Enabling early synchronization and timing advance information for lower layer triggered mobility

Abstract

Methods and devices in a wireless communication network perform cell switching with early synchronization and / or timing advance for a lower-layer triggered mobility (LTM) configuration. The cell switching with early synchronization includes a service base station (S-BS) transmitting (718) a random access channel, RACH, configuration to a first user equipment, UE, (102) via a serving cell (124A), transmitting (750), to the first UE (102), a first physical downlink control channel, PDCCH, order instructing the first UE (102) to transmit a first random access, RA, preamble on a candidate cell (125), which is configured for an LTM procedure, the first PDCCH order including at least one of: a first RA preamble index, a first physical random access channel, PRACH, mask index, or a first synchronization signal block, SSB, index, and receiving (712), the RACH configuration, a PDCCH order information, or SSB positions in burst for the candidate cell.

Description

Patent ApplicationAttorney Docket Number 0683-100-WOENABLING EARLY SYNCHRONIZATION AND TIMING ADVANCE INFORMATION FOR LOWER LAYER TRIGGERED MOBILITYFIELD 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 3rdGeneration Partnership Program (3GPP) communication systems, which are configured to enable early synchronization and timing advance information for mobility.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, the Packet Data Convergence Protocol (PDCP) sublayer of the 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 user device, also known as a user equipment (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 dual connectivity (DC), the cells associated with the BS operating a master node (MN) definePatent ApplicationAttorney Docket Number 0683-100-WO a master cell group (MCG), and the cells associated with the BS operating as a secondary node (SN) define a secondary cell group (SCG). SRB1 resources carry RRC messages, which in some cases include NAS messages over the dedicated control channel (DCCH). SRB2 resources support RRC messages that include logged measurement information or NAS messages, also over the DCCH but with lower priority than the SRB1 resources. More generally, SRB1 and SRB2 resources allow the UE and the MN to exchange RRC messages related to the MN. The SRB1 and SRB2 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] The UE, in some scenarios, may concurrently utilize resources of multiple radio access network (RAN) nodes (e.g., BSs or components of a distributed BS), interconnected by a backhaul. When these network nodes (i.e., the BSs or their components) 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 an MN that covers a primary cell (PCell), and the other BS operates as an 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. Under certain conditions, one BS and / or the UE determines that the UE should establish a radio connection with another BS. For example, one BS may determine to hand the UE over to the second BS, and initiate a handover procedure.

[0006] When the UE moves from coverage area of one cell to coverage area of another cell in a RAN, at some point, the RAN performs a serving cell change 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, thePatent ApplicationAttorney Docket Number 0683-100-WORAN transmits an RRC reconfiguration message configuring Reconfiguration with Synchronization (e.g., the RRC reconfiguration message includes a ReconfigurationWithSync information element (IE)) for changing the serving cell (e.g., PCell or PSCell). If the UE operates in carrier aggregation (CA) of at least one secondary cell (SCell) with the PCell or PSCell, the RAN has to release the at least one SCell due to the change of the PCell or PSCell. The serving cell change involves complete L2 (and L1 ) resets, leading to longer latency, and larger overhead and longer interruption time. Thus, 3GPP has introduced the L1 / L2 Triggered Mobility (LTM) (may also be referred to as lower-layer triggered mobility) feature to reduce the latency in mobility.

[0007] While a BS of the RAN communicates with the UE via a serving cell, the BS receives one or more L3 (e.g., RRC) measurement results from the UE. The BS may include a central unit (CU) and one or more distributed units (DUs). One of the DU(s) operating the serving cell is a serving DU. Based on the L3 measurement result(s), the BS determines to configure an LTM candidate cell for an LTM cell switch. To configure the LTM candidate cell for the UE, the BS transmits an LTM candidate configuration to the UE, via an RRC signaling, configuring the LTM candidate cell. Later on, the BS receives one or more L1 measurement results from the UE. Based on the one or more L1 measurement result(s), the BS determines that the LTM candidate cell qualifies to be a serving cell for the UE. Therefore, the BS transmits an LTM cell switch command to the UE to command the UE to perform the LTM cell switch to the LTM candidate cell. The UE performs a cell change from the serving cell to the LTM candidate cell in response to the LTM cell switch command. If the LTM candidate cell is operated by the serving DU, the LTM cell switch is an intra-CU intra-DU LTM cell switch. If the LTM candidate cell is operated by a candidate DU in the DU(s), the LTM cell switch is an intra-CU inter-DU LTM cell switch. 3GPP has enabled the intra-CU intra-DU LTM cell switch and intra-CU inter-DU LTN cell switch in Release 18 specifications. 3GPP is standardizing the inter-CU LTM cell switch.

[0008] Specifically, to trigger the UE to perform early uplink synchronization with an LTM candidate cell of a candidate BS, the source BS (e.g., an aggregated BS or a DU) may transmit a physical downlink control channel (PDCCH) order to the UE,Patent ApplicationAttorney Docket Number 0683-100-WO including a random access (RA) preamble index. The RA preamble index indicates a particular RA preamble. The UE transmits the RA preamble on the LTM candidate cell on a physical RA channel (PRACH) occasion. The candidate BS receives the RA preamble on the PRACH occasion via the LTM candidate cell. The candidate BS derives a first timing advance (TA) value based on the received RA preamble. The candidate BS also calculates a first RA radio network temporary identifier (RA-RNTI) based on the PRACH occasion and a mapping of synchronization signal block (SSB) indexes to PRACH occasions. The candidate BS transmits the first TA value, a cell ID of the LTM candidate cell, the RA preamble index, and the first RA-RNTI as first TA information to the source BS. However, the source BS does not know the mapping of the SSB indexes to PRACH occasions used by the candidate BS. Therefore, the source BS is not able to calculate an RA-RNTI that is identical to the first RA-RNTI calculated by the candidate BS.

[0009] Therefore, in some embodiments, the source BS may discard the TA value. In other embodiments, the candidate BS may transmit to the source BS a second TA information including: a second TA value, the cell ID, the RA preamble index, and a second RA-RNTI, together with the first TA information. The source BS might calculate an RA-RNTI identical to the second RA-RNTI but not identical to the first RA-RNTI. The source BS incorrectly identifies the second TA value for the UE as the candidate BS provides the second TA value for another UE. Thus, for this scenario, the RAN fails performing the LTM cell switch.SUMMARY

[0010] According to an embodiment, a wireless communication method is performed by a BS and includes transmitting a RACH configuration to a first UE via a serving cell, which is configured by a source distributed unit (S-DU) of the BS, and transmitting, to the first UE, a first PDCCH order instructing the first UE to transmit a first RA preamble on a candidate cell, which is configured by a candidate distributed unit (C- DU) of the BS for an LTM procedure, the first PDCCH order including at least one of a first RA preamble index, a first PRACH mask index, or a first SSB, index.

[0011] According to another embodiment, a wireless communication method is performed by a candidate base station (C-BS), and the method includes receiving, atPatent ApplicationAttorney Docket Number 0683-100-WO the C-BS, a message from a S-BS, requesting early synchronization information for an LTM procedure, and transmitting to the S-BS or a DU of the S-BS or another BS or a DU of the another BS, a message including a RACH configuration, a PDCCH order information, or SSB positions in burst configuration, the SSB positions in burst configuration being for calculating one or more random access-radio network temporary identifiers (RA-RNTIs).

[0012] According to yet another embodiment, a wireless communication method is performed by a DU of a BS, and the method includes receiving a first message from a CU of the BS. When the first message includes a request for early synchronization information for an LTM cell switching, the method further includes, in a second message for the CU, a RACH configuration, a PDCCH order information, or SSB positions in burst configuration for early synchronization with the DU, and transmitting the second message to the CU. When the first message omits the request for early synchronization information for the LTM cell switching, the method further includes a configuration unrelated to early synchronization information in a third message for the CU, and transmitting the third message to the CU.

[0013] According to still another embodiment, a wireless communication method is performed by a first BS, and the method includes receiving a first message from a second BS. When the first message includes a request for early synchronization information for an LTM cell switching, the method further includes, in a second message for the second BS, a RACH configuration, a PDCCH order information, or SSB positions in a burst configuration for early synchronization with the first BS, and transmitting the second message to the second BS. When the first message omits the request for early synchronization information for the LTM cell switching, the method includes a configuration unrelated to early the synchronization information in a third message for the second BS, and transmitting the third message to the second BS.

[0014] According to another embodiment, a wireless communication method is performed by a first RAN node, and the method includes transmitting a first message to a second RAN node to request early synchronization for LTM cell switching for a first candidate cell for UE, receiving a second message from the second RAN node including a RACH configuration, a PDCCH order information, or SSB positions in aPatent ApplicationAttorney Docket Number 0683-1 OO-WO burst, for the first candidate cell for UE, transmitting a third message to a third RAN node to request early synchronization for a second candidate cell for the UE, receiving a fourth message, from the third RAN node, including a second RACH configuration, a second PDCCH order information, and second SSB positions in burst, for the second candidate cell, for the UE, transmitting a fifth message to a DU including the first RACH configuration, the first PDCCH order information, the first SSB positions in burst, an identifier (ID) for the first candidate cell, the second RACH configuration, the second PDCCH order information, the second SSB positions in burst, or the ID for the second candidate cell, for the UE, and transmitting to the UE, via the DU, the first RACH configuration, the first SSB positions in burst for the first configuration cell, the second RACH configuration, or the second SSB positions in burst for the second configuration cell.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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.

[0016] FIG. 1 A is a block diagram of an example system in which an RAN and a UE may implement the techniques of this document for managing conditional procedures related to an SN;

[0017] FIG. 1 B is a block diagram of a communication system that uses four BSs;

[0018] FIG. 1 C is a block diagram of an example BS including a CU and a DU that may operate in the system of FIG. 1A;

[0019] FIG. 2A is a block diagram of an example protocol stack according to which the UE of FIG. 1 A communicates with BSs;

[0020] 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;

[0021] FIG. 3 is a signal diagram illustrating an LTM procedure with early synchronization performed by a UE in communication with a BS including a DU and a CU according to an embodiment.Patent ApplicationAttorney Docket Number 0683-100-WO

[0022] FIG. 4 is a signal diagram illustrating an LTM procedure with early synchronization performed by a UE in communication with a BS including a source-DU (S-DU), a candidate DU (C-DU), and a CU, according to an embodiment.

[0023] FIG. 5 is a signal diagram illustrating an LTM procedure with early synchronization performed by a UE for hand over from a serving BS to a candidate BS including a DU and a CU, according to other embodiments.

[0024] FIGs. 6A to 6D are signal diagrams illustrating an LTM with early synchronization performed by a UE in communication with master node and secondary node BSs, and a candidate BS including a DU and a CU, according to various embodiments.

[0025] FIGs. 7A and 7B are flow diagrams illustrating the LTM procedure with early synchronization performed by a source DU and a source CU of a BS, according to other embodiments.

[0026] FIG. 8 is a flow diagram illustrating the LTM procedure with early synchronization performed by a source DU and a source CU of a BS with two UEs, according to various embodiments.

[0027] FIG. 9 is a flow diagram illustrating the LTM procedure with early synchronization performed by a DU and CU of a BS according to various embodiments.

[0028] FIGs. 10A and 10B are flow diagram illustrating the LTM procedure with early synchronization performed by two BSs according to various embodiments.

[0029] FIG. 11 is a flow diagram illustrating the LTM procedure with early synchronization performed by a DU of a BS according to various embodiments.

[0030] FIG. 12 is a flow diagram illustrating the LTM procedure with early synchronization performed by a first BS in communication with a second BS, according to various embodiments.

[0031] FIG. 13 is a flow diagram illustrating the LTM procedure with early synchronization performed by a first RAN node in communication with a second RAN node, according to various embodiments.

[0032] FIGs. 14A and 14B illustrate SSB indexes to PRACH occasion mapping according to an embodiment.Patent ApplicationAttorney Docket Number 0683-100-WODETAILED DESCRIPTION

[0033] Methods and devices described in this section embody techniques related to early synchronization and timing advance information association for low layer triggered mobility. Prior to discussing the various embodiments associated with the early synchronization and timing advance, a wireless communication system in which these embodiments may be performed is discussed.

[0034] FIG. 1A depicts an example wireless communication system 100 in which communication devices may implement various techniques discussed in the next embodiments. The wireless communication system 100 includes a UE 102, a first BS 104A, a second BS 106A, and a core network (CN) 110. The UE 102 initially connects to the first BS 104A. In some scenarios, the first BS 104A may perform an SN addition to configure the UE 102 to operate in DC with the first BS 104A and the second BS 106A. The BSs 104A and 106A operate as an MN and an SN for the UE 102, respectively.

[0035] In various configurations of the wireless communication system 100, the first BS 104A may be implemented as a master eNB (MeNB) or a master gNB (MgNB), and the second BS 106A may be implemented as a secondary gNB (SgNB). These roles may be switched for the BSs 104A and 106A. In one embodiment, the BSs 104A and 106A may be replaced by the BSs 104B and 106B (illustrated in FIG. 1 B) for the above roles. In another embodiment, any of the four BSs may be the MeNB, MgNB, SgNB, MN, SN, etc. The UE 102 may communicate with the first BS 104A and the second BS 106A via the same RAT such as EUTRA or NR or sixth generation (6G), or different RATs. When the first BS 104A is an MeNB and the second BS 106A is an SgNB, the UE 102 may be in EUTRA-NR DC (EN-DC) with the MeNB and the SgNB.

[0036] In some cases, an MeNB or an SeNB is implemented as an ng-eNB rather than an eNB. When the first BS 104A is a Master ng-eNB (Mng-eNB) and the second BS 106A is a SgNB, the UE 102 may be in next generation (NG) EUTRA-NR DC (NGEN-DC) with the Mng-eNB and the SgNB. When the first BS 104A is an MgNB and the second BS 106A is an SgNB, the UE 102 may be in NR-NR DC (NR-DC) with the MgNB and the SgNB. When the first BS 104A is an MgNB and the second BS 106A is a Secondary ng-Patent ApplicationAttorney Docket Number 0683-100-WO eNB (Sng-eNB), the UE 102 may be in NR-EUTRA DC (NE-DC) with the MgNB and the Sng-eNB.

[0037] In the scenarios where the network hands over the UE 102 from the first BS 104A to the second BS 106A, the BSs 104A and 106A operate as a source BS (S-BS) and a target (or candidate) BS (T-BS or C-BS), respectively. The UE 102 may operate in DC with the first BS 104A and an additional BS 104B, shown in FIG. 1 B, for example, prior to the handover. The UE 102 may continue to operate in DC with the second BS 106A and the additional BS 104B or operate in single connectivity (SC) with the second BS 106A, after completing the handover. The BSs 104A and 106A in this case operate as a source MN (S-MN) and a target (or candidate) MN (T-MN or C-MN), respectively. FIG. 1 B illustrates a case when there are two BSs 104A and 104B that support two corresponding cells 124A and 124B and two BSs 106A and 106B that support two corresponding cells 126A and 126B, and the UE may communicate with any of these BSs via corresponding cells 124A, 124B, 126A, and 126B.

[0038] 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, or a 6G (not shown). The BS 104A (104B or 106A or 106B) 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 scenarios discussed below, the BSs 104A and 106A 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 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic, etc., and the MME 114 is configured to manage authentication, registration, paging, and other related functions. The PGW 116 provides connectivity from the UE to one or more external packet data networks, e g., an Internet network and / or an Internet Protocol (IP) Multimedia Subsystem (IMS) network. The 5GC 160 includes a User Plane Function (UPF) 162, an Access and Mobility Management (AMF) 164, and / or Session Management Function (SMF) 166. The UPF 162 is generally configured to transfer user-plane packets related to audio calls, video calls, Internet traffic,Patent ApplicationAttorney Docket Number 0683-100-WO etc., the AMF 164 is configured to manage authentication, registration, paging, and other related functions, and the SMF 166 is configured to manage PDU sessions.

[0039] As illustrated in FIG. 1A, the first BS 104A supports cell 124A, and the second BS 106A supports a cell 126A. The cells 124A and 126A may partially overlap, so that the UE 102 may communicate in DC with the first BS 104A and the second BS 106A, where one of the BSs 104A and 106A is an MN and the other is an SN. The first BS 104A may support additional cell(s) such as cells 125, and the second BS 106A may support additional cell(s) (not shown in FIG. 1A). The cells 124A and 125 may partially overlap, so that the UE 102 may communicate in carrier aggregation (CA) with the first BS 104A. The first BS 104A may operate the cells 124A and 125 via one or more transmit and receive points (TRPs). More particularly, when the UE 102 is in DC with the first BS 104A and the second BS 106A, one of the BSs 104A and 106A operates as an MeNB, an Mng-eNB, or an MgNB, and the other operates as an SgNB or an Sng-eNB.

[0040] The wireless communication network 100 may include any suitable number of BSs (see FIG. 1 B) supporting NR cells and / or EUTRA cells or 6G 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 document may also apply to other suitable radio access and / or core network technologies such as 6G radio access and / or 6G core network or 5G NR-6G DC.

[0041] With continued reference to FIG. 1A, the first BS 104A is equipped with processing hardware 130 that may include one or more general-purpose processors (e.g., CPUs) 131 and a non-transitory computer-readable memory 132 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 may also include a transceiver 133 for communication with the CN, other BSs and / or UEs. 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. UE 102) via one or more cells (e.g., the cell(s) 124A and 125) and / or one or more TRPs. The PHY controller 134 is also configured to receive data and control signal on physical uplink (UL) channels and / or UL referencePatent ApplicationAttorney Docket Number 0683-100-WO signals with the one or more user devices via one or more cells (e.g., the cell(s) 124A and 125) and / or one or more TRPs. The processing hardware 130 may also include a Medium Access Controller (MAC) controller 135 configured to perform MAC functions with one or more user devices. The MAC functions include an RA procedure, managing UL timing advance (TA) 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 LTM related functions as described below. The processing hardware 130 may further include an RRC controller 136 to implement procedures and messaging at the RRC sublayer of the protocol communication stack. For example, the RRC controller 136 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 104A operates as an MN relative to an SN or as an SN relative to an MN. The second BS 106A may include processing hardware 140 that is similar to processing hardware 130. In particular, components 141 , 142, 143, 144, 145, and 146 may be similar to the components 131 , 132, 133, 134, 135, and 136, respectively.

[0042] The UE 102 is equipped with processing hardware 150 that may include one or more general-purpose processors 151 such as CPUs and non-transitory computer- readable memory 152 storing machine-readable instructions executable on the one or more general-purpose processors, and / or special-purpose processing units. The processing hardware 150 also includes a transceiver 153. A PHY controller 154 is configured to receive data and control signal on physical DL channels and / or DL reference signals with the BS 104A or 106A via one or more cells (e.g. , the cell(s) 124A, 125, and / or 126A) and / or one or more TRPs. The processing hardware 150 may further include a MAC controller 155 configured to perform MAC functions with BS 104A or 106A. 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 BS 104A or 106A. In another example, the MAC functions include LTM related functions as described below. The processing hardware 150 may further include an RRC controller 156 to implement procedures and messaging at the RRC sublayer of the protocol communication stack.Patent ApplicationAttorney Docket Number 0683-100-WO

[0043] 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 (BS 104A) or at the SN (BS 106A). 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.

[0044] FIG. 1 C depicts an embodiment of a distributed BS such as the first BS 104A, second BS 104B, BS 106A, or BS 106B. The BS in this embodiment may include a CU 172 and one or more DUs 174 (only one shown for simplicity), as illustrated in FIG.1 C. 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 the processing hardware 130. In another example, the CU 172 is equipped with the processing hardware 140. The processing hardware 140 in an example embodiment includes an SN RRC controller 146 configured to manage or control one or more RRC configurations and / or RRC procedures when the second BS 106A 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 in an example embodiment 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 106A operates as an MN or an SN. The process hardware may include further a physical layer controller configured to manage or control one or more physical layer operations or procedures.

[0045] 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 230 or a gNB 232 (e.g., one or more of the BSs 104A, 104B, 106A, 106B). In the example stack 200, a PHY 202A of EUTRA provides transport channels to the EUTRA MAC sublayer 204A, which in turn provides logical channels to the EUTRA RLC sublayer 206A. The EUTRA RLCPatent ApplicationAttorney Docket Number 0683-100-WO 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 an 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.

[0046] 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.”

[0047] On a control plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 may provide signaling radio bearers (SRBs) or RRC sublayer (not shown in FIG. 2A) to exchange RRC messages or non-access-stratum (NAS) messages, for example. On a user plane, the EUTRA PDCP sublayer 208 and the NR PDCP sublayer 210 may provide Data Radio Bearers (DRBs) to support data exchange. Data exchanged on the NR PDCP sublayer 210 may be SDAP PDUs, Internet Protocol (IP) packets or Ethernet packets.

[0048] FIG. 2B illustrates, in a simplified manner, an example protocol stack 250, 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 104A or 106A 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 thePatent ApplicationAttorney Docket Number 0683-100-WODU. 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.

[0049] Next, several example scenarios are discussed in which the BS operating in the system of FIGs. 1 A and 1 B transmits a configuration to the UE 102 and later activates a configuration for communication between the UE 102 and another BS or another component (DU) of the same BS. The events and / or acts in FIGs. 3-6D that are similar are labeled with similar reference numbers (e.g., event 302 in FIG. 3 is similar to event 402 of FIG. 4 and event 502 of FIG. 5, event 390 in FIG.3 is similar to event 490 of FIG. 4 and event 590 of FIG. 5, etc.), 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.

[0050] FIG. 3 illustrates a scenario 300 in which the BS 104A includes a CU 172 and DU 174, and the DU 174 operates the cell 124A. The UE 102 initially communicates 302 with the DU 174 on a serving cell (e.g., the cell 124A), using a serving DU configuration, and communicates with the CU 172 via the DU 174, using a serving CU configuration. The DU 174 is a serving or a source DU (S-DU) for the UE 102. In other words, the DU 174 is a serving DU (S-DU) that communicates with the UE 102. In some embodiments, the UE 102 communicates in carrier aggregation (CA) with the DU 174 on the cell 124A and other cell(s) (e.g., cell 124D shown in FIG. 1 B) using the serving DU configuration. The DU 174 operates the other cell(s). The cell 124A and / or the other cell(s) are serving cell(s) for the UE 102. In other embodiments, the UE 102 communicates with the DU 174 only on the cell 124A. In some embodiments, the UE 102 communicates with the DU 174 on the cell 124A and / or other cell(s) (i.e. , serving cell(s)) via one or multiple TRPs. In the following description, events 394, 324, 350, 352, 354, and 326 occur on the serving cell(s). 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 additional cell(s) associated with thePatent ApplicationAttorney Docket Number 0683-100-WOPCell or a SCell. In the following description, the first BS 104A may be the DU 174, the CU 172, or the DU 174 and CU 172.

[0051] The UE 102 may transmit 302 UL PDUs and / or UL control signals to first BS 104A 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 BS 104A via radio bearers which may include SRBs and / or DRB(s). The BS 104A may configure the radio bearers to the UE 102. In some embodiments, UL control signals include UL control information, channel state information, hybrid automatic repeat request (HARQ) acknowledgements (ACKs), HARQ negative ACKs, scheduling request(s) and / or sounding reference signal(s). Similarly, the UE 102 may receive DL PDUs and / or DL control signals from the BS 104A 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, channel state information reference signal(s) (CSI-RS(s)), and / or tracking reference signal(s)). The BS 104A 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.

[0052] In some embodiments, the serving DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some embodiments, the serving DU configuration includes at least one first non-LTM TCI state configuration for the serving cell(s). In some embodiments, the DU 174 may transmit these configuration parameters and / or the first non-LTM TCI state configuration(s) to the CU 172. The CU 172 generates one or more messages (e.g., RRC reconfiguration message(s)) including the configuration parameters and / or the first non- LTM TCI state configuration(s) and transmits the one or more messages to the UE 102 via the DU 174. In other embodiments, the DU 174 directly transmits the configuration parameters and / or the first non-LTM TCI state configuration(s) to the UE 102. 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, thePatent ApplicationAttorney Docket Number 0683-100-WO serving CU configuration includes a MeasConfig IE and / or a RadioBearerConfig IE defined in 3GPP TS 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE. The radio configuration parameters or the RadioBearerConfig IE configures one or more DRBs. In some embodiments, the serving DU configuration includes a CSI-MeasConfig IE or configuration 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 BS 104A and the remaining portion of these configuration parameters from the BS 104.

[0053] In some embodiments, the DU 174 and the UE 102 communicate with each other using first non-LTM TCI state configuration(s), e.g., in the events 302, 318, 320, 324,350, 354, and / or 326. In some embodiments, the DU 174 transmits at least one first non-LTM TCI States Activation / Deactivation command (e.g., MAC CE) to the UE 102 to activate the first non-LTM TCI state configuration(s). The UE 102 activates the first non- LTM TCI state configuration(s) in response to the first non-LTM TCI States Activation / Deactivation command(s). In some embodiments, the DU 174 includes a serving cell ID (e.g., a serving cell index) in each of the first non-LTM TCI States Activation / Deactivation command(s) to identify the first non-LTM TCI state configuration(s). Each of the serving cell ID(s) indicates a respective serving cell of the serving cell(s). In some embodiments, the serving DU configuration includes the serving cell ID(s) and configures association(s) between the serving cell ID(s) and the first non-LTM TCI state configuration(s).

