WO2025213847A1

WO2025213847A1 - Subsequent conditional ltm and pdcp re-establishment

Info

Publication number: WO2025213847A1
Application number: PCT/CN2024/140415
Authority: WO
Inventors: Lianhai WU; Shuigen Yang; Mingzeng Dai; Le Yan
Original assignee: Lenovo Beijing Ltd
Current assignee: Lenovo Beijing Ltd
Priority date: 2024-12-18
Filing date: 2024-12-18
Publication date: 2025-10-16
Anticipated expiration: 2027-06-18

Abstract

Various aspects of the present disclosure relate to subsequent conditional LTM and PDCP re-establishment. In one aspect, a first network node transmits a first request message to a second network node. The first message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update. In turn, the first network node receives a first response message from the second network node. With this solution, at least one condition for subsequent conditional LTM can be provided to the second network node.

Description

SUBSEQUENT CONDITIONAL LTM AND PDCP RE-ESTABLISHMENT

TECHNICAL FIELD

The present disclosure relates to wireless communications, and more specifically to network nodes and methods for supporting subsequent conditional layer 1 (L1) or layer 2 (L2) triggered mobility (LTM) and packet data convergence protocol (PDCP) re-establishment.

BACKGROUND

A wireless communications system may include one or multiple network communication devices, such as base stations, which may be otherwise known as an eNodeB (eNB) , a next-generation NodeB (gNB) , or other suitable terminology. Each network communication devices, such as a base station may support wireless communications for one or multiple user communication devices, which may be otherwise known as user equipment (UE) , or other suitable terminology. The wireless communications system may support wireless communications with one or multiple user communication devices by utilizing resources of the wireless communication system (e.g., time resources (e.g., symbols, slots, subframes, frames, or the like) or frequency resources (e.g., subcarriers, carriers) . Additionally, the wireless communications system may support wireless communications across various radio access technologies including third generation (3G) radio access technology, fourth generation (4G) radio access technology, fifth generation (5G) radio access technology, among other suitable radio access technologies beyond 5G (e.g., sixth generation (6G) ) .

When the UE moves from one cell to another cell, at some point a serving cell change needs to be performed. In the legacy, a serving cell change is done by explicit radio resource configuration (RRC) reconfiguration signalling to trigger synchronization of a target cell based on layer 3 (L3) measurements report. It leads to longer latency, larger overhead, and longer interruption time.

In order to reduce the latency, overhead, and interruption time, LTM was proposed to change a serving cell via L1 or L2 signalling. LTM may refer to a switch procedure of a primary cell of a master cell group (also referred to as PCell) or a primary cell of a secondary cell group (also referred to as PSCell) , wherein a network node triggers the procedure via a medium access control (MAC) control element (CE) based on L1 measurements.

In order to reduce signaling exchange during LTM, conditional LTM was proposed. With respect to the conditional LTM, the network node may configure the UE with a condition for LTM and the UE performs the serving cell change only when the condition is met.

SUMMARY

The present disclosure relates to network nodes and methods that support subsequent conditional LTM and PDCP re-establishment. With the network nodes and methods, at least one condition for subsequent conditional LTM can be provided to a candidate gNB and a UE can determine whether to perform PDCP re-establishment or security key update.

Some implementations of a first network node described herein may include a processor and a transceiver coupled to the processor, wherein the processor is configured to: transmit a first request message via the transceiver to a second network node, wherein the first message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or identifiers (IDs) for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and receive a first response message via the transceiver from the second network node.

In some implementations, the first request message further comprises at least one of the following: capability of a UE which indicates that the UE supports at least one of layer 1 condition based LTM or layer 3 condition based LTM, or a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node.

In some implementations, the request for at least one condition indicates the second network node to generate one of the following: at least one condition for subsequent conditional LTM from a candidate cell prepared by the second network node to each of the at least one candidate cell prepared by at least one other network node, at least one layer 1 condition for the subsequent conditional LTM, or at least one layer 3 condition for the subsequent conditional LTM.

In some implementations, the first request message comprises the request for the at least one condition for the subsequent conditional LTM from a candidate cell prepared by the second network node to each of the at least one candidate cell prepared by at least one other network node, and the first response message comprises the at least one condition for the subsequent conditional LTM.

In some implementations, both layer 1 condition based LTM and layer 3 condition based LTM are supported by a UE. In such implementations, a first priority of the layer 1 condition based LTM is higher than a second priority of the layer 3 condition based LTM, and the at least one condition comprises at least one layer 1 condition for LTM.

In some implementations, the first network node comprises a central unit (CU) of a source master node (MN) , and the second network node comprises one of the following: a candidate distributed unit (DU) of the source MN, or a CU of a candidate MN.

In some implementations, the first network node comprises a central unit (CU) of a source master node (MN) , and the second network node comprises a CU of a candidate secondary node (SN) .

In some implementations, the processor is further configured to: receive a message from a CU of a source SN, In some implementations, the message comprises at least one of the following: an ID of a candidate cell belonging to the candidate SN, an indication indicating conditional LTM is initiated, a type of the at least one condition for initial conditional LTM related to cell switch from a current serving cell to a candidate cell prepared by another candidate SN, suggestion that the request for the at least one condition for conditional LTM is to be transmitted to the CU of the candidate SN, or at least one ID for the at least one candidate cell related to PDCP re-establishment or security update which is assigned by the source SN.

In some implementations, the first network node comprises a central unit (CU) of a source secondary node (SN) , and the second network node comprises a candidate distributed unit (DU) of the source SN.

In some implementations, the first request message comprises the IDs for the serving cell and at least one candidate cell related to PDCP re-establishment or security key update. In such implementations, the processor is further configured to: transmit, to a CU of a source master node (MN) , a request for at least one ID for the at least one candidate cell related to PDCP re-establishment or security key update.

In some implementations, the processor is further configured to: determine an ID for the serving cell as at least one ID for the at least one candidate cell.

In some implementations, the processor is further configured to: transmit, to a fourth network node, the IDs for the serving cell and at least one candidate cell related to PDCP re-establishment or security key update.

In some implementations, the first network node comprises a central unit (CU) of a source master node (MN) , and the fourth network node comprises a source distributed unit (DU) of the source MN.

In some implementations, the first network node comprises a CU of a source secondary node (SN) , and the fourth network node comprises a source DU of the source SN.

In some implementations, the processor is further configured to: transmit, to a UE, the IDs for the serving cell and at least one candidate cell related to PDCP re-establishment or security key update.

Some implementations of a second network node described herein may include a processor and a transceiver coupled to the processor, wherein the processor is configured to: receive a first request message via the transceiver to from a first network node, wherein the first request message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and transmit a first response message via the transceiver to the first network node.

In some implementations, the first network node comprises a central unit (CU) of a source master node (MN) , and the second network node comprises a candidate distributed unit (DU) of the source MN.

In some implementations, the first network node comprises a central unit (CU) of a source master node (MN) , and the second network node comprises one of the following: a CU of a candidate MN, or a CU of a candidate secondary node (SN) .

In some implementations, the processor is further configured to: determine a type of the at least one condition.

In some implementations, the type of the at least one condition comprises one of the following: layer 1 condition, layer 3 condition, or a combination of layer 1 condition and layer 3 condition.

In some implementations, in the combination of layer 1 condition and layer 3 condition, a UE is triggered to execute conditional LTM when both layer 1 condition and layer 3 condition are met.

In some implementations, in the combination of layer 1 condition and layer 3 condition, a UE is triggered to execute conditional LTM when either layer 1 condition or layer 3 condition is met.

In some implementations, the processor is further configured to: transmit a second request message to a third network node, wherein the second request message comprises at least one of the following: capability of a UE which indicates that the UE supports at least one of layer 1 condition based LTM or layer 3 condition based LTM, a type of a condition for initial conditional LTM from a current serving cell to a candidate cell provided by the second network node, a request for at least one layer 1 condition for conditional LTM for the at least one candidate cell, or the list of the at least one candidate cell, the IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and receive a second response message from the DU of the candidate MN, wherein the second response message comprises the at least one layer 1 condition.

In some implementations, the third network node comprises a distributed unit (DU) of the candidate MN or a DU of a candidate SN.

In some implementations, the processor is further configured to: generate at least one layer 3 condition for conditional LTM for the at least one candidate cell.

In some implementations, the processor is configured to generate the at least one layer 3 condition based on capability of a UE, wherein the capability indicates that the UE supports at least one of layer 1 condition based LTM or layer 3 condition based LTM.

In some implementations, the first response message further comprises at least one of the following: LTM candidate configuration for a first candidate cell prepared by the CU of the source NM or a CU of a source SN, or a condition for initial conditional LTM from a source cell to the first candidate cell.

Some implementations of a third network node described herein may include a processor and a transceiver coupled to the processor, wherein the processor is configured to: receive a second request message via the transceiver to from a second network node, wherein the second request message comprises at least one of the following: a request for at least one layer 1 condition for conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and transmit a second response message via the transceiver to the second network node.

In some implementations, the second request message further comprises at least one of the following: capability of a UE which indicates that the UE supports at least one of layer 1 condition based LTM or layer 3 condition based LTM, or a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node.

In some implementations, the second network node comprises a central unit (CU) of a candidate master node (MN) , and the third network node comprises a distributed unit (DU) of the candidate MN.

In some implementations, the second network node comprises a CU of a candidate secondary node (SN) , and the third network node comprises a distributed unit (DU) of the candidate SN.

Some implementations of a method described herein may include: transmitting a first request message to a second network node, wherein the first message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and receiving a first response message from the second network node.

Some implementations of a method described herein may include: receiving a first request message to from a first network node, wherein the first request message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and transmitting a first response message to the first network node.

Some implementations of a method described herein may include: receiving a second request message to from a second network node, wherein the second request message comprises at least one of the following: a request for at least one layer 1 condition for conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and transmitting a second response message to the second network node.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates an example of a wireless communications system that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure;

Fig. 2 illustrates another example of a wireless communications system that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure;

Figs. 3A, 3B, 3C and 3D illustrate a further example of a wireless communications system that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure, respectively;

Figs. 4 to 12 illustrate a signaling diagram illustrating an example process that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure, respectively;

Fig. 13 illustrates an example of a device that supports subsequent conditional LTM and PDCP re-establishment in accordance with some aspects of the present disclosure; and

Figs. 14, 15 and 16 illustrate a flowchart of a method that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure, respectively.

DETAILED DESCRIPTION

Principles of the present disclosure will now be described with reference to some embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein may be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

References in the present disclosure to “one embodiment, ” “an example embodiment, ” “an embodiment, ” “some embodiments, ” and the like indicate that the embodiment (s) described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases do not necessarily refer to the same embodiment (s) . Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” or the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element could also be termed as a second element, and similarly, a second element could also be termed as a first element, without departing from the scope of embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a” , “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” , “comprising” , “has” , “having” , “includes” and/or “including” , when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

As described above, in order to reduce signaling exchange during LTM, conditional LTM was proposed. 3GPP agreed to support initial conditional LTM and subsequent conditional LTM.

A conditional LTM configuration of each candidate cell may include the execution condition for initial conditional LTM, which is generated by the initial source cell to trigger the conditional LTM cell switching from source cell to the candidate cell.

Consider an example for Inter-CU conditional LTM. A source cell#0 of gNB#0 prepares a candidate cell#1 belonging to gNB#1. The execution condition for initial conditional LTM is generated by the initial source cell#0 to trigger the conditional LTM cell switching from source cell to the candidate cell#1.

The conditional LTM configuration of each candidate cell (e.g., cell#1) may include execution conditions for subsequent conditional LTM, which is generated by the candidate cell (e.g., cell#2 or cell#3) to trigger the conditional LTM for other candidate cells (e.g., cell#1) when the candidate cell (e.g., cell#2 or cell#3) becomes a serving cell.

Therefore, there is a need to study how to provide at least one condition for subsequent conditional LTM to a candidate gNB.

In addition, 3GPP agreed that Release 19 Set ID is configured for a candidate configuration. If the Release 19 Set IDs are different for the source cell and the target cell, a UE performs PDCP re-establishment or security key update. Therefore, there is a need to study whether Release 19 Set ID should be transmitted to a target CU for determining whether to perform PDCP re-establishment or security key update.

In view of the above, the present disclosure provides a solution that supports subsequent conditional LTM and PDCP re-establishment. In this solution, a first network node transmits a first request message to a second network node. The first message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update. In turn, the first network node receives a first response message from the second network node. With this solution, at least one condition for subsequent conditional LTM can be provided to the second network node (such as a candidate gNB) . In this way, subsequent conditional LTM can be achieved. In addition, IDs for a serving cell and at least one candidate cell can be transmitted to a target CU for determining whether to perform PDCP re-establishment or security key update.

Aspects of the present disclosure are described in the context of a wireless communications system.

Fig. 1 illustrates an example of a wireless communications system 100 that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The wireless communications system 100 may include one at least one of network entities 102 (also referred to as network equipment (NE) ) , one or more terminal devices or UEs 104, a core network 106, and a packet data network 108. The wireless communications system 100 may support various radio access technologies. In some implementations, the wireless communications system 100 may be a 4G network, such as an LTE network or an LTE-advanced (LTE-A) network. In some other implementations, the wireless communications system 100 may be a 5G network, such as an NR network. In other implementations, the wireless communications system 100 may be a combination of a 4G network and a 5G network, or other suitable radio access technology including institute of electrical and electronics engineers (IEEE) 802.11 (Wi-Fi) , IEEE 802.16 (WiMAX) , IEEE 802.20. The wireless communications system 100 may support radio access technologies beyond 5G. Additionally, the wireless communications system 100 may support technologies, such as time division multiple access (TDMA) , frequency division multiple access (FDMA) , or code division multiple access (CDMA) , etc.

The network entities 102 may be dispersed throughout a geographic region to form the wireless communications system 100. One or more of the network entities 102 described herein may be or include or may be referred to as a network node, a base station (BS) , a network element, a radio access network (RAN) node, a base transceiver station, an access point, a NodeB, an eNodeB (eNB) , a next-generation NodeB (gNB) , or other suitable terminology. A network entity 102 and a UE 104 may communicate via a communication link 110, which may be a wireless or wired connection. For example, a network entity 102 and a UE 104 may perform wireless communication (e.g., receive signaling, transmit signaling) over a Uu interface. The network entities 102 may be collectively referred to as network entities 102 or individually referred to as a network entity 102. Hereinafter, some implementations of the present disclosure will be described by taking a gNB as an example of the network entity 102. Thus, the network entity 102 may be used interchangeably with the gNB 102.

A network entity 102 may provide a geographic coverage area 112 for which the network entity 102 may support services (e.g., voice, video, packet data, messaging, broadcast, etc. ) for one or more UEs 104 within the geographic coverage area 112. For example, a network entity 102 and a UE 104 may support wireless communication of signals related to services (e.g., voice, video, packet data, messaging, broadcast, etc. ) according to one or multiple radio access technologies. In some implementations, a network entity 102 may be moveable, for example, a satellite associated with a non-terrestrial network. In some implementations, different geographic coverage areas 112 associated with the same or different radio access technologies may overlap, but the different geographic coverage areas 112 may be associated with different network entities 102. Information and signals described herein may be represented using any of a variety of different technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that may be referenced throughout the description may be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

The one or more UEs 104 may be dispersed throughout a geographic region of the wireless communications system 100. A UE 104 may include or may be referred to as a mobile device, a wireless device, a remote device, a remote unit, a handheld device, or a subscriber device, or some other suitable terminology. In some implementations, the UE 104 may be referred to as a unit, a station, a terminal, or a client, among other examples. Additionally, or alternatively, the UE 104 may be referred to as an internet-of-things (IoT) device, an internet-of-everything (IoE) device, or machine-type communication (MTC) device, among other examples. In some implementations, a UE 104 may be stationary in the wireless communications system 100. In some other implementations, a UE 104 may be mobile in the wireless communications system 100.

