Communication device, base station, and communication method

Abstract

A communication device (100) according to an embodiment comprises: a reception unit that uses an RRC message to receive, from a base station, setting information pertaining to an LTM and including first information indicating a preamble index used in an RA procedure, and receives, from the base station, a cell change command media access control MAC CE that indicates a cell change and includes information for identifying the setting information; and a control unit which, when the cell change command MAC CE is received, executes the RA procedure to a target cell corresponding to information for identifying the setting information. When second information expressing the preamble index is included in the cell change command MAC CE, the control unit executes the RA procedure by using the preamble index which is selected on the basis of the second information.

Description

Communication device, base station, and communication method CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims the benefit of priority from patent application serial number 2023-130224, filed August 9, 2023, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to a communication device, a base station, and a communication method.

[0003] In a mobile communication system that complies with the technical specifications of 3GPP (registered trademark; the same applies hereinafter) (Third Generation Partnership Project), a standardization project for mobile communication systems, the introduction of L1 (Layer 1) / L2 (Layer 2) triggered mobility (LTM) is planned (see, for example, Non-Patent Document 1). In LTM, a base station changes the serving cell of a communication device by transmitting a cell switch command to the communication device via a media access control control element (MAC CE) based on an L1 measurement report received from the communication device. Compared to a cell change based on a radio resource control (RRC) message, the communication device can dynamically perform a cell change and reduce mobility delay.

[0004] In LTM, for example, early synchronization, in which a communication device synchronizes with a candidate cell before receiving a cell change command, and LTM execution, in which a communication device executes a cell change in response to a cell change command based on an L1 measurement report, can be performed.

[0005] In performing LTM, it has been agreed that both a method of performing a random access procedure between a communication device and a base station (hereinafter referred to as RACH-based LTM) and a method of performing uplink transmission by a communication device without performing a random access procedure between the communication device and a base station (hereinafter referred to as RACH-less LTM) are supported.

[0006] 3GPP TSG-RAN WG2 Meeting #121, R2-2302039, “38.300 running CR for introduction of NR further mobility enhancements”

[0007] A communication device according to a first aspect includes: a receiving unit that receives, from a base station, configuration information related to Layer 1 / Layer 2 triggered mobility (LTM), the configuration information including first information indicating a preamble index used in a random access (RA) procedure using a radio resource control (RRC) message; and a cell change command media access control (MAC) control element (CE) that includes information for identifying the configuration information and instructs a cell change from the base station. When the cell change command MAC CE is received, the control unit executes the RA procedure for a target cell corresponding to the information for identifying the configuration information. When the cell change command MAC CE includes second information indicating the preamble index, the control unit executes the RA procedure using the preamble index determined based on the second information.

[0008] A base station according to a second aspect includes: a transmitter that transmits configuration information related to Layer 1 / Layer 2 triggered mobility (LTM), the configuration information including first information indicating a preamble index used in a random access (RA) procedure to a communication device using a radio resource control (RRC) message; and transmits a cell change command media access control (MAC) control element (CE) to the communication device, the cell change command including information for identifying the configuration information and instructing a cell change; and a controller that includes second information indicating the preamble index in the cell change command MAC CE.

[0009] A communication method according to a third aspect is a communication method executed by a communication device, comprising the steps of: receiving, from a base station, configuration information related to Layer 1 / Layer 2 triggered mobility (LTM), using a radio resource control (RRC) message, the configuration information including first information indicating a preamble index used in a random access (RA) procedure; receiving, from the base station, a cell change command media access control (MAC) control element (CE) including information for identifying the configuration information and instructing a cell change; performing, when the cell change command MAC CE is received, the RA procedure for a target cell corresponding to the information for identifying the configuration information; and, when the cell change command MAC CE includes second information indicating the preamble index, performing the RA procedure using the preamble index determined based on the second information.

[0010] Objects, features, advantages, etc. of the present disclosure will become clearer from the following detailed description taken in conjunction with the accompanying drawings. FIG. 1 is a diagram illustrating a configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram illustrating an example configuration of a protocol stack according to an embodiment. FIG. 3 is a diagram illustrating an overview of LTM. FIG. 4 is a diagram illustrating a configuration of a UE according to an embodiment. FIG. 5 is a diagram illustrating a configuration of a base station according to an embodiment. FIG. 6 is a sequence diagram illustrating an example operation according to an embodiment. FIG. 7 is a flowchart (part 1) illustrating an example operation according to an embodiment. FIG. 8 is a flowchart (part 2) illustrating an example operation according to an embodiment. FIG. 9 is a flowchart (part 3) illustrating an example operation according to an embodiment.

[0011] A mobile communication system according to an embodiment will be described with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

[0012] However, when a communication device performs RACH-based LTM, the RACH resource used in the random access procedure is not defined. Therefore, the communication device may not be able to properly perform RACH-based LTM, and cell change to the target cell may fail in LTM.

[0013] Therefore, one object is to provide a communication device, a base station, and a communication method that can appropriately execute RACH-based LTM.

[0014] (System Configuration) First, the configuration of a mobile communication system 1 according to this embodiment will be described with reference to Fig. 1. The mobile communication system 1 is, for example, a system that complies with the 3GPP Technical Specification (TS). In the following, the mobile communication system 1 will be described using as an example a 5th Generation System (5G system) of the 3GPP standard, i.e., a mobile communication system based on NR (NR (New Radio) radio access).

[0015] The mobile communication system 1 includes a network 10 and a user equipment (UE) 100 that communicates with the network 10. The network 10 includes a next generation radio access network (NG-RAN) 20, which is a 5G radio access network, and a 5G core network (5GC) 30, which is a 5G core network.

[0016] The UE 100 is a communication device that communicates via the base station 200. The UE 100 may be a device used by a user. The UE 100 may be a mobile device such as a mobile phone terminal such as a smartphone, a tablet terminal, a laptop PC, a communication module, or a communication card. The UE 100 may be a vehicle (e.g., a car, a train, etc.) or a device provided therein. The UE 100 may be a transport vehicle other than a vehicle (e.g., a ship, an airplane, etc.) or a device provided therein. The UE 100 may be a sensor or a device provided therein. The UE 100 may be called a terminal, a terminal device, a mobile station, a mobile terminal, a mobile device, a mobile unit, a subscriber station, a subscriber terminal, a subscriber device, a subscriber unit, a wireless station, a wireless terminal, a wireless device, a wireless unit, a remote station, a remote terminal, a remote device, or a remote unit. The UE 100 is an example of a terminal, and the terminal may include factory equipment, etc.

[0017] The NG-RAN 20 includes multiple base stations 200. Each base station 200 manages at least one cell. A cell constitutes the smallest unit of a communication area. One cell belongs to one frequency (carrier frequency). The term "cell" may refer to wireless communication resources or to the communication target of the UE 100. Each base station 200 can perform wireless communication with the UE 100 located in its own cell. The base station 200 communicates with the UE 100 using a RAN protocol stack. Details of the protocol stack will be described later. The base station 200 is also connected to other base stations 200 (which may be referred to as neighboring base stations) via an Xn interface. The base station 200 communicates with neighboring base stations via the Xn interface. The base station 200 provides NR user plane and control plane protocol termination for the UE 100 and is connected to the 5GC 30 via an NG interface. Such an NR base station 200 is sometimes referred to as a gNodeB (gNB).

[0018] The 5GC 30 includes a core network device 300. The core network device 300 includes, for example, an AMF (Access and Mobility Management Function) and / or a UPF (User Plane Function). The AMF performs mobility management for the UE 100. The UPF provides functions specialized for U-plane processing. The AMF and the UPF are connected to the base station 200 via an NG interface.

[0019] (Configuration Example of Protocol Stack) Next, a configuration example of a protocol stack according to this embodiment will be described with reference to FIG.

