Managing a transmission configuration indicator state for lower layer triggered mobility

Abstract

Methods and devices operate within a radio access network to facilitate a fast serving cell change using a lower layer triggered mobility, LTM, procedure, reducing latency and overhead relative to L3-triggered cell-switching procedures. LTM execution is triggered by an L1 measurement report. Methods and devices according to various embodiments, exchange LTM-related configurations that include an LTM identity, ID, and at least one LTM transmission configuration indicator, TCI, state configuration. The LTM TCI state configuration is associated with the LTM ID, or with a TCI state ID, or with a candidate cell ID.

Description

MANAGING A TRANSMISSION CONFIGURATION INDICATOR STATE FOR LOWER LAYER TRIGGERED MOBILITYCROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of and priority to U.S. Provisional Application Serial No. 63 / 546,984, entitled “MANAGING A TRANSMISSION CONFIGURATION INDICATOR STATE FOR LOWER LAYER TRIGGERED MOBILITY” and filed on November 2, 2024, which is expressly incorporated by reference herein in its entirety.FIELD OF THE DISCLOSURE

[0002] This document relates to wireless communications and, more particularly, to configuring and activating a transmission configuration indicator (TCI) state for a user equipment (UE) before, during, and after lower layer triggered mobility (LTM).BACKGROUND

[0003] This background description is provided for the purpose of generally presenting the context of the embodiments later discussed. 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 document.

[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 3rdGeneration Partnership Project (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 UE, to a base station, BS) as well as in the downlink direction (from the BS to the UE). Further, the PDCP sublayer provides signaling radio bearers (SRBs) and data radio bearers (DRBs) to the Radio Resource Control (RRC) sublayer. Generally speaking, the UEand a BS can use SRBs to exchange RRC messages as well as non-access stratum (NAS) messages, and can use DRBs to transport data on a user plane.

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

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

[0007] When the UE moves from coverage area of one cell to another cell in a RAN, at some point a serving cell change has to be performed for the UE. Toperform 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 a RRC reconfiguration message configuring Reconfiguration with Synchronization (e.g., the RRC reconfiguration message includes a ReconfigurationWithSync IE) for change of the serving cell (e.g., PCell or PSCell). In cases where the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN has to release the at least one SCell due to the change of the PCell or PSCell. The serving cell change involves complete layer 2 (L2) (and layer 1 (L1)) resets, leading to longer latency, larger overhead, and longer interruption time. Thus, 3GPP recently launched a new work item to develop new mobility techniques for serving cell changes. These techniques aim to reduce latency and overhead, and are called lower-layer triggered mobility (LTM) cell switch, or faster serving cell switching. LTM may also be referred to as L1 / L2 triggered mobility.

[0008] The LTM, which is also known as network-triggered mobility or network- initiated mobility, is a technique applicable to the field of mobile networking and wireless communication. It refers to a type of mobility management in which the decision to hand off the UE from one NE or BS to another is primarily determined by the lower layers of the network protocol stack, such as the physical and data link layers. In LTM, the network infrastructure, such as the BSs or NEs, initiates and controls the handover process based on a lower-layer-related (L1) criteria like signal strength, quality, and resource availability. When a UE connection quality deteriorates beyond a certain threshold, the network infrastructure decides to trigger a handoff and directs the UE to switch to a different NE or BS that can provide a better connection.

[0009] This approach is in contrast to higher layer triggered mobility, where the decision to hand off is primarily made by the UE itself or an upper-layer network entity, such as a Mobility Management Entity (MME) in Long Term Evolution (LTE) / 4G or a Mobility Anchor Point in Mobile IP. In higher layer triggered mobility, the UE actively scans for better networks and makes decisions based on higher- layer parameters, such as network load, service quality, or user preferences.

[0010] While the RAN communicates with the UE via a serving cell, the RAN receives one or more layer 3 (e.g., RRC) measurement results from the UE. Basedon the layer 3 (L3) measurement result(s), the RAN determines to configure an LTM candidate cell for LTM cell switch. To configure the LTM candidate cell for the UE, the RAN transmits an LTM configuration configuring the LTM candidate cell to the UE via RRC signaling. Later, the RAN receives one or more layer 1 (L1) measurement results from the UE. Based on the one or more L1 measurement result(s), the RAN determines that the LTM candidate cell qualifies to be a serving cell for the UE. Therefore, the RAN transmits an LTM cell switch command to the UE to command the UE to perform the LTM cell switch to the LTM candidate cell. The UE performs a cell change from the serving cell to the LTM candidate cell in response to the LTM cell switch command. In response to the cell change, the UE disconnects from the serving cell and accesses the LTM candidate cell. After the UE successfully accesses the LTM candidate cell, the UE communicates with the RAN via the LTM candidate cell and the LTM candidate cell becomes a new serving cell for the UE.

[0011] After the RAN configures the LTM candidate cell and before transmitting the LTM cell switch command, the RAN might activate one or more TCI states of the candidate cell in advance, before the candidate cell becomes the serving cell. Note that a TCI state is related to the management of control information used in the downlink (from the BS to the UE) for transmission on physical downlink shared channels (PDSCHs). TCI plays a role in managing beamforming, spatial multiplexing, and other Multiple-Input Multiple-Output (MIMO) techniques to enhance the efficiency and performance of the network. This allows the UE to be DL synchronized with the candidate cell, thereby facilitating a faster cell switch to one of those cells when the UE performs an LTM cell switch to the candidate cell. In 3GPP R2-2311250, a candidate cell TCI states activation / deactivation MAC CE is specified for the RAN to activate and deactivate one or more TCI states of an LTM candidate cell as shown below.AN LTM RRC running change request (CR) is described in 3GPP R2-2310885 and the physical cell identity (PCI) description is provided in 3GPP TS 38.331.

[0012] As described above, the candidate cell identifier, ID, in the MAC CE is 3 bits while the candidate cell ID for the LTM (i.e., ltm-CandidatePCI-r18) is 10 bits to represent a value of 0, ... , 1007. The existing networks are not configured for converting the 10 bits into 3 bits in the candidate cell ID field in the MAC CE. In addition, the existing RAN is not configured to manage TCI states of the candidate cell for the UE after the candidate cell becomes a serving cell for the UE.SUMMARY

[0013] Recently developed mobility techniques known as LTM reduce conventional cell switching latency and overhead because, for the LTM, the UE doesnot require explicit layer-3 RRC signaling. LTM execution may be triggered by an L1 or L2 measurement report. According to various embodiments, an LTM ID is used for identifying both LTM distributed unit, DU, configurations and LTM TCI state configurations. According to other various embodiments, a candidate cell ID, when used for LTM related procedures, is calculated based on a PCI value according to a given formula. Thus, the long bit PCI (e.g., 1O-bit) is converted into a short bit candidate cell ID (e.g., 3-bit) and the LTM commands convey the long bit PCI value via the required short bit field without ambiguity. According to yet other various embodiments, the UE determines whether the candidate cell is a serving cell. Based on this determination, the UE selectively exchanges signals with the RAN, using the one or more of the LTM TCI state configurations.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 A is a block diagram of an example system in which a RAN and a UE can implement the techniques of this document for managing conditional procedures related to LTM procedures;

[0015] FIG. 1 B is a block diagram of an example BS including a centralized unit (CU) and a distributed unit (DU) that can operate in the system of FIG. 1 A;

[0016] FIG. 2 is a block diagram illustrating structural elements of a UE and an BS configured to perform methods for managing LTM configurations and TCI states according to an embodiment.

[0017] FIG. 3 illustrates a first scenario for a UE and a network entity (NE) operating according to an embodiment.

[0018] FIG. 4 illustrates a second scenario for a UE and an NE operating according to another embodiment.

[0019] FIGs. 5A and 5B illustrate third scenarios for UEs and NEs operating according to other embodiments.

[0020] FIGs. 6A and 6B illustrate fourth scenarios for UEs and NEs operating according to yet other embodiments.

[0021] FIGs. 7A and 7B illustrate fifth scenarios for UEs and NEs operating according to some embodiments.

[0022] FIGs. 8A and 8B illustrate sixth scenarios for UEs and NEs operating according to some other embodiments.

[0023] FIGs. 9A to 91 depict flow diagrams illustrating methods performed by the BS according to various embodiments.

[0024] FIGs. 10A to 10C depict flow diagrams illustrating methods performed by a serving DU of the BS according to various embodiments.

[0025] FIGs. 11 A to 11 B depict flow diagrams illustrating methods performed by a target DU according to various embodiments.

[0026] FIGs. 12A to 12C depict flow diagrams illustrating other methods performed by the serving DU of the BS according to various embodiments.

[0027] FIGs. 13A and 13B depict flow diagrams illustrating methods performed by a CU of the BS according to various embodiments.

[0028] FIGs. 14A to 141 depict flow diagrams illustrating methods performed by the UE according to various embodiments.

[0029] FIGs. 15A to 15D depict flow diagrams illustrating other methods performed by the UE, after a target cell becomes a serving cell, according to various embodiments.DETAILED DESCRIPTION OF THE DRAWINGS

[0030] 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 first BS 104, a second BS 106 and a core network (CN) 110. The UE 102 initially connects to the first BS 104. In some scenarios, the first BS 104 can perform an SN addition to configure the UE 102 to operate in dual connectivity (DC) with the first BS 104 and the second BS 106. The first and second BS 104 and 106 operate as an MN and an SN for the UE 102, respectively.

[0031] In various configurations of the wireless communication system 100, the first BS 104 can be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the second BS 106 can be implemented as a secondary gNB (SgNB). The UE 102 can communicate with the first BS 104 and the second BS 106 via the same RAT such as EUTRA or NR, or different RATs. When the first BS 104 is an MeNB and the second BS 106 is a SgNB, the UE 102 can be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0032] In some cases, an MeNB or an SeNB is implemented as an ng-eNB rather than an eNB. When the first BS 104 is a Master ng-eNB (Mng-eNB) and the second BS 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 first BS 104 is an MgNB and the second BS 106 is an SgNB, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the first BS 104 is an MgNB and the second BS 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.

[0033] In the scenarios where the UE 102 hands over from the first BS 104 to the second BS 106, the first and second BS 104 and 106 operate as the source BS (S- BS) and a target BS (T-BS), respectively. The UE 102 can operate in DC with the first BS 104 and an additional BS (not shown in FIG. 1 A) for example prior to the handover. The UE 102 can continue to operate in DC with the second BS 106 and the additional BS or operate in single connectivity (SC) with the second BS 106, after completing the handover. The BSs 104 and 106 in this case operate as a source MN (S-MN) and a target MN (T-MN), respectively.

[0034] A core network (CN) 110 can be an evolved packet core (EPC) 111 or a fifth-generation core (5GC) 160, both of which are depicted in FIG. 1A. The first BS 104 can be an eNB supporting an S1 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 BSs 104 and 106 can support an X2 orXn 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 transferuser-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.

[0035] As illustrated in FIG. 1A, the first BS 104 supports cell 124A, and the second BS 106 supports a cell 126. Note that the shape and sizes of the cells are not at scale and the cells may have various shapes. The cells 124A and 126 can partially overlap, so that the UE 102 can communicate in DC with the first BS 104 and the second BS 106, where one of the BSs 104 and 106 is an MN and the other is an SN. The first BS 104 can support additional cell(s) such as cells 124B and 124C, and the second BS 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 first BS 104. The first BS 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 first BS 104 and the second BS 106, one of the BSs 104 and 106 operates as an MeNB, an Mng-eNB or an MgNB, and the other operates as an SgNB or an Sng-eNB.

[0036] In general, the wireless communication network 100 can include any suitable number of BSs supporting NR cells and / or EUTRA cells. More particularly, the EPC 111 or the 5GC 160 can be connected to any suitable number of BSs 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 document 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.

[0037] With continued reference to FIG. 1A, the first BS 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 PHYcontroller 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 devices via one or more cells (e.g., the cell(s) 124A, 124B and / or 124C) and / or one or more TRPs. The processing hardware 130 in an example implementation includes a MAC controller 134 configured to perform MAC functions with one or more user devices. The MAC functions include a random access (RA) procedure, managing UL timing advance for the one or more user devices, and / or communicating UL / DL MAC PDUs with the one or more user devices. The MAC functions include lower triggered mobility (LTM) related functions as described below. The processing hardware 130 can further include an RRC controller 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 first BS 104 operates as an MN relative to an SN or as an SN relative to an MN. The second BS 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.

[0038] 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 first BS 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 first BS 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 first BS 104 or second BS 106. For example, the MAC functions include a random access procedure, managing UL timing advance for the one or more user devices, and communicating UL / DL MAC PDUs with the first BS 104 or 106. In another example, the MAC functions include LTM related functions as described below. The processing hardware 150 canfurther include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.

[0039] 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 BS) and / or downlink (from a BS to the UE 102) direction.

[0040] FIG. 1 B depicts an example distributed implementation of a BS such as the first BS 104 or 106. The BS 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 second BS 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 second BS 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.

[0041] FIG. 2 is a block diagram illustrating structural elements of a UE and an NE (e.g., BS) configured to perform methods for managing LTM according to an embodiment. NE 204 (which may be operated as 104, 106 in Figure 1A, 170 in Figure 1 B) and UE 102 communicate wirelessly. NE 204 may be a BS, but moregenerally, the term “network entity” stands for a wireless device with a well-defined network functionality (e.g., BS’s functionality is connecting UEs to the core network including managing communications to and from the UEs).

[0042] NE 204 may provide the functionality of an gNB (i.e., a 5G or 6G base station). NE 204’s functionality may be distributed across multiple entities (e.g., a central unit, CU, a distributed unit, DU, and a radio unit, RU). NE 204 includes antennas, a Radio Frequency (RF) front end 281 and a transceiver 282 for communicating with UE 102 and other UEs and NEs. NE 104 / 106’s antennas and RF front end 281 can be tuned to one or more frequency bands (e.g., subcarriers), for example as defined by 3GPP LTE, 5G NR, and 6G communication standards and implemented by transceiver 282.

[0043] NE 204 further includes processor(s) 283 and computer-readable storage media (CRM) 284. Processor(s) 283 can include single or multiple-core processors, and CRM 284 includes any suitable memory / storage except propagating signals. For example, memory / storage can include random-access memory (RAM), static RAM (SRAM), dynamic RAM (DRAM), non-volatile RAM (NVRAM), read-only memory (ROM), and / or flash memory. CRM 214 stores device data 285, which includes network scheduling data, radio resource management data, applications, and / or an operating system, which are executable by processor(s) 283 to enable wireless communication with UE 102 as well as with other NEs and UEs.

[0044] CRM 284 also stores an L1 measurement configurer 286 and LTM control- related executable instructions 287. NE 104 / 106 also includes inter-base station interface 288 and core-network interface 289. Inter-base station interface 288 can be a standardized interface, such as an Xn and / or X2 interface, for exchanging userplane and control-plane data with another NE (e.g., in case of a handover). Corenetwork interface 289 enables NE’s user-plane data and control-plane information exchange with core network functions and / or entities.

[0045] UE 102 includes antennas connected to an RF front end 291 , and a transceiver 292. The UE may include multiple transceivers for supporting various technologies. The antennas and RF front end 291 can be tuned to one or more frequency bands (e.g., subcarriers), for example, as defined by 3GPP LTE, 5G NR, and 6G communication standards and implemented by respective transceivers. UE 102 also includes one or more processor(s) 293, and computer-readable storagemedia (CRM) 294. Processor(s) 293 may be single or multiple-core processors, and CRM 294 includes any suitable memory / storage other than propagating signals. For example, memory / storage can include random-access memory (RAM), static RAM, dynamic RAM, non-volatile RAM, read-only memory (ROM), and / or flash memory. CRM 294 stores device data 295 necessary for UE’s communications, L1 measurement and report generator 296, and LTM-control-related executable instructions 297.

[0046] In some embodiments, the NE’s and the UE’s L1 measurement and LTM execution may be implemented not only as software but also as hardware logic and / or circuitry.

[0047] Next, several example scenarios in which the BS 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 BS. 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 the figures and discussed below, any of the alternative implementations discussed with respect to a particular event (e.g., for messaging and processing) may apply to events labeled with similar reference numbers in other figures.

[0048] Referring first to FIG. 3, in a scenario 300, the first BS 104 includes a CU 172 and a DU 174 and the DU 174 operates the cell 124A. The UE 102 initially communicates 302 with the DU 174 on the cell 124A using a serving DU configuration, and communicates with the CU 172 via the DU 174, e.g., using a serving CU configuration. In other words, the DU 174 is a serving DU that communicates with the UE 102. In some implementations, the UE 102 in carrier aggregation (CA) communicates with the DU 174 on the cell 124A and other cell(s) (e.g., cell 124D not shown in FIG. 1A) using the serving DU configuration. The DU 174 operates the other cell(s). The cell 124A and / or the other cell(s) are serving cell(s) for the UE 102. 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 ormultiple TRPs. In some implementations, the cell 124A can be a PCell. In such cases, the other cell(s) include SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In other implementations, the cell 124A can be a SCell, and one of the other cell(s) is a PCell. In such cases, the rest includes SCell(s) and / or additional cell(s) associated with the PCell or a SCell. In the following description, the first BS 104 can be the DU 174, the CU 172 or the DU 174 and CU 172.

[0049] In the event 302, the UE 102 can transmit UL PDUs and / or UL control signals to the first BS 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 first BS 104 via radio bearers which can include SRBs and / or DRB(s). The first BS 104 can configure the radio bearers to the UE 102. In some implementations, UL control signals include UL control information, channel state information, hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, scheduling request(s) and / or sounding reference signal(s). Similarly, the UE 102 can receive DL PDUs and / or DL control signals from the first BS 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 step, channel state information reference signal(s) (CSI-RS(s)), and / or tracking reference signal(s)). The first BS 104 can transmit the DCIs on physical downlink control channel(s) (PDCCH(s)) monitored by the UE 102, on the cell 124A and / or other cell(s) via one or multiple TRPs.

[0050] In some implementations, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the serving DU configuration includes at least one first non-LTM TCI state configuration for the serving cell(s). The term “at least one first configuration” is used in this document to mean one or more configurations from a given set of configurations (the first set in this example). The term “non-LTM TCI state configuration” means a TCI state configuration that is used with no LTM, i.e. , the TCI state configuration used with legacy 5G networks, for example L3 messaging (higher layer) instead of L1 / L2 messaging (lower layer). Note that the term “at least one” is used in this document to mean one element of the set or plural elements of the set. In some implementations, the DU 174 can transmitthese configuration parameters and / or the first non-LTM TCI state configuration(s) to the CU 172. The CU 172 generates one or more messages (e.g., RRC reconfiguration message(s)) including the configuration parameters and / or the first non-LTM TCI state configuration(s) 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 and / or the first non-LTM TCI state configuration(s) to the UE 102 directly. In some implementations, the serving DU configuration is CellGroupConfig IE 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 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 CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and reporting. In other implementations, the serving CU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and reporting. In some implementations, the UE 102 receives the serving CU configuration or the configuration parameters in the serving CU configuration from the CU 172 via the DU 174. In other implementations, the UE 102 receives a portion of the serving CU configuration and / or a portion of the serving DU configuration from a BS other than the first BS 104 and the remaining portion of these configuration parameters from the first BS 104.

[0051] In some implementations, the UE 102 and DU 174 communicate with each other using the first non-LTM TCI state configuration(s), e.g., in the events 302, 318, 320, 324, 325, 330, and / or 331. In some implementations, the DU 174 transmits at least one first non-LTM TCI states activation / deactivation command to the UE 102 to activate some of the first non-LTM TCI state configuration(s). The UE 102 activates the some of the first non-LTM TCI state configuration(s) in response to the first non- LTM TCI states activation / deactivation command(s). In some implementations, the DU 174 indicates deactivation of some of the first non-LTM TCI state configuration(s) in some of the first non-LTM TCI states activation / deactivation command(s). The UE102 and DU 174 communicate with each other using the activated non-LTM TCI state configuration(s), e.g., in the events 302, 318, 320, 324, 325, 330, and / or 331.

[0052] In some implementations, each of the first non-LTM TCI states activation / deactivation command(s) is a MAC CE. The MAC CE(s) may include one or more TCI states activation / deactivation for UE-specific PDSCH MAC CEs, one or more TCI state indication for UE-specific PDCCH MAC CEs, one or more PUCCH spatial relation activation / deactivation MAC CEs, one or more enhanced TCI states activation / deactivation for UE-specific PDSCH MAC CEs, one or more Enhanced PUCCH Spatial Relation Activation / deactivation MAC CEs, one or more Enhanced TCI states indication for UE-specific PDCCH MAC CEs, one or more PUCCH spatial relation activation / deactivation for multiple TRP PUCCH repetition MAC CEs, and / or one or more unified TCI states activation / deactivation MAC CEs.

[0053] In some implementations, the DU 174 includes a serving cell ID (e.g., a serving cell index; however, while a cell ID is a unique identifier assigned to each cell, the cell index refers to an identifier used to access or reference a specific cell, and a cell index may not be necessarily a unique identifier) in each of the first non- LTM TCI states activation / deactivation command(s) to identify the first non-LTM TCI state configuration(s). Each of the serving cell ID(s) indicates a respective serving cell of the serving cell(s). In some implementations, the serving DU configuration includes the serving cell ID(s) and configures association(s) between the serving cell ID(s) and the first non-LTM TCI state configuration(s).

[0054] While communicating with the first BS 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 (L1) 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 non-serving 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 F1 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 L1 measurement report(s) to the CU 172. The at least one serving cell includes the cell 124A and / or other cell(s), and the at least one nonserving cell includes the cell 124B and / or cell 124C. In some implementations, theserving 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 I E(s)) and / or L1 measurement configuration(s). The L1 measurement configuration(s) (e.g., CSI-MeasConfig I E(s)) can include L1 measurement resource configuration(s) and / or L1 measurement reporting configuration(s). The L1 measurement resource configuration(s) can configure reference signal(s) and / or resources of the reference signal(s) for the UE 102 to measure and obtain L1 measurement results. In some implementations, the reference signal(s) includes CSI-RS(s) and / or Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Step(s) (SSB(s)). For example, the L1 measurement resource configuration(s) is / are CSI-ResourceConfig I E(s). In another example, the L1 measurement reporting configuration(s) configures way(s) the UE 102 uses to transmit L1 measurement results / reports. For example, the L1 measurement report configuration(s) is / are CSI-ReportConfig IE(s). For example, The UE 102 transmits the L3 measurement report(s) to the CU 172 via the DU 174 in accordance with the L3 measurement configuration(s). The UE 102 transmits the L1 measurement report(s) to the DU 174 in accordance with the L1 measurement configuration(s) or L1 measurement reporting configuration(s). In one implementation, the DU 174 does not transmit the L1 measurement report(s) to the CU 172.

[0055] In some implementations, the L1 measurement configuration(s) are new RRC IE(s) defined in 3GPP TS 38.331 for a lower layer triggered mobility (LTM). In some implementations, the L1 measurement resource configuration(s) are new RRC I E(s) defined in 3GPP TS 38.331 for the LTM. In some implementations, the L1 measurement reporting configuration(s) are new RRC I E(s) defined in 3GPP TS 38.331 for the LTM. In some implementations, each of the L1 measurement reporting configuration(s) can include a trigger event configuration configuring a trigger event to trigger the UE 102 to transmit a L1 measurement report. If the UE102 detects the trigger event, the UE 102 transmits a L1 measurement report to the DU 174.

[0056] In some implementations, (each of) the L1 measurement report(s) can include at least one L1 measurement result. In some implementations, the at least L1 measurement result includes at least one L1 -reference signal received power (L1- RSRP) value and / or at least one L1- Signal to Interference Noise Ratio (L1-SINR) value. For each of the L1 measurement report(s), the UE 102 transmits a PUCCH transmission including the L1 measurement report to the DU 174, in some implementations. That is, the UE 102 transmits the each of the L1 measurement report(s) on a PUCCH to the DU 174. In other implementations, for each of the L1 measurement report(s), the UE 102 transmits a PUSCH transmission including the L1 measurement report to the DU 174. That is, the UE 102 transmits the each of the L1 measurement report(s) on a PUSCH to the DU 174. In yet other implementations, the UE 102 transmits a portion of the L1 measurement report(s) on PUCCH(s) and the rest of the L1 measurement report(s) on physical UL shared channel(s) (PUSCH(s)) to the DU 174. That is, for each of the portion of the L1 measurement report(s), the UE 102 transmits a PUCCH transmission including the L1 measurement report to the DU 174, and for each of the rest of the L1 measurement report(s), the UE 102 transmits a PUSCH transmission including the L1 measurement report to the DU 174. In some implementations, each of the L1 measurement report(s) is a part of CSI (i.e. , a CSI component) or CSI. In some implementations, the UE 102 can include other CSI component(s) in (each of) the PUCCH transmission(s) and / or PUSCH transmission(s) described above. In one implementation, the other CSI component(s) include such as a channel quality indicator (CQI), a Precoding Matrix Indicator (PMI), a CSI-RS Resource Indicator (CRI), a SSB Resource Indicator (SSBRI), a Layer Indicator (LI), and / or a Rank Indicator (Rl). In some implementations, the UE 102 does not transmit the L1 measurement report(s) in format of RRC message(s) to the DU 174.

[0057] In some implementations, each of the L3 measurement report(s) can include at least one L3 measurement result. In some implementations, the at least one L3 measurement result includes at least one RSRP (value) and / or at least one SI NR (value). In one implementation, the UE 102 transmits each of the L3 measurement report(s) on a PUSCH to the CU 172 via the DU 174. In someimplementations, each of the L3 measurement report(s) can be a RRC message (e.g., MeasurementReport message). In some implementations, each of the L3 measurement configuration(s) includes a particular measurement identity (e.g., measld) and each of the L3 measurement report(s) includes a particular measurement identity in a particular L3 measurement configuration. When the CU 172 receives a L3 measurement report including a measurement identity and a L3 measurement result from the UE 102 via the DU 174, the CU 172 can determine that the L3 measurement report is associated to a L3 measurement configuration identified by the measurement identity.

[0058] In some alternative implementations, for each of the at least one measurement report (e.g., L1 measurement report(s)), the UE 102 transmits a MAC control element (CE) including the measurement report to the DU 174 in the event 304. To transmit the MAC CE(s), the UE 102 generate one or more MAC PDUs each including one or more of the MAC CE(s) to the DU 174 in the event 304.

