WO2025173465A1 - Distributed unit, central unit, wireless terminal, and methods therefor - Google Patents

Abstract

In the present invention, a distributed unit (DU) of a radio access network (RAN) node receives, from a central unit (CU) of the RAN node, a first message for requesting preparation of a first candidate cell for L1/L2-triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells that include the first candidate cell. The DU determines, on the basis of whether or not the first message includes a first display which is related to a conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM which has been requested by the first message are the subject of the conditional LTM or the subject of a normal LTM. This is useful for providing, for example, details of the operations of the CU and a candidate DU for preparing the conditional LTM.

Description

Distributed unit, central unit, wireless terminal, and methods thereof

This disclosure relates to wireless communication systems, and more particularly to wireless terminal mobility.

The 3rd Generation Partnership Project (3GPP (registered trademark)) Release 18 specifies the mechanisms and procedures for Layer-1 (L1)/Layer-2 (L2) Triggered Mobility (LTM) (see, for example, non-patent literature 1-6). When a wireless terminal (i.e., User Equipment (UE)) in the Radio Resource Control (RRC)_CONNECTED state moves from the coverage area of one cell to another, a serving cell change must be performed at some point. Serving cell changes, as specified in 3GPP Release 17 and earlier, are triggered by Layer-3 (L3) measurements and involve reconfiguration with synchronization triggered by RRC signaling for changes in the Primary Cell (PCell) and Primary Secondary Cell Group (SCG) Cell (PSCell), and the release and addition of Secondary Cells (SCells), if applicable.

In contrast, LTM is a procedure in which a base station (i.e., gNB) receives L1 measurement reports from a UE and, based on these, the gNB changes one or more serving cells of the UE through L2 signaling, specifically Medium Access Control (MAC) Control Element (MAC CE). The gNB prepares one or more candidate cells and provides the candidate cell configurations to the UE through an RRC message. An LTM cell switch is then triggered when the gNB selects one of the candidate cell configurations as the target configuration for LTM. The gNB sends a Cell Switch Command MAC CE to the UE. The Cell Switch Command MAC CE indicates the target configuration selected by the gNB (which corresponds to one target cell). In response to receiving the Cell Switch Command MAC CE, the UE initiates a cell switch to the target cell. The UE performs a Random Access Channel (RACH)-less LTM cell switch or a RACH-based LTM cell switch. Subsequent LTM between candidate cells (i.e., after an LTM is triggered, the UE does not release other candidate cell configurations) can be performed without RRC reconfiguration. Candidate cell configurations can only be added, modified, or released by the network (i.e., gNB) via RRC signaling.

LTM supports both intra-gNB Distributed Unit (gNB-DU) mobility and intra-gNB-CU inter-gNB-DU mobility. LTM supports inter-frequency mobility as well as intra-frequency mobility. LTM supports the following scenarios: PCell change in non-Carrier Aggregation (CA) scenarios; PCell change without SCell change in CA scenarios; PCell change with SCell change in CA scenarios; and Dual Connectivity scenarios. PCell change with SCell change in CA scenarios includes a) cases where the target PCell or target SCell(s) is not the current serving cell (i.e., CA-to-CA scenario with PCell change), b) cases where the target PCell is the current SCell, and c) cases where the target SCell is the current PCell. The Dual Connectivity scenario includes at least a PSCell change without Master Node (MN) involvement.

Non-patent document 2 discloses the procedure for inter-gNB-DU LTM, i.e., LTM in which a UE moves from one gNB-DU to another within the same gNB-CU. The gNB-CU receives an L3 measurement report from the UE and decides to start LTM preparation (or LTM configuration). The gNB-CU sends one or more UE CONTEXT SETUP REQUEST messages to a candidate gNB-DU regarding the preparation of one or more candidate cells. If multiple candidate cells are prepared, the gNB-CU uses multiple UE Context Setup procedures, each for one candidate cell. If the candidate gNB-DU accepts the LTM configuration request, it responds to the gNB-CU with one or more UE CONTEXT SETUP REPONSE messages. Each of the one or more UE CONTEXT SETUP REPONSE messages contains RRC configuration for a corresponding accepted candidate cell.

Non-patent document 6 proposes improvements to support LTM for F1 Application Protocol (F1AP) messages sent from a gNB-CU to a gNB-DU. Specifically, non-patent document 6 discloses that a UE CONTEXT SETUP REQUEST message sent from a gNB-CU to a gNB-DU may include an LTM Information Setup information element (IE), an LTM Configuration ID Mapping List IE, an Early Sync Information Request IE, and a Source gNB-DU ID IE. In addition, non-patent document 6 discloses that the UE CONTEXT MODIFICATION REQUEST message sent from the gNB-CU to the gNB-DU may include an LTM Information Modify IE, an LTM Configuration ID Mapping List IE, an Early Sync Information Request IE, an Early Sync Information List IE, and an LTM Cells To Be Released List IE. Furthermore, non-patent document 6 discloses that the UE CONTEXT SETUP RESPONSE and UE CONTEXT SETUP RESPONSE messages sent from the gNB-DU to the gNB-CU may include an Early Sync Information IE and an LTM Configuration IE.

3GPP plans to consider extensions to LTM for 3GPP Release 19 (see, for example, Non-Patent Document 7). LTM extensions under consideration include conditional LTM (CLTM), which may also be referred to by other names such as UE-triggered LTM. 3GPP aims to support CLTM, which includes defining the conditions that will be evaluated by the UE to trigger CLTM (CLTM execution).

Non-patent Documents 8-11 disclose findings and proposals regarding CLTM. Non-patent Document 8 states that when CLTM is introduced, the LTM mechanisms of 3GPP Release 18, such as UE-based TA (not early TA) and RACH-less operation, can be reused to perform handovers with low latency.

Non-Patent Document 9 describes the features and advantages of conditional reconfiguration, or L3 conditional mobility, and states that CLTM can be considered to improve robustness. Non-Patent Document 9 discloses that potential enhancements for CLTM include L1 measurement-based execution conditions and enhanced procedures such as early TA acquisition.

Non-patent document 10 states that CLTM, i.e., UE-initiated LTM execution based on configured conditions, can be effective in improving the robustness of LTM. Non-patent document 10 includes the following description regarding CLTM: The UE autonomously executes LTM when configured conditions are met. The configured conditions relate, for example, to L1/L2-based triggers and Beam Failure Detection (BFD). For CLTM execution, resources to be used in the target cell may be specified, regardless of whether source cell notification is present. Resources to be used in the target cell include, for example, configured Scheduling Request (SR), Sunding Reference Signal (SRS) or Configured Grant (CG), and Dynamic Grant (DG) for intra-DU cases. For target cell synchronization, early synchronization (before conditional LTM is performed) may be required, which can be UE-based synchronization or an early LTM RACH with a Random Access Response (RAR) or MAC CE providing TA.

Non-patent document 11 includes the following description regarding CLTM: Applicable CLTM scenarios include Contention-based Random Access (CBRA)-based CLTM, Contention-free RA (CFRA)-based CLTM, and RACH-less CLTM. For CFRA-based CLTM, provisioning and validity management of CFRA resources need to be considered. For RACH-less CLTM, both RA-based and UE-based TA acquisition are supported for early TA acquisition. For RA-based early TA acquisition, RA including RAR is used as the baseline. For beam indication, pre-beam indication from the network is considered. In CLTM, it is important to reduce candidate cell management operations. For example, it is possible to reduce Channel State Information (CSI)-related operations and TA acquisition operations based on L3 measurements of candidate cells. 3GPP Release 18 Regarding coexistence of LTM and CLTM, dynamic activation of CLTM evaluation for configured candidate cells is considered.

MediaTek Inc., vivo, "Introduction of NR further mobility enhancements in TS 38.300", R2-2313832, 3GPP TSG-RAN WG2 Meeting #124, Chicago, USA, November 13-17, 2023 Huawei, Ericsson, Nokia, Nokia Shanghai Bell, ZTE, NEC, LG Electronics, Lenovo, Samsung, CATT, Google, "Intr oduction of L1L2Mob and S-CPAC", R3-238088, 3GPP TSG-RAN WG3 Meeting #122, Chicago, USA, November 13-17, 2023 ZTE Corporation, Sanechips, CATT, "Introduction of NR further mobility enhancements in TS 37.340", R2-2313647, 3GPP TSG-RAN WG2 Meeting #124, Chicago, USA, November 13-17, 2023 Ericsson, “Introduction of further NR mobility enhancements”, R2-2314056, 3GPP TSG-RAN WG2 Meeting #124, Chicago, USA, November 13-17, 2023 Huawei, HiSilicon, "Introduction of NR further mobility enhancements in TS 38.321", R2-2314040, 3GPP TSG-RAN WG2 Meeting #124, Chicago, USA, November 13-17, 2023 Ericsson, Huawei, Nokia, Nokia Shanghai Bell, ZTE, NEC, LG Electronics Inc., Lenovo, CATT, Samsung, Qualcomm Incorporate d, “Additions for L1/L2 triggered mobility”, R3-238152, 3GPP TSG-RAN WG3 Meeting #122, Chicago, USA, November 13-17, 2023 Intel, “New WID: NR mobility enhancements Phase 4”, RP-234036, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023 Samsung, “Scope of Mobility Enhancements in Rel-19”, RP-232916, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023 vivo, "Views on Rel-19 Mobility enhancements (RAN2-led)", RP-233056, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023 Qualcomm Incorporated, “Views on scope for NR Mobility enhancements in Rel-19”, RP-233214, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023 LG Electronics, “Work scope of mobility enhancements in Rel-19”, RP-233466, 3GPP TSG RAN Meeting #102, Edinburgh, Scotland, December 11-15, 2023

The inventors have considered supporting CLTM in cellular networks and have identified various challenges. One of these challenges relates to signaling between a CU (e.g., gNB-CU) and a DU (e.g., gNB-DU) for CLTM. It is currently unclear how a CU and one or more DUs operate to prepare for CLTM between multiple candidate cells.

One of the objectives that the embodiments disclosed in this specification aim to achieve is to provide an apparatus, method, and program that contributes to solving at least one of the multiple problems related to CLTM, including the problems described above. It should be noted that this objective is only one of the multiple objectives that the multiple embodiments disclosed in this specification aim to achieve. Other objectives or objectives and novel features will become apparent from the description of this specification or the accompanying drawings.

A first aspect is directed to a distributed unit (DU) of a Radio Access Network (RAN) node. The DU is configured to receive, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for LTM of a wireless terminal among a plurality of candidate cells including the first candidate cell. The DU is configured to determine whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM, based on whether the first message includes a first indication related to conditional LTM.

A second aspect is directed to a method performed by a DU of a RAN node, the method comprising the steps of:
(a) receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for LTM of a wireless terminal among a plurality of candidate cells including the first candidate cell; and (b) the DU determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM.

A third aspect is directed to a CU of a RAN node. The CU is configured to send a first message to a DU of the RAN node, requesting preparation of a first candidate cell for LTM of a radio terminal among multiple candidate cells including the first candidate cell. The first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM, based on whether the first message includes a first indication related to conditional LTM.

A fourth aspect is directed to a method performed by a CU of a RAN node. The method includes sending a first message to a DU of the RAN node, requesting preparation of a first candidate cell for LTM of a radio terminal among a plurality of candidate cells including the first candidate cell. The first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM, based on whether the first message includes a first indication related to conditional LTM.

A fifth aspect is directed to a wireless terminal. The wireless terminal is configured to evaluate an execution condition for conditional LTM for each of one or more candidate cells. The wireless terminal is configured to perform a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell. With regard to the cell switch, the wireless terminal is configured to determine whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether the reference signal beam for which the execution condition for the one candidate cell is determined to be met was used to acquire the valid Timing Advance value in the early Timing Advance acquisition procedure performed for the one candidate cell.

A sixth aspect is directed to a method performed by a wireless terminal. The method includes: (a) evaluating an execution condition for conditional LTM for each of one or more candidate cells; and (b) performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell. Here, performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether the reference signal beam for which the execution condition for the one candidate cell is determined to be met was used to acquire the valid Timing Advance value in the early Timing Advance acquisition procedure performed for the one candidate cell.