[0054] While communicating with the BS 104A, the UE 102 transmits 304 at least one measurement report to the DU 174. In some embodiments, the measurement report(s) includes measurement results for at least one serving cell (e.g., the cell 124A) of the UE 102 and / or at least one non-serving cell. For each of the measurement report(s), the DU 174 transmits 306 a (first) DU-to-CU message including the measurement report to the CU 172. In some embodiments, the DU-to-CU message(s) of the event 306 is / are F1Patent ApplicationAttorney Docket Number 0683-100-WO application protocol (F1AP) message(s) (e.g., UL RRC Message Transfer message(s)). The 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 additional cell(s). In some embodiments, the serving CU configuration includes at least one measurement configuration. In accordance with the measurement configuration(s), the UE 102 performs measurements and transmits 304 the measurement report(s) to the DU 174. In some embodiments, the measurement configuration(s) includes Layer 3 (L3) measurement configuration(s) (e.g., MeasConfig IE(s)) and the measurement report(s) include L3 measurement report(s).

[0055] After (e.g., in response to) receiving one or some of the measurement report(s) from the UE 102, the CU 172 determines to prepare a first cell (e.g., cell 1 such as the cell 124B) as an LTM candidate (or target) cell for the UE 102. In some embodiments, the BS 104A determines to prepare the first cell for the UE 102 because the measurement report(s) indicates that the first cell could be used by the BS 104A to communicate with the UE 102. In some embodiments, the BS 104A determines to prepare the first cell for the UE 102 because the measurement report(s) indicates that the first cell qualifies to be an LTM 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, the first cell is better in strength and / or quality than the serving cell (e.g., cell 124A), and / or is better in strength and / or quality than the serving cell by a first predetermined threshold, the CU 172 determines to prepare the first cell for the UE 102. Alternatively, the CU 172 determines to prepare the first cell for the UE 102 regardless of whether a measure report is received from the UE 102 or not.

[0056] In response to determining 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. For example, the cell ID 1 is cell global identity (CGI). In another example, the cell ID is a portion of the CGI. In yet another example, the cell ID is a physical cell ID (PCI). In some embodiments, the CU 172 includes an LTM indicator in the first CU-to-DU message to request the DU 174 to prepare the first cell for LTM. In somePatent ApplicationAttorney Docket Number 0683-100-WO embodiments, the CU 172 includes the LTM indicator in an LTM Information Setup IE and includes the LTM Information Setup IE in the first CU-to-DU message. In yet other embodiments, the CU 172 includes the LTM indicator in an LTM Information Modify IE and includes the LTM Information Modify IE in the first CU-to-DU message.

[0057] In response to the first CU-to-DU message, the DU 174 generates a first LTM DU configuration (referred to herein after as LTM DU configuration 1) for the UE 102, which configures the first cell for LTM. In some embodiments, the CU 172 includes a first LTM configuration ID (i.e., referred to herein after as LTM ID 1 ) in the first CU-to-DU message and the DU 174 associates the LTM ID 1 and / or the cell ID 1 with the LTM DU configuration 1. The DU 174 then transmits 310 a second DU-to-CU message including the LTM DU configuration 1 to the CU 172 in response to the first CU-to-DU message. The events 308 and 310 are collectively referred to in FIG. 3 as an LTM preparation procedure 390.

[0058] In some embodiments, the DU 174 includes, in the first DU-to-CU message, the cell ID 1 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. In cases where the CU 172 performs multiple LTM preparation procedures (e.g., the procedure 390 and the LTM preparation procedure 2, ... , N described below) with the DU 174 to prepare multiple LTM candidate cells, the CU 172 may determine that the LTM DU configuration 1 is configured for or associated with the first cell, based on the cell ID 1 in the first DU-to- CU message.

[0059] In some embodiments, the CU 172 does not include an LTM reference DU configuration in the first CU-to-DU message. In such cases, the DU 174 generates an LTM reference DU configuration and includes the LTM reference DU configuration in the first DU-to-CU message. In some embodiments, the DU 174 generates the LTM DU configuration 1 as a delta configuration to augment the LTM reference DU configuration. In other embodiments, the DU 174 generates the LTM DU configuration 1 as a complete configuration, i.e., not on top of the LTM reference DU configuration.

[0060] In some embodiments, the CU 172 includes an LTM reference DU configuration request in the first CU-to-DU message, and the DU 174 generates the LTM reference DU configuration and includes the LTM reference DU configuration in the firstPatent ApplicationAttorney Docket Number 0683-100-WODU-to-CU message in response to the request. In some embodiments, the CU 172 determines whether the UE 102 supports an LTM reference configuration. If the CU 172 determines that the UE 102 supports an LTM reference configuration, the CU 172 includes the LTM reference DU configuration request in the first CU-to-DU message. The DU 174 includes the LTM reference DU configuration in the first DU-to-CU message in response to the LTM reference DU configuration request. Otherwise, if the CU 172 determines that the UE 102 does not support an LTM reference configuration, the CU 172 does not include the LTM reference DU configuration request in the first CU-to-DU message. In this case, the DU 174 may generate the LTM DU configuration 1 as a complete configuration and may not include a / the LTM reference DU configuration in the first DU-to-CU message.

[0061] In other embodiments, the CU 172 transmits an additional CU-to-DU message including the LTM reference DU configuration request to the DU 174 instead of the first CU-to-DU message. In response, the DU 174 includes an additional DU-to-CU message including the LTM reference DU configuration to the CU 172. In yet other embodiments, the DU 174 determines whether the UE 102 supports an LTM reference configuration. If the DU 174 determines that the UE 102 supports an LTM reference configuration, the DU 174 includes the LTM reference DU configuration in the first DU-to- CU message. Otherwise, if the DU 174 determines that the UE 102 does not support an LTM reference configuration, the DU 174 does not include a / the LTM reference DU configuration in the first DU-to-CU message.

[0062] In some embodiments, the CU 172 includes an LTM reference DU configuration in the first CU-to-DU message. In some embodiments, the CU 172 receives the LTM reference DU configuration from an additional DU during an LTM preparation procedure as described above and later for FIG. 4. In other embodiments, the CU 172 is preconfigured with the LTM reference DU configuration. In some embodiments, the DU 174 generates the LTM DU configuration 1 as a delta configuration to augment the LTM reference DU configuration. In other embodiments, the DU 174 ignores the LTM reference DU configuration and generates the LTM DU configuration 1 as a complete configuration, i.e., not on top of the LTM reference DU configuration.

[0063] If the DU 174 generates the LTM DU configuration 1 as a complete configuration, the DU 174 may include a complete configuration indication in the first DU-Patent ApplicationAttorney Docket Number 0683-100-WO to-CU message to indicate that the LTM DU configuration 1 is a complete configuration. In some embodiments, if the first CU-to-DU message does not include a / the LTM reference DU configuration, the CU 172 may determine that the LTM DU configuration 1 as a complete configuration. Otherwise, if the first CU-to-DU message includes a / the LTM reference DU configuration, the CU 172 may determine that the LTM DU configuration 1 is a delta configuration.

[0064] In some embodiments, the LTM reference DU configuration is different from the serving DU configuration. In some embodiments, a portion of the LTM reference DU configuration is the same as a portion of the serving DU configuration and the rest of the LTM reference DU configuration is different from the rest of the serving DU configuration. In yet other embodiments, the LTM reference DU configuration is the same as the serving DU configuration. In some embodiments, the LTM reference DU configuration includes physical layer configuration parameters, MAC configuration parameters, and / or RLC configuration parameters. In some embodiments, the LTM reference DU configuration is the CellGroupConfig IE defined in 3GPP TS 38.331. In other embodiments, the LTM reference DU configuration includes configuration parameters in the CellGroupConfig IE. In some embodiments, the LTM reference DU configuration includes a CSI-MeasConfig IE or configuration parameters for CSI measurement and / or reporting.

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

[0066] To prepare the first cell as an LTM candidate cell for the UE 102, the CU 172 may transmit 312 a second CU-to-DU message to the DU 174, including a CSI resource configuration (e.g., CSI resource configuration 1 ) and / or an LTM SSB configuration (i.e., LTM SSB configuration 1 ) to request the DU 174 to generate one or more CSI report configurations (e.g., (LTM) CSI report configuration(s) 1 ). The CSI resource configuration (e.g., (LTM) CSI resource configuration(s) 1) includes configuration parameters configuring at least one reference signal (RS) transmitted on the first cell. ThePatent ApplicationAttorney Docket Number 0683-100-WORS(s) include SSB(s) and / or CSI-RS(s). The LTM SSB configuration include SSB configuration parameters configuring an SSB frequency, an SSB subcarrier spacing, an SSB periodicity, an SSB half frame index, an SSB System Frame Number (SFN) offset, an SFN initialization time, SSB positions in burst (e.g., ssb-PositionsInBurst) and / or SSB transmit power for SSB(s) transmitted on the first cell. The SSB positions in burst (also called “SSB positions in burst configuration”) indicates the time domain positions of the transmitted SSBs in a half frame with SSB blocks as defined in TS 38.213.

[0067] After (e.g., in response to) receiving the CSI resource configuration, the DU 174 generates one or more CSI report configurations (e.g., (LTM) CSI report configuration(s) 1 ) based on the CSI resource configuration and includes the CSI report configuration(s) in a serving DU configuration (referred to as a second serving DU configuration to distinguish from the serving DU configuration in event 302). In some embodiments, the CSI report configuration(s) configures the UE 102 to transmit CSI reports based on measurements of the RS(s). The DU 174 transmits 314 a second DU-to- CU message including the second serving DU configuration to the CU 172. In some embodiments, the CSI resource configuration comprises (e.g., is or includes) one or more LTM-CSI-ResourceConfig-r18 lEs. In other embodiments, the CSI resource configuration comprises an ltm-CSI-ResourceConfigToAddModList e\d / \E. In some embodiments, the second serving DU configuration is a CellGroupConfig IE.

[0068] In some embodiments, the CU 172 includes the cell ID 1 and / or the LTM ID 1 in the second CU-to-DU message. In one embodiment, the CU 172 does so to indicate that the CSI resource configuration is / are associated with the first cell. In another embodiment, the CU 172 does so for the DU 174 to associate the LTM ID 1 with the first cell, the cell ID 1 , the LTM DU configuration 1 , and / or the CSI report configuration(s). Based on the above embodiment(s), the DU 174 may associate the LTM ID 1 and / or the cell ID 1 with configurations (e.g., LTM DU configuration 1 , the CSI resource configuration, and / or the CSI report configuration(s)) related to the first cell. In such embodiments, the CU 172 may or may not include the LTM ID 1 in the first CU-to-DU message.

[0069] In some alternative embodiments, the CU 172 includes the CSI resource configuration in the first CU-to-DU message and the DU 174 includes the CSI report configuration(s) in the first DU-to-CU message.Patent ApplicationAttorney Docket Number 0683-100-WO

[0070] In some embodiments, the DU 174 transmits the LTM SSB configuration or the SSB configuration parameters to the CU 172, e.g., in the first DU-to-CU message, the second DU-to-CU message, or an additional DU-to-CU message. In some embodiments, the DU 174 transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other embodiments, the DU 174 transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message or the second CU-to-DU message.

[0071] Events 312 and 314 are collectively referred to in FIG. 3 as an LTM CSI report configuration and / or LTM ID configuration procedure 392.

[0072] After receiving the first DU-to-CU message, the CU 172 generates a first LTM candidate configuration (i.e., LTM candidate configuration 1 ) including the LTM DU configuration 1 and generates a first RRC reconfiguration message including the LTM candidate configuration 1 and the LTM ID 1 . In some embodiments, the CU 172 includes LTM CU configuration 1 in the LTM candidate configuration 1 . In other embodiments, the CU 172 does not include an LTM CU configuration in the LTM candidate configuration 1. The CU 172 transmits 316 a third CU-to-DU message including the first RRC reconfiguration message to the DU 174. In turn, the DU 174 transmits 318 the first RRC reconfiguration message to the UE 102. In response, the UE 102 transmits 320 a first RRC reconfiguration complete message to the DU 174. The DU 174 then transmits 322 a third DU-to-CU message including the first RRC reconfiguration complete message to the CU 172.

[0073] If the first DU-to-CU message includes the LTM reference DU configuration, the CU 172 generates an LTM reference configuration including the LTM reference DU configuration. In such cases, the CU 172 may include the LTM reference configuration in the first RRC reconfiguration message. In some embodiments, the CU 172 includes an LTM reference CU configuration in the LTM reference configuration. In such cases, the CU 172 may generate the LTM CU configuration 1 as a delta configuration based on the LTM reference CU configuration. In other embodiments, the CU 172 does not include an LTM reference CU configuration in the LTM reference configuration. In such cases, the CU 172 may generate the LTM CU configuration 1 as a complete configuration. Alternatively, thePatent ApplicationAttorney Docket Number 0683-100-WOCU 172 transmits a second RRC reconfiguration message including the LTM reference configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a second RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322. In some embodiments, if the CU 172 does not receive an LTM reference DU configuration, the CU 172 may generate an LTM reference configuration including only the LTM reference CU configuration. In other embodiments, if the CU 172 does not receive an LTM reference DU configuration, the CU 172 may not generate an LTM reference configuration.

[0074] In some embodiments, if the first DU-to-CU message includes the complete configuration indication, the CU 172 may determine that the LTM DU configuration 1 is a complete configuration. Otherwise, if the first DU-to-CU message does not include the complete configuration indication, the CU 172 may determine that the LTM DU configuration 1 is a delta configuration. In some embodiments, if the LTM DU configuration 1 is a complete configuration, the CU 172 generates the LTM candidate configuration 1 as a complete configuration. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates the LTM candidate configuration 1 as a delta configuration. If the LTM candidate configuration 1 is a complete configuration, the CU 172 includes, in the first RRC reconfiguration message, a complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration. If the LTM candidate configuration 1 is a delta configuration, the CU 172 excludes the complete configuration indication from the first RRC reconfiguration message to indicate that the LTM candidate configuration 1 is a delta configuration.

[0075] If the CU 172 performs the procedure 392, the CU 172 may include the second serving DU configuration in the first RRC reconfiguration message. Alternatively, the CU 172 transmits a third RRC reconfiguration message including the second serving DU configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a third RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322.

[0076] In some embodiments, the CU 172 includes the CSI resource configuration in the first RRC reconfiguration message, the second RRC reconfiguration message, or the third RRC reconfiguration message. In other embodiments, the CU 172 transmits aPatent ApplicationAttorney Docket Number 0683-100-WO fourth RRC reconfiguration message including the CSI resource configuration to the UE 102 via the DU 174, similar to the events 316 and 318. In response, the UE 102 transmits a fourth RRC reconfiguration complete message to the UE 102 via the DU 174, similar to the events 320 and 322.

[0077] In some embodiments, the DU 174 transmits a DU-to-CU message to the CU 172, including early synchronization information for the UE 102. The DU-to-CU message may be the first DU-to-CU message, the second DU-to-CU message, or a fourth DU-to-CU message. In some embodiments, the DU 174 transmits the fourth DU-to-CU message in response to receiving a fourth CU-to-DU message from the CU 172. In other embodiments, the DU 174 transmits the fourth DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message or the second CU-to-DU message. In one embodiment, the DU 174 does so, if the DU 174 determines that the UE 102 supports (i.e., is capable of) early UL synchronization with an LTM candidate cell (e.g., early TA acquisition with an LTM candidate cell, early RA on an LTM candidate cell, or UE measured TA). Otherwise, if the DU 174 determines that the UE 102 does not support the early UL synchronization with an LTM candidate cell, the DU 174 does not transmit the early synchronization information to the CU 172.

[0078] In other embodiments, the CU 172 transmits a CU-to-DU message including an early synchronization information request (e.g., an IE) to the DU 174, and the DU 174 includes the early synchronization information in the DU-to-CU message in response to the early synchronization information request. The CU-to-DU message may be the first CU-to-DU message, the second CU-to-DU message, or the fourth CU-to-DU message. In one embodiment, the CU 172 does so if the CU 172 determines that the UE 102 supports the early UL synchronization with an LTM candidate cell. Otherwise, if the CU 172 determines that the UE 102 does not support the early UL synchronization with an LTM candidate cell, the CU 172 does not request the DU 174 to provide the early synchronization information for the UE 102. If the CU 172 receives the early synchronization information, the CU 172 includes the early synchronization information in the first, second, third, or fourth RRC reconfiguration message. Alternatively, the CU 172 transmits a fifth RRC reconfiguration message including the early synchronization information to the UE 102 via the DU 174, similar to the events 316 and 318. In response,Patent ApplicationAttorney Docket Number 0683-100-WO the UE 102 transmits a fifth RRC reconfiguration complete message to the CU 172 via the DU 174, similar to the events 320 and 322.

[0079] In some embodiments, the early synchronization information includes a RACH configuration (i.e., RACH configuration 1 ) and / or one or more TCI state configurations (i.e., TCI state configuration(s) 1 ). In some embodiments, the early synchronization information request may include a request for a RACH configuration. If the early synchronization information request includes the request for a RACH configuration, the DU 174 includes the RACH configuration in the early synchronization information or in the DU-to-CU message (e.g., be the first, second, or fourth DU-to-CU message).Otherwise, if the early synchronization information request does not include the request for a RACH configuration, the DU 174 neither includes the RACH configuration in the early synchronization information nor in the DU-to-CU message.

[0080] In some embodiments, the CU 172 includes, in the first, second, third, fourth, and / or fifth RRC reconfiguration messages, one or more other LTM related configurations for the first cell. For example, the other LTM related configuration(s) include a PCI of the first cell and / or the LTM SSB configuration.

[0081] The events 316, 318, 320, and 322 in FIG. 3 are collectively referred to as an LTM configuration delivery procedure 394. The second, third, fourth, and / or fifth RRC reconfiguration message(s) and the second, third, fourth, and / or fifth RRC reconfiguration complete message(s), the related CU-to-DU message(s), and / or the related DU-to-CU message(s) are also considered as part of the LTM configuration delivery procedure 394. In some embodiments, the RRC reconfiguration message and the RRC reconfiguration complete message described above are an RRCReconfiguration message and an RRCReconfigurationComplete message, respectively.

[0082] 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. In some embodiments, the second CU-to-DU message is a UE Context Modification Request message, and the second DU-to-CU message is a UE Context Modification Response message or a 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 UEPatent ApplicationAttorney Docket Number 0683-100-WOContext Modification Required message. In some embodiments, the third CU-to-DU message is a DL RRC Message Transfer message. In other embodiments, the third CU- to-DU message is a UE Context Modification Request message. In some embodiments, the third DU-to-CU message is a UL RRC Message Transfer message. In other embodiments, the third DU-to-CU message is a UE Context Modification Response message.

[0083] In some embodiments, the LTM reference CU configuration is different from the serving CU configuration. In some embodiments, a portion of the LTM reference CU configuration is the same as a portion of the serving CU configuration and the rest of the LTM reference CU configuration is different from the rest of the serving CU configuration. In yet other embodiments, the LTM reference CU configuration is the same as the serving CU configuration.

[0084] In some embodiments, the LTM reference CU configuration 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 defined in 3GPP TS 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE.

[0085] In some embodiments, the LTM CU configuration 1 and / or the LTM reference CU configuration include PDCP configuration parameters, measurement configuration parameters, and / or radio bearer configuration parameters. In some embodiments, the LTM CU configuration 1 or the LTM reference CU configuration includes a MeasConfig IE and / or a RadioBearerConfig IE defined in 3GPP TS 38.331 or includes configuration parameters in the MeasConfig IE and / or RadioBearerConfig IE.

[0086] 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 I E(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 DUPatent ApplicationAttorney Docket Number 0683-100-WO configuration 1 is CellG roupConfig IE defined in 3GPP TS 38.331. In other embodiments, the LTM DU configuration 1 includes configuration parameters in the CellGroupConfig IE.

[0087] In some embodiments, the LTM DU configuration 1 includes a first L1 measurement configuration (e.g., a CSI-MeasConfig IE) and / or at least one first TCI state configuration. In other embodiments, the LTM CU configuration 1 includes the first TCI state configuration(s). In some embodiments, the first L1 measurement configuration includes at least one first RS resource configuration and / or at least one first report configuration. In some embodiments, the first RS resource configuration(s) 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 first RS resource configuration(s) includes an RS resource configuration ID. In some embodiments, the first RS resource configuration(s) is / are (similar to) CSI-ResourceConfig IE(s). In some embodiments, the first report configuration(s) configures one or more UL resources (e.g., PUCCH resources or PUSCH resources) on the first cell for the UE 102 to transmit measurement results (e.g., CSI reports or LTM CSI reports). In some embodiments, each of the first report configuration(s) includes one or more RS resource configuration IDs identifying one or more RS resource configurations included in the first RS resource configuration(s). In some embodiments, each of the first TCI state configuration(s) configures a TCI state that associates one or two DL RSs with a corresponding quasi-colocation (QCL) type. The DL RS(s) are associated with the cell 1 .

[0088] After receiving the LTM-related configurations and the second serving DU configuration or after receiving the RRC reconfiguration message(s) described above, the UE 102 performs measurements on at least one first RS, generates at least one first L1 measurement result based on the measurements, and transmits 324 at least one first L1 measurement report including the first L1 measurement result(s) to the DU 174. The first RS(s) may include SSB(s) and / or CSI-RS(s). In some embodiments, the first RS(s) and / or transmission pattern(s) of the first RS(s) are configured in the CSI report configuration(s), the LTM SSB configuration, and / or the CSI resource configuration. The UE 102 performs the measurements on the first RS(s) in accordance with the CSI report configuration(s), the LTM SSB configuration, and / or the CSI resource configuration.Patent ApplicationAttorney Docket Number 0683-100-WO

[0089] After receiving the LTM-related configurations and the second serving DU configuration or after receiving the RRC reconfiguration message(s) described above, the UE 102 performs measurements on at least one second RS, generates at least one second L1 measurement result based on the measurements, and transmits at least one second L1 measurement report including the first L1 measurement result(s) to the DU 174. The second RS(s) may include SSB(s) and / or CSI-RS(s). In some embodiments, the second RS(s) and / or transmission pattern(s) of the second RS(s) are configured in one or more second CSI report configurations and / or one or more second CSI resource configuration that are included in the serving DU configuration 302 and / or the second serving DU configuration. The UE 102 performs the measurements on the second RS(s) in accordance with the second CSI report configuration(s) and / or the second CSI resource configuration(s). The second CSI report configuration(s) may include non-LTM CSI report configuration(s) and / or LTM CSI report configuration(s). The second CSI resource configuration(s) may include non-LTM CSI resource configuration(s) and / or LTM CSI resource configuration(s).

[0090] After transmitting the RACH configuration to the UE 102 via the CU 172, the DU 174 may transmit 350 a PDCCH order to the UE 102 to command the UE 102 to transmit an RA preamble on the first cell. In response to the PDCCH order, the UE 102 transmits 352 the RA preamble on the first cell. The DU 174 includes PDCCH order information in the PDCCH order. The PDCCH order information includes an RA preamble index (e.g., a first RA preamble index), a UL or supplemental UL (UL / SUL) indicator, an SSB index, and / or a physical RACH (PRACH) mask index. In one embodiment, the SSB index is a unique number assigned to an SSB in an SSB set. In some embodiments, the DU 174 indicates the LTM ID 1 in the PDCCH order to indicate the first cell. The UE 102 identifies the first cell based on the LTM ID 1 in the PDCCH order and transmits 352 to the DU 174, the RA preamble on the first cell, using the PDCCH order information. Correspondingly, the DU 174 receives 352 the RA preamble in accordance with the PDCCH order information. In some embodiments, the DU 174 may determine the SSB index, based on L1 measurement report(s) 324, and / or the CSI resource configuration, the CSI report configuration, and / or the LTM SSB configuration. In some embodiments, the L1 measurement report(s) may include the SSB index. In other embodiments, the L1Patent ApplicationAttorney Docket Number 0683-100-WO measurement report(s) include an SS / PBCH Block Resource Indicator (SSBRI) corresponding to the SSB index. Thus, the DU 174 determines the SSB index based on the SSBRI.

[0091] In some embodiments, the PDCCH order includes a RA preamble index, a UL / SUL indicator, an SSB index, a PRACH mask index, and a cell indicator. In some embodiments, the cell indicator is log2C + 1)] bit-long and indicates the cell for the corresponding PRACH transmission if the UE is configured with higher layer parameter EarlyUISyncConfig, where C is the number of candidate cells configured with higher layer parameter EarlyUISyncConfig-, 0 bit otherwise. The bit field index 0 of the cell indicator field is mapped to the serving cell, and other bit field indexes are mapped to the candidate cells configured with higher layer parameter EarlyUISyncConfig according to an ascending order of a candidate identity configured by the LTM ID (e.g., Itm-Candidateld), with the bit field index 1 mapped to the candidate cell with the smallest candidate identity.

