WO2025151569A1

WO2025151569A1 - Managing lower layer triggered mobility during a failure

Info

Publication number: WO2025151569A1
Application number: PCT/US2025/010832
Authority: WO
Inventors: Chih-Hsiang Wu; Teming Chen
Original assignee: Google LLC
Current assignee: Google LLC
Priority date: 2024-01-08
Filing date: 2025-01-08
Publication date: 2025-07-17
Anticipated expiration: 2026-07-08

Abstract

A user equipment (UE) communicates with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG). The UE performs a lower-layer triggered mobility (LTM) cell switch to a candidate cell associated with the SCG, according to an LTM configuration; and transmits, via one of the MCG or the SCG, an indication that the UE performed the LTM cell switch, based on whether the UE has suspended a transmission on the MCG.

Description

MANAGING LOWER LAYER TRIGGERED MOBILITY DURING A FAILURE

REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of the filing date of provisional U.S. Patent Application No. 63/618,899 entitled “Managing Lower Layer Triggered Mobility During a Failure,” filed on January 8, 2024 and provisional U.S. Patent Application No. 63/567,419 entitled “Managing Lower Layer Triggered Mobility During a Failure,” filed on March 19, 2024. The entire contents of the provisional applications are hereby expressly incorporated herein by reference.

FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to managing lower layer triggered mobility during a failure.

BACKGROUND

[0003] This background description is provided for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0004] In telecommunication systems, the Packet Data Convergence Protocol (PDCP) sublayer of the radio protocol stack provides services such as transfer of user-plane data, ciphering, integrity protection, etc. For example, the PDCP layer defined for the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface (see 3GPP specification TS 36.323) and New Radio (NR) (see 3GPP specification TS 38.323) provides sequencing of protocol data units (PDUs) in the uplink direction (from a user device, also known as a user equipment (UE), to a base station) as well as in the downlink direction (from the base station to the UE). Further, the PDCP sublayer provides signaling radio bearers (SRBs) and data radio bearers (DRBs) to the Radio Resource Control (RRC) sublayer. Generally speaking, the UE and a base station can use SRBs to exchange RRC messages as well as non-access stratum (NAS) messages, and can use DRBs to transport data on a user plane.

[0005] UEs can use several types of SRBs and DRBs. When operating in dual connectivity (DC), the cells associated with the base station operating the master node (MN) define a master cell group (MCG), and the cells associated with the base station operating as the secondary node (SN) define the secondary cell group (SCG). So-called SRB1 resources carry RRC messages, which in some cases include NAS messages over the dedicated control channel (DCCH), and SRB2 resources support RRC messages that include logged measurement information or NAS messages, also over the DCCH but with lower priority than SRB1 resources. More generally, SRB1 and SRB2 resources allow the UE and the MN to exchange RRC messages related to the MN and embed RRC messages related to the SN, and also can be referred to as MCG SRBs. SRB3 resources allow the UE and the SN to exchange RRC messages related to the SN, and can be referred to as SCG SRBs. Split SRBs allow the UE to exchange RRC messages directly with the MN via lower layer resources of the MN and the SN. Further, DRBs using the lower-layer resources of only the MN can be referred as MCG DRBs, DRBs using the lower-layer resources of only the SN can be referred as SCG DRBs, and DRBs using the lower-layer resources of both the MCG and the SCG can be referred to as split DRBs.

[0006] The UE in some scenarios can concurrently utilize resources of multiple radio access network (RAN) nodes (e.g., base stations or components of a distributed base station), interconnected by a backhaul. When these network nodes support different radio access technologies (RATs), this type of connectivity is referred to as Multi-Radio Dual Connectivity (MR-DC). When a UE operates in MR-DC, one base station operates as a master node (MN) that covers a primary cell (PCell), and the other base station operates as a secondary node (SN) that covers a primary secondary cell (PSCell). The UE communicates with the MN (via the PCell) and the SN (via the PSCell). In other scenarios, the UE utilizes resources of one base station at a time. One base station and/or the UE determines that the UE should establish a radio connection with another base station. For example, one base station can determine to hand the UE over to the second base station, and initiate a handover procedure.

[0007] When the UE moves from coverage area of one cell to another cell in a RAN, at some point a serving cell change has to be performed for the UE. To perform the serving cell change, the RAN configures the UE to transmit Layer 3 (L3) measurement results. Based on L3 measurement results received from the UE, the RAN transmits an RRC reconfiguration message configuring Reconfiguration with Synchronization (e.g., the RRC reconfiguration message includes ^ ReconfigurationWithSync IE) for change of the serving cell (e.g., PCell or PSCell). In cases where the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN has to release the at least one SCell due to the change of the PCell or PSCell. The serving cell change involves complete L2 (and LI) resets, leading to longer latency, larger overhead and longer interruption time. Thus, 3GPP recently launched a new work item, described in RP-221799, to develop new mobility techniques for serving cell changes. These techniques aim to reduce latency and overhead, and are called low-layer triggered mobility (LTM) cell switch, or faster serving cell switching.

[0008] While the RAN communicates with the UE via the serving cell, the RAN receives one or more layer 3 (e.g., RRC) measurement results from the UE. Based on the layer 3 (L3) measurement result(s), the RAN determines to configure an LTM candidate cell for LTM cell switch. To configure the LTM candidate cell for the UE, the RAN transmits an LTM configuration configuring the LTM candidate cell to the UE via RRC signaling. In some implementations, the RAN includes the configuration parameters for the first radio bearer in the LTM configuration. Later on, the RAN receives one or more layer 1 (LI) measurement results from the UE. Based on the one or more LI measurement result(s), the RAN determines that the LTM candidate cell qualifies to be a serving cell for the UE. Therefore, the RAN transmits an LTM cell switch command to the UE to command the UE to perform the LTM cell switch to the LTM candidate cell. The UE performs a cell change from the serving cell to the LTM candidate cell in response to the LTM cell switch command as described in 3GPP R2-2313672.

[0009] When the UE operates in a MR-DC with a MN and a SN of the RAN, the UE can receive an LTM candidate configuration for an SCG from the SN via the MN or directly. The MN transmits a fast MCG link recovery configuration to the UE to enable fast MCG link recovery. At a later, the UE can encounter an MCG failure with the MN while communicating with the SN. Because the UE is configured with the fast MCG link recovery, the UE maintains the connection (i.e., continues communication) with the SN during the MCG failure. During the MCG failure, the SN may transmit an LTM command to the UE to command the UE to perform an LTM cell switch to a SCG candidate cell (i.e., an LTM candidate cell configured by the SN). The UE performs the LTM cell switch to the SCG candidate cell in accordance with the LTM command. To perform the LTM cell switch, the UE must send an RRC reconfiguration complete message to the MN via the MCG. However, the UE fails to transmit the RRC reconfiguration complete message because of the MCG failure. The failure to transmit the RRC reconfiguration complete message in turn causes failure of the LTM cell switch.

SUMMARY

[0010] An example embodiment of the techniques of this disclosure is a method implemented in a user equipment (UE), the method comprising: communicating with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); performing a lower-layer triggered mobility (LTM) cell switch to a candidate cell associated with the SCG, according to an LTM configuration; and transmitting, via one of the MCG or the SCG, an indication that the UE performed the LTM cell switch, based on whether the UE has suspended a transmission on the MCG.

[0011] Another example embodiment of these techniques is a method implemented in a user equipment (UE). The method comprises communicating with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); receiving, from the RAN, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell associated with the SCG; detecting an MCG failure associated with the MCG; receiving, via the SCG and subsequently to the detecting of the MCG failure but prior to recovering the MCG, an LTM command indicating that the UE is to initiate an LTM cell switch to the candidate cell; and one of: discarding the LTM command, or performing an MCG failure information procedure after completing the LTM cell switch.

[0012] Another example embodiment of these techniques is a method implemented in a user equipment (UE). The method comprises communicating with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); receiving, from the RAN, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell associated with the SCG; detecting an SCG failure associated with the SCG; suspending a transmission on the SCG in response to the detecting of the SCG failure; receiving, from the RAN and subsequently to the detecting of the SCG failure but prior to recovering the SCG, an LTM command indicating that the UE is to initiate an LTM cell switch to the candidate cell; performing the LTM cell switch to the candidate cell; and resuming the transmission via the SCG after the LTM cell switch. [0013] Yet another example embodiment of these techniques is a method implemented in a user equipment (UE). The method comprises communicating with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); receiving, from the RAN, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell associated with the MCG; detecting an MCG failure associated with the MCG; determining, subsequently to the detecting of the MCG failure but prior to recovering the MCG, that the UE is to initiate an LTM cell switch to the candidate cell; and performing the LTM switch to the candidate cell in response to the determining.

[0014] Still another example embodiment of these techniques is a method implemented in a radio access network (RAN). The method comprises communicating with a user equipment (UE) in dual connectivity (DC) via (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); transmitting, to the UE, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell associated with the SCG; receiving an indication of an MCG failure for the UE; and refraining from causing the UE to initiate an LTM cell switch to the candidate cell, prior to a recovery of the MCG for the UE.

[0015] Another example embodiment of these techniques is an apparatus comprising processing hardware and configured to implement one of the methods above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Fig. 1 A is a block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing conditional procedures related to a secondary node (SN);

[0017] Fig. IB is a block diagram of an example base station including a centralized unit (CU) and a distributed unit (DU) that can operate in the system of Fig. 1 A;

[0018] Fig. 2A is a block diagram of an example protocol stack according to which the UE of Fig. 1 A communicates with base stations;

[0019] Fig. 2B is a block diagram of an example protocol stack according to which the UE of Fig. 1 A communicates with a CU and a DU; [0020] Fig. 3 is a messaging diagram of an example scenario in which a UE communicates with a distributed base station and performs an LTM cell switch in response to a command from the base station;

[0021] Fig. 4 is a messaging diagram of an example scenario generally similar to that of Fig. 3, but in which the base station includes a source DU and a target DU, and the candidate cell for an LTM cell switch is associated with the target DU;

[0022] Figs. 5A-8B are messaging diagrams of example scenarios in which a UE performs an LTM cell switch in a dual connectivity scenario;

[0023] Fig. 9A is a flow diagram of an example method in a UE for processing an LTM command after detecting a failure of the MCG, which includes discarding the first LTM command received prior to an MCG recovery but performing an LTM cell switch in response to a second LTM command receiving after the MCG recovery;

[0024] Fig. 9B is a flow diagram of example method similar to that of Fig. 9A, but according to which the UE releases the LTM configuration in response to a message from the RAN related to MCG recovery;

[0025] Fig. 9C is a flow diagram of example method similar to that of Fig. 9A, but according to which the UE re-initiates a procedure for reporting MCG failure after comprising an LTM cell switch to an SCG cell;

[0026] Figs. 10A-G are flow diagrams of example methods for processing an LTM command in view of such factors as suspension of MCG transmission, UE configuration with respect to transmitting an RRC message via an MCG in response to an LTM command, or configuration of SRB over SCG;

[0027] Fig. 11 is a flow diagram of an example method in a UE for detecting an SCG failure when the UE stores one or more LTM candidate configurations;

[0028] Figs. 12A-C are flow diagrams of example methods in a UE for detecting an MCG failure when the UE stores one or more LTM candidate configurations;

[0029] Figs. 13A-C are flow diagrams of example methods in a RAN for managing an LTM cell switch when the UE encounters a failure on the MCG or the SCG;

[0030] Figs. 14 is a flow diagram of an example method in a CU for managing an LTM cell switch; and [0031] Figs. 15 is a flow diagram of an example method in a DCU for managing an LTM cell switch.

DETAILED DESCRIPTION OF THE DRAWINGS

[0032] Fig. 1 A depicts an example wireless communication system 100 in which communication devices can implement these techniques. The wireless communication system 100 includes a UE 102, a base station (BS) 104, a base station 106 and a core network (CN) 110. The UE 102 initially connects to the base station 104. In some scenarios, the base station 104 can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104 and the base station 106. The base stations 104 and 106 operate as an MN and an SN for the UE 102, respectively.

[0033] In various configurations of the wireless communication system 100, the base station 104 can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106 can be implemented as a secondary gNB (SgNB). The UE 102 can communicate with the base station 104 and the base station 106 via the same RAT such as EUTRA or NR, or different RATs. When the base station 104 is an MeNB and the base station 106 is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0034] In some cases, an MeNB or an SeNB is implemented as an ng-eNB rather than an eNB. When the base station 104 is a Master ng-eNB (Mng-eNB) and the base station 106 is a SgNB, the UE 102 can be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. When the base station 104 is an MgNB and the base station 106 is an SgNB, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the base station 104 is an MgNB and the base station 106 is a Secondary ng-eNB (Sng-eNB), the UE 102 may be in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB.

[0035] In the scenarios where the UE 102 hands over from the base station 104 to the base station 106, the base stations 104 and 106 operate as the source base station (S-BS) and a target base station (T-BS), respectively. The UE 102 can operate in DC with the base station 104 and an additional base station (not shown in Fig. 1 A) for example prior to the handover. The UE 102 can continue to operate in DC with the base station 106 and the additional base station or operate in single connectivity (SC) with the base station 106, after completing the handover. The base stations 104 and 106 in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively. [0036] A core network (CN) 110 can be an evolved packet core (EPC) 111 or a fifthgeneration core (5GC) 160, both of which are depicted in Fig. 1 A. The base station 104 can be an eNB supporting an SI interface for communicating with the EPC 111, an ng-eNB supporting an NG interface for communicating with the 5GC 160, or a gNB that supports an NR radio interface as well as an NG interface for communicating with the 5GC 160. To directly exchange messages with each other during the scenarios discussed below, the base stations 104 and 106 can support an X2 or Xn interface. Among other components, the EPC 111 can include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, and a Packet Data Network Gateway (PGW) 116. The SGW 112 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME 114 is configured to manage authentication, registration, paging, and other related functions. The PGW 116 provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and/or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The 5GC 160 includes a User Plane Function (UPF) 162 and an Access and Mobility Management (AMF) 164, and/or Session Management Function (SMF) 166. The UPF 162 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the SMF 166 is configured to manage PDU sessions.

[0037] As illustrated in Fig. 1 A, the base station 104 supports cell 124A, and the base station 106 supports a cell 126. The cells 124A and 126 can partially overlap, so that the UE 102 can communicate in DC with the base station 104 and the base station 106, where one of the base stations 104 and 106 is an MN and the other is an SN. The base station 104 can support additional cell(s) such as cells 124B and 124C, and the base station 106 can support additional cell(s) (not shown in Fig. 1 A). The cells 124A, 124B and 124C can partially overlap, so that the UE 102 can communicate in carrier aggregation (CA) with the base station 104. The base station 104 can operate the cells 124A, 124B and 124C via one or more transmit and receive points (TRPs). More particularly, when the UE 102 is in DC with the base station 104 and the base station 106, one of the base stations 104 and 106 operates as an MeNB, an Mng-eNB or an MgNB, and the other operates as an SgNB or an Sng-eNB.

[0038] In general, the wireless communication network 100 can include any suitable number of base stations supporting NR cells and/or EUTRA cells. More particularly, the

EPC 111 or the 5GC 160 can be connected to any suitable number of base stations supporting NR cells and/or EUTRA cells. Although the examples below refer specifically to specific CN types (EPC, 5GC) and RAT types (5GNR and EUTRA), in general the techniques of this disclosure also can apply to other suitable radio access and/or core network technologies such as sixth generation (6G) radio access and/or 6G core network or 5GNR-6G DC.

[0039] With continued reference to Fig. 1A, the base station 104 is equipped with processing hardware 130 that can include one or more general-purpose processors (e.g., CPUs) and a non-transitory computer-readable memory storing instructions that the one or more general-purpose processors execute. Additionally or alternatively, the processing hardware 130 can include special-purpose processing units. The processing hardware 130 can include a PHY controller 132 configured to transmit data and control signal on physical downlink (DL) channels and DL reference signals with one or more user devices (e.g. UE 102) via one or more cells (e.g., the cell(s) 124A, 124B and/or 124C) and/or one or more TRPs. The PHY controller 132 is also configured to receive data and control signal on physical uplink (UL) channels and/or UL reference signals with the one or more user devices via one or more cells (e.g., the cell(s) 124A, 124B and/or 124C) and/or one or more TRPs. The processing hardware 130 in an example implementation includes a MAC controller 134 configured to perform MAC functions with one or more user devices. The MAC functions include a random access (RA) procedure, managing UL timing advance (TA) for the one or more user devices, and/or communicating UL/DL MAC PDUs with the one or more user devices. The MAC functions include lower triggered mobility (LTM) related functions as described below. The processing hardware 130 can further include an RRC controller 136 to implement procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller 132 may be configured to support RRC messaging associated with handover procedures, and/or to support the necessary operations when the base station 104 operates as an MN relative to an SN or as an SN relative to an MN. The base station 106 can include processing hardware 140 that is similar to processing hardware 130. In particular, components 142, 144, and 146 can be similar to the components 132, 134, and 136, respectively.

[0040] The UE 102 is equipped with processing hardware 150 that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and/or special-purpose processing units. The PHY controller 152 is also configured to receive data and control signal on physical DL channels and/or DL reference signals with the base station 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and/or 126) and/or one or more TRPs. The PHY controller 152 is also configured to transmit data and control signal on physical UL channels and/or UL reference signals with the base station 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and/or 126) and/or one or more TRPs. The processing hardware 150 in an example implementation includes a MAC controller 154 configured to perform MAC functions with base station 104 or 106. For example, the MAC functions includes a random access procedure, managing UL timing advance for the one or more user devices, and communicating UL/DL MAC PDUs with the base station 104 or 106. In another example, the MAC functions includes LTM related functions as described below. The processing hardware 150 can further include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0041] In operation, the UE 102 in DC can use a radio bearer (e.g., a DRB or an SRB) that at different times terminates at the MN 104 or the SN 106. The UE 102 can apply one or more security keys when communicating on the radio bearer, in the uplink (UL) (from the UE 102 to a base station) and/or downlink (from a base station to the UE 102) direction.

[0042] Fig. IB depicts an example distributed implementation of a base station such as the base station 104 or 106. The base station in this implementation can include a centralized unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 is equipped with processing hardware that can include one or more general -purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and/or special-purpose processing units. In one example, the CU 172 is equipped with the processing hardware 130. In another example, the CU 172 is equipped with the processing hardware 140. The processing hardware 140 in an example implementation includes an SN RRC controller 142 configured to manage or control one or more RRC configurations and/or RRC procedures when the base station 106 operates as an SN. The DU 174 is also equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and/or special-purpose processing units. In some examples, the processing hardware in an example implementation includes a medium access control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure) and a radio link control (REC) controller configured to manage or control one or more RLC operations or procedures when the base station 106 operates as an MN or an SN. The process hardware may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0043] Fig. 2A illustrates, in a simplified manner, an example protocol stack 200 according to which the UE 102 can communicate with an eNB/ng-eNB or a gNB (e.g., one or more of the base stations 104, 106).

[0044] In the example stack 200, a physical layer (PHY) 202 A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLC sublayer 206A in turn provides RLC channels to an EUTRA PDCP sublayer 208 and, in some cases, to an NR PDCP sublayer 210. Similarly, the NR PHY 202B provides transport channels to the NR MAC sublayer 204B, which in turn provides logical channels to the NR RLC sublayer 206B. The NR RLC sublayer 206B in turn provides data transfer services to the NR PDCP sublayer 210. The NR PDCP sublayer 210 in turn can provide data transfer services to Service Data Adaptation Protocol (SDAP) 212 or a radio resource control (RRC) sublayer (not shown in Fig. 2A). The UE 102, in some implementations, supports both the EUTRA and the NR stack as shown in Fig. 2A, to support handover between EUTRA and NR base stations and/or to support DC over EUTRA and NR interfaces. Further, as illustrated in Fig. 2A, the UE 102 can support layering of NR PDCP 210 over EUTRA RLC 206 A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0045] The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the PDCP layer 208 or 210) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer 206A or 206B) that can be referred to as protocol data units (PDUs). Except where the difference between SDUs and PDUs is relevant, this disclosure for simplicity refers to both SDUs and PDUs as “packets.”

[0046] On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide signaling radio bearers (SRBs) or RRC sublayer (not shown in Fig. 2 A) to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0047] Fig. 2B illustrates, in a simplified manner, an example protocol stack 250, which the UE 102 can communicate with a DU (e.g., DU 174) and a CU (e.g., CU 172). The radio protocol stack 200 is functionally split as shown by the radio protocol stack 250 in Fig. 2B. The CU at any of the base stations 104 or 106 can hold all the control and upper layer functionalities (e.g., RRC 214, SDAP 212, NR PDCP 210), while the lower layer operations (e.g., NR RLC 206B, NR MAC 204B, and NR PHY 202B) are delegated to the DU. To support connection to a 5GC, NR PDCP 210 provides SRBs to RRC 214, and NR PDCP 210 provides DRBs to SDAP 212 and SRBs to RRC 214.

[0048] Next, several example scenarios in which the base station operating in the system of Fig. 1 A transmits a configuration to the UE 102 and later activates a configuration for communication between the UE 102 and base station. Generally speaking, events in Figs. 3- 7B that are similar are labeled with similar reference numbers e.g., event 316 is similar to event 416 of Figs 4A and 4B, event 516 of Fig. 5 A, event 517 of Fig. 5B, event 616 of Fig. 6A, event 617 of Fig. 6B, event 716 of Fig. 7A, and event 717 of Fig. 7B), with differences discussed below where appropriate. With the exception of the differences shown in the figures and discussed below, any of the alternative implementations discussed with respect to a particular event (e.g., for messaging and processing) may apply to events labeled with similar reference numbers in other figures.

[0049] Referring first to Fig. 3, in a scenario 300, the base station 104 includes a CU 172 and a DU 174 and the DU 174 operates the cell 124 A. The UE 102 initially communicates 302 with the DU 174 on the cell 124 A using a serving DU configuration, and communicates with the CU 172 via the DU 174, e.g., using a serving CU configuration. In other words, the DU 174 is a serving DU that is communicating with the UE 102. In some implementations, the UE 102 in carrier aggregation (CA) communicates with the DU 174 on the cell 124 A and other cell(s) (e.g., cell 124D not shown in Fig. 1 A) using the serving DU configuration. The DU 174 operates the other cell(s). The cell 124A and/or the other cell(s) are serving cell(s) for the UE 102. In other implementations, the UE 102 in communicates with the DU 174 on the cell 124A only. In some implementations, the UE 102 communicates with the DU 174 on the cell 124A and/or other cell(s) via one or multiple TRPs. In some implementations, the cell 124A can be a PCell. In such cases, the other cell(s) include SCell(s) and/or additional cell(s) associated with the PCell or a SCell. In other implementations, the cell 124A can be a SCell, and one of the other cell(s) is a PCell. In such cases, the rest includes SCell(s) and/or additional cell(s) associated with the PCell or a SCell. In the following description, the base station 104 can be the DU 174, the CU 172 or the DU 174 and CU 172.

[0050] In the event 302, the UE 102 can transmit UL PDUs and/or UL control signals to the base station 104 on the cell 124A and/or other cell(s) via one or multiple TRPs. In some implementations, the UE 102 communicates UL PDUs and/or DL PDUs with the base station 104 via radio bearers which can include SRBs and/or DRB(s). The base station 104 can configure the radio bearers to the UE 102. In some implementations, UL control signals include UL control information, channel state information, hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, scheduling request(s) and/or sounding reference signal(s). Similarly, the UE 102 can receive DL PDUs and/or DL control signals from the base station 104 on the cell 124A and/or other cell(s) via one or multiple TRPs. In some implementations, the DL control signals include downlink control information (DCIs) and reference signals (e.g., synchronization signal block, channel state information reference signal(s) (CSI-RS(s)), and/or tracking reference signal(s)). The base station 104 can transmit the DCIs on physical downlink control channel(s) (PDCCH(s)) monitored by the UE 102, on the cell 124A and/or other cell(s) via one or multiple TRPs.

[0051] In some implementations, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and/or RLC configuration parameters. In some implementations, the serving DU configuration includes at least one first non-LTM TCI state configuration for the serving cell(s). In some implementations, the DU 174 can transmit these configuration parameters and/or the first non-LTM TCI state configuration(s) to the CU 172. The CU 172 generates one or more messages (e.g., RRC reconfiguration message(s)) including the configuration parameters and/or the first non-LTM TCI state configuration(s) and transmits the one or more messages to the UE 102 via the DU 174. In other implementations, the DU 174 transmits the configuration parameters and/or the first non-LTM TCI state configuration(s) to the UE 102 directly. In some implementations, the serving DU configuration is CellGroupConfig ^E defined in 3GPP specification 38.331. In other implementations, the serving DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the serving CU configuration includes PDCP configuration parameters, measurement configuration parameters, and/or radio bearer configuration parameters. In some implementations, the serving CU configuration includes a MeasConfig IE and/or a RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConfig IE and/or RadioBearerConfig IE. In some implementations, the serving DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. In other implementations, the serving CU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and reporting. In some implementations, the UE 102 receives the serving CU configuration or the configuration parameters in the serving CU configuration from the CU 172 via the DU 174. In other implementations, the UE 102 receives a portion of the serving CU configuration and/or a portion of the serving DU configuration from a base station other than the base station 104 and the remaining portion of these configuration parameters from the base station 104.

[0052] In some implementations, the UE 102 and DU 174 communicates with each other using the first non-LTM TCI state configuration(s), e.g., in the events 302, 318, 320, 324, 325, 330, and/or 331. In some implementations, the DU 174 transmits at least one first non- LTM TCI States Activation/Deactivation command to the UE 102 to activate some of the first non-LTM TCI state configuration(s). The UE 102 activates the some of the first non- LTM TCI state configuration(s) in response to the first non-LTM TCI States Activation/Deactivation command(s). In some implementations, the DU 174 indicates deactivation of some of the first non-LTM TCI state configuration(s) in some of the first non- LTM TCI States Activation/Deactivation command(s). The UE 102 and DU 174 communicate with each other using the activated non-LTM TCI state configuration(s), e.g., in the events 302, 318, 320, 324, 325, 330, and/or 331.