A seventh aspect is directed to a program. The program includes a set of instructions (software code) that, when loaded into a computer, causes the computer to perform the method according to the second, fourth, or sixth aspect described above.

The above-described aspects provide an apparatus, method, and program that contribute to solving at least one of the multiple problems related to CLTM, including the problems described above.

FIG. 1 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 1 illustrates an example configuration of a wireless communication system according to one or more embodiments. FIG. 1 illustrates an example of a signaling procedure for LTM, in accordance with one or more embodiments. FIG. 1 illustrates an example signaling procedure for conditional LTM, in accordance with one or more embodiments. 1 is a flowchart illustrating an example of the operation of a DU in accordance with one or more embodiments. 10 is a flowchart illustrating an example of the operation of a CU in accordance with one or more embodiments. FIG. 1 illustrates an example of signaling between a CU and a candidate DU, in accordance with one or more embodiments. A figure showing an example format of a UE CONTEXT SETUP REQUEST message relating to one or more embodiments. A figure showing an example format of a UE CONTEXT SETUP REQUEST message relating to one or more embodiments. A figure showing an example format of a UE CONTEXT SETUP REQUEST message relating to one or more embodiments. A figure showing an example format of a UE CONTEXT SETUP REQUEST message relating to one or more embodiments. A figure showing an example of the format of a DU to CU RRC Information information element relating to one or more embodiments. A figure showing an example format of a UE CONTEXT SETUP RESPONSE message relating to one or more embodiments. FIG. 1 illustrates an example of signaling between a CU, a source DU, and a candidate DU, in accordance with one or more embodiments. FIG. 1 illustrates an example of signaling between a CU and a candidate DU, in accordance with one or more embodiments. 1 is a flowchart illustrating an example of UE operation in accordance with one or more embodiments. FIG. 2 is a block diagram illustrating an example configuration of a CU, a CU-CP, a CU-UP, and a DU, in accordance with one or more embodiments. FIG. 1 is a block diagram illustrating an example configuration of a UE in accordance with one or more embodiments.

Specific embodiments will be described in detail below with reference to the drawings. In each drawing, identical or corresponding elements are designated by the same reference numerals, and duplicate explanations will be omitted as necessary for clarity.

The multiple embodiments described below may be used independently, or two or more embodiments may be combined as appropriate. These multiple embodiments may have novel features that are different from each other. Therefore, these multiple embodiments may contribute to achieving different objectives or solving different problems, and may contribute to achieving different effects from each other.

Each drawing is merely an example for describing one or more embodiments. Each drawing does not relate to only one particular embodiment, but may also relate to one or more other embodiments. As will be understood by those skilled in the art, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings to create, for example, an embodiment not explicitly shown or described. Not all features or steps shown in any one drawing are necessarily required to describe an exemplary embodiment, and some features or steps may be omitted. The order of steps described in any drawing may be changed as appropriate.

The following embodiments are described primarily with the 3GPP 5th Generation Mobile Communication System (5G system) in mind. However, these embodiments may also be applied to other wireless communication systems that support technologies similar to 3GPP LTM.

As used herein, depending on the context, "if" may be interpreted to mean "when," "while," "at or around the time," "after," "upon," "in response to determining," "in accord with a determination," or "in response to detecting." These expressions may be interpreted to have the same meaning, depending on the context.

First, the configuration and operation of multiple network elements common to multiple embodiments will be described. Figure 1 shows an example configuration of a wireless communication system related to multiple embodiments. In the example of Figure 1, the wireless communication system includes a gNB-CU 10, gNB-DUs 21 and 22, TRPs 31 to 34, and a UE 40. The UE 40 may also be referred to by other terms such as a radio terminal, a mobile terminal, a mobile station, or a wireless transmit receive unit (WTRU). Each element (network function) shown in Figure 1 can be implemented, for example, as a network element on dedicated hardware, as a software instance running on dedicated hardware, or as a virtualized function instantiated on an application platform.

The gNB-CU10 and gNB-DUs 21 and 22 correspond to one gNB1. In other words, the gNB1 includes the gNB-CU10 and gNB-DUs 21 and 22. Alternatively, the gNB1 includes TRPs 31 to 34 in addition to the gNB-CU10 and gNB-DUs 21 and 22. The gNB1 is an NG-RAN node. The gNB1 may also be referred to as a RAN node, base station, radio station, or access point. The gNB-CU10, the gNB-DUs 21 and 22, and the TRPs 31 to 34 may each be referred to as a RAN node.

gNB1 may be an en-gNB, which provides NR user plane and control plane protocol termination to the UE and operates as a secondary node for Evolved Universal Terrestrial Radio Access (E-UTRA)-NR Dual Connectivity (EN-DC).

The gNB-CU10 is a logical node that controls the operation of one or more gNB-DUs (e.g., gNB-DUs 21 and 22). The gNB-CU10 hosts the RRC, Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) protocols of gNB1 (or the RRC and PDCP protocols of the gNB). If gNB1 is an en-gNB, the gNB-CU10 hosts the RRC and PDCP protocols of the en-gNB. The gNB-CU10 may include a Control Plane (CP) Unit (i.e., gNB-CU-CP) and one or more User Plane (UP) Units (i.e., gNB-CU-UPs).

Each of gNB-DUs 21 and 22 is a logical node that hosts the Radio Link Control (RLC) layer and MAC layer of gNB1 and hosts part of the Physical (PHY) layer of gNB1, i.e., the upper PHY layer. The remaining PHY layer signal processing, i.e., the lower PHY layer, is located in TRPs 31 to 34. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU. In the example of Figure 1, gNB-DU 21 is connected to TRPs 31 and 32, while gNB-DU 22 is connected to TRPs 33 and 34. TRPs 31 to 34 provide separate cells 51 to 54, respectively. In other words, gNB-DU 21 provides multiple cells 51 and 52, and TRPs 31 and 32 correspond to cells 51 and 52, respectively. Similarly, gNB-DU 22 provides multiple cells 53 and 54, and TRPs 33 and 34 correspond to cells 53 and 54, respectively.

Each of the TRPs 31 to 34 can communicate with the UE 40 using beams. The TRPs 31 to 34 may also be referred to as Radio Units (RUs) or Remote Radio Heads (RRHs). Each of the TRPs 31 to 34 provides lower PHY layer signal processing and analog Radio Frequency (RF) signal processing. Each TRP includes or is connected to one or more antenna arrays. Each TRP has multiple RF chains equal to or less than the total number of antenna elements included in the one or more antenna arrays. Each TRP further includes a Digital Front End (DFE). The DFE provides lower PHY layer signal processing and digital radio signal processing. The lower PHY layer signal processing includes, for example, fast Fourier Transform (FFT) and inverse FFT (IFFT). The lower PHY layer signal processing may further include Cyclic Prefix (CP) addition and removal, and Physical RACH (PRACH) extraction or filtering. Digital radio signal processing may include, for example, digital pre-distortion (DPD), crest factor reduction (CFR), digital up-conversion (DUC), digital down-conversion (DDC), and transmit and receive baseband channel filters. The DFE may perform digital baseband precoding for beamforming. If a hybrid beamforming scheme is employed, an analog beamformer circuit or analog precoder (e.g., phase shifter matrix) may be located between one or more antenna arrays and multiple RF chains.

The interface between gNB-CU10 and each of gNB-DU21 and 22 is an F1 interface. A direct interface, connection, or backhaul may be provided to communicatively connect gNB-DU21 and gNB-DU22. Similarly, a direct interface, connection, or backhaul may be provided to communicatively connect two TRPs serving adjacent cells, for example, between TRPs 31 and 32, between TRPs 32 and 33, and between TRPs 33 and 34.

Figure 2 shows an example configuration of gNB1. In the example of Figure 2, gNB-CU10 includes gNB-CU-CP11 and one or more gNB-CU UPs 12. gNB-CU-CP11 is a logical node that hosts the control plane portion of the RRC and PDCP protocols of gNB-CU10. gNB-CU-CP11 terminates the E1 interface connected to each gNB-CU-UP and the F1-C interface connected to each gNB-DU. The E1 interface uses the E1 Application Protocol (E1AP). The F1-C interface uses the F1 Application Protocol (F1AP). In addition, gNB-CU-CP11 terminates the NG-C interface connected to a control plane node (i.e., Access and Mobility management Function (AMF)) in the core network.

gNB-CU-UP12 is a logical node that hosts the user plane portion of the PDCP protocol of gNB-CU10 for the en-gNB, or the user plane portion of the PDCP protocol and SDAP protocol of gNB-CU10 for the gNB. gNB-CU-UP12 terminates the E1 interface connected to gNB-CU-CP11 and the F1-U interface connected to each gNB-DU. The F1-U interface uses a General Packet Radio Service Tunneling Protocol User Plane (GTP-U) tunnel. gNB-CU-UP12 also terminates the NG-U interface connected to a user plane node (i.e., User Plane Function (UPF)) in the core network.

gNB1 and UE 40 support LTM (normal LTM and CLTM). In this specification, the term "LTM" refers to a broad concept that includes both normal LTM (normal LTM) and conditional LTM. The term "normal LTM (or normal LTM)" means non-conditional LTM as defined in 3GPP Release 18. Specifically, normal LTM is an LTM in which UE 40 performs an LTM cell switch in response to UE 40 receiving a Layer 1 or Layer 2 cell switch command from a source DU. In contrast, in CLTM, UE 40 evaluates the execution conditions set by the network, and performs an LTM cell switch in response to UE 40 determining that the execution conditions are met.

Normal LTM is a procedure in which gNB1 receives L1 measurement reports from UE40 and, based on these, gNB changes one or more serving cells (e.g., cell groups) of UE40 through L1 or L2 signaling (e.g., MAC CE). gNB1 prepares one or more candidate cells and provides candidate cell configurations to UE40 through RRC messages. LTM cell switching is then triggered when gNB1 selects one of the candidate cell configurations as the target configuration for normal LTM. Candidate cell configurations can only be added, changed, or released by the network (i.e., gNB1) via RRC signaling. However, as an exception, UE40 may autonomously release or remove at least part of the candidate cell configurations only in specified situations or when specified conditions are met.

In both normal LTM and CLTM, the LTM candidate cell configuration may be provided on top of the reference configuration or as a delta configuration to the reference configuration. The reference configuration is managed separately from the delta configuration of each candidate cell, and the UE 40 stores the reference configuration as a separate configuration from the delta configuration of each candidate cell. In both normal LTM and CLTM, security is not updated during LTM (or LTM execution or LTM cell switch execution). In both normal LTM and CLTM, subsequent LTM between candidate cells (i.e., after LTM is triggered, the UE 40 does not release other candidate cell configurations) can be performed without RRC reconfiguration.

In both normal LTM and CLTM, the LTM candidate cell configuration includes multiple candidate Transmission Configuration Indicator (TCI) state configurations. Each candidate TCI state configuration indicates the reference signal that serves as the basis for path loss for at least one of the Physical Downlink Control Channel (PDCCH), Physical Downlink Shared Channel (PDSCH), Physical Uplink Control Channel (PUCCH), and Physical Uplink Sheared Channel (PUSCH) in the corresponding candidate TCI state.

The TCI state (or TCI state ID or TCI state setting) indicates the Quasi Co-Location (QCL) relationship between the antenna port used for downlink or uplink transmission and the antenna port used for transmitting a particular reference signal. Two antenna ports are said to be QCLed (Quasi Co-located) if the characteristics of the channel through which symbols on one antenna port are transmitted can be inferred from the channel through which symbols on the other antenna port are transmitted. QCL is an indicator of the statistical properties of a signal or channel. If two antenna ports or two signals transmitted on these two antenna ports are QCLed, it means that these two signals have passed through similar radio channels that share similar characteristics in terms of at least one of Doppler shift, Doppler spread, average delay, delay spread, and spatial reception (Rx) parameter. If two antenna ports are QCLed, the two signals transmitted on these two antenna ports can be considered to reach the receiver through similar channels. Therefore, if the receiver can detect one signal and understand its channel characteristics, those channel characteristics can help it detect the other signal.

