Generating a lower layer triggered cell switch configuration

Abstract

A distributed unit (DU) of a distributed base station that includes the DU and a central unit (CU) receives, from the CU, a request to prepare a cell for mobility by a user equipment (UE) and generates, at the DU and in response to the request, a DU configuration. The generating of the DU configuration includes generating a first configuration for mobility or a second configuration for mobility, depending on whether the request includes a lower-layer triggered mobility (LTM) indication. The DU then transmits, to the CU, the DU configuration that (i) includes the first configuration for mobility or (ii) includes the second configuration for mobility and excludes the first configuration for mobility.

Description

GENERATING A LOWER LAYER TRIGGERED CELL SWITCH CONFIGURATIONCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of the filing date of provisional U.S. Patent Application No. 63 / 582,454, entitled “Generating a Lower Layer Triggered Cell Switch Configuration,” filed on September 13, 2023. The entire content of the provisional application is hereby expressly incorporated herein by reference.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to selecting a configuration for communication upon a lower layer triggered cell switch.BACKGROUND

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

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

[0005] UEs use several types of SRBs and DRBs. When operating in dual connectivity (DC), the cells associated with the base station operating the master node (MN) define a master cell group (MCG), and the cells associated with the base station operating as thesecondary node (SN) define the secondary cell group (SCG). SRB1 resources carry RRC messages, which in some cases include NAS messages, over the dedicated control channel (DCCH), and SRB2 resources support RRC messages that include logged measurement information or NAS messages, also over the DCCH but with lower priority than SRB 1 resources. More generally, SRB1 and SRB2 resources allow the UE and the MN to exchange RRC messages related to the MN and embed RRC messages related to the SN, and also can be referred to as MCG SRBs. SRB3 resources allow the UE and the SN to exchange RRC messages related to the SN; SRB3 resources can be referred to as SCG SRBs. Split SRBs allow the UE to exchange RRC messages directly with the MN via lower layer resources of the MN and the SN. Further, DRBs using the lower-layer resources of only the MN can be referred as MCG DRBs, DRBs using the lower-layer resources of only the SN can be referred as SCG DRBs, and DRBs using the lower-layer resources of both the MCG and the SCG can be referred to as split DRBs.

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

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

[0008] In some scenarios, a distributed base station that includes a central unit (CU) and at least one distributed unit (DU) operates communicates with a UE, and the DU operates as a serving DU. The CU can prepare multiple cells for LTM (as candidate LTM cells) for the UE. The candidate LTM cells can be associated with one or more DUs (e.g., the serving DU and / or one or more candidate DUs). These one or more DUs generate respective LTM configurations, each including a random access channel (RACH) or RACH-less access configuration. The CU then transmits the multiple LTM configurations to the UE. After the CU transmits the LTM configurations to the UE, the serving DU receives one or more LI or L2 measurement results from the UE. The serving DU determines that one of the candidate LTM cells qualifies to be a new serving cell, based on the one or more measurement results. In response to the determination, the DU transmits an LTM command to the UE, so as to instruct the UE to connect to the qualified cell.

[0009] However, it is not clear how the DU should handle preparation requests from the CU so that the DU can generate LTM-specific DU configuration(s) to avoid configuration errorsSUMMARY

[0010] An example embodiment of the techniques of this disclosure is a method implemented in a DU of a distributed base station that includes the DU and a CU. The method comprises receiving, from the CU, a request to prepare a cell for mobility by a UE; generating, at the DU and in response to the request, a DU configuration, including generating a first configuration for mobility or a second configuration for mobility, depending on whether the request includes a lower-layer triggered mobility (LTM) indication; and transmitting, to the CU, the DU configuration that (i) includes the first configuration for mobility or (ii) includes the second configuration for mobility and excludes the first configuration for mobility.

[0011] Another example embodiment of these techniques is a method implemented in CU of a distributed base station that includes the CU and a DU. The method comprisestransmitting, to the CU, a request to prepare a cell for mobility by a UE; receiving, in a first instance when the request includes an LTM indication, a first DU configuration that includes the first configuration for mobility; and receiving, in a second instance when the request does not include the LTM indication, a second DU configuration that includes a second configuration for mobility and excludes the first configuration for mobility.

[0012] Still another embodiment of these techniques is a method for generating a configuration for mobility for a user equipment (UE), implemented in a distributed unit (DU) of a radio access network (RAN) node. The method comprises receiving, at the DU, a cell mobility message from a central unit (CU) of the RAN node; in a first instance, when the cell mobility message includes a lower layer mobility indication, generating, at the DU, a DU configuration including a first configuration for mobility and excluding a second configuration for mobility; in a second instance, when the cell mobility message does not include a lower layer mobility indication, generating, at the DU, the DU configuration including the second configuration and excluding the first configuration; and transmitting, from the DU to the CU, the DU configuration.

[0013] Yet another example embodiment of these techniques is a method for providing a configuration for mobility for a UE via a DU, implemented in a CU of a RAN node. The method comprises generating, at the CU, a mobility message including a lower layer mobility indication; transmitting, from the CU to the DU, the mobility message; receiving, at the CU from the DU, a DU configuration including a first configuration for mobility; and transmitting, from the CU to the UE via the DU, the DU configuration including the first configuration and excluding a second configuration for mobility.

[0014] Another example embodiment of these techniques is a network node comprising a transceiver and processing hardware configured to implement one of the methods above.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Fig. 1 A is a block diagram of an example system in which a radio access network (RAN) and a user device can implement the techniques of this disclosure for managing LTM configuration;

[0016] Fig. IB is a block diagram of an example base station including a centralized unit (CU) and a distributed unit (DU) that can operate in the system of Fig. 1 A;

[0017] Fig. 2A is a block diagram of an example protocol stack according to which the UE of Fig. 1 A communicates with base stations;

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

[0019] Fig. 3 is a messaging diagram of an example scenario in which a UE receives an LTM configuration from a distributed unit (DU) of a distributed base station and accesses a candidate cell of the DU in accordance with the LTM configuration;

[0020] Fig. 4 is a messaging diagram of an example scenario generally similar to that of Fig. 3, but in which the candidate cell is associated with another DU of the distributed base station;

[0021] Fig. 5A is a messaging diagram of an example scenario generally similar to that of Fig. 3, but in which the UE operates in dual connectivity, and the candidate cell is associated with a secondary node (SN);

[0022] Fig. 5B is a messaging diagram of an example scenario generally similar to that of Fig. 5 A, but in which the SN performs LTM configuration via the main node (MN) rather than directly;

[0023] Fig. 6A is a messaging diagram of an example scenario generally similar to that of Fig. 3, but in which the UE operates in dual connectivity, and the candidate cell is associated with a secondary node (SN);

[0024] Fig. 6B is a messaging diagram of an example scenario generally similar to that of Fig. 6A, but in which the SN performs LTM configuration via the MN rather than directly;

[0025] Fig. 7A is a messaging diagram of an example scenario generally similar to that of Fig. 4, but in which the MN and the SN are implemented in a same base station;

[0026] Fig. 7B is a messaging diagram of an example scenario generally similar to that of Fig. 7A, but in which the SN performs LTM configuration via the MN DU (M-DU) rather than directly;

[0027] Fig. 8A is a messaging diagram of an example scenario generally similar to that of Fig. 3, but in which the MN and the SN are implemented in different respective DUs of a same base station, and the candidate cell is associated with yet another DU of the distributed base station;

[0028] Fig. 8B is a messaging diagram of an example scenario generally similar to that of Fig. 9A, but in which the SN performs LTM configuration via the M-DU rather than directly;

[0001] Fig. 9 is a flow diagram of an example method for generating an LTM DU configuration, which can be implemented in a DU;

[0002] Fig. 10 is a flow diagram of an example method according to which a DU generates a DU configuration including either a first configuration or a second configuration, depending on the request from the CU;

[0003] Fig. 11 A is a flow diagram of an example method according to which a DU generates a DU configuration with either an LTM cell switch information or a reconfiguration with sync configuration, depending on whether a UE Context Modification Request message from the CU includes an LTM indicator;

[0004] Fig. 1 IB is a flow diagram of an example method similar to that of Fig. 11 A, but according to which the CU provides the LTM indicator in, or omits the LTM indicator from, a UE Context Setup Request message;

[0005] Fig. 11C is a flow diagram of an example method similar to that of Fig. 1 IB, but according to which the CU transmits, to the DU, a CG configuration information IE rather than a handover preparation IE to request preparation for mobility;

[0006] Fig. 12 is a flow diagram of an example method for preparing a cell for LTM, which can be implemented in CU;

[0007] Fig. 13 A is a flow diagram of an example method according to which a CU prepares a cell for LTM using an LTM indicator and by removing the reconfiguration with sync configuration from the received LTM DU configuration, which can be implemented in a CU;

[0008] Fig. 13B is a flow diagram of an example method similar to that of Fig. 13 A, but according to which the CU uses a CG configuration information IE rather than a handover preparation IE;

[0009] Fig. 14A is a flow diagram of an example method according to which a CU determines whether to include, or refrain from including, handover preparation information in a CU-to-DU message, depending on whether mobility preparation relates to LTM; and

[0010] Fig. 14B is a flow diagram of an example method similar to that of Fig. 14A, but according to which the CU includes, or refrain from including, CG configuration in a CU-to- DU message, depending on whether mobility preparation relates to LTM.DETAILED DESCRIPTION OF THE DRAWINGS

[0011] Generally speaking, a DU can implement one or more of the techniques discussed herein to determine the type of configuration (e.g., lower-layer configuration, higher-layer configuration) to include in a DU configuration when preparing a cell for mobility, for a UE. The CU can implement one or more of these techniques to indicate, to the DU, the type of mobility for which the CU is preparing the UE, and receive a DU configuration that includes lower-layer configuration and / or higher-layer configuration.

[0012] For example, according to one approach, LTM procedures do not rely on legacy (i.e., mobility techniques available prior to the introduction of LTM) reconfiguration with sync procedure. Because the DU is generally responsible for the lower layer RRC configuration, the DU generates a CellGroupConfig including an LTM-CellSw itchinfo IE while excluding or refraining from including a reconfigurationWithSync IE. Thus, the specification for the UE Context Setup procedure and the UE Context Modification procedure can include the requirement that, for certain operations such as the DC operation, the CG-Configlnfo IE shall be included in the CU to DU RRC Information IE at the gNB acting as secondary node; if the CG-Configlnfo IE is included in the UE CONTEXT SETUP REQUEST message, the gNB-DU shall regard it as a reconfiguration with sync as defined in TS 38.331 except for LTM. Further, the specification can include the requirement that, if the HandoverPreparationlnformation IE is included in the CU to DU RRC Information IE in the UE CONTEXT SETUP REQUEST message, the gNB-DU of the gNB acting as master node shall regard it as a reconfiguration with sync as defined in TS 38.331 except for LTM. Still further, the specification can include the requirement that, if the LTM Indicator IE is contained in the LTM Information to be Setup IE included in the UE CONTEXT SETUP REQUEST message, the gNB-DU shall, if supported, consider that the request concerns LTM for the included SpCell ID IE and shall include it as the Requested Target Cell ID IE and generate a corresponding CellGroupConfig IE in the UE CONTEXT SETUP RESPONSE message.

[0013] Fig. 1 A depicts an example wireless communication system 100 in which a user equipment (UE) can implement early timing advance (TA) acquisition. The wirelesscommunication system 100 includes a UE 102, a base station (BS) 104, a base station 106 and a core network (CN) 110. The UE 102 initially connects to the base station 104. In some scenarios, the base station 104 can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104 and the base station 106. The base stations 104 and 106 operate as an MN and an SN for the UE 102, respectively.

[0014] In various configurations of the wireless communication system 100, the base station 104 can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the base station 106 can be implemented as a secondary gNB (SgNB). The UE 102 can communicate with the base station 104 and the base station 106 via the same RAT such as EUTRA or NR, or different RATs. When the base station 104 is an MeNB and the base station 106 is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0015] In some cases, an MeNB or an SeNB is implemented as an ng-eNB rather than an eNB. When the base station 104 is a Master ng-eNB (Mng-eNB) and the base station 106 is a SgNB, the UE 102 can be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. When the base station 104 is an MgNB and the base station 106 is an SgNB, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the base station 104 is an MgNB and the base station 106 is a Secondary ng-eNB (Sng-eNB), the UE 102 may be in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB.

[0016] In the scenarios where the UE 102 hands over from the base station 104 to the base station 106, the base stations 104 and 106 operate as the source base station (S-BS) and a target base station (T-BS), respectively. The UE 102 can operate in DC with the base station 104 and an additional base station (not shown in Fig. 1 A) prior to the handover, for example. The UE 102 can continue to operate in DC with the base station 106 and the additional base station, or operate in single connectivity (SC) with the base station 106, after completing the handover. The base stations 104 and 106 in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively.

[0017] A core network (CN) 110 can be an evolved packet core (EPC) 111 or a fifthgeneration core (5GC) 160, both of which are depicted in Fig. 1 A. The base station 104 can be an eNB supporting an SI interface for communicating with the EPC 111, an ng-eNB supporting an NG interface for communicating with the 5GC 160, or a gNB that supports an NR radio interface as well as an NG interface for communicating with the 5GC 160. Todirectly exchange messages with each other during the scenarios discussed below, the base stations 104 and 106 can support an X2 or Xn interface. Among other components, the EPC 111 can include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, and a Packet Data Network Gateway (PGW) 116. The SGW 112 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME 114 is configured to manage authentication, registration, paging, and other related functions. The PGW 116 provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and / or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The 5GC 160 includes a User Plane Function (UPF) 162 and an Access and Mobility Management (AMF) 164, and / or Session Management Function (SMF) 166. The UPF 162 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the SMF 166 is configured to manage PDU sessions.

[0018] As illustrated in Fig. 1 A, the base station 104 supports a cell 124A, and the base station 106 supports a cell 126. The cells 124A and 126 can partially overlap, so that the UE 102 can communicate in DC with the base station 104 and the base station 106, where one of the base stations 104 and 106 is an MN and the other is an SN. The base station 104 can support additional cell(s) such as cells 124B and 124C, and the base station 106 can support additional cell(s) (not shown in Fig. 1 A). The cells 124A, 124B and 124C can partially overlap, so that the UE 102 can communicate in carrier aggregation (CA) with the base station 104. The base station 104 can operate the cells 124A, 124B and 124C via one or more transmit and receive points (TRPs). More particularly, when the UE 102 is in DC with the base station 104 and the base station 106, one of the base stations 104 and 106 operates as an MeNB, an Mng-eNB or an MgNB, and the other operates as an SgNB or an Sng-eNB.

[0019] In general, the wireless communication network 100 can include any suitable number of base stations supporting NR cells and / or EUTRA cells. More particularly, the EPC 111 or the 5GC 160 can be connected to any suitable number of base stations supporting NR cells and / or EUTRA cells. Although the examples below refer specifically to specific CN types (EPC, 5GC) and RAT types (5GNR and EUTRA), in general the techniques of this disclosure also can apply to other suitable radio access and / or core network technologies such as sixth generation (6G) radio access and / or 6G core network or 5GNR-6G DC.

[0020] With continued reference to Fig. 1A, the base station 104 is equipped with processing hardware 130 that can include one or more general-purpose processors (e.g., CPUs) and a non-transitory computer-readable memory storing instructions that the one or more general-purpose processors execute. Additionally or alternatively, the processing hardware 130 can include special-purpose processing units.

[0021] The processing hardware 130 can implement an LTM controller 132 to support LTM procedures. The LTM controller 132 can be implemented as respective sets of instructions executable by one or more processors, for example. The processing hardware 130 can also implement additional components such as a PHY controller (not shown) configured to transmit data and control signal on physical downlink (DL) channels and DL reference signals with one or more user devices (e.g. UE 102) via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The PHY controller can be configured to receive data and control signal on physical uplink (UL) channels and / or UL reference signals with the one or more user devices via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The processing hardware 130 can also implement a MAC controller (not shown) configured to perform MAC functions with one or more user devices. The MAC functions include a random access (RA) procedure, managing UL timing advance for the one or more user devices, and / or communicating UL / DL MAC PDUs with the one or more user devices. The MAC functions include lower triggered mobility (LTM) related functions as described below. The processing hardware 130 can further include an RRC controller (not shown) to implement procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller may be configured to support RRC messaging associated with handover procedures, and / or to support the necessary operations when the base station 104 operates as an MN relative to an SN or as an SN relative to an MN. The base station 106 can include processing hardware 140 that is similar to processing hardware 130. In particular, components 142, 144, and 146 can be similar to the components 132 and 134, , respectively.

[0022] The UE 102 is equipped with processing hardware 150 that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special -purpose processing units. The processing hardware 150 can implement an LTM controller 152 to support LTM procedures in the serving cell and / or atarget cell. The LTM controller 152 can be implemented as respective sets of instructions executable by one or more processors, for example.

[0023] The processing hardware 150 can also implement additional components such as a PHY controller (not shown) configured to receive data and control signal on physical DL channels and / or DL reference signals with the base station 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126) and / or one or more TRPs. The PHY controller can be configured to transmit data and control signal on physical UL channels and / or UL reference signals with the base station 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126) and / or one or more TRPs. The processing hardware 150 in an example implementation includes a MAC controller (not shown) configured to perform MAC functions with base station 104 or 106. For example, the MAC functions includes a random access procedure, managing UL timing advance for the one or more user devices, and communicating UL / DL MAC PDUs with the base station 104 or 106. In another example, the MAC functions includes LTM related functions as described below. The processing hardware 150 can further include an RRC controller (not shown) to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0024] In operation, the UE 102 in DC can use a radio bearer (e.g., a DRB or an SRB) that at different times terminates at the MN 104 or the SN 106. The UE 102 can apply one or more security keys when communicating on the radio bearer, in the uplink (UL) (from the UE 102 to a base station) and / or downlink (from a base station to the UE 102) direction.

[0025] Fig. IB depicts an example distributed implementation of a base station such as the base station 104 or 106. The base station in this implementation can include a centralized unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 is equipped with processing hardware that can include one or more general -purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In one example, the CU 172 is equipped with the processing hardware 130. In another example, the CU 172 is equipped with the processing hardware 140. The processing hardware 140 in an example implementation includes an SN RRC controller 142 configured to manage or control one or more RRC configurations and / or RRC procedures when the base station 106 operates as an SN. The DU 174 is also equipped with processing hardware thatcan include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In some examples, the processing hardware in an example implementation includes a medium access control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure) and a radio link control (RLC) controller configured to manage or control one or more RLC operations or procedures when the base station 106 operates as an MN or an SN. The process hardware may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0026] Fig. 2A illustrates, in a simplified manner, an example protocol stack 200 according to which the UE 102 can communicate with an eNB / ng-eNB 230 or a gNB 232 (e.g., one or more of the base stations 104, 106).

[0027] In the example stack 200, a physical layer (PHY) 202 A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLC sublayer 206A in turn provides RLC channels to an EUTRA PDCP sublayer 208 and, in some cases, to an NR PDCP sublayer 210. Similarly, the NR PHY 202B provides transport channels to the NR MAC sublayer 204B, which in turn provides logical channels to the NR RLC sublayer 206B. The NR RLC sublayer 206B in turn provides data transfer services to the NR PDCP sublayer 210. The NR PDCP sublayer 210 in turn can provide data transfer services to Service Data Adaptation Protocol (SDAP) 212 or a radio resource control (RRC) sublayer (not shown in Fig. 2A). The UE 102, in some implementations, supports both the EUTRA and the NR stack as shown in Fig. 2A, to support handover between EUTRA and NR base stations and / or to support DC over EUTRA and NR interfaces. Further, as illustrated in Fig. 2A, the UE 102 can support layering of NR PDCP 210 over EUTRA RLC 206 A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0028] The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the PDCP layer 208 or 210) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer 206A or 206B) that can be referred to as protocol data units (PDUs). Exceptwhere the difference between SDUs and PDUs is relevant, this disclosure for simplicity refers to both SDUs and PDUs as “packets.”

[0029] On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide signaling radio bearers (SRBs) or RRC sublayer (not shown in Fig. 2 A) to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 can provide Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0030] Fig. 2B illustrates, in a simplified manner, an example protocol stack 250, which the UE 102 can communicate with a DU (e.g., DU 174) and a CU (e.g., CU 172). The radio protocol stack 200 is functionally split as shown by the radio protocol stack 250 in Fig. 2B. The CU at any of the base stations 104 or 106 can hold all the control and upper layer functionalities (e.g., RRC 214, SDAP 212, NR PDCP 210), while the lower layer operations (e.g., NR RLC 206B, NR MAC 204B, and NR PHY 202B) are delegated to the DU. To support connection to a 5GC, NR PDCP 210 provides SRBs to RRC 214, and NR PDCP 210 provides DRBs to SDAP 212 and SRBs to RRC 214.

[0031] Next, several example scenarios in which the base station operating in the system of Fig. 1 A transmits a configuration to the UE 102 and later activates a configuration for communication between the UE 102 and base station. Generally speaking, events in Figs. 3- 7B that are similar are labeled with similar reference numbers e.g., event 316 is similar to event 416 of Figs 4A and 4B, event 516 of Fig. 5 A, event 517 of Fig. 5B, event 616 of Fig. 6A, event 617 of Fig. 6B, event 716 of Fig. 7A, and event 717 of Fig. 7B), with differences discussed below where appropriate. With the exception of the differences shown in the figures and discussed below, any of the alternative implementations discussed with respect to a particular event (e.g., for messaging and processing) may apply to events labeled with similar reference numbers in other figures.

[0032] Referring first to Fig. 3, in a scenario 300, the base station 104 includes a CU 172 and a DU 174, and the DU 174 operates the cell 124 A. The UE 102 initially communicates 302 with the DU 174 on the cell 124 A using a serving DU configuration, and communicates with the CU 172 via the DU 174, e.g., using a serving CU configuration. In other words, the DU 174 is a serving DU that is communicating with the UE 102. In some implementations, the UE 102 in carrier aggregation (CA) communicates with the DU 174 on the cell 124 A andother cell(s) (e.g., cell 124D not shown in Fig. 1 A) using the serving DU configuration. The DU 174 operates the other cell(s). In other implementations, the UE 102 in communicates with the DU 174 on the cell 124A only. In some implementations, the UE 102 communicates with the DU 174 on the cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the cell 124 A can be a PCell. In such cases, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In other implementations, the cell 124A can be a SCell, and one of the other cell(s) is a PCell. In such cases, the rest includes SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In the following description, the base station 104 can be the DU 174, the CU 172 or the DU 174 and CU 172.

[0033] In the event 302, the UE 102 can transmit UL PDUs and / or UL control signals to the base station 104 on the cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the UE 102 communicates UL PDUs and / or DL PDUs with the base station 104 via radio bearers which can include SRBs and / or DRB(s). The base station 104 can configure the radio bearers to the UE 102. In some implementations, UL control signals include UL control information, channel state information, hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, scheduling request(s) and / or sounding reference signal(s). Similarly, the UE 102 can receive DL PDUs and / or DL control signals from the base station 104 on the cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the DL control signals include downlink control information (DCIs) and reference signals (e.g., synchronization signal block, channel state information reference signal(s) (CSI-RS(s)), and / or tracking reference signal(s)). The base station 104 can transmit the DCIs on physical downlink control channel(s) (PDCCH(s)) monitored by the UE 102, on the cell 124A and / or other cell(s) via one or multiple TRPs.