The one or more UEs 104 may be devices in different forms or having different capabilities. Some examples of UEs 104 are illustrated in Fig. 1. A UE 104 may be capable of communicating with various types of devices, such as the network entities 102, other UEs 104, or network equipment (e.g., the core network 106, the packet data network 108, a relay device, an integrated access and backhaul (IAB) node, or another network equipment) , as shown in Fig. 1. Additionally, or alternatively, a UE 104 may support communication with other network entities 102 or UEs 104, which may act as relays in the wireless communications system 100.

A UE 104 may also be able to support wireless communication directly with other UEs 104 over a communication link 114. For example, a UE 104 may support wireless communication directly with another UE 104 over a device-to-device (D2D) communication link. In some implementations, such as vehicle-to-vehicle (V2V) deployments, vehicle-to-everything (V2X) deployments, or cellular-V2X deployments, the communication link 114 may be referred to as a sidelink. For example, a UE 104 may support wireless communication directly with another UE 104 over a PC5 interface.

A network entity 102 may support communications with the core network 106, or with another network entity 102, or both. For example, a network entity 102 may interface with the core network 106 through one or more backhaul links 116 (e.g., via an S1, N2, N2, or another network interface) . The network entities 102 may communicate with each other over the backhaul links 116 (e.g., via an X2, Xn, or another network interface) . In some implementations, the network entities 102 may communicate with each other directly (e.g., between the network entities 102) . In some other implementations, the network entities 102 may communicate with each other or indirectly (e.g., via the core network 106) . In some implementations, one or more network entities 102 may include subcomponents, such as an access network entity, which may be an example of an access node controller (ANC) . An ANC may communicate with the one or more UEs 104 through one or more other access network transmission entities, which may be referred to as a radio heads, smart radio heads, or transmission-reception points (TRPs) .

In some implementations, a network entity 102 may be configured in a disaggregated architecture, which may be configured to utilize a protocol stack physically or logically distributed among two or more network entities 102, such as an integrated access backhaul (IAB) network, an open radio access network (O-RAN) (e.g., a network configuration sponsored by the O-RAN Alliance) , or a virtualized RAN (vRAN) (e.g., a cloud RAN (C-RAN) ) . For example, a network entity 102 may include one or more of a central unit (CU) , a distributed unit (DU) , a radio unit (RU) , a RAN intelligent controller (RIC) (e.g., a near-real time RIC (Near-RT RIC) , a non-real time RIC (Non-RT RIC) ) , a service management and orchestration (SMO) system, or any combination thereof.

An RU may also be referred to as a radio head, a smart radio head, a remote radio head (RRH) , a remote radio unit (RRU) , or a transmission reception point (TRP) . One or more components of the network entities 102 in a disaggregated RAN architecture may be co-located, or one or more components of the network entities 102 may be located in distributed locations (e.g., separate physical locations) . In some implementations, one or more network entities 102 of a disaggregated RAN architecture may be implemented as virtual units (e.g., a virtual CU (VCU) , a virtual DU (VDU) , a virtual RU (VRU) ) .

Split of functionality between a CU, a DU, and an RU may be flexible and may support different functionalities depending upon which functions (e.g., network layer functions, protocol layer functions, baseband functions, radio frequency functions, and any combinations thereof) are performed at a CU, a DU, or an RU. For example, a functional split of a protocol stack may be employed between a CU and a DU such that the CU may support one or more layers of the protocol stack and the DU may support one or more different layers of the protocol stack. In some implementations, the CU may host upper protocol layer (e.g., an L3, an L2) functionality and signaling (e.g., radio resource control (RRC) , service data adaption protocol (SDAP) , packet data convergence protocol (PDCP) ) . The CU may be connected to one or more DUs or RUs, and the one or more DUs or RUs may host lower protocol layers, such as an L1 (e.g., physical (PHY) layer) or an L2 (e.g., radio link control (RLC) layer, medium access control (MAC) layer) functionality and signaling, and may each be at least partially controlled by the CU.

Additionally, or alternatively, a functional split of the protocol stack may be employed between a DU and an RU such that the DU may support one or more layers of the protocol stack and the RU may support one or more different layers of the protocol stack. The DU may support one or multiple different cells (e.g., via one or more RUs) . In some implementations, a functional split between a CU and a DU, or between a DU and an RU may be within a protocol layer (e.g., some functions for a protocol layer may be performed by one of a CU, a DU, or an RU, while other functions of the protocol layer are performed by a different one of the CU, the DU, or the RU) .

A CU may be functionally split further into CU control plane (CU-CP) and CU user plane (CU-UP) functions. A CU may be connected to one or more DUs via a midhaul communication link (e.g., F1, F1-C, F1-U) , and a DU may be connected to one or more RUs via a fronthaul communication link (e.g., open fronthaul (FH) interface) . In some implementations, a midhaul communication link or a fronthaul communication link may be implemented in accordance with an interface (e.g., a channel) between layers of a protocol stack supported by respective network entities 102 that are in communication via such communication links.

The core network 106 may support user authentication, access authorization, tracking, connectivity, and other access, routing, or mobility functions. The core network 106 may be an evolved packet core (EPC) , or a 5G core (5GC) , which may include a control plane entity that manages access and mobility (e.g., a mobility management entity (MME) , an access and mobility management functions (AMF) ) and a user plane entity that routes packets or interconnects to external networks (e.g., a serving gateway (S-GW) , a packet data network (PDN) gateway (P-GW) , or a user plane function (UPF) ) . In some implementations, the control plane entity may manage non-access stratum (NAS) functions, such as mobility, authentication, and bearer management (e.g., data bearers, signal bearers, etc. ) for the one or more UEs 104 served by the one or more network entities 102 associated with the core network 106.

The core network 106 may communicate with the packet data network 108 over one or more backhaul links 116 (e.g., via an S1, N2, N3, or another network interface) . The packet data network 108 may include an application server 118. In some implementations, one or more UEs 104 may communicate with the application server 118. A UE 104 may establish a session (e.g., a protocol data unit (PDU) session, or the like) with the core network 106 via a network entity 102. The core network 106 may route traffic (e.g., control information, data, and the like) between the UE 104 and the application server 118 using the established session (e.g., the established PDU session) . The PDU session may be an example of a logical connection between the UE 104 and the core network 106 (e.g., one or more network functions of the core network 106) .

In the wireless communications system 100, the network entities 102 and the UEs 104 may use resources of the wireless communications system 100 (e.g., time resources (e.g., symbols, slots, subframes, frames, or the like) or frequency resources (e.g., subcarriers, carriers) ) to perform various operations (e.g., wireless communications) . In some implementations, the network entities 102 and the UEs 104 may support different resource structures. For example, the network entities 102 and the UEs 104 may support different frame structures. In some implementations, such as in 4G, the network entities 102 and the UEs 104 may support a single frame structure. In some other implementations, such as in 5G and among other suitable radio access technologies, the network entities 102 and the UEs 104 may support various frame structures (i.e., multiple frame structures) . The network entities 102 and the UEs 104 may support various frame structures based on one or more numerologies.

One or more numerologies may be supported in the wireless communications system 100, and a numerology may include a subcarrier spacing and a cyclic prefix. A first numerology (e.g., μ=0) may be associated with a first subcarrier spacing (e.g., 15 kHz) and a normal cyclic prefix. In some implementations, the first numerology (e.g., μ=0) associated with the first subcarrier spacing (e.g., 15 kHz) may utilize one slot per subframe. A second numerology (e.g., μ=1) may be associated with a second subcarrier spacing (e.g., 30 kHz) and a normal cyclic prefix. A third numerology (e.g., μ=2) may be associated with a third subcarrier spacing (e.g., 60 kHz) and a normal cyclic prefix or an extended cyclic prefix. A fourth numerology (e.g., μ=3) may be associated with a fourth subcarrier spacing (e.g., 120 kHz) and a normal cyclic prefix. A fifth numerology (e.g., μ=4) may be associated with a fifth subcarrier spacing (e.g., 240 kHz) and a normal cyclic prefix.

A time interval of a resource (e.g., a communication resource) may be organized according to frames (also referred to as radio frames) . Each frame may have a duration, for example, a 10 millisecond (ms) duration. In some implementations, each frame may include multiple subframes. For example, each frame may include 10 subframes, and each subframe may have a duration, for example, a 1 ms duration. In some implementations, each frame may have the same duration. In some implementations, each subframe of a frame may have the same duration.

Additionally or alternatively, a time interval of a resource (e.g., a communication resource) may be organized according to slots. For example, a subframe may include a number (e.g., quantity) of slots. The number of slots in each subframe may also depend on the one or more numerologies supported in the wireless communications system 100. For instance, the first, second, third, fourth, and fifth numerologies (i.e., μ=0, μ=1, μ=2, μ=3, μ=4) associated with respective subcarrier spacings of 15 kHz, 30 kHz, 60 kHz, 120 kHz, and 240 kHz may utilize a single slot per subframe, two slots per subframe, four slots per subframe, eight slots per subframe, and 16 slots per subframe, respectively. Each slot may include a number (e.g., quantity) of symbols (e.g., OFDM symbols) . In some implementations, the number (e.g., quantity) of slots for a subframe may depend on a numerology. For a normal cyclic prefix, a slot may include 14 symbols. For an extended cyclic prefix (e.g., applicable for 60 kHz subcarrier spacing) , a slot may include 12 symbols. The relationship between the number of symbols per slot, the number of slots per subframe, and the number of slots per frame for a normal cyclic prefix and an extended cyclic prefix may depend on a numerology. It should be understood that reference to a first numerology (e.g., μ=0) associated with a first subcarrier spacing (e.g., 15 kHz) may be used interchangeably between subframes and slots.

In the wireless communications system 100, an electromagnetic (EM) spectrum may be split, based on frequency or wavelength, into various classes, frequency bands, frequency channels, etc. By way of example, the wireless communications system 100 may support one or multiple operating frequency bands, such as frequency range designations FR1 (410 MHz –7.125 GHz) , FR2 (24.25 GHz –52.6 GHz) , FR3 (7.125 GHz –24.25 GHz) , FR4 (52.6 GHz –114.25 GHz) , FR4a or FR4-1 (52.6 GHz –71 GHz) , and FR5 (114.25 GHz –300 GHz) . In some implementations, the network entities 102 and the UEs 104 may perform wireless communications over one or more of the operating frequency bands. In some implementations, FR1 may be used by the network entities 102 and the UEs 104, among other equipment or devices for cellular communications traffic (e.g., control information, data) . In some implementations, FR2 may be used by the network entities 102 and the UEs 104, among other equipment or devices for short-range, high data rate capabilities.

FR1 may be associated with one or multiple numerologies (e.g., at least three numerologies) . For example, FR1 may be associated with a first numerology (e.g., μ=0) , which includes 15 kHz subcarrier spacing; a second numerology (e.g., μ=1) , which includes 30 kHz subcarrier spacing; and a third numerology (e.g., μ=2) , which includes 60 kHz subcarrier spacing. FR2 may be associated with one or multiple numerologies (e.g., at least 2 numerologies) . For example, FR2 may be associated with a third numerology (e.g., μ=2) , which includes 60 kHz subcarrier spacing; and a fourth numerology (e.g., μ=3) , which includes 120 kHz subcarrier spacing.

Fig. 2 illustrates another example of a wireless communications system 200 that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. As shown in Fig. 2, the wireless communications system 200 may comprise a first network node 210, a second network node 220 and a third network node 230.

The first network node 210 transmits a first request message to the second network node 220. The first message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update. In turn, the first network node 210 receives a first response message from the second network node 220.

In some implementations, the first network node 210 may comprise or may be implemented as a CU of a source MN, and the second network node 220 may comprise or may be implemented as a candidate DU of the source MN. This will be described with reference to Fig. 3A.

Alternatively, in some implementations, the first network node 210 may comprise or may be implemented as a CU of a source SN, and the second network node 220 may comprise or may be implemented as a candidate DU of the source SN. This will be described with reference to Fig. 3B.

Alternatively, in some implementations, the first network node 210 may comprise or may be implemented as a CU of a source MN, and the second network node 220 may comprise or may be implemented as a CU of a candidate MN. This will be described with reference to Fig. 3C.

Alternatively, in some implementations, the first network node 210 may comprise or may be implemented as a CU of a source MN, and the second network node 220 may comprise or may be implemented as a CU of a candidate SN. This will be described with reference to Fig. 3D.

Hereinafter, for brevity, a CU of a source MN is also referred to as a source MN-CU, and a candidate DU of a source MN is also referred to as a candidate MN-DU. A CU of a source SN is also referred to as a source SN-CU, and a candidate DU of a source SN is also referred to as a candidate SN-DU. A CU of a candidate MN is also referred to as a candidate MN-CU. A CU of a candidate SN is also referred to as a candidate SN-CU.

Fig. 3A illustrates another example of a wireless communications system 300A that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The wireless communications system 300A may be considered as an example implementation of the wireless communications system 100 or 200.

As shown in Fig. 3A, the wireless communications system 300A may comprise the gNB 102-1, the gNB 102-2 and the UE 104 in Fig. 1.

In some implementations, the gNB 102-1 may comprise a gNB-CU 310 as well as a gNB-DU 312 and a gNB-DU 314. The gNB 102-2 may comprise a gNB-CU 320 as well as a gNB-DU 322 and a gNB-DU 324.

In some implementations, a gNB-CU may be a logical node hosting RRC, SDAP and PDCP protocols of the gNB or RRC and PDCP protocols of the en-gNB that controls the operation of one or more gNB-DUs. The gNB-CU terminates the F1 interface connected to the gNB-DU.

In some implementations, a gNB-DU may be a logical node hosting RLC, MAC and PHY layers of the gNB or en-gNB, and its operation is partly controlled by gNB-CU. One gNB-DU supports one or multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected with the gNB-CU.

In some implementations, the UE 104 may be is in dual connection (DC) with the gNB 102-1 and the gNB 102-2. For example, the UE 104 may access a PCell provided the gNB-DU 312 and a PSCell provided by the gNB-DU 322.

In some implementations, the gNB 102-1 may be implemented as an MN, and the gNB 102-2 may be implemented as an SN. The gNB 102-1 may provide an MCG and the gNB 102-2 may provide an SCG.

In such implementations, the gNB 102-1 and the gNB 102-2 are also referred to as an MN 102-1 and an SN 102-2, respectively. The gNB-CU 310, the gNB-DU 312 and the gNB-DU 314 are also referred to as an MN-CU 310, an MN-DU 312 and an MN-DU 314, respectively. Alternatively, the gNB-CU 310, the gNB-DU 312 and the gNB-DU 314 are also referred to as a CU 310 of the MN 102-1, a DU 312 of the MN 102-1 and a DU 314 of the MN 102-1, respectively.

In such implementations, the gNB-CU 32, the gNB-DU 322 and the gNB-DU 324 are also referred to as an SN-CU 320, an SN-DU 322 and an SN-DU 324, respectively. Alternatively, the gNB-CU 320, the gNB-DU 322 and the gNB-DU 324 are also referred to as a CU 320 of the SN 102-2, a DU 322 of the SN 102-2 and a DU 324 of the SN 102-2, respectively.

