Communication device, base station, and communication method

Abstract

A communication device (100) according to one embodiment comprises: a reception unit (112) that receives, from base stations (200, 201), a radio resource control (RRC) message which triggers a handover to a target cell; and a control unit (120) that, on the basis of the RRC message, determines a physical random access channel (PRACH) occasion in a random access procedure in the target cell. The RRC message includes control information for controlling a change in the period of the PRACH occasion through signaling in a layer lower than an RRC layer in the target cell. The control unit determines the PRACH occasion on the basis of the control 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 No. 2023-187085, filed October 31, 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] 3GPP (Third Generation Partnership Project, registered trademark; the same applies hereinafter), a standardization project for mobile communication systems, is discussing network energy saving (NES). As one NES technique, dynamic adaptation, which dynamically changes the period of physical random access channel (PRACH) opportunities (hereinafter referred to as PRACH period), has been proposed (see, for example, Non-Patent Document 1).

[0004] Dynamic adaptation of PRACH opportunities, for example, by changing the PRACH periodicity via downlink control information (DCI), allows the PRACH periodicity to be changed at shorter intervals than, for example, by updating the system information block, thereby saving energy in the network.

[0005] "RWS-230156" (On NW Energy Savings for Rel-19)

[0006] A communication device according to a first aspect includes a receiver that receives a Radio Resource Control (RRC) message from a base station that triggers a handover to a target cell, and a controller that determines a Physical Random Access Channel (PRACH) opportunity in a random access procedure in the target cell based on the RRC message. The RRC message includes control information for controlling a change in a periodicity of the PRACH opportunity through signaling in a layer lower than the RRC layer in the target cell. The controller determines the PRACH opportunity based on the control information.

[0007] A base station according to a second aspect includes a transmitter configured to transmit a radio resource control (RRC) message to a communication device, the RRC message triggering a handover to a target cell. The RRC message is used by the communication device to determine a physical random access channel (PRACH) opportunity in a random access procedure in the target cell. The RRC message includes control information for controlling a change in a periodicity of the PRACH opportunity by signaling in a layer lower than the RRC layer in the target cell.

[0008] A communication method according to a third aspect is a communication method executed by a communication device. The communication method includes the steps of receiving a Radio Resource Control (RRC) message from a base station that triggers a handover to a target cell, and determining a Physical Random Access Channel (PRACH) opportunity in a random access procedure in the target cell based on the RRC message. The RRC message includes control information for controlling a change in the periodicity of the PRACH opportunity through signaling in a layer lower than the RRC layer in the target cell. In the determining step, the PRACH opportunity is determined based on the control information.

[0009] 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 a configuration of a UE according to an embodiment. FIG. 4 is a diagram illustrating a configuration of a base station according to an embodiment. FIG. 5 is a sequence diagram (part 1) for describing an example operation according to the first embodiment. FIG. 6 is a diagram for describing the first embodiment. FIG. 7 is a sequence diagram (part 2) for describing an example operation according to the first embodiment. FIG. 8 is a flowchart for describing an example operation according to the first embodiment. FIG. 9 is a flowchart (part 1) for describing an example operation according to the second embodiment. FIG. 10 is a flowchart (part 2) for describing an example operation according to the second embodiment.

[0010] 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.

[0011] An object of the present disclosure is to provide a communication device, a base station, and a communication method that are capable of appropriately performing dynamic adaptation of PRACH opportunities.

[0012] (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).

[0013] 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.

[0014] 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 (e.g., a Vehicle UE). The UE 100 may be a transport vehicle other than a vehicle (e.g., a ship, an airplane, etc.) or a device provided therein (e.g., an Aerial UE). The UE 100 may be a sensor or a device provided therein. Note that the UE 100 may be referred to by other names such as 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. Furthermore, the UE 100 is an example of a terminal, and the terminal may include factory equipment or the like.

[0015] The NG-RAN 20 includes multiple base stations 200. Each base station 200 manages at least one cell. One or more base stations 200 may correspond to one or more cells. A base station 200 may be replaced with a cell, or a cell may be replaced with a base station 200. 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 a 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. Furthermore, the base station 200 is connected to other base stations 200 (which may be referred to as neighbor base stations) via an Xn interface. The base station 200 communicates with the neighbor base stations via the Xn interface. In addition, 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).