[0092] In some embodiments, the DU 174 determines whether to transmit the PDCCH order based on the L1 measurement result(s) 324. In some embodiments, if the L1 measurement result(s) indicate that the first cell qualifies for the UE 102 to perform RA for early UL synchronization, the DU 174 transmits the PDCCH order. Otherwise, if the L1 measurement result(s) indicate that the first cell does not qualify for the UE 102 to perform RA for early UL synchronization, the DU 174 refrains from transmitting the PDCCH order. In other embodiments, if the L1 measurement result(s) indicate that the first cell qualifies for the UE 102 to access, the DU 174 transmits the PDCCH order. Otherwise, if the L1 measurement result(s) indicate that the first cell does not qualify for the UE 102 to access, the DU 174 refrains from transmitting the PDCCH order. In yet other embodiments, the DU 174 transmits the PDCCH order after receiving 320 the RRC reconfiguration complete message, regardless of the L1 measurement result(s) 324.

[0093] After transmitting 324 the L1 measurement report(s) or transmitting 352 the RA preamble, the UE 102 may transmit 354 an additional L1 measurement report(s) to the DU 174, similar to the event 324. In one embodiment, the DU 174 determines to command the UE 102 to perform an LTM cell switch to the first cell based on the additional L1 measurement report(s) and / or the L1 measurement report(s) 324. In response to the determination, the DU 174 generates an LTM Cell Switch Command (e.g., a MAC CE)Patent ApplicationAttorney Docket Number 0683-100-WO including the LTM ID 1 and transmits 326 the LTM Cell Switch Command to the UE 102. In response to the determination, the DU 174 may transmit 328 a DU-to-CU Cell Switch Notification message to the CU 172. In response to the LTM Cell Switch Command, the UE 102 performs an LTM cell switch to the first cell. In the LTM cell switch, the UE 102 accesses 332 the first cell and transmits 336 an RRC reconfiguration complete message to the DU 174 via the first cell. The DU 174 transmits 338 a DU-to-CU message (e.g., UL RRC Message Transfer message) including the RRC reconfiguration complete message to the CU 172. When the UE 102 receives the LTM Cell Switch Command, the UE 102 identifies the LTM candidate configuration 1 from the LTM ID 1 and accesses 332 the first cell using the LTM candidate configuration 1. Depending on embodiments, the UE 102 may stop communicating on the serving cell(s) in response to the LTM Cell Switch Command. In turn, the DU 174 transmits a fifth DU-to-CU message including the RRC reconfiguration complete message to the CU 172. When the DU 174 detects the UE 102 accesses the first cell in the event 332, the DU 174 may transmit 334 an Access Success message to the CU 172 to indicate that the UE 102 has accessed the first cell.

[0094] In some embodiments, the DU 174 includes, in the LTM Cell Switch Command, a TA value for UL synchronization with the first cell. In one embodiment, the DU 174 derives the TA value based on the RA preamble (e.g., reception timing of the RA preamble). In another embodiment, the DU 174 derives the TA value from an UL transmission on the serving cell (e.g., the cell 124A) from the UE 102. The UE 102 applies the TA value to synchronize with the first cell in UL transmission. After applying the TA value, the UE 102 transmits 340 the first UL transmission on the first cell based on the LTM candidate configuration 1 without performing an RA procedure on the first cell. In some embodiments, the UE 102 transmits the first UL transmission on the first cell using a UL grant. In such cases, the first UL transmission is a PUSCH transmission. In some embodiments, the PUSCH transmission includes the RRC reconfiguration complete message 336. In some embodiments, the UL grant is a configured grant and the LTM candidate configuration 1 or the LTM DU configuration 1 includes the configured grant configuration configuring the configured grant. In other embodiments, the UL grant is a dynamic grant that the UE 102 receives on a PDCCH on the first cell. After transmitting the first UL transmission, the UE 102 receives a PDCCH transmission addressing to a C-RNTIPatent ApplicationAttorney Docket Number 0683-100-WO of the UE 102 and determines that the LTM cell switch is completed successfully in response to receiving the PDCCH transmission.

[0095] The PDCCH transmission may include a UL grant or a DL assignment. In the case of the UL grant, the UE 102 transmits a PUSCH transmission to the DU 174 on the first cell using the UL grant. In the case of the DL assignment, the DU 174 transmits a PDSCH transmission to the UE 102 on the first cell in accordance with the DL assignment. The DU 174 may transmit 334 the Access Success message to the CU 172 after receiving (e.g., in response to) the first UL transmission, transmitting the PDCCH transmission, receiving the PUSH transmission or transmitting the PDSCH transmission.

[0096] In other embodiments, the DU 174 does not include a TA value in the LTM Cell Switch Command. If the LTM Cell Switch Command does not include a / the TA value, the UE 102 performs 332 an RA procedure on the first cell in accordance with the RA configuration parameters. In some embodiments, the RA configuration parameters are included in the LTM candidate configuration 1 or the LTM DU configuration 1 . In some embodiments, the RA configuration parameters configure PRACH resources, an association between SSB and PRACH resources, and / or one or more PRACH occasions. If the UE 102 successfully completes the RA procedure, the UE 102 determines the LTM cell switch to the first cell is completed successfully. Depending on embodiments and / or the RA configuration parameters, the RA procedure may be a four-step RA procedure or a two-step RA procedure. During the four-step RA procedure, the UE 102 transmits a Message 3 on the first cell and the DU 174 transmits a Message 4 on the first cell to the UE 102 in response. During the two-step RA procedure, the UE 102 transmits a Message A on the first cell and the DU 174 transmits a Message B to the UE 102 on the first cell in response. The UE 102 may include the RRC reconfiguration complete message 336 in the Message 3 or Message A. Alternatively, the UE 102 transmits 336 the RRC reconfiguration complete message after completing the RA procedure. The DU 174 may transmit 334 the Access Success message to the CU 172, after receiving the Message 3, Message A or the RRC reconfiguration complete message 336 or transmitting the Message 4 or Message B.

[0097] After successfully completing the LTM cell switch to the first cell as described above, the UE 102 communicates 340 with the DU 174 and the CU 172 via thePatent ApplicationAttorney Docket Number 0683-100-WO first cell, using the LTM candidate configuration 1 . In the case of the LTM reference configuration, the UE 102 applies the LTM reference configuration first and then applies the LTM candidate configuration 1 to augment the LTM reference configuration.

[0098] In some embodiments, each of the TCI state configuration(s) includes a TCI state ID. In some embodiments, the DU 174 includes, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI state ID indicating a first one of the TCI state configuration(s). The UE 102 identifies the first one of the TCI state configuration(s) based on the first TCI state ID and applies the first TCI state configuration to communicate UL transmissions and / or DL transmissions with the DU 174 in the events 332, 336, and / or 340. The DU 174 applies the first TCI state configuration to communicate UL transmissions and / or DL transmissions with the UE 102 in the events 332, 336, and / or 340. In other embodiments, in case that separate TCI states are used, the DL TCI State and the UL TCI state use different TCI State IDs. In such cases, the DU 174 includes, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI State ID for DL and / or a second TCI State ID for UL. The UE 102 identifies the first and the second of the TCI state configuration(s) based on the first and / or second TCI state ID and applies the first and / or the second TCI state configuration to communicate DL transmissions and UL transmissions, respectively, with the DU 174 in the events 332, 336, and / or 340. The DU 174 applies the first and / or the second TCI state configuration to communicate DL transmissions and UL transmissions, respectively, with the UE 102 in the events 332, 336, and / or 340.

[0099] In some embodiments, the CU 172 may prepare additional cell(s) (i.e., cell(s) 2, ... , N) as LTM candidate cell(s) for the UE 102 with the DU 174, before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 390 or 392, as described above, where N is an integer larger than 1 . For example, the CU 172 performs additional LTM preparation procedure(s) 2, ... , N with the DU 174 to prepare the cell(s) 2, ... , N respectively. Each of the LTM preparation procedure(s) 2, ... , N is similar to the procedure 390. In the LTM preparation procedure(s) 2, ... , N, the CU 172 receives LTM DU configuration(s) 2, ... , N configuring the cell(s) 2, ... , N for LTM, respectively. The CU 172 generates LTM candidate configuration(s) 2, ... , N including the LTM DU configuration(s) 2, ... N, respectively. The CU 172 assigns LTM ID(s) 2, ... , N to identify thePatent ApplicationAttorney Docket Number 0683-100-WOLTM DU configuration(s) 2, , N and the LTM candidate configuration(s) 2, ... , N, respectively. The CU 172 may obtain CSI resource configuration 2, ... , N and perform CSI report configuration and / or LTM ID configuration procedure(s) 2, ... , N with the DU 174 to obtain the CSI report configuration(s) 2, ... , N, respectively, as described with regard to the CSI resource configuration 1 and the CSI report configuration(s) 1 . The CU 172 may obtain RACH configuration 2, ... , N for the cell(s) 2, ... , N respectively, as described for the RACH configuration 1. The CU 172 may obtain TCI state configuration(s) 2, ... , N for the cell(s) 2, ... , N respectively, as described for the TCI state configuration(s) 1 . Each of the CSI report configuration and / or LTM ID configuration procedure(s) 2, ... , N is similar to the procedure 392. The CU 172 may obtain LTM SSB configuration 2, ... , N for the cell(s) 2, ... , N, respectively, as described for the LTM SSB configuration 1. In some embodiments, the CU 172 may perform LTM configuration delivery procedure 2, ... , N with the UE 102 to transmit a list of the {LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained)}, ... , {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained)}, respectively. Each of the LTM configuration delivery procedure 2, ... , N is similar to the procedure 394. In other embodiments, the CU 172 includes the list in the first RRC reconfiguration message.

[0100] In some embodiments, after receiving 334 the Access Success message or receiving 338 the DU-to-CU message, the CU 172 may transmit 342 a CU-to-DU message to the DU 174. In one embodiment, the CU 172 transmits 342 the CU-to-DU message to release radio resources and / or configurations of the serving cell(s) configured for the UE 102. In another embodiment, the CU 172 transmits 342 the CU-to-DU message to release some of the LTM candidate cell(s) 2, ... , N. In response to the CU-to-DU message 342, the DU 174 transmits 344 a DU-to-CU message to the CU 172. In some embodiments, the CU-to-DU message 342 and the DU-to-CU message 344 are a UE Context Modification Request message and a UE Context Modification Response message, respectively

[0101] In some embodiments, an LTM ID in a PDCCH order, an LTM Cell Switch Command, and an RRC reconfiguration message are represented in different formats. ForPatent ApplicationAttorney Docket Number 0683-100-WO example, the PDCCH order or the LTM Cell Switch Command includes a first field to include the LTM ID 1 and the first RRC reconfiguration message includes a second field to include the LTM ID 1. In some embodiments, the first field and the second field have different formats or coding schemes. For example, the first field uses a binary format (i.e., 3 bits) with a value range of 0, ... , 7 and the second field uses an integer format with a value range of 1 , ... , 8. In this example, the first field with binary value 000b is equivalent to the second field with integer value 1 , the first field with binary value 001b is equivalent to the second field with integer value 2, ... , the first field with binary value 111 b is equivalent to the second field with integer value 8.

[0102] The events 304, 306, 390, 392, 394, and 324 are collectively referred to in FIG. 3 as an intra-CU intra-DU LTM configuration procedure 396. The events 304, 306, 390, 392, 394, 324, 350, 352, 354, 326, 328, 332, 334, 336, 338, and 340 are collectively referred to in FIG. 3 as an intra-CU intra-DU LTM procedure 380.

[0103] FIG. 4 shows a scenario 400 in which the BS 104A includes a CU 172, a serving S-DU 174A, and a candidate DU (C-DU) 174B. The S-DU 174A operates the cell 124A and optionally additional cell(s), while the C-DU 174B operates a first cell (e.g., cell 125). The scenario 400 is an intra-CU inter-DU scenario, similar to the scenario 300. Thus, the descriptions for the scenario 300 may generally apply to the scenario 400. Some descriptions for the DU 174 in FIG. 3 may apply to the S-DU 174A in FIG. 4, and some descriptions for the DU 174 in FIG. 3 may apply to the C-DU 174B. The differences between the scenarios 300 and 400 are described below.

[0104] Initially, the UE 102 communicates 402 with the S-DU 174A on one or more serving cells (e.g., the cell 124A and / or other cell(s)) using a serving DU configuration and communicates with the CU 172 via the S-DU 174A using a serving CU configuration. In some embodiments, the CU 172 and S-DU 174A might perform the LTM configuration procedure 396 or the LTM procedure 380 with the UE 102, as described above with regard to FIG. 3. For procedure 380, the UE 102 may perform an LTM cell switch to the first cell (e.g., cell 124B) as described in FIG. 3. Upon successfully completing the LTM cell switch, the first cell becomes a serving cell and cell 124A and / or the other cell(s) is / are no longer serving cell(s) for the UE 102. For procedure 396, the UE 102 does not perform an LTM cell switch. During communication 402, the UE 102 transmits 404, 406 at leastPatent ApplicationAttorney Docket Number 0683-100-WO one measurement report (e.g., L3 measurement report(s)) to the CU 172 via the S-Dll 174A. Based on the measurement report(s), the CU 172 determines to prepare cell 1 (e.g., cell 125 operated by the C-DU 174B) for LTM for the UE 102. Cell 1 is identified by a cell ID (i.e., cell ID 1 ). In response to the determination, the CU 172 performs 490 an LTM preparation procedure with the C-DU 174B to (request the C-DU 174B to) prepare the cell 1 as an LTM candidate cell for the UE 102. In the LTM preparation procedure 490, the CU 172 transmits a first CU-to-DU message including a cell ID 1 of the cell 1 to the C-DU 174B to request the C-DU 174B to prepare the cell 1 as an LTM candidate cell for the UE 102, similar to the event 308. In response, the C-DU 174B transmits a first DU-to-CU message including an LTM DU configuration (e.g., LTM DU configuration 1 ) to the CU 172, similar to the event 310. The CU 172 may or may not request an LTM reference DU configuration in the first CU-to-DU message, as described in FIG. 3. The C-DU 174B may or may not include an LTM reference DU configuration in the first DU-to-CU message, as described in FIG. 3.

[0105] In some embodiments, if the CU 172 receives an LTM reference DU configuration from the S-DU 174A as described in FIG. 3, the CU 172 may include the LTM reference DU configuration in the first CU-to-DU message and the C-DU 174B may generate the LTM DU configuration as a delta configuration based on the LTM reference DU configuration. In such cases, the C-DU 174B does not transmit an LTM reference DU configuration for the UE 102 to the CU 172. In other embodiments, the CU 172 receives an LTM reference DU configuration from the C-DU 174B, e.g., in the first DU-to-CU message or an additional DU-to-CU message as described in FIG. 3. In such cases, the CU 172 may generate an LTM reference configuration including the LTM reference DU configuration. The CU 172 may or may not include an LTM reference CU configuration in the LTM reference configuration.

[0106] To prepare cell 1 for LTM, the CU 172 may perform 492 an LTM CSI report configuration and / or LTM ID configuration procedure with the S-DU 174A. For the procedure 492, the CU 172 transmits a second CU-to-DU message including a CSI resource configuration (e.g., CSI resource configuration 1 ) and / or an LTM SSB configuration (i.e., LTM SSB configuration 1 ) to the S-DU 174A, similar to the event 312. In response, the S-DU 174A transmits a second DU-to-CU message including one or morePatent ApplicationAttorney Docket Number 0683-100-WOCSI report configurations (e.g., CSI report configuration(s) 1) to the CU 172. In some embodiments, the CU 172 generates an LTM candidate configuration (e.g., LTM candidate configuration 1 ) including the LTM DU configuration and assigns an LTM ID (e.g., LTM ID 1 ) for identifying the LTM DU configuration and / or the LTM candidate configuration as described in FIG. 3. In some embodiments, the CU 172 includes {the LTM ID 1 , the cell ID 1 } as a tuple in the second CU-to-DU message. In some embodiments, the LTM SSB configuration or SSB configuration parameters for the cell 1 might include at least one of an SSB frequency, an SSB subcarrier spacing, an SSB transmit power, an SSB periodicity, an SSB half frame index, an SSB, an SFN offset, and an SFN initialization time, and a SSB positions in burst configuration (e.g., a bit map). The SSB positions in burst configuration indicates the time domain positions of the transmitted SSBs in a half frame with SSB blocks as defined in TS 38.213.

[0107] To prepare cell 1 as an LTM candidate cell for the UE 102, the CU 172 may receive early synchronization information for the cell 1 in a DU-to-CU message (e.g., the first DU-to-CU message or an additional DU-to-CU message) from the C-DU 174B. In some embodiments, the C-DU 174B transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other embodiments, the C-DU 174B transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message. The early synchronization information includes an RACH configuration (e.g., RACH configuration 1 ) and / or at least one TCI state configuration (e.g., TCI state configuration(s) 1), as described in FIG. 3. In some embodiments, the C-DU 174B includes in the early synchronization information or in the DU-to-CU message, the PDCCH order information (PDCCH order information 1 ) for early UL synchronization with the first cell. In some embodiments, the PDCCH order information includes multiple RA preamble indexes (e.g., the first RA preamble index and additional RA preamble index(es)).

[0108] In some embodiments, the CU 172 may receive the LTM SSB configuration or SSB configuration parameters in the LTM SSB configuration from the C-DU 174B, e.g., in the first DU-to-CU message or an additional DU-to-CU message. In some embodiments, the CU 172 may receive a PCI of the cell 1 from the C-DU 174B in the first DU-to-CU message or the additional DU-to-CU message. In some embodiments, the C-Patent ApplicationAttorney Docket Number 0683-100-WODU 174B transmits the additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other embodiments, the C-DU 174B transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message.

[0109] As described in FIG. 3, the CU 172 performs 494 LTM configuration delivery procedure with the UE 102 to transmit the LTM ID 1 and the LTM candidate configuration to the UE 102. In some embodiments, the CU 172 transmits {LTM ID, the LTM candidate configuration} as a tuple in a first RRC reconfiguration message in the procedure 494. Depending on the embodiments, the CU 172 may include the LTM reference configuration, the CSI report configuration(s), the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 to the UE 102 in the first RRC reconfiguration message and / or other RRC reconfiguration message(s) transmitted to the UE 102, as described for FIG. 3. The CU 172 includes the LTM ID in the first RRC reconfiguration or the other RRC reconfiguration message(s) to indicate the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 are associated with the cell 1 . For example, the CU 172 includes the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 in the tuple. In another example, the CU 172 includes {LTM ID, the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1} as a tuple in the other RRC reconfiguration message(s). In response to each of the other RRC reconfiguration message(s), the UE 102 transmits an RRC reconfiguration complete message to the CU 172 via the S-DU 174A.

[0110] In some embodiments, the PDCCH order information includes a frequency domain resource assignment, an RA preamble index, an UL / SUL indicator, an SSB index and / or a PRACH mask index. In some embodiment, the PDCCH order information is a dedicated RACH configuration and resources that the C-DU 174B reserves (e.g., in the form of a RACH-ConfigDedicated or rach-ConfigDedicated IE or field as defined in the TS 38.331 ). The CU 172 may transmit a CU-to-DU message (e.g., the second CU-to-DU message or an additional CU-to-DU message) including the PDCCH order information toPatent ApplicationAttorney Docket Number 0683-1 OO-WO the S-DU 174A. In some embodiments, the CU 172 includes the LTM ID 1 or the cell ID 1 in the CU-to-DU message to indicate that the PDCCH order information is associated with the LTM ID 1 or the cell ID 1 . For example, the CU 172 includes {the cell ID 1 , the PDCCH order information} as a tuple in the CU-to-DU message. In the case of the additional CU- to-DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response. The S-DU 174A transmits 450 a PDCCH order to the UE 102, based on the PDCCH order information and / or the RACH configuration. For example, the PDCCH order includes the PDCCH order information. In another example, the S-DU 174A determines the content of the PDCCH order based on the PDCCH order information and / or the RACH configuration and / or the L1 measurement report(s). In some embodiments, the S-DU 174A may determine a first SSB index included in the PDCCH order (i.e., a first PDCCH order), based on L1 measurement report(s) 424, the CSI resource configuration, the CSI report configuration, the LTM SSB configuration, and / or the PDCCH order information. In some embodiments, the S-DU 174A determines a first PRACH mask index and / or a first UL / SUL indicator, based on the RACH configuration. In some embodiments, the RACH configuration is the Early UL Sync Configuration IE or the Early UL Sync Configuration for SUL IE. In some embodiments, the RACH configuration includes a parameter (e.g., ssb-PerRACH-Occasion) which indicates at most 8 PRACH occasions for a SSB. In other embodiments, the S-DU 174A determines the first PRACH mask index based on the PDCCH order information. The first PRACH mask index indicates one or more RACH occasions associated with the first SSB index for the PRACH transmission as specified in TS 38.321 . The S-DU 174A includes the first SSB index, the first PRACH mask index and the first UL / SUL indicator in the first PDCCH order. For multiple RA preamble indexes configured in the PDCCH order information, the S-DU 174A selects one (e.g., the first RA preamble index) of the RA preamble indexes and include the selected RA preamble index in the first PDCCH order. In some embodiments, the S-DU 174A includes the LTM ID 1 (e.g., an indication of the LTM ID1 ) in the first PDCCH order to indicate the cell 1 . In the case of the additional CU-to-DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response. The UE 102 transmits 452 a first RA preamble to the C-DU 174B on the cell 1 , using the RACH configuration and / or the PDCCH order. The first RA preamble is identified or indicated byPatent ApplicationAttorney Docket Number 0683-100-WO the first RA preamble index. The C-Dll 174B derives a first TA value based on the first RA preamble. The C-DU 174B transmits 456 a DU-CU TA Information Transfer message including the first TA value to the CU 172. The CU 172 in turn transmits 458 a CU-DU TA Information Transfer message including the TA value to the S-DU 174A. In some embodiments, the C-DU 174B includes in the message 458, the cell ID 1 , the first RA preamble index, a first RA radio network temporary identifier (RA-RNTI), and / or a DU ID of the S-DU 174A in the message 456. In such cases, the CU 172 includes the cell ID 1 , the first RA preamble index, the first RA-RNTI, and / or the DU ID of the S-DU 174A.

[0111] In some embodiments, the C-DU 174B determines the first RA-RNTI based on a PRACH occasion in which the C-DU 174B receives the RA preamble 452. In some embodiments, the C-DU 174B calculates the first RA-RNTI as:RA-RNTI = 1 + s_id + 14 x t_id + 14 x 80 x fjd + 14 x 80 x 8 x ul_carrier_id where s_id is the index of the first OFDM symbol of the PRACH occasion (0 < s_id < 14), t_id is the index of the first slot of the PRACH occasion in a system frame (0 < t_id < 80), where the subcarrier spacing to determine t_id is based on the value of specified in clause 5.3.2 in 3GPP TS 38.211 for p = {0, 1 , 2, 3}, and for p = {5, 6}, t_id is the index of the 120 kHz slot in a system frame that contains the PRACH occasion (0 < t_id < 80), f_id is the index of the PRACH occasion in the frequency domain (0 < f_id < 8), and ul_carrier_id is the UL carrier used for the RA Preamble transmission (0 for NUL carrier, and 1 for SUL carrier).

[0112] In some embodiments, the S-DU 174A determines whether the first TA value is for the UE 102 based on the cell ID 1 , the first RA preamble index, and / or the first RA-RNTI in the CU-DU TA Information Transfer message. In some embodiments, the S- DU 174A only configures the first RA preamble index for the UE 102 and does not configure the first RA preamble index for other UE(s). In such cases, the S-DU 174A might determine the first TA value is for the UE 102 because the first RA preamble index received in the CU-DU TA Information Transfer message is identical to the first RA preamble index in the PDCCH order. If the CU-DU TA Information Transfer message includes a second RA preamble index associated with the first TA value instead of the first RA preamble index, the S-DU 174A determines the first TA value is not provided for the UE 102. In other embodiments, the S-DU 174A configures the first RA preamble index forPatent ApplicationAttorney Docket Number 0683-100-WO the UE 102 and other UE(s) to transmit on different cells. That is, the UE 102 is the only UE that transmits the first RA preamble on the cell 1 and the other UE(s) transmit the first RA preamble on cell(s) other than the cell 1 . In such cases, the S-Dll 174A might determine the TA value is for the UE 102 based on the cell ID 1 and the first RA preamble index.

