Enabling a fast cell change across distributed units

Abstract

A centralized unit (CU) of a distributed radio access network (RAN) node can implement a method for managing lower layer triggered mobility protocol procedure(s). The method includes: (i) determining, at the CU, to prepare a user equipment (UE) for lower layer triggered mobility (LTM) from a first distributed unit (DU) to a second DU; (ii) transmitting, to the second DU and responsive to the determining, a reference LTM configuration; (iii) receiving, at the CU from the second DU, an LTM configuration based on the reference LTM configuration; and (iv) transmitting, from the CU to the UE, the LTM configuration.

Description

ENABLING A FAST CELL CHANGE ACROSS DISTRIBUTED UNITSCROSS-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 / 483,253 entitled “ENABLING A FAST CELL CHANGE ACROSS DISTRIBUTED UNITS,” filed on February 3, 2023, as well as provisional U.S. Patent Application No. 63 / 482,018 entitled “LOWER LAYER TRIGGERED MOBILITY WITH LOW OVERHEAD SIGNALING,” filed on January 27, 2023. The entire contents of the provisional applications are hereby expressly incorporated herein by reference.FIELD OF THE DISCLOSURE

[0002] This disclosure relates to wireless communications and, more particularly, to enabling a fast serving cell change across different distributed units (DUs) for a user equipment (UE) using a control signaling of a protocol layer lower than a radio resource control (RRC) protocol layer.BACKGROUND

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

[0004] In telecommunication systems, the Packet Data Convergence Protocol (PDCP) sublayer of the radio protocol stack provides services such as transfer of user-plane data, ciphering, integrity protection, etc. For example, the PDCP layer defined for the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface (see 3GPP technical specification (TS) 36.323) and New Radio (NR) (see 3GPP 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, in some examples, the UE and a base station 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] Depending on the scenario, UEs use several types of SRBs and DRBs. When operating in dual connectivity (DC), the cells associated with the base station operating the master node (MN) define a master cell group (MCG), and the cells associated with the base station operating as the secondary node (SN) define the secondary cell group (SCG). SRB1 resources carry RRC messages, which in some cases include NAS messages over the dedicated control channel (DCCH), and SRB2 resources support RRC messages that include logged measurement information or NAS messages, also over the DCCH but with lower priority than 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. The SRB1 and SRB 2 resources 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, concurrently utilizes resources of multiple radio access network (RAN) nodes (e.g., base stations or components of a distributed base station), interconnected by a backhaul. When such 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 determines 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 another cell in a RAN, the RAN should configure the UE for a serving cell change. To perform the serving cell change, the RAN configures the UE to transmit Layer 3 (L3) measurement results. Based on L3 measurement results received from the UE, the RAN transmits an RRC reconfiguration message, configuring Reconfiguration with Synchronization (e.g., the RRC reconfigurationmessage includes a ReconfigurationWithSync IE) for the change of the serving cell (e.g., PCell or PSCell). In cases where the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN releases the at least one SCell due to the change of the PCell or PSCell. The serving cell change involves complete L2 (and LI) resets, leading to longer latency, larger overhead, and longer interruption time. Thus, it is desirable to develop new mobility techniques to reduce latency and overhead for fast serving cell change.

[0008] However, it is not clear how to perform a serving cell using a lower layer signaling (i.e., lower layer triggered mobility (LTM)) functionality at the UE and a disaggregated base station. In some scenarios, the RAN prepares multiple cells for LTM for the UE and, accordingly, transmits multiple LTM configurations, each configuring a particular cell. The multiple LTM configurations cause a significant signaling overhead to the UE and RAN. To reduce the signaling overhead, the RAN can generate each of the multiple LTM configurations as a delta configuration based on a serving configuration (i.e., the latest serving configuration) that the RAN and UE use to communicate with each other. After providing the multiple LTM configurations to the UE, the RAN updates the serving configuration, which, depending on the scenario, causes the RAN to update the multiple LTM configurations. In some cases, the RAN frequently updates the serving configuration, which, depending on the scenario, causes frequent updates to the LTM configurations. In some scenarios, frequently updating the LTM configurations causes a significant signaling overhead to the RAN and UE.SUMMARY

[0009] In some embodiments, this disclosure describes techniques to mitigate the signaling overhead by using a reference LTM configuration at the RAN to generate the LTM configurations instead of the serving LTM configuration. In particular, this disclosure describes, in some embodiments, how to generate or obtain the reference LTM configuration in scenarios with multiple distributed units (DUs).

[0010] An example embodiment of the techniques of this disclosure is a method implemented in a centralized unit (CU) of a distributed base station, the method comprising: determining, at the CU, to prepare a user equipment (UE) for lower layer triggered mobility (LTM) from a first distributed unit (DU) to a second DU; transmitting, to the second DU and responsive to the determining, a reference LTM configuration; receiving, at the CU from thesecond DU, an LTM configuration based on the reference LTM configuration; and transmitting, from the CU to the UE, the LTM configuration.

[0011] Another example embodiment of these techniques is a method implemented in a DU of a distributed base station, the method comprising: receiving, at the DU from the CU, a reference lower layer triggered mobility (LTM) configuration; generating, at the DU, an LTM configuration based on the reference LTM configuration; and transmitting, from the DU to the CU, the LTM configuration.

[0012] Another example embodiment of these techniques is a method implemented in a CU of a distributed base station, the method comprising: determining, at the CU, to prepare a first distributed unit (DU) for lower layer triggered mobility; transmitting, from the CU to a second DU, a request for lower layer triggered mobility preparation; receiving, at the CU from the second DU, a reference lower layer triggered mobility configuration; and transmitting, to the DU for the UE, an LTM configuration based on the reference LTM configuration.

[0013] Another example embodiment of these techniques is a distributed base station comprising processing hardware and configured to implement the method above.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] 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 conditional procedures related to a secondary node (SN);

[0015] 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;

[0016] Fig. 2A is a block diagram of an example protocol stack according to which the UE of Fig. 1A communicates with base stations;

[0017] 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

[0018] Fig. 3 is a messaging diagram of an example scenario where a CU provides a reference lower layer triggered mobility configures to a DU for generating a configuration for a UE;

[0019] Fig. 4 is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the base station includes a source DU (S-DU) and target DU (T-DU);

[0020] Fig. 5A is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the UE communicates in DC with an MN and an SN;

[0021] Fig. 5B is a messaging diagram of an example scenario similar to that of Fig. 5A, but in which the CU provides the reference lower layer triggered mobility configuration to the UE via the MN;

[0022] Fig. 6A is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the CU communicates with an S-DU and a T-DU in the SN;

[0023] Fig. 6B is a messaging diagram of an example scenario similar to that of Fig. 6A, but in which the CU provides the reference lower layer triggered mobility configuration to the UE via the MN;

[0024] Fig. 7A is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the CU communicates with an M-DU and an S-DU;

[0025] Fig. 7B is a messaging diagram of an example scenario similar to that of Fig. 7A, but in which the CU provides the reference lower layer triggered mobility configuration to the UE via the M-DU;

[0026] Fig. 8A is a messaging diagram of an example scenario similar to that of Fig. 3, but in which the CU communicates with an M-DU, an S-DU, and a T-DU;

[0027] Fig. 8B is a messaging diagram of an example scenario similar to that of Fig. 8A, but in which the CU provides the reference lower layer triggered mobility configuration to the UE via the M-DU;

[0028] Fig. 9 is a flow diagram depicting an example method, implemented in a CU, in which the CU transmits a reference lower layer triggered mobility configuration to a DU and receives an LTM configuration;

[0029] Fig. 10 is a flow diagram depicting an example method, implemented in a DU, in which the DU receives a reference lower layer triggered mobility configuration from the CU and generates at least one LTM configuration based on the reference lower layer triggered mobility configuration;

[0030] Fig. 11 is a flow diagram depicting an example method, implemented in a CU, in which the CU determines whether to include a reference lower layer triggered mobility configuration based on whether a second cell is operated by a first DU via which the CU communicates with a UE;

[0031] Fig. 12A is a flow diagram depicting an example method, implemented in a DU, in which the DU determines whether generate a reference lower layer triggered mobility configuration based on whether the DU receives a reference lower layer triggered mobility configuration from the CU;

[0032] Fig. 12B is a flow diagram depicting an example method, similar to that of Fig. 12A, but in which the DU additionally makes the determination based on whether the DU has already stored a reference lower layer triggered mobility configuration;

[0033] Fig. 13 is a flow diagram depicting an example method, implemented in a CU, in which the CU communicates with a UE via a first DU and obtains a reference lower layer triggered mobility from a second DU; and

[0034] Fig. 14 is a flow diagram depicting an example method, implemented in a base station, in which a first DU generates a first reference lower layer triggered mobility configuration and a second DU generates a second lower layer triggered mobility configuration.DETAILED DESCRIPTION OF THE DRAWINGS

[0035] Fig. 1A depicts an example wireless communication system 100 in which communication devices can implement these techniques. The wireless communication system 100 includes a UE 102, a base station (BS) 104, a base station 106 and a core network (CN) 110. The UE 102 initially connects to the base station 104. In some scenarios, the base station 104 can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the base station 104 and the base station 106. The base stations 104 and 106 operate as an MN and an SN for the UE 102, respectively.

[0036] 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 basestation 106 is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0037] 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.

[0038] 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) for example prior to the handover. The UE 102 can continue to operate in DC with the base station 106 and the additional base station or operate in single connectivity (SC) with the base station 106, after completing the handover. The base stations 104 and 106 in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively.

[0039] 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 the MME 114 is configured to manage authentication, registration, paging, and other related functions. The PGW 116 provides connectivity from the UE to one or more external packet data networks, e.g., an Internet network and / or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The 5GC 160 includes a User Plane Function (UPF) 162 and an Access and Mobility Management (AMF) 164, and / or Session Management Function (SMF)166. The UPF 162 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., the AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the SMF 166 is configured to manage PDU sessions.

[0040] As illustrated in Fig. 1A, the base station 104 supports cell 124A, and the base station 106 supports a cell 126. The cells 124A and 126 can partially overlap, so that the UE 102 can communicate in DC with the base station 104 and the base station 106, where one of the base stations 104 and 106 is an MN and the other is an SN. The base station 104 can support additional cell(s) such as cells 124B and 124C, and the base station 106 can support additional cell(s) (not shown in Fig. 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.

[0041] 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.

[0042] With continued reference to Fig. 1A, the base station 104 is equipped with processing hardware 130 that can include one or more general-purpose processors (e.g., CPUs) and a non-transitory computer-readable memory storing instructions that the one or more general-purpose processors execute. Additionally or alternatively, the processing hardware 130 can include special-purpose processing units. The processing hardware 130 can include a PHY controller 132 configured to transmit data and control signal on physical downlink (DL) channels and DL reference signals with one or more user devices (e.g., UE 102) via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The PHY controller 132 is also configured to receive data and control signal on physical uplink (UL) channels and / or UL reference signals with the one or more user devicesvia one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The processing hardware 130 in an example implementation includes a MAC controller 134 configured to perform MAC functions with one or more user devices. The MAC functions includes 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 processing hardware 130 can further include an RRC controller 136 to implement procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller 132 may be configured to support RRC messaging associated with handover procedures, and / or to support the necessary operations when the base station 104 operates as an MN relative to an SN or as an SN relative to an MN. The base station 106 can include processing hardware 140 that is similar to processing hardware 130. In particular, components 142, 144, and 146 can be similar to the components 132, 134, and 136, respectively.

[0043] The UE 102 is equipped with processing hardware 150 that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. The PHY controller 152 is also configured to receive data and control signal on physical DL channels and / or DL reference signals with the base station 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126) and / or one or more TRPs. The PHY controller 152 is also configured to transmit data and control signal on physical UL channels and / or UL reference signals with the base station 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C and / or 126) and / or one or more TRPs. The processing hardware 150 in an example implementation includes a MAC controller 154 configured to perform MAC functions with base station 104 or 106. Lor 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. The processing hardware 150 can further include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0044] 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.

[0045] Fig. IB depicts an example distributed implementation of a base station such as the base station 104 or 106. The base station in this implementation can include a centralized unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 is equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In one example, the CU 172 is equipped with the processing hardware 130. In another example, the CU 172 is equipped with the processing hardware 140. The processing hardware 140 in an example implementation includes an SN RRC controller 142 configured to manage or control one or more RRC configurations and / or RRC procedures when the base station 106 operates as an SN. The DU 174 is also equipped with processing hardware that can include one or more general-purpose processors such as CPUs and non-transitory computer-readable memory storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. In some examples, the processing hardware in an example implementation includes a medium access control (MAC) controller configured to manage or control one or more MAC operations or procedures (e.g., a random access procedure) and a radio link control (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.

[0046] 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).

[0047] 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 inFig. 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.

[0048] 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.”

[0049] 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 Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 can be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0050] 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.