[0020] The protocol of the wireless section between UE 100 and base station 200 includes a physical (PHY) layer, a medium access control (MAC) layer, a radio link control (RLC) layer, a packet data convergence protocol (PDCP) layer, and a radio resource control (RRC) layer.

[0021] The PHY layer performs encoding / decoding, modulation / demodulation, antenna mapping / demapping, and resource mapping / demapping. Data and control information are transmitted between the PHY layer of the UE 100 and the PHY layer of the base station 200 via a physical channel.

[0022] The MAC layer performs data priority control, retransmission processing using Hybrid ARQ (HARQ), random access procedures, etc. Data and control information are transmitted between the MAC layer of UE 100 and the MAC layer of base station 200 via a transport channel. The MAC layer of base station 200 includes a scheduler. The scheduler determines the uplink and downlink transport format (transport block size, modulation and coding scheme (MCS)) and the resources to be allocated to UE 100.

[0023] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and the PHY layer. Data and control information are transmitted between the RLC layer of the UE 100 and the RLC layer of the base station 200 via logical channels.

[0024] The PDCP layer performs header compression / decompression and encryption / decryption.

[0025] A Service Data Adaptation Protocol (SDAP) layer may be provided as an upper layer above the PDCP layer. The SDAP layer maps IP flows, which are units for Quality of Service (QoS) control by the core network, to radio bearers, which are units for QoS control by an Access Stratum (AS).

[0026] The RRC layer controls logical channels, transport channels, and physical channels according to the establishment, re-establishment, and release of radio bearers. RRC signaling for various settings is transmitted between the RRC layer of the UE 100 and the RRC layer of the base station 200. When an RRC connection exists between the RRC of the UE 100 and the RRC of the base station 200, the UE 100 is in an RRC connected state. When there is no RRC connection between the RRC of the UE 100 and the RRC of the base station 200, the UE 100 is in an RRC idle state. When the RRC connection between the RRC of the UE 100 and the RRC of the base station 200 is suspended, the UE 100 is in an RRC inactive state.

[0027] The NAS layer, which is located above the RRC layer in the UE 100, performs session management and mobility management for the UE 100. NAS signaling is transmitted between the NAS layer of the UE 100 and the NAS layer of the core network device 300.

[0028] The UE 100 has an application layer and the like in addition to the radio interface protocol.

[0029] (Radio Frame Configuration) In a 5G system, downlink transmission and uplink transmission are configured within a radio frame having a duration of 10 ms. For example, a radio frame is represented by a system frame number (SFN) ranging from 0 to 1023. For example, a radio frame is configured with 10 subframes. For example, one subframe may be 1 ms. Furthermore, one subframe may be configured with one or more slots. For example, the number of symbols that make up one slot is 14 for a normal CP (Cyclic Prefix) and 12 for an extended CP. Furthermore, the number of slots that make up one subframe varies depending on the set subcarrier spacing. For example, for a normal CP, if the subcarrier spacing is set to 15 kHz, the number of slots per subframe is 1 (i.e., 14 symbols); if the subcarrier spacing is set to 30 kHz, the number of slots per subframe is 2 (i.e., 28 symbols); if the subcarrier spacing is set to 60 kHz, the number of slots per subframe is 4 (i.e., 56 symbols); and if the subcarrier spacing is set to 120 kHz, the number of slots per subframe is 8 (i.e., 128 symbols). Furthermore, if the subcarrier spacing is set to 60 kHz for an extended CP, the number of slots per subframe is 4 (i.e., 48 symbols). That is, the number of slots constituting one subframe is determined based on the subcarrier spacing set by the base station 200. Furthermore, the number of symbols constituting one subframe is determined based on the subcarrier spacing set by the base station 200. That is, the number of symbols constituting a 1 ms subframe is determined based on the subcarrier spacing set by the base station 200, and the length of each symbol (length in the time direction) changes.

[0030] (LTM) In a mobile communication system 1 conforming to the technical specifications of 3GPP, introduction of L1 (Layer 1) / L2 (Layer 2) triggered mobility (LTM) is planned. As shown in Fig. 3, in LTM, the following operations can be performed.

[0031] Step S10: LTM Preparation The UE 100 in the RRC connected state may perform the following operation as an operation for LTM preparation.

[0032] Step S11: The UE 100 transmits a measurement report message to the base station 200. The base station 200 determines to use the LTM and starts candidate cell preparation.

[0033] Step S12: The base station 200 transmits an RRC reconfiguration message including LTM candidate cell configuration of one or more candidate cells.

[0034] Step S13: The UE 100 stores the LTM candidate cell configuration. The UE 100 transmits an RRC reconfiguration complete (RRCReconfigurationComplete) message to the base station 200.

[0035] Step S20: Early synchronization The UE 100 may perform the following operation as the early synchronization operation.

[0036] Step S21: Before receiving the cell switching command, the UE 100 performs downlink (DL) synchronization with the candidate cell. The UE 100 may perform DL synchronization based on a synchronization signal (SS) and a physical broadcast channel (PBCH) block (SSB).

[0037] Step S22: Before receiving the cell switch command, the UE 100 performs timing advance (TA) acquisition. The UE 100 may perform TA acquisition based on a PDCCH order (specifically, a PDCCH ordered RACH). The PDCCH order may be triggered only by the source cell.

[0038] Step S30: LTM execution The UE 100 may execute the following operation as the LTM execution operation.

[0039] Step S31: The UE 100 performs L1 measurement on the candidate cell configured by the LTM candidate cell configuration. The UL 100 transmits a lower-layer measurement report based on the L1 measurement to the base station 200.

[0040] Step S32: The base station 200 determines to perform a cell change to the target cell. The base station 200 transmits a MAC CE that triggers the cell change by including a candidate configuration index of the target cell. The UE 100 switches the configuration of the target cell.

[0041] Step S33: If the cell change needs to include the execution of a random access (RA) procedure, the UE 100 executes the RA procedure toward the target cell.

[0042] Step S40: LTM Completion The UE 100 may perform the following operation as an operation for completing LTM.

[0043] Step S41: The UE 100 indicates that the cell change to the target cell has been successfully completed.

[0044] It should be noted that UE 100 may execute steps S20 to S40 multiple times for subsequent LTM cell switching based on the configuration provided in step S12 without releasing the configuration.

[0045] Incidentally, in the execution of LTM, it has been agreed that both a method of executing an RA procedure between the UE 100 and the base station 200 (hereinafter referred to as RACH-based LTM) and a method of the UE 100 performing uplink transmission without executing an RA procedure between the UE 100 and the base station 200 (hereinafter referred to as RACH-less LTM) are supported.

[0046] However, when the UE 100 performs the RACH-based LTM, the random access channel (RACH) resources used in the RA procedure are not defined. Therefore, the UE 100 may not be able to properly perform the RACH-based LTM, and there is a concern that the cell change to the target cell in the LTM may fail. In one embodiment described later, an operation for enabling the RACH-based LTM to be properly performed will be described.

[0047] (Configuration of User Equipment) The configuration of the UE 100 according to the embodiment will be described with reference to Fig. 4. The UE 100 includes a communication unit 110 and a control unit 120.

[0048] The communication unit 110 performs wireless communication with the base station 200 by transmitting and receiving radio signals to and from the base station 200. The communication unit 110 has at least one transmission unit 111 and at least one reception unit 112. The transmission unit 111 and the reception unit 112 may be configured to include multiple antennas and RF (Radio Frequency) circuits. The antenna converts a signal into radio waves and radiates the radio waves into space. The antenna also receives radio waves in space and converts the radio waves into a signal. The RF circuit performs analog processing of the signal transmitted and received via the antenna. The RF circuit may include a high-frequency filter, an amplifier, a modulator, a low-pass filter, etc.