[0034] In some implementations, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the DU 174 can transmit these configuration parameters to the CU 172. The CU 172 generates one or more messages (e.g., RRC reconfiguration message(s)) including the configuration parameters and transmits the one or more messages to the UE 102 via the DU 174. In other implementations, the DU 174 transmits the configuration parameters to the UE 102 directly. In some implementations, the serving DU configuration is CellGroupConfig ^E (e.g., as defined in 3GPP specification 38.331). In other implementations, the serving DU configuration includes configurationparameters in the CellGroupConfig IE. In some implementations, the serving CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the serving CU configuration includes a MeasConfig IE and / or a RadioBear er Config IE (e.g., as defined in 3GPP specification 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some implementations, the serving DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. In other implementations, the serving CU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and reporting. In some implementations, the UE 102 receives the serving CU configuration or the configuration parameters in the serving CU configuration from the CU 172 via the DU 174. In other implementations, the UE 102 receives a portion of the serving CU configuration and / or a portion of the serving DU configuration from a base station other than the base station 104 and the remaining portion of these configuration parameters from the base station 104.

[0035] While communicating with the base station 104, the UE 102 transmits 304 at least one measurement report to the DU 174. In some implementations, the at least one measurement report includes Layer 1 (LI) measurement report(s) and / or Layer 3 (L3) measurement report(s) for at least one serving cell of the UE 102 and / or at least one nonserving cell. For each of the L3 measurement report(s), the DU 174 transmits 306 a DU-to- CU message including the L3 measurement report to the CU 172. In some implementations, the DU-to-CU message(s) of the event 306 is / are Fl application protocol (F1AP) message(s) (e.g., UL RRC Message Transfer message(s)). In some implementations, the DU 174 does not transmit or refrains from transmitting the LI measurement report(s) to the CU 172. The at least one serving cell includes the cell 124A and / or other cell(s), and the at least one nonserving cell includes the cell 124B and / or cell 124C. In some implementations, the serving DU configuration or the serving CU configuration includes at least one measurement configuration. In some implementations, the UE 102 receives one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration from the CU 172 via the DU 174 in the event 302. In accordance with the at least one measurement configuration, the UE 102 performs measurements and transmits 304 the at least one measurement report to the DU 174. In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfigIE(s)) and / or LI measurement configuration(s). The LI measurement configuration(s) (e.g., CSI-MeasConfig IE(s)) can include LI measurement resource configuration(s) and / or LI measurement reporting configuration(s). The LI measurement resource configuration(s) can configure reference signal(s) and / or resources of the reference signal(s) for the UE 102 to measure and obtain LI measurement results. In some implementations, the reference signal(s) includes CSLRS(s) and / or Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Block(s) (SSB(s)). For example, the LI measurement resource configuration(s) is / are CSI-ResourceConfig IE(s). In another example, the LI measurement reporting configuration(s) configures way(s) the UE 102 uses to transmit LI measurement results / reports. For example, the LI measurement report configuration(s) is / are CSI- ReportConfig IE(s). For example, The UE 102 transmits the L3 measurement report(s) to the CU 172 via the DU 174 in accordance with the L3 measurement configuration(s). The UE 102 transmits the LI measurement report(s) to the DU 174 in accordance with the LI measurement configuration(s) or LI measurement reporting configuration(s). In one implementations, the DU 174 does not transmit the LI measurement report(s) to the CU 172.

[0036] In some implementations, the LI measurement configuration(s) are new RRC IE(s) (e.g., as defined in 3GPP specification 38.331 vl8.0.0 and / or later version(s)) for a lower layer triggered mobility (LTM). In some implementations, the LI measurement resource configuration(s) are new RRC IE(s) (e.g., defined in 3GPP specification 38.331 vl8.0.0 and / or later version(s)) for the LTM. In some implementations, the LI measurement reporting configuration(s) are new RRC IE(s) (e.g., as defined in 3GPP specification 38.331 V18.0.0 and / or later version(s)) for the LTM. In some implementations, each of the LI measurement reporting configuration(s) can include a trigger event configuration configuring a trigger event to trigger the UE 102 to transmit a LI measurement report. If the UE 102 detects the trigger event, the UE 102 transmits a LI measurement report to the DU 174.

[0037] In some implementations, (each of) the LI measurement report(s) can include at least one LI measurement result. In some implementations, the at least LI measurement result includes at least one LI -reference signal received power (Ll-RSRP) value and / or at least one LI- Signal to Interference Noise Ratio (Ll-SINR) value. For each of the LI measurement report(s), the UE 102 transmits a PUCCH transmission including the LI measurement report to the DU 174, in some implementations. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUCCH to the DU 174. In other implementations, for each of the LI measurement report(s), the UE 102 transmits a PUSCHtransmission including the LI measurement report to the DU 174. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUSCH to the DU 174. In yet other implementations, the UE 102 transmits a portion of the LI measurement report(s) on PUCCH(s) and the rest of the LI measurement report(s) on physical UL shared channel(s) (PUSCH(s)) to the DU 174. That is, for each of the portion of the LI measurement report(s), the UE 102 transmits a PUCCH transmission including the LI measurement report to the DU 174, and for each of the rest of the LI measurement report(s), the UE 102 transmits a PUSCH transmission including the LI measurement report to the DU 174. In some implementations, each of the LI measurement report(s) is a part of CSI (i.e., a CSI component) or CSI. In some implementations, the UE 102 can include other CSI component(s) in (each of) the PUCCH transmission(s) and / or PUSCH transmission(s) described above. In one implementation, the other CSI component(s) include such as a channel quality indicator (CQI), a Precoding Matrix Indicator (PMI), a CSLRS Resource Indicator (CRI), a SSB Resource Indicator (SSBRI), a Layer Indicator (LI), and / or a Rank Indicator (RI). In some implementations, the UE 102 does not transmit the LI measurement report(s) in format of RRC message(s) to the DU 174.

[0038] In some implementations, each of the L3 measurement report(s) can include at least one L3 measurement result. In some implementations, the at least one L3 measurement result includes at least one RSRP (value) and / or at least one SINR (value). In one implementation, the UE 102 transmits each of the L3 measurement report(s) on a PUSCH to the CU 172 via the DU 174. In some implementations, each of the L3 measurement report(s) can be an RRC message (e.g., MeasurementReport message). In some implementations, each of the L3 measurement configuration(s) includes a particular measurement identity (e.g., measld) and each of the L3 measurement report(s) includes a particular measurement identity in a particular L3 measurement configuration. When the CU 172 receives a L3 measurement report including a measurement identity and a L3 measurement result from the UE 102 via the DU 174, the CU 172 can determine that the L3 measurement report is associated to a L3 measurement configuration identified by the measurement identity.

[0039] In some alternative implementations, for each of the at least one measurement report (e.g., LI measurement report(s)), the UE 102 transmits a MAC control element (CE) including the measurement report to the DU 174 in the event 304. To transmit the MAC CE(s), the UE 102 generate one or more MAC PDUs each including one or more of the MAC CE(s) to the DU 174 in the event 304.

[0040] In some implementations, the UE 102 performs measurements on one or more reference signals in accordance with the at least one measurement configuration. The one or more reference signals can include one or more Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Blocks (SSBs) and / or one or more CSI-RSs. The UE 102 obtains the at least one LI measurement result and / or at least one L3 measurement result from the measurements. The DU 174 transmits the one or more reference signals on the cell 124A and other cell(s) (e.g., the cell 124B, the cell 124C and / or cell(s) not shown in Fig. 1 A).

[0041] After (e.g., in response to) receiving one or some of the at least one measurement report from the UE 102, the base station 104 (i.e., the CU 172 or DU 174) determines to prepare a first cell (e.g., the cell 124B) for LTM for the UE 102. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell could be used by the base station 104 to communicate with the UE 102. In some implementations, the base station 104 determines to prepare the first cell for the UE 102 because the at least one measurement report indicates that the first cell qualifies to be a candidate cell that could be used for communication with the UE 102. In some implementations, if the L3 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than strength and / or quality of the cell 124A, and / or is better than strength and / or quality of the cell 124 A by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. In other implementations, if the LI measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than signal strength and / or quality of the cell 124A, and / or is better than signal strength and / or quality of the cell 124A by a first predetermined threshold, the DU 174 determines to prepare the first cell for the UE 102. Alternatively, the base station 104 determines to prepare the first cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0042] In cases where the CU 172 determines to prepare the first cell for LTM, the CU 172 transmits 308 a first CU-to-DU message to the DU 174 to prepare the first cell for the UE 102. In some implementations, the CU 172 includes a cell identity (ID) 1 of the first cell in the first CU-to-DU message to request the DU 174 to prepare the first cell for LTM for the UE 102. For example, the cell ID 1 is a cell global identity (CGI). In another example, the cell ID is a portion of the CGI. In yet another example, the cell ID is a physical cell ID (PCI). In some implementations, the CU 172 includes an LTM indicator in the first CU-to-DUmessage to indicate the DU 174 to prepare the first cell for LTM. In some implementations, the LTM indicator is an LTM Information to be Setup IE o LTM Information to be Modification IE. In other implementations, the LTM indicator is a specific LTM Indicator IE in the LTM Information to be Setup IE or LTM Information to be Modification IE. In response to the first CU-to-DU message, the DU 174 generates a first LTM DU configuration (referred to herein after as LTM DU configuration 1) for the UE 102, which configures the first cell for LTM. The DU 174 then transmits 310 a first DU-to-CU message including the LTM DU configuration 1 to the CU 172 in response to the first CU-to-DU message. In some implementations, the DU 174 includes the cell ID 1 together with the LTM DU configuration 1 in an IE of the first DU-to-CU message to indicate that the LTM DU configuration 1 is associated with the first cell (i.e., the cell ID 1). In cases where the DU 174 determines to prepare the first cell, the DU 174 initiates transmission of the first DU-to-CU message to the CU 172 instead of in response to a CU-to-DU message received from the CU 172.

[0043] In some implementations, the DU 174 includes, in the first DU-to-CU message, the cell ID 1 to indicate that the LTM DU configuration 1 is configured for or associated with the first cell. The CU 172 identifies the LTM DU configuration 1 is configured for or associated with the first cell. In some scenarios and implementations, the CU 172 includes additional cell ID(s) (e.g., cell ID(s) 2, . . ., N) in the first CU-to-DU message to prepare additional cell(s) (e.g., cell(s) 2, . . ., N) for LTM for the UE 102, and the DU 174 includes additional LTM DU configuration(s) (e.g., LTM DU configuration(s) 2, . . ., N) each configuring a particular cell of the additional cell(s), as described below. In such cases, the DU 174 includes, in the first DU-to-CU message, the additional cell ID(s) respectively associated with the additional LTM DU configuration(s) to indicate that which LTM DU configuration is associated to which cell (ID). The cell(s) 1 and / or 2, . . ., N are candidate cell(s). In some implementations, the CU 172 associates the LTM DU configuration(s) 1, . . ., N with the cell ID(s) 1, ..., N, respectively.

[0044] In some implementations, the DU 174 includes, in the first DU-to-CU message, a UE ID 1 to indicate that the DU 174 configures the UE ID 1 for communication with the UE 102 on the first cell. In some cases of preparing additional cell(s) (e.g., cell(s) 2, . . ., N) for LTM for the UE 102 in the first CU-to-DU message, the DU 174 includes UE ID(s) 2, . . . , N for communication with the UE 102 on the cell(s) 2, . . . , N in the first DU-to-CU message, respectively. In some implementations, the UE ID(s) 1, . . ., N are cell radio network temporary identifier (C-RNTI). In some implementations, the DU 174 includes the UE ID(s)1, . . . , N in the LTM DU configuration(s) 1, . . . , N, respectively. In some implementations, the DU 174 includes the UE ID(s) 1, . . N in the first DU-to-CU message, and includes the UE ID(s) 1, . . . , N in the LTM DU configurations(s) 1, . . . , N respectively. In some implementations, the CU 172 stores the UE ID(s) 1, . . . ., N and associates the UE ID(s) 1, . . ., N with the LTM DU configured on(s) 1, . . . , N and / or the cell ID(s) 1, . . . , N, respectively.

[0045] In some implementations, the CU 172 does not include a (reference) LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, . . ., N (i.e., non-reference LTM DU configuration(s)) based on the reference LTM DU configuration, and includes the reference LTM DU configuration in the first DU-to-CU message. In other implementations, the CU 172 includes a reference LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates the LTM DU configured on(s) 1, and / or 2, . . ., N which are delta configured on(s) to augment the reference LTM DU configuration. In yet other implementations, the CU 172 includes a reference LTM DU configuration (e.g., a first reference LTM DU configuration) in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration (e.g., a second reference LTM DU configuration) replacing the first reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, . . ., N based on the second reference LTM DU configuration, and includes the second reference LTM DU configuration in the first DU-to-CU message.

[0046] In some implementations, the reference LTM DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the reference LTM DU configuration is or includes a CellGroupConfig IE (e.g., as defined in 3GPP specification 38.331). In other implementations, the reference LTM DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the reference LTM DU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0047] In some implementations, the reference LTM DU configuration is different from the serving DU configuration. In some implementations, a portion of the reference LTM DU configuration is the same as a portion of the serving DU configuration and the rest of the reference LTM DU configuration is different from the rest of the serving DU configuration.In other implementations, the reference LTM DU configuration is the same as the serving DU configuration.

[0048] After receiving the first DU-to-CU message, the CU 172 generates an RRC reconfiguration message (e.g., an RRCReconfiguration message) including the LTM DU configuration 1 and transmits 316 a second CU-to-DU message including the RRC reconfiguration message to the DU 174. In some implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316. In other implementations, the CU 172 does not include a / the reference LTM DU configuration in the RRC reconfiguration message 316. In some implementations, if the CU 172 transmits the reference LTM DU configuration to the UE 102 during the event 302, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316. In other implementations, if the CU 172 receives the reference LTM DU configuration from the DU 174, the CU 172 includes the LTM DU configuration in the RRC reconfiguration message 316. Otherwise, if the CU 172 does not receive a reference LTM DU configuration from the DU 174, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316.

[0049] In some implementations, the CU 172 includes the LTM DU configuration 1 and / or the LTM CU configuration 1 in a first container (e.g., a field / IE) and includes the first container (e.g., LTM configuration 1) in the RRC reconfiguration message of the events 316 and 318. In such cases, the CU 172 generates the first container. The first container is to indicate the UE 102 not to apply the LTM DU configuration 1 and / or the LTM CU configuration 1 immediately. In some scenarios or implementations, the UE 102 receives an RRC reconfiguration message (e.g., the RRC reconfiguration message of the event 318) including a configuration (e.g., the LTM DU configuration 1). If the configuration is included in the first container, the UE 102 refrains from immediately applying the configuration. Otherwise, if the configuration is not included in the first container, the UE 102 can apply the configuration immediately. In some implementations, the first container includes or is a first addition or modification list (e.g., Itm-ConfigToAddModList field, Itm- CandidateToAddModList field, or Itm-CandidateConfigToAddModList field). The CU 172 includes the LTM DU configuration 1 and / or the LTM CU configuration 1 in a first element (referred to herein after as element 1) of the first addition or modification list. In some implementations, the CU 172 generates an RRC message (e.g., RRCRecconfiguration message) including the LTM DU configuration 1 and / or the LTM CU configuration 1, andincludes the RRC message in the element 1. In some implementations, the element 1 is an addition or modification IE (e.g., LTM-ConfigToAddMod IE, LTM-Candidate IE, LTM- CandidateToAddMod IE or LTM-CandidateConfigToAddMod IE). When the UE 102 receives the first addition or modification list, the UE 102 can store the first addition or modification list, e.g., in a variable in its random access memory (RAM). In other alternative implementations, the DU 174 generates the first container and includes the first container in the first DU-to-CU message. In yet other alternative implementations, the DU 174 generates the element 1 and includes the element 1 in the first DU-to-CU message.

[0050] In some implementations, the CU 172 includes an LTM CU configuration 1 in the RRC reconfiguration message 316, the first container or the element 1, where the LTM CU configuration 1 associated with the LTM DU configuration 1. To associate the LTM CU configuration 1 with the LTM DU configuration 1, the CU 172 can include the LTM CU configuration 1 and the LTM DU configuration in the element 1. In some implementations, the CU 172 includes LTM CU configuration(s) 2, . . ., N in the RRC reconfiguration message 316 or the second container, where the LTM CU configuration(s) 2, . . . , N associated with the LTM DU configuration(s) 2, . . . , N, respectively. To associate the LTM CU configuration(s) 2, . . . , N with the LTM DU configured on(s) 2, . . . , N , the CU 172 can include the LTM CU configured on(s) 2, . . . , N and the LTM DU configured on(s) in the element(s) 2, . . . , N, respectively. In other implementations, the CU 172 includes, in the element(s) 2, . . ., N, the LTM CU configured on(s) 2, . . . , N associated with the LTM DU configured on(s) 2, . . . , N, respectively. Alternatively, the CU 172 does not include, in the RRC reconfiguration message 316, LTM CU configured on(s) for some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, . . . , N.

[0051] After receiving the RRC reconfiguration message 316, the DU 174 transmits 318 the RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 an RRC reconfiguration complete message (e.g., an RRCReconfigurationComplete message) to the DU 174, which in turn transmits 322 a second DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some implementations, the CU 172 performs security protection (e.g., integrity protection and / or encryption) on the RRC reconfiguration message. For example, the CU 172 generates a message authentication code for integrity (MAC-I) for the RRC reconfiguration message, encrypts the RRC reconfiguration message and the MAC-I to obtain an encrypted RRC reconfiguration message and an encrypted MAC-I, and transmits a PDCP PDU including the encrypted RRCreconfiguration message and encrypted MAC-I to the UE 102 via the DU 174 in the events 316 and 318. When the UE 102 receives the PDCP PDU from the CU 172 via the DU 174 (i.e., events 316 and 318), the UE 102 decrypts the encrypted RRC reconfiguration and encrypted MAC-I to obtain the RRC reconfiguration message and MAC-I and verifies whether the MAC-I is valid. If the UE 102 verifies the MAC-I is invalid, the UE 102 discards or ignores the RRC reconfiguration message. In some implementations, the UE 102 can perform an RRC connection reestablishment procedure in response to the invalid MAC-I. Otherwise, if the UE 102 verifies the MAC-I is valid, the UE 102 can process the RRC reconfiguration. The UE 102 refrains from applying (i.e., executing) the LTM DU configuration 1 until receiving an LTM command activating the LTM DU configuration 1 as described for events 330, 350.

[0052] The events 308 and 310 are collectively referred to in Fig. 3 as an LTM preparation procedure 390. The events 316, 318, 320, 322 are collectively referred to in Fig. 3 as an LTM configuration delivery procedure 394.

[0053] In some implementations, the first CU-to-DU message is a UE Context Modification Request message, and the first DU-to-CU message is a UE Context Modification Response message or UE Context Modification Required message. In the case of the UE Context Modification Required message, the CU 172 can transmit a UE Context Modification Confirm message to the DU 174 in response to UE Context Modification Required message. In some implementations, the second CU-to-DU message is a / ) / . RRC Message Transfer message. In other implementations, the second CU-to-DU message is a UE Context Modification Request message and the DU 174 can transmit a second DU-to-CU message (e.g., UE Context Modification Response message) to the CU 172 in response to the second CU-to-DU message.

[0054] In some implementations, the CU 172 can include a reference LTM CU configuration in the RRC reconfiguration message 316 or the first container. In some implementations, the CU 172 generates the LTM CU configuration 1 (i.e., non-reference LTM CU configuration) as a delta configuration to augment the reference LTM CU configuration. Similarly, in further implementations, the CU 172 generates some or all of the LTM CU configuration(s) 2, . . . , N as delta configuration(s) to augment the reference LTM CU configuration. Alternatively, in the RRC reconfiguration message 316 or the first container, the CU 172 includes the reference LTM CU configuration and does not include anon-reference LTM CU configuration. In some implementations, the CU 172 includes the reference LTM CU configuration and / or the reference LTM DU configuration in an additional container (e.g., reference LTM configuration) and include the additional container in the RRC reconfiguration message 316.

[0055] In some implementations, the reference LTM CU configuration is different from the serving CU configuration. In some implementations, a portion of the reference LTM CU configuration is the same as a portion of the serving CU configuration and the rest of the reference LTM CU configuration is different from the rest of the serving CU configuration. In yet other implementations, the reference LTM CU configuration is the same as the serving LTM CU configuration.

[0056] In some implementations, the CU 172 includes, in the RRC reconfiguration message, a first LTM ID (referred to herein after as ID 1) for identifying the LTM DU configuration 1 or the element 1. In some implementations, the CU 172 includes the ID 1 in the first container or element 1. In some implementations, the CU 172 assigns the ID 1.

[0057] In some implementations, the CU 172 can transmit the ID 1 to the DU 174, and the DU 174 associates the ID 1 with the LTM DU configuration 1 and / or the cell ID 1. In some implementations, the CU 172 includes the ID 1 in the first CU-to-DU message. In other implementations, after receiving the first DU-to-CU message, the CU 172 transmits 312 a third CU-to-DU message including the ID 1 to the DU 174 instead of including the ID 1 in the first CU-to-DU message. In some implementations, in the third CU-to-DU message, the CU 172 can include the LTM DU configuration 1 and the ID 1 and indicate the association between the ID 1 and LTM DU configuration 1. Thus, the DU 174 can directly associate the ID 1 with the LTM DU configuration 1. In other implementations, in the third CU-to-DU message, the CU 172 can include the cell ID 1 and the ID 1 (i.e., the first LTM ID) and indicate the association between the cell ID 1 and the ID 1. Thus, the DU 174 can associate the ID 1 with the LTM DU configuration 1, based on the association between the cell ID 1 and the ID 1 and the association between the cell ID 1 and the LTM DU configuration 1. In yet other implementations, in the third CU-to-DU message, the CU 172 can include the LTM DU configuration 1, the cell ID 1 and / or the ID 1 and indicate the association between the ID 1, LTM DU configuration 1 and / or the cell ID 1. In some implementations, the DU 174 can transmit 314 a third DU-to-CU message to the CU 172 in response to the third CU-to-DU message. In some implementations, the third CU-to-DU message and third DU-to-CUmessage are UE Context Modification Request message and UE Context Modification Response message. The events 312 and 314 are collectively referred to in Fig. 3 as an LTM ID assignment procedure 392. In other implementations, the CU 172 can include the ID 1, the cell ID 1 and / or the LTM DU configuration 1 in the second CU-to-DU message as described above. Thus, the third CU-to-DU message can be omitted.

[0058] In cases where the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 can include the ID 1 in the LTM DU configuration 1, first container or element 1. Alternatively, the DU 174 does not include the ID 1 in the LTM DU configuration 1, first container and / or element 1.

[0059] In some implementations, the CU 172 includes the reference LTM DU configuration in the first container. For example, the CU 172 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In other implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316 and outside the first container. For example, the CU 172 generates a third container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the third container in the RRC reconfiguration message 316. In yet other implementations, the DU 174 includes the reference LTM DU configuration in the first container. For example, the DU 174 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In yet other implementations, the DU 174 generates a fourth container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the fourth container in the first DU-to-CU message 310. In such cases, the CU 172 includes the fourth container in the RRC reconfiguration message 316. Alternatively, the CU 172 retrieves the reference LTM DU configuration and the LTM DU configuration 1 from the fourth container and includes the reference LTM DU configuration and the LTM DU configuration 1 as described above.

[0060] In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM DU configuration. In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM CU configuration.