[0053] In some implementations, each of the first non-LTM TCI States Activation/Deactivation command(s) is a MAC CE. The MAC CE(s) may include one or more TCI States Activation/Deactivation for UE-specific PDSCH MAC CEs, one or more TCI State Indication for UE-specific PDCCH MAC CEs, one or more PUCCH spatial relation Activation/Deactivation MAC CEs, one or more Enhanced TCI States Activation/Deactivation for UE-specific PDSCH MAC CEs, one or more Enhanced PUCCH Spatial Relation Activation/Deactivation MAC CEs, one or more Enhanced TCI States Indication for UE-specific PDCCH MAC CEs, one or more PUCCH spatial relation Activation/Deactivation for multiple TRP PUCCH repetition MAC CEs, and/or one or more Unified TCI States Activation/Deactivation MAC CEs. [0054] In some implementations, the DU 174 includes a serving cell ID (e.g., a serving cell index) in each of the first non-LTM TCI States Activation/Deactivation command(s) to identify the first non-LTM TCI state configuration(s). Each of the serving cell ID(s) indicates a respective serving cell of the serving cell(s). In some implementations, the serving DU configuration includes the serving cell ID(s) and configures association(s) between the serving cell ID(s) and the first non-LTM TCI state configuration(s).

[0055] While communicating with the base station 104, the UE 102 transmits 304 at least one measurement report to the DU 174. In some implementations, the at least one measurement report includes Layer 1 (LI) measurement report(s) and/or Layer 3 (L3) measurement report(s) for at least one serving cell of the UE 102 and/or at least one nonserving cell. For each of the L3 measurement report(s), the DU 174 transmits 306 a DU-to- CU message including the L3 measurement report to the CU 172. In some implementations, the DU-to-CU message(s) of the event 306 is/are Fl application protocol (F1AP) message(s) (e.g., UL RRC Message Transfer message(s)). In some implementations, the DU 174 does not transmit or refrains from transmitting the LI measurement report(s) to the CU 172. The at least one serving cell includes the cell 124A and/or other cell(s), and the at least one nonserving cell includes the cell 124B and/or cell 124C. In some implementations, the serving DU configuration or the serving CU configuration includes at least one measurement configuration. In some implementations, the UE 102 receives one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration from the CU 172 via the DU 174 in the event 302. In accordance with the at least one measurement configuration, the UE 102 performs measurements and transmits 304 the at least one measurement report to the DU 174. In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)) and/or LI measurement configuration(s). The LI measurement configuration(s) (e.g., CSI-MeasConfig IE(s)) can include LI measurement resource configuration(s) and/or LI measurement reporting configuration(s). The LI measurement resource configuration(s) can configure reference signal(s) and/or resources of the reference signal(s) for the UE 102 to measure and obtain LI measurement results. In some implementations, the reference signal(s) includes CSLRS(s) and/or Synchronization Signal (SS)/ Physical Broadcast Channel (PBCH) Resource Block(s) (SSB(s)). For example, the LI measurement resource configuration(s) is/are CSI-ResourceConfig IE(s). In another example, the LI measurement reporting configuration(s) configures way(s) the UE 102 uses to transmit LI measurement results/reports. For example, the LI measurement report configuration(s) is/are CSI- ReportConfig IE(s). For example, The UE 102 transmits the L3 measurement report(s) to the CU 172 via the DU 174 in accordance with the L3 measurement configuration(s). The UE 102 transmits the LI measurement report(s) to the DU 174 in accordance with the LI measurement configuration(s) or LI measurement reporting configuration(s). In one implementations, the DU 174 does not transmit the LI measurement report(s) to the CU 172.

[0056] In some implementations, the LI measurement configuration(s) are new RRC IE(s) defined in 3GPP specification 38.331 vl8.0.0 and/or later version for a lower layer triggered mobility (LTM). In some implementations, the LI measurement resource configuration(s) are new RRC IE(s) defined in 3GPP specification 38.331 vl8.0.0 and/or later version for the LTM. In some implementations, the LI measurement reporting configuration(s) are new RRC IE(s) defined in 3GPP specification 38.331 vl8.0.0 and/or later version for the LTM. In some implementations, each of the LI measurement reporting configuration(s) can include a trigger event configuration configuring a trigger event to trigger the UE 102 to transmit a LI measurement report. If the UE 102 detects the trigger event, the UE 102 transmits a LI measurement report to the DU 174.

[0057] In some implementations, (each of) the LI measurement report(s) can include at least one LI measurement result. In some implementations, the at least LI measurement result includes at least one LI -reference signal received power (Ll-RSRP) value and/or at least one LI- Signal to Interference Noise Ratio (Ll-SINR) value. For each of the LI measurement report(s), the UE 102 transmits a PUCCH transmission including the LI measurement report to the DU 174, in some implementations. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUCCH to the DU 174. In other implementations, for each of the LI measurement report(s), the UE 102 transmits a PUSCH transmission including the LI measurement report to the DU 174. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUSCH to the DU 174. In yet other implementations, the UE 102 transmits a portion of the LI measurement report(s) on PUCCH(s) and the rest of the LI measurement report(s) on physical UL shared channel(s) (PUSCH(s)) to the DU 174. That is, for each of the portion of the LI measurement report(s), the UE 102 transmits a PUCCH transmission including the LI measurement report to the DU 174, and for each of the rest of the LI measurement report(s), the UE 102 transmits a PUSCH transmission including the LI measurement report to the DU 174. In some implementations, each of the LI measurement report(s) is a part of CSI (i.e., a CSI component) or CSI. In some implementations, the UE 102 can include other CSI component(s) in (each of) the PUCCH transmission(s) and/or PUSCH transmission(s) described above. In one implementation, the other CSI component(s) include such as a channel quality indicator (CQI), a Precoding Matrix Indicator (PMI), a CSI-RS Resource Indicator (CRI), a SSB Resource Indicator (SSBRI), a Layer Indicator (LI), and/or a Rank Indicator (RI). In some implementations, the UE 102 does not transmit the LI measurement report(s) in format of RRC message(s) to the DU 174.

[0058] In some implementations, each of the L3 measurement report(s) can include at least one L3 measurement result. In some implementations, the at least one L3 measurement result includes at least one RSRP (value) and/or at least one SINR (value). In one implementation, the UE 102 transmits each of the L3 measurement report(s) on a PUSCH to the CU 172 via the DU 174. In some implementations, each of the L3 measurement report(s) can bean RRC message (e.g., MeasurementReport message). In some implementations, each of the L3 measurement configuration(s) includes a particular measurement identity (e.g., measld) and each of the L3 measurement report(s) includes a particular measurement identity in a particular L3 measurement configuration. When the CU 172 receives a L3 measurement report including a measurement identity and a L3 measurement result from the UE 102 via the DU 174, the CU 172 can determine that the L3 measurement report is associated to a L3 measurement configuration identified by the measurement identity.

[0059] In some alternative implementations, for each of the at least one measurement report (e.g., LI measurement report(s)), the UE 102 transmits a MAC control element (CE) including the measurement report to the DU 174 in the event 304. To transmit the MAC CE(s), the UE 102 generate one or more MAC PDUs each including one or more of the MAC CE(s) to the DU 174 in the event 304.

[0060] In some implementations, the UE 102 performs measurements on one or more reference signals in accordance with the at least one measurement configuration. The one or more reference signals can include one or more Synchronization Signal (SS)/ Physical Broadcast Channel (PBCH) Resource Blocks (SSBs) and/or one or more CSI-RSs. The UE 102 obtains the at least one LI measurement result and/or at least one L3 measurement result from the measurements. The DU 174 transmits the one or more reference signals on the cell 124A and other cell(s) (e.g., the cell 124B, the cell 124C and/or cell(s) not shown in Fig. 1 A). [0061] After (e.g., in response to) receiving one or some of the at least one measurement report from the UE 102, the CU 172 determines to prepare a first cell (e.g., the cell 124B) for LTM for the UE 102. In other words, the first cell is an LTM candidate cell. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell could be used by the base station 104 to communicate with the UE 102. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell qualifies to be a candidate cell that could be used for communication with the UE 102. In some implementations, if the L3 measurement report(s) indicates that signal strength and/or quality of the first cell is above a first predetermined threshold, is better than strength and/or quality of the cell 124A, and/or is better than strength and/or quality of the cell 124A by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. In other implementations, if the LI measurement report(s) indicates that signal strength and/or quality of the first cell is above a first predetermined threshold, is better than signal strength and/or quality of the cell 124A, and/or is better than signal strength and/or quality of the cell 124A by a first predetermined threshold, the DU 174 determines to prepare the first cell for the UE 102. Alternatively, the base station 104 determines to prepare the first cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0062] In the case that the CU 172 determines to prepare the first cell for LTM, the CU 172 transmits 308 a first CU-to-DU message to the DU 174 to prepare the first cell for the UE 102. In some implementations, the CU 172 includes a cell identity (ID) 1 of the first cell in the first CU-to-DU message to request the DU 174 to prepare the first cell for LTM for the UE 102. For example, the cell ID 1 is cell global identity (CGI). In another example, the cell ID is a portion of the CGI. In yet another example, the cell ID is a physical cell ID (PCI). In some implementations, the CU 172 includes an LTM indicator in the first CU-to-DU message to indicate the DU 174 to prepare the first cell for LTM. In some implementations, the LTM indicator is an LTM Information to be Setup IE or LTM Information to be Modified IE. In other implementations, the CU 172 includes the LTM indicator in an LTM Information to be Setup IE and includes the LTM Information to be Setup IE in the first CU-to-DU message. In yet other implementations, the CU 172 includes the LTM indicator in an LTM Information to be Modified IE and includes the LTM Information to be Modified IE in the first CU-to-DU message. In response to the first CU-to-DU message, the DU 174 generates a first LTM DU configuration (referred to herein after as LTM DU configuration 1) for the UE 102, which configures the first cell for LTM. The DU 174 then transmits 310 a first DU-to-CU message including the LTM DU configuration 1 to the CU 172 in response to the first CU-to-DU message. In some implementations, the DU 174 can include the cell ID 1 together with the LTM DU configuration 1 in the first DU-to-CU message to indicate that the LTM DU configuration 1 is associated with the first cell (i.e., the cell ID 1). In the case that the DU 174 determines to prepare the first cell, the DU 174 initiates transmission of the first DU-to-CU message to the CU 172 instead of in response to a CU-to-DU message received from the CU 172.

[0063] In some implementations, the DU 174 includes, in the first DU-to-CU message, the cell ID of the first cell associated with the LTM DU configuration 1 to indicate that the LTM DU configuration 1 is configured for or associated with the first cell. The CU 172 identifies the LTM DU configuration 1 is configured for or associated with the first cell. In some scenarios and implementations, the CU 172 can include additional cell ID(s) (e.g., cell ID(s) 2, . . ., N) in the first CU-to-DU message to prepare additional cell(s) (e.g., cell(s) 2, . . ., N) for LTM for the UE 102, and the DU 174 includes additional LTM DU configuration(s) (e.g., LTM DU configuration(s) 2, . . . , N) each configuring a particular cell of the additional cell(s), as described below. In such cases, the DU 174 includes, in the first DU-to-CU message, the additional cell ID(s) respectively associated with the additional LTM DU configuration(s) to indicate that which LTM DU configuration is associated to which cell (ID). The cell(s) 1 and/or 2, . . . , N are candidate cell(s).

[0064] In some implementations, the CU 172 does not include a (reference) LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration, generates the LTM DU configuration(s) 1 and/or 2, . . ., N (i.e., nonreference LTM DU configuration(s)) based on the reference LTM DU configuration, and includes the reference LTM DU configuration in the first DU-to-CU message. In other implementations, the CU 172 includes a reference LTM DU configuration in the first CU-to- DU message. In such cases, the DU 174 generates the LTM DU configuration(s) 1, and/or 2, . . . , N which are delta configuration(s) to augment the reference LTM DU configuration. In yet other implementations, the CU 172 includes a reference LTM DU configuration (e.g., a first reference LTM DU configuration) in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration (e.g., a second reference LTM DU configuration) replacing the first reference LTM DU configuration, generates the LTM DU configuration(s) 1 and/or 2, . . N based on the second reference LTM DU configuration, and includes the second reference LTM DU configuration in the first DU-to-CU message.

[0065] In some implementations, the reference LTM DU configuration includes physical layer configuration parameters, MAC configuration parameters, and/or RLC configuration parameters. In some implementations, the reference LTM DU configuration is CellGroupConfig IE defined in 3 GPP specification 38.331. In other implementations, the reference LTM DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the reference LTM DU configuration includes a CSI- MeasConfig IE or configuration parameters for channel state information (CSI) measurement and/or reporting.

[0066] In some implementations, the reference LTM DU configuration is different from the serving DU configuration. In some implementations, a portion of the reference LTM DU configuration is the same as a portion of the serving DU configuration and the rest of the reference LTM DU configuration is different from the rest of the serving DU configuration. In other implementations, the reference LTM DU configuration is the same as the serving DU configuration.

[0067] After receiving the first DU-to-CU message, the CU 172 generates an RRC reconfiguration message (e.g., an RRCReconfiguration message) including the LTM DU configuration 1 and transmits 316 a second CU-to-DU message including the RRC reconfiguration message to the DU 174. In some implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316. In other implementations, the CU 172 does not include a/the reference LTM DU configuration in the RRC reconfiguration message 316. In some implementations, if the CU 172 transmits the reference LTM DU configuration to the UE 102 during the event 302, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316. In other implementations, if the CU 172 receives the reference LTM DU configuration from the DU 174, the CU 172 includes the LTM DU configuration in the RRC reconfiguration message 316. Otherwise, if the CU 172 does not receive a reference LTM DU configuration from the DU 174, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316.

[0068] In some implementations, the CU 172 includes the LTM DU configuration 1 and/or the LTM CU configuration 1 in a first container (e.g., a field/IE) and includes the first container (e.g., LTM configuration 1) in the RRC reconfiguration message of the events 316 and 318. In such cases, the CU 172 generates the first container. The first container is to indicate the UE 102 not to apply the LTM DU configuration 1 and/or the LTM CU configuration 1 immediately. In some scenarios or implementations, the UE 102 receives an RRC reconfiguration message (e.g., the RRC reconfiguration message of the event 318) including a configuration (e.g., the LTM DU configuration 1). If the configuration is included in the first container, the UE 102 refrains from immediately applying the configuration. Otherwise, if the configuration is not included in the first container, the UE 102 can apply the configuration immediately. In some implementations, the first container includes or is a first addition or modification list (e.g., Itm-CandidateToAddModList field or LTM- CandidateToAddModList IE). The CU 172 includes the LTM DU configuration 1 and/or the LTM CU configuration 1 in a first element (referred to herein after as element 1) of the first addition or modification list. In some implementations, the CU 172 generates an RRC message (e.g., RRCRecconfiguration message) including the LTM DU configuration 1 and/or the LTM CU configuration 1, and includes the RRC message in the element 1. In some implementations, the element 1 is an addition or modification IE (e.g., LTM- ConfigToAddMod IE, LTM-Candidate IE, LTM-CandidateToAddMod IE or LTM- CandidateConfigToAddMod IE). When the UE 102 receives the first addition or modification list, the UE 102 can store the first addition or modification list, e.g., in a variable in its random access memory (RAM). In other alternative implementations, the DU 174 generates the first container and includes the first container in the first DU-to-CU message. In yet other alternative implementations, the DU 174 generates the element 1 and includes the element 1 in the first DU-to-CU message.

[0069] In some implementations, the CU 172 includes an LTM CU configuration 1 in the RRC reconfiguration message 316, the first container or the element 1, where the LTM CU configuration 1 associated with the LTM DU configuration 1. To associate the LTM CU configuration 1 with the LTM DU configuration 1, the CU 172 can include the LTM CU configuration 1 and the LTM DU configuration in the element 1. In some implementations, the CU 172 includes LTM CU configuration(s) 2, . . ., N in the RRC reconfiguration message 316 or the second container, where the LTM CU configuration(s) 2, . . . , N associated with the LTM DU configuration(s) 2, . . . , N, respectively. To associate the LTM CU configuration(s) 2, . . . , N with the LTM DU configuration(s) 2, . . . , N , the CU 172 can include the LTM CU configuration(s) 2, . . . , N and the LTM DU configuration(s) in the element(s) 2, . . . , N, respectively. In other implementations, the CU 172 includes, in the element(s) 2, . . ., N, the LTM CU configuration(s) 2, . . . , N associated with the LTM DU configuration(s) 2, . . . , N, respectively. Alternatively, the CU 172 does not include, in the RRC reconfiguration message 316, LTM CU configured on(s) for some or all of the LTM DU configuration 1 and/or LTM DU configuration(s) 2, . . . , N.

[0070] After receiving the RRC reconfiguration message 316, the DU 174 transmits 318 the RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320an RRC reconfiguration complete message (e.g., an RRCReconfigurationComplete message) to the DU 174, which in turn transmits 322 a second DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some implementations, the CU 172 performs security protection (e.g., integrity protection and/or encryption) on the RRC reconfiguration message. For example, the CU 172 generates a message authentication code for integrity (MAC-I) for the RRC reconfiguration message, encrypts the RRC reconfiguration message and the MAC-I to obtain an encrypted RRC reconfiguration message and an encrypted MAC-I, and transmits a PDCP PDU including the encrypted RRC reconfiguration message and encrypted MAC-I to the UE 102 via the DU 174 in the events 316 and 318. When the UE 102 receives the PDCP PDU from the CU 172 via the DU 174 (i.e., events 316 and 318), the UE 102 decrypts the encrypted RRC reconfiguration and encrypted MAC-I to obtain the RRC reconfiguration message and MAC-I and verifies whether the MAC-I is valid. If the UE 102 verifies the MAC-I is invalid, the UE 102 discards or ignores the RRC reconfiguration message. In some implementations, the UE 102 can perform an RRC connection reestablishment procedure in response to the invalid MAC-I. Otherwise, if the UE 102 verifies the MAC-I is valid, the UE 102 can process the RRC reconfiguration. The UE 102 refrains from applying (i.e., executing) the LTM DU configuration 1 until receiving an LTM command activating the LTM DU configuration 1 as described for events 330, 350.

[0071] The events 308 (optional) and 310 are collectively referred to in Fig. 3 as an LTM preparation procedure 390. The events 316, 318, 320, 322 are collectively referred to in Fig. 3 as an LTM configuration delivery procedure 394.

[0072] In some implementations, the first CU-to-DU message is a UE Context Setup Request message, and the first DU-to-CU message is a UE Context Setup Response message. In some implementations, the first CU-to-DU message is a UE Context Modification Request message, and the first DU-to-CU message is a UE Context Modification Response message or UE Context Modification Required message. In the case of the UE Context Modification Required message, the CU 172 can transmit a UE Context Modification Confirm message to the DU 174 in response to UE Context Modification Required message. In some implementations, the second CU-to-DU message is a DL RRC Message Transfer message. In other implementations, the second CU-to-DU message is a UE Context Modification Request message. In some implementations, the second DU-to-CU message is a UL RRC Message Transfer message. In other implementations, the second DU-to-CU message is a UE Context Modification Response message.

[0073] In some implementations, the CU 172 can include a reference LTM CU configuration in the RRC reconfiguration message 316 or the first container. In some implementations, the CU 172 can generate the LTM CU configuration 1 (i.e., non-reference LTM CU configuration) as a delta configuration to augment the reference LTM CU configuration. Similarly, the CU 172 can generate some or all of the LTM CU configuration(s) 2, . . . , N as delta configuration(s) to augment the reference LTM CU configuration. Alternatively, in the RRC reconfiguration message 316 or the first container, the CU 172 includes the reference LTM CU configuration and does not include a nonreference LTM CU configuration. In some implementations, the CU 172 includes the reference LTM CU configuration and/or the reference LTM DU configuration in an additional container (e.g., reference LTM configuration) and include the additional container in the RRC reconfiguration message 316 or the first container.

[0074] In some implementations, the reference LTM CU configuration is different from the serving CU configuration. In some implementations, a portion of the reference LTM CU configuration is the same as a portion of the serving CU configuration and the rest of the reference LTM CU configuration is different from the rest of the serving CU configuration. In yet other implementations, the reference LTM CU configuration is the same as the serving LTM CU configuration.

[0075] In some implementations, the CU 172 includes, in the RRC reconfiguration message, a first LTM ID (referred to herein after as ID 1) for identifying the LTM DU configuration 1 or the element 1. In some implementations, the CU 172 includes the ID 1 in the first container or element 1. In some implementations, the CU 172 assigns the ID 1. [0076] In some implementations, the CU 172 can transmit the ID 1 to the DU 174, and the DU 174 associates the ID 1 with the LTM DU configuration 1 and/or the cell ID 1. In some implementations, the CU 172 includes the ID 1 in the first CU-to-DU message. In other implementations, after receiving the first DU-to-CU message, the CU 172 transmits 312 a third CU-to-DU message including the ID 1 to the DU 174 instead of including the ID 1 in the first CU-to-DU message. In some implementations, in the third CU-to-DU message, the CU 172 can include the LTM DU configuration 1 and the ID 1 and indicate the association between the ID 1 and LTM DU configuration 1. Thus, the DU 174 can directly associate the ID 1 with the LTM DU configuration 1. In other implementations, in the third CU-to-DU message, the CU 172 can include the cell ID 1 and the ID 1 (i.e., the first LTM ID) and indicate the association between the cell ID 1 and the ID 1. Thus, the DU 174 can associate the ID 1 with the LTM DU configuration 1, based on the association between the cell ID 1 and the ID 1 and the association between the cell ID 1 and the LTM DU configuration 1. In yet other implementations, in the third CU-to-DU message, the CU 172 can include the LTM DU configuration 1, the cell ID 1 and/or the ID 1 and indicate the association between the ID 1, LTM DU configuration 1 and/or the cell ID 1. In some implementations, the DU 174 can transmit 314 a third DU-to-CU message to the CU 172 in response to the third CU-to-DU message. In some implementations, the third CU-to-DU message and third DU-to-CU message are UE Context Modification Request message and UE Context Modification Response message. In some implementations, the CU 172 can include the ID 1, the cell ID 1 and/or the LTM DU configuration 1 in the second CU-to-DU message as described above. Thus, the third CU-to-DU message can be omitted. In some implementations, the third DU- to-CU message is a UE Context Modification Required message. In such cases, the CU 172 transmits a UE Context Modification Confirm message to the DU 174 in response to the UE Context Modification Required message.

[0077] In some implementations, the events 312 (optional) and/or 314 (optional) are collectively referred to in Fig. 3 as an LTM ID assignment procedure 392.

[0078] In the case that the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 can include the ID 1 in the LTM DU configuration 1, first container or element 1. Alternatively, the DU 174 does not include the ID 1 in the LTM DU configuration 1, first container and/or element 1. [0079] In some implementations, the CU 172 includes the reference LTM DU configuration in the first container. For example, the CU 172 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In other implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316 and outside the first container. For example, the CU 172 generates a third container (e.g., a field/IE) to include the first container and the reference LTM DU configuration and includes the third container in the RRC reconfiguration message 316. In yet other implementations, the DU 174 includes the reference LTM DU configuration in the first container. For example, the DU 174 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In yet other implementations, the DU 174 generates a fourth container (e.g., a field/IE) to include the first container and the reference LTM DU configuration and includes the fourth container in the first DU-to-CU message 310. In such cases, the CU 172 includes the fourth container in the RRC reconfiguration message 316. Alternatively, the CU 172 retrieves the reference LTM DU configuration and the LTM DU configuration 1 from the fourth container and includes the reference LTM DU configuration and the LTM DU configuration 1 as described above.

[0080] In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM DU configuration. In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM CU configuration.

[0081] In some implementations, the LTM DU configuration 1 includes a plurality of configuration parameters for the UE 102 to communicate with the DU 174 on the first cell. In some implementations, the plurality of configuration parameters include physical layer configuration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE) and/or RLC configuration parameters (e.g., RLC-BearerConfig IE(s)). In some further implementations, the plurality of configuration parameters include a special cell configuration (e.g., SpCellConfig E) and/or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration 1 is CellGroupConfig ^E defined in 3GPP specification 38.331. In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE. [0082] In some implementations, the LTM CU configuration 1 includes PDCP configuration parameters, measurement configuration parameters, and/or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 includes a MeasConfig IE and/or a RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConfig IE and/or RadioBearerConfig IE. In some implementations, the LTM DU configuration 1 includes LI measurement configuration 1 (e.g., a CSI-MeasConfig IE) and/or at least one configuration indicator (TCI) state configuration. In other implementations, the LTM CU configuration 1 includes the LI measurement configuration and/or the TCI state configuration(s) 1. In some implementations, the LI measurement configuration includes at least one reference signal (RS) resource configuration 1 and/or at least one report configuration 1. In some implementations, the RS resource configuration(s) 1 configures one or more RSs or one or more RS resources associated with the cell 1. The RS(s) includes SSB(s) and/or CSI-RS(s). The RS resource(s) includes SSB resource(s) and/or CSI-RS resource(s). In some implementations, each of the RS resource configuration(s) 1 includes an RS resource configuration ID. In some implementations, the RS resource configuration(s) 1 is/are (similar to) CSI-ResourceConfig l Xfi). In some implementations, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. In some implementations, each of the TCI state configuration(s) 1 configures a TCI state that associates one or two DL RSs with a corresponding quasi -colocation (QCL) type. The DL RS(s) are associated with the cell 1.

[0083] In some implementations, the DU 174 includes the LI measurement configuration 1 and/or the TCI state configuration(s) 1 in a serving DU configuration 1 (e.g., non-LTM DU configuration). In some implementations, the DU 174 includes the serving DU configuration in the first DU-to-CU message. In other implementations, the DU 174 transmits an additional DU-to-CU message including the serving DU configuration to the CU 172. In some implementations, the additional DU-to-CU message is a UE Context Modification Required message. In some implementations, the CU 172 includes the serving DU configuration 1 in the RRC reconfiguration message 316, 318. In other implementations, the CU 172 transmits another RRC reconfiguration message including the serving DU configuration to the UE 102 via the DU 174.

[0084] In some implementations, the DU 174 includes a random access configuration in the LTM DU configuration 1. In other implementations, the DU 174 does not include a random access configuration in the LTM DU configuration 1. In some implementations, if the cell 124 A and first cell are not synchronized, the DU 174 determines to include the random access configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the random access configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. If the LTM DU configuration 1 includes the random access configuration, the UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration, as described below. Otherwise, if the LTM DU configuration 1 does not include the random access configuration or indicates the UE 102 to skip a random access procedure in LTM, the UE 102 skips or refrains from performing the random access procedure of the event 332 in response to the LTM DU configuration 1 excluding the random access configuration.

