WO2024168867A1

WO2024168867A1 - Method and apparatus for beam indication in lower layer centric mobility procedure in a wireless communication system

Info

Publication number: WO2024168867A1
Application number: PCT/CN2023/076924
Authority: WO
Inventors: Yushu Zhang; Jia-Hong Liou
Original assignee: Google LLC
Current assignee: Google LLC
Priority date: 2023-02-17
Filing date: 2023-02-17
Publication date: 2024-08-22
Anticipated expiration: 2025-08-17
Also published as: EP4649718A1

Abstract

In the context of lower layer centric mobility, a network entity provides a beam indication to a user equipment (UE) during switching from a source cell to a target cell using a signaling. Methods, techniques, systems, and devices are disclosed for beam indication during the lower layer centric mobility operations. The signaling techniques herein are also useful for the UE reporting the capability regarding maintaining active transmission configuration indicator (TCI) states in the source cell and the target cell. In addition, the disclosed methods enable the network entity and the UE to track pathloss signals during the switching from the source cell to the target cell.

Description

METHOD AND APPARATUS FOR BEAM INDICATION IN LOWER LAYER CENTRIC MOBILITY PROCEDURE IN A WIRELESS COMMUNICATION SYSTEM

FIELD

This disclosure relates generally to wireless communications and, more particularly, to L1/L2 mobility signaling.

BACKGROUND

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.

Procedures related to multiple-transmit-reception-point (mTRP) scenario and interaction between serving cell and neighboring cell have been established in current practices. For example, inter-cell beam management and inter-cell mTRP. For these two procedures, at least one of concerned scenarios is a UE can communicate with a base station (BS) in a serving cell and/or a neighboring cell. A neighboring cell could be a cell broadcasting a physical cell ID (PCI) different from that of the serving cell. The UE can be served by the BS via two TRPs (or two TRP clusters/sets) , where one is located in the serving cell and the other is located in the neighboring cell.

For inter-cell beam management, the beam indication framework may use a unified TCI framework (e.g., according to Release 17 of 3^rd Generation Partnership Project (3GPP) ) . The BS may indicate and/or configure the UE a serving beam (e.g., a unified TCI state) . The unified TCI state is transmitted from the serving cell or a neighboring cell. However, the BS does not serve or communicate with the UE via one active TCI state from the serving cell and another one active TCI state from the neighboring cell at the same time (e.g., in the same slot) .

In inter-cell mTRP cases, such as according to the existing framework, the BS may indicate and/or configure the UE a serving beam (e.g., a TCI state) for each cell. The TCI state for the source cell is transmitted from the serving cell. The TCI state for the target cell is transmitted from the neighboring cell. The BS may then transmit DL data to the UE using the two beams indicated by the two TCI states. As such, lower layer mobility procedures are to be improved.

SUMMARY

The present disclosure provides methods, systems, and techniques related to the beam indication in lower layer centric mobility procedure (LLCMP) , such as L1/L2 trigger mobility (LTM) . LLCMP can involve a base station, BS, to signal beams usable in candidate cells and configured beam activation and/or indication to a user equipment, UE, when the UE is moving from a source cell (e.g., a coverage area of a current transmission reception point, TRP) to a target cell (e.g., another TRP) . In LLCMP, the BS and the UE communicate for or perform the cell switching using lower layer signaling without involving higher layer reconfiguration. The lower layer signaling also allows the BS and the UE to maintain and/or track transmission configuration indication (TCI) states corresponding to beams usable for communicating there-between and pathloss reference signals. In some cases, the UE reports the capability for maintaining/tracking active TCI states and pathloss RSs so that the BS may signal accordingly. The lower layer centric mobility procedure disclosed herein provides an efficient and reliable cell switching procedure.

According to general aspects of this disclosure, a BS may provide a beam indication to a UE during switching from a source cell to a target cell using a signaling. The signaling may also be used for the UE reporting the capability regarding maintaining active TCI states in the source cell and the target cell. The disclosed methods also enable the BS and UE to track pathloss signals during the switching from the source cell to the target cell.

In multiple-TRP (mTRP) scenarios, a UE interacts with both a TRP in a current serving cell and the other TRP in a neighboring cell. As such, the UE needs to perform inter-cell beam management and inter-cell mTRP signaling. For these procedures, a UE may communicate with a base station, BS, in a serving cell and/or a neighboring cell (e.g., the BS providing TRPs for both cells) . The neighboring cell may broadcast a physical cell identifier (PCI) different from the PCI of the serving cell. This way, the BS serves the UE via the two TRPs (or two TRP clusters/sets) , one TRP located in the serving cell (also referred to as the current cell or the source cell) and the other located in the neighboring cell (also referred to as the target cell as the UE moves to the neighboring cell) .

For example, in aspects of this disclosure, before cell switching, the BS may have configured one or more candidate cell configurations in the UE. The BS then transmits a cell switch command (CSC) to the UE. Based on the CSC, the UE may determine which candidate cell configuration to apply and which (target) cell to move in (when the UE moves from source cell to target cell) . The present disclosure provides methods and techniques for specific signaling and beam indication examples, including, for example, (1) how a BS performs beam indication for the target cell, and (2) how the UE receives and applies the beam indication.

In some cases, the disclosed method includes an example in which the beam indication signal being transmitted together with the CSC (e.g., they are in the same slot or in the same PDSCH) . In other cases, the disclosed method includes an example in which the beam indication signal being transmitted separate from the CSC. Furthermore, upon completing or during the cell switching, the UE may, in some cases, maintain active TCI states with the source cell. The present disclosure provides methods regarding when the UE may stop maintaining the active TCI states in the source cell. In some cases, the example methods may depend on UE capability regarding the number of active TCI states in the source cell and target cell (i.e., a candidate cell indicated by a CSC) . The UE may report this capability so that the BS may provide proper configuration.

Aspects of this disclosure include a wireless communication method by a UE. The example method includes obtaining, from a network entity, NE, via a source cell, candidate cell configurations of candidate cells. The UE receives, from the NE, a cell switch command, CSC, that indicates a target cell among the candidate cells. The UE activates TCI states associated with the target cell. The UE identifies at least one of the activated TCI states. The UE applies the at least one of the activated TCI states to communicate with the NE via the target cell.

Aspects of this disclosure include a wireless communication method by a network entity. The example method includes transmitting, to a user equipment, UE, via a source cell, candidate cell configurations of candidate cells. The network entity transmits, to the UE, a cell switch command, CSC, that indicates a target cell among the candidate cells. The network entity communicates with the UE via the target cell using activated beams.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1A is a block diagram of an example system in which a distributed base station and/or a user equipment (UE) can implement the techniques of this disclosure.

Fig. 1B is a block diagram of an example base station including a central unit (CU) and a distributed unit (DU) of a distributed base station that can operate in the system of Fig. 1A.

Fig. 2A is a block diagram of an example protocol stack according to which the UE of Figs. 1A-B can communicate with base stations.

Fig. 2B is a block diagram of an example protocol stack according to which the UE of Figs. 1A-B can communicate with a DU and a CU of a base station.

Fig. 3A illustrates a signaling diagram between the UE 102 and the BS 104 for beam indication, in accordance with aspects of this disclosure.

Fig. 3B illustrates a signaling diagram between the UE 102 and the BS 104 for beam indication, in accordance with aspects of this disclosure.

Fig. 3C illustrates a signaling diagram between the UE 102 and the BS 104 for beam indication, in accordance with aspects of this disclosure.

Fig. 3D illustrates a signaling diagram between the UE 102 and the BS 104 for beam indication, in accordance with aspects of this disclosure.

Fig. 4A illustrates a signaling diagram between the UE 102 and the BS 104 for beam indication, in accordance with aspects of this disclosure.

Fig. 4B illustrates a signaling diagram between the UE 102 and the BS 104 for beam indication, in accordance with aspects of this disclosure.

Fig. 5A illustrates a signaling diagram between the UE 102 and the BS 104 for beam indication, in accordance with aspects of this disclosure.

Fig. 5B illustrates a signaling diagram between the UE 102 and the BS 104 for beam indication, in accordance with aspects of this disclosure.

Fig. 6 illustrates a lower layer centric mobility operation scenario, in accordance with aspects of this disclosure.

Fig. 7 illustrates an example flowchart of a method performed by a network entity, in accordance with aspects of this disclosure.

Fig. 8 illustrates an example flowchart of a method performed by a network entity, in accordance with aspects of this disclosure.

Fig. 9 is a diagram illustrating a hardware implementation for an example UE apparatus.

Fig. 10 is a diagram illustrating a hardware implementation for one or more example network entities.

Like numerals indicate like elements.

DETAILED DESCRIPTION

For L1/L2 Triggered Mobility (LTM) , or in general, for lower layer centric mobility, the present disclosure concerns how a network entity (e.g., a base station, BS) may (1) perform beam indication and (2) maintain active TCI states in a source cell during beam switching from a source cell to a target cell.

Regarding beam indication, the legacy uses, after RRC configuration of TCI state, the MAC CE for beam activation, and DCI for beam indication. In the LTM scenario, this disclosure introduces the use of cell switch command (CSC) to perform the beam indication instead of using the DCI. Because the CSC is one type of MAC CE, the CSC may activate TCI states according to different options/assumptions (depending on future agreement) .

For example, in a first aspect, the CSC activates two or more TCI states. The CSC indicates a TCI state by a rule based method (e.g., activating a rule-specified one of the multiple activated TCI states) without CSC indication.

Regarding CSC indication, when the CSC is scheduled by a DCI, the DCI can indicate the beam (so indication prior to activation regarding the target cell beam) . The DCI may include a TCI field or bit field of the DCI. These options may coexist and be used with different DCI formats.

In a second aspect, the CSC activates one TCI state. For example, the activated TCI state is the indicated TCI state.

In a third aspect, the CSC does not activate any TCI state. For example, the TCI states activation may be indicated by the DCI scheduling the CSC, indicated by a DCI not scheduling the CSC, indicated by the CSC (i.e., separating beam activation from indication) , indicated by another MAC CE, and limiting the TCI state list to include only one TCI state.

Because CSC does not activate TCI state, the activation is performed by the network entity sending: (1) one MAC CE for both the source and the target cells; or (2) two MAC CEs respectively for each of the source and the target cells.

Regarding the single MAC CE situation, one mapping table (TCI code point differentiation) may be provided, or two mapping tables (e.g., UE determines which to use based on CSC scheduling) may be provided.

Regarding the two MAC CEs situation, two mapping tables are provided and the UE determines which to use based on CSC scheduling.

Regarding active TCI states maintenance (associated with pathloss reference signal tracking, one-to-one relationship) , the UE maintains active TCI states in the current cell when the total active TCI states for both the source and the target cells does not exceed the UE’s capability; and stops maintaining the active TCI states in the current cell when the total active TCI states for both the source and the target cells exceeds the US’s capability.

Regarding the UE capability, the LTM procedure may require the UE to support two or more active TCI states (X) . When not performing LTM procedure, the UE may support a maximum active TCI states number that is one less than the maximum active TCI states number for LTM procedure (X-1) ; or the UE continues to support X.

In some aspects regarding special occasions, when the UE supports only one active TCI state, then the UE stops maintaining that TCI state when: receiving CSC or beam indication, transmitting ACK for CSC or beam indication, upon completing LTM, and receiving indication other than beam indication.

In some cases, whether to maintain active TCI state in current cell may be decoupled from monitoring PDCCH in the current cell.

This disclosure provides ideas of handling issues or performing procedures related to a lower layer centric mobility procedure. With ideas mentioned in this disclosure, UE and/or BS can perform procedure related to beam indication, maintaining/tracking TCI states and pathloss RSs, and reporting UE capability for maintaining/tracking active TCI states and pathloss RSs. An efficient and reliable cell switching procedure can be provided from this disclosure.

For inter-cell beam management, the concerned beam indication framework is Rel-17 unified TCI framework. The BS can indicate and/or configure the UE a serving beam or unified TCI state, which is transmitted from the serving cell or the neighboring cell. However, the BS does not serve or communicate with the UE via one active TCI state from the serving cell and another one active TCI state from the neighboring cell at the same time (e.g., in the same slot) .

For inter-cell mTRP, the concerned beam indication framework is Rel-15/16 TCI framework. The BS can indicate and/or configure the UE a serving beam or Rel-15/16 TCI state, which is transmitted from the serving cell, and another one serving beam or Rel-15/16 TCI state, which is transmitted from the neighboring cell. The BS could transmit DL data to the UE by these two beams (or Rel-15/16 TCI state) .

For NR Rel-18, 3GPP has agreed a working item (WI) targeting mobility enhancement, one target of which is for a lower layer centric mobility procedure (or a L1/L2 triggered mobility (LTM) procedure) . The lower layer centric mobility is intended for reducing latency when performing cell switching. In legacy, cell switching may require many higher layer message exchange and reconfiguration, which also induces longer latency. A lower layer centric mobility procedure can help resolve this latency issue. Before cell switching, the BS may have configured one or more candidate cell configurations to the UE. Afterwards, the BS could transmit a cell switch command (CSC) to the UE, and the UE can realize which candidate cell configuration to apply and which cell to move in (i.e., UE moves from source cell to target cell) . However, there are still some holes in the lower layer centric mobility, which are left to fill in.