[0061] In some implementations, the LTM DU configuration 1 includes a plurality of configuration parameters for the UE 102 to communicate with the DU 174 on the first cell.In some implementations, the plurality of configuration parameters include physical layer configuration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE) and / or RLC configuration parameters (e.g., RLC-BearerConfig IE(s)). In some further implementations, the plurality of configuration parameters include a special cell configuration (e.g., SpCellConfig E) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration 1 is CellGroupConfig ^E (e.g., as defined in 3GPP specification 38.331). In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0062] In some implementations, the LTM CU configuration 1 includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 includes a MeasConfig IE and / or a RadioBearerConfig IE (e.g., as defined in 3GPP specification 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some implementations, the LTM DU configuration 1 includes LI measurement configuration 1 (e.g., a CSI-MeasConfig IE) and / or at least one configuration indicator (TCI) state configuration. In other implementations, the LTM CU configuration 1 includes the LI measurement configuration and / or the TCI state configuration(s) 1. In some implementations, the LI measurement configuration includes at least one reference signal (RS) resource configuration 1 and / or at least one report configuration 1. In some implementations, the RS resource configuration(s) 1 configures one or more RSs or one or more RS resources associated with the cell 1. The RS(s) includes SSB(s) and / or CSI-RS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the RS resource configuration(s) 1 includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) 1 is / are (similar to) CSI-ResourceConfig lPfi). In some implementations, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. In some implementations, each of the TCI state configuration(s) 1 configures a TCI state that associates one or two DL RSs with a corresponding quasi -colocation (QCL) type. The DL RS(s) are associated with the cell 1.

[0063] In some implementations, the DU 174 includes the LI measurement configuration 1 and / or the TCI state configuration(s) 1 in a serving DU configuration 1 (e.g., non-LTM DU configuration). In some implementations, the DU 174 includes the serving DU configuration in the first DU-to-CU message. In other implementations, the DU 174 transmits an additional DU-to-CU message including the serving DU configuration to the CU 172. In some implementations, the additional DU-to-CU message is a UE Context Modification Required message. In some implementations, the CU 172 includes the serving DU configuration 1 in the RRC reconfiguration message 316, 318. In other implementations, the CU 172 transmits another RRC reconfiguration message including the serving DU configuration to the UE 102 via the DU 174.

[0064] In some implementations, the DU 174 includes a random access configuration in the LTM DU configuration 1. In other implementations, the DU 174 does not include a random access configuration in the LTM DU configuration 1. In some implementations, if the cell 124 A and first cell are not synchronized, the DU 174 determines to include the random access configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the random access configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines not to include the random access configuration in the LTM DU configuration 1. In some implementations, if the LTM DU configuration 1 includes the random access configuration, the UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration, as described below. Otherwise, if the LTM DU configuration 1 does not include the random access configuration or indicates the UE 102 to skip a random access procedure in LTM, the UE 102 skips or refrains from performing the random access procedure of the event 332 in response to the LTM DU configuration 1 excluding the random access configuration.

[0065] In some implementations, the DU 174 includes random access configuration parameters in the LTM DU configuration 1 and / or the reference LTM DU configuration regardless of whether the cell 124 A and first cell are synchronized or not. In some implementations, the UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration parameters, as described below. In someimplementations, the random access configuration parameters configure physical random access channel (PRACH) resources, an association between SSB and PRACH resources, and / or one or more PRACH occasions.

[0066] In some implementations, if the cell 124 A and first cell are synchronized, the DU 174 determines to include, in the LTM DU configuration 1, a first indication configuring the UE 102 not to perform a random access procedure on the first cell. Otherwise, if the cell 124 A and first cell are not synchronized, the DU 174 determines not to include the first indication in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to include the first indication in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to not include the first indication in the LTM DU configuration 1. If the LTM DU configuration 1 includes the first indication, the UE 102 skips or refrains from performing the random access procedure of the event 332 in accordance with or in response to the first indication. Otherwise, if the LTM DU configuration 1 does not include the first indication, the UE 102 performs the random access procedure in accordance with the random access configuration in the event 332, in response to the LTM DU configuration 1 excluding the first indication, as described below.

[0067] In some implementations, the DU 174 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In other implementations, the DU 174 does not include a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In some implementations, the DU 174 includes an LTM cell switch information in the LTM DU configuration 1. In some implementations, the DU 174 includes the random access configuration (parameters) in the LTM cell switch information (e.g., Itm-CellSw itchinfo field or LTM-CellSw itchinfo IE). In some implementations, if the cell 124 A and first cell are not synchronized, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the cell 124 A and first cell are synchronized, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 hassynchronized in UL with the first cell, the DU 174 determines not to include the reconfiguration with sync configuration in the LTM DU configuration 1. In some implementations, if the LTM DU configuration 1 includes the reconfiguration with sync configuration, the UE 102 performs the random access procedure in the event 332 as described below, in response to or in accordance with the reconfiguration with sync configuration. Otherwise, if the LTM DU configuration 1 does not include the reconfiguration with sync configuration, the UE 102 skips or refrains from performing the random access procedure of the event 332.

[0068] In some implementations, the DU 174 includes a cell ID (i.e., cell ID 1) of cell 1 (i.e., the first cell) in the LTM DU configuration 1. In one implementation, the cell ID 1 can be a PCI. In another implementation, the cell ID 1 is a CGI. In some implementations, the cell ID 1 included in the LTM DU configuration l is a PCI, while the cell ID 1 included in the first CU-to-DU message is a CGI. In some further implementations, the LTM DU configuration 1 includes a cell index 1 indexing the cell ID 1 or the first cell. The cell index 1 is not a cell ID. The cell index takes fewer bits than the cell ID. In some implementations, the CU 172 sets the cell index 1 to a value and includes the cell index 1 in the first CU-to-DU message of the event 308.

[0069] In some implementations, after (e.g., in response to) receiving one or some of the at least one measurement report of the event 304, the base station 104 (i.e., the CU 172 or DU 174) determines to prepare additional cell(s) (i.e., cell(s) 2, . . ., N) of the base station 104 for LTM for the UE 102. In one implementation, the base station 104 determines to prepare the additional cell(s) for LTM for the UE 102 because the at least one measurement report indicates that the additional cell(s) could be used by the base station 104 to communicate with the UE 102. The additional cell(s) can include the cell 124C and / or cell(s) other than the cells 124A, 124B and 124C. In some implementations, if the L3 measurement report(s) indicates that signal strength and / or quality of a particular cell of the additional cell(s) is above a respective predetermined threshold and / or is better than the cell 124A, the CU 172 determines to prepare the particular cell for LTM for the UE 102. In other implementations, if the LI measurement report(s) indicates that signal strength and / or quality of a particular cell of the additional cell(s) is above a first predetermined threshold and / or is better than the cell 124A, the DU 174 determines to prepare the particular cell for LTM for the UE 102. In one implementation, the respective predetermined threshold(s) for the additional cells can be different from the first predetermined threshold. In another implementation, the respectivepredetermined threshold(s) for the additional cell(s) can be the same as the first predetermined threshold. In some implementations, the respective predetermined thresholds for the additional cells can be the same or different. Alternatively, the base station 104 determines to prepare the additional cell(s) for the UE 102 regardless of whether a measurement report is received from the UE 102 or not.

[0070] In cases where the CU 172 determines to prepare the additional cell(s), the CU 172 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the DU 174 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390. In cases where the DU 174 determines to prepare the additional cell(s), the DU 174 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the CU 172 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390.

[0071] In some implementations, the CU 172 and DU 174 perform LTM preparation procedure(s) 2, . . . , N to prepare the cell(s) 2, . . . , N, respectively, similar to the procedure 390. In some such implementations, the CU 172 includes the cell ID(s) 2, . . ., N in CU-to- DU message(s) 2, . . . , N in the LTM preparation procedure(s) 2, . . . , N, respectively, similar to the first CU-to-DU message. In the LTM preparation procedure(s) 2, . . . , N, the DU 174 generates LTM DU configuration(s) 2, . . . , N configuring the cell(s) 2, . . . , N and includes the LTM DU configured on(s) 2, . . ., N in DU-to-CU message(s) 2, .., N, respectively, as described for the LTM DU configuration 1. In cases where the DU 174 receives the CU-to- DU message(s) 2, . . . , N, the DU-to-CU message(s) 2, . . . , N responds to the CU-to-DU message(s) 2, . . ., N, respectively . “N” is an integer and larger than one. For example, “N” is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 14, 15 or 16. In another example, the maximum number of “N” is 4, 8, 16 or 32. Examples and implementations of the LTM DU configuration 1 can apply to the LTM DU configured on(s) 2, . . . , N.

[0072] In other implementations, the CU 172 and DU 174 perform a single LTM preparation procedure (i.e., the LTM preparation procedure 390) to prepare the cell(s) 1, 2, . . ., N. In such cases, the DU 174 includes the LTM DU configured on(s) 1, 2, . . ., N for the cell(s) 1, 2, . . ., N, respectively in the first DU-to-CU message. In some implementations, in the first DU-to-CU message, the DU 174 includes the cell ID(s) 1, 2, . . ., N respectively associated with the LTM DU configured on(s) 1, 2, . . . , N to indicate that the LTM DUconfiguration(s) 1, 2, . . ., N are configured for the cell ID(s) 1, 2, . . ., N, respectively. In cases where the CU 172 determines to perform the LTM preparation procedure 390, the CU 172 includes the cell ID(s) 1, 2, . . ., N in the first CU-to-DU message to request the DU 174 to prepare the cell(s) 1, 2, ..., N, respectively, for LTM.

[0073] After receiving the LTM DU configuration(s) 2, . . . , N from the DU 174, the CU 172 can include the LTM DU configuration(s) 2, . . . , N in the first container. In some implementations, the CU 172 can include the LTM DU configuration(s) 2, . . ., N in element(s) 2, . . . , N, respectively, and includes the element(s) 2, . . . , N in the first container. In some implementations, the CU 172 includes, in the RRC reconfiguration message, LTM ID(s) (i.e., ID(s) 2, . . . , N) for identifying the LTM DU configuration(s) 2, . . . , N, respectively. In some implementations, the CU 172 includes the ID(s) 2, . . . , N in the first container. For example, the CU 172 can include the ID(s) 2, . . . , N and LTM DU configuration(s) 2, . . . , N in the element(s) 2, . . . , N in the first addition or modification list.

[0074] In some implementations, the CU 172 assigns the ID(s) 2, . . . , N for the LTM DU configuration(s) 2, . . ., N, respectively. In other implementations, the CU 172 receives the ID(s) 2, . . . , N from the DU 174 in the first DU-to-CU message of the procedure 390. In yet other implementations, the CU 172 receives, from the DU 174, the ID(s) 2, . . ., N in the DU- to-CU message(s) 2, . . . , N of the LTM preparation procedure(s) 2, . . . , N, respectively.

[0075] In some implementations, the CU 172 can perform an LTM ID assignment procedure with the DU 174 for each of the LTM DU configuration(s) 2, . . ., N, similar to the procedure 392. In other implementations, the CU 172 can include the ID(s) 2, . . ., N and the LTM DU configuration(s) 2, . . ., N in the third CU-to-DU message and indicate the association between the ID(s) 2, . . . , N and the LTM DU configuration(s) 2, . . . , N, respectively. Thus, the DU 174 can associate the LTM DU configuration(s) 2, . . . , N with the ID(s) 2, . . ., N, respectively. In yet other implementations, the CU 172 can include the cell ID(s) 2, . . . , N and the ID(s) 2, . . . , N in the third CU-to-DU message and indicate the association between the cell ID(s) 2, . . . , N and the ID(s) 2, . . . , N, respectively. Thus, the DU 174 can associate the LTM DU configuration(s) 2, . . . , N with the ID(s) 2, . . . , N, respectively, based on the association between the cell ID(s) 2, . . . , N and the ID(s) 2, . . . , N and the association between the cell ID(s) 2, . . . , N and the LTM DU configuration(s) 2, . . . , N, respectively. In other implementations, the CU 172 can include the ID(s) 2, . . ., N, the cell ID(s) 2, . . . , N and / or the LTM DU configuration(s) 2, . . . , N in the second CU-to-DUmessage as described above. Thus, the third CU-to-DU message can be omitted. In yet other implementations, the CU 172 can include the ID(s) 2, . . ., N in the first CU-to-DU message and indicate the ID(s) 2, . . . , N is / are respectively associated with the cell ID(s) 2, . . . , N. In one implementation, the DU 174 includes the ID(s) 2, . . ., N in the LTM DU configuration(s) 2, . . . , N. Thus, the CU 172 does not include the ID(s) 2, . . . , N in the RRC reconfiguration message, first container and / or element(s) 2, . . ., N.

[0076] In some alternative implementations, the DU 174 assigns the ID(s) 2, . . ., N. In some implementations, the DU 174 includes the ID(s) 2, . . ., N in the first DU-to-CU message of the procedure 390. In yet other implementations, the DU 174 includes the ID(s) 2, . . . , N in the DU-to-CU message(s) 2, . . . , N of the LTM preparation procedure(s) 2, . . . ,N. The CU 172 can include the ID(s) 2, . . . , N in the RRC reconfiguration message. In other implementations, the DU 174 includes the ID(s) 2, . . ., N in the LTM DU configuration(s) 2, . . . , N. Thus, the CU 172 does not include an ID (e.g., LTM ID) identifying each of the LTM DU configuration(s) 2, . . ., N in the RRC reconfiguration message, first container and / or element 1.

[0077] In some alternative implementations, the CU 172 can generate a second container including the LTM DU configuration(s) 2, . . . , N or element(s) 2, . . . , N instead of using the first container. The CU 172 then transmits an additional RRC reconfiguration message including the second container to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits an additional RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some implementations, the second container can be a second addition or modification list (e.g., Itm- ConfigToAddModList field, LTM-ConfigToAddModList IE, Itm- CandidateConfigToAddModList field, or LTM-CandidateConfigToAddModList ^E), and each of the element(s) 2, . . ., N can be an addition or modification IE (e.g., Itm-ConfigToAddMod field, LTM-ConfigToAddMod IE, Itm-CandidateConfigToAddMod field, or LTM- CandidateConfigToAddMod IE). When the UE 102 receives the second addition or modification list, the UE 102 can store the second addition or modification list together with the first addition or modification list, e.g., in a variable in its random access memory (RAM).

[0078] In some implementations, the DU 174 includes cell ID(s) 2, . . . , N in the LTM DU configuration(s) 2, . . . , N to identify the cell(s) 2, . . . , N, respectively. In one implementation, each of the cell ID(s) 2, . . . , N is a PCI. In some further implementations, the LTM DUconfiguration(s) 2, . . . , N includes cell index(es) 2 , . . . , N indexing the cell ID(s) 2, . . . , N or the cell(s) 2, . . . , N, respectively. In some cases where the CU 172 prepares the cell(s) 2, . . . , N for LTM in the procedure 390, the CU 172 sets the cell index(es) 2, . . N to different value(s) and includes the cell index(es) 2, . . . , N in the first CU-to CU-to-DU message of the event 308. In some cases where the CU 172 prepares the cell(s) 2, . . ., N in the additional LTM preparation procedure(s), the CU 172 sets the cell index(es) 2, . . ., N to different values and include the cell index(es) 2, . . . , N in CU-to-DU message(s) of the additional LTM preparation procedure(s). The CU 172 sets the cell index(es) 1, . . ., N to different values. In some implementations, the cell ID(s) 1, . . ., N in the LTM DU configuration(s) 1, . . ., N are different from the cell ID(s) 1, . . ., N in the CU-to-DU message(s) described above.

[0079] In some implementations, each of the LTM DU configuration(s) 1, . . ., N includes physical configuration parameters, MAC configuration parameters, RLC configuration parameters and / or LI measurement configuration(s). In some implementations, each of the LTM DU configuration(s) 1, . . ., N can be a CellGroupConfig IE (e.g., as defined in 3GPP specification 38.331). In other implementations, each of the LTM DU configuration(s) 1, . . . , N include configuration parameters included in a CellGroupConfig IE (e.g., as defined in 3 GPP specification 38.331). In some further implementations, the plurality of configuration parameters in each of the LTM DU configuration(s) include a particular special cell configuration (e.g., SpCellConfig E) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration(s) 1, . . ., N are CellGroupConfig IE(s) (e.g., as defined in 3GPP specification 38.331). In other implementations, the LTM DU configuration(s) 1, . . ., N include configuration parameters in the CellGroupConfig IE.

[0080] In some implementations, the CU 172 can include one or more additional LTM CU configurations in at least one of the element(s) 2, . . . , N, the first container or the second container. Each of the additional LTM CU configurations are associated with a particular LTM DU configuration of the LTM DU configuration(s) 2, . . . , N. Examples and implementations of the additional LTM CU configurations are similar to the LTM CU configuration 1.

[0081] In some implementations, the CU 172 determines to release the LTM DU configuration M of the LTM DU configuration(s) 1, . . . , N (or the element M of the element(s) 1, . . . , M). 1 < M < N. In response to the determination, the CU 172 transmits anRRC reconfiguration message to the UE 102 via the DU 174 to indicate the UE 102 to release the LTM DU configuration M or element M. In one implementation, the CU 172 generates a release list including the ID (i.e., LTM ID) M for releasing the LTM DU configuration M or element M and includes the release list in the RRC reconfiguration message. In response to the RRC reconfiguration message, the UE 102 releases the LTM DU configuration M or element M and transmits an RRC reconfiguration complete message to the CU 172 via the DU 174. In response to the determination, the CU 172 transmits a CU-to-DU message to the DU 174 to indicate the DU 174 to release the LTM DU configuration M. To indicate the DU 174 to release the LTM DU configuration M, the CU 172 can include the cell ID M or the ID (i.e., LTM ID) M in a release indication (e.g., a field or IE) in the CU-to-DU message. In response, the DU 174 releases the LTM DU configuration M and transmits a DU-to-CU message to the CU 172. In some implementations, the CU-to-DU message and DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0082] In other implementations, the DU 174 determines to release the LTM DU configuration K. In response to the determination, the DU 174 transmits a DU-to-CU message to the CU 172 to release the LTM DU configuration K. To indicate the LTM DU configuration K is released, the DU 174 can include the cell ID K or the ID (i.e., LTM ID) K in a release indication (e.g., a field or IE) in the DU-to-CU message. 1 < K < N. After (e.g., in response to) receiving the DU-to-CU message, the CU 172 generates a release list including the ID (i.e., LTM ID) K to release the LTM DU configuration K or element K and transmits an RRC reconfiguration message including the release list to the UE 102 via the DU 174. In response, the UE 102 releases the LTM DU configuration K or element K and transmits an RRC reconfiguration complete message to the UE 102 via the DU 174. The CU 172 can transmit a CU-to-DU message to the DU 174 in response to the DU-to-CU message. In some implementations, the DU-to-CU message and CU-to-DU message are a UE Context Modification Required message and a UE Context Modification Confirm message, respectively.

[0083] After receiving the RRC reconfiguration in the event 318 or transmitting the RRC reconfiguration complete message in the event 320, the UE 102 transmits 324 at least one measurement report to the DU 174, similar to the event 304. In some implementations, the DU 174 may transmit 326 a DU-to-CU message including the at least one measurement report to the CU 172, similar to the event 306. In other implementations, the DU 174 doesnot transmit the at least one measurement report to the CU 172. In some implementations, the at least one measurement report of the event 324 include LI measurement report(s) or L3 measurement repot(s), as described for the event 304. In some implementations, the UE 102 transmits 324 the at least one measurement report on PUCCH(s) and / or PUSCH(s) to the DU 174, similar to the event 304. In other implementations, the UE 102 transmits 324 at least one MAC CE including the at least one measurement report to the DU 174, similar to the event 304. In some implementations, the UE 102 does not transmit the LI measurement report(s) in format of RRC message(s) to the DU 174.

[0084] In some implementations, the UE 102 transmits 324 the at least one measurement report to the DU 174 in accordance with at least one measurement configuration. The at least one measurement configuration configures the UE 102 to perform measurements and report measurement results. The CU 172 transmits the at least one measurement configuration to the UE 102 via the DU 174. For example, the CU 172 can transmit one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration to the UE 102 via the DU 174 in the event 302 and / or 316 and / or after the event 306 or 316. The one or more RRC messages may or may not include the RRC reconfiguration message of the event 316. In accordance with the at least one measurement configuration, the UE 102 performs measurements on one or more reference signals. The one or more reference signals can include one or more SSBs and / or one or more CSI-RSs. The UE 102 obtains the at least one LI measurement result and / or at least one L3 measurement result from the measurements and includes the at least one LI measurement result and / or at least one L3 measurement result in the at least measurement report of the event 324. The DU 174 transmits the one or more reference signals on the cell 124A, the cell 1 and / or the cell(s) 2, . . . , N. The one or more reference signals can be CSI-RS(s) or SSB(s).

[0085] In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)), as described for the event 304. In other implementations, the at least one measurement configuration includes or is LI measurement configuration(s), as described above. In yet other implementations, the LI measurement configuration(s) can be CSI-MeasConfig IE(s) (e.g., as defined in 3GPP specification 38.331 vl8.0.0 and / or later versions). The LI measurement configuration(s) can include RS resource configuration(s) and / or report configuration(s). The UE 102 transmits 324 the LI measurement report(s) on UL resources (e.g., PUCCH resources or PUSCH resources) to the DU 174 in accordance with the report configuration(s). The DU174 receives the LI measurement report(s) on the UL resources in accordance with the report configuration(s). In some implementations, the report configuration(s) are or are similar to CSI-ReportConfig IE(s). In other implementations, each of the report configuration(s) is a new RRC IE. In some implementations, (each of) the report configuration(s) configures periodically reporting and / or event-triggered reporting of the LI measurement result(s).

[0086] In some implementations, the LI measurement report(s) is / are CSI report(s). In other implementations, the LI measurement report(s) is / are MAC CE(s). In some implementations, each of the measurement report(s) includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) and / or the report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). Depending on the implementation, the quantized measurement values include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0087] In yet other implementations, the at least one measurement configuration includes new-type measurement configuration(s) (e.g., LTM measurement configuration(s)). The new-type measurement configuration can be newly defined (e.g., as defined in a 3GPP specification vl 8.0.0 and / or later versions). In some implementations, the new-type measurement configuration(s) includes reference signal resource configuration(s) configuring resources where the DU 174 transmits reference signal(s). For example, the reference signal resource configuration(s) include CSI-RS(s) and / or SSB(s). In one implementation, the reference signal resource configuration(s) is / are CSI-ResourceConfig E(s). In another implementation, the new-type measurement configuration(s) include measurement report configuration(s), as described above. The UE 102 transmits the measurement report(s) on PUCCH(s) or MAC CE(s) to the DU 174 in accordance with the measurement report configuration(s). The DU 174 receives the measurement report(s) on PUCCH(s) or MAC CE(s) in accordance with the measurement report configuration(s). In such cases, the measurement report(s) can be LI measurement report(s) or new-type measurement report(s) (e.g., LTM measurement report(s)). In some implementations, the new-type measurementconfiguration includes configuration parameters newly defined (e.g., as defined in a 3GPP specification vl 8.0.0 and / or later versions).

[0088] After (e.g., in response to) receiving the at least one measurement report in the event 324, the DU 174 generates a first LTM command to activate the LTM DU configuration 1 (i.e., the first LTM command commands the UE 102 to apply the LTM DU configuration 1 or to perform a serving cell change to the cell 1). The DU 174 then transmits 330 the first LTM command to the UE 102. In some implementations, the DU 174 transmits the first LTM command on the cell 124A to the UE 102. In other implementations, the DU 174 transmits the first LTM command on the cell 124D to the UE 102. In some implementations, the DU 174 can include the ID 1 in the first LTM command to indicate the LTM DU configuration 1 or element 1, and the UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 in accordance with the ID 1.