[0085] In some implementations, the DU 174 includes random access configuration parameters in the LTM DU configuration 1 and/or the reference LTM DU configuration regardless of whether the cell 124 A and first cell are synchronized or not. The UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration parameters, as described below. In some implementations, the random access configuration parameters configure physical random access channel (PRACH) resources, an association between SSB and PRACH resources, and/or one or more PRACH occasions.

[0086] In some implementations, if the cell 124 A and first cell are synchronized, the DU 174 determines to include, in the LTM DU configuration 1, a first indication configuring the UE 102 not to perform a random access procedure on the first cell. Otherwise, if the cell 124 A and first cell are not synchronized, the DU 174 determines to not include the first indication in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to include the first indication in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to not include the first indication in the LTM DU configuration 1. If the LTM DU configuration 1 includes the first indication, the UE 102 skips or refrains from performing the random access procedure of the event 332 in accordance with or in response to the first indication. Otherwise, if the LTM DU configuration 1 does not include the first indication, the UE 102 performs the random access procedure in accordance with the random access configuration in the event 332, in response to the LTM DU configuration 1 excluding the first indication, as described below.

[0087] In some implementations, the DU 174 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In other implementations, the DU 174 does not include a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In some implementations, the DU 174 includes an LTM cell switch information in the first LTM DU configuration 1. In some implementations, the DU 174 includes the random access configuration (parameters) in the LTM cell switch information (e.g., Itm-CellSw itchinfo field or LTM-CellSw itchinfo IE). In some implementations, if the cell 124 A and first cell are not synchronized, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1. In some implementations, if the LTM DU configuration 1 includes the reconfiguration with sync configuration, the UE 102 performs the random access procedure in the event 332 as described below, in response to or in accordance with the reconfiguration with sync configuration. Otherwise, if the LTM DU configuration 1 does not include the reconfiguration with sync configuration, the UE 102 skips or refrains from performing the random access procedure of the event 332. In some implementations, the DU 174 includes a cell ID (i.e., cell ID 1) of cell 1 (i.e., the first cell) in the LTM DU configuration 1. In one implementation, the cell ID 1 can be a PCI. In another implementation, the cell ID 1 is a CGI. In some implementations, the cell ID 1 included in the LTM DU configuration l is a PCI, while the cell ID 1 included in the first CU-to-DU message is a CGI. In some further implementations, the LTM DU configuration 1 includes a cell index 1 indexing the cell ID 1 or the first cell. The cell index 1 is not a cell ID. The cell index takes fewer bits than the cell ID. In some implementations, the CU 172 sets the cell index 1 to a value and includes the cell index 1 in the first CU-to-DU message of the event 308.

[0088] In some implementations, after (e.g., in response to) receiving one or some of the at least one measurement report of the event 304, the base station 104 (i.e., the CU 172 or DU 174) determines to prepare additional cell(s) (i.e., cell(s) 2, . . ., N) of the base station 104 for LTM for the UE 102. In one implementation, the base station 104 determines to prepare the additional cell(s) for LTM for the UE 102 because the at least one measurement report indicates that the additional cell(s) could be used by the base station 104 to communicate with the UE 102. The additional cell(s) can include the cell 124C and/or cell(s) other than the cells 124A, 124B and 124C. In some implementations, if the L3 measurement report(s) indicates that signal strength and/or quality of a particular cell of the additional cell(s) is above a respective predetermined threshold and/or is better than the cell 124A, the CU 172 determines to prepare the particular cell for LTM for the UE 102. In other implementations, if the LI measurement report(s) indicates that signal strength and/or quality of a particular cell of the additional cell(s) is above a first predetermined threshold and/or is better than the cell 124A, the DU 174 determines to prepare the particular cell for LTM for the UE 102. In one implementation, the respective predetermined threshold(s) for the additional cells can be different from the first predetermined threshold. In another implementation, the respective predetermined threshold(s) for the additional cell(s) can be the same as the first predetermined threshold. In some implementations, the respective predetermined thresholds for the additional cells can be the same or different. Alternatively, the base station 104 determines to prepare the additional cell(s) for the UE 102 regardless of whether a measurement report is received from the UE 102 or not.

[0089] In the case that the CU 172 determines to prepare the additional cell(s), the CU 172 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the DU 174 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390. In the case that the DU 174 determines to prepare the additional cell(s), the DU 174 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the CU 172 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390.

[0090] In some implementations, the CU 172 and DU 174 perform LTM preparation procedure(s) 2, . . . , N to prepare the cell(s) 2, . . . , N, respectively, similar to the procedure 390. The CU 172 can include the cell ID(s) 2, . . . , N in CU-to-DU message(s) 2, . . . , N in the LTM preparation procedure(s) 2, . . . , N, respectively, similar to the first CU-to-DU message. In the LTM preparation procedure(s) 2, . . . , N, the DU 174 generates LTM DU configuration(s) 2, . . . , N configuring the cell(s) 2, . . . , N and includes the LTM DU configuration(s) 2, . . ., N in DU-to-CU message(s) 2, .., N, respectively, as described for the LTM DU configuration 1. In the case that the DU 174 receives the CU-to-DU message(s) 2, . . . , N, the DU-to-CU message(s) 2, . . . , N responds to the CU-to-DU message(s) 2, . . . , N, respectively . “N” is an integer and larger than one. For example, “N” is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 14, 15 or 16. In another example, the maximum number of “N” is 4, 8, 16 or 32. Examples and implementations of the LTM DU configuration 1 can apply to the LTM DU configuration(s) 2, . . . , N.

[0091] In other implementations, the CU 172 and DU 174 performs a single LTM preparation procedure (i.e., the LTM preparation procedure 390) to prepare the cell(s) 1, 2, . . ., N. In such cases, the DU 174 includes the LTM DU configuration(s) 1, 2, . . ., N for the cell(s) 1, 2, . . . , N, respectively in the first DU-to-CU message. In the first DU-to-CU message, the DU 174 can include the cell ID(s) 1, 2, . . ., N respectively associated with the LTM DU configuration(s) 1, 2, . . . , N to indicate that the LTM DU configuration(s) 1, 2, . . . , N are configured for the cell ID(s) 1, 2, . . ., N, respectively. In the case that the CU 172 determines to perform the LTM preparation procedure 390, the CU 172 includes the cell ID(s) 1, 2, . . ., N in the first CU-to-DU message to request the DU 174 to prepare the cell(s) 1, 2, ..., N, respectively, for LTM.

[0092] After receiving the LTM DU configuration(s) 2, . . . , N from the DU 174, the CU 172 can include the LTM DU configuration(s) 2, . . ., N in the first container. In some implementations, the CU 172 can include the LTM DU configuration(s) 2, . . ., N in element(s) 2, . . . , N, respectively, and includes the element(s) 2, . . . , N in the first container. In some implementations, the CU 172 includes, in the RRC reconfiguration message, LTM ID(s) (i.e., ID(s) 2, . . . , N) for identifying the LTM DU configuration(s) 2, . . . , N, respectively. In some implementations, the CU 172 includes the ID(s) 2, . . N in the first container. For example, the CU 172 can include the ID(s) 2, . . ., N and LTM DU configuration(s) 2, . . . , N in the element(s) 2, . . . , N in the first addition or modification list.

[0093] In some implementations, the CU 172 assigns the ID(s) 2, . . . , N for the LTM DU configuration(s) 2, . . ., N, respectively. In other implementations, the CU 172 receives the ID(s) 2, . . ., N from the DU 174 in the first DU-to-CU message of the procedure 390. In yet other implementations, the CU 172 receives from the DU 174 the ID(s) 2, . . ., N in the DU- to-CU message(s) 2, . . . , N of the LTM preparation procedure(s) 2, . . . , N, respectively.

[0094] In some implementations, the CU 172 can perform an LTM ID assignment procedure with the DU 174 for each of the LTM DU configuration(s) 2, . . ., N, similar to the procedure 392. In other implementations, the CU 172 can include the ID(s) 2, . . ., N and the LTM DU configuration(s) 2, . . ., N in the third CU-to-DU message and indicate the association between the ID(s) 2, . . . , N and the LTM DU configuration(s) 2, . . . , N, respectively. Thus, the DU 174 can associate the LTM DU configuration(s) 2, . . . , N with the ID(s) 2, . . ., N, respectively. In yet other implementations, the CU 172 can include the cell ID(s) 2, . . . , N and the ID(s) 2, . . . , N in the third CU-to-DU message and indicate the association between the cell ID(s) 2, . . . , N and the ID(s) 2, . . . , N, respectively. Thus, the DU 174 can associate the LTM DU configuration(s) 2, . . . , N with the ID(s) 2, . . . , N, respectively, based on the association between the cell ID(s) 2, . . . , N and the ID(s) 2, . . . , N and the association between the cell ID(s) 2, . . . , N and the LTM DU configuration(s) 2, . . . , N, respectively. In other implementations, the CU 172 can include the ID(s) 2, . . ., N, the cell ID(s) 2, . . . , N and/or the LTM DU configuration(s) 2, . . . , N in the second CU-to-DU message as described above. Thus, the third CU-to-DU message can be omitted. In yet other implementations, the CU 172 can include the ID(s) 2, . . ., N in the first CU-to-DU message and indicate the ID(s) 2, . . . , N is/are respectively associated with the cell ID(s) 2, . . . , N. In one implementation, the DU 174 includes the ID(s) 2, . . ., N in the LTM DU configuration(s) 2, . . . , N. Thus, the CU 172 does not include the ID(s) 2, . . . , N in the RRC reconfiguration message, first container and/or element(s) 2, . . ., N.

[0095] In some alternative implementations, the DU 174 assigns the ID(s) 2, . . ., N. In some implementations, the DU 174 includes the ID(s) 2, . . ., N in the first DU-to-CU message of the procedure 390. In yet other implementations, the DU 174 includes the ID(s) 2, . . ., N in the DU-to-CU message(s) 2, . . . , N of the LTM preparation procedure(s) 2, . . . ,N. The CU 172 can include the ID(s) 2, . . N in the RRC reconfiguration message. In other implementations, the DU 174 includes the ID(s) 2, . . N in the LTM DU configuration(s) 2, . . N. Thus, the CU 172 does not include an ID (e.g., LTM ID) identifying each of the LTM DU configuration(s) 2, . . ., N in the RRC reconfiguration message, first container and/or element 1.

[0096] In some alternative implementations, the CU 172 can generate a second container including the LTM DU configuration(s) 2, . . . , N or element(s) 2, . . . , N instead of using the first container. The CU 172 then transmits an additional RRC reconfiguration message including the second container to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits an additional RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some implementations, the second container is or includes a second addition or modification list (e.g., Itm- ConfigToAddModList field, LTM-ConfigToAddModList IE, Itm- CandidateConfigToAddModList field, or LTM-CandidateConfigToAddModList ^E), and each of the element(s) 2, . . ., N can be an addition or modification IE (e.g., Itm-ConfigToAddMod field, LTM-ConfigToAddMod IE, Itm-CandidateConfigToAddMod field, or LTM- CandidateConfigToAddMod IE). When the UE 102 receives the second addition or modification list, the UE 102 can store the second addition or modification list together with the first addition or modification list, e.g., in a variable in its random access memory (RAM).

[0097] In some implementations, the DU 174 includes cell ID(s) 2, . . . , N in the LTM DU configuration(s) 2, . . ., N to identify the cell(s) 2, . . ., N, respectively. In one implementation, each of the cell ID(s) 2, . . . , N is a PCI. In some further implementations, the LTM DU configuration(s) 2, . . . , N includes cell index(es) 2 , . . . , N indexing the cell ID(s) 2, . . . , N or the cell(s) 2, . . . , N, respectively. In the case that the CU 172 prepares the cell(s) 2, . . . , N for LTM in the procedure 390, the CU 172 can set the cell index(es) 2, . . ., N to different value(s) and include the cell index(es) 2, . . ., N in the first CU-to CU-to-DU message of the event 308. In the case that the CU 172 prepares the cell(s) 2, . . . , N in the additional LTM preparation procedure(s), the CU 172 can set the cell index(es) 2, . . ., N to different values and include the cell index(es) 2, . . . , N in CU-to-DU message(s) of the additional LTM preparation procedure(s). The CU 172 sets the cell index(es) 1, . . ., N to different values. In some implementations, the cell ID(s) 1, . . ., N in the LTM DU configuration(s) 1, . . ., N are different from the cell ID(s) 1, . . ., N in the CU-to-DU message(s) described above. [0098] In some implementations, each of the LTM DU configuration(s) 1, . . N includes physical configuration parameters, MAC configuration parameters, RLC configuration parameters and/or LI measurement configuration(s). In some implementations, each of the LTM DU configuration(s) 1, . . ., N can be a CellGroupConfig IE as defined in 3GPP specification 38.331. In other implementations, each of the LTM DU configuration(s) 1, . . . , N include configuration parameters included in a CellGroupConfig IE as defined in 3 GPP specification 38.331. In some further implementations, the plurality of configuration parameters in each of the LTM DU configuration(s) include a particular special cell configuration (e.g., SpCellConfig E) and/or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration(s) 1, . . ., N are CellGroupConfig IE(s) defined in 3GPP specification 38.331. In other implementations, the LTM DU configuration(s) 1, . . ., N include configuration parameters in the CellGroupConfig IE.

[0099] In some implementations, the CU 172 can include one or more additional LTM CU configurations in at least one of the element(s) 2, . . . , N, the first container or the second container. Each of the additional LTM CU configurations are associated with a particular LTM DU configuration of the LTM DU configuration(s) 2, . . . , N. Examples and implementations of the additional LTM CU configurations are similar to the LTM CU configuration 1.

[0100] In some implementations, the CU 172 determines to release the LTM DU configuration M of the LTM DU configuration(s) 1, . . . , N (or the element M of the element(s) 1, . . . , M). 1 < M < N. In response to the determination, the CU 172 transmits an RRC reconfiguration message to the UE 102 via the DU 174 to indicate the UE 102 to release the LTM DU configuration M or element M. In one implementation, the CU 172 generates a release list including the ID (i.e., LTM ID) M for releasing the LTM DU configuration M or element M and includes the release list in the RRC reconfiguration message. In response to the RRC reconfiguration message, the UE 102 releases the LTM DU configuration M or element M and transmits an RRC reconfiguration complete message to the CU 172 via the DU 174. In response to the determination, the CU 172 transmits a CU-to-DU message to the DU 174 to indicate the DU 174 to release the LTM DU configuration M. To indicate the DU 174 to release the LTM DU configuration M, the CU 172 can include the cell ID M or the ID (i.e., LTM ID) M in a release indication (e.g., a field or IE) in the CU-to-DU message. In response, the DU 174 releases the LTM DU configuration M and transmits a DU-to-CU message to the CU 172. In some implementations, the CU-to-DU message and DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0101] In other implementations, the DU 174 determines to release the LTM DU configuration K. In response to the determination, the DU 174 transmits a DU-to-CU message to the CU 172 to release the LTM DU configuration K. To indicate the LTM DU configuration K is released, the DU 174 can include the cell ID K or the ID (i.e., LTM ID) K in a release indication (e.g., a field or IE) in the DU-to-CU message. 1 < K < N. After (e.g., in response to) receiving the DU-to-CU message, the CU 172 generates a release list including the ID (i.e., LTM ID) K to release the LTM DU configuration K or element K and transmits an RRC reconfiguration message including the release list to the UE 102 via the DU 174. In response, the UE 102 releases the LTM DU configuration K or element K and transmits an RRC reconfiguration complete message to the UE 102 via the DU 174. The CU 172 can transmit a CU-to-DU message to the DU 174 in response to the DU-to-CU message. In some implementations, the DU-to-CU message and CU-to-DU message are a UE Context Modification Required message and a UE Context Modification Confirm message, respectively.

[0102] After receiving the RRC reconfiguration in the event 318 or transmitting the RRC reconfiguration complete message in the event 320, the UE 102 transmits 324 at least one measurement report to the DU 174, similar to the event 304. In some implementations, the DU 174 may transmit 326 a DU-to-CU message including the at least one measurement report to the CU 172, similar to the event 306. In other implementations, the DU 174 does not transmit the at least one measurement report to the CU 172. In some implementations, the at least one measurement report of the event 324 include LI measurement report(s) or L3 measurement repot(s), as described for the event 304. In some implementations, the UE 102 transmits 324 the at least one measurement report on PUCCH(s) and/or PUSCH(s) to the DU 174, similar to the event 304. In other implementations, the UE 102 transmits 324 at least one MAC CE including the at least one measurement report to the DU 174, similar to the event 304. In some implementations, the UE 102 does not transmit the LI measurement report(s) in format of RRC message(s) to the DU 174.

[0103] In some implementations, the UE 102 transmits 324 the at least one measurement report to the DU 174 in accordance with at least one measurement configuration. The at least one measurement configuration configures the UE 102 to perform measurements and report measurement results. The CU 172 transmits the at least one measurement configuration to the UE 102 via the DU 174. For example, the CU 172 can transmit one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration to the UE 102 via the DU 174 in the event 302 and/or 316 and/or after the event 306 or 316. The one or more RRC messages may or may not include the RRC reconfiguration message of the event 316. In accordance with the at least one measurement configuration, the UE 102 performs measurements on one or more reference signals. The one or more reference signals can include one or more SSBs and/or one or more CSI-RSs. The UE 102 obtains the at least one LI measurement result and/or at least one L3 measurement result from the measurements and includes the at least one LI measurement result and/or at least one L3 measurement result in the at least measurement report of the event 324. The DU 174 transmits the one or more reference signals on the cell 124A, the cell 1 and/or the cell(s) 2, . . ., N. The one or more reference signals can be CSI-RS(s) or SSB(s).

[0104] In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)), as described for the event 304. In other implementations, the at least one measurement configuration includes or is LI measurement configuration(s), as described above. In yet other implementations, the LI measurement configuration(s) can be CSI-MeasConfig IE(s) defined in 3GPP specification 38.331 V18.0.0 and/or later versions. The LI measurement configuration(s) can include RS resource configuration(s) and/or report configuration(s). The UE 102 transmits 324 the LI measurement report(s) on UL resources (e.g., PUCCH resources or PUSCH resources) to the DU 174 in accordance with the report configuration(s). The DU 174 receives the LI measurement report(s) on the UL resources in accordance with the report configuration(s). In some implementations, the report configuration(s) are or are similar to CSI-ReportConfig IE(s). In other implementations, each of the report configuration(s) is a new RRC IE. In some implementations, (each of) the report configuration(s) configures periodically reporting and/or event-triggered reporting of the LI measurement result(s).

[0105] In some implementations, the LI measurement report(s) is/are CSI report(s). In other implementations, the LI measurement report(s) is/are MAC CE(s). In some implementations, each of the measurement report(s) includes one or more RS resource indicators and/or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) and/or the report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and/or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values can include one or more Ll-RSRP values and/or one or more Ll-SINR values.

[0106] In yet other implementations, the at least one measurement configuration includes new-type measurement configuration(s) (e.g., LTM measurement configuration(s)). The new-type measurement configuration can be newly defined in a 3GPP specification vl 8.0.0 and/or later versions. In some implementations, the new-type measurement configuration(s) includes reference signal resource configuration(s) configuring resources where the DU 174 transmits reference signal(s). For example, the reference signal resource configuration(s) include CSI-RS(s) and/or SSB(s). In one implementation, the reference signal resource configuration(s) is/are CSI-ResourceConfig IE(s). In another implementation, the new-type measurement configuration(s) include measurement report configuration(s), as described above. The UE 102 transmits the measurement report(s) on PUCCH(s) or MAC CE(s) to the DU 174 in accordance with the measurement report configuration(s). The DU 174 receives the measurement report(s) on PUCCH(s) or MAC CE(s) in accordance with the measurement report configuration(s). In such cases, the measurement report(s) can be LI measurement report(s) or new-type measurement report(s) (e.g., LTM measurement report(s)). In some implementations, the new-type measurement configuration includes configuration parameters newly defined in a 3GPP specification vl 8.0.0 and/or later versions.

[0107] After (e.g., in response to) receiving the measurement report(s) in the event 324, the DU 174 generates a first LTM command to activate the LTM DU configuration 1 (i.e., the first LTM command commands the UE 102 to apply the LTM DU configuration 1 or to perform a serving cell change to the cell 1). The DU 174 then transmits 330 the first LTM command to the UE 102. In some implementations, the DU 174 transmits the first LTM command on the cell 124A to the UE 102. In other implementations, the DU 174 transmits the first LTM command on the cell 124D to the UE 102. In some implementations, the DU 174 can include the ID 1 in the first LTM command to indicate the LTM DU configuration 1 or element 1, and the UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 in accordance with the ID 1. [0108] In other implementations, the DU 174 can include the cell index 1 indexing the cell ID 1 in the first LTM command. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1, based on the cell index 1. Before receiving the first LTM command, the UE 102 retrieves the cell index 1 from the LTM DU configuration 1 or element 1, and establishes an association 1 between the cell index 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell index 1, before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell index 1 and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell index(es) 2, . . . , N from the LTM DU configuration(s) or element(s) 2, . . . , N and establishes association(s) 2, . . . , N between the cell index(es) 2, . . . , N and the LTM DU configuration(s) or element(s) 2, . . . , N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, . . ., N to obtain the cell index(es) 2, . . . , N, before receiving the first LTM command.

[0109] In yet other implementations, the DU 174 includes cell ID 1 in the first LTM command, where the cell ID 1 identifies the cell 1. In some implementations, the cell ID 1 included in the first LTM command is the same as the cell ID 1 included in the first CU-to- DU message. In other implementations, the DU 174 determines the cell ID 1 (e.g., PCI) included in the first LTM command from the cell ID 1 (e.g., CGI) received in the first CU-to- DU message. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1, based on the cell ID 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID 1 from the LTM DU configuration 1 or element 1, and establishes an association 1 between the cell ID 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell ID 1, before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell ID 1 (received in the first LTM command) and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID(es) 2, . . . , N from the LTM DU configuration(s) or element(s) 2, . . . , N and establishes association(s) 2, . . . , N between the cell ID(es) 2, . . . , N and the LTM DU configuration(s) or element(s) 2, . . ., N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, . . . , N to obtain the cell ID(es) 2, . . . , N, before receiving the first LTM command. In some implementations, the DU 174 has a mapping table to store mappings between the PCI(s) 1, . . . , N and the CGI(s) 1, . . . , N for the cell(s) 1, N, respectively.

[0110] In yet other implementations, the DU 174 can include a bit map in the first LTM command to activate the LTM DU configuration 1, instead of the ID 1 or cell index 1. The number of bits in the bit map is larger than or equal to “N”. In one implementation, bit 1, . . . , N corresponds to the cell index(es) 1, . . ., N, the ID(s) 1, . . ., N, the LTM DU configuration(s) 1, . . ., N or the element(s) 1, . . ., N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 1) in the bit map to a first value to indicate the cell index 1, the ID 1, the LTM DU configuration 1 or the element 1. Thus, the UE 102 can determine the cell index 1, the ID 1, LTM DU configuration 1, or element 1 in accordance with the bit 1 set to the first value in the bit map. In another implementation, bit 0, . . . , N-l corresponds to the cell index(es) 1, . . . , N, the ID(s) 1, . . . , N, the LTM DU configuration(s) 1, . . . , N or the element (s) 1, . . . , N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 0) in the bit map to a first value to indicate the cell index 1, the ID 1 the LTM DU configuration 1 or the element 1. Thus, the UE 102 can determine the cell index 1, the ID 1 LTM DU configuration 1 or element 1 in accordance with the bit 0 set to the first value in the bit map. In such implementations, the DU 174 sets the remaining bits in the bit map to a second value to indicate that the rest of the LTM DU configuration(s) 1, . . . , N is/are not activated. In some implementations, the first value is one and the second value is zero. In other implementations, the first value is zero and the second value is one. Generally, if the DU 174 determines to activate the LTM DU configuration L or change a serving cell to the cell L for the UE 102, the DU 174 can set the corresponding bit (e.g., bit L or bit Z-7) in the bit map to the first value and set the remaining bits to the second value, where 1 <L < N. In some implementations, the DU 174 sets at most one bit in the bit map to the first value.

[OHl] After determining or identifying the LTM DU configuration 1 or element 1, the UE 102 then applies the LTM DU configuration 1 and/or LTM CU configuration, after (e.g., in response to) receiving the first LTM command.

[0112] In some implementations, the at least one measurement report (e.g., LI measurement report(s) or new-type measurement report(s)) of the event 324 includes at least one measurement result for the first cell, TRP(s) of the first cell or reference signal(s) transmitted on the first cell. The reference signal(s) can be CSI-RS(s) or SSB(s). The DU 174 determines to activate the LTM DU configuration 1 or transmit the first LTM command, based on the at least one measurement result. In some implementations, the DU 174 determines to activate the LTM DU configuration 1 because, when or if the at least one measurement result is above a second predetermined threshold. In some implementations, the at least one measurement result includes Ll-RSRP value(s), Ll-RSRQ value(s) and/or Ll-SINR value(s). In other implementations, the at least one measurement result includes RSRP value(s), RSRQ value(s) and/or SINR value(s) for the new-type measurement report(s). In some implementations, the second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is larger than the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell is suitable for communication with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This indicates that the first cell is suitable for communication with the UE 102. Thus, the DU 174 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold for the UE 102.

[0113] In some implementations, the at least one measurement report (e.g., L3 measurement report(s)) of the events 324 and 326 includes at least one measurement result for the first cell. The CU 172 determines to activate the LTM DU configuration 1 or transmit the first LTM command, because the at least one measurement result indicates that signal strength or quality of the first cell is above a second predetermined threshold. The second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is larger than the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell is suitable for communication with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This also indicates that the first cell is suitable for communication with the UE 102. Thus, the CU 172 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold. In response to the determination, the CU 172 transmits 328 a fourth CU-to-DU message to the DU 174 to activate the LTM DU configuration 1 or trigger a serving cell change to the cell 1 for the UE 102. In some implementations, the CU 172 includes the ID 1 in the fourth CU-to-DU message. In other implementations, the CU 172 includes the cell index 1 in the fourth CU-to- DU message. In response to the fourth CU-to-DU message, the DU 174 transmits 330 the first LTM command to the UE 102 and optionally transmits a fourth DU-to-CU message to the CU 172. In some implementations, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the cell index 1. In other implementations, the CU 172 can include the cell ID 1 in the fourth CU-to-DU message. Thus, the DU 174 determines to activate the LTM DU configuration 1 in accordance with the cell ID 1. In yet other implementations, the CU 172 can include the ID 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the ID 1. In some implementations, the fourth CU-to-DU message and fourth DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In other implementations, the fourth CU-to-DU message and/or fourth DU-to- CU message are new interface messages, e.g., Fl application protocol (F1AP) messages defined in 3GPP specification 38.473 vl8.0.0 and/or later versions.