[0016] 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.

[0017] (Configuration Example of Protocol Stack) Next, a configuration example of a protocol stack according to this embodiment will be described with reference to FIG.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The PDCP layer performs header compression / decompression and encryption / decryption.

[0023] 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).

[0024] 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.

[0025] 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.

[0026] The UE 100 has an application layer and the like in addition to the radio interface protocol.

[0027] (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., 112 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.

[0028] (Determination of PRACH Transmission Opportunity) An example of determination of a PRACH transmission opportunity will be described. For example, when performing a random access (RA) procedure, the UE 100 determines a PRACH opportunity (or referred to as a PRACH transmission opportunity).

[0029] The UE 100 may receive, for example, (a) initial access from an RRC idle state, (b) an RRC Connection Re-establishment procedure, (c) arrival of downlink data or uplink data during an RRC connected state when the uplink synchronization status is “asynchronous”, (d) arrival of uplink data when there are no physical uplink control channel (PUCCH) resources for a scheduling request (SR) available, (e) an SR failure, (f) a request by the RRC at synchronization reconfiguration (e.g., handover), (g) an RRC connection resume procedure from an RRC inactive state, (h) a procedure to establish timing adjustment of a secondary timing advance group (TAG), (i) other system information (OTHER The RA procedure may be performed if it is triggered by any of the following events: (i) a request for SI, (j) beam failure recovery, (k) consistent uplink listen-before-talk (UL LBT) failure in the SpCell, (l) small data transmission (SDT) in the RRC inactive state, (m) positioning purposes during the RRC connected state that require an RA procedure (e.g., when a timing advance is required for UE positioning), etc.

[0030] In the RA procedure, the UE 100 determines resources for PRACH transmission (i.e., PRACH opportunities) using, for example, a plurality of predefined random access configurations and random access (RA) parameters included in a system information block type 1 (SIB1) message.

[0031] The random access (RA) configuration is specified by a table (RA configuration table) that indicates the association between a PRACH preamble format, a time domain allocation configuration of a PRACH opportunity, and a PRACH configuration index. The UE 100 stores the table in advance. The PRACH preamble format is "Preamble format." The time domain allocation configuration of a PRACH opportunity is, for example, "Preamble format," "n ｆ mod x = y”, “Subframe number”, “Starting symbol”, “Number of PRACH slots within a subframe”, “Number of time-domain PRACH occasions within a PRACH slot”, and “PRACH duration”.

[0032] The RA parameters are specified, for example, by RACH configuration common information (e.g., RACH-ConfigCommon, RACH-ConfigCommonTwoStepRA) used to specify random access parameters. "RACH-ConfigCommon" may be information used to specify cell-specific random-access parameters. "RACH-ConfigCommonTwoStepRA" may be information used to specify cell-specific two-step random access type parameters.

[0033] The RACH configuration common information may include, for example, a PRACH configuration index (e.g., prach-ConfigurationIndex, msgA-PRACH-ConfigurationIndex(-r16)), information on the number of PRACH transmission opportunities (e.g., msg1-FDM, msgA-RO-FDM(-r16)), etc. "msg1-FDM" may indicate the number of PRACH transmission opportunities that are FDM-multiplexed in one instance. "msgA-RO-FDM" may indicate the number of msgA PRACH transmission opportunities that are Frequency-Division Multiplexed in one instance. The PRACH configuration index indicates which PRACH opportunity of an RA configuration is to be used in PRACH transmission from among a plurality of RA configurations defined in the RA configuration table. The UE 100 determines the PRACH opportunity using the RA configuration indicated by the PRACH configuration index.

[0034] In addition, the UE 100 maps a synchronization signal (SS) and a physical broadcast channel (PBCH) block (SSB) index (hereinafter, sometimes referred to as an SSB index) to a PRACH opportunity.