A particular downlink transmission is, for example, a PDCCH transmission or a PDSCH transmission. A particular uplink transmission is, for example, a PUCCH transmission or a PUSCH transmission. A particular reference signal is, for example, a Synchronization Signal (SS)/Physical Broadcast Channel (PBCH) block (SSB) or a Channel State Information (CSI) Reference Signal (CSI-RS).

The TCI state indicates, for example, the QCL relationship between the antenna port used for PDSCH transmission and the antenna port used for transmitting a specific SSB or a specific CSI-RS. Additionally or alternatively, the TCI state indicates the QCL relationship between the antenna port used for PDCCH transmission and the antenna port used for transmitting a specific SSB or a specific CSI-RS. In other words, the TCI state indicates, for example, the QCL relationship between the Demodulation Reference Signal (DMRS) port used for demodulating the PDSCH or PDCCH and a specific downlink SSB or CSI-RS port.

LTM (regular LTM and CLTM) supports both intra-gNB-DU mobility and intra-gNB-CU inter-gNB-DU mobility. LTM supports not only intra-frequency mobility but also inter-frequency mobility. LTM supports the following scenarios: PCell change in non-CA scenarios; PCell change without SCell change in CA scenarios; PCell change with SCell change in CA scenarios; and Dual Connectivity scenarios. PCell change with SCell change in CA scenarios includes a) cases where the target PCell or target SCell(s) is not the current serving cell (i.e., CA-to-CA scenario with PCell change), b) cases where the target PCell is the current SCell, and c) cases where the target SCell is the current PCell. The Dual Connectivity scenario includes at least a PSCell change without MN involvement.

The mobility 120 shown in Figure 1 is intra-DU (intra-DU) LTM. Specifically, the UE 40 moves from the beam of cell 52 of TRP32 associated with the same gNB-DU21 to the beam of cell 51 of TRP31. In contrast, the mobility 140 shown in Figure 1 is inter-DU (inter-DU) LTM. Specifically, the UE 40 moves from the beam of cell 52 of TRP32 associated with gNB-DU21 to the beam of cell 53 of TRP33 associated with another gNB-DU22.

Before and after the LTM cell switch, the termination points of the radio bearers (e.g., Signaling Radio Bearers (SRBs), Data Radio Bearers (DRBs)) for UE 40 are fixed at gNB-CU10 and remain unchanged. One or more QoS flows belonging to UE 40's PDU Session pass through the same gNB-CU10 (e.g., gNB-CU-UP) after the LTM cell switch as before the switch. Therefore, the radio bearer configuration may be inherited or maintained in UE 40 and gNB1 (i.e., gNB-CU10, or gNB-CU10 and (target) gNB-DU21 or 22) before and after the LTM. Alternatively, the target gNB-DU (e.g., gNB-DU22) or gNB-CU10 may transmit the radio bearer configuration for the target cell to the UE 40 via the source gNB-DU (e.g., gNB-DU21) in preparation for LTM. If the UE 40 does not receive explicit radio bearer configuration for after the LTM cell switch from the gNB1 (e.g., gNB-CU10 or target gNB-DU), it may carry over the radio bearer configuration in the serving cell to the target cell after the LTM cell switch. In other words, the UE 40 may continue to use the radio bearer configuration in the serving cell in the target cell after the LTM cell switch.

The control plane handling for normal LTM is described in more detail below. The cell switch command (or cell switch trigger information) sent by gNB1 to UE40 may be conveyed in a MAC CE (i.e., LTM Cell Switch Command MAC CE). This MAC CE contains at least an index (i.e., Target Configuration ID) of a candidate target configuration associated with a target cell selected by gNB1 from one or more prepared LTM candidate cells. Simultaneously with the LTM triggered by the MAC CE, activation of one or more SCells associated with the candidate target configuration may be performed. UE40 may perform CBRA or CFRA during the cell switch.

The Cell Switch Command MAC CE is sent by gNB1 to UE40 to trigger an LTM cell switch by UE40 to the target cell selected by gNB1. The Cell Switch Command MAC CE includes, among other fields, a Target Configuration ID field, a Timing Advance Command field, a TCI state ID field, an Uplink (UL) TCI state ID field, and a Random Access Preamble index field.

The Target Configuration ID field indicates the index of the candidate target configuration to be applied to the LTM cell switch. The candidate target configuration is the candidate cell configuration of the target cell selected by gNB1.

The Timing Advance Command field indicates whether a Timing Advance (TA) is valid for the LTM target cell (i.e., the Special Cell (SpCell) corresponding to the target configuration indicated in the Target Configuration ID field). If the value of the Timing Advance Command field is set to FFF, this field indicates that no valid timing adjustment is available for the TA Group (TAG) of the LTM target cell. Otherwise, this field indicates the TA value used to control the amount of timing adjustment that the MAC entity of UE 40 must apply, and indicates that UE 40 can skip the random access procedure for that LTM cell switch.

The TCI state ID field indicates and activates the TCI state of the LTM target cell (i.e., the SpCell of the target configuration indicated in the Target Configuration ID field). The TCI state indicated by the TCI state ID field is for the joint TCI state or the downlink TCI state. The UL TCI state ID field indicates and activates the uplink TCI state of the LTM target cell.

The Random Access Preamble index field indicates the random access preamble index of the contention-free random access resources.

If the UE 40 has a valid Timing Advance (TA) of the target cell and does not need to acquire the TA of the target cell during an LTM cell switch, the UE 40 can also skip the random access procedure. An LTM cell switch procedure in which the UE skips the random access procedure is called RACH-less LTM. The UE 40 can acquire the TA through early TA acquisition. Early TA acquisition is triggered by a Physical Downlink Control Channel (PDCCH) order or achieved by UE-based TA measurement.

In early TA acquisition via PDCCH order, gNB1 (e.g., source DU) triggers UE40 to perform CFRA to a candidate cell via a PDCCH order via the serving cell. UE40 transmits a first random access message (i.e., a random access preamble) to the candidate cell. To minimize data interruption in the serving cell due to the CFRA to the candidate cell, UE40 does not monitor or receive a random access response from the candidate cell. The candidate cell does not transmit a random access response to the CFRA. The TA value of the candidate cell is indicated to UE40 by the LTM Cell Switch Command MAC CE. Note that the TA value of the candidate cell is indicated to the LTM Cell Switch Command MAC CE only when the candidate cell is selected as a target cell for the cell switch. Alternatively, the TA value of the candidate cell may be refined so as to be indicated to the LTM Cell Switch Command MAC CE regardless of whether the candidate cell is selected as a target cell for the cell switch.

UE-based TA measurement is configured in UE 40 by RRC. In UE-based TA measurement, UE 40 derives the TA of the candidate cell based on the reception timing difference between the current serving cell and the candidate cell and the TA value of the current serving cell.

Figure 3 shows an example of the overall procedure for normal LTM. Subsequent LTMs are performed by repeating the procedures of early synchronization, LTM execution, and LTM completion after each LTM is completed, without releasing other candidate cell settings. Note that early synchronization is intended to allow UE 40 to synchronize with the candidate cell before the LTM execution phase and skip the random access procedure during the LTM execution phase. However, early synchronization is optional and does not necessarily have to be performed.

Steps 301 to 304 are the LTM preparation phase. In step 301, UE 40, which is RRC_CONNECTED, sends an L3 measurement report to gNB1. Specifically, UE 40 sends a MeasurementReport message to gNB1. The MeasurementReport message indicates the L3 measurement results. The MeasurementReport message may indicate the measurement results of the serving cell and neighboring cells. The measurement results for each cell include Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), or Signal-to-Interference and Noise Ratio (SINR), or any combination of these.

In step 302, based on the L3 measurement report, gNB1 decides to use LTM and starts preparing one or more LTM candidate cells. An LTM candidate cell may also be referred to as an LTM candidate target cell. In step 303, gNB1 sends an RRCReconfiguration message to UE40, including the configuration of one or more LTM candidate cells. In step 304, UE40 stores the configuration of one or more LTM candidate cells and sends an RRCReconfigurationComplete message to gNB1.

Step 305 is the early synchronization phase. UE 40 may perform downlink (DL) synchronization and uplink (UL) TA acquisition with one or more candidate cells before receiving the LTM cell switch command.

Steps 306 to 310 are the LTM execution phase. In step 306, UE 40 performs L1 measurements on the configured LTM candidate cells and sends L1 measurement reports to gNB1. The L1 measurement reports may be carried by L1 signaling (e.g., Uplink Control Information (UCI)) or MAC CE. In step 307, gNB1 decides to perform an LTM cell switch to one of the prepared candidate cells and sends an LTM cell switch command (i.e., LTM Cell Switch Command MAC CE) to UE 40, including an identifier of the target cell (e.g., LTM candidate ID) (step 308). The LTM switch command includes the Target Configuration ID associated with the target cell and triggers the LTM cell switch in UE 40. In step 309, UE 40 switches to the target cell configuration specified by gNB1. In other words, the UE 40 detaches from the source cell and applies the target cell configuration. In step 310, if TA is not available, the UE 40 performs a random access procedure toward the target cell.

Step 311 is the LTM completion phase. UE 40 completes the LTM cell switch procedure by sending an RRCReconfigurationComplete message to the target cell. Alternatively, if UE 40 performs a random access procedure in the LTM execution phase, UE 40 determines that the execution of the LTM cell switch has been completed successfully when the random access procedure has been completed successfully. In the case of RACH-less LTM, UE 40 determines that the execution of the LTM cell switch has been completed successfully when UE 40 determines that the network has successfully received the first uplink data.

Figure 4 shows an example of the overall procedure for CLTM. Subsequent CLTMs are performed by repeating the procedure of early synchronization, CLTM execution, and CLTM completion, without releasing other candidate cell settings after each CLTM is completed. Note that early synchronization is intended to allow UE 40 to synchronize with the candidate cell before the CLTM execution phase and skip the random access procedure during the CLTM execution phase. However, early synchronization is optional and does not necessarily have to be performed.

Steps 401 to 404 are the CLTM preparation phase. In step 401, UE 40, which is in the RRC_CONNECTED state, sends an L3 measurement report to gNB 1. Step 401 may be the same as step 301 in Figure 3.

In step 402, based on the L3 measurement report, gNB1 decides to use CLTM and starts preparing one or more CLTM candidate cells. A CLTM candidate cell may also be referred to as a CLTM candidate target cell. In step 403, gNB1 sends an RRCReconfiguration message to UE40, which includes the configuration of one or more CLTM candidate cells and the CLTM execution conditions for each candidate cell. In step 404, UE40 stores the CLTM candidate cell configuration and the CLTM execution conditions, and sends an RRCReconfigurationComplete message to gNB1.

In addition, gNB1 may decide to use both normal LTM and CLTM. CLTM cell switch may be used for some of the multiple candidate cells prepared in steps 402 and 403, and normal LTM cell switch may be used for the rest. For example, a CLTM cell switch triggered by UE40 determining that an execution condition is met may be applied to a cell switch from a source cell (serving cell) or a first candidate cell to another candidate cell, while a normal LTM cell switch triggered by an LTM cell switch command by gNB1 may be applied to a cell switch from a second candidate cell to another candidate cell. In another example, a CLTM cell switch may be applied to a cell switch from a source cell to a first candidate cell, while a normal LTM cell switch may be applied to a cell switch from a source cell to a second candidate cell.

Additionally or alternatively, CLTM cell switch and normal LTM may be used for the purpose of cell switch from a source cell to the same candidate cell, or cell switch between the same candidate cell pair. In this case, UE 40 may perform a cell switch triggered by either the satisfaction of a CLTM execution condition or the receipt of an LTM cell switch command from gNB1, whichever occurs first. Note that even when UE 40 performs an LTM cell switch triggered by an LTM cell switch command received from gNB1, it also retains CLTM-specific settings (e.g., CLTM execution conditions) for subsequent CLTM.