In some implementations, the UE 104 may perform intra-CU MCG conditional LTM. In other words, the UE 104 may perform, based on an execution condition, a cell switch from a PCell (i.e., a source cell) provided by the MN-DU 312 to a PCell (i.e., a candidate cell) provided by the MN-DU 314. In such implementations, the MN-DU 312 and the MN-DU 314 are also referred to as a source MN-DU 312 and a candidate MN-DU 314.

Fig. 3B illustrates another example of a wireless communications system 300B that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The wireless communications system 300B may be considered as an example implementation of the wireless communications system 100 or 200.

The wireless communications system 300B is different from the wireless communications system 300A in that the UE 104 may perform intra-CU SCG conditional LTM. In other words, the UE 104 may perform, based on an execution condition, a cell switch from a PSCell (i.e., a source cell) provided by the SN-DU 322 to a PSCell (i.e., a candidate cell) provided by the SN-DU 324. In such implementations, the SN-DU 322 and the SN-DU 324 are also referred to as a source SN-DU 322 and a candidate SN-DU 324.

Fig. 3C illustrates another example of a wireless communications system 300C that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The wireless communications system 300C may be considered as an example implementation of the wireless communications system 100 or 200.

The wireless communications system 300C is different from the wireless communications system 300A and 300B in that the wireless communications system 300C further comprises a gNB 102-3 not shown in Fig. 1. The gNB 102-3 may comprise a gNB-CU 330 and a gNB-DU 332. The gNB 102-3 may be implemented as a candidate MN. Thus, the gNB 102-3 is also referred to as a candidate MN 102-3.

In some implementations, the UE 104 may perform inter-CU MCG conditional LTM. In other words, the UE 104 may perform, based on an execution condition, a cell switch from a PCell (i.e., a source cell) provided by the MN-DU 312 of the MN 102-1 to a PCell (i.e., a candidate cell) provided by the MN-DU 332 of the candidate MN 102-3. In such implementations, the MN-DU 312 and the MN-DU 314 are also referred to as a source MN-DU 312 and a candidate MN-DU 332.

Fig. 3D illustrates another example of a wireless communications system 300D that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The wireless communications system 300D may be considered as an example implementation of the wireless communications system 100 or 200.

The wireless communications system 300D is different from the wireless communications system 300A and 300B in that the wireless communications system 300D further comprises a gNB 102-4 not shown in Fig. 1. The gNB 102-4 may comprise a gNB-CU 340 and a gNB-DU 342. The gNB 102-4 may be implemented as a candidate SN. Thus, the gNB 102-4 is also referred to as a candidate SN 102-4.

In some implementations, the UE 104 may perform inter-CU SCG conditional LTM. In other words, the UE 104 may perform, based on an execution condition, a cell switch from a PSCell (i.e., a source cell) provided by the SN-DU 322 of the SN 102-2 to a PCell (i.e., a candidate cell) provided by the SN-DU 342 of the candidate SN 102-4. In such implementations, the SN-DU 322 and the SN-DU 342 are also referred to as a source SN-DU 322 and a candidate SN-DU 342.

Fig. 4 illustrates a signaling diagram illustrating an example process 400 that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The process 400 may involve the first network node 210 and the second network node 220 in Fig. 1.

As shown in Fig. 4, the first network node 210 transmits 410 a first request message to the second network node 220. The first request message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update. Hereinafter, an ID for a serving cell or an ID for a candidate cell related to PDCP re-establishment or security key update is also referred to as a “new ID” .

In turn, the first network node 210 receives 440 a first response message from the second network node 220.

In some implementations, the second network node 220 may transmit 420 a second request message to the third network node 230. The second request message comprises at least one of the following: a request for at least one layer 1 condition for conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update.

In some implementations, the second network node 220 may receive 430 a second response message from the third network node 230.

In some implementations, the UE 104 may transmit capability of the UE 104 to the first network node 210 (such as the MN 102-1) . For example, the UE 104 may transmit the capability of the UE 104 to the MN 102-1 if the UE 104 receives the enquiry from the MN 102-1. The capability of the UE 104 indicates that the UE 104 supports at least one of L1 condition based LTM or L3 condition based LTM.

In some implementations, the capability of the UE 104 may comprise at least one of the following: first information, second information or third information.

In some implementations, the first information indicates whether the UE 104 supports L1 condition based LTM. The second information indicates whether the UE 104 supports L1 condition-based MCG LTM. The third information indicate whether the UE 104 supports L1 condition-based SCG LTM.

In some implementations, in the above three information, the UE 104 may further indicate what L1 event (also referred to as L1 condition) will be supported. The L1 condition could be at least one of the following.
◆ Event#A for LTM: Beam of serving cell becomes worse than absolute
threshold;
◆ Event#B for LTM: Beam of candidate cell becomes amount of offset
better than beam of serving cell;
◆ Event#C for LTM: Beam of candidate cell becomes better than absolute
threshold; or
◆ Event#D for LTM: Beam of serving cell becomes worse than absolute
threshold1 AND Beam of candidate cell becomes better than another absolute threshold2.

In some implementations, the capability of the UE 104 may further comprise at least one of the following: fourth information, fifth information or sixth information.

In some implementations, the fourth information indicates whether the UE 104 supports L3 condition based LTM. The fifth information indicates whether the UE 104 supports L3 condition-based MCG LTM. The sixth information indicates whether the UE 104 supports L3 condition-based SCG LTM.

In some implementations, in the above three information, the UE 104 may further indicate what L3 event (also referred to as L3 condition) will be supported. The L3 condition could be at least one of the following.
◆ Event A1: Serving cell becomes better than absolute threshold;
◆ Event A2: Serving cell becomes worse than absolute threshold;
◆ Event A3: Neighbour becomes amount of offset better than PCell/PSCell;
◆ Event A4: Neighbour becomes better than absolute threshold;
◆ Event A5: PCell/PSCell becomes worse than absolute threshold1 AND
Neighbour/SCell becomes better than another absolute threshold2;
◆ Event A6: Neighbour becomes amount of offset better than SCell;
◆ Event D1: Distance between UE and a reference location
referenceLocation1 becomes larger than configured threshold distanceThreshFromReference1 and distance between UE and a reference location referenceLocation2 becomes shorter than configured threshold distanceThreshFromReference2;
◆ Event D2: Distance between UE and the serving cell moving reference
location determined based on movingReferenceLocation and its corresponding satellite ephemeris and epoch time broadcast in SIB19 becomes larger than configured threshold distanceThreshFromReference1 and distance between UE and a moving reference location determined based on referenceLocation and its corresponding satellite ephemeris and epoch time for the neighbor cell provided in the associated MeasObjectNR becomes shorter than configured threshold distanceThreshFromReference2;
◆ CondEvent A3: Conditional reconfiguration candidate becomes amount
of offset better than PCell/PSCell;
◆ CondEvent A4: Conditional reconfiguration candidate becomes better
than absolute threshold where condEventA4 can also be used for current PSCell (i.e., in case it is configured as candidate PSCell for CondEvent A4 evaluation) for CHO with candidate SCG (s) case;
◆ CondEvent A5: PCell/PSCell becomes worse than absolute threshold1
AND Conditional reconfiguration candidate becomes better than another absolute threshold2;
◆ CondEvent D1: Distance between UE and a reference location
referenceLocation1 becomes larger than configured threshold distanceThreshFromReference1 and distance between UE and a reference location referenceLocation2 of conditional reconfiguration candidate becomes shorter than configured threshold distanceThreshFromReference2;
◆ CondEvent D2: Distance between UE and the serving cell moving
reference location determined based on movingReferenceLocation and its corresponding satellite ephemeris and epoch time broadcast in SIB19 becomes larger than configured threshold distanceThreshFromReference1 and distance between UE and a moving reference location determined based on referenceLocation and its corresponding satellite ephemeris and epoch time for the conditional reconfiguration candidate provided in the associated MeasObjectNR becomes shorter than configured threshold distanceThreshFromReference2;
◆ CondEvent T1: Time measured at UE becomes more than configured
threshold t1-Threshold but is less than t1-Threshold + duration;
◆ Event X1: Serving L2 user equipment (UE) to network (NW) (U2N)
Relay UE becomes worse than absolute threshold1 AND NR Cell becomes better than another absolute threshold2;
◆ Event X2: Serving L2 U2N Relay UE becomes worse than absolute
threshold;
◆ For event I1, measurement reporting event is based on cross link
interference (CLI) measurement results, which can either be derived based on sounding reference signal (SRS) -reference signal received power (RSRP) or cross link interference-received signal strength indicator (CLI-RSSI) ;
◆ Event I1: Interference becomes higher than absolute threshold;
◆ The reporting events concerning Aerial UE altitude are labelled HN with
N equal to 1 and 2. Additionally, the reporting events concerning Aerial UE altitude and the neighboring cell measurements simultaneously are labelled AMHN with M equal to 3, 4, 5 and N equal to 1, 2;
◆ Event H1: Aerial UE altitude becomes higher than a threshold;
◆ Event H2: Aerial UE altitude becomes lower than a threshold;
◆ Event A3H1: Neighbour becomes offset better than SpCell and the Aerial
UE altitude becomes higher than a threshold;
◆ Event A3H2: Neighbour becomes offset better than SpCell and the Aerial
UE altitude becomes lower than a threshold;
◆ Event A4H1: Neighbour becomes better than threshold1 and the Aerial
UE altitude becomes higher than a threshold2;
◆ Event A4H2: Neighbour becomes better than threshold1 and the Aerial
UE altitude becomes lower than a threshold2;
◆ Event A5H1: SpCell becomes worse than threshold1 and neighbour
becomes better than threshold2 and the Aerial UE altitude becomes higher than a threshold3;
◆ Event A5H2: SpCell becomes worse than threshold1 and neighbour
becomes better than threshold2 and the Aerial UE altitude becomes lower than a threshold3.

In some implementations, the first network node 210 (such as the MN 102-1) may transmit the capability of the UE 104 to the second network node 220 (such as the SN 102-2) . Then, the SN 102-2 can determine condition type and generate a condition based on the capability of the UE 104 for SCG LTM. If a type of the condition is L1 condition, the SN-CU 320 can request the SN-DU 322 to provide the L1 condition. Otherwise, the SN-CU 320 itself provides L3 condition.

In some implementations, the UE 104 receives a configuration related to L1 measurement report or L3 measurement report from the MN 102-1. If SCG is configured, the UE 104 may receive the configuration related to L1 measurement report or L3 measurement report from the SN 102-2 as well. The configuration from the SN 102-2 is configured for SCG LTM purpose.

Fig. 5 illustrates a signaling diagram illustrating an example process 500 that supports subsequent conditional LTM in accordance with aspects of the present disclosure. The process 500 may be considered as an example implementation of the process 400. For the purpose of discussion, the process 500 will be described with reference to Fig. 3A. The process 500 may involve the MN-CU 310, the source MN-DU 312, the candidate MN-DU 314 and the UE 104 in Fig. 3A.

Generally, in the process 500, the UE 104 may perform intra-CU MCG conditional LTM. In other words, the UE 104 may perform, based on an execution condition, a cell switch from a PCell (i.e., a source cell) provided by the MN-DU 312 to a PCell (i.e., a candidate cell) prepared by the candidate MN-DU 314. The source cell is also referred to as a current serving cell.

As shown in Fig. 5, after the MN-CU 310 receives a measurement report from the UE 104, the MN-CU 310 determines 510 to prepare a candidate cell, e.g., a candidate cell#1 prepared by the candidate MN-DU 314.

The MN-CU 310 transmits 515 the first request message to a candidate MN-DU for each candidate cell. For example, the MN-CU 310 may transmit the first request message to the candidate MN-DU 314 providing the candidate cell#1. The MN-CU 310 may also transmit the first request message to a further MN-DU (not shown) of the MN-CU 310 and the further MN-DU provides a candidate cell#2. It is assumed that a source cell is a source cell#0 provided by the source MN-DU 312.

In some implementations, the first request message may comprise a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell.

In some implementations, the first request message towards the candidate MN-DU 314 may comprise an ID of a candidate cell, e.g., an ID of the candidate cell#1.

Alternatively or additionally, in some implementations, the first request message may comprise the capability of the UE 104. The capability of the UE 104 indicates that the UE 104 supports at least one of L1 condition based LTM or L3 condition based LTM. In such implementations, the candidate MN-DU 314 may determine a type of the at least one condition for subsequent conditional LTM based on the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as or different from the type of the condition for initial conditional LTM.

Alternatively or additionally, in some implementations, the first request message may comprise a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node (e.g., from the source cell#0 to the candidate cell#1) . In such implementations, the candidate MN-DU 314 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM. Alternatively, the candidate MN-DU 314 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM and the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as the type of the condition for initial conditional LTM.

In some implementations, the request for at least one condition may indicate the candidate MN-DU 314 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 314 to each of the at least one candidate cell prepared by at least one other MN-DU. For example, the request for at least one condition may indicate the candidate MN-DU 314 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by a further MN-DU of the MN 102-1 or at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by a further MN-DU of other MN than the MN 102-1. In such implementations, the candidate MN-DU 314 may determine the type of the at least one condition to be generated.

Alternatively or additionally, in some implementations, the request for at least one condition may indicate the candidate MN-DU 314 to generate at least one L1 condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 314 to each of the at least one candidate cell prepared by at least one other MN-DU. In such implementations, the MN-CU 310 may determine the type of the at least one condition to be generated.

In some implementations, the first request message may comprise a UE CONTEXT SETUP REQUEST message.

In some implementations, the UE CONTEXT SETUP REQUEST message may comprise an LTM Multiple Target DU List IE comprising the list of at least one candidate cell. Upon receiving the UE CONTEXT SETUP REQUEST message, the candidate MN-DU 314 shall, if supported, consider that the information in the IE pertains to a list of candidate cells suggested for other candidate MN-DUs and the information may also be prepared for subsequent LTM. For example, other candidate MN-DUs may comprise a further MN-DU of the MN 102-1 and/or a further MN-DU of other MN than the MN 102-1.

Alternatively or additionally, in some implementations, the first request message may comprise a CSI resource configuration for subsequent LTM.

In some implementations, the MN-CU 310 may provide the LTM configuration ID mapping list to the candidate MN-DU 314.

Alternatively or additionally, in some implementations, the first request message may comprise a request for PRACH resources from the candidate MN-DU 314.

In some implementations, the MN-CU 310 may request, via the first request message, the candidate MN-DU 314 to provide the lower layer configuration for the purpose of generating the reference configuration.

In some implementations, the MN-CU 310 may provide, via the first request message, the lower layer part of the reference configuration to the candidate MN-DU 314.

With continued reference to Fig. 5, if the candidate MN-DU 314 accepts the request for at least one condition for subsequent conditional LTM, the candidate MN-DU 314 transmits 520 the first response message to the MN-CU 310. The first response message comprises the at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 314 to each of the at least one candidate cell prepared by at least one other MN-DU.

In some implementations, both L1 condition based LTM and L3 condition based LTM are supported by the UE 104. In such implementations, it may be predefined that a first priority of the L1 condition based LTM is higher than a second priority of the L3 condition based LTM. Thus, the candidate MN-DU 314 may generate at least one L1 condition for the subsequent conditional LTM.

