Devices and methods for managing lower layer triggered mobility configuration and dual connectivity

Abstract

Methods and devices in a wireless communication network perform a cell switching based on a lower-layer triggered mobility (LTM) configuration. A user equipment (UE), which is in dual connectivity with a radio access network (RAN) node, receives (904) at least one LTM configuration from the RAN node, for switching from a first or a second serving cell to a first candidate cell. The UE performs (908) the cell switch based on the LTM configuration and an indicator, received from the RAN node. Based on the indicator, the UE determines (909B) whether to release a first cell group, associated with the first serving cell, or a second cell group, associated with the second serving cell.

Description

DEVICES AND METHODS FOR MANAGING LOWER LAYER TRIGGERED MOBILITY CONFIGURATION AND DUAL CONNECTIVITYFIELD OF THE DISCLOSURE

[0001] This document generally describes methods and devices operating in wireless communication systems such as (but not limited to) the ones described in 5G standard documents, known as 3GPP communication systems, and, more particularly, to managing lower-layer triggered mobility (LTM) configurations when a user equipment (UE) is capable of dual connectivity (DC).BACKGROUND

[0002] This background description is provided for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.

[0003] In telecommunication systems, a Packet Data Convergence Protocol (PDCP) sublayer of a radio protocol stack provides services such as transfer of userplane data, ciphering, integrity protection, etc. For example, the PDCP layer defined for the Evolved Universal Terrestrial Radio Access (EUTRA) radio interface (see 3GPP technical specification (TS) 36.323) and New Radio (NR) (see 3GPP TS 38.323) provides sequencing of protocol data units (PDUs) in the uplink direction (from a 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. The UE and BS may use SRBs to exchange RRC messages as well as non-access stratum (NAS) messages and may use DRBs to transport data on a user plane.

[0004] UEs may use several types of SRBs and DRBs. When operating in DC, the cells associated with the BS operating a master node (MN) define a master cell group (MCG), and cells associated with a BS operating as a secondary node (SN)define a 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 may be referred to as MCG SRBs. SRB3 resources allow the UE and the SN to exchange RRC messages related to the SN and may 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 may be referred as MCG DRBs, DRBs using the lower-layer resources of only the SN may be referred as SCG DRBs, and DRBs using the lower- layer resources of both the MCG and the SCG may be referred to as split DRBs.

[0005] In some scenarios, the UE may concurrently utilize resources of multiple radio access network (RAN) nodes (e.g., BSs or components of a distributed base station), interconnected by a backhaul. When these network nodes support different radio access technologies (RATs), this type of connectivity is referred to as Multi-Radio Dual Connectivity (MR-DC). When a UE operates in MR-DC, one BS operates as the MN that covers a primary cell (PCell), and the other BS operates as the SN that covers a primary secondary cell (PSCell). The UE communicates with the MN (via the PCell) and with the SN (via the PSCell). In other scenarios, the UE utilizes resources of one BS at a time.

[0006] Sometimes, the BS and / or the UE determines that the UE should establish a radio connection with another BS. For example, a first BS may determine to hand the UE over to a second BS, and initiate a handover procedure. When the UE moves from coverage area of one cell to another cell in a RAN, a serving cell change has to be performed for the UE. To perform the serving cell change, the RAN configures the UE to transmit Layer 3 (L3) measurement results. Based on L3 measurement results received from the UE, the RAN transmits an RRC reconfiguration message configuring Reconfiguration with Synchronization (e.g., the RRC reconfiguration message includes a ReconfigurationWithSync information element (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 SCell due to the change of the PCell or PSCell. The serving cell change involves complete L2 (and L1 ) resets, leading to long latency, large overhead, and long interruption time. Thus, 3GPP developed new mobility techniques for serving cell changes. These techniques aim to reduce latency and overhead and are called LTM, or faster serving cell switching.

[0007] In LTM, the UE switches from a serving cell to a candidate cell based on an L1 measurement report, without the L1 and L2 reset. When the UE operates in DC, an LTM configuration addresses the UE switch from a first serving cell (e.g., a primary cell of the master node) to a candidate cell (e.g., a candidate primary cell) in a first cell group (e.g., master cell group). However, the LTM configuration does not address what happens with the communication between the UE and a second serving cell (e.g., a primary secondary cell of the secondary node) from a second cell group (e.g., a secondary cell group), after or during the first serving cell switch.SUMMARY

[0008] The use of LTM configurations by the UE reduces conventional cell switching latency and overhead because, the LTM does not require L1 and L2 resets, reestablishment and / or random access. To address the communication status between the UE and first and second serving cells in DC, after a cell switch from the first serving cell to a candidate cell, the LTM configuration includes an indicator that instructs the UE how to handle the second serving cell (and a second cell group (CG) associated with the second serving cell). In one embodiment, a RAN configures the UE, through the LTM configuration and the indicator, to automatically release the connection with the second CG after the first serving cell switch. In another embodiment, the RAN configures the UE to check whether the LTM configuration indicates the release of the second CG, and based on this determination, the UE releases or maintains the connection with the second CG. In yet another embodiment, the RAN configures the UE to check whether the candidate cell belongs to a first CG associated with the first serving cell, and based on this determination, to release ormaintain the connection to the second CG. In still another embodiment, the RAN configures the UE to check whether the LTM configuration is received via the first CG of the first serving cell, and based on this determination, to release or maintain the connection to the second CG.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one or more embodiments and, together with the description, explain these embodiments.

[0010] FIG. 1 A is a block diagram of an example system in which devices communicating via a RAN can implement LTM configuration based cell switching for a UE.

[0011] FIG. 1 B is a block diagram of an example base station including a centralized unit (CU) and a distributed unit (DU) that can operate in the system of FIG. 1A.

[0012] FIG. 2A is a block diagram of an example protocol stack according to which the UE of FIG. 1 A communicates with base stations.

[0013] FIG. 2B is a block diagram of an example protocol stack according to which the UE of FIG. 1 A communicates with a CU and a DU.

[0014] FIG. 3 is a signal diagram illustrating an LTM performed by a UE in communication with a BS including a DU and a CU according to an embodiment.

[0015] FIG. 4 is a signal diagram illustrating an LTM performed by a UE in communication with a BS including a source-DU (S-DU), a target DU (T-DU), and a CU according to an embodiment.

[0016] FIGs. 5A and 5B are signal diagrams illustrating an LTM performed by a UE in dual connectivity (DC) with a master node (MN) and a secondary node (SN) including a DU and a CU according to other embodiments.

[0017] FIGs. 6A and 6B are signal diagrams illustrating an LTM performed by a UE in DC with an MN and an SN including an S-DU, a T-DU, and a CU according to various embodiments.

[0018] FIGs. 7A and 7B are signal diagrams illustrating an LTM performed by a UE in DC with a distributed BS including a master-DU (M-DU), a secondary DU (S-DU), and a CU according to other embodiments.

[0019] FIGs. 8A and 8B are signal diagrams illustrating an LTM performed by a UE in DC with a distributed BS including an M-DU, an S-DU, a T-DU, and a CU according to various embodiments.

[0020] FIGs. 9A to 9D depict flow diagrams of a UE method for LTM configuration based cell switching in DC according to various embodiments.

[0021] FIG. 9E depicts a flow diagram of a RAN method for managing LTM configuration based cell switching in DC according to an embodiment.

[0022] FIGs. 10A to 10C depict flow diagrams of a UE method for LTM configuration based cell switching in DC according to various embodiments.

[0023] FIG. 11 depicts a flow diagram of a UE method for determining whether an LTM configuration is associated with a first or a second cell group according to an embodiment.

[0024] FIG. 12 depicts a flow diagram of a UE method for determining whether an LTM configuration is associated with a first or a second cell group, based on a radio resource control (RRC) message, according to an embodiment.

[0025] FIGs. 13A to 13C depict flow diagrams of a UE RRC layer method for LTM configuration based cell switching in DC according to various embodiments.

[0026] FIGs. 14A to 14C depict flow diagrams of a UE medium access control (MAC) layer method for LTM configuration based cell switching in DC according to various embodiments.

[0027] FIGs. 15A and 15B depict flow diagrams of a UE method for LTM configuration based cell switching in DC when simultaneous LTM commands are received, according to various embodiments.DETAILED DESCRIPTION

[0028] Methods and devices described in this section embody techniques for preparing a UE and / or a BS or a portion of the BS for LTM based cell change / switch while performing DC. Before discussing these techniques, an example wireless communication system 100 is introduced.

[0029] The embodiment descriptions in this section refer to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The detailed descriptions do not preclude other embodiments within the scope of the appended claims. The embodiments are not limited to the described configurations but may be extended to other arrangements.

[0030] Reference throughout this section to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification are not necessarily all referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[0031] FIG. 1A depicts an example wireless communication system 100 in which communication devices may 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 embodiments, the first BS 104 may perform an SN addition to configure the UE 102 to operate in DC with the first BS 104 and the second BS 106. The BSs 104 and 106 operate as an MN and an SN for the UE 102, respectively.

[0032] In various configurations of the wireless communication system 100, the first BS 104 may be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the second BS 106 may be implemented as a secondary gNB (SgNB). The UE 102 may 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 may be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0033] In some embodiments, 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 LIE 102 may 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.

[0034] In the embodiments where the network hands over the UE 102 from the first BS 104 to the second BS 106, the BSs 104 and 106 operate as the source BS (S-BS) and the target BS (T-BS), respectively. The UE 102 may operate in DC with the first BS 104 and an additional BS (not shown in FIG. 1A), for example, prior to the handover. The UE 102 may 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.

[0035] The CN 110 may 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 may 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 embodiments discussed below, the BSs 104 and 106 may support an X2 or Xn interface. Among other components, the EPC 111 may include a Serving Gateway (SGW) 112, a Mobility Management Entity (MME) 114, and a Packet Data Network Gateway (PGW) 116. The SGW 112 transfers user-plane packets related to audio calls, video calls, Internet traffic, etc. The MME 114 manages 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 transfersuser-plane packets related to audio calls, video calls, Internet traffic, etc. The AMF 164 manages authentication, registration, paging, and other related functions, and the SMF 166 manages PDU sessions.

[0036] As also illustrated in FIG. 1 A, the first BS 104 supports cells 124A to 124C, and the second BS 106 supports cells 126A and 126B. Cells 124A and 126A may partially overlap, so that the UE 102 may 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 may support additional cell(s), and the second BS 106 may support additional cell(s). The cells 124A, 124B, and 124C may partially overlap, so that the UE 102 may communicate in carrier aggregation (CA) with the first BS 104. The first BS 104 may operate the cells 124A, 124B, and 124C via one or more transmit and receive points (TRPs). The same is true for the second BS 106 and its cells. 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.

[0037] The wireless communication network 100 may include any suitable number of BSs supporting NR cells and / or EUTRA cells. More particularly, the EPC 111 or the 5GC 160 may 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), the techniques of this disclosure also may 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.

[0038] Still with regard to FIG. 1A, the first BS 104 is equipped with processing hardware 130 that may include one or more general-purpose processors (e.g., CPUs) 132 and a non-transitory computer-readable memory (CRM) 133 storing instructions that the one or more general-purpose processors execute. Additionally, or alternatively, the processing hardware 130 may include special-purpose processing units. The processing hardware 130 may include a PHY controller 134 configured to transmit data and control signal on physical downlink (DL) channels and DL reference signals with one or more user devices (e g., the UE 102) via one or more cells (e.g., the cell(s) 124A, 124B, and / or 124C) and / or one or more TRPs. The PHY controller 134 is also configured to receive data andcontrol 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 embodiment, includes a medium access control (MAC) controller 136 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 may further include an RRC controller (not shown) to support procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller may be configured to support RRC messaging associated with LTM configuration procedures, 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 first BS 104 further includes a transceiver 138 for communicating with the UE 102. The second BS 106 may include processing hardware 140 that is similar to processing hardware 130. In particular, components 142, 143, 144, 146, and 148 may be similar to the components 132, 133, 134, 136, and 138, respectively.

[0039] The UE 102 is equipped with processing hardware 150 that may include one or more general-purpose processors 152 such as CPUs and non-transitory computer- readable memory 153 storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. The PHY controller 154 is also configured to receive data and control signal on physical DL channels and / or DL reference signals with the BSs 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C, 126A, and / or 126B) and / or one or more TRPs. The PHY controller 154 is also configured to transmit data and control signal on physical UL channels and / or UL reference signals with the BSs 104 or 106 via one or more cells (e.g., the cell(s) 124A, 124B, 124C, 126A, and / or 126B) and / or one or more TRPs. The processing hardware 150 in an example embodiment includes a MAC controller 156 configured to perform MAC functions with BS 104 or 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 BSs 104 or 106. In anotherexample, the MAC functions include LTM related functions as described below. The processing hardware 150 may further include an RRC controller (not shown) to support LTM configuration procedures, handover procedures, DC operation and messaging at the RRC sublayer of the protocol communication stack. The UE further includes a transceiver 158 for communicating with the BSs 104 and / or 106.

[0040] In operation, the UE 102 in DC may 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 may 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.

[0041] FIG. 1 B depicts a distributed BS 170, for example, one or both of the first BS 104 or 106. The BS 170 may include, in this embodiment, a centralized unit (CU) 172 and one or more distributed units (DUs) 174. The CU 172 may include a CU control plane (CU- CP) unit 172A and a CU user plane (CU-UP) unit 172, that communicate to each other via an E1 interface. The units 172A and 172B communicate with the DU 174 via F1-C / W1-C interfaces. The BS 170, or one of its components CU 172 or DU 174 are sometimes called, in this document, a RAN node. The CU 172 is equipped with processing hardware that may 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 processing hardware 130. In another example, the CU 172 is equipped with processing hardware 140. The processing hardware 140, in an example embodiment, includes an SN RRC controller 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 may 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 includes a 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. Theprocess hardware may further include a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0042] FIG. 2A illustrates, in a simplified manner, an example protocol stack 200 according to which the UE 102 may communicate with an eNB / ng-eNB or a gNB (e.g., one or more of the BSs 104, 106). In the example stack 200, a physical layer (PHY) 202A of ELITRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLC sublayer 206A in turn provides RLC channels to an EUTRA PDCP sublayer 208 and, in some cases, to an NR PDCP sublayer 210. Similarly, the NR PHY 202B provides transport channels to the NR MAC sublayer 204B, which in turn provides logical channels to the NR RLC sublayer 206B. The NR RLC sublayer 206B in turn provides data transfer services to the NR PDCP sublayer 210. The NR PDCP sublayer 210 in turn may provide data transfer services to Service Data Adaptation Protocol (SDAP) 212 or a radio resource control (RRC) sublayer (not shown in FIG. 2A). The UE 102, in some embodiments, supports both the EUTRA and the NR stack as shown in FIG. 2A, to support handover between EUTRA and NR BSs and / or to support DC over EUTRA and NR interfaces. Further, as illustrated in FIG. 2A, the UE 102 may support layering of NR PDCP 210 over EUTRA RLC 206A, and SDAP sublayer 212 over the NR PDCP sublayer 210.

[0043] The EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 receive packets (e.g., from an Internet Protocol (IP) layer, layered directly or indirectly over the PDCP layer 208 or 210) that may be referred to as service data units (SDUs), and output packets (e.g., to the RLC layer 206A or 206B) that may be referred to as protocol data units (PDUs). Except where the difference between SDUs and PDUs is relevant, this disclosure for simplicity refers to both SDUs and PDUs as “packets.”