Step 405 is the early synchronization phase. UE 40 may perform DL synchronization and UL TA acquisition with one or more candidate cells. Step 405 may be performed in parallel with step 406, described below.

Step 406 is the CLTM evaluation phase. UE 40 evaluates the CLTM execution conditions for each candidate cell.

Steps 407 and 408 are the CLTM execution phase. In step 407, UE 40 determines that the execution conditions are met for one of the candidate cells and decides to perform a cell switch to that candidate cell. UE 40 detaches from the source cell and applies the target cell configuration. In step 408, if TA is not available, UE 40 performs a random access procedure toward the target cell.

In some implementations, in step 4071, after UE40 determines that an execution condition is met for any candidate cell (i.e., target cell) (and before detaching from the source cell), UE40 may send L1 or L2 (L1/L2) signaling to gNB1 (e.g., source DU) in the source cell. The L1/L2 signaling includes an identifier or index (e.g., Target Configuration ID) indicating the target cell or indicating a candidate target configuration associated with the target cell. The L1/L2 signaling in step 4071 may further indicate that the cell switch by UE40 via CLTM is performed in a RACH-less or CFRA-based manner. The L1/L2 signaling may be a MAC CE. The MAC CE may be named, for example, CLTM Indication MAC CE or CLTM Triggering Indication MAC CE. Alternatively, the L1/L2 signaling may be UCI on the PUCCH.

The L1/L2 signaling in step 4071 enables UE 40 to inform gNB 1 that the CLTM execution conditions have been met for the target cell or that a CLTM cell switch to the target cell has been initiated. However, step 4071 may be omitted.

After or in response to receiving the L1/L2 signaling of step 4071, the source DU may notify the CU of the initiation of a CLTM cell switch. This notification may include the target cell ID. This notification may be made using an F1AP message, such as a DU-CU CELL SWITCH NOTIFICATION message. Furthermore, the CU may notify a candidate DU (i.e., target DU) serving the target cell of the initiation of a CLTM cell switch to the target cell. The notification from the CU to the target DU may include the target cell ID. This notification may be made using an F1AP message, such as a CU-DU CELL SWITCH NOTIFICATION message. In other words, the source DU may notify the target DU via the CU of the initiation of a CLTM cell switch to the target cell. These signalings enable the target DU to know that UE 40 has initiated a CLTM cell switch to the target cell. In other words, these signalings allow the target DU to know that the cell switch to the target cell initiated by the UE 40 will be based on CLTM rather than the usual LTM.

Step 409 is the CLTM completion phase. Step 409 may be similar to step 311 in Figure 3.

First Embodiment
A configuration example of a wireless communication system according to this embodiment is similar to the configuration example described with reference to Figures 1 and 2. This embodiment provides details of signaling between a CU (e.g., gNB-CU 10) and a DU (e.g., gNB-DUs 21 or 22) performed to prepare CLTM between multiple candidate cells.

Figure 5 shows an example of the operation of a candidate DU (e.g., gNB-DU 21 or 22) that provides a candidate cell for CLTM. In the case of intra-DU CLTM, the candidate DU is naturally the same as the DU that provides the source cell. In addition, even in the case of intra-CU inter-DU CLTM, the DU that provides the source cell may further provide other candidate cells. Furthermore, the source cell may be prepared as one of the candidate cells for a subsequent CLTM. Therefore, in the case of intra-CU inter-DU CLTM, the candidate DU may be different from or the same as the DU that provides the source cell.

In step 501, the candidate DU receives a first message from the CU requesting preparation of a first candidate cell. The first message receives a first message from the CU requesting preparation of a first candidate cell for LTM of the UE 40 among multiple candidate cells including the first candidate cell. The first candidate cell may be the same as the source cell. Alternatively, one of the multiple candidate cells excluding the first candidate cell may be the same as the source cell. In other words, the first candidate cell or another candidate cell included in the multiple candidate cells may be the same as the source cell of the first LTM in the LTM requested by the first message. The first message may include a first indication related to CLTM. The first message may be an F1AP message, specifically a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message.

In step 502, the candidate DU determines whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to CLTM or normal LTM, based on whether the first message includes a first indication related to CLTM. Specifically, if the first message in step 501 includes the above-mentioned first indication, the candidate DU may consider one or more cell switches from the first candidate cell to one or more other candidate cells to be subject to CLTM. On the other hand, if the first message does not include the first indication, the candidate DU may consider these one or more cell switches to be subject to normal LTM.

FIG. 6 shows an example of the operation of a CU (e.g., gNB-CU10). In step 601, the CU decides to initiate LTM configuration. As described with respect to step 302 in FIG. 3 and step 402 in FIG. 4, the CU may decide to use regular LTM, CLTM, or both based on one or more L3 measurement reports from the UE 40. As described above, the CU may decide to use both regular LTM and CLTM. CLTM cell switch may be used for some of multiple candidate cells, and regular LTM cell switch may be used for the rest. For example, CLTM cell switch may be applied to a cell switch from a source cell or a first candidate cell to another candidate cell, while regular LTM cell switch may be applied to a cell switch from a second candidate cell to another candidate cell.

In step 602, the CU sends a first message to a candidate DU (e.g., gNB-DU 21 or 22) requesting preparation of a first candidate cell for LTM of the UE 40 among multiple candidate cells, including the first candidate cell. The first message indicates to the candidate DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to CLTM or normal LTM, based on whether the first message includes a first indication related to CLTM. Specifically, if the first message includes the above-mentioned first indication, the first message may cause the candidate DU to consider one or more cell switches from the first candidate cell to one or more other candidate cells to be subject to CLTM. On the other hand, if the first message does not include the first indication, the first message may cause the candidate DU to consider these one or more cell switches to be subject to normal LTM.

The operations of the CU and candidate DU described with reference to Figures 5 and 6 can provide details of the operations of the CU and candidate DU for preparing a CLTM. Furthermore, these operations of the CU and candidate DU help to reuse the first message for both preparing a normal LTM and preparing a CLTM. In other words, these operations of the CU and candidate DU make it possible to reuse the first message for preparing a normal LTM for preparing a CLTM.

The operations of the CU and candidate DU described with reference to Figures 5 and 6 may be modified as follows. The first message received by the candidate DU in step 501 of Figure 5 may include a second indication related to CLTM for an (inbound) cell switch from the candidate cell of another candidate DU to the first candidate cell of the candidate DU. Similarly, the first message sent by the CU to the candidate DU in step 602 of Figure 6 may include a second indication related to CLTM for an (inbound) cell switch from the candidate cell of another candidate DU to the first candidate cell of the candidate DU. The second indication may indicate whether CLTM, normal LTM, or both are planned or configured for the cell switch from the other candidate cell to the first candidate cell.

The first message in step 501 of FIG. 5 and step 602 of FIG. 6 may include a second indication in addition to the first indication described above. Alternatively, the first message in step 501 of FIG. 5 and step 601 of FIG. 6 may include the second indication without including the first indication. Alternatively, the first message in step 501 of FIG. 5 and step 602 of FIG. 6 may include a single common indication that serves as both the first indication and the second indication. The second indication may be included in a subsequent message (not shown) sent from the CU to the candidate DU, different from the first message.

The candidate DU may determine whether an (inbound) cell switch from another cell (i.e., another candidate cell or source cell) to the first candidate cell provided by the candidate DU is subject to normal LTM, CLTM, or both, based on whether the received message includes the second indication. Alternatively, the candidate DU may determine this based on the content of the second indication. This allows the candidate DU to know in advance whether CLTM or normal LTM is planned for the subsequent (inbound) cell switch from the candidate DU to the first candidate cell, and to make any necessary preparations in advance (e.g., a waiting method for access from UE 40 to the first candidate cell). Note that the node managing the other cell (e.g., another candidate DU or source DU) may generate the execution conditions evaluated by UE 40 for a CLTM cell switch from the other cell (i.e., other candidate cell or source cell) to the first candidate cell.

The candidate DU may generate a second message based on the first message and send the second message to the CU. The second message typically contains cell configuration of the first candidate cell prepared for LTM or CLTM. The second message may be an F1AP message, specifically a UE CONTEXT SETUP RESPONSE message or a UE CONTEXT MODIFICATION RESPONSE message.

In one implementation, the candidate DU may generate execution conditions to be evaluated by the UE 40 for a CLTM cell switch from a first candidate cell to another candidate cell. In this case, if one or more cell switches from the first candidate cell to one or more other candidate cells are subject to CLTM, the candidate DU may include one or more CLTM execution conditions for these one or more cell switches in the second message, in addition to the LTM configuration for the first candidate cell. On the other hand, if these one or more cell switches are subject to normal LTM, the candidate DU may include the LTM configuration for the first candidate cell in the second message without including one or more CLTM execution conditions in the second message. According to this operation, the candidate DU can determine whether or not it is necessary to generate CLTM execution conditions based on whether or not the first message includes a specific indication.

In another implementation, the CU may generate execution conditions to be evaluated by the UE 40 for a CLTM cell switch from a first candidate cell to another candidate cell. In this case, the candidate DU may provide the CU with suggestion information (or assist information) that is used, useful, or assists the CU in generating the execution conditions. If one or more cell switches from the first candidate cell to one or more other candidate cells are subject to CLTM, the candidate DU may include suggestion information for CLTM in the second message in addition to the LTM configuration for the first candidate cell. On the other hand, if these one or more cell switches are normally subject to LTM, the candidate DU may include the LTM configuration for the first candidate cell in the second message without including suggestion information in the second message. According to this operation, the candidate DU can determine whether or not it is necessary to generate suggestion information based on whether or not the first message includes a specific indication.

The proposed information may be taken into consideration by the CU to determine one or more execution conditions for one or more cell switches from the first candidate cell to one or more other candidate cells. The CU may determine one or more execution conditions for these one or more cell switches based on the proposed information. The proposed information may indicate, for example, one or more proposed events (i.e., events that trigger CLTM), proposed parameters (e.g., offsets or thresholds), or a combination thereof. The one or more proposed parameters may include, for example, an offset or threshold to be applied to radio quality (e.g., RSRP) for an execution condition related to radio quality.

In some implementations, CLTM may be applied only to one or more cell pairs among a plurality of candidate cells configured for LTM, and normal LTM may be applied to the remaining one or more cell pairs. In this case, the first message or the above-mentioned indication included in the first message (i.e., the first indication or the second indication, or both) may explicitly indicate which cell pairs included in the plurality of candidate cells are subject to CLTM. In other words, or alternatively, the first message or the above-mentioned first indication may explicitly indicate which one or more of the plurality of candidate cells, excluding the first candidate cell, are subject to CLTM in a cell switch from the first candidate cell. This enables the candidate DU to know which candidate cells will be subject to CLTM in a cell switch from the first candidate cell, and can assist the candidate DU in generating CLTM execution conditions (or the above-mentioned proposal information).

In one implementation, the above-mentioned first indication included in the first message may indicate to the candidate DU whether one or more cell switches from the first candidate cell to one or more other candidate cells are subject to CLTM. Furthermore, the first message or the first indication may further indicate to the candidate DU whether generation of execution conditions is required if these one or more cell switches are subject to CLTM. This enables the candidate DU to know whether it is necessary to generate CLTM execution conditions for CTLM cell switches from the first candidate cell to other cells.

The above-mentioned indication (i.e., the first indication or the second indication, or both) included in the first message may be an indication of one or more execution condition requests for one or more cell switches. Alternatively, the indication (i.e., the first indication or the second indication, or both) may be an indication of CLTM.

As mentioned above, the first message may be a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message. In this case, the above-mentioned indication (i.e., the first indication or the second indication, or both) may be included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message. The above-mentioned indication may be included in an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message. Alternatively, the above-mentioned indication (i.e., the first indication or the second indication, or both) may be an information element included in the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message, separately from the LTM Information Setup information element or the LTM Information Modify information element.

