Configuring early timing advance acquisition

Abstract

A distributed unit (DU) of a distributed base station that also includes a central unit (CU) receiving, from the CU, a request to prepare a target cell for a low-layer triggered mobility (LTM) cell switch by a user equipment (UE) communicating in a serving cell. The DU determines that the UE supports early timing advance (TA) acquisition and transmits, to the UE in the serving cell, a command to transmit a random access preamble in the target cell for the early TA acquisition.

Description

CONFIGURING EARLY TIMING ADVANCE ACQUISITIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of the filing date of provisional U.S. Patent Application No 63 / 513,568, entitled “Configuring Early Timing Advance Acquisition,” filed on July 13, 2023 and provisional U.S. Patent Application No. 63 / 580,316, entitled “Configuring Early Timing Advance Acquisition,” filed on September 1, 2023. The entire contents of the provisional application are hereby expressly incorporated herein by reference.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to configuring a user equipment (UE) to perform early timing advance acquisition with a radio access network (RAN).BACKGROUND

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

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

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

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

[0007] When the UE moves from 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 this end, the RAN configures the UE to transmit Layer 3 (L3) measurement results. Using the L3 measurement results from the UE, the RAN transmits an RRC reconfiguration message configuring Reconfiguration with Synchronization (e.g., the RRCreconfiguration message includes a ReconfigurationWithSync IE) for a 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 RAN has to release the at least one SCell due to the change of the PCell or PSCell. The serving cell change involves complete L2 (and LI) resets, leading to longer latency, larger overhead, and longer interruption time. For these reasons, 3GPP proposed to develop new mobility techniques for serving cell changes. These techniques aim to reduce latency and overhead and are called low-layer triggered mobility (LTM), or faster serving cell switching.

[0008] When a UE switches from a serving cell to a target cell in a RAN, the UE has to perform a random access procedure in order to synchronize with the target cell in the uplink direction, i.e., in the direction from the UE to the RAN. The UE can start communicating data with the RAN via the target cell only after the UE successfully completes the random access procedure. As a result, an interruption in data communication occurs during the serving cell switch. If the UE could obtain a timing advance value (TA) for synchronization with the target cell before switching to the target cell, the UE could avoid this interruption. However, it is not clear how the RAN should configured the UE to obtain uplink synchronization with the target cell prior to connecting to the serving cell, especially when a base station providing the serving cell and / or a target cell is a distributed base station including a central unit (CU) and or more distributed units (DUs).SUMMARY

[0009] An example embodiment of the techniques of this disclosure is a method implemented in a distributed unit (DU) of a distributed base station that also includes a central unit (CU). The method comprises receiving, from the CU, a request to prepare a target cell for a low-layer triggered mobility (LTM) cell switch by a user equipment (UE) communicating in a serving cell; determining that the UE supports early timing advance (TA) acquisition; and transmitting, to the UE serving cell, a command to transmit a random access preamble in the target cell for the early TA acquisition.

[0010] Another example embodiment of these techniques is a method implemented in a central unit (CU) of a distributed base station that also equipped with one or more distributed unit (DUs) including a serving DU. The method comprises receiving a DU-to-CU message including an LTM DU configuration related to a target cell and a random access configuration parameter for configuring a UE for early TA acquisition in the target cell;associating the LTM DU configuration with an LTM identifier (ID); and transmitting, to the serving DU, the LTM ID and the random access configuration parameter.

[0011] Still another example embodiment of these techniques is a node in a communication network comprising processing hardware and configured to implement one of the methods above.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Fig. 1A 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 early timing advance (TA) acquisition;

[0013] 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;

[0014] Fig. 2A is a block diagram of an example protocol stack according to which the UE of Fig. 1A communicates with base stations;

[0015] Fig. 2B is a block diagram of an example protocol stack according to which the UE of Fig. 1A communicates with a CU and a DU; and

[0016] 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;

[0017] 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;

[0018] 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);

[0019] Fig. 5B is a messaging diagram of an example scenario generally similar to that of Fig. 5A, but in which the SN performs LTM configuration via the main node (MN) rather than directly;

[0020] 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);

[0021] 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;

[0022] 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;

[0023] 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;

[0024] 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;

[0025] 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;

[0026] Fig. 9A is a flow diagram of an example method for configuring a UE to transmit a random access preamble for early TA acquisition, which can be implemented in a DU;

[0027] Fig. 9B is a flow diagram of a method similar to that of Fig. 9A, but here the DU receives an LTM ID separately from the request to prepare a cell for LTM;

[0028] Fig. 9C is a flow diagram of a method similar to that of Fig. 9A, but here the DU includes a cell ID rather than the LTM ID in the command to transmit a random access preamble in the target cell;

[0029] Fig. 9D is a flow diagram of a method similar to that of Fig. 9A, but here the DU receives an LTM ID separately from the request to prepare a cell for LTM and includes a cell ID rather than the LTM ID in the command to transmit a random access preamble in the target cell;

[0030] Fig. 9E is a flow diagram of a method similar to that of Fig. 9A, but here the DU includes a cell index rather than the LTM ID in the command to transmit a random access preamble in the target cell;

[0031] Fig. 9F is a flow diagram of a method similar to that of Fig. 9A, but here the DU receives an LTM ID separately from the request to prepare a cell for LTM and includes a cellindex rather than the LTM ID in the command to transmit a random access preamble in the target cell;

[0032] Fig. 10A is a flow diagram of an example method for configuring a UE to transmit a random access preamble for early TA acquisition and activating the LTM cell change procedure, which can be implemented in a DU;

[0033] Fig. 10B is a flow diagram of a method similar to that of Fig. 10A, but here the DU receives an LTM ID and random access configuration parameters in separate messages;

[0034] Fig. 10C is a flow diagram of a method similar to that of Fig. 10A, but here the DU includes a cell ID rather than the LTM ID in the command to transmit a random access preamble in the target cell;

[0035] Fig. 10D is a flow diagram of a method similar to that of Fig. 10A, but here the DU receives an LTM ID and random access configuration parameters in separate messages and includes a cell ID rather than the LTM ID in the command to transmit a random access preamble in the target cell;

[0036] Fig. 10E is a flow diagram of a method similar to that of Fig. 10A, but here the DU includes a cell index rather than the LTM ID in the command to transmit a random access preamble in the target cell;

[0037] Fig. 10F is a flow diagram of a method similar to that of Fig. 10A, but here the DU receives an LTM ID and random access configuration parameters in separate messages and includes a cell index rather than the LTM ID in the command to transmit a random access preamble in the target cell;

[0038] Fig. 11 A is a flow diagram of an example method for configuring a UE for early TA acquisition, which can be implemented in a CU;

[0039] Fig. 1 IB is a flow diagram of a method similar to that of Fig. 11 A, but here the CU transmits, to the serving DU, an LTM ID and random access configuration parameters in separate messages;

[0040] Fig. 12 a flow diagram of an example method in a CU, according to which the CU determines whether to include random access configuration parameters for early TA acquisition in a message to a DU based on whether the UE supports early TA acquisition;

[0041] Fig. 13 a flow diagram of an example method in a CU, according to which the CU determines whether to request random access configuration parameters for early TA acquisition from the target DU based on whether the UE supports early TA acquisition;

[0042] Fig. 14A is a flow diagram of an example method for generating an LTM DU configuration including random access configuration parameters for early TA acquisition, which can be implemented in a DU;

[0043] Fig. 14B is a flow diagram of a method similar to that of Fig. 14A, but here the DU transmits, to the CU, the LTM DU configuration and the random access configuration parameters for early TA acquisition in separate messages;

[0044] Fig. 15A is a flow diagram of an example method for providing a TA and an indication of the target cell to a UE, which can be implemented in a DU;

[0045] Fig. 15B is a flow diagram of a method similar to that of Fig. 15 A, but here the DU generates an identifier of the target cell based on the identifier of the target cell received from the CU;

[0046] Fig. 16A is a flow diagram of an example method for providing a TA to a UE via the serving DU, which can be implemented in a CU; and

[0047] Fig. 16B is a flow diagram of a method similar to that of Fig. 15 A, but here the CU generates an identifier of the target cell based on the identifier of the target cell received from the DU.DETAILED DESCRIPTION OF THE DRAWINGS

[0048] A radio access network (RAN) node of this disclosure can implement the techniques discussed below to acquire a timing advance (TA) early, prior to performing a low-layer triggered mobility (LTM) cell change from the currently serving cell to a new (“target” or “candidate”) cell, so as to make the LTM cell change more efficient.

[0049] Fig. 1A depicts an example wireless communication system 100 in which a user equipment (UE) can implement early timing advance (TA) acquisition. The wireless communication system 100 includes a UE 102, a base station (BS) 104, a base station 106 and a core network (CN) 110. The UE 102 initially connects to the base station 104. In some scenarios, the base station 104 can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104 and the base station 106. The base stations 104 and 106 operate as an MN and an SN for the UE 102, respectively.

[0050] 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.

[0051] 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.

[0052] 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. 1A) 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.

[0053] 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. 1A. The base station 104 can be an eNB supporting an SI interface for communicating with the EPC 111, an ng-eNB supporting an NG interface for communicating with the 5GC 160, or a gNB that supports an NR radio interface as well as an NG interface for communicating with the 5GC 160. To directly exchange messages with each other during the scenarios discussed below, the base stations 104 and 106 can support an X2 or Xn interface. Among other components, the EPC 111 can include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, and a Packet Data Network Gateway (PGW) 116. The SGW 112 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and theMME 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.

[0054] As illustrated in Fig. 1A, 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. 1A). 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.

[0055] 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 (5G NR 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 5G NR-6G DC.

[0056] 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.

[0057] The processing hardware 130 can implement an LTM controller 132 to support LTM procedures and a TA acquisition controller 134 to support early TA acquisition at UEs. The LTM controller 132 and the TA acquisition controller 134 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. Lor 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.

[0058] 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 and a TA acquisition controller 154 to support early TA acquisition in the serving cell and / or a target cell. The LTM controller 152 and the TA acquisition controller 154 can be implemented as respective sets of instructions executable by one or more processors, for example.

[0059] 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 DLchannels 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.

[0060] 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.

[0061] Fig. IB depicts an example distributed implementation of a base station such as the base station 104 or 106. The base station in this implementation can include a centralized unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 is equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In one example, the CU 172 is equipped with the processing hardware 130. In another example, the CU 172 is equipped with the processing hardware 140. The processing hardware 140 in an example implementation includes an SN RRC controller 142 configured to manage or control one or more RRC configurations and / or RRC procedures when the base station 106 operates as an SN. The DU 174 is also equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In some examples, the processing hardware in an example implementation includes a medium access control (MAC) controller configured to manage or control one or more MAC operations orprocedures (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.

[0062] Fig. 2A illustrates, in a simplified manner, an example protocol stack 200 according to which the UE 102 can communicate with an eNB / ng-eNB or a gNB (e.g., one or more of the base stations 104, 106).

[0063] In the example stack 200, a physical layer (PHY) 202A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLC sublayer 206A in turn provides RLC channels to 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.

[0064] The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the PDCP layer 208 or 210) that can be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer 206A or 206B) that can be referred to as protocol data units (PDUs). Except where the difference between SDUs and PDUs is relevant, this disclosure for simplicity refers to both SDUs and PDUs as “packets.”

[0065] 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. 2A) 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 DataRadio 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.

[0066] 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.

[0067] Next, several example LTM scenarios for certain RAN node topologies are discussed with reference to Figs. 3 - 8B. Generally speaking, events in Figs. 3-8B 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. 5A, 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.

[0068] 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 124A. The UE 102 initially communicates 302 with the DU 174 on the cell 124A 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 124A and other cell(s) (e.g., cell 124D not shown in Fig. 1A) 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 124A can be a PCell. In such cases, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In other implementations, the cell 124A can be a SCell, and one of the other cell(s) is a PCell. In suchcases, 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.

[0069] During 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) (CSLRS(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.

[0070] 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 IE defined in 3GPP specification 38.331. In other implementations, the serving DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the serving CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the serving CU configuration includes a MeasConfig IE and / or a RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some implementations, the serving DU configuration includes a CSl-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. Inother implementations, the serving CU configuration includes a CSl-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.

[0071] While communicating with the base station 104, the UE 102 transmits 304 at least one measurement report to the DU 174. In some implementations, the at least one measurement report includes Layer 1 (LI) measurement report(s) and / or Layer 3 (L3) measurement report(s) for at least one serving cell of the UE 102 and / or at least one nonserving cell. For each of the L3 measurement report(s), the DU 174 transmits 306 a DU-to- CU message including the L3 measurement report to the CU 172. In some implementations, the DU-to-CU message(s) of the event 306 is / are Fl application protocol (F1AP) message(s) (e.g., UL RRC Message Transfer message(s)). In some implementations, the DU 174 does not transmit or refrains from transmitting the LI measurement report(s) to the CU 172. The at least one serving cell includes the cell 124A and / or other cell(s), and the at least one nonserving cell includes the cell 124B and / or cell 124C. In some implementations, the serving DU configuration or the serving CU configuration includes at least one measurement configuration. In some implementations, the UE 102 receives one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration from the CU 172 via the DU 174 in the event 302. In accordance with the at least one measurement configuration, the UE 102 performs measurements and transmits 304 the at least one measurement report to the DU 174. In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)) and / or LI measurement configuration(s). The LI measurement configuration(s) (e.g., CSl-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 CSl-ResourceConfig IE(s). In another example, the LI measurementreporting 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 CS1- 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.

[0072] In some implementations, the LI measurement configuration(s) are dedicated, special-purpose RRC IE(s) defined in a relevant 3GPP specification such as TS 38.331 specifically for a lower layer triggered mobility (LTM). In some implementations, the LI measurement resource configuration(s) are dedicated, special-purpose RRC IE(s) defined in a relevant 3GPP specification such as TS 38.331 specifically for the LTM. In some implementations, the LI measurement reporting configuration(s) are dedicated, specialpurpose RRC IE(s) defined in a relevant 3GPP specification such as TS 38.331 specifically 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.

[0073] In some implementations, (each of) the LI measurement report(s) can include at least one LI measurement result. In some implementations, the at least LI measurement result includes at least one LI -reference signal received power (Ll-RSRP) value and / or at least one LI- Signal to Interference Noise Ratio (Ll-SINR) value. For each of the LI measurement report(s), the UE 102 transmits a PUCCH transmission including the LI measurement report to the DU 174, in some implementations. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUCCH to the DU 174. In other implementations, for each of the LI measurement report(s), the UE 102 transmits a PUSCH transmission including the LI measurement report to the DU 174. That is, the UE 102 transmits the each of the LI measurement report(s) on a PUSCH to the DU 174. In yet other implementations, the UE 102 transmits a portion of the LI measurement report(s) on PUCCH(s) and the rest of the LI measurement report(s) on physical UL shared channel(s) (PUSCH(s)) to the DU 174. That is, for each of the portion of the LI measurement report(s), the UE 102 transmits a PUCCH transmission including the LI measurement report to the DU 174, and for each of the rest of the LI measurement report(s), the UE 102 transmits a PUSCHtransmission 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.

[0074] 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 a 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.

[0075] 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.

[0076] 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 CSLRSs. The UE 102 obtains the at least one LI measurement result and / or at least one L3 measurement resultfrom 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. 1A).

[0077] 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 124A by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. In other implementations, if the LI measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than signal strength and / or quality of the cell 124 A, 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.