[0089] In other implementations, the DU 174 can include the cell index 1 indexing the cell ID 1 in the first LTM command. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1, based on the cell index 1. Before receiving the first LTM command, the UE 102 retrieves the cell index 1 from the LTM DU configuration 1 or element 1, and establishes an association 1 between the cell index 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell index 1, before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell index 1 and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell index(es) 2, . . . , N from the LTM DU configuration(s) or element(s) 2, . . . , N and establishes association(s) 2, . . . , N between the cell index(es) 2, . . . , N and the LTM DU configuration(s) or element(s) 2, . . . , N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, . . ., N to obtain the cell index(es) 2, . . . , N, before receiving the first LTM command.

[0090] In yet other implementations, the DU 174 includes cell ID 1 in the first LTM command, where the cell ID 1 identifies the cell 1. In some implementations, the cell ID 1 included in the first LTM command is the same as the cell ID 1 included in the first CU-to- DU message. In other implementations, the DU 174 determines the cell ID 1 (e.g., PCI) included in the first LTM command from the cell ID 1 (e.g., CGI) received in the first CU-to- DU message. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 orelement 1, based on the cell ID 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID 1 from the LTM DU configuration 1 or element 1, and establishes an association 1 between the cell ID 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell ID 1, before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell ID 1 (received in the first LTM command) and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID(es) 2, . . . , N from the LTM DU configuration(s) or element(s) 2, . . . , N and establishes association(s) 2, . . . , N between the cell ID(es) 2, . . . , N and the LTM DU configuration(s) or element(s) 2, . . ., N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, . . . , N to obtain the cell ID(es) 2, . . . , N, before receiving the first LTM command. In some implementations, the DU 174 has a mapping table to store mappings between the PCI(s) 1, . . . , N and the CGI(s) 1, . . . , N for the cell(s) 1, ..., N, respectively.

[0091] In yet other implementations, the DU 174 can include a bit map in the first LTM command to activate the LTM DU configuration 1, instead of the ID 1 or cell index 1. The number of bits in the bit map is larger than or equal to “N”. In one implementation, bit 1, . . . , N corresponds to the cell index(es) 1, . . ., N, the ID(s) 1, . . ., N, the LTM DU configuration(s) 1, . . ., N or the element(s) 1, . . ., N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 1) in the bit map to a first value to indicate the cell index 1, the ID 1, the LTM DU configuration 1 or the element 1. Thus, the UE 102 can determine the cell index 1, the ID 1, LTM DU configuration 1, or element 1 in accordance with the bit 1 set to the first value in the bit map. In another implementation, bit 0, . . . , N-l corresponds to the cell index(es) 1, . . . , N, the ID(s) 1, . . . , N, the LTM DU configuration(s) 1, . . . , N or the element (s) 1, . . . , N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 0) in the bit map to a first value to indicate the cell index 1, the ID 1 the LTM DU configuration 1 or the element 1. Thus, the UE 102 can determine the cell index 1, the ID 1 LTM DU configuration 1 or element 1 in accordance with the bit 0 set to the first value in the bit map. In such implementations, the DU 174 sets the remaining bits in the bit map to a second value to indicate that the rest of the LTM DU configuration(s) 1, . . . , N is / are not activated. In some implementations, the first value is one and the second value is zero. In other implementations, the first value is zero and the second value is one. Generally, if the DU 174 determines to activate the LTM DU configuration L or change a serving cell to the cell L forthe UE 102, the DU 174 can set the corresponding bit (e.g., bit L or bit Z-7) in the bit map to the first value and set the remaining bits to the second value, where 1 <L < N. In some implementations, the DU 174 sets at most one bit in the bit map to the first value.

[0092] After determining or identifying the LTM DU configuration 1 or element 1, the UE 102 then applies the LTM DU configuration 1 and / or LTM CU configuration, after (e.g., in response to) receiving the first LTM command.

[0093] In some implementations, the at least one measurement report (e.g., LI measurement report(s) or new-type measurement report(s)) of the event 324 includes at least one measurement result for the first cell, TRP(s) of the first cell or reference signal(s) transmitted on the first cell. The reference signal(s) can be CSI-RS(s) or SSB(s). The DU 174 determines to activate the LTM DU configuration 1 or transmit the first LTM command, based on the at least one measurement result. In some implementations, the DU 174 determines to activate the LTM DU configuration 1 because, when or if the at least one measurement result is above a second predetermined threshold. In some implementations, the at least one measurement result includes Ll-RSRP value(s), Ll-RSRQ value(s) and / or Ll-SINR value(s). In other implementations, the at least one measurement result includes RSRP value(s), RSRQ value(s) and / or SINR value(s) for the new-type measurement report(s). In some implementations, the second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is larger than the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell is suitable for communication with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This indicates that the first cell is suitable for communication with the UE 102. Thus, the DU 174 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold for the UE 102.

[0094] In some implementations, the at least one measurement report (e.g., L3 measurement report(s)) of the events 324 and 326 includes at least one measurement result for the first cell. The CU 172 determines to activate the LTM DU configuration 1 or transmit the first LTM command, because the at least one measurement result indicates that signalstrength or quality of the first cell is above a second predetermined threshold. The second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is larger than the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell is suitable for communication with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This also indicates that the first cell is suitable for communication with the UE 102. Thus, the CU 172 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold. In response to the determination, the CU 172 transmits 328 a fourth CU-to-DU message to the DU 174 to activate the LTM DU configuration 1 or trigger a serving cell change to the cell 1 for the UE 102. In some implementations, the CU 172 includes the ID 1 in the fourth CU-to-DU message. In other implementations, the CU 172 includes the cell index 1 in the fourth CU-to- DU message. In response to the fourth CU-to-DU message, the DU 174 transmits 330 the first LTM command to the UE 102 and, depending on the implementation, transmits a fourth DU-to-CU message to the CU 172. In some implementations, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the cell index 1. In other implementations, the CU 172 can include the cell ID 1 in the fourth CU-to-DU message. Thus, the DU 174 determines to activate the LTM DU configuration 1 in accordance with the cell ID 1. In yet other implementations, the CU 172 can include the ID 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the ID 1. In some implementations, the fourth CU-to-DU message and fourth DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In other implementations, the fourth CU-to-DU message and / or fourth DU-to-CU message are new interface messages, (e.g., Fl application protocol (F1AP) messages (e.g., as defined in 3GPP specification 38.473 vl8.0.0 and / or later versions)).

[0095] In some implementations, when or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 330, the DU 174 transmits 329 to theCU 172 a DU-to-CU message indicating LTM (being) executed. In some implementations, the DU 174 includes the cell ID 1 or the ID 1 (i.e., LTM ID) in the DU-to-CU message 329 to indicate that the DU 174 is to activate the LTM DU configuration 1 or trigger a fast serving cell change (i.e., an LTM serving cell change). The DU can transmit the DU-to-CU message 329 to the CU 172 before or after transmitting the LTM command 330.

[0096] In some implementations, the first LTM command is a MAC CE included in a MAC PDU that the UE 102 receives from the DU 174 in the event 330. The MAC CE can be a new MAC CE (e.g., as defined in 3GPP specification 38.321 vl8.0.0 and / or later versions). In one implementation, the DU 174 includes a subheader identifying the new MAC CE in the MAC PDU and the UE 102 identifies the new MAC CE in the MAC PDU in accordance with the subheader. The subheader can include a logical channel ID or extended logical channel ID (e.g., as defined in a 3 GPP specification) to identify the new MAC CE. For example, the logical channel ID or extended logical channel ID are newly defined (e.g., as defined in 3GPP specification 38.321 vl8.0.0 and / or later versions). In other implementations, the first LTM command is a DCI that the UE 102 receives on a PDCCH from the DU 174 in the event 330. The DU 174 generates a CRC for the DCI, scrambles the CRC with a first C-RNTI of the UE 102, and transmits the DCI and scrambled CRC on the PDCCH in the event 330. In one implementation, a format of the DCI can be an existing DCI format (e.g., as defined in a 3GPP specification (e.g., 38.212)). In another implementation, the format of the DCI can be a new DCI format (e.g., as defined in a 3GPP specification (e.g., 38.212 vl 8.0.0 or later versions)). In some implementations, the DU 174 assigns the first C-RNTI for communication with the UE 102 on the cell 124 A.

[0097] In some implementations, the DU 174 does not perform security protection (e.g., integrity protection and / or encryption) on the first LTM command. This speeds up processing the first LTM command in the UE 102 because the UE 102 does not perform security check (e.g., decryption and / or integrity check) on the first LTM command.

[0098] In some implementations, after receiving the first LTM command, the UE 102 may transmit 331 an acknowledgement to the DU 174 on the cell 124A or cell 124D to indicate that the UE 102 receives the first LTM command. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE (e.g., as defined in 3GPP specification 38.321 vl7.2.0 and / or later versions). In another example, the MAC CE is anew MAC CE (e.g., as defined in 3GPP specification 38.321 V18.0.0 and / or later versions). In yet other implementations, the acknowledgement is a PUCCH transmission.

[0099] In some implementations, the CU 172 transmits 316 the RRC reconfiguration message in response to the L3 measurement report 306 for the first cell. To configure the UE 102 to transmit the L3 measurement report 306, the CU 172 can transmit a first RRC reconfiguration message including the L3 measurement configuration (e.g., MeasConfig IE) to the UE 102 before the event 306. In some implementations, the DU 174 transmits 330 the first LTM command in response to the LI measurement report(s) 324 for the first cell. To configure the UE 102 to transmit the LI or new-type measurement report(s) 324, the CU 172 can transmit a second RRC reconfiguration message including the LI or new-type measurement configuration(s) to the UE 102. In some implementations, the first and second RRC reconfiguration messages can be the same message (i.e., the same instance). In other implementations, the first and second RRC reconfiguration messages are different messages. In some implementations, the second RRC reconfiguration message is the RRC reconfiguration message of the event 316. In other implementations, the second RRC reconfiguration message is different from the RRC reconfiguration message of the event 316.

[0100] After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 the first cell. The UE 102 identifies the LTM DU configuration 1 in accordance with the LTM ID 1, the cell ID 1 or the cell index 1 received in the first LTM command and applies the LTM DU configuration 1 to communicate with the DU 174 on the first cell. In some implementations, the UE 102 disconnects from the cell 124A, after (e.g., in response to) receiving the first LTM command or after transmitting 331 the acknowledgement. In some implementations, the UE 102 stops communicating on the cell 124A after (e.g., in response to) receiving 330 the first LTM command or transmitting 331 the acknowledgement. In some implementations, the UE 102 accesses 332 the first cell by performing a random access procedure on the first cell with the DU 174, in response to receiving the first LTM command. In other implementations, the UE 102 skips a random access procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174 in the event 332, after (e.g., in response to) receiving the first LTM command. In some implementations, the UE 102 transmits the first transmission using configuration parameters included in the LTM DU configuration 1. In some implementations, the configuration parameters include a PUSCH configuration, a PUCCH configuration and / or a UL grant.

[0101] In some implementations, the DU 174 configures the access of the UE 102 to the first cell, including whether or not the UE 102 performs a random access procedure, in the LTM DU configuration 1. When receiving the first LTM command, the UE 102 determines whether to perform a random access procedure on the first cell in accordance with the LTM DU configuration 1. If the LTM DU configuration 1 configures the UE 102 to perform a random access procedure, the UE 102 performs a random access procedure on the first cell in the event 332, in order to connect to the first cell. For example, the LTM DU configuration 1 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) to configure that the UE 102 performs a random access procedure when the UE 102 receives an LTM command for the first cell. In other implementations, in the LTM DU configuration 1, the DU 174 configures the UE 102 to skip a random access procedure for an LTM serving cell change to the first cell. In such cases, after receiving the first LTM command, the UE 102 skips the random access procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174 in the event 332. In some implementations, the DU 174 excludes a reconfiguration with sync configuration in the LTM DU configuration 1 to configure the UE 102 skipping a random access procedure for an LTM serving cell change to the first cell. In other implementations, the DU 174 includes an indication in the LTM DU configuration 1 to indicate skipping a random access procedure for an LTM serving cell change to the first cell.

[0102] In other implementations, the LTM DU configuration 1 includes the reconfiguration with sync configuration or the random access configuration for an LTM serving cell change to the first cell. In such cases, the DU 174 configures whether the UE 102 performs a random access procedure on the first cell in an LTM command. Thus, the UE 102 determines whether to perform a random access procedure on the first cell in the event 332 in accordance with the first LTM command. In some implementations, the DU 174 includes, in the first LTM command, an indication (e.g., a field) indicating skipping a random access procedure. In response to the indication or the first LTM command including the indication, the UE 102 skips a random access procedure and directly transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to access the first cell. In other implementations, the DU 174 excludes the indication in the first LTM command to configure the UE 102 to perform a random access procedure. In response to the first LTM command excluding the indication, the UE 102 performs a random access procedure on the first cell to access the first cell. In some other implementations, the DU 174includes a timing advance (TA) value in the first LTM command to indicate skipping a random access procedure. In response to receiving the TA value or the first LTM command including the TA value, the UE 102 skips a random access procedure and transmits the first transmission on the first cell to access the first cell, using the timing advance value. In yet other implementations, the DU 174 excludes, in the first LTM command, a timing advance value to configure the UE 102 to perform a random access procedure. In response to the first LTM command excluding a timing advance command, the UE 102 performs a random access procedure on the first cell to access the first cell.

[0103] In some implementations, the random access procedure is a four-step random access procedure. In other implementations, the random access procedure is a two-step random access procedure. In some implementations, the random access procedure is a contention-free random access procedure. In other implementations, the random access procedure is a contention-based random access procedure. In cases where the random access procedure is a four-step random access procedure, the UE 102 transmits a Message 3 including a UE ID to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., a Message 4) to the UE 102 in response to the Message 3. In cases where the random access procedure is a two-step random access procedure, the UE 102 transmits a Message A including the UE ID to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., Message B) to the UE 102 in response to the Message A. In some implementations, when the UE 102 receives the contention resolution message from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell). In some implementations, the LTM DU configuration 1 includes a second C-RNTI and the UE ID is the second C-RNTI of the UE 102. In such implementations, the contention resolution message is a PDCCH transmission addressed to the second C-RNTI. In other implementations, the LTM DU configuration 1 does not include a C-RNTI, the UE ID is the first C-RNTI. In such implementations, the contention resolution message is a PDCCH transmission addressed to the first C-RNTI. In some implementations, the DU 174 includes the second C-RNTI in the reconfiguration with sync configuration. In other implementations, the DU 174 includes the second C-RNTI in the LTM cell switch information.

[0104] In cases where the LTM DU configuration 1 includes a dedicated random access preamble, the random access procedure is a contention free random access procedure. Insuch cases, the UE 102 transmits the dedicated random access preamble to the DU 174 via the first cell. When the UE 102 receives a random access response including an ID of the dedicated random access preamble from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell).

[0105] If the DU 174 configures the UE 102 to perform a random access procedure on the first cell as described above, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives Message 3, Message A, or the dedicated preamble in the random access procedure. If the DU 174 configures the UE 102 to skip a random access procedure, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives the first transmission.

[0106] In some implementations, the UE 102 transmits the first transmission (e.g., the PUSCH transmission) on the first cell using a UL grant. In some implementations, the first LTM command includes the UL grant. In other implementations, when the UE 102 performs an LTM serving cell change to the first cell in response to the first LTM command, the UE 102 receives a first DCI including the UL grant on a PDCCH on the first cell. In some implementations, the UE 102 attempts to receive the first DCI or the UL grant by monitoring one or more PDCCHs on the first cell in accordance with the LTM DU configuration 1, when the UE 102 switches to the first cell in response to the first LTM command. While monitoring one or more PDCCHs on the first cell, the UE 102 receives the first DCI and a CRC of the first DCI on the PDCCH. In cases where the LTM DU configuration 1 includes the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the second C-RNTI. In cases where the LTM DU configuration 1 does not include the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the first C-RNTI.

[0107] In some implementations, the CU 172 transmits at least one first TCI state configuration to the UE 102 via the DU 174. In some implementations, each of the first TCI state configuration(s) configures a TCI state for the UE 102 to transmit and / or receive data and / or control signal on the first cell. Each TCI state associates one or two DL RSs with a corresponding QCL type and the DL RS(s) are, in some implementations, associated with a particular cell of the cell(s) 1, . . ., N. In some implementations, the CU 172 receives a DU- to-CU message including the first TCI state configuration(s) from the DU 174 and transmitsan RRC message including the first TCI state configured on(s) to the UE 102 via the DU 174. In further implementations, the DU 174 includes the first TCI state configured on(s) in a serving DU configuration (e.g., CellGroupConfig IE) and includes the serving DU configuration in the DU-to-CU message. In some implementations, the DU 174 includes the LTM DU configuration 1 in a first interface protocol lE / field in the message 312, and includes the serving DU configuration in a second interface protocol lE / field in the DU-to- CU message.

[0108] In some implementations, the first interface protocol lE / field is defined as part of a format of the DU-to-CU message. The CU 172 includes the serving DU configuration in the RRC message. In some implementations, the CU 172 refrains from including the serving DU configuration in a container for LTM (e.g., the first container). In other implementations, the CU 172 includes the first TCI state configured on(s) in an element for LTM, an addition or modification list for LTM, or a container, similar to the element 1, the first addition or modification list, or the first container respectively. In some implementations, the RRC message is the RRC reconfiguration message 316, 318 or another RRC reconfiguration message (not shown in Fig. 3). In some implementations, the DU-to-CU message is the message 312, the message 314, a UE Context Modification Response message, or a UE Context Modification Required message. In some implementations, the DU 174 also includes the first TCI state configured on(s) in the LTM DU configuration 1. In other implementations, the DU 174 refrains from including the first TCI state configured on(s) in the LTM DU configuration 1.

[0109] In some implementations, the first interface protocol lE / field is a first F1AP lE / field and the second interface protocol lE / field is a second Fl AP lE / field. In some implementations, one of the first F1AP lE / field and the second F1AP lE / field is a F1AP CellGroupConfig lE / field and the other is not the F1AP CellGroupConfig lE / field. In some implementations, the DU 174 includes the first Fl AP lE / field in a DU to CU RRC Information IE in the message 312 and includes the second F1AP lE / field in the DU to CU RRC Information IE in the DU-to-CU message. In other implementations, neither the first F1AP lE / field nor the second F1AP IE is a F1AP CellGroupConfig lE / field. In other implementations, the second Fl AP lE / field is the DU to CU RRC Information IE and the first F1AP lE / field is a new IE specific for including an LTM DU configuration.

[0110] In some implementations, after (e.g., in response to) receiving the first LTM command or while accessing 332 the first cell, the UE 102 monitors one or more PDCCHs on the first cell using some or all of the first TCI state configuration(s). In some implementations, each of the first TCI state configuration(s) includes a TCI state ID identifying the corresponding TCI state configuration. For example, the first TCI state configuration(s) includes TCI state configuration(s) 1, ..., L, where L is a positive integer larger than zero. The TCI state configuration(s) 1, . . . , L include TCI state ID(s) 1, . . . , L identifying the TCI state configuration(s) 1, . . ., L, respectively. The DU 174 includes the TCI state ID 1 in the first LTM command to indicate to the UE 102 to apply the TCI state configuration 1 to communicate on the first cell. After (e.g., in response to) receiving the first LTM command, the UE 102 accesses and / or communicates on the first cell using the TCI state configuration 1 in accordance with the TCI state ID 1. For example, the UE 102 monitors one or more PDCCHs and / or transmits the first transmission, using the TCI state configuration 1. In some implementations, the DU 174 detects that the UE 102 accesses the first cell and communicates with the UE 102 on the first cell, based on the TCI state configuration 1. For example, the DU 174 receives the first transmission from the UE 102 on the first cell, based on the TCI state configuration 1.[OHl] In some implementations, the DU 174 includes the TCI state ID 2 in the first LTM command to indicate to the UE 102 to apply the TCI state configuration 2 to communicate on the first cell, in addition to the TCI state ID 1. After (e.g., in response to) receiving the first LTM command, the UE 102 accesses and / or communicates on the first cell using the TCI state configurations 1 and 2 in accordance with the TCI state ID 1 and the TCI state ID 2. For example, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and transmits the first transmission on the first cell using the TCI state configuration 2. In another example, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and the TCI state configuration 2 and transmits the first transmission on the first cell using one of the TCI state configuration 1 and the TCI state configuration 2. In some implementations, the DU 174 detects that the UE 102 accesses the first cell and communicates with the UE 102 on the first cell, based on the TCI state configuration 1 and / or the TCI state configuration 2. For example, the DU 174 receives the first transmission from the UE 102 on the first cell, based on one of the TCI state configuration 1 and the TCI state configuration 2.

[0112] In some alternative implementations, the DU 174 does not include a TCI state ID in the first LTM command. In such cases, the UE lOcommunicates on the first cell with the first DU using the at least one first TCI state, after (e.g., in response to) receiving the first LTM command. In some implementations, the DU 174 detects that the UE 102 accesses the first cell and communicates with the UE 102 on the first cell, based on the first TCI state configuration(s).

[0113] In some implementations, before transmitting the first LTM command, the DU 174 transmits one or more activation commands to activate some or all of the first TCI state configuration(s). In some implementations, each of the activation command(s) is a MAC CE. In other implementations, each of the activation command(s) is a DCI. In some implementations, the DU 174 includes the TCI state ID 1 and / or TCI state ID 2 in the activation command(s) to activate the TCI state configuration 1 and / or the TCI state configuration 2, respectively. Accordingly, the UE 102 determines or identifies that the TCI state configuration 1 and / or the TCI state configuration 2 is / are activated upon receiving the activation command(s). In other implementations, the DU 174 includes all the TCI state ID(s) for the first TCI state configuration(s) in the activation command(s). Accordingly, the UE 102 determines or identifies that the first TCI state configuration(s) is / are activated upon receiving the activation command(s). In some implementations, the DU 174 refrains from including, in the first LTM command, a TCI state ID for a TCI state configuration that the DU 174 has not activated for the UE 102. In some implementations, the DU 174 includes the cell ID 1 or the cell index 1 in the activation command(s). Based on the cell ID 1 or cell index 1, and the one or more TCI state IDs in the activation command(s), the UE 102 determines that the activation command(s) activates the one or more TCI state configurations in the first TCI state configuration(s), where each of the TCI state ID(s) identifies a particular TCI state configuration of the TCI state configuration(s).

[0114] In some implementations, the UE 102 communicates with the DU 174 on the cell 124A (e.g., events 302, 304, 318, 320, 324, 330), using one or more TCI state configurations. In some implementations, each of the TCI state configuration(s) configures a TCI state for the UE 102 to transmit and / or receive data and / or control signal on the cell 124 A. In some implementations, the UE 102 stops using the TCI configuration(s) upon receiving the first LTM command.

[0115] After successfully accessing the first cell, the UE 102 communicates 336 with the DU 174 on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the DU 174. In such cases, the DU 174 communicates 336 with the UE 102 on the first cell using the LTM DU configuration 1. In some scenarios or implementations, the UE 102 communicates 336 PUSCH transmissions, PDSCH transmissions, PUCCH transmissions, PDCCH transmissions, and / or sounding reference signal (SRS) transmissions with the DU 174 on the first cell. In some implementations, the UE 102 uses some or all of the first TCI state configuration(s) to perform 336 the communication with the DU 174. Similarly, the DU 174 uses some or all of the first TCI state configuration(s) to perform 336 the communication with the UE 102. In some implementations, the DU 174 includes one or more additional TCI state configurations in the LTM DU configuration 1. In some such cases, the DU 174 transmits one or more activation commands to the UE 102 via the first cell in the event 336 to activate the additional TCI state configuration(s). The UE 102 determines that the additional TCI state configuration(s) is / are activated upon receiving the activation command(s). In some implementations, each of the activation command(s) is a MAC CE. In other implementations, each of the activation command(s) is a DCI. After receiving the activation command(s), the UE 102 uses the additional TCI state configuration(s) to communicate with the DU 174 on the first cell. Similarly, after transmitting the activation command(s), the DU 174 uses the additional TCI state configuration(s) to communicate with the UE 102 on the first cell.