[0044] On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 may provide SRBs or RRC sublayer (not shown in FIG. 2A) to exchange RRC messages or NAS messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 may provide DRBs to support data exchange. Data exchanged on the NR PDCP sublayer 210 may be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0045] FIG. 2B illustrates, in a simplified manner, an example protocol stack 250, in which the UE 102 may communicate with a DU (e.g., DU 174) and a CU (e.g., CU 172). The radio protocol stack 200 is functionally split as shown by the radio protocol stack 250 in FIG. 2B. The CU at any of the BSs 104 or 106 may hold all the control and upper layer functionalities (e.g., RRC 214, SDAP 212, NR PDCP 210), while the lower layer operations (e.g., NR RLC 206B, NR MAC 204B, and NR PHY 202B) are delegated to the DU. To support connection to a 5GC, NR PDCP 210 provides SRBs to RRC 214, and NR PDCP 210 provides DRBs to SDAP 212 and SRBs to RRC 214.

[0046] Several embodiments are now discussed in which the BSs operating in the system of FIG. 1 A transmit a configuration to the UE 102 and later activate the configuration for communication between the UE 102 and the BSs. The events or steps in FIGs. 3-8B that are similar, are labeled with similar reference numbers (e.g., event 316 is similar to event 416 of FIGs 4A and 4B, event 516 of FIG. 5A, event 517 of FIG. 5B, event 616 of FIG. 6A, event 617 of FIG. 6B, event 716 of FIG. 7A, and event 717 of FIG. 7B), with differences discussed below where appropriate. With the exception of the differences shown in the figures and discussed below, any of the alternative embodiments 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.

[0047] Referring to FIG. 3, which shows a signal diagram 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 (i.e. , serving cell) 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 embodiments, the UE 102 communicates in CA with the DU 174 on the cell 124A and other cell(s) (e.g., cell 124C) using the serving DU configuration. In other embodiments, the UE 102 communicates with the DU 174 on cell 124A only. In some embodiments, the UE 102 communicates with the DU 174 on the cell 124A and / or other cell(s) via one or multiple TRPs. In some embodiments, the cell 124A may 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 embodiments, the cell 124A may be a SCell, and one of the other cell(s) is a PCell. In such cases, the rest includes SCell(s) and / or additionalcell(s) associated with the PCell or a SCell. In the following description, the first BS 104 may be the DU 174, the CU 172, or the DU 174 and CU 172.

[0048] In the event 302, the UE 102 may 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 embodiments, the UE 102 communicates UL PDUs and / or DL PDUs with the first BS 104 via radio bearers which may include SRBs and / or DRB(s). The BS 104 may configure the radio bearers to the UE 102. In some embodiments, UL control signals include UL control information, channel state information (CSI), hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, scheduling request(s) and / or sounding reference signal(s). Similarly, the UE 102 may 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 embodiments, the DL control signals include downlink control information (DCIs) and reference signals (e.g., synchronization signal block(s), channel state information reference signal(s) (CSI-RS(s)), and / or tracking reference signal(s)). The first BS 104 may 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.

[0049] In some embodiments, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some embodiments, the DU 174 may transmit these configuration parameters to the CU 172. The CU 172 generates one or more messages (e.g., RRC reconfiguration message(s)) including the configuration parameters and transmits one or more messages to the UE 102 via the DU 174. In other embodiments, the DU 174 transmits the configuration parameters to the UE 102 directly. In some embodiments, the serving DU configuration is CellGroupConfig IE defined in 3GPP TS 38.331. In other embodiments, the serving DU configuration includes configuration parameters in the CellGroupConfig IE. In some embodiments, the serving CU configuration includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some embodiments, the serving CU configuration includes a MeasConfig IE and / or a RadioBearerConfig IE (e.g., defined in 3GPP TS 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some embodiments, the serving DU configuration includes a CSI-MeasConfig IE orconfiguration parameters for CSI measurement and reporting. In other embodiments, the serving CU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and reporting. In some embodiments, 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 embodiments, 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.

[0050] While communicating with the first BS 104, the UE 102 transmits 304 at least one measurement report to the DU 174. In some embodiments, 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 nonserving cell. For each of the L3 measurement report(s), the DU 174 transmits 306 a DU-to- CU message including the L3 measurement report to the CU 172. In some embodiments, 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 embodiments, the DU 174 does not transmit or refrains from transmitting the L1 measurement report(s) to the CU 172. At least one serving cell includes the cell 124A and / or other cell(s), and the at least one non-serving cell includes the cell 124B and / or cell 124C. In some embodiments, the serving DU configuration or the serving CU configuration includes at least one measurement configuration. In some embodiments, the UE 102 receives one or more RRC messages (e.g., RRCReconfiguration message(s)) including at least one measurement configuration from the CU 172 via the DU 174, in the event 302. Based on the at least one measurement configuration, the UE 102 performs measurements and transmits 304 the at least one measurement report to the DU 174.

[0051] In some embodiments, at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)) and / or L1 measurement configuration(s). The L1 measurement configuration(s) (e.g., CSI-MeasConfig IE(s)) may include L1 measurement resource configuration(s) and / or L1 measurement reporting configuration(s). The L1 measurement resource configuration(s) may configure reference signal(s) and / or resources of the reference signal(s) for the UE 102 to measure and obtainL1 measurement results. In some embodiments, the reference signal(s) includes CSI- RS(s) and / or Synchronization Signal (SS) / Physical Broadcast Channel (PBCH) Resource Block(s) (SSB(s)). For example, the L1 measurement resource configuration(s) is / are CS / - ResourceConfig IE(s). In another example, the L1 measurement reporting configuration(s) configures way(s) the UE 102 transmits 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 embodiment, the DU 174 does not transmit the L1 measurement report(s) to the CU 172.

[0052] In some embodiments, the L1 measurement configuration(s) are RRC IE(s) defined in 3GPP TS 38.331 for a lower layer triggered mobility (LTM). In some embodiments, the L1 measurement resource configuration(s) are RRC I E(s) defined in 3GPP TS 38.331 for the LTM. In some embodiments, the L1 measurement reporting configuration(s) are RRC IE(s) (e.g., defined in 3GPP TS 38.331 ) for the LTM. In some embodiments, each of the L1 measurement reporting configuration(s) may include a trigger event configuration configuring a trigger event to trigger the UE 102 to transmit a L1 measurement report. If UE 102 detects the trigger event, the UE 102 transmits an L1 measurement report to DU 174.

[0053] In some embodiments, (each of) the L1 measurement report(s) may include at least one L1 measurement result. In some embodiments, 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 plus Noise Ratio (L1-SINR) value. In some embodiments, for each of the L1 measurement report(s), the UE 102 transmits a PUCCH transmission including the L1 measurement report to the DU 174. That is, the UE 102 transmits each of the L1 measurement report(s) on a PUCCH to the DU 174. In other embodiments, 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 each of the L1 measurement report(s) on a PUSCH to the DU 174. In yet other embodiments, the UE 102 transmits a portion of the L1 measurement report(s) onPUCCH(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 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 remaining portion of the L1 measurement report(s), the UE 102 transmits a PUSCH transmission including the L1 measurement report to the DU 174. In some embodiments, each of the L1 measurement report(s) is a part of a CSI report (i.e. , a CSI component) or a CSI report. In some embodiments, the UE 102 may include other CSI component(s) in (each of) the PUCCH transmission(s) and / or PUSCH transmission(s) described above. In one embodiment, the other CSI component(s) include 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 embodiments, the UE 102 does not transmit the L1 measurement report(s) in an RRC message(s) to the DU 174.

[0054] In some embodiments, each of the L3 measurement report(s) may include at least one L3 measurement result. In some embodiments, the at least one L3 measurement result includes at least one RSRP (value) and / or at least one SINR (value). In one embodiment, the UE 102 transmits each of the L3 measurement report(s) on a PUSCH to the CU 172, via the DU 174. In some embodiments, each of the L3 measurement report(s) may be an RRC message (e.g., MeasurementReport message). In some embodiments, 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 may determine that the L3 measurement report is associated with an L3 measurement configuration identified by the measurement identity.

[0055] In some alternative embodiments, for each of the at least one measurement report (e.g., L1 measurement report(s)), the UE 102 transmits 304 a MAC control element (CE) including the measurement report to DU 174. To transmit 304 the MAC CE(s) to the DU 174, the UE 102 generates one or more MAC PDUs, each including one or more of the MAC CE(s).

[0056] In some embodiments, the UE 102 performs measurements on one or more reference signals in accordance with at least one measurement configuration. The one or more reference signals may include one or more SS / PBCH Blocks (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 one or more reference signals on cell 124A and other cell(s) (e.g., the cell 124B, the cell 124C, and / or cell(s)).

[0057] 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 or target cell (e.g., cell 124B in FIG. 1 A) for LTM for the UE 102. In some embodiments, 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 embodiments, 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 embodiments, if the L3 measurement report(s) indicates that signal strength and / or quality of the first cell is above a first predetermined threshold, is better than 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 CU 172 determines to prepare the first cell for the UE 102. In other embodiments, 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.

[0058] If 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 embodiments, 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, cell ID 1 is a cell global identity (CGI). In another example, the cell ID 1is a portion of the CGI. In yet another example, the cell ID 1 is a physical cell ID (PCI). In some embodiments, 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 embodiments, 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 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 some embodiments, the DU 174 may 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 ). If 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, in response to a CU-to-DU message received from the CU 172.

[0059] In some embodiments, the DU 174 includes, in the first DU-to-CU message, the cell ID of the first cell associated with the LTM DU configuration 1 , to indicate that the LTM DU configuration 1 is configured for or associated with the first cell. The CU 172 identifies the LTM DU configuration 1 is configured for or associated with the first cell. In some embodiments, the CU 172 may 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).

[0060] In some embodiments, 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 embodiments, the CU 172 does not include a reference LTM DUconfiguration in the first CU-to-DU message. In such cases, the DU 174 generates the LTM DU configuration(s) 1 and / or 2, .... N (i.e., non-reference LTM DU configuration(s)) as complete LTM DU configuration(s). In yet other embodiments, 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 embodiments, 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.

[0061] In some embodiments, the reference LTM DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some embodiments, the reference LTM DU configuration is CellGroupConfig IE defined in 3GPP TS 38.331. In other embodiments, the reference LTM DU configuration includes configuration parameters in the CellGroupConfig IE. In some embodiments, the reference LTM DU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and / or reporting.

[0062] In some embodiments, the reference LTM DU configuration is different from the serving DU configuration. In some embodiments, 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 embodiments, the reference LTM DU configuration is the same as the serving DU configuration.

[0063] After receiving the first DU-to-CU message, the CU 172 generates an RRC reconfiguration message (e.g., an RRCReconfiguration message) including the LTM DU configuration 1 and transmits 316 to the DU 174 a second CU-to-DU message, including the RRC reconfiguration message. In some embodiments, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message. In other embodiments, the CU 172 does not include a / the reference LTM DU configuration in theRRC reconfiguration message. In some embodiments, if the CU 172 transmits 302 the reference LTM DU configuration to the UE 102, the CU 172 does not include the reference LTM DU configuration in the RRC reconfiguration message. In other embodiments, 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. 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.

[0064] In some embodiments, 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 instructs the UE 102 not to immediately apply the LTM DU configuration 1 and / or the LTM CU configuration 1. In some embodiments, the UE 102 receives an RRC reconfiguration message (e.g., the RRC reconfiguration message of the event 318) including a configuration (e.g., the LTM DU configuration 1 ). If the configuration is included in the first container and the RRC reconfiguration message includes the first container, the UE 102 refrains from applying the configuration. Otherwise, if the configuration is not included in the first container, the UE 102 may immediately apply the configuration. In some embodiments, the first container includes or is a first addition or modification list (e.g., Itm- ConfigToAddModList field, ltm-CandidateToAddModListf\e\d, or Itm- CandidateConfigToAddModList \e\d). 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 embodiments, 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 embodiments, 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 may store the first addition or modification list, e.g., in a variable in its random access memory (RAM). In other alternative embodiments, the DU174 generates the first container and includes the first container in the first DU-to-CU message. In yet other alternative embodiments, the DU 174 generates the element 1 and includes element 1 in the first DU-to-CU message.

[0065] In some embodiments, 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 is associated with the LTM DU configuration 1 . To associate theLTM CU configuration 1 with the LTM DU configuration 1 , the CU 172 may include theLTM CU configuration 1 and the LTM DU configuration in the element 1 . In some embodiments, 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 are 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 may include the LTM CU configuration(s) 2, ... , N and the LTM DU configuration(s) in element(s) 2, ... , N, respectively. In other embodiments, 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.

[0066] After receiving the RRC reconfiguration message 316, the DU 174 transmits 318 the RRC reconfiguration message to UE 102. In response, the UE 102 transmits 320 an RRC reconfiguration complete message (e.g., an RRCReconfigurationComplete message) to the DU 174, which in turn transmits 322 to the CU 172 a second DU-to-CU message including the RRC reconfiguration complete message. In some embodiments, 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 encryptedRRC reconfiguration and encrypted MAC-1 to obtain the RRC reconfiguration message and MAC-1 and verifies whether the MAC-1 is valid. If the UE 102 verifies the MAC-I is invalid, the UE 102 discards or ignores the RRC reconfiguration message. In some embodiments, the UE 102 may perform an RRC connection reestablishment procedure in response to the invalid MAC-I. Otherwise, if the UE 102 verifies the MAC-I is valid, the UE 102 may 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.

[0067] The events 308 (optional) and 310 are collectively referred to in FIG. 3 as an LTM preparation procedure 390. The events 316, 318, 320, and 322 are collectively referred to in FIG. 3 as an LTM configuration delivery procedure 394.

[0068] In some embodiments, 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 may transmit a UE Context Modification Confirm message to the DU 174 in response to UE Context Modification Required message. In some embodiments, the second CU-to-DU message is a DL RRC Message Transfer message. In other embodiments, the second CU-to-DU message is a UE Context Modification Request message, and the DU 174 may transmit a second DU-to-CU message (e.g., UE Context Modification Response message) to the CU 172 in response to the second CU-to-DU message.

[0069] In some embodiments, the CU 172 may include a reference LTM CU configuration in the RRC reconfiguration message 316 or the first container. Additionally, the CU 172 may generate the LTM CU configuration 1 (i.e., non-reference LTM CU configuration) as a delta configuration, to augment the reference LTM CU configuration. Similarly, the CU 172 may generate some or all of the LTM CU configuration(s) 2, ... , N as delta configuration(s), to augment the reference LTM CU configuration. Alternatively, in the RRC reconfiguration message 316 or the first container, the CU 172 includes the reference LTM CU configuration and does not include a non-reference LTM CU configuration. In some embodiments, 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 includes the additional container in the RRC reconfiguration message 316.

[0070] In some embodiments, the reference LTM CU configuration is different from the serving CU configuration. In some embodiments, 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 embodiments, the reference LTM CU configuration is the same as the serving CU configuration.

[0071] In some embodiments, the CU 172 includes a first LTM ID (referred to herein after as ID 1 ) in the RRC reconfiguration message, for identifying the LTM DU configuration 1 or the element 1. In some embodiments, the CU 172 includes the ID 1 in the first container or element 1 . In some embodiments, the CU 172 assigns the ID 1.