[0078] In the case that the CU 172 determines to prepare the first cell for LTM, the CU 172 transmits 308 a first CU-to-DU message to the DU 174 to prepare the first cell for the UE 102. In some implementations, the CU 172 includes a cell identity (ID) 1 of the first cell in the first CU-to-DU message to request the DU 174 to prepare the first cell for LTM for the UE 102. For example, the cell ID 1 is cell global identity (CGI). In another example, the cell ID is a portion of the CGI. In yet another example, the cell ID is a physical cell ID (PCI). In response to the first CU-to-DU message, the DU 174 generates a first LTM DU configuration (referred to herein after as LTM DU configuration 1) for the UE 102, which configures the first cell for LTM. The DU 174 then transmits 310 a first DU-to-CU message including the LTM DU configuration 1 to the CU 172 in response to the first CU-to-DU message. In some implementations, the DU 174 can include the cell ID 1 together with the LTM DU configuration 1 in an IE of the first DU-to-CU message to indicate that the LTM DUconfiguration 1 is associated with the first cell (i.e., the cell ID 1). In the case that the DU 174 determines to prepare the first cell, the DU 174 initiates transmission of the first DU-to-CU message to the CU 172 instead of in response to a CU-to-DU message received from the CU 172.

[0079] In some implementations, the DU 174 includes, in the first DU-to-CU message, the cell ID of the first cell associated with the LTM DU configuration 1 to indicate that the LTM DU configuration 1 is configured for or associated with the first cell. The CU 172 identifies the LTM DU configuration 1 is configured for or associated with the first cell. In some scenarios and implementations, the CU 172 can include additional cell ID(s) (e.g., cell ID(s) 2, ..., N) in the first CU-to-DU message to prepare additional cell(s) (e.g., cell(s) 2, ..., N) for LTM for the UE 102, and the DU 174 includes additional LTM DU configuration(s) (e.g., LTM DU configuration(s) 2, ..., N) each configuring a particular cell of the additional cell(s), as described below. In such cases, the DU 174 includes, in the first DU-to-CU message, the additional cell ID(s) respectively associated with the additional LTM DU configuration(s) to indicate that which LTM DU configuration is associated to which cell (ID). The cell(s) 1 and / or 2, ..., N are candidate cell(s).

[0080] In some implementations, the CU 172 does not include a (reference) LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, ..., N (i.e., nonreference LTM DU configuration(s)) based on the reference LTM DU configuration, and includes the reference LTM DU configuration in the first DU-to-CU message. In other implementations, the CU 172 includes a reference LTM DU configuration in the first CU-to- DU message. In such cases, the DU 174 generates the LTM DU configuration(s) 1, and / or 2, ..., N which are delta configuration(s) to augment the reference LTM DU configuration. In yet other implementations, the CU 172 includes a reference LTM DU configuration (e.g., a first reference LTM DU configuration) in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration (e.g., a second reference LTM DU configuration) replacing the first reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, ..., N based on the second reference LTM DU configuration, and includes the second reference LTM DU configuration in the first DU-to-CU message.

[0081] In some implementations, the reference LTM DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configurationparameters. In some implementations, the reference LTM DU configuration is CellGroupConfig IE 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 CS1- MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0082] 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.

[0083] After receiving the first DU-to-CU message, the CU 172 generates a 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.

[0084] 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 aRRC 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, and includes the RRC message in the element 1. In some implementations, the element 1 is an addition or modification IE (e.g., LTM-ConfigToAddMod IE, LTM-Candidate IE, LTM- CandidateToAddMod IE or LTM-CandidateConfigToAddMod IE). When the UE 102 receives the first addition or modification list, the UE 102 can store the first addition or modification list, e.g., in a variable in its random access memory (RAM). In other alternative implementations, the DU 174 generates the first container and includes the first container in the first DU-to-CU message. In yet other alternative implementations, the DU 174 generates the element 1 and includes the element 1 in the first DU-to-CU message.

[0085] In some implementations, the CU 172 includes a LTM CU configuration 1 in the RRC reconfiguration message 316, the first container or the element 1, where the LTM CU configuration 1 associated with the LTM DU configuration 1. To associate the LTM CU configuration 1 with the LTM DU configuration 1, the CU 172 can include the LTM CU configuration 1 and the LTM DU configuration in the element 1. In some implementations, the CU 172 includes LTM CU configuration(s) 2, ..., N in the RRC reconfiguration message 316 or the second container, where the LTM CU configuration(s) 2, ..., N associated with the LTM DU configuration(s) 2, ..., N, respectively. To associate the LTM CU configuration(s) 2, ..., N with the LTM DU configuration(s) 2, ..., N , the CU 172 can include the LTM CU configuration(s) 2, ..., N and the LTM DU configuration(s) in the element(s) 2, ..., N, respectively. In other implementations, the CU 172 includes, in the element(s) 2, ..., N, the LTM CU configuration(s) 2, ..., N associated with the LTM DU configuration(s) 2, ..., N, respectively. Alternatively, the CU 172 does not include, in the RRC reconfigurationmessage 316, LTM CU configuration(s) for some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, .. N.

[0086] 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 a RRC reconfiguration complete message (e.g., an RRCReconfigurationComplete message) to the DU 174, which in turn transmits 322 a second DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some implementations, the CU 172 performs security protection (e.g., integrity protection and / or encryption) on the RRC reconfiguration message. For example, the CU 172 generates a message authentication code for integrity (MAC-I) for the RRC reconfiguration message, encrypts the RRC reconfiguration message and the MAC-I to obtain an encrypted RRC reconfiguration message and an encrypted MAC-I, and transmits a PDCP PDU including the encrypted RRC reconfiguration message and encrypted MAC-I to the UE 102 via the DU 174 in the events 316 and 318. When the UE 102 receives the PDCP PDU from the CU 172 via the DU 174 (i.e., events 316 and 318), the UE 102 decrypts the encrypted RRC reconfiguration and encrypted MAC-I to obtain the RRC reconfiguration message and MAC-I and verifies whether the MAC-I is valid. If the UE 102 verifies the MAC-I is invalid, the UE 102 discards or ignores the RRC reconfiguration message. In some implementations, the UE 102 can perform a 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 a LTM command activating the LTM DU configuration 1 as described for events 330, 350.

[0087] The events 308 (optional) and 310 are collectively referred to in Fig. 3 as a LTM preparation procedure 390. The events 316, 318, 320, 322 are collectively referred to in Fig. 3 as a LTM configuration delivery procedure 394.

[0088] 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 DE RRCMessage 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.

[0089] 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 may generate the LTM CU configuration 1 (i.e., non-reference LTM CU configuration) as a delta configuration to augment the reference LTM CU configuration. Similarly, the CU 172 may generate some or all of the LTM CU configuration(s) 2, ..., N as delta configuration(s) to augment the reference LTM CU configuration. Alternatively, in the RRC reconfiguration message 316 or the first container, the CU 172 includes the reference LTM CU configuration and does not include a nonreference LTM CU configuration. In some implementations, the CU 172 includes the reference LTM CU configuration and / or the reference LTM DU configuration in an additional container (e.g., reference LTM configuration) and include the additional container in the RRC reconfiguration message 316.

[0090] 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.

[0091] 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.

[0092] 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, theCU 172 can include the LTM DU configuration 1 and the ID 1 and indicate the association between the ID 1 and LTM DU configuration 1. Thus, the DU 174 can directly associate the ID 1 with the LTM DU configuration 1. In other implementations, in the third CU-to-DU message, the CU 172 can include the cell ID 1 and the ID 1 (i.e., the first LTM ID) and indicate the association between the cell ID 1 and the ID 1. Thus, the DU 174 can associate the ID 1 with the LTM DU configuration 1, based on the association between the cell ID 1 and the ID 1 and the association between the cell ID 1 and the LTM DU configuration 1. In yet other implementations, in the third CU-to-DU message, the CU 172 can include the LTM DU configuration 1, the cell ID 1 and / or the ID 1 and indicate the association between the ID 1, LTM DU configuration 1 and / or the cell ID 1. In some implementations, the DU 174 can transmit 314 a third DU-to-CU message to the CU 172 in response to the third CU-to-DU message. In some implementations, the third CU-to-DU message and third DU-to-CU message are UE Context Modification Request message and UE Context Modification Response message. The events 312 (optional) and 314 (optional) are collectively referred to in Fig. 3 as a 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.

[0093] In the case that the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 can include the ID 1 in the LTM DU configuration 1, first container or element 1. Alternatively, the DU 174 does not include the ID 1 in the LTM DU configuration 1, first container and / or element 1.

[0094] 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 firstcontainer 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.

[0095] 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.

[0096] 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 IE) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration 1 is CellGroupConfig IE defined in 3GPP specification 38.331. In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0097] In some implementations, the LTM CU configuration 1 includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 includes a MeasConfig IE and / or a RadioBearerConfig IE defined in 3GPP specification 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some implementations, the LTM DU configuration 1 includes LI measurement configuration 1 (e.g., a CSl-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 CSLRS(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) CSl-ResourceConfig IE(s). 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.

[0098] 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.

[0099] 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 124A and first cell are not synchronized, the DU 174 determines to include the random access configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the random access configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. If the LTM DU configuration 1 includes the random access configuration,the UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration, as described below. Otherwise, if the LTM DU configuration 1 does not include the random access configuration or indicates the UE 102 to skip a random access procedure in LTM, the UE 102 skips or refrains from performing the random access procedure of the event 332 in response to the LTM DU configuration 1 excluding the random access configuration.

[0100] 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 124A and first cell are synchronized or not. The UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration parameters, as described below. In some implementations, the random access configuration parameters configure physical random access channel (PRACH) resources, an association between SSB and PRACH resources, and / or one or more PRACH occasions.

[0101] In some implementations, if the cell 124A 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 124A and first cell are not synchronized, the DU 174 determines to not include the first indication in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to include the first indication in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to not include the first indication in the LTM DU configuration 1. If the LTM DU configuration 1 includes the first indication, the UE 102 skips or refrains from performing the random access procedure of the event 332 in accordance with or in response to the first indication. Otherwise, if the LTM DU configuration 1 does not include the first indication, the UE 102 performs the random access procedure in accordance with the random access configuration in the event 332, in response to the LTM DU configuration 1 excluding the first indication, as described below.

[0102] 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 1or special cell configuration. In some implementations, if the cell 124A and first cell are not synchronized, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1. In some implementations, if the LTM DU configuration 1 includes the reconfiguration with sync configuration, the UE 102 performs the random access procedure in the event 332 as described below, in response to or in accordance with the reconfiguration with sync configuration. Otherwise, if the LTM DU configuration 1 does not include the reconfiguration with sync configuration, the UE 102 skips or refrains from performing the random access procedure of the event 332. In some implementations, the DU 174 includes a cell ID (i.e., cell ID 1) of cell 1 (i.e., the first cell) in the LTM DU configuration 1. In one implementation, the cell ID 1 can be a PCI. In another implementation, the cell ID 1 is a CGI. In some implementations, the cell ID 1 included in the LTM DU configuration 1 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.

[0103] 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 172determines to prepare the particular cell for LTM for the UE 102. In other implementations, if the LI measurement report(s) indicates that signal strength and / or quality of a particular cell of the additional cell(s) is above a first predetermined threshold and / or is better than the cell 124A, the DU 174 determines to prepare the particular cell for LTM for the UE 102. In one implementation, the respective predetermined threshold(s) for the additional cells can be different from the first predetermined threshold. In another implementation, the respective predetermined threshold(s) for the additional cell(s) can be the same as the first predetermined threshold. In some implementations, the respective predetermined thresholds for the additional cells can be the same or different. Alternatively, the base station 104 determines to prepare the additional cell(s) for the UE 102 regardless of whether a measurement report is received from the UE 102 or not.

[0104] In the case that the CU 172 determines to prepare the additional cell(s), the CU 172 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the DU 174 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390. In the case that the DU 174 determines to prepare the additional cell(s), the DU 174 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the CU 172 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390.

[0105] In some implementations, the CU 172 and DU 174 perform LTM preparation procedure(s) 2, ..., N to prepare the cell(s) 2, ..., N, respectively, similar to the procedure 390. The CU 172 can include the cell ID(s) 2, ..., N in CU-to-DU message(s) 2, ..., N in the LTM preparation procedure(s) 2, ..., N, respectively, similar to the first CU-to-DU message. In the LTM preparation procedure(s) 2, ..., N, the DU 174 generates LTM DU configuration(s) 2, ..., N configuring the cell(s) 2, ..., N and includes the LTM DU configuration(s) 2, ..., N in DU-to-CU message(s) 2, .., N, respectively, as described for the LTM DU configuration 1. In the case that the DU 174 receives the CU-to-DU message(s) 2, ..., N, the DU-to-CU message(s) 2, ..., N responds to the CU-to-DU message(s) 2, ..., N, respectively . “N” is an integer and larger than one. Lor example, “N” is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 14, 15 or 16. In another example, the maximum number of “N” is 4, 8, 16 or 32. Examples and implementations of the LTM DU configuration 1 can apply to the LTM DU configuration(s) 2, ..., N.

[0106] In other implementations, the CU 172 and DU 174 performs a single LTM preparation procedure (i.e., the LTM preparation procedure 390) to prepare the cell(s) 1, 2, .. N. In such cases, the DU 174 includes the LTM DU configuration(s) 1, 2, ..., N for the cell(s) 1, 2, ..., N, respectively in the first DU-to-CU message. In the first DU-to-CU message, the DU 174 can include the cell ID(s) 1, 2, ..., N respectively associated with the LTM DU configuration(s) 1, 2, ..., N to indicate that the LTM DU configuration(s) 1, 2, ..., N are configured for the cell ID(s) 1, 2, ..., N, respectively. In the case that the CU 172 determines to perform the LTM preparation procedure 390, the CU 172 includes the cell ID(s) 1, 2, ..., N in the first CU-to-DU message to request the DU 174 to prepare the cell(s) 1, 2, ..., N, respectively, for LTM.

[0107] 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.

[0108] 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.

[0109] In some implementations, the CU 172 can perform a 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 theassociation between the cell ID(s) 2, .. N and the ID(s) 2, .. N, respectively. Thus, the DU 174 can associate the LTM DU configuration(s) 2, .. N with the ID(s) 2, .. N, respectively, based on the association between the cell ID(s) 2, ..., N and the ID(s) 2, ..., N and the association between the cell ID(s) 2, ..., N and the LTM DU configuration(s) 2, ..., N, respectively. In other implementations, the CU 172 can include the ID(s) 2, ..., N, the cell ID(s) 2, ..., N and / or the LTM DU configuration(s) 2, ..., N in the second CU-to-DU message as described above. Thus, the third CU-to-DU message can be omitted. In yet other implementations, the CU 172 can include the ID(s) 2, ..., N in the first CU-to-DU message and indicate the ID(s) 2, ..., N is / are respectively associated with the cell ID(s) 2, ..., N. In one implementation, the DU 174 includes the ID(s) 2, ..., N in the LTM DU configuration(s) 2, ..., N. Thus, the CU 172 does not include the ID(s) 2, ..., N in the RRC reconfiguration message, first container and / or element(s) 2, ..., N.

[0110] 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.

[0111] 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 IE), 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 ormodification 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).