[0116] In cases where the UE 102 receives the reference LTM DU configuration as described above, the UE 102 communicates 336 with and the DU 174 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the UE 102 communicates 336 with the DU 174 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration. Similarly, the DU 174 communicates 336 with the UE 102 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the DU 174 communicates 336 with the UE 102 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration.

[0117] In cases where the UE 102 receives neither the LTM CU configuration 1 nor a / the reference LTM CU configuration, the UE 102 communicates 336 with the CU 172 via theDU 174 using the serving CU configuration. Correspondingly, if the CU 172 neither transmits the LTM CU configuration 1 nor a / the reference CU configuration to the UE 102, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving CU configuration. In cases where the UE 102 receives the LTM CU configuration 1 and the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1.

[0118] In cases where the UE 102 receives the LTM CU configuration 1 and does not receive the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1. If the LTM CU configuration 1 is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the LTM CU configuration 1 instead of the serving CU configuration. In some implementations, if the UE 102 does not receive a / the reference LTM CU configuration from the base station 104, the UE 102 determines that the LTM CU configuration l is a full configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a full configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In other implementations, the CU 172 includes a first indication (e.g., a field or IE) in the LTM CU configuration 1, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration l is a full configuration. If the LTM CU configuration l is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the LTM CU configuration 1 and at least a portion of the serving CU configuration not augmented by the LTM CU configuration 1. In some implementations, if the UE 102 does not receive a / the reference LTM CU configuration from the base station 104, the UE 102 determines that the LTM CU configuration l is a delta configuration to augment the serving CU configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a delta configuration to augment the serving CU configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In someimplementations, the CU 172 indicates that the LTM CU configuration 1 is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the LTM CU configuration 1, the first container, the element 1 and / or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the LTM CU configuration 1, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration l is a delta configuration to augment the serving CU configuration. In some implementations, the CU 172 indicates that the LTM CU configuration 1 is a full configuration, by excluding the second indication in the LTM CU configuration 1, the first container, the element 1 and / or the RRC reconfiguration message 316.

[0119] In cases where the UE 102 receives the reference LTM CU configuration and does not receive the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the reference LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the reference LTM CU configuration. If the reference LTM CU configuration is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration instead of the serving CU configuration. In some implementations, the UE 102 and CU 172 determine that the reference LTM CU configuration 1 is a full configuration (e.g., as specified in a 3GPP specification (e.g., 3GPP specification 38.331 vl8.0.0 or later version)). In other implementations, the CU 172 includes a first indication (e.g., a field or IE) in the reference LTM CU configuration, the first container or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a full configuration. If the reference LTM CU configuration is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration and at least a portion of the serving CU configuration not augmented by the reference LTM CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the reference LTM CU configuration, the first container, the element 1 and / or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the reference LTM CU configuration, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a delta configuration to augment the serving CU configuration. In some implementations, theCU 172 indicates that the reference LTM CU configuration is a full configuration, by excluding the second indication in the reference LTM CU configuration, the first container, the element 1 and / or the RRC reconfiguration message 316.

[0120] In cases where the UE 102 neither receives the reference LTM CU configuration and nor the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving LTM CU configuration.

[0121] In some implementations, the UE 102 transmits an RRC message to the CU 172 via the DU 174 and the first cell to indicate that the UE 102 applies the LTM DU configuration 1. In cases where the UE 102 performs the random access procedure 332, the UE 102 can include the RRC message in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC message after completing the random access procedure. In cases where the UE 102 skip the random access procedure 332, the UE 102 includes the RRC message in the first PUSCH transmission. In some implementations, if the UE 102 maintains communication on the cell 124A with the base station 104 (i.e., the UE 102 does not disconnect from the cell 124A), the UE 102 can transmit the RRC message to the base station 104 via the cell 124 A. When the DU 174 receives the RRC message, the DU 174 transmits the RRC message to the CU 172.

[0122] In some implementations, the UE 102 includes the LTM ID 1 in the RRC message. Upon receiving the RRC message including the LTM ID 1, the CU 172 determines that the UE 102 performs an LTM cell switch to the cell 1 and is using the LTM DU configuration 1 and / or the LTM CU configuration 1 to communicate with the base station 104. In other implementations, the UE 102 includes the UE ID 1 in the RRC message. Upon receiving the RRC message including the UE ID 1, the CU 172 determines that the UE 102 performs an LTM cell switch to the cell 1 and is using the LTM DU configuration 1 and / or the LTM CU configuration 1 to communicate with the base station 104. In some implementations, the RRC message is an RRC reconfiguration complete message (e.g., RRCReconfigurationComplete message). In other implementations, the UE 102 includes neither an LTM ID nor a UE ID in the RRC message.

[0123] In other implementations, the UE 102 refrains from transmitting the RRC message to the base station 104 in response to applying the LTM DU configuration 1 or receiving thefirst LTM command. In such cases, the UE 102 can include or transmit data in the Message 3, Message A or PUSCH transmission as described above. The UE 102 can generate a MAC PDU and / or a RLC PDU including the data and transmits or includes the MAC PDU and / or RLC PDU in the PUSCH transmission. For example, the data can be a PDCP PDU, a SDAP PDU, a LTE Positioning Protocol (LPP) PDU, an RRC PDU and / or a NAS PDU. The RRC PDU includes a UL-DCCH-Message excluding an RRC reconfiguration complete message. The NAS PDU includes a Mobility Management (MM) message or a Session Management (SM) message. The MM message can be a 5G MM message or a 6G MM message, and the SM message can be a 5G SM message or a 6G SM message. When the DU 174 receives the data, the DU 174 transmits the data to the CU 172.

[0124] When the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 can transmit 334 a DU-to-CU message (e.g., Access Success message) to the CU 172 (e.g., a CP of the CU 172). In some implementations, the DU 174 can include the cell ID 1 of the first cell in the DU-to-CU message of the event 334. The cell ID can be a PCI or a CGI. Thus, the CU 172 determines that the UE 102 connects to the first cell upon receiving the DU-to-CU message of the event 334. When the DU 174 determines that the UE 102 successfully connect to the first cell in the event 332 or 336, the DU 174 can transmit a DL Data Delivery Status message or frame to the CU 172 (e.g., a UP of the CU 172). In some implementations, when or after the CU 172 receives the DU-to-CU message 329, the CU 172 stops or suspends transmitting DL data for the UE 102 to the DU 174 until receiving the DU-to-CU message 334. Depending on the implementation, the CU 172 does so because the DU 174 cannot buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. After receiving the DU-to-CU message 334, the CU 172 continues or resumes transmitting DL data for the UE 102 to the DU 174. In other implementations, when the CU 172 receives the DU-to-CU message 329, the CU 172 continues transmitting DL data for the UE 102 to the DU 174. In some implementations, the CU 172 does so because the DU 174 can buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. When or after the DU 174 detects that UE 102 accesses the cell 1, the DU 174 transmits the DL data to the UE 102 via the cell 1.

[0125] In some implementations, when determining that the UE 102 connects to the first cell, transmitting 330 the first LTM command, or receiving 331 the acknowledgement, the DU 174 can stop communicating with the UE 102 on the cell 124A and / or release resources of the cell 124 A configured for the UE 102.

[0126] In some implementations, the DU 174 can generate some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, N as full configuration(s) to replace the serving DU configuration. If the LTM DU configuration l is a full configuration, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 instead of the serving DU configuration. In some implementations, the DU 174 includes an indication indicating that the LTM DU configuration 1 is a full configuration in the LTM DU configuration 1. In each of the LTM DU configured on(s) 2, . . . , N, the DU 174 can include an indication to indicate that the corresponding DU configuration is a full configuration. Each of the indication(s) in the LTM DU configured on(s) 1, . . ., N can be a field or IE (i.e., the same field or IE). In other implementations, the CU 172 can include, in the RRC reconfiguration message of the events 316, 318, a single indication indicating that the LTM DU configuration(s) 1 and / or 2, . . ., N is / are full configuration(s). In the case of the second container, the CU 172 can include, in the additional RRC reconfiguration message, a single indication indicating that the LTM DU configuration(s) 2, . . ., N is / are full configured on(s). In yet other implementations, the CU 172 can include, in the first container, a single indication indicating that the LTM DU configuration(s) 1 and / or 2, . . ., N is / are full configuration(s). In yet other implementations, for each of the LTM DU configuration(s) 2, . . ., N, the CU 172 can include, in the first container, a particular indication indicating the corresponding LTM DU configuration is a full configuration. In the case of the second container, the CU 172 can include, in the second container, a single indication indicating that the LTM DU configuration(s) 2, . . . , N is / are full configuration(s). In yet other implementations, the CU 172 can include, in the element 1, includes an indication indicating that the LTM DU configuration 1 is a full configuration. In each of the element(s) 2, . . ., N, the CU 172 can include an indication indicating that the corresponding LTM DU configuration is a full configuration. The UE 102 can determine that the LTM DU configuration 1 and / or LTM DU configuration(s) 2, . . ., N is / are full configuration(s) based on the indication(s) above. In some implementations, each of the indication(s) above is different from a currently defined fullConfig field (e.g., as defined in the current 3GPP specification). In some implementations, each of the indication(s) above is a currently defined fullConfig field (e.g., as defined in the current 3 GPP specification). In cases where the LTM DU configuration 1 is a full configuration, the UE 102 in the event 336 does not apply the reference LTM DU configuration if received from the base station 104, e.g., in theRRC reconfiguration message 318. In some such cases, the DU 174 does not include a / the reference LTM DU configuration in the first DU-to-CU message 310.

[0127] In other implementations, the DU 174 can generate the LTM DU configuration 1 and / or LTM DU configuration(s) 2, . . ., N as delta configuration(s) that augment (a portion of) the reference LTM DU configuration. In other words, the DU 174 generates the LTM DU configuration(s) 1, . . .N based on the reference LTM DU configuration. For example, if the LTM DU configuration 1 is a delta configuration, the UE 102 and DU 174 augment (the portion of) the reference LTM DU configuration with the LTM DU configuration 1. Thus, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 and unaugment portion of the reference LTM DU configuration. In some implementations, the LTM DU configuration(s) 1, and / or 2. . ., N, first container, second container or element(s) 1, . . . , N exclude indication(s) indicating that the LTM DU configuration(s) 1, and / or 2. . ., N is / are full configuration(s) to indicate that the LTM DU configuration(s) 1 and / or 2, . . ., N is / are delta configuration(s). The UE 102 can determine that each of the LTM DU configuration(s) 1 and / or 2, . . ., N is a delta configuration based on that the indication is excluded in the LTM DU configuration(s) 1 and / or 2, . . ,,N, first container, second container or element(s) 1 and / or 2, . . ., N.

[0128] In some implementations, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and / or the LTM DU configuration(s) 2, . . . , N, the UE 102 determines that the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, . . ., N are full configuration(s). Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM DU configuration for the UE 102 and / or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, . . ., N as full configuration(s).

[0129] In other implementations, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and / or the LTM DU configuration(s) 2, . . . , N, the UE 102 determines that the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, . . . , N are delta configuration(s) to augment the serving DU configuration. In such cases, the UE 102 communicates 336 with the DU 174 in accordance with the LTM DU configuration 1 and at least a portion of the serving DU configuration not augmented by LTM DU configuration 1. Correspondingly, if the DU 174 does not obtain a reference LTMDU configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM DU configuration for the UE 102 and / or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, . . N as delta configuration(s) to augment the serving DU configuration. In such cases, the DU 174 communicates 336 with the UE 102 in accordance with the LTM DU configuration 1 and the at least a portion of the serving DU configuration.

[0130] In some implementations, the UE 102 uses a UE MAC entity (e.g., MAC 204B) to communicate with a DU MAC entity (e.g., MAC 204B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331). In some implementations, the UE 102 resets the UE MAC entity, after or in response to receiving the first LTM command and before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 resets the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

[0131] In some implementations, when the UE 102 resets the UE MAC entity, the UE 102 performs at least one of the following actions for the UE MAC entity (i.e., UE MAC reset or full UE MAC reset): (i) initialize Bj for configured logical channel(s) to zero; (ii) stop one or more timers; (iii) consider timeAlignmentTimer(s) as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (iv) set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0; (v) set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1; (vi) flush Msg3 buffer; (vii) flush MSGA buffer; (viii) cancel, if any, triggered Scheduling Request procedure; (ix) cancel, if any, triggered Buffer Status Reporting procedure; (x) cancel, if any, triggered Power Headroom Reporting procedure; (xi) cancel, if any, triggered consistent LBT failure; (xii) cancel, if any, triggered BFR; (xiii) cancel, if any, triggered Sidelink Buffer Status Reporting procedure; (xiv) cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure; (xv) cancel, if any, triggered Timing Advance Reporting procedure; (xvi) cancel, if any, triggered Recommended bit rate query procedure; (xvii) cancel, if any, triggered configured uplink grant confirmation; (xviii) cancel, if any, triggered configured sidelink grant confirmation; (xix) cancel, if any, triggered Desired Guard Symbol query; (xx) cancel, if any, triggered Positioning Measurement Gap Activation / Deactivation Request procedure; (xxi) flush soft buffers for DL HARQ process(es); (xxii) for each of the DL HARQ process(es), consider the next receivedtransmission for a TB as the very first transmission; (xxiii) release, if any, Temporary C- RNTI; and (xxiv) reset one or more counters (e.g., BFI COUNTERs and / or LBT COUNTERs).

[0132] In some implementations, when the DU 174 resets the DU MAC entity, the DU 174 performs at least one of the following actions for the DU MAC entity (i.e., DU MAC reset or full DU MAC reset): (i) stop one or more timers; (ii) consider limeAlignmenlTimer( , that the DU 174 starts and / or maintains for the UE 102, as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (iii) set NDI(s) for DL HARQ process(es) to value 0; (iv) flush soft buffers for UL HARQ process(es); (v) for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission; (vi) reset one or more counters (e g., BFI COUNTERs and / or LBT COUNTERs).

[0133] Depending on implementations, the UE 102 can determine to partially or fully reset the UE MAC entity. In some implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 fully resets the UE MAC entity (i.e., a full UE MAC reset). In the full UE MAC reset, the UE 102 performs some or all of the actions described above. In other implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 partially resets the UE MAC entity (i.e., a partial UE MAC reset). In the partial UE MAC reset, the UE 102 performs a subset or portion of the some or all of the actions in the full UE MAC reset.

[0134] In some implementations, the partial UE MAC reset includes at least one of the following actions: (i) consider timeAlignmentTimer(s) of the UE 102 as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (ii) flush Msg3 buffer; (iii) flush MSGA buffer; (iv) release, if any, Temporary C-RNTI; and (v) reset one or more counters (e.g., BFI COUNTERs and / or LBT COUNTERs).

[0135] In some implementations, the partial UE MAC reset further includes at least one of the following actions: (i) cancel, if any, triggered Scheduling Request procedure; (ii) cancel, if any, triggered Buffer Status Reporting procedure; (iii) cancel, if any, triggered Power Headroom Reporting procedure; (iv) cancel, if any, triggered consistent LBT failure; (v) cancel, if any, triggered BFR; (vi) cancel, if any, triggered Sidelink Buffer Status Reporting procedure; (vii) cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure;(viii) cancel, if any, triggered Timing Advance Reporting procedure; (ix) cancel, if any, triggered Recommended bit rate query procedure; (x) cancel, if any, triggered configured uplink grant confirmation; (xi) cancel, if any, triggered configured sidelink grant confirmation; (xii) cancel, if any, triggered Desired Guard Symbol query; and (xiii) cancel, if any, triggered Positioning Measurement Gap Activation / Deactivation Request procedure;

[0136] In some implementations, the partial UE MAC reset further includes at least one of the following actions: (i) stop a first portion of the one or more timers and retain the rest of the one or more timers; (ii) set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0; (iii) set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1; (iv) flush soft buffers for DL HARQ process(es); and (v) for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission;

[0137] Depending on implementations, the DU 174 can determine to partially or fully reset the DU MAC entity. In some implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 fully resets the DU MAC entity (i.e., a full DU MAC reset). In the full DU MAC reset, the DU 174 performs some or all of the actions described above. In other implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 partially resets the DU MAC entity (i.e., a partial DU MAC reset). In the partial DU MAC reset, the DU 174 performs a subset or portion of the some or all of the actions in the full DU MAC reset.

[0138] In some implementations, the partial DU MAC reset includes at least one of the following actions in the partial MAC reset: (i) consider limeAlignmenlTimer( , that the DU 174 starts and / or maintains for the UE 102, as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (ii) reset one or more counters (e.g., BFI COUNTERs and / or LBT COUNTERs)

[0139] In some implementations, when the partial DU MAC reset includes at least one of the following actions for the MAC entity (i.e., DU MAC reset): (i)stop a first portion of the one or more timers and retain the rest of the one or more timers; (ii) set NDI(s) for DL HARQ process(es) to value 0; (iii) flush soft buffers for UL HARQ process(es); (iv)for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission; (v) reset one or more counters (e.g., BFI COUNTERs and / or LBT COUNTERs).

[0140] In other implementations, the UE 102 refrains from resetting the UE MAC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from resetting the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the UE MAC entity (not reset). Similarly, the DU 174 communicates with the UE 102 using the DU MAC entity (not reset) on the first cell during or after the random access procedure 332 or after determining that the UE 102 connects to the first cell.

[0141] In some implementations, the UE 102 uses at least one UE RLC entity (e.g., RLC 206B) to communicate RLC PDUs with at least one DU RLC entity (e.g., RLC 206B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331). In some implementations, the UE 102 reestablishes some or all of the at least one UE RLC entity, after or in response to receiving the first LTM command and before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 reestablishes some or all of the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

[0142] In some implementations, the LTM DU configuration 1 may or may not include one or more RLC reestablishment indications (e.g., reestablishRLC field(s)) configuring the UE 102 to reestablish some or all of the at least one UE RLC entity. If the LTM DU configuration 1 includes the a RLC reestablishment indication configuring the UE 102 to reestablish a first UE RLC entity, of the at least one UE RLC entity, that the UE 102 uses to communicate RLC PDU(s) with the DU 174, the UE 102 reestablishes the first UE RLC entity in response to the RLC reestablishment indication and the first LTM command. In some implementations, the UE 102 can reestablish the first UE RLC entity before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In other implementations, the UE 102 can reestablish the first UE RLC entity while or after performing 332 the random access procedure. Otherwise if the LTM DU configuration 1 does not include the RLC reestablishment indication, the UE 102 refrains from reestablishing the first UE RLC entity in response to the first LTM command.

[0143] In some implementations, when the UE 102 reestablishes the first UE RLC entity, the UE 102 performs at least one of the following actions for the first UE RLC entity: (i)discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any; (ii) stop and reset timer(s), if running; and (iii) reset state variables to initial values. In some implementations, the state variables and timer(s) are currently defined (e.g., as defined in 3 GPP specification 38.322).

[0144] Otherwise, if the LTM DU configuration 1 does not include the RLC reestablishment indication for the first UE RLC entity, the UE 102 refrains from reestablishing the first UE RLC entity upon or when receiving the first LTM command. In other words, the UE 102 refrains from preforming the actions for reestablishing the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. In some implementations, if the LTM DU configuration 1 or element 1 does not include the RLC reestablishment indication and includes an indication indicating that the configuration l is a full configuration, the UE 102 can reestablish the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. Otherwise, if the LTM DU configuration 1 or element 1 does not include the RLC reestablishment indication and the indication indicating that the configuration 1 is a full configuration, the UE 102 refrains from reestablishing the first UE RLC entity upon or when receiving the first LTM command.

[0145] Similarly, the DU 174 reestablishes some or all of at least one DU RLC entity (e.g., NR RLC 206B) that the DU 174 uses to communicate with the at least one UE RLC entity of the UE 102 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331) in response to the RLC reestablishment indication. In some implementations, the DU 174 reestablishes a first DU RLC entity of the at least one DU RLC entity after transmitting the first LTM command, receiving an acknowledgement for the first LTM command from the UE 102, or determining that the UE 102 connects to the first cell. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. In yet other implementations, the acknowledgement is a PUCCH transmission. In some implementations, when the base station 104 reestablishes the first DU RLC entity, the DU 174 performs at least one of the following actions for the first DU RLC entity: (i) discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any; (ii) stop and reset timer(s), if running; (iii)reset state variables to initial values. In some implementations, the state variables and timer(s) are currently defined (e.g., as defined in 3GPP specification 38.322).

[0146] In other implementations, the UE 102 refrains from reestablishing some or all of the at least one UE RLC entity in response to receiving the first LTM command. Similarly, theDU 174 refrains from reestablishing some or more of the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the some or all of the at least one UE RLC entity (not reestablished). For example, the some or all of the at least one UE RLC entity includes the first UE RLC entity and / or a second UE RLC entity. Similarly, the DU 174 communicates with the UE 102 using the some or all of the at least one DU RLC entity (not reestablished) on the first cell during or after the random access procedure 332 or after determining that the UE 102 connects to the first cell. For example, the some or all of the at least one DU RLC entity includes the first DU RLC entity and / or a second DU RLC entity.

[0147] In some implementations, the UE 102 uses at least one UE PDCP entity (e.g., PDCP 210) to communicate UL PDCP PDUs and / or DL PDCP PDUs with at least one CU PDCP entity (e.g., PDCP 210) of the CU 172 in the event 302. In some implementations, the UE 102 performs a PDCP recovery procedure for some or all of the at least one UE PDCP entity, after or in response to receiving the first LTM command. For example, the UE 102 performs a PDCP recovery procedure for a first UE PDCP entity of the at least one UE PDCP entity, after or in response to receiving the first LTM command. In the PDCP recovery procedure, the UE 102 may or may not reestablish the first UE PDCP entity. After or in response to performing the PDCP recovery procedure, the UE 102 can retransmit at least a portion of the UL PDCP PDUs to the CU 172 via the DU 174 and the first cell in the event 336. Similarly, the CU 172 performs a PDCP recovery procedure for some or all of the at least one CU PDCP entity after or in response to transmitting the first LTM command. For example, the CU 172 performs a PDCP recovery procedure for a first CU PDCP entity of the at least one CU PDCP entity, after or in response to transmitting the first LTM command. In some implementations, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DU-to-CU message 329 or 334. In other implementations, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DL Data Delivery Status message. In the PDCP recovery procedure, the CU 172 may or may not reestablish the first CU PDCP entity. After or in response to performing the PDCP recovery procedure, the CU 172 can retransmit at least a portion of the DL PDCP PDUs to the UE 102 via the DU 174 and the first cell in the event 336.

[0148] In other implementations, the UE 102 refrains from reestablishing some or all of the at least one UE PDCP entity in response to receiving the first LTM command. For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 refrains from reestablishing some or more of the at least one CU PDCP entity, after (e.g., in response to) receiving the DU-to-CU message 329 or 340 or after (e.g., in response to) receiving the DL Data Delivery Status message. In other words, the UE 102 communicates with the CU 172 via the DU 174 and the first cell using the some or all of the at least one UE PDCP entity (not reestablished). For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 communicates with the UE 102 using the some or all of the at least one CU PDCP entity (not reestablished) via the DU 174 and the first cell. For example, the some or all of the at least one CU PDCP entity includes the first CU PDCP entity and / or a second CU PDCP entity.