[0072] In some embodiments, the CU 172 transmits 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 embodiments, the CU 172 includes the ID 1 in the first CU-to-DU message. In other embodiments, after receiving the first DU-to-CU message, the CU 172 transmits 312 a third CU-to-DU message including the ID 1 to the DU 174 instead of including the ID 1 in the first CU-to-DU message. In some embodiments, in the third CU-to-DU message, the CU 172 may 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 may directly associate the ID 1 with the LTM DU configuration 1 . In other embodiments, in the third CU-to-DU message, the CU 172 may 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 may 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 embodiments, in the third CU-to-DU message, the CU 172 may include the LTM DU configuration 1 , the cell ID 1 , and / or the ID 1 and indicates the association between the ID 1 , LTM DU configuration 1 , and / or the cell ID 1 . In some embodiments, the DU 174 may transmit 314 a third DU-to-CU message to the CU 172, in response to the third CU-to-DU message. In some embodiments, the third CU-to-DU message and third DU-to-CU message are UE Context Modification Request messageand UE Context Modification Response message, respectively. The events 312 (optional) and 314 (optional) are collectively referred to in FIG. 3 as an LTM ID assignment procedure 392. In other embodiments, the CU 172 may 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 may be omitted.

[0073] In the case that the CU 172 includes the ID 1 in the first CU-to-DU message, the DU 174 may 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.

[0074] In some embodiments, 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 embodiments, the CU 172 includes the reference LTM DU configuration in the RRC reconfiguration message 316 and outside the first container. For example, the CU 172 generates a third container (e.g., a field / IE) to include the first container and the reference LTM DU configuration and includes the third container in the RRC reconfiguration message 316. In yet other embodiments, 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 embodiments, 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, 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.

[0075] In some embodiments, neither the CU 172 nor the DU 174 assigns an ID to identify the reference LTM DU configuration. In some embodiments, neither the CU 172 nor the DU 174 assigns an ID to identify the reference LTM CU configuration.

[0076] In some embodiments, 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 embodiments, the plurality of configuration parameters includes physical layer configuration parameters (e.g., PhysicalCellGroupConfig IE), MAC layer configuration parameters (e.g., MAC-CellGroupConfig IE) and / or RLC configuration parameters (e.g., RLC-BearerConfig IE(s)). In some further embodiments, the plurality of configuration parameters includes a special cell configuration (e.g., SpCellConfig IE) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some embodiments, the LTM DU configuration 1 is CellGroupConfig IE defined in 3GPP TS 38.331 . In other embodiments, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0077] In some embodiments, the LTM CU configuration 1 includes PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some embodiments, the LTM CU configuration 1 includes a MeasConfig IE and / or a RadioBearerConfig IE (e.g., defined in 3GPP TS 38.331) or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. In some embodiments, the LTM DU configuration 1 includes L1 measurement configuration 1 (e.g., a CSI-MeasConfig IE) and / or at least one TCI state configuration. In other embodiments, the LTM CU configuration 1 includes the L1 measurement configuration and / or the TCI state configuration(s) 1. In some embodiments, the L1 measurement configuration includes at least one reference signal (RS) resource configuration 1 and / or at least one report configuration 1. In some embodiments, 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 embodiments, each of the RS resource configuration(s) 1 includes an RS resource configuration ID. In some embodiments, the RS resource configuration(s) 1 is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on cell 1 for the UE 102 to transmit measurement results. In some embodiments, 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 embodiments, each of the TCI state configuration(s) 1 configures a TCI state that associates one or two DLRSs with a corresponding quasi-colocation (QCL) type. The DL RS(s) are associated with cell 1.

[0078] In some embodiments, 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 embodiments, the DU 174 includes the serving DU configuration in the first DU-to-CU message. In other embodiments, the DU 174 transmits an additional DU-to-CU message including the serving DU configuration to the CU 172. In some embodiments, the additional DU-to-CU message is a UE Context Modification Required message. In some embodiments, the CU 172 includes the serving DU configuration 1 in the RRC reconfiguration message 316, 318. In other embodiments, the CU 172 transmits another RRC reconfiguration message, including the serving DU configuration, to the UE 102 via the DU 174.

[0079] In some embodiments, the DU 174 includes a random access configuration in the LTM DU configuration 1 . In other embodiments, the DU 174 does not include a random access configuration in the LTM DU configuration 1. In some embodiments, 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 embodiments, 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 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 instructs 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 , which excludes the random access configuration.

[0080] In some embodiments, 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 embodiments, 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.

[0081] In some embodiments, 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 embodiments, if the DU 174 determines that the UE 102 has synchronized in UL with the first cell, the DU 174 determines to include the first indication in the LTM DU configuration 1. Otherwise, if the DU 174 determines that the UE 102 has not synchronized in UL with the first cell, the DU 174 determines to not include the first indication in the LTM DU configuration 1 . If the LTM DU configuration 1 includes the first indication, the UE 102 skips or refrains from performing the random access procedure of the event 332, in accordance with or in response to the first indication. Otherwise, if the LTM DU configuration 1 does not include the first indication, the UE 102 performs the random access procedure in accordance with the random access configuration in the event 332, in response to the LTM DU configuration 1 excluding the first indication, as described below.

[0082] In some embodiments, 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 embodiments, 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 embodiments, the DU 174 includes an LTM cell switch information in the first LTM DU configuration 1. In some embodiments, the DU 174 includes the random access configuration (parameters) in the LTM cell switch information (e.g., Itm-Cell Switch Info field or LTM-Cell Switch Info IE). In some embodiments, if the cell124A 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 embodiments, 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 embodiments, 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 event 332. In some embodiments, the DU 174 includes a cell ID (i.e., cell ID 1) of cell 1 (i.e., the first cell) in the LTM DU configuration 1. In one embodiment, the cell ID 1 may be a PCI. In another embodiment, the cell ID 1 is a CGI. In some embodiments, 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 embodiments, the LTM DU configuration 1 includes a cell index 1 indexing the cell ID 1 or the first cell. Cell index 1 is not a cell ID. The cell index takes fewer bits than the cell ID. In some embodiments, 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.

[0083] In some embodiments, 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 embodiment, 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) may include the cell 124C and / or cell(s) 126B, other than the cells 124A, 124B, and / or 124C. In some embodiments, if the L3 measurementreport(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 embodiments, 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 embodiment, the respective predetermined threshold(s) for the additional cells may be different from the first predetermined threshold. In another embodiment, the respective predetermined threshold(s) for the additional cell(s) may be the same as the first predetermined threshold. In some embodiments, the respective predetermined thresholds for the additional cells may 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.

[0084] 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.

[0085] In some embodiments, 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 may 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, where “N” is an integer 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 embodiments of the LTM DU configuration 1 may apply to the LTM DU configuration(s) 2, ... , N.

[0086] In other embodiments, the CU 172 and DU 174 perform a single LTM preparation procedure (i.e. , the LTM preparation procedure 390) to prepare the cell(s) 1 , 2, ... , N. In such cases, the DU 174 includes the LTM DU 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 may 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.

[0087] After receiving the LTM DU configuration(s) 2, ... , N from the DU 174, the CU 172 may include the LTM DU configuration(s) 2, ... , N in the first container. In some embodiments, the CU 172 may 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 embodiments, 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 embodiments, the CU 172 includes the ID(s) 2, ... , N in the first container. For example, the CU 172 may 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.

[0088] In some embodiments, the CU 172 assigns the ID(s) 2, ... , N for the LTM DU configuration(s) 2, ... , N, respectively. In other embodiments, 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 embodiments, 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.

[0089] In some embodiments, the CU 172 performs 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 embodiments, the CU 172 may include the ID(s) 2, ... , N and the LTM DU configuration(s) 2, ... , N in the third CU-to-DU message and indicate theassociation between the ID(s) 2, , N and the LTM DU configuration(s) 2, ... , N, respectively. Thus, the DU 174 may associate the LTM DU configuration(s) 2, ... , N with the ID(s) 2, ... , N, respectively. In yet other embodiments, the CU 172 may 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 may 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 embodiments, the CU 172 may 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 may be omitted. In yet other embodiments, the CU 172 may 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 embodiment, the DU 174 includes the ID(s) 2, ... , N in the LTM DU configuration(s) 2, ... , N. Thus, the CU 172 does not include the ID(s) 2, ... , N in the RRC reconfiguration message, first container, and / or element(s) 2, ... , N.

[0090] In some alternative embodiments, the DU 174 assigns the ID(s) 2, ... , N. In some embodiments, the DU 174 includes the ID(s) 2, ... , N in the first DU-to-CU message of the procedure 390. In yet other embodiments, 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 may include the ID(s) 2, ... , N in the RRC reconfiguration message. In other embodiments, 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.

[0091] In some alternative embodiments, the CU 172 generates 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 someembodiments, the second container may include or be a second addition or modification list (e.g., Itm-ConfigToAddModList field, LTM-ConfigToAddModList IE, Itm- CandidateConfigToAddModList field, or LTM-CandidateConfigToAddModList IE), and each of the element(s) 2, ... , N may be an addition or modification IE (e.g., Itm- ConfigToAddMod field, LTM-ConfigToAddMod IE, ltm-CandidateConfigToAddMod \e\d, or LTM-CandidateConfigToAddMod IE). When the UE 102 receives the second addition or modification list, the UE 102 may 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).

[0092] In some embodiments, 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 embodiment, each of the cell ID(s) 2, ... , N is a PCI. In some further embodiments, 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 may set the cell index(es) 2, ... , N to different value(s) and include the cell index(es) 2, ... , N in the first CU-to CU-to-DU message of the event 308. In the case that the CU 172 prepares the cell(s) 2, ... , N in the additional LTM preparation procedure(s), the CU 172 may 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 embodiments, 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.

[0093] In some embodiments, 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 embodiments, each of the LTM DU configuration(s) 1 , ... , N may be a CellGroupConfig IE as defined in 3GPP TS 38.331 . In other embodiments, each of the LTM DU configuration(s) 1 , ... , N includes configuration parameters included in a CellGroupConfig IE as defined in 3GPP TS 38.331 . In some further embodiments, the plurality of configuration parameters in each of the LTM DU configuration(s) includes a particularspecial cell configuration (e.g., SpCellConfig IE) and / or one or more SCell configurations (e.g., SCellConfig IE(s)). In some embodiments, the LTM DU configuration(s) 1 , N are CellGroupConfig IE(s) as defined in 3GPP TS 38.331. In other embodiments, the LTM DU configuration(s) 1 , ... , N include configuration parameters in the CellGroupConfig IE.

[0094] In some embodiments, the CU 172 includes 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 embodiments of the additional LTM CU configurations are similar to the LTM CU configuration 1 .

[0095] In some embodiments, 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 , ... , N). 1 < M < N. In response to the determination, the CU 172 transmits an RRC reconfiguration message to the UE 102, via the DU 174, to instruct the UE 102 to release the LTM DU configuration M or element M. In one embodiment, the CU 172 generates a release list including the ID (i.e. , LTM ID) M for releasing the LTM DU configuration M or element M and includes the release list in the RRC reconfiguration message. In response to the RRC reconfiguration message, the UE 102 releases the LTM DU configuration M or element M and transmits an RRC reconfiguration complete message to the CU 172, via the DU 174. In response to the determination, the CU 172 transmits a CU-to-DU message to the DU 174 to instruct the DU 174 to release the LTM DU configuration M. To instruct the DU 174 to release the LTM DU configuration M, the CU 172 may 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 embodiments, 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.

[0096] In other embodiments, 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 DUconfiguration K is released, the DU 174 may 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, where 1 < K < N. After (e.g., in response to) receiving the DU-to-CU message, the CU 172 generates a release list including the ID (i.e., LTM ID) K to release the LTM DU configuration K or element K and transmits an RRC reconfiguration message including the release list to the UE 102 via the DU 174. In response, the UE 102 releases the LTM DU configuration K or element K and transmits an RRC reconfiguration complete message to the UE 102 via the DU 174. The CU 172 may transmit a CU-to-DU message to the DU 174 in response to the DU-to- CU message. In some embodiments, 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.

[0097] After receiving the RRC reconfiguration in event 318 or transmitting the RRC reconfiguration complete message in event 320, the UE 102 transmits 324 at least one measurement report to DU 174, similar to event 304. In some embodiments, the DU 174 may transmit 326 a DU-to-CU message including at least one measurement report to the CU 172, similar to event 306. In other embodiments, the DU 174 does not transmit at least one measurement report to the CU 172. In some embodiments, the at least one measurement report of the event 324 includes L1 measurement report(s) or L3 measurement repot(s), as described for the event 304. In some embodiments, 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 embodiments, 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 embodiments, the UE 102 does not transmit the L1 measurement report(s) in format of RRC message(s) to the DU 174.

[0098] In some embodiments, the UE 102 transmits 324 the at least one measurement report to 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 may 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 theevent 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 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 may 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 cell 124A, cell 1 , and / or cell(s) 2, ... , N. The one or more reference signals may be CSI-RS(s) or SSB(s).

[0099] In some embodiments, the at least one measurement configuration includes L3 measurement configuration(s) (e.g., MeasConfig IE(s)), as described for the event 304. In other embodiments, the at least one measurement configuration includes or is L1 measurement configuration(s), as described above. In yet other embodiments, the L1 measurement configuration(s) may be CSI-MeasConfig IE(s) defined in 3GPP TS 38.331. The L1 measurement configuration(s) may 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 PUSCH resources) 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 embodiments, the report configuration(s) are similar to CSI-ReportConfig I E(s). In other embodiments, each of the report configuration(s) is a new RRC IE. In some embodiments, (each of) the report configuration(s) configures periodically reporting and / or event-triggered reporting of the L1 measurement result(s).

[0100] In some embodiments, the L1 measurement report(s) is / are CSI report(s). In other embodiments, the L1 measurement report(s) is / are MAC CE(s). In some embodiments, 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 embodiments, 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 embodiments, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values may include one or more L1-RSRP values and / or one or more L1-SINR values.

[0101] In yet other embodiments, the at least one measurement configuration includes new-type measurement configuration(s) (e.g., LTM measurement configuration(s)). The new-type measurement configuration may be newly defined in a 3GPP TS. In some embodiments, 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 embodiment, the reference signal resource configuration(s) is / are CSI-ResourceConfig IE(s). In another embodiment, the new-type measurement configuration(s) include measurement report configuration(s), as described above. The UE 102 transmits the measurement report(s) on PUCCH(s) or MAC CE(s) to the DU 174 in accordance with the measurement report configuration(s). The DU 174 receives the measurement report(s) on PUCCH(s) or MAC CE(s) in accordance with the measurement report configuration(s). In such cases, the measurement report(s) may be L1 measurement report(s) or new-type measurement report(s) (e.g., LTM measurement report(s)). In some embodiments, the new-type measurement configuration includes configuration parameters newly defined in a 3GPP TS.

[0102] After (e.g., in response to) receiving the at least one measurement report in the event 324, the DU 174 generates a first LTM command to activate the LTM DU configuration 1 (i.e., the first LTM command instructs 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 UE 102. In some embodiments, the DU 174 transmits the first LTM command on cell 124A (e.g., the serving PCell) to the UE 102. In other embodiments, the DU 174 transmits the first LTM command on cell 124C (e.g., the serving SCell) to the UE 102. In some embodiments, the DU 174 may include the ID 1 in the first LTM command to indicate the LTM DU configuration 1 or element 1 , and the UE102 determines (e.g., identifies) the LTM DU configuration 1 or element 1 in accordance with the ID 1.

[0103] In other embodiments, the DU 174 includes the cell index 1 indexing the cell ID 1 in the first LTM command. In this case, 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.