[0035] The SSB indexes are mapped to valid PRACH opportunities using parameters (e.g., the number of SSBs associated with one PRACH occasion, the number of contention-based preambles per SSB per valid PRACH opportunity) provided by the RACH configuration common information (e.g., ssb-perRACH-OccasionAndCB-PreamblesPerSSB included in RACH-ConfigCommon and / or msgA-SSB-PerRACH-OccasionAndCB-PreamblesPerSSB included in RACH-ConfigCommonTwoStepRA), for example in the following order:

[0036] First, in ascending order of preamble index within a single PRACH opportunity. Second, in ascending order of frequency resource index for frequency multiplexed PRACH occasions. Third, in ascending order of time resources for time multiplexed PRACH occasions within a PRACH slot. Fourth, in ascending order of index for PRACH slots. An association period is specified when the UE 100 maps to this association period. The association period is the smallest value within a set determined by the PRACH configuration period. The association period starts from frame 0. Within an association period, a predetermined number of SSB indices are mapped to a PRACH opportunity at least once. The UE 100 acquires the predetermined number from information (e.g., ssb-PositionsInBurst) in SIB1 or serving cell configuration common information (e.g., ServingCellConfigCommon). Note that in a set determined by a PRACH configuration period, the table associates the PRACH configuration period (ms) with the association period (the number of PRACH configuration periods).

[0037] If there is a PRACH opportunity or a set of PRACH preambles that is not mapped to a predetermined number of SSB indices after an integer number of SSB indices to PRACH opportunity mapping cycles within an association period, then the SSB index is not mapped to that PRACH opportunity or set of PRACH preambles.

[0038] An association pattern period includes one or more association periods. The association pattern period is determined so that the pattern between PRACH opportunities and SSB indices repeats every 160 msec. PRACH opportunities that are not associated with an SSB index after an integer number of association periods are not used for PRACH transmission.

[0039] (Configuration of User Equipment) The configuration of the UE 100 according to the embodiment will be described with reference to Fig. 3. The UE 100 includes a communication unit 110 and a control unit 120.

[0040] 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.

[0041] 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.

[0042] In the UE 100 configured in this manner, the receiver 112 of the UE 100 receives a radio resource control (RRC) message from the base station 200 that triggers a handover to the target cell. The controller 120 of the UE 100 determines a PRACH opportunity in the RA procedure in the target cell based on the RRC message. The RRC message includes control information for controlling a change in the periodicity of the PRACH opportunity through signaling in a layer lower than the RRC layer in the target cell. The controller 120 determines the PRACH opportunity based on the control information. As a result, even if, for example, synchronization reconfiguration information for the target cell includes conventional RA parameters and RA parameters for dynamic adaptation, the UE 100 can appropriately determine a PRACH opportunity based on the control information and perform dynamic adaptation of the PRACH opportunity.

[0043] (Configuration of Base Station) The configuration of the base station 200 according to this embodiment will be described with reference to Fig. 4. The base station 200 includes a communication unit 210, a network communication unit 220, and a control unit 230.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] In base station 200 configured in this manner, transmitter 211 transmits to UE 100 an RRC message that triggers handover to the target cell. The RRC message is used by UE 100 to determine a PRACH opportunity in a random access procedure in the target cell. The RRC message includes control information for controlling a change in the periodicity of the PRACH opportunity by signaling in a layer lower than the RRC layer in the target cell. As a result, even if, for example, synchronization reconfiguration information for the target cell includes a first RA parameter and a second RA parameter, UE 100 can appropriately determine a PRACH opportunity based on the control information and can perform dynamic adaptation of the PRACH opportunity.

[0048] First Embodiment A first embodiment will be described with reference to Figures 5 to 8. Previous descriptions may be omitted.

[0049] Specific operations related to dynamic adaptation of PRACH opportunities are not specified. Therefore, when UE 100 executes handover to a target cell, for example, there is a concern that dynamic adaptation of PRACH opportunities may not be properly executed in the target cell. Therefore, an operation for enabling dynamic adaptation of PRACH opportunities to be properly executed will be described.

[0050] 5 , UE 100 is in an RRC connected state with a cell managed by base station 200. Note that, for UE 100, communication with base station 200 may be communication with the cell. Therefore, for UE 100, receiving information / messages, etc. from base station 200 may be receiving information / messages, etc. from the cell, and transmitting information / messages, etc. to base station 200 may be transmitting information / messages, etc. to the cell.

[0051] Step S101: The transmitter 111 of the UE 100 transmits a measurement report to the base station 201. The receiver 212 of the base station 201 receives the measurement report from the UE 100.

[0052] Based on the measurement report, the control unit 230 of the base station 201 decides to hand over the UE 100. The control unit 230 determines the cell of the base station 202, which is to be the target base station, as the target cell.