[0049] The control unit 120 performs various controls in the UE 100. The control unit 120 controls communication with the base station 200 via the communication unit 110. The operations of the UE 100 described above and below may be operations controlled by the control unit 120. The control unit 120 may include at least one processor capable of executing a program and a memory that stores the program. The processor may execute the program to perform the operations of the control unit 120. The control unit 120 may include a digital signal processor that performs digital processing of signals transmitted and received via the antenna and the RF circuit. The digital processing includes processing of a RAN protocol stack. The memory stores the program executed by the processor, parameters related to the program, and data related to the program. The memory may include at least one of read-only memory (ROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), random access memory (RAM), and flash memory. All or a portion of the memory may be contained within the processor.

[0050] In the UE 100 configured in this manner, the receiver 112 receives a cell change command that triggers a cell change from the base station 200 by MAC CE. The controller 120 executes an RA procedure between the UE 100 and the target cell based on the cell change command. The controller 120 determines a RACH resource for the RA procedure according to a predefined rule or an instruction from the base station 200. This allows the base station 200 to clearly grasp the RACH resource used by the UE 100, which makes it easier for the cell change to the target cell to succeed in LTM compared to a case where the RACH resource used by the UE 100 is unclear, and the RACH-based LTM is executed appropriately.

[0051] (Configuration of Base Station) The configuration of the base station 200 according to this embodiment will be described with reference to Fig. 5. The base station 200 includes a communication unit 210, a network communication unit 220, and a control unit 230.

[0052] The communication unit 210 receives, for example, a radio signal from the UE 100 and transmits the radio signal to the UE 100. The communication unit 210 has at least one transmission unit 211 and at least one reception unit 212. The transmission unit 211 and the reception unit 212 may be configured to include an RF circuit. The RF circuit performs analog processing of signals transmitted and received via an antenna. The RF circuit may include a high-frequency filter, an amplifier, a modulator, a low-pass filter, etc.

[0053] The network communication unit 220 transmits and receives signals to and from the network. For example, the network communication unit 220 receives signals from adjacent base stations connected via an Xn interface, which is an interface between base stations, and transmits the signals to the adjacent base stations. The network communication unit 220 also receives signals from the core network device 300 connected via an NG interface, and transmits the signals to the core network device 300.

[0054] The control unit 230 performs various controls in the base station 200. The control unit 230 controls, for example, communication with the UE 100 via the communication unit 210. The control unit 230 also controls, for example, communication with a node (e.g., a neighboring base station, the core network device 300) via the network communication unit 220. The operations of the base station 200 described above and below may be controlled by the control unit 230. The control unit 230 may include at least one processor capable of executing a program and a memory that stores the program. The processor may execute the program to perform the operations of the control unit 230. The control unit 230 may include a digital signal processor that performs digital processing of signals transmitted and received via the antenna and the RF circuit. The digital processing includes processing of a RAN protocol stack. The memory stores programs executed by the processor, parameters related to the programs, and data related to the programs. All or a part of the memory may be included in the processor.

[0055] In the base station 200 configured in this manner, the transmitter 211 transmits a cell change command that triggers a cell change to the UE 100 by using a MAC CE. The controller 230 executes an RA procedure between the UE 100 and the target cell based on the cell change command. The controller 230 may perform control to instruct the UE 100 about the RACH resource for the RA procedure. This allows the base station 200 to clearly grasp the RACH resource used by the UE 100. Therefore, compared to a case where the RACH resource used by the UE 100 is unclear, the cell change to the target cell is more likely to be successful in LTM, and the RACH-based LTM is executed appropriately.

[0056] (Operation Example) An operation example will be described with reference to Fig. 6 to Fig. 9. Previous descriptions may be omitted. The UE 100 is in an RRC connected state with a cell (source cell) managed by the base station 200. Thereafter, the UE 100 performs communication with the base station 200 in the source cell until a cell change to a target cell is performed.

[0057] Step S101: The transmitter 111 of the UE 100 transmits a measurement report (message) to the base station 200. The receiver 212 of the base station 200 receives the measurement report from the UE 100.

[0058] The control unit 230 of the base station 200 determines whether to use LTM. The control unit 230 may determine whether to use LTM based on, for example, a measurement report. If the control unit 230 determines to use LTM, it starts candidate cell preparation.

[0059] As candidate cell preparation, the control unit 230 may select a candidate cell for the target cell in LTM based on the measurement report. The control unit 230 may select a candidate cell, for example, from among cells managed by the base station 200. The control unit 230 may also generate setting information related to LTM (hereinafter, LTM setting information). The control unit 230 may include the generated LTM setting information in, for example, an RRC reconfiguration message. That is, the control unit 230 may instruct the UE 100 to perform LTM (an operation related to LTM) by including the LTM setting information in the RRC reconfiguration message. The UE 100 may perform LTM (an operation related to LTM) when the LTM setting information is included in the RRC reconfiguration message.

[0060] The control unit 230 may include, in the LTM setting information (e.g., LTM-Config), at least any one of information for example, a list for releasing a candidate cell (hereinafter referred to as an LTM candidate release list (e.g., ltm-CandidateToReleaseList)) and a list for adding or changing a candidate cell (hereinafter referred to as an LTM addition change list (e.g., ltm-CandidateToAddModList)). The LTM addition change list may be a list configured by information of one or more candidate cells (e.g., LTM-Candidate). The candidate cell information may include, for example, at least any one of the following information: - Identifier of the candidate cell (e.g., ltm-CandidateId) - Configuration information related to the candidate cell (e.g., ltm-CandidateConfig) - Information indicating whether the configuration information related to the candidate cell is a complete configuration (Complete Configuration) or a differential configuration (Delta-Configuration) (e.g., ltm-ConfigComplete) - Configuration information for setting information to be used for early synchronization (e.g., ltm-EarlyUlSyncConfig) - Cell identifier for not performing L2 reset when changing cells (e.g., ltm-NoResetID) - List for adding / changing information to be used for early synchronization (e.g., ltm-Candidate-Tci-States-ToAddModList) Identifier for clearing (deleting) information used for early synchronization (e.g., ltm-Candidate-Tci-States-ToReleaseList)

[0061] The identifier of the candidate cell may be an identifier of the candidate cell configuration. Furthermore, the configuration information regarding the candidate cell (hereinafter, candidate cell configuration information) may include an RRC configuration configured in the UE 100. Furthermore, the candidate cell configuration information may include cell group configuration information (e.g., CellGroupConfig) including serving cell configuration information (e.g., ServingCellConfig) and the like. Note that the candidate cell configuration information may correspond to the LTM candidate cell configuration included in the RRC reconfiguration message in the above-mentioned step S12.

[0062] The setting information for setting information to be used for early synchronization (hereinafter referred to as early synchronization setting information) may include second setting information regarding the setting of RACH resources to be used for uplink synchronization with a candidate cell in early synchronization performed before receiving a cell change command, or may be the second setting information.

[0063] Step S102: The transmitter 211 of the base station 200 transmits an RRC reconfiguration message including the LTM setting information to the UE 100. The receiver 112 of the UE 100 receives the RRC reconfiguration message from the base station 200. This enables the receiver 112 of the UE 100 to receive the candidate cell information included in the LTM setting information from the base station 200 via the RRC message. The controller 120 of the UE 100 stores the LTM setting information.

[0064] Step S103: The transmitter 111 of the UE 100 transmits an RRC reconfiguration completion message to the base station 200. The receiver 212 of the base station 200 receives the RRC reconfiguration completion message from the UE 100.

[0065] Step S104: As an early synchronization operation, downlink synchronization with each candidate cell may be performed. The control unit 120 of the UE 100 performs downlink synchronization based on, for example, an SSB transmitted from each candidate cell.