In some implementations, the first response message may further comprise L1 condition for initial conditional LTM. For example, the first response message may further comprise L1 condition for initial cell switch from the source cell#0 to the candidate cell#1.

In some implementations, the first response message may further comprise the generated lower layer RRC configurations for the accepted target candidate cell.

In some implementations, the first response message may comprise a UE CONTEXT SETUP RESPONSE message. The UE CONTEXT SETUP RESPONSE message may comprise the at least one condition for subsequent conditional LTM related to the list of at least one candidate cell.

In some implementations, if a candidate cell in the list of at least one candidate cell is cancelled, the MN-CU 310 may indicate it (cancellation of the candidate cell) to the candidate MN-DU 314 via e.g. UE CONTEXT MODIFICATION REQUEST message. For example, the UE CONTEXT MODIFICATION REQUEST message may comprise the LTM Multiple Target DU List IE comprising an updated list of the at least one candidate cell. For example, the updated list of the at least one candidate cell may be transmitted to the candidate MN-DU 314 for updating purpose.

In turn, the MN-CU 310 may transmit 525 to the source MN-DU 312 a message, e.g., UE CONTEXT MODIFICATION REQUEST message. The message may comprise an indication to indicate the candidate cell is condition based LTM.

The MN-CU 310 may transmit 530 an RRC reconfiguration message related to candidate cell#1 to the UE 104 via the source MN-DU 312.

In some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#1) ;
● LTM candidate configuration for the candidate cell#1;
● Condition#1 of cell switch from the source cell#0 to the candidate cell#1,
wherein the condition could be L1 condition or L3 condition;
● Condition#2 of cell switch from candidate cell#2 to candidate cell#1,
wherein the condition could be L1 condition or L3 condition; or
● Condition#3 of cell switch from candidate cell#3 to candidate cell#1, the
condition could be L1 condition or L3 condition.

Alternatively or additionally, in some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#2) ,
● LTM candidate configuration for the candidate cell#2;
● Condition#4 of cell switch from the source cell#0 to the candidate cell#2,
wherein the condition could be L1 condition or L3 condition;
● Condition#5 of cell switch from the candidate cell#1 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition (wherein Condition#5 is generated by the candidate MN-DU 314) ; or
● Condition#6 of cell switch from the candidate cell#3 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition.

In some implementations, the LTM configuration may comprise the LTM candidate configuration.

In some implementations, the LTM candidate configuration may comprise at least one of the following: measurement configuration, CSI resource, RACH configuration, MAC configuration, Physical layer configuration, RLC configuration or PDCP configuration.

The UE 104 starts 535 to evaluate the at least one condition according to the configuration.

In some implementations, when the UE 104 is served by the cell#0, the UE 104 evaluates the condition#1. The UE 104 does not evaluate the condition#2 and the condition#3. After the UE 104 is triggered to switch from the cell#0 to the candidate cell#2, the UE 104 starts to evaluate the condition#2 since the current serving cell is cell#2.

Fig. 6 illustrates a signaling diagram illustrating an example process 600 that supports subsequent conditional LTM in accordance with aspects of the present disclosure. The process 600 may be considered as an example implementation of the process 400. For the purpose of discussion, the process 600 will be described with reference to Fig. 3A. The process 600 may involve the SN-CU 320, the source SN-DU 322, the candidate SN-DU 324 and the UE 104 in Fig. 3B.

Generally, in the process 600, the UE 104 may perform intra-CU SCG conditional LTM. In other words, the UE 104 may perform, based on an execution condition, a cell switch from a PSCell (i.e., a source cell) provided by the SN-DU 322 to a PSCell (i.e., a candidate cell) prepared by the candidate SN-DU 324. The source cell is also referred to as a current serving cell.

As shown in Fig. 6, after the SN-CU 320 receives a measurement report from the UE 104, the SN-CU 320 determines 610 to prepare a candidate cell, e.g., a candidate cell#1 prepared by the candidate SN-DU 324.

The SN-CU 320 transmits 615 the first request message to a candidate SN-DU for each candidate cell. For example, the SN-CU 320 may transmit the first request message to the candidate SN-DU 324 providing the candidate cell#1. The SN-CU 320 may also transmit the first request message to a further SN-DU (not shown) of the SN-CU 320 and the further SN-DU provides a candidate cell#2. It is assumed that a source cell is a source cell#0 provided by the source SN-DU 322.

In some implementations, the first request message towards the candidate SN-DU 324 may comprise an ID of a candidate cell, e.g., an ID of the candidate cell#1.

Alternatively or additionally, in some implementations, the first request message may comprise the capability of the UE 104. The capability of the UE 104 indicates that the UE 104 supports at least one of L1 condition based LTM or L3 condition based LTM. In such implementations, the candidate SN-DU 324 may determine a type of the at least one condition for subsequent conditional LTM based on the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as or different from the type of the condition for initial conditional LTM.

Alternatively or additionally, in some implementations, the first request message may comprise a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node (e.g., from the source cell#0 to the candidate cell#1) . In such implementations, the candidate SN-DU 324 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM. Alternatively, the candidate SN-DU 324 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM and the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as the type of the condition for initial conditional LTM.

In some implementations, the request for at least one condition may indicate the candidate SN-DU 324 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 324 to each of the at least one candidate cell prepared by at least one other SN-DU. For example, the request for at least one condition may indicate the candidate SN-DU 324 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by a further SN-DU of the SN 102-2 or at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by a further SN-DU of other SN than the SN 102-2. In such implementations, the candidate SN-DU 324 may determine the type of the at least one condition to be generated.

Alternatively or additionally, in some implementations, the request for at least one condition may indicate the candidate SN-DU 324 to generate at least one L1 condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 324 to each of the at least one candidate cell prepared by at least one other SN-DU. In such implementations, the SN-CU 320 may determine the type of the at least one condition to be generated.

In some implementations, the UE CONTEXT SETUP REQUEST message may comprise an LTM Multiple Target DU List IE comprising the list of at least one candidate cell. Upon receiving the UE CONTEXT SETUP REQUEST message, the candidate SN-DU 324 shall, if supported, consider that the information in the IE pertains to a list of candidate cells suggested for other candidate SN-DUs and the information may also be prepared for subsequent LTM. For example, other candidate SN-DUs may comprise a further SN-DU of the SN 102-2 and/or a further SN-DU of other SN than the SN 102-2.

In some implementations, the SN-CU 320 may provide the LTM configuration ID mapping list to the candidate SN-DU 324.

Alternatively or additionally, in some implementations, the first request message may comprise a request for PRACH resources from the candidate SN-DU 324.

In some implementations, the SN-CU 320 may request, via the first request message, the candidate SN-DU 324 to provide the lower layer configuration for the purpose of generating the reference configuration.

In some implementations, the SN-CU 320 may provide, via the first request message, the lower layer part of the reference configuration to the candidate SN-DU 324.

With continued reference to Fig. 6, if the candidate SN-DU 324 accepts the request for at least one condition for subsequent conditional LTM, the candidate SN-DU 324 transmits 620 the first response message to the SN-CU 320. The first response message comprises the at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 324 to each of the at least one candidate cell prepared by at least one other SN-DU.

In some implementations, both L1 condition based LTM and L3 condition based LTM are supported by the UE 104. In such implementations, it may be predefined that a first priority of the L1 condition based LTM is higher than a second priority of the L3 condition based LTM. Thus, the candidate SN-DU 324 may generate at least one L1 condition for the subsequent conditional LTM.

In some implementations, if a candidate cell in the list of at least one candidate cell is cancelled, the SN-CU 320 may indicate it (e.g. cancellation of the candidate cell) to the candidate SN-DU 324 via e.g. UE CONTEXT MODIFICATION REQUEST message. For example, the UE CONTEXT MODIFICATION REQUEST message may comprise the LTM Multiple Target DU List IE comprising an updated list of the at least one candidate cell. For example, the updated list of the at least one candidate cell may be transmitted to the candidate SN-DU 324 for updating purpose.

In turn, the SN-CU 320 may transmit 625 to the source SN-DU 322 a message, e.g., UE CONTEXT MODIFICATION REQUEST message. The message may comprise an indication to indicate the candidate cell is condition based LTM.

The SN-CU 320 may transmit 630 an RRC reconfiguration message related to candidate cell#1 to the UE 104 via the source SN-DU 322.

Alternatively or additionally, in some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#2) ,
● LTM candidate configuration for the candidate cell#2;
● Condition#4 of cell switch from the source cell#0 to the candidate cell#2,
wherein the condition could be L1 condition or L3 condition;
● Condition#5 of cell switch from the candidate cell#1 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition (wherein Condition#5 is generated by the candidate SN-DU 324) ; or
● Condition#6 of cell switch from the candidate cell#3 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition.

The UE 104 starts 635 to evaluate the at least one condition according to the configuration.

Fig. 7 illustrates a signaling diagram illustrating an example process 700 that supports subsequent conditional LTM in accordance with aspects of the present disclosure. The process 700 may be considered as an example implementation of the process 400. For the purpose of discussion, the process 700 will be described with reference to Fig. 3C. The process 700 may involve the MN-CU 310, the source MN-DU 312, the candidate MN-DU 314 and the UE 104 in Fig. 3C.

Generally, in the process 700, the UE 104 may perform inter-CU MCG conditional LTM. In other words, the UE 104 may perform, based on an execution condition, a cell switch from a PCell (i.e., a source cell) provided by the MN-DU 312 of the source MN 102-1 to a PCell (i.e., a candidate cell) prepared by the candidate MN-DU 332 of the candidate MN 102-3. The source cell is also referred to as a current serving cell.

As shown in Fig. 7, after the MN-CU 310 receives a measurement report from the UE 104, the MN-CU 310 determines 710 to prepare a candidate cell, e.g., a candidate cell#1 prepared by the candidate MN-DU 332.

The source MN-CU 310 transmits 715 the first request message to the candidate MN-CU 330 for each candidate cell via Xn interface. For example, the candidate cell may comprise the candidate cell#1 prepared by the candidate MN-DU 332. It is assumed that a source cell is a source cell#0 provided by the source MN-DU 312.

In some implementations, the first request message towards the candidate MN-CU 330 may comprise an ID of a candidate cell, e.g., an ID of the candidate cell#1.

Alternatively or additionally, in some implementations, the first request message may comprise the capability of the UE 104. The capability of the UE 104 indicates that the UE 104 supports at least one of L1 condition based LTM or L3 condition based LTM. In such implementations, the candidate MN-CU 330 may determine a type of the at least one condition for subsequent conditional LTM based on the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as or different from the type of the condition for initial conditional LTM.

Alternatively or additionally, in some implementations, the first request message may comprise a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node (e.g., from the source cell#0 to the candidate cell#1) . In such implementations, the candidate MN-CU 330 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM. Alternatively, the candidate MN-CU 330 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM and the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as the type of the condition for initial conditional LTM.

In some implementations, the request for at least one condition may indicate the candidate MN-CU 330 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 332 of the candidate MN-CU 330 to each of the at least one candidate cell prepared by at least one other MN. For example, the request for at least one condition may indicate the candidate MN-CU 330 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by other candidate MN than the candidate MN 102-3. In such implementations, the candidate MN-CU 330 may determine the type of the at least one condition to be generated.

Alternatively or additionally, in some implementations, the request for at least one condition may indicate the candidate MN-CU 330 to generate at least one L1 condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 332 of the candidate MN-CU 330 to each of the at least one candidate cell prepared by at least one other candidate MN. In such implementations, the MN-CU 310 may determine the type of the at least one condition to be generated.

In some implementations, the first request message may comprise a handover request message.

In some implementations, the handover request message may comprise an LTM Multiple Target NG-RAN Node List IE comprising the list of at least one candidate cell. Upon receiving the handover request message, the candidate MN-CU 330 shall, if supported, consider that the information in the IE pertains to a list of candidate cells suggested for other candidate MN and the information may also be prepared for subsequent LTM. For example, other candidate MN may comprise an MN different from the candidate MN 102-3.

In some implementations, if a candidate cell in the list of at least one candidate cell is cancelled, the MN-CU 310 may indicate it (cancellation of the candidate cell) to the candidate MN-CU 330 via LTM CONFIGURATION UPDATE message. For example, the LTM CONFIGURATION UPDATE message may comprise the LTM Multiple Target NG-RAN Node List IE comprising an updated list of the at least one candidate cell. For example, the updated list of the at least one candidate cell may be transmitted to the candidate MN-CU 330 for updating purpose.

In some implementations, after the candidate MN-CU 330 receives the first request message from the source MN-CU 310, the candidate MN-CU 330 may determine 720 a type of the at least one condition for subsequent conditional LTM related to the list of at least one candidate cell based on the information in the first request message. Alternatively, the candidate MN-CU 330 may determine 720 the type of the at least one condition for subsequent conditional LTM without considering the information in the first request message.

In some implementations, the type of the at least one condition comprises one of the following: L1 condition, L3 condition, or a combination of L1 condition and L3 condition.

In some implementations, if the candidate MN-CU 330 determines that a type of the at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell#2 prepared by other MN is L3 condition, the candidate MN-CU 330 may generate the at least one condition. If the candidate MN-CU 330 determines that the type of the at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell#2 prepared by other MN is L1 condition, the candidate MN-CU 330 may request the candidate MN-DU 332 to generate the at least one condition.

In some implementations, in the combination of L1 condition and L3 condition, the UE 104 is triggered to execute conditional LTM when both L1 condition and L3 condition are met.

Alternatively, in some implementations, in the combination of L1 condition and L3 condition, the UE 104 is triggered to execute conditional LTM when either L1 condition or L3 condition is met.

In some implementations, after the candidate MN-CU 330 receives the first request message from the source MN-CU 310, the candidate MN-CU 330 may transmit a second request message to a DU of a candidate MN for each candidate cell. For example, the candidate MN-CU 330 may transmit 725 the second request message to the candidate MN-DU 332 providing the candidate cell#1.

In some implementations, the second request message may comprise a request for at least one L1 condition for conditional LTM related to the list of at least one candidate cell.

In some implementations, the second request message towards the candidate MN-DU 332 may comprise an ID of a candidate cell, e.g., an ID of the candidate cell#1.

Alternatively or additionally, in some implementations, the second request message may comprise the capability of the UE 104. The capability of the UE 104 indicates that the UE 104 supports at least one of L1 condition based LTM or L3 condition based LTM. In such implementations, the candidate MN-DU 332 may determine a type of the at least one condition for subsequent conditional LTM based on the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as or different from the type of the condition for initial conditional LTM.

Alternatively or additionally, in some implementations, the second request message may comprise a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node (e.g., from the source cell#0 to the candidate cell#1) . In such implementations, the candidate MN-DU 332 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM. Alternatively, the candidate MN-DU 332 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM and the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as the type of the condition for initial conditional LTM.

In some implementations, the request for at least one condition may indicate the candidate MN-DU 332 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 332 to each of the at least one candidate cell prepared by at least one other MN-DU. For example, the request for at least one condition may indicate the candidate MN-DU 332 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by a further MN-DU of the MN 102-1 or at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by a further MN-DU of other MN than the MN 102-1. In such implementations, the candidate MN-DU 332 may determine the type of the at least one condition to be generated.

Alternatively or additionally, in some implementations, the request for at least one condition may indicate the candidate MN-DU 332 to generate at least one L1 condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 332 to each of the at least one candidate cell prepared by at least one other MN-DU. In such implementations, the MN-CU 310 may determine the type of the at least one condition to be generated.

In some implementations, the second request message may comprise a UE CONTEXT SETUP REQUEST message.