[0051] Next, several example scenarios in which the base station operating in the system of Fig. 1A transmits a configuration to the UE 102 and later activates a configuration for communication between the UE 102 and base station. Generally speaking, events in Figs. 3- 7B that are similar are labeled with similar reference numbers e.g., event 316 is similar to event 416 of Figs 4A and 4B, event 516 of Fig. 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 thefigures 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.

[0052] 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 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 is a PCell. In such cases, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or an SCell. In other implementations, the cell 124A is an SCell, and one of the other cell(s) is a PCell. In such cases, the rest of the cells include SCell(s) and / or additional cell(s) associated with the PCell or an SCell. In the following description, depending on the implementation, the base station 104 is the DU 174, the CU 172, or the DU 174 and CU 172.

[0053] In some implementations, in the event 302, the UE 102 transmits 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 include SRBs and / or DRB(s). In further implementations, the base station 104 configures the radio bearers for 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, in further implementations the UE 102 receives DL PDUs and / or DL control signals from the base station 104 on the cell 124A and / or other cell(s) via one or multiple TRPs. In some implementations, the DL control signals include downlink control information (DCIs) and reference signals (e.g., synchronization signal block, channel state information reference signal(s) (CSI-RS(s)), and / or tracking reference signal(s)). In some implementations, the base station 104 transmits 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.

[0054] 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 transmits the 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 (e.g., defined in 3GPP TS 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 (e.g., defined in 3GPP TS 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. In other implementations, the serving CU configuration includes a CSl-MeasConfig IE or configuration parameters for channel state information (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.

[0055] While communicating with the base station 104, the UE 102 transmits 304 at least one measurement report to the DU 174. In some implementations, the at least one measurement report includes Layer 1 (LI) measurement report(s) and / or Layer 3 (L3) measurement report(s) for at least one serving cell of the UE 102 and / or at least one nonserving cell. For each of the L3 measurement report(s), the DU 174 transmits 306 a DU-to- CU message including the L3 measurement report to the CU 172. In some implementations, the DU-to-CU message(s) of the event 306 is / are Fl application protocol (F1AP) message(s) (e.g., UL RRC Message Transfer message(s)). In some implementations, the DU 174 does not transmit or refrains from transmitting the LI measurement report(s) to the CU 172. Theat 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). In some implementations, the LI measurement configuration(s) (e.g., CSl-MeasConfig IE(s)) includes LI measurement resource configuration(s) and / or LI measurement reporting configuration(s). In further implementations, the LI measurement resource configuration(s) configure resources of reference signal(s) (e.g., CSLRS(s)) for the UE 102 to measure and obtain LI measurement results. Lor example, the LI measurement resource configuration(s) is / are CS1- ResourceConfig IE(s). In another example, the LI measurement reporting configuration(s) configure way(s) the UE 102 uses to transmit LI measurement results / reports. Lor example, the LI measurement report configuration(s) is / are CSl-ReportConfig IE(s). Lor 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 some implementations, the DU 174 does not transmit the LI measurement report(s) to the CU 172.

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

[0057] In some implementations, (each of) the LI measurement report(s) includes 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 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 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 remainder of the LI measurement report(s), the UE 102 transmits a PUSCH transmission including the LI measurement report to the DU 174. In some implementations, each of the LI measurement report(s) Is a part of the channel state information (CSI) (i.e., a CSI component) or CSI. In some implementations, the UE 102 includes other CSI component(s) in (each of) the PUCCH transmission(s) and / or PUSCH transmission(s) described above. In some implementations, the other CSI component(s) include a channel quality indicator (CQI), a Precoding Matrix Indicator (PMI), a CSLRS Resource Indicator (CRI), a Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Block 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 the format of RRC message(s) to the DU 174. In some implementations, each of the LI measurement report(s) includes an LI event ID to identify or indicate the trigger LI event. Alternatively, each of the LI measurement report(s) does not include an LI event ID to identify or indicate the trigger LI event.

[0058] In some implementations, each of the L3 measurement report(s) includes 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 some implementations, 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) is an RRC message (e.g., MeasurementReport message). In some implementations, each ofthe 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. In some implementations, when the CU 172 receives an L3 measurement report, including a measurement identity and an L3 measurement result, from the UE 102 via the DU 174, the CU 172 determines that the L3 measurement report is associated with an L3 measurement configuration identified by the measurement identity.

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

[0060] In some implementations, the UE 102 performs measurements on one or more reference signals in accordance with the at least one measurement configuration. Depending on the implementation, the one or more reference signals include one or more Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Blocks (SSBs) and / or one or more CSI-RSs. The UE 102 obtains the at least one LI measurement result and / or at least one L3 measurement result from the measurements. The DU 174 transmits the one or more reference signals on the cell 124A and other cell(s) (e.g., the cell 124B, the cell 124C, and / or cell(s) not shown in Fig. 1A).

[0061] After (e.g., in response to) receiving one or some of the at least one measurement report(s) 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 cellfor the UE 102. In other implementations, if the LI measurement report(s) indicate 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.

[0062] In cases where the CU 172 determines to prepare the first cell for LTM, the CU 172 transmits 308 a first CU-to-DU message to the DU 174 to prepare the first cell for the UE 102. In some implementations, the CU 172 includes a cell identity (ID) 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 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 configuration (referred to hereinafter as LTM 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 configuration 1, to the CU 172 in response to the first CU-to-DU message. In cases where the DU 174 determines to prepare the first cell, the DU 174 initiates transmission of the first DU-to-CU message to the CU 172 instead of in response to a CU-to-DU message received from the CU 172.

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

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

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

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

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

[0068] After receiving the RRC reconfiguration message 316, the DU 174 transmits 318 the RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 an RRC reconfiguration complete message (e.g., an RRCReconfigurationComplete message) to the DU 174, which in turn transmits 322 a second DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some implementations, the CU 172 performs security protection (e.g., integrity protection and / or encryption) on the RRC reconfiguration message. For example, the CU 172 generates a message authentication code for integrity (MAC-I) for the RRC reconfiguration message, encrypts the RRC reconfiguration message and the MAC-I to obtain an encrypted RRC reconfiguration message and an encrypted MAC-I, and transmits a PDCP PDU including the encrypted 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 performs an RRC connection reestablishment procedure in response to the invalid MAC-I. Otherwise, in further implementations, if the UE 102 verifies the MAC-I is valid, the UE 102 processes the RRC reconfiguration. The UE 102 refrains from applying (i.e., executing) the LTM configuration 1 until receiving a configuration activation command activating the LTM configuration 1 (e.g., the event 330).

[0069] The events 308 (optional) and 310 are collectively referred to in Fig. 3 as an LTM preparation procedure 390. The events 316, 318, 320, 322 are collectively referred to in Fig. 3 as an LTM configuration delivery procedure 394.

[0070] In some implementations, the DU 174 transmits the reference LTM configuration to the UE 102 in procedures similar to the procedures 390 and 392 before receiving the first CU-to-DU message. In such cases, the DU 174 does not include the reference LTM configuration in the first DU-to-CU message.

[0071] In some implementations, in the case that the CU 172 performs the multiple LTM preparation procedures 390, the DU 174 includes the reference LTM configuration in the first DU-to-CU message in the first LTM preparation procedure of the LTM preparation procedures 390. In some such cases, the DU 174 does not include the reference LTM configuration in DU-to-CU messages in the rest of the LTM preparation procedures 390.

[0072] 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 some cases including the UE Context Modification Required message, the CU 172 transmits 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 RRC Message Transfer message. In other implementations, the second CU-to-DU message is a UE Context Modification Request message, and the DU 174 transmits 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.

[0073] In some implementations, the CU 172 includes the LTM configuration 1 in a first container (e.g., a field / IE) and includes the first container 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 to the UE 102 not to apply the LTM configuration 1 immediately. In some scenarios or implementations, the UE 102 receives an RRC reconfiguration message (e.g., the RRC reconfiguration message of the event 318) including a configuration (e.g., the LTM configuration 1). If the configuration is included in the first container, the UE 102 refrains from immediately applying the configuration. Otherwise, in further implementations, if the configuration is not included in the first container, the UE 102 applies the configuration immediately. In some implementations, the first container is a firstaddition or modification list (e.g., Itm-ConfigToAddModList field, LTM- ConfigToAddModList IE, Itm-CandidateConfigToAddModList field, or LTM- CandidateConfigToAddModList IE). The CU 172 includes the LTM configuration 1 in a first element (referred to herein after as element 1) of the first addition or modification list. For example, the element 1 is an addition or modification IE (Itm-ConfigToAddMod field, LTM- ConfigToAddMod IE, Itm-CandidateConfigToAddMod field, or LTM- CandidateConfigToAddMod IE). In some implementations, when the UE 102 receives the first addition or modification list, the UE 102 stores the first addition or modification list (e.g., in a variable in the 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.The CU assigns an ID for the LTM configuration 1

[0074] 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 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. In other implementations, the CU 172 receives the ID 1 from the DU 174 in the first DU-to-CU message, as described below.

[0075] In some implementations where the CU 172 assigns or generates the ID 1, the CU 172 transmits the ID 1 to the DU 174, and the DU 174 associates the ID 1 with the LTM configuration 1. In some implementations, in the first CU-to-DU message, the CU 172 includes the ID 1 and indicates that the ID 1 is associated with the LTM configuration 1. In other implementations, after receiving the first DU-to-CU message, the CU 172 transmits 312 a third CU-to-DU message including the ID 1 to the DU 174 instead of including the ID 1 in the first CU-to-DU message. In some implementations, in the third CU-to-DU message, the CU 172 includes the LTM configuration 1 and the ID 1. The CU 172 further indicates the association between the ID 1 and LTM configuration 1. Thus, the DU 174 directly associates the ID 1 with the LTM configuration 1. In other implementations, in the third CU-to-DU message, the CU 172 includes the cell ID 1 and the ID 1 (i.e., the first LTM ID), and indicates the association between the cell ID 1 and the ID 1. Thus, in some such implementations, the DU 174 associates the ID 1 with the LTM configuration 1 based on theassociation between the cell ID 1 and the ID 1 and the association between the cell ID 1 and the LTM configuration 1. In yet other implementations, in the third CU-to-DU message, the CU 172 includes the LTM configuration 1, the cell ID 1, and the ID 1, and indicates the association between the ID 1, LTM configuration 1, and the cell ID 1. In some implementations, the DU 174 transmits 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 a 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 an LTM ID assignment procedure 392. In other implementations, the CU 172 includes the ID 1, the cell ID 1, and / or the LTM configuration 1 in the second CU-to-DU message, as described above. Thus, the CU 172 can omit the third CU-to-DU message.

[0076] In some implementations where the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 includes the ID 1 in the LTM configuration 1, first container or element 1. Alternatively, the DU 174 does not include the ID 1 in the LTM configuration 1, first container and / or element 1.DU assigns an ID for the LTM configuration 1

[0077] In some alternative implementations, the DU 174 assigns the ID 1 identifying the LTM configuration 1. In some implementations, the DU 174 includes the ID 1 in the first DU-to-CU message. In some implementations, the CU 172 includes the ID 1 in the RRC reconfiguration message as described above. In other implementations, the DU 174 includes the ID 1 in the LTM configuration 1, first container, or element 1. Thus, the CU 172 does not include an ID identifying the LTM configuration 1 in the RRC reconfiguration message, first container and / or element 1.

[0078] In some implementations, the CU 172 includes the reference LTM configuration in the first container. For example, the CU 172 includes the reference LTM configuration in a field of the first container, different from a field of the first container including the LTM configuration 1. In other implementations, the CU 172 includes the reference LTM 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 configuration and includes the third container in the RRC reconfiguration message 316. In yet other implementations, the DU 174 includes thereference LTM configuration in the first container. For example, the DU 174 includes the reference LTM configuration in a field of the first container, different from a field of the first container including the LTM configuration 1. In yet other implementations, the DU 174 generates a fourth container (e.g., a field / IE) to include the first container and the reference LTM 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 configuration and the LTM configuration 1 from the fourth container and includes the reference LTM DU configuration and the LTM DU configuration 1 as described above.

[0079] In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM configuration. In such cases, there is no ID for the reference LTM configuration.

[0080] In some implementations, the LTM 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 includes 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 includes 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 configuration 1 is a CellGroupConfig IE (e.g., defined in 3GPP TS 38.331). In other implementations, the LTM configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0081] In some implementations, the DU 174 includes a random access configuration in the LTM configuration 1. In other implementations, the DU 174 does not include a random access configuration in the LTM 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 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 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 configuration 1. Otherwise, if the DU 174 determines thatthe UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the random access configuration in the LTM configuration 1. If the LTM 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 configuration 1 does not include the random access configuration, the UE 102 skips or refrains from performing the random access procedure of the event 332 in response to the LTM configuration 1 excluding the random access configuration.

[0082] In some implementations, the DU 174 includes random access configuration parameters in the LTM configuration 1 and / or the reference LTM 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.

[0083] In some implementations, if the cell 124A and first cell are synchronized, the DU 174 determines to include, in the LTM 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 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 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 configuration 1. If the LTM 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 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 configuration 1 excluding the first indication, as described below.