[0066] Step S105: Uplink synchronization may be performed as an operation of early synchronization. The transmission unit 211 of the base station 200 may transmit, for example, to the UE 100, a physical downlink control channel (PDCCH) order (i.e., downlink control information (DCI)) that starts an RA procedure for early synchronization in each candidate cell configured for the UE 100 by the candidate cell configuration information. The reception unit 112 of the UE 100 may receive the PDCCH order from the base station 200. Note that the PDCCH order in early synchronization may be a PDCCH order (PDCCH ordered-RACH for TA Acquisition without RAR) used to acquire a TA value without an RA response.

[0067] The control unit 120 of the UE 100 may start the RA procedure based on the PDCCH order. The control unit 120 may control the RA procedure based on the early synchronization setting information.

[0068] In each candidate cell, the transmitter 111 of the UE 100 transmits an RA preamble (message 1) on a physical random access channel (PRACH) to the base station 200. The receiver 212 of the base station 200 receives the RA preamble from the UE 100 in each candidate cell.

[0069] The control unit 230 of the UE 100 may use an RA preamble based on the early synchronization setting information, or may use an RA preamble based on information included in the PDCCH order. For example, the control unit 230 of the base station 200 may include a preamble index in the PDCCH order, and may further include an SSB index. The preamble index indicates which RA preamble to use. The SSB index indicates the SSB used to determine the RACH opportunity for PRACH transmission. The control unit 120 of the UE 100 may determine the RA preamble based on the preamble index (and the SSB index). The control unit 120 may use, for example, other information included in the PDCCH order and / or other information included in the early synchronization setting information to transmit the RA preamble.

[0070] The control unit 230 of the base station 200 calculates a timing advance (TA) value based on the RA preamble from the UE 100. The control unit 230 may execute control to omit transmission of an RA response (i.e., message 2) that is a response to the RA preamble.

[0071] Step S106: After performing L1 measurement in each candidate cell configured by the candidate cell configuration information, the transmitter 111 of UE 100 transmits an L1 measurement report to base station 200. The receiver 212 of base station 200 receives the L1 measurement report from UE 100. The L1 measurement report is a measurement report of a lower layer based on the L1 measurement. The L1 measurement report is transmitted in a layer lower than the RRC layer. Note that the measurement report in step S101 is transmitted in the RRC layer.

[0072] The control unit 230 of the base station 200 determines a target cell in the LTM (i.e., an LTM target cell) based on the L1 measurement report. In addition, the control unit 230 may determine whether to cause the UE 100 to execute a RACH-less LTM in which the UE 100 performs uplink transmission without executing an RA procedure between the UE 100 and the base station 200, or to cause the UE 100 to execute a RACH-based LTM in which the RA procedure between the UE 100 and the base station 200.

[0073] When the control unit 230 calculates the TA value in the target cell by performing early synchronization, the control unit 230 may determine to cause the UE 100 to execute the RACH-less LTM. When the control unit 230 sets a valid value as the TA value in the target cell in a MAC CE for transmitting a cell change command described later, the control unit 230 may determine to cause the UE 100 to execute the RACH-less LTM. On the other hand, when the TA value in the target cell has not been calculated, the control unit 230 may determine to cause the UE 100 to execute the RACH-based LTM. When the control unit 230 sets an invalid value as the TA value in the target cell in the MAC CE, the control unit 230 may determine to cause the UE 100 to execute the RACH-based LTM. In this operation example, the description will proceed assuming that the control unit 230 determines to cause the UE 100 to execute the RACH-based LTM.

[0074] The control unit 230 generates a MAC CE for transmitting the cell change command. This MAC CE may be referred to as an LTM cell change command MAC CE, for example. This MAC CE may also be referred to as a cell change command (i.e., may be a cell change command). Hereinafter, the LTM cell change command MAC CE may be referred to as a cell change command as appropriate. The cell change command may include, for example, at least one of the following information (i.e., fields):

[0075] a target configuration identifier (Target Configuration ID) indicating the index of the candidate target configuration to apply to the LTM cell change; a timing advance command (Timing Advance Command) indicating whether the TA for the LTM target cell is valid; a transmission configuration indication (TCI state ID) state identifier indicating and activating the TCI state for the LTM target cell; an uplink TCI state identifier indicating and activating the uplink TCI state for the LTM target cell (UL TCI state ID); an identifier of the downlink bandwidth portion to be activated in the LTM target cell (DL BWP ID); an identifier of the uplink bandwidth portion to be activated in the LTM target cell (UL BWP ID). The target setting identifier may be the identifier of a candidate cell that will become the target cell after the change, among the identifiers of the candidate cells included in the above-mentioned candidate cell information.

[0076] The Timing Advance Command (field) may indicate whether a TA (TA value) is valid for a target cell (e.g., SpCell) corresponding to the target configuration (i.e., candidate cell configuration information) indicated by the Target Configuration Identifier (field). When a predetermined value (e.g., FFF) is set as the value of this field, this field may indicate that valid timing adjustment is not available for the primary timing advance group (PTAG) of the LTM target cell. In this case, the UE 100 needs to perform an RA procedure to the LTM target cell. That is, the UE 100 performs RACH-based LTM. On the other hand, when a value other than the predetermined value (e.g., FFF) is set as the value of this field, this field indicates an index value (i.e., TA value) used to control the amount of timing adjustment to be applied by the MAC entity of the UE 100. That is, the timing advance command (field) indicates that the RA procedure for the LTM cell change can be skipped. In this case, the UE 100 performs RACH-less LTM. Here, the predetermined value may be defined in advance by a specification or the like and may be a known value between the base station 200 and the UE 100.

[0077] In this operation example, the explanation will proceed assuming that the control unit 230 of the base station 200 sets a predetermined value indicating that the TA value is invalid in the timing advance command.

[0078] Step S107: The transmitting unit 211 of the base station 200 transmits the cell change command by MAC CE to the UE 100. The receiving unit 112 of the UE 100 receives the cell change command from the base station 200 by MAC CE.

[0079] The control unit 120 of the UE 100 switches the setting of the target cell based on the identifier of the candidate cell (i.e., the target setting identifier) ​​included in the cell change command (MAC CE). For example, the control unit 120 applies the candidate cell setting information associated with the identifier of the candidate cell that is the same as the target setting identifier included in the cell change command (MAC CE).

[0080] The control unit 120 determines whether to execute the RACH-based LTM or the RACH-less LTM based on the value included in the timing advance command. If a predetermined value (e.g., FFF) is set in the timing advance command, the control unit 120 determines to execute the RACH-based LTM. On the other hand, if a value other than the predetermined value (e.g., FFF) is set in the timing advance command, the control unit 120 determines to execute the RACH-less LTM. In this operation example, the description will proceed assuming that the control unit 120 has determined to execute the RACH-based LTM.

[0081] Step S108: The control unit 120 of the UE 100 determines a random access channel (RACH) resource for the RA procedure. The control unit 120 determines the RACH resource in accordance with, for example, a predetermined rule or an instruction from the base station 200.

[0082] For example, when the candidate cell information includes second configuration information regarding the configuration of a RACH resource used for uplink synchronization with a candidate cell in early synchronization, the control unit 120 may determine, as the RACH resource, either the first RACH resource configured by the candidate cell configuration information regarding the configuration of the candidate cell (hereinafter, sometimes referred to as first configuration information) or the second RACH resource configured by the second configuration information. The control unit 120 can determine the RACH resource by, for example, any of the following methods.

[0083] In the first method, the UE 100 determines the second RACH resource as the RACH resource in accordance with a predetermined rule, with priority over the first RACH resource. For example, as shown in Fig. 7A, the control unit 120 may perform the following operations. Fig. 7A is a flowchart illustrating the first method for determining the RACH resource.

[0084] Step S211: The control unit 120 determines whether the information about the candidate cell includes the second setting information. If the information about the candidate cell includes the second setting information, the control unit 120 executes the process of step S212. On the other hand, if the information about the candidate cell does not include the second setting information, the control unit 120 executes the process of step S213.