[0053] Step S102: The network communication unit 220 of the base station 201 transmits a handover request message requesting preparation of resources for handover to the base station 202. The network communication unit 220 of the base station 202 receives the handover request message from the base station 201.

[0054] The control unit 230 of the base station 202 may determine whether to approve the handover based on, for example, the handover request message. If the control unit 230 approves the handover, it may execute the following process. If the control unit 230 does not approve the handover, it may send a handover preparation failure message to the source base station (i.e., the base station 201) to notify the base station 201 that the handover preparation has failed.

[0055] Step S103: The network communication unit 220 of the base station 202 transmits a Handover Request Acknowledge message to the base station 201 to inform the source base station (i.e., the base station 201) of the prepared resources at the target. The network communication unit 220 of the base station 201 receives the Handover Request Acknowledge message from the base station 202. The Handover Request Acknowledge message may include (at least a part of) the control information described below.

[0056] Step S104: The transmitter 211 of the base station 201 transmits an RRC reconfiguration message to the UE 100 as an RRC message that triggers a handover to the target cell. The receiver 112 of the UE 100 receives the RRC reconfiguration message from the base station 201. The RRC message that triggers a handover to the target cell may be referred to as a handover command.

[0057] The control unit 230 of the base station 201 may include, in the RRC reconfiguration message, control information for controlling a change in the periodicity of PRACH opportunities by signaling in a layer lower than the RRC layer in the target cell. The control unit 230 may include the control information, for example, in information on reconfiguration involving synchronization (hereinafter, sometimes referred to as synchronization reconfiguration information) included in the RRC reconfiguration message. The synchronization reconfiguration information (e.g., ReconfigurationWithSync) may indicate parameters for synchronization reconfiguration to the target cell (e.g., an Sp cell).

[0058] The control information may be configuration information related to dynamic adaptation (hereinafter referred to as DA configuration information). Here, the dynamic adaptation may be referred to as dynamic RACH adaptation, for example. The dynamic adaptation may be, for example, at least one of the following operations (or definitions):

[0059] The UE 100 switches the random access (RA) configuration through signaling in a layer lower than the RRC layer. Here, the signaling in the layer lower than the RRC layer may include a MAC CE transmitted in the MAC layer. That is, information used to switch the RA configuration may be included in the MAC CE. For example, a logical channel identifier (LCID) may be defined for identifying information used to switch the RA configuration. The information used to switch the RA configuration identified by the LCID may be included in the MAC CE. Furthermore, the signaling in the layer lower than the RRC layer may include downlink control information (also referred to as a downlink control information format) transmitted on a PDCCH in the physical layer. That is, downlink control information (downlink control information format) including information used to switch the RA configuration may be transmitted on the PDCCH. For example, the UE 100 may monitor the PDCCH in a search space configured for downlink control information (downlink control information format) including information used to switch the RA configuration, and may receive downlink control information including information used to switch the RA configuration. Here, a radio network temporary identifier (RNTI) may be defined, in which a cyclic redundancy check (CRC) (also referred to as a CRC parity bit) added to the downlink control information including information used to switch the RA configuration is scrambled. For example, the base station 200 may transmit system information including information for configuring the search space and / or information for configuring the RNTI (RNTI value). Here, the RNTI (RNTI value) may be calculated by the UE 100. For example, the RNTI (RNTI value) may be calculated by the UE 100 based on the PRACH configuration. For example, the RNTI (RNTI value) may be calculated using the transmission timing (SFN, subframe, slot, and / or symbol) of the random access preamble (message 1) determined based on the PRACH configuration.

[0060] - UE100 supports multiple PRACH configurations.

[0061] A plurality of PRACH configurations are configured for one cell in the UE 100. Here, one cell may include a downlink cell and / or an uplink cell. Furthermore, configuring a plurality of PRACH configurations may include configuring a plurality of PRACH configurations based on a plurality of PRACH configurations included in RACH configuration common information for one cell.

[0062] A plurality of PRACH configurations are configured in UE 100 for one bandwidth portion (BWP). Here, one BWP may include a downlink BWP and / or an uplink BWP. That is, a plurality of PRACH configurations may be configured for each of one or more BWPs (downlink BWP and / or uplink BWP) in one cell. Furthermore, configuring a plurality of PRACH configurations may include configuring a plurality of PRACH configurations based on a plurality of PRACH configurations included in RACH configuration common information for one BWP.