[0114] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 330, the DU 174 can transmit 329 to the CU 172 a DU-to- CU message indicating LTM (being) executed. In some implementations, the DU-to-CU message is an LTM Cell Change Notification message. In some implementations, the DU 174 includes the cell ID 1 or the ID 1 (i.e., LTM ID) in the DU-to-CU message 329 to indicate that the DU 174 is to activate the LTM DU configuration 1 or trigger a fast serving cell change (i.e., an LTM serving cell change or an LTM cell switch). The DU can transmit the DU-to-CU message 329 to the CU 172 before or after transmitting the LTM command 330.

[0115] In some implementations, the first LTM command is a MAC CE included in a MAC PDU that the UE 102 receives from the DU 174 in the event 330. The MAC CE can be a new MAC CE defined in 3GPP specification 38.321 vl8.0.0 and/or later versions. In one implementation, the DU 174 includes a subheader identifying the new MAC CE in the MAC PDU and the UE 102 identifies the new MAC CE in the MAC PDU in accordance with the subheader. The subheader can include a logical channel ID or extended logical channel ID defined in a 3GPP specification to identify the new MAC CE. For example, the logical channel ID or extended logical channel ID are newly defined in 3GPP specification 38.321 vl 8.0.0 and/or later versions. In other implementations, the first LTM command is a DCI that the UE 102 receives on a PDCCH from the DU 174 in the event 330. The DU 174 generates a cyclic redundancy check (CRC) for the DCI, scrambles the CRC with a first C- RNTI of the UE 102, and transmits the DCI and scrambled CRC on the PDCCH in the event 330. In one implementation, a format of the DCI can be an existing DCI format defined in a 3GPP specification (e.g., 38.212). In another implementation, the format of the DCI can be a new DCI format defined in a 3GPP specification (e.g., 38.212 V18.0.0 or later versions).

[0116] In some implementations, the DU 174 does not perform security protection (e.g., integrity protection and/or encryption) on the first LTM command. This speeds up processing the first LTM command in the UE 102 because the UE 102 does not perform security check (e.g., decryption and/or integrity check) on the first LTM command.

[0117] In some implementations, after receiving the first LTM command, the UE 102 may transmit 331 an acknowledgement to the DU 174 on the cell 124A or cell 124D to indicate that the UE 102 receives the first LTM command. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE defined in 3GPP specification 38.321 vl7.2.0 and/or later versions. In another example, the MAC CE is a new MAC CE defined in 3GPP specification 38.321 vl8.0.0 and/or later versions. In yet other implementations, the acknowledgement is a PUCCH transmission.

[0118] In some implementations, the CU 172 transmits 316 the RRC reconfiguration message in response to the L3 measurement report 306 for the first cell. To configure the UE 102 to transmit the L3 measurement report 306, the CU 172 can transmit a first RRC reconfiguration message including the L3 measurement configuration (e.g., MeasConfig IE) to the UE 102 before the event 306. In some implementations, the DU 174 transmits 330 the first LTM command in response to the LI measurement report(s) 324 for the first cell. To configure the UE 102 to transmit the LI or new-type measurement report(s) 324, the CU 172 can transmit a second RRC reconfiguration message including the LI or new-type measurement configuration(s) to the UE 102. In some implementations, the first and second RRC reconfiguration messages can be the same message (i.e., the same instance). In other implementations, the first and second RRC reconfiguration messages are different messages. In some implementations, the second RRC reconfiguration message is the RRC reconfiguration message of the event 316. In other implementations, the second RRC reconfiguration message is different from the RRC reconfiguration message of the event 316.

[0119] After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 the first cell. The UE 102 identifies the LTM DU configuration 1 in accordance with the ID 1, the cell ID 1 or the cell index 1 received in the first LTM command and applies the LTM DU configuration 1 to communicate with the DU 174 on the first cell. In some implementations, the UE 102 disconnects from the cell 124A, after (e.g., in response to) receiving the first LTM command or after transmitting 331 the acknowledgement. In some implementations, the UE 102 stops communicating on the cell 124A after (e.g., in response to) receiving 330 the first LTM command or transmitting 331 the acknowledgement. In some implementations, the UE 102 accesses the first cell by performing a random access procedure on the first cell with the DU 174, in response to receiving the first LTM command. In other implementations, the UE 102 skips a random access procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174, after (e.g., in response to) receiving the first LTM command.

[0120] In some implementations, the DU 174 configures the access of the UE 102 to the first cell, including whether or not the UE 102 performs a random access procedure, in the LTM DU configuration 1. When receiving the first LTM command, the UE 102 determines whether to perform a random access procedure on the first cell in accordance with the LTM DU configuration 1. If the LTM DU configuration 1 configures the UE 102 to perform a random access procedure, the UE 102 performs a random access procedure on the first cell in the event 332, in order to connect to the first cell. For example, the LTM DU configuration 1 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) to configure that the UE 102 performs a random access procedure when the UE 102 receivesan LTM command for the first cell. In other implementations, in the LTM DU configuration 1, the DU 174 configures the UE 102 to skip the random access procedure for an LTM serving cell change to the first cell. In such cases, after receiving the first LTM command, the UE 102 skips the random access procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174 in the event 332. In some implementations, the DU 174 excludes a reconfiguration with sync configuration in the LTM DU configuration 1 to configure the UE 102 skipping a random access procedure for an LTM serving cell change to the first cell. [0121] In other implementations, the LTM DU configuration 1 includes the reconfiguration with sync configuration or the random access configuration. In such cases, the DU 174 configures whether the UE 102 performs a random access procedure on the first cell in an LTM command (e.g., the first LTM command). Thus, the UE 102 determines whether to perform the random access procedure on the first cell in the event 332 in accordance with the first LTM command. In some implementations, the DU 174 includes, in the first LTM command, an indication (e.g., a field) indicating skipping a random access procedure. In response to the indication or the first LTM command including the indication, the UE 102 skips a random access procedure and directly transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to access the first cell. In other implementations, the DU 174 excludes the indication in the first LTM command to configure the UE 102 to perform a random access procedure. In response to the first LTM command excluding the indication, the UE 102 performs a random access procedure on the first cell to access the first cell. In some other implementations, the DU 174 includes a timing advance value in the first LTM command to indicate skipping a random access procedure. In response to receiving the timing advance value or the first LTM command including the timing advance value, the UE 102 skips a random access procedure and transmits the first transmission on the first cell to access the first cell, using the timing advance value. In yet other implementations, the DU 174 excludes, in the first LTM command, a timing advance value to configure the UE 102 to perform a random access procedure. In response to the first LTM command excluding a timing advance command, the UE 102 performs a random access procedure on the first cell to access the first cell.

[0122] In some implementations, the random access procedure is a four-step random access procedure. In other implementations, the random access procedure is a two-step random access procedure. In some implementations, the random access procedure is a contention-free random access procedure. In other implementations, the random access procedure is a contention-based random access procedure. In cases where the random access procedure is a four-step random access procedure, the UE 102 transmits a Message 3 including a UE identity to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., a Message 4) to the UE 102 in response to the Message 3. In cases where the random access procedure is a two-step random access procedure, the UE 102 transmits a Message A including the UE identity to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., Message B) to the UE 102 in response to the Message A. In some implementations, when the UE 102 receives the contention resolution message from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell). In some implementations, the LTM DU configuration 1 includes a second C-RNTI and the UE identity is the second C-RNTI of the UE 102. In such implementations, the contention resolution message is a PDCCH transmission addressed to the second C-RNTI. In other implementations, the LTM DU configuration 1 does not include a C-RNTI, the UE identity is the first C-RNTI. In such implementations, the contention resolution message is a PDCCH transmission addressed to the first C-RNTI. In some implementations, the DU 174 includes the second C-RNTI in the reconfiguration with sync configuration. In other implementations, the DU 174 includes the second C-RNTI in the LTM cell switch information.

[0123] In cases where the LTM DU configuration 1 includes a dedicated random access preamble, the random access procedure is a contention free random access procedure. In such cases, the UE 102 transmits the dedicated random access preamble to the DU 174 via the first cell. When the UE 102 receives a random access response including an ID of the dedicated random access preamble from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell).

[0124] If the DU 174 configures the UE 102 to perform a random access procedure on the first cell as described above, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives Message 3, Message A, or the dedicated preamble in the random access procedure. If the DU 174 configures the UE 102 to skip a random access procedure, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives the first transmission.

[0125] In some implementations, the UE 102 transmits the first transmission (e.g., the PUSCH transmission) on the first cell using a UL grant. In some implementations, the first LTM command includes the UL grant. In other implementations, when the UE 102 performs an LTM serving cell change to the first cell in response to the first LTM command, the UE 102 receives a first DCI including the UL grant on a PDCCH on the first cell. In some implementations, the UE 102 attempts to receive the first DCI or the UL grant by monitoring one or more PDCCHs on the first cell in accordance with the LTM DU configuration 1, when the UE 102 switches to the first cell in response to the first LTM command. While monitoring one or more PDCCHs on the first cell, the UE 102 receives the first DCI and a CRC of the first DCI on the PDCCH. In the case that the LTM DU configuration 1 includes the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the second C-RNTI. In the case that the LTM DU configuration 1 does not include the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the first C-RNTI.

[0126] In some implementations, the CU 172 transmits at least one first TCI state configuration (e.g., LTM TCI state configuration) for the first cell to the UE 102 via the DU 174. In some implementations, each of the first TCI state configuration(s) configures a TCI state for the UE 102 to transmit and/or receive data and/or control signal on the first cell. Each TCI state associates or includes one or two DL RSs with a corresponding QCL type and the DL RS(s) can be associated with a particular cell of the cell(s) 1, . . . , N. The DL RS(s) include SSB(s) and/or tracking reference signal(s) (TRS(s)). In some implementations, the CU 172 receives a DU-to-CU message including the first TCI state configuration(s) from the DU 174 and transmits an RRC message including the first TCI state configuration(s) to the UE 102 via the DU 174. In further implementations, the DU 174 includes the first TCI state configuration(s) in a serving DU configuration (e.g., CellGroupConfig ^E) and includes the serving DU configuration in the DU-to-CU message. In some implementations, the DU-to- CU message is the DU-to-CU message 310 or the DU-to-CU message 314. In other implementations, the DU-to-CU message is a message different from the messages 310, 314. For example, the DU-to-CU message is a UE Context Modification Response message or a UE Context Modification Required message.

[0127] In some implementations, the DU 174 includes the LTM DU configuration 1 in a first interface protocol lE/field in the DU-to-CU message 310, and includes the serving DU configuration in a second interface protocol lE/field in the DU-to-CU message 314. In some implementations, the events 312 (optional) and/or 314 (optional) are collectively referred to in Fig. 3 as an LTM TCI state configuration procedure 392.

[0128] In some implementations, the CU 172 includes the serving DU configuration in the RRC message. In some implementations, the CU 172 refrains from including the serving DU configuration in a container for LTM (e.g., the first container). In some implementations, the CU 172 includes the LTM ID 1 and the first LTM TCI state configuration(s) in an element for LTM, an addition or modification list for LTM, or a container, and the CU 172 includes the element, addition or modification list for LTM, or the container in the RRC message, similar to the element 1, the first addition or modification list, or the first container respectively. In some implementations, the RRC message is the RRC reconfiguration message 316, 318. In such cases, the CU 172 may include the first LTM TCI state configuration(s) in the element 1. In other implementations, the RRC reconfiguration is another RRC reconfiguration message (not shown in Fig. 3). In some implementations, the DU 174 also includes the first TCI state configuration(s) in the LTM DU configuration 1. In other implementations, the DU 174 refrains from including the first TCI state configuration(s) in the LTM DU configuration 1.

[0129] In some implementations, the first interface protocol lE/field is a first F1AP lE/field and the second interface protocol lE/field is a second Fl AP lE/field. In some implementations, one of the first F1AP lE/field and the second F1AP lE/field is a F1AP CellGroupConfig lE/field and the other is not the F1AP CellGroupConfig lE/field. In some implementations, the DU 174 includes the first Fl AP lE/field in a DU to CU RRC Information IE in the message 314 and includes the second F1AP lE/field in the DU to CU RRC Information IE in the DU-to-CU message. In other implementations, neither the first F1AP lE/field nor the second F1AP IE is a F1AP CellGroupConfig lE/field. In other implementations, the second Fl AP lE/field is the DU to CU RRC Information IE and the first F1AP lE/field is a new IE specific for including an LTM DU configuration.

[0130] In some implementations, the DU 174 transmits 325 at least one first LTM TCI states Activation/Deactivation command to the UE 102 to activate some of the first LTM TCI state configuration(s). The UE 102 activates the some of the first LTM TCI state configuration(s) in response to the first LTM TCI States Activation/Deactivation command(s). In some implementations, the DU 174 indicates deactivation of some of the first LTM TCI state configuration(s) in some of the first LTM TCI States Activation/Deactivation command(s). In some implementations, the DU 174 transmits one or more DL RSs on the candidate cell(s) using the activated LTM TCI state configuration(s) or the first LTM TCI state configuration(s). The DL RS(s) may include one or more SSBs and/or one or more TRSs. In some implementations, the UE 102 receives the DL RS(s) using the activated LTM TCI state configuration(s). The UE 102 may obtain LI measurement results from the received DL RS(s) and transmits the LI measurement results to the DU 174. The UE 102 may obtain L3 measurement results from the received DL RS(s) and transmits the L3 measurement results to the CU 172 via the DU 174. In some implementations, the DU 174 refrains from using the first LTM TCI state configured on(s) to communicate with the UE 102 on the serving cell(s). In some implementations, the UE 102 refrains from using the first LTM TCI state configured on(s) to communicate with the DU 174 on the serving cell(s).

[0131] In some implementations, each of the first LTM TCI States Activation/Deactivation command(s) is a MAC CE (e.g., Candidate Cell TCI States Activation/Deactivation command). In some implementations, the DU 174 includes the LTM ID 1 in each of the first LTM TCI States Activation/Deactivation command(s) to identify the first LTM TCI state configured on(s). In other implementations, the DU 174 includes a candidate cell index (e.g., the cell index 1) in each of the first LTM TCI States Activation/Deactivation command(s) to identify the first LTM TCI state configuration(s). In such cases, the candidate cell index is different from the LTM ID 1. In some implementations, each of the first LTM TCI state configured on(s) may include the candidate cell index. Alternatively, the CU 172 includes the candidate cell index in the RRC message including the first LTM TCI state configuration(s). For example, the CU 172 includes the candidate cell index in the element 1. In some alternative implementations, the UE 102 and the DU 174 determines the candidate cell index from the PCI of the first cell. In such cases, the base station 104 does not transmit the candidate cell index to the UE 102.

[0132] In some implementations, after (e.g., in response to) receiving the first LTM command or accessing 332 the first cell, the UE 102 performs DL reception (e.g., monitors one or more PDCCHs) or UL transmission on the first cell using some or all of the first LTM TCI state configuration(s) in the event 336. In other implementations, after (e.g., in response to) receiving the first LTM command or accessing 332 the first cell, the UE 102 performs DL reception (e.g., monitors one or more PDCCHs) or UL transmission on the first cell without using the first LTM TCI state configuration(s) in the event 336.

[0133] In some implementations, each of the first LTM TCI state configuration(s) includes a TCI state ID identifying the corresponding TCI state configuration. For example, the first LTM TCI state configuration(s) includes LTM TCI state configuration(s) 1, ..., L, where L is a positive integer larger than zero. The LTM TCI state configuration(s) 1, . . . , L include TCI state ID(s) 1, . . ., L identifying the LTM TCI state configuration(s) 1, . . ., L, respectively. In some implementations, the DU 174 includes the TCI state ID 1 in the first LTM command to indicate to the UE 102 to activate the LTM TCI state configuration 1 to communicate on the first cell. The UE 102 activates the LTM TCI state configuration 1 in response to receiving the TCI state ID 1 in the first LTM command. In some implementations, the UE 102 accesses 332 on the first cell using the (activated) LTM TCI state configuration 1. In other implementations, the UE 102 accesses 332 on the first cell without using the first LTM TCI state configuration(s). In some implementations, the UE 102 communicates 336 on the first cell using the (activated) LTM TCI state configuration 1. In some implementations, the DU 174 communicates 336 with the UE 102 on the first cell, using the activated LTM TCI state configurations 1.

[0134] In some implementations, in the events 332 and/or 336, the UE 102 monitors one or more PDCCHs, receives one or more DL RSs, receives one or more PDSCH transmissions, and/or transmits the first transmission and/or one or more additional transmissions, using the LTM TCI state configuration 1. In some implementations, the DU 174 detects 332 that the UE 102 accesses the first cell and/or communicates 336 with the UE 102 on the first cell, based on the LTM TCI state configuration 1. In some implementations, the DU 174 receives 332 the first transmission and/or 336 the additional transmission(s) from the UE 102 on the first cell, based on the TCI state configuration 1. In other implementations, in the events 332 and/or 336, the DU 174 transmits one or more PDCCHs, one or more PDSCH transmissions, and/or one or more DL RSs, based on the LTM TCI state configuration 1.

[0135] In some implementations, the DU 174 includes the TCI state ID 2 in the first LTM command to indicate to the UE 102 to activate the TCI state configuration 2 to communicate on the first cell, in addition to the TCI state ID 1. The UE 102 activates the LTM TCI state configuration 1 in response to receiving the TCI state ID 1 in the first LTM command, and activates the LTM TCI state configuration 2 in response to receiving the TCI state ID 2 in the first LTM command. After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 and/or communicates 336 on the first cell using the activated LTM TCI state configurations 1 and 2. After (e.g., in response to) transmitting the first LTM command or receiving the acknowledgement 331, the DU 174 communicates with the UE 102 on the first cell in the events 332 and/or 336, using the activated LTM TCI state configurations 1 and 2.

[0136] In some implementations, after applying one or more TCI state configurations (e.g., the TCI state configuration(s) 1 and/or 2) indicated in an LTM command (e.g., the first LTM command), the UE 102 takes time (e.g., beam application time or cell switch delay) to acquire TCI state(s) configured in the TCI state configuration(s) (e.g., synchronize and/or receive DL RS(s) configured in the TCI state configuration(s)). The time to acquire TCI state(s) is considered as a switch delay. In such cases, the DU 174 takes the switch delay into account when communicating with the UE 102 on the first cell in the events 332 and/or 336. For example, after transmitting the first LTM command or receiving the acknowledgement 331, the DU 174 starts to communicate with the UE 102 on the first cell in the events 332 and/or 336 after the switch delay, using the activated LTM TCI state configuration(s) 1 and/or 2.

[0137] In some implementations, the UE 102 monitors one or more PDCCHs, receives one or more DL RSs, and/or receives one or more PDSCH transmissions from the DU 174 on the first cell using the LTM TCI state configuration 1 and transmits the first transmission and/or one or more additional transmissions on the first cell to the DU 174 using the LTM TCI state configuration 2. In such implementations, the DU 174 transmits one or more control signals one or more PDCCHs, one or more DL RSs, and/or one or more PDSCH transmissions to the UE 102 on the first cell using the LTM TCI state configuration 1 and receives the first transmission and/or one or more additional transmissions on the first cell from the UE 102 using the LTM TCI state configuration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DCI.

[0138] In other implementations, the UE 102 monitors one or more PDCCHs from the DU 174 on the first cell using the LTM TCI state configuration 1 and receives one or more PDSCH transmissions from the DU 174 on the first cell using the LTM TCI state configuration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DCI. In such implementations, the DU 174 transmits one or more control signals on one or more PDCCHs on the first cell to the UE 102 using the LTM TCI state configuration 1 and transmits one or more PDSCH transmissions to the UE 102 on the first cell using the LTM TCI state configuration 2. In some implementations, the UE 102 transmits the first transmission and/or one or more additional transmissions to the DU 174 on the first cell, using the LTM TCI state configuration 1. In such implementations, the DU 174 receives the first transmission and/or one or more additional transmissions from the UE 102 on the first cell, using the LTM TCI state configuration 1. In other implementations, the UE 102 may transmit the first transmission and/or one or more additional transmissions to the DU 174 on the first cell, using the LTM TCI state configuration 2. In such implementations, the DU 174 receives the first transmission and/or one or more additional transmissions from the UE 102 on the first cell, using the LTM TCI state configuration 2.

[0139] In yet other implementations, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and the TCI state configuration 2, and transmits the first transmission and/or one or more additional transmissions on the first cell using one of the TCI state configuration 1 and the TCI state configuration 2. In such implementations, the DU 174 transmits one or more control signals on one or more PDCCHs receives the first transmission and/or one or more additional transmissions from the UE 102 on the first cell, using the LTM TCI state configuration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DCI.

[0140] In some implementations, the CU 172 receives a CN-to-BS message including a UE capability IE of the UE 102 from a CN (e.g., the CN 110 or the AMF 164), e.g., during the event 302. For example, the CN-to-BS message is a NG application protocol (NGAP) message. In other implementations, the CU 172 receives a BS-to-BS message including the UE capability IE from another base station (e.g., the base station 106), e.g., before the event 302. In yet other implementations, the CU 172 receives a UE Capability Information message including the UE capability IE from the UE 102, via the DU 174 or another DU e.g., during the event 302. In some implementations, the DU 174 receives the UE capability IE (e.g., UE-NR-Capability or UE-6G-Capability) of the UE 102 from the CU 172, e.g., during the event 302.

[0141] In some implementations, the UE capability IE indicates that the UE 102 supports RACH-less LTM. Thus, based on the indication of supporting Random Access Channel-less (RACH-less) LTM, the DU 174 configures and/or activates one or more LTM TCI state configurations for the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support RACH-less LTM, the DU 174 refrains from configuring and/or activating an LTM TCI state configuration for the UE 102. For example, the DU 174 refrains from including an LTM TCI state configuration for the UE 102 in the DU-to-CU message(s) described above. Accordingly, the CU 712 does not transmit an LTM TCI state configuration to the UE 102. For example, the CU 172 does not include an LTM TCI state configuration in the RRC reconfiguration message 316, 318.

[0142] In other implementations, the UE capability IE indicates that the UE supports early timing advance (TA) acquisition. Based on the indication of supporting early TA acquisition, the DU 174 configures and/or activates one or more LTM TCI state configurations for the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support the early TA acquisition, the DU 174 refrains from configuring and/or activating an LTM TCI state configuration for the UE 102. For example, the DU 174 refrains from including an LTM TCI state configuration for the UE 102 in the DU-to-CU message(s) described above. Accordingly, the CU 712 does not transmit tan LTM TCI state configuration to the UE 102. For example, the CU 172 does not include an LTM TCI state configuration in the RRC reconfiguration message 316, 318.

[0143] In yet other implementations, the UE capability IE indicates that the UE supports a UE-based TA acquisition (e.g., the UE acquires UL synchronization based on reference signal time difference (RSTD) measurements). Based on the indication of supporting the UE-based TA acquisition, the DU 174 configures and/or activates one or more LTM TCI state configurations for the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support the UE-based TA acquisition, the DU 174 refrains from configuring and/or activating an LTM TCI state configurations for the UE 102. For example, the DU 174 refrains from including an LTM TCI state configuration for the UE 102 in the DU-to-CU message(s) described above. Accordingly, the CU 712 does not transmit an LTM TCI state configuration to the UE 102. For example, the CU 172 does not include an LTM TCI state configuration in the RRC reconfiguration message 316, 318.

[0144] In yet other implementations, the UE capability IE indicates that the UE supports LTM TCI states. Based on the indication of supporting LTM TCI states, the DU 174 configures and/or activates one or more LTM TCI state configurations for the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support LTM TCI states, the DU 174 refrains from configuring and/or activating an LTM TCI state configuration for the UE 102. For example, the DU 174 refrains from including an LTM TCI state configuration for the UE 102 in the DU-to-CU message(s) described above. Accordingly, the CU 712 does not transmit an LTM TCI state configuration to the UE 102. For example, the CU 172 does not include an LTM TCI state configuration in the RRC reconfiguration message 316, 318.

[0145] In yet other implementations, the DU 174 does not determine whether to provide an LTM TCI state configuration for the UE 102. The DU 174 provides the LTM TCI state configuration(s) for the UE 102 to the CU 172 as described above. The CU 172 determines whether to transmit the first LTM TCI state configuration(s) to the UE 102. In some implementations, based on the indication of supporting RACH-less LTM, the CU 172 transmits the first LTM TCI state configuration(s) to the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support RACH- less LTM, the CU 172 refrains from transmitting an LTM TCI state configuration to the UE 102. For example, the CU 172 refrains from transmitting the first LTM TCI state configuration(s) to the UE 102. For example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message 316, 318.

[0146] In other implementations, based on the indication of supporting the early TA acquisition, the CU 172 transmits the first LTM TCI state configuration(s) to the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support the early TA acquisition, the CU 172 refrains from transmitting an LTM TCI state configuration to the UE 102. For example, the CU 172 refrains from transmitting the first LTM TCI state configuration(s) to the UE 102. For example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message 316, 318.

[0147] In yet other implementations, based on the indication of supporting the UE-based TA acquisition, the CU 172 transmits the first LTM TCI state configuration(s) to the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support the UE-based TA acquisition, the CU 172 refrains from transmitting an LTM TCI state configuration to the UE 102. For example, the CU 172 refrains from transmitting the first LTM TCI state configuration(s) to the UE 102. For example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message 316, 318.

[0148] In yet other implementations, based on the indication of supporting the LTM TCI states, the CU 172 transmits the first LTM TCI state configuration(s) to the UE 102 as described above. In some implementations, if the UE capability IE indicates that the UE 102 does not support LTM TCI states, the CU 172 refrains from transmitting an LTM TCI state configuration to the UE 102. For example, the CU 172 refrains from transmitting the first LTM TCI state configuration(s) to the UE 102. For example, the CU 172 refrains from including the first LTM TCI state configuration(s) in the RRC reconfiguration message 316, 318. [0149] In some alternative implementations, the DU 174 may not activate or may determine to not activate a (LTM) TCI state configuration in the first LTM command. In such cases, the DU 174 does not include a TCI state ID in the first LTM command. Thus, when the UE 102 receives the first LTM command not including a TCI state configuration, the UE 102 refrains from using the first LTM TCI configuration(s) to access and/or communicate on the first cell.