[0085] The control unit 120 may determine whether or not the second RACH resource is configured based on the second configuration information. If the second RACH resource is configured, the control unit 120 may execute the process of step S212. On the other hand, if the second RACH resource is not configured, the control unit 120 executes the process of step S213.

[0086] Step S212: The control unit 120 uses the second RACH resource set by the second setting information. Therefore, when the second setting information is included in the information of the candidate cell, the control unit 120 determines the second RACH resource as the RACH resource.

[0087] Step S213: The control unit 120 uses the first RACH resource configured by the first configuration information. Therefore, if the second configuration information is not included in the candidate cell information, the control unit 120 determines the first RACH resource as the RACH resource.

[0088] In the second method, the UE 100 determines the first RACH resource as the RACH resource according to a predefined rule. For example, as shown in Fig. 7B, the control unit 120 may perform the following operations. Fig. 7B is a flowchart illustrating the second method for determining the RACH resource.

[0089] Step S221: The control unit 120 uses the first RACH resource configured by the first configuration information. Therefore, the control unit 120 determines the first RACH resource as the RACH resource regardless of whether the second configuration information is included in the candidate cell information.

[0090] In the third method, UE 100 determines the RACH resource in accordance with an instruction from base station 200. Control unit 230 of base station 200 performs control to instruct UE 100 about the RACH resource. Control unit 230 may control transmission unit 211 to transmit instruction information to UE 100.

[0091] As shown in FIG. 8, the control unit 120 of the UE 100 may perform the following operations.

[0092] Step S231: As in step S211, the control unit 120 determines whether the information about the candidate cell includes the second setting information. If the information about the candidate cell includes the second setting information, the control unit 120 executes the process of step S232. On the other hand, if the information about the candidate cell does not include the second setting information, the control unit 120 executes the process of step S234.

[0093] Step S232: The control unit 120 determines whether or not there is an instruction to use the second RACH resource. When the receiving unit 112 receives information (hereinafter referred to as instruction information) from the base station 200 instructing the use of either the first RACH resource or the second RACH resource as the RACH resource for the RA procedure, the control unit 120 determines whether or not there is an instruction to use the second RACH resource based on the instruction information.

[0094] For example, when the instruction information instructs the use of the second RACH resource, the control unit 120 determines that there is an instruction to use the second RACH resource. On the other hand, when the instruction information instructs the use of the first RACH resource, the control unit 120 determines that there is no instruction to use the second RACH resource. Furthermore, when the control unit 120 has not received instruction information from the base station 200, it determines that there is no instruction to use the second RACH resource.

[0095] The instruction information may be included in the RRC message. The instruction information may be information common to each candidate cell set in the UE 100 as a candidate for the target cell. Therefore, the instruction information may be set commonly for each candidate cell. The control unit 230 of the base station 200 may include the instruction information in a field arranged in parallel to a field in the LTM setting information in which the LTM candidate release list is set, instead of in each candidate cell setting information, for example.

[0096] The instruction information may be information that is individual to each candidate cell that is set in the UE 100 as a candidate for the target cell. Therefore, the instruction information may be set individually for each candidate cell. The control unit 230 of the base station 200 may, for example, include the instruction information in each piece of first setting information, or may include the instruction information in each piece of second setting information. When the instruction information is included in both the first setting information and the second setting information, the control unit 120 may, for example, prioritize the second setting information. Alternatively, when the instruction information is included in both the first setting information and the second setting information, the control unit 120 may, for example, prioritize the first setting information. The control unit 120 may ignore the instruction information that is not prioritized.

[0097] Furthermore, the instruction information may be included in the cell change command. When the instruction information is included in both the cell change command and the RRC message, the control unit 120 may determine the RACH resource indicated by the instruction information included in the cell change command as the RACH resource. Therefore, the instruction information included in the cell change command may be prioritized over the instruction information included in each (or one) of the first setting information and the second setting information. In this case, the control unit 120 may ignore the instruction information included in each (or one) of the first setting information and the second setting information.

[0098] If the prioritized instruction information indicates that the second RACH resource is to be used, the control unit 120 determines that there is an instruction to use the second RACH resource. Otherwise, the control unit 120 determines that there is no instruction to use the second RACH resource.

[0099] Step S233: As in step S212, the control unit 120 uses the second RACH resource set by the second setting information, and therefore determines the second RACH resource as the RACH resource.

[0100] Step S234: As in step S213, the control unit 120 uses the first RACH resource set by the first setting information, and therefore determines the first RACH resource as the RACH resource.

[0101] As described above, after determining the RACH resource to be used, the control unit 120 executes the following process. Note that the control unit 120 executes the following process in the RA procedure.

[0102] Step S109: The control unit 120 of the UE 100 executes an RA procedure based on the cell change command. The control unit 120 may determine whether to execute contention-free random access (CFRA) or contention-based random access (CBRA) as the RA procedure based on the RACH resource to be used. The control unit 120 may make the determination as follows, for example, as shown in FIG. 9 .

[0103] Step S310: The control unit 120 determines whether or not to use the second RACH resource. If the second RACH resource is to be used, the control unit 120 executes the process of step S320. On the other hand, the control unit 120 determines whether or not to use the first RACH resource. If the first RACH resource is to be used, the control unit 120 executes the process of step S320.

[0104] Step S320: The control unit 120 executes CFRA. Therefore, when the control unit 120 determines the second RACH resource as the RACH resource, the control unit 120 executes CFRA as the RA procedure.

[0105] When performing CFRA, the control unit 120 may use, in addition to the second RACH resource set by the second setting information, the resource set (or assigned) by the following information as the RACH resource.

[0106] First, when the control unit 120 receives a PDCCH order for a candidate cell corresponding to the target cell in early synchronization, the control unit 120 may determine the RACH resource using information included in the PDCCH order. For example, when performing CFRA as the RA procedure, the control unit 120 may use, as the RACH resource, an RA preamble determined based on a preamble index included in the PDCCH order in early synchronization.

[0107] Furthermore, when the PDCCH order further includes an SSB index, the control unit 120 may determine the RA preamble based on the SSB index in addition to the preamble index. The control unit 120 may determine the RA preamble based on the measurement result of the SSB indicated by the SSB index.

[0108] Furthermore, the control unit 120 may use other information included in the PDCCH order (e.g., an uplink / supplemental uplink indicator (UL / SUL indicator) indicating an uplink carrier in a cell transmitting the PRACH, a PRACH mask index indicating a RACH opportunity associated with an SSB indicated by an SSB index, etc.) to determine the RACH resource. Alternatively, the control unit 120 may ignore other information included in the PDCCH order.

[0109] Second, the control unit 120 may determine the RACH resource using information included in the cell change command. For example, when CFRA is executed as the RA procedure, the control unit 120 may use the RA preamble determined based on the preamble index included in the cell change command as the RACH resource. Therefore, the control unit 230 of the base station 200 may include the preamble index in the cell change command.

[0110] Furthermore, when the cell change command further includes an SSB index, the control unit 120 may determine the RA preamble based on the SSB index in addition to the preamble index. Therefore, the control unit 230 of the base station 200 may include the SSB index in the cell change command.

[0111] Furthermore, the control unit 120 may use other information included in the cell change command (for example, an uplink / supplemental uplink indicator (UL / SUL indicator), a PRACH mask index, etc.) to determine the RACH resource.

[0112] The control unit 120 may prioritize one of the information included in the PDCCH order and the information included in the cell change command. For example, the control unit 120 may determine an RA preamble using a preamble index included in the cell change command, without using a preamble index included in the PDCCH order. For example, when a preamble index is not included in the cell change command, the control unit 120 may determine an RA preamble using a preamble index included in the PDCCH order. Furthermore, even when the RACH resource is determined using information included in the cell change command, the control unit 120 may determine the RACH resource using information not included in the cell change command but included in the PDCCH order. Alternatively, the control unit 120 may prioritize the information included in the PDCCH order over the information included in the cell change command.