[0149] In some implementations, after determining that the UE 102 connects to the first cell, the CU 172 can transmit 338 a CU-to-DU message (e.g., a UE Context Modification Request message) to the DU 174 to indicate the DU 174 to stop communicating with the UE 102 and / or to release or suspend resources, of the cell 124A, configured for the UE 102. In response, the DU 174 can stop communicating on the cell 124A with the UE 102 and / or release or suspend resources, of the cell 124A, configured for the UE 102, and transmit 340 a DU-to-CU message (e.g., a UE Context Modification Response message) to the CU-172. The events 338 and 340 are collectively referred to in Fig. 3 as a resource release procedure 396.

[0150] In some implementations, after or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351, 352, 354 and / or 356 occur, similar to the events 324, 326, 328, 330, 331, 332, 334 and / or 336, respectively. The UE 102 transmits 344 at least one measurement report to the DU 174. The at least one measurement report includes at least one measurement result for a second cell (i.e., the cell 2). The at least one measurement result indicates that the second cell is suitable for communication with UE 102 and / or the first cell is not suitable for communication with the UE 102. After (e.g., in response to) receiving the at least one measurement report, the DU 174 determines to activate the LTM DU configuration 2 and generates a second LTM command to activate the LTM DU configuration 2 (i.e., the second LTM command commands the UE 102 to apply the LTM DU configuration 2). The DU 174 then transmits 350 the second LTM command to the UE on the first cell to the UE 102.

[0151] In some implementations, when or in response to determining to activate the LTM DU configuration 2 or transmit the second LTM command, the DU 174 transmits 349 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some implementations, the DU 174 includes the cell ID 2 or the ID 2 (i.e., LTM ID) in the DU-to-CU message 349 to indicate that the DU 174 is to activate the LTM DU configuration 2. The DU can transmit the DU-to-CU message 349 to the CU 172 before or after transmitting the LTM command 350.

[0152] The descriptions for the events 324, 326, 328, 330, 331, 332, 334 and / or 336 can be applied to the events 344, 346, 348, 350, 351, 352, 354 and / or 356 with simple changes. For example, “ cell 124 A”, “first LTM command”, “first cell”, “ID 1”, “LTM DU configuration 1” and / or “LTM CU configuration 1” are replaced with “first cell”, “second LTM command” and “second cell”, “ID 2”, “LTM DU configuration 2” and / or “LTM CU configuration 2”, respectively.

[0153] The events 344, 346, 348, 350, 351, 352, 354 are collectively referred to in Fig. 3 as an LTM execution procedure 398. The events 304, 306, 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, 356 are collectively referred to in Fig. 3 as an LTM DU configuration and / or activation procedure 380.

[0154] Referring next to Fig. 4, in a scenario 400, the base station 104 includes a CU 172, a source DU (S-DU) 174A and a target DU (T-DU) 174B. The S-DU 174A operates the cell 124 A and, in some implementations, additional cell(s), while the T-DU 174B operates a first cell (e.g., cell 124C). The scenario 400 is similar to the scenario 300. Thus, the descriptions for the scenario 300 can generally apply to the scenario 400. The differences between the scenarios 300 and 400 are described below.

[0155] Initially, the UE 102 communicates 402 with the S-DU 174A on cell 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174 A. The S- DU 174A is a serving DU similar to the DU 174 in Fig. 3 A. During the communication 402, the UE 102 transmits 404, 406 at least one measurement report (e.g., L3 measurement report(s)) to the CU 172 via the S-DU 174 A. Based on the at least one measurement report, the CU 172 determines to prepare cell(s) 1, . . ., N (operated by the T-DU 174B) for LTM for the UE 102, where N is a positive integer larger than 0 or 1. The cell(s) 1, . . . , N are identified by cell ID(s) 1, . . ., N, respectively. In response to the determination, the CU 172 performs 490 an LTM preparation procedure with the T-DU 174B to (request the T-DU 174Bto) prepare cell(s) 1, . . . , N for LTM for the UE 102. N can be a positive integer larger than zero or 1. In the LTM preparation procedure 490, the CU 172 transmits a CU-to-DU message including the cell ID(s) 1, . . N to the T-DU 174B to request the T-DU 174B to prepare the cell(s) 1, . . . , N for LTM for the UE 102, similar to the event 308. In response, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) 1, . . . , N to the CU 172, similar to the event 310. The LTM DU configuration(s) 1, . . . , N configures the cell(s) 1, . . ., N for LTM, respectively. In details, the LTM DU configuration(s) 1, . . ., N include configuration parameters for communication on the cell(s) 1, . . ., N, respectively. In some implementations, the CU-to-DU message and DU-to-CU message in the procedure 490 are UE Context Setup Request message and UE Context Setup Response message, respectively. The CU 172 then transmits the LTM DU configuration(s) 1, . . ., N in an RRC reconfiguration message in an LTM configuration delivery procedure 494, similar to the LTM configuration delivery procedure 394. In some implementations, the T-DU 174B can include cell index(es) 1, . . ., N in the LTM DU configuration(s) 1, . . ., N, respectively. In some implementations, the CU 172 can set the cell index(es) 1, . . ., N to different values and include the cell index(es) 1, . . ., N in the CU-to-DU message of the procedure 490.

[0156] In some implementations, after performing the LTM preparation procedure 490, the CU 172 performs an additional LTM preparation procedure(s) with the T-DU 174B to prepare cell(s) N+l, . . . , N+M for LTM for the UE 102, similar to the procedure 490. M is a positive integer larger than zero. In some implementations, the CU 172 determines to do so based on one or more measurement reports received from the UE 102 via the S-DU 174 A, similar to the events 404, 406. In the additional LTM preparation procedure, the CU 172 transmits a CU-to-DU message including cell ID(s) N+l, . . ., N+M to the T-DU 174B to request the T-DU 174B to prepare the cell(s) N+l, . . . , N+M for LTM for the UE 102. The cell ID(s) N+l, . . . , N+M identifies the cell ID(s) N+l, . . . , N+M, respectively. In response to the CU-to-DU message, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) N+l, . . . , N+M to the CU 172. The LTM DU configuration(s) N+l, . . . , N+M configures the cell(s) N+l, . . . , N+M for LTM, respectively. In details, the LTM DU configuration(s) N+l, . . ., N+M include configuration parameters for communication on the cell(s) N+l, . . . , N+M, respectively. The CU 172 then transmits the LTM DU configuration(s) N+l, . . ., N+M in an RRC reconfiguration message in an additional LTMconfiguration delivery procedure, similar to the LTM configuration delivery procedure 394 or 494.

[0157] In some implementations, the LTM preparation procedure 490 is a UE Context Setup procedure, and the additional LTM preparation procedure is a UE Context Modification procedure. In other implementations, the LTM preparation procedure 490 and the additional LTM preparation procedure(s) are UE Context Setup procedures. The UE Context Setup procedures can take place in parallel between the CU and the DU and the procedures can be differentiated by the SpCell ID IE and the Requested Target Cell ID IE in the UE Context Setup Request message and the UE Context Setup Request Acknowledge message, respectively.

[0158] In some implementations, the CU 172 and S-DU 174 A performs the procedure 380 with the UE 102, as described for Fig. 3. In the procedure 380, the CU 172 and S-DU 174 A performs the procedure(s) 390 and / or 392 to prepare cell(s) of the S-DU 174A for LTM for the UE 102. Note, the value N in the procedure 380 or described for Fig. 3 can be the same as or different from the value N described for Fig. 4. In the procedure 390, the CU 172, in some implementations, receives the first DU-to-CU message including the reference LTM DU configuration from the S-DU 174A in the event 310. In other implementations, the CU 172 and S-DU 174A does not perform the procedure 380 with the UE 102. In such cases, the CU 172 can perform 488 a reference LTM DU configuration query procedure with the S-DU 174A to obtain a reference LTM DU configuration. In the procedure 488, the CU 172 transmits 460 a CU-to-DU message to the S-DU 174A to request or query a reference LTM DU configuration. In some implementations, the CU 172 can include an indication in the CU-to-DU message to request or query a reference LTM DU configuration. In response to the indication or CU-to-DU message 460, the S-DU 174 A transmits 462 a DU-to-CU message including a reference LTM DU configuration to the CU 172. In some implementations, the indication is a reference LTM DU configuration query indication. In other implementations, the indication is an LTM indication, and the CU 172 includes a query indication (e.g., GNB-DU Configuration Query IE) in the CU-to-DU message. After receiving the reference LTM DU configuration (i.e., either in the procedure 390 or in the procedure 488), the CU 172 includes the reference LTM DU configuration (received from the S-DU 174A) in the CU-to-DU message in the LTM preparation procedure 490. The T-DU 174B generates the LTM DU configuration(s) 1, . . . , N based on the reference LTM DU configuration received from the CU 172. In such cases, the T-DU 174B does not include areference LTM DU configuration in the DU-to-CU message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. The CU 172 in some implementations does not include the reference LTM DU configuration in CU-to-DU message in the additional LTM preparation procedure with the T- DU 174B. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+l, . . . , N+M based on the reference LTM DU configuration received from the CU 172.

[0159] In some implementations, the CU 172 does not provide a reference LTM DU configuration to the T-DU 174B in the LTM preparation procedure 490. In such cases, the T- DU 174B generates a reference LTM DU configuration and generates the LTM DU configuration(s) 1, . . . , N based on the reference LTM DU configuration. In such cases, the T-DU 174B includes the reference LTM DU configuration in the DU-to-CU message in the procedure 490. The CU 172 transmits the reference LTM DU configuration in the RRC reconfiguration message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+l, . . ., N+M based on the reference LTM DU configuration. In some such cases, the T-DU 174B does not include the reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. In some implementations, the reference LTM DU configuration generated by the T-DU 174B is different from the reference LTM DU configuration generated by the S-DU 174A. In other implementations, the reference LTM DU configuration generated by the T-DU 174B is the same as the reference LTM DU configuration generated by the S-DU 174 A.

[0160] In some implementations, the CU 172 includes the LTM DU configuration(s) 1, . . ., N of the procedure 380 in the CU-to-DU message of the procedure 490, and the T-DU 174B generates the LTM DU configuration(s) 1, . . . , N and / or N+l, . . . , N+M, considering or based on configuration(s) in the LTM DU configuration(s) of the procedure 380.

[0161] In some implementations, the LTM DU configuration X of the procedure 380 includes at least one reference signal (RS) resource configuration X, where 1 < X < N. Each of the RS resource configuration(s) X configures one or more RSs or one or more RS resources associated with the cell X of the S-DU 174A. The RS(s) includes SSB(s) and / or CSI-RS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). Insome implementations, each of the RS resource configuration(s) X includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) X is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the LTM DU configuration X includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI- ResourceConfig IE(s). The T-DU 174B generates at least one report configuration 1 for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the report configuration(s) 1 in the LTM DU configuration 1. In some implementations, the report configuration(s) 1 is / are (similar to) CSI-ReportConfig IE(s). In some implementations, the T-DU 174B generates at least one RS resource configuration 1, considering or based on the RS resource configuration(s) X and includes the RS resource configuration(s) 1 in the LTM DU configuration 1. In some implementations, the T-DU 174B includes the RS resource configuration(s) X in the RS resource configuration(s) 1. In other implementations, the T-DU 174B includes each of the RS resource configuration(s) X in the RS resource configuration(s) 1, except the RS resource configuration ID(s) in the RS resource configuration(s) X. The T-DU 174B assigns a RS resource configuration ID to a value for each of the RS resource configuration(s) 1 (including the RS resource configuration(s) X) and includes the RS resource configuration ID in the corresponding RS resource configuration.

[0162] In some implementations, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124 A, the UE 102 communicates with the S-DU 174B (i.e., the T-DU 17B becomes a S-DU for the UE 102) and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the report configuration(s) 1. Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the report configuration(s) 1. In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) 1 and / or the report configuration(s) 1 and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s)indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). Depending on the implementation, the quantized measurement values include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0163] In some implementations, the T-DU 174B also includes additional RS resource configuration(s) in the LTM DU configuration 1. Each of the additional RS resource configuration(s) configures one or more additional RSs or one or more additional RS resources associated with the cell 1. The additional RS(s) includes SSB(s) and / or CSI-RS(s). The additional RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the additional RS resource configuration(s) includes a RS resource configuration ID. In some implementations, the additional RS resource configuration(s) is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the T-DU 174B includes the CSI-ResourceConfig IE(s) in the CSI-MeasConfig IE. The T-DU 174B generates at least one additional report configuration for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the additional report configuration(s) in the LTM DU configuration 1. In some implementations, the additional report configuration(s) is / are (similar to) CSI-ReportConfig IE(s).

[0164] In some implementations, the additional report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the additional report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the additional RS resource configuration(s). After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124 A, the UE 102 communicates 436 with the S-DU 174B and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the additional report configuration(s). Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the additional report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the additional RS(s) or the additional RS resource(s) in accordance with the additional RS resource configuration(s) and / or the additional report configuration(s) and obtains the quantized measurement values from the measurements. Insome implementations, the RS resource indicator(s) indicates the additional RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). Depending on the implementation, the quantized measurement values include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0165] Similarly, the T-DU 174B can generate RS resource configuration(s) 2, . . ., N, and / or N+l, . . . , N+M and / or report configuration(s) 2, . . . , N, and / or N+l, . . . , N+M, considering or based on the RS resource configuration(s) X, and include the RS resource configuration(s) 2, . . . , N, and / or N+l, . . . , N+M and / or the report configuration(s) 2, . . . , N, and / or N+l, . . . , N+M in the LTM DU configuration(s) 2, . . . , N, and / or N+l, . . . , N+M, respectively, as described above.

[0166] In other implementations, the LTM DU configuration X of the procedure 380 includes at least one TCI state configuration X, where 1 < X < N. Each of the TCI state configuration(s) X configures a TCI state that associates one or two DL RSs with a corresponding QCL type. In some implementations, the DL RS(s) can be associated with the cell X operated by the S-DU 174A. In some implementations, each of the TCI state configuration(s) X includes a TCI state ID. In some implementations, each of the TCI state configuration(s) X is a TCI-State IE. In some implementations, the TCI state configuration(s) X includes / is / are an ul-TCI-ToAddModList-r 17 field, one or more TCI-UL-State-r 17 IES, a dl-OrJointTCI-StateToAddModList-rl7 field, one or more TCI-State IEs, TCI- ActivatedConfig IE and / or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration X includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) X. In some implementations, the T-DU 174B generates at least one TCI state configuration 1, considering or based on the TCI state configuration(s) X and includes the TCI state configuration(s) 1 in the LTM DU configuration 1. In some implementations, the TCI state configuration(s) 1 includes the TCI state configuration(s) X. In other implementations, the T-DU 174B includes each of the TCI state configuration(s) X in the TCI state configuration(s) 1, except the TCI state ID(s) in the TCI state configuration(s) X. The T-DU 174B assigns a TCI state ID to a value for each of the TCI state configuration(s) 1 (including the TCI state configuration(s) X) and includes the TCI state ID in the corresponding TCI state configuration. In some implementations, while the UE 102 and the S-DU 174B communicate 436 with one another, the S-DU 174B transmits anLTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell X. The S-DU 174B includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell X, where the TCI state configuration is one of the TCI state configuration(s) X or includes configurations of one of the TCI state configuration(s) X.

[0167] Similarly, the T-DU 174B can generate TCI state configuration(s) 2, . . N, considering or based on the RS resource configuration(s) X, and include the TCI state configuration(s) 2, . . . , N, and / or N+l, . . . , N+M in the LTM DU configured on(s) 2, . . . , N, and / or N+l, N+M, respectively, as described above.

[0168] In some implementations, in cases where the CU 172 performs the procedure 380 after performing the procedure 490, the CU 172 includes the LTM DU configured on(s) 1, . . ., N of the procedure 490 in the CU-to-DU message of the procedure 380, and the S-DU 174 A generates the LTM DU configured on(s) 1, . . ., N of the procedure 380, considering or based on configurations in the LTM DU configuration(s) of the procedure 490, in a similar way as described above.

[0169] In some implementations, the CU 172 assigns ID(s) 1, . . ., N identifying the LTM DU configured on(s) 1, . . ., N (received from the T-DU 174B), respectively, and performs the procedure 492 with the T-DU 174B to provide the ID(s) 1, . . . , N and / or cell ID(s) 1, . . . , N to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) 1, . . . , N with the LTM DU configured on(s) 1, . . . , N and / or the cell ID(s) 1, . . . , N, respectively. In other implementations, the T-DU 174B assigns ID(s) 1, . . ., N identifying the LTM DU configuration(s) 1, . . ., N (generated by the T-DU 174B), respectively and includes the ID(s) 1, . . . , N in the DU-to-CU message of the procedure 490, similar to the event 310. In some implementations, the CU 172 assigns ID(s) N+l, . . ., N+M identifying the LTM DU configuration(s) N+l, . . ., N+M, respectively, and performs a procedure (similar to the procedure 492) with the T-DU 174B to provide the ID(s) N+l, . . ., N+M and / or cell ID(s) N+l, . . ., N+M to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) N+l, . . ., N+M with the LTM DU configuration(s) N+l, . . ., N+M and / or the cell ID(s) N+l, . . ., N+M, respectively. In other implementations, the T-DU 174B assigns ID(s) N+l, . . . , N+M identifying the LTM DU configured on(s) N+l, . . . , N+M, respectively and includes the ID(s) 1, . . ., N in the DU-to-CU message of the additional LTM preparation procedure, similar to the event 310.

[0170] In some implementations, the CU 172 transmits 412 a CU-to-DU message including the ID(s) 1, . . N to the S-DU 174A and receives 414 a DU-to-CU message from the S-DU 174 A in response. The CU-to-DU message 412 and DU-to-CU message 414 are collectively referred to in Fig. 4 as an LTM ID transfer procedure 493 or an LTM cell index transfer procedure 493. In some implementations, the message 412 and message 414 can be UE Context Modification Request message and UE Context Modification Response message, respectively. In some implementations, the CU 172 includes the LTM DU configuration(s) 1, . . . , N and / or cell ID(s) 1, . . . , N in the CU-to-DU message 412. In one implementation, the CU 172 includes the ID(s) 1, . . ., N in the CU-to-DU message 412. In another implementation, the CU 172 includes the cell index(es) 1, . . ., N in the CU-to-DU message 412. In some alternative implementations, the CU 172 can perform multiple LTM ID transfer procedures to transmit the ID(s) 1, . . . , N, cell ID(s) 1, . . . , N and / or LTM DU configuration(s) 1, . . ., N to the S-DU 174 A. In each of the procedures, the CU 172 includes particular portion of the ID(s) 1, . . . , N, cell ID(s) 1, . . . , N and / or LTM DU configuration(s) 1, . . . , N in a CU- to-DU message similar to the message 412. Thus, the S-DU 174A associates the ID(s) 1, . . ., N with the LTM DU configured on(s) 1, . . . , N and / or the cell ID(s) 1, . . . , N, respectively. In other alternative implementations, the CU 172 can perform multiple LTM cell index transfer procedures to transmit the cell index(es) 1, . . . , N, cell ID(s) 1, . . . , N and / or LTM DU configured on(s) 1, . . ., N to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the cell index(es) 1, . . . , N, cell ID(s) 1, . . . , N and / or LTM DU configuration(s) 1, . . ., N in a CU-to-DU message similar to the message 412. Thus, the S- DU 174 A associates the cell index(es) 1, . . ., N with the LTM DU configured on(s) 1, . . ., N and / or the cell ID(s) 1, . . ., N, respectively.

[0171] In some implementations, the S-DU 174 A generates a first serving DU configuration, based on the LTM DU configuration(s) 1, 2,... , and / or N, and includes the first serving DU configuration in the DU-to-CU message 414. In some implementations, the first serving DU configuration including configurations updating (e.g., augmenting, modifying or replacing) the serving DU configuration 402. In other implementations, the first serving DU configuration includes configurations that are not included in the serving DU configuration 402. The CU 172 transmits an RRC reconfiguration message including the first serving DU configuration to the UE 102. The UE 102 applies the first serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRCreconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174 A using configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. The following are example implementations of generating the first serving DU configuration based on the LTM DU configuration 1, . . . , N.

[0172] In some implementations, the LTM DU configuration Y of the procedure 490 includes at least one RS resource configuration Y, where 1 < Y < N. Each of the RS resource configuration(s) Y configures one or more RSs or one or more RS resources associated with the cell Y of the T-DU 174B. The RS(s) includes SSB(s) and / or CSI-RS(s). The RS resource(s) includes SSB resource(s) and / or CSLRS resource(s). In some implementations, each of the RS resource configuration(s) Y includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) Y is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the LTM DU configuration Y includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI-ResourceConfig IE(s). The S-DU 174A generates at least one serving report configuration for reporting, on the cell 124 A, measurement results of the RS(s) or RS resource(s) and includes the serving report configuration(s) in the first serving DU configuration. In some implementations, the serving report configuration(s) is / are (similar to) CSI-ReportConfig IE(s). In some implementations, the S-DU 174 A generates at least one serving RS resource configuration, considering or based on the RS resource configuration(s) Y and includes the serving RS resource configuration(s) in the first serving DU configuration. In some implementations, the S-DU 174 A includes the RS resource configuration(s) Y in the serving RS resource configuration(s). In other implementations, the S-DU 174A includes each of the RS resource configuration(s) Y in the serving RS resource configuration(s), except the RS resource configuration ID(s) in the RS resource configuration(s) Y. The S-DU 174 A assigns a RS resource configuration ID to a value for each of the serving RS resource configuration(s) (including the RS resource configuration(s) Y) and includes the RS resource configuration ID in the corresponding serving RS resource configuration.

[0173] In some implementations, the serving report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 124A for the UE 102 to transmit measurement results. In some implementations, each of the serving report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the serving RS resource configuration(s). Whilethe UE 102 communicates with the S-DU 174 A, the UE 102 transmits measurement results on the UL resource(s) via the cell 124 A to the S-DU 174 A, in accordance with the serving report configuration(s) (e.g., event 424). Correspondingly, the S-DU 174A receives the measurement results on the UL resource (s) via the cell 124 A from the UE 102, in accordance with the serving report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the serving RS resource configuration(s) and / or the serving report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). Depending on the implementation, the quantized measurement values include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0174] In other implementations, the LTM DU configuration Y of the procedure 490 includes at least one TCI state configuration Y, where 1 < Y < N. Each of the TCI state configuration(s) Y configures a TCI state that associates one or two DL RSs with a corresponding QCL type. In some implementations, the DL RS(s) can be associated with the cell Y operated by the T-DU 174B. In some implementations, each of the TCI state configuration(s) Y includes a TCI state ID. In some implementations, each of the TCI state configuration(s) Y is a TCI-State IE. In some implementations, the TCI state configuration(s) Y includes / is / are an ul-TCI-ToAddModList-r 17 field, one or more TCI-UL-State-r 17 IES, a dl-OrJointTCI-StateToAddModList-rl7 field, one or more TCI-State IEs, TCI- ActivatedConfig IE and / or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration Y includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configured on(s) Y. In some implementations, the S-DU 174A generates at least one serving TCI state configuration, considering or based on the TCI state configuration(s) Y and includes the serving TCI state configuration(s) in the first serving DU configuration. In some implementations, the serving TCI state configuration(s) 1 includes the TCI state configured on(s) Y. In other implementations, the S-DU 174 A includes each of the TCI state configuration(s) Y in the serving TCI state configuration(s), except the TCI state ID(s) in the TCI state configured on(s) Y. The S-DU 174A assigns a TCI state ID to a value for each ofthe serving TCI state configuration(s) (including the TCI state configuration(s) Y) and includes the TCI state ID in the corresponding serving TCI state configuration. In some implementations, while the S-DU 174A communicate 436 with the UE 102, the S-DU 174A transmits an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell Y. The S-DU 174A includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell Y, where the TCI state configuration is one of the TCI state configuration(s) Y or includes configurations of one of the TCI state configuration(s) Y.