[0104] In yet other embodiments, the DU 174 includes cell ID 1 in the first LTM command, where the cell ID 1 identifies the cell 1 . In some embodiments, the cell ID 1 included in the first LTM command is the same as the cell ID 1 included in the first CU-to- DU message. In other embodiments, 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, ... , Nand 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 embodiments, the DU 174 stores 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.

[0105] In yet other embodiments, the DU 174 includes 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 embodiment, 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 may 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 embodiment, bit 0, ... , N-1 corresponds to the cell index(es) 1 , ... , N, the ID(s) 1 , ... , N, the LTM DU configuration(s) 1 , ... , N, or the element (s) 1 , ... , N, respectively, and the DU 174 sets a corresponding bit (e.g., bit 0) in the bit map to a first value to indicate the cell index 1 , the ID 1 the LTM DU configuration 1 , or the element 1. Thus, the UE 102 may determine the cell index 1 , the ID 1 LTM DU configuration 1 , or element 1 in accordance with the bit 0 set to the first value in the bit map. In such embodiments, 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 embodiments, the first value is one and the second value is zero. In other embodiments, 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 may 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 embodiments, the DU 174 sets at most one bit in the bit map to the first value.

[0106] After determining or identifying the LTM DU configuration 1 or element 1 , the UE 102 applies the LTM DU configuration 1 and / or LTM CU configuration, after (e.g., in response to) receiving the first LTM command.

[0107] In some embodiments, 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) may 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 embodiments, 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 embodiments, the at least one measurement result includes L1-RSRP value(s), L1 -RSRQ value(s), and / or L1-SINR value(s). In other embodiments, 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 embodiments, the second predetermined threshold is different from the first predetermined threshold. In one embodiment, 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 embodiment, the second predetermined threshold is equal to the first predetermined threshold. In this case, the at least one measurement result indicates that the first cell has been continuously above the second predetermined threshold or the first predetermined threshold. This indicates that the first cell is suitable for communication with 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.

[0108] In some embodiments, the at least one measurement report (e.g., L3 measurement report(s)) of 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 embodiment, the second predetermined threshold is larger than the first predetermined threshold. In such an embodiment, the measurement report of the event 326 indicates that signal strength or quality of the first cell is suitable for communication with the UE 102. Inanother embodiment, the second predetermined threshold is equal to the first predetermined threshold. In such an embodiment, the 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 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, when above the second predetermined threshold. In response to the determination, 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 one embodiment, a serving cell change invokes only L1 report(s) while a handover invokes L3 report(s). In some embodiments, the CU 172 includes the ID 1 in the fourth CU-to-DU message. In other embodiments, 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 embodiments, the CU 172 includes the cell index 1 in the fourth CU-to-DU message. Thus, the DU 174 may determine to activate the LTM DU configuration 1 in accordance with the cell index 1 . In other embodiments, the CU 172 may 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 embodiments, the CU 172 may include the ID 1 in the fourth CU-to-DU message. Thus, the DU 174 may determine to activate the LTM DU configuration 1 in accordance with the ID 1. In some embodiments, 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 embodiments, 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.

[0109] When or in response to determining to activate the LTM DU configuration 1 or transmit the first LTM command 330, the DU 174 may transmit 329 to the CU 172 a DU- to-CU message indicating LTM (being) executed. In some embodiments, 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 activates the LTM DU configuration 1 or triggers a fast serving cell change(i. e. , an LTM serving cell change). Note that serving cell change or switch is faster than a handover procedure. The DU may transmit the DU-to-CU message 329 to the CU 172 before or after transmitting the LTM command 330.

[0110] In some embodiments, the first LTM command is a MAC CE included in a MAC PDU that the UE 102 receives 330 from the DU 174. The MAC CE may be a new MAC CE defined in 3GPP TS 38.321. In one embodiment, 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 may include a logical channel ID or extended logical channel ID defined in a 3GPP TS to identify the new MAC CE. For example, the logical channel ID or extended logical channel ID are newly defined in 3GPP TS 38.321 . In other embodiments, the first LTM command is a DCI that the UE 102 receives on a PDCCH from the DU 174 in the event 330. The DU 174 generates a CRC for the DCI, scrambles the CRC with a first C-RNTI of the UE 102, and transmits 330 the DCI and scrambled CRC on the PDCCH. In one embodiment, a format of the DCI may be an existing DCI format defined in a 3GPP TS (e.g., 3GPP TS 38.212). In another embodiment, the format of the DCI may be a new DCI format defined in a 3GPP TS (e.g., 3GPP TS 38.212).

[0111] In some embodiments, 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.

[0112] In some embodiments, after receiving the first LTM command, the UE 102 transmits 331 an acknowledgement to the DU 174 on the cell 124A (e.g., serving PCell) or cell 124D (e.g., serving SCell) to indicate that the UE 102 receives the first LTM command. In some embodiments, the acknowledgement is a HARQ ACK. In other embodiments, 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 embodiments, the acknowledgement is a PUCCH transmission.

[0113] In some embodiments, the CU 172 transmits 316 the RRC reconfiguration message in response to the L3 measurement report 306 for the first cell. To configure theUE 102 to transmit the L3 measurement report 306, the CU 172 may 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 embodiments, 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 may transmit a second RRC reconfiguration message including the L1 or new- type measurement configuration(s) to the UE 102. In some embodiments, the first and second RRC reconfiguration messages may be the same message (i.e., the same instance). In other embodiments, the first and second RRC reconfiguration messages are different messages. In some embodiments, the second RRC reconfiguration message is the RRC reconfiguration message of event 316. In other embodiments, the second RRC reconfiguration message is different from the RRC reconfiguration message of event 316.

[0114] After (e.g., in response to) receiving the first LTM command, the UE 102 accesses 332 the first cell. The UE 102 identifies the LTM DU configuration 1 in accordance with the ID 1 , the cell ID 1 , or the cell index 1 received in the first LTM command and applies the LTM DU configuration 1 to communicate with the DU 174 on the first cell. In some embodiments, 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 embodiments, the UE 102 stops communicating on cell 124A after (e.g., in response to) receiving 330 the first LTM command or transmitting 331 the acknowledgement. In some embodiments, the UE 102 accesses the first cell (target 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 embodiments, 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.

[0115] In some embodiments, the DU 174 configures the access of the UE 102 to the first cell, including whether or not the UE 102 performs a random access procedure, in the LTM DU configuration 1. When receiving the first LTM command, the UE 102 determines whether to perform a random access procedure on the first cell in accordance with the LTM DU configuration 1. If the LTM DU configuration 1 configures the UE 102 toperform 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 embodiments, 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 332 the first transmission (e.g., a PUSCH transmission or a PUCCH transmission) on the first cell to the DU 174. In some embodiments, 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.

[0116] In other embodiments, 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 (e.g., the first LTM command). Thus, the UE 102 determines whether to perform the random access procedure on the first cell in event 332 in accordance with the first LTM command. In some embodiments, 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 embodiments, 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 embodiments, 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 andtransmits the first transmission on the first cell to access the first cell, using the provided timing advance value. In yet other embodiments, 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.

[0117] In some embodiments, the random access procedure is a four-step random access procedure. In other embodiments, the random access procedure is a two-step random access procedure. In some embodiments, the random access procedure is a contention-free random access procedure. In other embodiments, the random access procedure is a contention-based random access procedure. In cases where the random access procedure is a four-step random access procedure, the UE 102 transmits a Message 3 including a UE identity to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., a Message 4) to the UE 102 in response to the Message 3. In cases where the random access procedure is a two-step random access procedure, the UE 102 transmits a Message A including the UE identity to the DU 174 via the first cell in the random access procedure. The DU 174 transmits a contention resolution message (e.g., Message B) to the UE 102 in response to Message A. In some embodiments, 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 embodiments, 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 embodiments, the contention resolution message is a PDCCH transmission addressed to the second C-RNTI. In other embodiments, the LTM DU configuration 1 does not include a C-RNTI, the UE identity is the first C-RNTI. In such embodiments, the contention resolution message is a PDCCH transmission addressed to the first C-RNTI. In some embodiments, the DU 174 includes the second C-RNTI in the reconfiguration with sync configuration. In other embodiments, the DU 174 includes the second C-RNTI in the LTM cell switch information.

[0118] In cases where the LTM DU configuration 1 or the first LTM command configures a dedicated random access preamble, the random access procedure is acontention 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 completed the random access procedure (i.e., the UE 102 successfully accesses the first cell).

[0119] 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.

[0120] In some embodiments, the UE 102 transmits the first transmission (e.g., the PUSCH transmission) on the first cell using a UL grant. In some embodiments, the first LTM command includes the UL grant. In other embodiments, 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 embodiments, the UE 102 attempts to receive the first DCI or the UL grant by monitoring one or more PDCCHs on the first cell in accordance with the LTM DU configuration 1 , when the UE 102 switches to the first cell in response to the first LTM command. While monitoring one or more PDCCHs on the first cell, the UE 102 receives the first DCI and a CRC of the first DCI on the PDCCH. In 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 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.

[0121] In some embodiments, the CU 172 transmits at least one first TCI state configuration to the UE 102 via the DU 174. In some embodiments, each of the first TCI state configuration(s) configures a TCI state for the UE 102 to transmit and / or receive data and / or control signal on the first cell. Each TCI state associates one or two DL RSs with a corresponding QCL type, and the DL RS(s) may be associated with a particular cell of thecell(s) 1 , N. In some embodiments, the CU 172 receives a DU-to-CU message including the first TCI state configuration(s) from the DU 174 and transmits an RRC message including the first TCI state configuration(s) to the UE 102, via the DU 174. In further embodiments, 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 embodiments, the DU 174 includes the LTM DU configuration 1 in a first interface protocol lE / field in the message 312 and includes the serving DU configuration in a second interface protocol I E / field in the DU-to-CU message.

[0122] In some embodiments, the first interface protocol I E / field is defined as part of a format of the DU-to-CU message. The CU 172 includes the serving DU configuration in the RRC message. In some embodiments, the CU 172 refrains from including the serving DU configuration in a container for LTM (e.g., the first container). In other embodiments, the CU 172 includes the first TCI state configuration(s) in an element for LTM, an addition or modification list for LTM, or a container, similar to the element 1 , the first addition or modification list, or the first container respectively. In some embodiments, the RRC message is the RRC reconfiguration message 316, 318 or another RRC reconfiguration message (not shown in FIG. 3). In some embodiments, the DU-to-CU message is the message 312, the message 314, a UE Context Modification Response message, or a UE Context Modification Required message. In some embodiments, the DU 174 also includes the first TCI state configuration(s) in the LTM DU configuration 1 . In other embodiments, the DU 174 refrains from including the first TCI state configuration(s) in the LTM DU configuration 1 .

[0123] In some embodiments, the first interface protocol I E / field is a first F1AP lE / field and the second interface protocol lE / field is a second F1 AP lE / field. In some embodiments, one of the first F1 AP lE / field and the second F1 AP lE / field is a F1AP CellGroupConfig lE / field, and the other is not the F1AP CellGroupConfig lE / field. In some embodiments, the DU 174 includes the first F1AP lE / field in a DU to CU RRC Information IE in the message 312 and includes the second F1AP lE / field in the DU to CU RRC Information IE in the DU-to-CU message. In other embodiments, neither the first F1 AP lE / field nor the second F1 AP IE is a F1 AP CellGroupConfig I E / field. In other embodiments,the second F1 AP I E / field is the DU to CU RRC Information IE and the first F1 AP lE / field is a new IE specific for including an LTM DU configuration.

[0124] In some embodiments, after (e.g., in response to) receiving the first LTM command or while accessing 332 the first cell, the UE 102 monitors one or more PDCCHs on the first cell using some or all of the first TCI state configuration(s). In some embodiments, each of the first TCI state configuration(s) includes a TCI state ID identifying the corresponding TCI state configuration. For example, the first TCI state configuration(s) includes TCI state configuration(s) 1 , ..., L, where L is a positive integer larger than zero. The TCI state configuration(s) 1 , ... , L include TCI state ID(s) 1 , ... , L identifying the TCI state configuration(s) 1 , ... , L, respectively. The DU 174 includes the TCI state ID 1 in the first LTM command to request the UE 102 to apply the TCI state configuration 1 to communicate on the first cell. After (e.g., in response to) receiving the first LTM command, the UE 102 accesses and / or communicates on the first cell using the TCI state configuration 1 in accordance with the TCI state ID 1 . For example, the UE 102 monitors one or more PDCCHs and / or transmits the first transmission, using the TCI state configuration 1 . In some embodiments, the DU 174 detects that the UE 102 accesses the first cell and communicates with the UE 102 on the first cell, based on the TCI state configuration 1 . For example, the DU 174 receives the first transmission from the UE 102 on the first cell, based on the TCI state configuration 1 .

[0125] In some embodiments, the DU 174 includes the TCI state ID 2 in the first LTM command to request the UE 102 to apply the TCI state configuration 2 to communicate on the first cell, in addition to the TCI state ID 1 . After (e.g., in response to) receiving the first LTM command, the UE 102 accesses and / or communicates on the first cell using the TCI state configurations 1 and 2 in accordance with the TCI state ID 1 and the TCI state ID 2. For example, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and transmits the first transmission on the first cell using the TCI state configuration 2. In another example, the UE 102 monitors one or more PDCCHs on the first cell using the TCI state configuration 1 and the TCI state configuration 2 and transmits the first transmission on the first cell using one of the TCI state configuration 1 and the TCI state configuration 2. In some embodiments, the DU 174 detects that the UE 102 accessed the first cell and communicates with the UE 102 on thefirst cell, based on the TCI state configuration 1 and / or the TCI state configuration 2. For example, the DU 174 receives the first transmission from the UE 102 on the first cell, based on one of the TCI state configuration 1 and the TCI state configuration 2.

[0126] In some alternative embodiments, the DU 174 does not include a TCI state ID in the first LTM command. In such cases, the UE 102 communicates on the first cell with the first DU using the at least one first TCI state, after (e.g., in response to) receiving the first LTM command. In some embodiments, the DU 174 detects that the UE 102 accessed the first cell and communicates with the UE 102 on the first cell, based on the first TCI state configuration(s).

[0127] In some embodiments, before transmitting the first LTM command, the DU 174 transmits one or more activation commands to activate some or all of the first TCI state configuration(s). In some embodiments, each of the activation command(s) is a MAC CE. In other embodiments, each of the activation command(s) is a DCL In some embodiments, the DU 174 includes the TCI state ID 1 and / or TCI state ID 2 in the activation command(s) to activate the TCI state configuration 1 and / or the TCI state configuration 2, respectively. Accordingly, the UE 102 determines or identifies that the TCI state configuration 1 and / or the TCI state configuration 2 is / are activated upon receiving the activation command(s). In other embodiments, the DU 174 includes all the TCI state ID(s) for the first TCI state configuration(s) in the activation command(s). Accordingly, the UE 102 determines or identifies that the first TCI state configuration(s) is / are activated upon receiving the activation command(s). In some embodiments, the DU 174 refrains from including, in the first LTM command, a TCI state ID for a TCI state configuration that the DU 174 has not activated for the UE 102. In some embodiments, the DU 174 includes the cell ID 1 or the cell index 1 in the activation command(s). Based on the cell ID 1 or cell index 1 , and the one or more TCI state IDs in the activation command(s), the UE 102 determines that the activation command(s) activates the one or more TCI state configurations in the first TCI state configuration(s), where each of the TCI state ID(s) identifies a particular TCI state configuration of the TCI state configuration(s).