[0113] Furthermore, the control unit 120 may prioritize information included in the cell change command over information set by the second setting information. Furthermore, the control unit 120 may prioritize information included in the PDCCH order over information set by the second setting information. Since the control unit 120 can use the latest information received after the RRC message, it becomes possible to appropriately execute the RA procedure.

[0114] The transmitter 111 of the UE 100 uses the determined RACH resource to transmit an RA preamble to the base station 200 (target cell). The receiver 212 of the base station 200 receives the RA preamble from the UE 100 in the target cell.

[0115] Thereafter, the transmitting unit 211 of the base station 200, in the target cell, transmits an RA response to the UE 100. The receiving unit 112 of the UE 100 receives the RA response from the base station 200 (target cell).

[0116] Step S330: The control unit 120 executes CBRA. Therefore, when the control unit 120 determines the first RACH resource as the RACH resource, the control unit 120 executes CBRA as the RA procedure.

[0117] The control unit 120 uses a first RACH resource configured in first configuration information associated with a candidate cell corresponding to the target cell. The control unit 120 uses, for example, an RA preamble determined based on a preamble index included in the first configuration information as the RACH resource.

[0118] The control unit 120 of the UE 100 may execute a 4-step RA type CBRA or may execute a 2-step RA type CBRA.

[0119] The control unit 120 of the UE 100 uses the determined RACH resource to transmit an RA preamble to the base station 200 (target cell). The receiving unit 212 of the base station 200 receives the RA preamble from the UE 100 in the target cell.

[0120] Transmitter 211 of base station 200 transmits an RA response (i.e., message 2) to UE 100 in the target cell. Receiver 112 of UE 100 receives the RA response from base station 200 (target cell). Alternatively, transmitter 211 of base station 200 transmits a contention resolution (i.e., message B) to UE 100 in the target cell. Receiver 112 of UE 100 receives message B from base station 200 (target cell).

[0121] When the RA response is received, the transmitter 111 of the UE 100 transmits a scheduled transmission (i.e., message 3) to the base station 200. The receiver 212 of the base station 200 receives message 3 from the UE 100 in the target cell.

[0122] When message 3 is received, transmitter 211 of base station 200 transmits a contention resolution (i.e., message 4) in the target cell to UE 100. Receiver 112 of UE 100 receives message 4 from base station 200 (target cell).

[0123] Step S110: The control unit 120 of the UE 100 determines that the RACH has been completed normally, that is, that the RA procedure has been successful, and therefore determines that the LTM execution has been completed normally.

[0124] In CFRA, control unit 230 of base station 200 determines that LTM execution has been completed successfully based on reception of an RA preamble in the target cell. In CBRA, control unit 230 determines that LTM execution has been completed successfully based on reception of message 3 or message B in the target cell. This results in LTM completion.

[0125] As described above, the receiving unit 112 of the UE 100 receives a cell change command that triggers a cell change from the base station 200 by using the MAC CE. The control unit 120 executes the RA procedure between the UE 100 and the target cell based on the cell change command. The control unit 120 determines the RACH resource for the RA procedure according to a predetermined rule or an instruction from the base station 200. This allows the base station 200 to clearly grasp the RACH resource used by the UE 100, which makes it easier for the cell change to the target cell to be successful in LTM compared to a case where the RACH resource used by the UE 100 is unclear, and the RACH-based LTM is executed appropriately.

[0126] Furthermore, the receiver 112 may receive information about a candidate cell that is a candidate for the target cell from the base station 200 via an RRC message. The information about the candidate cell may include first configuration information related to the configuration of the candidate cell. When the information about the candidate cell includes second configuration information related to the configuration of a RACH resource used for uplink synchronization with the candidate cell in early synchronization performed before receiving a cell change command, the controller 120 may determine, as the RACH resource, either the first RACH resource configured by the first configuration information or the second RACH resource configured by the second configuration information. As a result, the UE 100 uses either the first RACH resource or the second RACH resource as the RACH resource, and the base station 200 can clearly grasp the RACH resource used by the UE 100.

[0127] Here, when two RACH resources, the first RACH resource and the second RACH resource, can be configured in the UE 100, it is currently unclear which resource should be used as the RACH resource in the RACH-based LTM. Therefore, the UE 100 can determine the RACH resource as follows.

[0128] When the second setting information is included in the candidate cell information, the control unit 120 determines the second RACH resource as the RACH resource. Therefore, the UE 100 and the base station 200 know to use the second RACH resource out of the first RACH resource and the second RACH resource, and can appropriately perform the RACH-based LTM.

[0129] Furthermore, when the second configuration information is not included in the candidate cell information, the control unit 120 determines the first RACH resource as the RACH resource. Therefore, the UE 100 and the base station 200 know to use the first RACH resource, and can appropriately perform the RACH-based LTM.

[0130] Furthermore, the control unit 120 determines the first RACH resource as the RACH resource regardless of whether the second configuration information is included in the candidate cell information. As a result, even if the second RACH resource is configured, the UE 100 knows to use the first RACH resource, and can appropriately perform the RACH-based LTM.

[0131] Furthermore, the receiving unit 112 may receive instruction information instructing the base station 200 to use either the first RACH resource or the second RACH resource as the RACH resource for the RA procedure from the base station 200. This allows the RACH resource used by the base station 200 to be controlled.

[0132] The instruction information may be included in an RRC message, which allows flexible instruction of the RACH resource to be used since the RRC message contains more information than the lower layer.

[0133] The instruction information may also be included in the cell change command. Since the cell change command is received immediately before the cell change, the cell change command can instruct the base station 200 to use an available RACH resource, for example, so that the RA procedure can be performed appropriately.

[0134] Furthermore, when both the cell change command and the RRC message include instruction information, the control unit 120 may determine the RACH resource indicated by the instruction information included in the cell change command as the RACH resource. This allows the UE 100 to use a valid RACH resource determined immediately before the cell change.

[0135] Furthermore, when determining the second RACH resource as the RACH resource, the control unit 120 may execute CFRA as the RA procedure. When determining the first RACH resource as the RACH resource, the control unit 120 may execute CBRA as the RA procedure. The second RACH resource is information regarding the configuration of a RACH resource used for uplink synchronization with a candidate cell in early synchronization, and therefore may include information usable for CFRA. Therefore, the control unit 120 can appropriately execute RACH-based LTM by executing CFRA using information usable for CFRA.

[0136] Furthermore, the receiving unit 112 may receive a PDCCH order from the base station 200 in early synchronization. When executing CFRA as the RA procedure, the control unit 120 may use, as the RACH resource, an RA preamble determined based on a preamble index included in the PDCCH order. This makes it possible to determine a contention-free RA preamble using the preamble index included in the PDCCH order. As a result, the RA procedure is more likely to be successful, and a cell change to a target cell in LTM is more likely to be successful.

[0137] Furthermore, when the control unit 120 executes CFRA as the RA procedure, the control unit 120 may use, as the RACH resource, an RA preamble determined based on a preamble index included in the cell change command. This allows the UE 100 to use a valid preamble index determined immediately before the cell change.

[0138] Furthermore, when executing CBRA as the RA procedure, the control unit 120 may use, as the RACH resource, an RA preamble determined based on a preamble index included in the first configuration information. This allows the UE 100 to determine the RA preamble based on a preamble index previously assigned by candidate cell configuration information regarding the configuration of the candidate cell, and allows the UE 100 to appropriately perform the RACH-based LTM.

[0139] Furthermore, the transmission unit 211 of the base station 200 transmits a cell change command that triggers a cell change to the UE 100 by using a MAC CE. The control unit 230 executes an RA procedure between the UE 100 and the target cell based on the cell change command. The control unit 230 may perform control to instruct the UE 100 about the RACH resource for the RA procedure. This allows the base station 200 to clearly grasp the RACH resource used by the UE 100, which makes it easier for the cell change to the target cell to be successful in LTM compared to a case where the RACH resource used by the UE 100 is unclear, and the RACH-based LTM is executed appropriately.