In NR Rel-17, several procedures have been introduced, which are related to multiple-TRP (mTRP) scenario and interaction between serving cell and neighboring cell. For example, inter-cell beam management and inter-cell mTRP. For these two procedures, at least one of concerned scenarios is a UE can communicate with a base station (BS) in a serving cell and/or a neighboring cell. A neighboring cell could be a cell broadcasting a physical cell ID (PCI) different from that of the serving cell. The UE can be served by the BS via two TRPs (or two TRP clusters/sets) , where one is located in the serving cell and the other is located in the neighboring cell.

One issue considered in this disclosure is related to how a BS performs beam indication for target cell, and how also UE receives and applies the beam indication. The solutions may differ depending on whether the beam indication signal is transmitted together with the cell switch command (e.g., they are in the same slot or in the same PDSCH) . Furthermore, when to stop maintaining active TCI states in current cell (or source cell) . How to repot UE capability for the number of active TCI states in the source cell and target cell (i.e., a candidate cell indicated by a CSC) could be issues as well. We could also take similar concerns for tracking pathloss RS.

Referring first to Fig. 1A, an example of wireless communication system 100 includes a UE 102, a base station (BS) 104, a base station 106, and a core network (CN) 110. The base stations 104 and 106 can operate in a RAN 105 connected to the core network (CN) 110. The CN 110 can be implemented as an evolved packet core (EPC) 111 or a fifth generation (5G) core (5GC) 160, for example. The CN 110 can also be implemented as a sixth generation (6G) core in another example.

The base station 104 can cover one or more cells (e.g., cells 124 and 125) with one or more transmit and/or receive points (TRPs) , and the base station 106 can similarly cover one or more cells (e.g., cell 126) with one or more TRPs. For example, the base station 104 operates cell 124 with TRPs 107-1 and 107-2 and operates cell 125 with TRP 107-3, and the base station 106 operates cell 126 with TRPs 108-1 and 108-2. The cells 124 and 125 are operated on the same carrier frequency/frequencies. The cell 126 can be operated on the same carrier frequency/frequencies as the cells 124 and 125. Alternatively, the cell 126 can be operated on different carrier frequency/frequencies from the cells 124 and 125. In some implementations, the base station 104 connects each of the TRPs 107-1, 107-2 and 107-3 via a fiber connection or an Ethernet connection. If the base station 104 is a gNB, the cells 124 and 125 are NR cells. If the base station 104 is an (ng-) eNB, the cells 124 and 125 are evolved universal terrestrial radio access (EUTRA) cells. Similarly, if the base station 106 is a gNB, the cell 126 is an NR cell, and if the base station 106 is an (ng-) eNB, the cell 126 is an EUTRA cell. The cells 124, 125, and 126 can be in the same Radio Access Network Notification Areas (RNA) or different RNAs. In general, the RAN 105 can include any number of base stations, and each of the base stations can cover one, two, three, or any other suitable number of cells. The UE 102 can support at least a 5G NR (or simply, “NR” ) or E-UTRA air interface to communicate with the base station 104 via the TRP 107-1, TRP 107-2 and/or TRP-3. Similarly, the UE 102 can support at least a 5G NR (or simply, “NR” ) or E-UTRA air interface to communicate with the base station 106 via the TRP 108-1 and/or TRP 108-2. Each of the base stations 104, 106 can connect to the CN 110 via an interface (e.g., S1 or NG interface) . The base stations 104 and 106 also can be interconnected via an interface (e.g., X2 or Xn interface) for interconnecting NG RAN nodes.

When a base station (e.g., the base station 104 or 106) transmits DL data via a TRP (e.g., the TRP 107-1, TRP 107-2, TRP 107-3, TRP 108-1 or TRP 108-2) , the base station 104 can generate a packet including the data transmit the packet to the TRP 107-1. For example, the packet can be a fronthaul transport protocol data unit. The TRP extracts the data from the packet and transmits the data. In some implementations, the base station 104 can include control information for time-critical control and management information directly related to the data in the packet, and the TRP can transmit the data in accordance with the control information. In some implementations, the data includes In-phase and Quadrature (IQ) data, a physical layer bit sequence, or a MAC PDU. When the TRP receives data from a UE (e.g., UE 102) , the TRP generates a packet including the data and transmit the packet to the base station 104. In some implementations, the data includes IQ data, a physical layer bit sequence, or a MAC PDU.

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 in general is 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 102 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 Function (AMF) 164, and/or Session Management Function (SMF) 166. Generally, the UPF 162 is 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.

As illustrated in Fig. 1A, the base station 104 supports cells 124 and 125, and the base station 106 supports a cell 126. The cells 124, 125, and 126 can partially overlap, so that the UE 102 can select, reselect, or hand over from one of the cells 124, 125, and 126 to another. To directly exchange messages or information, the base station 104 and base station 106 can support an X2 or Xn interface. In general, the CN 110 can connect to any suitable number of base stations supporting NR cells and/or EUTRA cells.

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 DL channels and DL reference signals with one or more user devices (e.g., UE 102) via one or more TRPs (e.g., TRP 107-1, TRP 107-2 and/or TRP 107-3) . The PHY controller 132 is also configured to receive data and control signal on physical UL channels and/or UL reference signals with the one or more user devices via the one or more TRPs (e.g., TRP 107-1, TRP 107-2 and/or TRP 107-3) . The processing hardware 130 in an example implementation includes a MAC controller 134 configured to perform a random access (RA) procedure with one or more user devices, manage UL timing advance for the one or more user devices, receive UL MAC PDUs from the one or more user devices, and transmit DL MAC PDUs to the one or more user devices. 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. 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.

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 TRPs (e.g., TRP 107-1, TRP 107-2, TRP 107-3, TRP 108-1 and/or TRP 108-2) . 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 the one or more TRPs (e.g., TRP 107-1, TRP 107-2, TRP 107-3, TRP 108-1 and/or TRP 108-2) . The processing hardware 150 in an example implementation includes a MAC controller 154 configured to perform a random access procedure with base station 104 or 106, manage UL timing advance for the one or more user devices, transmit UL MAC PDUs to the base station 104 or 106, and receive DL MAC PDUs from the base station 104 or 106. 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.

Fig. 1B depicts an example distributed or disaggregated implementation of one or both of the base stations 104, 106. In this implementation, each of the base station 104 and/or 106 includes a central unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 includes processing hardware, such as one or more general-purpose processors (e.g., CPUs) and a computer-readable memory storing machine-readable instructions executable on the general-purpose processor (s) , and/or special-purpose processing units. For example, the CU 172 can include a PDCP controller (e.g., PDCP controller 134, 144) , an RRC controller (e.g., RRC controller 136, 146) , and/or an RRC inactive controller (e.g., RRC inactive controller 138, 148) . In some implementations, the CU 172 can include an RLC controller configured to manage or control one or more RLC operations or procedures. In other implementations, the CU 172 does not include an RLC controller.

Each of the DUs 174 also includes processing hardware that can include one or more general-purpose processors (e.g., CPUs) and computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and/or special-purpose processing units. For example, the processing hardware can include a MAC controller (e.g., MAC controller 132, 142) configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure) , and/or an RLC controller configured to manage or control one or more RLC operations or procedures. The processing hardware can also include a physical layer controller configured to manage or control one or more physical layer operations or procedures.

In some implementations, the RAN 105 supports Integrated Access and Backhaul (IAB) functionality. In some implementations, the DU 174 operates as an (IAB) -node, and the CU 172 operates as an IAB-donor.

In some implementations, the CU 172 can include a logical node CU-CP 172A that hosts the control plane part of the PDCP protocol of the CU 172. The CU 172 can also include logical node (s) CU-UP 172B that hosts the user plane part of the PDCP protocol and/or SDAP protocol of the CU 172. The CU-CP 172A can transmit control information (e.g., RRC messages, F1 application protocol messages) , and the CU-UP 172B can transmit data packets (e.g., SDAP PDUs or IP packets) .

The CU-CP 172A can be connected to multiple CU-UPs 172B through the E1 interface. The CU-CP 172A selects the appropriate CU-UP 172B for the requested services for the UE 102. In some implementations, a single CU-UP 172B can be connected to multiple CU-CPs 172A through the E1 interface. If the CU-CP 172A and DU (s) 174 belong to a gNB, the CU-CP 172A can be connected to one or more DU 174s through an F1-C interface and/or an F1-U interface. If the CU-CP 172A and DU (s) 174 belong to an ng-eNB, the CU-CP 172A can be connected to DU (s) 174 through a W1-C interface and/or a W1-U interface. In some implementations, one DU 174 can be connected to multiple CU-UPs 172B under the control of the same CU-CP 172A. In such implementations, the connectivity between a CU-UP 172B and a DU 174 is established by the CU-CP 172A using Bearer Context Management functions.

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 both of the base stations 104, 106) .

In the example stack 200, a physical layer (PHY) 202A 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 a 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 the SDAP sublayer 212 or an 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 dual connectivity (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 206A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

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

On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide signaling radio bearers (SRBs) to the RRC sublayer (not shown in Fig. 2A) to exchange RRC messages or 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, IP packets, or Ethernet packets.

Thus, it is possible to functionally split the radio protocol stack, as shown by the radio protocol stack 250 in Fig. 2B. The CU at one or both of the base stations 104, 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.

Applicable scenario

Next, several example scenarios that involve various components of Fig. 1A and relate to lower layer centric mobility are discussed with reference to Figs. 3A-3D. Generally, events in Figs. 3A-3D that can be the same are labeled with the same reference numbers. In scenario 300A to 300D, the BS 104 could communicate with the UE 102 via TRP 107-1, 107-2 or 107-3.

In scenario 300A in Fig. 3A, the UE 102 could transmit or report UE capability 310 for supporting UE capability for supporting lower layer centric mobility procedure. Then, the BS 104 could transmit or configure RRC configuration (s) 320 to enable function of lower layer centric mobility procedure and/or configure candidate cell configuration (s) . The BS 104 could further transmit or configure RRC configuration (s) 322 of configuring one or more TCI states for configured candidate cell (s) . In some cases, 320 and 322 could be the same RRC message. Then, the BS 104 could further transmit a cell switch command (CSC) for indicating a target cell from candidate cell (s) and activating more than one configured TCI state (s) for the target cell. Further, the BS 104 transmits a beam indication to indicate that which activated TCI state (s) are applied/used for the target cell. In response, the UE transmits an ACK for the beam indication. In block 360, the UE applies TCI state (s) indicated by the beam indication to perform DL reception and/or UL transmission in the target cell.

In scenario 300B in Fig. 3B, the difference from Fig. 3A is block 350 and 362. The UE determines or derives which activated TCI state (s) is applied/used to perform DL reception and/or UL transmission in the target cell. This could imply that no further signal (e.g., beam indication) is transmitted by the BS to indicate which activated TCI state (s) is applied/used for the target cell. In block 362, the UE applies determined/derived TCI state (s) to perform DL reception and/or UL transmission in the target cell.

In scenario 300C in Fig. 3C, the difference from Fig. 3A is message 326 and block 364. The BS could transmit a cell switch command (CSC) 326 for indicating a target cell from candidate cell (s) and activating one or more than one configured TCI state (s) for the target cell. Then, in block 364, the UE applies TCI state (s) activated by the beam indication to perform DL reception and/or UL transmission in the target cell. This could imply that no further signal (e.g., beam indication) is transmitted by the BS to indicate which activated TCI state (s) is applied/used for the target cell. This could also imply that the UE does not determine or derive which activated TCI state (s) is for the target cell.

In scenario 300D in Fig. 3D, the difference from Fig. 3A is message 328. The BS transmits a MAC-CE 328 to activate configured TCI state (s) for a target cell from candidate cell (s) , where the MAC-CE 328 is not a CSC.

General description

//this section mentions some general descriptions applicable for methods, embodiments and implementations provided in this disclosure

Some general descriptions are given below, which can be applied for flow diagrams and/or embodiments mentioned in the following paragraphs or sessions.

//description of TRP identifier

In some implementations, a TRP (e.g., TRP 107-1, TRP 107-2, TRP 107-3, TRP 108-1 and/or TRP 108-2) can be associated with or identified by a TRP identifier. In some implementations, a base station (e.g., the base station 104 or 106) includes or configures a TRP identifier in UL configuration (s) that the base station transmits to a UE (e.g., the UE 102) for UL transmission (s) via a TRP identified by the TRP identifier. In some implementation, the UL configuration (s) include downlink control information (DCI) transmitted on a PDCCH, and/or physical uplink shared channel (PUSCH) configuration, physical uplink control channel (PUCCH) configuration and/or sounding reference signal (SRS) configuration included in a RRC message (e.g., RRC reconfiguration message or a RRC resume message) that the base station transmits to the UE. In some implementations, the UL transmission (s) include PUSCH transmission (s) , PUCCH transmission (s) and/or SRS transmission (s) . In some implementations, the base station includes a TRP identifier in DL configuration (s) that the base station transmits to the UE 102 for DL transmission (s) via a TRP identified by the TRP identifier. In one implementation, the DL configuration (s) include DCI transmitted on a PDCCH, and/or channel state information (CSI) resource configuration, physical downlink shared channel (PDSCH) configuration (s) and/or physical downlink control channel (PDCCH) configuration (s) included in a RRC message (e.g., RRC reconfiguration message or a RRC resume message) that the base station transmits to the UE. In some implementations, the DL transmission (s) include CSI reference signal (CSI-RS) transmission (s) , synchronization signal block (SSB) transmission (s) , PDSCH transmission (s) and/or PDCCH transmission (s) .