[0128] In some embodiments, the UE 102 communicates with the DU 174 on the cell 124A (e.g., events 302, 304, 318, 320, 324, and 330), using one or more TCI state configurations. In some embodiments, each of the TCI state configuration(s) configures aTCI state for the UE 102 to transmit and / or receive data and / or control signal on cell 124A. In some embodiments, the UE 102 stops using the TCI configuration(s) upon receiving the first LTM command.

[0129] 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 embodiments, the UE 102 communicates 336 PUSCH transmissions, PDSCH transmissions, PUCCH transmissions, PDCCH transmissions, and / or sounding reference signal (SRS) transmissions with the DU 174 on the first cell. In some embodiments, the UE 102 uses some or all of the first TCI state configuration(s) to perform 336 the communication with the DU 174. Similarly, the DU 174 uses some or all of the first TCI state configuration(s) to perform 336 the communication with the UE 102. In some embodiments, the DU 174 includes one or more additional TCI state configurations in the LTM DU configuration 1 . In such cases, the DU 174 may transmit 336 one or more activation commands to the UE 102 via the first cell, to activate the additional TCI state configuration(s). The UE 102 determines that the additional TCI state configuration(s) is / are activated upon receiving the activation command(s). In some embodiments, each of the activation command(s) is a MAC CE. In other embodiments, each of the activation command(s) is a DCI. After receiving the activation command(s), the UE 102 uses the additional TCI state configuration(s) to communicate with the DU 174 on the first cell. Similarly, after transmitting the activation command(s), the DU 174 uses the additional TCI state configuration(s) to communicate with the UE 102 on the first cell.

[0130] In 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 the reference LTM DU configuration. In other words, the UE 102 communicates 336 with the DU 174 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration. Similarly, the DU 174 communicates 336 with the UE 102 on the first cell in accordance with the LTM DU configuration 1 and at least a portion of the reference LTM DU configuration. In other words, the DU 174 communicates 336with the UE 102 in accordance with configuration parameters in the LTM DU configuration 1 and the reference LTM DU configuration.

[0131] In 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.

[0132] In 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 (i.e., a complete configuration without referring to a reference LTM CU configuration), the UE 102 and CU 172 communicate 336 with each other via the DU 174 using the LTM CU configuration 1 instead of the serving CU configuration. In some embodiments, if the UE 102 does not receive a / the reference LTM CU configuration from the base station 104, the UE 102 determines that the LTM CU configuration 1 is a full configuration. Correspondingly, if the CU 172 determines to configure or configures the LTM CU configuration 1 as a full configuration, the CU 172 does not transmit a / the reference LTM CU configuration to the UE 102. In other embodiments, 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 communicate 336 with each other via the DU 174 using the LTM CUconfiguration 1 and at least a portion of the serving CU configuration not augmented by the LTM CU configuration 1. In some embodiments, 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 embodiments, the CU 172 indicates that the LTM CU configuration 1 is a delta configuration to augment 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 embodiments, 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.

[0133] In case 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 embodiments, 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 embodiments, 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 communicate 336 with each other via the DU 174 using thereference LTM CU configuration and at least a portion of the serving CU configuration not augmented by the reference LTM CU configuration. In some embodiments, the CU 172 indicates that the reference LTM CU configuration is a delta configuration to augment 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 embodiments, 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.

[0134] In case the UE 102 neither receives the reference LTM CU configuration, 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 CU configuration. In this case, the CU 172 communicates 336 with the UE 102 via the DU 174 using the serving CU configuration.

[0135] In some embodiments, the UE 102 transmits an RRC message (e.g., RRC reconfiguration complete message) to the CU 172 via the DU 174 and the first cell to indicate that the UE 102 applies the LTM DU configuration 1. In case that the UE 102 performs the random access procedure 332, the UE 102 may include the RRC message in the Message 3 or Message A. Alternatively, the UE 102 transmits the RRC message after completing the random access procedure. In the case that the UE 102 skips the random access procedure 332, the UE 102 includes the RRC message in a PUSCH transmission of the at least one PUSCH transmission. In some embodiments, if the UE 102 maintains communication on the cell 124A with the base station 104 (i.e., the UE 102 does not disconnect from the cell 124A), the UE 102 may 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.

[0136] In other embodiments, 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 may include or transmit datain the Message 3, Message A, or PUSCH transmission as described above. The UE 102 may generate a MAC PDU and / or a RLC PDU including the data and transmit or includes the MAC PDU and / or RLC PDU in the PUSCH transmission. For example, the data may be a PDCP PDU, a SDAP PDU, an LTE Positioning Protocol (LPP) PDU, an RRC PDU, and / or a NAS PDU. The RRC PDU includes a UL-DCCH-Message excluding an RRC reconfiguration complete message. The NAS PDU includes a Mobility Management (MM) message or a Session Management (SM) message. The MM message may be a 5G MM message or a 6G MM message, and the SM message may 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.

[0137] When the DU 174 determines that the UE 102 successfully connects to the first cell in the event 332 or 336, the DU 174 may 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 embodiments, the DU 174 may include the cell ID 1 of the first cell in the DU-to-CU message of the event 334. The cell ID may be a PCI or a CGI. Thus, 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 may transmit a DL Data Delivery Status message or frame to the CU 172 (e.g., a UP of the CU 172). In some embodiments, when or after the CU 172 receives the DU-to-CU message 329, the CU 172 may stop or suspend transmitting DL data for the UE 102 to the DU 174 until receiving the DU-to-CU message 334. The CU 172 may do so because the DU 174 may not 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 embodiments, when the CU 172 receives the DU-to-CU message 329, the CU 172 may continue transmitting DL data for the UE 102 to the DU 174. The CU 172 may do so because the DU 174 may 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 accessed cell 1 , the DU 174 transmits the DL data to the UE 102 via the cell 1 .

[0138] In some embodiments, 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 may stop communicating with the UE 102 on the cell 124A and / or release resources of the cell 124A configured for the UE 102.

[0139] In some embodiments, the DU 174 generates some or all of the LTM DU configuration 1 and / or LTM DU configuration(s) 2, N as full configuration(s) (i.e., complete configuration(s) without referring to a reference LTM 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 embodiments, the DU 174 includes an indication indicating that the LTM DU configuration 1 is a full configuration in the LTM DU configuration 1 . In each of the LTM DU configuration(s) 2, ... , N, the DU 174 may 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 may be a field or IE (i.e., the same field or IE). In other embodiments, the CU 172 may 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 may 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 embodiments, the CU 172 may 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 embodiments, for each of the LTM DU configuration(s) 2, ... , N, the CU 172 may include, in the first container, a particular indication indicating the corresponding LTM DU configuration is a full configuration. In the case of the second container, the CU 172 may 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 embodiments, the CU 172 may include, in the element 1 , an indication indicating that the LTM DU configuration 1 is a full configuration. In each of the element(s) 2, ... , N, the CU 172 may include an indication indicating that the corresponding LTM DU configuration is a full configuration. The UE 102 may 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 embodiments, each of the indication(s) above is different from a fullConfig field defined in the current 3GPP specification. In some embodiments, each of the indication(s) above is a fullConfig fielddefined in the current 3GPP TS. In the case that the LTM DU configuration 1 is a full configuration, the UE 102 in the event 336 does not apply the reference LTM DU configuration if received from the base station 104, e.g., in the RRC reconfiguration message 318. In such cases, the DU 174 may not include a / the reference LTM DU configuration in the first DU-to-CU message 310.

[0140] In other embodiments, the DU 174 generates 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 embodiments, 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 may determine that each of the LTM DU configuration(s) 1 and / or 2, ... , N is a delta configuration, and 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.

[0141] In some embodiments, 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).

[0142] In other embodiments, 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 DUconfiguration(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.

[0143] In some embodiments, 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 embodiments, 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 embodiments, 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.

[0144] In some embodiments, 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 Message 3 (Msg3) buffer;• flush Message A (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 Listen Before Talk (LBT) failure;• cancel, if any, triggered Beam Failure Recovery (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; and / or• reset one or more counters (e.g., BFI_COUNTERs and / or LBT_COUNTERs).

[0145] In some embodiments, 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).

[0146] Depending on the embodiment, the UE 102 determines to partially or fully reset the UE MAC entity. In some embodiments, 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 embodiments, 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 or all of the actions in the full UE MAC reset.

[0147] In some embodiments, 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).

[0148] In some embodiments, 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.

[0149] In some embodiments, 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.

[0150] Depending on the embodiment, the DU 174 determines to partially or fully reset the DU MAC entity. In some embodiments, 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 embodiments, 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.

[0151] In some embodiments, 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).

[0152] In some embodiments, 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).

[0153] In other embodiments, 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.

[0154] In some embodiments, 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 embodiments, 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 embodiments, the DU 174 reestablishes some or all of the at least one DU RLC entity after (e.g., in response to) transmitting the first LTM command, receiving the acknowledgement 331 or determining that the UE 102 connects to the first cell.

[0155] In some embodiments, 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 RLC reestablishment indication configuring the UE 102 toreestablish 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 embodiments, the UE 102 may 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 embodiments, the UE 102 may 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.

[0156] In some embodiments, 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.

[0157] In some embodiments, the state variables and timer(s) are defined in 3GPP TS 38.322.

[0158] 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 performing the actions for reestablishing the first UE RLC entity of the UE 102 upon or when receiving the first LTM command. In some embodiments, if the LTM DU configuration 1 or element 1 does not include the RLC reestablishment indication and includes an indication indicating that the configuration 1 is a full configuration, the UE 102 may 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.

[0159] 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 RLCentity 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 embodiments, 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 embodiments, the acknowledgement is a HARQ ACK. In other embodiments, the acknowledgement is a MAC CE. In yet other embodiments, the acknowledgement is a PUCCH transmission. In some embodiments, when the base station 104 reestablishes the first DU RLC entity, the DU 174 performs at least one of the following actions for the first DU RLC entity:• discard RLC SDU(s), RLC SDU segment(s), and RLC PDU(s), if any;• stop and reset timer(s), if running;• reset state variables to initial values.

[0160] In some embodiments, the state variables and timer(s) are defined in 3GPP TS 38.322.

[0161] In other embodiments, 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 some or all of the at least one UE RLC entity (not reestablished). For example, 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 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, some or all of the at least one DU RLC entity includes the first DU RLC entity and / or a second DU RLC entity.

[0162] In some embodiments, the UE 102 uses at least one UE PDCP entity (e.g., PDCP 210) to communicate 302 UL PDCP PDUs and / or DL PDCP PDUs with at least one CU PDCP entity (e.g., PDCP 210) of the CU 172. In some embodiments, the UE 102performs 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 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 may retransmit 336 at least a portion of the UL PDCP PDUs to the CU 172 via the DU 174 and the first cell. 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 embodiments, 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 embodiments, 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, 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 may retransmit 336 at least a portion of the DL PDCP PDUs to the UE 102 via the DU 174 and the first cell.

[0163] In other embodiments, 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, some or all of the at least one UE PDCP entity includes the first UE PDCP entity and / or a second UE PDCP entity. Similarly, the CU 172 refrains from reestablishing some or more of the at least one CU PDCP entity, after (e.g., in response to) receiving the DU- to-CU message 329 or 340 or after (e.g., in response to) receiving the DL Data Delivery Status message. In other words, the UE 102 communicates with the CU 172 via the DU 174 and the first cell using the some or all of the at least one UE PDCP entity (not reestablished). For example, 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 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.

[0164] In some embodiments, after determining that the UE 102 connects to the first cell, the CU 172 transmits 338 a CU-to-DU message (e.g., a UE Context Modification Request message) to the DU 174 to indicate 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 may 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.

[0165] After or while communicating with the DU 174 on the first cell, events 344, 346, 348, 350, 351 , 352, 354, and / or 356 may occur, similar to the events 324, 326, 328, 330, 331 , 332, 334, and / or 336, respectively. The UE 102 transmits 344 at least one measurement report to the DU 174. The at least one measurement report includes at least one measurement result for a second cell (i.e. , 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 requests the UE 102 to apply the LTM DU configuration 2). The DU 174 then transmits 350 the second LTM command to the UE on the first cell to the UE 102.

[0166] When or in response to determining to activate the LTM DU configuration 2 or transmitting the second LTM command, the DU 174 may transmit 349 to the CU 172 a DU-to-CU message indicating LTM (being) executed. In some embodiments, 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 may transmit the DU- to-CU message 349 to the CU 172 before or after transmitting the LTM command 350.

[0167] The descriptions for events 324, 326, 328, 330, 331 , 332, 334, and / or 336 may be applied to 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”, “secondLTM command”, “second cell”, “ID 2”, “LTM DU configuration 2”, and / or “LTM CU configuration 2”, respectively.

[0168] The events 344, 346, 348, 350, 351 , 352, and 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, and 356 are collectively referred to in FIG. 3 as an LTM DU configuration and / or activation procedure 380.

[0169] FIG. 4 shows a signal diagram 400, in which 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). Embodiment 400 is similar to the embodiment 300. Thus, the descriptions for the embodiment 300 may generally apply to the embodiment 400. The differences between the embodiments 300 and 400 are described below.

[0170] Initially, a UE 102 communicates 402 with the S-DU 174A on cell 124A using a serving DU configuration and communicates with the CU 172 via the S-DU 174A. The S-DU 174A is a serving DU similar to the DU 174 in FIG. 3A. During communication 402, the UE 102 transmits 404, 406 at least one measurement report (e.g., L3 or L1 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-DU 174B to) prepare cell(s) 1 , ... , N for LTM for the UE 102, where N may 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. The LTM DU configuration(s) 1 , ... , N include configuration parameters for communication on the cell(s) 1 , ... , N, respectively. In some embodiments, the CU-to-DU message and DU- to-CU message in procedure 490 are UE Context Setup Request message and UEContext Setup Response message, respectively. The CU 172 then transmits the LTM DU configuration(s) 1 , N in an RRC reconfiguration message in an LTM configuration delivery procedure 494, similar to the LTM configuration delivery procedure 394. In some embodiments, the T-DU 174B may include cell index(es) 1 , ... , N in the LTM DU configuration(s) 1 , ... , N, respectively. In some embodiments, the CU 172 may 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.

[0171] After performing the LTM preparation procedure 490, the CU 172 may perform 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, where M is a positive integer larger than zero. The CU 172 may determine to do so based on one or more measurement reports received from the UE 102 via the S-DU 174A, similar to the events 404, 406. In the additional LTM preparation procedure, the CU 172 transmits a CU-to-DU message including cell ID(s) N+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. The LTM DU configuration(s) N+1 , ... , N+M include configuration 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 an RRC reconfiguration message in an additional LTM configuration delivery procedure, similar to the LTM configuration delivery procedure 394 or 494.

[0172] In some embodiments, the LTM preparation procedure 490 is a UE Context Setup procedure, and the additional LTM preparation procedure is a UE Context Modification procedure.