[0112] In some implementations, the DU 174 includes cell ID(s) 2, ..., N in the LTM DU configuration(s) 2, ..., N to identify the cell(s) 2, ..., N, respectively. In one implementation, each of the cell ID(s) 2, ..., N is a PCI. In some further implementations, the LTM DU configuration(s) 2, ..., N includes cell index(es) 2 , ..., N indexing the cell ID(s) 2, ..., N or the cell(s) 2, ..., N, respectively. In the case that the CU 172 prepares the cell(s) 2, ..., N for LTM in the procedure 390, the CU 172 can set the cell index(es) 2, ..., N to different value(s) and include the cell index(es) 2, ..., N in the first CU-to CU-to-DU message of the event 308. In the case that the CU 172 prepares the cell(s) 2, ..., N in the additional LTM preparation procedure(s), the CU 172 can set the cell index(es) 2, ..., N to different values and include the cell index(es) 2, ..., N in CU-to-DU message(s) of the additional LTM preparation procedure(s). The CU 172 sets the cell index(es) 1, ..., N to different values. In some implementations, the cell ID(s) 1, ..., N in the LTM DU configuration(s) 1, ..., N are different from the cell ID(s) 1, ..., N in the CU-to-DU message(s) described above.

[0113] In some implementations, each of the LTM DU configuration(s) 1, ..., N includes physical configuration parameters, MAC configuration parameters, RLC configuration parameters and / or LI measurement configuration(s). In some implementations, each of the LTM DU configuration(s) 1, ..., N can be a CellGroupConfig IE as defined in 3GPP specification 38.331. In other implementations, each of the LTM DU configuration(s) 1, ..., N include configuration parameters included in a CellGroupConfig IE as defined in 3GPP 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 IE) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some implementations, the LTM DU configuration(s) 1, ..., N are CellGroupConfig IE(s) defined in 3GPP specification 38.331. In other implementations, the LTM DU configuration(s) 1, ..., N include configuration parameters in the CellGroupConfig IE.

[0114] 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 andimplementations of the additional LTM CU configurations are similar to the LTM CU configuration 1.

[0115] 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 a RRC reconfiguration message to the UE 102 via the DU 174 to indicate the UE 102 to release the LTM DU configuration M or element M. In one implementation, the CU 172 generates a release list including the ID (i.e., LTM ID) M for releasing the LTM DU configuration M or element M and includes the release list in the RRC reconfiguration message. In response to the RRC reconfiguration message, the UE 102 releases the LTM DU configuration M or element M and transmits a 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.

[0116] 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 a 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 a 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.

[0117] After receiving the RRC reconfiguration in the event 318 or transmitting the RRC reconfiguration complete message in the event 320, the UE 102 transmits 324 at least one measurement report to the DU 174, similar to the event 304. In some implementations, the DU 174 may transmit 326 a DU-to-CU message including the at least one measurement report to the CU 172, similar to the event 306. In other implementations, the DU 174 does not transmit the at least one measurement report to the CU 172. In some implementations, the at least one measurement report of the event 324 include LI measurement report(s) or L3 measurement repot(s), as described for the event 304. In some implementations, the UE 102 transmits 324 the at least one measurement report on PUCCH(s) and / or PUSCH(s) to the DU 174, similar to the event 304. In other implementations, the UE 102 transmits 324 at least one MAC CE including the at least one measurement report to the DU 174, similar to the event 304. In some implementations, the UE 102 does not transmit the LI measurement report(s) in format of RRC message(s) to the DU 174.

[0118] 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 include or omit 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).

[0119] 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 LImeasurement configuration(s) can be CSl-MeasConfig IE(s) defined in a relevant 3GPP specification such as TS 38.331. The LI measurement configuration(s) can include RS resource configuration(s) and / or report configuration(s). The UE 102 transmits 324 the LI measurement report(s) on UL resources (e.g., PUCCH resources or PUSCH resources) to the DU 174 in accordance with the report configuration(s). The DU 174 receives the LI measurement report(s) on the UL resources in accordance with the report configuration(s). In some implementations, the report configuration(s) are or are similar to CSl-ReportConfig IE(s). In other implementations, each of the report configuration(s) is a dedicated 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).

[0120] 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 CSLRS resource indicators (CRI(s)). The quantized measurement values may include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0121] In yet other implementations, the at least one measurement configuration includes dedicated, special-purpose -type measurement configuration(s) (e.g., LTM measurement configuration(s))specifically defined for LTM in a relevant 3GPP specification. In some implementations, the dedicated, special-purpose -type measurement configuration(s) includes reference signal resource configuration(s) configuring resources where the DU 174 transmits reference signal(s). Lor example, the reference signal resource configuration(s) include CSL RS(s) and / or SSB(s). In one implementation, the reference signal resource configuration(s) is / are CSl-ResourceConfig IE(s). In another implementation, the dedicated, special-purpose - 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 receivesthe 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 dedicated, special-purpose -type measurement report(s) (e.g., LTM measurement report(s)). In some implementations, the dedicated, special-purpose -type measurement configuration includes configuration parameters defined for the purpose of LTM in a relevant 3GPP specification.

[0122] 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.

[0123] 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.

[0124] 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 1included in the first LTM command is the same as the cell ID 1 included in the first CU-to- DU message. In other implementations, the DU 174 determines the cell ID 1 (e.g., PCI) included in the first LTM command from the cell ID 1 (e.g., CGI) received in the first CU-to- DU message. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1, based on the cell ID 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID 1 from the LTM DU configuration 1 or element 1, and establishes an association 1 between the cell ID 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell ID 1, before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell ID 1 (received in the first LTM command) and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell ID(es) 2, ..., N from the LTM DU configuration(s) or element(s) 2, ..., N and establishes association(s) 2, ..., N between the cell ID(es) 2, ..., N and the LTM DU configuration(s) or element(s) 2, ..., N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, ..., N to obtain the cell ID(es) 2, ..., N, before receiving the first LTM command. In some implementations, the DU 174 has a mapping table to store mappings between the PCI(s) 1, ..., N and the CGI(s) 1, ..., N for the cell(s) 1, ..., N, respectively.

[0125] 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 toindicate that the rest of the LTM DU configuration(s) 1, .. N is / are not activated. In some implementations, the first value is one and the second value is zero. In other implementations, the first value is zero and the second value is one. Generally, if the DU 174 determines to activate the LTM DU configuration L or change a serving cell to the cell L for the UE 102, the DU 174 can set the corresponding bit (e.g., bit L or bit L-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.

[0126] 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.

[0127] In some implementations, the at least one measurement report (e.g., LI measurement report(s) or dedicated, special-purpose -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 CSLRS(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 dedicated, special-purpose -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.

[0128] In some implementations, the at least one measurement report (e.g., L3 measurement report(s)) of the events 324 and 326 includes at least one measurement result for the first cell. The CU 172 determines to activate the LTM DU configuration 1 or transmit the first LTM command, because the at least one measurement result indicates that signal strength or quality of the first cell is above a second predetermined threshold. The second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is larger than the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell is suitable for communication with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This also indicates that the first cell is suitable for communication with the UE 102. Thus, the CU 172 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold. In response to the determination, the CU 172 transmits 328 a fourth CU-to-DU message to the DU 174 to activate the LTM DU configuration 1 or trigger a serving cell change to the cell 1 for the UE 102. In some implementations, the CU 172 includes the ID 1 in the fourth CU-to-DU message. In other implementations, the CU 172 includes the cell index 1 in the fourth CU-to- DU message. In response to the fourth CU-to-DU message, the DU 174 transmits 330 the first LTM command to the UE 102 and optionally transmits a fourth DU-to-CU message to the CU 172. In some implementations, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the cell index 1. In other implementations, the CU 172 can include the cell ID 1 in the fourth CU-to-DU message. Thus, the DU 174 determines to activate the LTM DU configuration 1 in accordance with the cell ID 1. In yet other implementations, the CU 172 can include the ID 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the ID 1. In some implementations, the fourth CU-to-DU message and fourth DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In other implementations, the fourth CU-to-DU message and / or fourth DU-to- CU message are dedicated, special-purpose interface messages, e.g., El application protocol(F1AP) messages defined in a relevant 3GPP specification such as TS 38.473 specifically in connection with the procedures described herein .

[0129] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 330, the DU 174 may transmit 329 to the CU 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., a 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.

[0130] 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 dedicated, special-purpose MAC CE defined in a relevant 3GPP specification such as TS 38.321. In one implementation, the DU 174 includes a subheader identifying the new MAC CE in the MAC PDU and the UE 102 identifies the new MAC CE in the MAC PDU in accordance with the subheader. The subheader can include a logical channel ID or extended logical channel ID defined in a 3GPP specification to identify the new MAC CE. For example, the logical channel ID or extended logical channel ID are dedicated, specialpurpose defined in a relevant 3GPP specification such as TS 38.321. In other implementations, the first LTM command is a DO that the UE 102 receives on a PDCCH from the DU 174 in the event 330. The DU 174 generates a CRC for the DO, scrambles the CRC with a first C-RNTI of the UE 102, and transmits the DCI and scrambled CRC on the PDCCH in the event 330. In one implementation, a format of the DCI can be an existing DCI format defined in a 3GPP specification (e.g., 38.212). In another implementation, the format of the DCI can be a dedicated, special-purpose DCI format defined in a relevant 3GPP specification (e.g., TS 38.212).

[0131] 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.

[0132] 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, theacknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE defined in 3GPP specification 38.321 vl7.2.0 and / or later versions. In another example, the MAC CE is a dedicated, special-purpose MAC CE defined in a relevant 3GPP specification such as TS 38.321. In yet other implementations, the acknowledgement is a PUCCH transmission.

[0133] 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., a 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 dedicated, special-purpose -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.

[0134] After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 the first cell. The UE 102 identifies the LTM DU configuration 1 in accordance with the ID 1, the cell ID 1 or the cell index 1 received in the first LTM command and applies the LTM DU configuration 1 to communicate with the DU 174 on the first cell. In some implementations, the UE 102 disconnects from the cell 124A, after (e.g., in response to) receiving the first LTM command or after transmitting 331 the acknowledgement. In some implementations, the UE 102 stops communicating on the cell 124A after (e.g., in response to) receiving 330 the first LTM command or transmitting 331 the acknowledgement. In some implementations, the UE 102 accesses the first cell by performing a random access procedure on the first cell with the DU 174, in response to receiving the first LTM command. In other implementations, the UE 102 skips a random access procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174, after (e.g., in response to) receiving the first LTM command.

[0135] 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 (e.g., 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 a LTM command for the first cell. In other implementations, in the LTM DU configuration 1, the DU 174 configures the UE 102 to skip the random access procedure for a 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 a LTM serving cell change to the first cell.

[0136] In other implementations, the LTM DU configuration 1 includes the reconfiguration with sync configuration or the random access configuration. In such cases, the DU 174 configures whether the UE 102 performs a random access procedure on the first cell in a LTM command. Thus, the UE 102 determines whether to perform the random access procedure on the first cell in the event 332 in accordance with the first LTM command. In some implementations, the DU 174 includes, in the first LTM command, an indication (e.g., a field) indicating skipping a random access procedure. In response to the indication or the first LTM command including the indication, the UE 102 skips a random access procedure and directly transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to access the first cell. In other implementations, the DU 174 excludes the indication in the first LTM command to configure the UE 102 to perform a random access procedure. In response to the first LTM command excluding the indication, the UE 102 performs a random access procedure on the first cell to access the first cell. In some other implementations, the DU 174 includes a timing advance value in the first LTM command to indicate skipping a random access procedure. In response to receiving the timing advance value or the first LTM command including the timing advance value, the UE102 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.

[0137] In some implementations, the random access procedure is a four-step random access procedure. In other implementations, the random access procedure is a two-step random access procedure. In some implementations, the random access procedure is a contention-free random access procedure. In other implementations, the random access procedure is a contention-based random access procedure. In cases where the random access procedure is a four-step random access procedure, the UE 102 transmits a Message 3 including a UE identity to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., a Message 4) to the UE 102 in response to the Message 3. In cases where the random access procedure is a two-step random access procedure, the UE 102 transmits a Message A including the UE identity to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., Message B) to the UE 102 in response to the Message A. In some implementations, when the UE 102 receives the contention resolution message from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell). In some implementations, the LTM DU configuration 1 includes a second C-RNTI and the UE identity is the second C-RNTI of the UE 102. In such implementations, the contention resolution message is a PDCCH transmission addressed to the second C-RNTI. In other implementations, the LTM DU configuration 1 does not include a C-RNTI, the UE identity is the first C-RNTI. In such implementations, the contention resolution message is a PDCCH transmission addressed to the first C-RNTI.

[0138] In cases where the LTM DU configuration 1 includes a dedicated random access preamble, the random access procedure is a contention free random access procedure. In such cases, the UE 102 transmits the dedicated random access preamble to the DU 174 via the first cell. When the UE 102 receives a random access response including an ID of the dedicated random access preamble from the DU 174 on the first cell, the UE 102 determinesthat the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell).

[0139] 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.

[0140] 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 a LTM serving cell change to the first cell in response to the first LTM command, the UE 102 receives a first DCI including the UL grant on a PDCCH on the first cell. In some implementations, the UE 102 attempts to receive the first DCI or the UL grant by monitoring one or more PDCCHs on the first cell in accordance with the LTM DU configuration 1, when the UE 102 switches to the first cell in response to the first LTM command. While monitoring one or more PDCCHs on the first cell, the UE 102 receives the first DCI and a CRC of the first DCI on the PDCCH. In the case that the LTM DU configuration 1 includes the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the second C-RNTI. In the case that the LTM DU configuration 1 does not include the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the first C-RNTI.

[0141] 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) may be 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 transmits a RRC message including the first TCI state configuration(s) to the UE 102 via the DU 174. In further implementations, the DU 174 includes the first TCI state configuration(s) in a serving DU configuration (e.g., CellGroupConfig IE) and includes the serving DU configuration in theDU-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.

[0142] 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 configuration(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 Eig. 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 configuration(s) in the LTM DU configuration 1. In other implementations, the DU 174 refrains from including the first TCI state configuration(s) in the LTM DU configuration 1.

[0143] In some implementations, the first interface protocol lE / field is a first E1AP lE / field and the second interface protocol lE / field is a second E1AP lE / field. In some implementations, one of the first L1AP lE / field and the second L1AP lE / field is a L1AP CellGroupConfig lE / field and the other is not the L1AP CellGroupConfig lE / field. In some implementations, the DU 174 includes the first L1AP lE / field in a DU to CU RRC Information IE in the message 312 and includes the second E1AP lE / field in the DU to CU RRC Information IE in the DU-to-CU message. In other implementations, neither the first E1AP lE / field nor the second E1AP IE is a F1AP CellGroupConfig lE / field. In other implementations, the second F1AP lE / field is the DU to CU RRC Information IE and the first F1AP lE / field is a dedicated IE specifically defined for including a LTM DU configuration.

[0144] 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 stateconfiguration(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.

[0145] 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.

[0146] In some alternative implementations, the DU 174 may 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).

[0147] In some implementations, before transmitting the first LTM command, the DU 174 may transmit 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).

[0148] 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 124A. In some implementations, the UE 102 stops using the TCI configuration(s) upon receiving the first LTM command.

[0149] 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) toperform 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 such cases, the DU 174 may transmit 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.

[0150] In the case that the UE 102 receives the reference LTM DU configuration as described above, the UE 102 communicates 336 with and the DU 174 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the UE 102 communicates 336 with the DU 174 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration. Similarly, the DU 174 communicates 336 with the UE 102 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the DU 174 communicates 336 with the UE 102 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration.