[0059] In some implementations, the UE 102 performs measurements on one or more reference signals in accordance with the at least one measurement configuration. The one or more reference signals can include one or more Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Steps (SSBs) and / or one or more CSI-RSs. The UE 102 obtains the at least one L1 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).

[0060] After (e.g., in response to) receiving one or some of the at least one measurement report from the UE 102, the first BS 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 first BS 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 first BS 104 to communicate with the UE 102. In some implementations, the first BS 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 strengthand / or quality of the first cell is above a first predetermined threshold, is better than strength and / or quality of the cell 124A, and / or is better than strength and / or quality of the cell 124A by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. In other implementations, if the L1 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than signal strength and / or quality of the cell 124A, and / or is better than signal strength and / or quality of the cell 124A by a first predetermined threshold, the DU 174 determines to prepare the first cell for the UE 102. Alternatively, the first BS 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.

[0061] In the case that the CU 172 determines to prepare the first cell for LTM, the CU 172 transmits 308 a first CU-to-DU message to the DU 174 to prepare the first cell for the UE 102. In some implementations, the CU 172 includes a cell identity (ID) 1 of the first cell in the first CU-to-DU message to request the DU 174 to prepare the first cell for LTM for the UE 102. For example, the cell ID 1 is cell global identity (CGI). In another example, the cell ID is a portion of the CGI. In yet another example, the cell ID is a physical cell ID (PCI). In some implementations, the CU 172 includes an LTM indicator in the first CU-to-DU message to indicate the DU 174 to prepare the first cell for LTM. In some implementations, the LTM indicator is an LTM Information to be Setup IE or LTM Information to be Modification IE. In response to the first CU-to-DU message, the DU 174 generates a first LTM DU configuration (referred to herein after as LTM DU configuration 1) for the UE 102, which configures the first cell for LTM. The DU 174 then transmits 310 a first DU-to-CU message including the LTM DU configuration 1 to the CU 172 in response to the first CU-to- DU message. In some implementations, the DU 174 can include the cell ID 1 together with the LTM DU configuration 1 in an IE of the first DU-to-CU message to indicate that the LTM DU configuration 1 is associated with the first cell (i.e., the cell ID 1). In the case that the DU 174 determines to prepare the first cell, the DU 174 initiates transmission of the first DU-to-CU message to the CU 172 instead of in response to a CU-to-DU message received from the CU 172.

[0062] In some implementations, the DU 174 includes, in the first DU-to-CU message, the cell ID of the first cell associated with the LTM DU configuration 1 to indicate that the LTM DU configuration 1 is configured for or associated with the firstcell. The CU 172 identifies the LTM DU configuration 1 is configured for or associated with the first cell. In some scenarios and implementations, the CU 172 can include additional cell ID(s) (e.g., cell ID(s) 2, ..., N) in the first CU-to-DU message to prepare additional cell(s) (e.g., cell(s) 2, ... , N) for LTM for the UE 102, and the DU 174 includes additional LTM DU configuration(s) (e.g., LTM DU configuration(s) 2, ..., N) each configuring a particular cell of the additional cell(s), as described below. In such cases, the DU 174 includes, in the first DU-to-CU message, the additional cell ID(s) respectively associated with the additional LTM DU configuration(s) to indicate which LTM DU configuration is associated to which cell (ID). The cell(s) 1 and / or 2, ... , N are candidate cell(s).

[0063] In some implementations, the CU 172 does not include a (reference) LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, ... , N (i.e., non-reference LTM DU configuration(s)) based on the reference LTM DU configuration, and includes the reference LTM DU configuration in the first DU-to-CU message. In other implementations, the CU 172 includes a reference LTM DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates the LTM DU configuration(s) 1 , and / or 2, ..., N which are delta configuration(s) to augment the reference LTM DU configuration. In yet other implementations, the CU 172 includes a reference LTM DU configuration (e.g., a first reference LTM DU configuration) in the first CU-to-DU message. In such cases, the DU 174 generates a reference LTM DU configuration (e.g., a second reference LTM DU configuration) replacing the first reference LTM DU configuration, generates the LTM DU configuration(s) 1 and / or 2, ... , N based on the second reference LTM DU configuration, and includes the second reference LTM DU configuration in the first DU-to-CU message.

[0064] In some implementations, the reference LTM DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some implementations, the reference LTM DU configuration is CellGroupConfig IE defined in 3GPP TS 38.331. In other implementations, the reference LTM DU configuration includes configuration parameters in the CellGroupConfig IE. In some implementations, the reference LTMDU configuration includes a CSI-MeasConfig IE or configuration parameters for channel state information (CSI) measurement and / or reporting.

[0065] In some implementations, the reference LTM DU configuration is different from the serving DU configuration. In some implementations, a portion of the reference LTM DU configuration is the same as a portion of the serving DU configuration and the rest of the reference LTM DU configuration is different from the rest of the serving DU configuration. In other implementations, the reference LTM DU configuration is the same as the serving DU configuration.

[0066] After receiving the first DU-to-CU message, the CU 172 generates a RRC reconfiguration message (e.g., an RRCReconfiguration message) including the LTM DU configuration 1 and transmits 316 a second CU-to-DU message including the RRC reconfiguration message to the DU 174. In some implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316. In other implementations, the CU 172 does not include a / the reference LTM DU configuration in the RRC reconfiguration message 316. In some implementations, if the CU 172 transmits the reference LTM DU configuration to the UE 102 during the event 302, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316. In other implementations, if the CU 172 receives the reference LTM DU configuration from the DU 174, the CU 172 includes the LTM DU configuration in the RRC reconfiguration message 316. Otherwise, if the CU 172 does not receive a reference LTM DU configuration from the DU 174, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message 316.

[0067] In some implementations, the CU 172 includes the LTM DU configuration 1 and / or the LTM CU configuration 1 in a first container (e.g., a field / IE) and includes the first container (e.g., LTM configuration 1) in the RRC reconfiguration message of the events 316 and 318. In such cases, the CU 172 generates the first container. The first container is to indicate the UE 102 not to apply the LTM DU configuration 1 and / or the LTM CU configuration 1 immediately. In some scenarios or implementations, the UE 102 receives a RRC reconfiguration message (e.g., the RRC reconfiguration message of the event 318) including a configuration (e.g., the LTM DU configuration 1). If the configuration is included in the first container, the UE 102 refrains from immediately applying the configuration. Otherwise, if theconfiguration is not included in the first container, the UE 102 can apply the configuration immediately. In some implementations, the first container includes or is a first addition or modification list (e.g., Itm-CandidateToAddModList e or LTM- CandidateToAddModList IE). The CU 172 includes the LTM DU configuration 1 and / or the LTM CU configuration 1 in a first element (referred to herein after as element 1) of the first addition or modification list. In some implementations, the CU 172 generates an RRC message (e.g., RRCRecconfiguration message) including the LTM DU configuration 1 and / or the LTM CU configuration 1 , and includes the RRC message in the element 1. In some implementations, the element 1 is an addition or modification IE (e.g., LTM-ConfigToAddMod IE, LTM-Candidate IE, LTM- CandidateToAddMod IE or LTM-CandidateConfigToAddMod IE). When the UE 102 receives the first addition or modification list, the UE 102 can store the first addition or modification list, e.g., in a variable in its random access memory (RAM). In other alternative implementations, the DU 174 generates the first container and includes the first container in the first DU-to-CU message. In yet other alternative implementations, the DU 174 generates the element 1 and includes the element 1 in the first DU-to-CU message.

[0068] In some implementations, the CU 172 includes an LTM CU configuration 1 in the RRC reconfiguration message 316, the first container or the element 1 , where the LTM CU configuration 1 associated with the LTM DU configuration 1. To associate the LTM CU configuration 1 with the LTM DU configuration 1 , the CU 172 can include the LTM CU configuration 1 and the LTM DU configuration in the element 1. In some implementations, the CU 172 includes LTM CU configuration(s) 2, ..., N in the RRC reconfiguration message 316 or the second container, where the LTM CU configuration(s) 2, ... , N associated with the LTM DU configuration(s) 2, ..., N, respectively. To associate the LTM CU configuration(s) 2, ... , N with the LTM DU configuration(s) 2, ..., N , the CU 172 can include the LTM CU configuration(s) 2, ..., N and the LTM DU configuration(s) in the element(s) 2, ... , N, respectively. In other implementations, the CU 172 includes, in the element(s) 2, ... , N, the LTM CU configuration(s) 2, ..., N associated with the LTM DU configuration(s) 2, .... N, respectively. Alternatively, the CU 172 does not include, in the RRC reconfiguration message 316, LTM CU configuration(s) for some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ... , N.

[0069] After receiving the RRC reconfiguration message 316, the DU 174 transmits 318 the RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 a RRC reconfiguration complete message (e.g., an RRCReconfigurationComplete message) to the DU 174, which in turn transmits 322 a second DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some implementations, the CU 172 performs security protection (e.g., integrity protection and / or encryption) on the RRC reconfiguration message. For example, the CU 172 generates a message authentication code for integrity (MAC-I) for the RRC reconfiguration message, encrypts the RRC reconfiguration message and the MAC-I to obtain an encrypted RRC reconfiguration message and an encrypted MAC-I, and transmits a PDCP PDU including the encrypted RRC reconfiguration message and encrypted MAC-I to the UE 102 via the DU 174 in the events 316 and 318. When the UE 102 receives the PDCP PDU from the CU 172 via the DU 174 (i.e. , events 316 and 318), the UE 102 decrypts the encrypted RRC reconfiguration and encrypted MAC-I to obtain the RRC reconfiguration message and MAC-I and verifies whether the MAC-I is valid. If the UE 102 verifies the MAC-I is invalid, the UE 102 discards or ignores the RRC reconfiguration message. In some implementations, the UE 102 can perform a RRC connection reestablishment procedure in response to the invalid MAC-I. Otherwise, if the UE 102 verifies the MAC-I is valid, the UE 102 can process the RRC reconfiguration. The UE 102 refrains from applying (i.e., executing) the LTM DU configuration 1 until receiving an LTM command activating the LTM DU configuration 1 as described for events 330, 350.

[0070] 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.

[0071] In some implementations, the first CU-to-DU message is a UE Context Modification Request message, and the first DU-to-CU message is a UE Context Modification Response message or UE Context Modification Required message. In the case of the UE Context Modification Required message, the CU 172 can transmit a UE Context Modification Confirm message to the DU 174 in response to UE Context Modification Required message. In some implementations, the second CU- to-DU message is a DL RRC Message Transfer message. In other implementations,the second CU-to-DU message is a UE Context Modification Request message. In some implementations, the second DU-to-CU message is a UL RRC Message Transfer message. In other implementations, the second DU-to-CU message is a UE Context Modification Response message.

[0072] In some implementations, the CU 172 can include a reference LTM CU configuration in the RRC reconfiguration message 316 or the first container. In some implementations, the CU 172 might generate the LTM CU configuration 1 (i.e., nonreference LTM CU configuration) as a delta configuration to augment the reference LTM CU configuration. Similarly, the CU 172 might generate some or all of the LTM CU configuration(s) 2, ..., N as delta configuration(s) to augment the reference LTM CU configuration. Alternatively, in the RRC reconfiguration message 316 or the first container, the CU 172 includes the reference LTM CU configuration and does not include a non-reference LTM CU configuration. In some implementations, the CU 172 includes the reference LTM CU configuration and / or the reference LTM DU configuration in an additional container (e.g., reference LTM configuration) and include the additional container in the RRC reconfiguration message 316.

[0073] In some implementations, the reference LTM CU configuration is different from the serving CU configuration. In some implementations, a portion of the reference LTM CU configuration is the same as a portion of the serving CU configuration and the rest of the reference LTM CU configuration is different from the rest of the serving CU configuration. In yet other implementations, the reference LTM CU configuration is the same as the serving LTM CU configuration.

[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 DU configuration 1 or the element 1. In some implementations, the CU 172 includes the ID 1 in the first container or element 1 . In some implementations, the CU 172 assigns the ID 1 .

[0075] In some implementations, the CU 172 can transmit the ID 1 to the DU 174, and the DU 174 associates the ID 1 with the LTM DU configuration 1 and / or the cell ID 1. In some implementations, the CU 172 includes the ID 1 in the first CU-to-DU message. In other implementations, after receiving the first DU-to-CU message, the CU 172 transmits 312 a third CU-to-DU message including the ID 1 to the DU 174 instead of including the ID 1 in the first CU-to-DU message. In someimplementations, in the third CU-to-DU message, the Gil 172 can include the LTM DU configuration 1 and the ID 1 and indicate the association between the ID 1 and LTM DU configuration 1. Thus, the DU 174 can directly associate the ID 1 with the LTM DU configuration 1. In other implementations, in the third CU-to-DU message, the CU 172 can include the cell ID 1 and the ID 1 (i.e. , the first LTM ID) and indicate the association between the cell ID 1 and the ID 1. Thus, the DU 174 can associate the ID 1 with the LTM DU configuration 1 , based on the association between the cell ID 1 and the ID 1 and the association between the cell ID 1 and the LTM DU configuration 1 . In yet other implementations, in the third CU-to-DU message, the CU 172 can include the LTM DU configuration 1 , the cell ID 1 and / or the ID 1 and indicate the association between the ID 1 , LTM DU configuration 1 and / or the cell ID 1. In some implementations, the DU 174 can transmit 314 a third DU-to-CU message to the CU 172 in response to the third CU-to-DU message. In some implementations, the third CU-to-DU message and third DU-to-CU message are UE Context Modification Request message and UE Context Modification Response message. In some implementations, the CU 172 can include the ID 1 , the cell ID 1 and / or the LTM DU configuration 1 in the second CU-to-DU message as described above. Thus, the third CU-to-DU message can be omitted. In some implementations, the third DU-to-CU message is a UE Context Modification Required message. In such cases, the CU 172 transmits a UE Context Modification Confirm message to the DU 174 in response to the UE Context Modification Required message.

[0076] In some implementations, the events 312 (optional) and / or 314 (optional) are collectively referred to in FIG. 3 as an LTM ID assignment procedure 392.

[0077] In the case that the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 can include the ID 1 in the LTM DU configuration 1 , first container or element 1. Alternatively, the DU 174 does not include the ID 1 in the LTM DU configuration 1 , first container and / or element 1 .

[0078] In some implementations, the CU 172 includes the reference LTM DU configuration in the first container. For example, the CU 172 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In other implementations, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316 and outside the first container. For example, the CU 172 generates athird container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the third container in the RRC reconfiguration message 316. In yet other implementations, the DU 174 includes the reference LTM DU configuration in the first container. For example, the DU 174 includes the reference LTM DU configuration in a field of the first container, different from a field of the first container including the LTM DU configuration 1. In yet other implementations, the DU 174 generates a fourth container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the fourth container in the first DU-to-CU message 310. In such cases, the CU 172 includes the fourth container in the RRC reconfiguration message 316. Alternatively, the CU 172 retrieves the reference LTM DU configuration and the LTM DU configuration 1 from the fourth container and includes the reference LTM DU configuration and the LTM DU configuration 1 as described above.

[0079] In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM DU configuration. In some implementations, neither the CU 172 nor the DU 174 assign an ID to identify the reference LTM CU configuration.

[0080] In some implementations, the LTM DU configuration 1 includes a plurality of configuration parameters for the UE 102 to communicate with the DU 174 on the first cell. In some implementations, the plurality of configuration parameters include physical layer configuration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE) and / or RLC configuration parameters (e.g., RLC-BearerConfig I E(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 I E(s)). In some implementations, the LTM DU configuration 1 is CellGroupConfig IE defined in 3GPP TS 38.331. In other implementations, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0081] In some implementations, the LTM CU configuration 1 includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some implementations, the LTM CU configuration 1 includes a MeasConfig IE and / or a RadioBearerConfig IE defined in 3GPP TS 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some implementations, the LTM DU configuration 1includes L1 measurement configuration 1 (e.g., a CSI-MeasConfig IE) and / or at least one configuration indicator (TCI) state configuration. In other implementations, the LTM CU configuration 1 includes the L1 measurement configuration and / or the TCI state configuration(s) 1. In some implementations, the L1 measurement configuration includes at least one reference signal (RS) resource configuration 1 and / or at least one report configuration 1. In some implementations, the RS resource configuration(s) 1 configures one or more RSs or one or more RS resources associated with the cell 1. The RS(s) includes SSB(s) and / or CSI-RS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the RS resource configuration(s) 1 includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) 1 is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PLISCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. In some implementations, each of the TCI state configuration(s) 1 configures a TCI state that associates one or two DL RSs with a corresponding quasi-colocation (QCL) type. The DL RS(s) are associated with the cell 1.

[0082] In some implementations, the DU 174 includes the L1 measurement configuration 1 and / or the TCI state configuration(s) 1 in a serving DU configuration 1 (e.g., non-LTM DU configuration). In some implementations, the DU 174 includes the serving DU configuration in the first DU-to-CU message. In other implementations, the DU 174 transmits an additional DU-to-CU message including the serving DU configuration to the CU 172. In some implementations, the additional DU-to-CU message is a UE Context Modification Required message. In some implementations, the CU 172 includes the serving DU configuration 1 in the RRC reconfiguration message 316, 318. In other implementations, the CU 172 transmits another RRC reconfiguration message including the serving DU configuration to the UE 102 via the DU 174.

[0083] In some implementations, the DU 174 includes a random access configuration in the LTM DU configuration 1. In other implementations, the DU 174does not include a random access configuration in the LTM DU configuration 1. In some implementations, if the cell 124A and first cell are not synchronized, the DU 174 determines to include the random access configuration in the LTM DU configuration 1 . Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the random access configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the random access configuration in the LTM DU configuration 1. If the LTM DU configuration 1 includes the random access configuration, the UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration, as described below. Otherwise, if the LTM DU configuration 1 does not include the random access configuration or indicates the UE 102 to skip a random access procedure in LTM, the UE 102 skips or refrains from performing the random access procedure of the event 332 in response to the LTM DU configuration 1 excluding the random access configuration.

[0084] In some implementations, the DU 174 includes random access configuration parameters in the LTM DU configuration 1 and / or the reference LTM DU configuration regardless of whether the cell 124A and first cell are synchronized or not. The UE 102 performs the random access procedure in the event 332 in accordance with the random access configuration parameters, as described below. In some implementations, the random access configuration parameters configure physical random access channel (PRACH) resources, an association between SSB and PRACH resources, and / or one or more PRACH occasions.

[0085] In some implementations, if the cell 124A and first cell are synchronized, the DU 174 determines to include, in the LTM DU configuration 1 , a first indication configuring the UE 102 not to perform a random access procedure on the first cell. Otherwise, if the cell 124A and first cell are not synchronized, the DU 174 determines to not include the first indication in the LTM DU configuration 1 . In other implementations, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to include the first indication in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has notsynchronized in UL with the first cell, the DU 174 determines to not include the first indication in the LTM DU configuration 1. If the LTM DU configuration 1 includes the first indication, the UE 102 skips or refrains from performing the random access procedure of the event 332 in accordance with or in response to the first indication. Otherwise, if the LTM DU configuration 1 does not include the first indication, the UE 102 performs the random access procedure in accordance with the random access configuration in the event 332, in response to the LTM DU configuration 1 excluding the first indication, as described below.

[0086] In some implementations, the DU 174 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In other implementations, the DU 174 does not include a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) in the LTM DU configuration 1 or special cell configuration. In some implementations, the DU 174 includes an LTM cell switch information in the first LTM DU configuration 1. In some implementations, the DU 174 includes the random access configuration (parameters) in the LTM cell switch information (e.g., Itm-CellSwitchlnfo field or LTM- Cell Switch Info IE). In some implementations, if the cell 124A and first cell are not synchronized, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the cell 124A and first cell are synchronized, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1. In other implementations, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to include the reconfiguration with sync configuration in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to not include the reconfiguration with sync configuration in the LTM DU configuration 1 . In some implementations, if the LTM DU configuration 1 includes the reconfiguration with sync configuration, the UE 102 performs the random access procedure in the event 332 as described below, in response to or in accordance with the reconfiguration with sync configuration. Otherwise, if the LTM DU configuration 1 does not include the reconfiguration with sync configuration, the UE 102 skips or refrains from performing the random access procedure of the event 332. In some implementations, the DU 174 includes a cell ID (i.e., cell ID 1) of cell 1 (i.e., the firstcell) in the LTM DU configuration 1. In one implementation, the cell ID 1 can be a PCI. In another implementation, the cell ID 1 is a CGI. In some implementations, the cell ID 1 included in the LTM DU configuration 1 is a PCI, while the cell ID 1 included in the first CU-to-DU message is a CGI. In some further implementations, the LTM DU configuration 1 includes a cell index 1 indexing the cell ID 1 or the first cell. The cell index 1 is not a cell ID. The cell index takes fewer bits than the cell ID. In some implementations, the CU 172 sets the cell index 1 to a value and includes the cell index 1 in the first CU-to-DU message of the event 308.

[0087] 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 first BS 104 (i.e., the CU 172 or DU 174) determines to prepare additional cell(s) (i.e., cell(s) 2, ... , N) of the first BS 104 for LTM for the UE 102. In one implementation, the first BS 104 determines to prepare the additional cell(s) for LTM for the UE 102 because the at least one measurement report indicates that the additional cell(s) could be used by the first BS 104 to communicate with the UE 102. The additional cell(s) can include the cell 124C and / or cell(s) other than the cells 124A, 124B and 124C. In some implementations, if the L3 measurement report(s) indicates that signal strength and / or quality of a particular cell of the additional cell(s) is above a respective predetermined threshold and / or is better than the cell 124A, the CU 172 determines to prepare the particular cell for LTM for the UE 102. In other implementations, if the L1 measurement report(s) indicates that signal strength and / or quality of a particular cell of the additional cell(s) is above a first predetermined threshold and / or is better than the cell 124A, the DU 174 determines to prepare the particular cell for LTM for the UE 102. In one implementation, the respective predetermined threshold(s) for the additional cells can be different from the first predetermined threshold. In another implementation, the respective predetermined threshold(s) for the additional cell(s) can be the same as the first predetermined threshold. In some implementations, the respective predetermined thresholds for the additional cells can be the same or different. Alternatively, the first BS 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.

[0088] In the case that the CU 172 determines to prepare the additional cell(s), the CU 172 initiates and performs at least one additional LTM preparation procedure(LTM preparation procedure(s)) with the DU 174 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390. In the case that the DU 174 determines to prepare the additional cell(s), the DU 174 initiates and performs at least one additional LTM preparation procedure (LTM preparation procedure(s)) with the CU 172 to prepare the additional cell(s) for LTM, where each of the LTM preparation procedure(s) is similar to the procedure 390.

[0089] In some implementations, the CU 172 and DU 174 perform LTM preparation procedure(s) 2, ... , N to prepare the cell(s) 2, ... , N, respectively, similar to the procedure 390. The CU 172 can include the cell ID(s) 2, ... , N in CU-to-DU message(s) 2, ..., N in the LTM preparation procedure(s) 2, ... , N, respectively, similar to the first CU-to-DU message. In the LTM preparation procedure(s) 2, ..., N, the DU 174 generates LTM DU configuration(s) 2, ... , N configuring the cell(s) 2, ... , N and includes the LTM DU configuration(s) 2, ... , N in DU-to-CU message(s) 2, ... , N, respectively, as described for the LTM DU configuration 1 . In the case that the DU 174 receives the CU-to-DU message(s) 2, ... , N, the DU-to-CU message(s) 2, ... , N responds to the CU-to-DU message(s) 2, .... N, respectively. “N” is an integer and larger than one. For example, “N” is 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 , 12, 13 14, 15 or 16. In another example, the maximum number of “N” is 4, 8, 16 or 32. Examples and implementations of the LTM DU configuration 1 can apply to the LTM DU configuration(s) 2, ..., N.

[0090] In other implementations, the CU 172 and DU 174 performs a single LTM preparation procedure (i.e. , the LTM preparation procedure 390) to prepare the cell(s) 1 , 2, ..., N. In such cases, the DU 174 includes the LTM DU configuration(s) 1 , 2, ... , N for the cell(s) 1 , 2, ... , N, respectively in the first DU-to-CU message. In the first DU-to-CU message, the DU 174 can include the cell ID(s) 1 , 2, .... N respectively associated with the LTM DU configuration(s) 1 , 2, ... , N to indicate that the LTM DU configuration(s) 1 , 2, ..., N are configured for the cell ID(s) 1 , 2, ..., N, respectively. In the case that the CU 172 determines to perform the LTM preparation procedure 390, the CU 172 includes the cell ID(s) 1 , 2, ..., N in the first CU-to-DU message to request the DU 174 to prepare the cell(s) 1 , 2, ..., N, respectively, for LTM.

[0091] After receiving the LTM DU configuration(s) 2, ... , N from the DU 174, the CU 172 can include the LTM DU configuration(s) 2, ..., N in the first container. Insome implementations, the CU 172 can include the LTM DU configuration(s) 2, N in element(s) 2, N, respectively, and includes the element(s) 2, ... , N in the first container. In some implementations, the CU 172 includes, in the RRC reconfiguration message, LTM ID(s) (i.e. , ID(s) 2, ..., N) for identifying the LTM DU configuration(s) 2, ..., N, respectively. In some implementations, the CU 172 includes the ID(s) 2, ... , N in the first container. For example, the CU 172 can include the ID(s) 2, ... , N and LTM DU configuration(s) 2, ..., N in the element(s) 2, ... , N in the first addition or modification list.

[0092] In some implementations, the CU 172 assigns the ID(s) 2, ... , N for the LTM DU configuration(s) 2, ... , N, respectively. In other implementations, the CU 172 receives the ID(s) 2, ... , N from the DU 174 in the first DU-to-CU message of the procedure 390. In yet other implementations, the CU 172 receives from the DU 174 the ID(s) 2, ... , N in the DU-to-CU message(s) 2, ... , N of the LTM preparation procedure(s) 2, ... , N, respectively.