[0173] In some embodiments, the CU 172 and S-DU 174A perform procedure 380 with the UE 102, as described for FIG. 3. In procedure 380, the CU 172 and S-DU 174A perform 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 may be the same as or different from the value N described for FIG. 4. In procedure 390, the CU 172may receive the first DU-to-CU message including the reference LTM DU configuration from the S-DU 174A in event 310. In other embodiments, the CU 172 and S-DU 174A do not perform procedure 380 with the UE 102. In such cases, the CU 172 may perform 488 a reference LTM DU configuration query procedure with the S-DU 174A to obtain a reference LTM DU configuration. In 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 embodiments, the CU 172 may 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 embodiments, the indication is a reference LTM DU configuration query indication. In other embodiments, the indication is an LTM indication, and the CU 172 may include a query indication (e.g., GNB-DU Configuration Query IE) in the CU-to-DU message. After receiving the reference LTM DU configuration (i.e., either in the procedure 390 or in the procedure 488), the CU 172 includes the reference LTM DU configuration (received from the S-DU 174A) in the CU-to- DU message in the LTM preparation procedure 490. The T-DU 174B generates the LTM DU configuration(s) 1 , ... , N based on the reference LTM DU configuration received from the CU 172. In such cases, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in procedure 490. In the case of the additional LTM preparation procedure, the T-DU 174B does not include a reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. The CU 172 may not include the reference LTM DU configuration in CU-to-DU message in the additional LTM preparation procedure with the T-DU 174B. In the case of the additional LTM preparation procedure, the T-DU 174B generates the LTM DU configuration(s) N+1 , ... , N+M based on the reference LTM DU configuration received from the CU 172.

[0174] In some embodiments, 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 procedure 490. The CU 172 transmits the reference LTM DU configuration in the RRCreconfiguration message in 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 may not include the reference LTM DU configuration in the DU-to-CU message in the additional LTM preparation procedure. In some embodiments, 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 embodiments, 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.

[0175] In some embodiments, 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.

[0176] In some embodiments, an LTM DU configuration X of the procedure 380 includes at least one 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 embodiments, each of the RS resource configuration(s) X includes an RS resource configuration ID. In some embodiments, the RS resource configuration(s) X is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the LTM DU configuration X includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI- ResourceConfig IE(s). The T-DU 174B generates at least one report configuration 1 for reporting, on 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 embodiments, the report configuration(s) 1 is / are (similar to) CSI-ReportConfig IE(s). In some embodiments, 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 embodiments, the T-DU 174B includes the RS resource configuration(s) X in the RS resource configuration(s) 1 . In other embodiments, the T-DU 174B includes each of the RS resource configuration(s) X in theRS resource configuration(s) 1 , except the RS resource configuration ID(s) in the RS resource configuration(s) X. The T-DU 174B assigns an 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.

[0177] In some embodiments, the report configuration(s) 1 configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on cell 1 for the UE 102 to transmit measurement results. In some embodiments, 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 cell 1 from the UE 102, in accordance with the report configuration(s) 1 . In some embodiments, each of the measurement results includes one or more RS resource indicators and / or one or more quantized measurement values. The UE 102 performs measurements on the RS(s) or the RS resource(s) in accordance with the RS resource configuration(s) 1 and / or the report configuration(s) 1 and obtains the quantized measurement values from the measurements. In some embodiments, 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 embodiments, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values may include one or more L1-RSRP values and / or one or more L1-SINR values.

[0178] In some embodiments, 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 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). Insome embodiments, each of the additional RS resource configuration(s) includes an RS resource configuration ID. In some embodiments, the additional RS resource configuration(s) is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the T- Dll 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 cell 1 of the T- Dll 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 embodiments, the additional report configuration(s) is / are (similar to) CSI-ReportConfig IE(s).

[0179] In some embodiments, the additional report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on cell 1 for the UE 102 to transmit measurement results. In some embodiments, 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 cell 1 , in accordance with the additional report configuration(s).Correspondingly, the S-DU 174B receives the measurement results on the UL resource (s) via cell 1 , from the UE 102, in accordance with the additional report configuration(s). In some embodiments, 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 embodiments, 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 embodiments, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values may include one or more L1-RSRP values and / or one or more L1 -SINR values.

[0180] Similarly, the T-DU 174B may 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.

[0181] In other embodiments, an LTM DU configuration X of the procedure 380 includes at least one TCI state configuration X, where 1 < X < N. Each of the TCI state configuration(s) X configures a TCI state that associates one or two DL RSs with a corresponding QCL type. In some embodiments, the DL RS(s) may be associated with the cell X operated by the S-DU 174A. In some embodiments, each of the TCI state configuration(s) X includes a TCI state ID. In some embodiments, each of the TCI state configuration(s) X is a TCI-State IE. In some embodiments, the TCI state configuration(s) X 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-StatesToAddModList field. In some embodiments, the LTM DU configuration X includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) X. In some embodiments, the T-DU 174B generates at least one TCI state configuration 1 , considering or based on the TCI state configuration(s) X and includes the TCI state configuration(s) 1 in the LTM DU configuration 1 . In some embodiments, the TCI state configuration(s) 1 includes the TCI state configuration(s) X. In other embodiments, the T-DU 174B includes each of the TCI state configuration(s) X in the TCI state configuration(s) 1 , except the TCI state ID(s) in the TCI state configuration(s) X. The T-DU 174B assigns a TCI state ID to a value for each of the TCI state configuration(s) 1 (including the TCI state configuration(s) X) and includes the TCI state ID in the corresponding TCI state configuration. While the UE 102 and the S-DU 174B communicate 436 with one another, the S-DU 174B may transmit an LTM command to the UE 102 to command the UE 102 to perform a fast serving cell change to 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.

[0182] Similarly, the T-DU 174B may 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.

[0183] In some embodiments, 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.

[0184] In some embodiments, 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 embodiments, 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 embodiments, the CU 172 assigns 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 embodiments, 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.

[0185] In some embodiments, 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. 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 transferprocedure 493. In some embodiments, the message 412 and message 414 may be UE Context Modification Request message and UE Context Modification Response message, respectively. In some embodiments, 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 embodiment, the CU 172 includes the ID(s) 1 , ... , N in the CU-to-DU message 412. In another embodiment, the CU 172 includes the cell index(es) 1 , ... , N in the CU-to-DU message 412. In some alternative embodiments, the CU 172 may 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 a 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 embodiments, the CU 172 may 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 a particular portion of the cell index(es) 1 , ... , N, cell ID(s) 1 , ... , N, and / or LTM DU configuration(s) 1 , ... , N in a CU-to-DU message similar to the message 412. Thus, the S-DU 174A associates the cell index(es) 1 , ... , N with the LTM DU configuration(s) 1 , ... , N and / or the cell ID(s) 1 , ... , N, respectively.

[0186] In some embodiments, 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 embodiments, the first serving DU configuration includes configurations updating (e.g., augmenting, modifying or replacing) the serving DU configuration 402. In other embodiments, the first serving DU configuration includes configurations that are not included in the serving DU configuration 402. The CU 172 transmits an RRC reconfiguration message including the first serving DU configuration to the UE 102. The UE 102 applies the first serving DU configuration to communicate with the S-DU 174A upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is similar to the RRC reconfiguration message in procedure 494. Depending on the embodiment, the UE 102 communicates with the S-DU 174A using configurations included in the serving DUconfiguration 402 and not updated by the first serving DU configuration. The following are example embodiments of generating the first serving DU configuration based on the LTM DU configuration 1 , N.

[0187] In some embodiments, the LTM DU configuration Y of 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 embodiments, each of the RS resource configuration(s) Y includes an RS resource configuration ID. In some embodiments, the RS resource configuration(s) Y is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the LTM DU configuration Y includes a CSI-MeasConfig IE and the CSI-MeasConfig IE includes the CSI- ResourceConfig IE(s). The S-DU 174A generates at least one serving report configuration for reporting, on the cell 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 embodiments, the serving report configuration(s) is / are (similar to) CSI -ReportConfig IE(s). In some embodiments, the S-DU 174A generates at least one serving RS resource configuration, considering or based on the RS resource configuration(s) Y and includes the serving RS resource configuration(s) in the first serving DU configuration. In some embodiments, the S-DU 174A includes the RS resource configuration(s) Y in the serving RS resource configuration(s). In other embodiments, 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 an 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.

[0188] In some embodiments, the serving report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on cell 124A for the UE 102 to transmit measurement results. In some embodiments, 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-Dll 174A, the UE 102 transmits measurement results on the UL resource(s) via the cell 124A to the S-DU 174A, in accordance with the serving report configuration(s) (e.g., event 424). Correspondingly, the S-DU 174A receives the measurement results on the UL resource (s) via the cell 124A from the UE 102, in accordance with the serving report configuration(s). In some embodiments, 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 embodiments, 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 embodiments, the RS resource indicator(s) includes one or more SSB resource indicators (SSBRI(s)) and / or one or more CSI-RS resource indicators (CRI(s)). The quantized measurement values may include one or more L1-RSRP values and / or one or more L1-SINR values.

[0189] In other embodiments, the LTM DU configuration Y of the procedure 490 includes at least one TCI state configuration Y, where 1 < Y < N. Each of the TCI state configuration(s) Y configures a TCI state that associates one or two DL RSs with a corresponding QCL type. In some embodiments, the DL RS(s) may be associated with the cell Y operated by the T-DU 174B. In some embodiments, each of the TCI state configuration(s) Y includes a TCI state ID. In some embodiments, each of the TCI state configuration(s) Y is a TCI-State IE. In some embodiments, 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-StatesToAddModList field. In some embodiments, the LTM DU configuration Y includes a PDSCH-Config IE and the PDSCH-Config IE includes the TCI state configuration(s) Y. In some embodiments, 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 embodiments, the serving TCI state configuration(s) 1 includes the TCI state configuration(s) Y. In other embodiments, the S-DU 174A includes each of the TCI stateconfiguration(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 communicates 436 with the UE 102, the S-DU 174A may transmit an LTM command to the UE 102 to request 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.

[0190] In some embodiments, 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 embodiments, the CU 172 includes 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 embodiments, the CU 172 may 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 a 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 embodiments, 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 embodiments, the second serving DU configuration includes 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 embodiments, the second serving DU configuration includes configurations that are not included in the first serving DU configuration. The CU 172 transmits an RRC reconfiguration message including the second serving DU configuration to the UE 102 viathe S-DU 174A. The UE 102 applies the second serving DU configuration to communicate with the S-DU 174A upon receiving the RRC reconfiguration message. For example, the RRC reconfiguration message is or is similar to the RRC reconfiguration message in procedure 494. Depending on embodiments, 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 embodiments, 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 embodiments, 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.

[0191] In some embodiments, in case that the CU 172 and S-DU 174A perform the procedure 380 with the UE 102, value(s) of the ID(s) 1 , ... , N of the procedure 380 are different from value(s) of the ID(s) 1 , ...., N, and the ID(s) N+1 , ... , N+M described for the embodiment 400. In some embodiments, 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 embodiment 400. In some embodiments, 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 embodiment 400.

[0192] Later, the UE 102 may transmit 424 at least one measurement report to the S-DU 174A, similar to event 324. The 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 embodiments, the first measurement result(s) may be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on cell 1 . Likewise, the second measurement result(s) may be or include RSRP, RSRQ and / or SINR that the UE 102 obtains from reference signal(s) transmitted on cell 124A. In some embodiments, theevent 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 may transmit 430 a first LTM command (i.e. , LTM command 1) including the ID 1 to the UE 102 to order the UE 102 to perform a serving cell change to the cell 1 of the T-DU 174B. In some embodiments, the first LTM command includes the ID 1 (i.e., LTM ID). In other embodiments, 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 cell 1 , from a serving cell, in accordance with the LTM DU configuration 1. After (e.g., in response to) receiving the first LTM command, the UE 102 may or may 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 may communicate 436 with the T-DU 174B on the first cell using the LTM DU configuration 1 and / or reference LTM DU configuration and communicates with the CU 172 via the T-DU 174B, similar to the event 336. If a serving cell change occurs in procedure 380, the serving cell may be 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 on the LTM ID 1 , as described above 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 on the cell index 1 , as described above 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 cell 1 .

[0193] When or in response to determining to activate the LTM DU configuration 1 or transmitting the first LTM command 430, the S-DU 174A may transmit 429 to the CU 172 a DU-to-CU message indicating the LTM (being) executed. In some embodiments, 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 may transmit the DU-to-CU message 429 to the CU 172 before or after transmitting the LTM command 430. In some embodiments, when or after the CU 172 receives the DU-to-CU message 429, the CU 172 may stop or suspendtransmitting 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 accessed cell 1 , the T-DU 174B transmits the DL data to the UE 102 via the cell 1.

[0194] The resource release procedure 496 may be similar to the procedure 396. Alternatively, in the resource release procedure 496, the CU 172 may 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.

[0195] The events 380, 404, 406, 490, 492, 494, 494, 424, 426, 428, 429, 430, 431 , 432, 434, 436, 496, 498, and 456 are collectively referred to in FIG. 4 as an LTM configuration and / or activation procedure 480.

[0196] Referring next to FIG. 5A, in an embodiment 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 embodiment 500A is similar to the embodiment 300, except that the embodiment 500A is a DC embodiment and the embodiment 300 is a single connectivity (SC) embodiment. The MN 106 may include a CU and a DU similar to the base station 104 of FIG. 3.

[0197] Initially, a UE 102 is in DC communicates with MN 106 and with SN 104. In 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 event 302. In some alternative embodiments, the UE 102 does not communicate with the CU 172 via the DU 174 in the event 302. In some embodiments, the UE 102 in DC may communicate 502 UL PDUs and / or DL PDUs with the MN 106 and / or SN 104 via radio bearers which may include SRBs and / or DRB(s). The MN 106 and / or the SN 104 may 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 radioresources) in accordance with a MN configuration (i.e. , MCG configuration). In some embodiments, the serving DU configuration is an SN configuration (i.e., SCG configuration). In the MN configuration, the MN 106 configures the MCG which includes at least one serving cell (e.g., the cell 126A and / or other cell(s), e.g., cell 126B) 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 embodiments, 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 in FIG. 3, the serving DU configuration includes multiple configuration parameters. In some embodiments, 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.

[0198] While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 may perform 580 an LTM DU configuration and / or activation procedure with the UE 102, similar to the procedures 380 and / or 480. In some embodiments, while communicating in DC with the MN 106 and SN 104, the UE 102 may transmit 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 embodiments, while communicating in DC with the MN 106 and SN 104, the UE 102 may 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 embodiments, 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 embodiment, the at least one SN message includes RRC Transfer message(s) and / or SN Modification Request message(s).

[0199] After (e.g., in response to) receiving the 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 LTMcommand 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, the DU 174 and / or CU 172 may 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.

[0200] The events 504, 506, 505, 507, 590, 592, 594, 524, 526, 528, 529, 530, 531 , 532, 534, 536, 596, 598, and 556 are collectively referred to in FIG. 5A as an LTM DU configuration and / or activation procedure 581 .

[0201] Referring next to FIG. 5B, an embodiment 500B is generally similar to the embodiment 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 embodiments, the SN 104 generates a first SN message (e.g., SN Modification Required message, SN Modification Required message, or RRC Transfer message) including the RRC reconfiguration message and transmits the first SN message to the MN 106 in the event 517. The MN 106 generates an MN RRC message including the RRC reconfiguration message and transmits 519 the MN RRC message to UE 102. In response, the UE 102 generates an MN RRC response message including the RRC reconfiguration complete message and transmits 521 the MN RRC response message to MN 106. In some embodiments, the MN 106 generates a second SN message (e.g., SA / Reconfiguration Complete message or RRC Transfer message) including the RRC reconfiguration complete message and transmits 523 the second SN message to the SN 104. In some embodiments, the MN RRC message and MN RRC response message maybe an RRC reconfiguration message and an RRC reconfiguration complete message, respectively.