In some implementations, the UE CONTEXT SETUP REQUEST message may comprise an LTM Multiple Target DU List IE comprising the list of at least one candidate cell. Upon receiving the UE CONTEXT SETUP REQUEST message, the candidate MN-DU 332 shall, if supported, consider that the information in the IE pertains to a list of candidate cells suggested for other candidate MN-DUs and the information may also be prepared for subsequent LTM. For example, other candidate MN-DUs may comprise a further MN-DU of other MN than the MN 102-1 and the MN 102-3.

Alternatively or additionally, in some implementations, the second request message may comprise a CSI resource configuration for subsequent LTM.

In some implementations, the MN-CU 310 may provide the LTM configuration ID mapping list to the candidate MN-DU 332.

Alternatively or additionally, in some implementations, the second request message may comprise a request for PRACH resources from the candidate MN-DU 332.

In some implementations, the MN-CU 330 may request, via the second request message, the candidate MN-DU 332 to provide the lower layer configuration for the purpose of generating the reference configuration.

In some implementations, the MN-CU 330 may provide, via the second request message, the lower layer part of the reference configuration to the candidate MN-DU 332.

With continued reference to Fig. 7, if the candidate MN-DU 332 accepts the request for at least one condition for subsequent conditional LTM, the candidate MN-DU 332 transmits 730 a second response message to the MN-CU 330. The second response message comprises the at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 332 to each of the at least one candidate cell prepared by at least one other MN-DU.

In some implementations, both L1 condition based LTM and L3 condition based LTM are supported by the UE 104. In such implementations, it may be predefined that a first priority of the L1 condition based LTM is higher than a second priority of the L3 condition based LTM. Thus, the candidate MN-DU 332 may generate at least one L1 condition for the subsequent conditional LTM.

In some implementations, the second response message may further comprise L1 condition for initial conditional LTM. For example, the second response message may further comprise L1 condition for initial cell switch from the source cell#0 to the candidate cell#1.

In some implementations, the second response message may further comprise the generated lower layer RRC configurations for the accepted target candidate cell.

In some implementations, the second response message may comprise a UE CONTEXT SETUP RESPONSE message. The UE CONTEXT SETUP RESPONSE message may comprise the at least one condition for subsequent conditional LTM related to the list of at least one candidate cell.

After the candidate MN-CU 330 receives the second response message from the candidate MN-DU 332, the candidate MN-CU 330 may transmit 735 a first response message to the source MN-CU 310.

In some implementations, the first response message may comprise at least LTM candidate configuration for the candidate cell#1.

In some implementations, the first response message may comprise a condition for initial conditional LTM. For example, the first response message may further comprise a condition for initial cell switch from the source cell#0 to the candidate cell#1.

In some implementations, the first response message may comprise the at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate MN-DU 332 to each of the at least one candidate cell prepared by at least one other MN.

In some implementations, the first response message may comprise a condition for conditional LTM from a candidate cell belonging to the MN-CU 330 to a candidate cell belonging to other MN.

In some implementations, the first response message may comprise a handover request acknowledge.

In turn, the MN-CU 310 may transmit 740 to the source MN-DU 312 a message, e.g., UE CONTEXT MODIFICATION REQUEST message. The message may comprise an indication to indicate the candidate cell is condition based LTM.

The MN-CU 310 may transmit 745 an RRC reconfiguration message related to candidate cell#1 to the UE 104 via the source MN-DU 312.

In some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#1) ;
● LTM candidate configuration for the candidate cell#1;
● Condition#1 of cell switching from the source cell#0 to the candidate
cell#1, wherein the condition could be L1 condition or L3 condition;
● Condition#2 of cell switching from candidate cell#2 to candidate cell#1,
wherein the condition could be L1 condition or L3 condition; or
● Condition#3 of cell switching from candidate cell#3 to candidate cell#1,
the condition could be L1 condition or L3 condition.

Alternatively or additionally, in some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#2) ,
● LTM candidate configuration for the candidate cell#2;
● Condition#4 of cell switching from the source cell#0 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition;
● Condition#5 of cell switching from the candidate cell#1 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition (wherein Condition#5 is generated by the candidate MN-CU 330 or the candidate MN-DU 332) ; or
● Condition#6 of cell switching from the candidate cell#3 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition.

In some implementations, the LTM configuration may comprise the LTM candidate configuration and the at least one condition for LTM as described above.

The UE 104 starts 750 to evaluate the at least one condition according to the configuration.

Fig. 8 illustrates a signaling diagram illustrating an example process 800 that supports subsequent conditional LTM in accordance with aspects of the present disclosure. The process 800 may be considered as an example implementation of the process 400. For the purpose of discussion, the process 800 will be described with reference to Fig. 3D. The process 800 may involve the source SN-DU 322, the source SN-CU 320, the source MN-CU 310, the candidate SN-CU 340, the candidate SN-DU 342 and the UE 104 in Fig. 3D.

Generally, in the process 800, the UE 104 may perform inter-CU SCG conditional LTM. In other words, the UE 104 may perform, based on an execution condition, a cell switch from a PSCell (i.e., a source cell) provided by the SN-DU 322 of the source SN 102-2 to a PSCell (i.e., a candidate cell) prepared by the candidate SN-DU 342 of the candidate SN 102-4. The source cell is also referred to as a current serving cell. The cell switch is initiated by the source SN 102-2.

As shown in Fig. 8, after the SN-CU 320 receives a measurement report from the UE 104, the SN-CU 320 determines 810 to prepare a candidate cell, e.g., a candidate cell#1 prepared by the candidate SN-DU 342.

The source SN-CU 320 transmits 815 a message to the source MN-CU 310.

In some implementations, the message may comprise an SN Change Required message.

In some implementations, the message may comprise an indication indicating conditional LTM is initiated.

For example, the source SN 102-2 initiates a subsequent LTM procedure for candidate PSCell (s) in other (candidate SN (s) ) by sending the SN Change Required message, which contains the indication indicating conditional LTM is initiated. The message also contains candidate node ID (s) and may include an SCG reference configuration (to support delta configuration) , and contains the measurements results which may include cells that are not LTM candidates. The message also includes a list of proposed PSCell candidates recommended by the source SN 102-2, including execution conditions for the initial evaluation, the upper limit for the number of PSCells that can be prepared by each candidate SN, and may also include the SCG measurement configurations for subsequent LTM (e.g. measurement ID (s) to be used for subsequent LTM) . The source SN 102-2 may also propose data forwarding to the MN 102-1 or other candidate SN (s) for subsequent LTM.

Alternatively or additionally, in some implementations, the message may comprise an ID of the candidate cell#1 belonging to the candidate SN 102-4.

Alternatively or additionally, in some implementations, the message may comprise at least one condition for initial conditional LTM related to cell switch from a current serving cell to a candidate cell prepared by another candidate SN.

Alternatively or additionally, in some implementations, the message may comprise a type of the at least one condition for initial conditional LTM related to cell switch from a current serving cell to a candidate cell prepared by another candidate SN.

Alternatively or additionally, in some implementations, the message may comprise a type of the at least one condition for subsequent conditional LTM.

Alternatively or additionally, in some implementations, the message may comprise suggestion that the request for the at least one condition for conditional LTM is to be transmitted to the candidate SN-CU 340. In other words, the source SN-CU 320 may suggest the source MN-CU 310 to request the candidate SN 102-4 to generate L1 condition or L3 condition for each candidate cell for subsequent LTM.

For example, the candidate cell is a candidate cell#1 proposed by the source SN 102-2. The execution condition for cell switch from a candidate cell#2 to the candidate cell#1 should be either L1 condition or L3 condition. This execution should be generated by the candidate SN 102-4 serving the candidate cell#2. Therefore, the source MN 102-1 should request the candidate SN 102-4 to generate a condition for cell switch from the candidate cell#2 to the candidate cell#1.

In turn, the source MN-CU 310 transmits 820 the first request message to the candidate SN 102-4 via Xn interface. For example, the first request message may comprise an SN Addition request.

In some implementations, the MN 102-1 (e.g., the source MN-CU 310) may request each candidate SN to allocate resources for the UE 104 by means of the SN Addition procedure (s) , indicating the request is for conditional LTM, and the measurements results which may include cells that are not LTM candidates received from the source SN 102-2 to the candidate SN, and indicating a list of proposed PSCell candidates to the candidate SN (s) received from the source SN 102-2, but not including execution conditions. The MN 102-1 also includes information of other candidate SN (s) , and for each candidate SN, a list of proposed PSCell candidates recommended by the source SN 102-2 for the candidate SN to select the PSCell (s) for the following execution of subsequent LTM. The source MN 102-1 also provides the upper limit for the number of PSCells that can be prepared by each candidate SN. Within the list of PSCells suggested by the source SN 102-2, the candidate SN decides the list of PSCell (s) to prepare (considering the maximum number indicated by the MN 102-1) and, for each prepared PSCell, the candidate SN decides other SCG SCells and provides the new corresponding SCG radio resource configuration to the MN 102-1 in an NR RRCReconfiguration message contained in the SN Addition Request Acknowledge message with the prepared PSCell ID (s) . For each prepared PSCell, the candidate SN also decides the list of PSCell (s) and associated execution conditions proposed for the following execution of subsequent LTM. If data forwarding is needed, the candidate SN provides data forwarding addresses to the MN 102-1. The candidate SN may also propose data forwarding to the MN 102-1 or other candidate SN (s) for subsequent condition LTM. The candidate SN may include an indication that the SCG radio resource configuration of a prepared PSCell is a complete candidate configuration, i.e. that it is not a delta configuration with respect to the SCG reference configuration. For the prepared PSCell (s) and the proposed PSCell (s) for the following execution of subsequent LTM, the candidate SN can either accept or reject each of the candidate cells suggested by the source SN 102-2, i.e., it cannot configure any alternative candidates.

For example, the source MN-CU 310 transmits the first request message (e.g., the SN Addition request message) to a candidate SN-CU (e.g., the candidate SN-CU 340) for each candidate cell via Xn interface. For example, the candidate cell may be a candidate cell#1 of the candidate DU 342 of the candidate SN-CU 340. It is assumed that a source cell is a source cell#0 of the source SN 102-2. The source MN-CU 310 may also transmit the first request message to a further candidate SN-CU for a candidate cell#2.

In some implementations, the first request message towards the candidate SN-CU 340 may comprise an ID of a candidate cell, e.g., an ID of the candidate cell#1.

Alternatively or additionally, in some implementations, the first request message may comprise the capability of the UE 104. The capability of the UE 104 indicates that the UE 104 supports at least one of L1 condition based LTM or L3 condition based LTM.

Alternatively or additionally, in some implementations, the first request message may comprise a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node (e.g., from the source cell#0 to the candidate cell#1) . In such implementations, the candidate SN-CU 340 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM. Alternatively, the candidate SN-CU 340 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM and the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as the type of the condition for initial conditional LTM.

In some implementations, the request for at least one condition may indicate the candidate SN-CU 340 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 342 of the candidate SN-CU 340 to each of the at least one candidate cell prepared by at least one other SN. For example, the request for at least one condition may indicate the candidate SN-CU 340 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by other candidate SN than the candidate SN 102-4. In such implementations, the candidate SN-CU 340 may determine the type of the at least one condition to be generated.

Alternatively or additionally, in some implementations, the request for at least one condition may indicate the candidate SN-CU 340 to generate at least one L1 condition or L3 condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 342 of the candidate SN-CU 340 to each of the at least one candidate cell prepared by at least one other candidate SN. In such implementations, the candidate SN-CU 340 may determine the type of the at least one condition to be generated.

In some implementations, the first request message may comprise an SN Addition request message.

In some implementations, the SN Addition request message may comprise an LTM Multiple Target NG-RAN Node List IE comprising the list of at least one candidate cell. Upon receiving the SN Addition request message, the candidate SN-CU 340 shall, if supported, consider that the information in the IE pertains to a list of candidate cells suggested for other candidate SN and the information may also be prepared for subsequent LTM. For example, other candidate SN may comprise an SN different from the candidate SN 102-4.

In some implementations, if a candidate cell in the list of at least one candidate cell is cancelled, the MN-CU 310 may indicate it (cancellation of the candidate cell) to the candidate SN-CU 340 via LTM CONFIGURATION UPDATE message. For example, the LTM CONFIGURATION UPDATE message may comprise the LTM Multiple Target NG-RAN Node List IE comprising an updated list of the at least one candidate cell. For example, the updated list of the at least one candidate cell may be transmitted to the candidate SN-CU 340 for updating purpose.

In some implementations, after the candidate SN-CU 340 receives the first request message from the source MN-CU 310, the candidate SN-CU 340 may determine 825 a type of the at least one condition for subsequent conditional LTM related to the list of at least one candidate cell based on the information in the first request message. Alternatively, the candidate SN-CU 340 may determine 825 the type of the at least one condition for subsequent conditional LTM without considering the information in the first request message.

In some implementations, if the candidate SN-CU 340 determines that a type of the at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell#2 prepared by other MN is L3 condition, the candidate SN-CU 340 may generate the at least one condition. If the candidate SN-CU 340 determines that the type of the at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell#2 prepared by other MN is L1 condition, the candidate SN-CU 340 may request the candidate SN-DU 342 to generate the at least one condition.

In some implementations, after the candidate SN-CU 340 receives the first request message from the source MN-CU 310, the candidate SN-CU 340 may transmit a second request message to a DU of a candidate SN for each candidate cell. For example, the candidate SN-CU 340 may transmit 830 the second request message to the candidate SN-DU 342 providing the candidate cell#1.

In some implementations, the second request message towards the candidate SN-DU 342 may comprise an ID of a candidate cell, e.g., an ID of the candidate cell#1.

Alternatively or additionally, in some implementations, the second request message may comprise the capability of the UE 104. The capability of the UE 104 indicates that the UE 104 supports at least one of L1 condition based LTM or L3 condition based LTM. In such implementations, the candidate SN-DU 342 may determine a type of the at least one condition for subsequent conditional LTM based on the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as or different from the type of the condition for initial conditional LTM.

Alternatively or additionally, in some implementations, the second request message may comprise a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node (e.g., from the source cell#0 to the candidate cell#1) . In such implementations, the candidate SN-DU 342 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM. Alternatively, the candidate SN-DU 342 may determine a type of the at least one condition for subsequent conditional LTM based on the type of the condition for initial conditional LTM and the capability of the UE 104. In such implementations, the type of the at least one condition for subsequent conditional LTM may be the same as the type of the condition for initial conditional LTM.

In some implementations, the request for at least one condition may indicate the candidate SN-DU 342 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 342 to each of the at least one candidate cell prepared by at least one other SN-DU. For example, the request for at least one condition may indicate the candidate SN-DU 342 to generate at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by a further SN-DU of the SN 102-4 or at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell prepared by a further SN-DU of other SN than the SN 102-4. In such implementations, the candidate SN-DU 342 may determine the type of the at least one condition to be generated.

Alternatively or additionally, in some implementations, the request for at least one condition may indicate the candidate SN-DU 342 to generate at least one L1 condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 342 to each of the at least one candidate cell prepared by at least one other SN-DU. In such implementations, the SN-CU 340 may determine the type of the at least one condition to be generated.