[0084] In some implementations, the DU 174 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM 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 configuration 1 or 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 configurationin the LTM 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 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 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 configuration 1. In some implementations, if the LTM 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 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 configuration 1. In some implementations, the cell ID 1 is a PCI. In another implementation, the cell ID 1 is a CGI. In some further implementations, the LTM configuration 1 includes a cell index 1 (e.g., a serving cell index or LTM cell index) indexing the cell ID 1 or the first cell (e.g., the cell index 1 is not a cell ID).

[0085] 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 some implementations, 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 base station 104 can use the additional cell(s) to communicate with the UE 102. In some implementations, the additional cell(s) 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) indicate that signal strength and / or quality of a particular cell of the additional cell(s) is above a respective predetermined threshold and / or is better than the cell 124A, the CU 172 determines to prepare the particular cell for LTM for the UE 102. In other implementations, if the LI measurement report(s) indicate 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 some implementations, the respective predetermined threshold(s) for theadditional cells are different from the first predetermined threshold. In further implementations, the respective predetermined threshold(s) for the additional cell(s) are the same as the first predetermined threshold. In some implementations, the respective predetermined thresholds for the additional cells are 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.

[0086] In cases where the CU 172 determines to prepare the additional cell(s), the CU 172 initiates and performs at least one additional LTM preparation procedure with the DU 174 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390. In cases where the DU 174 determines to prepare the additional cell(s), the DU 174 initiates and performs at least one additional LTM preparation procedure 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.

[0087] In some implementations, the CU 172 and DU 174 perform LTM preparation procedure(s) 2, ..., N to prepare the cell(s) 2, ..., N, respectively, similar to the procedure 390. In some implementations, the CU 172 includes the cell ID(s) 2, ..., N in CU-to-DU message(s) 2, ..., N in the LTM preparation procedure(s) 2, ..., N, respectively, similar to the first CU-to-DU message. In the LTM preparation procedure(s) 2, ..., N, the DU 174 generates LTM configuration(s) 2, ..., N configuring the cell(s) 2, ..., N and includes the LTM configuration(s) 2, ..., N in DU-to-CU message(s) 2, .., N, respectively, as described for the LTM configuration 1. In cases where the DU 174 receives the CU-to-DU message(s) 2, ..., N, the DU-to-CU message(s) 2, ..., N responds to the CU-to-DU message(s) 2, ..., N, respectively. “N” is an integer and larger than one. Lor example, “N” is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13 14, 15, 16, etc. In another example, the maximum number of “N” is 4, 8, 16, 32, etc. Examples and implementations of the LTM configuration 1 can apply to the LTM configuration(s) 2, ..., N.

[0088] 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 configuration(s) 1, 2, ..., N for the cell(s) 1, 2, ..., N, respectively in the first DU-to-CU message. In some implementations, in the first DU-to-CU message, the DU 174 includes the cell ID(s) 1, 2, ..., N respectively associated with the LTM configuration(s) 1, 2, ..., N to indicate that the LTMconfiguration(s) 1, 2, .. N are configured for the cell ID(s) 1, 2, ..., N, respectively. In cases where the CU 172 determines to perform the LTM preparation procedure 390, the CU 172 includes the cell ID(s) 1, 2, ..., N in the first CU-to-DU message to request the DU 174 to prepare the cell(s) 1, 2, ..., N, respectively, for LTM.

[0089] In some implementations, after receiving the LTM configuration(s) 2, ..., N from the DU 174, the CU 172 includes the LTM configuration(s) 2, ..., N in the first container. In some implementations, the CU 172 includes the LTM 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 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 includes the ID(s) 2, ..., N and LTM configuration(s) 2, ..., N in the element(s) 2, ... , N in the first addition or modification list.

[0090] In some implementations, the CU 172 assigns the ID(s) 2, ..., N for the LTM 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.

[0091] In some implementations, the CU 172 performs an LTM ID assignment procedure with the DU 174 for each of the LTM configuration(s) 2, ..., N, similar to the procedure 392. In other implementations, the CU 172 includes the ID(s) 2, ..., N and the LTM configuration(s) 2, ..., N in the third CU-to-DU message and indicates the association between the ID(s) 2, ..., N and the LTM configuration(s) 2, ..., N, respectively. Thus, in some implementations, the DU 174 associates the LTM configuration(s) 2, ..., N with the ID(s) 2, ..., N, respectively. In yet other implementations, the CU 172 includes the cell ID(s) 2, ..., N and the ID(s) 2, ..., N in the third CU-to-DU message and indicates the association between the cell ID(s) 2, ..., N and the ID(s) 2, ..., N, respectively. Thus, in further implementations, the DU 174 associates the LTM 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 configuration(s) 2, ..., N, respectively. In other implementations, the CU 172 includes the ID(s) 2, ..., N, the cell ID(s) 2, ..., N and / or the LTM configuration(s) 2, ..., N in the second CU-to-DU 1message as described above. Thus, the CU 172 can omit the third CU-to-DU message. In yet other implementations, the CU 172 includes the ID(s) 2, ..., N in the first CU-to-DU message and indicates that the ID(s) 2, ..., N are respectively associated with the cell ID(s) 2, ..., N. In some implementations, the DU 174 includes the ID(s) 2, ..., N in the LTM 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.

[0092] 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. In some implementations, the CU 172 includes 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 configuration(s) 2, ..., N. Thus, the CU 172 does not include an ID (e.g., LTM ID) identifying each of the LTM configuration(s) 2, ..., N in the RRC reconfiguration message, first container, and / or element 1.

[0093] In some alternative implementations, the CU 172 generates a second container including the LTM configuration(s) 2, ..., N or element(s) 2, ..., N instead of using the first container. The CU 172 then transmits an additional RRC reconfiguration message, including the second container, to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits an additional RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some implementations, the second container is 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 is an addition or modification IE (e.g., Itm-ConfigToAddMod field, LTM-ConfigToAddMod l , Itm- CandidateConfigToAddMod field, or LTM-CandidateConfigToAddMod IE). In some implementations, when the UE 102 receives the second addition or modification list, the UE 102 stores the second addition or modification list together with the first addition or modification list (e.g., in a variable in the random access memory (RAM)).

[0094] In some implementations, the DU 174 includes cell ID(s) 2, ..., N in the LTM configuration(s) 2, ..., N to identify the cell(s) 2, ..., N, respectively. In some implementations, each of the cell ID(s) 2, ..., N is a PCI. In some further implementations,the LTM configuration(s) 2, .. N includes (serving) cell index(es) 2 , .. N indexing the cell ID(s) 2, .. N or the cell(s) 2, .. N, respectively. In some implementations, the cell ID(s) 1, .. N in the LTM configuration(s) 1, .. N are different from the cell ID(s) 1, .. N in the CU-to-DU message(s) described above.

[0095] In some implementations, each of the LTM 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 configuration(s) 1, ..., N is a CellGroupConfig IE (e.g., as defined in 3GPP TS 38.331). In other implementations, each of the LTM configuration(s) 1, ..., N include configuration parameters included in a CellGroupConfig IE (e.g., as defined in 3GPP TS 38.331). In some further implementations, the plurality of configuration parameters in each of the LTM 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 configuration(s) 1, ..., N are CellGroupConfig IE(s) (e.g., defined in 3GPP TS 38.331). In other implementations, the LTM configuration(s) 1, ..., N include configuration parameters in the CellGroupConfig IE.

[0096] In some implementations, the CU 172 determines to release the LTM configuration M of the LTM configuration(s) 1, ..., N (or the element M of the element(s) 1, ..., M), where 1 < M < N. In response to the determination, the CU 172 transmits an RRC reconfiguration message to the UE 102 via the DU 174 to indicate to the UE 102 to release the LTM configuration M or element M. In some implementations, the CU 172 generates a release list including the ID (i.e., LTM ID) M for releasing the LTM 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 configuration M or element M and transmits an RRC reconfiguration complete message to the CU 172 via the DU 174. In response to the determination, the CU 172 transmits a CU-to-DU message to the DU 174 to indicate to the DU 174 to release the LTM configuration M. In some implementations, to indicate to the DU 174 to release the LTM configuration M, the CU 172 includes 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 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.

[0097] In other implementations, the DU 174 determines to release the LTM configuration K. In response to the determination, the DU 174 transmits a DU-to-CU message to the CU 172 to release the LTM configuration K. In some implementations, to indicate that the LTM configuration K is released, the DU 174 includes 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. Further, 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 configuration K or element K and transmits an RRC reconfiguration message including the release list to the UE 102 via the DU 174. In response, the UE 102 releases the LTM configuration K or element K and transmits an RRC reconfiguration complete message to the UE 102 via the DU 174. In some implementations, the CU 172 transmits 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.

[0098] 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 transmits 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 includes 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.

[0099] 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 transmits one or more RRC messages (e.g., RRCReconfiguration message(s)), including the at least one measurementconfiguration, to the UE 102 via the DU 174 in the event 302 and / or 316 and / or after the event 306 or 316. Depending on the implementation, the one or more RRC messages do or do not include the RRC reconfiguration message of the event 316. In accordance with the at least one measurement configuration, the UE 102 performs measurements on one or more reference signals. In some implementations, the one or more reference signals 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. Depending on the implementation, the one or more reference signals are CSI-RS(s) or SSB(s).

[0100] 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 LI measurement configuration(s), as described for the event 304. For example, the LI measurement configuration(s) are CSI-MeasConfig IE(s) (e.g., defined in 3GPP TS 38.331 vl8.0.0 and / or later versions). In some implementations, the LI measurement configuration(s) include measurement report configuration(s). The UE 102 transmits the LI measurement report(s) on PUCCH(s) or MAC CE(s) to the DU 174 in accordance with the measurement report configuration(s). The DU 174 receives the LI measurement report(s) on PUCCH(s) or MAC CE(s) in accordance with the measurement report configuration(s). In some implementations, the measurement report configuration(s) are CSl-ReportConfig IE(s). In other implementations, each of the measurement report configuration(s) is a new RRC IE. In some implementations, (each of) the measurement report configuration(s) configures periodically reporting and / or event-triggered reporting of the LI measurement result(s).

[0101] In yet other implementations, the at least one measurement configuration includes new-type measurement configuration(s) (e.g., LTM measurement configuration(s)). In some implementations, the new-type measurement configuration(s) are newly defined (e.g., in 3GPP TS v 18.0.0 and / or later versions). In some implementations, the new-type measurement configuration(s) include reference signal resource configuration(s) configuring resources where the DU 174 transmits reference signal(s). For example, the reference signal resource configuration(s) include CSLRS(s) and / or SSB(s). In some implementations, the reference signal resource configuration(s) are CSl-ResourceConfig IE(s). In anotherimplementation, the new-type measurement configuration(s) include measurement report configuration(s), as described above. The UE 102 transmits the measurement report(s) on PUCCH(s) or MAC CE(s) to the DU 174 in accordance with the measurement report configuration(s). The DU 174 receives the measurement report(s) on PUCCH(s) or MAC CE(s) in accordance with the measurement report configuration(s). In some such cases, the measurement report(s) are LI measurement report(s) or new-type measurement report(s) (e.g., LTM measurement report(s)). In some implementations, the new-type measurement configuration includes configuration parameters newly defined (e.g., in a 3GPP TS v 18.0.0 and / or later versions).

[0102] 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 configuration 1 (i.e., the first LTM command commands the UE 102 to apply the LTM 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 includes the ID 1 in the first LTM command to indicate the LTM configuration 1, and the UE 102 determines (e.g., identifies) the LTM configuration 1 or element 1 in accordance with the ID 1. In other implementations, the DU 174 includes the cell index 1 indexing the cell ID 1 in the first LTM command. The UE 102 determines (e.g., identifies) the LTM configuration 1 or element 1 based on the cell index 1. After determining the LTM configuration 1 or element 1, the UE 102 then applies the LTM configuration 1 in response to receiving the first LTM command.

[0103] In yet other implementations, the DU 174 includes a bit map in the first LTM command to activate the LTM 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 some implementations, bit 1, ..., N corresponds to the LTM 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 ID 1, the LTM configuration 1, or the element 1. Thus, in some such implementations, the UE 102 determines the ID 1, LTM configuration 1, or element 1 in accordance with the bit 1 set to the first value in the bit map. In further implementations, bit 0, ..., N-l corresponds to the LTM 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 firstvalue to indicate the ID 1 or the LTM configuration 1. Thus, in some such implementations, the UE 102 determines the ID 1 or LTM configuration 1 in accordance with the bit 0 set to the first value in the bit map. In such implementations, the DU 174 sets the remaining bits in the bit map to a second value to indicate that the rest of the LTM configuration(s) 1, ..., N 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, depending on the implementation, if the DU 174 determines to activate the LTM configuration L, the DU 174 sets the corresponding bit (e.g., bit L or bit L-7) in the bit map to the first value and sets the remaining bits to the second value, where 1 <L <N.