[0151] In the case that the UE 102 receives neither the LTM CU configuration 1 nor a / the reference LTM CU configuration, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving CU configuration. Correspondingly, if the CU 172 neither transmits the LTM CU configuration 1 nor a / the reference CU configuration to the UE 102, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving CU configuration. In the case that the UE 102 receives the LTM CU configuration 1 and the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CUconfiguration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1.

[0152] In the case that the UE 102 receives the LTM CU configuration 1 and does not receive the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1. If the LTM CU configuration 1 is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the LTM CU configuration 1 instead of the serving CU configuration. In some implementations, if the UE 102 does not receive a / the reference LTM CU configuration from the base station 104, the UE 102 determines that the LTM CU configuration 1 is a full configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a full configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In other implementations, the CU 172 includes a first indication (e.g., a field or IE) in the LTM CU configuration 1, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration 1 is a full configuration. If the LTM CU configuration 1 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 1 is a delta configuration to augment the serving CU configuration.Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a delta configuration to augment the serving CU configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In some implementations, the CU 172 indicates that the LTM CU configuration 1 is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the LTM CU configuration 1, the first container, the element 1 and / or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the LTM CU configuration 1, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration 1 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 thesecond indication in the LTM CU configuration 1 , the first container, the element 1 and / or the RRC reconfiguration message 316.

[0153] In the case that the UE 102 receives the reference LTM CU configuration and does not receive the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the reference LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the reference LTM CU configuration. If the reference LTM CU configuration is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration instead of the serving CU configuration. In some implementations, the UE 102 and CU 172 determine that the reference LTM CU configuration 1 is a full configuration as specified in a 3GPP specification (e.g., 3GPP specification TS 38.331). In other implementations, the CU 172 includes a first indication (e.g., a field or IE) in the reference LTM CU configuration, the first container or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a full configuration. If the reference LTM CU configuration is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration and at least a portion of the serving CU configuration not augmented by the reference LTM CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the reference LTM CU configuration, the first container, the element 1 and / or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the reference LTM CU configuration, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a delta configuration to augment the serving CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a full configuration, by excluding the second indication in the reference LTM CU configuration, the first container, the element 1 and / or the RRC reconfiguration message 316.

[0154] In the case that the UE 102 neither receives the reference LTM CU configuration and nor the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving LTM CU configuration.

[0155] In some implementations, the UE 102 transmits a RRC message (e.g., RRC reconfiguration complete 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 the case that the UE 102 performs the random access procedure 332, the UE 102 can include the RRC message in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC message after completing the random access procedure. In the case that the UE 102 skip the random access procedure 332, the UE 102 includes the RRC message in a PUSCH transmission of the at least one PUSCH transmission. In some implementations, if the UE 102 maintains communication on the cell 124A with the base station 104 (i.e., the UE 102 does not disconnect from the cell 124A), the UE 102 can transmit the RRC message to the base station 104 via the cell 124A. When the DU 174 receives the RRC message, the DU 174 transmits the RRC message to the CU 172.

[0156] In other implementations, the UE 102 refrains from transmitting the RRC message to the base station 104 in response to applying the LTM DU configuration 1 or receiving the first LTM command. In such cases, the UE 102 can include or transmit data in the Message 3, Message A or PUSCH transmission as described above. The UE 102 can generate a MAC PDU and / or a 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, a RRC PDU and / or a NAS PDU. The RRC PDU includes a UL-DCCH-Message excluding a 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.

[0157] 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 may stop or suspend transmitting DL data for the UE 102 to theDU 174 until receiving the DU-to-CU message 334. The CU 172 may do so because the DU 174 cannot buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. After receiving the DU-to-CU message 334, the CU 172 continues or resumes transmitting DL data for the UE 102 to the DU 174. In other implementations, when the CU 172 receives the DU-to-CU message 329, the CU 172 may continue transmitting DL data for the UE 102 to the DU 174. The CU 172 may do so because the DU 174 can buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. When or after the DU 174 detects that UE 102 accesses the cell 1, the DU 174 transmits the DL data to the UE 102 via the cell 1.

[0158] 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.

[0159] 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 1 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 configuration(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 configuration(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 configuration(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 thatthe 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 fullConfig field defined in the current 3GPP specification. In some implementations, each of the indication(s) above is fullConfig field defined in the current 3GPP specification. In the case that 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 the RRC reconfiguration message 318. In such cases, the DU 174 may not include a / the reference LTM DU configuration in the first DU-to-CU message 310.

[0160] 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.

[0161] 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 notobtain 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).

[0162] In other implementations, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and / or the LTM DU configuration(s) 2, ..., N, the UE 102 determines that the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, ..., N are delta configuration(s) to augment the serving DU configuration. In such cases, the UE 102 communicates 336 with the DU 174 in accordance with the LTM DU configuration 1 and at least a portion of the serving DU configuration not augmented by LTM DU configuration 1. Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM DU configuration for the UE 102 and / or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, ..., N as delta configuration(s) to augment the serving DU configuration. In such cases, the DU 174 communicates 336 with the UE 102 in accordance with the LTM DU configuration 1 and the at least a portion of the serving DU configuration.

[0163] 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.

[0164] In some implementations, when the UE 102 resets the UE MAC entity, the UE 102 performs at least one of the following actions for the UE MAC entity (i.e., UE MAC reset or full UE MAC reset):• initialize Bj for configured logical channel(s) to zero; stop one or more timers;• consider limeAlignmenlTimer( ) as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1);• set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0;• set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1 ;• flush Msg3 buffer;• flush MSGA buffer;• cancel, if any, triggered Scheduling Request procedure;• cancel, if any, triggered Buffer Status Reporting procedure;• cancel, if any, triggered Power Headroom Reporting procedure;• cancel, if any, triggered consistent LBT failure;• cancel, if any, triggered BFR;• cancel, if any, triggered Sidelink Buffer Status Reporting procedure;• cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure;• cancel, if any, triggered Timing Advance Reporting procedure;• cancel, if any, triggered Recommended bit rate query procedure;• cancel, if any, triggered configured uplink grant confirmation;• cancel, if any, triggered configured sidelink grant confirmation;• cancel, if any, triggered Desired Guard Symbol query;• cancel, if any, triggered Positioning Measurement Gap Activation / Deactivation Request procedure;• flush soft buffers for DL HARQ process(es);• for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission;• release, if any, Temporary C-RNTI;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0165] In some implementations, when the DU 174 resets the DU MAC entity, the DU 174 performs at least one of the following actions for the DU MAC entity (i.e., DU MAC reset or full DU MAC reset):• stop one or more timers;• consider timeAlignmentTimer(s), that the DU 174 starts and / or maintains for the UE 102, as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1);• set NDI(s) for DL HARQ process(es) to value 0;• flush soft buffers for UL HARQ process(es);• for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs)

[0166] 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.

[0167] In some implementations, the partial UE MAC reset includes at least one of the following actions:• consider timeAlignmentTimeris) of the UE 102 as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1);• flush Msg3 buffer;• flush MSGA buffer;• release, if any, Temporary C-RNTI;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0168] In some implementations, the partial UE MAC reset further includes at least one of the following actions:• cancel, if any, triggered Scheduling Request procedure;• cancel, if any, triggered Buffer Status Reporting procedure;• cancel, if any, triggered Power Headroom Reporting procedure;• cancel, if any, triggered consistent LBT failure;• cancel, if any, triggered BFR;• cancel, if any, triggered Sidelink Buffer Status Reporting procedure;• cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure;• cancel, if any, triggered Timing Advance Reporting procedure;• cancel, if any, triggered Recommended bit rate query procedure;• cancel, if any, triggered configured uplink grant confirmation;• cancel, if any, triggered configured sidelink grant confirmation;• cancel, if any, triggered Desired Guard Symbol query;• cancel, if any, triggered Positioning Measurement Gap Activation / Deactivation Request procedure;

[0169] In some implementations, the partial UE MAC reset further includes at least one of the following actions:• stop a first portion of the one or more timers and retain the rest of the one or more timers;• set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0;• set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1 ;• flush soft buffers for DL HARQ process(es);• for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission;

[0170] 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.

[0171] In some implementations, the partial DU MAC reset includes at least one of the following actions in the partial MAC reset:• consider timeAlignmentTimer(s), 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);• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs)

[0172] 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):• stop a first portion of the one or more timers and retain the rest of the one or more timers;• set NDI(s) for DL HARQ process(es) to value 0;• flush soft buffers for UL HARQ process(es);• for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs)

[0173] 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 DUMAC 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.

[0174] 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.

[0175] In some implementations, the LTM DU configuration 1 may include or omit 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.

[0176] 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:• discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any;• stop and reset timer(s), if running;• reset state variables to initial values.In some implementations, the state variables and timer(s) are defined in 3GPP specification 38.322.

[0177] 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 1 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.

[0178] 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:• discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any;• stop and reset timer(s), if running;• reset state variables to initial values.In some implementations, the state variables and timer(s) are defined in 3GPP specification 38.322.

[0179] 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, the DU 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.

[0180] 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 reestablish or refrain from reestablishing 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 reestablish or refrain from reestablishing 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.

[0181] 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.

[0182] In some implementations, after determining that the UE 102 connects to the first cell, the CU 172 can transmit 338 a CU-to-DU message (e.g., a UE Context Modification Request message) to the DU 174 to indicate the DU 174 to stop communicating with the UE 102 and / or to release or suspend resources, of the cell 124A, configured for the UE 102. In response, the DU 174 can stop communicating on the cell 124A with the UE 102 and / or release or suspend resources, of the cell 124A, configured for the UE 102, and transmit 340 a DU-to-CU message (e.g., a UE Context Modification Response message) to the CU-172. The events 338 (optional) and 340 (optional) are collectively referred to in Fig. 3 as a resource release procedure 396.

[0183] After or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351, 352, 354 and / or 356 may 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.

[0184] When or in response to determining to activate the LTM DU configuration 2 or transmit the second LTM command, the DU 174 may transmit 349 to the CU 172 a DU-to- CU message indicating LTM (being) executed. In some implementations, the DU 174 includes the cell ID 2 or the ID 2 (i.e., LTM ID) in the DU-to-CU message 349 to indicate that the DU 174 is to activate the LTM DU configuration 2. The DU can transmit the DU-to- CU message 349 to the CU 172 before or after transmitting the LTM command 350.

[0185] The discussion of the events 324, 326, 328, 330, 331, 332, 334 and / or 336 can apply to the events 344, 346, 348, 350, 351, 352, 354 and / or 356 with simple changes, at least partially. For example, “ cell 124A”, “first LTM command”, “first cell”, “ID 1”, “LTM DU configuration 1” and / or “LTM CU configuration 1” are replaced with “first cell”, “second LTM command” and “second cell”, “ID 2”, “LTM DU configuration 2” and / or “LTM CU configuration 2”, respectively.

[0186] The events 344, 346, 348, 350, 351, 352, 354 are collectively referred to in Fig. 3 as a 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 a LTM DU configuration and / or activation procedure 380.

[0187] 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 124A and optionally additional cell(s), while the T-DU 174B operates a first cell (e.g., cell 124C). The scenario 400 is similar to the scenario 300. Thus, the at least some of the discussion of the scenario 300 can generally apply to the scenario 400. The differences between the scenarios 300 and 400 are described below.

[0188] 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 174A. The S-DU 174A is a serving DU similar to the DU 174 in Fig. 3A. 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 174A. 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 a LTM preparation procedure with the T-DU 174B to (request the T-DU 174B to) prepare cell(s) 1, ..., N for LTM for the UE 102. N can be a positive integer larger than zero or 1. Inthe 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 a RRC reconfiguration message in a 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.

[0189] After performing the LTM preparation procedure 490, the CU 172 may perform an additional LTM preparation procedure(s) with the T-DU 174B to prepare cell(s) N+l, ..., N+M for LTM for the UE 102, similar to the procedure 490. M is a positive integer larger than zero. The CU 172 may determine to do so based on one or more measurement reports received from the UE 102 via the S-DU 174A, similar to the events 404, 406. In the additional LTM preparation procedure, the CU 172 transmits a CU-to-DU message including cell ID(s) N+l, ..., N+M to the T-DU 174B to request the T-DU 174B to prepare the cell(s) N+l, ..., N+M for LTM for the UE 102. The cell ID(s) N+l, ..., N+M identifies the cell ID(s) N+l, ..., N+M, respectively. In response to the CU-to-DU message, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) N+l, ..., N+M to the CU 172. The LTM DU configuration(s) N+l, ..., N+M configures the cell(s) N+l, ..., N+M for LTM, respectively. In details, the LTM DU configuration(s) N+l, ..., N+M include configuration parameters for communication on the cell(s) N+l, ..., N+M, respectively. The CU 172 then transmits the LTM DU configuration(s) N+l, ..., N+M in a RRC reconfiguration message in an additional LTM configuration delivery procedure, similar to the LTM configuration delivery procedure 394 or 494.

[0190] 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.

[0191] In some implementations, the CU 172 and S-DU 174A may perform the procedure 380 with the UE 102, as described for Fig. 3. In the procedure 380, the CU 172 and S-DU 174A performs the procedure(s) 390 and / or 392 to prepare cell(s) of the S-DU 174A for LTM for the UE 102. Note, the value N in the procedure 380 or described for Fig. 3 can be the same as or different from the value N described for Fig. 4. In the procedure 390, the CU 172 may receive the first DU-to-CU message including the reference LTM DU configuration from the S-DU 174A in the event 310. In other implementations, the CU 172 and S-DU 174A does not perform the procedure 380 with the UE 102. In such cases, the CU 172 can perform 488 a reference LTM DU configuration query procedure with the S-DU 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 174A transmits 462 a DU-to-CU message including a reference LTM DU configuration to the CU 172. In some implementations, the indication is a reference LTM DU configuration query indication. In other implementations, the indication is a LTM indication, and the CU 172 may include a query indication (e.g., GNB-DU Configuration Query IE) in the CU-to-DU message. After receiving the reference LTM DU configuration (i.e., either in the procedure 390 or in the procedure 488), the CU 172 includes the reference LTM DU configuration (received from the S-DU 174A) in the CU-to-DU message in the LTM preparation procedure 490. The T-DU 174B generates the LTM DU configuration(s) 1, ..., N based on the reference LTM DU configuration received from the CU 172. In such cases, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. The CU 172 may 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.

[0192] In some implementations, the CU 172 does not provide a reference LTM DU configuration to the T-DU 174B in the LTM preparation procedure 490. In such cases, the T- DU 174B generates a reference LTM DU configuration and generates the LTM DU configuration(s) 1, ..., N based on the reference LTM DU configuration. In such cases, the T- DU 174B includes the reference LTM DU configuration in the DU-to-CU message in the procedure 490. The CU 172 transmits the reference LTM DU configuration in the RRC reconfiguration message in the procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+l, ..., N+M based on the reference LTM DU configuration. In this case, the T-DU 174B may 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 174A.

[0193] 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.

[0194] 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 CSLRS(s). The RS resource(s) includes SSB resource(s) and / or CSLRS resource(s). In some implementations, each of the RS resource configuration(s) X includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) X is / are (similar to) CSl-ResourceConfig IE(s). In some implementations, the LTM DU configuration X includes a CSl-MeasConfig IE and the CSl-MeasConfig IE includes the CSl- 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) CSl-ReportConfig IE(s). In some implementations, the T-DU 174B generates at least one RS resourceconfiguration 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.

[0195] 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 a LTM serving cell change to the cell 1 from the cell 124A, the UE 102 communicates with the S-DU 174B (i.e., the T-DU 17B becomes a S-DU for the UE 102) and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the report configuration(s) 1. Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the report configuration(s) 1. In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) 1 and / or the report configuration(s) 1 and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values may include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0196] 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) CSl-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) CSl-ReportConfig IE(s).