[0063] Multiple PRACH configurations are configured in UE 100 for one subcarrier spacing. Here, one subcarrier spacing may include the subcarrier spacing configured for the downlink BWP and / or the uplink BWP. That is, multiple PRACH configurations may be configured for one subcarrier spacing configured for each of one or more BWPs (downlink BWP and / or uplink BWP) in one cell. Furthermore, one subcarrier spacing may include the subcarrier spacing of the PRACH (also referred to as the subcarrier spacing for the PRACH transmission (message 1)). That is, multiple PRACH configurations may be configured for one subcarrier spacing configured for the PRACH. Here, information for configuring the subcarrier spacing of the PRACH may be included in the RACH configuration common information. That is, one common subcarrier spacing (e.g., one subcarrier spacing configured for one BWP and / or one subcarrier spacing of the PRACH) may be used for multiple PRACH configurations.

[0064] A plurality of PRACH configurations for one component carrier are configured in the UE 100. Here, one component carrier may include a downlink component carrier and / or an uplink component carrier.

[0065] Change of PRACH configuration based on signaling in layers lower than the RRC layer

[0066] The PRACH configuration is a configuration related to control of PRACH transmission. The PRACH configuration may include, for example, RA configuration. The PRACH configuration may include parameters related to control of PRACH transmission. The PRACH configuration may include, for example, at least one of a PRACH preamble index, a preamble SCS (Subcarrier Spacing), a PRACH resource (time resource, frequency resource), and / or a period (cycle) of a PRACH opportunity. The PRACH configuration may include, for example, RA parameters related to control of PRACH transmission.

[0067] First, the control information (or DA configuration information) may include a specific random access (RA) configuration that is used to configure the periodicity of PRACH opportunities and is used exclusively when changing the periodicity of PRACH opportunities through lower layer signaling. The specific RA configuration may be an RA configuration dedicated to dynamic adaptation. The specific RA configuration may include, for example, a PRACH preamble format dedicated to dynamic adaptation and a time domain allocation configuration of PRACH opportunities dedicated to dynamic adaptation. The specific RA configuration may include a PRACH configuration index dedicated to dynamic adaptation as an index described below.

[0068] The DA configuration information may include configuration information for configuring multiple RA configurations for determining PRACH opportunities in the UE 100. Note that the multiple RA configurations may be configured by (only) a normal RA configuration that is not a specific RA configuration, may be configured by (only) a specific RA configuration described below, or may be configured by a combination of the normal RA configuration and the specific RA configuration. Note that the normal RA configuration may be a configuration that can be configured even in a UE 100 (which may be referred to as a legacy UE) that does not support dynamic adaptation (i.e., does not have the capability of dynamic adaptation). The normal RA configuration may be, for example, an RA configuration specified in a technical specification of a release earlier than the technical specification of the release in which dynamic adaptation was introduced. Note that the normal RA configuration may be referred to as a first RA configuration, and the specific RA configuration may be referred to as a second RA configuration.

[0069] The DA configuration information may include, for example, a list (hereinafter referred to as a RACH adaptation configuration list) consisting of multiple specific RA configurations that are used to set the periodicity of PRACH opportunities and are changed by lower layer signaling, as configuration information for setting multiple RA configurations to UE 100.

[0070] As shown in Fig. 6, for example, a RACH adaptation configuration list (e.g., RACHAdaptation-ConfigList(-r19)) may be included in the synchronization reconfiguration information. The synchronization reconfiguration information may include the RACH adaptation configuration list separately from RACH configuration dedicated information (e.g., rach-ConfigDedicated) including the first RA parameters (see E1 in Fig. 6). The specific RA configuration may be referred to as, for example, RACH adaptation configuration information (e.g., RACHAdaptation-Config(-r19)), or may be a configuration specified by the RACH adaptation configuration information. The RACH adaptation configuration information may include, for example, RACH configuration common information (e.g., rach-ConfigCommon(-r19)) including the second RA parameters (see E2 in Fig. 6).