[0104] In some implementations, the at least one measurement report (e.g., LI measurement report(s) or new-type measurement report(s)) of the event 324 includes at least one measurement result for the first cell, TRP(s) of the first cell or reference signal(s) transmitted on the first cell. In some implementations, the reference signal(s) are CSLRS(s) or SSB(s). The DU 174 determines to activate the LTM 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 configuration 1 because, when, or if the at least one measurement result is above a second predetermined threshold. In some implementations, the at least one measurement result includes Ll-RSRP value(s), Ll-RSRQ value(s) and / or Ll-SINR value(s). In other implementations, the at least one measurement result includes RSRP value(s), RSRQ value(s), and / or SINR value(s) for the new-type measurement report(s). In some implementations, the second predetermined threshold is different from the first predetermined threshold. In some implementations, 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 such cases, the at least one measurement result indicates that the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. Such indicates that the first cell is suitable for communication with the UE 102. Thus, the DU 174 determines to activate the LTM configuration 1 in response to the signal strength or quality of the first cell being above the second predetermined threshold for the UE 102.

[0105] 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 resultfor the first cell. The CU 172 determines to activate the LTM 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 some implementations, 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 further implementations, 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, further indicating that the first cell is suitable for communication with the UE 102. Thus, the CU 172 determines to activate the LTM configuration 1 in response to the signal strength or quality of the first cell being 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 configuration 1. 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, in some such implementations, the DU 174 determines to activate the LTM configuration 1 in accordance with the cell index 1. In other implementations, the CU 172 includes the cell ID 1 in the fourth CU-to-DU message. Thus, the DU 174 determines to activate the LTM configuration 1 in accordance with the cell ID 1. In yet other implementations, the CU 172 includes the ID 1 in the fourth CU-to-DU message. Thus, in some such implementations, the DU 174 determines to activate the LTM configuration 1 in accordance with the ID 1. In some implementations, the fourth CU-to-DU message and fourth DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In other implementations, the fourth CU-to-DU message and / or fourth DU-to-CU message are new interface messages (e.g., El application protocol (E1AP) messages (e.g., defined in 3GPP TS 38.473 vl8.0.0 and / or later versions)).

[0106] In some implementations, when or in response to determining to activate the LTM configuration 1 or transmit the first LTM command, the DU 174 transmits 329 to the CU 172 a DU-to-CU message indicating that LTM is (being) executed. In some implementations, theDU 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 configuration 1. Depending on the implementation, the DU transmits the DU-to-CU message 329 to the CU 172 before or after transmitting the LTM command 330.

[0107] 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. In some implementations, the MAC CE is a new MAC CE (e.g., defined in 3GPP TS 38.321 vl8.0.0 and / or later versions). In some implementations, 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. In some implementations, the subheader includes a logical channel ID or extended logical channel ID (e.g., defined in a 3GPP TS) to identify the new MAC CE. For example, the logical channel ID or extended logical channel ID are newly defined (e.g., in 3GPP TS 38.321 vl8.0.0 and / or later versions). 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 some implementations, a format of the DCI is an existing DCI format (e.g., defined in a 3GPP TS (e.g., 38.212)). In further implementations, the format of the DCI is a new DCI format (e.g., defined in a 3GPP TS (e.g., 38.212 vl8.0.0 and / or later versions)).

[0108] 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 a security check (e.g., decryption and / or integrity check) on the first LTM command.

[0109] In some implementations, after receiving the first LTM command, the UE 102 transmits 331 an acknowledgement to the DU 174 on the cell 124A or cell 124D to indicate that the UE 102 receives the first LTM command. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE (e.g., defined in 3GPP TS 38.321 vl7.2.0 and / or later versions). In another example, the MAC CE is a new MAC CE (e.g., defined in 3GPP TS 38.321 vl8.0.0 and / or later versions). In yet other implementations, the acknowledgement is a PUCCH transmission.

[0110] In some implementations, the CU 172 transmits 316 the RRC reconfiguration message in response to the L3 measurement report 306 for the first cell. In some implementations, to configure the UE 102 to transmit the L3 measurement report 306, the CU 172 transmits 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. In some implementations, to configure the UE 102 to transmit the LI or new-type measurement report(s) 324, the CU 172 transmits 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 are 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.

[0111] After (e.g., in response to) receiving the first LTM command, the UE 102 identifies the LTM configuration 1 in accordance with the ID 1 and applies the LTM configuration 1. In some implementations, the UE 102 performs 332 a random access procedure on the first cell with the DU 174 in response to applying the LTM configuration 1 or receiving the first LTM command. 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 the acknowledgement. In other words, 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 such cases, the UE 102 performs 332 the random access procedure after disconnecting from the cell 124A. In some implementations, the UE 102 determines whether to perform the random access procedure in accordance with the LTM configuration 1. In some implementations, if the LTM configuration 1 configures the UE 102 to perform a random access procedure, the UE 102 performs the random access procedure in the event 332. For example, the LTM configuration 1 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) to configure the UE 102 to perform a random access procedure. Otherwise, if the LTM configuration 1 does not configure the UE 102 to perform a random access procedure or configures the UE 102 to skip a random access procedure, the UE 102 refrains from performing a random access procedure with the DU 174upon receiving the first LTM command. In such cases, the UE 102 skips the event 316. For example, if the LTM configuration 1 excludes a reconfiguration with sync configuration, the LTM configuration 1 configures the UE 102 not to perform a random access procedure. 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.

[0112] In cases where the UE 102 performs 332 the random access procedure, the UE 102 communicates 336 with the DU 174 on the first cell using the LTM configuration 1 and reference LTM configuration, and communicates with the CU 172 via the DU 174, after successfully completing the random access procedure. In such cases, the DU 174 communicates with the UE 102 on the first cell using the LTM configuration 1 in the event 332 and / or event 336. In some scenarios or implementations, the UE 102 communicates UL PDUs, DL PDUs, and / or physical layer signals (e.g., PUCCH transmissions and PDCCH transmissions) with the base station 104 in the event 336. In some implementations, the UE 102 determines that the UE 102 successfully completes the random access procedure when the UE 102 receives a contention resolution from the DU 174. 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. 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. In some implementations, if the LTM configuration 1 includes a second C-RNTI, the UE identity is the second C-RNTI of the UE 102. Otherwise, if the LTM configuration 1 does not include a C-RNTI, the UE identity is the first C-RNTI. In cases where the random access procedure is a contention free random access procedure, the UE 102 transmits the dedicated random access preamble to the DU 174 via the first cell. In such cases, the LTM configuration 1 includes the dedicated random access preamble.

[0113] The DU 174 identifies or determines that the UE 102 connects to the first cell upon receiving the UE identity or the dedicated preamble from the UE 102 in the random access procedure 332.

[0114] In cases where the UE 102 skips the random access procedure, the UE 102 directly communicates 336 with the DU 174 on the first cell in accordance with the LTM configuration 1 and communicates with the CU 172 via the DU 174, after (e.g., in response to) receiving the first LTM command. For example, the UE 102 directly communicates UL PDUs, DL PDUs, and / or physical layer signals (e.g., PUCCH transmissions and PDCCH transmissions) with the base station 104 in the event 336. In some implementations, the DU 174 includes, in the LTM configuration 1, configuration parameters configuring resources for the UE 102 to transmit the at least one PUCCH or PUSCH transmission, and the UE 102 transmits the at least one PUCCH or PUSCH transmission on the resources, using the configuration parameters, to indicate that the UE 102 connects to the first cell. In other implementations, the DU 174 transmits, to the UE 102, at least one DCI on a PDCCH on the first cell to command the UE 102 to transmit the at least one PUCCH or PUSCH transmission, after transmitting the first LTM command. The at least one DCI configures resources for the UE 102 to transmit the at least one PUCCH or PUSCH transmission, and the UE 102 transmits the at least one PUCCH or PUSCH transmission on the resources. The DU 174 identifies or determines that the UE 102 connects to the first cell upon receiving the PUCCH or PUSCH transmission. The DU 174 identifies or determines that the UE 102 connects to the first cell upon receiving the PUCCH or PUSCH transmission on the resources configured in the LTM configuration 1 or the at least one DCI.

[0115] In cases where the UE 102 receives the reference LTM configuration as described above, the UE 102 communicates 336 with the DU 174 on the first cell in accordance with the LTM configuration 1 and at least a portion of the reference LTM configuration. In other words, the UE 102 communicates 336 with the DU 174 in accordance with configuration parameters in the LTM configuration 1 and the reference LTM configuration. Similarly, the DU 174 communicates 336 with the UE 102 on the first cell in accordance with the LTM configuration 1 and at least a portion of the reference LTM configuration. In other words, the DU 174 communicates 336 with the UE 102 in accordance with configuration parameters in the LTM configuration 1 and the reference LTM configuration.

[0116] In some implementations, the UE 102 transmits an RRC message (e.g., RRC reconfiguration complete message) to the CU 172 via the DU 174 and the first cell to indicate that the UE 102 applies the LTM configuration 1. In some implementations where the UE 102 performs the random access procedure 332, the UE 102 includes the RRC message in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC message aftercompleting the random access procedure. In cases where the UE 102 skips 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 transmits 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.

[0117] In other implementations, the UE 102 refrains from transmitting the RRC message to the base station 104 in response to applying the LTM configuration 1 or receiving the first LTM command. In some such cases, the UE 102 includes or transmits data in the Message 3, Message A or PUSCH transmission as described above. In some implementations, the UE 102 generates a MAC PDU and / or an RLC PDU, including the data, and transmits or includes the MAC PDU and / or RLC PDU in the PUSCH transmission. For example, depending on the implementation, the data is a PDCP PDU, an SDAP PDU, an LTE Positioning Protocol (LPP) PDU, an RRC PDU, and / or a NAS PDU. The RRC PDU includes a UL-DCCH-Message excluding an RRC reconfiguration complete message. The NAS PDU includes a Mobility Management (MM) message or a Session Management (SM) message. Depending on the implementation, the MM message is a 5G MM message or a 6G MM message, and the SM message is 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.

[0118] In some implementations, when the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 transmits 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 includes the cell ID 1 of the first cell in the DU-to-CU message of the event 334. In some implementations, the cell ID is 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. In some implementations, when the DU 174 determines that the UE 102 successfully connect to the first cell in the event 332 or 336, the DU 174 transmits a DL Data Delivery Status message or frame to the CU 172 (e.g., a UP of the CU 172).

[0119] 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, theDU 174 stops communicating with the UE 102 on the cell 124A and / or releases resources of the cell 124 A configured for the UE 102.

[0120] In some implementations, the DU 174 generates some or all of the LTM configuration 1 and / or LTM configuration(s) 2, N as full configuration(s) to replace the serving DU configuration. If the LTM configuration 1 is a full configuration, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM configuration 1 instead of the serving DU configuration. In some implementations, the DU 174 includes an indication that the LTM configuration l is a full configuration in the LTM configuration 1. In some implementations, in each of the LTM configuration(s) 2, ..., N, the DU 174 includes an indication to indicate that the corresponding DU configuration is a full configuration. In some implementations, each of the indication(s) in the LTM configuration(s) 1, ..., N is a field or IE (i.e., the same field or IE). In other implementations, the CU 172 includes, in the RRC reconfiguration message of the events 316, 318, a single indication that the LTM configuration(s) 1 and / or 2, ..., N is / are full configuration(s). In some cases, for the second container, the CU 172 includes, in the additional RRC reconfiguration message, a single indication that the LTM configuration(s) 2, ..., N is / are full configuration(s). In yet other implementations, the CU 172 includes, in the first container, a single indication that the LTM configuration(s) 1 and / or 2, ..., N is / are full configuration(s). In yet other implementations, for each of the LTM configuration(s) 2, ..., N, the CU 172 includes, in the first container, a particular indication that the corresponding LTM configuration is a full configuration. In some cases, for the second container, the CU 172 includes, in the second container, a single indication that the LTM configuration(s) 2, ..., N is / are full configuration(s). In yet other implementations, the CU 172 includes, in the element 1, an indication that the LTM configuration 1 is a full configuration. In some implementations, in each of the element(s) 2, ..., N, the CU 172 includes an indication that the corresponding LTM configuration is a full configuration. In some implementations, the UE 102 determines that the LTM configuration 1 and / or LTM configuration(s) 2, ..., N are full configuration(s) based on the indication(s) above. In some implementations, each of the indication(s) above is different from a fullConfig field (e.g., as defined in the current 3GPP TS). In some implementations, each of the indication(s) above is a fullConfig field (e.g., as defined in the current 3GPP TS). In cases where the LTM configuration 1 is a full configuration, the UE 102 in the event 336 does not apply the reference LTM configuration if received from the base station 104 (e.g., inthe RRC reconfiguration message 318). In some such cases, the DU 174 does not include a reference LTM configuration in the first DU-to-CU message 310.