[0202] The events 504, 506, 505, 507, 590, 592, 594, 517, 519, 521 , 523, 524, 526, 528, 529, 530, 531 , 532, 534, 536, 596, 598, and 556 are collectively referred to in FIG. 5B as an LTM DU configuration and / or activation procedure 582.

[0203] Referring next to FIG. 6A, in embodiment 600A, the second BS 106 operates as an MN, and the first BS 104 operates as an SN, similar to the embodiments 300-500B. The SN 104 includes a CU 172, an S-DU 174A and a T-DU 174B, similar to the base station 104 in embodiment 400. While the UE 102 communicates in DC with the MN 106 and SN 104, the MN 106 may 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 CU 172 may 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.

[0204] Referring next to FIG. 6B, embodiment 600B is similar to the embodiments 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.

[0205] Referring next to FIG. 7A, in an embodiment 700A, the first BS 104 operates as an MN and an SN, similar to the embodiments 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.

[0206] In the embodiment 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 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 event 302. Events 704 and 706 are similar to events 304 and 306. In some embodiments, the UE 102 may transmit 705 at least one measurement report to the M-DU 174A, similar to event 304. The M-DU 174A inturn transmits 707 at least one DU-to-CU message including the at les tone measurement report to the CU 172, similar to event 306. While the UE 102 communicates in DC with the M-DU 174A and S-DU 174B, the CU 172 may perform 780 an LTM DU configuration and / or activation procedure with the UE 102 via the M-DU 174A, similar to the procedure 380.

[0207] The events 704, 706, 705, 707, 790, 792, 794, 724, 726, 728, 729, 730, 731 , 732, 734, 736, 796, 798, and 756 are collectively referred to in FIG. 7A as an LTM configuration and / or activation procedure 781 .

[0208] Referring next to FIG. 7B, an embodiment 700B is similar to the embodiments 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.

[0209] The events 704, 706, 705, 707, 790, 792, 794, 717, 719, 721 , 723, 724, 726, 728, 729, 730, 731 , 732, 734, 736, 796, 798, and 756 are collectively referred to in FIG. 7B as an LTM DU configuration and / or activation procedure 782.

[0210] Referring next to FIG. 8A, in an embodiment 800A, the first BS 104 operates as an MN and an SN, similar to the embodiments 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 may 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 may 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.

[0211] Referring next to FIG. 8B, an embodiment 800B is similar to the embodiments 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.

[0212] Next, several methods that may be performed by a UE, which is configured to handle an LTM configuration, LTM execution, and DC, are discussed with reference toFIGs. 9A-15B. Descriptions for FIGs. 3-8B may apply to any of FIGs. 9A-15B. Note that if a given step is explained with regard to a corresponding method, the description of that step, when reused for another method, is omitted for simplicity.

[0213] FIG. 9A is a flow chart of a method 900A, which may be implemented by a UE (e.g., the UE 102 in FIGs. 3-8B). The method 900A begins with the UE 102 communicating 902 with a RAN (e.g., BS 104 or 106 or RAN 105) via a first serving cell (e.g., 124A) and a second serving cell (126A), where the first serving cell and the second serving cell belong to a first CG and a second CG, respectively (e.g., events 502, 602, 702, 802). The UE receives 904 an LTM configuration from the RAN (e.g., events 316, 318, 394, 380, 580, 680, 780, 880). The UE receives 906 an LTM command from the RAN, commanding the UE to apply the LTM configuration (e.g., events 330, 430, 580, 680, 780, 880). The UE performs 908 a serving cell, change from the first serving cell to a candidate cell, in accordance with the received LTM configuration, in response to the LTM command (e.g., events 332, 432, 580, 680, 780, 880). After the serving cell change, the UE communicates with the RAN via the candidate cell (e.g., events, 336, 436, 580, 680, 780, 880). The UE releases 910 the second CG in response to the LTM command. In other words, the UE releases the connection with the second CG after the cell switch.

[0214] In some embodiments, the RAN may include one or more RAN nodes communicating with the UE. Each of the RAN node(s) may be a BS (e.g., 104, 106 or 170) or a DU (e.g., 174). In some embodiments, a first RAN node (e.g., MN or M-DU) of the RAN operates the first CG and configures the first CG for the UE, and a second RAN node (e.g., SN or secondary DU) of the RAN operates the second CG and configures the second CG for the UE. In some embodiments, the first CG is an MCG and the second CG is an SCG. In some embodiments, the first serving cell is a PCell and the second serving cell is a PSCell. In some embodiments, the first RAN node operates the candidate cell. In some embodiments, the candidate cell belongs to the first CG.

[0215] FIG. 9B is a flow chart of a method 900B similar to the method 900A, except that the method 900B includes blocks 909B and 911 . At block 909B, the UE determines whether the LTM configuration indicates releasing the second CG. If the UE determines that the LTM configuration indicates releasing the second CG at block 909B, the method proceeds to blocks 910. Otherwise, if the UE determines that the LTM configuration doesnot indicate releasing the second CG at block 909B, the method proceeds to block 911. The UE continues communicating 911 with the RAN node via the second CG (e.g., the second serving cell) during and / or after the serving cell change (e.g., events 504, 594, 517, 519, 524, 530, 604, 694, 617, 619, 624, 630, 704, 794, 717, 719, 724, 730, 804, 894, 817, 819, 824, and / or 830). That is, the UE communicates 911 with the RAN node via the candidate cell and the second CG during and / or after the serving cell change.

[0216] FIG. 9C is a flow chart of a method 900C similar to the method 900B, except that the method 900C include blocks 907 and 909C instead of blocks 908 and 909B. The UE performs 907 a serving cell change to a candidate cell in accordance with the LTM configuration, in response to the LTM command. The UE then determines 909C whether the candidate cell belongs to the first CG (e.g., the candidate cell is operated by the MN). If the UE determines 909C that the candidate cell belongs to the first CG, the method proceeds to block 910. Otherwise, if the UE determines that the candidate cell belongs to the second CG (e.g., the candidate cell is operated by the SN), the method proceeds to block 911 .

[0217] In some embodiments, the UE receives an additional LTM configuration from the RAN node (e.g., events 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, and / or 819), in addition to the LTM configuration. In some embodiments, the LTM command at block 906 is similar to event 316, 318, 394, 380, 580, 680, 780, or 880. In other embodiments, the LTM command at block 906 is similar to event 530, 630, 730 or 830.

[0218] FIG. 9D is a flow chart of a method 900D similar to the methods 900B-900C, except that the method 900D includes block 909D instead of blocks 909B and 909C. The UE determines 909D that the UE received the LTM command via the first CG (e.g., the UE determines whether the UE received the LTM command from the MN or the SN). If the UE determines 909D that the UE received the LTM command via the first CG (e.g., the first serving cell), the method proceeds to block 910. Otherwise, if the UE determines 909D that the UE received the LTM command via the second CG (e.g., the second serving cell), the method proceeds to block 911 .

[0219] FIG. 9E is a flow chart of a method 900E performed by the RAN (e.g., elements 104, 106, 170, 172, or 174 discussed above with regard to FIG. 1A) formanaging a UE operating in DC when cell switching based on an LTM configuration. The RAN communicates with the UE via a first serving cell (e.g., 124A) and a second serving cell (e.g., 126A). The first serving cell belongs to a first CG and the second serving cell belongs to a second CG. The RAN sends 903 an LTM configuration to the UE to be used for the cell switching. The RAN sends 905 an LTM command requesting the UE to apply the LTM configuration for the cell switching.

[0220] The method 900E may be modified so that the at least one LTM configuration includes first and second LTM configurations, and the first and second LTM configurations include information about whether the LTM command is associated with the first CG or the second CG. The method may further include transmitting the first LTM command via the first CG or the second CG, wherein the indicator is related to the transmitting of the first LTM command via the first CG or the second CG, where the at least one LTM configuration includes first and second LTM configurations. The method may also include transmitting a second LTM command while transmitting the first LTM command, the second LTM command instructing the UE to perform a cell switch from the second serving cell to a second candidate cell, and / or transmitting to the UE, a radio resource control, RRC, reconfiguration message via a first signaling radio bearer, SRB, or a second SRB. The method may also include transmitting an indication, from a medium access control, MAC, entity, indicating the first LTM command and one of: an LTM identifier, ID, a cell index, or a cell ID, and / or transmitting the first LTM command using a first medium access control, MAC, entity or a second MAC entity, and / or communicating with the UE via the first serving cell and the second serving cell in dual connectivity operation. The cell switching is then performed by the UE as discussed above with regard to methods illustrated in FIGs. 9A to 9D. Description for the RAN as described for FIGs. 9A-9D can apply to the RAN in FIG. 9E.

[0221] FIG. 10A is a flow chart of a method 1000A, which may be performed by aUE (e.g., the UE 102 in FIGs. 3-8B). The method 1000A begins with the UE communicating 1002 with a RAN (or RAN node) via a first serving cell and a second serving cell, where the first serving cell and the second serving cell belong to a first CG and a second CG, respectively (e.g., events 502, 602, 702, 802). The UE receives 1004 at least one first LTM configuration and at least one second LTM configuration from the RAN.In some embodiments, the UE receives the first LTM configuration(s) from an MN of the RAN (e.g., events 316, 318, 394, 380, 580, 680, 780, 880) and receives the second LTM configuration(s) from an SN of the RAN (e.g., events 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, 819).

[0222] The UE determines 1006 that the first LTM configuration(s) is / are associated with a first CG. The UE also determines 1008 that the second LTM configuration(s) is / are associated with a second CG. The UE receives 1010 an LTM command from the RAN (e.g., events 330, 430, 580, 680, 780, 880) and UE determines 1012 that the LTM command is associated with the first CG (or with the second CG). The UE identifies 1014 an LTM configuration from the first LTM configuration(s), based on the LTM command and the first CG. The UE performs 1016 a serving cell change from the first serving cell to a candidate cell in accordance with the identified LTM configuration, in response to the LTM command (e.g., events 332, 432, 580, 680, 780, 880). Then, the UE communicates 1018 with the RAN node on the candidate cell (e.g., events, 336, 436, 580, 680, 780, 880) and releases 1020 the second CG in response to the LTM command.

[0223] The determination 1006 in FIG. 10A may be replaced / modified as illustrated in FIGs. 11 and 12. For example, the UE determines 1106 that the first LTM configuration(s) is / are associated with the first CG, as described in FIG. 11 . In some embodiments, the UE determines 1106 that the second LTM configuration(s) is / are associated with the second CG, as also described in FIG. 11 . In some embodiments, the first CG is an MCG and the second CG is an SCG. In some embodiments, the UE determines 1208 that the first LTM configuration(s) is / are associated with the MCG as described in FIG. 12. In some embodiments, the UE determines 1209 that the second LTM configuration(s) is / are associated with the SCG, as also described for FIG. 12. The embodiments illustrated in FIGs. 11 and 12 are discussed in more detail later.

[0224] FIG. 10B is a flow chart of a method 1000B similar to the method 1000A, except that the method 1000B includes blocks 1019B and 1021. The UE determines 1019B whether the identified LTM configuration indicates releasing the second CG. If the UE determines 1019B that the identified LTM configuration indicates releasing the second CG, the method proceeds to block 1020, where the UE releases the second CG in response to the LTM command. Otherwise, if the UE determines 1019B that the identifiedLTM configuration does not indicate releasing the second CG, the method proceeds to block 1021 , where the UE continues communicating with the RAN node via the second CG during and / or after the serving cell change.

[0225] FIG. 10C is a flow chart of a method 1000C similar to the method 1000B, except that the method 1000C includes block 1019C instead of block 1019B. The UE determines 1019C whether the first CG is an MCG. If the UE determines that the first CG is an MCG, the method proceeds to block 1020, which is similar to block 910. Otherwise, if the UE determines 1019C that the first CG is an SCG, the method proceeds to block 1021 , which is similar to block 911. Examples and embodiments described for FIGs. 9A-9E may apply to FIG. 10A-10C.

[0226] FIG. 11 is a flow chart of a method 1100, which may be performed by a UE (e.g., the UE 102). The method 1100 starts with the UE communicating 1102 with a RAN (e.g., events 502, 602, 702, 802). The UE receives 1104 one or more LTM configurations from the RAN (e.g., events 316, 318, 394, 380, 580, 680, 780, 880, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, and / or 819). The UE determines 1106 whether the UE received the LTM configuration(s) in a configuration for a first CG or a second CG. If the UE determines 1106 that the UE received the LTM configuration(s) in a configuration for the first CG, the method proceeds to block 1108, where the UE determines that the LTM configuration(s) is / are associated with the first CG. Otherwise, if the UE determines 1106 that the UE received the LTM configuration(s) in a configuration for the second CG, the method proceeds to block 1109, where the UE determines that the LTM configuration(s) is / are associated with the second CG. Examples and embodiments described for FIGs. 9A-10C may apply to FIG. 11.

[0227] FIG. 12 is a flow chart of a method 1200, which may be performed by a UE (e.g., the UE 102 in FIGs. 3-8B). The method 1200 starts with the UE communicating 1202 with a RAN (e.g., events 502, 602, 702, 802). The UE receives 1204 an RRC reconfiguration message including an LTM configuration from the RAN node (e.g., events 316, 318, 394, 380, 580, 680, 780, 880, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, and / or 819). The UE determines 1206 whether the UE received the RRC reconfiguration message via a first SRB or a second SRB. In some embodiments, the first SRB is an SRB1 and the second SRB is an SRB3.

[0228] If the UE determines 1206 that the UE received the RRC reconfiguration message via the first SRB, the method proceeds to block 1207. Otherwise, if the UE determines 1206 that the UE received the RRC reconfiguration message via the second SRB, the method proceeds to block 1209. The UE determines 1207 whether the UE received the RRC reconfiguration message in an RRC message. If the UE determines 1207 that the UE received the RRC reconfiguration message in an RRC message, the method proceeds to block 1209. Otherwise, if the UE determines 1207 that the UE received the RRC reconfiguration message not included in an RRC message, the method proceeds to block 1208, where the UE determines that the LTM configuration is associated with an MCG. At block 1209, the UE determines that the LTM configuration is associated with an SCG.

[0229] In some embodiments, the RRC reconfiguration message is a first RRC reconfiguration message and the UE may receive a second RRC reconfiguration message including the first RRC reconfiguration message. In this case, the UE determines that the received RRC reconfiguration message (i.e. , the first RRC reconfiguration message) is embedded in an RRC message (i.e., the second RRC reconfiguration message).

[0230] FIG. 13A is a flow chart of a method 1300A, which may be performed by an RRC protocol layer of a UE (e.g., the RRC 214 of the UE 102). To simplify the following description, the RRC protocol layer is referred to as RRC. The method 1300A starts with the RRC receiving 1302 at least one first LTM configuration and at least one second LTM configuration from the RAN (e.g., events 316, 318, 394, 380, 580, 680, 780, 880, 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, and / or 819). The RRC determines 1304 that the first LTM configuration(s) is associated with a first CG. The RRC determines 1306 that the second LTM configuration(s) is associated with a second CG. The RRC receives 1308A an indication from a MAC entity, indicating an LTM command is received and including an LTM ID. The RRC determines 1310 whether the MAC entity is associated with the first CG or the second CG. If the RRC determines 1310 that the MAC entity is associated with the first CG, the method proceeds to block 1312A, where the RRC identifies an LTM configuration from the first LTM configuration(s), based on the LTM ID. Otherwise, if the RRC determines 1310 that the MAC entity is associated with the second CG, the method proceeds to block 1314A. At block 1314A, the RRC identifies an LTMconfiguration from the second LTM configuration(s), based on the LTM ID. Then, the RRC performs 1316 an LTM cell switch procedure in accordance with the identified LTM configuration. The method proceeds to block 1316 from block 1314A as well as from block 1312A.