[0113] In yet other embodiments, the S-DU 174A configures the first RA preamble index for the UE 102 and other UE(s) to transmit on the cell 1 in different time and / or frequency resources (e.g., PRACH occasions). The time and / or frequency resources may be represented in s_id, t_id and / or f_id as described above for the C-DU 174B. In such cases, the S-DU 174A determines whether the first TA value is for the UE 102 based on the cell ID 1 , the first RA preamble index and the first RA-RNTI. Based on the first RA preamble index and the cell ID 1 in the CU-DU TA Information Transfer message, the S- DU 174A might determine that the first TA value is derived from the first RA preamble transmitted on the cell 1 . The S-DU 174A determines whether the first TA value is for the UE 102 or the other UE based on the first RA-RNTI. In some embodiments, the S-DU 174A calculates one or more RA-RNTIs (i.e., values) based on time resource(s) (e.g., allowed PRACH occasion(s)) configured in the first PDCCH order. If the first RA-RNTI (i.e., value) is (equal to) one of the calculated RA-RNTI(s) (i.e., value(s)), the S-DU 174A determines the first RA-RNTI addresses the UE 102. The S-DU 174A determines that the first TA value is for the UE 102 in response to determining that the first RA-RNTI addresses the UE 102. Otherwise, if the first RA-RNTI (i.e., value) is not one of the calculated RA-RNTI(s) (i.e., value(s)), the received RA-RNTI might address the other UE (e.g., an UE not shown in FIG. 1A and FIG. 4). The S-DU 174A might transmit a second PDCCH order to the other UE, including the first RA preamble index, a second PRACH mask, and the LTM ID 1.

[0114] In yet other embodiments, the S-DU 174A calculates the one or more RA- RNTIs based on the allowed PRACH occasion(s) corresponding to both the first SSB index and the first PRACH mask index configured in the first PDCCH order. To determine the allowed PRACH occasion(s), the S-DU 174A obtains the exact transmitted SSBs from the SSB positions in burst and constructs / obtains the mapping of the SSB indexes to valid PRACH occasions as specified in the TS 38.213 and TS 38.212. The constructedPatent ApplicationAttorney Docket Number 0683-100-WO mapping of SSB indexes may be illustrated as in Figs. 14A or 14B. The S-DU 174A calculates the one or more RA-RNTI(s) based on the determination of the allowed PRACH occasion(s) similar to the calculation of the first RA-RNTI above. The S-DU 174A determines that the first TA value is for the UE 102 in response to determining that the first RA-RNTI addresses the UE 102.

[0115] In some embodiments, the S-DU 174A does not receive in the UE Context Modification Request message (e.g., the step 412) the SSB positions in a burst for the cell 1 from the CU 172. Instead, the S-DU 174A receives the SSB positions in a burst in a CU- DU TA Information Transfer message (e.g., the step 458 and in the TA Information IE) from the CU 172. In such embodiment, the S-DU 174A might calculate the one or more RA-RNTI(s) after it receives the CU-DU TA Information Transfer message.

[0116] In some embodiments, the S-DU 174A does not have the SSB positions in a burst for the cell 1 from the CU 172. The S-DU 174A might instead infer the exact SSBs transmitted by the C-DU 174B on cell 1 by the LTM CSI SSB resource set (e.g., LTM-CSI- SSB-ResourceSet) in the LTM CSI resource configuration (e.g., LTM-CSI- ResourceConfig) which it received from the CU 172. The LTM CSI SSB resource set is used to indicate on SSB resources (e.g., in tuple of {SSB index, LTM ID}) from one or more LTM candidate cells. In such embodiments, the CU 172 needs to generate the LTM CSI SSB resource set using all the SSB indexes indicated in the SSB positions in burst it receives from the C-DU(s) for the candidate cell(s) for LTM. For example, a first C-DU indicates {SSB1 , SSB2, SSB3, SSB4, SSB5} in the SSB positions in burst of cell 1 (associated with LTM ID1 ) to the CU 172 and a second C-DU indicates {SSB2, SSB4, SSB6} in the SSB positions in burst of cell 2 (associated with LTM ID2). The CU 172 includes the ({SSB1 , ID1}, {SSB2, ID1}, {SSB3, ID1}, {SSB4, ID1}, {SSB5, ID1}, {SSB2, ID2}, {SSB4, ID2}, {SSB6, ID2}) in the SSB resource set within the LTM CSI resource configuration. Otherwise, the S-DU 174A might fail to correctly map the SSB indexes to PRACH occasions and fail to calculate a RA-RNTI matching the first RA-RNTI. The S-DU 174A may then refrain from including the received TA value in the LTM cell switch command to the UE.

[0117] In other embodiments, the S-DU 174A might instead infer the exact SSBs transmitted by the C-DU 174B on cell 1 by the CFRA SSB resource (e.g., CFRA-SSB-Patent ApplicationAttorney Docket Number 0683-100-WOResource) in a dedicated RACH configuration (e.g., RACH-ConfigDedicated) the S-DU 174A receives in a RACH Configuration or a PDCCH order information from the C-DU 174B via the CU 172. In such embodiments, the C-DU 174B needs to generate the CFRA SSB resource list using all the SSB indexes as in the SSB positions in burst for the candidate cell 1 for LTM. For example, if the SSB positions in burst is '11100000,’ the C- DU 174B needs to include the SSB 0, SSB 1 , SSB2 in the CFRA SSB resource list.

[0118] In response to determining to command the UE 102 to perform an LTM cell switch to the cell 1 , the S-DU 174A transmits 426 the LTM Cell Switch Command including the LTM ID 1 to the UE 102. If the S-DU 174A receives a TA value as described above, the S-DU 174A may include the TA value in the LTM Cell Switch Command. The S-DU 174A may include a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates the first one of the TCI state configurations.

[0119] In response to determining to command the UE 102 to perform an LTM cell switch or transmitting 426 the LTM Cell Switch Command, the S-DU 174A transmits 428 a DU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 performs an LTM cell switch to the cell 1 . In response, the CU 172 may transmit 430 a CU- DU Cell Switch Notification message to the C-DU 174B to indicate that the UE 102 performs an LTM cell switch to the cell 1 . In some embodiments, the S-DU 174A includes the first TCI state ID in the DU-CU Cell Switch Notification message and the CU 172 in turn includes the first TCI state ID in the CU-to-DU Cell Switch Notification message. The UE 102 and the C-DU 174B identify the first one of the TCI state configurations based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 432, 436 and / or 440.

[0120] In other embodiments, in case that separate TCI states are used, the DL TCI State and the UL TCI state uses different TCI State IDs. In such cases, the S-DU 174A includes, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI State ID for DL and / or a second TCI State ID for UL. The CU 172, in response to the DU-CU Cell Switch Notification message, in turn includes the first TCI State ID and / or the second TCI state ID in the CU-DU Cell Switch Notification message to the C-DU 174B. The UE 102 identifies the first and / or the second of the TCI state configuration(s) based on the first and / or second TCI state ID and applies the first and / orPatent ApplicationAttorney Docket Number 0683-100-WO second TCI state configuration to communicate DL transmissions and / or UL transmissions, respectively, with the C-DU 174B in the events 432, 436, and / or 440. The C-DU 174B applies the first and / or the second TCI state configuration to communicate DL transmissions and / or UL transmissions, respectively, with the UE 102 in the events 432, 436, and / or 440.

[0121] In some embodiments, each of the TCI state configuration(s) includes or is associated with a TCI state ID. In some embodiments, the CU 172 may transmit a CU-to- DU message (e.g., the second CU-to-DU message or an additional CU-to-DU message) including the TCI state configuration(s) and / or the associated TCI state ID(s) to the S-DU 174A. In some embodiments, the CU 172 includes the LTM ID 1 or the cell ID 1 in the CU- to-DU message to indicate that the TCI state configuration(s) is associated with the LTM ID 1 or the cell ID 1. For example, the CU 172 includes {the cell ID 1 , the TCI state configuration(s)} as a tuple in the CU-to-DU message. In the case of the additional CU-to- DU message, the S-DU 174A may transmit an additional DU-to-CU message to the CU 172 in response. In some embodiments, the S-DU 174A includes, in the LTM Cell Switch Command 426, a first TCI state ID indicating a first one of the TCI state configurations. In some embodiments, the S-DU 174A determines the first TCI state configuration or the fist TCI state ID. The UE 102 identifies the one of the TCI state configurations based on the first TCI state ID and applies the first TCI state configuration in UL transmissions and / or DL receptions in the events 432, 436 and / or 440.

[0122] In some embodiments, the CU 172 may prepare additional cell(s) (i.e., cell(s) 2, ... , N) as LTM candidate cell(s) for the UE 102 with the C-DU 174B, before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 490 or 492, as described for FIG. 3.

[0123] In some embodiments, the first CU-to-DU message and the first DU-to-CU message are a UE Context Setup Request message and a UE Context Setup Response message. In some embodiments, the first CU-to-DU message and the first DU-to-CU message are a UE Context Modification Request message and a UE Context Modification Response message. 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. In other embodiments, the LTM procedure 490 and the additionPatent ApplicationAttorney Docket Number 0683-100-WOLTM preparation procedures are UE Context Setup procedures. In yet other embodiments, the LTM procedure 490 and the addition LTM preparation procedures are UE Context Modification procedures.

[0124] The events 404, 406, 490, 492, 494, 494, and 424 are collectively referred to, in FIG. 4, as an intra-CU inter-DU LTM configuration procedure 496. The events 404, 406, 490, 492, 494, 494, 424, 450, 452, 454456, 458, 426, 428, 430, 432, 434, 436, 438, 440, 442, and 444 are collectively referred to, in FIG. 4, as an intra-CU inter-DU LTM procedure 480.

[0125] Referring next to FIG. 5, in a scenario 500, the BS 104A operates as a serving or source BS (S-BS), and the BS 106A operates as a candidate BS (C-BS). The C-BS 106A includes a CU 172 and a DU 174. In some embodiments, the S-BS 104A may include a DU and a CU, as described above with respect to FIG. 3. In other embodiments, the S-BS 104A may include an S-DU, a C-DU and a CU, as described above with respect to FIG. 4. The scenario 500 is similar to the scenarios 300 and 400, except that the scenario 500 is an inter-CU scenario (i.e. , inter-BS scenario) while the scenarios 300 and 400 are intra-CU (i.e., intra-BS) scenarios. The S-BS 104A may include a CU and a DU (not shown in FIG. 5), similar to the BS 104A of Figs. 3 and 4. Initially, the UE 102 communicates 502 with the S-BS 104A via serving cell(s) using a serving configuration. In some embodiments, the S-BS 104A includes a S-DU and a CU and the serving configuration may include a serving CU configuration and a serving DU configuration, as described for Figs. 3 and 4. While the communicating 502 with the UE 102, the S-BS 104A might perform 580 intra-CU LTM procedure(s) with the UE 102, similar to the procedures 380 and / or 480. Alternatively, while the communicating 502 with the UE 102, the S-BS 104A might perform 596 intra-CU LTM configuration procedure(s) with the UE 102, similar to the procedures 396 and / or 496.

[0126] While communicating with the S-BS 104A, the UE 102 transmits 504 at least one measurement report to the S-BS 104. The measurement report(s) include measurement results for a serving cell of the UE 102 and / or at least one non-serving cell (e.g., cell 126A). The S-BS 104A determines to prepare a first cell (e.g., the cell 126A) as an LTM candidate cell for the UE 102, based on the measurement report(s). For example, the measurement report(s) include a PCI of the first cell and measurement result(s) of thePatent ApplicationAttorney Docket Number 0683-100-WG cell 126A. The S-BS 104A identifies that the first cell is operated by the BS 106A based on the PCI, and determines that the first cell qualifies for LTM preparation based on the measurement result(s).

[0127] After (e.g., in response to) determining to prepare the first cell as an LTM candidate cell for the UE 102, the S-BS 104A (e.g., the CU of the S-BS 104) generates a Handover Request message including a first cell ID (i.e. , cell ID 1) of the first cell (i.e. , cell 1 ). The S-BS 104A transmits 505 the Handover Request message to the CU 172. In some embodiments, the Handover Request message includes an LTM indicator indicating the Handover Request message concerns LTM for the first cell ID. After (e.g., in response to) receiving the Handover Request message, the CU 172 performs an LTM preparation procedure 590 with the DU 174 to prepare the first cell as an LTM candidate cell for the UE 102, similar to the procedure 390 or 490. In the procedure 590, the CU 172 transmits a first CU-to-DU message including the first cell ID to the DU 174 to request preparing the first cell, similar to the event 308. In response, the CU 172 may receive a first DU-to-CU message including an LTM DU configuration 1 from the DU 174, similar to the event 310. The CU 172 generates a first LTM candidate configuration (LTM candidate configuration 1 ). In response to the Handover Request message, the CU 172 transmits 507 a Handover Request Acknowledge message including the first LTM candidate configuration to the S- BS 104. In some embodiments, the CU 172 includes the first cell ID in the Handover Request Acknowledge message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID). In some embodiments, the CU 172 includes the SSB positions in burst (e.g., ssb-PositionslnBurst-r18 or a Xn-interface bitmap field / IE signaling the SSB positions in burst) corresponding to the first cell in the Handover Request Acknowledge message to indicate the exact SSB indexes the C-BS 106A or the DU 174 sent on the first cell. In other embodiments, the CU 172 does not include the SSB positions in burst corresponding to the first cell in the Handover Request Acknowledge message but implicitly signal this information in a dedicated RACH configuration or in an LTM CSI resource configuration as described in the FIG. 4.

[0128] The events 505, 590, and 507 are collectively referred to in FIG. 5 as an inter-CU LTM preparation procedure (or called inter-MN LTM preparation procedure) 598.Patent ApplicationAttorney Docket Number 0683-100-WO

[0129] In some embodiments, the Handover Request message includes a DU ID of the S-DU of the S-BS 104. In such cases, the CU 172 includes the DU ID in the first CU- to-DU message. In some embodiments, the Handover Request message includes a BS ID of the S-BS 104. When receiving the BS ID, the CU 172 may include the BS ID in the first CU-to-DU message. For example, the BS ID is a gNB ID.

[0130] The CU 172 may or may not request an LTM reference DU configuration in the procedure 590, as described for Figs. 3 and 4. The DU 174 may or may not transmit an LTM reference DU configuration to the CU 172 in the procedure 590, as described for Figs. 3 and 4. In some embodiments, the S-BS 104A (e.g., the CU of the S-BS 104) may obtain an LTM reference configuration, as described for Figs. 3 and 4. In other embodiments, the S-BS 104A may receive an LTM reference configuration from another BS (not shown in FIG. 5) in another inter-CU LTM preparation procedure as described above and below. If the S-BS 104A obtains an LTM reference configuration, the S-BS 104A may include the LTM reference configuration (S-BS generated LTM reference configuration) in the Handover Request message. In some embodiments, the S-BS 104A includes the LTM reference configuration in the inter-node RRC message HandoverPreparationlnformation or as an Xn Application Protocol (XnAP) IE or field and includes the inter-node RRC message or the XnAP IE in the Handover Request message. Alternatively, the S-BS 104A determines to request or cause the C-BS 106A to provide a complete LTM candidate configuration so that the S-BS 104A does not include the LTM reference configuration in the Handover Request message. If the S-BS 104A does not obtain an LTM reference configuration, the S-BS 104A does not include an LTM reference configuration in the Handover Request message. If the Handover Request message includes an LTM reference configuration, the CU 172 may include the LTM reference configuration in the first CU-to-DU message. The DU 174 may extract an LTM reference DU configuration from the LTM reference configuration. Alternatively, the CU 172 extracts an LTM reference DU configuration from the LTM reference configuration and includes the LTM reference DU configuration in the first CU-to-DU message. The DU 174 may generate an LTM DU configuration as a delta configuration based on the LTM reference DU configuration, as described for FIG. 3. Alternatively, the DU 174 may ignore the LTMPatent ApplicationAttorney Docket Number 0683-1 OO-WO reference (DU) configuration and generate an LTM DU configuration as a complete configuration, as described in FIG. 3.

[0131] Otherwise, if the Handover Request message does not include an LTM reference configuration, the CU 172 may or may not receive an LTM reference DU configuration from the DU 174 as described for FIG. 3. If the CU 172 receives an LTM reference DU configuration (e.g., in the first DU-to-CU message), the CU 172 generates an LTM reference configuration (C-BS generated LTM reference configuration) including the LTM reference DU configuration. The CU 172 may include an LTM reference CU configuration (candidate CU (C-CU) generated LTM reference CU configuration). Otherwise, if the CU 172 does not receive an LTM reference DU configuration from the DU 174 as described for FIG. 3, the CU 172 does not generate an LTM reference configuration. Alternatively, the CU 172 generates an LTM reference configuration (C-BS generated LTM reference configuration) only including a C-CU generated LTM reference CU configuration. In cases where the CU 172 generates an LTM reference configuration (C-BS generated LTM reference configuration), the CU 172 includes the C-BS generated LTM reference configuration in the Handover Request Acknowledge message.

[0132] In some embodiments, if the LTM DU configuration 1 is a complete configuration, the CU 172 generates the LTM candidate configuration 1 as a complete configuration. The CU 172 may include a complete configuration indication (e.g., a BS-to- BS interface protocol field / IE) in the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a complete configuration. In some embodiments, the BS-to-BS interface protocol is an Xn application protocol defined in 3GPP specification 38.423. In some embodiments, the complete configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other embodiments, the complete configuration indication is an existing field / IE defined in 3GPP specification 38.423. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates the LTM candidate configuration 1 as a delta configuration. The CU 172 may exclude the complete configuration indication from the Handover Request Acknowledge message to indicate that the LTM candidate configuration 1 is a delta configuration.Alternatively, the CU 172 may include a delta configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the Handover Request Acknowledge message to indicate thatPatent ApplicationAttorney Docket Number 0683-100-WO the LTM candidate configuration 1 is a delta configuration. In some embodiments, the BS- to-BS interface protocol is an Xn application protocol defined in 3GPP specification 38.423. In some embodiments, the delta configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other embodiments, the delta configuration indication is an existing field / IE defined in 3GPP specification 38.423. In some embodiments, the BS-to-BS interface protocol field / IE have two values (i.e. , a first value and a second value). The BS-to-BS interface protocol field / IE set to the first value is the complete configuration indication and the BS-to-BS interface protocol field / IE set to the second value is the delta configuration indication.

[0133] In some embodiments, the S-BS 104A is preconfigured with a CSI resource configuration (e.g., (LTM) CSI resource configuration 1 ) and / or an LTM SSB configuration (LTM SSB configuration 1) for the first cell. In other embodiments, the S-BS 104A receives the CSI resource configuration and / or the LTM SSB configuration from an 0AM (Operations, Administration and Maintenance) node. In yet other embodiments, the S-BS 104A receives the CSI resource configuration and / or the LTM SSB configuration from the CU 172. For example, the CU 172 includes the CSI resource configuration and / or the LTM SSB configuration in the Handover Request Acknowledge message. In some embodiments, the CU 172 includes a PCI (PCI 1 ) of the first cell in the Handover Request Acknowledge message. To prepare the first cell as a candidate LTM cell for the UE 102, the CU of the S-BS 104A performs an LTM CSI report configuration and / or LTM ID configuration procedure (not shown in FIG. 5) with a S-DU of the S-BS 104A, similar to the procedure 392. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-BS 104A transmits the CSI resource configuration and / or the LTM SSB configuration to the S-DU of the S-BS 104. In response, the CU of the S-BS 104A receives one or more CSI report configurations for the UE 102 from the S-DU of the S-BS 104. In some embodiments, the CU of the S-BS 104A receives the CSI report configuration(s) in a second serving DU configuration from the S-DU.

[0134] To prepare the first cell as an LTM candidate cell for the UE 102, the CU 172 may receive early synchronization information (early synchronization information 1 ) for the first cell from the DU 174 in a DU-to-CU message (e.g., the first DU-to-CU message or an additional DU-to-CU message). In some embodiments, the DU 174 transmits thePatent ApplicationAttorney Docket Number 0683-100-WO additional DU-to-CU message in response to receiving an additional CU-to-DU message from the CU 172. In other embodiments, the DU 174 transmits the additional DU-to-CU message (e.g., a UE Context Modification Required message) in response to receiving the first CU-to-DU message. The CU 172 includes the early synchronization information in the Handover Request Acknowledge message. The early synchronization information includes a RACH configuration (RACH configuration 1 ) and / or at least one TCI state configuration (TCI state configuration(s) 1). In some embodiments, the DU 174 includes, in the early synchronization information or in the DU-to-CU message, PDCCH order information for early UL synchronization with the first cell. The CU 172 includes the PDCCH order information in the Handover Request Acknowledge message.

[0135] In some embodiments, the CU 172 assigns an LTM ID (e.g., LTM ID 1 ) for identifying the first LTM candidate configuration and includes the LTM ID in the Handover Request Acknowledge message. In other embodiments, the S-BS 104A assigns an LTM ID (e.g., LTM ID 1 ) for identifying the first LTM candidate configuration.

[0136] After (e.g., in response to) receiving the Handover Request Acknowledge message, the S-BS 104A (e.g., the CU of the S-BS 104) transmits 518 a first RRC reconfiguration message to the UE 102, including {the LTM ID 1 , the LTM candidate configuration 1} as a tuple, similar to the event 318. If the Handover Request Acknowledge message includes the LTM reference configuration, the S-BS 104A may include the LTM reference configuration in the first RRC reconfiguration message. The S-BS 104A may include the CSI resource configuration 1 , the TCI state configuration(s) 1 , the RACH configuration 1 , and / or the LTM SSB configuration 1 in the tuple, if received in the Handover Request Acknowledge message. Alternatively, the S-BS 104A transmits one or more additional RRC reconfiguration message(s) to the UE 102, including the CSI resource configuration 1 , the TCI state configuration(s) 1 , the RACH configuration 1 , the LTM SSB configuration 1 , and / or the PCI of the first cell. In each of the additional RRC reconfiguration message(s), the S-BS 104A includes the LTM ID 1 to indicate that the CSI resource configuration 1 , the TCI state configuration(s) 1 , the RACH configuration 1 , the LTM SSB configuration 1 , and / or the PCI of the first cell are associated with the first cell or configured for the first cell.Patent ApplicationAttorney Docket Number 0683-100-WO

[0137] Then, the UE 102 transmits 520 a first RRC reconfiguration complete message to the S-BS 104A, in response to the first RRC reconfiguration message. The UE 102 transmits one or more additional RRC reconfiguration complete message(s) to the S-BS 104A in response to each of the additional RRC reconfiguration complete message(s) noted above. The RRC reconfiguration message(s) (i.e. , the first RRC reconfiguration message and / or the additional RRC reconfiguration message(s)) and the RRC reconfiguration complete message(s) (i.e., the first RRC reconfiguration complete message and / or the additional RRC reconfiguration complete message(s)) form an LTM configuration delivery procedure. The S-BS 104A may include the second serving DU configuration in the first RRC reconfiguration message or one or the additional RRC reconfiguration message(s).

[0138] In some embodiments, if the Handover Request Acknowledge message includes the complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration, the S-BS 104A includes, in the first RRC reconfiguration message, a complete configuration indication (e.g., an RRC field / IE) to indicate that the LTM candidate configuration 1 is a complete configuration. Otherwise, if the Handover Request Acknowledge message does not include the complete configuration indication or includes the delta configuration indication to indicate that the LTM candidate configuration 1 is a delta configuration, the S-BS 104A excludes or does not include, in the first RRC reconfiguration message, the complete configuration indication (e.g., an RRC field / IE) to indicate that the LTM candidate configuration 1 is a delta configuration.

[0139] If the Handover Request Acknowledge message includes the PDCCH order information (PDCCH order information 1 ), the S-BS 104A transmits 550 a PDCCH order, based on the RACH configuration and / or the PDCCH order information. If the S-BS 104A is a distributed BS, the CU of the S-BS 104A may transmit the PDCCH order information to the S-DU of the S-BS 104. For example, the S-BS 104A or the S-DU of the S-BS 104A transmits 550 the PDCCH order to the UE 102, including the PDCCH order information. In some embodiments, the S-BS 104A or the S-DU of the S-BS 104A may determine an SSB index included in the PDCCH order, based on the L1 measurement report(s) 524, and / or the CSI resource configuration, the CSI report configuration, and / or the LTM SSBPatent ApplicationAttorney Docket Number 0683-100-WO configuration. In some embodiments, the S-DU or the S-BS 104A includes the LTM ID 1 in the PDCCH order, to indicate the first cell. In some embodiments, the S-DU or the S-BS 104A includes an RA preamble index, a PRACH mask index, and / or an UL / SUL indicator in the PDCCH order. The RA preamble index indicates a particular RA preamble. The S- BS 104A determines or selects the RA preamble index based on the PDCCH order information. The PRACH mask index indicates one or more allowed PRACH occasions for the UE 102 to transmit the RA preamble.