FIG. 7 shows an example of signaling between a CU and a candidate DU for preparing LTM (CLTM or CLTM and normal LTM). The CU 701 shown in FIG. 7 may be gNB-CU 10 in FIGS. 1 and 2, and the candidate DU 702 shown in FIG. 7 may be gNB-DU 21 or 22 in FIGS. 1 and 2. In step 721, the CU 701 decides to initiate CLTM configuration. In other words, the CU 701 decides to use CLTM and initiates preparation of one or more CLTM candidate cells. The CU 701 may decide to initiate CLTM configuration based on one or more L3 measurement reports from the UE 40. Step 721 may correspond to step 601 in FIG. 6.

In step 722, the CU 701 sends a UE CONTEXT SETUP REQUEST message to the candidate DU 702. The UE CONTEXT SETUP REQUEST message includes the LTM Information Setup IE and further includes a new field or IE. This new field or IE indicates that the message or LTM preparation is for CLTM. This new field or IE may be included in the LTM Information Setup IE, or may be included in the UE CONTEXT SETUP REQUEST message separately from the LTM Information Setup IE. Step 722 may correspond to step 501 in Figure 5 and step 602 in Figure 6.

In step 723, the candidate DU 702 sends a UE CONTEXT SETUP RESPONSE message to the CU 701. The UE CONTEXT SETUP RESPONSE message includes a DU To CU RRC Information IE. The DU To CU RRC Information IE contains the RRC information sent from the candidate DU 702 to the CU 701. The RRC information includes the configuration of the candidate cell or the configuration of the cell group (CellGroupConfig) that includes the candidate cell. The UE CONTEXT SETUP RESPONSE message further includes an LTM Configuration IE. The LTM Configuration IE includes the time and frequency configuration of SSB or CSI-RS. In addition, the UE CONTEXT SETUP RESPONSE message includes a new F1AP IE or a new field or IE in the DU To CU RRC Information IE (RRC Container). This new F1AP IE, or a new field or IE in the DU To CU RRC Information IE, contains one or more CLTM execution conditions. These one or more CLTM execution conditions are used and evaluated by the UE 40 to determine the execution of one or more subsequent CLTM cell switches from the candidate cell for which preparation has been requested in the UE CONTEXT SETUP REQUEST message to one or more other candidate cells.

Note that if the candidate DU 702 is the same as the source DU providing the source cell, a UE CONTEXT MODIFICATION REQUEST message is used instead of the UE CONTEXT SETUP REQUEST message (step 722), and a UE CONTEXT MODIFICATION REPONSE message is used instead of the UE CONTEXT SETUP REPONSE message (step 723). The UE CONTEXT MODIFICATION REQUEST message may include an LTM Information Modify IE instead of an LTM Information Setup IE. The new field or IE described with respect to step 722 may be included in the LTM Information Modify IE or may be included in the UE CONTEXT MODIFICATION REQUEST message separately from the LTM Information Modify IE.

The operations of the CU701 and candidate DU702 described with reference to Figure 7 can provide details of the operations of the CU701 and candidate DU702 for preparing a CLTM. Furthermore, these operations of the CU701 and candidate DU702 help to reuse the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message for both preparing a normal LTM and preparing a CLTM. In other words, these operations of the CU701 and candidate DU702 make it possible to reuse the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message for preparing a normal LTM for preparing a CLTM.

8 to 11 show specific examples of the new fields or IEs included in the UE CONTEXT SETUP REQUEST message described with respect to step 722. In the example of FIG. 8, the UE CONTEXT SETUP REQUEST message includes a Conditional LTM Information Request IE 801 apart from the LTM Information Setup IE. The Conditional LTM Information Request IE 801 can optionally include a Request for Execution Condition IE 802. If the Request for Execution Condition IE 802 set to "true" is included in the Conditional LTM Information Request IE 801 included in the UE CONTEXT SETUP REQUEST message, the candidate DU 702 considers the request to be related to CLTM and that the generation of a CLTM execution condition is required. The candidate DU 702 then includes the CLTM execution conditions in the UE CONTEXT SETUP RESPONSE message.

In the example of Figure 9, the UE CONTEXT SETUP REQUEST message can include a Request for Execution Condition IE 901 in the LTM Information Setup IE. If the Request for Execution Condition IE 901 set to "true" is included in the LTM Information Setup IE included in the UE CONTEXT SETUP REQUEST message, the candidate DU 702 considers the request to be related to CLTM and that the generation of a CLTM execution condition is required. The candidate DU 702 then includes the CLTM execution condition in the UE CONTEXT SETUP RESPONSE message.

In the example of Figure 10, the UE CONTEXT SETUP REQUEST message may include a Conditional LTM Indicator IE 1001 in the LTM Information Setup IE. If the Conditional LTM Indicator IE 1001 set to "true" is included in the LTM Information Setup IE included in the UE CONTEXT SETUP REQUEST message, the candidate DU 702 considers the request to be related to CLTM. Specifically, the candidate DU 702 may recognize that an (outbound) LTM cell switch from a candidate cell provided by the candidate DU 702 to another candidate cell is subject to CLTM. Additionally or alternatively, the candidate DU 702 may recognize that a CLTM is scheduled or configured in an (inbound) LTM cell switch from another candidate cell to the candidate cell provided by the candidate DU 702. The candidate DU 702 may include the CLTM execution conditions in the UE CONTEXT SETUP RESPONSE message. Alternatively, the candidate DU 702 may include the above-mentioned proposal information in the UE CONTEXT SETUP RESPONSE message.

11, the LTM Indicator IE 1101 included in the UE CONTEXT SETUP REQUEST message is enhanced compared to that in 3GPP Release 18. The LTM Indicator IE 1101 may be set to the value "CLTM". If the LTM Indicator IE 1101 set to "CLTM" is included in the LTM Information Setup IE included in the UE CONTEXT SETUP REQUEST message, the candidate DU 702 considers the request to be related to CLTM. Specifically, the candidate DU 702 may recognize that an (outbound) LTM cell switch from a candidate cell provided by the candidate DU 702 to another candidate cell is subject to CLTM. Additionally or alternatively, the candidate DU 702 may recognize that a CLTM is planned for an (inbound) LTM cell switch from another candidate cell to the candidate cell provided by the candidate DU 702. The candidate DU 702 may include the CLTM execution conditions in the UE CONTEXT SETUP RESPONSE message. Alternatively, the candidate DU 702 may include the above-mentioned proposal information in the UE CONTEXT SETUP RESPONSE message.

Figures 12 and 13 show specific examples of the new fields or IEs included in the UE CONTEXT SETUP RESPONSE message described with respect to step 723. Figure 12 is an example of the DU To CU RRC Information IE included in the UE CONTEXT SETUP RESPONSE message. In the example of Figure 12, the DU To CU RRC Information IE may include a ConditionalLTM-Configuration field or IE 1201. The ConditionalLTM-Configuration field or IE 1201 includes or indicates one or more CLTM execution conditions generated by the candidate DU.

In the example of Figure 13, the UE CONTEXT SETUP RESPONSE message may include a Conditional LTM Configuration IE 1301 within the LTM Configuration IE. The Conditional LTM Configuration IE 1301 includes or indicates one or more CLTM execution conditions generated by the candidate DU.

As in the examples described with reference to Figures 8 to 11, the UE CONTEXT MODIFICATION REQUEST message may be extended to include the new fields or IEs described with reference to step 722. As in the examples described with reference to Figures 12 and 13, the UE CONTEXT MODIFICATION RESPONSE message may be extended to include the new fields or IEs described with reference to step 723.

Figure 14 shows an example of signaling between a CU, source DU, and candidate DU for preparing LTM (CLTM or CLTM and regular LTM). CU 1401 shown in Figure 14 may be gNB-CU 10 of Figures 1 and 2. Source DU 1402 shown in Figure 14 may be gNB-DU 21 of Figures 1 and 2. Two candidate DUs 1403 and 1404 shown in Figure 14 may be gNB-DU 22 of Figures 1 and 2.

In step 1421, source DU 1402 sends a UL RRC MESSAGE TRANSFER message carrying the L3 measurement report received from the UE to CU 1401. In step 1422, CU 1401 decides to initiate CLTM configuration. In other words, CU 1401 decides to use CLTM and starts preparing one or more CLTM candidate cells. CU 1401 may decide to initiate CLTM configuration based on one or more L3 measurement reports from UE 40. Step 1422 may correspond to step 601 in FIG. 6.

In step 1423, CU 1401 sends a UE CONTEXT SETUP REQUEST message to each of candidate DUs 1403 and 1404. Step 1423 is similar to step 722 in FIG. 7. Step 1423 may correspond to step 501 in FIG. 5 and step 602 in FIG. 6.

In step 1424, each of the candidate DUs 1403 and 1404 sends a UE CONTEXT SETUP RESPONSE message to CU 1401. Step 1424 is similar to step 723 in Figure 7.

In step 1425, the CU 1401 sends a UE CONTEXT MODIFICATION REQUEST message to the source DU 1402. The UE CONTEXT MODIFICATION REQUEST message requests the source DU 1402 to prepare the source cell or another cell provided by the source DU 1402 as a CLTM candidate cell. Step 1425 is similar to step 722 of FIG. 7. The new fields or IEs described with respect to step 722 may be included in the LTM Information Modify IE or may be included in the UE CONTEXT MODIFICATION REQUEST message separately from the LTM Information Modify IE. Furthermore, the UE CONTEXT MODIFICATION REQUEST message may include information indicating whether CLTM, normal LTM, or both are planned or configured for the cell switch from the candidate cell of another candidate DU to the source cell or another cell provided by the source DU 1402.

7. In step 1426, the source DU 1402 sends a UE CONTEXT MODIFICATION RESPONSE message to the CU 1401. The UE CONTEXT MODIFICATION RESPONSE message includes a DU To CU RRC Information IE. The DU To CU RRC Information IE contains the RRC information sent from the source DU 1402 to the CU 1401. The RRC information includes the configuration of candidate cells (i.e., source cells or other cells provided by the source DU 1402) or the configuration of a cell group (CellGroupConfig) that includes the candidate cells. Step 1426 is similar to step 723 of Figure 7. The UE CONTEXT MODIFICATION RESPONSE message of step 1426 is extended to include the new fields or IEs described with respect to step 723. Additionally, the UE CONTEXT MODIFICATION RESPONSE message (or DU To CU RRC Information IE) may include execution conditions for CLTM to the source cell or other cells served by the source DU 1402.

Although omitted in FIG. 14, after steps 1425 and 1426, CU 1401 further sends a UE CONTEXT MODIFICATION REQUEST message to source DU 1402, and source DU 1402 further sends a UE CONTEXT MODIFICATION RESPONSE message to CU 1401. The additional UE CONTEXT MODIFICATION REQUEST message, not shown, includes information collected from candidate DUs 1403 and 1404 (e.g., collected CSI reporting settings and RACH configuration settings, as well as TCI state settings of candidate cells accepted by other DUs). The additional UE CONTEXT MODIFICATION RESPONSE message, not shown, may include updated lower layer settings (e.g., including CSI reporting settings).

An additional UE CONTEXT MODIFICATION REQUEST message, not shown, may indicate, on a candidate cell-by-candidate cell basis, whether normal LTM or CLTM is to be applied to each cell switch from the source cell to one or more candidate cells. This enables the source DU 1402 to recognize the type of cell switch (i.e., normal LTM or CLTM) to be applied to each candidate cell and to take action according to the cell switch type for each candidate cell. Furthermore, an additional UE CONTEXT MODIFICATION REQUEST message, not shown, may include information indicating whether CLTM, normal LTM, or both are planned or configured for a cell switch from a candidate cell of another candidate DU to the source cell or other cells served by the source DU 1402.

In step 1427, the CU 1401 may send a UE CONTEXT MODIFICATION REQUEST message to each candidate DU. The message includes CSI reporting configuration, TCI status information, RACH configuration, and LTM configuration IDs of the candidate cells of the other candidate DUs. The CU 1401 may further provide the lower layer portion of the reference configuration to each candidate DU. The CU 1401 may further provide the updated CSI resource configuration to each candidate DU. The message may further include information indicating whether CLTM, normal LTM, or both are planned or configured for the cell switch from the candidate cells of the other candidate DUs to the candidate cell provided by each candidate DU. In step 1428, each candidate DU responds with a UE CONTEXT MODIFICATION RESPONSE message including the updated lower layer configuration. Each candidate DU may also send the updated CSI reporting configuration.
Steps 1427 and 1428 may be omitted.