[0150] In some implementations, if the UE capability IE indicates that the UE 102 does not support the RACH-less LTM, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability IE indicates that the UE 102 supports the RACH-less LTM, the DU 174 includes the one or more TCI state IDs (e.g., the TCI state ID 1 and/or the TCI state ID 2) in the first LTM command as described above.

[0151] In other implementations, if the DU 174 does not configure LTM TCI state configurations for the first cell for the UE 102, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the DU 174 configures one or more LTM TCI state configurations (e.g., the first LTM TCI state configuration(s)), the DU 174 includes one or more LTM TCI state IDs (e.g., the TCI state ID 1 and/or the TCI state ID 2) in the first LTM command.

[0152] In yet other implementations, if the UE capability IE indicates that the UE 102 does not support the early TA acquisition, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability indicates that the UE 102 supports the early TA acquisition, the DU 174 includes the TCI state ID 1 and/or the TCI state ID 2 in the first LTM command as described above.

[0153] In yet other implementations, if the UE capability IE indicates that the UE 102 does not support the UE-based TA acquisition, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability indicates that the UE 102 supports the early TA acquisition, the DU 174 includes the TCI state ID 1 and/or the TCI state ID 2 in the first LTM command as described above.

[0154] In yet other implementations, if the UE capability IE indicates that the UE 102 does not support LTM TCI states, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability indicates that the UE 102 supports LTM TCI states, the DU 174 includes the TCI state ID 1 and/or the TCI state ID 2 in the first LTM command as described above. [0155] In some implementations, the UE 102 stops using or deactivates the first non-LTM TCI configuration(s) upon receiving the first LTM command.

[0156] After successfully accessing the first cell, the UE 102 communicates 336 with the DU 174 on the first cell using the LTM DU configuration 1 and/or reference LTM DU configuration and communicates with the CU 172 via the DU 174. In such cases, the DU 174 communicates 336 with the UE 102 on the first cell using the LTM DU configuration 1. In some scenarios or implementations, the UE 102 communicates 336 PUSCH transmissions, PDSCH transmissions, PUCCH transmissions, PDCCH transmissions, and/or sounding reference signal (SRS) transmissions with the DU 174 on the first cell.

[0157] In the case that the UE 102 receives the reference LTM DU configuration as described above, the UE 102 communicates 336 with and the DU 174 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the UE 102 communicates 336 with the DU 174 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration. Similarly, the DU 174 communicates 336 with the UE 102 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the DU 174 communicates 336 with the UE 102 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration.

[0158] In the case that the UE 102 receives neither the LTM CU configuration 1 nor a/the reference LTM CU configuration, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving CU configuration. Correspondingly, if the CU 172 neither transmits the LTM CU configuration 1 nor a/the reference CU configuration to the UE 102, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving CU configuration. In the case that the UE 102 receives the LTM CU configuration 1 and the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1. [0159] In the case that the UE 102 receives the LTM CU configuration 1 and does not receive the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1. If the LTM CU configuration 1 is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the LTM CU configuration 1 instead of the serving CU configuration. In some implementations, if the UE 102 does not receive a/the reference LTM CU configuration from the base station 104, the UE 102 determines that the LTM CU configuration 1 is a full configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a full configuration, the CU 172 does not transmit a/the reference LTM CU configuration to the UE 102. In other implementations, the CU 172 includes a first indication (e.g., a field or IE) in the LTM CU configuration 1, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration l is a full configuration. If the LTM CU configuration l is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the LTM CU configuration 1 and at least a portion of the serving CU configuration not augmented by the LTM CU configuration 1. In some implementations, if the UE 102 does not receive a/the reference LTM CU configuration from the base station 104, the UE 102 determines that the LTM CU configuration l is a delta configuration to augment the serving CU configuration.

Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a delta configuration to augment the serving CU configuration, the CU 172 does not transmit a/the reference LTM CU configuration to the UE 102. In some implementations, the CU 172 indicates that the LTM CU configuration 1 is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the LTM CU configuration 1, the first container, the element 1 and/or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the LTM CU configuration 1, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration l is a delta configuration to augment the serving CU configuration. In some implementations, the CU 172 indicates that the LTM CU configuration 1 is a full configuration, by excluding the second indication in the LTM CU configuration 1, the first container, the element 1 and/or the RRC reconfiguration message 316. [0160] In the case that the UE 102 receives the reference LTM CU configuration and does not receive the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the reference LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the reference LTM CU configuration. If the reference LTM CU configuration is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration instead of the serving CU configuration. In some implementations, the UE 102 and CU 172 determine that the reference LTM CU configuration 1 is a full configuration as specified in a 3GPP specification (e.g., 3GPP specification 38.331 vl8.0.0 or later version). In other implementations, the CU 172 includes a first indication (e.g., a field or IE) in the reference LTM CU configuration, the first container or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a full configuration. If the reference LTM CU configuration is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration and at least a portion of the serving CU configuration not augmented by the reference LTM CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the reference LTM CU configuration, the first container, the element 1 and/or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the reference LTM CU configuration, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a delta configuration to augment the serving CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a full configuration, by excluding the second indication in the reference LTM CU configuration, the first container, the element 1 and/or the RRC reconfiguration message 316.

[0161] In the case that the UE 102 neither receives the reference LTM CU configuration and nor the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving LTM CU configuration.

[0162] In some implementations, the DU 174 includes or configures at least one second non-LTM TCI state configuration for the first cell in the LTM DU configuration 1. While communicating with the UE 102 at event 332 or 336, the DU 174 may transmit a second non- LTM TCI States Activation/Deactivation command on the first cell to the UE 102 to activate the second non-LTM TCI state configuration(s) and/or deactivate the activated LTM TCI state configuration(s). In some implementations, the DU 174 includes a serving cell index for the first cell in the second non-LTM TCI States Activation/Deactivation command. The DU 174 includes the serving cell index in the LTM DU configuration 1. In some implementations, the UE 102 stops using or deactivates the (activated) LTM TCI state configuration(s) in response to receiving the second non-LTM TCI States Activation/Deactivation command. In some implementations, the second non-LTM TCI States Activation/Deactivation command(s) is a MAC CE. The MAC CE may be a TCI States Activation/Deactivation for UE-specific PDSCH MAC CE, a TCI State Indication for UE-specific PDCCH MAC CEs, a PUCCH spatial relation Activation/Deactivation MAC CEs, an Enhanced TCI States Activation/Deactivation for UE-specific PDSCH MAC CE, an Enhanced PUCCH Spatial Relation Activation/Deactivation MAC CE, an Enhanced TCI States Indication for UE-specific PDCCH MAC CE, an PUCCH spatial relation Activation/Deactivation for multiple TRP PUCCH repetition MAC CE, or an Unified TCI States Activation/Deactivation MAC CE.

[0163] In some implementations, the second non-LTM state configuration(s) may be Rel- 15/16 TCI state configuration(s) (i.e., not a unified joint/DL/UL TCI state). This imply that the BS 104 may configure Rel-15/16 beam indication framework for the first cell. Non- LTM TCI state configurations activated/indicated by the second non-LTM TCI States Activation/Deactivation command(s) may be only applicable to a channel or RS (PDSCH/PDCCH/CSI-RS/PUCCH/SRS). In such implementations, if the UE 102 receives a second non-LTM TCI States Activation/Deactivation command, the UE would stop or use the first LTM TCI state for channels or RSs, which are applicable to share/follow/apply unified TCI states. For example, if the UE 102 receives an Enhanced TCI States Indication for UE-specific PDCCH MAC CE, the UE 102 would stop or use the first LTM TCI state for at least one of other channels or RSs applicable to share/follow/apply unified TCI states as well (e.g., PDSCH, PUSCH, PUCCH, CSI-RS or SRS). If the UE 102 receives a second non- LTM TCI States Activation/Deactivation command, the UE 102 may deactivate the activated first LTM TCI state configuration(s).

[0164] In some implementations, the second non-LTM TCI state configuration(s) includes at least one TCI state configured in the first LTM TCI state configuration(s). In other implementations, TCI state(s) in the second non-LTM TCI state configuration(s) is/are different from the TCI(s) in the first LTM TCI state configuration(s). In some implementations, the second non-LTM TCI state configuration(s) configure more TCI states than the first LTM TCI state configurations(s). In some other implementations, TCI state(s) in the second non-LTM TCI state configuration(s) is/are identical with the TCI(s) in the first LTM TCI state configuration(s). The BS 104/CU 172/DU 174 may notify the UE 102 in an RRC message or signal, whether first LTM TCI state configuration(s) is identical or different or a subset of the second non-LTM TCI state configuration(s).

[0165] In some implementations, the first LTM TCI state configuration(s) for the first cell is a subset of the second non-LTM TCI state configuration(s) for the first cell. In some implementations, TCI state IDs of the first LTM TCI state configuration(s) for the first cell are not overlapped or identical with those of the second non-LTM TCI state configuration(s) for the first cell. This may imply that when the UE 102 receives the second non-LTM TCI States Activation/Deactivation command(s), the UE 102 considers/determines that the TCI state ID(s) indicated in the second non-LTM TCI States Activation/Deactivation command(s) refer to the first LTM TCI state configuration(s) for the first cell or the second non-LTM TCI state configurations for the first cell. For example, TCI state IDs of the first LTM TCI state configuration(s) for the first cell ranges from #000 to #007; TCI state IDs of the second non- LTM TCI state configurations for the first cell ranges from #008 to #015. In such example, if the second non-LTM TCI States Activation/Deactivation command indicates TCI state ID #001, the UE 102 activates the first LTM TCI state configuration identified by TCI state ID #001; if the second non-LTM TCI States Activation/Deactivation command indicates TCI state ID #012, the UE 102 activates the second non-LTM TCI state configuration identified by TCI state ID #012. In some implementations, the UE 102 combines or catenate the first LTM TCI state configuration(s) for the first cell and the second non-LTM TCI state configurations for the first cell for non-LTM TCI state activation/indicate purpose. In some implementations, the UE 102 considers or determines the first LTM TCI state configuration(s) for the first cell as the non-LTM TCI state configurations for the first cell.

[0166] In some implementations, the DU 174 may not include or configure the at least one second non-LTM TCI state configuration for the first cell in the LTM DU configuration 1. In such cases, the UE 102 considers or determines the at least one first TCI state configuration(s) (e.g., LTM TCI state configuration) for the first cell as the non-LTM TCI state configurations for the first cell. This may imply that when the UE 102 receives the second non-LTM TCI States Activation/Deactivation command(s), the UE 102 considers/ determines that the TCI state ID(s) indicated in the second non-LTM TCI States Activation/Deactivation command(s) refer to the first LTM TCI state configuration(s) for the first cell. For example, if the second non-LTM TCI States Activation/Deactivation command indicates TCI state ID #000, the UE 102 activates and/or applies the first TCI state configuration (e.g., LTM TCI state configuration) identified by TCI state ID #000, and performs non-LTM communication in the first cell.

[0167] In some implementations, if a first LTM TCI state configuration associates or includes a SSB corresponding to QCL type A, the UE 102 refrains from using such TCI state configuration for non-LTM purpose or communication in the first cell. In some implementations, the UE 102 may consider or determine a first LTM TCI state configuration(s) for the first cell as a non-LTM TCI state configurations for the first cell, unless it includes or associates a SSB corresponding to QCL type A.

[0168] In some implementations, when or while the DU 174 communicates 332, 336 with the UE 102 on the first cell, the DU 174 refrains from transmitting an LTM TCI States Activation/Deactivation command to the UE 102 to activate an LTM TCI state configuration for the first cell or associated with the LTM ID 1. In other implementations, when or while the DU 174 communicates 332, 336 with the UE 102 on the first cell, the DU 174 transmits a second LTM TCI States Activation/Deactivation command to the UE 102 to activate at least one LTM TCI state configuration in the first LTM TCI state configuration(s) that is/are not activated by the first LTM command. In response to the second LTM TCI States Activation/Deactivation command, the UE 102 activates the LTM TCI state configuration(s) indicated in the second LTM TCI States Activation/Deactivation command. In the second LTM TCI States Activation/Deactivation command, the DU 174 may deactivate the LTM TCI state configuration(s) activated in the first LTM command, in some implementations. In such cases, the UE 102 deactivate the LTM TCI state configuration(s) activated in the first LTM command, in response. The UE 102 and the DU 174 communicate with each other on the first cell using the LTM TCI state configuration(s) activated by the second LTM TCI States Activation/Deactivation command, as described above.

[0169] In some implementations, the UE 102 transmits an RRC message (e.g., RRC reconfiguration complete message) to the CU 172 via the DU 174 and the first cell, e.g., to indicate that the UE 102 applies an LTM candidate configuration (e.g., the LTM DU configuration 1 and/or the LTM CU configuration 1). In the case that the UE 102 performs the random access procedure 332, the UE 102 can include the RRC message in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC message after completing the random access procedure. In the case that the UE 102 skip the random access procedure 332, the UE 102 includes the RRC message in a PUSCH transmission (e.g., the first transmission) of the at least one PUSCH transmission. In some implementations, if the UE 102 maintains communication on the cell 124A with the base station 104 (i.e., the UE 102 does not disconnect from the cell 124A), the UE 102 can transmit the RRC message to the base station 104 via the cell 124 A. When the DU 174 receives the RRC message, the DU 174 transmits the RRC message to the CU 172.

[0170] In other implementations, the UE 102 refrains from transmitting the RRC message to the base station 104 in response to applying the LTM DU configuration 1 or receiving the first LTM command. In such cases, the UE 102 can include or transmit data in the Message 3, Message A or PUSCH transmission as described above. The UE 102 can generate a MAC PDU and/or a REC PDU including the data and transmits or includes the MAC PDU and/or RLC PDU in the PUSCH transmission. For example, the data can be a PDCP PDU, a SDAP PDU, a LTE Positioning Protocol (LPP) PDU, an RRC PDU and/or a NAS PDU. The RRC PDU includes a UL-DCCH-Message excluding an RRC reconfiguration complete message. The NAS PDU includes a Mobility Management (MM) message or a Session Management (SM) message. The MM message can be a 5G MM message or a 6G MM message, and the SM message can be a 5G SM message or a 6G SM message. When the DU 174 receives the data, the DU 174 transmits the data to the CU 172.

[0171] When the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 can transmit 334 a DU-to-CU message (e.g., Access Success message) to the CU 172 (e.g., a CP of the CU 172). In some implementations, the DU 174 can include the cell ID 1 of the first cell in the DU-to-CU message of the event 334. The cell ID can be a PCI or a CGI. Thus, the CU 172 determines that the UE 102 connects to the first cell upon receiving the DU-to-CU message of the event 334. When the DU 174 determines that the UE 102 successfully connect to the first cell in the event 332 or 336, the DU 174 can transmit a DL Data Delivery Status message or frame to the CU 172 (e.g., a UP of the CU 172). In some implementations, when or after the CU 172 receives the DU-to-CU message 329, the CU 172 can stop or suspend transmitting DL data for the UE 102 to the DU 174 until receiving the DU-to-CU message 334. The CU 172 can do so because the DU 174 cannot buffer DL data for the UE 102 during the LTM execution in the events 330 and/or 332. After receiving the DU-to-CU message 334, the CU 172 continues or resumes transmitting DL data for the UE 102 to the DU 174. In other implementations, when the CU 172 receives the DU-to-CU message 329, the CU 172 can continue transmitting DL data for the UE 102 to the DU 174. The CU 172 can do so because the DU 174 can buffer DL data for the UE 102 during the LTM execution in the events 330 and/or 332. When or after the DU 174 detects that UE 102 accesses the cell 1, the DU 174 transmits the DL data to the UE 102 via the cell 1.

[0172] In some implementations, when determining that the UE 102 connects to the first cell, transmitting 330 the first LTM command, or receiving 331 the acknowledgement, the DU 174 can stop communicating with the UE 102 on the cell 124A and/or release resources of the cell 124 A configured for the UE 102.

[0173] In some implementations, the DU 174 can generate some or all of the LTM DU configuration 1 and/or LTM DU configuration(s) 2, ..., N as full configuration(s) to replace the serving DU configuration. If the LTM DU configuration l is a full configuration, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 instead of the serving DU configuration. In some implementations, the DU 174 includes an indication indicating that the LTM DU configuration 1 is a full configuration in the LTM DU configuration 1. In each of the LTM DU configured on(s) 2, . . . , N, the DU 174 can include an indication to indicate that the corresponding DU configuration is a full configuration. Each of the indication(s) in the LTM DU configured on(s) 1, . . ., N can be a field or IE (i.e., the same field or IE). In other implementations, the CU 172 can include, in the RRC reconfiguration message of the events 316, 318, a single indication indicating that the LTM DU configuration(s) 1 and/or 2, . . ., N is/are full configuration(s). In the case of the second container, the CU 172 can include, in the additional RRC reconfiguration message, a single indication indicating that the LTM DU configuration(s) 2, . . ., N is/are full configured on(s). In yet other implementations, the CU 172 can include, in the first container, a single indication indicating that the LTM DU configuration(s) 1 and/or 2, . . ., N is/are full configuration(s). In yet other implementations, for each of the LTM DU configuration(s) 2, . . ., N, the CU 172 can include, in the first container, a particular indication indicating the corresponding LTM DU configuration is a full configuration. In the case of the second container, the CU 172 can include, in the second container, a single indication indicating that the LTM DU configuration(s) 2, . . ., N is/are full configuration(s). In yet other implementations, the CU 172 can include, in the element 1, includes an indication indicating that the LTM DU configuration 1 is a full configuration. In each of the element(s) 2, . . ., N, the CU 172 can include an indication indicating that the corresponding LTM DU configuration is a full configuration. The UE 102 can determine that the LTM DU configuration 1 and/or LTM DU configuration(s) 2, . . ., N is/are full configuration(s) based on the indication(s) above. In some implementations, each of the indication(s) above is different from a fullConfig field defined in the current 3GPP specification. In some implementations, each of the indication(s) above is a fullConfig field defined in the current 3GPP specification. In the case that the LTM DU configuration l is a full configuration, the UE 102 in the event 336 does not apply the reference LTM DU configuration if received from the base station 104, e.g., in the RRC reconfiguration message 318. In such cases, the DU 174 can not include a/the reference LTM DU configuration in the first DU-to-CU message 310.

[0174] In other implementations, the DU 174 can generate the LTM DU configuration 1 and/or LTM DU configuration(s) 2, . . ., N as delta configuration(s) that augment (a portion of) the reference LTM DU configuration. In other words, the DU 174 generates the LTM DU configuration(s) 1, . . .N based on the reference LTM DU configuration. For example, if the LTM DU configuration 1 is a delta configuration, the UE 102 and DU 174 augment (the portion of) the reference LTM DU configuration with the LTM DU configuration 1. Thus, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 and unaugment portion of the reference LTM DU configuration. In some implementations, the LTM DU configuration(s) 1, and/or 2. . ., N, first container, second container or element(s) 1, . . . , N exclude indication(s) indicating that the LTM DU configuration(s) 1, and/or 2. . ., N is/are full configuration(s) to indicate that the LTM DU configuration(s) 1 and/or 2, . . ., N is/are delta configuration(s). The UE 102 can determine that each of the LTM DU configuration(s) 1 and/or 2, . . ., N is a delta configuration based on that the indication is excluded in the LTM DU configuration(s) 1 and/or 2, . . ,,N, first container, second container or element(s) 1 and/or 2, . . ., N.

[0175] In some implementations, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and/or the LTM DU configuration(s) 2, . . . , N, the UE 102 determines that the LTM DU configuration 1, and/or the LTM DU configuration(s) 2, . . ., N are full configuration(s). Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM DU configuration for the UE 102 and/or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1, and/or the LTM DU configuration(s) 2, . . N as full configuration(s).

[0176] In other implementations, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and/or the LTM DU configuration(s) 2, . . . , N, the UE 102 determines that the LTM DU configuration 1, and/or the LTM DU configuration(s) 2, . . . , N are delta configuration(s) to augment the serving DU configuration. In such cases, the UE 102 communicates 336 with the DU 174 in accordance with the LTM DU configuration 1 and at least a portion of the serving DU configuration not augmented by LTM DU configuration 1. Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM DU configuration for the UE 102 and/or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1, and/or the LTM DU configuration(s) 2, . . ., N as delta configuration(s) to augment the serving DU configuration. In such cases, the DU 174 communicates 336 with the UE 102 in accordance with the LTM DU configuration 1 and the at least a portion of the serving DU configuration.

[0177] In some implementations, the UE 102 uses a UE MAC entity (e.g., MAC 204B) to communicate with a DU MAC entity (e.g., MAC 204B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330 and/or 331). In some implementations, the UE 102 resets the UE MAC entity, after or in response to receiving the first LTM command and before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 resets the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

[0178] In some implementations, when the UE 102 resets the UE MAC entity, the UE 102 performs at least one of the following actions for the UE MAC entity (i.e., UE MAC reset or full UE MAC reset): initialize Bj for configured logical channel(s) to zero; stop one or more timers; • consider timeAlignmentTimer s) as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1);

• set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0;

• set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1;

• flush Msg3 buffer;

• flush MSGA buffer;

• cancel, if any, triggered Scheduling Request procedure;

• cancel, if any, triggered Buffer Status Reporting procedure;

• cancel, if any, triggered Power Headroom Reporting procedure;

• cancel, if any, triggered consistent LBT failure;

• cancel, if any, triggered BFR;

• cancel, if any, triggered Sidelink Buffer Status Reporting procedure;

• cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure;

• cancel, if any, triggered Timing Advance Reporting procedure;

• cancel, if any, triggered Recommended bit rate query procedure;

• cancel, if any, triggered configured uplink grant confirmation;

• cancel, if any, triggered configured sidelink grant confirmation;

• cancel, if any, triggered Desired Guard Symbol query;

• cancel, if any, triggered Positioning Measurement Gap Activation/Deactivation Request procedure;

• flush soft buffers for DL HARQ process(es);

• for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission; release, if any, Temporary C-RNTI; • reset one or more counters (e.g., BFI COUNTERs and/or LBT COUNTERs).

[0179] In some implementations, when the DU 174 resets the DU MAC entity, the DU 174 performs at least one of the following actions for the DU MAC entity (i.e., DU MAC reset or full DU MAC reset):

• stop one or more timers;

• consider limeAlignmenlTimer( , that the DU 174 starts and/or maintains for the UE 102, as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1);

• set NDI(s) for DL HARQ process(es) to value 0;

• flush soft buffers for UL HARQ process(es);

• for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission;

• reset one or more counters (e g., BFI COUNTERs and/or LBT COUNTERs)

[0180] Depending on implementations, the UE 102 can determine to partially or fully reset the UE MAC entity. In some implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 fully resets the UE MAC entity (i.e., a full UE MAC reset). In the full UE MAC reset, the UE 102 performs some or all of the actions described above. In other implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 partially resets the UE MAC entity (i.e., a partial UE MAC reset). In the partial UE MAC reset, the UE 102 performs a subset or portion of the some or all of the actions in the full UE MAC reset.

[0181] In some implementations, the partial UE MAC reset includes at least one of the following actions:

• consider timeAlignmentTimer(s) of the UE 102 as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1);

• flush Msg3 buffer;

• flush MSGA buffer; release, if any, Temporary C-RNTI; • reset one or more counters (e g., BFI COUNTERs and/or LBT COUNTERs).

[0182] In some implementations, the partial UE MAC reset further includes at least one of the following actions:

• cancel, if any, triggered Scheduling Request procedure;

• cancel, if any, triggered Buffer Status Reporting procedure;

• cancel, if any, triggered Power Headroom Reporting procedure;

• cancel, if any, triggered consistent LBT failure;

• cancel, if any, triggered BFR;

• cancel, if any, triggered Sidelink Buffer Status Reporting procedure;

• cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure;

• cancel, if any, triggered Timing Advance Reporting procedure;

• cancel, if any, triggered Recommended bit rate query procedure;

• cancel, if any, triggered configured uplink grant confirmation;

• cancel, if any, triggered configured sidelink grant confirmation;

• cancel, if any, triggered Desired Guard Symbol query;

[0183] In some implementations, the partial UE MAC reset further includes at least one of the following actions:

• stop a first portion of the one or more timers and retain the rest of the one or more timers;

• set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0;

• set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1; flush soft buffers for DL HARQ process(es); for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission; [0184] Depending on implementations, the DU 174 can determine to partially or fully reset the DU MAC entity. In some implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 fully resets the DU MAC entity (i.e., a full DU MAC reset). In the full DU MAC reset, the DU 174 performs some or all of the actions described above. In other implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 partially resets the DU MAC entity (i.e., a partial DU MAC reset). In the partial DU MAC reset, the DU 174 performs a subset or portion of the some or all of the actions in the full DU MAC reset.

[0185] In some implementations, the partial DU MAC reset includes at least one of the following actions in the partial MAC reset:

• reset one or more counters (e.g., BFI COUNTERs and/or LBT COUNTERs)

[0186] In some implementations, when the partial DU MAC reset includes at least one of the following actions for the MAC entity (i.e., DU MAC reset):

• set NDI(s) for DL HARQ process(es) to value 0;

• flush soft buffers for UL HARQ process(es);

• reset one or more counters (e.g., BFI COUNTERs and/or LBT COUNTERs)

[0187] In other implementations, the UE 102 refrains from resetting the UE MAC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from resetting the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the UE MAC entity (not reset). Similarly, the DU 174 communicates with the UE 102 using the DU MAC entity (not reset) on the first cell during or after the random access procedure 332 or after determining that the UE 102 connects to the first cell.

[0188] In some implementations, the UE 102 uses at least one UE RLC entity (e.g., RLC 206B) to communicate RLC PDUs with at least one DU RLC entity (e.g., RLC 206B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330 and/or 331). In some implementations, the UE 102 reestablishes the at least one UE RLC entity, after or in response to receiving the first LTM command and before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 correspondingly reestablishes the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

[0189] In some implementations, the UE 102 can reestablish the at least one UE RLC entity before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In other implementations, the UE 102 can reestablish the at least one UE RLC entity while or after performing 332 the random access procedure. In some implementations, the DU 174 reestablishes the at least one DU RLC entity after transmitting the first LTM command, receiving an acknowledgement for the first LTM command from the UE 102, or determining that the UE 102 connects to the first cell. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. In yet other implementations, the acknowledgement is a PUCCH transmission.