[0140] The UE 102 transmits 552 an RA preamble to the DU 174 on the first cell in response to the PDCCH order, using the RACH configuration and / or the PDCCH order information. The DU 174 derives a TA value based on the RA preamble. The DU 174 transmits 556 to the CU 172 a DU-CU TA Information Transfer message including the TA value. The CU 172 transmits 558 a CU-CU TA Information Transfer message including the TA value, to the S-BS 104A (e.g., the CU of the S-BS 104). In some embodiments, the DU 174 includes in the message 556, the cell ID 1 , the RA preamble index, an RA-RNTI, the DU ID of the S-DU of the S-BS 104A, and / or the BS ID of the S-BS 104A. In some embodiments, the DU 174 does not include the BS ID in the message 556. In some embodiments, the CU 172 includes, in the message 558, the cell ID 1 , the RA preamble index, the RA-RNTI, the DU ID of the S-DU, and / or the BS ID of the S-BS 104A. In some embodiments, the CU 172 does not include the BS ID in the message 558.

[0141] The CU of the S-BS 104A transmits, to the S-DU of the S-BS 104, a CU-DU TA Information Transfer message including the TA value, the cell ID 1 , the RA preamble index, the RA-RNTI, and / or the DU ID of the S-DU, and / or the BS ID of the S-BS 104A. In some embodiments, the CU of the S-BS 104A does not include the BS ID in the CU-DU TA Information Transfer message. In some embodiments, based on the allowed PRACH occasion(s), the S-BS 104A or the S-DU calculates one or more RA-RNTI(s) (i.e. , values), respectively. The S-BS 104A or the S-DU, after receiving the CU-CU TA Information Transfer message or the CU-DU TA Information Transfer message, determines if the received RA-RNTI is (equal to) one of the calculated RA-RNTI(s). If the received RA-RNTI is (equal to) one of the calculated RA-RNTI(s), the S-BS 104A or the S-DU identifies a TA value for the UE 102 and may include the TA value in the LTM Cell Switch Command 526, similar to the event 426 with respect to FIG. 4.Patent ApplicationAttorney Docket Number 0683-100-WO

[0142] The example embodiments described for the S-DU 174A in FIG.4 may apply to the S-BS 104A or S-DU in FIG. 5 for the determination of one or more (allowed) PRACH occasion(s), the calculation of the RA-RNTI(s) for the PRACH occasion(s), and the association of a TA value to a UE considering the cell ID, the RA preamble index, and / or the received RA-RNTI, etc.

[0143] In some embodiments, the CU 172 determines an address (e.g., an IP address) of the S-BS 104A or the CU of the S-BS 104A, based on the BS ID of the S-BS 104. In other embodiments, the CU 172 determines an address (e.g., an IP address) of the S-BS 104A or the CU of the S-BS 104A, based on the DU ID of the S-DU of the S-BS 104. For these embodiments, the CU 172 sends the CU-CU TA Information Transfer message to the S-BS 104A or the CU of the S-BS 104A in accordance with the determined address.

[0144] In response to determining to instruct the UE 102 to perform an LTM cell switch to the first cell, e.g., based on the measurement report(s) 524 and / or 554, the S-DU or the S-BS 104A transmits 526 the LTM Cell Switch Command including the LTM ID 1 to the UE 102. In response to the LTM Cell Switch Command, the UE 102 may stop communication on the serving cell(s). In response to the LTM Cell Switch Command, the UE 102 accesses 532 the first cell and transmits 536 an RRC reconfiguration complete message to DU 174. The DU 174 in turn transmits 538 to the CU 172 a DU-to-CU message including the RRC reconfiguration complete message. After receiving 538 the DU-to-CU message or the RRC reconfiguration complete message, the C-BS 106A communicates 540 with the UE 102 in accordance with the first LTM candidate configuration and / or the LTM reference configuration.

[0145] In some embodiments, the UE 102 includes the LTM ID 1 in the RRC reconfiguration complete message 536 to indicate that the UE 102 applies the first LTM candidate configuration. In accordance with the LTM ID 1 , the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration. In other embodiments, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration based on the first cell ID included in the Access Success message 534. In such embodiments, the CU 172 maintains or stores association information between the first cell ID, and the first LTM candidate configuration and / or the LTM reference configuration. When the CU 172 receives the first cell ID in the Access SuccessPatent ApplicationAttorney Docket Number 0683-100-WO message, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration in accordance with the first cell ID and the association information.

[0146] In some embodiments, if the S-Dll or the S-BS 104A receives a TA value as described above, the S-Dll or the S-BS 104A may include the TA value in the LTM Cell Switch Command. In some embodiments, the S-Dll or the S-BS 104A includes a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates the first one of the TCI state configuration(s).

[0147] In response to determining to request the UE 102 to perform the LTM cell switch or transmitting 526 the LTM Cell Switch Command, the S-DU of the S-BS 104A transmits a DU-CU Cell Switch Notification message to the CU of the S-BS 104A to indicate that the UE 102 performs or is performing an LTM cell switch to the first cell. In response to receiving the DU-CU Cell Switch Notification message, the CU of the S-BS 104A transmits 527 a CU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 performs an LTM cell switch to the first cell. In response, the CU 172 transmits 530 a CU-DU Cell Switch Notification message to the DU 174 to indicate that the UE 102 performs an LTM cell switch to the first cell. In some embodiments, the S-BS 104A includes the first TCI state ID in the CU-CU Cell Switch Notification message and the CU 172 then includes the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the DU 174 identify the first one of the TCI state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 532, 536, and / or 540. In other embodiments, if separate TCI states are used, the DL TCI state and the UL TCI state uses different TCI state IDs. In such cases, the S-DU of the S-BS 104A includes, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI state ID for DL and / or a second TCI state ID for UL. The CU of the S-BS 104A, in response to the DU-CU Cell Switch Notification message, includes the first TCI state ID and / or the second TCI state ID in the CU-CU Cell Switch Notification message to the CU 172. The CU 172 then includes the first TCI state ID and / or the second TCI state ID in the CU-DU Cell Switch Notification message to the DU 174. The UE 102 identifies the first and / or the second TCI state configuration(s) based on the first and / or second TCI state ID and applies the first and / or second TCI state configuration to communicate, with the DU 174,Patent ApplicationAttorney Docket Number 0683-100-WODL transmissions and / or UL transmissions, respectively, in the events 532, 536, and / or 540. The DU 174 applies the first and / or the second TCI state configuration to communicate DL transmissions and / or UL transmissions, respectively, with the UE 102 in the events 532, 536, and / or 540.

[0148] In some embodiments, after (e.g., in response to) determining to request the UE 102 to perform the LTM cell switch, transmitting 526 the LTM Cell Switch Command, or receiving 527 the DU-CU Cell Switch Notification message, the S-BS 104A (e.g., the CU of the S-BS 104) transmits 531 one or more Early Status Transfer messages to the CU 172, each including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE 102 and the S-BS 104A communicate 502 data with each other. In some embodiments, after receiving 534 the Access Success message or receiving 538 the DU- to-CU message or the RRC reconfiguration complete message, the CU 172 transmits 539 an LTM Success message to the S-BS 104A (e.g., the CU of the S-BS 104) to indicate that the LTM cell switch was successfully completed. In some embodiments, the LTM Success message is a Handover Success message. In some embodiments, the CU 172 includes the first cell ID in the LTM Success message. In other embodiments, the CU 172 does not transmit a BS-to-BS message to the S-BS 104A (e.g., the CU of the S-BS 104) to indicate that the LTM cell switch is completed successfully.

[0149] In some embodiments, after (e.g., in response to) determining to request the UE 102 to perform the LTM cell switch, transmitting 526 the LTM Cell Switch Command, receiving 527 the DU-CU Cell Switch Notification message, or receiving 539 the LTM Success message, the S-BS 104A (e.g., the CU of the S-BS 104) transmits 541 an SN Status Transfer message to the CU 172, including a DL COUNT value and / or a UL COUNT value for a / the DRB over which the UE 102 and the S-BS 104A communicate 502 data with each other.

[0150] In some embodiments, after (e.g., in response to) receiving 534 the Access Success message, receiving 538 the DU-to-CU message or the RRC reconfiguration complete message, or receiving 541 the SN Status Transfer message, the CU 172 transmits 543 a UE Context Release message to the S-BS 104. In response to the UE Context Release message, the S-BS 104A releases a UE context of the UE 102.Patent ApplicationAttorney Docket Number 0683-1 OO-WO

[0151] In some embodiments, the S-BS 104A (e.g., the CU of the S-BS 104) may prepare additional cell(s) (i.e., cell(s) 2, N) as LTM candidate cell(s) for the UE 102 with the CU 172, before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 598, as described above. The cell(s) 2, ... , N are identified by cell ID(s) 2, , N, respectively and operated by the DU 174 and / or other DU(s) of the C-BS 106A, where N is an integer larger than 1. For example, the S-BS 104A performs additional inter-CU LTM preparation procedure(s) 2, ... , N with the CU 172 to prepare the cell(s) 2, ... , N, respectively. Each of the inter-CU LTM preparation procedure(s) 2, ... , N is similar to the procedure 598. In the inter-CU LTM preparation procedure(s) 2, ... , N, the S- BS 104A receives LTM candidate configuration(s) 2, ... , N configuring the cell(s) 2, ... , N for LTM, respectively. As described above, the S-BS 104A or the C-BS 106A assigns LTM ID(s) 2, ... , N to identify the LTM candidate configuration(s) 2, ... , N, respectively. The S- BS 104A may obtain CSI resource configuration 2, ... , N for the cell(s) 2, ... , N respectively, as described for the CSI resource configuration 1 . The S-BS 104A may obtain CSI report configuration(s) 2, ... , N or the cell(s) 2, ... , N, respectively, as described for the CSI report configuration(s) 1 . The S-BS 104A may obtain RACH configuration 2, ... , N for the cell(s) 2, ... , N respectively, as described for the RACH configuration 1. The S-BS 104A may obtain TCI state configuration(s) 2, .... N for the cell(s) 2, ... , N respectively, as described for the TCI state configuration(s) 1 . The S-BS 104A may obtain LTM SSB configuration 2, ... , N for the cell(s) 2, ... , N, respectively, as described for LTM SSB configuration 1 . The S-BS 104A may obtain PCI(s) 2, ... , N for the cell(s) 2, .... N respectively, as described for the PC1 1. In some embodiments, the S-BS 104A may perform LTM configuration delivery procedure 2, ... , N, with the UE 102, to transmit a list of the {LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained), the PCI 2 (if obtained)}, .... {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained), the PCI N (if obtained)}, respectively. Each of the LTM configuration delivery procedure 2, ... , N is similar to the procedures 394, 494, and / or 594.Patent ApplicationAttorney Docket Number 0683-100-WOIn other embodiments, the S-BS 104A includes the list in the first RRC reconfiguration message.

[0152] In other embodiments, the S-BS 104A performs the procedure 598 with the CU 172 to prepare one or more of the cell(s) 1 , ... , N as LTM candidate cell(s) for the UE 102. In such embodiments, the S-BS 104A includes the cell ID(s) 1 , ... , N in the Handover Request message 505 for LTM, as described for the cell ID 1 . In some embodiments, upon receiving the Handover Request message, the CU 172 determines or selects the cell(s) 1 , ... , M from the cell(s) 1 , ... , N as LTM candidate cell(s), where M is a positive integer and M < N. In other embodiments, CU 172 prepares the cell(s) 1 , ... , N for LTM as requested in the Handover Request message. The CU 172 performs LTM preparation procedure(s) 2, ... , M with the DU 172 to prepare the cell(s) 2, ... , M as LTM candidate cell(s) for the UE 102, respectively. The LTM preparation procedure(s) 2, ... , M are similar to the procedure 590 that the CU 172 performs with the DU 174 to prepare the cell 1 . The CU 172 obtains the LTM candidate configuration(s) 2, ... , M for the cell(s) 2, ... , M as a result of the LTM preparation procedure(s) 2, ... , M respectively, similar to obtaining the LTM candidate configuration 1 . The C-BS 106A may generate the LTM candidate configuration(s) 2, ... , M as complete configuration(s) or generate delta configuration(s) based on the LTM reference configuration, as described for the LTM candidate configuration 1. The CU 172 includes the LTM candidate configuration(s) 2, ... , M in the Handover Request Acknowledge message. In some embodiments, the CU 172 or the S- BS 104A assigns LTM ID(s) 2, ... , M to identify the LTM preparation procedure(s) 2, ... , M respectively, as described for the LTM ID 1. If the CU 172 assigns the LTM ID(s) 1 , ... , M, the CU 172 includes the LTM ID(s) 1 , ... , M with the LTM candidate configuration(s) 1 , ... , M, respectively in the Handover Request Acknowledge message, as described for the LTM ID 1 and the LTM candidate configuration 1.

[0153] In some embodiments, the CU 172 obtains early synchronization information 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the early synchronization information 1. The CU 172 includes the early synchronization information 2, ... , M in the Handover Request Acknowledge message. In some embodiments, the CU 172 or the S- BS 104A obtains CSI resource configuration(s) 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the CSI resource configuration 1 . If the CU 172 obtains thePatent ApplicationAttorney Docket Number 0683-100-WOCSI resource configuration(s) 2, M, the CU 172 includes the CSI resource configuration(s) 2, M in the Handover Request Acknowledge message.

[0154] In some embodiments, the CU 172 or the S-BS 104A obtains LTM SSB configuration(s) 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the LTM SSB configuration 1. If the CU 172 obtains the LTM SSB configuration(s) 2, ... , M, the CU 172 includes the LTM SSB configuration(s) 2, ... , M in the Handover Request Acknowledge message. In some embodiments, the CU 172 or the S-BS 104A obtains PCI(s) 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the PCI 1 . If the CU 172 obtains the PCI(s) 2, ... , M, the CU 172 includes the PCI(s) 2, ... , M in the Handover Request Acknowledge message.

[0155] In some embodiments, the CU 172 includes a list of {the cell ID 1 , the LTM ID 1 (if obtained or optional), the LTM candidate configuration 1 , the CSI resource configuration 1 (if obtained or optional), the TCI state configuration 1 (if obtained or optional), the early synchronization information 1 (if obtained or optional), the LTM SSB configuration 1 (if obtained or optional), PCI 1 (if obtained or optional)}, ... , {the cell ID M, the LTM ID M (if obtained or optional), the LTM candidate configuration M, the CSI resource configuration M (if obtained or optional), the TCI state configuration M (if obtained or optional), the early synchronization information M (if obtained or optional), the LTM SSB configuration M (if obtained or optional), the PCI M (if obtained or optional)} in the Handover Request Acknowledge message.

[0156] In some embodiments, the CU 172 obtains PDCCH order information 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the PDCCH order information 1. In one embodiment, the CU 172 includes the PDCCH order information 2, ... , M in the Handover Request Acknowledge message. In another embodiment, the CU 172 includes the PDCCH order information 2, ... , M in the early synchronization information 2, ... , M, respectively. The S-BS 104A may obtain RACH configuration 2, TCI state configuration(s) 2, and / or the PDCCH order information 2, ...., RACH configuration M, TCI state configuration(s) M, and / or the PDCCH order information M from the early synchronization information 2, ... , M, respectively or from the Handover Request Acknowledge message.

[0157] In some embodiments, the S-BS 104A may perform LTM configuration delivery procedure 2, ... , M with the UE 102 to transmit a list of the {LTM ID 2, the LTMPatent ApplicationAttorney Docket Number 0683-100-WO candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained), the PCI 2 (if obtained)}, ... , {the LTM ID M, the LTM candidate configuration M, the CSI resource configuration M, the TCI state configuration(s) M (if obtained), the RACH configuration M (if obtained), the LTM SSB configuration M (if obtained), the PCI M (if obtained)} to the UE 102, respectively. Each of the LTM configuration delivery procedure 2, ... , M is similar to the procedures 394, 494, and / or 594. In other embodiments, the S-BS 104A includes the list in the first RRC reconfiguration message.

[0158] In some embodiments, the S-BS 104A may include measurement result(s) 1 , ... , N for the cell(s) 1 , ... , N respectively in the Handover Request message. The S-BS 104A receives the measurement result(s) from the UE 102. The C-BS 106A may select or determine the cell(s) 1 , ...M, based on the measurement result(s) 1 , ... , N. In other embodiments, the C-BS 106A may select or determine the cell(s) 1 , ... M, based on one or more other factors (e.g., capacity or load of the cell(s) 1 , ... , N and / or a maximum number of LTM candidate cell(s)). In one embodiment, the maximum number is included in the Handover Request message. In another embodiment, the maximum number is a predetermined number.

[0159] In some embodiments, instead of a Handover Request Acknowledge message, the C-BS 106A (or the CU 172 of the C-BS 106A) transmits to the S-BS 104A the SSB positions in burst(s) for the cell(s) it serves in a Served Cell Information NR IE in an Xn Setup Request message, an Xn Setup Response message, an NG-RAN Node Configuration Update message, or an NG-RAN Node Configuration Update Acknowledge message. In other embodiments, instead of a Handover Request Acknowledge message, the C-BS 106A (or the CU 172 of the C-BS 106) transmits to the S-BS 104A the SSB positions in burst for the cell accessed by the UE for early UL synchronization in a CU-to- CU TA Information Transfer message.

[0160] FIG. 6A illustrates a scenario 600A in which the BS 104B operates as an MN, the BS 106A operates as a candidate SN (C-SN), and the BS 104A operates as a serving or source SN (S-SN). The C-SN 106A includes a CU 172 and a DU 174. The MN 104B may include a CU and a DU (not shown in FIG. 6A), similar to the BS 104A in FIG.Patent ApplicationAttorney Docket Number 0683-100-WG3. The S-SN 104A may include a CU and a DU (not shown in FIG. 6A), similar to the C-SN 106A. The scenario 600A is similar to the scenario 500, except that the scenario 600A is a SN scenario and the scenario 500 is a MN scenario.

[0161] Initially, the UE 102 in DC communicates 602 with the MN 104B and with the S-SN 104A. In some embodiments, the UE 102 communicates with the DU of the S-SN 104A on cell 124A using a serving DU configuration, and communicates with the CU of the S-SN 104A via the DU of the S-SN 104A using a serving CU configuration, similar to the event 302. In some embodiments, the UE 102 in DC may communicate 602 UL PDUs and / or DL PDUs with the MN 104B and / or S-SN 104A via radio bearers which may include SRBs and / or DRB(s). The MN 104B and / or the S-SN 104A may configure the radio bearers to the UE 102. The UE 102 in DC communicates 602 UL PDUs and / or DL PDUs with the S-SN 104A on an SCG (i.e., SCG radio resources) that the S-SN 104A configures for communication with the UE 102. The UE 102 in DC communicates UL PDUs and / or DL PDUs with the MN 104B on an MCG (i.e., MCG radio resources) 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 104B configures the MCG, which includes at least one serving cell (e.g., the cell 124B and / or other cell(s)) operated by the MN 104B. In the serving DU configuration, the S-SN 104A configures the SCG, which includes at least one serving cell (e.g., the cell 124A and / or other cell(s)) operated by the S-SN 104A. 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 104B. As described with regard to 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 S-SN 104A, e.g., via the MN 104B and / or on an SRB (e.g., SRB3) that the MN 104B or S-SN 104A configures to exchange RRC messages between the UE 102 and the S-SN 104A.

[0162] While the UE 102 communicates in DC with the MN 104B and S-SN 104A, the S-SN 104A may perform 696 an intra-CU LTM configuration procedure with the UE 102, similar to the procedures 396 and / or 496. While the UE 102 communicates in DC with the MN 104B and S-SN 104A, the S-SN 104A may perform 680 an intra-CU LTMPatent ApplicationAttorney Docket Number 0683-100-WO procedure with the UE 102, similar to the procedures 380 and / or 480. In the procedure 696 or 680, the CU of the S-SN 104A may transmit one or more RRC reconfiguration messages, each including one or more LTM candidate configurations, to the UE 102, via the SRB3, similar to the procedure 394 or 494. Alternatively, the CU of the S-SN 104A may transmit one or more RRC reconfiguration messages, each including one or more LTM candidate configurations, to the UE 102, via the MN 104B. In response to each of the RRC reconfiguration message(s), the UE 102 transmits an RRC reconfiguration complete message to the S-SN 104A, via the MN 104B. In the procedure 680, the S-DU of the S-SN 104A may perform the early uplink synchronization procedure with the UE 102 and a C- DU, similar to the procedures 480.

[0163] While communicating in DC with the MN 104B and S-SN 104A, the UE 102 may directly transmit 604A at least one measurement report to the S-SN 104A, e.g. via the SRB3, similar to the events 304 / 306, the events 404 / 406, and the event 504. Alternatively, the UE 102 may transmit the measurement report(s) to the MN 104B. The MN 104B generates at least one SN message, including the measurement report(s), and transmits the SN message(s) to the CU 172. In one embodiment, the SN message(s) include RRC Transfer message(s) and / or SN Modification Request message(s). The S-SN 104A (e.g., the CU of the S-SN 104A) generates a measurement configuration to configure the UE 102 to transmit the measurement report(s) and directly transmits the measurement report to the UE 102 (e.g., via the S-DU of the S-SN 104A or via the MN 104B).

[0164] After (e.g., in response to) receiving one or some of the measurement report(s) from the UE 102, the S-SN 104A (e.g., the CU of the S-SN 104A) determines to prepare a first cell (e.g., the cell 126A) as an LTM candidate cell for the UE 102. In response to the determination, the S-SN 104A generates an SN Required message (a first SN Required message) including a first cell ID (e.g., cell ID 1 ) of the first cell (e.g., cell 1 ) and / or a target SN ID indicating the C-SN 106A. In some embodiments, the SN Required message includes an LTM indicator indicating the SN Required message concerns LTM for the first cell ID. The S-SN 104A transmits 603 the SN Required message to the MN 104B. After (e.g., in response to) receiving the SN Required message, the MN 104B transmits 605 an SN Request message (a first SN Request message), including the first cell ID, to the CU 172, to request preparing the first cell as an LTM candidate cell for thePatent ApplicationAttorney Docket Number 0683-100-WOUE 102. In response to the SN Request message, the CU 172 performs an LTM preparation procedure 690 with the DU 174 to prepare the first cell as an LTM candidate cell for the UE 102, similar to the procedure 390, 490, or 590. In the procedure 690, the CU 172 transmits a first CU-to-DU message, including the first cell ID, to the DU 174 to request preparing the first cell, similar to the event 308. In response, the CU 172 may receive, from the DU 174, a first DU-to-CU message including an LTM DU configuration 1 , similar to the event 310. The CU 172 generates a first LTM candidate configuration (LTM candidate configuration 1 ). In response to the SN Request message, the CU 172 transmits 607, to the MN 104B, an SN Request Acknowledge message (a first SN Request Acknowledge message) including the first LTM candidate configuration, the RACH configuration, and / or the PDCCH order Information, and / or the SSB positions in burst. In some embodiments, the CU 172 includes the first cell ID in the SN Request Acknowledge message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID). The MN 104B transmits 609A to the S-SN 104A, an SN Confirm message (e.g., a first SN Confirm message) including the first LTM candidate configuration, the RACH configuration, and / or the PDCCH order Information, and / or the SSB positions in burst. In some embodiments, the MN 104B includes the first cell ID in the SN Confirm message to indicate that the first LTM candidate configuration is provided for or associated with the first cell (ID). The events 603, 605, 690, 607, and 609A are collectively referred to, in FIG. 6A, as an SN-initiated inter-SN LTM preparation procedure 698A.

[0165] In some embodiments, the SN Required message and the SN Confirm message are an S / V Change Required message and an SN Change Confirm message, respectively. In other embodiments, the SN Required message and the SN Confirm message are an SN Modification Required message and an SN Modification Confirm message, respectively. In some embodiments, the SN Request message and the SN Request Acknowledge message are an SN Addition Request message and an SN Addition Request Acknowledge message, respectively. In other embodiments, the SN Request message and the SN Request Acknowledge message are an SN Modification Request message and an SN Modification Request Acknowledge message, respectively.Patent ApplicationAttorney Docket Number 0683-100-WO

[0166] In some embodiments, the SN Required message includes a DU ID of the S-DU of the S-SN 104A. In such cases, the MN 104B may include the DU ID in the SN Request message and the CU 172 may include the DU ID in the first CU-to-DU message. In other embodiments, the SN Required message includes a first BS ID of the S-SN 104A. In some embodiments, the MN 104B may include the first BS ID in the SN Request message. When receiving the first BS ID, the CU 172 may include the first BS ID in the first CU-to-DU message. In some embodiments, the MN 104B may include a second BS ID of the MN 104B in the SN Request message. When receiving the second BS ID, the CU 172 may include the second BS ID in the first CU-to-DU message. In some embodiments, the first BS ID and the second BS ID are gNB IDs.