[0093] In some implementations, the CU 172 can perform an LTM ID assignment procedure with the DU 174 for each of the LTM DU configuration(s) 2, ... , N, similar to the procedure 392. In other implementations, the CU 172 can include the ID(s) 2, ... , N and the LTM DU configuration(s) 2, ... , N in the third CU-to-DU message and indicate the association between the ID(s) 2, ... , N and the LTM DU configuration(s) 2, ..., N, respectively. Thus, the DU 174 can associate the LTM DU configuration(s) 2, ..., N with the ID(s) 2, ... , N, respectively. In yet other implementations, the CU 172 can include the cell ID(s) 2, ..., N and the ID(s) 2, ..., N in the third CU-to-DU message and indicate the association between the cell ID(s) 2, ... , N and the ID(s) 2, ... , N, respectively. Thus, the DU 174 can associate the LTM DU configuration(s) 2, ... , N with the ID(s) 2, ..., N, respectively, based on the association between the cell ID(s) 2, ..., N and the ID(s) 2, .... N and the association between the cell ID(s) 2, .... N and the LTM DU configuration(s) 2, ... , N, respectively. In other implementations, the CU 172 can include the ID(s) 2, ..., N, the cell ID(s) 2, ... , N and / or the LTM DU configuration(s) 2, ..., N in the second CU-to-DU message as described above.Thus, the third CU-to-DU message can be omitted. In yet other implementations, the CU 172 can include the ID(s) 2, ... , N in the first CU-to-DU message and indicate the ID(s) 2, ..., N is / are respectively associated with the cell ID(s) 2, ... , N. In one implementation, the DU 174 includes the ID(s) 2, ... , N in the LTM DUconfiguration(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.

[0094] In some alternative implementations, the DU 174 assigns the ID(s) 2, ... , N. In some implementations, the DU 174 includes the ID(s) 2, ..., N in the first DU-to- CU message of the procedure 390. In yet other implementations, the DU 174 includes the ID(s) 2, ... , N in the DU-to-CU message(s) 2, ... , N of the LTM preparation procedure(s) 2, ... , N. The CU 172 can include the ID(s) 2, .... N in the RRC reconfiguration message. In other implementations, the DU 174 includes the ID(s) 2, ..., N in the LTM DU configuration(s) 2, ... , N. Thus, the CU 172 does not include an ID (e.g., LTM ID) identifying each of the LTM DU configuration(s) 2, ... , N in the RRC reconfiguration message, first container and / or element 1 .

[0095] In some alternative implementations, the CU 172 can generate a second container including the LTM DU configuration(s) 2, ... , N or element(s) 2, ... , N instead of using the first container. The CU 172 then transmits an additional RRC reconfiguration message including the second container to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits an additional RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some implementations, the second container can be a second addition or modification list (e.g., Itm-ConfigToAddModList field, LTM-ConfigToAddModList IE, ltm-CandidateConfigToAddModList^e\d, or LTM- CandidateConfigToAddModList IE), and each of the element(s) 2, ... , N can be an addition or modification IE (e.g., Itm-ConfigToAddMod field, LTM-ConfigToAddMod IE, Itm-CandidateConfigToAddMod field, or LTM-CandidateConfigToAddMod IE). When the UE 102 receives the second addition or modification list, the UE 102 can store the second addition or modification list together with the first addition or modification list, e.g., in a variable in its random access memory (RAM).

[0096] In some implementations, the DU 174 includes cell ID(s) 2, ..., N in the LTM DU configuration(s) 2, ... , N to identify the cell(s) 2, ..., N, respectively. In one implementation, each of the cell ID(s) 2, ... , N is a PCI. In some further implementations, the LTM DU configuration(s) 2, ... , N includes cell index(es) 2 , ... , N indexing the cell ID(s) 2, ..., N or the cell(s) 2, ..., N, respectively. In the case that the CU 172 prepares the cell(s) 2, ... , N for LTM in the procedure 390, the CU 172 can set the cell index(es) 2, ... , N to different value(s) and include the cell index(es)2, ... , N in the first CU-to CU-to-DU message of the event 308. I n the case that the CU 172 prepares the cell(s) 2, .... N in the additional LTM preparation procedure(s), the CU 172 can set the cell index(es) 2, ... , N to different values and include the cell index(es) 2, N in CU-to-DU message(s) of the additional LTM preparation procedure(s). The CU 172 sets the cell index(es) 1 , N to different values. In some implementations, the cell ID(s) 1 , ... , N in the LTM DU configuration(s) 1 , ... , N are different from the cell ID(s) 1 , ... , N in the CU-to-DU message(s) described above.

[0097] In some implementations, each of the LTM DU configuration(s) 1 , .... N includes physical configuration parameters, MAC configuration parameters, RLC configuration parameters and / or L1 measurement configuration(s). In some implementations, each of the LTM DU configuration(s) 1 , ..., N can be a CellGroupConfig IE as defined in 3GPP TS 38.331. In other implementations, each of the LTM DU configuration(s) 1 , ..., N include configuration parameters included in a CellGroupConfig IE as defined in 3GPP TS 38.331. In some further implementations, the plurality of configuration parameters in each of the LTM DU configuration(s) include a particular special cell configuration (e.g., SpCellConflg IE) and / or one or more SCell configurations (e.g., SCellConfig I E(s)). In some implementations, the LTM DU configuration(s) 1 , ... , N are CellGroupConfig IE(s) defined in 3GPP TS 38.331. In other implementations, the LTM DU configuration(s) 1 , ..., N include configuration parameters in the CellGroupConfig IE.

[0098] In some implementations, the CU 172 can include one or more additional LTM CU configurations in at least one of the element(s) 2, ..., N, the first container or the second container. Each of the additional LTM CU configurations are associated with a particular LTM DU configuration of the LTM DU configuration(s) 2, ... , N. Examples and implementations of the additional LTM CU configurations are similar to the LTM CU configuration 1 .

[0099] In some implementations, the CU 172 determines to release the LTM DU configuration M of the LTM DU configuration(s) 1 , ..., N (or the element M of the element(s) 1 , ... , M). 1 < M < N. In response to the determination, the CU 172 transmits a RRC reconfiguration message to the UE 102 via the DU 174 to indicate the UE 102 to release the LTM DU configuration M or element M. In one implementation, the CU 172 generates a release list including the ID (i.e., LTM ID) M for releasing the LTM DU configuration M or element M and includes the release listin the RRC reconfiguration message. In response to the RRC reconfiguration message, the UE 102 releases the LTM DU configuration M or element M and transmits a RRC reconfiguration complete message to the CU 172 via the DU 174. In response to the determination, the CU 172 transmits a CU-to-DU message to the DU 174 to indicate the DU 174 to release the LTM DU configuration M. To indicate the DU 174 to release the LTM DU configuration M, the CU 172 can include the cell ID M or the ID (i.e., LTM ID) M in a release indication (e.g., a field or IE) in the CU-to- DU message. In response, the DU 174 releases the LTM DU configuration M and transmits a DU-to-CU message to the CU 172. In some implementations, the CU-to- DU message and DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively.

[0100] In other implementations, the DU 174 determines to release the LTM DU configuration K. In response to the determination, the DU 174 transmits a DU-to-CU message to the CU 172 to release the LTM DU configuration K. To indicate the LTM DU configuration K is released, the DU 174 can include the cell ID K or the ID (i.e., LTM ID) K in a release indication (e.g., a field or IE) in the DU-to-CU message. 1 < K < N. After (e.g., in response to) receiving the DU-to-CU message, the CU 172 generates a release list including the ID (i.e., LTM ID) K to release the LTM DU configuration K or element K and transmits a RRC reconfiguration message including the release list to the UE 102 via the DU 174. In response, the UE 102 releases the LTM DU configuration K or element K and transmits a RRC reconfiguration complete message to the UE 102 via the DU 174. The CU 172 can transmit a CU-to-DU message to the DU 174 in response to the DU-to-CU message. In some implementations, the DU-to-CU message and CU-to-DU message are a UE Context Modification Required message and a UE Context Modification Confirm message, respectively.

[0101] After receiving the RRC reconfiguration in the event 318 or transmitting the RRC reconfiguration complete message in the event 320, the UE 102 transmits 324 at least one measurement report to the DU 174, similar to the event 304. In some implementations, the DU 174 may transmit 326 a DU-to-CU message including the at least one measurement report to the CU 172, similar to the event 306. In other implementations, the DU 174 does not transmit the at least one measurement report to the CU 172. In some implementations, the at least one measurement report of theevent 324 include L1 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 L1 measurement report(s) in format of RRC message(s) to the DU 174.

[0102] In some implementations, the UE 102 transmits 324 the at least one measurement report to the DU 174 in accordance with at least one measurement configuration. The at least one measurement configuration configures the UE 102 to perform measurements and report measurement results. The CU 172 transmits the at least one measurement configuration to the UE 102 via the DU 174. For example, the CU 172 can transmit one or more RRC messages (e.g., RRCReconfiguration message(s)) including the at least one measurement configuration to the UE 102 via the DU 174 in the event 302 and / or 316 and / or after the event 306 or 316. The one or more RRC messages may or may not include the RRC reconfiguration message of the event 316. In accordance with the at least one measurement configuration, the UE 102 performs measurements on one or more reference signals. The one or more reference signals can include one or more SSBs and / or one or more CSI-RSs. The UE 102 obtains the at least one L1 measurement result and / or at least one L3 measurement result from the measurements and includes the at least one L1 measurement result and / or at least one L3 measurement result in the at least measurement report of the event 324. The DU 174 transmits the one or more reference signals on the cell 124A, the cell 1 and / or the cell(s) 2, ... , N. The one or more reference signals can be CSI-RS(s) or SSB(s).

[0103] In some implementations, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig I E(s)), as described for the event 304. In other implementations, the at least one measurement configuration includes or is L1 measurement configuration(s), as described above. In yet other implementations, the L1 measurement configuration(s) can be CSI-MeasConfig I E(s) defined in 3GPP TS 38.331. The L1 measurement configuration(s) can include RS resource configuration(s) and / or report configuration(s). The UE 102 transmits 324 the L1 measurement report(s) on UL resources (e.g., PUCCH resources or PUSCHresources) to the DU 174 in accordance with the report configuration(s). The DU 174 receives the L1 measurement report(s) on the UL resources in accordance with the report configuration(s). In some implementations, the report configuration(s) are or are similar to CSI-ReportConfig IE(s). In other implementations, each of the report configuration(s) is a new RRC IE. In some implementations, (each of) the report configuration(s) configures periodically reporting and / or event-triggered reporting of the L1 measurement result(s).

[0104] In some implementations, the L1 measurement report(s) is / are CSI report(s). In other implementations, the L1 measurement report(s) is / are MAC CE(s). In some implementations, each of the measurement report(s) includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) and / or the report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values might include one or more L1-RSRP values and / or one or more L1-SINR values.

[0105] In yet other implementations, the at least one measurement configuration includes new-type measurement configuration(s) (e.g., LTM measurement configuration(s)). The new-type measurement configuration can be newly defined in a 3GPP specification. In some implementations, the new-type measurement configuration(s) includes reference signal resource configuration(s) configuring resources where the DU 174 transmits reference signal(s). For example, the reference signal resource configuration(s) include CSI-RS(s) and / or SSB(s). In one implementation, the reference signal resource configuration(s) is / are CSI- ResourceConfig IE(s). In another implementation, the new-type measurement configuration(s) include measurement report configuration(s), as described above. The UE 102 transmits the measurement report(s) on PUCCH(s) or MAC CE(s) to the DU 174 in accordance with the measurement report configuration(s). The DU 174 receives the measurement report(s) on PUCCH(s) or MAC CE(s) in accordance withthe measurement report configuration(s). In such cases, the measurement report(s) can be L1 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 in a 3GPP specification.

[0106] After (e.g., in response to) receiving the measurement report(s) in the event 324, the DU 174 generates a first LTM command to activate the LTM DU configuration 1 (i.e. , the first LTM command commands the UE 102 to apply the LTM DU configuration 1 or to perform a serving cell change to the cell 1). The DU 174 then transmits 330 the first LTM command to the UE 102. In some implementations, the DU 174 transmits the first LTM command on the cell 124A to the UE 102. In other implementations, the DU 174 transmits the first LTM command on the cell 124D to the UE 102. In some implementations, the DU 174 can include the ID 1 in the first LTM command to indicate the LTM DU configuration 1 or element 1 , and the UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 in accordance with the ID 1 .

[0107] In other implementations, the DU 174 can include the cell index 1 indexing the cell ID 1 in the first LTM command. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 , based on the cell index 1 . Before receiving the first LTM command, the UE 102 retrieves the cell index 1 from the LTM DU configuration 1 or element 1 , and establishes an association 1 between the cell index 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell index 1 , before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell index 1 and the association 1. Before receiving the first LTM command, the UE 102 retrieves the cell index(es) 2, ..., N from the LTM DU configuration(s) or element(s) 2, ... , N and establishes association(s) 2, ... , N between the cell index(es) 2, ... , N and the LTM DU configuration(s) or element(s) 2, ..., N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, ..., N to obtain the cell index(es) 2, ... , N, before receiving the first LTM command.

[0108] In yet other implementations, the DU 174 includes cell ID 1 in the first LTM command, where the cell ID 1 identifies the cell 1. In some implementations, the cellID 1 included in the first LTM command is the same as the cell ID 1 included in the first CU-to-DU message. In other implementations, the DU 174 determines the cell ID 1 (e.g., PCI) included in the first LTM command from the cell ID 1 (e.g., CGI) received in the first CU-to-DU message. The UE 102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 , based on the cell ID 1 . Before receiving the first LTM command, the UE 102 retrieves the cell ID 1 from the LTM DU configuration 1 or element 1 , and establishes an association 1 between the cell ID 1 and the LTM DU configuration 1 or element 1. In other words, the UE 102 decodes the LTM DU configuration 1 or element 1 to obtain the cell ID 1 , before receiving the first LTM command. Thus, the UE 102 identifies the LTM DU configuration 1 or element 1 in accordance with the cell ID 1 (received in the first LTM command) and the association 1 . Before receiving the first LTM command, the UE 102 retrieves the cell ID(es) 2, ..., N from the LTM DU configuration(s) or element(s) 2, ... , N and establishes association(s) 2, ..., N between the cell ID(es) 2, ... , N and the LTM DU configuration(s) or element(s) 2, ..., N, respectively. In other words, the UE 102 decodes the LTM DU configuration(s) or element(s) 2, ... , N to obtain the cell ID(es) 2, ..., N, before receiving the first LTM command. In some implementations, the DU 174 has a mapping table to store mappings between the PCI(s) 1 , ... , N and the CGI(s) 1 , ..., N for the cell(s) 1 , ... , N, respectively.

[0109] In yet other implementations, the DU 174 can include a bit map in the first LTM command to activate the LTM DU configuration 1 , instead of the ID 1 or cell index 1 . The number of bits in the bit map is larger than or equal to “N”. In one implementation, bit 1 , ..., N corresponds to the cell index(es) 1 , ... , N, the ID(s) 1 , ... , N, the LTM DU configuration(s) 1 , ..., N or the element(s) 1 , ..., N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 1) in the bit map to a first value to indicate the cell index 1 , the ID 1 , the LTM DU configuration 1 or the element 1. Thus, the UE 102 can determine the cell index 1 , the ID 1 , LTM DU configuration 1 , or element 1 in accordance with the bit 1 set to the first value in the bit map. In another implementation, bit O, ... , N-1 corresponds to the cell index(es) 1 , ... , N, the ID(s) 1 , ..., N, the LTM DU configuration(s) 1 , .... N orthe element (s) 1 , ..., N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 0) in the bit map to a first value to indicate the cell index 1 , the ID 1 the LTM DU configuration 1 or the element 1. Thus, the UE 102 can determine the cell index 1 , the ID 1 LTM DUconfiguration 1 or element 1 in accordance with the bit 0 set to the first value in the bit map. In such implementations, the DU 174 sets the remaining bits in the bit map to a second value to indicate that the rest of the LTM DU configuration(s) 1 , N is / are not activated. In some implementations, the first value is one and the second value is zero. In other implementations, the first value is zero and the second value is one. Generally, if the DU 174 determines to activate the LTM DU configuration L or change a serving cell to the cell L for the UE 102, the DU 174 can set the corresponding bit (e.g., bit L or bit L-1) in the bit map to the first value and set the remaining bits to the second value, where 1 < L < N. In some implementations, the DU 174 sets at most one bit in the bit map to the first value.

[0110] After determining or identifying the LTM DU configuration 1 or element 1 , the UE 102 then applies the LTM DU configuration 1 and / or LTM CU configuration, after (e.g., in response to) receiving the first LTM command.

[0111] In some implementations, the at least one measurement report (e.g., L1 measurement report(s) or new-type measurement report(s)) of the event 324 includes at least one measurement result for the first cell, TRP(s) of the first cell or reference signal(s) transmitted on the first cell. The reference signal(s) can be CSI- RS(s) or SSB(s). The DU 174 determines to activate the LTM DU configuration 1 or transmit the first LTM command, based on the at least one measurement result. In some implementations, the DU 174 determines to activate the LTM DU configuration 1 because, when or if the at least one measurement result is above a second predetermined threshold. In some implementations, the at least one measurement result includes L1-RSRP value(s), L1-RSRQ value(s) and / or L1-SINR value(s). In other implementations, the at least one measurement result includes RSRP value(s), RSRQ value(s) and / or SINR value(s) for the new-type measurement report(s). In some implementations, the second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is larger than the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell is suitable for communication with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This indicates that thefirst cell is suitable for communication with the UE 102. Thus, the DU 174 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold for the UE 102.

[0112] In some implementations, the at least one measurement report (e.g., L3 measurement report(s)) of the events 324 and 326 includes at least one measurement result for the first cell. The CU 172 determines to activate the LTM DU configuration 1 or transmit the first LTM command, because the at least one measurement result indicates that signal strength or quality of the first cell is above a second predetermined threshold. The second predetermined threshold is different from the first predetermined threshold. In one implementation, the second predetermined threshold is larger than the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell is suitable for communication with the UE 102. In another implementation, the second predetermined threshold is equal to the first predetermined threshold. In such an implementation, the at least one measurement report of the event 326 indicates that signal strength or quality of the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This also indicates that the first cell is suitable for communication with the UE 102. Thus, the CU 172 determines to activate the LTM DU configuration 1 in response to that signal strength or quality of the first cell is above the second predetermined threshold. In response to the determination, the CU 172 transmits 328 a fourth CU-to-DU message to the DU 174 to activate the LTM DU configuration 1 or trigger a serving cell change to the cell 1 for the UE 102. In some implementations, the CU 172 includes the ID 1 in the fourth CU-to-DU message. In other implementations, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. In response to the fourth CU-to-DU message, the DU 174 transmits 330 the first LTM command to the UE 102 and optionally transmits a fourth DU-to-CU message to the CU 172. In some implementations, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the cell index 1 . In other implementations, the CU 172 can include the cell ID 1 in the fourth CU-to-DU message. Thus, the DU 174 determines to activate the LTM DU configuration 1 in accordance with the cell ID 1 . In yet other implementations, the CU 172 can includethe ID 1 in the fourth CU-to-DU message. Thus, the DU 174 can determine to activate the LTM DU configuration 1 in accordance with the ID 1. In some implementations, the fourth CU-to-DU message and fourth DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message, respectively. In other implementations, the fourth CU-to-DU message and / or fourth DU-to-CU message are new interface messages, e.g., F1 application protocol (F1AP) messages defined in 3GPP TS 38.473.

[0113] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 330, the DU 174 might transmit 329 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some implementations, the DU-to-CU message is an LTM cell change notification message. In some implementations, the DU 174 includes the cell ID 1 or the ID 1 (i.e., LTM ID) in the DU-to-CU message 329 to indicate that the DU 174 is to activate the LTM DU configuration 1 or trigger a fast-serving cell change (i.e., an LTM serving cell change). The DU can transmit the DU-to-CU message 329 to the CU 172 before or after transmitting the LTM command 330.

[0114] In some implementations, the first LTM command is a MAC CE included in a MAC PDU that the UE 102 receives from the DU 174 in the event 330. The MAC CE can be a new MAC CE defined in 3GPP TS 38.321. In one implementation, the DU 174 includes a subheader identifying the new MAC CE in the MAC PDU and the UE 102 identifies the new MAC CE in the MAC PDU in accordance with the subheader. The subheader can include a logical channel ID or extended logical channel ID defined in a 3GPP specification to identify the new MAC CE. For example, the logical channel ID or extended logical channel ID are newly defined in 3GPP TS 38.321 . In other implementations, the first LTM command is a DCI that the UE 102 receives on a PDCCH from the DU 174 in the event 330. The DU 174 generates a cyclic redundancy check (CRC) for the DCI, scrambles the CRC with a first C-RNTI of the UE 102, and transmits the DCI and scrambled CRC on the PDCCH in the event 330. In one implementation, a format of the DCI can be an existing DCI format defined in a 3GPP specification (e.g., 38.212). In another implementation, the format of the DCI can be a new DCI format defined in a 3GPP specification (e.g., 3GPP TS 38.212).

[0115] In some implementations, the DU 174 does not perform security protection (e.g., integrity protection and / or encryption) on the first LTM command. This speeds up processing the first LTM command in the UE 102 because the UE 102 does not perform security check (e.g., decryption and / or integrity check) on the first LTM command.

[0116] In some implementations, after receiving the first LTM command, the UE 102 may transmit 331 an acknowledgement to the DU 174 on the cell 124A or cell 124D to indicate that the UE 102 receives the first LTM command. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. For example, the MAC CE is an existing MAC CE defined in 3GPP TS 38.321. In another example, the MAC CE is a new MAC CE defined in 3GPP TS 38.321. In yet other implementations, the acknowledgement is a PUCCH transmission.

[0117] In some implementations, the CU 172 transmits 316 the RRC reconfiguration message in response to the L3 measurement report 306 for the first cell. To configure the UE 102 to transmit the L3 measurement report 306, the CU 172 can transmit a first RRC reconfiguration message including the L3 measurement configuration (e.g., a MeasConfig IE) to the UE 102 before the event 306. In some implementations, the DU 174 transmits 330 the first LTM command in response to the L1 measurement report(s) 324 for the first cell. To configure the UE 102 to transmit the L1 or new-type measurement report(s) 324, the CU 172 can transmit a second RRC reconfiguration message including the L1 or new-type measurement configuration(s) to the UE 102. In some implementations, the first and second RRC reconfiguration messages can be the same message (i.e., the same instance). In other implementations, the first and second RRC reconfiguration messages are different messages. In some implementations, the second RRC reconfiguration message is the RRC reconfiguration message of the event 316. In other implementations, the second RRC reconfiguration message is different from the RRC reconfiguration message of the event 316.

[0118] After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 the first cell. The UE 102 identifies the LTM DU configuration 1 in accordance with the ID 1 , the cell ID 1 or the cell index 1 received in the first LTM command and applies the LTM DU configuration 1 to communicate with the DU 174on the first cell. In some implementations, the UE 102 disconnects from the cell 124A, after (e.g., in response to) receiving the first LTM command or after transmitting 331 the acknowledgement. In some implementations, the UE 102 stops communicating on the cell 124A after (e.g., in response to) receiving 330 the first LTM command or transmitting 331 the acknowledgement. In some implementations, the UE 102 accesses the first cell by performing a random access procedure on the first cell with the DU 174, in response to receiving the first LTM command. In other implementations, the UE 102 skips a random access procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174, after (e.g., in response to) receiving the first LTM command.

[0119] In some implementations, the DU 174 configures the access of the UE 102 to the first cell, including whether or not the UE 102 performs a random access procedure, in the LTM DU configuration 1. When receiving the first LTM command (e.g., the first LTM command), the UE 102 determines whether to perform a random access procedure on the first cell in accordance with the LTM DU configuration 1. If the LTM DU configuration 1 configures the UE 102 to perform a random access procedure, the UE 102 performs a random access procedure on the first cell in the event 332, in order to connect to the first cell. For example, the LTM DU configuration 1 includes a reconfiguration with sync configuration (e.g., ReconfigurationWithSync IE) to configure that the UE 102 performs a random access procedure when the UE 102 receives an LTM command for the first cell. In other implementations, in the LTM DU configuration 1 , the DU 174 configures the UE 102 to skip the random access procedure for an LTM serving cell change to the first cell. In such cases, after receiving the first LTM command, the UE 102 skips the random access procedure and transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174 in the event 332. In some implementations, the DU 174 excludes a reconfiguration with sync configuration in the LTM DU configuration 1 to configure the UE 102 skipping a random access procedure for an LTM serving cell change to the first cell.

[0120] In other implementations, the LTM DU configuration 1 includes the reconfiguration with sync configuration or the random access configuration. In such cases, the DU 174 configures whether the UE 102 performs a random access procedure on the first cell in an LTM command. Thus, the UE 102 determineswhether to perform the random access procedure on the first cell in the event 332 in accordance with the first LTM command. In some implementations, the DU 174 includes, in the first LTM command, an indication (e.g., a field) indicating skipping a random access procedure. In response to the indication or the first LTM command including the indication, the UE 102 skips a random access procedure and directly transmits the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to access the first cell. In other implementations, the DU 174 excludes the indication in the first LTM command to configure the UE 102 to perform a random access procedure. In response to the first LTM command excluding the indication, the UE 102 performs a random access procedure on the first cell to access the first cell. In some other implementations, the DU 174 includes a timing advance value in the first LTM command to indicate skipping a random access procedure. In response to receiving the timing advance value or the first LTM command including the timing advance value, the UE 102 skips a random access procedure and transmits the first transmission on the first cell to access the first cell, using the timing advance value. In yet other implementations, the DU 174 excludes, in the first LTM command, a timing advance value to configure the UE 102 to perform a random access procedure. In response to the first LTM command excluding a timing advance command, the UE 102 performs a random access procedure on the first cell to access the first cell.

[0121] In some implementations, the random access procedure is a four-step random access procedure. In other implementations, the random access procedure is a two-step random access procedure. In some implementations, the random access procedure is a contention-free random access procedure. In other implementations, the random access procedure is a contention-based random access procedure. In cases where the random access procedure is a four-step random access procedure, the UE 102 transmits a Message 3 including a UE identity to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., a Message 4) to the UE 102 in response to the Message 3. In cases where the random access procedure is a two- step random access procedure, the UE 102 transmits a Message A including the UE identity to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., Message B) to the UE 102 inresponse to the Message A. In some implementations, when the UE 102 receives the contention resolution message from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell). In some implementations, the LTM DU configuration 1 includes a second C-RNTI and the UE identity is the second C-RNTI of the UE 102. In such implementations, the contention resolution message is a PDCCH transmission addressed to the second C-RNTI. In other implementations, the LTM DU configuration 1 does not include a C-RNTI, the UE identity is the first C-RNTI. In such implementations, the contention resolution message is a PDCCH transmission addressed to the first C-RNTI. In some implementations, the DU 174 includes the second C-RNTI in the reconfiguration with sync configuration. In other implementations, the DU 174 includes the second C- RNTI in the LTM cell switch information.