[0140] (Other Embodiments) In the above-described embodiment, the UE 100 may use the first RACH resource configured by the first configuration information (that is, candidate cell configuration information) in the CFRA.

[0141] In the above-described embodiment, the UE 100 may determine the RACH resource according to a predefined rule until receiving instruction information from the base station 200. When receiving the instruction information, the UE 100 may determine the RACH resource according to the instruction from the base station 200.

[0142] In the above-described embodiment, an NR-based mobile communication system has been described as an example of the mobile communication system 1. However, the mobile communication system 1 is not limited to this example. The mobile communication system 1 may be a system compliant with the TS of either LTE (Long Term Evolution) or another generation system (e.g., 6th generation) of the 3GPP standard. The base station 200 may be an eNB that provides E-UTRA user plane and control plane protocol termination toward the UE 100 in LTE. The mobile communication system 1 may be a system compliant with the TS of a standard other than the 3GPP standard. The base station 200 may be an IAB (Integrated Access and Backhaul) donor or an IAB node.

[0143] In the above-described embodiment, an NR-based mobile communication system has been described as an example of the mobile communication system 1. However, the mobile communication system 1 is not limited to this example. The mobile communication system 1 may be a system conforming to the TS of either LTE or another generation system (e.g., 6th generation) of the 3GPP standard. The base station 200 may be an eNB that provides E-UTRA user plane and control plane protocol termination for the UE 100 in LTE. The mobile communication system 1 may be a system conforming to the TS of a standard other than the 3GPP standard.

[0144] The steps in the operations of the above-described embodiments do not necessarily have to be executed in chronological order according to the order depicted in the flow diagrams or sequence diagrams. For example, the steps in the operations may be executed in an order different from that depicted in the flow diagrams or sequence diagrams, or may be executed in parallel. Some of the steps in the operations may be deleted, or additional steps may be added to the process. Furthermore, the above-described operational flows are not limited to being executed independently, but may be executed by combining two or more operational flows. For example, some steps of one operational flow may be added to another operational flow, or some steps of one operational flow may be replaced with some steps of another operational flow.

[0145] A program may be provided that causes a computer to execute each process performed by the UE 100 or the base station 200. The program may be recorded on a computer-readable medium. Using the computer-readable medium, the program can be installed on a computer. Here, the computer-readable medium on which the program is recorded may be a non-transitory recording medium. The non-transitory recording medium is not particularly limited, and may be, for example, a recording medium such as a CD-ROM (Compact Disk Read Only Memory) or a DVD-ROM (Digital Versatile Disc Read Only Memory). Furthermore, circuits that execute each process performed by the UE 100 or the base station 200 may be integrated, and at least a part of the UE 100 or the base station 200 may be configured as a semiconductor integrated circuit (chip set, SoC (System On Chip)).

[0146] In the above-described embodiments, "transmit" may mean performing processing at least one layer in a protocol stack used for transmission, or may mean physically transmitting a signal wirelessly or via a wired connection. Alternatively, "transmit" may mean a combination of performing processing at least one layer and physically transmitting a signal wirelessly or via a wired connection. Similarly, "receive" may mean performing processing at least one layer in a protocol stack used for reception, or may mean physically receiving a signal wirelessly or via a wired connection. Alternatively, "receive" may mean a combination of processing at least one layer and physically receiving a signal wirelessly or via a wired connection. Similarly, "obtain / acquire" may mean obtaining information from stored information, obtaining information from information received from another node, or obtaining information by generating the information. Similarly, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless expressly stated otherwise. The term "based on" means both "based only on" and "based at least in part on." Similarly, the term "depending on" means both "depending only on" and "depending at least in part on." Similarly, "include" and "comprise" do not mean including only the listed items, but may mean including only the listed items or may include additional items in addition to the listed items. Similarly, in this disclosure, "or" does not mean an exclusive or, but rather a logical or. Furthermore, any reference to elements using designations such as "first," "second," etc., as used in this disclosure does not generally limit the quantity or order of those elements. These designations may be used in this disclosure as a convenient method of distinguishing between two or more elements.Thus, a reference to a first and a second element does not imply that only two elements may be employed therein or that the first element must precede the second element in some way. In this disclosure, where articles are added by translation, such as a, an, and the in English, these articles shall include the plural unless the context clearly indicates otherwise.

[0147] Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure.

[0148] (Additional Notes) Additional notes will be given regarding the features of the above-described embodiment.

[0149] (Supplementary Note 1) A communication device comprising: a receiver unit that receives a cell change command that triggers a cell change from a base station by a media access control (MAC) control element (CE); and a controller that executes a random access (RA) procedure between the communication device and a target cell based on the cell change command, wherein the controller determines a random access channel (RACH) resource for the RA procedure according to a predefined rule or an instruction from the base station.

[0150] (Supplementary Note 2) The communication device according to Supplementary Note 1, wherein the receiving unit receives information about a candidate cell that is a candidate for the target cell from the base station by a Radio Resource Control (RRC) message, the information about the candidate cell includes first setting information about setting the candidate cell, and the control unit determines, when the information about the candidate cell includes second setting information about setting the RACH resource used for uplink synchronization with the candidate cell in early synchronization performed before receiving the cell change command, to use either a first RACH resource set by the first setting information or a second RACH resource set by the second setting information as the RACH resource.

[0151] (Supplementary Note 3) The communication device according to Supplementary Note 2, wherein the control unit determines the second RACH resource as the RACH resource when the second setting information is included in the information of the candidate cell.

[0152] (Supplementary Note 4) The communication device according to Supplementary Note 2 or 3, wherein the control unit determines the first RACH resource as the RACH resource when the second setting information is not included in the information of the candidate cell.

[0153] (Supplementary Note 5) The communication device according to Supplementary Note 2, wherein the control unit determines the first RACH resource as the RACH resource regardless of whether the second setting information is included in the information of the candidate cell.

[0154] (Supplementary Note 6) The communication device according to any one of Supplementary Notes 2 to 5, wherein the receiving unit receives, from the base station, instruction information instructing use of either the first RACH resource or the second RACH resource as the RACH resource for the RA procedure.

[0155] (Supplementary Note 7) The communication device according to Supplementary Note 6, wherein the instruction information is included in the RRC message.

[0156] (Supplementary Note 8) The communication device according to Supplementary Note 6 or 7, wherein the instruction information is included in the cell change command.

[0157] (Supplementary Note 9) The communication device according to Supplementary Note 8, wherein, when the instruction information is included in both the cell change command and the RRC message, the controller determines, as the RACH resource, a RACH resource indicated by the instruction information included in the cell change command.

[0158] (Supplementary Note 10) The communication device according to any one of Supplementary Notes 2 to 9, wherein the control unit: when determining the second RACH resource as the RACH resource, executes contention-free random access (CFRA) as the RA procedure; and when determining the first RACH resource as the RACH resource, executes contention-based random access (CBRA) as the RA procedure.

[0159] (Supplementary Note 11) The communication device according to Supplementary Note 10, wherein the receiving unit receives a Physical Downlink Control Channel (PDCCH) order from the base station in the early synchronization, and the control unit, when executing the CFRA as the RA procedure, uses an RA preamble determined based on a preamble index included in the PDCCH order as the RACH resource.

[0160] (Supplementary Note 12) The communication device according to Supplementary Note 10 or 11, wherein when the CFRA is executed as the RA procedure, the controller uses, as the RACH resource, an RA preamble determined based on a preamble index included in the cell change command.

[0161] (Supplementary Note 13) The communication device according to any one of Supplementary Notes 10 to 12, wherein when the CBRA is executed as the RA procedure, the control unit uses, as the RACH resource, an RA preamble determined based on a preamble index included in the first configuration information.