[0167] The CU 172 may or may not request an LTM reference DU configuration in the procedure 690, as described for FIGs. 3, 4, and 5. The DU 174 may or may not transmit an LTM reference DU configuration to the CU 172 in the procedure 690, as described for FIGs. 3, 4, and 5. In some embodiments, the S-SN 104A (e.g., the CU of the S-SN 104A) may obtain an LTM reference configuration, as described for FIGs. 3 and 4. In other embodiments, the S-SN 104A may receive an LTM reference configuration from the MN 106B (not shown in FIG. 6A) in another inter-SN LTM preparation procedure as described above and below. If the S-SN 104A obtains an LTM reference configuration, the S-SN 104A may include the LTM reference configuration (S-SN generated LTM reference configuration) in the SN Required message. In turn, the MN 104B includes the LTM reference configuration in the SN Request message. Alternatively, the S-SN 104A determines to request or cause the C-SN 106A to provide a complete LTM candidate configuration so that the S-SN 104A does not transmit the LTM reference configuration to the C-SN 106A. If the S-SN 104A does not obtain an LTM reference configuration, the S- SN 104A does not include an LTM reference configuration in the SN Required message. If the SN Required message includes an LTM reference configuration, the MN 104B includes the LTM reference configuration in the SN Request message. Otherwise, if the SN Required message does not include an LTM reference configuration, the MN 104B may not include the LTM reference configuration in the SN Request message.

[0168] If the SN Request message includes an LTM reference configuration as described above, the CU 172 may include the LTM reference configuration in the first CU-Patent ApplicationAttorney Docket Number 0683-1 OO-WO to-DU message. Alternatively, the CU 172 may extract an LTM reference DU configuration from the LTM reference configuration and includes the LTM reference DU configuration in the first CU-to-DU message. Otherwise, if the SN Request message does not include an LTM reference configuration, the CU 172 may or may not receive an LTM reference DU configuration from the DU 174 as described for FIG. 3. If the CU 172 receives an LTM reference DU configuration (e.g., in the first DU-to-CU message), the CU 172 generates an LTM reference configuration (C-SN generated LTM reference configuration) including the LTM reference DU configuration. The CU 172 may include an LTM reference CU configuration (candidate CU (C-CU) generated LTM reference CU configuration). Otherwise, if the CU 172 does not receive an LTM reference DU configuration from the DU 174 as described for FIG. 3, the CU 172 does not generate an LTM reference configuration. Alternatively, the CU 172 generates an LTM reference configuration (C-SN generated LTM reference configuration) only including a C-CU generated LTM reference CU configuration. In cases where the CU 172 generates an LTM reference configuration (C-SN generated LTM reference configuration), the CU 172 includes the C-SN generated LTM reference configuration in the SN Request Acknowledge message.

[0169] In some embodiments, if the LTM DU configuration 1 is a complete configuration, the CU 172 generates the LTM candidate configuration 1 as a complete configuration. The CU 172 may include a complete configuration indication (e.g., a BS-to- BS interface protocol field / IE) in the SN Request Acknowledge message to indicate that the LTM candidate configuration 1 is a complete configuration. In some embodiments, the BS-to-BS interface protocol is an Xn application protocol defined in 3GPP TS 38.423. In some embodiments, the complete configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other embodiments, the complete configuration indication is an existing field / IE defined in 3GPP TS 38.423. Otherwise, if the LTM DU configuration 1 is a delta configuration, the CU 172 generates the LTM candidate configuration 1 as a delta configuration. The CU 172 may exclude the complete configuration indication from the SN Request Acknowledge message to indicate that the LTM candidate configuration 1 is a delta configuration. Alternatively, the CU 172 may include a delta configuration indication (e.g., a BS-to-BS interface protocol field / IE) in the SN Request Acknowledge message to indicate that the LTM candidate configuration 1Patent ApplicationAttorney Docket Number 0683-100-WO is a delta configuration. In some embodiments, the BS-to-BS interface protocol is an Xn application protocol defined in 3GPP TS 38.423. In some embodiments, the delta configuration indication is a new field / IE (e.g., LTM specific) to avoid an impact to non-LTM configurations. In other embodiments, the delta configuration indication is an existing field / IE defined in 3GPP TS 38.423. In some embodiments, the BS-to-BS interface protocol field / IE has two values (i.e. , a first value and a second value). The BS-to-BS interface protocol field / IE set to the first value is the complete configuration indication and the BS-to-BS interface protocol field / IE set to the second value is the delta configuration indication.

[0170] In some embodiments, the S-SN 104A is preconfigured with a CSI resource configuration (e.g., (LTM) CSI resource configuration 1 ) and / or an LTM SSB configuration (LTM SSB configuration 1) for the first cell. In yet another embodiment, the CU 172 receives the CSI resource configuration and / or the LTM SSB configuration from an 0AM (Operations, Administration and Maintenance) node. In yet other embodiments, the S-SN 104A receives the CSI resource configuration and / or the LTM SSB configuration from the CU 172. For example, the CU 172 includes the CSI resource configuration and / or the LTM SSB configuration in the SN Request Acknowledge message. In this case, the MN 104B may include the CSI resource configuration and / or the LTM SSB configuration in the SN Confirm message. In some embodiments, the CU 172 includes a PCI of the first cell in the SN Request Acknowledge message. In this case, the MN 104B may include the PCI of the first cell in the SN Confirm message. To prepare the first cell as a candidate LTM cell for the UE 102, the CU of the S-SN 104A performs an LTM CSI report configuration and / or LTM ID configuration procedure (not shown in FIG. 6A) with an S-DU of the S-SN 104A, similar to the procedure 392 or 492. In the LTM CSI report configuration and / or LTM ID configuration procedure, the CU of the S-SN 104A transmits the CSI resource configuration and / or the LTM SSB configuration to the S-DU of the S-SN 104A. In response, the CU of the S-SN 104A receives one or more CSI report configurations for the UE 102, from the S-DU of the S-SN 104A. In some embodiments, the S-SN 104A receives a second serving DU configuration including the CSI report configuration(s).

[0171] In some embodiments, the CU 172 receives early synchronization information for the first cell and / or PDCCH order information from the DU 174, asPatent ApplicationAttorney Docket Number 0683-100-WO described for FIG. 5. In some embodiments, the early synchronization information includes a RACH configuration (e.g., RACH configuration 1 ) and / or at least one TCI state configuration (e.g., TCI state configuration(s) 1). The CU 172 includes the early synchronization information and / or the PDCCH order information in the SN Request Acknowledge message. The MN 104B includes the early synchronization information and / or the PDCCH order information in the SN Confirm message.

[0172] In some embodiments, the CU 172 assigns an LTM ID (e.g., LTM ID 1 ) for identifying the first LTM candidate configuration and includes the LTM ID and / or an associated (or mapped) cell ID for the LTM ID in the SN Request Acknowledge message. The MN 104A includes the LTM ID and / or an associated (or mapped) cell ID for the LTM ID in the SN Confirm message. In other embodiments, the S-SN 104A assigns an LTM ID (e.g., LTM ID 1 ) for identifying the first LTM candidate configuration. In yet other embodiments, the MN 104B assigns an LTM ID (e.g., LTM ID 1 ) for identifying the first LTM candidate configuration. In such cases, the MN 104B may include the LTM ID in the SN Confirm message. After receiving or assigning the LTM ID, the CU of the S-SN 104A transmits the LTM ID and the first cell ID to the S-DU in an LTM ID configuration procedure, similar to the procedure 390, 392, or 492.

[0173] After (e.g., in response to) receiving the SN Confirm message, the S-SN 104A (e.g., the CU of the S-SN 104A) performs 694 LTM configuration delivery procedure with the UE 102 to transmit the LTM ID and the LTM candidate configuration to the UE 102. In some embodiments, the S-SN 104A transmits {LTM ID, the LTM candidate configuration} as a tuple in a first RRC reconfiguration message in the procedure 694. Depending on the embodiments, the S-SN 104A may include the LTM reference configuration, the CSI report configuration(s), the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration, and / or the PCI of the first cell to the UE 102 in the first RRC reconfiguration message and / or other RRC reconfiguration message(s) transmitted to the UE 102, as described for FIGs. 3 and 4. The S-SN 104A includes the LTM ID in the first RRC reconfiguration or the other RRC reconfiguration message(s) to indicate the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the first cell are associated with the first cell. For example, the S-SN 104A includes the CSIPatent ApplicationAttorney Docket Number 0683-100-WO resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1 in the tuple. In another example, the S-SN 104A includes {LTM ID 1 , the CSI resource configuration, the RACH configuration, the TCI state configuration(s), the LTM SSB configuration and / or the PCI of the cell 1} as a tuple in the other RRC reconfiguration message(s). In response to each of the other RRC reconfiguration message(s), the UE 102 transmits an RRC reconfiguration complete message to the CU 172 via the S-DU 174A.

[0174] In some embodiments, if the SN Required message includes the complete configuration indication to indicate that the LTM candidate configuration 1 is a complete configuration, the S-SN 104A includes, in the first RRC reconfiguration message, a complete configuration indication (e.g., an RRC field / IE) to indicate that the LTM candidate configuration 1 is a complete configuration. Otherwise, if the SN Required message does not include the complete configuration indication or includes the delta configuration indication to indicate that the LTM candidate configuration 1 is a delta configuration, the S- SN 104A excludes or does not include, in the first RRC reconfiguration message, the complete configuration indication (e.g., an RRC field / IE) to indicate that the LTM candidate configuration 1 is a delta configuration.

[0175] If the SN Confirm message includes the RACH configuration and / or the PDCCH order information (PDCCH order information 1), the S-SN 104A may transmit 650A a PDCCH order to the UE 102, based on the RACH configuration and / or the PDCCH order information. If the S-SN 104A is a distributed BS, the CU of the S-SN 104A may transmit the RACH configuration and / or the PDCCH order information to the S-DU of the S-SN 104A and the S-DU may transmit 650A the PDCCH order to the UE 102. For example, the S-SN 104A or the S-DU of the S-SN 104A determines a content of the PDCCH order based on the RACH configuration and / or the PDCCH order information and / or L1 measurement report(s). In some embodiments, the S-SN 104A or the S-DU may determine to transmit the PDCCH order, based on (e.g., in response to) the measurement report(s) 624A. In some embodiments, the S-SN 104A or the S-DU may determine a first SSB index included in the PDCCH order (i.e., a first PDCCH order), based on L1 measurement report(s) 624A, and / or the CSI resource configuration, the CSI report configuration and / or the LTM SSB configuration. In some embodiments, the S-DU or thePatent ApplicationAttorney Docket Number 0683-1 OO-WOS-SN 104A includes the LTM ID 1 in the first PDCCH order to indicate the first cell. The UE 102 transmits 652 a first RA preamble to the DU 174 on the first cell, using the RACH configuration and / or the PDCCH order information. The DU 174 or the C-SN 106A derives a first TA value based on the first RA preamble. The DU 174 transmits 656 a DU-CU TA Information Transfer message including the first TA value to the CU 172. The CU 172 transmits 657 a CU-CU TA Information Transfer message, including the TA value, to the MN 104B (e.g., the CU of the MN 104B). The MN 104B transmits 658 a CU-CU TA Information Transfer message, including the TA value, to the S-SN 104A. In some embodiments, the DU 174 includes the cell ID 1 , the first RA preamble index, a first RA- RNTI, and / or the DU ID of the S-DU of the S-SN 104A in the message 656. The DU 174 may additionally include the first BS ID and / or the second BS ID in the message 656. In some embodiments, the CU 172 includes the cell ID 1 , the first RA preamble index, the first RA-RNTI, and / or the DU ID of the S-DU in the message 657. In some embodiments, the CU 172 may additionally include the first BS ID and / or the second BS ID in the message 657. The MN 104B then includes the cell ID 1 , the first RA preamble index, the first RA-RNTI, and / or the DU ID of the S-DU in the message 658. In some embodiments, the MN 104B may additionally include the first BS ID and / or the second BS ID in the message 658.

[0176] The example embodiments described for the S-DU 174A of BS 104A or the S-BS 104A in FIGs. 4 and 5 apply to the S-SN 104A or the S-DU of the S-SN 104A in FIGs. 6A-6C for the determination of the one or more (allowed) PRACH occasion(s), the calculation of the RA-RNTI(s) for the PRACH occasion(s), and the association of a TA value to a UE considering the cell ID, the RA preamble index, and / or the received RA- RNTI, etc.

[0177] In some embodiments, the CU 172 determines an address (e.g., an IP address) of the MN 104B or the CU of the MN 104B, based on the second BS ID. Thus, the CU 172 transmits the message 657 to the MN 104B in accordance with the address. In some embodiments, the MN 104B determines an address (e.g., an IP address) of the S- SN 104A or the CU of S-SN 104A, based on the first BS ID. In other embodiments, the MN 104B determines an address (e.g., an IP address) of the S-SN 104A or the CU of the S-SN 104A, based on the DU ID of the S-DU of the S-SN 104A. For these embodiments,Patent ApplicationAttorney Docket Number 0683-100-WO the MN 104B sends 658 the CU-CU TA Information Transfer message to the S-SN 104A or the CU of the S-SN 104A in accordance with the address.

[0178] In response to determining to command the UE 102 to perform an LTM cell switch to the first cell, e.g., based on the L1 measurement report(s) 624A and / or 654A, the S-DU or the S-SN 104A transmits 626A to the UE the LTM Cell Switch Command including the LTM ID 1. In response to the LTM Cell Switch Command, the UE 102 may stop communication on the serving cell(s). In response to the LTM Cell Switch Command, the UE 102 accesses 632 the first cell and transmits 636A an RRC reconfiguration complete message to DU 174. The DU 174 in turn transmits 638 a DU-to-CU message including the RRC reconfiguration complete message to the CU 172. In some alternative embodiments, the UE 102 transmits the RRC reconfiguration complete message to the C- SN 106A via the MN 104B, instead of the DU 174. After receiving 638 the DU-to-CU message or the RRC reconfiguration complete message, the C-SN 106A communicates 640 with the UE 102 (which is in DC with the MN 104B and the C-SN 106A) in accordance with the first LTM candidate configuration and / or the LTM reference configuration. In some embodiments, the UE 102 includes the LTM ID 1 in the RRC reconfiguration complete message 636A to indicate that the UE 102 applies the first LTM candidate configuration. In accordance with the LTM ID 1 , the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration. In other embodiments, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration based on the first cell ID included in the Access Success message 634. In such embodiments, the CU 172 maintains or stores association information between the first cell ID and the first LTM candidate configuration and / or the LTM reference configuration. When the CU 172 receives the first cell ID in the Access Success message, the CU 172 identifies the first LTM candidate configuration and / or the LTM reference configuration in accordance with the first cell ID and the association information.

[0179] In some embodiments, if the S-DU or the S-SN 104A receives a TA value as described above, the S-DU or the S-SN 104A may include the TA value in the LTM Cell Switch Command. In some embodiments, the S-DU or the S-SN 104A includes a first TCI state ID in the LTM Cell Switch Command. The first TCI state ID indicates the first one of the TCI state configuration(s).Patent ApplicationAttorney Docket Number 0683-100-WO

[0180] In response to determining to command the UE 102 to perform the LTM cell switch or transmitting 626A the LTM Cell Switch Command, the S-DU of the S-SN 104A transmits a DU-CU Cell Switch Notification message to the CU of the S-SN 104A to indicate that the UE 102 performs an LTM cell switch to the first cell. In response to receiving the DU-CU Cell Switch Notification message, the CU of the S-SN 104A transmits 627A a CU-CU Cell Switch Notification message to the MN 104B to indicate that the UE 102 performs or is performing an LTM cell switch to the first cell. In response, the MN 104B transmits 628 a CU-CU Cell Switch Notification message to the CU 172 to indicate that the UE 102 performs or is performing an LTM cell switch to the first cell. In response, the CU 172 transmits 630 a CU-DU Cell Switch Notification message to the DU 174 to indicate that the UE 102 performs or is performing an LTM cell switch to the first cell. In some embodiments, the S-SN 104A includes the first TCI state ID in the CU-CU Cell Switch Notification message 627A. In such cases, the MN 104B includes the first TCI state ID in the CU-CU Cell Switch Notification message 628. The CU 172 then includes the first TCI state ID in the CU-DU Cell Switch Notification message. The UE 102 and the DU 174 identify the first one of the TCI state configuration(s) based on the first TCI state ID and apply the first TCI state configuration to communicate UL transmissions and / or DL transmissions in the events 632, 636A, and / or 640. In other embodiments, in case that separate TCI states are used, the DL TCI state and the UL TCI state use different TCI state IDs. In such cases, the S-DU of the S-SN 104A includes, in the DU-CU Cell Switch Notification message and / or the LTM Cell Switch Command, a first TCI state ID for DL and a second TCI state ID for UL that identify a first one and a second one of the TCI state configuration(s). The CU of the S-SN 104A, in response to the DU-CU Cell Switch Notification message, includes the first TCI state ID and the second TCI state ID in the CU-CU Cell Switch Notification message to the MN 104B. The MN 104B includes the first TCI state ID and the second TCI state ID in the CU-CU Cell Switch Notification message sent to the CU 172. The CU 172 then includes the first TCI state ID and the second TCI state ID in the CU-DU Cell Switch Notification message sent to the DU 174. The UE 102 identifies the first TCI state configuration and / or the second TCI state configuration based on the first TCI state ID and the second TCI state ID, respectively. The UE 102 applies the first TCI state configuration and the second TCI state configuration to communicate DLPatent ApplicationAttorney Docket Number 0683-100-WO transmissions and UL transmissions, respectively, with the DU 174 in the events 632, 636A, and / or 640. The DU 174 identifies the first TCI state configuration and the second the TCI state configuration based on the first TCI state ID and second TCI state ID, respectively. The DU 174 applies the first and / or the second TCI state configuration to communicate DL transmissions and / or UL transmissions, respectively, with the UE 102 in the events 632, 636A, and / or 640.

[0181] In some embodiments, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch or transmitting 626A the LTM Cell Switch Command, the S-SN 104A transmits 631 one or more Early Status Transfer messages to the MN 104B, each including a DL COUNT value or a DISCARD DL COUNT value for a DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other. The MN 104B transmits one or more Early Status Transfer messages to CU 172, each including the DL COUNT value or the DISCARD DL COUNT value for the DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other.

[0182] In some embodiments, after receiving 634 the Access Success message or receiving 638 the DU-to-CU message or the RRC reconfiguration complete message, the CU 172 transmits 639 an LTM Success message to the MN 104B (e.g., the CU of the MN 104B) to indicate that the LTM cell switch was successfully completed. In some embodiments, the LTM Success message is an SA / Modification Required message or a BS-to-BS Access Success message. In some embodiments, the CU 172 includes the first cell ID in the LTM Success message. In other embodiments, the CU 172 does not transmit a BS-to-BS message to the MN 104B (e.g., the CU of the MN 104B) to indicate that the LTM cell switch is completed successfully. In some embodiments, after (e.g., in response to) receiving the LTM Success message or receiving the RRC reconfiguration complete message from the UE 102, the MN 104B may transmit an SN message (as shown event 645 in FIG. 6C) to the S-SN 104A. The SN message may indicate that the LTM cell switch was successfully completed, and indicate the S-SN 104A to suspend communication with the UE 102, or indicate the S-SN 104A to release a UE context of the UE 102 and resources configured for the UE 102. The MN 104B may include the first cell ID in the SN message. In some embodiments, the SN message is an SN Modification Request message, an SN Release Request message, an SN Access Success message or the like.Patent ApplicationAttorney Docket Number 0683-100-WO

[0183] In some embodiments, after (e.g., in response to) determining to command the UE 102 to perform the LTM cell switch, transmitting 626A the LTM Cell Switch Command, receiving the DU-CU Cell Switch Notification message from the S-Dll, or receiving the SN message, the S-SN 104A (e.g., the CU of the S-SN 104A) transmits 641 an SN Status Transfer message to the MN 104B, including a DL COUNT value and / or a UL COUNT value for a / the DRB over which the UE 102 and the S-SN 104A communicate 602 data with each other. After (e.g., in response to) receiving the SN Status Transfer message 641 , the MN 104B transmits 642 an S / V Status Transfer message to the CU 172, including the DL COUNT value and / or the UL COUNT value.

[0184] In some embodiments, the S-SN 104A (e.g., the CU of the S-SN 104A) may prepare additional cell(s) (i.e., cell(s) 2, ... , N) as LTM candidate cell(s) for the UE 102 with the MN 104B and one or more C-SNs (including the C-SN 106A), before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 698A, as described above, where N is an integer larger than 1 . The cell(s) 2, ... , N may be operated by the C-SN(s). For example, the S-SN 104A performs additional inter-SN LTM preparation procedure(s) 2, ... , N with the MN 104B to prepare the cell(s) 2, ... N, respectively. Each of the inter-SN LTM preparation procedure(s) 2, ... , N is similar to the procedure 698A. In the inter-SN LTM preparation procedure(s) 2, ... , N, the S-SN 104A receives LTM candidate configuration(s) 2, ... , N configuring the cell(s) 2, ... , N for LTM, respectively. As described above, the MN 104B, S-SN 104A or C-SN(s) assign LTM ID(s) 2, ... , N to identify the LTM candidate configuration(s) 2, ... , N, respectively. The S-SN 104A may obtain CSI resource configuration 2, ... , N for the cell(s) 2, ... , N, respectively, as described for the CSI resource configuration 1 . The S-SN 104A may obtain CSI report configuration(s) 2, ... , N or the cell(s) 2, .... N, respectively, as described for the CSI report configuration(s) 1. The S-SN 104A may obtain RACH configuration 2, ... , N for the cell(s) 2, ... , N respectively, as described for the RACH configuration 1. The S-SN 104A may obtain TCI state configuration(s) 2, ... , N for the cell(s) 2, ... , N respectively, as described for the TCI state configuration(s) 1. The S-SN 104A may obtain LTM SSB configuration 2, ... , N for the cell(s) 2, ... , N, respectively, as described for LTM SSB configuration 1. In some embodiments, the S-SN 104A may perform LTM configuration delivery procedure 2, ... , N with the UE 102 to transmit the {LTM ID 2, the LTM candidate configuration 2, thePatent ApplicationAttorney Docket Number 0683-1 OO-WOCSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained)}, .... {the LTM ID N, the LTM candidate configuration N, the CSI resource configuration N, the TCI state configuration(s) N (if obtained), the RACH configuration N (if obtained), the LTM SSB configuration N (if obtained)}, respectively. Each of the LTM configuration delivery procedure 2, ... , N is similar to the procedures 394, 494, and / or 594. In other embodiments, the S-SN 104A includes the tuples in the first RRC reconfiguration message.

[0185] In some embodiments, an SN Required message and an SN Confirm message in each of the inter-SN LTM preparation procedure(s) 2, ... , N are an SN Modification Required message and an SN Modification Confirm message, respectively. In other embodiments, an SN Required message and an SN Confirm message in each of the inter-SN LTM preparation procedure(s) 2, ... , N are an SN Change Required message and an SN Change Confirm message, respectively. In some embodiments, an SN Request message and an SN Request Acknowledge message in each of the inter-SN LTM preparation procedure(s) 2, ... , N are an SN Addition Request message and an SN Addition Request Acknowledge message, respectively. In other embodiments, the SN Request message and the SN Request Acknowledge message, in each of the inter-SN LTM preparation procedure(s) 2, ... , N, are an SN Modification Request message and an SN Modification Request Acknowledge message, respectively. In some embodiments, the information provided in the SN Confirm message (e.g., LTM candidate configuration, LTM reference configuration, first cell ID, or LTM ID) are alternatively provided in an SN Modification Request message from the MN 104B to the S-SN 104A (i.e., similar to the event 609B which will be described in the scenario 600B).

[0186] In other embodiments, the S-SN 104A performs the procedure 698A with the CU 172 to prepare (one or more of) the cell 1 and cell(s) 2, ... , N as LTM candidate cell(s) for the UE 102. The cell(s) 2, ... , N are identified by cell ID(s) 2, ... , N respectively and operated by the DU 174 and / or other DU(s) of the C-SN 106A. In such embodiments, the S-SN 104A includes the cell ID(s) 2, ... , N in the SN Required message 603 for LTM and the MN 104B includes the cell ID(s) 2, ... , N in the SN Request message, as descried for the cell ID 1 above. In some embodiments, upon receiving the SN Request message,Patent ApplicationAttorney Docket Number 0683-1 OO-WO the CU 172 determines or selects the cell(s) 1 , ... , M from the cell(s) 1 , ... , N as LTM candidate cell(s), where M is a positive integer and M < N. In other embodiments, CU 172 prepares the cell(s) 1 , N for LTM as requested in the SN Request message. The CU 172 performs LTM preparation procedure(s) 2, M with the DU 172 to prepare the cell(s) 2, M as LTM candidate cell(s) for the UE 102, respectively. The LTM preparation procedure(s) 2, ... , M are similar to the procedure 690 that the CU 172 performs with the DU 174 to prepare the cell 1 . The CU 172 obtains the LTM candidate configuration(s) 2, ... , M for the cell(s) 2, ... , M as a result of the LTM preparation procedure(s) 2, ... , M respectively, similar to obtaining the LTM candidate configuration 1. The C-SN 106A may generate the LTM candidate configuration(s) 2, ... , M as complete configuration(s) or generate delta configuration(s) based on the LTM reference configuration, as described for the LTM candidate configuration 1. The CU 172 includes the LTM candidate configuration(s) 2, ... , M in the SN Request Acknowledge message. In some embodiments, the CU 172, the MN 104B, or the S-SN 104A assigns LTM ID(s) 2, ... , M to identify the LTM preparation procedure(s) 2, ... , M, respectively, as described for the LTM ID 1 and the LTM candidate configuration 1. If the CU 172 assigns the LTM ID(s) 1 , ... , M, the CU 172 includes the LTM ID(s) 1 , ... , M with the LTM candidate configuration(s) 1 , ... , M, respectively, in the SN Request Acknowledge message, as described for the LTM ID 1 and the LTM candidate configuration 1.