[0122] In cases where the LTM DU configuration 1 includes a dedicated random access preamble, the random access procedure is a contention free random access procedure. In such cases, the UE 102 transmits the dedicated random access preamble to the DU 174 via the first cell. When the UE 102 receives a random access response including an ID of the dedicated random access preamble from the DU 174 on the first cell, the UE 102 determines that the UE 102 successfully completes the random access procedure (i.e., the UE 102 successfully accesses the first cell).

[0123] If the DU 174 configures the UE 102 to perform a random access procedure on the first cell as described above, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives Message 3, Message A, or the dedicated preamble in the random access procedure. If the DU 174 configures the UE 102 to skip a random access procedure, the DU 174 will detect that the UE 102 has accessed the first cell when the DU 174 receives the first transmission.

[0124] In some implementations, the UE 102 transmits the first transmission (e.g., the PUSCH transmission) on the first cell using a UL grant. In some implementations, the first LTM command includes the UL grant. In other implementations, when the UE 102 performs an LTM serving cell change to the first cell in response to the first LTM command, the UE 102 receives a first DCI including the UL grant on a PDCCH on the first cell. In some implementations, the UE 102attempts to receive the first DCI or the UL grant by monitoring one or more PDCCHs on the first cell in accordance with the LTM DU configuration 1 , when the UE 102 switches to the first cell in response to the first LTM command. While monitoring one or more PDCCHs on the first cell, the UE 102 receives the first DCI and a CRC of the first DCI on the PDCCH. In the case that the LTM DU configuration 1 includes the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the second C-RNTI. In the case that the LTM DU configuration 1 does not include the second C-RNT, the UE 102 determines that the first DCI was sent for the UE 102, using the CRC and the first C-RNTI.

[0125] In some implementations, the CU 172 transmits at least one first TCI state configuration (e.g., LTM TCI state configuration) for the first cell to the UE 102 via the DU 174. In some implementations, each of the first TCI state configuration(s) configures a TCI state for the UE 102 to transmit and / or receive data and / or control signal on the first cell. Each TCI state associates or includes one or two DL RSs with a corresponding QCL type and the DL RS(s) might be associated with a particular cell of the cell(s) 1 , ... , N. The DL RS(s) include SSB(s) and / or tracking reference signal(s) (TRS(s)). In some implementations, the CU 172 receives a DU-to-CU message including the first TCI state configuration(s) from the DU 174 and transmits a RRC message including the first TCI state configuration(s) to the UE 102 via the DU 174. In further implementations, the DU 174 includes the first TCI state configuration(s) in a serving DU configuration (e.g., CellGroupConfig IE) and includes the serving DU configuration in the DU-to-CU message. In some implementations, the DU-to-CU message is the DU-to-CU message 310 or the DU- to-CU message 314. In other implementations, the DU-to-CU message is a message different from the messages 310, 314. For example, the DU-to-CU message is a UE Context Modification Response message or a UE Context Modification Required message.

[0126] In some implementations, the DU 174 includes the LTM DU configuration 1 in a first interface protocol I E / field in the DU-to-CU message 310, and includes the serving DU configuration in a second interface protocol I E / field in the DU-to-CU message 314. In some implementations, the events 312 (optional) and / or 314 (optional) are collectively referred to in FIG. 3 as an LTM TCI state configuration procedure 392.

[0127] In some implementations, the CU 172 includes the serving DU configuration in the RRC message. In some implementations, the CU 172 refrains from including the serving DU configuration in a container for LTM (e.g., the first container). In some implementations, the CU 172 includes the LTM ID 1 and the first LTM TCI state configuration(s) in an element for LTM, an addition or modification list for LTM, or a container, and the CU 172 includes the element, addition or modification list for LTM, or the container in the RRC message, similar to the element 1 , the first addition or modification list, or the first container respectively. In some implementations, the RRC message is the RRC reconfiguration message 316, 318. In such cases, the CU 172 may include the first LTM TCI state configuration(s) in the element 1 . In other implementations, the RRC reconfiguration is another RRC reconfiguration message (not shown in FIG. 3). In some implementations, the DU 174 also includes the first TCI state configuration(s) in the LTM DU configuration 1 . In other implementations, the DU 174 refrains from including the first TCI state configuration(s) in the LTM DU configuration 1.

[0128] In some implementations, the first interface protocol I E / field is a first F1 AP I E / field and the second interface protocol I E / field is a second F1AP lE / field. In some implementations, one of the first F1AP I E / field and the second F1AP I E / field is a F1 AP CellGroupConfig I E / field and the other is not the F1AP CellGroupConfig I E / field. In some implementations, the DU 174 includes the first F1AP I E / field in a DU to CU RRC Information IE in the message 314 and includes the second F1 AP I E / field in the DU to CU RRC Information IE in the DU-to-CU message. In other implementations, neither the first F1AP I E / field nor the second F1AP IE is a F1AP CellGroupConfig I E / field. In other implementations, the second F1AP I E / field is the DU to CU RRC Information IE and the first F1AP I E / field is a new IE specific for including an LTM DU configuration.

[0129] In some implementations, the DU 174 transmits 325 at least one first LTM TCI states Activation / deactivation command to the UE 102 to activate some of the first LTM TCI state configuration(s). The UE 102 activates the some of the first LTM TCI state configuration(s) in response to the first LTM TCI states activation / deactivation command(s). In some implementations, the DU 174 indicates deactivation of some of the first LTM TCI state configuration(s) in some of the first LTM TCI states activation / deactivation command(s). In some implementations, theDU 174 transmits one or more DL RSs on the candidate cell(s) using the activated LTM TCI state configuration(s) or the first LTM TCI state configuration(s). The DL RS(s) may include one or more SSBs and / or one or more TRSs. In some implementations, the UE 102 receives the DL RS(s) using the activated LTM TCI state configuration(s). The UE 102 may obtain L1 measurement results from the received DL RS(s) and transmits the L1 measurement results to the DU 174. The UE 102 may obtain L3 measurement results from the received DL RS(s) and transmit the L3 measurement results to the CU 172 via the DU 174. In some implementations, the DU 174 refrains from using the first LTM TCI state configuration(s) to communicate with the UE 102 on the serving cell(s). In some implementations, the UE 102 refrains from using the first LTM TCI state configuration(s) to communicate with the DU 174 on the serving cell(s).

[0130] In some implementations, each of the first LTM TCI states activation / deactivation command(s) is a MAC CE (e.g., Candidate Cell TCI states activation / deactivation command). In some implementations, the DU 174 includes the LTM ID 1 in each of the first LTM TCI states activation / deactivation command(s) to identify the first LTM TCI state configuration(s). In other implementations, the DU 174 includes a candidate cell index (e.g., the cell index 1 ) in each of the first LTM TCI states activation / deactivation command(s) to identify the first LTM TCI state configuration(s). In such cases, the candidate cell index is different from the LTM ID 1. In some implementations, each of the first LTM TCI state configuration(s) may include the candidate cell index. Alternatively, the CU 172 includes the candidate cell index in the RRC message including the first LTM TCI state configuration(s). For example, the CU 172 includes the candidate cell index in the element 1. In some alternative implementations, the UE 102 and the DU 174 determines the candidate cell index from the PCI of the first cell. In such cases, the first BS 104 does not transmit the candidate cell index to the UE 102.

[0131] In some implementations, after (e.g., in response to) receiving the first LTM command or accessing 332 the first cell, the UE 102 performs DL reception (e.g., monitors one or more PDCCHs) or UL transmission on the first cell using some or all of the first LTM TCI state configuration(s) in the event 336. In other implementations, after (e.g., in response to) receiving the first LTM command or accessing 332 the first cell, the UE 102 performs DL reception (e.g., monitors one or more PDCCHs) orUL transmission on the first cell without using the first LTM TCI state configuration(s) in the event 336.

[0132] In some implementations, each of the first LTM TCI state configuration(s) includes a TCI state ID identifying the corresponding TCI state configuration. For example, the first LTM TCI state configuration(s) includes LTM TCI state configuration(s) 1 , ..., L, where L is a positive integer larger than zero. The LTM TCI state configuration(s) 1 , ... , L include TCI state ID(s) 1 , .... L identifying the LTM TCI state configuration(s) 1 , ... , L, respectively. In some implementations, the DU 174 includes the TCI state ID 1 in the first LTM command to indicate to the UE 102 to activate the LTM TCI state configuration 1 to communicate on the first cell. The UE 102 activates the LTM TCI state configuration 1 in response to receiving the TCI state ID 1 in the first LTM command. In some implementations, the UE 102 accesses 332 on the first cell using the (activated) LTM TCI state configuration 1 . In other implementations, the UE 102 accesses 332 on the first cell without using the first LTM TCI state configuration(s). In some implementations, the UE 102 communicates 336 on the first cell using the (activated) LTM TCI state configuration 1 . In some implementations, the DU 174 communicates 336 with the UE 102 on the first cell, using the activated LTM TCI state configurations 1.

[0133] In some implementations, in the events 332 and / or 336, the UE 102 monitors one or more PDCCHs, receives one or more DL RSs, receives one or more PDSCH transmissions, and / or transmits the first transmission and / or one or more additional transmissions, using the LTM TCI state configuration 1. In some implementations, the DU 174 detects 332 that the UE 102 accesses the first cell and / or communicates 336 with the UE 102 on the first cell, based on the LTM TCI state configuration 1. In some implementations, the DU 174 receives 332 the first transmission and / or 336 the additional transmission(s) from the UE 102 on the first cell, based on the TCI state configuration 1. In other implementations, in the events 332 and / or 336, the DU 174 transmits one or more PDCCHs, one or more PDSCH transmissions, and / or one or more DL RSs, based on the LTM TCI state configuration 1.

[0134] In some implementations, the DU 174 includes the TCI state ID 2 in the first LTM command to indicate to the UE 102 to activate the TCI state configuration 2 to communicate on the first cell, in addition to the TCI state ID 1. The UE 102activates the LTM TCI state configuration 1 in response to receiving the TCI state ID 1 in the first LTM command, and activates the LTM TCI state configuration 2 in response to receiving the TCI state ID 2 in the first LTM command. After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 and / or communicates 336 on the first cell using the activated LTM TCI state configurations 1 and 2. After (e.g., in response to) transmitting the first LTM command or receiving the acknowledgement 331 , the DU 174 communicates with the UE 102 on the first cell in the events 332 and / or 336, using the activated LTM TCI state configurations 1 and 2.

[0135] In some implementations, after applying one or more TCI state configurations (e.g., the TCI state configuration(s) 1 and / or 2) indicated in an LTM command (e.g., the first LTM command), the UE 102 takes time (e.g., beam application time or cell switch delay) to acquire TCI state(s) configured in the TCI state configuration(s) (e.g., synchronize and / or receive DL RS(s) configured in the TCI state configuration(s)). The time to acquire TCI state(s) is considered as a switch delay. In such cases, the DU 174 takes the switch delay into account when communicating with the UE 102 on the first cell in the events 332 and / or 336. For example, after transmitting the first LTM command or receiving the acknowledgement 331 , the DU 174 starts to communicate with the UE 102 on the first cell in the events 332 and / or 336 after the switch delay, using the activated LTM TCI state configuration(s) 1 and / or 2.

[0136] In some implementations, the UE 102 monitors one or more PDCCHs, receives one or more DL RSs, and / or receives one or more PDSCH transmissions from the DU 174 on the first cell using the LTM TCI state configuration 1 and transmits the first transmission and / or one or more additional transmissions on the first cell to the DU 174 using the LTM TCI state configuration 2. In such implementations, the DU 174 transmits one or more control signals one or more PDCCHs, one or more DL RSs, and / or one or more PDSCH transmissions to the UE 102 on the first cell using the LTM TCI state configuration 1 and receives the first transmission and / or one or more additional transmissions on the first cell from the UE 102 using the LTM TCI state configuration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DCI.

[0137] In other implementations, the UE 102 monitors one or more PDCCHs from the DU 174 on the first cell using the LTM TCI state configuration 1 and receives one or more PDSCH transmissions from the DU 174 on the first cell using the LTM TCI state configuration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DCI. In such implementations, the DU 174 transmits one or more control signals on one or more PDCCHs on the first cell to the UE 102 using the LTM TCI state configuration 1 and transmits one or more PDSCH transmissions to the UE 102 on the first cell using the LTM TCI state configuration 2. In some implementations, the UE 102 transmits the first transmission and / or one or more additional transmissions to the DU 174 on the first cell, using the LTM TCI state configuration1. In such implementations, the DU 174 receives the first transmission and / or one or more additional transmissions from the UE 102 on the first cell, using the LTM TCI state configuration 1 . In other implementations, the UE 102 may transmit the first transmission and / or one or more additional transmissions to the DU 174 on the first cell, using the LTM TCI state configuration 2. In such implementations, the DU 174 receives the first transmission and / or one or more additional transmissions from the UE 102 on the first cell, using the LTM TCI state configuration 2.

[0138] In yet other implementations, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and the TCI state configuration 2, and transmits the first transmission and / or one or more additional transmissions on the first cell using one of the TCI state configuration 1 and the TCI state configuration2. In such implementations, the DU 174 transmits one or more control signals on one or more PDCCHs receives the first transmission and / or one or more additional transmissions from the UE 102 on the first cell, using the LTM TCI state configuration 2. Each of the control signal(s) includes a DCI and a scrambled CRC for the DCI.

[0139] In some implementations, the CU 172 receives a CN-to-BS message including a UE capability IE of the UE 102 from a CN (e.g., the CN 110 or the AMF 164), e.g., during the event 302. For example, the CN-to-BS message is a NG application protocol (NGAP) message. In other implementations, the CU 172 receives a BS-to-BS message including the UE capability IE from another BS (e.g., the second BS 106), e.g., before the event 302. In yet other implementations, the CU 172 receives a UE Capability Information message including the UE capability IEfrom the UE 102, via the DU 174 or another DU e.g., during the event 302. In some implementations, the DU 174 receives the UE capability IE (e.g., UE-NR-Capability or UE-6G-Capability) of the UE 102 from the CU 172, e.g., during the event 302.

[0140] In some alternative implementations, the DU 174 may not activate or may determine to not activate a (LTM) TCI state configuration in the first LTM command. In such cases, the DU 174 does not include a TCI state ID in the first LTM command. Thus, when the UE 102 receives the first LTM command not including a TCI state configuration, the UE 102 refrains from using the first LTM TCI configuration(s) to access and / or communicate on the first cell. In some implementations, if the UE capability IE indicates that the UE 102 does not support a Random Access Channel (RACH)-less LTM, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the UE capability IE indicates that the UE 102 supports the RACH-less LTM, the DU 174 includes the one or more TCI state IDs (e.g., the TCI state ID 1 and / or the TCI state ID 2) in the first LTM command. In other implementations, if the DU 174 does not configure LTM TCI state configurations for the first cell for the UE 102, the DU 174 does not include or refrains from including a TCI state ID in the first LTM command. Otherwise, if the DU 174 configures one or more LTM TCI state configurations (e.g., the first LTM TCI state configuration(s)), the DU 174 includes one or more LTM TCI state IDs (e.g., the TCI state ID 1 and / or the TCI state ID 2) in the first LTM command.

[0141] In some implementations, the UE 102 stops using or deactivates the first non-LTM TCI configuration(s) upon receiving the first LTM command.

[0142] After successfully accessing the first cell, the UE 102 communicates 336 with the DU 174 on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the DU 174. In such cases, the DU 174 communicates 336 with the UE 102 on the first cell using the LTM DU configuration 1. In some scenarios or implementations, the UE 102 communicates 336 PUSCH transmissions, PDSCH transmissions, PUCCH transmissions, PDCCH transmissions, and / or sounding reference signal (SRS) transmissions with the DU 174 on the first cell.

[0143] In the case that the UE 102 receives the reference LTM DU configuration as described above, the UE 102 communicates 336 with the DU 174 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of thereference LTM DU configuration. In other words, the UE 102 communicates 336 with the DU 174 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration. Similarly, the DU 174 communicates 336 with the UE 102 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the DU 174 communicates 336 with the UE 102 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration.

[0144] In the case that the UE 102 receives neither the LTM CU configuration 1 nor a / the reference LTM CU configuration, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving CU configuration. Correspondingly, if the CU 172 neither transmits the LTM CU configuration 1 nor a / the reference CU configuration to the UE 102, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving CU configuration. In the case that the UE 102 receives the LTM CU configuration 1 and the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1 and (at least a portion of) the reference LTM CU configuration not augmented by the LTM CU configuration 1 .

[0145] In the case that the UE 102 receives the LTM CU configuration 1 and does not receive the reference LTM CU configuration from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the LTM CU configuration 1. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the LTM CU configuration 1. If the LTM CU configuration 1 is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the LTM CU configuration 1 instead of the serving CU configuration. In some implementations, if the UE 102 does not receive a / the reference LTM CU configuration from the first BS 104, the UE 102 determines that the LTM CU configuration 1 is a full configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a full configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In otherimplementations, the CU 172 includes a first indication (e.g., a field or IE) in the LTM CU configuration 1 , the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration 1 is a full configuration. If the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the LTM CU configuration 1 and at least a portion of the serving CU configuration not augmented by the LTM CU configuration 1 . In some implementations, if the UE 102 does not receive a / the reference LTM CU configuration from the first BS 104, the UE 102 determines that the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a delta configuration to augment the serving CU configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In some implementations, the CU 172 indicates that the LTM CU configuration 1 is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the LTM CU configuration 1 , the first container, the element 1 and / or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the LTM CU configuration 1 , the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the LTM CU configuration 1 is a delta configuration to augment the serving CU configuration. In some implementations, the CU 172 indicates that the LTM CU configuration 1 is a full configuration, by excluding the second indication in the LTM CU configuration 1 , the first container, the element 1 and / or the RRC reconfiguration message 316.

[0146] In the case that the UE 102 receives the reference LTM CU configuration and does not receive the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the reference LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the reference LTM CU configuration. If the reference LTM CU configuration is a full configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration instead of the serving CU configuration. In some implementations, the UE 102 and CU 172 determine that the reference LTM CU configuration 1 is a full configuration as specified in a 3GPP specification (e.g., 3GPP TS 38.331). In other implementations,the CU 172 includes a first indication (e.g., a field or IE) in the reference LTM CU configuration, the first container or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a full configuration. If the reference LTM CU configuration is a delta configuration to augment the serving CU configuration, the UE 102 and CU 172 communicates 336 with each other via the DU 174 using the reference LTM CU configuration and at least a portion of the serving CU configuration not augmented by the reference LTM CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a delta configuration to augment to the serving CU configuration, by excluding the first indication in the reference LTM CU configuration, the first container, the element 1 and / or the RRC reconfiguration message 316. Alternatively, the CU 172 includes a second indication (e.g., a field or IE) in the reference LTM CU configuration, the first container, the element 1 or the RRC reconfiguration message 316 to indicate that the reference LTM CU configuration is a delta configuration to augment the serving CU configuration. In some implementations, the CU 172 indicates that the reference LTM CU configuration is a full configuration, by excluding the second indication in the reference LTM CU configuration, the first container, the element 1 and / or the RRC reconfiguration message 316.

[0147] In the case that the UE 102 neither receives the reference LTM CU configuration and nor the LTM CU configuration 1 from the CU 172, the UE 102 communicates 336 with the CU 172 via the DU 174 using the serving LTM CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving LTM CU configuration.

[0148] In some implementations, the DU 174 includes or configures at least one second non-LTM TCI state configuration for the first cell in the LTM DU configuration 1. While communicating with the UE 102 at event 332 or 336, the DU 174 may transmit a second non-LTM TCI states activation / deactivation command on the first cell to the UE 102 to activate the second non-LTM TCI state configuration(s) and / or deactivate the activated LTM TCI state configuration(s). In some implementations, the DU 174 includes a serving cell index for the first cell in the second non-LTM TCI states activation / deactivation command. The DU 174 includes the serving cell index in the LTM DU configuration 1 . In some implementations, the UE 102 stops using or deactivates the (activated) LTM TCI state configuration(s) in response to receivingthe second non-LTM TCI states activation / deactivation command. In some implementations, the second non-LTM TCI states activation / deactivation command(s) is a MAC CE. The MAC CE may be a TCI states activation / deactivation for UE-specific PDSCH MAC CE, a TCI state indication for UE-specific PDCCH MAC CEs, a PUCCH spatial relation activation / deactivation MAC CEs, an Enhanced TCI states activation / deactivation for UE-specific PDSCH MAC CE, an Enhanced PUCCH Spatial Relation activation / deactivation MAC CE, an Enhanced TCI states indication for UE-specific PDCCH MAC CE, an PUCCH spatial relation activation / deactivation for multiple TRP PUCCH repetition MAC CE, or an Unified TCI states activation / deactivation MAC CE.

[0149] In some implementations, the second non-LTM state configuration(s) may be Rel-15 / 16 TCI state configuration(s) (i.e., not a unified joint / DL / UL TCI state). This imply that the BS 104 may configure Rel-15 / 16 beam indication framework for the first cell. Non-LTM TCI state configurations activated / indicated by the second non- LTM TCI states activation / deactivation command(s) may be only applicable to a channel or RS (PDSCH / PDCCH / CSI-RS / PUCCH / SRS). In such implementations, if the UE 102 receives a second non-LTM TCI states activation / deactivation command, the UE would stop or use the first LTM TCI state for channels or RSs, which are applicable to share / follow / apply unified TCI states. For example, if the UE 102 receives an enhanced TCI states indication for UE-specific PDCCH MAC CE, the UE 102 would stop or use the first LTM TCI state for at least one of other channels or RSs applicable to share / follow / apply unified TCI states as well (e.g., PDSCH, PUSCH, PUCCH, CSI-RS or SRS). If the UE 102 receives a second non-LTM TCI states activation / deactivation command, the UE 102 may deactivate the activated first LTM TCI state configuration(s).

[0150] In some implementations, the second non-LTM TCI state configuration(s) includes at least one TCI state configured in the first LTM TCI state configuration(s). In other implementations, TCI state(s) in the second non-LTM TCI state configuration(s) is / are different from the TCI(s) in the first LTM TCI state configuration(s). In some implementations, the second non-LTM TCI state configuration(s) configure more TCI states than the first LTM TCI state configurations(s). In some other implementations, TCI state(s) in the second non- LTM TCI state configuration(s) is / are identical with the TCI(s) in the first LTM TCIstate configuration(s). The BS 104 / Cll 172 / DU 174 may notify the UE 102 in a RRC message or signal, whether first LTM TCI state configuration(s) is identical or different or a subset of the second non-LTM TCI state configuration(s).

[0151] In some implementations, the first LTM TCI state configuration(s) for the first cell is a subset of the second non-LTM TCI state configuration(s) for the first cell. In some implementations, TCI state IDs of the first LTM TCI state configuration(s) for the first cell are not overlapped or identical with those of the second non-LTM TCI state configuration(s) for the first cell. This may imply that when the UE 102 receives the second non-LTM TCI States Activation / deactivation command(s), the UE 102 considers / determines that the TCI state ID(s) indicated in the second non-LTM TCI States Activation / deactivation command(s) refer to the first LTM TCI state configuration(s) for the first cell or the second non-LTM TCI state configurations for the first cell. For example, TCI state IDs of the first LTM TCI state configuration(s) for the first cell ranges from #000 to #007; TCI state IDs of the second non-LTM TCI state configurations for the first cell ranges from #008 to #015. In such example, if the second non-LTM TCI States Activation / deactivation command indicates TCI state ID #001 , the UE 102 activates the first LTM TCI state configuration identified by TCI state ID #001 ; if the second non-LTM TCI states activation / deactivation command indicates TCI state ID #012, the UE 102 activates the second non-LTM TCI state configuration identified by TCI state ID #012. In some implementations, the UE 102 combines or catenate the first LTM TCI state configuration(s) for the first cell and the second non-LTM TCI state configurations for the first cell for non-LTM TCI state activation / indicate purpose. In some implementations, the UE 102 considers or determines the first LTM TCI state configuration(s) for the first cell as the non-LTM TCI state configurations for the first cell.

[0152] In some implementations, the DU 174 may not include or configure the at least one second non-LTM TCI state configuration for the first cell in the LTM DU configuration 1. In such cases, the UE 102 considers or determines the at least one first TCI state configuration(s) (e.g., LTM TCI state configuration) for the first cell as the non-LTM TCI state configurations for the first cell. This may imply that when the UE 102 receives the second non-LTM TCI states activation / deactivation command(s), the UE 102 considers / determines that the TCI state ID(s) indicated in the second non-LTM TCI states activation / deactivation command(s) refer to the firstLTM TCI state configuration(s) for the first cell. For example, if the second non-LTM TCI states activation / deactivation command indicates TCI state ID #000, the UE 102 activates and / or applies the first TCI state configuration (e.g., LTM TCI state configuration) identified by TCI state ID #000, and performs non-LTM communication in the first cell.

[0153] In some implementations, if a first LTM TCI state configuration associates or includes a SSB corresponding to QCL type A, the UE 102 refrains from using such TCI state configuration for non-LTM purpose or communication in the first cell. In some implementations, the UE 102 may consider or determine a first LTM TCI state configuration(s) for the first cell as a non-LTM TCI state configurations for the first cell, unless it includes or associates a SSB corresponding to QCL type A.

[0154] In some implementations, when or while the DU 174 communicates 332, 336 with the UE 102 on the first cell, the DU 174 refrains from transmitting an LTM TCI states activation / deactivation command to the UE 102 to activate an LTM TCI state configuration for the first cell or associated with the LTM ID 1. In other implementations, when or while the DU 174 communicates 332, 336 with the UE 102 on the first cell, the DU 174 transmits a second LTM TCI states activation / deactivation command to the UE 102 to activate at least one LTM TCI state configuration in the first LTM TCI state configuration(s) that is / are not activated by the first LTM command. In response to the second LTM TCI states activation / deactivation command, the UE 102 activates the LTM TCI state configuration(s) indicated in the second LTM TCI states activation / deactivation command. In the second LTM TCI states activation / deactivation command, the DU 174 may deactivate the LTM TCI state configuration(s) activated in the first LTM command, in some implementations. In such cases, the UE 102 deactivate the LTM TCI state configuration(s) activated in the first LTM command, in response. The UE 102 and the DU 174 communicate with each other on the first cell using the LTM TCI state configuration(s) activated by the second LTM TCI states activation / deactivation command, as described above.