In other implementations, the base station does not transmit/configure a TRP identifier to the UE and uses an implicit indication to indicating a TRP to the UE. In one implementation, the implicit indication can be one of the following configuration parameters: a CORESETPoolIndex, a value (candidate) of a CORESETPoolIndex, dataScramblingIdentityPDSCH, dataScramblingIdentityPDSCH2-r16, or PUCCH-ResourceGroup-r16. In such implementations, the UE derives a TRP (identifier) from the implicit indication. In some implementations, the base station transmits a RRC message (e.g., RRC reconfiguration message or a RRC resume message) including the configuration parameters to the UE.

//description of first and second TRP identifier

In some implementations, the BS configures or indicates the UE a first TRP identifier. In some implementations, the UE derives a first TRP identifier (value) . In some implementations, the BS configures or indicates the UE a second TRP identifier (value) . In some implementations, the UE derives a second TRP identifier (value) . In some implementations, the first TRP identifier can be associated with the first TRP. In some implementations, the second TRP identifier can be associated with the second TRP.

In some implementations, the base station configures that a serving cell is associated with the first TRP or the first TRP identifier (value) . In some implementations, the base station configures a first control resource set (CORESET) associated with the serving cell or first TRP. The base station can configure CORESETPoolIndex #0 to identify the first CORESET. In one implementation, the base station can transmit to the UE a RRC message (e.g., a RRC setup message, a RRC reconfiguration message or a RRC resume message) configuring the first CORESET and/or including the CORESETPoolIndex #0. Thus, the UE monitors a PDCCH on the first CORESET to receive DCIs from the base station, which implies that the UE monitors a PDCCH or receives DCIs via the first TRP from the base station (i.e., from the first TRP) . In such a case, the UE determines that CORESETPoolIndex #0 indicates a TRP (i.e., the first TRP) of the base station.

In one implementation, the base station configures that the serving cell associated with the second TRP or the second TRP identifier (value) . In other implementation, the second TAG is associated with a non-serving cell, and the base station indicates or configures the association in the second RRC message. In one implementation, the base station configures the non-serving cell associated with the second TRP or the second TRP identifier (value) . In some implementations, the base station configures a second CORESET is associated with the serving cell, non-serving cell or second TRP. The base station can configure CORESETPoolIndex #1 to identify the second CORESET. In one implementation, the base station can transmit to the UE a RRC message (e.g., a RRC setup message, a RRC reconfiguration message or a RRC resume message) configuring the second CORESET and/or including the CORESETPoolIndex #1. Thus, the UE monitors a PDCCH on the second CORESET to receive DCIs from the base station, which implies that the UE monitors a PDCCH or receives DCIs via the second TRP from the base station (i.e., from the second TRP) . In such a case, the UE determines that CORESETPoolIndex #1 indicates a TRP (i.e., the second TRP) .

//beam indication structure/procedure in serving cell, including RRC, MAC-CE and DCI

//RRC configuration

In some implementations, the BS can configure the UE one or more TCI state lists for a component carrier (CC) of a serving cell, where the CC could be PCell or SCell. For example, the BS can configure a joint TCI state list for a CC of a serving cell. For example, the BS can configure a DL TCI state list and/or a UL TCI state list for a CC of a serving cell. One joint TCI state list can comprise one or more joint TCI states. One DL TCI state list can comprise one or more DL TCI states. One UL TCI state list can comprise one or more UL TCI states.

In some implementations, the BS can configure the UE a RRC parameter unifiedTCI-StateType. The RRC parameter unifiedTCI-StateType can be a per-serving-cell configuration. The RRC parameter unifiedTCI-StateType can indicate which type of TCI state list (s) for a serving cell. For example, the RRC parameter unifiedTCI-StateType can indicate “joint” or “separate” . The RRC parameter unifiedTCI-StateType can provide one or more the following purpose:

- If the first RRC parameter for a CC of serving cell indicates “joint” , the BS could explicitly or implicitly configure the UE one or more joint TCI state list (s) for the CC of serving cell or the UE ;

- If the first RRC parameter for a CC of serving cell indicates “separate” , the BS could explicitly or implicitly configure the UE one or more DL TCI state list (s) for the CC of serving cell;

- If the first RRC parameter for a CC of serving cell indicates “separate” , the BS could explicitly or implicitly configure the UE one or more UL TCI state list (s) for the CC of serving cell.

In some implementations, if the BS explicitly configures the UE one or more TCI state list (s) for a CC of a serving cell, it could imply that

- the BS configures the one or more TCI state list (s) (explicitly) under RRC configuration (e.g., ServingCellConfig) for a CC of the serving cell.

In some implementations, if the BS implicitly configures the UE one or more TCI state list (s) for a CC of serving cell, it could imply at least one of the followings:

- the BS configures the one or more TCI state list (s) under RRC configuration (e.g., ServingCellConfig) for other serving cell (s) /CCs or a reference serving cell/CC;

- the UE refers the one or more TCI state list (s) for other serving cell (s) /CCs or a reference serving cell/CC;

- the UE determines that the one or more TCI state list (s) , which is for other serving cell/CCs or a reference serving cell/CC, is also for the CC of the serving cell.

//introduction of basic beam indication structure including RRC, MAC-CE and DCI

//MAC-CE activation

//the first MAC-CE could be a normal MAC-CE for TCI activation used in legacy

In some implementations, the BS can transmit a first MAC-CE to the UE when or after

- the BS configures the UE one or more TCI state list (s) for the CC of serving cell; and/or

- the UE refers or determines one or more TCI state list (s) for the CC of serving cell.

In some implementations, the first MAC-CE can activate or indicate one or more TCI states from the one or more TCI state list (s) . The one or more TCI states activated/indicated by the first MAC-CE can map to one or more TCI codepoints in a TCI field. In some cases, the UE can (directly) apply or use the one or more TCI states activated/indicated by the first MAC-CE for performing DL and/or UL transmission (subsequently) .

In some implementations, if the number of TCI states activated/indicated by the first MAC-CE is larger than one, those TCI states activated/indicated by the first MAC-CE can map to one or more TCI codepoints in a TCI field in a DCI. In some implementations, if the number of TCI states activated/indicated by the first MAC-CE is one, the UE can (directly) apply or use the TCI state activated/indicated by the first MAC-CE for performing DL and/or UL transmission (subsequently) . In some implementations,

- if the number of TCI states activated/indicated by the first MAC-CE is two, and/or

- if the two TCI states activated/indicated by the first MAC-CE are associated with different TRP identifier or applicable for different TRP,

the UE can (directly) apply or use these two TCI states activated/indicated by the first MAC-CE for performing corresponding DL and/or UL transmission (subsequently) .

In some implementations, one TCI state can be mapped to one TCI codepoint, based on the first MAC-CE. In some cases, more than one TCI states can be mapped to one TCI codepoint, based on the first MAC-CE. In some cases, the TCI codepoint can indicate one of the followings:

- one or more joint TCI states,

○ some could be TCI states associated with the first TRP, the other could be TCI states associated with the second TRP

- one or more DL TCI states,

- one or more UL TCI states,

- one or more DL TCI states and one or more UL TCI states.

In some cases, the number of joint TCI states indicated in a TCI codepoint by the BS can be up to 4. In some cases, the number of DL TCI states indicated in a TCI codepoint by the BS can be up to 4. In some cases, the number of UL TCI states indicated in a TCI codepoint by the BS can be up to 4.

For example, one of the followings can be mapped to a TCI codepoint:

- one joint TCI state associated with the first TRP, one joint TCI state associated with the second TRP,

- one DL TCI state associated with the first TRP, one UL TCI state associated with the second TRP,

- one DL TCI state associated with the first TRP, one DL TCI state associated with the second TRP,

- one UL TCI state associated with the first TRP, one UL TCI state associated with the second TRP,

- one DL TCI state and one UL TCI state associated with the first TRP, one joint TCI state associated with the second TRP,

- one DL TCI state and one UL TCI state associated with the first TRP, one DL TCI state associated with the second TRP,

- one DL TCI state and one UL TCI state associated with the first TRP, one ULTCI state associated with the second TRP.

//introduction of basic beam indication structure including RRC, MAC-CE and DCI

//beam indication by DCI singling

//the first DCI could be the DCI for TCI indication used in legacy

//the first acknowledgement signal could be used for indicating HARQ-ACK for legacy beam indication by DCI signaling

In some implementations, the UE can receive a first DCI indicating one or more TCI states. The first DCI can indicate one or more TCI states by the TCI field in the first DCI. In response to receiving the first DCI, the UE can transmit, to the BS, a first acknowledgement signal via a PUCCH or PUSCH transmission. In response to transmitting the first acknowledgement signal, the UE can apply or use the one or more TCI states activated/indicated by the first DCI for performing DL and/or UL transmission. In some cases, in response to transmitting the first acknowledgement signal, the UE can apply or use the one or more TCI states activated/indicated by the first DCI for performing DL and/or UL transmission, after a first application time period. In some cases, the UE can apply or use the one or more TCI states activated/indicated by the first DCI for performing DL and/or UL transmission, starting from a first slot.

//introduction of the first application time period and the first slot

In some cases, the first slot can be the earliest slot that is at least the first application time period after the last symbol of the PUCCH or PUSCH transmission. In some cases, the earliest slot (for determining the first slot) and/or the first application time period can be determined based on the active BWP with the smallest SCS among the active BWP (s) of the carrier/serving cell (s) applying the one or more TCI states. In some cases, the first application time period can be in unit of one of the followings: symbol, sub-slot, slot, sub-frame, frame, ms, or second. In some cases, the first application time period can be beamAppTime.

//beam indication by MAC-CE

//the second acknowledgement signal could be used for indicating HARQ-ACK for legacy beam indication by MAC-CE

In other implementations, the UE can receive the first MAC-CE indicating one or more TCI states. For example, the first MAC-CE might indicate one TCI state. For example, the first MAC-CE might indicate more than one TCI states, each of them can be associated with different TRP or TRP identifier. For example, the first MAC-CE might indicate two TCI states, where one is associated with the first TRP (identifier) and the other is associated with the second TRP (identifier) . In such cases, the UE might not receive a DCI indicating one or more TCI states for applying for subsequent DL and/or UL transmission. In response to receiving the first MAC-CE, the UE can transmit, to the BS, a second acknowledgement signal via a PUCCH or PUSCH transmission. In response to transmitting the second acknowledgement signal, the UE can apply or use the one or more TCI states activated/indicated by the first MAC-CE for performing DL and/or UL transmission. In some cases, in response to transmitting the second acknowledgement signal, the UE can apply or use the one or more TCI states activated/indicated by the first MAC-CE for performing DL and/or UL transmission, after a second application time period. In some cases, the UE can apply or use the one or more TCI states activated/indicated by the first MAC-CE for performing DL and/or UL transmission, starting from a second slot.

//introduction of the second application time period and the second slot

In some cases, the second slot can be the earliest slot that is at least the second application time period after the (last) slot of the PUCCH or PUSCH transmission. In some cases, the second application time period can beIn some cases, μ can be the SCS configuration for the PUCCH or PUSCH transmission; can be the subcarrier spacing configuration for k_mac with a value of 0 for frequency range 1, and k_mac is provided by K-Mac or k_mac=0 if K-Mac is not provided.

//introduction RRC parameter unifiedTCI-StateRef

In some cases, the BS can configure the UE a RRC parameter unifiedTCI-StateRef. The RRC parameter unifiedTCI-StateRef can be a per-cell or per-BWP configuration.

In some cases, if the BS configures, to the UE, the RRC parameter unifiedTCI-StateRef for a CC of serving cell and/or a BWP, it could imply one of the followings:

- the BS does not configure one or more TCI state list (s) under RRC configuration (e.g., ServingCellConfig) for the CC of serving cell and/or RRC configuration for the BWP;

- the UE refers one or more TCI state list (s) for the serving cell and/or the BWP from a reference serving cell/CC and/or a reference BWP;

- the UE determines that the one or more TCI state list (s) , which is for the reference serving cell/CC and/or the reference BWP, is also for the CC of serving cell and the BWP.

In some cases, the RRC parameter unifiedTCI-StateRef can at least indicate a cell index of the reference serving cell. In some cases, the RRC parameter unifiedTCI-StateRef can at least indicate a BWP ID of the reference BWP.

//description of candidate cell configuration

In some implementations, the BS could configure the UE one or more candidate cell configuration (s) . The one or more candidate cell configuration (s) could include information of neighboring cell (s) of the UE. The one or more candidate cell configuration (s) could include information of candidate target cell of the UE for performing a lower layer centric mobility procedure. A candidate cell configuration could comprise or be one of a RRCReconfiguration message, a CellGroupConfig IE or a SpCellConfig IE. A candidate cell configuration could comprise a candidate cell configuration ID. A candidate cell could be current configured/activated secondary cell (SCell) of the UE.

In some implementations, the candidate cell configuration could comprise one or more TCI state lists for a candidate cell.

//description of cell switch command (CSC)

//the second DCI is to schedule the CSC

In some implementations, the BS could transmit the UE a cell switch command. In one example, the BS could transmit the cell switch command via MAC-CE or PDSCH. In some implementations, the UE could receive a second DCI from the BS. The second DCI could schedule a PDSCH carrying the CSC.