[0187] In some embodiments, the CU 172 obtains early synchronization information 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the early synchronization information 1. The CU 172 includes the early synchronization information 2, ... , M in the SN Request Acknowledge message. In some embodiments, the CU 172 or the S-SN 104A obtains CSI resource configuration(s) 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the CSI resource configuration 1 . If the CU 172 obtains the CSI resource configuration(s) 2, ... , M, the CU 172 includes the CSI resource configuration(s) 2, ... , M in the SN Request Acknowledge message.

[0188] In some embodiments, the CU 172 or the S-SN 104A obtains LTM SSB configuration(s) 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the LTM SSB configuration 1. If the CU 172 obtains the LTM SSB configuration(s) 2, ... , M, the CU 172 includes the LTM SSB configuration(s) 2, ... , M in the SN Request AcknowledgePatent ApplicationAttorney Docket Number 0683-100-WO message. In some embodiments, the CU 172 or the S-SN 104A obtains PCI(s) 2, M for the cell(s) 2, , M, respectively, as described for the PCI 1 . If the CU 172 obtains the PCI(s) 2, ... , M, the CU 172 includes the PCI(s) 2, ... , M in the SN Request Acknowledge message.

[0189] In some embodiments, the CU 172 includes a list of {the cell ID 1 , the LTM ID 1 (if obtained or optional), the LTM candidate configuration 1 , the CSI resource configuration 1 (if obtained or optional), the TCI state configuration 1 (if obtained or optional), the early synchronization information 1 (if obtained or optional), the LTM SSB configuration 1 (if obtained or optional), PCI 1 (if obtained or optional)}, ... , {the cell ID M, the LTM ID M (if obtained or optional), the LTM candidate configuration M, the CSI resource configuration M (if obtained or optional), the TCI state configuration M (if obtained or optional), the early synchronization information M (if obtained or optional), the LTM SSB configuration M (if obtained or optional), the PCI M (if obtained or optional)} in the SN Request Acknowledge message. The MN 104B includes the list or a portion of the list in the SN Confirm message.

[0190] In some embodiments, the CU 172 obtains PDCCH order information 2, ... , M for the cell(s) 2, ... , M, respectively, as described for the PDCCH order information 1. In one embodiment, the CU 172 includes the PDCCH order information 2, ... , M in the SN Request Acknowledge message. In another embodiment, the CU 172 includes the PDCCH order information 2, ... , M in the early synchronization information 2, ... , M, respectively. The MN 104B may include the PDCCH order information 2, ... , M in the SN Confirm message as described for the PDCCH order information 1. The S-SN 104A may obtain RACH configuration 2, TCI state configuration(s) 2 and / or the PDCCH order information 2, ...., RACH configuration M, TCI state configuration(s) M and / or the PDCCH order information M from the early synchronization information 2, ... , M, respectively or from the SN Confirm message.

[0191] In some embodiments, the S-SN 104A may perform LTM configuration delivery procedure 2, ... , M with the UE 102 to transmit the tuples {LTM ID 2, the LTM candidate configuration 2, the CSI resource configuration 2 (if obtained), the TCI state configuration 2 (if obtained), the RACH configuration 2 (if obtained), the LTM SSB configuration 2 (if obtained), the PCI 2 (if obtained)}, ... , {the LTM ID M, the LTM candidatePatent ApplicationAttorney Docket Number 0683-100-WO configuration M, the CSI resource configuration M, the TCI state configuration(s) M (if obtained), the RACH configuration M (if obtained), the LTM SSB configuration M (if obtained), the PCI M (if obtained)}, respectively. Each of the LTM configuration delivery procedure 2, ... , M is similar to the procedures 394, 494, and / or 594. In other embodiments, the S-SN 104A includes the tuples in the first RRC reconfiguration message.

[0192] In some embodiments, the MN 104B may include measurement result(s) 1 , ... , N for the cell(s) 1 , ... , N, respectively in the SN Request message. In some embodiments, the MN 104B may receive the measurement result(s) from the UE 102 and / or in the SN Required message from the S-SN 104A. The C-SN 106A may select or determine the cell(s) 1 , ...M, based on the measurement result(s) 1 , ... , N. In other embodiments, the C-SN 106A may select or determine the cell(s) 1 , ... , M, based on other factors (e.g., capacity or load of the cell(s) 1 , ... , N and / or a maximum number of LTM candidate cell(s)). In one embodiment, the maximum number is included in the SN Request message. In another embodiment, the maximum number is a predetermined number. The events 626A, 627A, 628, 630, 631 , 632, 633, and 634 are collectively referred to in FIG. 6A as an LTM execution procedure 699.

[0193] FIG. 6B illustrates a scenario 600B which is generally similar to the scenario 600A, except that the scenario 600B includes events 604B, 609B, and 611 instead of events 603 and 609A. In the scenario 600B, the MN 104B initiates 698B inter-SN LTM preparation procedure, while in the scenario 600A, the S-SN 104A initiates 698A inter-SN LTM preparation procedure. While communicating in DC with the MN 104B and S-SN 104A, the UE 102 may transmit 604B at least one measurement report to the MN 104B, e.g., via the SRB1 , similar to the events 304 / 306, the events 404 / 406, and the event 504. If the MN 104B is a distributed BS, the MN 104B includes a CU and a DU. The CU of the MN 104B receives the measurement report(s) from the UE 102 via the DU of the MN 104B. The MN 104B (e.g., the CU of the MN 104B) generates a measurement configuration to configure the UE 102 to transmit the measurement report(s) and transmits the measurement configuration to the UE 102 (e.g., via the DU of the MN 104B).

[0194] After (e.g., in response to) receiving one or some of the measurement report(s) from the UE 102, the MN 104B (e.g., the CU of the MN 104B) determines toPatent ApplicationAttorney Docket Number 0683-100-WO prepare a first cell (e.g., the cell 124B) as an LTM candidate for the UE 102. In response to the determination, the MN 104B generates an SN Request message (a first SN Request message) including a first cell ID (e.g., cell ID 1 ) of the first cell (e.g., cell 1 ) and transmits 605 the SN Request message to the C-SN 106A. In response to the SN Request message, the CU 172 (decides and) performs the LTM preparation procedure 690 with the DU 174 and transmits 607 the SN Request Acknowledge message to the MN 104B, as described above with regard to FIG. 6A. After (e.g., in response to) receiving the message 607, the MN 104B transmits 609B an S / V Modification Request message to the S-SN 104A, including a first LTM candidate configuration (LTM candidate configuration 1 ), an LTM reference configuration, and / or the first cell ID, the RACH configuration, and / or the PDCCH order information, and / or the SSB positions in burst, similar to the event 609A. If the SN Request Acknowledge message includes LTM related configurations such as the RACH configuration, the TCI state configuration(s), the CSI resource configuration, the LTM SSB configuration, and / or the PCI of the first cell for configuring the first cell as an LTM candidate cell, the MN 104B includes the LTM related configurations in the SN Modification Request message. In response to the SN Modification Request message, the S-SN 104A transmits 611 an SN Modification Request Acknowledge message to the MN 104B and performs 694 the LTM configuration delivery procedure with the UE 102 to transmit the first LTM candidate configuration and / or the LTM reference configuration to the UE 102. The events 605, 690, 607, 609B, and 611 are collectively referred to in FIG. 6B as an MN-initiated inter-SN LTM preparation procedure 698B.

[0195] As described for FIG. 6A, the SN Request Acknowledge message 607 may include the PDCCH order information. If the SN Request Acknowledge message 607 includes the PDCCH order information, the MN 104B includes the PDCCH order information in the SN Modification Request message. If the SN Modification Request message includes the PDCCH order information, the S-SN 104A may transmit 650A a PDCCH order to the UE 102, based on the PDCCH order information, as described for FIG. 6A. If the SN Modification Request message includes the TCI state configuration(s), the S-SN 104A may include a first TCI state ID in the LTM Cell Switch Command as described for FIG. 6A.Patent ApplicationAttorney Docket Number 0683-100-WO

[0196] In some embodiments, the MN 104B (e.g., the CU of the MN 104B) may perform one or more LTM preparation procedures to prepare additional cell(s) (i.e., cell(s) 2, ... , N) as LTM candidate cell(s) for the UE 102 with the CU 172 or other C-SN(s), and each of the LTM preparation procedure is similar to the procedure 698B. The MN 104B may perform the LTM preparation procedure(s) before or after transmitting the LTM Cell Switch Command or during, before or after the procedure 698B.

[0197] In other embodiments, the MN 104B performs the procedure 698B with the CU 172 to prepare (one or more of) the cell 1 and cell(s) 2, ... , N as LTM candidate cell(s) for the UE 102, where N is an integer larger than 1. The cell(s) 2, ... , N are identified by cell ID(s) 2, ... , N, respectively and operated by the DU 174 and / or other DU(s) of the C- SN 106A. In such embodiments, the MN 104B includes the cell ID(s) 2, ... , N in the SN Request message 605, as descried for the cell ID 1 above.

[0198] FIG. 6C illustrates a scenario 600C which is generally similar to the scenarios 600A and 600B, except that the scenario 600C includes events 694C, 636C, and 645 instead of events 694A, 636A, and 638. In the scenario 600C, the MN 104B transmits to the UE 102, the second serving DU configuration (including the CSI report configuration), the LTM ID, the first LTM candidate configuration, the LTM reference configuration, the CSI resource configuration, the LTM SSB configuration, the RACH configuration, the TCI state configuration(s), and / or the PCI of the first cell for configuring the first cell as an LTM candidate cell in one or more RRC reconfiguration messages in the LTM configuration delivery procedure 694C, similar to the procedures 394, 494, or 594. In some embodiments, the MN 104B generates the RRC reconfiguration message(s) in the procedure 694C, while the S-SN 104A generates the RRC reconfiguration message(s) in the procedure 694A. In some embodiments, the MN 104B assigns the LTM ID in the scenario 600C, while the S-SN 104A assigns the LTM ID in the scenarios 600A and 600B.

[0199] When the UE 102 performs 699 the LTM execution procedure, the UE 102 transmits 636C an RRC reconfiguration message to the MN 104B, similar to the event 636A. In some embodiments, the UE 102 includes the LTM ID in the RRC reconfiguration complete message to indicate that the UE 102 applies the first LTM candidate configuration. After (e.g., in response to) receiving the RRC reconfiguration message, the MN 104B may transmit 645 the SN message to the S-SN 104A as described for FIG. 6A.Patent ApplicationAttorney Docket Number 0683-100-WOIn some embodiments, the MN 104B may include a first cell ID of the first cell in the SN message. The MN 104B may determine the first cell ID based on the LTM ID received in the RRC reconfiguration complete message.

[0200] FIG. 6D illustrates a scenario 600D which is generally similar to the scenarios 600A, 600B, and 600C, except that the scenario 600D includes events 624D, 650D, 654D, 626D, and 627D instead of events 624A, 650A, 654A, 626A, and 627A. The events 624D, 650D, 654D, and 626D are similar to the events 624A, 650A, 654A, and 626A respectively, except that the MN 104B is involved in the events 624D, 650D, 654D, and 626D, while the S-SN 104A is involved in the events 624A, 650A, 654A, and 626A. The event 627D is different from the 627A as in the event 627D, the MN 104B may transmit the CU-CU Cell Switch Notification message which may include the first TCI State ID and / or the second TCI State ID to the S-SN 104A.

[0201] The example embodiments described for the S-DU 174A of BS 104A or the S-BS 104A in FIGs. 4 and 5 apply to the MN 104B or the S-DU of the MN 104B in FIG. 6D for the determination of the one or more (allowed) PRACH occasion(s), the calculation of the one or more RA-RNTI(s) for the PRACH occasion(s), and the association of a TA value to a UE considering the cell ID, the RA preamble index, and / or the received RA- RNTI, etc.

[0202] In some embodiments, the MN 104B may generate the CSI report configuration(s) based on a CSI resource configuration, as described for S-SN 104A. The CSI resource configuration configures RS(s) transmitted on the first cell. The MN 104B transmits the CSI report configuration(s) to the UE 102 in the procedure 694C. In some embodiments, the MN 104B is preconfigured with CSI resource configuration. In other embodiments, the MN 104B receives the CSI resource configuration from an 0AM node. In yet other embodiments, the MN 104B receives the CSI resource configuration from the CU 172 or the S-SN 104A.

[0203] Next, several example methods, which may be performed by a RAN node (e.g., a BS, a DU, or a CU) for intra-CU or inter-CU LTM, are discussed with reference to FIGs. 7A-14B. Descriptions for FIGs. 3-6D may apply to any of the FIGs. 7A-14B. Similar steps are similarly labeled (e.g., 302, 402, 502, 602, etc.) and individual descriptions of these steps are therefore omitted.Patent ApplicationAttorney Docket Number 0683-100-WO

[0204] FIG. 7A illustrates a method 700A, which may be performed by a first RAN node (e.g., the S-DU 174A in FIG. 4, the S-BS 104A in FIG. 5, the S-SN 104A in Figs. 6A- 6C, or the MN 104B in FIG. 6D). The method 700A starts with the first RAN node receiving 712 a message (e.g., at least one of a RACH configuration, and / or a PDCCH order information, and / or SSB positions in burst) for a first cell for a first UE (e.g., UE 102). The first RAN node receives the message from a second RAN node (e.g., the CU 172 in FIG.4, the C-BS 104A or CU 172 in FIG. 5, the MN 104B in Figs. 6A-6C, or the C-SN 106A or CU 172 in FIG. 6D). The first RAN node transmits 718 the RACH configuration to the first UE. The first RAN node may construct 751 SSB indexes to PRACH occasions mapping based on the RACH configuration and / or the SSB positions in burst. The first RAN node determines 753 a first SSB index based on an L1 measurement report of the first UE and / or the PDCCH order information. The first RAN node determines 755 a first PRACH mask index based on the RACH configuration and / or the PDCCH order information and / or the SSB positions in burst. The first PRACH mask index indicates at least one first PRACH occasion(s) where the first UE is allowed to transmit an RA preamble. The first RAN node transmits 750 a first PDCCH order to the first UE, where the first PDCCH order includes a first RA preamble, the first PRACH mask index, and the first SSB index, and commands the first UE to transmit the first RA preamble on the first cell. Then, the first RAN node calculates 757 a first set of RA-RNTI(s) according to the allowed first PRACH occasion(s) and / or the SSB indexes to PRACH occasions mapping. The first RAN node receives 758 an interface message (e.g., CU-DU TA Information Transfer message or CU-to-CU TA Information Transfer message) including a first TA value and a first RA-RNTI from the second RAN node. The first RAN node determines 759 whether the first TA value is provided for the first UE, based on whether a value of the first RA-RNTI is equal to a value of one of the first set of RA-RNTI(s). The first RAN node transmits 726A an LTM cell switch command to the first UE, commanding the first UE to perform an LTM cell switch to the first cell.

[0205] In some embodiments, the steps 757 and 758 may be interchanged. In some embodiments, at step 757, the first RAN node calculates the first set of RA-RNTI(s) without referencing to the SSB indexes to PRACH occasions mapping (which might or might not be constructed at step 751 ). The first RAN node only calculates the first set ofPatent ApplicationAttorney Docket Number 0683-100-WORA-RNTI(s) based on the allowed first PRACH occasion(s), which are determined according to the RACH configuration and the first PRACH mask index. In such embodiment, the first RAN node uses the first set of RA-RNTI(s) to determine 759 whether the first TA value is provided for the first UE. In other embodiments, the first RAN node performs 751 and calculates a first set of RA-RNTI(s) according to the allowed first PRACH occasion(s) and the SSB indexes to PRACH occasions mapping. In such embodiment, the first RAN node uses the first set of RA-RNTI(s) to determine 759 whether the first TA value is provided for the first UE.

[0206] In some embodiments, the first RAN node (e.g., the S-BS 104A in FIG. 5) transmits at least one Handover Request message to the second RAN node, including an early sync information request to request early sync information (e.g., event 505). In response, the first RAN node (e.g., the S-BS 104A in FIG. 5) receives 712, from the second RAN node (e.g., the C-BS 106A in FIG. 5), at least one Handover Request Acknowledge message that includes the RACH configuration and / or the PDCCH order information and / or a SSB positions in burst. In other embodiments, the first RAN node (e.g., the S-DU 174A in FIG. 4) receives 712 from the second RAN node (e.g., the CU 172 in FIG. 4) at least one UE Context Modification Request message that includes the RACH configuration and / or the PDCCH order information and / or a SSB positions in burst. In yet another embodiments, the first RAN node (e.g., the S-SN 104A in Figs. 6A-6C) receives 712 from the second RAN node (e.g., the MN 104B in Figs. 6A-6C) an S-Node Modification Confirm message, or an S-Node Modification Request message that includes the RACH configuration and / or the PDCCH order information and / or a SSB positions in burst. In yet another embodiment, the first RAN node (e.g., the MN 104B in FIG. 6D) receives 712 from the second RAN node (e.g., C-SN 106A in FIG. 6D) an S-Node Modification Request Acknowledge message or an S-Node Addition Request Acknowledge message that includes the RACH configuration and / or the PDCCH order information and / or a SSB positions in burst.

[0207] In some embodiments, the first RAN node determines the content of the first PDCCH order for the UE based on the RACH configuration (e.g., EarlyUL-SyncConfig) and a preamble index list and / or the SSB positions in burst. In other embodiments, the first RAN node determines the content of the first PDCCH order for the UE based on thePatent ApplicationAttorney Docket Number 0683-100-WORACH configuration (e.g., EarlyUL-SyncConfig) and the PDCCH order information (e.g., RACH-ConfigDedicated) and / or the SSB positions in burst.

[0208] In some embodiments, the first RAN node, which acts as a source DU (e.g., S-DU 174A of FIG. 4), does not receive the SSB positions in burst but receives an LTM CSI resource configuration from the second RAN node, which acts as a CU (e.g., CU 172 of FIG. 4). In such case, if the first RAN node needs to construct the mapping of SSB indexes to valid PRACH occasions and calculate the corresponding RA-RNTI(s), the first RAN node infers the transmitted SSBs for the first cell, based on the LTM CSI resource configuration. In other embodiments, if the first RAN node receives a dedicated RACH configuration (e.g., RACH-ConfigDedicated as the PDCCH order information) for early uplink synchronization while the SSB positions in burst for the first cell is absent, the first RAN node infers the transmitted SSBs for the first cell, based on the dedicated RACH configuration for early uplink synchronization.

[0209] FIG. 7B illustrates an example method 700B similar to the method 700A, which may be performed by a first RAN node (e.g., the S-DU 174A in FIG. 4, the S-BS 104A in FIG. 5, the S-SN 104A in Figs. 6A-6C, or the MN 104B in FIG. 6D). The method 700B begins at block 712 and then proceeds to block 718. The first RAN node may construct 751 an SSB indexes to PRACH occasions mapping based on the RACH configuration and the SSB positions in burst. The flow proceeds to blocks 753, 755, 757, and 758, which were discussed above. The first RAN node determines 760 whether a value of the first RA-RNTI is equal to a value of one of the first set of RA-RNTI(s). If the value of the first RA-RNTI is equal to a value of one of the first set of RA-RNTI(s) (i.e. , “Yes” branch of block 760), the flow proceeds to block 725, where the first RAN node includes the first TA value in an LTM cell switch command for commanding the first UE to perform an LTM cell switch to the first cell. The flow proceeds from block 725 to block 726B where the first RAN node transmits the LTM cell switch command to the first UE. If the value of the first RA-RNTI is not equal to a value of one of the first set RA-RNTI(s) (i.e., “No” branch of block 760), the flow proceeds to block 726B directly from block 760. In other words, if the value of the first RA-RNTI is not equal to a value of one of first set of RA-RNTI(s) at block 760, the first RAN node refrains from including the TA value in thePatent ApplicationAttorney Docket Number 0683-100-WOLTM cell switch command. In such case, the UE may only perform a random access on the first cell during the LTM cell switch.

[0210] FIG. 8 illustrates a method 800 similar to the method 700A or 700B, which may be performed by a first RAN node (e.g., the S-DU 174A in FIG. 4, the S-BS 104A in FIG. 5, the S-SN 104A in Figs. 6A-6C, or the MN 104B in FIG. 6D). The method 800 begins with performing the actions noted in blocks 712, 718, 751 , 753, 755, 750, 757, and 758. At block 818, the first RAN node transmits the RACH configuration to a second UE. The first RAN node determines 853 a second SSB index based on an L1 measurement report of a second UE and / or the PDCCH order information. The first RAN node determines 855 a second PRACH mask index based on the RACH configuration, and / or the PDCCH order information, and / or the SSB positions in burst, where the second PRACH mask index indicates at least one second PRACH occasion(s) where the second UE is allowed to transmit an RA preamble. The first RAN node transmits 850 a second PDCCH order to the second UE, where the second PDCCH order includes, a second RA preamble index, the second PRACH mask index, and the second SSB index and commands the second UE to transmit the second RA preamble on the first cell. The first RAN node calculates 857 a second set of RA-RNTI(s) according to the allowed second PRACH occasion(s) and / or the SSB indexes to PRACH occasions mapping. The first RAN node receives 858 an interface message including a first TA value and a first RA-RNTI and a second TA value and a second RA-RNTI from the second RAN node. The first RAN node determines 859 whether the first TA value and the second TA value are provided for the first UE and the second UE, respectively, based on whether a value of the first RA- RNTI and a value of the second RA-RNTI are equal to a value of one of the first set of RA- RNTI(s) and a value of one of the second set of RA-RNTI(s), respectively. The first RAN node may transmit 726A an LTM cell switch command to the first UE, commanding the first UE to perform an LTM cell switch to the first cell. The first RAN node may transmit 826 an LTM cell switch command to the second UE, commanding the second UE to perform an LTM cell switch to the first cell.

[0211] In some embodiments, the first UE performs a RACH-less LTM cell switch to the first cell using the first TA value and the second UE performs a RACH-less LTM cell switch to the second cell. In some embodiments, the second SSB index may be the samePatent ApplicationAttorney Docket Number 0683-100-WO as or different from the first SSB index; the second PRACH mask index may be the same as or different from the first PRACH mask index; the second RA preamble index may be the same as or different from the first RA preamble index. To allow the first RAN node and the second RAN node to differentiate the UEs, the three parameters cannot be the same at the same time in the first PDCCH order and the second PDCCH order.

[0212] FIG. 9 illustrates a method 900, which may be performed by a first DU (e.g., the C-DU 174B of FIG. 4). The method 900 begins with the first DU receiving 908 a CU-to- DU message (e.g., UE Context Modification Request message) from a CU (e.g., the CU 172), where the CU-to-DU message requests early synchronization information. The first DU transmits 910, to the CU, a DU-to-CU message (e.g., UE Context Modification Response message) a RACH configuration, and / or a PDCCH order information and a SSB positions in a burst configuration for the cell, where the SSB positions in burst is provided for a second DU (e.g., the S-DU 174A) to calculate one or more RA-RNTI(s).

[0213] In some embodiments, the request for early synchronization information concerns a particular cell and the DU configures the RACH configuration, and / or PDCCH order information and SSB positions in burst configuration for the particular cell. In some embodiments, the first DU receives an RA preamble from a UE and derives a TA value. The first DU also calculates an RA-RNTI based on the RACH configuration, the SSB positions in burst, and the PRACH occasion on which the RA preamble is transmitted. The first DU transmits the RA-RNTI and the TA value to the second DU via the CU (e.g., by a DU-CU TA Information Transfer message and a CU-DU TA Information Transfer message). The value of the RA-RNTI should match the value of one of the RA-RNTI(s) calculated by the second DU so that the second DU is able to associate the UE with the TA value for early uplink synchronization.

[0214] FIG. 10A illustrates a method 1000A, which may be performed by a first BS (e.g. , the C-BS 106A of FIG. 5 or the C-SN 106A of FIG. 6D). The method 1000A starts with the first BS receiving 1008 a BS-to-BS message (e.g., Handover Request message, S-Node Addition Request message, or S-Node Modification Request message) from a second BS (e.g., the S-BS 104A of FIG. 5 or the MN 104B of FIG. 6D), where the BS-to- BS message requests early synchronization information. The first BS transmits 1010A, to the second BS, a BS-to-BS message (e.g., Handover Request Acknowledge message, S-Patent ApplicationAttorney Docket Number 0683-100-WONode Addition Request Acknowledge message, or S-Node Modification Request Acknowledge message) a RACH configuration, and / or a PDCCH order information and a SSB positions in burst configuration, where the SSB positions in burst is provided for the second BS or a DU of the second BS to calculate one or more RA-RNTI(s).