[0121] In other implementations, the DU 174 generates the LTM configuration 1 and / or LTM configuration(s) 2, ..., N as delta configuration(s) that augment at least a portion of the reference LTM configuration. In other words, the DU 174 generates the LTM configuration(s) 1, .. ,N based on the reference LTM configuration. For example, if the LTM configuration 1 is a delta configuration, the UE 102 and DU 174 augment at least the portion of the reference LTM configuration with the LTM configuration 1. Thus, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM configuration 1 and unaugmented portion of the reference LTM configuration. In some implementations, the LTM configuration(s) 1 and / or 2..., N, first container, second container, or element(s) 1, ..., N exclude indication(s) indicating that the LTM configuration(s) 1 and / or 2..., N are full configuration(s) to indicate that the LTM configuration(s) 1 and / or 2, ..., N are delta configuration(s). In some implementations, the UE 102 determines that each of the LTM configuration(s) 1 and / or 2, ..., N is a delta configuration based on the indication being excluded in the LTM configuration(s) 1 and / or 2, ..., N, first container, second container, or element(s) 1 and / or 2, ..., N.

[0122] In some implementations, if the UE 102 does not receive a reference LTM configuration for the LTM configuration 1 and / or the LTM configuration(s) 2, ..., N, the UE 102 determines that the LTM configuration 1, and / or the LTM configuration(s) 2, ..., N are full configuration(s). Correspondingly, if the DU 174 does not obtain a reference LTM configuration for the UE 102 (i.e., the DU 174 does not generate a reference LTM configuration for the UE 102 and / or receive a reference LTM configuration for the UE 102 from the CU 174), the DU 174 generates the LTM configuration 1, and / or the LTM configuration(s) 2, ..., N as full configuration(s).

[0123] In other implementations, if the UE 102 does not receive a reference LTM configuration for the LTM configuration 1 and / or the LTM configuration(s) 2, ..., N, the UE 102 determines that the LTM configuration 1 and / or the LTM 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 configuration 1 and at least a portion of the serving DU configuration not augmented by LTM configuration 1. Correspondingly, if the DU 174 does not obtain a reference LTM configuration for the UE102 (i.e., the DU 174 does not generate a reference LTM configuration for the UE 102 and / or receive a reference LTM configuration for the UE 102 from the CU 174), the DU 174 generates the LTM configuration 1 and / or the LTM 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 configuration 1 and the at least a portion of the serving DU configuration.

[0124] 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.

[0125] In some implementations, when the UE 102 resets the UE MAC entity, the UE 102 performs at least one of the following actions for the UE MAC entity (i.e., UE MAC reset or full UE MAC reset): (i) initialize Bj for configured logical channel(s) to zero; (ii) stop one or more timers; (iii) consider timeAlignmentTimeris) as expired if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (iv) set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0; (v) set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1; (vi) flush Msg3 buffer; (vii) flush MSGA buffer; (viii) cancel, if any, triggered Scheduling Request procedure; (ix) cancel, if any, triggered Buffer Status Reporting procedure; (x) cancel, if any, triggered Power Headroom Reporting procedure; (xi) cancel, if any, triggered consistent LBT failure; (xii) cancel, if any, triggered BFR; (xiii) cancel, if any, triggered Sidelink Buffer Status Reporting procedure; (xiv) cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure; (xv) cancel, if any, triggered Timing Advance Reporting procedure; (xvi) cancel, if any, triggered Recommended bit rate query procedure; (xvii) cancel, if any, triggered configured uplink grant confirmation; (xviii) cancel, if any, triggered configured sidelink grant confirmation; (xix) cancel, if any, triggered Desired Guard Symbol query; (xx) cancel, if any, triggered Positioning Measurement Gap Activation / Deactivation Request procedure; (xxi) flush soft buffers for DL HARQ process(es); (xxii) for each of the DL HARQ process(es), consider the next receivedtransmission for a TB as the very first transmission; (xxiii) release, if any, Temporary C- RNTI; and / or (xiv) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0126] In some implementations, when the DU 174 resets the DU MAC entity, the DU 174 performs at least one of the following actions for the DU MAC entity (i.e., DU MAC reset or full DU MAC reset): (i) stop one or more timers; (ii) consider limeAlignmenlTimer( ) that the DU 174 starts and / or maintains for the UE 102 as expired if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1); (iii) set NDI(s) for DL HARQ process(es) to value 0; (iv) flush soft buffers for UL HARQ process(es); (v) for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission; and / or (vi) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0127] Depending on implementations, the UE 102 determines 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.

[0128] In some implementations, the partial UE MAC reset includes at least one of the following actions: (i) 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); (ii) flush Msg3 buffer; (iii) flush MSGA buffer; (iv) release, if any, Temporary C-RNTI; and / or (v) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0129] In some implementations, the partial UE MAC reset further includes at least one of the following actions: (i) cancel, if any, triggered Scheduling Request procedure; (ii) cancel, if any, triggered Buffer Status Reporting procedure; (iii) cancel, if any, triggered Power Headroom Reporting procedure; (iv) cancel, if any, triggered consistent LBT failure; (v) cancel, if any, triggered BFR; (vi) cancel, if any, triggered Sidelink Buffer Status Reporting procedure; (vii) cancel, if any, triggered Pre-emptive Buffer Status Reporting procedure;(viii) cancel, if any, triggered Timing Advance Reporting procedure; (ix) cancel, if any, triggered Recommended bit rate query procedure; (x) cancel, if any, triggered configured uplink grant confirmation; (xi) cancel, if any, triggered configured sidelink grant confirmation; (xii) cancel, if any, triggered Desired Guard Symbol query; and / or (xiii) cancel, if any, triggered Positioning Measurement Gap Activation / Deactivation Request procedure.

[0130] In some implementations, the partial UE MAC reset further includes at least one of the following actions: (i) stop a first portion of the one or more timers and retain the rest of the one or more timers; (ii) set new data indicator(s) (NDI(s)) for UL HARQ process(es) to value 0; (iii) set NDI(s) for HARQ process ID(s) to value 0 for monitoring PDCCH in Sidelink resource allocation mode 1; (iv) flush soft buffers for DL HARQ process(es); and / or (v) for each of the DL HARQ process(es), consider the next received transmission for a TB as the very first transmission;

[0131] Depending on implementations, the DU 174 determines 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.

[0132] In some implementations, the partial DU MAC reset includes at least one of the following actions in the partial MAC reset: (i) consider limeAlignmenlTimer( ) that the DU 174 starts and / or maintains for the UE 102 as expired if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1) and / or (ii) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0133] In some implementations, when the partial DU MAC reset includes at least one of the following actions for the MAC entity (i.e., DU MAC reset): (i) stop a first portion of the one or more timers and retain the rest of the one or more timers; (ii) set NDI(s) for DL HARQ process(es) to value 0; (iii) flush soft buffers for UL HARQ process(es); (iv) for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission; and / or (v) reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0134] In other implementations, the UE 102 refrains from resetting the UE MAC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from resetting the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the UE MAC entity (not reset). Similarly, the DU 174 communicates with the UE 102 using the DU MAC entity (not reset) on the first cell during or after the random access procedure 332 or after determining that the UE 102 connects to the first cell.

[0135] 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.

[0136] In some implementations, the LTM configuration 1 does or does not include one or more RLC reestablishment indications (e.g., reestablishRLC field(s)) configuring the UE 102 to reestablish some or all of the at least one UE RLC entity. If the LTM configuration 1 includes the an 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 reestablishes 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 reestablishes the first UE RLC entity while or after performing 332 the random access procedure. Otherwise if the LTM 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.

[0137] In some implementations, when the UE 102 reestablishes the first UE RLC entity, the UE 102 performs at least one of the following actions for the first UE RLC entity: (i)discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any; (ii) stop and reset timer(s), if running; and / or (iii) reset state variables to initial values. In some implementations, the state variables and timer(s) are pre-defined (e.g., in 3GPP TS 38.322).

[0138] Otherwise, if the LTM 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 configuration 1 or element 1 does not include the RLC reestablishment indication and includes an indication that the configuration 1 is a full configuration, the UE 102 reestablishes the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. Otherwise, if the LTM 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.

[0139] Similarly, the DU 174 reestablishes some or all of at least one DU RLC entity (e.g., NR RLC 206B) that the DU 174 uses to communicate with the at least one UE RLC entity of the UE 102 (e.g., the events 302, 304, 318, 320, 324, 330, and / or 331) in response to the RLC reestablishment indication. In some implementations, the DU 174 reestablishes a first DU RLC entity of the at least one DU RLC entity after transmitting the first LTM command, receiving an acknowledgement for the first LTM command from the UE 102, or determining that the UE 102 connects to the first cell. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. In yet other implementations, the acknowledgement is a PUCCH transmission. In some implementations, when the base station 104 reestablishes the first DU RLC entity, the DU 174 performs at least one of the following actions for the first DU RLC entity: (i) discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any; (ii) stop and reset timer(s), if running; and / or (iii) reset state variables to initial values. In some implementations, the state variables and timer(s) are pre-defined (e.g., in 3GPP TS 38.322).

[0140] 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.

[0141] 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. Depending on the implementation, in the PDCP recovery procedure, the UE 102 does or does not reestablish the first UE PDCP entity. In some implementations, after or in response to performing the PDCP recovery procedure, the UE 102 retransmits 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. Depending on the implementation, in the PDCP recovery procedure, the CU 172 does or does not reestablish the first CU PDCP entity. In some implementations, after or in response to performing the PDCP recovery procedure, the CU 172 retransmits 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.

[0142] 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.

[0143] In some implementations, after determining that the UE 102 connects to the first cell, the CU 172 transmits 338 a CU-to-DU message (e.g., a UE Context Modification Request message) to the DU 174 to indicate to 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 some implementations, in response, the DU 174 stops communicating on the cell 124A with the UE 102 and / or releases or suspends resources, of the cell 124A, configured for the UE 102, and transmits 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.

[0144] Depending on the implementation, after or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351, 352, 354, and / or 356 occur, similar to the events 324, 326, 328, 330, 331, 332, 334, and / or 336, respectively. The UE 102 transmits 344 at least one measurement report to the DU 174. The at least one measurement report includes at least one measurement result for a second cell (i.e., the cell 2). The at least one measurement result indicates that the second cell is suitable for communication with UE 102 and / or the first cell is not suitable for communication with the UE 102. After (e.g., in response to) receiving the at least one measurement report, the DU 174 determines to activate the LTM configuration 2 and generates a second LTM command to activate the LTM configuration 2 (i.e., the second LTM command commands the UE 102 to apply the LTMconfiguration 2). The DU 174 then transmits 350 the second LTM command to the UE on the first cell to the UE 102.

[0145] In some implementations, when or in response to determining to activate the LTM configuration 2 or transmit the second LTM command, the DU 174 transmits 349 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some implementations, the DU 174 includes the cell ID 2 or the ID 2 (i.e., LTM ID) in the DU-to-CU message 349 to indicate that the DU 174 is to activate the LTM configuration 2. In some implementations, the DU transmits the DU-to-CU message 349 to the CU 172 before or after transmitting the LTM command 350.

[0146] The descriptions for the events 324, 326, 328, 330, 331, 332, 334, and / or 336 can be applied to the events 344, 346, 348, 350, 351, 352, 354, and / or 356 with simple changes. Lor example, “ cell 124A”, “first LTM command”, “first cell”, “ID 1”, and / or “LTM configuration 1” are replaced with “first cell”, “second LTM command”, “second cell”, “ID 2”, and / or “LTM configuration 2”, respectively.

[0147] The events 344, 346, 348, 350, 351, 352, 354 are collectively referred to in Eig. 3 as an LTM execution procedure 398. The events 304, 306, 390, 392, 394, 324, 326, 328, 329, 330, 331, 332, 334, 336, 396, 398, 356 are collectively referred to in Eig. 3 as an LTM configuration and / or activation procedure 380.

[0148] Referring next to Eig. 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 descriptions for the scenario 300 can generally apply to the scenario 400. The differences between the scenarios 300 and 400 are described below.

[0149] 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. 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 an LTM preparation procedure with the T-DU 174B to prepareand / or request the T-DU 174B to prepare cell(s) 1, .. N for LTM for the UE 102. In the LTM preparation procedure 490, the CU 172 transmits a CU-to-DU message, including the cell ID(s) 1, ..., N, to the T-DU 174B to request the T-DU 174B to prepare the cell(s) 1, ..., N for LTM for the UE 102. In response, the T-DU 174B transmits a DU-to-CU message including the LTM configuration(s) 1, ..., N to the CU 172 in response to the CU-to-DU message. The LTM configuration(s) 1, ..., N configure the cell(s) 1, ..., N for LTM, respectively. In particular, the LTM 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 a UE Context Setup Request message and UE Context Setup Response message, respectively. The CU 172 then transmits the LTM configuration(s) 1, ..., N in an RRC reconfiguration message in an LTM configuration delivery procedure 494, similar to the LTM configuration delivery procedure 394.

[0150] In some implementations, after performing the LTM preparation procedure 490, the CU 172 performs additional LTM preparation procedure(s) with the T-DU 174B to prepare cell(s) N+l, ..., N+M for LTM for the UE 102, where M is a positive integer larger than zero. In further implementations, the CU 172 determines 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(s), 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 identify 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-CU message including the LTM configuration(s) N+l, ..., N+M to the CU 172. The LTM configuration(s) N+l, ..., N+M configure the cell(s) N+l, ..., N+M for LTM, respectively. In particular, the LTM 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 configuration(s) N+l, ..., N+M in an RRC reconfiguration message in an additional LTM configuration delivery procedure, similar to the LTM configuration delivery procedure 394 or 494.