[0190] In other implementations, the UE 102 refrains from reestablishing the at least one UE RLC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from reestablishing the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the at least one UE RLC entity (not reestablished).

[0191] In some implementations, the UE 102 uses at least one UE PDCP entity (e.g., PDCP 210) to communicate UL PDCP PDUs and/or DL PDCP PDUs with at least one CU PDCP entity (e.g., PDCP 210) of the CU 172 in the event 302. In some implementations, the UE 102 performs a PDCP recovery procedure for some or all of the at least one UE PDCP entity, after or in response to receiving the first LTM command. For example, the UE 102 performs a PDCP recovery procedure for a first UE PDCP entity of the at least one UE PDCP entity, after or in response to receiving the first LTM command. In the PDCP recovery procedure, the UE 102 may or may not reestablish the first UE PDCP entity. After or in response to performing the PDCP recovery procedure, the UE 102 can retransmit at least a portion of the UL PDCP PDUs to the CU 172 via the DU 174 and the first cell in the event 336. Similarly, the CU 172 performs a PDCP recovery procedure for some or all of the at least one CU PDCP entity after or in response to transmitting the first LTM command. For example, the CU 172 performs a PDCP recovery procedure for a first CU PDCP entity of the at least one CU PDCP entity, after or in response to transmitting the first LTM command. In some implementations, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DU-to-CU message 329 or 334. In other implementations, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DL Data Delivery Status message. In the PDCP recovery procedure, the CU 172 may or may not reestablish the first CU PDCP entity. After or in response to performing the PDCP recovery procedure, the CU 172 can retransmit at least a portion of the DL PDCP PDUs to the UE 102 via the DU 174 and the first cell in the event 336.

[0192] In other implementations, the UE 102 refrains from reestablishing some or all of the at least one UE PDCP entity in response to receiving the first LTM command. For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and/or a second UE PDCP entity. Similarly, the CU 172 refrains from reestablishing some or more of the at least one CU PDCP entity, after (e.g., in response to) receiving the DU-to-CU message 329 or 340 or after (e.g., in response to) receiving the DL Data Delivery Status message. In other words, the UE 102 communicates with the CU 172 via the DU 174 and the first cell using the some or all of the at least one UE PDCP entity (not reestablished). For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and/or a second UE PDCP entity. Similarly, the CU 172 communicates with the UE 102 using the some or all of the at least one CU PDCP entity (not reestablished) via the DU 174 and the first cell. For example, the some or all of the at least one CU PDCP entity includes the first CU PDCP entity and/or a second CU PDCP entity.

[0193] In some implementations, after determining that the UE 102 connects to the first cell, the CU 172 can transmit 338 a CU-to-DU message (e.g., a UE Context Modification Request message) to the DU 174 to indicate the DU 174 to stop communicating with the UE 102 and/or to release or suspend resources, of the cell 124A, configured for the UE 102. In response, the DU 174 can stop communicating on the cell 124A with the UE 102 and/or release or suspend resources, of the cell 124A, configured for the UE 102, and transmit 340 a DU-to-CU message (e.g., a UE Context Modification Response message) to the CU-172. The events 338 (optional) and 340 (optional) are collectively referred to in Fig. 3 as a resource release or modification procedure 396.

[0194] After or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351, 352, 354 and/or 356 can occur, similar to the events 324, 326, 328, 330, 331, 332, 334 and/or 336, respectively. The UE 102 transmits 344 at least one measurement report to the DU 174. The at least one measurement report includes at least one measurement result for a second cell (i.e., the cell 2). The at least one measurement result indicates that the second cell is suitable for communication with UE 102 and/or the first cell is not suitable for communication with the UE 102. After (e.g., in response to) receiving the at least one measurement report, the DU 174 determines to activate the LTM DU configuration 2 and generates a second LTM command to activate the LTM DU configuration 2 (i.e., the second LTM command commands the UE 102 to apply the LTM DU configuration 2). The DU 174 then transmits 350 the second LTM command to the UE on the first cell to the UE 102.

[0195] When or in response to determining to activate the LTM DU configuration 2 or transmit the second LTM command, the DU 174 can transmit 349 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some implementations, the DU 174 includes the cell ID 2 or the ID 2 (i.e., LTM ID) in the DU-to-CU message 349 to indicate that the DU 174 is to activate the LTM DU configuration 2. The DU can transmit the DU-to-CU message 349 to the CU 172 before or after transmitting the LTM command 350.

[0196] At least some of the descriptions of the events 324, 326, 328, 330, 331, 332, 334 and/or 336 can apply to the events 344, 346, 348, 350, 351, 352, 354 and/or 356 with simple changes. For example, “ cell 124A”, “first LTM command”, “first cell”, “ID 1”, “LTM DU configuration 1” and/or “LTM CU configuration 1” are replaced with “first cell”, “second LTM command” and “second cell”, “ID 2”, “LTM DU configuration 2” and/or “LTM CU configuration 2”, respectively.

[0197] The events 344, 346, 348, 350, 351, 352, 354 are collectively referred to in Fig. 3 as an LTM execution procedure 398. The events 304, 306, 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, 356 are collectively referred to in Fig. 3 as an LTM DU configuration and/or activation procedure 380. [0198] Referring next to Fig. 4, in a scenario 400, the base station 104 includes a CU 172, a source DU (S-DU) 174A and a target DU (T-DU) 174B. The S-DU 174A operates the cell 124 A and optionally additional cell(s), while the T-DU 174B operates a first cell (e.g., cell 124C). The scenario 400 is similar to the scenario 300. Thus, the description for the scenario 300 can generally apply to the scenario 400. The differences between the scenarios 300 and 400 are described below.

[0199] Initially, the UE 102 communicates 402 with the S-DU 174A on cell 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174 A. The S-DU 174A is a serving DU similar to the DU 174 in Fig. 3 A. During the communication 402, the UE 102 transmits 404, 406 at least one measurement report (e.g., L3 measurement report(s)) to the CU 172 via the S-DU 174 A. Based on the at least one measurement report, the CU 172 determines to prepare cell(s) 1, . . ., N (operated by the T-DU 174B) for LTM for the UE 102, where N is a positive integer larger than 0 or 1. The cell(s) 1, . . ., N are identified by cell ID(s) 1, . . ., N, respectively. In response to the determination, the CU 172 performs 490an LTM preparation procedure with the T-DU 174B to (request the T-DU 174B to) prepare cell(s) 1, . . . , N for LTM for the UE 102. N can be a positive integer larger than zero or 1. In the LTM preparation procedure 490, the CU 172 transmits a CU-to-DU message including the cell ID(s) 1, . . ., N to the T-DU 174B to request the T-DU 174B to prepare the cell(s) 1, . . ., N for LTM for the UE 102, similar to the event 308. In response, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) 1, . . ., N to the CU 172, similar to the event 310. The LTM DU configuration(s) 1, . . . , N configures the cell(s) 1, . . ., N for LTM, respectively. In details, the LTM DU configuration(s) 1, . . ., N include configuration parameters for communication on the cell(s) 1, . . ., N, respectively. In some implementations, the CU-to-DU message and DU-to-CU message in the procedure 490 are UE Context Setup Request message and UE Context Setup Response message, respectively. The CU 172 then transmits the LTM DU configuration(s) 1, . . ., N in an RRC reconfiguration message in an LTM configuration delivery procedure 494, similar to the LTM configuration delivery procedure 394. In some implementations, the T-DU 174B can include cell index(es) 1, . . ., N in the LTM DU configuration(s) 1, . . ., N, respectively. In some implementations, the CU 172 can set the cell index(es) 1, . . ., N to different values and include the cell index(es) 1, . . . , N in the CU-to-DU message of the procedure 490.

[0200] After performing the LTM preparation procedure 490, the CU 172 can perform an additional LTM preparation procedure(s) with the T-DU 174B to prepare cell(s) N+l, . . ., N+M for LTM for the UE 102, similar to the procedure 490. M is a positive integer larger than zero. The CU 172 can determine to do so based on one or more measurement reports received from the UE 102 via the S-DU 174A, similar to the events 404, 406. In the additional LTM preparation procedure, the CU 172 transmits a CU-to-DU message including cell ID(s) N+l, . . ., N+M to the T-DU 174B to request the T-DU 174B to prepare the cell(s) N+l, . . . , N+M for LTM for the UE 102. The cell ID(s) N+l, . . . , N+M identifies the cell ID(s) N+l, . . ., N+M, respectively. In response to the CU-to-DU message, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) N+l, . . . , N+M to the CU 172. The LTM DU configuration(s) N+l, . . . , N+M configures the cell(s) N+l, . . . , N+M for LTM, respectively. In details, the LTM DU configuration(s) N+l, . . . , N+M include configuration parameters for communication on the cell(s) N+l, . . ., N+M, respectively. The CU 172 then transmits the LTM DU configuration(s) N+l, . . . , N+M in an RRC reconfiguration message in an additional LTM configuration delivery procedure, similar to the LTM configuration delivery procedure 394 or 494.

[0201] In some implementations, the LTM preparation procedure 490 is a UE Context Setup procedure and the additional LTM preparation procedure is a UE Context Modification procedure. In other implementations, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Setup procedures. In yet other implementations, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Modification procedures.

[0202] In some implementations, the CU 172 and S-DU 174 A can perform the procedure 380 with the UE 102, as described for Fig. 3. In the procedure 380, the CU 172 and S-DU 174A performs the procedure(s) 390 and/or 392 to prepare cell(s) of the S-DU 174A for LTM for the UE 102. Note, the value N in the procedure 380 or described for Fig. 3 can be the same as or different from the value N described for Fig. 4. In the procedure 390, the CU 172 can receive the first DU-to-CU message including the reference LTM DU configuration from the S-DU 174A in the event 310. In other implementations, the CU 172 and S-DU 174A does not perform the procedure 380 with the UE 102. In such cases, the CU 172 can perform 488 a reference LTM DU configuration query procedure with the S-DU 174 A to obtain a reference LTM DU configuration. In the procedure 488, the CU 172 transmits 460 a CU-to-DU message to the S-DU 174 A to request or query a reference LTM DU configuration. In some implementations, the CU 172 can include an indication in the CU-to-DU message to request or query a reference LTM DU configuration. In response to the indication or CU-to-DU message 460, the S-DU 174A transmits 462 a DU-to-CU message including a reference LTM DU configuration to the CU 172. In some implementations, the indication is a reference LTM DU configuration query indication. In other implementations, the indication is an LTM indication, and the CU 172 can include a query indication (e.g., GNB-DU Configuration Query IE) in the CU-to-DU message. After receiving the reference LTM DU configuration (i.e., either in the procedure 390 or in the procedure 488), the CU 172 includes the reference LTM DU configuration (received from the S-DU 174A) in the CU-to-DU message in the LTM preparation procedure 490. The T-DU 174B generates the LTM DU configuration(s) 1, . . ., N based on the reference LTM DU configuration received from the CU 172. In such cases, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. The CU 172 can not include the reference LTM DU configuration in CU-to-DU message in the additional LTM preparation procedure with the T-DU 174B. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+l, . . . , N+M based on the reference LTM DU configuration received from the CU 172.

[0203] In some implementations, the CU 172 does not provide a reference LTM DU configuration to the T-DU 174B in the LTM preparation procedure 490. In such cases, the T- DU 174B generates a reference LTM DU configuration and generates the LTM DU configuration(s) 1, . . ., N based on the reference LTM DU configuration. In such cases, the T- DU 174B includes the reference LTM DU configuration in the DU-to-CU message in the procedure 490. The CU 172 transmits the reference LTM DU configuration in the RRC reconfiguration message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+l, . . ., N+M based on the reference LTM DU configuration. In this case, the T-DU 174B can not include the reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. In some implementations, the reference LTM DU configuration generated by the T-DU 174B is different from the reference LTM DU configuration generated by the S-DU 174A. In other implementations, the reference LTM DU configuration generated by the T-DU 174B is the same as the reference LTM DU configuration generated by the S-DU 174 A. [0204] In some implementations, the CU 172 includes the LTM DU configuration(s) 1, . . N of the procedure 380 in the CU-to-DU message of the procedure 490, and the T-DU 174B generates the LTM DU configured on(s) 1, . . . , N and/or N+l, . . . , N+M, considering or based on configured on(s) in the LTM DU configured on(s) of the procedure 380.

[0205] In some implementations, the LTM DU configuration X of the procedure 380 includes at least one reference signal (RS) resource configuration X, where 1 < X < N. Each of the RS resource configuration(s) X configures one or more RSs or one or more RS resources associated with the cell X of the S-DU 174A. The RS(s) includes SSB(s) and/or CSI-RS(s). The RS resource(s) includes SSB resource(s) and/or CSI-RS resource(s). In some implementations, each of the RS resource configuration(s) X includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) X is/are (similar to) CSI-ResourceConfig IE(s). In some implementations, the LTM DU configuration X includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI- ResourceConfig IE(s). The T-DU 174B generates at least one report configuration 1 for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the report configured on(s) 1 in the LTM DU configuration 1. In some implementations, the report configuration(s) 1 is/are (similar to) CSI-ReportConfig IE(s). In some implementations, the T-DU 174B generates at least one RS resource configuration 1, considering or based on the RS resource configured on(s) X and includes the RS resource configuration(s) 1 in the LTM DU configuration 1. In some implementations, the T-DU 174B includes the RS resource configured on(s) X in the RS resource configuration(s) 1. In other implementations, the T-DU 174B includes each of the RS resource configured on(s) X in the RS resource configured on(s) 1, except the RS resource configuration ID(s) in the RS resource configured on(s) X. The T-DU 174B assigns a RS resource configuration ID to a value for each of the RS resource configuration(s) 1 (including the RS resource configuration(s) X) and includes the RS resource configuration ID in the corresponding RS resource configuration.

[0206] In some implementations, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configured on(s) 1. After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124 A, the UE 102 communicates with the S-DU 174B (i.e., the T-DU 17B becomes a S-DU for the UE 102) and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the report configuration(s) 1. Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the report configuration(s) 1. In some implementations, each of the measurement results includes one or more RS resource indicators and/or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) 1 and/or the report configuration(s) 1 and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and/or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values can include one or more Ll-RSRP values and/or one or more Ll-SINR values.

[0207] In some implementations, the T-DU 174B also includes additional RS resource configuration(s) in the LTM DU configuration 1. Each of the additional RS resource configuration(s) configures one or more additional RSs or one or more additional RS resources associated with the cell 1. The additional RS(s) includes SSB(s) and/or CSI-RS(s). The additional RS resource(s) includes SSB resource(s) and/or CSI-RS resource(s). In some implementations, each of the additional RS resource configuration(s) includes a RS resource configuration ID. In some implementations, the additional RS resource configuration(s) is/are (similar to) CSI-ResourceConfig IE(s). In some implementations, the T-DU 174B includes the CSI-ResourceConfig IE(s) in the CSI-MeasConfig IE. The T-DU 174B generates at least one additional report configuration for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the additional report configuration(s) in the LTM DU configuration 1. In some implementations, the additional report configuration(s) is/are (similar to) CSI-ReportConfig IE(s).

[0208] In some implementations, the additional report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the additional report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the additional RS resource configuration(s). After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124 A, the UE 102 communicates 436 with the S-DU 174B and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the additional report configuration(s). Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the additional report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and/or one or more quantized measurement values. The UE 102 performs measurements on the additional RS(s) or the additional RS resource(s) in accordance with the additional RS resource configuration(s) and/or the additional report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the additional RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and/or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values can include one or more Ll-RSRP values and/or one or more Ll-SINR values.

[0209] Similarly, the T-DU 174B can generate RS resource configuration(s) 2, . . ., N, and/or N+l, . . . , N+M and/or report configuration(s) 2, . . . , N, and/or N+l, . . . , N+M, considering or based on the RS resource configuration(s) X, and include the RS resource configuration(s) 2, . . . , N, and/or N+l, . . . , N+M and/or the report configuration(s) 2, . . . , N, and/or N+l, . . . , N+M in the LTM DU configuration(s) 2, . . . , N, and/or N+l, . . . , N+M, respectively, as described above.

[0210] In other implementations, the LTM DU configuration X of the procedure 380 includes at least one TCI state configuration X, where 1 < X < N. Each of the TCI state configuration(s) X configures a TCI state that associates or includes one or two DL RSs with a corresponding QCL type. In some implementations, the DL RS(s) can be associated with the cell X operated by the S-DU 174 A. In some implementations, each of the TCI state configuration(s) X includes a TCI state ID. In some implementations, each of the TCI state configuration(s) X is a TCI-State IE. In some implementations, the TCI state configuration(s) X includes/is/are an ul-TCI-ToAddModList-r 17 field, one or more TCI-UL-State-r 17 IES, a dl-OrJointTCI-StateToAddModList-rl7 field, one or more TCI-State IEs, TCI- ActivatedConfig IE and/or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration X includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) X. In some implementations, the T-DU 174B generates at least one TCI state configuration 1, considering or based on the TCI state configuration(s) X and includes the TCI state configuration(s) 1 in the LTM DU configuration 1. In some implementations, the TCI state configuration(s) 1 includes the TCI state configuration(s) X. In other implementations, the T-DU 174B includes each of the TCI state configuration(s) X in the TCI state configuration(s) 1, except the TCI state ID(s) in the TCI state configuration(s) X. The T-DU 174B assigns a TCI state ID to a value for each of the TCI state configuration(s) 1 (including the TCI state configuration(s) X) and includes the TCI state ID in the corresponding TCI state configuration. While the UE 102 and the S-DU 174B communicate 436 with one another, the S-DU 174B can transmit an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell X. The S- DU 174B includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell X, where the TCI state configuration is one of the TCI state configuration(s) X or includes configurations of one of the TCI state configuration(s) X.

[0211] Similarly, the T-DU 174B can generate TCI state configuration(s) 2, . . ., N, considering or based on the RS resource configuration(s) X, and include the TCI state configuration(s) 2, . . . , N, and/or N+l, . . . , N+M in the LTM DU configured on(s) 2, . . . , N, and/or N+l, ..., N+M, respectively, as described above.

[0212] In some implementations, in cases where the CU 172 performs the procedure 380 after performing the procedure 490, the CU 172 includes the LTM DU configured on(s) 1, . . ., N of the procedure 490 in the CU-to-DU message of the procedure 380, and the S-DU 174 A generates the LTM DU configured on(s) 1, . . ., N of the procedure 380, considering or based on configurations in the LTM DU configuration(s) of the procedure 490, in a similar way as described above.

[0213] In some implementations, the CU 172 assigns ID(s) 1, . . ., N identifying the LTM DU configured on(s) 1, . . ., N (received from the T-DU 174B), respectively, and performs the procedure 492 with the T-DU 174B to provide the ID(s) 1, . . . , N and/or cell ID(s) 1, . . . , N to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) 1, . . . , N with the LTM DU configured on(s) 1, . . . , N and/or the cell ID(s) 1, . . . , N, respectively. In other implementations, the T-DU 174B assigns ID(s) 1, . . ., N identifying the LTM DU configuration(s) 1, . . ., N (generated by the T-DU 174B), respectively and includes the ID(s) 1, . . . , N in the DU-to-CU message of the procedure 490, similar to the event 310. In some implementations, the CU 172 assigns ID(s) N+l, . . N+M identifying the LTM DU configuration(s) N+l, . . ., N+M, respectively, and performs a procedure (similar to the procedure 492) with the T-DU 174B to provide the ID(s) N+l, . . ., N+M and/or cell ID(s) N+l, . . ., N+M to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) N+l, . . ., N+M with the LTM DU configuration(s) N+l, . . ., N+M and/or the cell ID(s) N+l, . . ., N+M, respectively. In other implementations, the T-DU 174B assigns ID(s) N+l, . . . , N+M identifying the LTM DU configuration(s) N+l, . . . , N+M, respectively and includes the ID(s) 1, . . ., N in the DU-to-CU message of the additional LTM preparation procedure, similar to the event 310.

[0214] In some implementations, the CU 172 transmits 412 a CU-to-DU message including the ID(s) 1, . . ., N to the S-DU 174A and receives 414 a DU-to-CU message from the S-DU 174A in response. The CU-to-DU message 412 and DU-to-CU message 414 are collectively referred to in Fig. 4 as an LTM ID transfer procedure 493 or an LTM cell index transfer procedure 493. In some implementations, the message 412 and message 414 can be UE Context Modification Request message and UE Context Modification Response message, respectively. In some implementations, the CU 172 includes the LTM DU configuration(s) 1, . . ., N and/or cell ID(s) 1, . . ., N in the CU-to-DU message 412. In one implementation, the CU 172 includes the ID(s) 1, . . ., N in the CU-to-DU message 412. In another implementation, the CU 172 includes the cell index(es) 1, . . ., N in the CU-to-DU message 412. In some alternative implementations, the CU 172 can perform multiple LTM ID transfer procedures to transmit the ID(s) 1, . . . , N, cell ID(s) 1, . . . , N and/or LTM DU configuration(s) 1, . . ., N to the S-DU 174 A. In each of the procedures, the CU 172 includes particular portion of the ID(s) 1, . . . , N, cell ID(s) 1, . . . , N and/or LTM DU configuration(s) 1, . . . , N in a CU- to-DU message similar to the message 412. Thus, the S-DU 174A associates the ID(s) 1, . . ., N with the LTM DU configured on(s) 1, . . ., N and/or the cell ID(s) 1, . . ., N, respectively. In other alternative implementations, the CU 172 can perform multiple LTM cell index transfer procedures to transmit the cell index(es) 1, . . . , N, cell ID(s) 1, . . . , N and/or LTM DU configured on(s) 1, . . ., N to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the cell index(es) 1, . . . , N, cell ID(s) 1, . . . , N and/or LTM DU configuration(s) 1, . . ., N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the cell index(es) 1, . . ., N with the LTM DU configured on(s) 1, . . ., N and/or the cell ID(s) 1, . . ., N, respectively. [0215] In some implementations, the S-DU 174 A generates a first serving DU configuration, based on the LTM DU configuration(s) 1, 2,... , and/or N, and includes the first serving DU configuration in the DU-to-CU message 414. In some implementations, the first serving DU configuration including configurations updating (e.g., augmenting, modifying or replacing) the serving DU configuration 402. In other implementations, the first serving DU configuration includes configurations that are not included in the serving DU configuration 402. The CU 172 transmits an RRC reconfiguration message including the first serving DU configuration to the UE 102. The UE 102 applies the first serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174 A using configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. The following are example implementations of generating the first serving DU configuration based on the LTM DU configuration 1, . . . , N.

[0216] In some implementations, the LTM DU configuration Y of the procedure 490 includes at least one RS resource configuration Y, where 1 < Y < N. Each of the RS resource configuration(s) Y configures one or more RSs or one or more RS resources associated with the cell Y of the T-DU 174B. The RS(s) includes SSB(s) and/or CSI-RS(s). The RS resource(s) includes SSB resource(s) and/or CSLRS resource(s). In some implementations, each of the RS resource configuration(s) Y includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) Y is/are (similar to) CSI-ResourceConfig IE(s). In some implementations, the LTM DU configuration Y includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI-ResourceConfig IE(s). The S-DU 174A generates at least one serving report configuration for reporting, on the cell 124 A, measurement results of the RS(s) or RS resource(s) and includes the serving report configuration(s) in the first serving DU configuration. In some implementations, the serving report configuration(s) is/are (similar to) CSI-ReportConfig IE(s). In some implementations, the S-DU 174 A generates at least one serving RS resource configuration, considering or based on the RS resource configuration(s) Y and includes the serving RS resource configuration(s) in the first serving DU configuration. In some implementations, the S-DU 174 A includes the RS resource configuration(s) Y in the serving RS resource configuration(s). In other implementations, the S-DU 174A includes each of the RS resource configuration(s) Y in the serving RS resource configuration(s), except the RS resource configuration ID(s) in the RS resource configuration(s) Y. The S-DU 174 A assigns a RS resource configuration ID to a value for each of the serving RS resource configuration(s) (including the RS resource configuration(s) Y) and includes the RS resource configuration ID in the corresponding serving RS resource configuration.

[0217] In some implementations, the serving report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 124A for the UE 102 to transmit measurement results. In some implementations, each of the serving report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the serving RS resource configuration(s). While the UE 102 communicates with the S-DU 174 A, the UE 102 transmits measurement results on the UL resource(s) via the cell 124 A to the S-DU 174 A, in accordance with the serving report configuration(s) (e.g., event 424). Correspondingly, the S-DU 174A receives the measurement results on the UL resource (s) via the cell 124 A from the UE 102, in accordance with the serving report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and/or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the serving RS resource configuration(s) and/or the serving report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and/or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values can include one or more Ll-RSRP values and/or one or more Ll-SINR values.

[0218] In other implementations, the LTM DU configuration Y of the procedure 490 includes at least one TCI state configuration Y, where 1 < Y < N. Each of the TCI state configuration(s) Y configures a TCI state that associates or includes one or two DL RSs with a corresponding QCL type. In some implementations, the DL RS(s) can be associated with the cell Y operated by the T-DU 174B. In some implementations, each of the TCI state configuration(s) Y includes a TCI state ID. In some implementations, each of the TCI state configuration(s) Y is a TCI-State IE. In some implementations, the TCI state configuration(s) Y includes/is/are an ul-TCI-ToAddModList-r 17 field, one or more TCI-UL-State-r 17 IES, a dl-OrJointTCI-StateToAddModList-rl7 field, one or more TCI-State IES, TCI- ActivatedConfig IE and/or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration Y includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) Y. In some implementations, the S-DU 174A generates at least one serving TCI state configuration, considering or based on the TCI state configuration(s) Y and includes the serving TCI state configuration(s) in the first serving DU configuration. In some implementations, the serving TCI state configuration(s) 1 includes the TCI state configuration(s) Y. In other implementations, the S-DU 174 A includes each of the TCI state configuration(s) Y in the serving TCI state configuration(s), except the TCI state ID(s) in the TCI state configuration(s) Y. The S-DU 174A assigns a TCI state ID to a value for each of the serving TCI state configuration(s) (including the TCI state configuration(s) Y) and includes the TCI state ID in the corresponding serving TCI state configuration. While the S- DU 174 A communicate 436 with the UE 102, the S-DU 174 A can transmit an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell Y. The S-DU 174A includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell Y, where the TCI state configuration is one of the TCI state configuration(s) Y or includes configurations of one of the TCI state configuration(s) Y.