In step 1429, CU 1401 sends a DL RRC MESSAGE TRANSFER message to source DU 1402. This message includes an RRCReconfiguration message that includes the CLTM settings. Although not shown, source DU 1401 forwards the received RRCReconfiguration message to UE 40.

15 shows an example of signaling between a CU and a candidate DU for preparing LTM (CLTM or CLTM and normal LTM). CU1501 shown in FIG. 15 may be gNB-CU10 in FIG. 1 and FIG. 2, and candidate DU1502 shown in FIG. 15 may be gNB-DU21 or 22 in FIG. 1 and FIG. 2. In step 1521, CU1501 decides to initiate CLTM configuration. In other words, CU1501 decides to use CLTM and initiates preparation of one or more CLTM candidate cells. CU1501 may decide to initiate CLTM configuration based on one or more L3 measurement reports from UE40. In the example of FIG. 15, CU1501 further decides to generate one or more CLTM execution conditions by CU1501. CU1501 may generate the CLTM execution conditions based on the L3 measurement report (or L1 measurement report). Step 1521 may correspond to step 601 in FIG. 6.

In step 1522, CU701 sends a UE CONTEXT SETUP REQUEST message to candidate DU1502. The UE CONTEXT SETUP REQUEST message includes an LTM Information Setup IE and further includes a new field or IE. This new field or IE indicates that the message or LTM preparation is for CLTM. This new field or IE may be included in the LTM Information Setup IE, or may be included in the UE CONTEXT SETUP REQUEST message separately from the LTM Information Setup IE. Step 1522 may correspond to step 501 in Figure 5 and step 602 in Figure 6.

The UE CONTEXT SETUP REQUEST message of step 1522 may optionally indicate one or more CLTM execution conditions determined by CU 1501. The UE CONTEXT SETUP REQUEST message of step 1522 may optionally indicate one or more cell pairs, or a list of cell pairs, to which CLTM should be applied. If one or more cell pairs are not indicated, normal LTM as specified in 3GPP Release 18 may be applied to all cell pairs within a plurality of candidate cells or to all cell switches.

In step 1523, the candidate DU 1502 sends a UE CONTEXT SETUP RESPONSE message to the CU 1501. The UE CONTEXT SETUP RESPONSE message includes a DU To CU RRC Information IE. The DU To CU RRC Information IE contains the RRC information sent from the candidate DU 1502 to the CU 1501. The RRC information includes the configuration of the candidate cell or the configuration of the cell group (CellGroupConfig) that includes the candidate cell. The UE CONTEXT SETUP RESPONSE message further includes an LTM Configuration IE. The LTM Configuration IE includes the time and frequency configuration of SSB or CSI-RS. In addition, the UE CONTEXT SETUP RESPONSE message includes a new F1AP IE or a new field or IE in the DU To CU RRC Information IE (RRC Container). This new F1AP IE or a new field or IE within the DU To CU RRC Information IE may contain the proposed information described above.

Note that if the candidate DU 1502 is the same as the source DU providing the source cell, the UE CONTEXT MODIFICATION REQUEST message is used instead of the UE CONTEXT SETUP REQUEST message (step 1522), and the UE CONTEXT MODIFICATION REPONSE message is used instead of the UE CONTEXT SETUP REPONSE message (step 1523). The UE CONTEXT MODIFICATION REQUEST message may include an LTM Information Modify IE instead of an LTM Information Setup IE. The new field or IE described with respect to step 1522 may be included in the LTM Information Modify IE or may be included in the UE CONTEXT MODIFICATION REQUEST message separately from the LTM Information Modify IE.

Specific examples of new fields or IEs included in the UE CONTEXT SETUP REQUEST message described with respect to step 1522 may be similar to those shown in Figures 10 and 11.

The operations of CU1501 and candidate DU1502 described with reference to FIG. 15 can provide details of the operations of CU1501 and candidate DU1502 for preparing CLTM. Furthermore, these operations of CU1501 and candidate DU1502 help to reuse the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message for both preparing normal LTM and preparing CLTM. In other words, these operations of CU1501 and candidate DU1502 make it possible to reuse the UE CONTEXT SETUP REQUEST or UE CONTEXT MODIFICATION REQUEST message for preparing normal LTM for preparing CLTM.

Second Embodiment
The configuration example of the wireless communication system according to this embodiment is the same as the configuration example described with reference to Figures 1 and 2. This embodiment provides details of the use of a RACH-less LTM cell switch when the UE 40 determines that the CLTM execution condition is met.

FIG. 16 shows an example of the operation of UE 40. In step 1601, UE 40 evaluates the CLTM execution condition for each of one or more candidate cells. In step 1602, UE 40 determines whether the CLTM execution condition is met for one of the one or more candidate cells.

In step 1603, UE 40 determines whether to use a RACH-less cell switch procedure for a cell switch to the selected candidate cell. Specifically, UE 40 determines whether to use a RACH-less cell switch procedure based at least on whether UE 40 has a valid TA value and whether the reference signal beam for which the execution condition for the candidate cell was determined to be met was used to acquire a valid TA value in the early TA acquisition procedure performed for the candidate cell. The reference signal beam used to determine whether the execution condition for the candidate cell is met may be an SSB beam or a CSI-RS beam. An SSB beam may be expressed as SSB, and a CSI-RS beam may be expressed as CSI-RS. UE 40 performs a RACH-less cell switch procedure if UE 40 has a valid TA value and if the reference signal beam was used to acquire the valid TA value in the early TA acquisition procedure. In other words, UE 40 skips the random access procedure and accesses the selected candidate cell (i.e., target cell). Otherwise, the UE 40 performs a RACH-based cell switch using a random access procedure.

The operation of UE 40 described with reference to FIG. 16 can provide details of the use of a RACH-less LTM cell switch when UE 40 determines that the CLTM execution conditions are met. Specifically, the operation of UE 40 in FIG. 16 provides the following advantages, for example: A candidate cell selected as a target cell (or a candidate DU that manages the cell) can know in advance which uplink beam associated with which reference signal beam it should use to prepare to receive the (first) uplink signal in the cell switch procedure. In other words, the candidate cell (or the candidate DU that manages the cell) can know the beam that UE 40 will use to transmit the (first) uplink signal in the cell switch procedure from information about the reference signal associated with the random access preamble used by UE 40 in the early TA acquisition procedure. This is achieved because the correspondence between the reference signal beam, the beam of the random access preamble, and the beam of the uplink signal can be known in advance from their settings (or information thereon).

<Other embodiments>
CLTM may be valid only within a predetermined or specific group of cells. UE 40 may evaluate the CLTM execution conditions only for one or more candidate cells that belong to the same group as the current serving cell. For example, CLTM may be valid only within a group of cells served by the same DU (intra-DU cell group).

Next, example configurations of gNB-CU10, gNB-CU-CP11, gNB-CU-UP12, gNB-DUs21 and 22, and UE40 will be described below. Figure 17 is a block diagram showing an example configuration of gNB-CU10. The configurations of gNB-CU-CP11, gNB-CU-UP12, and gNB-DUs21 and 22 may also be similar to the configuration shown in Figure 17. In addition, the configurations of CUs (e.g., CUs 701, 1401, etc.) and DUs (e.g., DUs 702, 1402, 403, 1404, etc.) described in the above-mentioned embodiments may also be similar to the configuration shown in Figure 17.

Referring to FIG. 17, the gNB-CU10 includes a network interface 1701, a processor 1702, and a memory 1703. The network interface 1701 is used to communicate with network nodes (e.g., gNB-DUs, and control plane (CP) nodes and/or user plane (UP) nodes in the core network). The network interface 1701 may include multiple interfaces. The network interface 1701 may include, for example, an optical fiber interface for CU-DU communication and a network interface compliant with the IEEE 802.3 series.

Processor 1702 may include multiple processors. If gNB-CU10 is a gNB-CU-CP, processor 1702 performs, for example, control plane processing, such as processing related to NGAP, RRC, E1AP, and F1AP signaling. If gNB-CU10 includes a gNB-CU-UP, processor 1702 performs, for example, termination of the NG-U interface, termination of the F1-U interface, and data processing for the SDAP and PDCP layers.

In the case of gNB-DUs 21 and 22, the processor 1702 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communication. For example, the processor 1702 may include a modem processor (e.g., a Digital Signal Processor (DSP)) that performs digital baseband signal processing and a protocol stack processor (e.g., a Central Processing Unit (CPU) or a Micro Processing Unit (MPU)) that performs control plane processing. The digital baseband signal processing may include signal processing of the RLC, MAC, and PHY layers. The control plane processing may include processing of MAC CEs and DCIs. The processor 1702 may include a digital beamformer module for beamforming. The digital beamformer module may include a multiple-input multiple-output (MIMO) encoder and precoder.

Memory 1703 is composed of a combination of volatile memory and non-volatile memory. Volatile memory is, for example, Static Random Access Memory (SRAM) or Dynamic RAM (DRAM), or a combination thereof. Non-volatile memory is Mask Read Only Memory (MROM), Electrically Erasable Programmable ROM (EEPROM), flash memory, or a hard disk drive, or any combination thereof. Memory 1703 may include storage located remotely from processor 1702. In this case, processor 1702 may access memory 1703 via network interface 1701 or another I/O interface.

Memory 1703 may store one or more software modules (computer programs) 1704 containing instructions and data for performing the processing by gNB-CU10 described in the above-described embodiments. In some implementations, processor 1702 may be configured to read and execute one or more software modules 1704 from memory 1703, thereby performing the processing by gNB-CU10 described in the above-described embodiments.

Figure 18 is a block diagram showing an example configuration of UE 40. RF transceiver 1801 performs analog RF signal processing to communicate with TRPs. RF transceiver 1801 may include multiple transceivers. The analog RF signal processing performed by RF transceiver 1801 includes frequency up-conversion, frequency down-conversion, and amplification. RF transceiver 1801 is coupled to antenna array 1802 and baseband processor 1803. RF transceiver 1801 receives modulation symbol data (or OFDM symbol data) from baseband processor 1803, generates a transmit RF signal, and provides the transmit RF signal to antenna array 1802. RF transceiver 1801 also generates a baseband receive signal based on the receive RF signal received by antenna array 1802 and provides it to baseband processor 1803. RF transceiver 1801 may include an analog beamformer circuit for beamforming. The analog beamformer circuitry includes, for example, multiple phase shifters and multiple power amplifiers.

The baseband processor 1803 performs digital baseband signal processing (data plane processing) and control plane processing for wireless communications. Digital baseband signal processing includes (a) data compression/decompression, (b) data segmentation/concatenation, (c) transmission format (transmission frame) generation/decomposition, (d) transmission path encoding/decoding, (e) modulation (symbol mapping)/demodulation, and (f) generation of OFDM symbol data (baseband OFDM signal) using Inverse Fast Fourier Transform (IFFT). Control plane processing, on the other hand, includes communication management for Layer 1 (e.g., transmit power control), Layer 2 (e.g., radio resource management and hybrid automatic repeat request (HARQ) processing), and Layer 3 (e.g., signaling related to attachment, mobility, and call management).

For example, digital baseband signal processing by baseband processor 1803 may include signal processing of the SDAP layer, PDCP layer, RLC layer, MAC layer, and PHY layer. Furthermore, control plane processing by baseband processor 1803 may include processing of the Non-Access Stratum (NAS) protocol, RRC protocol, MAC CEs, and DCIs.

The baseband processor 1803 may perform MIMO encoding and precoding for beamforming.

The baseband processor 1803 may include a modem processor (e.g., DSP) that performs digital baseband signal processing and a protocol stack processor (e.g., CPU or MPU) that performs control plane processing. In this case, the protocol stack processor that performs control plane processing may be shared with the application processor 1804, which will be described later.