In some implementations, the cell switch command could indicate a target cell. In some implementations, the cell switch command could comprise a candidate cell configuration ID. It is noted that throughout this disclosure, a target cell could be or stand for a candidate cell indicated by a cell switch command. In response to receiving the cell switch command or after the action time of the cell switch command, the UE could perform lower layer centric mobility procedure based on the cell switch command. The UE could determine target cell and/or its corresponding configuration based on the candidate cell configuration ID indicated in the cell switch command. Upon completing the lower layer centric mobility procedure, the target cell indicated by the cell switch command could become a new serving cell or a PCell. Upon completing the lower layer centric mobility procedure, the UE moves from the source cell to the target cell. It is noted that throughout this disclosure, the source cell could be or stand for the (original or previous) serving cell before receiving the CSC or completing lower layer centric procedure.

Method/Embodiment/Implementation

Several ideas related to performing a lower layer centric mobility procedure are present in the following embodiments.

Embodiment 1

//How to perform beam indication for target cell in LTM

//RRC configuration of TCI states for candidate cell

In some implementations, the BS could configure to the UE one or more TCI state lists for a candidate cell. For example, the BS can configure a joint TCI state list for a candidate cell. For example, the BS can configure a DL TCI state list and/or a UL TCI state list for a candidate cell. One joint TCI state list can comprise one or more joint TCI states. One DL TCI state list can comprise one or more DL TCI states. One UL TCI state list can comprise one or more UL TCI states. In some implementations, the one or more TCI state lists for a candidate cell could be configured by the BS in one of the following:

- Corresponding candidate cell configuration for the candidate cell, and/or

- Serving cell configuration of the serving cell or the source cell (e.g., PDSCHConfig) , and/or

- A configuration comprising TCI state (s) for one or more candidate cell (s) .

//Assumption 1: CSC activates more than one TCI states from RRC-configured TCI pool

In some implementations, the BS could transmit to the UE a cell switch command (CSC) for performing or triggering a lower layer centric mobility. The CSC could indicate a target cell by indicating a candidate cell configuration (or its configuration ID) . A target cell could be one of configured candidate cell. The CSC could activate more than one TCI state (s) for the target cell from the one or more TCI state lists configured for the target cell.

In some implementations, the BS configures all the TCI state (s) activated by the CSC to be associated with the same physical cell identifier as the target cell (i.e., the candidate cell indicated in the CSC) . In some other implementations, the BS configures at least one of the TCI state (s) activated by the CSC to be associated with a different physical cell identifier (PCI) as the target cell (i.e., the candidate cell indicated in the CSC) . This could imply that the TCI state (s) activated by the CSC could be associated with either the target cell or other candidate cell (s) . Then the UE determines the one TCI state to be applied or used for the target cell based on the TCI state (s) associated with the same PCI as the target cell and/or one of the rules/methods below. In some implementations, the BS could configure or indicate the amount/number of candidate cell (s) associated with TCI state (s) activated by a CSC based on a UE capability reported by the UE.

After receiving activation of one or more TCI states by the CSC, one of the following alternatives could be used by the UE to determine or by the BS to indicate which activated TCI state (s) is applied or used for the target cell.

//alternative 1-1: Rule-based method

In some implementations, the UE could determine which TCI state (s) activated by the CSC is applied or used for the target cell or is the indicated TCI state (s) for the target cell by a rule-based method. For example, the first TCI state (s) activated in the CSC is applied or used for the target cell or is the indicated TCI state (s) for the target cell. For example, the UE could determine the last TCI state (s) activated in the CSC is applied or used for the target cell or is the indicated TCI state (s) for the target cell. For example, the UE could determine the TCI state (s) activated in the CSC with the lowest or lower TCI state ID is applied or used for the target cell or is the indicated TCI state (s) for the target cell. For example, the UE could determine the TCI state (s) activated in the CSC with the highest or higher TCI state ID is applied or used for the target cell or is the indicated TCI state (s) for the target cell. For example, the UE could determine TCI state (s) activated in the CSC is applied or used for the target cell or is the indicated TCI state (s) for the target cell, where the source RS (optionally for QCL-Type D) of the TCI state (s) is reported/measured with the largest or larger RSRP (or SINR) in the most recent beam report or CSI report for the target cell.

//alternative 1-2: Indication by the CSC

In some implementations, in addition to activating more than one TCI states, the CSC could indicate which activated TCI state (s) is applied or used for the target cell. In some implementations, in addition to activating more than one TCI states, the CSC could indicate which activated TCI state (s) is the indicated TCI state for the target cell.

//alternative 1-3: Indication by the DCI scheduling the CSC (the second DCI)

In some implementations, the second DCI could carry a TCI field for indicating TCI state (s) from the more than one TCI states activated by the CSC scheduled in the second DCI. The UE determines the TCI state (s) indicated in the second DCI is applied or used for the target cell or is the indicated TCI state (s) for the target cell.

//A bit/field in DCI to indicate that the scheduling DCI or the indicated TCI is for target cell or current cell

In some implementations, the second DCI could carry a field or bit (s) if the UE supports and/or the BS configures lower layer centric mobility. The field or bit (s) in the second DCI could indicate whether TCI states indicated in the TCI field is mapped to or associated with TCI states activated for the source cell (i.e., the original serving cell before receiving the CSC) or a target cell.

//TCI state indicated in the TCI field is for target cell if the scheduled PDSCH carries CSC

In some implementations, when the UE receives the second DCI, the UE could determine whether TCI states indicated in the TCI field is mapped to or associated with TCI states activated for the source cell or a target cell, based on the followings:

- If the second DCI schedules the CSC, the UE determines TCI states indicated in the TCI field is mapped to or associated with TCI states activated for the target cell (i.e., the candidate cell indicated by the CSC) ;

- Otherwise, the UE determines TCI states indicated in the TCI field is mapped to or associated with TCI states activated for the source cell.

//alternative 1-4: Combination of Alt 1-1/1-2 and Alt 1-3

In some implementations, if the second DCI is a DCI format 1_0 or a DCI format 1_1/1_2 without TCI field configured/present, the UE may apply implementations with beam indication related to rule-based method or CSC mentioned above to determine which TCI state activated by the CSC is applied or used for the target cell or is the indicated TCI state for the target cell.

In some implementations, if the second DCI is a DCI format 1_1/1_2 with TCI field configured/present, the UE may apply implementations with beam indication related to the DCI scheduling the CSC mentioned above to determine which TCI state activated by the CSC is applied or used for the target cell or is the indicated TCI state for the target cell.

In some implementations, the BS configures the UE a first RRC parameter indicating which method to determine which TCI state activated by the CSC is applied or used for the target cell or is the indicated TCI state for the target cell. For example, the first RRC parameter could indicate the rule-based method, CSC based method or DCI based indication above.

//Assumption 2: UE applies TCI state (s) activated from CSC without need of further indication, where CSC activates only one TCI state or CSC activates more than one TCI state

In some implementations, the CSC could activate only one TCI state for the target cell from the one or more TCI state lists configured for the target cell. After receiving activation of only one TCI state by the CSC, the UE could determine the only one TCI state activated by the CSC is applied or used for the target cell or is the indicated TCI state for the target cell.

In some implementations, the CSC could activate more than one TCI state for the target cell from the one or more TCI state lists configured for the target cell. After receiving activation of the more one TCI state by the CSC, the UE could determine the more than one TCI state activated by the CSC are (directly) applied or used for the target cell or are the indicated TCI state (s) for the target cell.

In some implementations, the UE does not receive further indication or signal to indicate that which TCI state (s) activated by the CSC is applied or used for the target cell or is the indicated TCI state (s) for the target cell.

//Assumption 3: CSC does not activate TCI state

//the second MAC-CE (not CSC) could activate TCI states for candidate cell

In some implementations, the CSC does not activate any TCI state for the target cell from the one or more TCI state lists configured for the target cell. In some implementations, the UE could receive a second MAC-CE from the BS. The second MAC-CE could activate one or more TCI state (s) for the target cell, which are selected from the one or more TCI state lists configured for the target cell. Optionally, the second MAC-CE could activate one or more TCI state (s) for one or more candidate cell (s) (including the target cell indicated by the CSC) , which are selected from the one or more TCI state lists configured for the one or more candidate cell (s) (including the target cell indicated by the CSC) . This could imply that the second MAC-CE could activate TCI state (s) for one or more candidate cell (s) (including the target cell indicated by the CSC) . In some implementations, the second MAC-CE is not a CSC.

The UE could use one of the following alternatives to determine which TCI state (s) activated by the second MAC-CE is applied or used for the target cell or is the indicated TCI state (s) for the target cell.

//alternative 3-1: The DCI scheduling the CSC (the second DCI) indicates TCI state from the set of active TCI states

In some implementations, the second DCI could indicate which TCI state (s) activated by the second MAC-CE is applied or used for the target cell or is the indicated TCI state (s) for the target cell.

//alternative 3-2: The CSC indicates one TCI state from the set of active TCI states

In some implementations, the CSC could indicate which TCI state (s) activated by the second MAC-CE is applied or used for the target cell or is the indicated TCI state (s) for the target cell.

//alternative 3-3: A DCI not scheduling the CSC indicates TCI state from the set of active TCI states

In some implementations, the UE could receive a third DCI. In some cases, the third DCI could be a DCI not scheduling the CSC. The third DCI could indicate which TCI state (s) activated by the second MAC-CE is applied or used for the target cell or is the indicated TCI state (s) for the target cell.

In some implementations, the third DCI could also be used (by the BS) to indicate which TCI state (s) activated by the second MAC-CE is applied or used for the source cell or is the indicated TCI state (s) for the source cell.

In some implementations, the third DCI could carry a field or bit (s) if the UE supports and/or the BS configures lower layer centric mobility. The field or bit (s) in the third DCI could indicate whether TCI states indicated in the TCI field is mapped to or associated with TCI states activated for the source cell or the target cell.

//alternative 3-4: A MAC-CE other than CSC indicates one TCI state from the set of active TCI states

In some implementations, the UE could receive a MAC-CE other than the CSC. The MAC-CE other than the CSC could indicate which TCI state (s) activated by the second MAC-CE is applied or used for the target cell or is the indicated TCI state (s) for the target cell. In some implementations, the MAC-CE other than the CSC could be the second MAC-CE. Optionally, the MAC-CE other than the CSC could be the second MAC-CE, if the second MAC-CE activates only one TCI state for the target cell.

//alternative 3-5: TCI state list for target cell only configures/includes one TCI state

In some implementations, TCI state list (s) for the target cell (i.e., the candidate cell indicated in the CSC) configures or includes only one TCI state. The UE could determine the only one TCI state configured for the target cell is applied or used for the target cell or is the indicated TCI state for the target cell.

In some implementations, TCI state list (s) for the target cell (i.e., the candidate cell indicated in the CSC) configures or includes more than one TCI state. The UE could determine the more than one TCI state configured for the target cell is applied or used for the target cell or is the indicated TCI state for the target cell.

In some implementations, the UE does not receive further indication or signal to indicate that which TCI state (s) is activated and applied/used for the target cell (i.e., the indicated TCI state (s) for the target cell) .

//How NW activates a set of active TCI states in different timing of transmitting the CSC

//Option 1: One MAC-CE (the second MAC-CE) for current cell and target cell

In some implementations, in addition to activating TCI state (s) for the target cell and/or one or more candidate cell (s) , the second MAC-CE could also activate one or more TCI states for the source cell.

//Option 2: Two MAC-CE separately for current cell (via other MAC-CE, e.g., the first MC-CE) and target cell (via the second MAC-CE)

In some implementations, the second MAC-CE does not activate one or more TCI states for the source cell. The BS could activate one or more TCI states for the source cell via a MAC-CE other than the second MAC-CE (e.g., the first MAC-CE) .

//One mapping table for TCI states mapped to TCI field codepoints

In some implementations, when the UE interprets a TCI field in a DCI, some TCI field codepoints could map to TCI states activated for the source cell, and other TCI field codepoints could map to TCI states activated for the target cell. Optionally, the UE could perform such behavior (s) when at least one of the followings is achieved:

- Beam indication for the target cell (i.e., which activated TCI state is indicated TCI state) is indicated by a DCI, and/or

- TCI states activation for the source cell and TCI states activation for the target cell are performed by the same MAC-CE (e.g., the second MAC-CE) .

In some implementations, the second MAC-CE could indicate or carry candidate cell configuration ID when activating TCI states for the target cell and/or one or more candidate cell (s) . In one example, the BS configures an index indicating a PCI in the second MAC CE. In another example, the BS configures a TCI state list ID in the second MAC CE. In such implementations, the UE could realize whether the indicated TCI state from the TCI field is intended for the source cell or the target cell.

In some implementations, if the UE supports or the BS configures one of the followings, bit length of TCI field in a DCI could increase to be more than 3 bits (e.g., 4 bits) :

- The second MAC-CE could activate TCI states for the source cell, and TCI states for the target cell, and/or

- Lower layer centric mobility (or L1/L2 triggered mobility) , and/or

In some implementations, the BS could configure the UE a second RRC parameter. The BS could use the second RRC parameter to indicate whether bit length of TCI field in a DCI increases to be more than 3 bits (e.g., 4 bits) .