[0175] In some implementations, the CU 172 transmits a CU-to-DU message including the ID(s) N+l, . . ., N+M to the S-DU 174A and receives a DU-to-CU message from the S-DU 174 A in response, similar to the CU-to-DU message 412 and the DU-to-CU message 414, respectively. In some implementations, the CU 172 includes the LTM DU configuration(s) N+l, . . ., N+M and / or cell ID(s) N+l, . . ., N+M in the CU-to-DU message. In some alternative implementations, the CU 172 can perform multiple LTM ID transfer procedures to transmit the ID(s) N+l, . . ., N+M, cell ID(s) N+l, . . ., N+M and / or LTM DU configuration(s) N+l, . . ., N+M to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the ID(s) N+l, . . . , N+M, cell ID(s) N+l, . . . , N+M and / or LTM DU configuration(s) 1, . . ., N in a CU-to-DU message similar to the message 412. Thus, the S- DU 174 A associates the ID(s) N+l, . . . , N+M with the LTM DU configured on(s) N+l, . . . , N+M and / or the cell ID(s) N+l, . . ., N+M, respectively. In some implementations, the S-DU 174 A generates a second serving DU configuration, based on the LTM DU configured on(s) N+l, N+2, . . . , and / or N+M, and includes the second serving DU configuration in the DU-to- CU message. In some implementations, the second serving DU configuration including configurations updating (e.g., augmenting, modifying or replacing) the first serving DU configuration and / or updating configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. In other implementations, the second serving DU configuration includes configurations that are not included in the first serving DU configuration. The CU 172 transmits an RRC reconfiguration message including the second serving DU configuration to the UE 102 via the S-DU 174 A. The UE 102 applies the second serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174 A using configurations included in the serving DUconfiguration 402 and / or the first serving DU configuration and not updated by the second serving DU configuration. In some implementations, the S-DU 174 A generates one or more new LI measurement configurations, based on LI measurement configuration(s) in the LTM DU configuration(s) N+l, N+2,. . . , and / or N+M, and includes the new LI measurement configuration(s) in the second serving DU configuration. In some implementations, the S- DU 174 A generates one or more new TCI state configuration, based on TCI state configuration(s) in the LTM DU configuration(s) N+l, N+2, . . . , and / or N+M, and includes the new TCI state configuration(s) in the second serving DU configuration.

[0176] In some implementations, in cases where the CU 172 and S-DU 174 A perform the procedure 380 with the UE 102, value(s) of the ID(s) 1, . . ., N of the procedure 380 are different from value(s) of the ID(s) 1, . . . ., N, and the ID(s) N+l ,...., N+M described for the scenario 400. In some implementations, in cases where the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the cell ID(s) 1, . . ., N of the procedure 380 are different from value(s) of the cell ID(s) 1, . . . ., N, and the cell ID(s) N+l ,...., N+M described for the scenario 400. In some implementations, in cases where the CU 172 and S- DU 174 A perform the procedure 380 with the UE 102, value(s) of the cell index(es) 1, . . ., N of the procedure 380 are different from value(s) of the cell index(es) 1, . . . ., N, and the cell index(es) N+l ,...., N+M described for the scenario 400.

[0177] Later in time, in some implementations, the UE 102 transmits 424 at least one measurement report to the S-DU 174A, similar to the event 324. The at least one measurement report (e.g., LI measurement report(s)) includes an event ID, first measurement result(s) for the cell 1 of the T-DU 174B, and / or includes second measurement result(s) for the cell 124 A. In some implementations, the first measurement result(s) can be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 1. Likewise, the second measurement result(s) can be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 124A. In some implementations, the event ID, RSRP, RSRQ and / or SINR are Ll-event ID, Ll- RSRP, Ll-RSRQ and / or Ll-SINR, respectively. Based on the first measurement result(s) and / or second measurement result(s), the S-DU 174A in some implementations transmits 430 a first LTM command (i.e., LTM command 1) including the ID 1 to the UE 102 to order the UE 102 to perform a serving cell change to the cell 1 of the T-DU 174B. In some implementations, the first LTM command includes the ID 1. In other implementations, the first LTM command includes the cell index 1. When the UE 102 receives the first LTMcommand, the UE 102 performs a serving cell change to the cell 1 from a serving cell in accordance with the LTM DU configuration 1. In some implementations, after (e.g., in response to) receiving the first LTM command, the UE 102 performs (or does not perform) 432 a random access procedure with the T-DU 174B, similar to the event 332. In some implementations, after (e.g., in response to) receiving the first LTM command or completing the random access procedure 432, the UE 102 communicates 436 with the T-DU 174B on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the T-DU 174B, similar to the event 336. If a serving cell change occurs in the procedure 380, the serving cell can be the cell 1 or cell 2 of the S-DU 174A. Otherwise, if no serving cell change occurs in the procedure 380 or the procedure 380 is not performed, the serving cell is the cell 124 A. If the first LTM command includes the ID 1, the UE 102 identifies the LTM DU configuration 1 and / or cell ID 1 (i.e., the cell 1), based the ID 1, as described for Fig. 3. If the first LTM command includes the cell index 1, the UE 102 identifies the LTM DU configuration 1, cell ID 1 (i.e., the cell 1) and / or LTM ID 1, based the cell index 1, as described for Fig. 3. The UE 102 applies the LTM DU configuration 1 to communicate with the T-DU 174B, after (e.g., in response to) receiving the first LTM command or successfully accessing the cell 1.

[0178] Depending on the implementation, when or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 430, the S-DU 174 A transmits 429 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some implementations, the S-DU 174A includes the cell ID 1 or the ID 1 (i.e., LTM ID) in the DU-to-CU message 429 to indicate that the S-DU 174A is to activate the LTM DU configuration 1 or trigger an LTM serving cell change. The S-DU 174 A can transmit the DU-to-CU message 429 to the CU 172 before or after transmitting the LTM command 430. In some implementations, when or after the CU 172 receives the DU-to-CU message 429, the CU 172 stops or suspends transmitting DL data for the UE 102 to the S-DU 174 A until receiving the DU-to-CU message 434. After receiving the DU-to-CU message 434, the CU 172 starts, continues or resumes transmitting DL data for the UE 102 to the T-DU 174B. When or after the T-DU 174B detects that UE 102 accesses the cell 1, the T-DU 174B transmits the DL data to the UE 102 via the cell 1.

[0179] The resource release procedure 496 can be similar to the procedure 396. Alternatively, in the resource release procedure 496, the CU 172 can transmit a CU-to-DU message (e.g., a UE Context Release Command message) to the S-DU 174 A to release a UEcontext of the UE 102. In response, the S-DU 174A releases a UE context of the UE 102 and transmits 440 a DU-to-CU message (e.g., a UE Context Release Complete message) to the CU-172.

[0180] The events 380, 404, 406, 490, 492, 494, 494, 424, 426, 428, 429, 430, 431, 432, 434, 436, 496, 498, 456 are collectively referred to in Fig. 4 as an LTM configuration and / or activation procedure 480.

[0181] Referring next to Fig. 5 A, in a scenario 500A, the base station 106 operates as an MN, and the base station 104 operates as an SN. The SN 104 includes a CU 172 and a DU 174. The scenario 500A is similar to the scenario 300, except that the scenario 500A is a DC scenario and the scenario 300 is a single connectivity (SC) scenario. The MN 106 can include a CU and a DU similar to the base station 104 of Fig. 3.

[0182] Initially, the UE 102 in DC communicates with the MN 106 and with SN 104. In the event 502, the UE 102 communicates with the DU 174 on cell 124A using a serving DU configuration and communicates with the CU 172 via the DU 174 using a serving CU configuration, similar to the event 302. In some alternative implementations, the UE 102 does not communicate with the CU 172 via the DU 174 in the event 302. In some implementations, the UE 102 in DC can communicate 502 UL PDUs and / or DL PDUs with the MN 106 and / or SN 104 via radio bearers which can include SRBs and / or DRB(s). The MN 106 and / or the SN 104 can configure the radio bearers to the UE 102. The UE 102 in DC communicates 502 UL PDUs and / or DL PDUs with the SN 104 on an SCG (i.e., SCG radio resources) that the SN 104 configures for communication with the UE 102. The UE 102 in DC communicates UL PDUs and / or DL PDUs with the MN 106 on an MCG (i.e., MCG radio resources) in accordance with a MN configuration (i.e., MCG configuration). In some implementations, the serving DU configuration is a SN configuration (i.e., SCG configuration). In the MN configuration, the MN 106 configures the MCG which includes at least one serving cell (e.g., the cell 126 and / or other cell(s)) operated by the MN 106. In the serving DU configuration, the SN 106 A configures the SCG which includes at least one serving cell (e.g., the cell 124A and / or other cell(s)) operated by the SN 104. In some implementations, the MN configuration includes multiple configuration parameters and the UE 102 receives the configuration parameters in one or more RRC messages from the MN 106. As described for Fig. 3, the serving DU configuration includes multiple configuration parameters. In some implementations, the UE 102 receives these configuration parameters inone or more RRC messages from the SN 104, e.g., via the MN 106 and / or on an SRB (e.g., SRB3) that the MN 106 or SN 104 configures to exchange RRC messages between the UE 102 and the SN 104.

[0183] While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 can perform 580 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. In some implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 can transmit the at least one measurement report to the CU 172 via the DU 174 and cell 124A in the events 504 and 506, similar to the events 304 and 306, respectively. In other implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 can transmit 505 at least one measurement report to the MN 106 via the cell 126. The MN 106 in turn transmits 507 the at least one measurement report to the CU 172. In some implementations, the MN 106 generates at least one SN message including the at least one measurement report and transmits the at least one SN message to the CU 172 in the event 507. In one implementation, the at least one SN message include RRC Transfer message(s) and / or SN Modification Request message(s).

[0184] After (e.g., in response to) receiving the at least one measurement report or while the SN 104 communicates with the UE 102, the SN 104 determines to prepare the first cell for the UE 102, as described for Fig. 3. The events 590, 592, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, and 556 are similar to the events 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, and 356, respectively. After receiving the first LTM command 530, transmitting the acknowledgement 531, or determining that the UE 102 successfully connects to the first cell 532 or 536, the UE 102 operating in DC with the MN 106 and SN 104 communicates 536 with the DU 174 on the first cell in accordance with the LTM DU configuration 1 and communicates 536 with the CU 172 via the DU 174, similar to the event 336. Later in time, the DU 174 and / or CU 172 can perform the LTM execution procedure 598 with the UE 102 to command the UE 102 to perform a cell change from the first cell to the second cell, similar to the procedure 398 or 498. As a result of the procedure 598, the UE 102 operating in DC with the MN 106 and SN 104 communicates 556 with the DU 174 on the second cell in accordance with the LTM DU configuration 2 and communicates 556 with the CU 172 via the DU 174, similar to the event 356.

[0185] The events 504, 506, 505, 507, 590, 592, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, 556 are collectively referred to in Fig. 5A as an LTM DU configuration and / or activation procedure 581.

[0186] Referring next to Fig. 5B, a scenario 500B is generally similar to the scenario 500A, except that the SN 104 transmits 517, 519 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 521, 523 the RRC reconfiguration complete message from the UE 102 via the MN 106. The RRC reconfiguration message 517, 519 is similar to the RRC reconfiguration message 316, 318. The RRC reconfiguration complete message 521, 523 is similar to the RRC reconfiguration message 320, 322. In some implementations, the SN 104 generates a first SN message (e.g., SN Modification Required message, SN Modification Required message, or RRC Transfer message) including the RRC reconfiguration message and transmits the first SN message to the MN 106 in the event 517. The MN 106 generates a MN RRC message including the RRC reconfiguration message and transmits 519 the MN RRC message to the UE 102. In response, the UE 102 generates a MN RRC response message including the RRC reconfiguration complete message and transmits 521 the MN RRC response message to the MN 106. In some implementations, the MN 106 generates a second SN message (e.g., SN Reconfiguration Complete message or RRC Transfer message) including the RRC reconfiguration complete message and transmits the second SN message to the SN 104 in the event 523. In some implementations, the MN RRC message and MN RRC response message can be an RRC reconfiguration message and an RRC reconfiguration complete message, respectively.

[0187] The events 504, 506, 505, 507, 590, 592, 594, 517, 519, 521, 523, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, 556 are collectively referred to in Fig. 5B as an LTM DU configuration and / or activation procedure 582.

[0188] Referring next to Fig. 6A, in a scenario 600A, the base station 106 operates as an MN, and the base station 104 operates as an SN, similar to the scenarios 300-500B. The SN 104 includes a CU 172, an S-DU 174A and a T-DU 174B, similar to the base station 104 in the scenario 400. While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 can perform 680 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. While the UE 102 communicates in DC with the M-DU 174 A and S-DU 174B, the CU 172 can perform 681 an LTM DU configurationand / or activation procedure with the UE 102 via the M-DU 174A or S-DU 174B, similar to the procedure 581 or 582.

[0189] Referring next to Fig. 6B, a scenario 600B similar to the scenarios 300-500B and 600 A, except that that the SN 104 transmits 617, 619 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 621, 623 the RRC reconfiguration complete message from the UE 102 via the MN 106.

[0190] Referring next to Fig. 7A, in a scenario 700A, the base station 104 operates as an MN and an SN, similar to the scenarios 300-600B. The base station 104 includes a CU 172, a master DU (M-DU) 174A and a secondary DU (S-DU) 174B. The CU 172 operates with the M-DU 174A as a MN, similar to the base station 104 in Fig. 3 or the MN 106 in Figs. 5A- 6B, and the CU 172 operates with the S-DU 174B as a SN, similar to the SN 104 in Figs. 5A- 6B.

[0191] In the scenario 700A, the UE 102 initially communicates 702 in DC with the M-DU 174A and S-DU 174B and communicates 702 with the CU 172 via the M-DU 174A and S- DU 174B. In the event 702, the UE 102 communicates with the S-DU 174B on cell 124 A using a serving DU configuration and communicates with the CU 172 via the S-DU 174B using a serving CU configuration, similar to the event 302. Events 704 and 706 are similar to the events 304 and 306. In some implementations, the UE 102 can transmit 705 at least one measurement report to the M-DU 174A, similar to the event 304. The M-DU 174A in turn transmits 707 at least one DU-to-CU message including the at les tone measurement report to the CU 172, similar to the event 306. While the UE 102 communicates in DC with the M- DU 174A and S-DU 174B, the CU 172 can perform 780 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380.

[0192] The events 704, 706, 705, 707, 790, 792, 794, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, 756 are collectively referred to in Fig. 7A as an LTM configuration and / or activation procedure 781.

[0193] Referring next to Fig. 7B, a scenario 700B similar to the scenarios 300-600B and 700A, except that that the CU 172 transmits 717, 719 the RRC reconfiguration message to the UE 102 via the M-DU 174 A and receives 721, 723 the RRC reconfiguration complete message from the UE 102 via the M-DU 174 A.

[0194] The events 704, 706, 705, 707, 790, 792, 794, 717, 719, 721, 723, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, 756 are collectively referred to in Fig. 7B as an LTM DU configuration and / or activation procedure 782.

[0195] Referring next to Fig. 8 A, in a scenario 800A, the base station 104 operates as an MN and an SN, similar to the scenarios 300-700B. The base station 104 includes a CU 172, a master DU (M-DU) 174A, a secondary DU (S-DU) 174B and a target secondary DU (T- DU) 174C. The CU 172 operates with the M-DU 174A as a MN and operates with the S-DU 174B as a SN. While the UE 102 communicates in DC with the M-DU 174 A and S-DU 174B, the CU 172 can perform 880 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 881 an LTM DU configuration and / or activation procedure with the UE 102 via the S-DU 174A, similar to the procedure 581 or 582.

[0196] Referring next to Fig. 8B, a scenario 800B similar to the scenarios 300-700B and 800 A, except that that the CU 172 transmits 817, 819 the RRC reconfiguration message to the UE 102 via the M-DU 174 A and receives 821, 823 the RRC reconfiguration complete message from the UE 102 via the M-DU 174 A.

[0197] Next, several example methods, that can be implemented in a RAN node such as a base station, a DU or a CU, to enable LTM, are discussed next with reference to Figs. 9-14B. Descriptions described for Figs. 3-8B can apply to Figs. 9-14B.

[0198] Fig. 9 illustrates an example method 900, which can be implemented by a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3-8B), for generating a DU configuration for a UE (e.g., the UE 102 in Figs. 3-8B).

[0199] The method 900 begins at block 902 where the DU in some implementations communicates with a UE (e.g., the UE 102) via a serving cell (e.g., event 302, 402, 502, 602, 702, 802, 380, 480, 580, 680, 780, 880, 581, 582, 681, 780, 880, or 881). At block 904, the DU receives, from a CU (e.g., the CU 172 of Figs. 3-8B), a first CU-to-DU message requesting preparation of a first cell for LTM for the UE (e.g., event 308, 390, 490, 590, 690, 790, or 890). At block 906, the DU generates a DU configuration that configures the first cell for LTM, including a first type of cell change configuration and excluding a second type of cell change configuration. In some implementations, the first type of cell change configuration and the second type of cell change configuration include a configurationspecific to lower layer mobility operations (e.g., LTM cell switch information) and a configuration agnostic / unrelated to lower layer mobility and / or associated with upper layer mobility operations (e.g., a reconfiguration with sync configuration), respectively. In some implementations, the first type of cell change configuration includes configuration parameters for accessing the first cell upon a serving cell change (e.g., an LTM cell switch). In some implementations, the second type of cell change configuration includes configuration parameters for accessing a cell upon a serving cell change (e.g., higher layer triggered mobility cell switch such as handover or PSCell change). For example, the LTM cell switch information is Itm-CellSw itchinfo field o LTM- CellSw itchinfo IE, and the reconfiguration with sync configuration is a reconfigurationWithSync field or a ReconfigurationWithSync IE.

[0200] At block 908, the DU transmits, to the CU, a first DU-to-CU message including the DU configuration (e.g., event 310, 390, 490, 590, 690, 790, or 890). At block 910, in some implementations, the DU transmits an LTM command to the UE to command the UE to perform an LTM cell switch to the first cell (e.g., event 330, 430, 530, 630, 730, or 830). At block 912, the DU detects that the UE accesses the first cell after transmitting the LTM command (e.g., event 332, 432, 532, 632, 732, or 832). At block 914, the DU transmits a second DU-to-CU message to the CU to indicate that the UE accesses the first cell (e.g., event 334, 434, 534, 634, 734, or 834). At block 916, the DU in some implementations communicates with the UE on the first cell and the DU configuration (e.g., event 336, 356, 436, 456, 536, 556, 636, 656, 736, 756, 836, or 856).

[0201] In some implementations, the DU is a serving DU (i.e., a source DU). In other implementations, the DU is a candidate DU. In the case of the candidate DU, block 910 is omitted.

[0202] In some implementations, the first CU-to-DU message is a UE Context Setup Request message, and the first DU-to-CU message is a UE Context Setup Response message. In some such implementations, the description for Fig. 11 A (e.g., as described below) applies to Fig. 9. In other implementations, the first CU-to-DU message is a UE Context Modification Request message, and the first DU-to-CU message is a UE Context Modification Response message. In some such implementations, the description for Figs.1 IB and 11C (e.g., as described below) applies to Fig. 9. In some implementations, the second DU-to-CU message is an Access Success message. In other implementations, the second DU-to-CU message is an LTM Cell Change Notification message.

[0203] In some implementations, at block 904, the first CU-to-DU message contains an LTM Indicator IE in the LTM Information to be Setup IE or in the LTM Information to be Modification IE.

[0204] In some implementations, the DU determines that the first CU-to-DU message does not request for reconfiguration with sync when the first CU-to-DU message includes an LTM indicator. Thus, the DU refrains from including a reconfiguration with sync configuration (e.g., the second configuration for mobility) in the DU configuration when the first CU-to- DU message includes an LTM indicator.

[0205] In some implementations, the DU configuration is an LTM DU configuration as described above. In some implementations, the DU configuration is a CellGroupConfig IE. In some implementations, the reconfigurationWithSync field or ReconfigurationWithSync IE is currently defined (e.g., in the 3GPP TS38.331vl7.5.0 and / or later versions). The ReconfigurationWithSync IE contains information for the UE to perform a cell switch (e.g., handover or PSCell change).

[0206] In an example implementation, the ReconfigurationWithSync IE is defined as follows: ReconfigurationWithSync ::= SEQUENCE { spCellConfigCommon ServingCellConfigCommon OPTIONAL — Need M, newUE-Identity RNTI-Value, t304 ENUMERATED {ms50, mslOO, msl50, ms200, ms500, mslOOO, ms2000, mslOOOO}, rach- ConfigDedicated CHOICE {uplink RACH-ConfigDedicated, supplementaryUplink RACH-ConfigDedicated} OPTIONAL, - Need N ..., [[smtc SSB-MTC OPTIONAL - Need S]], [[daps-UplinkPowerConfig-rl6 DAPS-UplinkPowerConfig-rl6 — Need N]], [[sl- PathSwitchConfig-rl7 SL-PathSwitchConfig-rl7 OPTIONAL — Cond DirectT olndirect-PathSwitch] } .

[0207] In some implementations, the Itm-CellSw itchinfo field or LTM-CellSw itchinfo IE is currently defined (e.g., as defined in the R2-2308435 or 3GPP RRC specification vl8.0.0 and / or later versions). The LTM-CellSw itchinfo IE contains information for the UE to perform a cell switch (i.e., an LTM cell switch).

[0208] In an example implementation, the LTM-CellSw itchinfo IE IE is defined as follows: LTM-CellSwitchInfo-rl8 ::= SEQUENCE { spCellConfigCommon-rl8 ServingCellConfigCommon OPTIONAL, — Need M newUE-Identity-rl8RNTI-Value, rach-ConfigDedicated-rl8 CHOICE { uplink-rl8 RACH-ConfigDedicated, supplementaryUplink-rl8 RACH-ConfigDedicated } OPTIONAL, — Need N ...}

[0209] Fig. 10 is a flow diagram of an example method 1000, similar to method 900, which can be implemented by a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3-8B), for generating a DU configuration for a UE (e.g., the UE 102 in Figs. 3-8B).

[0210] The method 1000 begins at block 1002 where the DU receives, from the CU (e.g., the CU 172 in Figs. 3-8B), a CU-to-DU message requesting preparation of a cell for mobility for a UE (e.g., event 308, 390, 490, 590, 690, 790, or 890). At block 1004, the DU determines whether the CU-to-DU message includes an LTM indicator. If the DU determines that the CU-to-DU message includes an LTM indicator at block 1004, the flow proceeds to block 1006, where the DU generates a DU configuration, including a first configuration and excluding a second configuration. The flow then proceeds to block 1010, where the DU transmits, to the CU, a DU-to-CU message including the DU configuration (e.g., event 310, 390, 490, 590, 690, 790, or 890). Otherwise, if the DU determines that the CU-to-DU message does not include an LTM indicator at block 1004, the flow instead proceeds to block 1008 where the DU generates a DU configuration including the second configuration. The flow then proceeds to block 1010.