[0155] In some implementations, the UE 102 transmits a RRC message (e.g., RRC reconfiguration complete message) to the CU 172 via the DU 174 and the first cell to indicate that the UE 102 applies the LTM DU configuration 1 . In the case that the UE 102 performs the random access procedure 332, the UE 102 can include theRRC message in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC message after completing the random access procedure. In the case that the UE 102 skip the random access procedure 332, the UE 102 includes the RRC message in a RUSCH transmission of the at least one PUSCH transmission. In some implementations, if the UE 102 maintains communication on the cell 124A with the first BS 104 (i.e. , the UE 102 does not disconnect from the cell 124A), the UE 102 can transmit the RRC message to the first BS 104 via the cell 124A. When the DU 174 receives the RRC message, the DU 174 transmits the RRC message to the CU 172.

[0156] In other implementations, the UE 102 refrains from transmitting the RRC message to the first BS 104 in response to applying the LTM DU configuration 1 or receiving the first LTM command. In such cases, the UE 102 can include or transmit data in the Message 3, Message A or PUSCH transmission as described above. The UE 102 can generate a MAC PDU and / or a RLC PDU including the data and transmits or includes the MAC PDU and / or RLC PDU in the PUSCH transmission. For example, the data can be a PDCP PDU, a SDAP PDU, a LTE Positioning Protocol (LPP) PDU, a RRC PDU and / or a NAS PDU. The RRC PDU includes a UL- DCCH-Message excluding a RRC reconfiguration complete message. The NAS PDU includes a Mobility Management (MM) message or a Session Management (SM) message. The MM message can be a 5G MM message or a 6G MM message, and the SM message can be a 5G SM message or a 6G SM message. When the DU 174 receives the data, the DU 174 transmits the data to the CU 172.

[0157] When the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 can transmit 334 a DU-to-CU message (e.g., access success message) to the CU 172 (e.g., a CP of the CU 172). In some implementations, the DU 174 can include the cell ID 1 of the first cell in the DU-to- CU message of the event 334. The cell ID can be a PCI or a CGI. Thus, the CU 172 determines that the UE 102 connects to the first cell upon receiving the DU-to-CU message of the event 334. When the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 can transmit a DL Data Delivery Status message or frame to the CU 172 (e.g., a UP of the CU 172). In some implementations, when or after the CU 172 receives the DU- to-CU message 329, the CU 172 might stop or suspend transmitting DL data for theUE 102 to the DU 174 until receiving the DU-to-CU message 334. The CU 172 might do so because the DU 174 cannot buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. After receiving the DU-to-CU message 334, the CU 172 continues or resumes transmitting DL data for the UE 102 to the DU 174. In other implementations, when the CU 172 receives the DU-to-CU message 329, the CU 172 might continue transmitting DL data for the UE 102 to the DU 174. The CU 172 might do so because the DU 174 can buffer DL data for the UE 102 during the LTM execution in the events 330 and / or 332. When or after the DU 174 detects that UE 102 accesses the cell 1 , the DU 174 transmits the DL data to the UE 102 via the cell 1 .

[0158] In some implementations, when determining that the UE 102 connects to the first cell, transmitting 330 the first LTM command, or receiving 331 the acknowledgement, the DU 174 can stop communicating with the UE 102 on the cell 124A and / or release resources of the cell 124A configured for the UE 102.

[0159] In some implementations, the DU 174 can generate some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ..., N as full configuration(s) to replace the serving DU configuration. If the LTM DU configuration 1 is a full configuration, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 instead of the serving DU configuration. In some implementations, the DU 174 includes an indication indicating that the LTM DU configuration 1 is a full configuration in the LTM DU configuration 1. In each of the LTM DU configu ratio n(s) 2, ... , N, the DU 174 can include an indication to indicate that the corresponding DU configuration is a full configuration. Each of the indication(s) in the LTM DU configuration(s) 1 , ... , N can be a field or IE (i.e. , the same field or IE). In other implementations, the CU 172 can include, in the RRC reconfiguration message of the events 316, 318, a single indication indicating that the LTM DU configuration(s) 1 and / or 2, ... , N is / are full configuration(s). In the case of the second container, the CU 172 can include, in the additional RRC reconfiguration message, a single indication indicating that the LTM DU configuration(s) 2, ..., N is / are full configuration(s). In yet other implementations, the CU 172 can include, in the first container, a single indication indicating that the LTM DU configuration(s) 1 and / or 2, ... , N is / are full configuration(s). In yet other implementations, for each of the LTM DU configuration(s) 2, .... N, the CU 172 caninclude, in the first container, a particular indication indicating the corresponding LTM DU configuration is a full configuration. In the case of the second container, the CU 172 can include, in the second container, a single indication indicating that the LTM DU configuration(s) 2, ... , N is / are full configuration(s). In yet other implementations, the CU 172 can include, in the element 1 , includes an indication indicating that the LTM DU configuration 1 is a full configuration. In each of the element(s) 2, ..., N, the CU 172 can include an indication indicating that the corresponding LTM DU configuration is a full configuration. The UE 102 can determine that the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ..., N is / are full configuration(s) based on the indication(s) above. In some implementations, each of the indication(s) above is different from a fullConfig field defined in the current 3GPP specification. In some implementations, each of the indication(s) above is a fullConfig field defined in the current 3GPP specification. In the case that the LTM DU configuration 1 is a full configuration, the UE 102 in the event 336 does not apply the reference LTM DU configuration if received from the first BS 104, e.g., in the RRC reconfiguration message 318. In such cases, the DU 174 might not include a / the reference LTM DU configuration in the first DU-to-CU message 310.

[0160] In other implementations, the DU 174 can generate the LTM DU configuration 1 and / or LTM DU configuration(s) 2, ..., N as delta configuration(s) that augment (a portion of) the reference LTM DU configuration. In other words, the DU 174 generates the LTM DU configuration(s) 1 , ...N based on the reference LTM DU configuration. For example, if the LTM DU configuration 1 is a delta configuration, the UE 102 and DU 174 augment (the portion of) the reference LTM DU configuration with the LTM DU configuration 1. Thus, the UE 102 and DU 174 communicate 336 with each other in accordance with the LTM DU configuration 1 and unaugment portion of the reference LTM DU configuration. In some implementations, the LTM DU configuration(s) 1 , and / or 2... , N, first container, second container or element(s) 1, ... , N exclude indication(s) indicating that the LTM DU configuration(s) 1 , and / or 2..., N is / are full configuration(s) to indicate that the LTM DU configuration(s) 1 and / or 2, ..., N is / are delta configuration(s). The UE 102 can determine that each of the LTM DU configuration(s) 1 and / or 2, ... , N is a delta configuration based on that the indication is excluded in the LTM DU configuration(s) 1 and / or 2, ..., N, first container, second container or element(s) 1 and / or 2, ... , N.

[0161] In some implementations, if the UE 102 does not receive a reference LTM DU configuration for the LTM DU configuration 1 and / or the LTM DU configuration(s) 2, N, the UE 102 determines that the LTM DU configuration 1, and / or the LTM DU configuration(s) 2, N are full configuration(s). Correspondingly, if the DU 174 does not obtain a reference LTM DU configuration for the UE 102 (i.e. , the DU 174 does not generate a reference LTM DU configuration for the UE 102 and / or receive a reference LTM DU configuration for the UE 102 from the CU 172), the DU 174 generates the LTM DU configuration 1 , and / or the LTM DU configuration(s) 2, ..., N as full configuration(s).

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

[0163] In some implementations, the UE 102 uses a UE MAC entity (e.g., MAC 204B) to communicate with a DU MAC entity (e.g., MAC 204B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331). In some implementations, the UE 102 resets the UE MAC entity, after or in response to receiving the first LTM command and before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 resets the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

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

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

[0166] Depending on implementation, the UE 102 can determine to partially or fully reset the UE MAC entity. In some implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 fully resets the UE MAC entity (i.e., a full UE MAC reset). In the full UE MAC reset, the UE 102 performs some or all of the actions described above. In other implementations, when the UE 102 resets the UE MAC entity as described above, the UE 102 partially resets the UE MAC entity (i.e., a partial UE MAC reset). In the partial UE MAC reset, the UE 102 performs a subset or portion of the some or all of the actions in the full UE MAC reset.

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

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

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

[0170] Depending on implementations, the DU 174 can determine to partially or fully reset the DU MAC entity. In some implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 fully resets the DU MAC entity (i.e., a full DU MAC reset). In the full DU MAC reset, the DU 174 performs some or all of the actions described above. In other implementations, when the DU 174 resets the DU MAC entity as described above, the DU 174 partially resets the DU MAC entity (i.e., a partial DU MAC reset). In the partial DU MAC reset, the DU 174 performs a subset or portion of the some or all of the actions in the full DU MAC reset.

[0171] In some implementations, the partial DU MAC reset includes at least one of the following actions in the partial MAC reset:• consider timeAlignmentTimer(s), that the DU 174 starts and / or maintains for the UE 102, as expired, if the UE 102 is configured to perform the random access procedure (e.g., the event 332) in the configuration (e.g., the configuration 1 );• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs)

[0172] In some implementations, when the partial DU MAC reset includes at least one of the following actions for the MAC entity (i.e., DU MAC reset):• stop a first portion of the one or more timers and retain the rest of the one or more timers;• set NDI(s) for DL HARQ process(es) to value 0;• flush soft buffers for UL HARQ process(es);• for each of the UL HARQ process(es), consider the next received transmission for a TB as the very first transmission;• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs)

[0173] In other implementations, the UE 102 refrains from resetting the UE MAC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from resetting the DU MAC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the UE MAC entity (not reset). Similarly, the DU 174 communicates with the UE 102 using the 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.

[0174] In some implementations, the UE 102 uses at least one UE RLC entity (e.g., RLC 206B) to communicate RLC PDUs with at least one DU RLC entity (e.g., RLC 206B) of the DU 174 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331). In some implementations, the UE 102 reestablishes some or all of the at least one UE RLC entity, after or in response to receiving the first LTM command and before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In some implementations, the DU 174 reestablishes some or allof the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

[0175] In some implementations, the LTM DU configuration 1 may or may not include one or more RLC reestablishment indications (e.g., reestablishRLC field(s)) configuring the UE 102 to reestablish some or all of the at least one UE RLC entity. If the LTM DU configuration 1 includes the a RLC reestablishment indication configuring the UE 102 to reestablish a first UE RLC entity, of the at least one UE RLC entity, that the UE 102 uses to communicate RLC PDU(s) with the DU 174, the UE 102 reestablishes the first UE RLC entity in response to the RLC reestablishment indication and the first LTM command. In some implementations, the UE 102 can reestablish the first UE RLC entity before performing 332 the random access procedure or communicating 336 with the DU 174 via the first cell. In other implementations, the UE 102 can reestablish the first UE RLC entity while or after performing 332 the random access procedure. Otherwise, if the LTM DU configuration 1 does not include the RLC reestablishment indication, the UE 102 refrains from reestablishing the first UE RLC entity in response to the first LTM command.

[0176] In some implementations, when the UE 102 reestablishes the first UE RLC entity, the UE 102 performs at least one of the following actions for the first UE RLC entity:• discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any;• stop and reset timer(s), if running;• reset state variables to initial values.In some implementations, the state variables and timer(s) are defined in 3GPP TS 38.322.

[0177] Otherwise, if the LTM DU configuration 1 does not include the RLC reestablishment indication for the first UE RLC entity, the UE 102 refrains from reestablishing the first UE RLC entity upon or when receiving the first LTM command. In other words, the UE 102 refrains from preforming the actions for reestablishing the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. In some implementations, if the LTM DU configuration 1 or element1 does not include the RLC reestablishment indication and includes an indication indicating that the configuration 1 is a full configuration, the UE 102 can reestablish the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. Otherwise, if the LTM DU configuration 1 or element 1 does not include the RLC reestablishment indication and the indication indicating that the configuration 1 is a full configuration, the UE 102 refrains from reestablishing the first UE RLC entity upon or when receiving the first LTM command.

[0178] Similarly, the DU 174 reestablishes some or all of at least one DU RLC entity (e.g., NR RLC 206B) that the DU 174 uses to communicate with the at least one UE RLC entity of the UE 102 (e.g., the events 302, 304, 318, 320, 324, 330 and / or 331) in response to the RLC reestablishment indication. In some implementations, the DU 174 reestablishes a first DU RLC entity of the at least one DU RLC entity after transmitting the first LTM command, receiving an acknowledgement for the first LTM command from the UE 102, or determining that the UE 102 connects to the first cell. In some implementations, the acknowledgement is a HARQ ACK. In other implementations, the acknowledgement is a MAC CE. In yet other implementations, the acknowledgement is a PUCCH transmission. In some implementations, when the first BS 104 reestablishes the first DU RLC entity, the DU 174 performs at least one of the following actions for the first DU RLC entity:• discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any;• stop and reset timer(s), if running;• reset state variables to initial values.In some implementations, the state variables and timer(s) are defined in 3GPP TS 38.322.

[0179] In other implementations, the UE 102 refrains from reestablishing some or all of the at least one UE RLC entity in response to receiving the first LTM command. Similarly, the DU 174 refrains from reestablishing some or more of the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell. In other words, the UE 102 communicates with the DU 174 on the first cell using the some or all of the at least one UE RLC entity (not reestablished). Forexample, the some or all of the at least one UE RLC entity includes the first UE RLC entity and / or a second UE RLC entity. Similarly, the DU 174 communicates with the UE 102 using the some or all of the at least one DU RLC entity (not reestablished) on the first cell during or after the random access procedure 332 or after determining that the UE 102 connects to the first cell. For example, the some or all of the at least one DU RLC entity includes the first DU RLC entity and / or a second DU RLC entity.

[0180] In some implementations, the UE 102 uses at least one UE PDCP entity (e.g., PDCP 210) to communicate UL PDCP PDUs and / or DL PDCP PDUs with at least one CU PDCP entity (e.g., PDCP 210) of the CU 172 in the event 302. In some implementations, the UE 102 performs a PDCP recovery procedure for some or all of the at least one UE PDCP entity, after or in response to receiving the first LTM command. For example, the UE 102 performs a PDCP recovery procedure for a first UE PDCP entity of the at least one UE PDCP entity, after or in response to receiving the first LTM command. In the PDCP recovery procedure, the UE 102 may or may not reestablish the first UE PDCP entity. After or in response to performing the PDCP recovery procedure, the UE 102 can retransmit at least a portion of the UL PDCP PDUs to the CU 172 via the DU 174 and the first cell in the event 336.Similarly, the CU 172 performs a PDCP recovery procedure for some or all of the at least one CU PDCP entity after or in response to transmitting the first LTM command. For example, the CU 172 performs a PDCP recovery procedure for a first CU PDCP entity of the at least one CU PDCP entity, after or in response to transmitting the first LTM command. In some implementations, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DU-to-CU message 329 or 334. In other implementations, the CU 172 performs the PDCP recovery procedure for the first CU PDCP entity in response to receiving the DL Data Delivery Status message. In the PDCP recovery procedure, the CU 172 may or may not reestablish the first CU PDCP entity. After or in response to performing the PDCP recovery procedure, the CU 172 can retransmit at least a portion of the DL PDCP PDUs to the UE 102 via the DU 174 and the first cell in the event 336.

[0181] In other implementations, the UE 102 refrains from reestablishing some or all of the at least one UE PDCP entity in response to receiving the first LTM command. For example, the some or all of the at least one UE PDCP entity includesthe first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 refrains from reestablishing some or more of the at least one CU PDCP entity, after (e.g., in response to) receiving the DU-to-CU message 329 or 340 or after (e.g., in response to) receiving the DL Data Delivery Status message. In other words, the UE 102 communicates with the CU 172 via the DU 174 and the first cell using the some or all of the at least one UE PDCP entity (not reestablished). For example, the some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 communicates with the UE 102 using the some or all of the at least one CU PDCP entity (not reestablished) via the DU 174 and the first cell. For example, the some or all of the at least one CU PDCP entity includes the first CU PDCP entity and / or a second CU PDCP entity.

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

[0183] After or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351 , 352, 354 and / or 356 might occur, similar to the events 324, 326, 328, 330, 331 , 332, 334 and / or 336, respectively. The UE 102 transmits 344 at least one measurement report to the DU 174. The at least one measurement report includes at least one measurement result for a second cell (i.e. , the cell 2). The at least one measurement result indicates that the second cell is suitable for communication with UE 102 and / or the first cell is not suitable for communication with the UE 102. After (e.g., in response to) receiving the at least one measurement report, the DU 174 determines to activate the LTM DU configuration 2 and generates a second LTM command to activate the LTM DU configuration 2 (i.e., the second LTM command commands the UE 102 to apply the LTM DU configuration 2). TheDU 174 then transmits 350 the second LTM command to the UE on the first cell to the UE 102.

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

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

[0186] The events 344, 346, 348, 350, 351 , 352, 354 are collectively referred to in FIG. 3 as an LTM execution procedure 398. The events 304, 306, 390, 392, 394, 324, 326, 328, 329, 330, 331 , 332, 334, 336, 396, 398, 356 are collectively referred to in FIG. 3 as an LTM DU configuration and / or activation procedure 380.

[0187] Referring next to FIG. 4, in a scenario 400, the first BS 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.

[0188] Initially, the UE 102 communicates 402 with the S-DU 174A on cell 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174A. The S-DU 174A is a serving DU similar to the DU 174 in FIG. 3. 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 (request the T-Dll 174B to) prepare cell(s) 1 , .... N for LTM for the UE 102. N can be a positive integer larger than zero or 1 . In the LTM preparation procedure 490, the CU 172 transmits a CU-to-DU message including the cell ID(s) 1 , ... , N to the T-DU 174B to request the T-DU 174B to prepare the cell(s) 1 , ... , N for LTM for the UE 102, similar to the event 308. In response, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) 1 , ... , N to the CU 172, similar to the event 310. The LTM DU configuration(s) 1 , ..., N configures the cell(s) 1 , ..., N for LTM, respectively. In details, the LTM DU configuration(s) 1 , ..., N include configuration parameters for communication on the cell(s) 1 , ... , N, respectively. In some implementations, the CU-to-DU message and DU-to-CU message in the procedure 490 are UE Context Setup Request message and UE Context Setup Response message, respectively. The CU 172 then transmits the LTM DU configuration(s) 1 , ... , N in a RRC reconfiguration message in an LTM configuration delivery procedure 494, similar to the LTM configuration delivery procedure 394. In some implementations, the T-DU 174B can include cell index(es) 1 , ..., N in the LTM DU configuration(s) 1 , ... , N, respectively. In some implementations, the CU 172 can set the cell index(es) 1 , ..., N to different values and include the cell index(es) 1 , ... , N in the CU-to-DU message of the procedure 490.

[0189] After performing the LTM preparation procedure 490, the CU 172 might perform an additional LTM preparation procedure(s) with the T-DU 174B to prepare cell(s) N+1 , ... , N+M for LTM for the UE 102, similar to the procedure 490. M is a positive integer larger than zero. The CU 172 might determine to do so based on one or more measurement reports received from the UE 102 via the S-DU 174A, similar to the events 404, 406. In the additional LTM preparation procedure, the CU 172 transmits a CU-to-DU message including cell ID(s) N+1 , ... , N+M to the T-DU 174B to request the T-DU 174B to prepare the cell(s) N+1 , ..., N+M for LTM for the UE 102. The cell ID(s) N+1 , ... , N+M identifies the cell ID(s) N+1 , ... , N+M, respectively. In response to the CU-to-DU message, the T-DU 174B transmits a DU-to-DU message including the LTM DU configuration(s) N+1 , ... , N+M to the CU 172. The LTM DU configuration(s) N+1 , ..., N+M configures the cell(s) N+1 , ... , N+M for LTM, respectively. In details, the LTM DU configuration(s) N+1 , ... , N+M includeconfiguration parameters for communication on the cell(s) N+1 , N+M, respectively. The CU 172 then transmits the LTM DU configuration(s) N+1 , N+M in a RRC reconfiguration message in an additional LTM configuration delivery procedure, similar to the LTM configuration delivery procedure 394 or 494.

[0190] In some implementations, the LTM preparation procedure 490 is a UE Context Setup procedure and the additional LTM preparation procedure is a UE Context Modification procedure.

[0191] In some implementations, the CU 172 and S-DU 174A might perform the procedure 380 with the UE 102, as described for FIG. 3. In the procedure 380, the CU 172 and S-DU 174A performs the procedure(s) 390 and / or 392 to prepare cell(s) of the S-DU 174A for LTM for the UE 102. Note, the value N in the procedure 380 or described for FIG. 3 can be the same as or different from the value N described for FIG. 4. In the procedure 390, the CU 172 might receive the first DU-to-CU message including the reference LTM DU configuration from the S-DU 174A in the event 310. In other implementations, the CU 172 and S-DU 174A does not perform the procedure 380 with the UE 102. In such cases, the CU 172 can perform 488 a reference LTM DU configuration query procedure with the S-DU 174A to obtain a reference LTM DU configuration. In the procedure 488, the CU 172 transmits 460 a CU-to-DU message to the S-DU 174A to request or query a reference LTM DU configuration. In some implementations, the CU 172 can include an indication in the CU-to-DU message to request or query a reference LTM DU configuration. In response to the indication or CU-to-DU message 460, the S-DU 174A transmits 462 a DU-to-CU message including a reference LTM DU configuration to the CU 172. In some implementations, the indication is a reference LTM DU configuration query indication. In other implementations, the indication is an LTM indication, and the CU 172 might include a query indication (e.g., GNB-DU Configuration Query IE) in the CU-to-DU message. After receiving the reference LTM DU configuration (i.e., either in the procedure 390 or in the procedure 488), the CU 172 includes the reference LTM DU configuration (received from the S-DU 174A) in the CU-to-DU message in the LTM preparation procedure 490. The T-DU 174B generates the LTM DU configuration(s) 1 , ..., N based on the reference LTM DU configuration received from the CU 172. In such cases, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the procedure 490. In the case of theadditional LTM preparation procedure, the T-Dll 174B does not include a reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. The CU 172 might not include the reference LTM DU configuration in CU- to-DU message in the additional LTM preparation procedure with the T-DU 174B. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+1 , ..., N+M based on the reference LTM DU configuration received from the CU 172.

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

[0193] In some implementations, the CU 172 includes the LTM DU configuration(s) 1 , ..., N of the procedure 380 in the CU-to-DU message of the procedure 490, and the T-DU 174B generates the LTM DU configuration(s) 1 , ..., N and / or N+1 , ... , N+M, considering or based on configuration(s) in the LTM DU configuration(s) of the procedure 380.

[0194] In some implementations, the LTM DU configuration X of the procedure 380 includes at least one reference signal (RS) resource configuration X, where 1 < X < N. Each of the RS resource configuration(s) X configures one or more RSs or one or more RS resources associated with the cell X of the S-DU 174A. The RS(s) includes SSB(s) and / or CSI-RS(s). The RS resource(s) includes SSB resource(s)and / or CSI-RS resource(s). In some implementations, each of the RS resource configuration(s) X includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) X is / are (similar to) CSI- ResourceConfig I E(s). In some implementations, the LTM DU configuration X includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI- ResourceConfig I E(s). The T-DU 174B generates at least one report configuration 1 for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the report configuration(s) 1 in the LTM DU configuration 1. In some implementations, the report configuration(s) 1 is / are (similar to) CSI-ReportConfig IE(s). In some implementations, the T-DU 174B generates at least one RS resource configuration 1 , considering or based on the RS resource configuration(s) X and includes the RS resource configuration(s) 1 in the LTM DU configuration 1. In some implementations, the T-DU 174B includes the RS resource configuration(s) X in the RS resource configuration(s) 1. In other implementations, the T-DU 174B includes each of the RS resource configuration(s) X in the RS resource configuration(s) 1 , except the RS resource configuration ID(s) in the RS resource configuration(s) X. The T-DU 174B assigns a RS resource configuration ID to a value for each of the RS resource configuration(s) 1 (including the RS resource configuration(s) X) and includes the RS resource configuration ID in the corresponding RS resource configuration.

[0195] In some implementations, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or RUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the report configuration(s) 1 includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the RS resource configuration(s) 1. After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124A, the UE 102 communicates with the S-DU 174B (i.e. , the T-DU 17B becomes a S-DU for the UE 102) and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the report configuration(s) 1. Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1 from the UE 102, in accordance with the report configuration(s) 1. In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantizedmeasurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) 1 and / or the report configuration(s) 1 and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values might include one or more L1-RSRP values and / or one or more L1-SINR values.

[0196] In some implementations, the T-DU 174B also includes additional RS resource configuration(s) in the LTM DU configuration 1. Each of the additional RS resource configuration(s) configures one or more additional RSs or one or more additional RS resources associated with the cell 1. The additional RS(s) includes SSB(s) and / or CSI-RS(s). The additional RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the additional RS resource configuration(s) includes a RS resource configuration ID. In some implementations, the additional RS resource configuration(s) is / are (similar to) CSI- ResourceConfig IE(s). In some implementations, the T-DU 174B includes the CSI- ResourceConfig IE(s) in the CSI-MeasConfig IE. The T-DU 174B generates at least one additional report configuration for reporting, on the cell 1 of the T-DU 174B, measurement results of the RS(s) or RS resource(s) and includes the additional report configuration(s) in the LTM DU configuration 1. In some implementations, the additional report configuration(s) is / are (similar to) CSI-ReportConfig IE(s).

[0197] In some implementations, the additional report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 1 for the UE 102 to transmit measurement results. In some implementations, each of the additional report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the additional RS resource configuration(s). After the UE 102 performs an LTM serving cell change to the cell 1 from the cell 124A, the UE 102 communicates 436 with the S-DU 174B and transmits measurement results on the UL resource(s) via the cell 1 to the S-DU 174B, in accordance with the additional report configuration(s). Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via the cell 1from the UE 102, in accordance with the additional report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the additional RS(s) or the additional RS resource(s) in accordance with the additional RS resource configuration(s) and / or the additional report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the additional RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values might include one or more L1-RSRP values and / or one or more L1-SINR values.

[0198] Similarly, the T-DU 174B can generate RS resource configuration(s) 2, ... , N, and / or N+1 , ... , N+M and / or report configuration(s) 2, ... , N, and / or N+1 , ... , N+M, considering or based on the RS resource configuration(s) X, and include the RS resource configuration(s) 2, ... , N, and / or N+1 , ... , N+M and / or the report configuration(s) 2, ..., N, and / or N+1 , ... , N+M in the LTM DU configuration(s) 2, ... , N, and / or N+1 , ... , N+M, respectively, as described above.