In some implementations, even that the second MAC-CE could activate one or more TCI states for the source cell and one or more TCI states for the target cell, when the UE interprets a TCI field in a DCI, all TCI field codepoints could map to TCI states activated for the source cell. Optionally, the UE could perform such behavior when one of the followings is achieved:

- Beam indication (i.e., which activated TCI state is indicated TCI state) for one or more candidate cell (s) (including the target cell) is indicated by a CSC, and/or

- When the second MAC-CE only activates one TCI state for one candidate cell.

//Two mapping tables for TCI states mapped to TCI field codepoints

In some implementations, when the UE interprets a TCI field in a DCI, all TCI field codepoints could map to either TCI states activated for the source cell or TCI states activated for one or more candidate cell (s) (including the target cell) . In such implementations, when the UE interprets a TCI field in a DCI, the UE determines that all the TCI field codepoints in the DCI are mapped to TCI state (s) activated for candidate cell (s) , if one of the following is achieved:

- One field or bit (s) in the DCI indicates the TCI field is intended for candidate cell (s) , and/or

- The DCI schedules a CSC, and/or

- DCI format of the DCI is a pre-specified or pre-configured or pre-determined DCI format.

In such implementations, when the UE interprets a TCI field in a DCI, the UE determines that all the TCI field codepoints in the DCI are mapped to TCI state (s) activated for the source cell, if one of the following is achieved:

- One field or bit (s) in the DCI indicates the TCI field is intended for the source cell, and/or

- The DCI does not schedule a CSC, and/or

- DCI format of the DCI is a pre-specified or pre-configured or pre-determined DCI format. In such implementations, TCI states for the source cell and TCI states for candidate cell (s) could be activated by the BS via the second MAC-CE. In such implementations, alternatively, TCI states for the source cell and TCI states for candidate cell (s) could be activated by the BS via different MAC-CE (e.g., the first MAC-CE for the source cell, and the second MAC-CE for candidate cell (s) ) .

//to describe cases that one or more than one activated TCI is indicated or applied for target cell

In the above implementations/methods, if one activated TCI state is indicated by the BS (or determined by the UE) to be applied or used for the target cell (i.e., the indicated TCI state for the target cell) , it could imply one of the followings:

- Joint TCI state mode is operated for the target cell, the one activated TCI state is a joint TCI state, and/or

- Separate TCI state mode is operated for the target cell, the one activated TCI state is a DL TCI state.

In the above implementations/methods, if two activated TCI states are indicated by the BS (or determined by the UE) to be applied or used for the target cell (i.e., the indicated TCI states for the target cell) , it could imply one of the followings:

- Separate TCI state mode is operated for the target cell, one of the two activated TCI states is DL TCI and the other is UL TCI, and/or

- Joint TCI state mode is operated for the target cell, one of the two activated TCI states is applied for UE specific channel/RS and the other is applied for common channel/RS.

In the above implementations/methods, if more than two activated TCI states are indicated by the BS (or determined by the UE) to be applied or used for the target cell (i.e., the indicated TCI states for the target cell) , it could imply one of the followings:

- Separate TCI state mode is operated for the target cell, each of the activated TCI states (could be DL or UL TCI) is applied for different type of DL or UL channel/RS.

From above mentioned implementations/cases, at least two examples could be implemented as shown in Fig. 4A and 4B.

Embodiment 2

//When to stop maintaining active TCI states and/or stop tracking pathloss RSs in current cell

//number of active TCI states

In some implementations, the number of active TCI states that the UE maintains in the serving cell or the source cell (or the number of TCI states activated for the serving cell or the source cell) is X. The number of TCI states activated for the target cell (or the number of active TCI states that the UE maintains in the target cell) is Y. In some implementations, the UE could report to the BS that the maximal number of active TCI states that the UE can maintain or the BS can activate is Z. In some other implementations, the UE could report to the BS the maximum number of active TCI states for the serving cell or the source cell, i.e., maximum value of X, and/or the maximum number of active TCI states for the target cell, i.e., maximum value of Y. The UE may report the UE capability on X, Y and Z per component carrier (CC) , per band or per band combination.

In some implementations, based on value Z, the BS is required to make sure that X is not larger than Z. If the BS configures X greater than Z, the UE can trigger RRC reconfiguration request procedure. In some implementations, based on value Z, the BS is required to make sure that Y is not larger than Z. If the BS configures Y greater than Z, the UE can trigger RRC reconfiguration request procedure.

//number of pathloss RSs

In some implementations, the number of pathloss RS that the UE tracks in the serving cell or the source cell (or the number of pathloss RS activated/indicated for the serving cell or the source cell) is P. The number of pathloss RS activated/indicated for the target cell (or the number of pathloss RS that the UE tracks in the target cell) is Q. In some implementations, the UE could report to the BS that the maximal number of pathloss RS that the UE can track or the BS can activate/indicate is R. In some other implementations, the UE could report to the BS the maximum number of pathloss reference signal resources for the serving cell or the source cell, i.e., maximum value of P, and/or the maximum number of pathloss reference signal resources for the target cell, i.e., maximum value of Q. The UE may report the UE capability on P, Q and R per component carrier (CC) , per band or per band combination.

In some implementations, based on value R, the BS is required to make sure that P is not larger than R. If the BS configures P greater than R, the UE can trigger RRC reconfiguration request procedure. In some implementations, based on value R, the BS is required to make sure that Q is not larger than R. If the BS configures Q greater than R, the UE can trigger RRC reconfiguration request procedure.

//cases of stopping maintaining partial active TCI state

In some implementations, the UE could stop maintaining partial active TCI states in the source cell such that the number of remaining maintained active TCI states in the source cell plus Y is not larger than Z. For an illustrative example in Fig. 6, assume X=2, Y=1, Z=2, the UE could stop maintaining one TCI state from X active TCI states in the source cell.

In some implementations, how UE determines which active TCI states to stop maintaining in the source cell could be based on one of the followings:

- TCI state (s) with lower TCI state ID or lower TCI codepoint ID;

- TCI state (s) with higher TCI state ID or higher TCI codepoint ID;

- A configuration or indication from the BS, e.g., the BS configures or indicates the priority for the TCI states;

- UE selection, where the UE may report to the BS which active TCI state (s) are maintained or not maintained via UCI reporting on a PUCCH/PUSCH or via MAC-CE.

//cases of stopping tracking partial pathloss RS

In some implementations, the UE could stop maintaining partial pathloss RSs in the source cell such that the number of remaining tracked pathloss RSs plus Q is not larger than R. For example, if P=2, Q=2, R=3, the UE could stop maintaining one pathloss RS from P pathloss RSs in the source cell.

In some implementations, how UE determines which pathloss RS to stop tracking in the source cell could be based on one of the followings:

- Pathloss RS (s) with lower RS ID or lower activation order;

- Pathloss RS (s) with higher RS ID or higher activation order;

- The configuration or indication from the BS, e.g., the BS configures or indicates the priority for the pathloss RS (s) ;

- UE selection, where the UE may report to the BS which pathloss RS (s) are maintained or not maintained via UCI reporting on a PUCCH/PUSCH or via MAC-CE.

//timing or event of stop maintaining active TCI state or stop tracking pathloss RS

In some implementations, the UE could stop maintaining all (or partial) active TCI states and/or stop tracking all (or partial) pathloss RSs in the source cell, based one of the following timings or events:

- After the UE receiving a CSC or transmitting ACK for a CSC, and/or

- After the UE receives beam indication for a candidate cell or transmitting ACK for beam indication for a candidate cell, and/or

- After action time of a CSC received by the UE, and/or

- After action time of beam indication received by the UE, and/or

- After completion of a lower layer centric mobility procedure triggered by a CSC, and/or

- Upon receiving an indication by MAC-CE or DCI from the BS.

In some implementations, before completion of a lower layer centric mobility procedure, only if X+Y>Z, the UE could stop maintaining all (or partial) active TCI states in the source cell, based on the timing/events mentioned in this embodiment.

In some other implementations, before completion of a lower layer centric mobility procedure, regardless of whether X+Y>Z, the UE could stop maintaining all (or partial) active TCI states in the source cell, based on the timing/events mentioned in this embodiment.

In some implementations, before completion of a lower layer centric mobility procedure, only if P+Q>R, the UE could stop tracking all (or partial) pathloss RSs in the source cell, based on the timing/events mentioned in this embodiment.

In some other implementations, before completion of a lower layer centric mobility procedure, regardless of whether P+Q>R, the UE could stop tracking all (or partial) pathloss RSs in the source cell, based on the timing/events mentioned in this embodiment.

In some implementations, whether to stop maintaining active TCI states and/or stop tracking pathloss RSs in the source cell could be independent of whether to stop PDCCH monitoring in the source cell.

From above mentioned implementations/cases, at least two examples could be implemented as shown in Fig. 5A and 5B.

Embodiment 2-1

//UE capability for the number of active TCI states for performing LTM procedure

In some implementations, if the UE supports the lower layer centric mobility procedure, the minimal number of active TCI states the UE can maintain or the BS can activate is N. In some implementations, to support the lower layer centric mobility procedure, the UE is required to support N active TCI states that the UE can maintain or the BS can activate. In some implementations, the support of N active TCI states could mean the support of N different QCL TypeD RS. In some cases, N is 2.

//Alt 1

In some implementations, the support of N active TCI states also applies when a lower layer centric mobility is not triggered or when a CSC or beam indication for a candidate cell is not transmitted. This could imply that the BS could activate TCI states based on the support of N even when the BS does not trigger a lower layer centric mobility or when the BS does not transmit a CSC or beam indication for a candidate cell. This could imply that the BS could activate TCI states for the serving cell or the source cell based on the support of N.

//Alt 2

In some implementations, the support of N active TCI states only applies when a lower layer centric mobility is triggered or when a CSC or beam indication for a candidate cell is transmitted. This could imply that the BS could only activate TCI states based on the support of N when (or after) the BS triggers a lower layer centric mobility or when (or after) the BS transmits a CSC or beam indication for a candidate cell. This could imply that the BS could not activate TCI states for the serving cell or the source cell based on the support of N. The number of active TCI states for the serving cell or the source cell (that the UE could maintain or the BS could activate) could be smaller than N.

Additional description

It is noted that throughout this disclosure, the UE may have one or more of the following attributes or behaviors. The following attributes or behaviors of the UE may also imply associated attributes or behaviors of a BS.

● The UE may be configured with and/or served by the BS in a serving cell.

● The UE may (be configured to) communicate with the BS in the serving cell.

● The UE may be configured with one or more serving cells by the BS, which may include the serving cell.

● The UE may be activated or be indicated, by the BS, to activate one or more serving cells, which may include the serving cell.

● The UE may be configured and/or indicated, by the BS, one or more BWP. The UE may be indicated and/or configured, by the BS, a BWP (in the serving cell) .

○ Optionally, the BWP may be activated as an active BWP.

○ Optionally, the BWP may be referred to an active BWP

○ Optionally, the BWP may be an active DL BWP.

○ Optionally, the BWP may be an active UL BWP.

○ Optionally, the BWP may be an initial BWP.

○ Optionally, the BWP may be a default BWP.

○ Optionally, the BWP may be a dormant BWP.

● The UE may be in one of RRC_CONNECTED state, RRC_INACTIVE state or RRC_IDLE state.

It is noted that throughout this disclosure, a neighboring cell can be referred to or replaced with one or some of the followings:

● Non-serving cell,

● A cell with PCI different that of the serving cell,

● A TRP associated with a PCI different from that of the serving cell.

It is noted that throughout this disclosure, action time of a signal could mean the actual timing when the signal is applicable or takes effect, which could be later than the timing of receiving this signal.

It is noted that throughout this disclosure, definition of a known and unknown TCI could be referred to 3GPP TS 38.133 V17.7.0 or newer version.

It is noted that throughout this disclosure, for case (s) that a BS configures or indicates the UE to operate with S-TRP mode in a serving cell or a BWP, or for case (s) that a serving cell or a BWP is operated with S-TRP mode, it can imply or be referred to be one of the followings:

- No TRP identifier or no TRP-related index is configured or indicated, by the BS, to any channel or RS in the serving cell or BWP, and/or

- (only) One TRP identifier or TRP-related index is configured or indicated, by the BS, to any channel or RS in the serving cell or BWP, and/or

- When the UE or the BS transmits/receives a transmission, (only) one TRP identifier or TRP-related index is configured or indicated or involved to the transmission or the beam/TCI state applied for the transmission.

It is noted that throughout this disclosure, for case (s) that a BS configures or indicates the UE to operate with M-TRP mode in a serving cell or a BWP, or for case (s) that a serving cell or a BWP is operated with M-TRP mod, it can imply or be referred to be one of the followings:

- More than one TRP identifier or TRP-related index is configured or indicated, by the BS, to at least one channel or RS in the serving cell or BWP, and/or

- One TRP identifier or TRP-related index is configured or indicated, by the BS, to one channel or RS in the serving cell or BWP; and the UE derives or determines another one TRP identifier or TRP-related index applied for or associated with at least one channel or RS in the serving cell or BWP, and/or

- When the UE or the BS transmits/receives a transmission, more than one TRP identifier or TRP-related index is configured or indicated or involved to the transmission or the beam/TCI state applied for the transmission.

It is noted that throughout this disclosure, for case (s) that a UE refers or determines a TCI state list (e.g., joint or DL or UL TCI state list) for a serving cell or BWP based on another one TCI state list, it could mean that the UE considers all or part of the another one TCI state list to be the TCI state list for the serving cell or BWP.