[0211] In some implementations, the first configuration includes configuration parameters for accessing the first cell upon a cell switch. In some implementations, the second configuration includes configuration parameters for accessing the first cell upon a cell switch. In some implementations, the first configuration is a first type of cell change configuration (e.g., a configuration specific to lower layer mobility operations) and the second configuration in a second type of cell change configuration (e.g., a configuration agnostic / unrelated to lower layer mobility operations and / or associated with upper layer mobility operations).

[0212] In some implementations, the CU-to-DU message is a UE Context Setup Request message, and the DU-to-CU message is a UE Context Setup Response message. In other implementations, the CU-to-DU message is a UE Context Modification Request message, and the DU-to-CU message is a UE Context Modification Response message. Examples and descriptions for Fig. 9 can apply to Fig. 10.

[0213] Fig. 11 A is a flow diagram of an example method 1100A, similar to the methods 900 or 1000, and can be implemented by a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3-8B), for generating an LTM DU configuration for a UE (e.g., the UE 102 in Figs. 3- 8B).

[0214] The method 1100 A begins at block 1102 A, where the DU receives, from a CU (e.g., the CU 172 in Figs. 3-8B), a UE Context Modification Request message including a cell ID for requesting preparing a first cell for mobility (i.e., a serving cell switch) for a UE (e.g., event 308, 390, 490, 590, 690, 790, 890). At block 1104A, the DU determines whether the UE Context Modification Request message includes an LTM indicator. If the DU determines that the UE Context Modification Request message includes an LTM indicator at block 1104A, the flow proceeds to block 1106. At block 1106, the DU generates an LTM DU configuration including an LTM cell switch information field or element (e.g., an LTM- CellSwitchlnfo lE / field) and excluding a reconfiguration with sync information field or element (e.g., a reconfigurationWithSync lE / field). Otherwise, if the DU determines that the UE Context Modification Request message does not include an LTM indicator at block 1104 A, the flow proceeds to block 1108. At block 1108, the DU generates an LTM DU configuration including the reconfiguration with sync information field or element (e.g., a reconfigurationWithSync lE / field). The flow proceeds to block 1110A from block 1106 as well as block 1108. At block 1110A, the DU transmits, to the CU, a UE Context Modification Response message including the DU configuration (e.g., event 390, 490, 590, 690, 790, 890).

[0215] In some implementations, the cell ID is a SpCell ID field / IE. In some implementations, at block 1102 A, the DU determines that the UE Context Modification Request message is not a request for a reconfiguration with sync configuration (e.g., reconfigurationWithSync lE / field) when the UE Context Modification Request message includes a SpCell ID and an LTM indicator. Thus, the DU refrains from including such a configuration and / or information element or field (e.g., a reconfigurationWithSync lE / field) in the DU configuration when the UE Context Modification Request message includes a SpCell ID and an LTM indicator.

[0216] Fig. 1 IB is a flow diagram of an example method 1100B similar to the method 1100A except that the method 1100B includes blocks 1102B, 1104B, and 1110B instead of blocks 1102 A, 1104 A, and 1110A. The differences are described below.

[0217] At block 1102B, the DU receives, from a CU, a UE Context Setup Request message including handover preparation information (e.g., a Handover Preparationinformation IE) for requesting preparation of a first cell for mobility (i.e., a serving cell switch) for a UE (e.g., event 308, 390, 490, 590, 690, 790, or 890). At block 1104B, the DU determines whether theUE Context Setup Request message includes an LTM indicator. If the DU determines that the UE Context Setup Request message includes an LTM indicator at block 1104B, the flow proceeds to block 1106. Otherwise, if the DU determines that the UE Context Setup Request message does not include an LTM indicator at block 1104B, the flow proceeds to block 1108. The flow proceeds to block 1110B from block 1106 as well as block 1108. At block 1 HOB, the DU transmits, to the CU, a UE Context Setup Response message including the DU configuration (e.g., event 310, 390, 490, 590, 690, 790, 890).

[0218] In some implementations, the DU determines that the UE Context Setup Request message does not request reconfiguration with sync when the UE Context Setup Request message includes handover preparation information (e.g., a HandoverPreparationlnformation IE) and an LTM indicator. Thus, the DU refrains from including a reconfigurationWithSync lE / field in the DU configuration when the UE Context Setup Request message includes a HandoverPreparationlnformation IE and an LTM indicator.

[0219] In some implementations, the HandoverPreparationlnformation IE is currently defined (e.g., as defined in the 3GPP TS 38.33 lvl5.0.0 and / or later versions).

[0220] Fig. 11C is a flow diagram of an example method 1100C similar to the methods 1100A or 1100B, except that the method 1100C includes blocks 1102C, 1104C, and 1110C instead. The differences are described below.

[0221] At block 1102C, the DU receives, from a CU, a UE Context Setup Request message including CG configuration information (e.g., a CG-Configlnfo IE) for requesting preparation of a first cell for mobility (i.e., a serving cell switch) for a UE (e.g., event 308, 390, 490, 590, 690, 790, or 890). At block 1104C, the DU determines whether the UE Context Setup Request message includes an LTM indicator. If the DU determines that the UE Context Setup Request message includes an LTM indicator at block 1104C, the flow proceeds to block 1106. Otherwise, if the DU determines that the UE Context Setup Request message does not include an LTM indicator, the flow proceeds to block 1108. The flow then proceeds to block 1110C from block 1106 as well as block 1108. At block 1110C, the DU transmits, to the CU, a UE Context Setup Response message including the DU configuration (e.g., event 310, 390, 490, 590, 690, 790, 890).

[0222] In some implementations, at block 1102C, the DU determines that the UE Context Setup Request message does not request for reconfiguration with sync when the UE Context Setup Request message includes CG configuration information (e.g., a CG-Configlnfo IE) andan LTM indicator. Thus, the DU refrains from including a reconfigurationWithSync lE / field in the DU configuration when the UE Context Setup Request message includes a CG- Configlnfo IE and an LTM indicator.

[0223] In some implementations, the CG-Configlnfo IE is currently defined (e.g., as defined in the 3GPP TS 38.33 lvl5.0.0 and / or later versions).

[0224] Examples and implementations described for Figs. 9-10 can apply to Figs. 11 A- 11C.

[0225] Fig. 12 illustrates an example method 1200, which can be implemented by a CU (e.g., the CU 172 in Figs. 3-8B) communicatively coupled in some implementations to a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3-8B), for requesting a DU configuration for a UE (e.g., the UE 102 in Figs. 3-8B).

[0226] The method 1200 begins at block 1202, where the CU in some implementations communicates with a UE via a serving DU (e.g., event 302, 402, 502, 602, 702, 802, 380, 480, 580, 680, 780, 880, 581, 582, 681, 780, 880, or 881). At block 1204, the CU generates a first CU-to-DU message to prepare a first cell for LTM for the UE, where the first CU-to-DU message includes an LTM indicator and excludes handover preparation information (e.g., HandoverPreparationlnformation IE). At block 1206, the CU transmits the first CU-to-DU message to a DU (the serving DU or a candidate DU) (e.g., event 308, 390, 490, 590, 690, 790, or 890). At block 1208, the CU receives a first DU-to-CU message, including a DU configuration, from the DU, where the DU configuration configures the first cell for LTM, includes a first type of cell switch configuration, and excludes a second type of cell switch configuration (e.g., event 310, 390, 490, 590, 690, 790, or 890). At block 1210, the CU transmits the DU configuration to the UE (e.g., event 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, or 819). In some implementations, the CU transmits the DU configuration to the UE via the serving DU. In other implementations, the CU transmits the DU configuration to the UE via another DU, another CU, or a base station.

[0227] Fig. 13A is a flow diagram of an example method 1300A, similar to method 1200, which can be implemented by a CU (e.g., the CU 172 in Figs. 3-8B) communicatively coupled in some implementations to a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3- 8B), for requesting an LTM DU configuration for a UE (e.g., the UE 102 in Figs. 3-8B).

[0228] The method 1300 A begins at block 1302, where the CU in some implementations communicates with a UE via a serving DU (e.g., event 302, 402, 502, 602, 702, 802, 380,480, 580, 680, 780, 880, 581, 582, 681, 780, 880, or 881). At block 1304, the CU generates a first CU-to-DU message to prepare a first cell for LTM for the UE, where the first CU-to-DU message includes an LTM indicator and handover preparation information (e.g., HandoverPreparationlnformation IE). At block 1306, the CU transmits the first CU-to-DU message to a DU (the serving DU or a candidate DU) (e.g., event 308, 390, 490, 590, 690, 790, or 890). At block 1308, the CU receives a first DU-to-CU message including a DU configuration from the DU, where the DU configuration configures the first cell for LTM, includes a first type of cell change configuration, and a second type of cell change configuration (e.g., event 310, 390, 490, 590, 690, 790, or 890). At block 1310, the CU removes the second type of cell change configuration from the DU configuration. At block 1312, the CU transmits the DU configuration to the UE (e.g., event 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, or 819).

[0229] In some implementations, the first CU-to-DU message and the first DU-to-CU message are a UE Context Setup Request message and a UE Context Setup Response message, respectively. In some implementations, the DU configuration and the second type of cell change configuration are and / or include a CellGroupConfig W and a ReconfigurationWithSync IE (e.g., as defined in 3GPP specification 38.331).

[0230] When a UE Context Setup Request message includes handover preparation information (e.g., ^ HandoverPreparationlnformation IE) (e.g., as described in section 8.3.1 in 3GPP specification 38.473), the DU shall regard the information (e.g., the HandoverPreparationlnformation IE) as a reconfiguration with sync (e.g., as defined in 3GPP specification 38.331). That is, when a UE Context Setup Request message includes a HandoverPreparationlnformation IE, the DU shall include the ReconfigurationWithSync IE in a CellGroupConfig IE and include the CellGroupConfig UE Context Setup Response message. The DU also includes the first type of cell change configuration (e.g., LTM cell switch information) in the CellGroupConfig IE. The CU then includes the CellGroupConfig IE in an RRC reconfiguration message (i.e., RRCReconfiguration message) and transmits the RRC reconfiguration message to the UE (e.g., as described in 3 GPP specification 38.331). If the CellGroupConfig IE includes both the ReconfigurationWithSync IE and the first type of cell change configuration, the UE may determine that the CellGroupConfig IE has an error because the UE does not know which one the UE should use to perform a serving cell change.

[0231] Fig. 13B is a flow diagram of an example method 1300B similar to the method 1300A, except that the method 1300B includes block 1305 instead of block 1304. The difference is that, at block 1305, the CU generates a first CU-to-DU message to prepare a first cell for LTM for the UE, where the first CU-to-DU message includes an LTM indicator and CG configuration information (e.g., a CG-Configlnfo IE).

[0232]

[0233] Fig. 14A is a flow diagram of an example method 1400A similar to the methods 1200, 1300A or 1300B, which can be implemented by a CU (e.g., the CU 172 in Figs. 3-8B) communicatively coupled in some implementations to a DU (e.g., the DU 174, 174A, 174B, or 174C in Figs. 3-8B), for requesting an LTM DU configuration for a UE (e.g., the UE 102 in Figs. 3-8B).

[0234] The method 1400 A begins at block 1402, where the CU in some implementations communicates with a UE via a serving DU on a PCell (e.g., event 302, 402, 580, 680, 780, or 880). In some implementations, the CU is a CU of an MN. At block 1404, the CU decides to transmit, to a first DU, a CU-to-DU message requesting preparing a first cell for mobility for a UE. At block 1406, the CU determines whether the mobility preparation is for LTM. If the CU determines that the mobility preparation is for LTM at block 1406, the flow proceeds to block 1408. At block 1408, the CU refrains from including handover preparation information (e.g., HandoverPreparationlnformation IE) in the CU-to-DU message. The flow then proceeds to block 1410 where the CU in some implementations includes a cell group configuration information element or field (e.g., a CellGroupConfig ^E) in the CU-to-DU message. Alternatively, the CU refrains from including the cell group configuration information (e.g., the CellGroupConfig ^E) in the CU-to-DU message.

[0235] Otherwise, if the CU determines that the mobility preparation is not for LTM (i.e., the mobility preparation is a higher layer triggered mobility preparation) at block 1406, the flow proceeds to block 1412. At block 1412, the CU includes handover preparation information (e.g., HandoverPreparationlnformation IE) in the CU-to-DU message. The flow then proceeds to block 1414, where the CU in some implementations refrains from including the cell group configuration information (e.g., a CellGroupConfig E) in the CU-to-DU message. The flow continues to proceed to block 1416 from block 1408 or 1410 as well as block 1412 or 1414. At block 1416, the CU transmits, to the first DU, the CU-to-DU message (e.g., event 310, 390, 490, 590, 690, 790, or 890).

[0236] Fig. 14B is a flow diagram of an example method 1400B, similar to the method 1400 A, except that the method 1400B includes blocks 1403, 1409, and 1413 instead of blocks 1402, 1408, and 1412. The differences are described below.

[0237] At block 1403, the CU in some implementations communicates with a UE via a serving DU on a PSCell (e.g., event 502, 602, 702 or 802). In some implementations, the CU is a CU of an SN. At block 1406, if the CU determines that the mobility preparation is for LTM at block 1406, the flow proceeds to block 1409. At block 1409, the CU refrains from including the CG configuration information (e.g., a CG-Configlnfo lE / field) in the CU-to-DU message. Otherwise, if the CU determines that the mobility preparation is not for LTM at block 1406, the flow proceeds to block 1413. At block 1413, the CU includes CG configuration information (e.g., a CG-Configlnfo lE / field) in the CU-to-DU message.

[0238] Examples and implementations described for Figs. 9-11C can apply to Figs. 12A- 14B.

[0239] The following list of examples reflects a variety of the embodiments explicitly contemplated by the present disclosure.

[0240] Example 1. A method, implemented in a DU of a RAN node, for generating a DU configuration for mobility for a UE the method comprising: receiving, at the DU, a cell mobility message from a CU of the RAN node; in a first instance, when the cell mobility message includes a lower layer mobility indication, generating, at the DU, a DU configuration including a first configuration for mobility and excluding a second configuration for mobility; in a second instance, when the cell mobility message does not include a lower layer mobility indication, generating, at the DU, the DU configuration including the second configuration and excluding the first configuration; and transmitting, from the DU to the CU, the DU configuration.

[0241] Example 2. The method of example 1, wherein the first configuration is a first configuration for mobility that is specific to lower layer mobility operations.

[0242] Example 3. The method of example 2, wherein the first configuration for mobility that is specific to lower layer mobility operations includes a lower layer cell switch information element.

[0243] Example 4. The method of any one of the preceding examples, wherein the second configuration is a second configuration for mobility that is associated with upper layer mobility operations.

[0244] Example s. The method of example 4, wherein the second configuration for mobility that is associated with upper layer mobility operations includes a synchronization reconfiguration information element.

[0245] Example 6. The method of any one of the preceding examples, wherein the cell mobility message is a CU-to-DU message requesting that the DU prepare a cell for mobility for the UE. 7.

[0246] Example 7. The method of any one of examples 1-5, wherein the cell mobility message is a UE context modification message.

[0247] Example 8. The method of example 7, wherein the UE context modification message includes a cell identifier indicative of a cell to which the UE should switch.

[0248] Example 9. The method of example 8, wherein the generating the DU configuration including the first configuration and the generating the DU configuration including the second configuration are further based on the cell identifier.

[0249] Example 10. The method of any one of examples 1-5, wherein the cell mobility message is a UE context setup message.

[0250] Example 11. The method of example 10, wherein the UE context setup message includes handover preparation information indicative of a cell to which the UE should switch.

[0251] Example 12. The method of example 11, wherein the generating the DU configuration including the first configuration and the generating the DU configuration including the second configuration are further based on the handover preparation information.

[0252] Example 13. The method of example 10, wherein the UE context setup message includes configured grant information indicative of a cell to which the UE should switch.

[0253] Example 14. The method of example 13, wherein the generating the DU configuration including the first configuration and the generating the DU configuration including the second configuration are further based on the configured grant information.

[0254] Example 15. A method, in a central unit (CU) of a radio access network (RAN) node, for providing a distributed unit (DU) configuration for mobility for a user equipment(UE) via a DU, the method comprising: generating, at the CU, a mobility message including a lower layer mobility indication; transmitting, from the CU to the DU, the mobility message; receiving, at the CU from the DU, a DU configuration including a first configuration for mobility; and transmitting, from the CU, the DU configuration including the first configuration and excluding a second configuration for mobility.

[0255] Example 16. The method of example 15, wherein the first configuration is a first configuration for mobility that is specific to lower layer mobility operations.

[0256] Example 17. The method of example 16, wherein the first configuration for mobility that is specific to lower layer mobility operations includes a lower layer cell switch information element.

[0257] Example 18. The method of any one of examples 15-17, wherein the second configuration is a second configuration for mobility that is associated with upper layer mobility operations.

[0258] Example 19. The method of example 18, wherein the second configuration for mobility that is associated with upper layer mobility operations includes a synchronization reconfiguration information element.

[0259] Example 20. The method of any one of examples 15-19, wherein the generating the mobility message includes: excluding handover preparation information in the mobility message.

[0260] Example 21. The method of example 20, wherein the DU configuration excludes a second configuration for mobility in response to the excluding the handover preparation information.

[0261] Example 22. The method of either of example 20 or 21, wherein the excluding the handover preparation information is in response to: determining to transmit a message to the DU requesting the DU to prepare a cell for a mobility operation other than a lower layer mobility operation.

[0262] Example 23. The method of any one of examples 15-19, wherein the generating the mobility message includes: including handover preparation information in the mobility message.

[0263] Example 24. The method of example 23, wherein the DU configuration includes a second configuration for mobility in response to the including the handover preparationinformation, the method further comprising: removing the second configuration from the DU configuration prior to transmitting the DU configuration.

[0264] Example 25. The method of either of examples 23 or 24, wherein the including the handover preparation information is in response to: determining to transmit a message to the DU requesting the DU to prepare a cell for a lower layer mobility operation.

[0265] Example 26. The method of any one of examples 15-19, wherein the generating the mobility message includes: including configured grant information in the mobility message.

[0266] Example 27. The method of example 26, wherein the DU configuration includes a second configuration for mobility in response to the including the configured grant information, the method further comprising: removing the second configuration from the DU configuration prior to transmitting the DU configuration.

[0267] Example 28. The method of either of examples 26 or 27, wherein the including the configured grant information is in response to: determining to transmit a message to the DU requesting the DU to prepare a cell for a lower layer mobility operation.

[0268] Example 29. The method of any one of examples 15-19, wherein the generating the mobility message includes: excluding configured grant information in the mobility message.

[0269] Example 30. The method of example 29, wherein the excluding the configured grant information is in response to: determining to transmit a message to the DU requesting the DU to prepare a cell for a mobility operation other than a lower layer mobility operation.

[0270] Example 31. The method of any one of examples 20-22, 29, or 30, wherein the generating the mobility message further includes: refraining from including a cell group configuration information element in the mobility message.

[0271] Example 32. The method of any one of examples 23-28, wherein the generating the mobility message further includes: including a cell group configuration information element in the mobility message.

[0272] Example 33. A network node comprising: a transceiver; and processing hardware configured to implement a method according to any one of the preceding examples.

[0273] The following description may be applied to the description above.

[0274] Generally speaking, description for one of the above figures can apply to another of the above figures. Examples, implementations and methods described above can be combined, if there is no conflict. An event or block described above can be optional or omitted. For example, an event or block with dashed lines in the figures can be optional. In some implementations, “message” is used and can be replaced by “information element (IE)”, and vice versa. In some implementations, “IE” is used and can be replaced by “field”, and vice versa. In some implementations, “configuration” can be replaced by “configurations” or “configuration parameters”, and vice versa. In some implementations, the “LTM command” can be replaced by “serving cell change command”, “Layer 1 / Layer 2 switching command”, “lower layer switching command” or “lower layer serving cell change command”. In some implementations, “some” means “one or more”. In some implementations, “at least one” means “one or more”. In some implementations, the “DU configuration” can be replaced by “cell group configuration”. In some implementations, the “cell index” can be replaced with “serving cell index”, “LTM cell index”, “special cell (SpCell) index”, “PCell index” or “PSCell index”. In some implementations, the “serving” can be replaced by “source”. In some implementations, the “measurement report” can be replaced by “measurement result(s)”. In some implementations, “identify” can be replaced with “determine” or vice versa.

[0275] A user device in which the techniques of this disclosure can be implemented (e.g., the UE 102) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an intemet-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0276] Certain embodiments are described in this disclosure as including logic or a number of components or modules. Modules may can be software modules (e.g., code, or machine- readable instructions stored on non-transitory machine-readable medium) or hardware modules. A hardware module is a tangible unit capable of performing certain operations andmay be configured or arranged in a certain manner. A hardware module can comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0277] When implemented in software, the techniques can be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software can be executed by one or more general -purpose processors or one or more special-purpose processors.

[0278] Upon reading this disclosure, those of skill in the art will appreciate still additional and alternative structural and functional designs for handling mobility between base stations through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

Claims

CLAIMS:

1. A method implemented in a distributed unit (DU) of a distributed base station that includes the DU and a central unit (CU), the method comprising: receiving, from the CU, a request to prepare a cell for mobility by a user equipment (UE); generating, at the DU and in response to the request, a DU configuration, including generating a first configuration for mobility or a second configuration for mobility, depending on whether the request includes a lower-layer triggered mobility (LTM) indication; and transmitting, to the CU, the DU configuration that (i) includes the first configuration for mobility or (ii) includes the second configuration for mobility and excludes the first configuration for mobility.

2. The method of claim 1, further comprising: wherein the first configuration is related to lower layer mobility operations.

3. The method of claim 1 or 2, further comprising: wherein the second configuration is unrelated to lower layer mobility operations.

4. The method of any of the preceding claims, further comprising: wherein the second configuration is related to upper layer mobility operations.

5. The method of claim 4, wherein the second configuration includes a reconfiguration with sync information.

6. The method of any of the preceding claims, wherein: the receiving of the request to prepare the cell for mobility includes receiving one of a UE Context Setup Request message or UE Context Modification Request message.

7. The method of any of the preceding claims, wherein: the transmitting of the DU configuration includes transmitting a UE Context Setup Response message or a UE Context Modification Response message.

8. The method of any of the preceding claims, further comprising: receiving, from the CU, handover preparation information.

9. A method implemented in central unit (CU) of a distributed base station that includes the CU and a distributed unit (DU), the method comprising: transmitting, to the CU, a request to prepare a cell for mobility by a user equipment (UE); receiving, in a first instance when the request includes a lower-layer triggered mobility (LTM) indication, a first DU configuration that includes the first configuration for mobility; and receiving, in a second instance when the request does not include the LTM indication, a second DU configuration that includes a second configuration for mobility and excludes the first configuration for mobility.

10. The method of claim 9, further comprising: wherein the first configuration is related to lower layer mobility operations11. The method of claim 9 or 10, further comprising: wherein the second configuration is related to upper layer mobility operations.

12. The method of claim 11, wherein the second configuration includes a reconfiguration with sync information.

13. The method of any of claims 9-12, further comprising: transmitting, to the DU, handover preparation information.

14. The method of any of claims 9-13, further comprising: transmitting, to the DU, an identifier of the cell.

15. A radio access network (RAN) node comprising: a transceiver; and processing hardware configured to implement a method according to any one of the preceding claims.

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