In some implementations, the UE CONTEXT SETUP REQUEST message may comprise an LTM Multiple Target DU List IE comprising the list of at least one candidate cell. Upon receiving the UE CONTEXT SETUP REQUEST message, the candidate SN-DU 342 shall, if supported, consider that the information in the IE pertains to a list of candidate cells suggested for other candidate SN-DUs and the information may also be prepared for subsequent LTM. For example, other candidate SN-DUs may comprise a further SN-DU of other SN than the SN 102-2 and the SN 102-4.

In some implementations, the SN-CU 340 may provide the LTM configuration ID mapping list to the candidate SN-DU 342.

Alternatively or additionally, in some implementations, the second request message may comprise a request for PRACH resources from the candidate SN-DU 342.

In some implementations, the SN-CU 340 may request, via the second request message, the candidate SN-DU 342 to provide the lower layer configuration for the purpose of generating the reference configuration.

In some implementations, the SN-CU 340 may provide, via the second request message, the lower layer part of the reference configuration to the candidate SN-DU 342.

With continued reference to Fig. 8, if the candidate SN-DU 342 accepts the request for at least one condition for subsequent conditional LTM, the candidate SN-DU 342 transmits 835 a second response message to the SN-CU 340. The second response message comprises the at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 342 to each of the at least one candidate cell prepared by at least one other SN-DU.

In some implementations, both L1 condition based LTM and L3 condition based LTM are supported by the UE 104. In such implementations, it may be predefined that a first priority of the L1 condition based LTM is higher than a second priority of the L3 condition based LTM. Thus, the candidate SN-DU 342 may generate at least one L1 condition for the subsequent conditional LTM.

After the candidate SN-CU 340 receives the second response message from the candidate SN-DU 342, the candidate SN-CU 340 may transmit 840 a first response message to the source MN-CU 310.

In some implementations, the first response message may comprise the at least one condition for subsequent conditional LTM from the candidate cell#1 prepared by the candidate SN-DU 342 to each of the at least one candidate cell prepared by at least one other MN.

In some implementations, if the candidate SN-CU 340 determines that a type of the at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell#2 prepared by other SN is L3 condition, the candidate SN-CU 340 may generate the at least one condition. If the candidate SN-CU 340 determines that the type of the at least one condition for subsequent conditional LTM from the candidate cell#1 to a candidate cell#2 prepared by other SN is L1 condition, the candidate SN-CU 340 may request the candidate SN-DU 342 to generate the at least one condition.

In some implementations, the first response message may comprise a condition for conditional LTM from a candidate cell belonging to the SN-CU 340 to a candidate cell belonging to other MN.

In some implementations, the first response message may comprise an SN addition request acknowledge message.

In turn, the MN-CU 310 may transmit 845 an RRC reconfiguration message related to candidate cell#1 to the UE 104 via the source MN-DU 312.

Alternatively or additionally, in some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#2) ,
● LTM candidate configuration for the candidate cell#2;
● Condition#4 of cell switching from the source cell#0 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition;
● Condition#5 of cell switching from the candidate cell#1 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition (wherein Condition#5 is generated by the candidate SN-CU 340 or the candidate SN-DU 342) ; or
● Condition#6 of cell switching from the candidate cell#3 to the candidate
cell#2, wherein the condition could be L1 condition or L3 condition.

In some implementations, the LTM configuration may comprise the LTM candidate configuration and the at least one condition for LTM as described above. In some implementations, the LTM candidate configuration may comprise at least one of the following: measurement configuration, CSI resource, RACH configuration, MAC configuration, Physical layer configuration, RLC configuration or PDCP configuration.

With continued reference to Fig. 8, the source MN-CU 310 may transmit a confirm message, e.g. SN Change Confirm message to the source SN-CU 320.

If an SN RRC response message is included, the source MN-CU 310 informs the source SN-CU 320 with the SN RRC reconfiguration complete message via SN Change Confirm message. The source MN-CU 310 may indicate the candidate PSCells accepted by each candidate SN to the source SN-CU 320 in the SN Change Confirm message.

The source MN-CU 310 transmits the SN Change Confirm message towards the source SN-CU 320 to indicate that condition LTM candidate is prepared, and in such case the source SN-CU 320 continues providing user data to the UE 104. If early data forwarding is applied, the MN-CU 310 informs the source SN-CU 320 the data forwarding address (es) , the source SN-CU 320, if applicable, together with the Early Status Transfer procedure, starts early data forwarding. The PDCP SDU forwarding may take place during early data forwarding. In case multiple candidate SNs are prepared, the MN-CU 310 includes a list of Target SN ID and list of data forwarding addresses to the source SN-CU 320.

The source SN-CU 320 may transmit a request message, e.g., UE CONTEXT MODIFICATION REQUEST message to the source SN-DU 322. The request message may include an indication to indicate the candidate cell is condition based LTM.

The UE 104 starts 855 to evaluate the at least one condition according to the configuration.

Fig. 9 illustrates a signaling diagram illustrating an example process 900 that supports PDCP re-establishment in accordance with aspects of the present disclosure. The process 900 may be considered as an example implementation of the process 400. For the purpose of discussion, the process 900 will be described with reference to Fig. 3A. The process 900 may involve the MN-CU 310, the source MN-DU 312, the candidate MN-DU 314 and the UE 104 in Fig. 3A.

Generally, in the process 900, the UE 104 may perform intra-CU MCG LTM. In other words, the UE 104 may perform a cell switch from a PCell (i.e., a source cell) provided by the MN-DU 312 to a PCell (i.e., a candidate cell) prepared by the candidate MN-DU 314. The source cell is also referred to as a current serving cell.

In addition, in the process 900, the UE 104 may transmit capability of the UE 104 to the first network node 210 (such as the MN 102-1) . For example, the UE 104 may transmit the capability of the UE 104 to the MN 102-1 if the UE 104 receives the enquiry from the MN 102-1.

In some implementations, the capability of the UE 104 may comprise information indicating the UE 104 supports to identify whether PDCP re-establishment or security key update should be performed. For example, network will configure a new ID for each cell including the serving cell and each candidate cell. If the new ID is different for the source serving cell and the candidate cell, the UE 104 performs PDCP re-establishment and/or security key update. For MCG LTM cell switch case, if the new IDs of the serving cell and the target cell have same values, the UE 104 further compares the LTMNo Reset ID for serving cell and LTM No Reset ID for candidate cell. If the LTM No Reset ID for serving cell is equal to the LTM No Reset ID for candidate cell, the UE 104 does not perform L2 reset, e.g., RLC re-establishment and PDCP data recovery. Otherwise, the UE 104 performs L2 reset, e.g., RLC re-establishment and PDCP data recovery.

The UE 104 may receive the configuration related to L1 measurement report or L3 measurement report from the MN 102-1. If SCG is configured, the UE 104 may receive the configuration related to L1 measurement report or L3 measurement report from the SN 102-2 as well. The configuration from the SN 102-2 is configured for SCG LTM purpose.

As shown in Fig. 9, after the MN-CU 310 receives a measurement report from the UE 104, the MN-CU 310 determines 910 to prepare a candidate cell, e.g., a candidate cell#1 prepared by the candidate MN-DU 314.

The MN-CU 310 transmits 915 the first request message to a candidate MN-DU for each candidate cell. For example, the MN-CU 310 may transmit the first request message to the candidate MN-DU 314 providing the candidate cell#1. The MN-CU 310 may also transmit the first request message to a further MN-DU (not shown) of the MN-CU 310 and the further MN-DU provides a candidate cell#2. It is assumed that a source cell is a source cell#0 provided by the source MN-DU 312.

In some implementations, the first request message may comprise IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update.

Alternatively or additionally, in some implementations, the first request message may comprise the capability of the UE 104. The capability of the UE 104 may comprise information indicating the UE 104 supports to identify whether PDCP re-establishment or security key update should be performed.

Alternatively or additionally, in some implementations, the first request message may comprise LTM No Reset ID for serving cell and LTM No Reset ID for candidate cell.

With continued reference to Fig. 9, if the candidate MN-DU 314 accepts the first request message, the candidate MN-DU 314 transmits 920 the first response message to the MN-CU 310. The first response message may comprise a UE CONTEXT SETUP RESPONSE message including at least the generated lower layer RRC configurations for the accepted target candidate cell.

In turn, the MN-CU 310 may transmit 925 to the source MN-DU 312 a message, e.g., UE CONTEXT MODIFICATION REQUEST message. The message may comprise the IDs for the serving cell and at least one candidate cell related to PDCP re-establishment or security key update.

The MN-CU 310 may transmit 930 an RRC reconfiguration message related to candidate cell#1 to the UE 104 via the source MN-DU 312.

In some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#1) ;
● LTM candidate configuration for the candidate cell#1;
● LTM no reset ID for serving cell e. g ltm-ServingCellNoResetID and
LTM no reset ID for candidate cell e.g. ltm-NoResetID; or
● the IDs for the serving cell and at least one candidate cell related to PDCP
re-establishment or security key update.

When the UE 104 receives LTM cell switching command towards a candidate cell or the condition for LTM candidate cell is met, the UE 104 performs 935 LTM cell switch.

In some implementations, when the UE 104 receives LTM cell switching command towards a candidate cell, the UE 104 will compare the new IDs for the source serving cell and the target cell. If the new ID is different for the source serving cell and the candidate cell, the UE 104 performs PDCP re-establishment and/or security key update. For MCG LTM cell switch case, if the new IDs of the serving cell and the target cell have same values, the UE 104 compares the LTM no reset ID for serving cell e.g. ltm-ServingCellNoResetID and LTM no reset ID for candidate cell e.g. ltm-NoResetID. If the LTM no reset ID for serving cell is equal to the LTM no reset ID for candidate cell, the UE 104 does not perform L2 reset e.g. RLC re-establishment and PDCP data recovery. Otherwise, the UE 104 performs L2 reset i.e. RLC re-establishment and PDCP data recovery.

Fig. 10 illustrates a signaling diagram illustrating an example process 1000 that supports PDCP re-establishment in accordance with aspects of the present disclosure. The process 1000 may be considered as an example implementation of the process 400. For the purpose of discussion, the process 1000 will be described with reference to Fig. 3B. The process 1000 may involve the SN-CU 320, the source SN-DU 322, the candidate SN-DU 324 and the UE 104 in Fig. 3B.

Generally, in the process 1000, the UE 104 may perform intra-CU SCG LTM. In other words, the UE 104 may perform a cell switch from a PSCell (i.e., a source cell) provided by the SN-DU 322 to a PSCell (i.e., a candidate cell) prepared by the candidate SN-DU 324. The source cell is also referred to as a current serving cell.

In addition, in the process 1000, the UE 104 may transmit capability of the UE 104 to the first network node 210 (such as the MN 102-1) . For example, the UE 104 may transmit the capability of the UE 104 to the MN 102-1 if the UE 104 receives the enquiry from the MN 102-1.

In some implementations, the capability of the UE 104 may comprise information indicating the UE 104 supports to identify whether PDCP re-establishment or security key update should be performed. For example, network will configure a new ID for each cell including the serving cell and each candidate cell. If the new ID is different for the source serving cell and the candidate cell, the UE 104 performs PDCP re-establishment and/or security key update. For MCG LTM cell switch case, if the new IDs of the serving cell and the target cell have same values, the UE 104 compares the LTM no reset ID for serving cell and LTM no reset ID for candidate cell. If the LTM no reset ID for serving cell is equal to the LTM no reset ID for candidate cell, the UE 104 does not perform L2 reset, e.g., RLC re-establishment and PDCP data recovery. Otherwise, the UE 104 performs L2 reset, e.g., RLC re-establishment and PDCP data recovery.

As shown in Fig. 10, after the SN-CU 320 receives a measurement report from the UE 104, the SN-CU 320 determines 1010 to prepare a candidate cell, e.g., a candidate cell#1 prepared by the candidate SN-DU 324.

In some implementations, regarding the co-existence of Intra-CU SCG LTM and Inter-CU SCG LTM, the new ID can also be configured to Intra-CU SCG LTM candidate cell.

In some implementations, after the SN-CU 320 itself configures an Intra-CU candidate cell, the SN-CU 320 may transmit, to the source MN-CU 310, a request for at least one ID for the at least one candidate cell related to PDCP re-establishment or security key update.

Alternatively, the SN-CU 320 may reuse a new ID for the source cell as an ID for Intra-CU candidate cell. In other words, the SN-CU 320 may determine a new ID for the serving cell as at least one new ID for the at least one candidate cell.

The SN-CU 320 transmits 1015 the first request message to a candidate SN-DU for each candidate cell. For example, the SN-CU 320 may transmit the first request message to the candidate SN-DU 324 providing the candidate cell#1. The SN-CU 320 may also transmit the first request message to a further SN-DU (not shown) of the SN-CU 320 and the further SN-DU provides a candidate cell#2. It is assumed that a source cell is a source cell#0 provided by the source SN-DU 322.

With continued reference to Fig. 10, if the candidate SN-DU 324 accepts the first request message, the candidate SN-DU 324 transmits 1020 the first response message to the SN-CU 320. The first response message may comprise a UE CONTEXT SETUP RESPONSE message including at least the generated lower layer RRC configurations for the accepted target candidate cell.

In turn, the SN-CU 320 may transmit 1025 to the source SN-DU 322 a message, e.g., UE CONTEXT MODIFICATION REQUEST message. The message may comprise the IDs for the serving cell and at least one candidate cell related to PDCP re-establishment or security key update.

The SN-CU 320 may transmit 1030 an RRC reconfiguration message related to candidate cell#1 to the UE 104 via the source SN-DU 322.

In some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#1) ;
● LTM candidate configuration for the candidate cell#1;
● LTM no reset ID for serving cell and LTM no reset ID for candidate cell;
or
● the IDs for the serving cell and at least one candidate cell related to PDCP
re-establishment or security key update.

When the UE 104 receives LTM cell switching command towards a candidate cell or the condition for LTM candidate cell is met, the UE 104 performs 1035 LTM cell switch.

In some implementations, when the UE 104 receives LTM cell switching command towards a candidate cell, the UE 104 will compare the new IDs for the source serving cell and the target cell. If the new ID is different for the source serving cell and the candidate cell, the UE 104 performs PDCP re-establishment and/or security key update. For MCG LTM cell switch case, if the new IDs of the serving cell and the target cell have same values, the UE 104 compares the LTM no reset ID for serving cell and ltm-NoResetID for candidate cell. If the LTM no reset ID for serving cell is equal to the ltm-NoResetID for candidate cell, the UE 104 does not perform L2 reset e.g. RLC re-establishment and PDCP data recovery. Otherwise, the UE 104 performs L2 reset i.e. RLC re-establishment and PDCP data recovery.

Fig. 11 illustrates a signaling diagram illustrating an example process 1100 that supports PDCP re-establishment in accordance with aspects of the present disclosure. The process 1100 may be considered as an example implementation of the process 400. For the purpose of discussion, the process 1100 will be described with reference to Fig. 3C. The process 1100 may involve the MN-CU 310, the source MN-DU 312, the candidate MN-DU 314 and the UE 104 in Fig. 3C.

Generally, in the process 1100, the UE 104 may perform inter-CU MCG conditional LTM. In other words, the UE 104 may perform a cell switch from a PCell (i.e., a source cell) provided by the MN-DU 312 of the source MN 102-1 to a PCell (i.e., a candidate cell) prepared by the candidate MN-DU 332 of the candidate MN 102-3. The source cell is also referred to as a current serving cell.

In addition, in the process 1100, the UE 104 may transmit capability of the UE 104 to the first network node 210 (such as the MN 102-1) . For example, the UE 104 may transmit the capability of the UE 104 to the MN 102-1 if the UE 104 receives the enquiry from the MN 102-1.