It is noted that throughout this disclosure, a joint TCI state can be referred to or replaced with at least one of the followings:

● A beam applicable for both one or more DL and UL transmission (s) , e.g., one or more DL channel, UL channel, DL RS and/or UL RS,

● Spatial filter for transmission and/or reception,

● Spatial parameters for transmission and/or reception,

● Spatial relationship for transmission and/or reception,

● Spatial assumption for transmission and/or reception

It is noted that throughout the document, a UL TCI state can be referred to or replaced with at least one of the followings:

● A beam (only) applicable for one or more UL transmission (s) , e.g., one or more UL channel and/or UL RS,

● UL beam,

● Configuration carrying or be associated with pathloss RS,

● Configuration carrying or be associated with UL power control parameters,

● Spatial relation

● Spatial transmitting filter,

● Transmission precoder,

● Spatial parameters,

● Spatial relationship.

It is noted that throughout this disclosure, a DL TCI state can be referred to or replaced with at least one of the followings:

● A beam (only) applicable for one or more DL transmission (s) , e.g., one or more DL channel (s) or DL RS (s)

● A TCI (only) applicable for one or more DL transmission (s) , e.g., one or more DL channel (s) or DL RS (s) ,

● A TCI associated with QCL type-D

● QCL assumption

● DL beam,

● Spatial receiving filter,

● Spatial parameters,

● Spatial relationship,

● Spatial assumption

It is noted that throughout this disclosure, a joint or DL or UL TCI state can be referred to or replaced with a common TCI state or a unified TCI state.

It is noted that throughout this disclosure, a DL TCI state can be different from a TCI state in Rel-15/16, where a TCI state in Rel-15/16 cannot be applied for one or more DL channel (s) or RS (s) at the same time.

It is noted that throughout this disclosure, a TCI state pool (e.g., joint TCI state pool, UL TCI state pool, DL TCI state pool) can be referred to or stand for a (RRC) configuration or a list, which may include or contain one or more TCI state (index) . It is noted that throughout this disclosure, “a TCI” can be referred to or replaced with “a TCI state” . It is noted that throughout this disclosure, “a TCI pool” can be referred to or replaced with “a TCI state pool” .

It is noted that throughout this disclosure, a TCI field could mean or be referred to a field used or applied or repurposed to indicate one or more TCI states.

It is noted that throughout this disclosure, “joint mode” or “joint TCI state mode” could mean or be referred to at least one of the followings:

● TCI field (s) or indicated TCI state (s) in a DCI format may refer/map to one of joint TCI state pool, DL TCI state pool or UL TCI state pool, and/or

● Beam indication (s) or indicated TCI state (s) are applied for both transmitting UL transmission and/or receiving DL transmission.

It is noted that throughout this disclosure, “separate mode” or “separate TCI state mode” could mean or be referred to at least one of the followings:

● Beam indication (s) or indicated TCI state (s) are applied either for (only) transmitting UL transmission or (only) receiving DL transmission.

It is noted that throughout this disclosure, “UL mode” or “UL-only TCI state mode” could mean or be referred to at least one of the followings:

● TCI field (s) or indicated TCI state (s) in a DCI format may refer/map to UL TCI state pool (joint TCI state pool) , and/or

● Beam indication (s) or indicated TCI state (s) are applied for (only) transmitting UL transmission.

It is noted that throughout this disclosure, “DL mode” or “DL-only TCI state mode” could mean or be referred to at least one of the followings:

● TCI field (s) or indicated TCI state (s) in a DCI format may refer/map to DL TCI state pool (joint TCI state pool) , and/or

● Beam indication (s) or indicated TCI state (s) are applied for (only) receiving DL transmission.

FIG. 7 illustrates a flowchart 700 of a method of wireless communication at a UE. With reference to FIGS. 1 and 9, the method may be performed by the UE 102, the UE apparatus 902, etc., which may include the memory 926', 906', 916, and which may correspond to the entire UE 102 or the entire UE apparatus 902, or a component of the UE 102 or the UE apparatus 902, such as the wireless baseband processor 926 and/or the application processor 906.

The UE 102 obtains 720, from a network entity, NE, via a source cell, candidate cell configurations of candidate cells. The UE 102 receives 724, from the NE, a cell switch command, CSC, that indicates a target cell among the candidate cells.

The UE activates 726 TCI states associated with the target cell. The UE identifies 730 at least one of the activated TCI states. The UE applies 760 the at least one of the activated TCI states to communicate with the NE via the target cell.

FIG. 7 describes a method from a UE-side of a wireless communication link, whereas FIG. 8 describes a method from a network-side of the wireless communication link.

FIG. 8 is a flowchart 800 of a method of wireless communication at a network entity. With reference to FIGS. 1 and 10, the method may be performed by one or more network entities 104, which may correspond to a base station or a unit of the base station, such as the RU 106, the DU 108, the CU 110, an RU processor 1006, a DU processor 1026, a CU processor 1046, etc. The one or more network entities 104 may include memory 1006’/1026’/1046’, which may correspond to an entirety of the one or more network entities 104, or a component of the one or more network entities 104, such as the RU processor 1006, the DU processor 1026, or the CU processor 1046.

The network entity 104 transmits 820, to a user equipment, UE, via a source cell, candidate cell configurations of candidate cells. The network entity transmits 824, to the UE, a cell switch command, CSC, that indicates a target cell among the candidate cells. The network entity communicates 860 with the UE via the target cell using activated beams.

A UE apparatus 902, as described in FIG. 9, may perform the method of flowchart 700. The one or more network entities 104, as described in FIG. 10, may perform the method of flowchart 800.

FIG. 9 is a diagram 900 illustrating an example of a hardware implementation for a UE apparatus 902. The UE apparatus 902 may be the UE 102, a component of the UE 102, or may implement UE functionality. The UE apparatus 902 may include an application processor 906, which may have on-chip memory 906’. In examples, the application processor 906 may be coupled to a secure digital (SD) card 908 and/or a display 910. The application processor 906 may also be coupled to a sensor (s) module 912, a power supply 914, an additional module of memory 916, a camera 918, and/or other related components. For example, the sensor (s) module 912 may control a barometric pressure sensor/altimeter, a motion sensor such as an inertial management unit (IMU) , a gyroscope, accelerometer (s) , a light detection and ranging (LIDAR) device, a radio-assisted detection and ranging (RADAR) device, a sound navigation and ranging (SONAR) device, a magnetometer, an audio device, and/or other technologies used for positioning.

The UE apparatus 902 may further include a wireless baseband processor 926, which may be referred to as a modem. The wireless baseband processor 926 may have on-chip memory 926'. Along with, and similar to, the application processor 906, the wireless baseband processor 926 may also be coupled to the sensor (s) module 912, the power supply 914, the additional module of memory 916, the camera 918, and/or other related components. The wireless baseband processor 926 may be additionally coupled to one or more subscriber identity module (SIM) card (s) 920 and/or one or more transceivers 930 (e.g., wireless RF transceivers) .

Within the one or more transceivers 930, the UE apparatus 902 may include a Bluetooth module 932, a WLAN module 934, an SPS module 936 (e.g., GNSS module) , and/or a cellular module 938. The Bluetooth module 932, the WLAN module 934, the SPS module 936, and the cellular module 938 may each include an on-chip transceiver (TRX) , or in some cases, just a transmitter (TX) or just a receiver (RX) . The Bluetooth module 932, the WLAN module 934, the SPS module 936, and the cellular module 938 may each include dedicated antennas and/or utilize antennas 940 for communication with one or more other nodes. For example, the UE apparatus 902 can communicate through the transceiver (s) 930 via the antennas 940 with another UE 102 (e.g., sidelink communication) and/or with a network entity 104 (e.g., uplink/downlink communication) , where the network entity 104 may correspond to a base station or a unit of the base station, such as the RU 106, the DU 108, or the CU 110.

The wireless baseband processor 926 and the application processor 906 may each include a computer-readable medium /memory 926', 906', respectively. The additional module of memory 916 may also be considered a computer-readable medium /memory. Each computer-readable medium /memory 926', 906', 916 may be non-transitory. The wireless baseband processor 926 and the application processor 906 may each be responsible for general processing, including execution of software stored on the computer-readable medium /memory 926', 906', 916. The software, when executed by the wireless baseband processor 926 /application processor 906, causes the wireless baseband processor 926 /application processor 906 to perform the various functions described herein. The computer-readable medium /memory may also be used for storing data that is manipulated by the wireless baseband processor 926 /application processor 906 when executing the software. The wireless baseband processor 926 /application processor 906 may be a component of the UE 102. The UE apparatus 902 may be a processor chip (e.g., modem and/or application) and include just the wireless baseband processor 926 and/or the application processor 906. In other examples, the UE apparatus 902 may be the entire UE 102 and include the additional modules of the apparatus 902.

As discussed in FIG. 1 and implemented with respect to FIG. 7, the beam indication manager 140 is configured to obtaining, from a network entity, NE, via a source cell, candidate cell configurations of candidate cells, receives, from the NE, a cell switch command, CSC, that indicates a target cell among the candidate cells; activates TCI states associated with the target cell; identifies at least one of the activated TCI states; and applies the at least one of the activated TCI states to communicate with the NE via the target cell.

The beam indication manager 140 may be within the application processor 906 (e.g., at 140a) , the wireless baseband processor 926 (e.g., at 140b) , or both the application processor 906 and the wireless baseband processor 926. The beam indication manager 140a-140b may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by one or more processors configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by the one or more processors, or a combination thereof.

FIG. 10 is a diagram 1000 illustrating an example of a hardware implementation for one or more network entities 104. The one or more network entities 104 may be a base station, a component of a base station, or may implement base station functionality. The one or more network entities 104 may include, or may correspond to, at least one of the RU 106, the DU, 108, or the CU 110. The CU 110 may include a CU processor 1046, which may have on-chip memory 1046'. In some aspects, the CU 110 may further include an additional module of memory 1056 and/or a communications interface 1048, both of which may be coupled to the CU processor 1046. The CU 110 can communicate with the DU 108 through a midhaul link 162, such as an F1 interface between the communications interface 1048 of the CU 110 and a communications interface 1028 of the DU 108.

The DU 108 may include a DU processor 1026, which may have on-chip memory 1026'. In some aspects, the DU 108 may further include an additional module of memory 1036 and/or the communications interface 1028, both of which may be coupled to the DU processor 1026. The DU 108 can communicate with the RU 106 through a fronthaul link 160 between the communications interface 1028 of the DU 108 and a communications interface 1008 of the RU 106.

The RU 106 may include an RU processor 1006, which may have on-chip memory 1006'. In some aspects, the RU 106 may further include an additional module of memory 1016, the communications interface 1008, and one or more transceivers 1030, all of which may be coupled to the RU processor 1006. The RU 106 may further include antennas 1040, which may be coupled to the one or more transceivers 1030, such that the RU 106 can communicate through the one or more transceivers 1030 via the antennas 1040 with the UE 102.

The on-chip memory 1006', 1026', 1046' and the additional modules of memory 1016, 1036, 1056 may each be considered a computer-readable medium /memory. Each computer-readable medium /memory may be non-transitory. Each of the processors 1006, 1026, 1046 is responsible for general processing, including execution of software stored on the computer-readable medium /memory. The software, when executed by the corresponding processor (s) 1006, 1026, 1046 causes the processor (s) 1006, 1026, 1046 to perform the various functions described herein. The computer-readable medium /memory may also be used for storing data that is manipulated by the processor (s) 1006, 1026, 1046 when executing the software. In examples, the beam indication manager 150 may sit at any of the one or more network entities 104, such as at the CU 110; both the CU 110 and the DU 108; each of the CU 110, the DU 108, and the RU 106; the DU 108; both the DU 108 and the RU 106; or the RU 106.

The beam indication manager 150 may perform various operations and signaling according to the examples provided herein and be within one or more processors of the one or more network entities 104, such as the RU processor 1006 (e.g., at 150a) , the DU processor 1026 (e.g., at 150b) , and/or the CU processor 1046 (e.g., at 150c) . The beam indication manager 150a-150c may be one or more hardware components specifically configured to carry out the stated processes/algorithm, implemented by one or more processors 1006, 1026, 1046 configured to perform the stated processes/algorithm, stored within a computer-readable medium for implementation by the one or more processors 1006, 1026, 1046, or a combination thereof.

The specific order or hierarchy of blocks in the processes and flowcharts disclosed herein are an illustration of example approaches. Hence, the specific order or hierarchy of blocks in the processes and flowcharts may be rearranged. Some blocks may also be combined or deleted. Dashed lines may indicate example/optional elements of the diagrams. The accompanying method claims present elements of the various blocks in an example order, and are not limited to the specific order or hierarchy presented in the claims, processes, and flowcharts.

The detailed description set forth herein describes various configurations in connection with the drawings and does not represent the only configurations in which the concepts described herein may be practiced. The detailed description includes specific details for the purpose of providing a thorough explanation of various concepts. However, these concepts may be practiced without these specific details. In some instances, well known structures and components are shown in block diagram form in order to avoid obscuring such concepts.

Aspects of wireless communication systems, such as telecommunication systems, are presented with reference to various apparatuses and methods. These apparatuses and methods are described in the following detailed description and are illustrated in the accompanying drawings by various blocks, components, circuits, processes, call flows, systems, algorithms, etc. (collectively referred to as “elements” ) . These elements may be implemented using electronic hardware, computer software, or combinations thereof. Whether such elements are implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system.