[0219] In some implementations, the CU 172 transmits a CU-to-DU message including the ID(s) N+l, . . ., N+M to the S-DU 174A and receives a DU-to-CU message from the S-DU 174 A in response, similar to the CU-to-DU message 412 and the DU-to-CU message 414, respectively. In some implementations, the CU 172 includes the LTM DU configuration(s) N+l, . . ., N+M and/or cell ID(s) N+l, . . ., N+M in the CU-to-DU message. In some alternative implementations, the CU 172 can perform multiple LTM ID transfer procedures to transmit the ID(s) N+l, . . ., N+M, cell ID(s) N+l, . . ., N+M and/or LTM DU configuration(s) N+l, . . ., N+M to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the ID(s) N+l, . . . , N+M, cell ID(s) N+l, . . . , N+M and/or LTM DU configuration(s) 1, . . ., N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174 A associates the ID(s) N+l, . . . , N+M with the LTM DU configured on(s) N+l, . . . , N+M and/or the cell ID(s) N+l, . . ., N+M, respectively. In some implementations, the S-DU 174A generates a second serving DU configuration, based on the LTM DU configured on(s) N+l, N+2, . . . , and/or N+M, and includes the second serving DU configuration in the DU-to-CU message. In some implementations, the second serving DU configuration including configurations updating (e.g., augmenting, modifying or replacing) the first serving DU configuration and/or updating configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. In other implementations, the second serving DU configuration includes configurations that are not included in the first serving DU configuration. The CU 172 transmits an RRC reconfiguration message including the second serving DU configuration to the UE 102 via the S-DU 174 A. The UE 102 applies the second serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174 A using configurations included in the serving DU configuration 402 and/or the first serving DU configuration and not updated by the second serving DU configuration. In some implementations, the S-DU 174 A generates one or more new LI measurement configurations, based on LI measurement configuration(s) in the LTM DU configuration(s) N+l, N+2,. . . , and/or N+M, and includes the new LI measurement configuration(s) in the second serving DU configuration. In some implementations, the S- DU 174 A generates one or more new TCI state configuration, based on TCI state configuration(s) in the LTM DU configuration(s) N+l, N+2, . . . , and/or N+M, and includes the new TCI state configuration(s) in the second serving DU configuration.

[0220] In some implementations, in the case that the CU 172 and S-DU 174 A perform the procedure 380 with the UE 102, value(s) of the ID(s) 1, . . ., N of the procedure 380 are different from value(s) of the ID(s) 1, . . . ., N, and the ID(s) N+l ,...., N+M described for the scenario 400. In some implementations, in the case that the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the cell ID(s) 1, . . ., N of the procedure 380 are different from value(s) of the cell ID(s) 1, . . . ., N, and the cell ID(s) N+l ,...., N+M described for the scenario 400. In some implementations, in the case that the CU 172 and S- DU 174 A perform the procedure 380 with the UE 102, value(s) of the cell index(es) 1, . . ., N of the procedure 380 are different from value(s) of the cell index(es) 1, . . . ., N, and the cell index(es) N+l ,...., N+M described for the scenario 400.

[0221] Later in time, the UE 102 can transmit 424 at least one measurement report to the S-DU 174A, similar to the event 324. The at least one measurement report (e.g., LI measurement report(s)) includes an event ID, first measurement result(s) for the cell 1 of the T-DU 174B, and/or includes second measurement result(s) for the cell 124A. In some implementations, the first measurement result(s) can be or include RSRP, RSRQ and/or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 1. Likewise, the second measurement result(s) can be or include RSRP, RSRQ and/or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 124 A. In some implementations, the event ID, RSRP, RSRQ and/or SINR are LI -event ID, LI -RSRP, LI -RSRQ and/or LI -SINR, respectively. Based on the first measurement result(s) and/or second measurement result(s), the S-DU 174A can transmit 430 a first LTM command (i.e., LTM command 1) including the ID 1 to the UE 102 to order the UE 102 to perform a serving cell change to the cell 1 of the T-DU 174B. In some implementations, the first LTM command includes the ID 1 (i.e., LTM ID). In other implementations, the first LTM command includes the cell index 1. When the UE 102 receives the first LTM command, the UE 102 performs a serving cell change to the cell 1 from a serving cell in accordance with the LTM DU configuration 1. After (e.g., in response to) receiving the first LTM command, the UE 102 can or can not perform 432 a random access procedure with the T-DU 174B, similar to the event 332. After (e.g., in response to) receiving the first LTM command or completing the random access procedure 432, the UE 102 can communicates 436 with the T-DU 174B on the first cell using the LTM DU configuration 1 and/or reference LTM DU configuration and communicates with the CU 172 via the T-DU 174B, similar to the event 336. If a serving cell change occurs in the procedure 380, the serving cell can be the cell 1 or cell 2 of the S-DU 174A. Otherwise, if no serving cell change occurs in the procedure 380 or the procedure 380 is not performed, the serving cell is the cell 124A. If the first LTM command includes the LTM ID 1, the UE 102 identifies the LTM DU configuration 1 and/or cell ID 1 (i.e., the cell 1), based the LTM ID 1, as described for Fig. 3. If the first LTM command includes the cell index 1, the UE 102 identifies the LTM DU configuration 1, cell ID 1 (i.e., the cell 1) and/or LTM ID 1, based the cell index 1, as described for Fig. 3. The UE 102 applies the LTM DU configuration 1 to communicate with the T-DU 174B, after (e.g., in response to) receiving the first LTM command or successfully accessing the cell 1.

[0222] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 430, the S-DU 174 A can transmit 429 to the CU 172 a DU- to-CU message indicating LTM (being) executed. In some implementations, the S-DU 174 A includes the cell ID 1 or the LTM ID 1 in the DU-to-CU message 429 to indicate that the S- DU 174A is to activate the LTM DU configuration 1 or trigger an LTM serving cell change. The S-DU 174 A can transmit the DU-to-CU message 429 to the CU 172 before or after transmitting the LTM command 430. In some implementations, when or after the CU 172 receives the DU-to-CU message 429, the CU 172 can stop or suspend transmitting DL data for the UE 102 to the S-DU 174A until receiving the DU-to-CU message 434. After receiving the DU-to-CU message 434, the CU 172 starts, continues or resumes transmitting DL data for the UE 102 to the T-DU 174B. When or after the T-DU 174B detects that UE 102 accesses the cell 1, the T-DU 174B transmits the DL data to the UE 102 via the cell 1.

[0223] The resource release procedure 496 can be similar to the procedure 396. Alternatively, in the resource release procedure 496, the CU 172 can transmit a CU-to-DU message (e.g., a UE Context Release Command message) to the S-DU 174 A to release a UE context of the UE 102. In response, the S-DU 174 A releases a UE context of the UE 102 and transmits 440 a DU-to-CU message (e.g., a UE Context Release Complete message) to the CU-172.

[0224] The events 380, 404, 406, 490, 492, 494, 494, 424, 426, 428, 429, 430, 431, 432, 434, 436, 496, 498, 456 are collectively referred to in Fig. 4 as an LTM configuration and/or activation procedure 480.

[0225] Referring next to Fig. 5 A, in a scenario 500A, the base station 106 operates as an MN, and the base station 104 operates as an SN. The SN 104 includes a CU 172 and a DU 174. The scenario 500A is similar to the scenario 300, except that the scenario 500A is a DC scenario and the scenario 300 is a single connectivity (SC) scenario. The MN 106 can include a CU and a DU similar to the base station 104 of Fig. 3.

[0226] Initially, the UE 102 in DC communicates with the MN 106 and with SN 104. In the event 502, the UE 102 communicates with the DU 174 on cell 124A using a serving DU configuration and communicates with the CU 172 via the DU 174 using a serving CU configuration, similar to the event 302. In some alternative implementations, the UE 102 does not communicate with the CU 172 via the DU 174 in the event 302. In some implementations, the UE 102 in DC can communicate 502 UL PDUs and/or DL PDUs with the MN 106 and/or SN 104 via radio bearers which can include SRBs and/or DRB(s). The MN 106 and/or the SN 104 can configure the radio bearers to the UE 102. The UE 102 in DC communicates 502 UL PDUs and/or DL PDUs with the SN 104 on an SCG (i.e., SCG radio resources) that the SN 104 configures for communication with the UE 102. The UE 102 in DC communicates UL PDUs and/or DL PDUs with the MN 106 on an MCG (i.e., MCG radio resources) in accordance with a MN configuration (i.e., MCG configuration). In some implementations, the serving DU configuration is a SN configuration (i.e., SCG configuration). In the MN configuration, the MN 106 configures the MCG which includes at least one serving cell (e.g., the cell 126 and/or other cell(s)) operated by the MN 106. In the serving DU configuration, the SN 106 A configures the SCG which includes at least one serving cell (e.g., the cell 124A and/or other cell(s)) operated by the SN 104. In some implementations, the MN configuration includes multiple configuration parameters and the UE 102 receives the configuration parameters in one or more RRC messages from the MN 106. As described for Fig. 3, the serving DU configuration includes multiple configuration parameters. In some implementations, the UE 102 receives these configuration parameters in one or more RRC messages from the SN 104, e.g., via the MN 106 and/or on an SRB (e.g., SRB3) that the MN 106 or SN 104 configures to exchange RRC messages between the UE 102 and the SN 104.

[0227] While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 can perform 580an LTM DU configuration and/or activation procedure with the UE 102, similar to the procedures 380 and/or 480. In some implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 can transmit the at least one measurement report to the CU 172 via the DU 174 and cell 124A in the events 504 and 506, similar to the events 304 and 306, respectively. In other implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 can transmit 505 at least one measurement report to the MN 106 via the cell 126. The MN 106 in turn transmits 507 the at least one measurement report to the CU 172. In some implementations, the MN 106 generates at least one SN message including the at least one measurement report and transmits the at least one SN message to the CU 172 in the event 507. In one implementation, the at least one SN message include RRC Transfer message(s) and/or SN Modification Request message(s).

[0228] After (e.g., in response to) receiving the at least one measurement report or while the SN 104 communicates with the UE 102, the SN 104 determines to prepare the first cell for the UE 102, as described for Fig. 3. The events 590, 592, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, and 556 are similar to the events 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, and 356, respectively. After receiving the first LTM command 530, transmitting the acknowledgement 531, or determining that the UE 102 successfully connects to the first cell 532 or 536, the UE 102 operating in DC with the MN 106 and SN 104 communicates 536 with the DU 174 on the first cell in accordance with the LTM DU configuration 1 and communicates 536 with the CU 172 via the DU 174, similar to the event 336. Later in time, the DU 174 and/or CU 172 can perform the LTM execution procedure 598 with the UE 102 to command the UE 102 to perform a cell change from the first cell to the second cell, similar to the procedure 398 or 498. As a result of the procedure 598, the UE 102 operating in DC with the MN 106 and SN 104 communicates 556 with the DU 174 on the second cell in accordance with the LTM DU configuration 2 and communicates 556 with the CU 172 via the DU 174, similar to the event 356.

[0229] In some implementations, the UE 102 transmits an RRC message (e.g., RRC reconfiguration complete message) to the CU 172 via the DU 174 and the first cell, e.g., to indicate that the UE 102 applies an LTM candidate configuration (e.g., the LTM DU configuration 1 and/or the LTM CU configuration 1) as described for Fig. 3. The first cell belongs to a secondary cell group (SCG).

[0230] The events 504, 506, 505, 507, 590, 592, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, 556 are collectively referred to in Fig. 5A as an LTM DU configuration and/or activation procedure 581.

[0231] Referring next to Fig. 5B, a scenario 500B is generally similar to the scenario 500A, except that the SN 104 transmits 517, 519 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 521, 523 the RRC reconfiguration complete message from the UE 102 via the MN 106. The RRC reconfiguration message 517, 519 is similar to the RRC reconfiguration message 316, 318. The RRC reconfiguration complete message 521, 523 is similar to the RRC reconfiguration message 320, 322. In some implementations, the SN 104 generates a first SN message (e.g., SN Modification Required message, SN Modification Required message, or RRC Transfer message) including the RRC reconfiguration message and transmits the first SN message to the MN 106 in the event 517. The MN 106 generates a MN RRC message including the RRC reconfiguration message and transmits 519 the MN RRC message to the UE 102. In response, the UE 102 generates a MN RRC response message including the RRC reconfiguration complete message and transmits 521 the MN RRC response message to the MN 106. In some implementations, the MN 106 generates a second SN message (e.g., SN Reconfiguration Complete message or RRC Transfer message) including the RRC reconfiguration complete message and transmits the second SN message to the SN 104 in the event 523. In some implementations, the MN RRC message and MN RRC response message can bean RRC reconfiguration message and an RRC reconfiguration complete message, respectively. [0232] In some implementations, the UE 102 transmits an RRC message (e.g., RRC reconfiguration complete message) to the CU 172 via the MN 106, e.g., to indicate that the UE 102 applies an LTM candidate configuration (e.g., the LTM DU configuration 1 and/or the LTM CU configuration 1) in response to receiving the LTM command 530. In one implementation, the UE 102 generates a MN container message (e.g., ULInformationTransferMRDC message) to include the RRC message and transmits the MN container message to the MN 106 via a serving cell 126 of a master cell group (MCG). The MN 106 retrieves the RRC message from the MN container message and transmits the RRC message to the CU 172.

[0233] The events 504, 506, 505, 507, 590, 592, 594, 517, 519, 521, 523, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, 556 are collectively referred to in Fig. 5B as an LTM DU configuration and/or activation procedure 582.

[0234] Referring next to Fig. 6 A, in a scenario 600 A, the base station 106 operates as an MN, and the base station 104 operates as an SN, similar to the scenarios 300-500B. The SN 104 includes a CU 172, an S-DU 174A and a T-DU 174B, similar to the base station 104 in the scenario 400. While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 can perform 680an LTM DU configuration and/or activation procedure with the UE 102, similar to the procedures 380 and/or 480. While the UE 102 communicates in DC with the M-DU 174 A and S-DU 174B, the CU 172 can perform 68 lan LTM DU configuration and/or activation procedure with the UE 102 via the M-DU 174A or S-DU 174B, similar to the procedure 581 or 582.

[0235] Referring next to Fig. 6B, a scenario 600B similar to the scenarios 300-500B and 600 A, except that that the SN 104 transmits 617, 619 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 621, 623 the RRC reconfiguration complete message from the UE 102 via the MN 106.

[0236] Referring next to Fig. 7A, in a scenario 700A, the base station 104 operates as an MN and an SN, similar to the scenarios 300-600B. The base station 104 includes a CU 172, a master DU (M-DU) 174 A and a secondary DU (S-DU) 174B. The CU 172 operates with the M-DU 174A as a MN, similar to the base station 104 in Fig. 3 or the MN 106 in Figs. 5A-6B, and the CU 172 operates with the S-DU 174B as a SN, similar to the SN 104 in Figs. 5A-6B.

[0237] In the scenario 700A, the UE 102 initially communicates 702 in DC with the M-DU

174A and S-DU 174B and communicates 702 with the CU 172 via the M-DU 174A and S- DU 174B. In the event 702, the UE 102 communicates with the S-DU 174B on cell 124 A using a serving DU configuration and communicates with the CU 172 via the S-DU 174B using a serving CU configuration, similar to the event 302. Events 704 and 706 are similar to the events 304 and 306. In some implementations, the UE 102 can transmit 705 at least one measurement report to the M-DU 174A, similar to the event 304. The M-DU 174A in turn transmits 707 at least one DU-to-CU message including the at les tone measurement report to the CU 172, similar to the event 306. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 780an LTM DU configuration and/or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380.

[0238] The events 704, 706, 705, 707, 790, 792, 794, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, 756 are collectively referred to in Fig. 7A as an LTM configuration and/or activation procedure 781.

[0239] Referring next to Fig. 7B, a scenario 700B similar to the scenarios 300-600B and 700A, except that that the CU 172 transmits 717, 719 the RRC reconfiguration message to the UE 102 via the M-DU 174 A and receives 721, 723 the RRC reconfiguration complete message from the UE 102 via the M-DU 174 A.

[0240] The events 704, 706, 705, 707, 790, 792, 794, 717, 719, 721, 723, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, 756 are collectively referred to in Fig. 7B as an LTM DU configuration and/or activation procedure 782.

[0241] Referring next to Fig. 8 A, in a scenario 800A, the base station 104 operates as an MN and an SN, similar to the scenarios 300-700B. The base station 104 includes a CU 172, a master DU (M-DU) 174A, a secondary DU (S-DU) 174B and a target secondary DU (T- DU) 174C. The CU 172 operates with the M-DU 174A as a MN and operates with the S-DU 174B as a SN. While the UE 102 communicates in DC with the M-DU 174 A and S-DU 174B, the CU 172 can perform 880an LTM DU configuration and/or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 88 lan LTM DU configuration and/or activation procedure with the UE 102 via the S-DU 174A, similar to the procedure 581 or 582.

[0242] Referring next to Fig. 8B, a scenario 800B similar to the scenarios 300-700B and 800 A, except that that the CU 172 transmits 817, 819 the RRC reconfiguration message to the UE 102 via the M-DU 174 A and receives 821, 823 the RRC reconfiguration complete message from the UE 102 via the M-DU 174 A.

[0243] Next, several example methods, which can be implemented in a RAN node (e.g., a base station, a DU or a CU) or a UE, for LTM, are discussed next with reference to Figs. 9A- 14. Descriptions described for Figs. 3-8B can apply to Figs. 9A-14. Similar steps are similarly labeled (e.g., 302, 402, 502, 602, 702, 802, 902, 1002, 1102, 1202, 1302, etc.) and individual descriptions are therefore omitted.

[0244] Fig. 9A illustrates an example method 900A, which can be implemented by a UE (e.g., the UE 102). The method 900A begins at block 902, where the UE communicates with a RAN via a MCG and a SCG (e.g., event 502, 602, 702 or 802). For example, the UE communicates with a MN and a SN of the RAN via the MCG and SCG, respectively. At block 918, the UE receives one or more LTM candidate configurations for the SCG from the RAN, where each of the LTM candidate configuration(s) configures a respective SCG candidate cell (e.g., event 594, 519, 694, 619, 794, 719, 894 or 819). At block 960, the UE detects a failure for the MCG (i.e., MCG failure). At block 962, the UE maintains the communication with the RAN via the SCG when detecting the failure for the MCG. At block 964, the UE initiates a MCG failure information procedure in response to detecting the failure for the MCG. At block 930, the UE receives a first LTM command from the RAN via the SCG after detecting the failure and before recovering the failure. At block 966, the UE discards the first LTM command. At block 968, the UE receives a first message recovering the failure from the RAN via the SCG. At block 970, the UE transmits a second message to the RAN via the MCG in response to the first message. At block 950, the UE receives a second LTM command from the RAN via the SCG after recovering the failure (e.g., event 598, 698, 798 or 898). At block 952, the UE performs an LTM cell switch to a second candidate SCG cell in response to the second LTM command (e.g., event 598, 698, 798 or 898).

[0245] The UE suspends transmission via the MCG (i.e., MCG transmission) in response to detecting the failure for the MCG. In some implementations, the UE suspends reception via the MCG (i.e., MCG reception) in response to detecting the failure for the MCG. In other implementations, the UE continues reception via the MCG after detecting the failure for the MCG. In some implementations, the UE operates in a connected state (e.g., RRC CONNECTED) performs all the actions in the blocks. In some implementations, all of the LTM candidate configuration(s) are SCG LTM candidate configuration(s) applying to or configured for the SCG. In such cases, each of the LTM DU configuration(s) configures a respective SCG candidate cell (e.g., a candidate PSCell for LTM).

[0246] In some implementations, upon initiating the MCG failure information procedure, the UE transmits a MCG failure information message to the RAN via the SCG to indicate the failure. When (e.g., in response to) receiving the MCG failure information message, the RAN transmits the first message to recover the failure.

[0247] In some implementations, the first message and the second message are an RRC reconfiguration message and an RRC reconfiguration complete message, respectively. In some implementations, the RAN includes a cell configuration (e.g., spCellConfig field or SpCellConfig IE) in the RRC reconfiguration message to configure a PCell. The UE accesses the PCell in accordance with the cell configuration. When the UE successfully connects to the PCell, the UE recovers the failure. In some implementations, the RAN does not include an LTM release configuration in the first message. In such cases, the UE retains the LTM candidate configuration(s) upon receiving the first message. In other implementations, the RAN includes one or more new LTM candidate configuration(s) in the first message. In such cases, the UE stores the new LTM candidate configuration(s). In one implementation, the new LTM candidate configuration(s) update some or all of the LTM candidate configuration(s). In such cases, the UE updates (e.g., modifies or replaces) some or all of the LTM candidate configuration(s) with the new LTM candidate configuration(s).

[0248] Based on the method 900 A, the UE refrains from performing an LTM cell switch to a SCG candidate cell during the failure for the MCG (i.e., MCG failure) to avoid a potential SCG failure of the LTM cell switch and wait for receiving the first message to recover the failure for the MCG. During the MCG failure, the UE discards any LTM command received from the RAN via the SCG to refrain from performing an LTM cell switch to a SCG candidate cell during a failure. After the UE recovers the MCG failure, the RAN may trigger an LTM cell switch for the UE as described in blocks 950 and 952.

[0249] Fig. 9B is a flow diagram of an example method 900B similar to the method 900A, except that method 900B includes block 972 instead of blocks 950 and 952. At block 972, the UE releases the LTM candidate configuration(s) in response to the first message.

[0250] In some implementations, the RAN includes an LTM release configuration in the first message to release the LTM candidate configuration(s). In such cases, the UE releases the LTM candidate configuration(s) in response to the LTM release configuration at block 972. The RAN releases the LTM candidate configuration(s) correspondingly in response to transmitting the LTM release configuration.

[0251] Fig. 9C is a flow diagram of an example method 900C similar to the method 900A, except that method 900C includes blocks 932 and 965 instead of block 966. At block 932, the UE performs an LTM cell switch to a first one of the candidate SCG cell(s) in response to the first LTM command. At block 965, the UE re-initiates the MCG failure information procedure after completing the LTM cell switch. In some implementations, if the UE determines that the RAN may not receive a MCG failure information message that the UE transmitted at block 964, the UE re-initiates the MCG failure information procedure (i.e., retransmits the MCG failure information message) to report the failure on the first candidate SCG cell. In other implementations, if the UE has not received an acknowledgement for the MCG failure information transmitted at block 964 before performing the LTM cell switch, the UE re-initiates the MCG failure information procedure. In yet other implementations, if the UE initiated transmission of the MCG failure information message during the last N second before performing the LTM cell switch or receiving the first LTM command, the UE re-initiates the MCG failure information procedure. In yet other implementations, the UE reinitiates the MCG failure information procedure after completing the LTM cell switch regardless of whether the RAN receives an MCG failure information message that the UE transmitted at block 964.

[0252] In some implementations, the UE is required to transmit an RRC message (e.g., RRC reconfiguration complete message) to the SN, e.g., to indicate that the UE applies the first LTM candidate configuration, in response to receiving the first LTM command. In cases where the UE is allowed to transmit SN RRC messages via the SCG (e.g., the UE is configured with a SRB over the SCG), the UE transmits the RRC message via the SRB over the SCG. In one implementation, the SRB is SRB3. In another implementation, the SRB is a split SRB 1.

[0253] In cases where the UE is not allowed to transmit SN RRC messages over the SCG (e.g., the UE is not configured with a SRB over the SCG or the UE does not support a SRB over the SCG), the UE transmits the RRC message via the MCG to the RAN after recovering the failure (i.e., blocks 968 and 970). In some implementations, the UE generates a MN container message to include the RRC message and transmit the MN container message via the MCG to the RAN. In such cases, the UE refrains from transmitting the RRC message via the MCG during the failure (period). If the UE attempts to transmit the RRC message via the MCG during the failure, the UE fails the attempt and ignores the attempt failure to avoid triggering an RRC connection reestablishment procedure. Alternatively, the UE skips transmitting the RRC message to the RAN via the MCG to avoid triggering an RRC connection reestablishment procedure.

[0254] Fig. 10A is a flow diagram of an example method 1000A, which can be implemented by a UE (e.g., the UE 102). The method 1000A begins with blocks 902 and 918 and can proceed to blocks 960, 962 and 964. The flow proceeds to block 1030 from block 918 or block 964. At block 1030, the UE receives a first LTM command from the RAN via the SCG. At block 1076A, the UE determines whether MCG transmission is suspended. If the MCG transmission is suspended (i.e., “Yes” branch of block 1076A), the flow proceeds to block 1068. Otherwise, if the MCG transmission is not suspended (i.e., “No” branch of block 1076A), the flow proceeds to block 1032.

[0255] Fig. 10B is a flow diagram of an example method 1000B similar to the method 1000A, except that method 1000B includes blocks 930 and 1076B instead of blocks 1030 and 1076A. At block 1076B, the UE determines whether the UE is required to transmit an RRC message via the MCG in response to the first LTM command. If the UE is required to transmit an RRC message via the MCG in response to the first LTM command (i.e., “Yes” branch of block 1076B), the flow proceeds to block 1068. Otherwise, if the UE is required to transmit an RRC message via the SCG in response to the first LTM command (i.e., “No” branch of block 1076B), the flow proceeds to block 1032.

[0256] In some implementations, the RRC message is an RRC reconfiguration complete message. If the UE is required to transmit an RRC message via the SCG in response to the first LTM command, the UE transmits the RRC message via the first candidate SCG cell to the RAN during or after the LTM cell switch.