[0162] (Supplementary Note 14) A base station comprising: a transmitter unit that transmits a cell change command that triggers a cell change to a communication device by a media access control (MAC) control element (CE); and a controller that executes a random access (RA) procedure between the communication device and a target cell based on the cell change command, wherein the controller controls to instruct the communication device about random access channel (RACH) resources for the RA procedure.

[0163] (Supplementary Note 15) A communication method executed by a communication device, comprising: receiving a cell change command that triggers a cell change from a base station by a media access control (MAC) control element (CE); and performing a random access (RA) procedure between the communication device and a target cell based on the cell change command, wherein in the step of performing the RA procedure, a random access channel (RACH) resource for the RA procedure is determined according to a predefined rule or an instruction from the base station.

[0164] (Supplementary Note 16) A communications device comprising: a receiving unit that receives, from a base station, configuration information related to Layer 1 / Layer 2 triggered mobility (LTM), the configuration information including first information indicating a preamble index used in a random access (RA) procedure by using a radio resource control (RRC) message; and receives, from the base station, a cell change command media access control (MAC) control element (CE) that includes information for identifying the configuration information and instructs a cell change; and a control unit that, when the cell change command MAC CE is received, executes the RA procedure for a target cell corresponding to the information for identifying the configuration information, wherein, when the cell change command MAC CE includes second information indicating the preamble index, the control unit executes the RA procedure using the preamble index determined based on the second information.

[0165] (Supplementary Note 17) The communication device according to Supplementary Note 16, wherein, when the cell change command MAC CE includes third information indicating an SSB index, the control unit executes the RA procedure using the SSB index determined based on the third information.

[0166] (Supplementary Note 18) The communication device according to Supplementary Note 17, wherein the cell change command MAC CE includes fourth information indicating use of the second information and the third information.

[0167] (Supplementary Note 19) The communication device according to any one of Supplementary Notes 16 to 18, wherein a target configuration identifier included in the cell change command MAC CE is set to a predetermined value.

[0168] (Supplementary Note 20) A base station comprising: a transmitter unit that transmits configuration information related to Layer 1 / Layer 2 triggered mobility (LTM), the configuration information including first information indicating a preamble index used in a random access (RA) procedure to a communication device using a radio resource control (RRC) message, and transmits a cell change command media access control (MAC) control element (CE) to the communication device, the cell change command including information for identifying the configuration information and instructing a cell change; and a controller that includes second information indicating the preamble index in the cell change command MAC CE.

[0169] (Supplementary Note 21) A communication method executed by a communication device, comprising: receiving, from a base station, configuration information related to Layer 1 / Layer 2 triggered mobility (LTM), the configuration information including first information indicating a preamble index used in a random access (RA) procedure, using a radio resource control (RRC) message; receiving, from the base station, a cell change command media access control (MAC) control element (CE) including information for identifying the configuration information and instructing a cell change; when the cell change command MAC CE is received, performing the RA procedure to a target cell corresponding to the information for identifying the configuration information; and when the cell change command MAC CE includes second information indicating the preamble index, performing the RA procedure using the preamble index determined based on the second information.

Claims

1. A communication device (100), A receiving unit (112) receives a radio resource control (RRC) message from a base station (200) that includes one or more settings related to a Layer 1 / Layer 2 triggered mobility (LTM) candidate cell, It comprises a control unit (120) and Each of the one or more settings includes an identifier for identifying the settings of a candidate cell, the settings of the candidate cell, and settings used to perform early uplink synchronization. The receiving unit is Based on the settings of the candidate cells, downlink control information (DCI) indicating that one candidate cell will perform transmission of a physical random access channel (PRACH) is received from the base station via the physical downlink control channel. The base station receives a cell change command media access control (MAC) control element (CE) for instructing a cell change, which includes information for identifying the settings of the candidate cell. The control unit, In the candidate cell indicated that, upon receiving the DCI, the transmission of the PRACH is performed using the resources of the random access (RA) channel based on the configuration information included in the settings used to perform the early uplink synchronization, according to the information including the preamble index and the synchronization signal and the index of the physical broadcast channel block (SSB) contained in the DCI, the transmission of the PRACH is performed. When the cell change command MAC CE is received, the PRACH transmission is performed in the candidate cell corresponding to the information for identifying the candidate cell's settings, using the RA channel resources based on the setting information included in the candidate cell's settings, according to the information indicating the preamble index and the information indicating the SSB index included in the cell change command MAC CE. Communication device.

2. The control unit transmits the PRACH in a candidate cell corresponding to the information for identifying the settings of the candidate cell, based on the fact that the field of the timing advance command included in the cell change command MAC CE indicates that no valid timing adjustment is available. The communication device according to claim 1.

3. A base station (200), A transmitting unit (211) transmits a radio resource control (RRC) message containing one or more settings related to a Layer 1 / Layer 2 triggered mobility (LTM) candidate cell to a communication device (100), The system comprises a control unit (230) and Each of the one or more settings includes an identifier for identifying the settings of a candidate cell, the settings of the candidate cell, and settings used to perform early uplink synchronization. The aforementioned transmitting unit Based on the settings of the candidate cells, downlink control information (DCI) indicating that transmission of a physical random access channel (PRACH) will be performed in one of the candidate cells is transmitted to the communication device via the physical downlink control channel. A cell change command media access control (MAC) control element (CE) for instructing a cell change, including information for identifying the settings of the candidate cell, is transmitted to the communication device. The control unit, When the DCI is transmitted, the transmission of the PRACH in one candidate cell is controlled to be performed using random access (RA) channel resources based on configuration information included in the settings used to perform the early uplink synchronization, according to information indicating the preamble index included in the DCI, the synchronization signal, and information indicating the index of the physical broadcast channel block (SSB). When the cell change command MAC CE is sent, the transmission of the PRACH in the candidate cell corresponding to the information for identifying the candidate cell's settings is controlled using the RA channel resources based on the setting information included in the candidate cell's settings, according to the information indicating the preamble index and the information indicating the SSB index included in the cell change command MAC CE. Base station.

4. The control unit controls the transmission of the PRACH in the candidate cell corresponding to the information for identifying the settings of the candidate cell, based on the fact that the field of the timing advance command included in the cell change command MAC CE indicates that no valid timing adjustment is available. The base station according to claim 3.

5. A communication method performed by a communication device (100), The process includes receiving a radio resource control (RRC) message from a base station (200) that includes one or more settings relating to a Layer 1 / Layer 2 triggered mobility (LTM) candidate cell, Each of the one or more settings includes an identifier for identifying the settings of a candidate cell, the settings of the candidate cell, and settings used to perform early uplink synchronization. The steps include receiving downlink control information (DCI) from the base station via the physical downlink control channel, indicating that one candidate cell configured based on the settings of the candidate cell will perform transmission of a physical random access channel (PRACH); The steps include receiving a cell change command media access control (MAC) control element (CE) from the base station to instruct a cell change, which includes information for identifying the settings of the candidate cell, The steps include: in one candidate cell that, upon receiving the DCI, transmits the PRACH using the resources of a random access (RA) channel based on configuration information included in the settings used to perform the early uplink synchronization, according to the information indicating the preamble index, the synchronization signal, and the index of the physical broadcast channel block (SSB) contained in the DCI; The process includes the step of, upon receiving the cell change command MAC CE, using the resources of the RA channel based on the setting information included in the candidate cell settings, to transmit the PRACH in the candidate cell corresponding to the information for identifying the candidate cell settings, according to the information indicating the preamble index and the information indicating the SSB index included in the cell change command MAC CE. Communication method.

6. The claim further includes the step of transmitting the PRACH in a candidate cell corresponding to information for identifying the settings of the candidate cell, based on the fact that a field of the timing advance command included in the cell change command MAC CE indicates that no valid timing adjustment is available. The communication method according to claim 5.