[0197] 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 a LTM serving cell change to the cell 1 from the cell 124A, the UE 102 communicates 436 with the S-DU 174B and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the additional report configuration(s). Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the additional report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the additional RS(s) or the additional RS resource(s) in accordance with the additional RS resource configuration(s) and / or the additional report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the additional RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values may include one or more Ll-RSRP values and / or one or more Ll-SINR values.

[0198] 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 resourceconfiguration(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.

[0199] 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 TCl-State IE. In some implementations, the TCI state configuration(s) X includes / is / are an ul-TCl-ToAddModList-rl7 field, one or more TCl-UL-State-rl7 IES, a dl-OrJointTCl-StateToAddModList-rl7 field, one or more TCl-State IEs, TC1- ActivatedConfig IE and / or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration X includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) X. In some implementations, the T-DU 174B generates at least one TCI state configuration 1, considering or based on the TCI state configuration(s) X and includes the TCI state configuration(s) 1 in the LTM DU configuration 1. In some implementations, the TCI state configuration(s) 1 includes the TCI state configuration(s) X. In other implementations, the T-DU 174B includes each of the TCI state configuration(s) X in the TCI state configuration(s) 1, except the TCI state ID(s) in the TCI state configuration(s) X. The T-DU 174B assigns a TCI state ID to a value for each of the TCI state configuration(s) 1 (including the TCI state configuration(s) X) and includes the TCI state ID in the corresponding TCI state configuration. While the UE 102 and the S-DU 174B communicate 436 with one another, the S-DU 174B may transmit a LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell X. The S- DU 174B includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell X, where the TCI state configuration is one of the TCI state configuration(s) X or includes configurations of one of the TCI state configuration(s) X.

[0200] 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 configuration(s) 2, ..., N, and / or N+l, ..., N+M, respectively, as described above.

[0201] 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 configuration(s) 1, ..., N of the procedure 490 in the CU-to-DU message of the procedure 380, and the S-DU 174A generates the LTM DU configuration(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.

[0202] In some implementations, the CU 172 assigns ID(s) 1, ..., N identifying the LTM DU configuration(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 configuration(s) 1, ..., N and / or the cell ID(s) 1, ..., N, respectively. In other implementations, the T-DU 174B assigns ID(s) 1, ..., N identifying the LTM DU configuration(s) 1, ..., N (generated by the T-DU 174B), respectively and includes the ID(s) 1, ..., N in the DU-to-CU message of the procedure 490, similar to the event 310. In some implementations, the CU 172 assigns ID(s) N+l, ..., N+M identifying the LTM DU configuration(s) N+l, ..., N+M, respectively, and performs a procedure (similar to the procedure 492) with the T-DU 174B to provide the ID(s) N+l, ..., N+M and / or cell ID(s) N+l, ..., N+M to the T-DU 174B, similar to the procedure 392. Thus, the T-DU 174B associates the ID(s) N+l, ..., N+M with the LTM DU configuration(s) N+l, ..., N+M and / or the cell ID(s) N+l, ..., N+M, respectively. In other implementations, the T-DU 174B assigns ID(s) N+l, ..., N+M identifying the LTM DU configuration(s) N+l, ..., N+M, respectively and includes the ID(s) 1, ..., N in the DU-to-CU message of the additional LTM preparation procedure, similar to the event 310.

[0203] In some implementations, the CU 172 transmits 412 a CU-to-DU message including the ID(s) 1, ..., N to the S-DU 174A and receives 414 a DU-to-CU message from the S-DU 174A in response. The CU-to-DU message 412 and DU-to-CU message 414 are collectively referred to in Fig. 4 as a LTM ID transfer procedure 493 or a 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 message412. 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 174A. 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 configuration(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 configuration(s) 1, ..., N to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the cell index(es) 1, ..., N, cell ID(s) 1, ..., N and / or LTM DU configuration(s) 1, ..., N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the cell index(es) 1, ..., N with the LTM DU configuration(s) 1, ..., N and / or the cell ID(s) 1, ..., N, respectively.

[0204] In some implementations, the S-DU 174A 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 a RRC reconfiguration message including the first serving DU configuration to the UE 102. The UE 102 applies the first serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174A 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.

[0205] 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 CSLRS(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) Y includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) Y is / are (similar to) CSl-ResourceConfig IE(s). In some implementations, the LTM DU configuration Y includes a CSl-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 124A, 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) CSl-ReportConfig IE(s). In some implementations, the S-DU 174A 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 174A 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 174A 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.

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

[0207] 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 TCl-State IE. In some implementations, the TCI state configuration(s) Y includes / is / are an ul-TCl-ToAddModList-rl7 field, one or more TCl-UL-State-rl7 IES, a dl-OrJointTCl-StateToAddModList-rl7 field, one or more TCl-State IEs, TC1- ActivatedConfig IE and / or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration Y includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) Y. In some implementations, the S-DU 174A generates at least one serving TCI state configuration, considering or based on the TCI state configuration(s) Y and includes the serving TCI state configuration(s) in the first serving DU configuration. In some implementations, the serving TCI state configuration(s) 1 includes the TCI state configuration(s) Y. In other implementations, the S-DU 174A includes each of the TCI state configuration(s) Y in the serving TCI state configuration(s), except the TCI state ID(s) in the TCI state configuration(s) Y. The S-DU 174A assigns a TCI state ID to a value for each of the serving TCI state configuration(s) (including the TCI state configuration(s) Y) and includes the TCI state ID in the corresponding serving TCI state configuration. While the S- DU 174A communicate 436 with the UE 102, the S-DU 174A may transmit a 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.

[0208] 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-DU174A 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 174A 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 some implementations, the S-DU 174A generates a second serving DU configuration, based on the LTM DU configuration(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 a RRC reconfiguration message including the second serving DU configuration to the UE 102 via the S-DU 174A. 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 174A using configurations included in the serving DU configuration 402 and / or the first serving DU configuration and not updated by the second serving DU configuration. In some implementations, the S-DU 174A 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 174A 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.

[0209] In some implementations, in the case that the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the ID(s) 1, ..., N of the procedure 380 aredifferent from value(s) of the ID(s) 1, ... N, and the ID(s) N+l N+M described for the scenario 400. In some implementations, in the case that the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the cell ID(s) 1, ..., N of the procedure 380 are different from value(s) of the cell ID(s) 1, N, and the cell ID(s) N+l N+M described for the scenario 400. In some implementations, in the case that the CU 172 and S- DU 174A 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.

[0210] At a later time, the UE 102 may transmit 424 at least one measurement report to the S-DU 174A, similar to the event 324. The at least one measurement report (e.g., LI measurement report(s)) includes an event ID, first measurement result(s) for the cell 1 of the T-DU 174B, and / or includes second measurement result(s) for the cell 124A. In some implementations, the first measurement result(s) can be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 1. Likewise, the second measurement result(s) can be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 124A. In some implementations, the event ID, RSRP, RSRQ and / or SINR are LI -event ID, LI -RSRP, LI -RSRQ and / or LI -SINR, respectively. Based on the first measurement result(s) and / or second measurement result(s), the S-DU 174A may transmit 430 a first LTM command (i.e., LTM command 1) including the ID 1 to the UE 102 to order the UE 102 to perform a serving cell change to the cell 1 of the T-DU 174B. In some implementations, the first LTM command includes the ID 1. In other implementations, the first LTM command includes the cell index 1. When the UE 102 receives the first LTM command, the UE 102 performs a serving cell change to the cell 1 from a serving cell in accordance with the LTM DU configuration 1. After (e.g., in response to) receiving the first LTM command, the UE 102 may perform 432 a random access procedure with the T-DU 174B, similar to the event 332, or omit this procedure. After (e.g., in response to) receiving the first LTM command or completing the random access procedure 432, the UE 102 may communicates 436 with the T-DU 174B on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the T-DU 174B, similar to the event 336. If a serving cell change occurs in the procedure 380, the serving cell can be the cell 1 or cell 2 of the S-DU 174A. Otherwise, if no serving cell change occurs in the procedure 380 or the procedure 380 is not performed, the serving cell is the cell 124A. If the first LTM command includes the ID 1, the UE 102identifies 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 Eig. 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.

[0211] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 430, the S-DU 174A may transmit 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 a LTM serving cell change. The S-DU 174A 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 may stop or suspend transmitting DL data for the UE 102 to the S-DU 174A until receiving the DU-to-CU message 434. After receiving the DU-to-CU message 434, the CU 172 starts, continues or resumes transmitting DL data for the UE 102 to the T-DU 174B. When or after the T-DU 174B detects that UE 102 accesses the cell 1, the T-DU 174B transmits the DL data to the UE 102 via the cell 1.

[0212] 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 174A to release a UE context 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.

[0213] 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 Eig. 4 as a LTM configuration and / or activation procedure 480.

[0214] Referring next to Eig. 5A, 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 Eig. 3.

[0215] Initially, the UE 102 in DC communicates with the MN 106 and with SN 104. In the event 502, the UE 102 communicates with the DU 174 on cell 124A using a serving DU configuration and communicates with the CU 172 via the DU 174 using a serving CU configuration, similar to the event 302. In some alternative implementations, the UE 102 does not communicate with the CU 172 via the DU 174 in the event 302. In some implementations, the UE 102 in DC can communicate 502 UL PDUs and / or DL PDUs with the MN 106 and / or SN 104 via radio bearers which can include SRBs and / or DRB(s). The MN 106 and / or the SN 104 can configure the radio bearers to the UE 102. The UE 102 in DC communicates 502 UL PDUs and / or DL PDUs with the SN 104 on an SCG (i.e., SCG radio resources) that the SN 104 configures for communication with the UE 102. The UE 102 in DC communicates UL PDUs and / or DL PDUs with the MN 106 on an MCG (i.e., MCG radio resources) in accordance with a MN configuration (i.e., MCG configuration). In some implementations, the serving DU configuration is a SN configuration (i.e., SCG configuration). In the MN configuration, the MN 106 configures the MCG which includes at least one serving cell (e.g., the cell 126 and / or other cell(s)) operated by the MN 106. In the serving DU configuration, the SN 106 A configures the SCG which includes at least one serving cell (e.g., the cell 124A and / or other cell(s)) operated by the SN 104. In some implementations, the MN configuration includes multiple configuration parameters and the UE 102 receives the configuration parameters in one or more RRC messages from the MN 106. As described for Fig. 3, the serving DU configuration includes multiple configuration parameters. In some implementations, the UE 102 receives these configuration parameters in one or more RRC messages from the SN 104, e.g., via the MN 106 and / or on an SRB e.g., SRB3) that the MN 106 or SN 104 configures to exchange RRC messages between the UE 102 and the SN 104.

[0216] While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 can perform 580 a 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 124 A 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 leastone 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).

[0217] 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. At a later 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.

[0218] 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 a LTM DU configuration and / or activation procedure 581.

[0219] 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 MNRRC 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 a RRC reconfiguration message and a RRC reconfiguration complete message, respectively.

[0220] 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 a LTM DU configuration and / or activation procedure 582.

[0221] 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 a 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 174A and S-DU 174B, the CU 172 can perform 681 a LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A or S-DU 174B, similar to the procedure 581 or 582.

[0222] Referring next to Fig. 6B, a scenario 600B similar to the scenarios 300-500B and 600A, 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.

[0223] 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.

[0224] 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 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174Busing 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 a LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380.

[0225] 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 a LTM configuration and / or activation procedure 781.

[0226] 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 174A and receives 721, 723 the RRC reconfiguration complete message from the UE 102 via the M-DU 174A.

[0227] 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 a LTM DU configuration and / or activation procedure 782.

[0228] Referring next to Fig. 8A, 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 174A and S-DU 174B, the CU 172 can perform 880 a 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 a LTM DU configuration and / or activation procedure with the UE 102 via the S-DU 174A, similar to the procedure 581 or 582.

[0229] Referring next to Fig. 8B, a scenario 800B similar to the scenarios 300-700B and 800A, except that that the CU 172 transmits 817, 819 the RRC reconfiguration message to the UE 102 via the M-DU 174A and receives 821, 823 the RRC reconfiguration complete message from the UE 102 via the M-DU 174A.

[0230] Next, several example methods, that can be implemented in a RAN node such as a base station, a DU or a CU, to enable early timing advance (TA) acquisition for LTM, are discussed with reference to Figs. 9A-16B. At least some of the discussion of Figs. 3-8B above can also apply to Figs. 9A-16B.

[0231] Fig. 9A illustrates an example method 900A, which can a DU (e.g., the DU 174, 174A, DU 174B or DU 174C in Figs. 3-8B) can implement to configure early TA acquisition for a UE (e.g., the UE 102 in Figs. 3-8B).

[0232] The method 900A begins at block 908, where the DU receives, from a CU, a first CU-to-DU message requesting preparation of a first cell for LTM, for the UE 102. The first CU-to-DU message includes a first LTM ID (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). At block 910, the DU transmits a first DU-to-CU message including a first LTM DU configuration configuring the first cell for LTM for the UE to the CU, in response to the first CU-to-DU message (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). At block 925, the DU associates the first LTM DU configuration with the first LTM ID. At block 927, the DU transmits a first command to the UE via the serving cell, where the first command commands the UE to transmit a random access preamble on the first cell and includes the first LTM ID. At block 953, the DU receives a first random access preamble on the first cell from the UE. At block 930, the DU transmits a LTM command to the UE via a serving cell, where the first LTM command includes the first LTM ID and includes a TA value (e.g., events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581, 582, 680, 681, 630, 698, 780, 730, 798, 880, 881, 830, 898). At block 932, the DU detects that the UE accesses the first cell after transmitting the LTM command (e.g., events 332, 352, 398, 380, 432, 452, 498, 480, 580, 532, 598, 581, 582, 680, 632, 698, 681, 780, 732, 798, 880, 881, 832, 898). At block 936, the DU communicates with the UE on the first cell using the TA value and the LTM configuration (e.g., events 336, 356, 380, 436, 456, 480, 536, 556, 580, 581, 582, 636, 656, 680, 681, 736, 756, 780, 836, 856, 880, 881).

[0233] In some implementations, the CU transmits a first message including the first LTM ID and the first LTM DU configuration to the UE (e.g., events 316, 318, 394, 380, 494, 480, 580, 594, 581, 517, 519, 582, 680, 681, 694, 780, 794, 717, 719, 880, 881, 894, 817, 819). In some implementations, the DU receives, from the CU, a second CU-to-DU message requesting preparation of a second cell for LTM for the UE, where the second CU-to-DUmessage includes a second LTM ID. In response to the second CU-to-DU message, the DU transmits a second DU-to-CU message including a second LTM DU configuration configuring the second cell for LTM for the UE to the CU. In some implementations, the DU associates the second LTM DU configuration or the second cell with the second LTM ID.

[0234] In some implementations, the DU transmits the first LTM command after receiving the first random access preamble. In some implementations, the DU refrains from transmitting a random access response to the UE in response to the first random access preamble.

[0235] In some implementations, the DU receives one or more lower layer measurement results for the first cell from the UE. In some implementations, if the DU determines that the lower layer measurement result(s) is above or equal to a first threshold, the DU transmits the first command at block 927. Otherwise, if the DU determines that the lower layer measurement result(s) for the first cell is below a second threshold, the DU refrains from transmitting, to the UE via the serving cell, a command commanding the UE to transmit a random access preamble for early TA acquisition on the first cell. In some implementations, the first threshold and the second threshold are the same threshold. In other implementations, the first threshold (value) is larger than the second threshold (value).