As shown in Fig. 11, after the MN-CU 310 receives a measurement report from the UE 104, the MN-CU 310 determines 1110 to prepare a candidate cell, e.g., a candidate cell#1 prepared by the candidate MN-DU 332.

The source MN-CU 310 transmits 1115 the first request message to the candidate MN-CU 330 for each candidate cell via Xn interface. For example, the candidate cell may comprise the candidate cell#1 prepared by the candidate MN-DU 332. It is assumed that a source cell is a source cell#0 provided by the source MN-DU 312.

In some implementations, the first request message may comprise the new IDs for the serving cell and at least one candidate cell.

For example, the first request message may comprise a new ID for the serving cell, a new ID for the candidate cell#1 and new IDs for other candidate cells. The other candidate cell may comprise candidate cells prepared by other candidate CU.

In some implementations, the new IDs may be updated before cell switch. For example, LTM configuration update message may be used to carry the new IDs for the candidate cells.

Alternatively, in some implementations, after cell switch towards the candidate cell#1 of the candidate MN-CU 330, the source MN 102-1 may transfer the new IDs for all candidate cells to the candidate MN-CU 330 related to the new serving cell.

In some implementations, after the candidate MN-CU 330 receives the first request message from the source MN-CU 310, the candidate MN-CU 330 may store 1120 the new IDs for the serving cell and at least one candidate cell.

In some implementations, the new IDs are used when the UE 104 is served by the candidate cell#1 (after the UE 104 switches from cell#0 to cell#1) . When the new ID for candidate cell is different from the new ID for the serving cell, the UE 104 performs PDCP re-establishment to all radio bearers. For example, when the new ID for a candidate cell#2 is different from the new ID for the serving cell (cell#1) , the UE 104 performs PDCP re-establishment to the related radio bearers.

In some implementations, Admission Control may be performed by the target gNB (e.g., the MN 102-3) . The target gNB prepares the handover with L1/L2 and sends the HANDOVER REQUEST ACKNOWLEDGE to the source Gnb (e.g., the MN 102-1) , which includes a transparent container to be sent to the UE 104 as an RRC message to perform the handover.

In some implementations, after the candidate MN-CU 330 receives the first request message from the source MN-CU 310, the candidate MN-CU 330 may transmit a second request message to a DU of a candidate MN for each candidate cell. For example, the candidate MN-CU 330 may transmit 1125 the second request message to the candidate MN-DU 332 providing the candidate cell#1.

In some implementations, the second request message may comprise the new IDs for the serving cell and at least one candidate cell.

Alternatively or additionally, in some implementations, the second request message may comprise the capability of the UE 104. The capability of the UE 104 may comprise information indicating the UE 104 supports to identify whether PDCP re-establishment or security key update should be performed.

Alternatively or additionally, in some implementations, the second request message may comprise an LTM No Reset ID for serving cell and LTM No Reset ID for candidate cell.

With continued reference to Fig. 11, if the candidate MN-DU 332 accepts the second request message, the candidate MN-DU 332 transmits 1130 a second response message to the MN-CU 330.

In some implementations, the second response message may comprise the generated lower layer RRC configurations for the accepted target candidate cell.

In some implementations, the second response message may comprise a UE CONTEXT SETUP RESPONSE message.

After the candidate MN-CU 330 receives the second response message from the candidate MN-DU 332, the candidate MN-CU 330 may transmit 1135 a first response message to the source MN-CU 310.

In turn, the MN-CU 310 may transmit 1140 to the source MN-DU 312 a message, e.g., UE CONTEXT MODIFICATION REQUEST message. The message may comprise the new IDs for the serving cell and at least one candidate cell.

In some implementations, the message may further comprise LTM No Reset ID for serving cell and LTM No Reset ID for candidate cell.

The MN-CU 310 may transmit 1145 an RRC reconfiguration message related to candidate cell#1 to the UE 104 via the source MN-DU 312.

In some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#1) ;
● LTM candidate configuration for the candidate cell#1;
● LTM No Reset ID for serving cell and LTM No Reset ID for candidate
cell; or
● the new IDs for the serving cell and at least one candidate cell.

When the UE 104 receives LTM cell switching command towards a candidate cell or the condition for LTM candidate cell is met, the UE 104 performs 1150 LTM cell switch.

Fig. 12 illustrates a signaling diagram illustrating an example process 1200 that supports PDCP re-establishment in accordance with aspects of the present disclosure. The process 1200 may be considered as an example implementation of the process 400. For the purpose of discussion, the process 1200 will be described with reference to Fig. 3D. The process 1200 may involve the source SN-DU 322, the source SN-CU 320, the source MN-CU 310, the candidate SN-CU 340, the candidate SN-DU 342 and the UE 104 in Fig. 3D.

Generally, in the process 1200, the UE 104 may perform inter-CU SCG LTM. In other words, the UE 104 may perform a cell switch from a PSCell (i.e., a source cell) provided by the SN-DU 322 of the source SN 102-2 to a PSCell (i.e., a candidate cell) prepared by the candidate SN-DU 342 of the candidate SN 102-4. The source cell is also referred to as a current serving cell. The cell switch is initiated by the source SN 102-2.

In addition, in the process 1200, the UE 104 may transmit capability of the UE 104 to the first network node 210 (such as the MN 102-1) . For example, the UE 104 may transmit the capability of the UE 104 to the MN 102-1 if the UE 104 receives the enquiry from the MN 102-1. The MN 102-1 may transfer the capability of the UE 104 to the SN 102-2.

As shown in Fig. 12, after the SN-CU 320 receives a measurement report from the UE 104, the SN-CU 320 determines 1210 to prepare a candidate cell, e.g., a candidate cell#1 prepared by the candidate SN-DU 342.

The source SN-CU 320 transmits 1215 a message to the source MN-CU 310.

In some implementations, the message may comprise the new IDs for the serving cell and at least one candidate cell.

For example, the source SN 102-2 initiates a subsequent LTM procedure for candidate PSCell (s) in other (candidate SN (s) ) by sending the SN Change Required message, which contains the new IDs for the serving cell and at least one candidate cell (in other words, the source SN 102-2 assigns a new ID for each of the at least one candidate cell) . The message also contains candidate node ID (s) and may include an SCG reference configuration (to support delta configuration) , and contains the measurements results which may include cells that are not LTM candidates. The message also includes a list of proposed PSCell candidates recommended by the source SN 102-2, including execution conditions for the initial evaluation, the upper limit for the number of PSCells that can be prepared by each candidate SN, and may also include the SCG measurement configurations for subsequent LTM (e.g. measurement ID (s) to be used for subsequent LTM) . The source SN 102-2 may also propose data forwarding to the MN 102-1 or other candidate SN (s) for subsequent LTM.

In turn, the source MN-CU 310 transmits 1220 the first request message to the candidate SN 102-4 via Xn interface. For example, the first request message may comprise an SN Addition request.

In some implementations, the MN 102-1 (e.g., the source MN-CU 310) may request each candidate SN to allocate resources for the UE 104 by means of the SN Addition procedure (s) , indicating the new ID for each candidate cell (the new ID could be assigned by the MN 102-1 itself. Alternatively, the new ID is from the action 1215 which is assigned by the source SN 102-2) , and the request may further include the measurements results which may include cells that are not LTM candidates received from the source SN 102-2 to the candidate SN, and indicating a list of proposed PSCell candidates to the candidate SN (s) received from the source SN 102-2. The MN 102-1 also includes information of other candidate SN (s) , and for each candidate SN, a list of proposed PSCell candidates recommended by the source SN 102-2 for the candidate SN to select the PSCell (s) for the following execution of subsequent LTM. The MN 102-1 also provides the upper limit for the number of PSCells that can be prepared by each candidate SN. Within the list of PSCells suggested by the source SN 102-2, the candidate SN decides the list of PSCell (s) to prepare (considering the maximum number indicated by the MN 102-1) and, for each prepared PSCell, the candidate SN decides other SCG SCells and provides the new corresponding SCG radio resource configuration to the MN 102-1 in an NR RRCReconfiguration message contained in the SN Addition Request Acknowledge message with the prepared PSCell ID (s) . If data forwarding is needed, the candidate SN provides data forwarding addresses to the MN. The candidate SN may also propose data forwarding to the MN or other candidate SN (s) for subsequent LTM. The candidate SN may include an indication that the SCG radio resource configuration of a prepared PSCell is a complete candidate configuration, i.e. that it is not a delta configuration with respect to the SCG reference configuration. For the prepared PSCell (s) and the proposed PSCell (s) for the following execution of subsequent LTM, the candidate SN can either accept or reject each of the candidate cells suggested by the source SN 102-2, i.e. it cannot configure any alternative candidates.

In some implementations, the new IDs may be updated before cell switching. For example, LTM configuration update message may be used to carry the new IDs for the candidate cells.

Alternatively, in some implementations, after cell switching towards the candidate cell#1 of the candidate SN-CU 340, the source MN 102-1 may transfer the new IDs for all candidate cells to the candidate SN-CU 340 related to the new serving cell.

In some implementations, after the candidate SN-CU 340 receives the first request message from the source MN-CU 310, the candidate SN-CU 340 may store 1225 the new IDs for the serving cell and at least one candidate cell.

In some implementations, after the candidate SN-CU 340 receives the first request message from the source MN-CU 310, the candidate SN-CU 340 may transmit a second request message to a DU of a candidate SN for each candidate cell. For example, the candidate SN-CU 340 may transmit 1230 the second request message to the candidate SN-DU 342 providing the candidate cell#1.

Alternatively or additionally, in some implementations, the second request message may comprise LTM No Reset ID for serving cell and LTM No Reset ID for candidate cell.

With continued reference to Fig. 12, if the candidate SN-DU 342 accepts the second request message, the candidate SN-DU 342 transmits 1235 a second response message to the SN-CU 340. The second response message may comprise the generated lower layer RRC configurations for the accepted target candidate cell.

After the candidate SN-CU 340 receives the second response message from the candidate SN-DU 342, the candidate SN-CU 340 may transmit 1240 a first response message to the source MN-CU 310.

In some implementations, the first response message may comprise the new IDs for a serving cell and at least one candidate cell.

In some implementations, the first response message may comprise candidate cell ID e.g., PCI, LTM candidate cell ID (such as the candidate cell#1) .

In some implementations, the first response message may comprise at least LTM candidate configuration for each candidate cell (such as the candidate cell#1) .

In some implementations, the first response message may comprise LTM No Reset ID for serving cell and LTM No Reset ID for candidate cell.

In turn, the MN-CU 310 may transmit 1245 an RRC reconfiguration message related to candidate cell#1 to the UE 104 via the source MN-DU 312.

In some implementations, the reconfiguration message may comprise at least one of the following:
● Candidate cell ID e.g., PCI, LTM candidate cell ID (e.g., candidate
cell#1) ;
● LTM candidate configuration for the candidate cell (e.g., candidate
cell#1) ;
● LTM No Reset ID for serving cell and LTM No Reset ID for candidate
cell; or
● The new IDs for a serving cell and at least one candidate cell.

With continued reference to Fig. 12, the source MN-CU 310 may transmit a confirm message, e.g. SN Change Confirm message to the source SN-CU 320.

If an SN RRC response message is included, the source MN-CU 310 informs the source SN-CU 320 with the SN RRCReconfigurationComplete message via SN Change Confirm message. The source MN-CU 310 may indicate the candidate PSCells accepted by each candidate SN to the source SN-CU 320 in the SN Change Confirm message.

The source SN-CU 320 may transmit a message, e.g., UE CONTEXT MODIFICATION REQUEST message to the source SN-DU 322. The message may include an indication to indicate the candidate cell is condition based LTM.

When the UE 104 receives LTM cell switching command towards a candidate cell or the condition for LTM candidate cell is met, the UE 104 performs 1255 LTM cell switch.

In some implementations, when the UE 104 receives LTM cell switching command towards a candidate cell, the UE 104 will compare the new IDs for the source serving cell and the target cell. If the new ID is different for the source serving cell and the candidate cell, the UE 104 performs PDCP re-establishment and/or security key update. For MCG LTM cell switch case, if the new IDs of the serving cell and the target cell have same values, the UE 104 compares the LTM no reset ID for serving cell and LTM no reset ID for candidate cell. If the LTM no reset ID for serving cell is equal to the LTM no reset ID for candidate cell, the UE 104 does not perform L2 reset e.g. RLC re-establishment and PDCP data recovery. Otherwise, the UE 104 performs L2 reset i.e. RLC re-establishment and PDCP data recovery.

In some implementations, for NTN-NTN mobility, the interruption time and the signalling overhead are big drivers towards an efficient seamless service continuity. RACH-less HO and satellite switch with re-sync procedures were introduced to this end. However, more can be done to achieve seamless soft satellite switching and to reduce inter-cell interruption time and overhead. RACHless and condition based LTM can be used to achieve the above target.

It shall be noted that the above implementations can be used to Non-terrestrial networks (NTN) system as well.

NTN refer to networks, or segments of networks, using an airborne or spaceborne vehicle for transmission.

In some implementations, spaceborne vehicles may comprise satellites (including Low Earth Orbiting (LEO) satellites, Medium Earth Orbiting (MEO) satellites, Geostationary Earth Orbiting (GEO) satellites as well as Highly Elliptical Orbiting (HEO) satellites) .

In some implementations, airborne vehicles may comprise High Altitude Platforms (HAPs) encompassing Unmanned Aircraft Systems (UAS) including Lighter than Air UAS (LTA) , Heavier than Air UAS (HTA) , all operating in altitudes typically between 8 and 50 km, quasi-stationary.

NTN supports the following additional trigger conditions upon which UE may execute CHO to a candidate cell:

- The RRM measurement-based event A4;

- A time-based trigger condition;

- A location-based trigger condition.

Time-based or location-based trigger conditions may be configured independently from the measurement condition for CHO in NTN in at least hard satellite switch case where the service discontinuity gap time length is assumed to be zero or negligible.

For NTN-NTN mobility, the interruption time and the signalling overhead are big drivers towards an efficient seamless service continuity. RACH-less HO and satellite switch with re-sync procedures were introduced to this end. However, more can be done to achieve seamless soft satellite switching and to reduce inter-cell interruption time and overhead.

Fig. 13 illustrates an example of a device 1300 that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The device 1300 may be an example of a network entity 102 or a UE 104 as described herein. The device 1300 may support wireless communication with one or more network entities 102, UEs 104, or any combination thereof. The device 1300 may include components for bi-directional communications including components for transmitting and receiving communications, such as a processor 1302, a memory 1304, a transceiver 1306, and, optionally, an I/O controller 1308. These components may be in electronic communication or otherwise coupled (e.g., operatively, communicatively, functionally, electronically, electrically) via one or more interfaces (e.g., buses) .

The processor 1302, the memory 1304, the transceiver 1306, or various combinations thereof or various components thereof may be examples of means for performing various aspects of the present disclosure as described herein. For example, the processor 1302, the memory 1304, the transceiver 1306, or various combinations or components thereof may support a method for performing one or more of the operations described herein.

In some implementations, the processor 1302, the memory 1304, the transceiver 1306, or various combinations or components thereof may be implemented in hardware (e.g., in communications management circuitry) . The hardware may include a processor, a digital signal processor (DSP) , an application-specific integrated circuit (ASIC) , a field-programmable gate array (FPGA) or other programmable logic device, a discrete gate or transistor logic, discrete hardware components, or any combination thereof configured as or otherwise supporting a means for performing the functions described in the present disclosure. In some implementations, the processor 1302 and the memory 1304 coupled with the processor 1302 may be configured to perform one or more of the functions described herein (e.g., executing, by the processor 1302, instructions stored in the memory 1304) .