[0071] Each of the multiple specific RA configurations may be associated with an index. For example, the RACH adaptation configuration information may include an index. The index may be included in the RACH configuration common information, or may be included in the RACH adaptation configuration information in parallel with the RACH configuration common information. This may associate the index with the specific RA configuration. The index may be used, for example, to specify the specific RA configuration by lower layer signaling. The index may be, for example, an identifier of the specific RA configuration and / or an identifier of the RACH adaptation configuration information. The index may be a PRACH configuration index.

[0072] Note that (at least a part of) the specific RA configuration may be predefined in the technical specifications. For example, a specific RA configuration table dedicated to dynamic adaptation may be predefined in the technical specifications. The specific RA configuration table may indicate a link between (at least a part of) the specific RA configuration and a PRACH configuration index. The specific RA configuration (at least a part of) may include, for example, at least one of a PRACH preamble format and a time domain allocation setting for PRACH opportunities. The control unit 120 of the UE 100 may store (at least a part of) the specific RA configuration in advance. The specific RA configuration (at least a part of) may be, for example, "Preamble format", "n ｆ mod x = y”, “Subframe number”, “Starting symbol”, “Number of PRACH slots within a subframe”, “Number of time-domain PRACH occasions within a PRACH slot”, or “PRACH duration”.

[0073] Second, the control information (or DA configuration information) may include specific random access (RA) parameters that are used exclusively when the periodicity of PRACH opportunities is changed by lower layer signaling. The specific RA parameters may include dedicated RA parameters (hereinafter, sometimes referred to as second RA parameters) that are applied (used) only during dynamic adaptation. The second RA parameters may be RA parameters that are changed by lower layer signaling. The second RA parameters may include, as retransmission parameters, specific retransmission parameters (hereinafter, sometimes referred to as second retransmission parameters) that are used exclusively when the periodicity of PRACH opportunities is changed by lower layer signaling. Note that RA parameters that are not dedicated to dynamic adaptation may be referred to as first RA parameters.

[0074] The retransmission parameters are RA parameters used to control the retransmission of RA preambles on PRACH opportunities in the RA procedure, and may include, for example, the maximum number of RA preambles, the receive window length, and (the value for) a contention resolution timer. The retransmission parameters may include RA parameters for controlling the transmission power of the RA preamble. The retransmission parameters do not have to include RA parameters for controlling the transmission power of the RA preamble.

[0075] The second retransmission parameter may be included in, for example, at least one of (i) information used to set parameters related to dynamic adaptation (hereinafter referred to as RACHAdaptation setting information (e.g., RACHAdaptation-Config(-r19))), (ii) RACH setting common information (e.g., RACH-ConfigCommon-r19), and (iii) RACH setting general information (e.g., RACH-ConfigGeneric-r19). The DA setting information may be any of the information (i) to (iii). The RACH setting common information and the RACH setting general information including the second retransmission parameter may be information newly specified in a technical specification after the release in which dynamic adaptation was introduced.

[0076] The second retransmission parameters may include, for example, at least one of the maximum number of RA preambles (e.g., preambleTransMaxRACHAdaptation(-r19)), the receive window length (e.g., Ra-ResponseWindowRACHAdaptation(-r19)), and (a value for) a contention resolution timer (e.g., Ra-ContentionResolutionTimerRACHAdaptation(-r19)). The second retransmission parameters may include an RA parameter for controlling the transmission power of the RA preamble. The second retransmission parameters may not include an RA parameter for controlling the transmission power of the RA preamble.

[0077] The maximum value of the maximum number of RA preambles of the second retransmission parameter may be greater than the maximum value of the maximum number of RA preambles of the first retransmission parameter described below. The maximum value of the receive window length of the second retransmission parameter may be greater than the maximum value of the receive window length of the first retransmission parameter. The maximum value of the contention resolution timer (value for) of the second retransmission parameter may be greater than the maximum value of the contention resolution timer (value for) of the first retransmission parameter.

[0078] Third, the control information (or DA setting information) may include information indicating whether the second RA setting and / or the second RA parameters are used (hereinafter referred to as availability information). The availability information may be information indicating whether the second RA setting and / or the second RA parameters are used. The availability information may be information indicating whether the second RA setting and / or the second RA parameters are permitted. The availability information may be information indicating whether execution of dynamic adaptation is permitted.