[0257] Fig. 10C is a flow diagram of an example method 1000C similar to the method 1000B, except that method 1000C includes blocks 1076C instead of block 1076B. At block 1076C, the UE determines whether a SRB over the SCG (e.g., SRB3) is configured. If the SRB over the SCG is not configured (i.e., “No” branch of block 1076C), the flow proceeds to block 1068. Otherwise, if the SRB over the SCG is configured (i.e., “Yes” branch of block 1076C), the flow proceeds to block 1032. [0258] Fig. 10D is a flow diagram of an example method WOOD similar to the method 1000A, except that method WOOD includes blocks 1082 and 1084 instead of block 1068. The flow proceeds to block 1032 from block 1030 and proceeds to block 1076A from block 1-32. If the MCG transmission is not suspended (i.e., “No” branch of block 1076A), the flow proceeds to block 1082. At block 1082, the UE transmits an RRC message via the MCG to the RAN to indicate that the UE performs the LTM cell switch. In some implementations, the UE generates a MN container message (e.g., ULInformationTransferMRDC message) to include the RRC message and transmits the MN container message to the RAN via the MCG. Otherwise, if the MCG transmission is suspended (i.e., “Yes” branch of block 1076A), the flow proceeds to block 1084. At block 1084, the UE skips transmitting the RRC message (i.e., the UE refrains from transmitting the RRC message). In some implementations, the RRC message is an RRC reconfiguration message.

[0259] In some implementations, the UE transmits the RRC message when or after resuming the MCG transmission. In other words, the UE delays transmission of the RRC message until resuming the MCG transmission. In other implementations, the UE skips transmitting the RRC message even when or after resuming the MCG transmission.

[0260] Fig. 10E is a flow diagram of an example method 1000E similar to the methods 1000A, 1000B and WOOD, except that method 1000E includes 1082 and 1084 instead of block 968. If the UE is required to transmit

[0261] an RRC message via the SCG in response to the first LTM command (i.e., “No” branch of block 1076B), the flow proceeds to block 1083. At block 1083, the UE transmits an RRC message via the SCG to the RAN to indicate that the UE performs the LTM cell switch. Otherwise, if the UE is required to transmit an RRC message via the MCG in response to the first LTM command (i.e., “Yes” branch of block 1076B), the flow proceeds to block 1084.

[0262] In some implementations, the UE transmits the RRC message when or after recovering the failure. In other words, the UE delays transmission of the RRC message until recovering the failure. In other implementations, the UE skips transmitting the RRC message even when or after recovering the failure.

[0263] Fig. 10F is a flow diagram of an example method WOOF similar to the methods WOO A, 1000C, WOOD and 1000E.

[0264] Fig. 10G is a flow diagram of an example method 1000G similar to the methods 1000A, 1000C, lOOOD, 1000E and lOOOF. If the UE does not suspend the MCG transmission (i.e., “No” branch of block 1076A), the flow proceeds to block 1082. Otherwise, if the UE has suspended the MCG transmission (i.e., “Yes” branch of block 1076A), the flow proceeds to block 1083.

[0265] Examples and implementations described for Fig. 9A can apply to Figs. 10A-10G.

[0266] Fig. 11 is a flow diagram of an example method 1100, which can be implemented by a UE (e.g., the UE 102). The method 1100 begins with block 1102 and 1108. The flow proceeds to block 1160 from block 1108. At block 1160, the UE detects a failure for the SCG. At block 1161, the UE suspends transmission via the SCG (i.e., SCG transmission) in response to detecting the failure for the SCG. In some implementations, the UE continues reception via the SCG after detecting the failure for the SCG. At block 1162, the UE maintains the communication with the RAN via the MCG when detecting the failure for the SCG. At block 1164, the UE initiates a SCG failure information procedure in response to detecting the failure for the SCG. In some implementations, the UE transmits a SCG failure information message to the RAN via the MCG in response to initiating the SCG failure information procedure. The flow proceeds to blocks 1130 and 1132 to block 1164. At block 1136, the UE resumes transmission via the SCG (i.e., SCG transmission) upon completing the LTM cell switch. The UE communicates with the RAN via the first SCG candidate cell after resuming transmission via the SCG.

[0267] Fig. 12A is a flow diagram of an example method 1200A, which can be implemented by a UE (e.g., the UE 102). The method 1200A includes blocks 1202, 1260, 1262, and 1264 described in Fig. 9A (as blocks 902, 960, 962, and 964). The flow begins at block 1202 and proceeds to block 1218. At block 1218, the UE receives one or more LTM candidate configurations for the MCG from the RAN, where each of the LTM candidate configuration(s) configures a respective MCG candidate cell. The flow proceeds to blocks 960, 1261, 962, and 964 from block 1218. At block 1261, the UE suspends transmission via the MCG (i.e., MCG transmission) in response to detecting the failure for the MCG. At block 1230, the UE receives a first LTM command from the RAN via the MCG after detecting the failure and before recovering the failure. At block 1232, the UE performs an LTM cell switch to a first one of the MCG candidate cell(s) in response to the first LTM command. Upon completing the LTM cell switch, the UE recovers the failure. At block 1236, the UE resumes transmission via the MCG (i.e., MCG transmission) upon completing the LTM cell switch. The UE communicates with the RAN via the first MCG candidate cell after resuming transmission via the MCG.

[0268] Fig. 12B is a flow diagram of an example method 1200B similar to the method 1200A, except that method 1200B includes block 1233B instead of blocks 1230 and 1232. At block 1233, the UE performs an LTM cell switch to a first one of the MCG candidate cell(s) to recover the failure.

[0269] In some implementations, the UE performs a cell selection upon detecting the failure for the MCG and selects the first MCG candidate cell in the cell selection. Upon selecting the first MCG candidate cell, the UE initiates the LTM cell switch to the first MCG candidate cell. Unlike Fig. 12A, the UE initiates the LTM cell switch without receiving an LTM command.

[0270] Fig. 12C is a flow diagram of an example method 1200C similar to the methods 1200 A and 1200B, except that method 1200C includes blocks 1274 and 1233C instead of blocks 1230 and 1232. At block 1274, the UE detects a failure for the SCG (i.e., the SCG failure) during the failure for the MCG. At block 1233C, the UE performs an LTM cell switch to a first MCG candidate cell to recover the failure for the MCG, in response to detecting the failure for the SCG. In other words, the UE refrains from performing an LTM cell switch to a MCG candidate cell during the failure for the MCG while communicating with the RAN via the SCG.

[0271] Fig. 12D is a flow diagram of an example method 1200D similar to the methods 1200A, 1200B and 1200C, except that method 1200D includes blocks 1269 and 1273 instead of blocks 1230, 1232 and 1274. At block 1269, the UE determines whether the UE detects a failure for the SCG during the failure for the MCG. If the UE detects a failure for the SCG during the failure for the MCG, the flow proceeds to blocks 1233C and 1236. Otherwise, if the UE does not detect a SCG failure for the SCG, the flow proceeds to block 1273. At block 1273, the UE refrains from performing an LTM cell switch to a MCG candidate cell to recover the failure for the MCG while communicating with the RAN via the SCG.

[0272] Fig. 12E is a flow diagram of an example method 1200E similar to the methods 1200A, 1200B, 1200C and 1200D, except that method 1200E includes blocks 1271 and 1289 instead of blocks 1230, 1232, 1269 and 1273. At block 1271, the UE determines whether the UE is configured with an attempt LTM switch configuration. If the UE is configured with an attempt LTM switch configuration (i.e., “Yes” branch of block 1271), the flow proceeds to block 1233C and 1236. Otherwise, if the UE is not configured with an attempt LTM switch configuration (i.e., “No” branch of block 1271), the flow proceeds to block 1289. At block 1289, the UE performs an RRC connection reestablishment procedure in response to detecting the failure for the SCG.

[0273] In some implementations, the attempt LTM switch configuration (e.g., attemptLTM-Switch field) configures the UE to perform an LTM cell switch to a MCG candidate cell during a MCG failure if the UE selects the MCG candidate cell in a cell selection triggered by detecting a SCG failure.

[0274] Descriptions for Fig. 9A can apply to Figs. 12A, 12B, 12C, 12D and 12E.

[0275] Fig. 13A is a flow diagram of an example method 1300A, which can be implemented by a RAN (e.g., the RAN 105 or the base station 104 or 106). The method 1300 A begins at block 1302, where the RAN communicates with a UE via a MCG and a SCG e.g., event 502, 602, 702 or 802). At block 1318, the RAN transmits one or more LTM candidate configurations for the SCG to the UE, where each of the LTM candidate configuration(s) configures a respective SCG candidate cell (e.g., event 594, 519, 694, 619, 794, 719, 894 or 819). At block 1364, the RAN receives a MCG failure information message via the SCG from the UE, indicating a failure for the MCG. At block 1324, the RAN receives at least one first measurement result from the UE via the SCG after receiving the MCG failure information message (e.g., event 524, 624, 724 or 824). At block 1367A, the RAN refrains from transmitting an LTM command to the UE before recovering the failure, e.g., even when the first measurement result(s) indicates a candidate SCG cell qualifies for an LTM cell switch. At block 1368, the RAN transmits a first message to the UE via the SCG to recover the failure. At block 1370, the RAN receives a second message from the UE via the MCG in response to the first message. At block 1344, the RAN receives at least one second measurement result from the UE via the SCG after recovering the failure (e.g., event 598, 698, 798 or 898). At block 1350, the RAN transmits an LTM command to the UE via the SCG in response to the second measurement result(s) (e.g., event 598, 698, 798 or 898). At block 1352, the RAN performs an LTM cell switch with the UE on a first one of the SCG candidate cell(s) (e.g., event 598, 698, 798 or 898).

[0276] Fig. 13B is a flow diagram of an example method 13006 similar to the method 1300 A, except that method 1300B includes block 1367B instead of block 1367 A. At block 1367B, the RAN ignores or discard the first measurement result(s) before recovering the failure.

[0277] Fig. 13C is a flow diagram of an example method 1300C similar to the method 1300A, except that method 1300C includes block 1372 instead of blocks 1344, 1350 and 1352. At block 1372, the RAN releases the LTM candidate configuration(s) in response to transmitting the first message.

[0278] In some implementations, the RAN includes an LTM release configuration in the first message to release the LTM candidate configuration(s). In such cases, the UE releases the LTM candidate configuration(s) in response to the LTM release configuration. The RAN releases the LTM candidate configuration(s) correspondingly in response to transmitting the LTM release configuration at block 1372.

[0279] At least some of the discussion of Figs. 9A and 9B can also apply to the Figs. 13A-

13C.

[0280] Fig. 14 is a flow diagram of an example method 1400, which can be implemented by a CU (e.g., the CU 172). The method 1400 begins at block 1402, where the CU communicates with a UE. At block 1410, the CU receives one or more LTM DU configurations from at least one DU, where each of the LTM DU configuration(s) configures a respective LTM candidate cell (e.g., events 310, 390, 490, 590, 690, 790, and/or 890). At block 1412, the CU transmits to a serving DU, at least one CU-to-DU message for the LTM candidate cell(s) for the UE (e.g., events 308, 390, 312, 392, 412, 493, 590, 592, 693, 790, 792, and/or 893). At block 1416, the CU transmits one or more LTM candidate configurations to the UE, where each of the LTM candidate configuration(s) including a respective one of the LTM DU configuration(s) (e.g., events 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, and/or 819). At block 1485, the CU transmits a first CU-to-DU message to a serving DU to suspend triggering an LTM cell switch for the UE, e.g., in response to receiving the MCG failure information message. At block 1486, the CU transmits a second CU-to-DU message to the serving DU to resume triggering an LTM cell switch for the UE, e.g., after receiving the second message.

[0281] The CU may transmit the first CU-to-DU message to the serving DU for different reason(s). In some implementations, the CU receives a failure information message from the UE, indicating a failure. For example, the failure information message is a MCG failure information message and the failure is a MCG failure as described above. The CU may transmit the first CU-to-DU message in response to receiving the failure information message indicating the failure. After receiving the message, the CU transmits a first message to the UE to recover the failure and receives a second message from the UE in response to the first message as described above. The CU may transmit the second CU-to-DU message in response to receiving the second message. In other implementations, the CU transmits the first CU-to-DU message because the CU determines to update a serving configuration (e.g., a serving CU configuration and/or a serving DU configuration) or radio resources for the UE. After updating the serving configuration or radio resources for the UE, the CU may transmit the second CU-to-DU message to the serving DU.

[0282] In some implementations, the CU includes an indication in the first CU-to-DU message to indicate the serving DU to suspend triggering an LTM cell switch. In response to the first CU-to-DU message or the indication, the serving DU suspends triggering an LTM cell switch for the UE. The serving DU may transmit a first DU-to-CU message to the CU in response to the first CU-to-DU message. In some implementations, the CU includes an indication in the second CU-to-DU message to indicate the serving DU to resume triggering an LTM cell switch. In response to the second CU-to-DU message or the indication, the serving DU resumes triggering an LTM cell switch for the UE. The serving DU may transmit a second DU-to-CU message to the CU in response to the second CU-to-DU message.

[0283] In some implementations, the first CU-to-DU message and the second CU-to-DU messages are Fl Application Protocol (F1AP) messages. In some implementations, the first CU-to-DU message and the second CU-to-DU messages are UE Context Modification Request messages, and the first DU-to-CU message and the second DU-to-CU messages are UE Context Modification Response messages.

[0284] In some implementations, the at least one DU includes the serving DU and/or one or more candidate DUs (e.g., the T-DU 174B or T-DU 174C in Figs. 4, 6A, 6B, 8A, and/or 8B).

[0285] Fig. 15 is a flow diagram of an example method 1500, which can be implemented by a serving DU (e.g., the DU 174 in Figs. 3, 5A and 5B, the S-DU 174A in Figs. 4, 6A and 6B, or the S-DU 174B in Figs. 7A, 7B, 8 A and 8B). The method 1500 begins at block 1502, where the serving DU communicates with a UE and a CU. At block 1512, the serving DU receives, from the CU, at least one CU-to-DU message for one or more LTM candidate cells for the UE (e.g., events 308, 390, 312, 392, 412, 493, 590, 592, 693, 790, 792, and/or 893). At block 1514, the serving DU transmits a configuration to the UE via the CU, configuring uplink resources for CSI reports (e.g., events 314, 392, 414, 493, 592, 693, 792, and/or 893). At block 1585, the serving DU receives a first CU-to-DU message from the CU to suspend triggering an LTM cell switch for the UE. At block 1587, the serving DU suspends triggering an LTM cell switch for the UE in response to the first CU-to-DU message. At block 1586, the serving DU receives a second CU-to-DU message from the CU to resume triggering an LTM cell switch for the UE. At block 1588, the serving DU resumes triggering an LTM cell switch. At block 1530, the serving DU transmits an LTM command to the UE to command the UE to perform an LTM cell switch after resuming triggering an LTM cell switch.

[0286] In some implementations, when the serving DU suspends triggering an LTM cell switch for the UE, the serving DU ignores or discards measurement results (e.g., event 324, 424, 524, 624, 724, or 824) received from the UE. When the serving DU resumes triggering an LTM cell switch for the UE, the serving DU uses measurements results (e.g., event 324, 424, 524, 624, 724, or 824) received from the UE to determine whether to trigger an LTM cell switch for the UE (i.e., send an LTM command to the UE). In other implementations, when the serving DU suspends triggering an LTM cell switch for the UE, the serving DU refrains from sending an LTM command to the UE to trigger an LTM cell switch. When the serving DU resumes triggering an LTM cell switch for the UE, the serving DU is allowed to send an LTM command to the UE to trigger an LTM cell switch.

[0287] Descriptions for the RAN or base station in Figs. 9A-14 can apply to the Fig. 15.

[0288] Generally speaking, description for one of the above figures can apply to another of the above figures. Examples, implementations and methods described above can be combined, if there is no conflict. An event or block described above can be optional or omitted. For example, an event or block with dashed lines in the figures can be optional. The description described from the perspective of the receiving node also applies to the sending node. For example, a description that a receiving node (e.g., DU) receives a message from a sending node (e.g., CU) may be replaced by the sending node sending a message to the receiving node. Similarly, a description that a receiving node (e.g., CU) receives a message from a sending node (e.g., DU) may be replaced by the sending node sending a message to the receiving node.

[0289] In some implementations, “message” is used and can be replaced by “information element (IE)”, and vice versa. In some implementations, “IE” is used and can be replaced by “field”, and vice versa. In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters”, and vice versa. In some implementations, the “LTM command” can be replaced by “serving cell change command”, “Layer 1/Layer 2 LTM cell switch command”, “lower layer switching command” or “lower layer serving cell change command”. In some implementations, “some” means “one or more”. In some implementations, “at least one” means “one or more”. In some implementations, the “DU configuration” can be replaced by “cell group configuration”. In some implementations, the “cell index” can be replaced with “serving cell index”, “LTM cell index”, “special cell (SpCell) index”, “PCell index” or “PSCell index”. In some implementations, the “serving” can be replaced by “source”. In some implementations, the “measurement report” can be replaced by “measurement result(s)” or “CSI report”. In some implementations, the “early TA acquisition” can be replaced by “early UL timing synchronization” or “early UL synchronization”. In some implementations, the “early TA acquisition on a/the candidate cell” can be replaced by “early UL timing synchronization with a/the candidate cell” or “early UL synchronization with a/the candidate cell."

[0290] The following list of examples reflects a variety of the embodiments explicitly contemplated by the present disclosure.

[0291] Example 1. A method implemented in a user equipment (UE), the method comprising: communicating with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); receiving, from the RAN, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell associated with the SCG; detecting an MCG failure associated with the MCG; receiving, via the SCG and subsequently to the detecting of the MCG failure but prior to recovering the MCG, an LTM command indicating that the UE is to initiate an LTM cell switch to the candidate cell; and one of discarding the LTM command, or performing an MCG failure information procedure after completing the LTM cell switch.

[0292] Example 2. The method of example 1, wherein: the LTM command is a first LTM command; the method further comprising: receiving, subsequently to the recovering of the MCG, a second LTM command indicating that the UE is to initiate the LTM switch to the candidate cell; and performing the LTM switch to the candidate cell using the LTM candidate configuration. [0293] Example 3. The method of example 1, further comprising: releasing the LTM candidate configuration.

[0294] Example 4. The method of example 3, wherein: the releasing is in response to receiving an LTM release configuration from the RAN.

[0295] Example 5. The method of example 4, wherein: the LTM release configuration is included in a radio resource control (RRC) reconfiguration message.

[0296] Example 6. The method of example 1, further comprising: initiating the MCG failure information procedure in response to the detecting of the MCG failure; wherein the performing of the MCG failure information procedure after completing the LTM cell switch includes re-initiating the MCG failure information procedure.

[0297] Example 7. The method of example 6, wherein: the initiating the MCG failure information procedure includes transmitting, to the RAN, an MCG failure information message; and the re-initiating the MCG failure information procedure includes determining that the RAN did not receive the MCG failure information message.

[0298] Example 8. The method of example 7, wherein the determining that the RAN did not receive the failure information message includes: failing to receive an acknowledgement to the MCG failure information message.

[0299] Example 9. The method of any of examples 6-8, further comprising: transmitting, to the RAN, an indication that the UE applied the LTM configuration in the LTM cell switch.

[0300] Example 10. The method of example 9, wherein: the indication is transmitted to the SN over one of a signaling radio bearer 3 (SRB3) or a split SRB.

[0301] Example 11. The method of example 9, wherein: the indication is transmitted to the MN subsequently to the recovering of the MCG.

[0302] Example 12. The method of any of examples 6-8, further comprising: subsequently to the LTM cell switch, transmitting, via the MCG and in response to determining that the MCG is not suspended, an indication that the UE applied the LTM configuration in the LTM cell switch.

[0303] Example 13. The method of any of examples 6-8, further comprising: subsequently to the LTM cell switch, transmitting, via the SCG and in response to determining that the UE is not configured to transmit an RRC message via the MCG in response to the LTM command, an indication that the UE applied the LTM configuration in the LTM cell switch.

[0304] Example 14. The method of any of examples 6-8, further comprising: subsequently to the LTM cell switch, transmitting, via the SCG and in response to determining that an SRB is configured for the SCG, an indication that the UE applied the LTM configuration in the LTM cell switch.

[0305] Example 15. The method of any of examples 1-11, wherein: the discarding of the LTM command is in response to determining that a transmission on the MCG is suspended.

[0306] Example 16. The method of any of examples 1-11, wherein: the discarding of the LTM command is in response to determining that the UE is configured to transmit an RRC message via the MCG in response to the LTM command.

[0307] Example 17. The method of any of examples 1-11, wherein: the discarding of the LTM command is in response to determining that an SRB is configured for the SCG.

[0308] Example 18. The method of any of the preceding examples, further comprising: subsequently to the detecting of the MCG failure and prior to recovering the MCG, continuing to communicate with the RAN via the SCG.

[0309] Example 19. The method of any of the preceding examples, wherein the candidate cell is an SCG cell associated with the SN.

[0310] Example 20. A method implemented in a user equipment (UE), the method comprising: communicating with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); receiving, from the RAN, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell associated with the SCG; detecting an SCG failure associated with the SCG; suspending a transmission on the SCG in response to the detecting of the SCG failure; receiving, from the RAN and subsequently to the detecting of the SCG failure but prior to recovering the SCG, an LTM command indicating that the UE is to initiate an LTM cell switch to the candidate cell; performing the LTM cell switch to the candidate cell; and resuming the transmission via the SCG after the LTM cell switch.

[0311] Example 21. The method of example 20, further comprising: subsequently to the detecting of the SCG failure and prior to recovering the SCG, continuing to communicate with the RAN via the MCG. [0312] Example 22. The method of example 20, further comprising: in response to the detecting of the SCG failure, initiating an SCG failure information procedure.

[0313] Example 23. A method implemented in a user equipment (UE), the method comprising: communicating with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); receiving, from the RAN, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell associated with the MCG; detecting an MCG failure associated with the MCG; determining, subsequently to the detecting of the MCG failure but prior to recovering the MCG, that the UE is to initiate an LTM cell switch to the candidate cell; and performing the LTM switch to the candidate cell in response to the determining.

[0314] Example 24. The method of example 23, further comprising: subsequently to the detecting of the MCG failure and prior to recovering the MCG, continuing to communicate with the RAN via the SCG.

[0315] Example 25. The method of example 23 or 24, wherein: the determining that the UE is to initiate the LTM cell switch to the candidate cell includes receiving an LTM command from the RAN.

[0316] Example 26. The method of example 23 or 24, wherein: the determining that the UE is to initiate the LTM cell switch to the candidate cell includes determining to recover the MCG by performing the LTM cell switch.

[0317] Example 27. The method of example 26, wherein the determining that the UE is to initiate the LTM cell switch includes not receiving an LTM command from the RAN.

[0318] Example 28. A method implemented in a radio access network (RAN), the method comprising: communicating with a user equipment (UE) in dual connectivity (DC) via (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); transmitting, to the UE, a low-layer triggered mobility (LTM) candidate configuration for a candidate cell associated with the SCG; receiving an indication of an MCG failure for the UE; and refraining from causing the UE to initiate an LTM cell switch to the candidate cell, prior to a recovery of the MCG for the UE.

[0319] Example 29. The method of example 28, wherein: the refraining incudes refraining from transmitting an LTM command to the UE. [0320] Example 30. The method of example 28, wherein: the refraining incudes discarding measurement results related to the candidate cells, from the UE.

[0321] Example 31. The method of any of examples 28-30, further comprising: releasing the LTM candidate configuration.

[0322] Example 32. The method of any of examples 28-30, further comprising: in response to the receiving of the indication of the MCG failure, transmitting, to the UE via the SCG, a request to recover the MCG.

[0323] Example 33. The method of example 32, further comprising: transmitting an LTM command to the UE in response to determining that the UE recovered the MCG.

[0324] Example 34. An apparatus comprising processing hardware and configured to implement a method of any of the preceding examples

[0325] A user device in which the techniques of this disclosure can be implemented (e.g., the UE 102) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an internet-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0326] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules may can be software modules (e.g., code, or machine- readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations and may be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0327] The term “or” as used herein is to be interpreted as an inclusive or meaning any one or any combination, unless expressly indicated otherwise, mutually exclusive, or indicated otherwise by context. Therefore, herein, the expression “A or B” means “A, B, or both A and B.”

[0328] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software can be executed by one or more general-purpose processors or one or more special-purpose processors.

[0329] Upon reading this disclosure, those of skill in the art will appreciate still additional and alternative structural and functional designs for handling mobility between base stations through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

Claims

What is claimed is:

1. A method implemented in a user equipment (UE), the method comprising: communicating with a radio access network (RAN) in dual connectivity (DC) with (i) a master node (MN) using a master cell group (MCG) and (ii) a secondary node (SN) using a secondary cell group (SCG); performing a lower-layer triggered mobility (LTM) cell switch to a candidate cell associated with the SCG, according to an LTM configuration; and transmitting, via one of the MCG or the SCG, an indication that the UE performed the LTM cell switch, based on whether the UE has suspended a transmission on the MCG.

2. The method of claim 1, wherein: the indication that the UE performed the LTM cell switch is transmitted via the MCG in response to determining that the UE has not suspended the transmission on the MCG.

3. The method of claim 2, wherein the indication that the UE performed the LTM cell switch is transmitted in an ULInformationTransferMRDC message.

4. The method of claim 3, wherein the ULInformationTransferMRDC message is transmitted in an MN container message.

5. The method of claim 1, wherein: the indication that the UE performed the LTM cell switch is transmitted via the SCG in response to determining that the UE has suspended the transmission on the MCG.

6. The method of any of the preceding claims, further comprising, prior to the performing of the LTM cell switch: receiving, from the RAN, the LTM configuration for the candidate cell.

7. The method of any of the preceding claims, further comprising, prior to the performing of the LTM cell switch: receiving, from the RAN, an LTM command indicating that the UE is to initiate the LTM cell switch to the candidate cell.

8. The method of claim 7, wherein the LTM command is received via the SCG.

9. The method of claim 7, wherein the LTM command is received subsequently to detecting failure of the MCG but prior to recovering the MCG.

10. The method of any of the preceding claims, further comprising: subsequently to detecting failure of the MCG and prior to recovering the MCG, continuing to communicate with the RAN via the SCG.

11. The method of any of claims 5-8, further comprising: suspending the transmission on the MCG in response to detecting failure of the MCG.

12. The method of claim 11, further comprising: transmitting, via the SCG, MCG failure information.

13. The method of any of claims 5-12, wherein: the indication that the UE performed the LTM cell switch is transmitted via the SN over a signaling radio bearer 3 (SRB3).

14. The method of any of claims 5-12, wherein: the indication that the UE performed the LTM cell switch is transmitted via the SN over a split signaling radio bearer (SRB).

15. A user equipment (UE) comprising: processing hardware; and a transceiver; wherein the UE is configured to implement a method of any of the preceding claims.