[0236] In some implementations, the DU obtains the first TA value for the UE and the first cell according to the time when the DU receives the first random access preamble. In some implementations, the DU transmits the first LTM command to the UE immediately after obtaining the first TA value. In other implementations, the DU transmits the first LTM command to the UE in a short time period after obtaining the first TA value. In yet other implementations, the DU receives one or more lower layer measurement results for the first cell from the UE after obtaining the first TA value. If the DU determines that the lower layer measurement result(s) is above or equal to a third threshold, the DU transmits the first LTM command at block 930. Otherwise, if the DU determines that the lower layer measurement result(s) for the first cell is below a fourth threshold, the DU refrains from transmitting a LTM command to the UE, where the LTM command commands the UE to perform a serving cell switch to the first cell from the serving cell, similar to the first LTM command. In some implementations, the third threshold and the fourth threshold are the same threshold. In other implementations, the third threshold (value) is larger than the fourth threshold (value). In some implementations, the third threshold and the first threshold are the same threshold. Inother implementations, the third threshold (value) is larger than the first threshold (value). In some implementations, the fourth threshold and the second threshold are the same threshold. In other implementations, the fourth threshold (value) is larger than the second threshold (value).

[0237] In some implementations, the DU receives one or more lower layer measurement results for the second cell from the UE. Because the DU determines that the lower layer measurement result(s) for the second cell is below the second threshold, the DU refrains from transmitting, to the UE via the serving cell, a command commanding the UE to transmit a random access preamble for early TA acquisition on the second cell. In some implementations, because the DU determines that the lower layer measurement result(s) is below the third threshold, the DU refrains from transmitting a LTM command to the UE, where the LTM command commands the UE to perform a serving cell switch to the second cell from the serving cell.

[0238] In some implementations, the first command is a PDCCH order or a DCI and the DU transmits the PDCCH or the DCI on a PDCCH to the UE. In some implementations, the DU generates the first command. In some implementations, the DU obtains a cyclic redundancy check (CRC) from the first command, scrambles the CRC with a UE ID of the UE, and transmits the first command and the scrambled CRC to the UE on a PDCCH. For example, the UE ID is a cell radio network temporary identifier (C-RNTI). In some implementations, the first command includes a first plurality of random access configuration parameters. In some implementations, the first plurality of random access configuration parameters includes a first random access preamble index, an indicator indicating a UL or a supplementary UL (SUL), a SSB index, and / or a physical random access channel (PRACH) mask index. The first random access preamble index indicates, identifies or indexes the first random access preamble. The UE selects or generates the first random access preamble in accordance with the first random access preamble index. In some implementations, the PRACH mask index configures one or more PRACH occasions. The UE determines a PRACH occasion to transmit the first random access preamble on the first cell in accordance with the SSB index and / or in the PRACH mask index. In some implementations, the indicator set to 0 indicates UL and the indicator set to 1 indicates SUL. The UE transmits the first random access preamble on UL or SUL of the first cell in accordance with the indicator. In some implementations, the first command includes an identifier for DCI formats and / or a frequency domain resource assignment field. In some implementations, the identifier for DCIformats may be set to zero for the first format and the second format. In some implementations, all the bits in the frequency domain resource assignment field are set to zero.

[0239] In some implementations, the first DU-to-CU message includes a second plurality of random access configuration parameters. In some implementations, the CU includes the second plurality of random access configuration parameters in the first message. In some implementations, the CU includes the first LTM ID, the first LTM DU configuration and the second plurality of random access configuration parameters in an element (e.g., a field or an IE) or a container (e.g., a field or an IE) and includes the element or container in the first message. In other implementations, the CU transmits a second message including the first LTM ID and the second plurality of random access configuration parameters to the UE. In some implementations, the CU includes the first LTM ID and the second plurality of random access configuration parameters in an element (e.g., a field or an IE) or a container (e.g., a field or an IE) and includes the element or element in the second message. In some implementations, the second message is a RRC reconfiguration message similar to the RRC reconfiguration message in events 316, 318, 394, 380, 494, 480, 580, 594, 581, 517, 519, 582, 680, 681, 694, 780, 794, 717, 719, 880, 881, 894, 817, 819.

[0240] In some implementations, the second plurality of random access configuration parameters include a PRACH root sequence index and / or a subcarrier spacing of PRACH. In some implementations, the UE generates or selects the first random access preamble using the PRACH root sequence index and the first random access preamble index. In some implementations, the UE transmits the first random access preamble on the first cell using the subcarrier spacing of PRACH. In some implementations, the second plurality of random access configuration parameters configure first random access resource (e.g., time resources (e.g., PRACH occasions), frequency resources, and / or random access preambles). In some implementations, the first LTM DU configuration includes the second plurality of random access configuration parameters. In other implementations, the first LTM DU configuration includes a third plurality of random access configuration parameters. In some implementations, the third plurality of random access configuration parameters configure second random access resources (e.g., time resources (e.g., PRACH occasions), frequency resources, and / or random access preambles). In some implementations, third random access resources may not overlap with the second random access resources. In other implementations, the third random access resources may overlap with the second randomaccess resources. In some implementations, third plurality of random access configuration parameters may be different from the second plurality of random access configuration parameters. In other implementations, a portion of or all of the second random access resources is the same as a portion or all of the first random access resources. In some implementations, the third plurality of random access configuration parameters include the PRACH root sequence index and / or the subcarrier spacing of PRACH that are included in the second plurality of random access configuration parameters.

[0241] In accordance with the first LTM ID in the first command, the UE identifies the first LTM DU configuration. The UE then determines the first cell is the cell where the UE is to transmit a random access preamble (i.e., the first random access preamble). In some implementations, the first LTM DU configuration includes a cell ID (e.g., PCI) of the first cell and the UE identifies the first cell based on the cell ID. In some implementations, the UE transmits the first random access preamble on the first cell, using 1) the second plurality of random access configuration parameters and 2) the indicator (e.g., indicating UL or SUL), the SSB index and / or the PRACH mask index. After transmitting the first command, the DU attempts to receive or receives the first random access preamble on the first cell using 1) the second plurality of random access configuration parameters and 2) the indicator (e.g., indicating UL or SUL), the SSB index and / or the PRACH mask index.

[0242] In some implementations, the DU determines whether the UE supports early TA acquisition. If the DU determines that 927 UE supports early TA acquisition, the DU transmits the first command at block 927 and attempts to receive or receives the first random access preamble at block 953. Otherwise, if the DU determines that the UE does not support early TA acquisition, the DU refrains from transmitting a command (e.g., the first command) to the UE to command the UE to transmit a random access preamble for early TA acquisition.

[0243] In some implementations, the DU receives, from the CU, a second CU-to-DU message requesting preparation of a second cell for LTM for the UE, where the second CU- to-DU message includes a second LTM ID (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). In response, the DU transmits a second DU-to-CU message including a second LTM DU configuration configuring the second cell for LTM for the UE to the CU (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). The DU associates the second LTM DU configuration with the second LTM ID. In some implementations, the DU determines not to configureearly TA acquisition for the UE, and in response to the determination, does not include random access configuration parameters for early TA acquisition in the second DU-to-CU message. The second LTM ID and the first LTM ID are set to different values.

[0244] In some implementations, the DU receives, from the CU, a third CU-to-DU message requesting preparation of the first cell for LTM for another UE (i.e., a second UE), where the third CU-to-DU message includes a third LTM ID (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). In response, the DU transmits a third DU-to-CU message including a third LTM DU configuration configuring the first cell for LTM for the second UE to the CU (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). In some implementations, the DU includes, in the third DU-to-CU message, the second plurality of random access configuration parameters for early TA acquisition for the second UE. In other implementations, the DU includes, in the third DU-to-CU message, the third plurality of random access configuration parameters for early TA acquisition for the second UE.

[0245] Fig. 9B is a flow diagram of an example method 900B similar to the method 900A, except that the method 900B includes blocks 909 and 911 instead of block 908. At block 909, the DU receives, from a CU, a first CU-to-DU message requesting preparation of a first cell for LTM for the UE. Block 909 is similar to block 908 except that the first CU-to-DU message in block 909 does not include a LTM ID. At block 911, the DU receives a first additional DU-to-CU message including a first LTM ID for the UE from the CU (e.g., events 312, 392, 380, 492, 480, 580, 592, 581, 582, 680, 692, 681, 780, 792, 880, 892, 881).

[0246] Fig. 9C is a flow diagram of an example method 900C similar to the method 900A, except that the method 900C includes block 909 instead of block 927. At block 909, the DU transmits a first command to the UE via the serving cell, where the first command commands the UE to transmit a random access preamble on the first cell and includes a first cell ID identifying the first cell. In accordance with the first cell ID in the first command, the UE identifies the first LTM DU configuration and determines the first cell is the cell where the UE is to transmit a random access preamble (i.e., the first random access preamble). In some implementations, the first LTM DU configuration includes the first cell ID of the first cell and the UE identifies the first LTM DU configuration based on the first cell ID.

[0247] Fig. 9D is a flow diagram of an example method 900D similar to the methods 900A, 900B, and 900C.

[0248] Fig. 9E is a flow diagram of an example method 900E similar to the method 900A, except that the method 900E includes blocks 907 instead of block 927. At block 907, the DU transmits a first command to the UE via the serving cell, where the first command commands the UE to transmit a random access preamble on the first cell and includes a first cell index indicating the first cell. In accordance with the first cell index in the first command, the UE identifies the first LTM DU configuration. In some implementations, the first LTM DU configuration includes a cell ID (e.g., PCI) of the first cell and the first cell index and the UE identifies the first LTM DU configuration based on the first cell index. The UE determines the first cell is the cell where the UE is to transmit a random access preamble (i.e., the first random access preamble), in accordance with the cell ID of the first cell.

[0249] Fig. 9F is a flow diagram of an example method 900D similar to the methods 900A, 900B, and 900D.

[0250] In some implementations, the DU in Figs. 9A-9F is a serving DU (e.g., the DU 174 in Figs. 3 and 5, S-DU 174A in Figs. 4, 6A and 6B, M-DU 174 or S-DU 174B in Figs. 7A, 7B, 8A and 8B ). Example and implementations described for the serving DU in Fig. 13 can apply to the DU in Figs. 9A-9F.

[0251] Fig. 10A illustrates an example method 1000A, which can be implemented by a DU (e.g., the DU 174, 174A, DU 174B or DU 174C in Figs. 3-8B), for configuring early TA acquisition for a UE (e.g., the UE 102 in Figs. 3-8B).

[0252] The method 1000A begins at block 1012, where the DU receives, from a CU, a first CU-to-DU message including a first LTM ID and a first plurality of random access configuration parameters for the UE (e.g., events 412, 493, 480, 580, 680, 693, 681, 880, 893, 881). At block 1027A, the DU transmits, to the UE via a serving cell, a first command to initiate random access on a target cell. The first command includes the first LTM ID and the first plurality of random access configuration parameters. At block 1030, the DU transmits an LTM command to the UE via the serving cell, where the LTM command includes the first LTM ID and includes a first TA value (e.g., events 430, 450, 498, 480, 580, 680, 681, 630, 698, 780, 880, 881, 830, 898). At block 1028, the DU receives a second CU-to-DU message for the UE from the CU. At block 1029, the DU transmits a second DU-to-CU message to the CU in response to the second CU-to-DU message.

[0253] In some implementations, the DU communicates with the UE via the serving cell (e.g., events 402, 502, 602, 702, 802, 480, 580, 680, 780, 880, 681, 780, 880, 881). In someimplementations, the first LTM ID identifies a first LTM DU configuration configuring a first cell for LTM and the first plurality of random access configuration parameters are configured for the UE to perform early TA acquisition on the first cell.

[0254] In some implementations, the second CU-to-DU message is to request to modify a UE context of the UE. The DU modifies the UE context in response to the second CU-to-DU message. In some implementations, the second CU-to-DU message and the second DU-to- CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In some implementations, the second CU-to- DU message is to request to prepare a second cell for LTM for the UE and the second DU-to- CU message includes a second LTM DU configuration, which configuring the second cell for the UE (e.g., events 308, 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). In some implementations, the second CU-to-DU message is to request or command to release a cell configured for LTM for the UE, and the DU releases the cell in response. In some implementations, the cell is the serving cell. In other implementations, the cell is not the serving cell. In some implementations, the second CU-to-DU message and the second DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0255] In other implementations, the second CU-to-DU message is to request to release a UE context of the UE. The DU releases the UE context in response to the second CU-to-DU message. In some implementations, the second CU-to-DU message and the second DU-to- CU message are a UE Context Release Command message and a UE Context Release Complete message.

[0256] In some implementations, the first CU-to-DU message includes first cell information of a first cell. In some implementations, the first cell information is a CGI. In other implementations, the first cell information is a PCI. In other implementations, the first CU-to-DU message includes a first LTM DU configuration associated with the first LTM ID.

[0257] In some implementations, the DU (i.e., a first DU) is a serving DU or a source DU for the UE. In some implementations, a second DU (e.g., a candidate DU or a target DU) operates the first cell. The CU receives the first plurality of random access configuration parameters from the second DU.

[0258] Fig. 10B is a flow diagram of an example method 1000B similar to the method 1000A, except that the method 1000B includes blocks 1012 and 1011 instead of block 1012.At block 1007, the DU receives, from a CU, a first CU-to-DU message including a first LTM ID for a UE. At block 1011, the DU receives, from a CU, a first additional CU-to-DU message including a first plurality of random access configuration for the UE.

[0259] In some implementations, the additional CU-to-DU message includes the first cell information. In such implementations, the DU determines the first LTM ID in accordance with an association between the first cell information and the first LTM ID and includes the first LTM ID in the first command. In some implementations, the additional CU-to-DU message includes the first LTM ID. In such cases, the DU includes the first LTM ID in the first command in accordance with the first LTM ID in the additional CU-to-DU message.

[0260] Eig. 10C is a flow diagram of an example method 1000C similar to the method 1000A, except that the method 1000C includes block 1027C instead of block 1027A. At block 1027C, the DU transmits a first command to the UE via a serving cell, where the first command includes a first cell ID identifying a first cell and the first plurality of random access configuration parameters. The first command does not include a LTM ID.

[0261] In some implementations, in cases where the first cell information includes a PCI of the first cell, the first cell ID is the PCI. In other implementations, in cases where the first cell information includes a CGI of the first cell, the first cell ID is a PCI of the first cell. In some implementations, the DU determines the PCI based on the CGI by looking up a mapping table including a mapping between the PCI and the CGI.

[0262] Pig. 10D is a flow diagram of an example method 1000D similar to the methods 1000A, 1000B and 1000C.

[0263] Pig. 10E is a flow diagram of an example method 1000E similar to the methods 1000A and 1000C, except that the method 1000E includes blocks 1027E instead of blocks 2027 A or 1027C. At block 1027E. the DU transmits a first command to the UE via a serving cell, where the first command includes a first cell index indicating a first cell and the first plurality of random access configuration parameters. The first command does not include a LTM ID. In some implementations, the first CU-to-DU message includes the first cell information and the first cell index.

[0264] Pig. 10P is a flow diagram of an example the method 1000P similar to the methods 1000A, 1000B, and 1000E.

[0265] At least some of the discussion of Figs. 9A-9F can apply to Figs. 10A-10F. Example and implementations described for the serving DU in Fig. 13 can apply to the DU in Figs. 10A-10E.