[0215] In some embodiments, the request for early synchronization information concerns a particular cell and the first BS configures the RACH configuration, and / or PDCCH order information and SSB positions in burst configuration for that particular cell. In some embodiments, the first BS receives an RA preamble from a UE and derives a TA value. The first BS also calculates an RA-RNTI based on the RACH configuration, the SSB positions in burst and the PRACH occasion on which the RA preamble is transmitted. The first BS transmits to the second BS the TA value and the RA-RNTI (e.g., by a CU-CU TA Information Transfer message). The value of the RA-RNTI should match the value of one of the RA-RNTI(s) calculated by the second BS or a DU of the second BS so that the second BS or the DU of the second BS is able to associate the UE with the TA value for early uplink synchronization.

[0216] FIG. 10B illustrates a method 1000B, which may be performed by a first BS (e.g., the C-SN 106A of Figs. 6A-6C). The method 1000B starts with the first BS receiving 1008 a BS-to-BS message (e.g., S-Node Addition Request message or S-Node Modification Request message) from a second BS (e.g., the MN 104B of Figs. 6A-6C), where the BS-to-BS message requests early synchronization information. The first BS transmits 101 OB to the second BS, a BS-to-BS message (e.g., S-Node Addition Request Acknowledge message or S-Node Modification Request Acknowledge message) a RACH configuration, and / or a PDCCH order information and a SSB positions in burst configuration, where the SSB positions in burst is provided for a third BS (e.g., the S-SN 104A of Figs. 6A-6C) or a DU of the third BS to calculate one or more RA-RNTI(s).

[0217] In some embodiments, the request for early synchronization information concerns a particular cell and the first BS configures the RACH configuration, and / or PDCCH order information and SSB positions in burst configuration for that particular cell. In some embodiments, the first BS receives an RA preamble from a UE and derives a TA value. The first BS also calculates a RA-RNTI based on the RACH configuration, the SSB positions in burst and the PRACH occasion on which the RA preamble is transmitted. ThePatent ApplicationAttorney Docket Number 0683-100-WO first BS transmits to the second BS the TA value and the RA-RNTI (e.g., by a CU-CU TA Information Transfer message) and the second BS further transmits the TA value and the RA-RNTI to the third BS. The value of the RA-RNTI should match the value of one of the RA-RNTI(s) calculated by the third BS or a DU of the third BS so that the third BS or the DU of the third BS is able to associate the UE with the TA value for early uplink synchronization.

[0218] In some embodiments, the SSB positions in burst (configuration) is contained in an SSB information which includes an SSB time / frequency configuration and a physical cell identifier (PCI). The SSB time / frequency configuration includes an SSB frequency, an SSB subcarrier spacing, an SSB transmit power, an SSB periodicity, an SSB half frame index, an SSB SFN offset, an SSB positions in burst, and an SFN initialization time.

[0219] FIG. 11 illustrates a method 1100, which may be performed by a DU (e.g., the C-DU 174B of FIG. 4). The method 1100 starts with the DU receiving 1108 a CU-to- DU message (e.g., UE Context Modification Request message) from a CU (e.g., the CU 172). The DU determines 1177 whether the CU-to-DU message requests early synchronization information for a cell. If the CU-to-DU message requests early synchronization information (i.e. , the ‘Yes’ branch of block 1177), the method proceeds to block 1178, where the DU includes a RACH configuration, and / or PDCCH order information and a SSB positions in burst configuration for early synchronization with the DU in a DU-to-CU message (e.g., UE Context Modification Response message). In some embodiments, the request for early synchronization information concerns a particular cell and the DU configures the RACH configuration, and / or PDCCH order information and SSB positions in burst configuration for that cell. The method proceeds to block 1179, where the DU includes one or more other configurations in the DU-to-CU message. The DU transmits 1107 the DU-to-CU message to the CU. If the CU-to-DU message does not request early synchronization information for a cell (i.e., the ‘No’ branch of block 1177), the method proceeds to block 1179 and then to block 1107.

[0220] In some embodiments, the “SSB positions in burst configuration for early synchronization with the DU” at block 1178 means that the SSB positions in burst configuration is used by the (ultimate) recipient (e.g., the S-DU 174A, the S-BS 104A, orPatent ApplicationAttorney Docket Number 0683-100-WO the MN 104B) to construct an SSB indexes to PRACH occasions mapping and calculate one or more RA-RNTI(s) associated with an SSB in the process of the early uplink synchronization.

[0221] FIG. 12 illustrates an LTM cell switch method 1200, which may be performed by a first BS (e.g., a C-BS 106A or the CU of the C-BS 106A of FIG. 5, or a C- SN 106A or the CU of the C-SN 106A of Figs. 6A-6D). The method 1200 starts with the first BS receiving 1208 a first BS-to-BS message (e.g., Handover Request message, S- Node Addition Request message, or S-Node Modification Request message) from a second BS (e.g., the S-BS 104A of FIG. 5 or the MN 104B of Figs. 6A-6D). The first BS determines 1277 whether the BS-to-BS message requests early synchronization information for an LTM cell switch. If the BS-to-BS message requests early synchronization information for a cell (i.e., the ‘Yes’ branch of block 1277), the flow proceeds to block 1278, where the first BS includes a RACH configuration, and / or PDCCH order information and a SSB positions in burst configuration for early synchronization with the first BS, in a second BS-to-BS message (e.g., Handover Request Acknowledge message, S-Node Addition Request Acknowledge message, or S-Node Modification Request Acknowledge message). In some embodiments, the early synchronization information request concerns a particular cell, and the first BS configures the RACH configuration, and / or PDCCH order information and SSB positions in burst configuration for that cell. The method proceeds to block 1279, where the first BS includes one or more other configurations in the second BS-to-BS message. Then, the first BS transmits 1207 the second BS-to-BS message to the second BS. If the BS-to-BS message does not request early synchronization information for a cell (i.e., the ‘No’ branch of block 1277), the method proceeds to block 1279 and then to block 1207.

[0222] In some embodiments, the “SSB positions in burst configuration for early synchronization with the first BS” at block 1278 means that the SSB positions in the burst configuration are used by the (ultimate) recipient (e.g., the S-DU 174A, the S-BS 104A, the MN 104B, or the S-SN 104A) to construct SSB indexes to PRACH occasions mapping and calculate one or more RA-RNTI(s) associated with an SSB in the process of the early uplink synchronization.Patent ApplicationAttorney Docket Number 0683-100-WO

[0223] In some embodiments, the CU does not include the SSB positions in burst it received from a C-DU, a C-BS, or a C-SN in a CU-to-DU message (e.g., UE Context Modification Request message) to the S-DU. The CU may, instead of including the SSB positions in burst, generate and include in the CU-to-DU message an LTM CSI resource configuration which contains an LTM CSI SSB resource set including all of the SSB indexes indicated in the SSB positions in burst it received at block 1107 or 1207. The CU transmits the CU-to-DU message including the LTM CSI resource configuration to the S- DU.

[0224] In other embodiments, the CU may, instead of including the SSB positions in burst in the UE Context Modification Request message, include the SSB positions in burst in the associated TA information for the first cell in the CU-DU TA Information Transfer message.

[0225] FIG. 13 illustrates a method 1300, which may be performed by a first RAN node (e.g., CU 172 in FIG. 4, the CU of the S-BS 104A in FIG. 5, the CU of the S-SN 104A in Figs. 6A-6C, or the CU of the MN 104B in FIG. 6D). The method 1300 starts with the first RAN node transmitting 1308 a first interface message to a second RAN node (e.g., the C-DU 174B in FIG. 4, the C-BS 106A in FIG. 5, the MN 104B in Figs. 6A-6C, or the C- SN 106A in FIG. 6D) to request early synchronization for a first cell for a first UE. The first RAN node receives 1310 a second interface message from the second RAN node including a first RACH configuration and / or a first PDCCH order information and a first SSB positions in burst, for the first cell, for the first UE. The first RAN node transmits 1309 a third interface message to a third RAN node to request early synchronization for a second cell for the first UE. The first RAN node receives 1311 a fourth interface message from the third RAN node including a second RACH configuration and / or a second PDCCH order information and a second SSB positions in burst, for the second cell, for the first UE. The first RAN node transmits 1312 a fifth interface message, to a DU, including the {first RACH configuration and / or the first PDCCH order information, the first SSB positions in burst, and the ID for the first cell} and the {second RACH configuration and / or the second PDCCH order information and the second SSB positions in burst, and the ID for the second cel I} for the first UE. The first RAN node transmits 1316 to the first UE, via the DU,Patent ApplicationAttorney Docket Number 0683-100-WO the first RACH configuration and the first SSB positions in burst for the first cell and the second RACH configuration and the second SSB positions in burst for the second cell.

[0226] In some embodiments, the third RAN node may be the same as or different from the second RAN node. In some embodiments, the {first RACH configuration and / or the first PDCCH order information, the first SSB positions in burst, and the ID for the first cell} are included as an item of an Early Sync Candidate Cell Information List. In some embodiments, the first RAN node, instead of including the SSB positions in burst at 1312, transmits to the DU the {first SSB positions in burst and first cell ID and other TA info} and / or {second SSB positions in burst and second cell ID and other TA info} in a CU-DU TA Information Transfer message. Examples and embodiments described for FIGs. 4-6D may apply to FIGs. 7A-13.

[0227] In some embodiments, the first and the second interface messages are a UE Context Setup Request message and a UE Context Setup Response message, respectively. In other implementations, the first and the second interface messages are a Ha ndo ver Req uest message and a Handover Request Acknowledge message, respectively. In yet other implementations, the first and the second interface messages are an S-Node Addition (or Modification) Request message and an S-Node Addition (or Modification) Request Acknowledge message, respectively. The third and the fourth interface messages may each be the same as or different from the first and the second interface messages, respectively.

[0228] FIG. 14A and FIG. 14B illustrate two example visualizations of the SSB indexes to PRACH occasion mapping, with the SSB positions in burst as ‘1111111 T and ‘1011011 T, respectively. For early uplink synchronization in LTM, the EarlyUL-SyncConfig IE contains the parameters such as the frequencylnfoUL, Itm-PRACH-SubcarrierSpacing, n-Timng AdvanceOffset, ssb-PerRACH-Occasion, and the rach-ConfigGeneric IE. The rach-ConfigGeneric IE further contains parameters such as the PRACH configuration index and the msg1-FDM, etc. An example from 3GPP TS 38.211 (Table 63.3.2-3: Random access configurations for FR1 and unpaired spectrum with the PRACH Configuration Index as ‘109’) is used for the illustrations in FIGs. 14A and 14B and a PRACH configuration period of ‘10ms’ and a subcarrier spacing of ‘30kHz’ are assumed. The PRACH Configuration Index indicates the available set of PRACH occasions for thePatent Application Attorney Docket Number 0683-1 OO-WO transmission of the RA preamble for Msg1 . From the content of the table, it may be interpreted as that every radio frame has PRACH slot(s); every subframe in the radio frame may have PRACH slot(s); the starting symbol of the PRACH slot is 9; every subframe has one PRACH slot; one PRACH slot has one time-domain PRACH occasion; the PRACH duration is 4-symbol long; etc. In such case, if the SSB positions in burst are ‘11111111 ,’ see FIG. 14A, 8 SSBs are transmitted and the last two PRACH occasions are invalid for RA preamble transmission (i. e. , no SSB indexes are mapped to the last two PRACH occasions). If the SSB positions in burst is ‘10110111 ,’ see FIG. 16B, 6 SSBs are transmitted and the last four PRACH occasions are invalid for RA preamble transmission.Table 6.3.3.2-3

[0229] The UE (e.g., the UE 102), the C-DU (e.g., the C-DU 174B), the S-DU (e.g., the S-DU 174A), the S-BS (e.g., the S-BS 104), the MN (e.g., the MN 104B), or the S-SN (e.g., S-SN 104A) each constructs and share the same result of mapping if RA-RNTI is needed to be calculated at each side. The RA-RNTI may be used as a way for resolution or identification among several RA-RNTI values associated with PRACH occasions so that the UE which transmits the RA preamble in that PRACH occasion may be identified. In some embodiments, for a first RAN node (e.g., the S-DU 174A or S-BS 104), it receives the EarlyUL-SyncConfig from a second RAN node (e.g., the CU 172 or C-BS 106) and obtains parameters such as the PRACH configuration index (e.g., with the value ‘109’), the ssb-perRACH-occasion (e.g., with the value ‘1 / 4’), and msg1 -FDM (e.g., with the value ‘4’), etc.

[0230] The first RAN node, which issues the PDCCH order, may construct the mapping combining also the information provided in the SSB positions in burst with thePatent ApplicationAttorney Docket Number 0683-100-WO above parameters and calculate one or more RA-RNTI(s) according to the mapping, as described in FIG. 4 and the mapping may be applied to any of the embodiments illustrated in FIGs. 4 to 13.

[0231] As discussed above, features from various embodiments may be combined to obtain additional methods. For example, features from at least the methods 700A, 700B, and 800 may be combined in the following method. A wireless communication method performed by a BS (e.g., 104A) includes transmitting 718 a RACH configuration to a first UE 102 via a serving cell 124A, and transmitting 750, to the first LIE, a first PDCCH order instructing the first UE to transmit a first RA preamble on a candidate cell 125, which is configured for an LTM procedure (by this BS or another BS), the first PDCCH order including at least one of: a first RA preamble index, a first PRACH mask index, or a first SSB index. The method may further include receiving 712, the RACH configuration, a PDCCH order information, or SSB positions in burst for the candidate cell.

[0232] The method may also include at least one of the following steps: determining the first SSB index based on a layer L1 measurement report received from the first UE or on the PDCCH order information, determining the first PRACH mask index based on the RACH configuration, the PDCCH order information, or the SSB positions in burst, where the first PRACH mask index indicates at least one first PRACH occasion for which the first UE is allowed to transmit the RA preamble, calculating a mapping of SSB indexes to PRACH occasions based on the RACH configuration and the SSB positions in burst, calculating a first set of RA-RNTIs, according to the first PRACH occasion or the SSB indexes to PRACH occasions mapping, receiving a first TA value and a first RA-RNTI from a second BS, adding the first TA value to an LTM cell switch command when determining that a value of the first RA-RNTI is equal to a value of one of the first set of RA-RNIs, and transmitting the LTM cell switch command to the first UE commanding the first UE to perform an LTM cell switch to the candidate cell. The method may further include one or more of the following steps: transmitting, to a second UE, a second PDCCH order instructing the second UE to transmit a second RA preamble on the candidate cell for the LTM procedure, the second PDCCH order including: a second RA preamble index, a second PRACH mask index, and a second SSB index, determining a second SSB index based on an L1 measurement report received from the second UE or on the secondPatent ApplicationAttorney Docket Number 0683-100-WOPDCCH order information, determining a second PRACH mask index based on the RACH configuration, the second PDCCH order information, or the second SSB positions in burst, wherein the second PRACH mask index indicates at least one second PRACH occasion for which the second UE is allowed to transmit the RA preamble, calculating a second set of RA-RNTIs, according to the second PRACH occasion or the SSB indexes to PRACH occasions mapping, receiving a message including the first TA value, a second TA value, the first RA-RNTI, and a second RA-RNTI, determining whether the first TA value and the second TA value are provided for the first UE and the second UE, respectively, based on the first and second RA-RNTI values being equal to corresponding values from the first and second sets of RA-RNTIs, respectively, transmitting a first LTM cell switch command to the first UE commanding the first UE to perform an LTM cell switch to the candidate cell, and transmitting a second LTM cell switch command to the second UE commanding the second UE to perform an LTM cell switch to the candidate cell.

[0233] According to another embodiment, a wireless communication method is performed by a first BS (e.g., 106A), and the method includes receiving 1208 a first message from a second BS (e.g., 104A), when the first message includes a request for early synchronization information for an LTM cell switch, including 1278, in a second message for the second BS, a RACH configuration, a PDCCH order information, or SSB positions in burst configuration for early synchronization with the first BS, and transmitting 1207 the second message to the second BS, and when the first message omits the request for early synchronization information for the LTM cell switch, including 1279 a configuration unrelated to the early synchronization information in a third message for the second BS, and transmitting 1207 the third message to the second BS.

[0234] A layer L1 , measurement report includes an SSB index or an SSB Resource Indicator (SSBRI) corresponding to the SSB index. The PDCCH order may further include an UL or a supplementary UL indicator, and a cell indicator. The SSB positions in burst indicate time domain positions of transmitted SSBs in a half frame with SSB blocks.

[0235] A communication device (102, 104) including a processor (151 , 131 ) and a transceiver (153, 133) is configured to execute the methods of claims 1 to 17.

[0236] The description for one of the above figures may apply to another of the above figures. Examples, embodiments and methods described above may be combined,Patent ApplicationAttorney Docket Number 0683-1 OO-WO 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. The description described from the perspective of the receiving node also applies to the sending node. For example, a description that a receiving node (e.g., DU) receives a message from a sending node (e.g., CU) may be replaced by the sending node sending a message to the receiving node. Similarly, a description that a receiving node (e.g., CU) receives a message from a sending node (e.g., DU) may be replaced by the sending node sending a message to the receiving node.

[0237] In some embodiments, the term “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, the “DU configuration” may be replaced by “cell group configuration”. In some embodiments, the “serving” may be replaced by “source”. In some embodiments, the “measurement report” may be replaced by “measurement result(s)” or “CSI report”. In some embodiments, the “early TA acquisition” may be replaced by “early UL timing synchronization” or “early UL synchronization”. In some embodiments, the “early TA acquisition on a / the candidate cell” may be replaced by “early UL timing synchronization with a / the candidate cell” or “early UL synchronization with a / the candidate cell”.“Handover Request’ and “Handover Request Acknowledge’’ described above are for illustration of the invention and may be replaced by messages with general names. For example, “Handover Request’ and “Handover Request Acknowledge" may be replaced by a first CU-to-CU message and a second CU-to-CU message, respectively. In another example, “Handover Request’ and “Handover Request Acknowledge” may be replaced by a first interface message and a second interface message, respectively. In yet another example, “Handover Request’ and “Handover Request Acknowledge" may be replaced by a first BS-to-BS message and a second BS-to-BS message, respectively. In some embodiments, “include” may be replaced by “comprise”. In some embodiments, “exclude” may be replaced by “refrain from including”.

[0238] A UE 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 aPatent ApplicationAttorney Docket Number 0683-1 OO-WO smartphone, a tablet computer, a laptop computer, a mobile gaming console, a point-of- sale (POS) terminal, a health monitoring device, a drone, a camera, a media-streaming dongle or another personal media device, a wearable device such as a smartwatch, a wireless hotspot, a femtocell, or a broadband router. Further, the user device in some cases may be embedded in an electronic system such as the head unit of a vehicle or an advanced driver assistance system (ADAS). Still further, the user device 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.

[0239] Certain embodiments are described in this disclosure 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 include dedicated circuitry or logic that is permanently configured (e.g., as a specialpurpose processor, such as a field programmable gate array (FPGA) or an applicationspecific integrated circuit (ASIC), a digital signal processor (DSP), etc.) to perform certain operations. A hardware module may also include 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. When implemented in software, the techniques 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.

[0240] Upon reading this document, those of skill in the art will appreciate still additional and alternative structural and functional designs for handling mobility between BSs through the principles disclosed herein. Thus, while particular embodiments and applications have been illustrated and described, it is to be understood that the disclosedPatent ApplicationAttorney Docket Number 0683-1 OO-WO embodiments are not limited to the precise construction and components disclosed herein. Various modifications, changes and variations, which will be apparent to those of ordinary skill in the art, may be made in the arrangement, operation and details of the method and apparatus disclosed herein without departing from the spirit and scope defined in the appended claims.

[0241] 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.

[0242] 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.

[0243] 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

Patent ApplicationAttorney Docket Number 0683-1 OO-WOWHAT IS CLAIMED IS:1 . A wireless communication method (700A, 700B) performed by a base station, BS, (104A), the method comprising: transmitting (718) a random access channel, RACH, configuration to a first user equipment, UE, (102) via a serving cell (124A); transmitting (750), to the first UE (102), a first physical downlink control channel, PDCCH, order instructing the first UE (102) to transmit a first random access, RA, preamble on a candidate cell (125), which is configured for a lower-layer triggered mobility, LTM, procedure, the first PDCCH order including at least one of: a first RA preamble index, a first physical random access channel, PRACH, mask index, or a first synchronization signal block, SSB, index; and receiving (712), the RACH configuration, a PDCCH order information, or SSB positions in burst for the candidate cell.

2. The method of Claim 1 , further comprising: determining the first SSB index based on a layer 1 , L1 , measurement report received from the first UE or on the PDCCH order information.

3. The method of Claim 2, further comprising: determining the first PRACH mask index based on the RACH configuration, the PDCCH order information, or the SSB positions in burst, wherein the first PRACH mask index indicates at least one first PRACH occasion for which the first UE is allowed to transmit the RA preamble.

4. The method of any of Claims 1 to 3, further comprising: calculating a mapping of SSB indexes to PRACH occasions based on the RACH configuration and the SSB positions in burst.

5. The method of Claim 4, further comprising:Patent ApplicationAttorney Docket Number 0683-1 OO-WO calculating a first set of RA-radio network temporary identifiers, RA-RNTIs, according to the first PRACH occasion or the SSB indexes to PRACH occasions mapping.

6. The method of Claim 5, further comprising: receiving a first TA value and a first RA-RNTI from a second BS.

7. The method of Claim 6, further comprising: adding the first TA value to an LTM cell switch command when determining that a value of the first RA-RNTI is equal to a value of one of the first set of RA-RNIs; and transmitting the LTM cell switch command to the first UE commanding the first UE to perform an LTM cell switch to the candidate cell.

8. The method of Claim 6, further comprising: transmitting, to a second UE, a second PDCCH order instructing the second UE to transmit a second RA preamble on the candidate cell for the LTM procedure, the second PDCCH order including: a second RA preamble index, a second PRACH mask index, and a second SSB index.

9. The method of Claim 8, further comprising: determining a second SSB index based on an L1 measurement report received from the second UE or on the second PDCCH order information.

10. The method of Claim 9, further comprising: determining a second PRACH mask index based on the RACH configuration, the second PDCCH order information, or the second SSB positions in burst, wherein the second PRACH mask index indicates at least one second PRACH occasion for which the second UE is allowed to transmit the RA preamble.11 . The method of Claim 10, further comprising:Patent ApplicationAttorney Docket Number 0683-1 OO-WO calculating a second set of RA-RNTIs, according to the second PRACH occasion or the SSB indexes to PRACH occasions mapping.

12. The method of Claim 11 , further comprising: receiving a message including the first TA value, a second TA value, the first RA- RNTI, and a second RA-RNTI.

13. The method of Claim 6, further comprising: determining whether the first TA value and the second TA value are provided for the first UE and the second UE, respectively, based on the first and second RA-RNTI values being equal to corresponding values from the first and second sets of RA-RNTIs, respectively; transmitting a first LTM cell switch command to the first UE commanding the first UE to perform an LTM cell switch to the candidate cell; and transmitting a second LTM cell switch command to the second UE commanding the second UE to perform an LTM cell switch to the candidate cell.

14. A wireless communication method (1200) performed by a first base station, BS, (106A), the method comprising: receiving (1208) a first message from a second BS (104A); when the first message includes a request for early synchronization information for a lower-layer triggered mobility, LTM, cell switch, including (1278), in a second message for the second BS (104A), a random access channel, RACH, configuration, a physical downlink control channel, PDCCH, order information, or synchronization signal block, SSB, positions in burst configuration for early synchronization with the first BS (104A), and transmitting (1207) the second message to the second BS (104A); and when the first message omits the request for early synchronization information for the LTM cell switch, including (1279) a configuration unrelated to the early synchronization information in a third message for the second BS (104A), and transmitting (1207) the third message to the second BS (104A).Patent ApplicationAttorney Docket Number 0683-1 OO-WO15. The method of Claim 14, wherein a layer 1 , L1 , measurement report includes an SSB index or an SSB Resource Indicator (SSBRI) corresponding to the SSB index.

16. The method of any of Claims 14 or 15, wherein the PDCCH order further includes an uplink, UL, or a supplementary UL, SUL, indicator, and a cell indicator.

17. The method of any of Claims 14 to 16, wherein the SSB positions in burst indicate time domain positions of transmitted SSBs in a half frame with SSB blocks.

18. A communication device (102, 104) comprising a processor (151 , 131 ) and a transceiver (153, 133) is configured to execute the methods of claims 1 to 17.

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