For example, the processor 1302 may support wireless communication at the device 1300 in accordance with examples as disclosed herein. The processor 1302 may be configured to operable to support a means for performing the following: transmitting a first request message to a second network node, wherein the first message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and receiving a first response message from the second network node.

Alternatively, in some implementations, the processor 1302 may be configured to operable to support a means for performing the following: receiving a first request message to from a first network node, wherein the first request message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and transmitting a first response message to the first network node.

Alternatively, in some implementations, the processor 1302 may be configured to operable to support a means for performing the following: receiving a second request message to from a second network node, wherein the second request message comprises at least one of the following: a request for at least one layer 1 condition for conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and transmitting a second response message to the second network node.

The processor 1302 may include an intelligent hardware device (e.g., a general-purpose processor, a DSP, a CPU, a microcontroller, an ASIC, an FPGA, a programmable logic device, a discrete gate or transistor logic component, a discrete hardware component, or any combination thereof) . In some implementations, the processor 1302 may be configured to operate a memory array using a memory controller. In some other implementations, a memory controller may be integrated into the processor 1302. The processor 1302 may be configured to execute computer-readable instructions stored in a memory (e.g., the memory 1304) to cause the device 1300 to perform various functions of the present disclosure.

The memory 1304 may include random access memory (RAM) and read-only memory (ROM) . The memory 1304 may store computer-readable, computer-executable code including instructions that, when executed by the processor 1302 cause the device 1300 to perform various functions described herein. The code may be stored in a non-transitory computer-readable medium such as system memory or another type of memory. In some implementations, the code may not be directly executable by the processor 1302 but may cause a computer (e.g., when compiled and executed) to perform functions described herein. In some implementations, the memory 1304 may include, among other things, a basic I/O system (BIOS) which may control basic hardware or software operation such as the interaction with peripheral components or devices.

The I/O controller 1308 may manage input and output signals for the device 1300. The I/O controller 1308 may also manage peripherals not integrated into the device M02. In some implementations, the I/O controller 1308 may represent a physical connection or port to an external peripheral. In some implementations, the I/O controller 1308 may utilize an operating system such as or another known operating system. In some implementations, the I/O controller 1308 may be implemented as part of a processor, such as the processor 1306. In some implementations, a user may interact with the device 1300 via the I/O controller 1308 or via hardware components controlled by the I/O controller 1308.

In some implementations, the device 1300 may include a single antenna 1310. However, in some other implementations, the device 1300 may have more than one antenna 1310 (i.e., multiple antennas) , including multiple antenna panels or antenna arrays, which may be capable of concurrently transmitting or receiving multiple wireless transmissions. The transceiver 1306 may communicate bi-directionally, via the one or more antennas 1310, wired, or wireless links as described herein. For example, the transceiver 1306 may represent a wireless transceiver and may communicate bi-directionally with another wireless transceiver. The transceiver 1306 may also include a modem to modulate the packets, to provide the modulated packets to one or more antennas 1310 for transmission, and to demodulate packets received from the one or more antennas 1310. The transceiver 1306 may include one or more transmit chains, one or more receive chains, or a combination thereof.

A transmit chain may be configured to generate and transmit signals (e.g., control information, data, packets) . The transmit chain may include at least one modulator for modulating data onto a carrier signal, preparing the signal for transmission over a wireless medium. The at least one modulator may be configured to support one or more techniques such as amplitude modulation (AM) , frequency modulation (FM) , or digital modulation schemes like phase-shift keying (PSK) or quadrature amplitude modulation (QAM) . The transmit chain may also include at least one power amplifier configured to amplify the modulated signal to an appropriate power level suitable for transmission over the wireless medium. The transmit chain may also include one or more antennas 1310 for transmitting the amplified signal into the air or wireless medium.

A receive chain may be configured to receive signals (e.g., control information, data, packets) over a wireless medium. For example, the receive chain may include one or more antennas 1310 for receive the signal over the air or wireless medium. The receive chain may include at least one amplifier (e.g., a low-noise amplifier (LNA) ) configured to amplify the received signal. The receive chain may include at least one demodulator configured to demodulate the receive signal and obtain the transmitted data by reversing the modulation technique applied during transmission of the signal. The receive chain may include at least one decoder for decoding the processing the demodulated signal to receive the transmitted data.

Fig. 14 illustrates a flowchart of a method 1400 that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The operations of the method 1400 may be implemented by a device or its components as described herein. For example, the operations of the method 1400 may be performed by a first network node as described herein. In some implementations, the device may execute a set of instructions to control the function elements of the device to perform the described functions. Additionally, or alternatively, the device may perform aspects of the described functions using special-purpose hardware.

At 1410, the method may transmitting a first request message to a second network node. The first message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update. The operations of 1410 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1410 may be performed by a device as described with reference to Fig. 2, 3A, 3B, 3C or 3D.

At 1420, the method may include receiving a first response message from the second network node. The operations of 1420 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1420 may be performed by a device as described with reference to Fig. 2, 3A, 3B, 3C or 3D.

Fig. 15 illustrates a flowchart of a method 1500 that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The operations of the method 1500 may be implemented by a device or its components as described herein. For example, the operations of the method 1500 may be performed by a second network node as described herein. In some implementations, the device may execute a set of instructions to control the function elements of the device to perform the described functions. Additionally, or alternatively, the device may perform aspects of the described functions using special-purpose hardware.

At 1510, the method may include receiving a first request message to from a first network node. The first request message comprises at least one of the following: a request for at least one condition for subsequent conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update. The operations of 1510 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1510 may be performed by a device as described with reference to Fig. 2, 3A, 3B, 3C or 3D.

At 1520, the method may include transmitting a first response message to the first network node. The operations of 1520 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1520 may be performed by a device as described with reference to Fig. 2, 3A, 3B, 3C or 3D.

Fig. 16 illustrates a flowchart of a method 1600 that supports subsequent conditional LTM and PDCP re-establishment in accordance with aspects of the present disclosure. The operations of the method 1600 may be implemented by a device or its components as described herein. For example, the operations of the method 1600 may be performed by the third network node as described herein. In some implementations, the device may execute a set of instructions to control the function elements of the device to perform the described functions. Additionally, or alternatively, the device may perform aspects of the described functions using special-purpose hardware.

At 1610, the method may include receiving a second request message to from a second network node. The second request message comprises at least one of the following: a request for at least one layer 1 condition for conditional LTM related to a list of at least one candidate cell, or IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update. The operations of 1610 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1610 may be performed by a device as described with reference to Fig. 2, 3A, 3B, 3C or 3D.

At 1620, the method may include transmitting a second response message to the second network node. The operations of 1620 may be performed in accordance with examples as described herein. In some implementations, aspects of the operations of 1620 may be performed by a device as described with reference to Fig. 2, 3A, 3B, 3C or 3D.

It shall be noted that implementations of the present disclosure which have been described with reference to Figs. 1 to 12 are also applicable to the device 1300 as well as the methods 1400, 1500 and 1600.

It should be noted that the methods described herein describes possible implementations, and that the operations and the steps may be rearranged or otherwise modified and that other implementations are possible. Further, aspects from two or more of the methods may be combined.

The various illustrative blocks and components described in connection with the disclosure herein may be implemented or performed with a general-purpose processor, a DSP, an ASIC, a CPU, an FPGA or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any processor, controller, microcontroller, or state machine. A processor may also be implemented as a combination of computing devices (e.g., a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

The functions described herein may be implemented in hardware, software executed by a processor, firmware, or any combination thereof. If implemented in software executed by a processor, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Other examples and implementations are within the scope of the disclosure and appended claims. For example, due to the nature of software, functions described herein may be implemented using software executed by a processor, hardware, firmware, hardwiring, or combinations of any of these. Features implementing functions may also be physically located at various positions, including being distributed such that portions of functions are implemented at different physical locations.

Computer-readable media includes both non-transitory computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A non-transitory storage medium may be any available medium that may be accessed by a general-purpose or special-purpose computer. By way of example, non-transitory computer-readable media may include RAM, ROM, electrically erasable programmable ROM (EEPROM) , flash memory, compact disk (CD) ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other non-transitory medium that may be used to carry or store desired program code means in the form of instructions or data structures and that may be accessed by a general-purpose or special-purpose computer, or a general-purpose or special-purpose processor.

As used herein, including in the claims, an article “a” before an element is unrestricted and understood to refer to “at least one” of those elements or “one or more” of those elements. The terms “a, ” “at least one, ” “one or more, ” and “at least one of one or more” may be interchangeable. As used herein, including in the claims, “or” as used in a list of items (e.g., a list of items prefaced by a phrase such as “at least one of” or “one or more of” or “one or both of” ) indicates an inclusive list such that, for example, a list of at least one of A, B, or C means A or B or C or AB or AC or BC or ABC (i.e., A and B and C) . Also, as used herein, the phrase “based on” shall not be construed as a reference to a closed set of conditions. For example, an example step that is described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure. In other words, as used herein, the phrase “based on” shall be construed in the same manner as the phrase “based at least in part on. Further, as used herein, including in the claims, a “set” may include one or more elements.

The description herein is provided to enable a person having ordinary skill in the art to make or use the disclosure. Various modifications to the disclosure will be apparent to a person having ordinary skill in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

Claims

A first network node, comprising:

a processor; and

a transceiver coupled to the processor,

wherein the processor is configured to:

transmit a first request message via the transceiver to a second network node, wherein the first request message comprises at least one of the following:

a request for at least one condition for subsequent conditional layer 1 or layer 2 triggered mobility (LTM) related to a list of at least one candidate cell, or

identifiers (IDs) for a serving cell and at least one candidate cell related to packet data convergence protocol (PDCP) re-establishment or security key update; and

receive a first response message via the transceiver from the second network node.
The first network node of claim 1, wherein the first request message further comprises at least one of the following:

capability of a user equipment (UE) which indicates that the UE supports at least one of layer 1 condition based LTM or layer 3 condition based LTM, or

a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node.
The first network node of claim 1, wherein the request for at least one condition indicates the second network node to generate one of the following:

at least one condition for subsequent conditional LTM from a candidate cell prepared by the second network node to each of at least one candidate cell prepared by at least one other network node,

at least one layer 1 condition for the subsequent conditional LTM, or

at least one layer 3 condition for the subsequent conditional LTM.
The first network node of claim 1, wherein the first request message comprises the request for the at least one condition for the subsequent conditional LTM from a candidate cell prepared by the second network node to each of the at least one candidate cell prepared by at least one other network node, and the first response message comprises the at least one condition for the subsequent conditional LTM.
The first network node of claim 1, wherein both layer 1 condition based LTM and layer 3 condition based LTM are supported by a user equipment (UE) ; and

wherein a first priority of the layer 1 condition based LTM is higher than a second priority of the layer 3 condition based LTM, and the at least one condition comprises at least one layer 1 condition for LTM.
The first network node of claim 1, wherein the first network node comprises a central unit (CU) of a source master node (MN) , and the second network node comprises one of the following:

a candidate distributed unit (DU) of the source MN, or

a CU of a candidate MN.
The first network node of claim 1, wherein the first network node comprises a central unit (CU) of a source master node (MN) , and the second network node comprises a CU of a candidate secondary node (SN) .
The first network node of claim 7, wherein the processor is further configured to:

receive a message via the transceiver from a CU of a source SN, wherein the message comprises at least one of the following:

an ID of a candidate cell belonging to the candidate SN,

an indication indicating conditional LTM is initiated,

a type of the at least one condition for initial conditional LTM related to cell switch from a current serving cell to a candidate cell prepared by another candidate SN,

suggestion that the request for the at least one condition for conditional LTM is to be transmitted to the CU of the candidate SN, or

at least one ID for the at least one candidate cell related to PDCP re-establishment or security key update which is assigned by the source SN.
The first network node of claim 1, wherein the first network node comprises a central unit (CU) of a source secondary node (SN) , and the second network node comprises a candidate distributed unit (DU) of the source SN.
The first network node of claim 9, wherein the first request message comprises the IDs for the serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and

wherein the processor is further configured to:

transmit, via the transceiver to a CU of a source master node (MN) , a request for at least one ID for the at least one candidate cell related to PDCP re-establishment or security key update.
The first network node of claim 9, wherein the processor is further configured to:

determine an ID for the serving cell as at least one ID for the at least one candidate cell.
The first network node of claim 1, wherein the processor is further configured to:

transmit, via the transceiver to a fourth network node, the IDs for the serving cell and at least one candidate cell related to PDCP re-establishment or security key update.
The first network node of claim 12, wherein the first network node comprises a central unit (CU) of a source master node (MN) , and the fourth network node comprises a source distributed unit (DU) of the source MN; or

wherein the first network node comprises a CU of a source secondary node (SN) , and the fourth network node comprises a source DU of the source SN.
The first network node of claim 1, wherein the processor is further configured to:

transmit, via the transceiver to a user equipment (UE) , the IDs for the serving cell and at least one candidate cell related to PDCP re-establishment or security key update.
A second network node, comprising:

a processor; and

a transceiver coupled to the processor,

wherein the processor is configured to:

receive a first request message via the transceiver to from a first network node, wherein the first request message comprises at least one of the following:

a request for at least one condition for subsequent conditional layer 1 or layer 2 triggered mobility (LTM) related to a list of at least one candidate cell, or

identifiers (IDs) for a serving cell and at least one candidate cell related to packet data convergence protocol (PDCP) re-establishment or security key update; and

transmit a first response message via the transceiver to the first network node.
The second network node of claim 15, wherein the first request message further comprises at least one of the following:

capability of a user equipment (UE) which indicates that the UE supports at least one of layer 1 condition based LTM or layer 3 condition based LTM, or

a type of a condition for initial conditional LTM from a current serving cell to a candidate cell prepared by the second network node.
The second network node of claim 15, wherein the request for at least one condition indicates the second network node to generate one of the following:

at least one condition for subsequent conditional LTM from a candidate cell prepared by the second network node to each of the at least one candidate cell prepared by at least one other network node,

at least one layer 1 condition for the subsequent conditional LTM, or

at least one layer 3 condition for the subsequent conditional LTM.
The second network node of claim 15, wherein the first request message comprises the request for the at least one condition for the subsequent conditional LTM from a candidate cell prepared by the second network node to each of the at least one candidate cell prepared by at least one other network node, and the first response message comprises the at least one condition for the subsequent conditional LTM.
A third network node, comprising:

a processor; and

a transceiver coupled to the processor,

wherein the processor is configured to:

receive a second request message via the transceiver to from a second network node, wherein the second request message comprises at least one of the following:

a request for at least one layer 1 condition for conditional layer 1 or layer 2 triggered mobility (LTM) related to a list of at least one candidate cell, or

IDs for a serving cell and at least one candidate cell related to PDCP re-establishment or security key update; and

transmit a second response message via the transceiver to the second network node.
A method performed by a first network node, comprising:

transmitting a first request message to a second network node, wherein the first message comprises at least one of the following:

a request for at least one condition for subsequent conditional layer 1 or layer 2 triggered mobility (LTM) related to a list of at least one candidate cell, or

identifiers (IDs) for a serving cell and at least one candidate cell related to packet data convergence protocol (PDCP) re-establishment or security key update; and

receiving a first response message from the second network node.