[0266] Fig. 11 A illustrates an example method 1100A, which can be implemented by a CU (e.g., the CU 172 in Figs. 3-8B), for configuring early TA acquisition for a UE (e.g., the UE 102 in Figs. 3-8B).

[0267] The method 1100A begins at block 1102, where the CU communicates with a UE via a serving DU (e.g., events 402, 502, 602, 702, 802, 480, 580, 680, 780, 880, 780, 880, 881). At block 1190, the CU receives, from a first DU, a first LTM DU configuration and a first plurality of random access configuration parameters for the UE (e.g., events 490, 480, 580, 680, 690, 780, 880, 890, 881). In some implementations, the first DU configures the first plurality of random access configuration parameters for early TA acquisition. At block 1125, the CU associates the first LTM DU configuration with a first LTM ID. At block 1194, the CU transmits the first LTM ID and the first LTM DU configuration to the UE (e.g., events 494, 480, 580, 594, 680, 694, 617, 619, 780, 880, 881, 894, 817, 819). In some implementations, the CU transmits the first LTM ID and the first LTM DU configuration via the serving DU. In other implementations, the CU transmits the LTM ID and the first LTM DU configuration to the UE via another DU or a base station. At block 1112, the CU transmits a first CU-to-DU message including the first LTM ID and the first plurality of random access configuration parameters to the serving DU (e.g., events 412, 493, 480, 580, 680, 693, 681, 880, 893, 881). At block 1195, the CU transmits a second CU-to-DU message for the UE to the serving DU. At block 1197, the CU receives a second DU-to-CU message from the serving DU in response to the second CU-to-DU message.

[0268] In some implementations, the CU transmits a CU-to-DU message including the first LTM ID to a second DU. In some implementations, the CU includes cell information of the first cell and / or the first LTM DU configuration in the CU-to-DU message.

[0269] Eig. 1 IB is a flow diagram of an example method 1100B similar to the method 1100A, except that the method 1100B includes blocks 1113 and 1111 instead of block 1112. At block 1113, the CU transmits a first CU-to-DU message including the first LTM ID to the serving DU (e.g., events 412, 493, 480, 580, 680, 693, 681, 880, 893, 881). At block 1111, the CU transmits a first additional CU-to-DU message including the first plurality of random access configuration parameters to the serving DU.

[0270] The discussion of Figs. 9A-9F and 10A-10F can apply to the Figs. 11A and 1 IB. Example and implementations described for Fig. 13 can apply to Figs. 11A and 1 IB.

[0271] Fig. 12 illustrates an example method 1200, which can be implemented by a CU (e.g., the CU 172 in Figs. 3-8B), for configuring early TA acquisition for a UE (e.g., the UE 102 in Figs. 3-8B).

[0272] The method 1200 begins at block 1202, where the CU communicates with a UE via a serving DU (e.g., events 302, 402, 502, 602, 702, 802, 380, 480, 580, 680, 780, 880, 581, 582, 681, 780, 880, 881). At block 1271, the CU initiates a LTM preparation procedure to prepare a first cell for LTM. At block 12061208 the CU includes a first cell ID of the first cell in a first CU-to-DU message in response to the initiation (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). At block 1273, the CU determines whether the UE supports early TA acquisition. If the CU determines that the UE supports early TA acquisition at block 1273, the flow proceeds to blocks 1275. At block 1275, the CU includes a request indication requesting random access configuration parameters for early TA acquisition in the first CU-to-DU message. The flow proceeds to block 1276 from block 1275. Otherwise, if the CU determines that the UE does not support early TA acquisition at block 1273, the flow skips block 1275 and proceeds to block 1276. At block 1276, the CU transmits the first CU-to-DU message to a first DU. The flow proceeds to block 1277A or 1277B from block 1276. At block 1277A, the CU performs actions as described in blocks 1190, 1125, 1028, 1112, 1195 and 1197. At block 1277B, the CU performs actions described in block 1190, 1125, 1028, 1113, 1111, 1195 and 1197. In some implementations, if the first CU-to-DU message does not include the request indication, the first DU does not transmit a plurality of random access configuration parameters for early TA acquisition to the CU. In such cases, the blocks 1113, 1112, 1111, 1195 and 1197 are omitted.

[0273] At the least some of the discussion of Figs. 9A-9F, 10A-10F and 11A and 11B can apply to Fig. 12, and at least some of the discussion of Fig. 13 can apply to Fig. 12.

[0274] Fig. 13 illustrates an example method 1300, which can be implemented by a CU (e.g., the CU 172 in Figs. 3-8B), for configuring early TA acquisition for a UE (e.g., the UE 102 in Figs. 3-8B).

[0275] The method 1300 begins at block 1302, where the CU communicates with the UE via a serving DU (e.g., events 302, 402, 502, 602, 702, 802, 380, 480, 580, 680, 780, 880,581, 582, 681, 780, 880, 881). At block 1308, the CU transmits, to a first DU, a first CU-to- DU message requesting preparation of LTM for a first cell for the UE (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). At block 1310, the CU receives, from the first DU, a first DU-to-CU message including a first LTM DU configuration for the UE (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). At block 1318, the CU transmits a first LTM ID and the first LTM DU configuration to the UE via the serving DU. In some implementations, the CU assigns the first LTM ID. In some implementations, the CU associates with the first LTM ID with the first LTM DU configuration. In some implementations, the CU includes the first LTM DU configuration in a first element, associates the first LTM ID with the first element and transmits the first LTM ID and the first element to the UE via the serving DU (e.g., events 316, 318, 394, 380, 494, 480, 580, 594, 581, 582, 680, 694, 617, 619, 780, 794, 880, 881, 894, 817, 819).

[0276] At block 1373, the CU determines whether the UE supports early TA acquisition. If the CU determines that the UE supports early TA acquisition at block 1373, the flow proceeds to block 1312. At block 1312, the CU transmits to, the first DU, a second CU-to- DU message including a request indication requesting random access configuration parameters for the UE (e.g., events 312, 392, 380, 492, 480, 580, 592, 581, 582, 680, 692, 681, 780, 792, 781, 880, 892, 881). In some implementations, the request indication requests random access configuration parameters for early TA acquisition on the first cell. At block 1314, the CU receives, from the first DU, a second DU-to-CU message including a first plurality of random access configuration parameters for the UE (e.g., events 314, 392, 380, 492, 480, 580, 592, 581, 582, 680, 692, 681, 780, 792, 781, 880, 892, 881). In some implementations, the first DU configures the first plurality of random access configuration parameters for early TA acquisition on the first cell, e.g., in response to the request indication. At block 1393, the CU transmits a third CU-to-DU message including the first plurality of random access configuration for the UE to a serving DU (e.g., events 412, 493, 480, 580, 680, 693, 681, 880, 893, 881). At block 1381, the CU receives a third DU-to-CU message from the first DU, including a first TA value for uplink synchronization with the UE on the first cell. At block 1383, the CU transmits a fourth CU-to-DU message including the first TA value for the UE to the serving DU. Otherwise, if the DU determines that the UE does not support early TA acquisition at block 1373, the flow ends.

[0277] In some implementations, the first DU is target DU or a candidate DU. In some implementations, the CU receives the second DU-to-CU message in response to the second CU-to-DU message. In some implementations, the CU-to-DU messages and DU-to-CU messages in the method 1300 are Fl application protocol messages. In some implementations, the second CU-to-DU message and the second DU-to-CU message are a UE Context Modification Request message or a UE Context Modification Response message, respectively. In some implementations, the CU receives a DU-to-CU response message from the serving DU in response to the third CU-to-DU message. In some implementations, the third CU-to-DU message and the DU-to-CU response message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In other implementations, the third CU-to-DU message and / or the DU-to-CU response message are dedicated, special-purpose F1AP messages defined in a relevant 3GPP specification such as TS 38.473. In some implementations, the third DU-to-CU message is a UE Context Modification Required message. In other implementations, the third DU-to-CU message is an Access Success message. In yet other implementations, the third DU-to-CU message is a dedicated, special-purpose Fl AP message defined in a relevant 3GPP specification such as TS 38.473. In some implementations, the CU receives a DU-to-CU response message from the serving DU in response to the fourth CU-to-DU message. In some implementations, the fourth CU-to-DU message and the DU-to-CU response 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 the DU-to-CU response message are dedicated, special-purpose F1AP messages defined in a relevant 3GPP specification such as TS 38.473.

[0278] In some implementations, the first DU assigns a first DU UE ID for the UE to uniquely identify the UE within the first DU. In some implementations, the serving DU assigns a second DU UE ID for the UE to uniquely identify the UE within the serving DU. In some implementations, the CU assigns a CU UE ID to uniquely identify the UE within the CU. In some implementations, the CU UE ID is a gNB-CU UE F1AP ID, and the first DU UE ID and the second DU UE ID are gNB-DU UE F1AP IDs. In some implementations, the messages exchanged between the CU and the first DU includes the CU UE ID and / or the first DU UE ID to indicate the messages for the UE. When the CU receives a DU-to-CU message including the CU UE ID from the first DU, the CU identifies the DU-to-CU message for the UE based on the CU UE ID. When the first DU receives a CU-to-DU message including thefirst DU UE ID from the CU, the DU identifies the CU-to-DU message for the UE based on the first DU UE ID. Similarly, the messages exchanged between the CU and the serving DU includes the second CU UE ID and / or the second DU UE ID to indicate the messages for the UE. When the CU receives a DU-to-CU message including the CU UE ID from the serving DU, the CU identifies the DU-to-CU message for the UE based on the CU UE ID. When the serving DU receives a CU-to-DU message including the second DU UE ID from the CU, the DU identifies the CU-to-DU message for the UE based on the second DU UE ID.

[0279] In some implementations, the CU includes the first LTM ID in the first CU-to-DU message and / or the second CU-to-DU message. In some implementations, the first DU includes the first LTM ID in the second DU-to-CU message or in the first plurality of random access configuration parameters. In other implementations, the first DU includes neither the first LTM ID in the second DU-to-CU message nor the first plurality of random access configuration parameters. In some implementations, the CU includes the first LTM ID in the third CU-to-DU message. In other implementations, the CU does not include a LTM ID (e.g., the first LTM ID) in the third CU-to-DU message.

[0280] In some implementations, the first DU includes a first cell ID (e.g., PCI) of the first cell in the first plurality of random access configuration parameters or in the second DU-to- CU message. In other implementations, the first DU includes neither a cell ID (e.g., the first cell ID) of the first cell in the second DU-to-CU message nor the first plurality of random access configuration parameters. In some implementations, the CU includes the first cell ID in the third CU-to-DU message. In other implementations, the CU does not include a cell ID (e.g., the first cell ID) in the third CU-to-DU message.

[0281] In some implementations, the first DU includes a first cell index in the first plurality of random access configuration parameters or in the second DU-to-CU message. The first cell index indicate the first cell. In other implementations, the first DU includes neither a cell index (e.g., the first cell index) of the first cell in the second DU-to-CU message nor the first plurality of random access configuration parameters. In some implementations, the CU includes the first cell index in the third CU-to-DU message. In other implementations, the CU does not include a cell index (e.g., the first cell index) in the third CU-to-DU message.

[0282] In some implementations, the second DU (e.g., the serving DU) transmits a first command (e.g., a DCI or PDCCH order) including the first plurality of random accessconfiguration parameters to the UE to command the UE to transmit a first random access preamble for early TA acquisition on the first cell.

[0283] In some implementations, the first plurality of random access configuration parameters include the first LTM ID as described above. In the case that the first plurality of random access configuration parameters do not include a LTM ID (e.g., the first LTM ID), the second DU receives the first LTM ID from the CU as described above and includes the first LTM ID in the first command. In accordance with the first LTM ID in the first command, the UE identifies the first LTM DU configuration. The UE then determines the first cell is the cell where the UE is to transmit a random access preamble (i.e., the first random access preamble). In some implementations, the first LTM DU configuration includes a cell ID (e.g., PCI) of the first cell and the UE identifies the first cell based on the cell ID.

[0284] In some implementations, the first plurality of random access configuration parameters include the first cell ID as described above. In the case that the first plurality of random access configuration parameters do not include a cell ID (e.g., the first cell ID), the second DU receives the first cell ID from the CU as described above and includes the first cell ID in the first command. In accordance with the first cell ID in the first command, the UE identifies the first LTM DU configuration and determines the first cell is the cell where the UE is to transmit a random access preamble (i.e., the first random access preamble). In some implementations, the first LTM DU configuration includes the first cell ID of the first cell and the UE identifies the first LTM DU configuration based on the first cell ID.

[0285] In some implementations, the first plurality of random access configuration parameters include the first cell index as described above. In the case that the first plurality of random access configuration parameters do not include a cell index (e.g., the first cell index), the second DU receives the first cell index from the CU as described above and includes the first cell index in the first command. In accordance with the first cell index in the first command, the UE identifies the first LTM DU configuration. In some implementations, the first LTM DU configuration includes a cell ID (e.g., PCI) of the first cell and the first cell index and the UE identifies the first LTM DU configuration based on the first cell index. The UE determines the first cell is the cell where the UE is to transmit a random access preamble (i.e., the first random access preamble), in accordance with the cell ID of the first cell.

[0286] In some implementations, the first plurality of random access configuration parameters includes a first random access preamble index, an indicator indicating a UL or a supplementary UL (SUL), a SSB index, and / or a physical random access channel (PRACH) mask index. The first random access preamble index indicates, identifies or indexes the first random access preamble. The UE selects or generates the first random access preamble in accordance with the first random access preamble index. In some implementations, the PRACH mask index configures one or more PRACH occasions. The UE determines a PRACH occasion to transmit the first random access preamble on the first cell in accordance with the SSB index and / or in the PRACH mask index. In some implementations, the indicator set to 0 indicates UL and the indicator set to 1 indicates SUL. The UE transmits the first random access preamble on UL or SUL of the first cell in accordance with the indicator. In some implementations, the first command includes an identifier for DCI formats and / or a frequency domain resource assignment field. In some implementations, the identifier for DCI formats may be set to zero for the first format and the second format. In some implementations, all the bits in the frequency domain resource assignment field are set to zero.

[0287] In some implementations, the first LTM DU configuration includes a second plurality of random access configuration parameters. In some implementations, the second plurality of random access configuration parameters include a PRACH root sequence index and / or a subcarrier spacing of PRACH. In some implementations, the UE generates or selects the first random access preamble using the PRACH root sequence index and the first random access preamble index. In some implementations, the UE transmits the first random access preamble on the first cell using the subcarrier spacing of PRACH. In some implementations, the first LTM DU configuration includes a RACH configuration that includes the second plurality of random access configuration parameters.

[0288] In some implementations, the UE transmits the first random access preamble on the first cell, using 1) the second plurality of random access configuration parameters and 2) the indicator (e.g., indicating UL or SUL), the SSB index and / or the PRACH mask index. In some implementations, the first DU attempts to receive or receives the first random access preamble on the first cell using 1) the second plurality of random access configuration parameters and 2) the indicator (e.g., indicating UL or SUL), the SSB index and / or the PRACH mask index.

[0289] In some implementations, the CU includes a first cell ID of the first cell in the second CU-to-DU message to indicate the request indication for the first cell. Based on the first cell ID, the first DU prepares the first plurality of random access configuration parameters for the first cell. In other implementations, the CU includes the first cell index in the second CU-to-DU message to indicate the request indication for the first cell. Based on the first cell index, the first DU prepares the first plurality of random access configuration parameters for the first cell. In yet other implementations, the CU includes the first LTM ID in the second CU-to-DU message to indicate the request indication for the first cell. Based on the first LTM ID, the first DU prepares the first plurality of random access configuration parameters for the first cell.