[0199] In other implementations, the LTM DU configuration X of the procedure 380 includes at least one TCI state configuration X, where 1 < X < N. Each of the TCI state configuration(s) X configures a TCI state that associates or includes one or two DL RSs with a corresponding QCL type. In some implementations, the DL RS(s) can be associated with the cell X operated by the S-DU 174A. In some implementations, each of the TCI state configuration(s) X includes a TCI state ID. In some implementations, each of the TCI state configuration(s) X is a TCI-State IE. In some implementations, the TCI state configuration(s) X includes / is / are an ul-TCI- ToAddModList-r17 ield, one or more TCI-UL-State-r17 lEs, a dl-OrJointTCI- StateToAddModList-r17 field, one or more TCI-State lEs, TCI-ActivatedConfig IE and / or a tci-StatesToAddModList field. In some implementations, the LTM DU configuration X includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) X. In some implementations, the T-DU 174B generates at least one TCI state configuration 1 , considering or based on the TCI stateconfiguration(s) X and includes the TCI state configuration(s) 1 in the LTM DU configuration 1. In some implementations, the TCI state configuration(s) 1 includes the TCI state configuration(s) X. In other implementations, the T-DU 174B includes each of the TCI state configuration(s) X in the TCI state config u ration (s) 1 , except the TCI state ID(s) in the TCI state configuration(s) X. The T-DU 174B assigns a TCI state ID to a value for each of the TCI state configuration(s) 1 (including the TCI state configuration(s) X) and includes the TCI state ID in the corresponding TCI state configuration. While the UE 102 and the S-DU 174B communicate 436 with one another, the S-DU 174B might transmit an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell X. The S-DU 174B includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell X, where the TCI state configuration is one of the TCI state configuration(s) X or includes configurations of one of the TCI state configuration(s) X.

[0200] Similarly, the T-DU 174B can generate TCI state configuration(s) 2, ... , N, considering or based on the RS resource configuration(s) X, and include the TCI state configuration(s) 2, ... , N, and / or N+1 , ..., N+M in the LTM DU configuration(s) 2, ..., N, and / or N+1 , ... , N+M, respectively, as described above.

[0201] In some implementations, in cases where the CU 172 performs the procedure 380 after performing the procedure 490, the CU 172 includes the LTM DU configuration(s) 1 , ..., N of the procedure 490 in the CU-to-DU message of the procedure 380, and the S-DU 174A generates the LTM DU configuration(s) 1 , ..., N of the procedure 380, considering or based on configurations in the LTM DU configuration(s) of the procedure 490, in a similar way as described above.

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

[0203] In some implementations, the CU 172 transmits 412 a CU-to-DU message including the ID(s) 1 , ... , N to the S-DU 174A and receives 414 a DU-to-CU message from the S-DU 174A in response. The CU-to-DU message 412 and DU-to-CU message 414 are collectively referred to in FIG. 4 as an LTM ID transfer procedure 493 or an LTM cell index transfer procedure 493. In some implementations, the message 412 and message 414 can be UE Context Modification Request message and UE Context Modification Response message, respectively. In some implementations, the CU 172 includes the LTM DU configuration(s) 1 , ... , N and / or cell ID(s) 1 , ... , N in the CU-to-DU message 412. In one implementation, the CU 172 includes the ID(s) 1 , ... , N in the CU-to-DU message 412. In another implementation, the CU 172 includes the cell index(es) 1 , ... , N in the CU-to-DU message 412. In some alternative implementations, the CU 172 can perform multiple LTM ID transfer procedures to transmit the ID(s) 1 , ... , N, cell ID(s) 1 , ..., N and / or LTM DU configuration(s) 1 , ..., N to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the ID(s) 1 , ..., N, cell ID(s) 1 , ... , N and / or LTM DU configuration(s) 1 , ..., N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the ID(s) 1 , .... N with the LTM DU configuration(s) 1 , .... N and / or the cell ID(s) 1 , ... , N, respectively. In other alternative implementations, the CU 172 can perform multiple LTM cell index transfer procedures to transmit the cell index(es) 1 , ... , N, cell ID(s) 1 , .... N and / or LTM DU configuration(s) 1 , ... , N to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the cell index(es) 1 , ..., N, cell ID(s) 1 , ... , N and / or LTM DU configuration(s) 1 , ... , N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associatesthe cell index(es) 1 , N with the LTM DU configuration(s) 1 , N and / or the cell ID(s) 1 , .... N, respectively.

[0204] In some implementations, the S-DU 174A generates a first serving DU configuration, based on the LTM DU configuration(s) 1 , 2, .... and / or N, and includes the first serving DU configuration in the DU-to-CU message 414. In some implementations, the first serving DU configuration including configurations updating (e.g., augmenting, modifying or replacing) the serving DU configuration 402. In other implementations, the first serving DU configuration includes configurations that are not included in the serving DU configuration 402. The CU 172 transmits a RRC reconfiguration message including the first serving DU configuration to the UE 102. The UE 102 applies the first serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174A using configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. The following are example implementations of generating the first serving DU configuration based on the LTM DU configuration 1 , ..., N.

[0205] In some implementations, the LTM DU configuration Y of the procedure 490 includes at least one RS resource configuration Y, where 1 < Y < N. Each of the RS resource configuration(s) Y configures one or more RSs or one or more RS resources associated with the cell Y of the T-DU 174B. The RS(s) includes SSB(s) and / or CSI-RS(s). The RS resource(s) includes SSB resource(s) and / or CSI-RS resource(s). In some implementations, each of the RS resource configuration(s) Y includes a RS resource configuration ID. In some implementations, the RS resource configuration(s) Y is / are (similar to) CSI-ResourceConfig IE(s). In some implementations, the LTM DU configuration Y includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI-ResourceConfig I E(s). The S-DU 174A generates at least one serving report configuration for reporting, on the cell 124A, measurement results of the RS(s) or RS resource(s) and includes the serving report configuration(s) in the first serving DU configuration. In some implementations, the serving report configuration(s) is / are (similar to) CSI-ReportConfig IE(s). In some implementations, the S-DU 174A generates at least one serving RS resourceconfiguration, considering or based on the RS resource configuration(s) Y and includes the serving RS resource configuration(s) in the first serving DU configuration. In some implementations, the S-DU 174A includes the RS resource configuration(s) Y in the serving RS resource configuration(s). In other implementations, the S-DU 174A includes each of the RS resource configuration(s) Y in the serving RS resource configuration(s), except the RS resource configuration ID(s) in the RS resource configuration(s) Y. The S-DU 174A assigns a RS resource configuration ID to a value for each of the serving RS resource configuration(s) (including the RS resource configuration(s) Y) and includes the RS resource configuration ID in the corresponding serving RS resource configuration.

[0206] In some implementations, the serving report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the cell 124A for the UE 102 to transmit measurement results. In some implementations, each of the serving report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the serving RS resource configuration(s). While the UE 102 communicates with the S- DU 174A, the UE 102 transmits measurement results on the UL resource(s) via the cell 124A to the S-DU 174A, in accordance with the serving report co nfigu ration (s) (e.g., event 424). Correspondingly, the S-DU 174A receives the measurement results on the UL resource (s) via the cell 124A from the UE 102, in accordance with the serving report configuration(s). In some implementations, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the serving RS resource configuration(s) and / or the serving report configuration(s) and obtains the quantized measurement values from the measurements. In some implementations, the RS resource indicator(s) indicates the RS(s) or a RS resource(s) where the UE 102 perform measurements or obtains the quantized measurement values. In some implementations, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values might include one or more L1-RSRP values and / or one or more L1-SINR values.

[0207] In other implementations, the LTM DU configuration Y of the procedure490 includes at least one TCI state configuration Y, where 1 < Y < N. Each of the TCI state configuration(s) Y configures a TCI state that associates or includes one or two DL RSs with a corresponding QCL type. In some implementations, the DL RS(s) can be associated with the cell Y operated by the T-DU 174B. In some implementations, each of the TCI state configuration(s) Y includes a TCI state ID. In some implementations, each of the TCI state configuration(s) Y is a TCI-State IE. In some implementations, the TCI state configuration(s) Y includes / is / are an ul-TCI- ToAddModList-r17 field, one or more TCI-UL-State-r17 lEs, a dl-OrJointTCI- StateToAddModList-r17 field, one or more TCI-State lEs, TCI-ActivatedConfig IE and / or a tci-StatesToAddModListf\e\d. In some implementations, the LTM DU configuration Y includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) Y. In some implementations, the S-DU 174A generates at least one serving TCI state configuration, considering or based on the TCI state configuration(s) Y and includes the serving TCI state configuration(s) in the first serving DU configuration. In some implementations, the serving TCI state configuration(s) 1 includes the TCI state configuration(s) Y. In other implementations, the S-DU 174A includes each of the TCI state configuration(s) Y in the serving TCI state configuration(s), except the TCI state ID(s) in the TCI state configuration(s) Y. The S-DU 174A assigns a TCI state ID to a value for each of the serving TCI state configuration(s) (including the TCI state configuration(s) Y) and includes the TCI state ID in the corresponding serving TCI state configuration. While the S-DU 174A communicate 436 with the UE 102, the S-DU 174A might transmit an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to the cell Y. The S-DU 174A includes a TCI state ID in the LTM command to indicate to the UE 102 to apply a TCI state configuration identified by the TCI state ID to communicate on the cell Y, where the TCI state configuration is one of the TCI state configuration(s) Y or includes configurations of one of the TCI state configuration(s) Y.

[0208] In some implementations, the CU 172 transmits a CU-to-DU message including the ID(s) N+1 , ... , 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 172includes the LTM DU configuration(s) N+1 , N+M and / or cell ID(s) N+1 , N+M in the CU-to-DU message. In some alternative implementations, the CU 172 can perform multiple LTM ID transfer procedures to transmit the ID(s) N+1 , .... N+M, cell ID(s) N+1 , ... , N+M and / or LTM DU configuration(s) N+1 , ... , N+M to the S-DU 174A. In each of the procedures, the CU 172 includes particular portion of the ID(s) N+1 , ... , N+M, cell ID(s) N+1 , ... , N+M and / or LTM DU configuration(s) 1 , ... , N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the ID(s) N+1 , ..., N+M with the LTM DU configuration(s) N+1 , ... , N+M and / or the cell ID(s) N+1 , ..., N+M, respectively. In some implementations, the S-DU 174A generates a second serving DU configuration, based on the LTM DU configuration(s) N+1 , N+2, ... , and / or N+M, and includes the second serving DU configuration in the DU-to-CU message. In some implementations, the second serving DU configuration including configurations updating (e.g., augmenting, modifying or replacing) the first serving DU configuration and / or updating configurations included in the serving DU configuration 402 and not updated by the first serving DU configuration. In other implementations, the second serving DU configuration includes configurations that are not included in the first serving DU configuration. The CU 172 transmits a RRC reconfiguration message including the second serving DU configuration to the UE 102 via the S-DU 174A. The UE 102 applies the second serving DU configuration to communicate with the serving DU upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in the procedure 494. Depending on implementations, the UE 102 communicates with the S-DU 174A using configurations included in the serving DU configuration 402 and / or the first serving DU configuration and not updated by the second serving DU configuration. In some implementations, the S- DU 174A generates one or more new L1 measurement configurations, based on L1 measurement configuration(s) in the LTM DU configuration(s) N+1 , N+2, ..., and / or N+M, and includes the new L1 measurement configuration(s) in the second serving DU configuration. In some implementations, the S-DU 174A generates one or more new TCI state configuration, based on TCI state configuration(s) in the LTM DU configuration(s) N+1 , N+2, ..., and / or N+M, and includes the new TCI state configuration(s) in the second serving DU configuration.

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

[0210] Later in time, the UE 102 might transmit 424 at least one measurement report to the S-DU 174A, similar to the event 324. The at least one measurement report (e.g., L1 measurement report(s)) includes an event ID, first measurement result(s) for the cell 1 of the T-DU 174B, and / or includes second measurement result(s) for the cell 124A. In some implementations, the first measurement result(s) can be or include RSRP, RSRQ and / or SI NR that the UE 102 obtains from reference signal(s) transmitted on the cell 1. Likewise, the second measurement result(s) can be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on the cell 124A. In some implementations, the event ID, RSRP, RSRQ and / or SINR are L1-event ID, L1-RSRP, L1-RSRQ and / or L1-SINR, respectively. Based on the first measurement result(s) and / or second measurement result(s), the S-DU 174A might transmit 430 a first LTM command (i.e. , LTM command 1) including the ID 1 to the UE 102 to order the UE 102 to perform a serving cell change to the cell 1 of the T-DU 174B. In some implementations, the first LTM command includes the ID 1 (i.e., LTM ID). In other implementations, the first LTM command includes the cell index 1 . When the UE 102 receives the first LTM command, the UE 102 performs a serving cell change to the cell 1 from a serving cell in accordance with the LTM DU configuration 1 . After (e.g., in response to) receiving the first LTM command, the UE 102 might or might not perform 432 a random access procedure with the T-DU 174B, similar to the event 332. After (e.g., in response to) receiving the first LTM command or completing the random access procedure 432, the UE 102 might communicates 436 with the T-DU 174B on the firstcell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the T-DU 174B, similar to the event 336. If a serving cell change occurs in the procedure 380, the serving cell can be the cell 1 or cell 2 of the S-DU 174A. Otherwise, if no serving cell change occurs in the procedure 380 or the procedure 380 is not performed, the serving cell is the cell 124A. If the first LTM command includes the LTM ID 1 , the UE 102 identifies the LTM DU configuration 1 and / or cell ID 1 (i.e., the cell 1), based the LTM ID 1 , as described for FIG. 3. If the first LTM command includes the cell index 1 , the UE 102 identifies the LTM DU configuration 1 , cell ID 1 (i.e., the cell 1) and / or LTM ID 1 , based the cell index 1 , as described for FIG. 3. The UE 102 applies the LTM DU configuration 1 to communicate with the T-DU 174B, after (e.g., in response to) receiving the first LTM command or successfully accessing the cell 1 .

[0211] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 430, the S-DU 174A might transmit 429 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some implementations, the S-DU 174A includes the cell ID 1 or the LTM ID 1 in the DU-to- CU message 429 to indicate that the S-DU 174A is to activate the LTM DU configuration 1 or trigger an LTM serving cell change. The S-DU 174A can transmit the DU-to-CU message 429 to the CU 172 before or after transmitting the LTM command 430. In some implementations, when or after the CU 172 receives the DU- to-CU message 429, the CU 172 might stop or suspend transmitting DL data for the UE 102 to the S-DU 174A until receiving the DU-to-CU message 434. After receiving the DU-to-CU message 434, the CU 172 starts, continues or resumes transmitting DL data for the UE 102 to the T-DU 174B. When or after the T-DU 174B detects that UE 102 accesses the cell 1 , the T-DU 174B transmits the DL data to the UE 102 via the cell 1 .

[0212] The resource release procedure 496 can be similar to the procedure 396. Alternatively, in the resource release procedure 496, the CU 172 can transmit a CU- to-DU message (e.g., a UE Context Release Command message) to the S-DU 174A to release a UE context of the UE 102. In response, the S-DU 174A releases a UE context of the UE 102 and transmits 440 a DU-to-CU message (e.g., a UE Context Release Complete message) to the CU-172.

[0213] The events 380, 404, 406, 490, 492, 494, 494, 424, 426, 428, 429, 430, 431 , 432, 434, 436, 496, 498, 456 are collectively referred to in FIG. 4 as an LTM configuration and / or activation procedure 480.

[0214] Referring next to FIG. 5A, in a scenario 500A, the second BS 106 operates as an MN, and the first BS 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 first BS 104 of FIG. 3.

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

[0216] While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 can perform 580 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. In some implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 can transmit the at least one measurement report to the CU 172 via the DU 174 and cell 124A in the events 504 and 506, similar to the events 304 and 306, respectively. In other implementations, while communicating in DC with the MN 106 and SN 104, the UE 102 can transmit 505 at least one measurement report to the MN 106 via the cell 126. The MN 106 in turn transmits 507 the at least one measurement report to the CU 172. In some implementations, the MN 106 generates at least one SN message including the at least one measurement report and transmits the at least one SN message to the CU 172 in the event 507. In one implementation, the at least one SN message include RRC Transfer message(s) and / or SN Modification Request message(s).

[0217] After (e.g., in response to) receiving the at least one measurement report or while the SN 104 communicates with the UE 102, the SN 104 determines to prepare the first cell for the UE 102, as described for FIG. 3. The events 590, 592, 594, 524, 526, 528, 529, 530, 531 , 532, 534, 536, 596, 598, and 556 are similar to the events 390, 392, 394, 324, 326, 328, 329, 330, 331 , 332, 334, 336, 396, 398, and 356, respectively. After receiving the first LTM command 530, transmitting the acknowledgement 531 , or determining that the UE 102 successfully connects to the first cell 532 or 536, the UE 102 operating in DC with the MN 106 and SN 104 communicates 536 with the DU 174 on the first cell in accordance with the LTM DU configuration 1 and communicates 536 with the CU 172 via the DU 174, similar to the event 336. Later in time, the DU 174 and / or CU 172 can perform the LTM execution procedure 598 with the UE 102 to command the UE 102 to perform a cell change from the first cell to the second cell, similar to the procedure 398 or 498. As a result of the procedure 598, the UE 102 operating in DC with the MN 106 and SN 104 communicates 556 with the DU 174 on the second cell in accordance with the LTM DU configuration 2 and communicates 556 with the CU 172 via the DU 174, similar to the event 356.

[0218] The events 504, 506, 505, 507, 590, 592, 594, 524, 526, 528, 529, 530, 531 , 532, 534, 536, 596, 598, 556 are collectively referred to in FIG. 5A as an LTM DU configuration and / or activation procedure 581 .

[0219] Referring next to FIG. 5B, a scenario 500B is generally similar to the scenario 500A, except that the SN 104 transmits 517, 519 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 521 , 523 the RRC reconfiguration complete message from the UE 102 via the MN 106. The RRC reconfiguration message 517, 519 is similar to the RRC reconfiguration message 316, 318. The RRC reconfiguration complete message 521 , 523 is similar to the RRC reconfiguration message 320, 322. In some implementations, the SN 104 generates a first SN message (e.g., S / V Modification Required message, SN Modification Required message, or RRC Transfer message) including the RRC reconfiguration message and transmits the first SN message to the MN 106 in the event 517. The MN 106 generates a MN RRC message including the RRC reconfiguration message and transmits 519 the MN RRC message to the UE 102. In response, the UE 102 generates a MN RRC response message including the RRC reconfiguration complete message and transmits 521 the MN RRC response message to the MN 106. In some implementations, the MN 106 generates a second SN message (e.g., SN Reconfiguration Complete message or RRC Transfer message) including the RRC reconfiguration complete message and transmits the second SN message to the SN 104 in the event 523. In some implementations, the MN RRC message and MN RRC response message can be a RRC reconfiguration message and a RRC reconfiguration complete message, respectively.

[0220] The events 504, 506, 505, 507, 590, 592, 594, 517, 519, 521 , 523, 524, 526, 528, 529, 530, 531 , 532, 534, 536, 596, 598, 556 are collectively referred to in FIG. 5B as an LTM DU configuration and / or activation procedure 582.

[0221] Referring next to FIG. 6A, in a scenario 600A, the second BS 106 operates as an MN, and the first BS 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 first BS 104 in the scenario 400. While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 can perform 680 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU172 can perform 681 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A or S-DU 174B, similar to the procedure 581 or 582.

[0222] Referring next to FIG. 6B, a scenario 600B similar to the scenarios 300- 500B and 600A, except that that the SN 104 transmits 617, 619 the RRC reconfiguration message to the UE 102 via the MN 106 and receives 621 , 623 the RRC reconfiguration complete message from the UE 102 via the MN 106.

[0223] Referring next to FIG. 7A, in a scenario 700A, the first BS 104 operates as an MN and an SN, similar to the scenarios 300-600B. The first BS 104 includes a CU 172, a master DU (M-DU) 174A and a secondary DU (S-DU) 174B. The CU 172 operates with the M-DU 174A as a MN, similar to the first BS 104 in FIG. 3 or the MN 106 in FIGs. 5A-6B, and the CU 172 operates with the S-DU 174B as a SN, similar to the SN 104 in FIGs. 5A-6B.

[0224] In the scenario 700A, the UE 102 initially communicates 702 in DC with the M-DU 174A and S-DU 174B and communicates 702 with the CU 172 via the M-DU 174A and S-DU 174B. In the event 702, the UE 102 communicates with the S-DU 174B on cell 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174B using a serving CU configuration, similar to the event 302.Events 704 and 706 are similar to the events 304 and 306. In some implementations, the UE 102 can transmit 705 at least one measurement report to the M-DU 174A, similar to the event 304. The M-DU 174A in turn transmits 707 at least one DU-to-CU message including the at les tone measurement report to the CU 172, similar to the event 306. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 780 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380.

[0225] The events 704, 706, 705, 707, 790, 792, 794, 724, 726, 728, 729, 730, 731 , 732, 734, 736, 796, 798, 756 are collectively referred to in FIG. 7A as an LTM configuration and / or activation procedure 781.

[0226] Referring next to FIG. 7B, a scenario 700B similar to the scenarios 300- 600B and 700A, except that that the CU 172 transmits 717, 719 the RRC reconfiguration message to the UE 102 via the M-DU 174A and receives 721 , 723 the RRC reconfiguration complete message from the UE 102 via the M-DU 174A.

[0227] The events 704, 706, 705, 707, 790, 792, 794, 717, 719, 721 , 723, 724, 726, 728, 729, 730, 731 , 732, 734, 736, 796, 798, 756 are collectively referred to in FIG. 7B as an LTM DU configuration and / or activation procedure 782.

[0228] Referring next to FIG. 8A, in a scenario 800A, the first BS 104 operates as an MN and an SN, similar to the scenarios 300-700B. The first BS 104 includes a CU 172, a master DU (M-DU) 174A, a secondary DU (S-DU) 174B, and a target secondary DU (T-DU) 174C. The CU 172 operates with the M-DU 174A as a MN and operates with the S-DU 174B as a SN. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 880 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 can perform 881 an LTM DU configuration and / or activation procedure with the UE 102 via the S-DU 174A, similar to the procedure 581 or 582.

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

[0230] Next, several example methods, which can be implemented in a RAN node (e.g., a BS, a DU or a CU) or a UE, for configuring and / or activating one or more TCI state configurations for an LTM candidate cell (i.e. , a cell for LTM), are discussed with reference to FIGs. 9A-15D. The descriptions for FIGs. 3-8B can apply to FIGs. 9A-15D.

[0231] FIG. 9A illustrates an example method 900A, which can be implemented by a BS (e.g., the first BS 104 or 106). The method 900A begins at step 902, where the BS communicates with a UE via a serving cell, using at least one first non-LTM TCI state configuration (e.g., events 302, 402, 502, 602, 702, 802). At step 904, the BS transmits an LTM ID, a first LTM DU configuration, and at least one first LTM TCI state configuration to the UE, where the first LTM DU configuration configures a candidate cell for LTM, each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell (e.g., events 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, 819). In some implementations, the LTM ID identifies the LTM DU configuration and the first LTM TCI state configuration(s). Insome implementations, the BS includes the LTM ID, the first LTM DU configuration, and the first LTM TCI state configuration(s) in a RRC reconfiguration message and transmits the RRC reconfiguration message to the UE. In other implementations, the BS transmits a first RRC reconfiguration message including the LTM ID and the first LTM DU configuration to the UE, and transmits a second RRC reconfiguration message including the LTM ID and the first LTM TCI state configuration(s) to the UE. The BS may do so because the UE or the BS does not support reception of segmented DL RRC messages.

[0232] In some implementations, the BS includes the LTM DU configuration in a DL RRC message and includes the DL RRC message in a first element (e.g., the element 1 described above). The BS includes the LTM ID in the first element. The BS transmits the first element to the UE at step 904. In some implementations, the BS includes the first LTM TCI state configuration(s) in the first element. In some implementations, the BS includes the first element in the (first) RRC reconfiguration message. In other implementations, the BS includes the first LTM TCI state configuration(s) in a second element instead of the first element. In such cases, the BS also includes the LTM ID in the second element to indicate the first LTM TCI state configuration(s) associated with the LTM ID. For example, the second element is an addition or modification IE (e.g., LTM-ConfigToAddMod IE, LTM-Candidate IE, LTM-CandidateToAddMod IE or LTM-CandidateConfigToAddMod IE). The BS transmits the second element to the UE at step 904. In some implementations, the BS includes the second element in the second RRC reconfiguration message.

[0233] At step 906, the BS generates a first LTM TCI states activation / deactivation command (also referred to as “LTM TCI states command) to activate one or more of the first LTM TCI state configurations, where the first LTM TCI states activation / deactivation command includes the LTM ID and at least one first TCI state ID and each of the first TCI state ID(s) identifies a respective one of the first LTM TCI state configuration(s) (e.g., events 325, 425, 525, 625, 725, 825). At step 908, the BS transmits the first LTM TCI states activation / deactivation command to the UE via the serving cell, using one of the first non-LTM TCI state configuration(s) (e.g., events 325, 425, 525, 625, 725, 825). At step 910, the BS transmits one or more reference signals on the candidate cell, using the (activated) first LTM TCI state configuration(s). At step 912, the BS transmits an LTM command to the UE via theserving cell using one of the first non-LTM TCI state configuration(s), where the LTM command includes the LTM ID and a TCI state ID, commanding the UE to perform an LTM cell switch and activate a TCI state configuration identified by the TCI state ID (e.g., events 330, 430, 530, 630, 730, 830). At step 914, the BS detects that the UE accesses the candidate cell (e.g., events 332, 432, 532, 632, 732, 832). At step 916, the BS communicates with the UE via the candidate cell, using the LTM DU configuration and the activated LTM TCI state configuration (e.g., events 336, 436, 536, 636, 736, 836). The activated LTM TCI state configuration is the LTM TCI state configuration activated by the LTM command at step 912.