[0151] 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.

[0152] In some implementations, the CU 172 and S-DU 174A 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. Depending on the implementation, the value N in the procedure 380 or described for Fig. 3 is same as or different from the value N described for Fig. 4. In some implementations, in the procedure 390, the CU 172 receives the first DU-to-CU message including the reference ETM configuration from the S-DU 174A in the event 310. In such cases, the CU 172 includes the reference ETM configuration (e.g., received from the S-DU 174A) in the CU-to-DU message in the ETM preparation procedure 490. The T-DU 174B generates the LTM configuration(s) 1, ..., N based on the reference LTM configuration received from the CU 172. In such cases, the T-DU 174B does not include a reference LTM configuration in the DU-to-CU message in the procedure 490. In cases regarding the additional LTM preparation procedure, the T-DU 174B does not include a reference LTM configuration in the DU-to-CU message in the additional LTM preparation procedure. In some implementations, the CU 172 does not include the reference LTM configuration in a CU-to-DU message in the additional LTM preparation procedure with the T-DU 174B. In cases regarding the additional LTM preparation procedure, the T-DU 174B generates the LTM configuration(s) N+l, ..., N+M based on the reference LTM configuration received from the CU 172.

[0153] In some implementations, the CU 172 does not provide a reference LTM configuration to the T-DU 174B in the LTM preparation procedure 490. In such cases, the T- DU 174B generates a reference LTM configuration and generates the LTM configuration(s) 1, ..., N based on the reference LTM configuration. In such cases, the T-DU 174B includes the reference LTM configuration in the DU-to-CU message in the procedure 490. The CU 172 transmits the reference LTM configuration in the RRC reconfiguration message in the procedure 490. In cases regarding the additional LTM preparation procedure, the T-DU 174B generates the LTM configuration(s) N+l, ... , N+M based on the reference LTM configuration. In some such cases, the T-DU 174B does not include the reference LTM configuration in the DU-to-CU message in the additional LTM preparation procedure. In some implementations, the reference LTM configuration that the T-DU 174B generates is different from the reference LTM configuration that the S-DU 174A generates. In other implementations, the reference LTM configuration that the T-DU 174B generates is the same as the reference LTM configuration that the S-DU 174A generates.

[0154] In some implementations, the CU 172 assigns ID(s) 1, ..., N identifying the LTM configuration(s) 1, ..., N (e.g., 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 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 configuration(s) 1, ..., N (e.g., 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 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 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 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.

[0155] In some implementations, the CU 172 transmits 412 a CU-to-DU message, including the ID(s) 1, ..., N, to the S-DU 174A and receives 414 a DU-to-CU message from the S-DU 174A in response. The CU-to-DU message 412 and DU-to-CU message 414 are collectively referred to in Fig. 4 as an LTM ID transfer procedure 493. In some implementations, the message 412 and message 414 are a UE Context Modification Request message and UE Context Modification Response message, respectively. In some implementations, the CU 172 includes the LTM configuration(s) 1, ..., N and / or cell ID(s) 1, ..., N in the CU-to-DU message 412. In some alternative implementations, the CU 172 performs multiple LTM ID transfer procedures to transmit the ID(s) 1, ..., N, cell ID(s) 1, ..., N and / or LTM 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 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 configuration(s) 1, ..., N and / or the cell ID(s) 1, ..., N, respectively.

[0156] In some implementations, the CU 172 transmits a CU-to-DU message, including the ID(s) N+l, ..., N+M, to the S-DU 174A and receives a DU-to-CU message from the S-DU 174A 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 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 performs multiple LTM ID transfer procedures to transmit the ID(s) N+l, ..., N+M, cell ID(s) N+l, ..., N+M and / or LTM 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 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 configuration(s) N+l, ..., N+M and / or the cell ID(s) N+l, ..., N+M, respectively.

[0157] In some implementations, later in time, the UE 102 transmits 424 at least one measurement report to the S-DU 174A, similar to the event 324. The at least one measurement report (e.g., LI measurement report(s)) includes an event ID, first measurement result(s) for the cell 1 of the T-DU 174B, and / or second measurement result(s) for the cell 124A. In some implementations, the first measurement result(s) are or include RSRP, RSRQ, and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 1. Likewise, in some implementations, the second measurement result(s) are or include RSRP, RSRQ, and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 124A. In some implementations, the event ID, RSRP, RSRQ, and / or SINR are Ll-event ID, Ll-RSRP, Ll-RSRQ, and / or Ll-SINR, respectively. In some implementations, based on the first measurement result(s) and / or second measurement result(s), the S-DU 174A transmits 430 a first LTM command (i.e., LTM command 1), including the ID 1, to the UE 102 to command the UE 102 to perform a cell change to the cell 1 of the T-DU 174B from the cell 124A. When the UE 102 receives the first LTM command, the UE 102 identifies an LTM configuration (e.g., LTM configuration 1) identified by the ID 1 and performs a cell change to the cell 1 from the cell 124 A in accordance with the LTM configuration 1. Depending on the implementation, after (e.g., in response to) receiving the first LTM command, the UE 102 does or does not perform 432 a random access procedure with the T-DU 174B, similar to the event 332. In some implementations, after (e.g., in response to) receiving the first LTM command or completing the random access procedure 432, the UE 102 communicates 436 with the T-DU 174B on the first cell using the LTM configuration 1 and / or reference LTM configuration and communicates with the CU 172 via the T-DU 174B, similar to the event 336.

[0158] The resource release procedure 496 can be similar to the procedure 396. Alternatively, in some implementations, in the resource release procedure 496, the CU 172 transmits 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.

[0159] The events 380, 404, 406, 490, 492, 494, 494, 424, 426, 428, 429, 430, 431, 432, 434, 436, 496, 498, 456 are collectively referred to in Fig. 4 as an LTM configuration and / or activation procedure 480.

[0160] Referring next to Fig. 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 Fig. 3.

[0161] Initially, the UE 102 in DC communicates with the MN 106 and with the 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 communicates 502 UL PDUs and / or DL PDUs with the MN 106 and / or SN 104 via radio bearers which, depending on the implementation, include SRBs and / or DRB(s). In some implementations, the MN 106 and / or the SN 104 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 an MN configuration (i.e., MCG configuration). In some implementations, the serving DU configuration is an 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 106A 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 includesmultiple 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 the 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).

[0162] In some implementations, while the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 performs 580 an LTM 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 transmits the at least one measurement report to the CU 172 via the DU 174 and cell 124A in the events 504 and 506, similar to the events 304 and 306, respectively. In other implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 transmits 505 at least one measurement report to the MN 106 via the cell 126. The MN 106 in turn transmits 507 the at least one measurement report to the CU 172. In some implementations, the MN 106 generates at least one SN message, including the at least one measurement report, and transmits the at least one SN message to the CU 172 in the event 507. In some implementatoins, the at least one SN message include RRC Transfer message(s) and / or SN Modification Request message(s).

[0163] 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 configuration 1 and communicates 536 with the CU 172 via the DU 174, similar to the event 336. In some implementations, later in time, the DU 174 and / or CU 172 performs 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 LTMconfiguration 2 and communicates 556 with the CU 172 via the DU 174, similar to the event 356.

[0164] The events 504, 506, 505, 507, 590, 592, 594, 594, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, 556 are collectively referred to in Fig. 5A as an LTM configuration and / or activation procedure 581.

[0165] 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 an 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 an MN RRC response message including the RRC reconfiguration complete message and transmits 521 the MN RRC response message to the MN 106. In some implementations, the MN 106 generates a second SN message (e.g., SN Reconfiguration Complete message or RRC Transfer message) including the RRC reconfiguration complete message and transmits the second SN message to the SN 104 in the event 523. In some implementations, the MN RRC message and MN RRC response message are an RRC reconfiguration message and an RRC reconfiguration complete message, respectively.

[0166] The events 504, 506, 505, 507, 590, 592, 594, 517, 519, 521, 523, 524, 526, 528, 529, 530, 531, 532, 534, 536, 596, 598, 556 are collectively referred to in Fig. 5B as an LTM configuration and / or activation procedure 582.

[0167] 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. In some implementations, while the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 performs 680 an LTM configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. In someimplementations, while the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 performs 681 an LTM 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.

[0168] Referring next to Fig. 6B, a scenario 600B is 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.

[0169] 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 an MN, similar to the base station 104 in the Fig. 3 or the MN 106 in Figs. 5A-6B, and the CU 172 operates with the S-DU 174B as an SN, similar to the SN 104 in Figs. 5A-6B.

[0170] 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 174B using a serving CU configuration, similar to the event 302. Events 704 and 706 are similar to the events 304 and 306. In some implementations, the UE 102 transmits 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 least one measurement report to the CU 172, similar to the event 306. In some implementations, while the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 performs 780 an LTM configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380.

[0171] The events 704, 706, 705, 707, 790, 792, 794, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, 756 are collectively referred to in Fig. 7A as an LTM configuration and / or activation procedure 781.

[0172] 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.

[0173] The events 704, 706, 705, 707, 790, 792, 794, 717, 719, 721, 723, 724, 726, 728, 729, 730, 731, 732, 734, 736, 796, 798, 756 are collectively referred to in Fig. 7B as an LTM DU configuration and / or activation procedure 782.

[0174] 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. In some implementations, while the UE 102 communicates in DC with the M- DU 174A and S-DU 174B, the CU 172 performs 880 an LTM configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380. In some implementations, while the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 performs 881 an LTM configuration and / or activation procedure with the UE 102 via the S-DU 174A, similar to the procedure 581 or 582.

[0175] 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.

[0176] Next, several example methods, that can be implemented in a RAN node such as a DU or a CU to support configuring a configuration for LTM, are discussed with reference to Figs. 9-14. Examples and implementations described for Figs. 3-8B can apply to Figs. 9-14.

[0177] Fig. 9 illustrates an example method 900, which a CU of a base station (e.g., the CU 172 of the base station 104) can implement, for communicating with a UE (e.g., the UE 102).

[0178] The method 900 begins at block 902, where the CU communicates with the UE via a first DU (e.g., events 302, 402, 602, 702, 802). At block 904, the CU receives a reference LTM configuration from the first DU (e.g., events 310, 390, 380 in Fig. 4, events 681, 682, 881, 882). At block 906, the CU transmits the reference LTM configuration to the UE via the first DU (e.g., events 316, 318, 394, 380 in Fig. 4, events 681, 682, 881, 882). At block 908, the CU transmits a first CU-to-DU message, including the reference LTM configuration, to request LTM preparation for the UE to a second DU (e.g., events 490, 690, 890). In some implementations, the CU includes at least one first cell ID in the first CU-to-DU message to request that the second DU prepare at least one first cell for LTM. The at least one first cellID identifies the at least one first cell. At block 910, the CU receives a first DU-to-CU message including at least one first LTM configuration from the second DU (e.g., events 490, 690, 890). At block 912, the CU transmits the at least one first LTM configuration to the UE via the first DU (e.g., events 494, 694, 894). Alternatively, the CU transmits the at least one first LTM configuration to the UE via a RAN node (e.g., events 617, 619, 817, 819). In some implementations, the RAN node is another DU or base station.

[0179] In some implementations, the at least one first cell ID and the at least one first cell include cell ID(s) 1, ..., N and cell(s) 1, ..., N, respectively. The cell ID(s) 1, ..., N identify the cell(s) 1, ..., N, respectively, where N is positive integer larger than zero. The at least one first LTM configuration includes LTM configuration(s) (i.e., non-reference LTM configuration(s)) 1, ..., N configuring the cell(s) 1, ..., N, respectively. In some implementations, the first CU-to-DU message and first DU-to-CU message are a UE Context Setup Request message and UE Context Setup Response message, respectively.

[0180] At block 914, the CU transmits a second CU-to-DU message requesting LTM preparation for the UE to the second DU (e.g., events 490, 690, 890). In some implementations, the CU includes at least one second cell ID in the second CU-to-DU message to request that the second DU prepare at least one second cell for LTM. The at least one second cell ID identifies the at least one second cell. In some implementations, the CU refrains from including the reference LTM configuration in the second CU-to-DU message, which prevents the second DU from determining that the at least one first LTM configuration is invalid or needs to be modified. In some implementations, the CU transmits the second CU-to-DU message after transmitting the first CU-to-DU message. At block 916, the CU receives a second DU-to-CU message including the at least one second LTM DU configuration from the second DU (e.g., events 490, 690, 890). At block 918, the CU transmits the at least one second LTM configuration to the UE via the first DU or second DU (e.g., events 494, 694, 617, 619, 894, 817, 819). The descriptions for the events 308 and 310 can apply to the second CU-to-DU message and second DU-to-CU message, respectively. Depending on the implementation, blocks 914, 916, and 918 are optional.