[0290] In some implementations, the CU includes a first cell ID of the first cell in the third CU-to-DU message to indicate the first plurality of random access configuration parameters for the first cell. Based on the first cell ID, the serving DU determines that the first plurality of random access configuration parameters for the first cell. In other implementations, the CU includes the first cell index in the third CU-to-DU message to indicate the first plurality of random access configuration parameters for the first cell. Based on the first cell index, the serving DU determines that the first plurality of random access configuration parameters for the first cell. In yet other implementations, the CU includes the first LTM ID in the third CU- to-DU message to indicate the first plurality of random access configuration parameters for the first cell. Based on the first LTM ID, the serving DU determines that the first plurality of random access configuration parameters for the first cell. In yet other implementations, the CU includes none of the first cell ID, the first cell index and / or the LTM ID in the third CU- to-DU message.

[0291] In some implementations, the first DU includes a first cell ID of the first cell in the third DU-to-CU message to indicate the first TA value for the first cell. Based on the first cell ID, the CU determines the first TA value for the first cell. In other implementations, the first DU includes the first cell index in the third DU-to-CU message to indicate the first TA value for the first cell. Based on the first cell index, the CU determines the first TA value for the first cell. In yet other implementations, the first DU includes the first LTM ID in the third DU-to-CU message to indicate the first TA value for the first cell. Based on the first LTM ID, the CU determines the first TA value for the first cell.

[0292] In some implementations, the CU includes a first cell ID of the first cell in the fourth CU-to-DU message to indicate the first TA value for the first cell. Based on the first cell ID, the serving DU identifies the first TA value for the first cell. In some implementations, when identifying the first TA value for the first cell and determining to command the UE to switch from a serving cell to the first cell, the serving DU transmits a first LTM command to the UE via the serving cell, where the first LTM command includes a first cell ID of the first cell and the first TA value. In other implementations, the CU includes the first cell index in the fourth CU-to-DU message to indicate the first TA value for the first cell. Based on the first cell index, the serving DU identifies the first TA value for the first cell. In some implementations, when identifying the first TA value for the first cell and determining to command the UE to switch from a serving cell to the first cell, the serving DU transmits a first LTM command including the first cell index and the first TA value to the UE via the serving cell. In yet other implementations, the CU includes the first LTM ID in the fourth CU-to-DU message to indicate the first TA value for the first cell. Based on the first LTM ID, the serving DU identifies the first TA value for the first cell. When identifying the first TA value for the first cell and determining to command the UE to switch from a serving cell to the first cell, the serving DU transmits a first LTM command including the first LTM ID and the first TA value to the UE via the serving cell.

[0293] In some implementations, the first cell ID is a PCI. In other implementations, the first cell ID is a CGI.

[0294] In some implementations, the CU performs actions to prepare a second cell for LTM with the first DU, similar to blocks 1302, 1308, 1310, 1318, 1373, 1312, 1314 and / or 1393. The CU performs the actions during or after preparing the first cell for LTM. In some implementations, the CU receives a second LTM DU configuration configuring the second cell for LTM from the first DU and transmits a second LTM DU and the second LTM DU configuration to the UE via the serving DU, similar to blocks 1308, 1310 and 1318. In some implementations, the CU receives a third plurality of random access configuration parameters for the UE, e.g., for early TA acquisition, from the first DU, and transmits the third plurality of random access configuration parameters to the serving DU, similar to blocks 1314 and 1393, respectively. In some implementations, the second LTM DU configuration includes a fourth plurality of random access configuration parameters. In some implementations, the fourth plurality of random access configuration parameters include a PRACH root sequence index and / or a subcarrier spacing of PRACH. In some implementations, the CU receive aDU-to-CU message from the first DU, including a second TA value for uplink synchronization with the UE on the second cell and transmits the second TA value to the serving DU, similar to blocks 1381 and 1383, respectively.

[0295] Fig. 14A illustrates an example method 1400A, which can be implemented by a DU (e.g., the DU 174, 174A, DU 174B or DU 174C in Figs. 3-8B), for configuring early TA acquisition for a UE (e.g., the UE 102 in Figs. 3-8B).

[0296] The method 1400A begins at block 1408, where the DU receives, from a CU, a first CU-to-DU message for the UE, requesting preparation of a first cell for LTM (e.g., events 308, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). At block 1410, the DU generates a first LTM DU configuration configuring the first cell for LTM for the UE, where the first LTM DU configuration includes a first plurality of random access configuration parameters (e.g., events 310, 390, 380, 490, 480, 580, 590, 581, 582, 680, 690, 681, 780, 790, 880, 890, 881). At block 1441, the DU generates a second plurality of random access configuration parameters for the UE. At block 1442, the DU transmits, to the CU, a first DU-to-CU message including the first LTM DU configuration and the second plurality of random access configuration parameters. At block 1453, the DU receives a first random access preamble on the first cell from the UE, based on the first plurality of random access configuration parameters and / or second plurality of random access configuration parameters. At block 1443, the DU obtains a first TA value based on the first random access preamble.

[0297] In some implementations, the DU obtains (e.g., calculates or derives) the first TA value for uplink synchronization with the UE on the first cell according to the time when the RAN receives the first random access preamble.

[0298] At block 1445, the DU transmits a second DU-to-CU message including the first TA value for the UE to the CU. At block 1432, the DU detects that the UE accesses the first cell (e.g., events 332, 352, 398, 380, 432, 452, 498, 480, 580, 532, 598, 581, 582, 680, 632, 698, 681, 780, 732, 798, 880, 881, 832, 898). At block 1436, the DU communicates with the UE on the first cell using the first TA value and the first LTM DU configuration (e.g., events 336, 356, 380, 436, 456, 480, 536, 556, 580, 581, 582, 636, 656, 680, 681, 736, 756, 780, 836, 856, 880, 881). In some implementations, the DU includes a first cell ID of the first cell in the second DU-to-CU message to indicate the first TA value for the first cell.

[0299] In some implementations, the first CU-to-DU message includes a request indication requesting random access configuration parameters for early TA acquisition and the DU includes the second plurality of random access configuration parameters in the first DU-to- CU message in response to the request indication.

[0300] Fig. 14B is a flow diagram of an example method 1400B similar to the method 1400A, except that method 1400B includes blocks 1461, 1465, and 1465 instead of block 1442. At block 1461, the DU transmits, to the CU, a first DU-to-CU message including the first LTM DU configuration.

[0301] In some implementations, at least some of the discussion of the first DU in Fig. 13 can apply to the DU in Figs. 14A and 14B.

[0302] Fig. 15A illustrates an example method 1500A, which can be implemented by a DU (e.g., the DU 174, 174A, DU 174B or DU 174C in Figs. 3-8B), for transmitting a TA value to a UE (e.g., the UE 102 in Figs. 3-8B).

[0303] The method 1500A begins at block 1567, where the DU receives, from a CU, a CU- to-DU message including a first ID and a first TA value for a UE, where the first TA value is associated with the first cell ID. At block 1527A, the DU transmits a command includes the first ID and the first TA value to the UE on a serving cell. In some implementations, the first ID is a LTM ID that indicates a LTM DU configuration or a LTM configuration configuring a cell, as described above. In other implementations, the first ID is a cell ID (e.g., PCI or CGI) of a cell as described above. In yet other implementations, the first ID is a cell index indicating a cell as described above.

[0304] Fig. 15B is a flow diagram of an example method 1500B similar to the method 1500A, except that method 1500B includes blocks 1568 and 1527B instead of block 1527A. At block 1503, the DU determine a second ID based on the first ID. At block 1505, the DU transmits a command including the second ID and the first TA value to the UE on a serving cell.

[0305] In some implementations, the DU stores or maintains an association or mapping between the first ID (value) and the second ID (value). Based on the first ID (value) and the association or mapping, the DU determines the second ID (value). In some implementations, the first ID is a cell ID (e.g., PCI or CGI) indicating a cell and the second ID is a LTM ID indicating a LTM DU configuration or a LTM configuration configuring the cell, as described above. In other implementations, the first ID is a cell ID of a cell (e.g., PCI orCGI) and the second ID is a cell index ID indicating the cell. In yet implementations, the first ID is a cell index indicating a cell and the second ID is a LTM ID indicating a LTM DU configuration or a LTM configuration configuring the cell, as described above.

[0306] In some implementations, the command in Figs. 15A and 15B is a LTM command (e.g., events 330, 350, 398, 380, 430, 450, 498, 480, 580, 530, 598, 581, 582, 680, 681, 630, 698, 780, 730, 798, 880, 881, 830, 898). In other implementations, the command in Figs. 15A and 15B is a MAC CE.

[0307] In some implementations, the DU in Figs. 15A and 15B is the serving DU in Fig. 13. In some implementations, at least some of the discussion of the serving DU above can apply to the DU in Figs. 15A and 15B. In some implementations, the discussion of the fourth CU-to-DU message in Fig. 13 can apply to the CU-to-DU message in Figs. 15A and 15B.

[0308] Fig. 16A illustrates an example method 1600A, which can be implemented by a CU (e.g., the CU 172 in Figs. 3-8B), for transmitting a TA value to a UE (e.g., the UE 102 in Figs. 3-8B).

[0309] The method 1600A begins at block 1667, where the CU receives, from a first DU, a DU-to-CU message including a first ID and a first TA value for a UE, where the first TA value is associated with the first cell ID. At block 1627 A, the CU transmits a CU-to-DU message including the first ID and the first TA value to a serving DU.

[0310] Fig. 16B is a flow diagram of an example method 1600B similar to the method 1500A, except that method 1600B includes blocks 1668 and 1627B instead of block 1627A. At block 1668, the CU determines a second ID based on the first ID. At block 1627B, the CU transmits a CU-to-DU message including the second ID and the first TA value to a serving DU. In some implementations, the CU stores or maintains an association or mapping between the first ID (value) and the second ID (value). Based on the first ID (value) and the association or mapping, the CU determines the second ID (value).

[0311] Examples and implementations described for Figs 15A and 15B can apply to Figs. 16A and 16B. In some implementations, the first DU and the serving DU in Figs. 16A and 16B are the first DU and the serving DU in Fig. 13, respectively. In some implementations, the discussion of the first DU and the serving DU above can apply to the first DU and the serving DU in Figs. 16A and 16B, respectively. In some implementations, the discussion of the fourth CU-to-DU message in Fig. 13 can apply to the CU-to-DU message in Figs. 16A and 16B.

[0312] The following list of examples reflects a variety of the embodiments explicitly contemplated by the present disclosure.

[0313] Example 1. A method in a DU of a distributed base station that also includes a central unit CU comprises obtaining an LTM DU configuration for a target cell; receiving, from the CU, an LTM identifier; and transmitting the LTM identifier to a UE, for obtaining a TA for the target cell when the UE performs an LTM cell change to the target cell, the LTM identifier associated with the LTM DU configuration.

[0314] Example 2. The method of example 1, further comprising associating the LTM identifier directly with the LTM DU configuration.

[0315] Example 3. The method of example 1, further comprising associating the LTM identifier with the target cell.

[0316] Example 4. The method of any of the preceding examples, further comprising: receiving, from the CU, a request to prepare the target cell for the LTM by the UE, where the obtaining of the LTM DU configuration at the DU is in response to the request.

[0317] Example 5. The method of example 4, where the request includes the LTM identifier.

[0318] Example 6. The method of example 4, where the request to prepare the target cell is included in a first CU-to-DU message; and the receiving of the LTM identifier includes receiving a second CU-to-DU message.

[0319] Example 7. The method of any of the preceding examples, further comprising transmitting to the UE, along with the LTM identifier, the TA.

[0320] Example 8. The method of example 7, further comprising communicating with the UE in the target cell according to the LTM DU configuration and the TA.

[0321] Example 9. The method of any of the preceding examples, further comprising transmitting, to the UE, a command in a serving cell, the command including an identifier of the target cell and indicating that the UE is to transmit a random access preamble in the target cell.

[0322] Example 10. A distributed unit (DU) of a distributed base station, the DU comprising a transceiver; and processing hardware configure to implement a method according to any of the preceding examples.

[0323] The following description may be applied to the description above.

[0324] 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, the “early TA acquisition” can be replaced by “early timing synchronization”, “early timing synchronization with a target cell”, “early TA value acquisition”, or “early TA value acquisition for a target cell”. In some implementations, the “early TA acquisition configuration” can be replaced by “early TA acquisition indication” or “early TA acquisition enabling indication”.

[0325] A user device in which the techniques of this disclosure can be implemented (e.g., the UE 102) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media- streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an 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.

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

[0327] 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.

[0328] Upon reading this disclosure, those of skill in the art will appreciate still additional and alternative structural and functional designs for handling mobility between base stations through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

Claims

What is claimed is:

1. A method implemented in a distributed unit (DU) of a distributed base station that also includes a central unit (CU), the method comprising: receiving, from the CU, a request to prepare a target cell for a low-layer triggered mobility (LTM) cell switch by a user equipment (UE) communicating in a serving cell; determining that the UE supports early timing advance (TA) acquisition; and transmitting, to the UE in the serving cell, a command to transmit a random access preamble in the target cell for the early TA acquisition.

2. The method of claim 1, further comprising: transmitting, to the CU, a random access configuration parameter for the UE.

3. The method of claim 2, wherein the random access configuration parameter is related to configuring the UE to perform the early TA acquisition.

4. The method of claim 2 or 3, further comprising: receiving, from the CU, the random access configuration parameter for the UE.

5. The method of claim 2 or 3, further comprising: receiving, from the CU, a request for random access configuration parameters, wherein the transmitting of the random access configuration parameter is in response to the receiving of the request.

6. The method of any of claims 2-5, wherein the transmitting of the random access configuration parameter includes transmitting one of a UE Context Setup Response message or a UE Context Modification Response.

7. The method of any of the preceding claims, further comprising: transmitting, to the CU, an LTM configuration for the target cell; and associating the LTM configuration with an LTM identifier assigned by the CU.

8. The method of claim 7, wherein:the transmitting of the command to the UE includes referencing the target cell using the LTM identifier.

9. The method of any of the preceding claims, wherein: the command includes (i) a downlink control information (DCI) message or (ii) a physical downlink control channel (PDCCH) order.

10. The method of any of the preceding claims, wherein the command to transmit the random access preamble in the target cell includes a cell index corresponding to the target cell.

11. A method implemented in a central unit (CU) of a distributed base station that also equipped with one or more distributed unit (DUs) including a serving DU, the method comprising: receiving a DU-to-CU message including an LTM DU configuration related to a target cell and a random access configuration parameter for configuring a UE for early TA acquisition in the target cell; associating the LTM DU configuration with an LTM identifier (ID); and transmitting, to the serving DU, the LTM ID and the random access configuration parameter.

12. The method of claim 11, wherein: the transmitting includes transmitting the LTM ID and the random access configuration parameter in a same CU-to-DU message.

13. The method of claim 11, wherein: the transmitting includes transmitting a first CU-to-DU message including the LTM ID and transmitting a second CU-to-DU message including the random access configuration parameter.

14. The method of any of claims 11-13, wherein: the DU-to-CU message is received from a target DU; and the CU-to-DU message is transmitted to a serving DU.

15. A node in a communication network comprising processing hardware and configured to implement a method of any of the preceding claims

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