An element, or any portion of an element, or any combination of elements may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs) , central processing units (CPUs) , application processors, digital signal processors (DSPs) , reduced instruction set computing (RISC) processors, systems-on-chip (SoC) , baseband processors, field programmable gate arrays (FPGAs) , programmable logic devices (PLDs) , state machines, gated logic, discrete hardware circuits, and other similar hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software, which may be referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, or any combination thereof.

If the functionality described herein is implemented in software, the functions may be stored on, or encoded as, one or more instructions or code on a computer-readable medium, such as a non-transitory computer-readable storage medium. Computer-readable media includes computer storage media and may include a random-access memory (RAM) , a read-only memory (ROM) , an electrically erasable programmable ROM (EEPROM) , optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of these types of computer-readable media, or any other medium that may be used to store computer executable code in the form of instructions or data structures that may be accessed by a computer. Storage media may be any available media that may be accessed by a computer.

Aspects, implementations, and/or use cases described herein may be implemented across many differing platform types, devices, systems, shapes, sizes, and packaging arrangements. For example, the aspects, implementations, and/or use cases may come about via integrated chip implementations and other non-module-component based devices, such as end-user devices, vehicles, communication devices, computing devices, industrial equipment, retail/purchasing devices, medical devices, artificial intelligence (AI) -enabled devices, machine learning (ML) -enabled devices, etc. The aspects, implementations, and/or use cases may range from chip-level or modular components to non-modular or non-chip-level implementations, and further to aggregate, distributed, or original equipment manufacturer (OEM) devices or systems incorporating one or more techniques described herein.

Devices incorporating the aspects and features described herein may also include additional components and features for the implementation and practice of the claimed and described aspects and features. For example, transmission and reception of wireless signals necessarily includes a number of components for analog and digital purposes, such as hardware components, antennas, RF-chains, power amplifiers, modulators, buffers, processor (s) , interleavers, adders/summers, etc. Techniques described herein may be practiced in a wide variety of devices, chip-level components, systems, distributed arrangements, aggregated or disaggregated components, end-user devices, etc., of varying configurations.

The description herein is provided to enable a person skilled in the art to practice the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not limited to the aspects described herein, but are to be interpreted in view of the full scope of the present disclosure consistent with the language of the claims.

Reference to an element in the singular does not mean “one and only one” unless specifically stated, but rather “one or more. ” Terms such as “if, ” “when, ” and “while” do not imply an immediate temporal relationship or reaction. That is, these phrases, e.g., “when, ” do not imply an immediate action in response to or during the occurrence of an action, but simply imply that if a condition is met then an action will occur, but without requiring a specific or immediate time constraint for the action to occur. The terms “may” , “might” , and “may” , as used in this disclosure, often carry certain connotations. For example, “may” refers to a permissible feature that may or may not occur, “might” refers to a feature that probably occurs, and “may” refers to a capability (e.g., capable of) . The phrase “For example” often carries a similar connotation to “may” and, therefore, “may” is sometimes excluded from sentences that include “for example” or other similar phrases.

Unless specifically stated otherwise, the term “some” refers to one or more. Combinations such as “at least one of A, B, or C” or “one or more of A, B, or C” include any combination of A, B, and/or C, such as A and B, A and C, B and C, or A and B and C, and may include multiples of A, multiples of B, and/or multiples of C, or may include A only, B only, or C only. Sets may be interpreted as a set of elements where the elements number one or more.

Unless otherwise specifically indicated, ordinal terms such as “first” and “second” do not necessarily imply an order in time, sequence, numerical value, etc., but are used to distinguish between different instances of a term or phrase that follows each ordinal term. Reference numbers, as used in the specification and figures, are sometimes cross-referenced among drawings to denote same or similar features. A feature that is exactly the same in multiple drawings may be labeled with the same reference number in the multiple drawings. A feature that is similar among the multiple drawings, but not exactly the same, may be labeled with reference numbers that have different leading numbers, but have one or more of the same trailing numbers (e.g., 206, 306, 406, etc., may refer to similar features in the drawings) . Sometimes an “X” is used to universally denote multiple variations of a feature. For instance, “X06” may universally refer to all reference numbers that end in “06” (e.g., 206, 306, 406, etc. ) .

It is noted that throughout this disclosure, a panel could mean that an antenna (port) group or an antenna (port) set. There may be more than one DL/UL beams associated with one panel. When one transmitting node (UE or NW) is performing a transmission via a panel, only one beam associated with the panel could be used to perform the transmission. For a transmitter comprising more than one panels, e.g., two panels, it may happen that two beams associated with the two panels respectively are used to perform a transmission.

It is noted that throughout this disclosure, a TRP identifier could mean or be referred to a (candidate) value of a TRP identifier. The first TRP identifier could be a first candidate value of a TRP identifier or a first TRP identifier value. The second TRP identifier could be a second candidate value of a TRP identifier or a second TRP identifier value.

It is noted that throughout this disclosure, a panel identifier could mean or be referred to a (candidate) value of a panel identifier. The first panel identifier could be a first candidate value of a panel identifier or a first panel identifier value. The second panel identifier could be a second candidate value of a panel identifier or a second panel identifier value.

It is noted that throughout this disclosure, when a procedure or description is related to a serving cell, it may mean the procedure or description is related to an active (DL/UL) BWP in the serving cell.

It is noted that throughout this disclosure, an expression of “X/Y” may include meaning of “X or Y” . It is noted that throughout this disclosure, an expression of “X/Y” may include meaning of “X and Y” . It is noted that throughout this disclosure, an expression of “X/Y” may include meaning of “X and/or Y” . It is noted that throughout this disclosure, an expression of “ (A) B” or “B (A) ” may include concept of “only B” . It is noted that throughout this disclosure, an expression of “ (A) B” or “B (A) ” may include concept of “A+B” or “B+A” .

It is noted that some or all of the foregoing or the following embodiments could be jointly combined or formed to be a new or another one embodiment.

It is noted that the foregoing or the following embodiments can be used to solve at least (but not limited to) the issue (s) or scenario (s) mentioned in this disclosure.

The following additional considerations may apply to the foregoing and the following discussions.

It is noted that any two or more than two of the foregoing or the following paragraphs, (sub) -bullets, points, actions, or claims described in each method/embodiment/implementation may be combined logically, reasonably, and properly to form a specific method.

It is noted that any sentence, paragraph, (sub) -bullet, point, action, or claim described in each of the foregoing or the following embodiment (s) /implementation (s) /concept (s) may be implemented independently and separately to form a specific method. Dependency, e.g., “based on” , “more specifically” , “where” or etc., in embodiment (s) /implementation (s) /concept (s) mentioned in this disclosure is just one possible embodiment which would not restrict the specific method.

It is noted that, some or all of the following terminology and assumption may be used hereafter.

● BS: a network central unit or a network node in NR which is used to control one or multiple TRPs which are associated with one or multiple cells. Communication between BS and TRP (s) is via fronthaul. BS may be referred to as central unit (CU) , eNB, gNB, or NodeB.

● TRP: a transmission and reception point provides network coverage and directly communicates with UEs. TRP may be referred to as distributed unit (DU) or network node.

● Cell: a cell is composed of one or multiple associated TRPs, i.e. coverage of the cell is composed of coverage of all associated TRP (s) . One cell is controlled by one BS. Cell may be referred to as TRP group (TRPG) .

● Serving beam: serving beam for a UE is a beam generated by a network node, e.g., TRP, which is configured to be used to communicate with the UE, e.g., for transmission and/or reception.

● Candidate beam: candidate beam for a UE is a candidate of a serving beam. Serving beam may or may not be candidate beam.

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 (IoT) 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.

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 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) ) 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.

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.

Structural and functional equivalents to elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are encompassed by the claims. The words “module, ” “mechanism, ” “element, ” “device, ” and the like may not be a substitute for the word “means. ” As such, no claim element is to be construed as a means plus function unless the element is expressly recited using the phrase “means for. ” As used herein, the phrase “based on” shall not be construed as a reference to a closed set of information, one or more conditions, one or more factors, or the like. In other words, the phrase “based on A” , where “A” may be information, a condition, a factor, or the like, shall be construed as “based at least on A” unless specifically recited differently.

The following examples are illustrative only and may be combined with other examples or teachings described herein, without limitation.

Examples

Example 1. A method for wireless communications by a user equipment, UE, the method comprising:

obtaining, from a network entity, NE, via a source cell, candidate cell configurations of candidate cells;

receiving, from the NE, a cell switch command, CSC, that indicates a target cell among the candidate cells;

activating TCI states associated with the target cell;

identifying at least one of the activated TCI states; and

applying the at least one of the activated TCI states to communicate with the NE via the target cell.

Example 2. The method of Example 1, wherein the identifying comprises receiving a beam indication from the NE, and selecting the at least one of the activated TCI states based on the beam indication.

Example 3. The method of Example 1, wherein the identifying comprises selecting the at least one of the activated TCI states using a predetermined rule, etc...

Example 4. The method of Example 1, wherein the obtaining of the configuration comprises: receiving, from the network entity, a radio resource control, RRC, message that configures at least one of:

enabling a lower layer centric mobility procedure;

providing the plurality of candidate cell configurations; or

providing the respective TCI states of the plurality of candidate cells.

Example 5. The method of Example 1, further comprising:

transmitting, to the network entity, an acknowledgement of the indication of the associated one or more TCI states of the target cell.

Example 6. The method of Example 2, wherein the receiving of the beam indication is performed substantially simultaneously with the receiving of the CSC.

Example 7. The method of Example 2, wherein the CSC includes the beam indication.

Example 8. The method of Example 2, wherein the receiving of the beam indication is performed using a field or a bit field of a control message.

Example 9. The method of any of Examples 1 to 8, wherein the receiving of the CSC comprises:

activating, by the received CSC in the UE, a single TCI state associated with the target cell; and

determining, by the UE, an indication of a specific TCI state of the target cell to be the activated single TCI state.

Example 10. The method of any of Examples 1 to 9, wherein the CSC includes a beam activation signal, and the activating of the TCI states is based on the beam activation signal..

Example 11. The method of Examples 1 to 10, wherein the activating comprises receiving a control message including a beam activation signal separate from the CSC.

Example 12. The method of Example 11, wherein the applying of the at least one of the associated one or more TCI states comprises at least one of:

using an indication of a specific TCI state in a downlink control information, DCI;

using a TCI state indicated in the CSC;

using an indication of a specific TCI state in a medium access control, MAC, control element, CE separate from the CSC; or

using a specific TCI state for the target cell when the configuration includes only one TCI state for the target cell.

Example 13. The method of Example 12, wherein the CSC has been scheduled by the DCI.

Example 14. The method of Example 13, wherein the activation signal comprises:

a single medium access control, MAC, control element, CE, for both a source cell and

the target cell included in the plurality of candidate cells; or

two MAC CEs respectively for each of the source cell and the target cell.

Example 15. The method of Example 14, further comprising:

interpreting a TCI field, in the DCI, TCI field codepoints mapped to one or more TCI states activated for the source cell, and other TCI field codepoints mapped to one or more TCI states activated for the target cell.

Example 16. The method of Example 14, further comprising:

interpreting a TCI field, in a DCI, TCI field codepoints mapped to either one or more TCI states activated for the source cell or one or more TCI states activated for the plurality of candidate cells including the target cell.

Example 17. The method of any of Examples 1 to 16, further comprising:

maintaining a predetermined number of active beams for the source cell and the target cell.

Example 18. The method of Example 17, wherein the maintaining includes terminating a subset of the active beams for the source cell if a sum of a first and a second number of the active beams for the target cell exceeds the predetermined number.

Example 19. The method of Example 17, further comprising:

transmitting, to the network entity, an indication of the UE’s capability regarding a number (X) of active TCI states that the UE maintains in the current cell, a number (Y) of TCI states activated for the target cell, and a number (Z) of maximum number of active TCI states that the UE is capable of maintaining, per component carrier, per band, or per band combination, wherein the terminating of the maintenance comprises determining that X + Y > Z.

Example 20. The method of Example 19, further comprising:

tracking a plurality of pathloss reference signals in the current cell and the target cell corresponding to the existing active TCI states and the activation of TCI states.

Example 21. The method of Example 20, further comprising:

terminating, at least partially, the tracking of the plurality of pathloss reference signals based on:

an activation order associated with the corresponding TCI states,

a priority indicated in the configuration; or

a selection by the UE associated with TCI states indication determination (462) .

Example 22. The method of Example 19, wherein the number Z equals to one and wherein the terminating of the maintenance is triggered by:

receiving the CSC or an indication of at least one of the associated one or more TCI states;

transmitting an acknowledgement message in response to the CSC or the indication of at least one of the associated one or more TCI states;

upon switching to the target cell; or

receiving a new TCI state indication other than the indication of at least one of the associated one or more TCI states.

Example 23. A method for wireless communications by a network entity, NE, the method comprising:

transmitting, to a user equipment, UE, via a source cell, candidate cell configurations of candidate cells;

transmitting, to the UE, a cell switch command, CSC, that indicates a target cell among the candidate cells; and

communicating with the UE via the target cell using activated beams.

Example 24. The method of Example 23, further comprising transmitting a beam indication to the UE for the UE to select the at least one of the activated beams based on the beam indication.