The application processor 1804 is also called a CPU, MPU, microprocessor, or processor core. The application processor 1804 may include multiple processors (multiple processor cores). The application processor 1804 realizes the various functions of the UE 40 by executing a system software program (operating system (OS)) and various application programs (e.g., a calling application, a web browser, a mailer, a camera operation application, a music playback application) read from the memory 1806 or a memory not shown.

In some implementations, the baseband processor 1803 and the application processor 1804 may be integrated on a single chip, as shown by the dashed line (1805) in Figure 18. In other words, the baseband processor 1803 and the application processor 1804 may be implemented as a single System on Chip (SoC) device 1805. An SoC device is sometimes called a System Large Scale Integration (LSI) or chipset.

Memory 1806 is volatile memory, non-volatile memory, or a combination thereof. Memory 1806 may include multiple physically independent memory devices. Volatile memory is, for example, SRAM or DRAM, or a combination thereof. Non-volatile memory is MROM, EEPROM, flash memory, or a hard disk drive, or any combination thereof. For example, memory 1806 may include an external memory device accessible from baseband processor 1803, application processor 1804, and SoC 1805. Memory 1806 may include an internal memory device integrated within baseband processor 1803, application processor 1804, or SoC 1805. Furthermore, memory 1806 may include memory within a Universal Integrated Circuit Card (UICC).

Memory 1806 may store one or more software modules (computer programs) 1807 containing instructions and data for performing the processing by UE 40 described in the above-described embodiments. In some implementations, baseband processor 1803 or application processor 1804 may be configured to read and execute the software modules 1807 from memory 1806, thereby performing the processing by UE 40 described using the drawings in the above-described embodiments.

Note that the control plane processing and operations performed by UE 40 described in the above embodiment can be realized by elements other than RF transceiver 1801 and antenna array 1802, namely, at least one of baseband processor 1803 and application processor 1804, and memory 1806 storing software module 1807.

As described using Figures 17 and 18, each of the processors possessed by the gNB-CUs, gNB-CU-CPs, gNB-CU-UPs, gNB-DUs, and UEs according to the above-described embodiments can execute one or more programs including instructions for causing a computer to perform the algorithms described using the drawings. The programs include instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The programs may be stored on a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technology, CD-ROM, digital versatile disk (DVD), Blu-ray (registered trademark) disc or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The programs may also be transmitted on a transitory computer-readable medium or a communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

The above-described embodiments are merely examples of the application of the technical ideas developed by the inventors. In other words, the technical ideas are not limited to the above-described embodiments, and various modifications are naturally possible.

For example, some or all of the above embodiments may also be described as, but are not limited to, the following appendices. Some or all of the elements (e.g., configurations and functions) described in appendices directed to devices (e.g., distributed units, central units, wireless terminals) may naturally also be described as appendices directed to methods and programs. For example, some or all of the elements described in appendices 2-16, which are subordinate to appendices 1, may also be described as appendices subordinate to appendices 17 and 18, due to the same subordinate relationship as appendices 2-16. Similarly, some or all of the elements described in appendices 20-34, which are subordinate to appendices 19, may also be described as appendices subordinate to appendices 35 and 36, due to the same subordinate relationship as appendices 20-34. Some or all of the elements described in any appendice may be applicable to various hardware, software, recording means for recording software, systems, and methods.

(Appendix 1)
A distributed unit (DU) of a radio access network (RAN) node, comprising:
means for receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell;
means for determining whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM;
DU equipped with.
(Appendix 2)
The determining means is
if the first message includes the first indication, deeming the one or more cell switches subject to the conditional LTM;
if the first message does not include the first indication, then deem the one or more cell switches to be subject to the normal LTM.
It is configured as follows:
DU as described in Appendix 1.
(Appendix 3)
means for generating a second message based on the first message;
means for sending the second message to the CU;
Furthermore,
The generating means comprises:
If the one or more cell switches are subject to the conditional LTM, include in the second message one or more execution conditions for the one or more cell switches in addition to the LTM configuration for the first candidate cell;
If the one or more cell switches are subject to the normal LTM, then the one or more execution conditions are not included in the second message, and an LTM configuration for the first candidate cell is included in the second message.
It is configured as follows:
DU according to Appendix 1 or 2.
(Appendix 4)
means for generating a second message based on the first message;
means for sending the second message to the CU;
Furthermore,
The generating means comprises:
If the one or more cell switches are subject to the conditional LTM, include, in addition to the LTM configuration for the first candidate cell, proposal information for the conditional LTM;
If the one or more cell switches are subject to the normal LTM, do not include the proposal information in the second message, and include an LTM configuration for the first candidate cell in the second message.
It is configured as follows:
DU according to Appendix 1 or 2.
(Appendix 5)
the suggestion information is taken into account by the CU to determine one or more performance conditions for the one or more cell switches.
DU as described in Appendix 4.
(Appendix 6)
The first message or the first indication explicitly indicates which one or more of the plurality of candidate cells, excluding the first candidate cell, are subject to the conditional LTM in a cell switch from the first candidate cell.
DU according to any one of appendices 1 to 5.
(Appendix 7)
The first message or the first indication explicitly indicates which cell pairs included in the plurality of candidate cells are subject to the conditional LTM.
DU according to any one of appendices 1 to 5.
(Appendix 8)
the first indication is an indication of one or more performance condition requirements for the one or more cell switches;
DU according to any one of appendices 1 to 7.
(Appendix 9)
the first representation is a representation of the conditional LTM;
DU according to any one of appendices 1 to 7.
(Appendix 10)
the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message;
The first indication is included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message or an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message;
DU according to any one of appendices 1 to 9.
(Appendix 11)
the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message;
The first indication is an information element included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message, separately from an LTM Information Setup information element or an LTM Information Modify information element.
DU according to any one of appendices 1 to 9.
(Appendix 12)
the first indication indicates to the DU whether the one or more cell switches are subject to the conditional LTM;
The first message or the first indication further indicates to the DU whether an execution condition is required to be generated if the one or more cell switches are subject to the conditional LTM.
DU according to any one of appendices 1 to 11.
(Appendix 13)
The first indication or a second indication included in the first message separately from the first indication indicates whether one or more cell switches from another cell to the first candidate cell are subject to conditional LTM.
DU according to any one of appendices 1 to 12.
(Appendix 14)
The conditional LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell in response to the wireless terminal determining that an execution condition is satisfied, and
The normal LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell, in response to the wireless terminal receiving a layer 1 or layer 2 cell switch command from a source DU, without depending on the execution condition.
DU according to any one of appendices 1 to 13.
(Appendix 15)
the LTM requested by the first message is an intra-DU LTM;
The DU is a DU that serves all of the plurality of candidate cells.
DU according to any one of appendices 1 to 14.
(Appendix 16)
the LTM requested by the first message is an inter-DU LTM;
The first candidate cell is different from the source cell of the first LTM in the LTM requested by the first message;
The DU is a candidate DU different from a source DU that serves the source cell.
DU according to any one of appendices 1 to 14.
(Appendix 17)
the LTM requested by the first message is an inter-DU LTM;
The first candidate cell is the same as the source cell of the first LTM in the LTM requested by the first message;
The DU is a source DU that serves the source cell.
DU according to any one of appendices 1 to 14.
(Appendix 18)
1. A method performed by a distributed unit (DU) of a radio access network (RAN) node, comprising:
receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM;
A method for providing the above.
(Appendix 19)
1. A program for causing a computer to perform a method for a distributed unit (DU) of a radio access network (RAN) node, the method comprising:
receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM;
A program that includes:
(Appendix 20)
A central unit (CU) of a radio access network (RAN) node, comprising:
means for sending a first message to a distributed unit (DU) of the RAN node, requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell;
The first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.
CU.
(Appendix 21)
the first message causes the DU to consider the one or more cell switches subject to the conditional LTM if the first message includes the first indication;
the first message causes the DU to consider the one or more cell switches to be subject to the normal LTM if the first message does not include the first indication.
21. The CU of claim 20.
(Appendix 22)
means for receiving a second message based on the first message from the DU;
If the one or more cell switches are subject to the conditional LTM, the second message includes one or more execution conditions for the one or more cell switches in addition to an LTM configuration for the first candidate cell;
If the one or more cell switches are subject to the normal LTM, the second message includes an LTM configuration for the first candidate cell without including the one or more execution conditions.
22. The CU of claim 20 or 21.
(Appendix 23)
further comprising means for receiving a second message based on the first message from the DU;
If the one or more cell switches are subject to the conditional LTM, the second message includes, in addition to an LTM configuration for the first candidate cell, proposal information for the conditional LTM;
If the one or more cell switches are subject to the normal LTM, the second message does not include the proposal information and includes an LTM configuration for the first candidate cell.
22. The CU of claim 20 or 21.
(Appendix 24)
means for determining one or more execution conditions for the one or more cell switches based on the proposal information;
24. The CU described in Appendix 23.
(Appendix 25)
The first message or the first indication explicitly indicates which one or more of the plurality of candidate cells, excluding the first candidate cell, are subject to the conditional LTM in a cell switch from the first candidate cell.
25. The CU of any one of appendices 20 to 24.
(Appendix 26)
The first message or the first indication explicitly indicates which cell pairs included in the plurality of candidate cells are subject to the conditional LTM.
25. The CU of any one of appendices 20 to 24.
(Appendix 27)
the first indication is an indication of one or more performance condition requirements for the one or more cell switches;
27. The CU of any one of appendices 20 to 26.
(Appendix 28)
the first representation is a representation of the conditional LTM;
27. The CU of any one of appendices 20 to 26.
(Appendix 29)
the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message;
The first indication is included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message or an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message;
29. The CU of any one of appendices 20 to 28.
(Appendix 30)
the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message;
The first indication is an information element included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message, separately from an LTM Information Setup information element or an LTM Information Modify information element.
29. The CU of any one of appendices 20 to 28.
(Appendix 31)
the indication indicates to the DU whether the one or more cell switches are subject to the conditional LTM;
The first message or the first indication further indicates to the DU whether an execution condition is required to be generated if the one or more cell switches are subject to the conditional LTM.
31. The CU of any one of appendices 20 to 30.
(Appendix 32)
The first indication or a second indication included in the first message separately from the first indication indicates whether one or more cell switches from another cell to the first candidate cell are subject to conditional LTM.
32. The CU of any one of appendices 20 to 31.
(Appendix 33)
The conditional LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell in response to the wireless terminal determining that an execution condition is satisfied, and
The normal LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell, in response to the wireless terminal receiving a layer 1 or layer 2 cell switch command from a source DU, without depending on the execution condition.
33. The CU of any one of appendices 20 to 32.
(Appendix 34)
the LTM requested by the first message is an intra-DU LTM;
The DU is a DU that serves all of the plurality of candidate cells.
34. The CU of any one of appendices 20 to 33.
(Appendix 35)
the LTM requested by the first message is an inter-DU LTM;
The first candidate cell is different from the source cell of the first LTM in the LTM requested by the first message;
The DU is a candidate DU different from a source DU that serves the source cell.
34. The CU of any one of appendices 20 to 33.
(Appendix 36)
the LTM requested by the first message is an inter-DU LTM;
The first candidate cell is the same as the source cell of the first LTM in the LTM requested by the first message;
The DU is a source DU that serves the source cell.
34. The CU of any one of appendices 20 to 33.
(Appendix 37)
1. A method performed by a Central Unit (CU) of a Radio Access Network (RAN) node, comprising:
sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell;
The first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.
method.
(Appendix 38)
1. A program for causing a computer to perform a method for a central unit (CU) of a radio access network (RAN) node, the method comprising:
sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell;
The first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.
program.
(Appendix 39)
A wireless terminal,
means for evaluating a condition for performing conditional Layer-1/Layer-2 triggered mobility (LTM) for each of the one or more candidate cells;
means for performing a cell switch to one of the one or more candidate cells if the execution condition is satisfied for the one of the one or more candidate cells;
Equipped with
the means for performing the cell switch is configured to determine whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for which the execution condition of the one candidate cell is determined to be satisfied has been used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.
Wireless terminal.
(Appendix 40)
The means for performing the cell switch includes:
performing a first cell switch procedure that skips a random access procedure if the wireless terminal has the valid Timing Advance value and if the reference signal beam was used to acquire the valid Timing Advance value in the early Timing Advance acquisition procedure;
otherwise, perform a second cell switch procedure using a random access procedure;
It is configured as follows:
40. The wireless terminal of claim 39.
(Appendix 41)
The reference signal beam is a Synchronization Signal (SS)/Physical Broadcast Channel (PBCH) block (SSB) beam or a Channel State Information (CSI) Reference Signal (CSI-RS) beam.
41. The wireless terminal of claim 39 or 40.
(Appendix 42)
1. A method performed by a wireless terminal, comprising:
evaluating an execution condition for conditional Layer-1/Layer-2 triggered mobility (LTM) for each of one or more candidate cells; and performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell;
Equipped with
performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for which the execution condition of the one candidate cell is determined to be satisfied has been used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.
method.
(Appendix 43)
A program for causing a computer to perform a method for a wireless terminal, comprising:
The method comprises:
evaluating an execution condition for conditional Layer-1/Layer-2 triggered mobility (LTM) for each of one or more candidate cells; and performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell;
Equipped with
performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for which the execution condition of the one candidate cell is determined to be satisfied has been used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.
program.