[0231] FIG. 13B is a flow chart of a method 1300B similar to the method 1300A, except that the method 1300B includes blocks 1308B, 1312B, and 1314B instead of blocks 1308A, 1312A, and 1314A. The RRC receives 1308B an indication from a MAC entity, indicating an LTM command is received and including a cell index. If the RRC determines 1310 that the MAC entity is associated with the first CG, the method proceeds to block 1312B, where the RRC identifies an LTM configuration from the first LTM configuration(s), based on the cell index. Otherwise, if the RRC determines 1310 that the MAC entity is associated with the second CG, the method proceeds to block 1314B, where the RRC identifies an LTM configuration from the second LTM configuration(s), based on the cell index. The method proceeds to block 1316 from block 1314B as well as 1312B.

[0232] FIG. 13C is a flow chart of a method 1300C similar to the method 1300A, except that the method 1300C includes blocks 1308C, 1312C, and 1314C instead of blocks 1308A, 1312A, and 1314A. The RRC receives 1308C an indication from a MAC entity, indicating an LTM command is received and including a cell ID. If the RRC determines 1310 that the MAC entity is associated with the first CG, the method proceeds to block 1312C, where the RRC identifies an LTM configuration from the first LTM configuration(s), based on the cell ID. Otherwise, if the RRC determines 1310 that the MAC entity is associated with the second CG, the method proceeds to block 1314C, where the RRC identifies an LTM configuration from the second LTM configuration(s), based on the cell ID. The method proceeds to block 1316 from block 1314C as well as from block 1312C.

[0233] FIG. 14A is a flow chart of a method 1400A, which may be performed by a UE (e.g., the UE 102 in FIGs. 3-8B). The method 1400A begins with the UE receiving 1402A an LTM command including an LTM ID from the RAN (e.g., events 330, 430, 530, 630, 730, 830). The UE determines 1404 whether the MAC received the LTM command using a first MAC entity or a second MAC entity. If the UE determines 1404 that the UEreceived the LTM command using the first MAC entity, the method proceeds to block 1406A, where the first MAC entity of the UE transmits an indication to an RRC protocol layer, the indication being associated with an LTM command being received by the first MAC entity and including the LTM ID. Otherwise, if the MAC determines 1404 that the UE received the LTM command using a second MAC entity, the method proceeds to block 1408A, where the second MAC entity of the UE transmits an indication to the RRC protocol layer, where the indication indicates that an LTM command is received by the second MAC entity and includes the LTM ID.

[0234] FIG. 14B is a flow chart of a method 1400B, similar to the method 1400A, except that method 1400B includes blocks 1402B, 1406B, and 1408B instead of blocks 1402A, 1406A, and 1408A. The method starts with the UE receiving 1402B an LTM command including a cell index from the RAN (e.g., events 330, 430, 530, 630, 730, and / or 830). If the UE determines 1404 that the UE received the LTM command using the first MAC entity, the method proceeds to block 1406B. The first MAC entity of the UE transmits 1406B an indication to an RRC protocol layer, where the indication indicates an LTM command is received by the first MAC entity and includes the cell index. Otherwise, if the MAC determines 1404 that the UE received the LTM command using a second MAC entity, the method proceeds to block 1408B. The second MAC entity of the UE transmits 1408B an indication to the RRC protocol layer, where the indication indicates an LTM command is received by the second MAC entity and includes the cell index.

[0235] FIG. 14C is a flow chart of a method 1400C, similar to the method 1400A, except that method 1400C includes blocks 1402C, 1406C, and 1408C instead of blocks 1402A, 1406A, and 1408A. The UE receives 1402C an LTM command including a cell ID from the RAN (e.g., events 330, 430, 530, 630, 730, and / or 830). If the UE determines 1404 that the UE received the LTM command using the first MAC entity, the method proceeds to block 1406C. The first MAC entity of the UE transmits 1406C an indication to an RRC protocol layer. The indication reveals that an LTM command is received by the first MAC entity and includes the cell ID. Otherwise, if the MAC determines 1404 that the UE received the LTM command using a second MAC entity, the method proceeds to block 1408C. The second MAC entity of the UE transmits 1408C an indication to the RRCprotocol layer. The indication reveals that an LTM command is received by the second MAC entity and includes the cell ID.

[0236] FIG. 15A is a flow chart of a method 1500A, which may be performed by a UE (e.g., the UE 102 in FIGs. 3-8B). Method 1500A begins with the UE communicating 1502 with a RAN (or RAN node) via a first serving cell and a second serving cell. The first serving cell and the second serving cell belong to a first CG and a second CG, respectively (e.g., events 502, 602, 702, and / or 802). The UE receives 1504 a first LTM configuration and a second LTM configuration from the RAN, where the first LTM configuration and the second LTM configuration are associated with the first CG and the second CG, respectively. In some embodiments, the UE receives the first LTM configuration from an MN of the RAN (e.g., events 316, 318, 394, 380, 580, 680, 780, and / or 880) and receives the second LTM configuration from an SN of the RAN (e.g., events 594, 517, 519, 694, 617, 619, 794, 717, 719, 894, 817, and / or 819).

[0237] The UE receives 1506 a first LTM command from the RAN, commanding the UE to perform a serving cell change from the first serving cell to a first candidate cell (e.g., events 330, 430, 580, 680, 780, and / or 880). The UE performs 1508 a serving cell change from the first serving cell to the first candidate cell, in accordance to the first LTM configuration, in response to the first LTM command (e.g., events 332, 432, 580, 680, 780, and / or 880). The UE receives 1510 a second LTM command from the RAN while performing the serving cell change. The second LTM command directs the UE to perform a serving cell change from the second serving cell to a second candidate cell (e.g., events 530, 630, 730, and / or 830). In this embodiment, the UE discards 1512 the second LTM command. That is, the UE refrains from performing a serving cell change in response to the second LTM command.

[0238] FIG. 15B is a flow chart of a method 1500B, similar to the method 1500A, except that method 1500B includes block 1513 instead of block 1512. The UE performs 1513 a serving cell change from the second serving cell to the second candidate cell in accordance with the second LTM configuration, in response to the second LTM command (e.g., events 532, 632, 732, and / or 832). In some embodiments, the UE performs the serving cell change from the second serving cell to the second candidate cell, after completing the serving cell change to the first candidate cell from the first serving cell. Inother embodiments, the UE performs the serving cell change from the second serving cell to the second candidate cell while performing the serving cell change to the first candidate cell from the first serving cell. Examples and embodiments described for FIGs. 9A-14C may apply to FIGs. 15A-15B.

[0239] The following description may be applied to any of the embodiments discussed above. Further, a description for one of the above figures may apply to another of the above figures. Examples, embodiments, and methods described above may be combined, if there is no conflict. An event or block described above may be optional or omitted. For example, an event or block with dashed lines in the figures may be optional. In some embodiments, “message” is used and may be replaced by “information element (IE)”, and vice versa. In some embodiments, “IE” is used and may be replaced by “field”, and vice versa. In some embodiments, “configuration” may be replaced by “configurations” or “configuration parameters”, and vice versa. In some embodiments, “lower layer” may be replaced by “Layer 1 / Layer 2”. In some embodiments, the “LTM command” may be replaced by “serving cell change command”, “Layer 1 / Layer 2 switching command”, “lower layer switching command” or “lower layer serving cell change command”. In some embodiments, “some” means “one or more”. In some embodiments, “at least one” means “one or more”. In some embodiments, the “DU configuration” may be replaced by “cell group configuration”. In some embodiments, the “cell index” may be replaced with “serving cell index”, “LTM cell index”, “special cell (SpCell) index”, “PCell index”, or “PSCell index”. In some embodiments, the “serving” may be replaced by “source”. In some embodiments, the “measurement report” may be replaced by “measurement result(s)”. In some embodiments, the “serving cell change” may be replaced by “serving cell switch”, “LTM cell switch” or “LTM cell switch execution”.

[0240] A user device in which the techniques of this disclosure may be implemented (e.g., the UE 102) may 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 headunit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device may operate as an internet-of-things (loT) device or a mobile-internet device (MID). Depending on the type, the user device may include one or more general-purpose processors, a computer-readable memory, a user interface, one or more network interfaces, one or more sensors, etc.

[0241] 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 may comprise dedicated circuitry or logic that is permanently configured (e.g., as a special-purpose processor, such as a field programmable gate array (FPGA) or an application-specific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also comprise programmable logic or circuitry (e.g., as encompassed within a general-purpose processor or other programmable processor) that is temporarily configured by software to perform certain operations. The decision to implement a hardware module in dedicated and permanently configured circuitry, or in temporarily configured circuitry (e.g., configured by software) may be driven by cost and time considerations.

[0242] When implemented in software, the techniques discussed above may be provided as part of the operating system, a library used by multiple applications, a particular software application, etc. The software may be executed by one or more general-purpose processors or one or more special-purpose processors.

[0243] Upon reading this document, those of skill in the art will appreciate additional or alternative structural and functional designs for handling mobility between base stations through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosed embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method andapparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

[0244] Numerical adjectives “first”, “second”, and “third” do not imply any order (are not ordinals) but are markers to distinguish separate instances of similar elements.References to the singular (e.g., “a” or “an”, “the”) should include the plural unless clearly indicated otherwise.

[0245] As used herein, a phrase referring to “at least one of’ or “one or more of” a list of items refers to any combination of those items, including single members. For example, “at least one of: a, b, or c” is intended to cover the possibilities of: a only, b only, c only, a combination of a and b, a combination of a and c, a combination of b and c, and a combination of a and b and c.

[0246] Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element may be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein. The methods or flowcharts may be implemented in a computer program, software or firmware tangibly embodied in a computer-readable storage medium for execution by a specifically programmed computer or processor.

Claims

WHAT IS CLAIMED IS:1 . A wireless communication method performed by a user equipment, UE, (102), the method comprising: receiving (904) at least one lower-layer triggered mobility, LTM, configuration from a radio access network, RAN, node (104), for switching from at least one of a first serving cell (124A) or a second serving cell (126A) to a first candidate cell (124B, 126B); performing (908) a cell switch, from the at least one of the first serving cell (124A) or the second serving cell (126A), to the first candidate cell (124B, 126B), based on a first indicator and a first LTM command received from the RAN node (104); and determining (909B), based on the first indicator, whether to release a first cell group, CG, associated with the first serving cell (124A) or a second CG associated with the second serving cell (126A).

2. The method of Claim 1 , further comprising: releasing or continue communicating with the first CG or the second CG based on the first indicator.

3. The method of Claim 1 or 2, wherein the first indicator includes information indicating the release of the first CG or the second CG.

4. The method of Claim 1 or 2, wherein the first indicator includes information about the first candidate cell belonging to the first CG or the second CG.

5. The method of Claim 1 or 2, further comprising: receiving the first LTM command via the first CG or the second CG, wherein the first indicator is related to the receiving of the first LTM command via the first CG or the second CG.

6. The method of any of Claims 1 to 5, wherein the at least one LTM configuration includes first and second LTM configurations, the method further comprising: determining whether the first LTM command is associated with the first CG or the second CG; identifying one of the first and second LTM configurations based on the first LTM command and the first CG or the second CG; and performing the cell switch based on the identified one of the first and second LTM configurations.

7. The method of Claim 6, further comprising: performing one of releasing or continue communicating with the first CG or the second CG based on an explicit indication included in the first LTM command or whether the first CG or the second CG is a master CG.

8. The method of any of Claims 1 to 7, further comprising: receiving a second LTM command while receiving the first LTM command, the second LTM command instructing the UE to perform a cell switch from the second serving cell to a second candidate cell; and discarding the second LTM command.

9. The method of any of Claims 1 to 7, further comprising: receiving a second LTM command while receiving the first LTM command, the second LTM command instructing the UE to perform a cell switch from the second serving cell to a second candidate cell; and performing the cell switch from the second serving cell to the second candidate cell in response to the second LTM command.

10. The method of any of Claims 1 to 9, further comprising: determining that the at least one LTM configuration is associated with the firstCG or the second CG based on a second indicator.11 . The method of Claim 10, wherein the second indicator is indicative of at least one of: whether the at least one LTM configuration is for the first CG or second GG; whether the at least one LTM configuration is included in a radio resource control, RRC, reconfiguration message or an RRC reconfiguration message embedded in an RRC message; an LTM identifier received from a medium access control, MAC, entity; a cell index received from a MAC entity; or a cell ID received from a MAC entity.

12. The method of any of Claims 1 to 10, further comprising: receiving a radio resource control, RRC, reconfiguration message via a first signaling radio bearer, SRB, or a second SRB.

13. The method of Claim 12, further comprising: determining that the at least one LTM configuration is associated with the second CG when (i) receiving RRC reconfiguration message via the second SRB or (ii) receiving the RRC reconfiguration message via the first SRB; or determining that the at least one LTM configuration is associated with the first CG when receiving the RRC reconfiguration message independent of the RRC message, via the first SRB.

14. The method of any of Claims 1 to 10, wherein the at least one LTM configuration includes first and second LTM configurations, the method further comprising: determining whether the first LTM command is associated with the first CG or the second CG; receiving an indication from a medium access control, MAC, entity indicating the first LTM command and at least one of: an LTM identifier, ID, a cell index, or a cell ID; anddetermining whether the MAC entity is associated with the first CG or the secondCG.

15. The method of Claim 14, further comprising: based on the at least one of: the LTM ID, the cell index, or the cell ID, identifying an LTM configuration from: the first LTM configuration, when the MAC entity is associated with the first CG, and the second LTM configuration, when the MAC entity is associated with the second CG; and performing the cell switch based on the identified LTM configuration.

16. The method of any of Claims 1 to 10, wherein the first LTM command includes at least one of: an LTM identifier, ID, a cell index, or a cell ID, the method further comprising: receiving the first LTM command using a first medium access control, MAC, entity or a second MAC entity; and transmitting, to an RRC protocol layer, an indication of the first LTM command being received by the first MAC entity or the second MAC entity and including an associated one of the LTM ID, the cell index, or the cell ID.

17. The method of any of Claims 1 to 16, further comprising: communicating with the RAN node via the first serving cell and the second serving cell in dual connectivity operation.

18. A wireless communication method (900E) performed by a radio access network, RAN, node (104), the method comprising: transmitting (903), to a user equipment, UE, (102), at least one lower-layer triggered mobility, LTM, configuration for switching from at least one of a first serving cell (124A) or a second serving cell (126A) to a candidate cell (124B, 126B); andtransmitting (905) a first LTM command instructing the UE (102) to perform a cell switch, from the at least one of the first serving cell (124A) or the second serving cell (126A), to the candidate cell (124B, 126B), based on an indicator, the indicator being associated with whether the at least one LTM configuration includes information about releasing or maintaining communication with a first cell group, CG, that includes the first serving cell (124A) or a second CG that includes the second serving cell (126A).

19. The method of Claim 18, wherein the indicator indicates at least one of: the releasing of the first CG or the second CG, the candidate cell belonging to the first CG or the second CG, or the first LTM command being received via the first CG or the second CG.

20. A communication device (102, 104) comprising a transceiver (156, 136), a processor (158, 138) and computer-readable storage media (160, 140) storing executable instructions for the processor to perform any of the methods recited in claims 1 -19, using the transceiver.

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