[0181] In some implementations, the at least one second cell ID and the at least one second cell include cell ID(s) N+l, ..., N+M and cell(s) N+l, ..., N+M, respectively. The cell ID(s) N+l, ..., N+M identify the cell(s) N+l, ..., N+M, respectively, where M is a positive integer larger than zero. The at least one second LTM configuration includes LTM configuration(s)(i.e., non-reference LTM configuration(s)) N+l, N+M configuring the cell(s) N+l, N+M, respectively. In some implementations, the second CU-to-DU message and second DU-to-CU message are a UE Context Modification Request message and UE Context Modification Response message, respectively.

[0182] In some implementations, the CU generates a first message (e.g., RRC reconfiguration message), including the reference LTM configuration, and transmits the first message to the UE via the first DU at block 906. In some implementations, the CU generates a second message (e.g., RRC reconfiguration message), including the at least one first LTM configuration, and transmits the second message to the UE via the first DU at block 912. Alternatively, the CU generates a single message (e.g., RRC reconfiguration message), including the reference LTM configuration and at least one first LTM configuration, and transmits the message to the UE via the first DU. In some implementations, the CU generates a third message (e.g., RRC reconfiguration message), including the at least one second LTM configuration, and transmits the third message to the UE via the first DU or second DU at block 918.

[0183] In some implementations, the CU assigns ID(s) 1, ..., N for the LTM configuration(s) 1, ..., N, respectively, and includes the ID(s) 1, ..., N in the first message or second message. In some implementations, the CU assigns ID(s) N+l, ..., N+M for the LTM configuration(s) N+l, ..., N+M, respectively, and includes the ID(s) N+l, ..., N+M in the third message. In some implementations, the CU refrains from assigning an ID for the reference LTM configuration.

[0184] In some implementations, the CU at block 904 performs an LTM preparation procedure with the first DU and receives the reference LTM configuration from the first DU in the LTM preparation procedure (e.g., events 390, 380 in Eig. 4; events 681, 682, 881, 882). In some implementations, in the LTM preparation procedure, the CU receives LTM configuration(s) configuring cell(s) of the first DU for LTM from the first DU (e.g., events 310, 390, 380 in Eig. 4; events 681, 682, 880, 881, 882) and transmits the LTM configuration(s) to the UE via the first DU (e.g., events 316, 318, 394, 380 in Eig. 4; events 480, 681, 682, 881, 882).

[0185] In some implementations, the first DU is a serving DU (e.g., the S-DU 174A inEigs. 4, 6A and 6B, and S-DU 174B in Eigs. 8A and 8B), and the second DU is a non-servingDU (e.g., the T-DU 174B in Eigs. 4, 6A and 6B, and T-DU 174C in Eigs. 8A and 8B). Insome implementations, the first DU communicates with the UE using a first serving DU configuration, before and / or when the receiving the first CU-to-DU message. In such cases, the first CU transmits the first message to the first DU, which in turn transmits the first message to the UE using the first serving DU configuration. In some implementations, the first DU communicates with the UE using a second serving DU configuration, before and / or when the receiving the second CU-to-DU message. In such cases, the CU transmits the second message to the first DU and transmits the second message to the UE using the second serving DU configuration. In some implementations, the second serving DU configuration is the same as the first serving DU configuration. In further implementations, the second serving DU configuration is different from the first serving DU configuration.

[0186] In some implementations, the first DU transmits an LTM command to the UE to command the UE to perform a cell change to the cell 1 of the second DU after transmitting the LTM configuration 1 to the UE. In response to the LTM command, the UE performs a cell change to the cell 1 from a serving cell of the first DU and communicates with the second DU via the cell 1 using the LTM reference configuration and LTM configuration 1 (e.g., events 432, 436, 632, 636, 832, 836). When the second DU detects that the UE accesses the cell 1, the second DU communicates with the UE on the cell 1 using the LTM reference configuration and LTM configuration 1 (e.g., events 432, 436, 632, 636, 832, 836). When the second DU detects that the UE accesses the cell 1, the second DU transmits a DU-to-CU message to the CU to indicate that the UE accesses the cell 1 or the second DU (e.g., event 429, 629, 829). After receiving the DU-to-CU message indicating that the UE accesses the cell 1 or the second DU, the CU communicates with the UE via the second DU (e.g., events 436, 636, 836). In some such cases, blocks 914, 916, and 918 occur after the UE communicates with the second DU via the cell 1, and the CU transmits the at least one second LTM configuration to the UE via the second DU and cell 1 using the LTM configuration 1.

[0187] In some implementations, the first serving DU configuration and second serving DU configuration are cell group configurations (e.g., CellGroupConfig IES). In other implementations, the first serving DU configuration and second serving DU configuration include configuration parameters in a CellGroupConfig IE (e.g., as defined in 3GPP TS 38.331). In some implementations, the LTM configuration(s) are cell group configurations (e.g., CellGroupConfig IEs).

[0188] In some implementations, the CU receives at least one first measurement report (e.g., L3 measurement report(s) such as RRC MeasurementReport message(s)) from the UE. The CU determines to request LTM preparation for the at least one first cell based on the at least one first measurement report and transmits the first CU-to-DU message to the second DU in response to the determination. For example, the at least one first measurement report indicates that signal strength and / or quality of the at least one first cell are above a first threshold. In some implementations, the first threshold is predetermined by the CU or preconfigured in the CU. In some implementations, the CU receives at least one second measurement report (e.g., L3 measurement report(s) such as RRC MeasurementReport message(s)) from the UE. The CU determines to request LTM preparation for the at least one second cell based on the at least one second measurement report and transmits the second CU-to-DU message to the second DU in response to the determination. For example, the at least one second measurement report indicates that signal strength and / or quality of the at least one second cell are above the first threshold.

[0189] In some implementations, the CU performs actions similar to blocks 906, 908, 910, 912, 914, and / or 916 with a third DU to prepare at least one third cell of the third DU for LTM for the UE. In some implementations, the CU receives at least one third measurement report (e.g., L3 measurement report(s) such as RRC MeasurementReport message(s)) from the UE. The CU determines to request LTM preparation for the at least one third cell based on the at least one third measurement report. For example, the at least one third measurement report indicates that signal strength and / or quality of the at least one third cell are above a second threshold. In some implementations, the second threshold is predetermined by the CU or preconfigured in the CU. In some implementations, the second threshold (value) is the same as the first threshold (value). In other implementations, the second threshold (value) is different from the first threshold (value).

[0190] The method 900 reduces overhead of managing the LTM-related configurations in the UE and RAN. With the method 900, the UE maintains a single reference configuration for LTM (i.e., the reference LTM configuration), which saves memory of the UE.

[0191] Fig. 10 illustrates an example method 1000, which a DU (e.g., the DU 174 of the base station 104 or 106) can implement, for communicating with a UE (e.g., the UE 102) and a CU (e.g., the CU 172 of the base station 104 or 106).

[0192] The method 1000 begins at block 1002, where the DU receives a first CU-to-DU message, including a reference LTM configuration, to request LTM preparation for a UE from the CU (e.g., events 308, 390 in event 380 in Fig. 4; events 490, 690, 890). At block 1004, the DU generates at least one first LTM configuration based on the reference LTM configuration (e.g., events 310, 390 in event 380 in Fig. 4; events 490, 690, 890). At block 1006, the DU transmits a first DU-to-CU message including the at least one first LTM configuration to the CU (e.g., events 310, 390 in event 380 in Fig. 4; events 490, 690, 890).

[0193] At block 1008, the DU receives a second CU-to-DU message requesting LTM preparation configuration for the UE from the CU (e.g., events 308, 390 in event 380 in Fig. 4; events 490, 690, 890). In some implementations, the second CU-to-DU message does not include a reference LTM configuration. At block 1010, the DU generates at least one second LTM configuration based on the reference LTM configuration (e.g., events 310, 390 in event 380 in Fig. 4; events 490, 690, 890). At block 1012, the DU transmits a second DU-to-CU message including the at least one second LTM configuration to the CU (e.g., events 310, 390 in event 380 in Fig. 4; events 490, 690, 890). At block 1014, the DU performs a random access procedure with the UE (e.g., events 432, 632, 832). At block 1016, the DU communicates with the UE using the reference LTM configuration and one of at least one first LTM configuration (e.g., events 436, 636, 836). Depending on the implementation, blocks 1008, 1010, 1012, and / or 1014 are optional.

[0194] In some implementations, the DU of the method 1000 is the second DU of the method 900, and thus, the descriptions related to the second DU in Fig. 9 can apply to the DU of the method 1000. Likewise, the descriptions for Fig. 10 can apply to Fig. 9.

[0195] In some implementations, the first CU-to-DU message and first DU-to-CU message are a UE Context Setup Request message and UE Context Setup Response message, respectively. In some implementations, the second CU-to-DU message and second DU-to- CU message are a UE Context Modification Request message and UE Context Modification Response message, respectively.

[0196] Fig. 11 illustrates a method 1100, which a CU (e.g., the CU 172 of the base station 104 or 106) can implement, for communicating with a UE (e.g., the UE 102).

[0197] The method 1100 begins at block 1102, where the CU communicates with the UE via a first DU and a first cell (e.g., events 302, 402, 502, 602, 702, 802). The first cell is a serving cell. At block 1104, the CU determines to prepare a second cell for LTM for the UE.The second cell is a non-serving cell. At block 1106, the CU determines whether the first DU operations the second cell. If the CU determines that the first DU does not operate the second cell (i.e., the CU determines that a second DU operates the second cell) at block 1106, the flow proceeds to block 1108. At block 1108, the CU includes a reference LTM configuration in a CU-to-DU message requesting LTM preparation for the UE (e.g., events 490, 480, 680, 690, 681, 880, 890, 881). At block 1110, the CU transmits the CU-to-DU message to the second DU. At block 1112, the CU receives a DU-to-CU message including at least one LTM configuration from the second DU UE (e.g., events 490, 480, 680, 690, 681, 880, 890, 881).

[0198] Otherwise, if the CU determines that the first DU operates the second cell at block 1006, the flow proceeds to block 1114. At block 1114, the CU refrains from including a reference LTM configuration in a CU-to-DU message requesting LTM preparation for the UE. At block 1116, the CU transmits a CU-to-DU message to a first DU (e.g., events 308, 390, 380, 580, 590, 581, 582, 780, 790, 781). At block 1118, the CU receives a DU-to-CU message including at least one LTM configuration from the first DU. The flow proceeds to block 1120 from block 1118 as well as block 1112. At block 1120, the CU transmits the at least one LTM configuration to the UE via the first DU (e.g., events 316, 318, 394, 494, 594, 694, 794, 894). Alternatively, the CU transmits the at least one LTM configuration to the UE via a RAN node (e.g., events 517, 519, 617, 619, 717, 719, 817, 819). In some implementations, the RAN node is another DU or base station.

[0199] In some implementations, the CU-to-DU message and DU-to-CU message are a UE Context Setup Request message and UE Context Setup Response message, respectively.

[0200] Fig. 12A illustrates a method 1200A, which a DU (e.g., the DU 174 of the base station 104 or 106) can implement, for communicating with a UE (e.g., the UE 102).

[0201] The method 1200A begins at block 1202, where the DU receives a CU-to-DU message to request LTM configuration for the UE from a CU (e.g., events 308, 390, 380, 580, 590, 581, 582, 780, 790, 781, 490, 480, 680, 690, 681, 880, 890, 881). At block 1204, the DU determines whether the CU-to-DU message includes a reference LTM configuration. If the DU determines that the CU-to-DU message does not include a reference LTM configuration at block 1204, the flow proceeds to block 1206. At block 1206, the DU generates a reference LTM configuration. At block 1208, the DU generates at least one LTM configuration based on the reference LTM configuration. At block 1210, the DU transmits aDU-to-CU message, including the at least one LTM configuration, to the CU (e.g., events 310, 390, 380, 580, 590, 581, 582, 780, 790, 781, 490, 480, 680, 690, 681, 880, 890, 881). Otherwise, if the DU determines that the CU-to-DU message includes a reference LTM configuration at block 1204, the flow proceeds to block 1208.

[0202] In some implementations, the CU-to-DU message and DU-to-CU message are UE Context Setup Request message and UE Context Setup Response message, respectively.

[0203] Fig. 12B illustrates an example method 1200B similar to the method 1200A, except that the method 1200B includes block 1205. If the DU determines that the CU-to-DU message does not include a reference LTM configuration at block 1204, the flow proceeds to block 1205. At block 1205, the DU determines whether the DU has a reference LTM configuration for the UE. If the DU determines that the DU has a reference LTM configuration for the UE at block 1205, the flow proceeds to block 1208. Otherwise, if the DU determines that the DU does not have a reference LTM configuration for the UE at block 1205, the flow proceeds to block 1206.

[0204] In some implementations, the DU has a reference LTM configuration at block 1205 because the DU receives another CU-to-DU message, including the reference LTM configuration, from the CU before receiving the CU-to-DU message at block 1202. In other implementations, the DU has a reference LTM configuration at block 1205 because the DU generates the reference LTM configuration before receiving the CU-to-DU message at block 1202.