This application claims priority based on Japanese Patent Application No. 2024-020584, filed February 14, 2024, the disclosure of which is incorporated herein in its entirety.

1 gNB
10 gNB-CU
11 gNB-CU-CP
12 gNB-CU-UP
21, 22 gNB-DU
31, 32, 33, 34 TRP
40UE
51, 52, 53, 54 Cell 120 LTM in DU
140 DU LTM
1702 Processor 1703 Memory 1803 Baseband processor 1804 Application processor 1806 Memory

Claims (43)

A distributed unit (DU) of a radio access network (RAN) node, comprising:
means for receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell;
means for determining whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM;
DU equipped with. The determining means is
if the first message includes the first indication, deeming the one or more cell switches subject to the conditional LTM;
if the first message does not include the first indication, then consider the one or more cell switches to be subject to the normal LTM.
It is configured as follows:
The DU according to claim 1. means for generating a second message based on the first message;
means for sending the second message to the CU;
Furthermore,
The generating means comprises:
If the one or more cell switches are subject to the conditional LTM, include in the second message one or more execution conditions for the one or more cell switches in addition to the LTM configuration for the first candidate cell;
If the one or more cell switches are subject to the normal LTM, then the one or more execution conditions are not included in the second message, and an LTM configuration for the first candidate cell is included in the second message.
It is configured as follows:
DU according to claim 1 or 2. means for generating a second message based on the first message;
means for sending the second message to the CU;
Furthermore,
The generating means comprises:
If the one or more cell switches are subject to the conditional LTM, include, in addition to the LTM configuration for the first candidate cell, proposal information for the conditional LTM;
If the one or more cell switches are subject to the normal LTM, do not include the proposal information in the second message, and include an LTM configuration for the first candidate cell in the second message.
It is configured as follows:
DU according to claim 1 or 2. the suggestion information is taken into account by the CU to determine one or more performance conditions for the one or more cell switches.
The DU according to claim 4. The first message or the first indication explicitly indicates which one or more of the plurality of candidate cells, excluding the first candidate cell, are subject to the conditional LTM in a cell switch from the first candidate cell.
The DU according to any one of claims 1 to 5. The first message or the first indication explicitly indicates which cell pairs included in the plurality of candidate cells are subject to the conditional LTM.
The DU according to any one of claims 1 to 5. the first indication is an indication of one or more performance condition requirements for the one or more cell switches;
The DU according to any one of claims 1 to 7. the first representation is a representation of the conditional LTM;
The DU according to any one of claims 1 to 7. the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message;
The first indication is included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message or an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message;
The DU according to any one of claims 1 to 9. the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message;
The first indication is an information element included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message, separately from an LTM Information Setup information element or an LTM Information Modify information element.
The DU according to any one of claims 1 to 9. the first indication indicates to the DU whether the one or more cell switches are subject to the conditional LTM;
The first message or the first indication further indicates to the DU whether an execution condition is required to be generated if the one or more cell switches are subject to the conditional LTM.
The DU according to any one of claims 1 to 11. The first indication or a second indication included in the first message separately from the first indication indicates whether one or more cell switches from another cell to the first candidate cell are subject to conditional LTM.
DU according to any one of claims 1 to 12. The conditional LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell in response to the wireless terminal determining that an execution condition is satisfied, and
The normal LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell, in response to the wireless terminal receiving a layer 1 or layer 2 cell switch command from a source DU, without depending on the execution condition.
The DU according to any one of claims 1 to 13. the LTM requested by the first message is an intra-DU LTM;
The DU is a DU that serves all of the plurality of candidate cells.
DU according to any one of claims 1 to 14. the LTM requested by the first message is an inter-DU LTM;
The first candidate cell is different from the source cell of the first LTM in the LTM requested by the first message;
The DU is a candidate DU different from a source DU that serves the source cell.
DU according to any one of claims 1 to 14. the LTM requested by the first message is an inter-DU LTM;
The first candidate cell is the same as the source cell of the first LTM in the LTM requested by the first message;
The DU is a source DU that serves the source cell.
DU according to any one of claims 1 to 14. 1. A method performed by a distributed unit (DU) of a radio access network (RAN) node, comprising:
receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM;
A method for providing the above. 1. A program for causing a computer to perform a method for a distributed unit (DU) of a radio access network (RAN) node, the method comprising:
receiving, from a central unit (CU) of the RAN node, a first message requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell; and determining, based on whether the first message includes a first indication related to conditional LTM, whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM;
A program that includes: A central unit (CU) of a radio access network (RAN) node, comprising:
means for sending a first message to a distributed unit (DU) of the RAN node, requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell;
The first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.
CU. the first message causes the DU to consider the one or more cell switches subject to the conditional LTM if the first message includes the first indication;
the first message causes the DU to consider the one or more cell switches to be subject to the normal LTM if the first message does not include the first indication.
The CU of claim 20. further comprising means for receiving a second message based on the first message from the DU;
If the one or more cell switches are subject to the conditional LTM, the second message includes one or more execution conditions for the one or more cell switches in addition to an LTM configuration for the first candidate cell;
If the one or more cell switches are subject to the normal LTM, the second message includes an LTM configuration for the first candidate cell without including the one or more execution conditions.
22. The CU according to claim 20 or 21. further comprising means for receiving a second message based on the first message from the DU;
If the one or more cell switches are subject to the conditional LTM, the second message includes, in addition to an LTM configuration for the first candidate cell, proposal information for the conditional LTM;
If the one or more cell switches are subject to the normal LTM, the second message does not include the proposal information and includes an LTM configuration for the first candidate cell.
22. The CU according to claim 20 or 21. means for determining one or more execution conditions for the one or more cell switches based on the proposal information;
The CU of claim 23. The first message or the first indication explicitly indicates which one or more of the plurality of candidate cells, excluding the first candidate cell, are subject to the conditional LTM in a cell switch from the first candidate cell.
The CU according to any one of claims 20 to 24. The first message or the first indication explicitly indicates which cell pairs included in the plurality of candidate cells are subject to the conditional LTM.
The CU according to any one of claims 20 to 24. the first indication is an indication of one or more performance condition requirements for the one or more cell switches;
The CU according to any one of claims 20 to 26. the first representation is a representation of the conditional LTM;
The CU according to any one of claims 20 to 26. the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message;
The first indication is included in an LTM Information Setup information element in the UE CONTEXT SETUP REQUEST message or an LTM Information Modify information element in the UE CONTEXT MODIFICATION REQUEST message;
The CU according to any one of claims 20 to 28. the first message is a UE CONTEXT SETUP REQUEST message or a UE CONTEXT MODIFICATION REQUEST message;
The first indication is an information element included in the UE CONTEXT SETUP REQUEST message or the UE CONTEXT MODIFICATION REQUEST message, separately from an LTM Information Setup information element or an LTM Information Modify information element.
The CU according to any one of claims 20 to 28. the indication indicates to the DU whether the one or more cell switches are subject to the conditional LTM;
The first message or the first indication further indicates to the DU whether an execution condition is required to be generated if the one or more cell switches are subject to the conditional LTM.
The CU according to any one of claims 20 to 30. The first indication or a second indication included in the first message separately from the first indication indicates whether one or more cell switches from another cell to the first candidate cell are subject to conditional LTM.
The CU according to any one of claims 20 to 31. The conditional LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell in response to the wireless terminal determining that an execution condition is satisfied, and
The normal LTM is an LTM in which the wireless terminal executes a cell switch from the first candidate cell to another cell, in response to the wireless terminal receiving a layer 1 or layer 2 cell switch command from a source DU, without depending on the execution condition.
The CU according to any one of claims 20 to 32. the LTM requested by the first message is an intra-DU LTM;
The DU is a DU that serves all of the plurality of candidate cells.
The CU according to any one of claims 20 to 33. the LTM requested by the first message is an inter-DU LTM;
The first candidate cell is different from the source cell of the first LTM in the LTM requested by the first message;
The DU is a candidate DU different from a source DU that serves the source cell.
The CU according to any one of claims 20 to 33. the LTM requested by the first message is an inter-DU LTM;
The first candidate cell is the same as the source cell of the first LTM in the LTM requested by the first message;
The DU is a source DU that serves the source cell.
The CU according to any one of claims 20 to 33. 1. A method performed by a Central Unit (CU) of a Radio Access Network (RAN) node, comprising:
sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell;
The first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.
method. 1. A program for causing a computer to perform a method for a central unit (CU) of a radio access network (RAN) node, the method comprising:
sending a first message to a distributed unit (DU) of the RAN node requesting preparation of a first candidate cell for Layer-1/Layer-2 triggered mobility (LTM) of a wireless terminal among a plurality of candidate cells including the first candidate cell;
The first message indicates to the DU whether one or more cell switches from the first candidate cell to one or more other candidate cells in the LTM requested by the first message are subject to conditional LTM or normal LTM based on whether the first message includes a first indication related to conditional LTM.
program. A wireless terminal,
means for evaluating a condition for performing conditional Layer-1/Layer-2 triggered mobility (LTM) for each of the one or more candidate cells;
means for performing a cell switch to one of the one or more candidate cells if the execution condition is satisfied for the one of the one or more candidate cells;
Equipped with
the means for performing the cell switch is configured to determine whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for which the execution condition of the one candidate cell is determined to be satisfied has been used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.
Wireless terminal. The means for performing the cell switch includes:
performing a first cell switch procedure that skips a random access procedure if the wireless terminal has the valid Timing Advance value and if the reference signal beam was used to acquire the valid Timing Advance value in the early Timing Advance acquisition procedure;
otherwise, perform a second cell switch procedure using a random access procedure;
It is configured as follows:
40. The wireless terminal of claim 39. The reference signal beam is a Synchronization Signal (SS)/Physical Broadcast Channel (PBCH) block (SSB) beam or a Channel State Information (CSI) Reference Signal (CSI-RS) beam.
41. A wireless terminal according to claim 39 or 40. 1. A method performed by a wireless terminal, comprising:
evaluating an execution condition for conditional Layer-1/Layer-2 triggered mobility (LTM) for each of one or more candidate cells; and performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell;
Equipped with
performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for which the execution condition of the one candidate cell is determined to be satisfied has been used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.
method. A program for causing a computer to perform a method for a wireless terminal, comprising:
The method comprises:
evaluating an execution condition for conditional Layer-1/Layer-2 triggered mobility (LTM) for each of one or more candidate cells; and performing a cell switch to one of the one or more candidate cells if the execution condition is met for the one candidate cell;
Equipped with
performing the cell switch includes determining whether to use a first cell switch procedure that skips a random access procedure based at least on whether the wireless terminal has a valid Timing Advance value and whether a reference signal beam for which the execution condition of the one candidate cell is determined to be satisfied has been used to acquire the valid Timing Advance value in an early Timing Advance acquisition procedure performed for the one candidate cell.
program.