Example 25. The method of Example 23, further comprising:

transmitting, to the UE, a radio resource control, RRC, message that configures at least one of:

enabling a lower layer centric mobility procedure;

providing the plurality of candidate cell configurations; or

providing the respective TCI states of the plurality of candidate cells.

Example 26. The method of Example 23, further comprising:

receiving, from the UE, an acknowledgement of the indication of the associated one or more TCI states of the target cell.

Example 27. The method of Example 24, wherein the transmitting of the beam indication is performed substantially simultaneously with the transmitting of the CSC.

Example 28. The method of Example 24, wherein the CSC includes the beam indication.

Example 29. The method of Example 24, wherein the transmitting of the beam indication is performed using a field or a bit field of a control message.

Example 30. The method of any of Examples 23 to 8, wherein the transmitting of the CSC comprises:

activating, by the received CSC in the UE, a single TCI state associated with the target cell.

Example 31. The method of any of Examples 23 to 9, wherein the CSC includes a beam activation signal, and the activating of the beams is based on the beam activation signal..

Example 32. The method of Example 30 or 31, wherein the activating comprises transmitting a control message including a beam activation signal separate from the CSC.

Example 33. The method of Example 32, further comprising scheduling the CSC via a downlink control information (DCI) .

Example 34. The method of Example 33, wherein the activation signal comprises:

the target cell included in the plurality of candidate cells; or

two MAC CEs respectively for each of the source cell and the target cell.

Example 35. The method of Example 23, further comprising:

receiving, from the UE, an indication of the UE’s capability regarding a number (X) of active TCI states that the UE maintains in the current cell, a number (Y) of TCI states activated for the target cell, and a number (Z) of maximum number of active TCI states that the UE is capable of maintaining, per component carrier, per band, or per band combination, wherein the terminating of the maintenance comprises determining that X + Y > Z.

Example 36. A wireless communication device comprising a communication interface, and signal processing hardware connected to the communication interface, configured to cooperatively perform any of the methods of Examples 1 to 35.

Topics

● Topic 1: Performing beam indication for target cell in LTM

○ Assumption 1: CSC activates more than one TCI states from RRC-configured TCI pool

○ Assumption 2: CSC activates only one TCI state

■ If activated, the activated TCI state is directly applied

○ Assumption 3: CSC does not activate TCI state

○ Note: These assumptions could co-exist

● For Assumption 1 (CSC activates more than one TCI states) , several alternatives are listed as below

○ Alt 1-1: Rule-based method

■ E.g., the first TCI state is applied, others TCIs are activated

○ Alt 1-2: Indication by the CSC as well

○ Alt 1-3: Indication by the DCI scheduling the CSC

■ SPEC should further specify: TCI field is for target cell if the scheduled PDSCH carries CSC, or

■ A bit/field in DCI to indicate that the scheduling DCI or the indicated TCI is for target cell or current cell

○ Alt 1-4: Combination of Alt 1-1/1-2 and Alt 1-3

■ If the scheduling DCI is DCI format 1_0, go with Alt 1-1 or Alt 1-2

■ If the scheduling DCI is DCI format 1_1 and 1_2 (with TCI field present) , go with Alt 1-3

● For Assumption 2 (CSC activates only one TCI state) , several alternatives are listed as below

○ Alt 2-1: CSC activates one TCI state from RRC-configured TCI pool

■ Note: The TCI state activated by the CSC is directly applied (i.e., indicated TCI state)

● For Assumption 3 (CSC does not activate TCI state) , several alternatives are listed as below

○ Note: NW could activate a set of active TCI states in different timing of transmitting the CSC

○ Alternatives

■ Alt 3-1: The DCI scheduling the CSC indicates TCI state from the set of active TCI states

■ Alt 3-2: The CSC indicates one TCI state from the set of active TCI states

■ Alt 3-3: A DCI not scheduling the CSC indicates TCI state from the set of active TCI states

■ Alt 3-4: A MAC-CE other than CSC indicates one TCI state from the set of active TCI states

■ Alt 3-5: TCI state list for target cell only configures/includes one TCI state

● The one TCI state is directly applied or used

○ How NW activates a set of active TCI states in different timing of transmitting the CSC

■ Option 1: One MAC-CE for current cell and target cell

● Before beam indication, NW has used one MAC-CE to activate at least one TCI state for current cell, and at least one TCI state for target cell

● For Alt 3-1 (via DCI) : Both TCI states for current cell and target cell are mapped to TCI field

○ One mapping table

■ UE can differentiate which TCI codepoint is for target cell

■ But the number of available TCI codepoints could be an issue

○ Two mapping table

■ UE determines which mapping table to use based on whether CSC is scheduled

● For Alt 3-2 (via CSC)

○ Only TCI states for current cell are mapped to TCI field

■ Option 2: Two MAC-CE separately for current cell and target cell

● Before beam indication, NW has used one MAC-CE to activate at least one TCI state for current cell, and the other MAC-CE to activate at least one TCI state for target cell

● Two mapping table

○ UE determines which mapping table to use based on whether CSC is scheduled

● Topic 2: When to stop maintaining active TCI states in current cell

○ Assume UE maintains X active TCI states in current cell, receives activation of Y active TCI states for target cell, and UE capability for maximal number of active TCI state (s) is Z

■ According UE capability, NW should make sure X<=Z, Y<=Z

○ When to stop maintaining X active TCI states?

■ Especially if X+Y>Z

■ For example, if UE supports only one active TCI, when to stop maintaining active TCI state in current cell?

● Alternatives

○ Alt 1: UE stops maintaining X active TCI state after receiving CSC or transmitting ACK for CSC

○ Alt 2: UE stops maintaining X active TCI state after receiving beam indication or transmitting ACK for beam indication

○ Alt 3: UE stops maintaining X active TCI state after action time of CSC

○ Alt 4: UE stops maintaining X active TCI state after action time of beam indication

○ Alt 5: UE stops maintaining X active TCI state after completion of LTM procedure

○ Alt 6: UE stops maintaining X active TCI state upon receiving further indication (which is other than beam indication)

● Note: Whether to maintain active TCI state in current cell could be decoupled with whether to monitor PDCCH in current cell

● Topic 2-1: UE capability for the number of active TCI states for performing LTM procedure

○ Whether “supporting two (or higher) active TCI state” is mandatory for supporting LTM?

■ Advantage: Able to keep connection with current cell until completion of LTM procedure

● Alternatives

○ Alt 1: Supporting two (or more) active TCI state is mandatory for supporting LTM

■ It can also apply for cases other than performing LTM procedure

○ Alt 2: Supporting two (or more) active TCI state is mandatory for supporting LTM

■ If not performing LTM procedure, the maximum number of supported active TCI sate could still be one or lower than the number reported for supporting LTM

Claims

A method for wireless communications by a user equipment, UE, the method comprising:

obtaining (320, 322) , from a network entity, NE, via a source cell, candidate cell configurations of candidate cells;

receiving (324) , from the NE, a cell switch command, CSC, that indicates a target cell among the candidate cells;

activating TCI states associated with the target cell;

identifying (330, 350) at least one of the activated TCI states; and

applying (360, 362, 364) the at least one of the activated TCI states to communicate with the NE via the target cell.
The method of claim 1, wherein the identifying comprises receiving a beam indication from the NE, and selecting the at least one of the activated TCI states based on the beam indication. (330)
The method of claim 1, wherein the identifying comprises selecting (350) the at least one of the activated TCI states using a predetermined rule, etc...
The method of claim 1, wherein the obtaining of the configuration comprises:

receiving, from the network entity, a radio resource control, RRC, message that configures at least one of:

enabling (320) a lower layer centric mobility procedure;

providing (320) the plurality of candidate cell configurations; or

providing (322) the respective TCI states of the plurality of candidate cells.
The method of claim 1, further comprising:

transmitting (340, 412) , to the network entity, an acknowledgement of the indication of the associated one or more TCI states of the target cell.
The method of claim 2, wherein the receiving of the beam indication is performed substantially simultaneously with the receiving of the CSC.
The method of claim 2, wherein the CSC includes the beam indication.
The method of claim 2, wherein the receiving of the beam indication is performed using a field or a bit field of a control message.
The method of any of claims 1 to 8, wherein the receiving of the CSC comprises:

activating, by the received CSC in the UE, a single TCI state associated with the target cell; and

determining (462) , by the UE, an indication of a specific TCI state of the target cell to be the activated single TCI state.
The method of any of claims 1 to 9, wherein the CSC includes a beam activation signal, and the activating of the TCI states is based on the beam activation signal..
The method of claims 1 to 10, wherein the activating comprises receiving a control message including a beam activation signal separate from the CSC.
The method of claim 11, wherein the applying of the at least one of the associated one or more TCI states comprises at least one of:

using an indication of a specific TCI state in a downlink control information, DCI;

using a TCI state indicated in the CSC;

using an indication of a specific TCI state in a medium access control, MAC, control element, CE separate from the CSC; or

using a specific TCI state for the target cell when the configuration includes only one TCI state for the target cell.
The method of claim 12, wherein the CSC has been scheduled by the DCI.
The method of claim 13, wherein the activation signal comprises:

a single medium access control, MAC, control element, CE, for both a source cell and the target cell included in the plurality of candidate cells; or

two MAC CEs respectively for each of the source cell and the target cell.
The method of claim 14, further comprising:

interpreting a TCI field, in the DCI, TCI field codepoints mapped to one or more TCI states activated for the source cell, and other TCI field codepoints mapped to one or more TCI states activated for the target cell.
The method of claim 14, further comprising:

interpreting a TCI field, in a DCI, TCI field codepoints mapped to either one or more TCI states activated for the source cell or one or more TCI states activated for the plurality of candidate cells including the target cell.
The method of any of claims 1 to 16, further comprising:

maintaining (582) a predetermined number of active beams for the source cell and the target cell.
The method of claim 17, wherein the maintaining includes terminating a subset of the active beams for the source cell if a sum of a first and a second number of the active beams for the target cell exceeds the predetermined number.
The method of claim 17, further comprising:

transmitting, to the network entity, an indication of the UE’s capability regarding a number (X) of active TCI states that the UE maintains in the current cell, a number (Y) of TCI states activated for the target cell, and a number (Z) of maximum number of active TCI states that the UE is capable of maintaining, per component carrier, per band, or per band combination, wherein the terminating of the maintenance comprises determining that X + Y > Z.
The method of claim 19, further comprising:

tracking a plurality of pathloss reference signals in the current cell and the target cell corresponding to the existing active TCI states and the activation of TCI states.
The method of claim 20, further comprising:

terminating, at least partially, the tracking of the plurality of pathloss reference signals based on:

an activation order associated with the corresponding TCI states,

a priority indicated in the configuration; or

a selection by the UE associated with TCI states indication determination (462) .
The method of claim 19, wherein the number Z equals to one and wherein the terminating of the maintenance is triggered by:

receiving the CSC or an indication of at least one of the associated one or more TCI states;

transmitting an acknowledgement message in response to the CSC or the indication of at least one of the associated one or more TCI states;

upon switching to the target cell; or

receiving a new TCI state indication other than the indication of at least one of the associated one or more TCI states.
A method for wireless communications by a network entity, NE, the method comprising:

transmitting (320, 322) , to a user equipment, UE, via a source cell, candidate cell configurations of candidate cells;

transmitting (324) , to the UE, a cell switch command, CSC, that indicates a target cell among the candidate cells; and

communicating with the UE via the target cell using activated beams.
The method of claim 23, further comprising transmitting a beam indication to the UE for the UE to select the at least one of the activated beams based on the beam indication.
The method of claim 23, further comprising:

transmitting, to the UE, a radio resource control, RRC, message that configures at least one of:

enabling (320) a lower layer centric mobility procedure;

providing (320) the plurality of candidate cell configurations; or

providing (322) the respective TCI states of the plurality of candidate cells.
The method of claim 23, further comprising:

receiving (340, 412) , from the UE, an acknowledgement of the indication of the associated one or more TCI states of the target cell.
The method of claim 24, wherein the transmitting of the beam indication is performed substantially simultaneously with the transmitting of the CSC.
The method of claim 24, wherein the CSC includes the beam indication.
The method of claim 24, wherein the transmitting of the beam indication is performed using a field or a bit field of a control message.
The method of any of claims 23 to 8, wherein the transmitting of the CSC comprises:

activating, by the received CSC in the UE, a single TCI state associated with the target cell.
The method of any of claims 23 to 9, wherein the CSC includes a beam activation signal, and the activating of the beams is based on the beam activation signal..
The method of claim 30 or 31, wherein the activating comprises transmitting a control message including a beam activation signal separate from the CSC.
The method of claim 32, further comprising scheduling the CSC via a downlink control information (DCI) .
The method of claim 33, wherein the activation signal comprises:

a single medium access control, MAC, control element, CE, for both a source cell and the target cell included in the plurality of candidate cells; or

two MAC CEs respectively for each of the source cell and the target cell.
The method of claim 23, further comprising:

receiving, from the UE, an indication of the UE’s capability regarding a number (X) of active TCI states that the UE maintains in the current cell, a number (Y) of TCI states activated for the target cell, and a number (Z) of maximum number of active TCI states that the UE is capable of maintaining, per component carrier, per band, or per band combination, wherein the terminating of the maintenance comprises determining that X + Y > Z.
A wireless communication device comprising a communication interface, and signal processing hardware connected to the communication interface, configured to cooperatively perform any of the methods of claims 1 to 35.