[0205] In some implementations, the DU of the methods 1200A and 1200B is the second DU of the method 900, and, as such, the descriptions related to the second DU in Fig. 9 can apply to the DU of the methods 1200A and 1200B. Likewise, the descriptions for Figs. 12A and 12B can apply to Fig. 9.

[0206] Fig. 13 illustrates an example method 1300, which a CU of a base station (e.g., the CU 172 of the base station 104) can implement, for communicating with a UE (e.g., the UE 102).

[0207] The method 1300 begins at block 1302, where the CU communicates with the UE via a first DU (e.g., events 402, 602, 802). At block 1304, the CU performs at least one first LTM preparation procedure with a second DU to obtain a first reference LTM configuration and at least one first LTM configuration for the UE from the second DU (e.g., events 490, 690, 890). In some implementations, the at least one first LTM configuration is a non-reference LTM configuration. At block 1306, the CU transmits the first reference LTM configuration and at least one first LTM configuration to the UE via the first DU (e.g., events 494, 694, 894). Alternatively, the CU transmits the first reference LTM configuration and at least one first LTM configuration to the UE via a RAN node (e.g., events 617, 619, 817, 819). The RAN node can be another DU or base station.

[0208] At block 1308, the CU performs at least one second LTM preparation procedure with the first DU to obtain a second reference LTM configuration and at least one second LTM configuration for the UE from the first DU (e.g., events 380, 390, 590, 581, 582, 681, 682, 790, 781, 782, 881, 882). In some implementations, the at least one second LTM configuration is a non-reference LTM configuration. At block 1310, the CU transmits the second reference LTM configuration and at least one second LTM configuration to the UE via the first DU (e.g., events 394, 594, 894). Alternatively, the CU transmits the second reference LTM configuration and at least one second LTM configuration to the UE via a RAN node (e.g., events 517, 519, 582, 682, 717, 719, 882). In some implementations, the RAN node is another DU or base station. Depending on the implementation, blocks 1308 and 1310 are optional.

[0209] In some implementations, the at least one first LTM preparation procedure occurs in parallel with the at least one second LTM preparation procedure. In other implementations, the at least one first LTM preparation procedure occurs before the at least one second LTM preparation procedure. In yet other implementations, the at least one first LTM preparation procedure occurs after the at least one second LTM preparation procedure.

[0210] With the method 1300, the first DU and second DU manage the first reference LTM configuration and second reference LTM configuration, respectively. An advantage of the method 1300 is that the LTM preparation for cell(s) of non-serving DUs has no dependency with the LTM preparation for cell(s) of a serving DU. Thus, the CU can prepare cell(s) of a non-serving DU without performing an LTM preparation with the serving DU, simplifying the LTM preparation with non-serving DUs.

[0211] In some implementations, the at least one first LTM preparation procedure includes a UE Context Setup procedure and optionally zero, one, or more UE Context Modification procedures. In some implementations, the at least one second LTM preparation procedure includes one or more UE Context Modification procedures.

[0212] In some implementations, the CU generates a first container (e.g., a field / IE) including the first reference LTM configuration, generates a first message including the first container, and transmits the first message to the UE via the first DU. In some implementations, the CU includes the at least one first LTM configuration in the first container. In other implementations, the CU generates a second container (e.g., a field / IE) including the at least one first LTM configuration. In some implementations, the CU includes the second container in the first message. In further implementations, the CU generates a second message including the second container and transmits the second message to the UE via the first DU.

[0213] In some implementations, the CU generates a third container (e.g., a field / IE) including the second reference LTM configuration, generates a third message including the third container, and transmits the third message to the UE via the first DU. In some implementations, the CU includes the at least one second LTM configuration in the third container. In other implementations, the CU generates a fourth container (e.g., a field / IE) including the at least one second LTM configuration. In some implementations, the CU includes the fourth container in the third message. In further implementations, the CU generates a fourth message including the fourth container and transmits the fourth message to the UE via the first DU.

[0214] In some implementations, the first container and the third container are different fields / IEs and, as such, the UE does not replace the first reference LTM configuration with the second reference LTM configuration. In other implementations, the first container and third container follow the same format (i.e., a field / IE), and the first container and third container include a first ID and a second ID, respectively. The first ID and the second ID follow the same format (i.e., a field / IE), and the CU sets the first ID and second ID to a first value and a second value, respectively. Because the first ID and the second ID have different values, the UE does not replace the first reference LTM configuration with the second reference LTM configuration or vice versa. Because the first ID and the second ID have different values, the UE does not replace the at least one first LTM configuration with the at least one second LTM configuration, or vice versa, if the first container and the third container include the at least one first LTM configuration and the at least one second LTM configuration, respectively. In some implementations, the first ID and the second ID identify the first reference LTM configuration and the second reference LTM configuration, respectively. In other implementations, the first ID and the second ID identify the second DUand the first DU, respectively. In yet other implementations, the first ID and the second ID identify a cell group of the second DU and a cell group of the first DU, respectively. In yet other implementations, the first ID and the second ID identify the first container and third container, respectively.

[0215] In some implementations, the second container and the fourth container are different fields / IEs and, as such, the UE does not replace the at least one first reference LTM configuration with the at least one second LTM configuration. In other implementations, the second container and the fourth container follow the same format (i.e., a field / IE), and the second container and fourth container include a third ID and a fourth ID, respectively. The third ID and the fourth ID follow the same format (i.e., a field / IE), and the CU sets the third ID and the fourth ID to a third value and a fourth value, respectively. Because the third ID and fourth ID have different values, the UE does not replace the at least one first LTM configuration with the at least one second LTM configuration. In some implementations, the third ID and the fourth ID identify the at least one first LTM configuration and the at least one second LTM configuration, respectively. In other implementations, the third ID and the fourth ID identify the second DU and the first DU, respectively. In yet other implementations, the third ID and the fourth ID identify a cell group of the second DU and a cell group of the first DU, respectively. In yet other implementations, the third ID and the fourth ID identify the second container and the fourth container, respectively.

[0216] In some alternative implementations, the second DU generates the first and / or second containers instead of the CU. In such cases, the CU receives the first and / or second containers from the second DU in the at least one first LTM preparation procedure. In some alternative implementations, the first DU generates the third and / or fourth containers instead of the CU. In such cases, the CU receives the third and / or fourth containers from the first DU in the at least one second LTM preparation procedure.

[0217] In some implementations, the descriptions for the first DU and second DU of Eig. 9 can apply to the first DU and second DU of Eig. 13, respectively.

[0218] Eig. 14 illustrates an example method 1400, which one or more DUs (e.g., the S- DU 174A and / or T-DU 174B of the base station 104 or 106 in Eigs. 4, 6, and / or 8) can implement, for communicating with a UE (e.g., the UE 102) and a CU (e.g., the CU 172 of the base station 104 or 106 in Figs. 4, 6, and / or 8).

[0219] The method 1400 begins at block 1402, where a first DU receives a first CU-to-DU message to request LTM preparation for a UE from a CU (e.g., events 490, 690, 890). At block 1404, the first DU generates a first reference LTM configuration (e.g., events 490, 690, 890). At block 1406, the first DU generates at least one first LTM configuration based on the first reference LTM configuration (e.g., events 490, 690, 890). At block 1408, the first DU transmits a first DU-to-CU message, including the at least one first LTM configuration, to the CU (e.g., events 490, 690, 890).

[0220] At block 1410, a second DU receives a second CU-to-DU message requesting LTM preparation configuration for the UE from the CU (e.g., events 390, 681, 682, 881, 882). At block 1412, the second DU generates a second reference LTM configuration (e.g., events 390, 681, 682, 881, 882). At block 1414, the second DU generates at least one second LTM configuration based on the second reference LTM configuration (e.g., events 390, 681, 682, 881, 882). At block 1416, the second DU transmits a second DU-to-CU message, including the at least one second LTM configuration, to the CU (e.g., events 390, 681, 682, 881, 882). At block 1418, the first DU performs a random access procedure with the UE (e.g., events 432, 632, 832). At block 1420, the first DU communicates with the UE using the reference LTM configuration and one of at least one first LTM configuration (e.g., events 436, 636, 836). Depending on the implementation, blocks 1410, 1412, 1414, 1416, 1418, and / or 1420 are optional.

[0221] In some implementations, blocks 1410, 1412, 1414, and 1416 occur in parallel with blocks 1402, 1404, 1406, and 1408. In other implementations, blocks 1410, 1412, 1414, and 1416 occur after blocks 1402, 1404, 1406, and 1408. In yet other implementations, blocks 1410, 1412, 1414, and 1416 occur before blocks 1402, 1404, 1406, and 1408.

[0222] In some implementations, the descriptions for the first DU and second DU of Eigs. 9 and 13 can apply to the second DU and first DU of Eig. 14, respectively. In other implementations, the descriptions for the first DU and second DU of Eigs. 9 and 13 can apply to the first DU and second DU of Eig. 14, respectively. In some implementations, the first DU, the second DU, and the CU form a disaggregated base station.

[0223] In some implementations, the first CU-to-DU message and first DU-to-CU message are a UE Context Setup Request message and UE Context Setup Response message, respectively. In other implementations, the first CU-to-DU message and first DU-to-CU message are a UE Context Modification Request message and UE Context ModificationResponse message, respectively. In some implementations, the second CU-to-DU message and second DU-to-CU message are a UE Context Modification Request message and UE Context Modification Response message, respectively. In other implementations, the second CU-to-DU message and second DU-to-CU message are a UE Context Setup Request message and UE Context Setup Response message, respectively.

[0224] In some implementations, the first DU receives a third CU-to-DU message requesting LTM preparation configuration for the UE from the CU (e.g., events 390, 690, 890). The first DU generates at least one third LTM configuration based on the first reference LTM configuration (e.g., events 390, 690, 890). The first DU transmits a third DU- to-CU message, including the at least one third LTM configuration, to the CU (e.g., events 390, 690, 890). In some implementations, the third CU-to-DU message and third DU-to-CU message are a UE Context Modification Request message and UE Context Modification Response message, respectively.

[0225] The following description may be applied to the description above.

[0226] 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”.

[0227] 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, afemtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an internet-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device can include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0228] 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.

[0229] 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.

[0230] 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 centralized unit (CU) of a distributed base station, the method comprising: determining, at the CU, to prepare a user equipment (UE) for lower layer triggered mobility (LTM) from a first distributed unit (DU) to a second DU; transmitting, to the second DU and responsive to the determining, a reference LTM configuration; receiving, at the CU from the second DU, an LTM configuration based on the reference LTM configuration; and transmitting, from the CU to the UE, the LTM configuration.

2. The method of claim 1, wherein: transmitting the LTM configuration includes transmitting a reconfiguration request including the LTM configuration.

3. The method of claim 1 or 2, further comprising: receiving, from the first DU, the reference LTM configuration.

4. The method of claim 2 or 3, wherein: transmitting the reconfiguration request to the UE includes transmitting the reconfiguration request from the CU to the UE via the first DU.

5. A method implemented in a distributed unit (DU) of a distributed base station, the method comprising: receiving, at the DU from a centralized unit (CU), a reference lower layer triggered mobility (LTM) configuration; generating, at the DU, an LTM configuration based on the reference LTM configuration; and transmitting, from the DU to the CU, the LTM configuration.

6. The method of claim 5, further comprising: receiving, at the DU, a reconfiguration request including the LTM configuration.

7. The method of claim 6, further comprising: transmitting, from the DU to a user equipment (UE), the LTM configuration.

8. The method of claim 7, wherein: transmitting, from the DU to the UE, the LTM configuration includes transmitting a reconfiguration request including the LTM configuration.

9. A method implemented in a centralized unit (CU) of a distributed base station, the method comprising: determining, at the CU, to prepare a first distributed unit (DU) for lower layer triggered mobility; transmitting, from the CU to a second DU, a request for lower layer triggered mobility (LTM) preparation; and receiving, at the CU from the second DU, a reference LTM configuration; and transmitting, to the first DU for a user equipment (UE), an LTM configuration based on the reference LTM configuration.

10. The method of claim 9, wherein: the request includes a user equipment (UE) context setup request.

11. The method of claim 10, wherein: receiving the reference LTM configuration includes receiving a UE context setup response including the LTM configuration.

12. The method of claim 9, wherein: transmitting the LTM configuration includes transmitting a reconfiguration request including the LTM configuration.

13. The method of claim 9, wherein the request is a first request for LTM preparation, the method further comprising: transmitting, from the CU to the second DU, a second request for LTM preparation; andreceiving, at the CU, a non-reference LTM configuration in response to the second request; wherein the LTM configuration based on the reference LTM configuration is the nonreference LTM configuration.

14. The method of claim 12 or 13, wherein: transmitting the reconfiguration request to the UE includes transmitting the reconfiguration request from the CU to the UE via the first DU.

15. A distributed base station comprising processing hardware and configured to implement a method according to any one of the preceding claims.

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