[0234] In some implementations, the UE performs a contention-based random access procedure on the candidate cell with the BS in response to the LTM command. The UE transmits a random access preamble on the candidate cell in the random access procedure. The BS associates the random access preamble with a SSB or a SSB index. The BS may include, in the LTM DU configuration, association information indicating association between the random access preamble and the SSB (index). The BS transmits the SSB on the candidate cell using a BS transmission beam. The UE receives the SSB on the candidate cell from the BS using a UE reception / receiving beam. The UE may receive and / or measure the SSB before receiving the LTM command. Alternatively, the UE may receive and / or measure the SSB after receiving the LTM command. The UE determines (e.g., selects) the random access preamble based on the SSB. The UE transmits the random access preamble on the candidate cell, using a UE transmission beam corresponding to or derived from the UE reception / receiving beam. The BS may receive the random access preamble using a BS reception / receiving beam. After transmitting the random access preamble, the UE monitors a PDCCH to receive a random access response. The UE may monitor the PDCCH using the UE reception / receiving beam. In response to receiving the random access preamble, the BS generates a DCI scheduling a PDSCH transmission including a random access response and transmits the DCI on a PDCCH to the UE. The BS may transmit the DCI on the PDCCH using the BS transmission beam. In some implementations, the BS refrains from using the first LTM TCI state configuration(s) to transmit the DCI and the PDSCH transmission. The random access response includes a random access preamble ID (or a preamble index) identifying the random access preamble,a UL grant, and a timing advance command. The UE adjusts UL transmission timing in accordance with the timing advance command. The UE transmits a UL PDU (e.g., a MAC PDU) to the BS in accordance with the UL grant and the UL transmission timing. The random access response may further include a TAG ID field. The UE may ignore or not use the TAG ID field, or the UE may determine the TAG ID field is a reserved / unused field, even the UE supports and / or operates two TA feature in source serving cell or S-DU. The UE may transmit the UL PDU using the UE transmission beam. In some implementations, the UE refrains from using the first LTM TCI state configuration(s) to transmit the UL PDU. In some implementations, the UE includes a UE identifier (e.g., C-RNTI) in the UL MAC PDU. In some implementations, after transmitting the UL PDU, the UE monitors a PDCCH in accordance with the first LTM TCI state configuration(s). After transmitting the UL PDU, the UE might monitor a PDCCH in accordance with the first LTM TCI state configuration(s), where the PDCCH schedules a new UL grant or a DL assignment indicating / confirming the UE identifier. In other implementations, the UE monitors a PDCCH using the UE reception / receiving beam. The BS receives the UL PDU from the UE in accordance with the UL grant. The BS may receive the UL PDU using the BS reception / receiving beam. The BS identifies the UE in accordance with the UE identifier. In response to receiving the UE identifier, the BS generates a DCI and a CRC for the DCI, scrambles the CRC with the UE identifier, and transmits the DCI and the scrambled CRC on a PDCCH to the UE. In some implementations, the BS transmits the DCI and the scrambled CRC, using one of the first LTM TCI state configuration(s). The UE receives the DCI and the scrambled CRC on the PDCCH, using one of the first LTM TCI state configuration(s) (i.e. , the same as the LTM TCI state configuration used by the BS to transmit the DCI and the scrambled CRC). When the UE receives the scrambled CRC and determines that the (scrambled) CRC is valid, the UE determines that the UE performs the LTM cell switch to the candidate cell successfully. In some implementations, the DCI schedules a PUSCH transmission. In such cases, the UE transmits a PUSCH transmission on the candidate cell. The BS receives the PUSCH transmission on the candidate cell in accordance with the DCI. After the BS successfully completes the contention-based random access procedure with the UE, the bases station may use the activated LTM TCI state configuration to communicate with the UE. Alternatively, after the BSsuccessfully completes the contention-based random access procedure with the UE, the BS uses the BS transmission beam and the BS reception / receiving beam to communication with UE instead of the activated LTM TCI state configuration.

[0235] In some implementations, a UE or BS using / deriving a transmission beam for transmission can refer to as the UE or BS using / deriving spatial transmission parameters / filters for transmission. In some implementations, a UE or BS using / deriving a reception or receiving beam for reception can refer to as that the UE or BS using / deriving spatial receiving / reception parameters or QCL assumption for reception.

[0236] In other implementations, the LTM command includes contention-free random access (CFRA) configuration parameters / fields. The CFRA configuration parameters may include a preamble index, a UL / supplemental UL (SUL) indicator, a SSB index, a PRACH Mask index, and / or a repetition number. The preamble index indicates a random access preamble. The UE determines the random access preamble in accordance with the preamble index. The UE determines a UL carrier or a SUL carrier of the candidate cell to transmit the random access preamble in accordance with the UL / SUL indicator. In some implementations, the LTM DU configuration includes a first plurality of configuration parameters and a second plurality of configuration parameters for the UL carrier and the SUL carrier respectively. For example, if the UL / SUL indicator indicates the UL carrier, the UE transmits the random access preamble on the UL carrier of the candidate cell, e.g., using the first plurality of configuration parameters. If the UL / SUL indicator indicates a SUL carrier, the UE transmits the random access preamble on the SUL carrier of the candidate cell, e.g., using the second plurality of configuration parameters. In some implementations, if the UE determines that the candidate cell does not support a SUL carrier (e.g., the LTM DU configuration does not include configuration parameters for the SUL carrier), the UE may ignore the UL / SUL indicator (or determine the UL / SUL indicator absent) and transmit the random access preamble on the UL carrier of the candidate cell, e.g., using the first plurality of configuration parameters. In other implementations, if the UE determines that the candidate cell does not support a SUL carrier (e.g., the LTM DU configuration does not include configuration parameters for the SUL carrier), the CFRA configuration parameters do not include a UL / SUL indicator and the UE transmits the random access preambleon the UL carrier of the candidate cell, e.g., using the first plurality of configuration parameters. In some implementations, the UE determines a pathloss reference signal (PL-RS) for determining UL transmit power for transmitting the random access preamble on the candidate cell. For example, the UE determines the PL-RS based on the SSB (index) indicated in the LTM command. For another example, the UE determines the PL-RS based on the first LTM TCI state configuration indicated / activated in the LTM command. In some implementations, the UE receives a SSB on the candidate cell from the BS, indicated by the SSB index from the LTM command. The UE may receive the SSB using a UE reception / receiving beam. In some implementations, the UE transmits the random access preamble on the candidate cell, using a UE transmission beam corresponding to or derived by the UE reception beam. In such cases, the UE monitors a PDCCH to receive a random access response using the UE reception / receiving beam, as described in the contention-based random access procedure above. For example, the UE may monitor a PDCCH to receive a random access response using the UE reception / receiving beam for receiving the SSB or the first LTM TCI state configuration indicated / activated in the LTM command.

[0237] In yet other implementations, when the UE performs an LTM cell switch to the candidate cell in response to receiving the LTM command, the UE skips a random access procedure and transmits a UL transmission (e.g., a PUSCH transmission) to the BS to access the candidate cell. In some implementations, the UE skips a random access procedure on the candidate cell because the UE has acquired UL synchronization on / with the candidate cell or the LTM command includes a (valid) timing advance command for the candidate cell. In some implementations, the LTM command includes a timing advance command for the candidate cell to indicate the UE to skip a random access procedure. The UE applies the timing advance command and skips a random access procedure when accessing the candidate cell in response to the LTM command. In other implementations, the LTM command includes an indication to indicate the UE to acquire UL synchronization with the candidate cell. The indication is not a timing advance command. In response to the indication, the UE acquires UL synchronization based on reference signal time difference (RSTD) measurements. The BS receives the UL transmission from the UE. In some implementations, the BSincludes a configured grant configuration in the LTM DU configuration and the UE transmits the UL transmission using a configured grant configured by the configured grant configuration. In other implementations, the UE receives a dynamic grant for the UE from the BS on the candidate cell and transmits the UL transmission in accordance with the dynamic grant. In response to receiving the UL transmission, the BS generates a DCI and a CRC for the DCI, scrambles the CRC with the UE identifier, and transmits the DCI and the scrambled CRC on a PDCCH to the UE. The DCI schedules a PUSCH transmission or a PDSCH transmission. In some implementations, the BS transmits the DCI and the scrambled CRC, using one of the first LTM TCI state configuration(s), e.g., the first LTM TCI state configuration indicated or derived from the LTM command. The UE receives the DCI and the scrambled CRC on the PDCCH, using one of the first LTM TCI state configuration(s) (i.e., the same as the LTM TCI state configuration used by the BS to transmit the DCI and the scrambled CRC). When the UE receives the scrambled CRC and determines that the (scrambled) CRC is valid, the UE determines that the UE performs the LTM cell switch to the candidate cell successfully. If the DCI schedules a PUSCH transmission, the UE transmits a PUSCH transmission on the candidate cell. The BS receives the PUSCH transmission on the candidate cell in accordance with the DCI. If the DCI schedules a PDSCH transmission, the BS transmits a PDSCH transmission on the candidate cell in accordance with the DCI. The UE receives a PDSCH transmission on the candidate cell in accordance with the DCI.

[0238] In some implementations, the LTM ID is an LTM candidate ID or an LTM configuration index. In some implementations, the BS configures the LTM ID to a value of 0, ... , 7. In such cases, the LTM ID is in a format of 3 bits. In some implementations, the BS transmits a cell ID (e.g., PCI) of the candidate cell to the UE. In some implementations, the PCI is in a format of 10 bits. The BS may include the cell ID in the first LTM DU configuration. The BS may include the cell ID in the RRC reconfiguration message, the first RRC reconfiguration message or the second RRC reconfiguration message described above. In some implementations, the reference signal(s) includes one or more SSBs, one or more CSI-RSs and / or one or more tracking reference signals. A tracking reference signal might be a CSI-RS for (time / frequency) tracking or a CSI-RS in a CSI resource set configured with higher layer parameter trs-lnfo.

[0239] In some implementations, the LTM TCI state configuration configures a TCI state. In some implementations, the first LTM TCI state configuration(s) includes the LTM TCI state configuration activated by the LTM command with the TCI state ID. In other implementations, the first LTM TCI state configuration(s) does not include the LTM TCI state configuration activated by the LTM command with the TCI state ID. The BS can transmit the LTM TCI state configuration to the UE before transmitting the LTM command. For example, the BS includes the LTM TCI state configuration in the RRC reconfiguration message, the first RRC reconfiguration message or the second RRC reconfiguration message. In another example, the BS transmits a third RRC reconfiguration message includes the LTM TCI state configuration to the UE.

[0240] In some implementations, the BS can transmit at least one second LTM TCI state configuration to the UE, where each of the second LTM TCI state configuration(s) configures a TCI state for the candidate cell as described for step 905 in FIG. 9B. In some implementations, the BS includes at least one second TCI state ID in the first LTM TCI states activation / deactivation command to activate the second TCI state configuration(s). Each of the second TCI state ID(s) identifies a respective one of the second LTM TCI state configuration(s). In other implementations, the BS does not include the second TCI state ID(s) in the first LTM TCI states activation / deactivation command. In some implementations, the BS includes the second TCI state ID(s) in the LTM command. In other implementations, the BS does not include the second TCI state ID(s) in the LTM command.

[0241] In some implementations, each LTM TCI state configuration (e.g., in the first and / or second TCI state configuration(s)) include a TCI state ID identifying the LTM TCI state configuration.

[0242] FIG. 9B is a flow diagram of an example method 900B similar to the method 900A, except that the method 900B includes steps 905, 918, 920 and 922. At step 905, the BS transmits the LTM ID and at least one second LTM TCI state configuration to the UE, where each of the second LTM TCI state configuration(s) configures a TCI state for the candidate cell. In some implementations, the LTM ID identifies the second LTM TCI state configuration(s). In some implementations, the BS includes the second LTM TCI state configuration(s) in the RRC reconfiguration message or the first RRC reconfiguration message described for FIG. 9A. In other implementations, the BS transmits a third RRC reconfiguration message includingthe LTM ID and the second LTM TCI state configuration(s) to the UE. In some implementations, the BS transmits the third RRC reconfiguration message to the UE before transmitting the LTM command or the first LTM TCI states activation / deactivation command. Next, the method follows steps 906, 908, 910, 912, 914, and 916, previously discussed. Steps 910, 912, 914, and 916 are mandatory in this embodiment.

[0243] At step 918, the BS generates a second LTM TCI states activation / deactivation command to activate the second LTM TCI state configuration(s), where the second LTM TCI states activation / deactivation command includes the LTM ID and at least one second TCI state ID and each of the second TCI state ID(s) identifies a respective one of the second LTM TCI state configuration(s). At step 920, the BS transmits the second LTM TCI states activation / deactivation command to the UE via the candidate cell, using the activated LTM TCI state configuration (e.g., event 336, 436, 536, 636, 736, 836). The activated LTM TCI state configuration is the LTM TCI state configuration activated by the LTM command at step 912. At step 922, the BS communicates with the UE via the candidate cell, using the second LTM TCI state configuration(s) (e.g., event 336, 436, 536, 636, 736, 836). In some embodiments, the BS may indicate deactivation of some or all of the first LTM TCI state configuration(s) in the second LTM TCI states activation / deactivation command.

[0244] FIG. 9C is a flow diagram of an example method 900C similar to the method 900A, except that the method 900C includes steps 917, 919 and 921. At step 917, the BS generates a non-LTM TCI states activation / deactivation command to activate at least one second non-LTM TCI state configuration, where the non-LTM TCI states activation / deactivation command includes a cell index of the candidate cell and at least one second TCI state ID and each of the second TCI state ID(s) identifies a respective one of the second non-LTM TCI state configuration(s) (e.g., event 336, 436, 536, 636, 736, 836). At step 919, the BS transmits the non-LTM TCI states activation / deactivation command to the UE via the candidate cell, using the activated LTM TCI state configuration (e.g., event 336, 436, 536, 636, 736, 836). The activated LTM TCI state configuration is the LTM TCI state configuration activated by the LTM command at step 912. At step 921 , the BS communicates with the UE viathe candidate cell, using the second non-LTM TCI state configuration(s) (e.g., event 336, 436, 536, 636, 736, 836).

[0245] In some implementations, the cell index of the candidate cell is neither a PCI nor an LTM ID. In some implementations, the cell index is a serving cell index. In some implementations, the BS configures the serving cell index to a value of 0, ..., 31 . In such cases, the serving cell index may be in a format of 5 bits. In some implementations, the BS uses the cell index to activate or deactivate a TCI state configuration of the candidate cell for the UE only when the candidate cell becomes a serving cell for the UE. In some implementations, the BS includes the cell index in the second non-LTM TCI state configuration(s).

[0246] In some implementations, the BS includes the second non-LTM TCI state configuration(s) in the LTM DU configuration. In other implementations, the BS transmits the second non-LTM TCI state configuration(s) to the UE via the candidate cell (i.e., a new serving cell). For example, the BS transmits a RRC reconfiguration including the second non-LTM TCI state configuration(s) to the UE via the candidate cell (i.e., a new serving cell).

[0247] FIG. 9D is a flow diagram of an example method 900D similar to the method 900A, except that the method 900D includes steps 903, 930 and 907 instead of steps 904 and 906. At step 903, the BS transmits an LTM ID, a first LTM DU configuration, a PCI, and at least one first LTM TCI state configuration to the UE, where the first LTM DU configuration configures a candidate cell for LTM, each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell, and the PCI is a PCI of the candidate cell. Step 903 is similar to step 904. In some implementations, the LTM ID identifies the LTM DU configuration and the first LTM TCI state configuration(s). At step 930, the BS determines a candidate cell ID based on a PCI of the candidate cell, as discussed in the next paragraph. At step 907, the BS generates a first LTM TCI states activation / deactivation command to activate the first LTM TCI state configuration(s), where the first LTM TCI states activation / deactivation command includes the candidate cell ID and at least one first TCI state ID and each of the first TCI state ID(s) identifies a respective one of the first LTM TCI state config u rati on (s) (e.g., events 325, 425, 525, 625, 725, 825).

[0248] In some implementations, the UE and the BS uses a formula and the PCI of the candidate cell to determine the candidate cell ID. For example, the formula is:Candidate cell ID = PCI value modulo 2number of bits of candidate cell lD.

[0249] For example, the candidate cell ID is 3 bits and the PCI is 10 bits. The UE and the BS generate the 3-bit candidate cell ID based on the 10-bit PCI and a formula. In this case, the formula is:Candidate cell ID = PCI value modulo 23.

[0250] FIG. 9E is a flow diagram of an example method 900E similar to the methods 900A, 900B and 900D, except that the method 900E includes step 938 instead of step 918. At step 938, the BS generates a second LTM TCI states activation / deactivation command to activate the second LTM TCI state configuration(s), where the second candidate LTM states activation / deactivation command includes the candidate cell ID and at least one second TCI state ID and each of the second TCI state ID(s) identifies a respective one of the second LTM TCI state configuration(s). Step 938 is similar to step 918.

[0251] FIG. 9F is a flow diagram of an example method 900F similar to the methods 900A, 900C and 900D. Method 900F begins at step 902, where the BS communicates with the UE via a serving cell, using at least one first non-LTM TCI state configuration (e.g., events 302, 402, 502, 602, 702, 802). At step 903, the BS transmits an LTM ID, a first LTM DU configuration, a PCI, and at least one first LTM TCI state configuration to the UE, where the first LTM DU configuration configures a candidate cell for LTM, each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell, and the PCI is a PCI of the candidate cell. Step 903 is similar to step 904. In some implementations, the LTM ID identifies the LTM DU configuration and the first LTM TCI state configuration(s). At step 930, the BS determines a candidate cell ID based on a PCI of the candidate cell. At step 907, the BS generates a first LTM TCI states activation / deactivation command to activate the first LTM TCI state configuration(s), where the first LTM TCI states activation / deactivation command includes the candidate cell ID and at least one first TCI state ID and each of the first TCI state ID(s) identifies a respective one of the first LTM TCI state configuration(s) (e.g., events 325, 425, 525, 625, 725, 825).

[0252] In some implementations, the UE and the BS uses a formula and the PCI of the candidate cell to determine the candidate cell ID. For example, the formula is: Candidate cell ID = PCI value modulo 2number of bits of candidate cel1 ID

[0253] For example, the candidate cell ID is 3 bits and the PCI is 10 bits. The UE and the BS generate the 3-bit candidate cell ID based on the 10-bit PCI and a formula. In this case, the formula is:Candidate cell ID = PCI value modulo 23.

[0254] Steps 910, 912, 914, and 916 are then performed and they are similar to the same steps in FIG. 9A discussed above. Next, at step 917, the BS generates a non-LTM TCI states activation / deactivation command to activate at least one second non-LTM TCI state configuration, where the non-LTM TCI states activation / deactivation command includes a cell index of the candidate cell and at least one second TCI state ID and each of the second TCI state ID(s) identifies a respective one of the second non-LTM TCI state configuration(s) (e.g., event 336, 436, 536, 636, 736, 836). At step 919, the BS transmits the non-LTM TCI states activation / deactivation command to the UE via the candidate cell, using the activated LTM TCI state configuration (e.g., event 336, 436, 536, 636, 736, 836). The activated LTM TCI state configuration is the LTM TCI state configuration activated by the LTM command at step 912. At step 921 , the BS communicates with the UE via the candidate cell, using the second non-LTM TCI state configuration(s) (e.g., event 336, 436, 536, 636, 736, 836).

[0255] FIG. 9G is a flow diagram of an example method 900G similar to the methods 900A and 900D, except that the method 900G includes step 944 instead of steps 904 and 930. At step 944, the BS transmits an LTM ID, a candidate cell ID, a PCI, a first LTM DU configuration and at least one first LTM TCI state configuration to the UE, where the first LTM DU configuration configures a candidate cell for LTM, each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell, and the PCI is PCI of the candidate cell. Step 944 is similar to step 904. In some implementations, the LTM ID identifies the LTM DU configuration and the candidate cell ID identifies the first LTM TCI state configuration(s). In one embodiment, the candidate cell ID is calculated based on the PCI, as discussed above with regard to step 930. In another embodiment, the candidate cell ID is not calculated based on the PCI. For example, the candidate cell ID is derived from or set to the LTM ID.

[0256] FIG. 9H is a flow diagram of an example method 900H that includes various steps of the methods 900A, 900B, 900D, 900E and 900G, arranged in a different way.

[0257] FIG. 9I is a flow diagram of an example method 900I that includes various steps of the methods 900A, 900C, 900D, 900F, and 900G, arranged in a different way.

[0258] FIG. 10A illustrates an example method 1000A, which can be implemented by a serving DU or a source DU (e.g., the DU 174, M-DU 174A or S-DU 174A in FIGs. 3-8B) communicating with a UE and a CU. The term “S-DU” is used to represent a serving DU or a source DU.

[0259] The method 1000A begins at step 1002, where the S-DU communicates with a UE via a serving cell, using at least one first non-LTM TCI state configuration (e.g., events 302, 402, 502, 602, 702, 802). At step 1004, the S-DU receives, from a CU, a first CU-to-DU message to request configuring a candidate cell for LTM for the UE (e.g., events 308, 390, 590, 790). At step 1006, the S-DU receives, from the CU, a second CU-to-DU message including an LTM ID for identifying LTM-related configurations for the candidate cell (e.g., events 308, 390, 312, 392, 590, 592, 790, 792). In some implementations, the first CU-to-DU message and the second CU-to- DU message are combined as a single CU-to-DU message. In some implementations, the LTM ID is an IE of an interface protocol. For example, the interface protocol is F1 Application Protocol (F1AP). In other implementations, the CU includes the LTM ID in an IE of an interface protocol and includes the IE in the second CU-to-DU message. For example, the interface protocol is F1AP. In yet other embodiments, the CU includes the LTM ID in a RRC IE and includes the RRC IE in the second CU-to-DU message. For example, the RRC IE is an LTM-CSI- ResourceConfig IE.

[0260] At step 1008, the S-DU generates an LTM DU configuration for the UE, where the LTM DU configuration configures the candidate cell for LTM (e.g., events 310, 390, 590, 790). In some implementations, the S-DU associates the LTM ID with the LTM DU configuration. In some implementations, the S-DU associates the LTM DU configuration and the LTM ID with a cell ID (e.g., CGI) of the candidate cell. At step 1010, the S-DU generates at least one first LTM TCI state configuration and associates the LTM ID with the first LTM TCI state configuration(s), where each ofthe first LTM TCI state configuration(s) configures a TCI state for the candidate cell (e.g., events 310, 390, 312, 392, 590, 592, 790, 792). At step 1012, the S-DU transmits a first DU-to-CU message, including the LTM DU configuration, to the CU (e.g., events 310, 390, 590, 790). At step 1014, the S-DU transmits, to the CU, a second DU-to-CU message including the first LTM TCI state configuration(s) (e.g., events 310, 390, 312, 392, 590, 592, 790, 792). At step 1016, the flow proceeds as previously discussed in steps 906 and 908. At step 1018, the flow proceeds as previously discussed in steps 912, 914 and 916.

[0261] Examples and implementations described for FIG. 9A-9C can apply to FIG. 10A.

[0262] FIG. 10B is a flow diagram of an example method 1000B similar to the method 1000A, except that the method 1000B includes steps 1009, 1011 and 1017 instead of steps 1010 and 1016. At step 1009, the S-DU generates at least one first LTM TCI state configuration, where each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell. At step 1011 , the S-DU associates the first LTM TCI state configuration(s) with a PCI of the candidate cell. At step 1017, the S-DU performs actions as described in steps 930, 907 and 908. Examples and implementations described for FIGs. 9A-9F can apply to FIG. 10B.

[0263] FIG. 10C is a flow diagram of an example method 1000C similar to the methods 1000A and 1000B, except that the method 1000C includes steps 1030 and 1015 instead of steps 1008, 1016 and 1017. At step 1030, the S-DU generates at least one first LTM TCI state configuration and a candidate cell ID, where each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell and the candidate cell ID identifies the first LTM TCI state configuration(s). At step 1015, the S-DU performs actions as described in steps 907 and 908. Examples and implementations described for FIGs. 9A-9I can apply to FIG. 10C.

[0264] FIG. 11A illustrates an example method 1100A, which can be implemented by a candidate DU (C-DU) (e.g., the T-DU 174B in FIGs. 4, 6A and 6B, or the T-DU 174C in FIG. 8A and 8B).

[0265] The method 1100A begins at step 1104, where the C-DU receives, from a CU, a first CU-to-DU message to request configuring a candidate cell for LTM for the UE. In some implementations, the first CU-to-DU message is a CU-to-DU message of the procedure 490, 690, or 890. At step 1106, the C-DU receives, from the CU, asecond CU-to-DU message including an LTM ID for identifying LTM-related configurations for the candidate cell. In some implementations, the second CU-to-DU message is a CU-to-DU message of the procedure 490, 492, 690, 692, 890, or 892. In some implementations, the first CU-to-DU message and the second CU-to-DU message are combined as a single CU-to-DU message.

[0266] At step 1108, the C-DU generates an LTM DU configuration for the UE, where the LTM DU configuration configures the candidate cell for LTM. In some implementations, the C-DU associates the LTM ID with the LTM DU configuration. In some implementations, the C-DU associates the LTM DU configuration and the LTM ID with a cell ID (e.g., CGI) of the candidate cell. At step 1110, the C-DU generates at least one first LTM TCI state configuration for the UE and associates the LTM ID with the first LTM TCI state configuration(s), where each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell. At step 1112, the C-DU transmits a first DU-to-CU message including the LTM DU configuration to the CU. In some implementations, the first DU-to-CU message is a DU-to-CU message of the procedure 490, 690, or 890. At step 1114, the C-DU transmits, to the CU, a second DU-to-CU message including the first LTM TCI state configuration(s). In some implementations, the second DU-to-CU message is a DU-to-CU message of the procedure 490, 492, 690, 692, 890, or 892. In some implementations, the first DU-to- CU message and the second DU-to-CU message are combined as a single DU-to- CU message.

[0267] At step 1116, the C-DU receives, from the CU, a third CU-to-DU message including at least one first TCI state ID, where each of the first TCI state ID(s) identifies a respective one of the first LTM TCI state configuration(s). At step 1118, the C-DU performs actions as described in steps 914 and 916. Based on the first TCI state I D(s), the C-DU identifies at least one respective LTM TCI state configuration. In some implementations, the third CU-to-DU message includes a cell ID (e.g., CGI) of the candidate cell. Based on the first TCI state ID(s) and the cell ID, the C-DU identifies at least one respective LTM TCI state configuration associated with the candidate cell. In some implementations, the third CU-to-DU message notifies that the UE performs or is performing an LTM cell switch to the candidate cell. In other implementations, the third CU-to-DU message notifies that the UE is or has been triggered to perform an LTM cell switch to the candidate cell. In someimplementations, the third CU-to-DU message is an LTM Cell Change Notification message.

[0268] Examples and implementations described for FIGs. 9A-9C and 10A can apply to FIG. 11A.

[0269] FIG. 11 B is a flow diagram of an example method 1100B similar to the method 1000A, except that the method 1100B includes steps 1130 and 1113 instead of step 1110 and 1114. At step 1130, the C-DU generates at least one first LTM TCI state configuration and a candidate cell ID for the UE and associate the LTM ID with the first LTM TCI state configuration(s), where each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell and the candidate cell ID identifies the first LTM TCI state configuration(s). At step 1113, the C-DU transmit, to the CU, a second DU-to-CU message including the first LTM TCI state configuration(s) and the candidate cell ID. Examples and implementations described for FIGs. 9A-9C, 10A, and FIGs. 9G-9I can apply to FIG. 11 B.

[0270] FIG. 12A illustrates an example method 1200A, which can be implemented by a serving DU or a source DU (e.g., the DU 174, M-DU 174A or S-174A in FIGs. 3- 8B) communicating with a UE and a CU. The term “S-DU” is used to represent a serving DU or a source DU.

[0271] The method 1200A begins at step 1202, where the S-DU communicates with a UE via a serving cell, using at least one first non-LTM TCI state configuration (e.g., events 402, 602, 802). At step 1204, the S-DU receives, from a CU, a first CU- to-DU message including an LTM ID for identifying LTM-related configurations for a candidate cell (e.g., events 460, 412, 488, 493, 688, 693, 888, 893). At step 1206, the S-DU receives, from the CU, a second CU-to-DU message including at least one first LTM TCI state configuration for the UE, where each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell (e.g., events 460, 412, 488, 493, 688, 693, 888, 893). In some implementations, the first CU-to-DU message and the second CU-to-DU message are combined as a single CU-to-DU message. At step 1208, the S-DU performs actions as described in steps 906 and 908. At step 1210, the S-DU performs actions as described in step 912.

[0272] In some implementations, the CU receives the first LTM TCI state configuration(s) from a C-DU as described for FIG. 11 A. Examples and implementations described for FIG. 9A-9C and 11 A can apply to FIG. 12A.

[0273] FIG. 12B is a flow diagram of an example method 1200B similar to the method 1200A, except that the method 1200B includes step 1209 instead of step 1208. At step 1209, the S-DU performs actions as described in steps 930, 907 and 908. Examples and implementations described for FIGs. 9A-9F can apply to FIG. 12B.

[0274] In some implementations, the second CU-to-DU message includes a PCI of the candidate cell. In other implementations, the second CU-to-DU message includes a CGI of the candidate cell and the S-DU determines the PCI based on the CGI.

[0275] FIG. 12C is a flow diagram of an example method 1200C similar to the methods 1200A and 1200B, except that the method 1200C includes steps 1205 and 1207 instead of steps 1206, 1208 and 1209. At step 1205, the S-DU receives, from the CU, a second CU-to-DU message including at least one first LTM TCI state configuration and a candidate cell ID for the UE, where each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell and the candidate cell ID identifies the first LTM TCI state configuration(s). At step 1207, the S-DU performs actions as described in steps 907 and 908. Examples and implementations described for FIGs. 9A-9I can apply to FIG. 12C.

[0276] FIG. 13A illustrates an example method 1300A, which can be implemented by a CU (e.g., the CU 172 in FIGs. 4, 6A, 6B, 8A and 8B), for configuring and / or activating one or more LTM TCI state configurations for communication with a UE (e.g., the UE 102 in FIGs. 4, 6A, 6B, 8A and 8B) before and / or after an LTM cell switch.

[0277] The method 1300A begins at step 1302, where the CU transmits, to a first DU, a first CU-to-DU message to request configuring a candidate cell for LTM for the UE (e.g., event). In some implementations, the first CU-to-DU message is a CU-to- DU message of the procedure 490, 690, or 890. At step 1304, the CU transmits, to the first DU, a second CU-to-DU message including an LTM ID for identifying LTM- related configurations for the candidate cell. In some implementations, the second CU-to-DU message is a CU-to-DU message of the procedure 490, 492, 690, 692, 890, or 892. In some implementations, the first CU-to-DU message and the second CU-to-DU message are combined as a single CU-to-DU message.

[0278] At step 1306, the CU receives a first DU-to-CU message including an LTM DU configuration from the first DU and associates the LTM ID with the LTM DU configuration. In some implementations, the first DU-to-CU message is a DU-to-CU message of the procedure 490, 690, or 890. In some implementations, the CU associates the LTM ID with an element including the LTM DU configuration as described above. At step 1308, the CU receives a second DU-to-CU message including at least one first LTM TCI state configuration from the first DU, where each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell. In some implementations, the second DU-to-CU message is a DU-to-CU message of the procedure 490, 492, 690, 692, 890, or 892. In some implementations, the first DU-to-CU message and the second DU-to-CU message are combined as a single DU-to-CU message. At step 1310, the CU associates the LTM ID with the first LTM TCI state configuration(s).

[0279] At step 1312, the CU transmits a third CU-to-DU message including the LTM ID to a second DU (e.g., events 412, 493, 693, 893). At step 1314, the CU transmits a fourth CU-to-DU message, including a cell ID of the candidate cell and the first LTM TCI state configuration(s), to the second DU (e.g., events 412, 493, 693, 893). In some implementations, the third CU-to-DU message and the fourth CU- to-DU message are combined as a single CU-to-DU message. At step 1316, the CU transmits a first RRC message including the LTM ID and the LTM DU configuration to the UE via a RAN node (e.g., events 494, 694, 617, 619, 894, 817, 819). At step 1318, the CU transmits a second RRC message including the LTM ID and the first LTM TCI state configuration(s) to the UE via the RAN node (e.g., events 494, 694, 617, 619, 894, 817, 819).

[0280] In some implementations, one of the first DU and the second DU is a S-DU and the other is a C-DU. In some implementations, the RAN node is a BS or a DU. The DU can be the serving / source DU, a master DU or a secondary DU. Examples and implementations described for FIGs. 9A-9F, 10A, 10B, 11 A, 12A, and 12B can apply to FIG. 13A.

[0281] FIG. 13B is a flow diagram of an example method 1300B similar to the method 1300A, except that the method 1300B includes steps 1309, 1313, and 1319 instead of steps 1308, 1314, and 1318. At step 1309, the CU receives a second DU- to-CU message including at least one first LTM TCI state configuration and acandidate cell ID from the first DU, where each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell and the candidate cell ID identifies the first LTM TCI state configuration(s). At step 1313, the CU transmits a fourth CU-to-DU message, including a CGI of the candidate cell, the first LTM TCI state configuration(s), and the candidate cell ID, to the second DU. At step 1319, the CU transmits a second RRC message including the LTM ID, the first LTM TCI state configuration(s), and the candidate cell ID to the UE via the RAN node.

[0282] Examples and implementations described for FIGs. 9G-9I, 10C, 11 B and 12C can apply to FIG. 13B.

[0283] FIG. 14A illustrates an example method 1400A, which can be implemented by a UE (e.g., the UE 102 in FIGs. 3-8B), for configuring and activating an LTM TCI state. The method 1400A begins at step 1402, where the UE communicates with a RAN via a serving cell, using at least one first non-LTM TCI state configuration. At step 1404, the UE receives an LTM ID, a first LTM DU configuration, and at least one first LTM TCI state configuration from the RAN, where the first LTM DU configuration configures a candidate cell for LTM, each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell (e.g., events 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, 819). In some implementations, the LTM ID identifies the LTM DU configuration and the first LTM TCI state configuration(s). At step 1406, the UE receives a first LTM TCI states activation / deactivation command from the RAN via the serving cell, using the first non-LTM TCI state configuration(s), where the first LTM TCI states activation / deactivation command includes the LTM ID and at least one first TCI state ID to activate the first LTM TCI state configuration(s). Each of the first TCI state ID(s) identifies a respective one of the first LTM TCI state configuration(s) (e.g., events 325, 425, 525, 625, 725, 825). At step 1408, the UE identifies the first LTM TCI state configuration(s), in accordance with the LTM ID and the first TCI state ID(s) included in the first TCI states activation / deactivation command. At step 1409, the UE activates the first LTM TCI state configuration(s) in response to the first TCI states activation / deactivation command. At step 1410, the UE receives one or more reference signals on the candidate cell, using the first LTM TCI state configuration(s). At step 1412, the UE receives an LTM command from the RAN via the serving cell using one of the first non-LTM TCI state configuration(s), where theLTM command includes the LTM ID and / or a TCI state ID, commanding the UE to perform an LTM cell switch and activate a TCI state configuration identified by the TCI state ID (e.g., events 330, 430, 530, 630, 730, 830). At step 1414, the UE accesses the candidate cell in response to receiving the LTM command (e.g., events 332, 432, 532, 632, 732, 832). At step 1416, the UE communicates with the RAN via the candidate cell, using the activated LTM TCI state configuration and the LTM DU configuration (e.g., events 336, 436, 536, 636, 736, 836).

[0284] The UE and RAN described in FIG. 14A can be the UE and BS described in FIG. 9A. Examples and implementations described for FIGs. 9A can apply to FIG. 14A.

[0285] FIG. 14B is a flow diagram of an example method 1400B similar to the method 1400A, except that the method 1400B includes steps 1405, 1418, 1420, 1422, and 1424. At step 1405, the UE receives the LTM ID and at least one second LTM TCI state configuration from the RAN, where the first LTM DU configuration configures the candidate cell for LTM, each of the second LTM TCI state configuration(s) configures a TCI state for the candidate cell. At step 1418, the UE receives a second LTM TCI states activation / deactivation command from the RAN via the candidate cell, using the activated LTM TCI state configuration, where the second LTM TCI states activation / deactivation command includes the LTM ID and at least one second TCI state ID to activate the second LTM TCI state configuration(s) and each of the second TCI state ID(s) identifies a respective one of the second LTM TCI state configuration(s). At step 1420, the UE identifies the second LTM TCI state configuration(s), in accordance with the LTM ID and the second TCI state ID(s) included in the second TCI states activation / deactivation command. At step 1422, the UE activates the second LTM TCI state configuration(s) in response to the second TCI states activation / deactivation command. At step 1424, the UE communicates with the RAN via the candidate cell, using the activated second LTM TCI state configuration(s).

[0286] The UE and RAN described in FIG. 14B can be the UE and BS described in FIG. 9B. Examples and implementations described for FIGs. 9A-9B can apply to FIG. 14B.

[0287] FIG. 14C is a flow diagram of an example method 1400C similar to the methods 1400A and 1400B, except that method 1400C includes step 1417, 1419and 1423. At step 1417, the UE receives a non-LTM TCI states activation / deactivation command from the RAN via the candidate cell, using the activated LTM TCI state configuration, where the non-LTM TCI states activation / deactivation command activates at least one second non-LTM TCI state configuration and includes a cell ID of the candidate cell and at least one second TCI state ID, and each of the second TCI state ID(s) identifies a respective one of the second non-LTM TCI state configuration(s).

[0288] The UE and RAN described in FIG. 14C can be the UE and BS described in FIG. 9C. Examples and implementations described for FIGs. 9A-9C can apply to FIG. 14C.

[0289] FIG. 14D is a flow diagram of an example method 14000 similar to the method 1400A, except that the method 14000 includes steps 1403, 1430, 1407 and 1440 instead of steps 1404 and 1406. At step 1403, the UE receives an LTM ID, a first LTM DU configuration, a PCI, and at least one first LTM TCI state configuration from the RAN, where the first LTM DU configuration configures a candidate cell for LTM, each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell, and the PCI is a PCI of the candidate cell. In some implementations, the LTM ID identifies the LTM DU configuration and the first LTM TCI state configuration(s). At step 1430, the UE determines a candidate cell ID based on the PCI. At step 1407, the UE receives a first LTM TCI states activation / deactivation command from the RAN via the serving cell, using one of the first non-LTM TCI state configuration(s), where the first LTM TCI states activation / deactivation command includes the candidate cell ID and at least one first TCI state ID to activate the first LTM TCI state configuration(s) and each of the first TCI state ID(s) identifies a respective one of the first LTM TCI state configuration(s). At step 1440, the UE identifies the first LTM TCI state configuration(s), in accordance with the candidate cell ID and the first TCI state ID(s) included in the first TCI states activation / deactivation command.

[0290] The UE and RAN described in FIG. 14D can be the UE and BS described in FIG. 9D. Examples and implementations described for FIGs. 9A-9D can apply to FIG. 14D.

[0291] FIG. 14E is a flow diagram of an example method 1400E similar to the methods 1400A, 1400B and 14000, except that the method 1400E includes step1438 and 1421 instead of step 1418. At step 1438, the UE receives a second LTM TCI states activation / deactivation command from the RAN via the candidate cell, using the activated LTM TCI state configuration, where the second LTM TCI states activation / deactivation command includes the candidate cell ID and at least one second TCI state ID to activate the second LTM TCI state configuration(s) and each of the second TCI state ID(s) identifies a respective one of the second LTM TCI state configuration(s). At step 1421 , the UE identifies the second LTM TCI state configuration(s), in accordance with the candidate cell ID and the second TCI state ID(s) included in the second TCI states activation / deactivation command.

[0292] The UE and RAN described in FIG. 14E can be the UE and BS described in FIG. 9E. Examples and implementations described for FIGs. 9A-9E can apply to FIG. 14E.

[0293] FIG. 14F is a flow diagram of an example method 1400F including various steps from the methods 1400A, 1400C and 14000, in a different order. The UE and RAN described in FIG. 14F can be the UE and BS described in FIG. 9F. Examples and implementations described for FIGs. 9A-9F can apply to FIG. 14F.

[0294] FIG. 14G is a flow diagram of an example method 1400G similar to the methods 1400A and 14000, except that the method 1400G includes step 1444 instead of steps 1404 and 1430. At step 1444, the UE receives an LTM ID, a candidate cell ID, a PCI, a first LTM DU configuration, and at least one first LTM TCI state configuration from the RAN, where the first LTM DU configuration configures a candidate cell for LTM, each of the first LTM TCI state configuration(s) configures a TCI state for the candidate cell, and the PCI is a PCI of the candidate cell. Step 1444 is similar to step 1404. The UE and RAN described in FIG. 14G can be the UE and BS described in FIG. 9G. Examples and implementations described for FIGs. 9A-9G can apply to FIG. 14G.

[0295] FIG. 14H is a flow diagram of an example method 1400H that includes steps from the methods 1400A, 1400B, 14000, 1400E and 1400G, but in a different order. The UE and RAN described in FIG. 14H can be the UE and BS described in FIG. 9H. Examples and implementations described for FIGs. 9A-9H can apply to FIG. 14H.

[0296] FIG. 141 is a flow diagram of an example method 1400H that includes steps from the methods 1400A, 1400C, 14000, 1400F, and 1400G, but in a differentorder. The UE and RAN described in FIG. 141 can be the UE and BS described in FIG. 91. Examples and implementations described for FIGs. 9A-9I can apply to FIG. 141.

[0297] FIG. 15A illustrates an example method 1500A, which can be implemented by a UE (e.g., the UE 102 in FIGs. 3-8B), for configuring and activating an LTM TCI state. The method 1500A begins at step 1502, where the UE receives an LTM ID, an LTM DU configuration, and at least one LTM TCI state configuration from the RAN, where the LTM DU configuration configures a candidate cell for LTM, each of the LTM TCI state configuration(s) configures a TCI state for the candidate cell, and the LTM ID identifies the LTM DU configuration (e.g., events 316, 318, 394, 494, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, 819). At optional step 1504, the UE receives an LTM TCI states activation / deactivation command from the RAN via the serving cell, where the LTM TCI states activation / deactivation command activates the LTM TCI state configuration(s) (e.g., events 325, 425, 525, 625, 725, 825). At optional step 1506, the UE activates the LTM TCI state configuration(s) in response to the LTM TCI states activation / deactivation command. At step 1508, the UE determines whether the candidate cell is a serving cell. If the UE determines that the candidate cell is a serving cell at step 1508, the flow proceeds to step 1510. At step 1510, the UE receives at least one DL transmission from the RAN and / or transmits at least one UL transmission to the RAN via the serving cell, using one of the LTM TCI state configuration(s) (e.g., event 336, 436, 536, 636, 736, 836).Otherwise, if the UE determines 1508 that the candidate cell is not a serving cell, the flow proceeds to step 1512. At step 1512, the UE refrains from using the LTM TCI state configuration(s) to receive DL transmissions and / or transmit UL transmissions.

[0298] FIG. 15B is a flow diagram of an example method 1500B similar to the method 1500A, except that the method 1500B includes step 1514 instead of step 1510 and steps 1504 and 1506 are not optional. If the UE determines 1508 that the candidate cell is a serving cell, the flow proceeds to step 1512. Otherwise, if the UE determines 1508 that the candidate cell is not a serving cell, the flow proceeds to step 1514. At step 1514, the UE performs actions as described in steps 1410, 1412, 1414 and 1416 of previous methods.

[0299] FIG. 15C is a flow diagram of an example method 1500C that includes step from the methods 1500A and 1500B, in a different order. If the UE determines 1508that the candidate cell is not a serving cell, the flow proceeds to step 1506. The flow may then proceed to step 1514. Otherwise, the flow proceeds to step 1512 discussed above.

[0300] FIG. 15D is a flow diagram of an example method 1500D similar to the method 1500A and 1500B, except that the method 15000 includes steps 1507, 1509 and 1511 instead of steps 1508 and 1510. At step 1507, the UE receives an LTM command from the RAN, commanding an LTM cell switch to the candidate cell (e.g., events 330, 430, 530, 630, 730, 830). At step 1509, the UE determines whether the LTM command includes a first TCI state ID to activate one of the TCI state configuration(s). If the UE determines that the LTM command includes a TCI state ID at step 1509, the flow proceeds to step 1511 . At step 1511 , the UE receives at least one DL transmission from the RAN and / or transmit at least one UL transmission to the RAN via the candidate cell, using an LTM TCI state configuration identified by the TCI state ID. Otherwise, if the UE determines 1509 that the LTM command does not include a TCI state ID, the flow proceeds to step 1512.

[0301] Examples and implementations described for FIGs. 9A-9I and 14A-14I can apply to Figs 15A-15D.

[0302] The following description may be applied to the embodiments discussed above. The 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 step described above can be optional or omitted, especially if the step is shown with a dash line. 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 LTM cell switch command”, “lower layer switching command” or “lower layer serving cell change command”. In some implementations, “some” means “one or more”. In some implementations, “at least one” means “one or more”. In some implementations, the “DU configuration” can be replaced by “cell group configuration”. In some implementations, the “cell index” can be replaced with “serving cell index”, “LTM cell index”, “special cell (SpCell) index”, “PCell index” or“PSCell index”. In some implementations, the “serving” can be replaced by “source”. In some implementations, the “measurement report” can be replaced by “measurement result(s)”. In some implementations, the “early TA acquisition” can be replaced by “early UL timing synchronization” or “early UL synchronization”. In some implementations, the “early TA acquisition on a / the candidate cell” can be replaced by “early UL timing synchronization with a / the candidate cell” or “early UL synchronization with a / the candidate cell”.

[0303] A user device in which the techniques of this document can be implemented (e.g., the UE 102) can be any suitable device capable of wireless communications such as a smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of-sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device can operate as an internet- of-things (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.

[0304] Certain embodiments are described in this document as including logic or a number of components or modules. Modules may 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, orin temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0305] 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.

[0306] Upon reading this document, those of skill in the art will appreciate additional and alternative structural and functional designs for handling mobility between BSs 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 (900A to 900I) for wireless communication, performed by a base station, BS, (104), configured for lower layer triggered mobility, LTM, the method comprising: transmitting (904), to a user equipment, UE, (102), via a serving cell (124A), an LTM identity, ID, a first LTM distributed unit, DU, configuration, and one or more first LTM transmission configuration indicator, TCI, state configurations, the LTM ID, the first LTM DU configuration, and each of the one or more LTM TCI state configurations being related to a candidate cell (124B); and transmitting (908) a first LTM TCI states command, via the serving cell, to activate a first LTM TCI state configuration of the one or more first LTM TCI state configurations, the first LTM TCI states command including the LTM ID and at least one first TCI state ID, and the first TCI state ID identifying a selected one of the one or more first LTM TCI state configurations.

2. The method of Claim 1 , wherein the transmitting the LTM ID, the first LTM DU configuration, and the one or more first LTM TCI state configurations and the transmitting the first LTM TCI states command employ at least one first non-LTM TCI state configuration.

3. The method of any of Claims 1 or 2, wherein the transmitting the LTM ID, the first LTM DU configuration, and the one or more first LTM TCI state configurations includes transmitting a second LTM TCI state configuration, the method further comprising: transmitting a second LTM TCI states command via the candidate cell, using the first LTM TCI state configuration, to activate the second LTM TCI state configuration.

4. The method of any of Claims 1 or 2, further comprising: transmitting a non-LTM TCI states command via the candidate cell, using the first LTM TCI state configuration, to activate a second non-LTM TCI state configuration,wherein the non-LTM TCI states command includes a cell index of the candidate cell and at least one second TCI state ID, which identifies a specific second non-LTM TCI state configuration.

5. The method of any of Claims 1 or 2, wherein the transmitting the LTM ID, the first LTM DU configuration, and the one or more first LTM TCI state configurations further includes transmitting a physical cell identity, PCI, of the candidate cell.

6. The method of Claim 5, further comprising: determining (930) a candidate cell ID based on the PCI, wherein the first LTM TCI states command includes the candidate cell ID.

7. The method of Claim 5, further comprising: transmitting the LTM ID and at least one second LTM TCI state configuration to the UE, wherein the second LTM TCI state configuration configures a TCI state for the candidate cell.

8. The method of Claim 7, further comprising: transmitting a second LTM TCI states command to activate the at least one second LTM TCI state configuration, the second LTM TCI states command including the candidate cell ID and at least one second TCI state ID.

9. The method of Claim 5, further comprising: transmitting a non-LTM TCI states command to the UE, via the candidate cell, using the LTM TCI state configuration, to activate at least one second non-LTM TCI state configuration, wherein the non-LTM TCI states command includes a cell index of the candidate cell and at least one second TCI state ID, wherein the second TCI state ID identifies a corresponding state of the at least one second non-LTM TCI state configuration.

10. The method of any of Claims 1 or 2, wherein the transmitting the LTM ID, the first LTM DU configuration, and the one or more first LTM TCI state configurations further includes transmitting a candidate cell ID and a physical cell identity, PCI, of the candidate cell, and wherein the transmitting the first LTM TCI states command further includes transmitting the candidate cell ID, the method further comprising: transmitting at least one second LTM TCI state configuration to the UE, to configure a corresponding TCI state of the candidate cell; and transmitting a second LTM TCI states command to activate the at least one second LTM TCI state configuration, wherein the second LTM TCI states command includes the candidate cell ID and at least one second TCI state ID, and the second TCI state ID identifies the at least one second LTM TCI state configuration.

11. A method (1400A to 14001) for wireless communication, performed by a user equipment, UE, (102), configured for lower layer triggered mobility, LTM, the method comprising:Receiving (1404), from a base station, BS, (104), via a serving cell (124A), an LTM identity, ID, a first LTM distributed unit, DU, configuration, and one or more first LTM transmission configuration indicator, TCI, state configurations, the LTM ID, the first LTM DU configuration, and each of the one or more LTM TCI state configurations configuring a candidate cell (124B); and receiving (1406) a first LTM TCI states command, via the serving cell, to activate a first LTM TCI state configuration of the one or more LTM TCI state configurations, the first LTM TCI states command including the LTM ID and at least one first TCI state ID, and the first TCI state ID identifying a selected one of the one or more first LTM TCI state configurations.

12. The method of Claim 11 , wherein the receiving the LTM ID, the first LTM DU configuration, and the one or more first LTM TCI state configurations and the receiving the first LTM TCI states command employ at least one first non-LTM TCI state configuration.

13. The method of any of Claims 11 or 12, wherein the receiving the LTM ID, the first LTM DU configuration, and the one or more first LTM TCI state configurations includes receiving a second LTM TCI state configuration, the method further comprising: receiving a second LTM TCI states command via the candidate cell, using the first LTM TCI state configuration, to activate the second LTM TCI state configuration.

14. The method of any of Claims 11 or 12, further comprising: receiving a non-LTM TCI states command via the candidate cell, using the LTM TCI state configuration, to activate a second non-LTM TCI state configuration, wherein the non-LTM TCI states command includes a cell index of the candidate cell and at least one second TCI state ID, which identifies a selected second non-LTM TCI state configuration.

15. The method of any of Claims 11 or 12, wherein the receiving the LTM ID, the first LTM DU configuration, and the one or more first LTM TCI state configurations further includes receiving a physical cell identity, PCI, of the candidate cell.

16. The method of Claim 15, further comprising: receiving the LTM ID and at least one second LTM TCI state configuration to the UE, wherein the second LTM TCI state configuration configures a TCI state for the candidate cell.

17. The method of Claim 15, further comprising: receiving a non-LTM TCI states command, via the candidate cell, using the LTM TCI state configuration, to activate at least one second non-LTM TCI state configuration, wherein the non-LTM TCI states command includes a cell index of the candidate cell and at least one second TCI state ID, which identifies a corresponding state of the at least one second non-LTM TCI state configuration.

18. The method of any of Claims 11 or 12, wherein the receiving the LTM ID, the first LTM DU configuration, and the one or more first LTM TCI state configurations further includes receiving a candidate cell ID and a physical cell identity, PCI, of the candidate cell, and wherein the receiving the first LTM TCI states command further includes receiving the candidate cell ID, the method further comprising: receiving at least one second LTM TCI state configuration to configure a corresponding TCI state of the candidate cell; and receiving a second LTM TCI states command to activate the at least one second LTM TCI state configuration, wherein the second LTM TCI states command includes the candidate cell ID and at least one second TCI state ID, and the second TCI state ID identifies the at least one second LTM TCI state configuration.

19. A communication device (102, 204) comprising a transceiver (292, 282), a processor (293, 283) and computer-readable storage media (294, 284) storing executable instructions for the processor to perform any of the methods recited in claims 1-18, using the transceiver.

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