[0079] Fourth, the control information (or DA setting information) may include information indicating a validity period of the second RA setting and / or the second RA parameters (hereinafter, referred to as period information). The period information may indicate the validity period by, for example, at least one of a system frame number, a subframe number, a slot number, a symbol number, the number of radio frames, the number of subframes, the number of slots, and the number of symbols. The period information may indicate, for example, the validity period of at least one of dynamic adaptation, the second RA parameters, and the second RA retransmission parameters. The period information may indicate, for example, the timing at which dynamic adaptation is performed.

[0080] The synchronization reconfiguration information may include information on random access configuration used for reconfiguration involving synchronization (hereinafter, referred to as RACH configuration individual information) (see FIG. 6). The RACH configuration individual information may be information used to identify individual RA parameters (for example, RACH-ConfigDedicated).

[0081] The RACH configuration dedicated information may include information on parameters for a contention-free random access (CFRA) procedure for the target cell (hereinafter, CFRA information (e.g., CFRA, CFRA-TwoStep)). The CFRA information may include information on RA opportunities for the CFRA procedure (hereinafter, opportunity information (e.g., occasions, occasionsTwoStepRA)). The opportunity information may include information on the configuration of (contention-free) RA opportunities for the CFRA procedure. This information may be RACH configuration general information (e.g., RACH-ConfigGeneric) used to specify random access parameters for both regular random access and beam failure recovery. Furthermore, the opportunity information may include information indicating the number of SSBs per RACH opportunity (for example, ssb-perRACH-Occasion, ssb-PerRACH-OccasionTwoStep). Note that the RA parameters included in the RACH configuration individual information may be the first RA parameters for the CFRA procedure.

[0082] Furthermore, the synchronization reconfiguration information may include information used to configure cell-specific parameters of the serving cell of UE 100 (hereinafter referred to as serving cell configuration common information (e.g., ServingCellConfigCommon)) (see FIG. 6). The serving cell configuration common information may include information used to identify random access parameters (e.g., RACH configuration common information). The RA parameters included in the RACH configuration common information may be first RA parameters for the CFRA procedure. Note that the RACH configuration common information may be included in information used to configure common parameters of the uplink bandwidth portion (BWP) (hereinafter, BWP uplink common information (e.g., BWP-UplinkCommon)).

[0083] The control unit 120 of the UE 100 initiates handover to the target cell based on the reception of the RRC message. In this operation example, the control unit 120 switches the serving cell from the source cell of the base station 201 to the target cell of the base station 202. The control unit 120 may perform the operation of step S105.

[0084] Step S105: The control unit 120 of the UE 100 executes the RA procedure for the target cell. Details of the operation of step S105 will be described later.

[0085] Step S106: The control unit 120 of the UE 100 transfers the RRC connection from the source cell to the target cell. Then, the transmission unit 111 of the UE 100 transmits an RRC reconfiguration complete message to the base station 202. The reception unit 212 of the base station 201 receives the RRC reconfiguration complete message from the UE 100.

[0086] Next, the RA procedure will be described in detail with reference to FIGS.

[0087] Step S111: The control unit 120 of the UE 100 determines an RA setting and RA parameters to be used in the RA procedure in the target cell based on the control information. The control unit 120 may determine the RA setting and RA parameters, for example, as shown in FIG. 8 .

[0088] Step S121: The control unit 120 determines whether the RRC message that triggers the handover includes the second RA configuration and / or second RA parameters of the target cell.

[0089] When the RRC message includes the second RA configuration, the control unit 120 may perform the process of step S122 for the RA configuration. On the other hand, when the RRC message does not include the second RA configuration, the control unit 120 may perform the process of step S126 for the RA configuration.

[0090] Furthermore, if the RRC message includes the second RA parameters, the control unit 120 may execute the process of step S122 for the RA parameters. If the RRC message does not include the second RA parameters, the control unit 120 may execute the process of step S126 for the RA parameters.

[0091] In addition, the control unit 120 may determine whether the synchronization reconfiguration information associated with the target cell identifier (e.g., a serving cell index that uniquely identifies the serving cell) includes the second RA setting and / or second RA parameters of the target cell.

[0092] Step S122: The control unit 120 determines whether or not to execute a CBRA procedure in the target cell. If the CBRA procedure is to be executed, the control unit 120 may execute the process of step S123. If the CBRA procedure is to be executed, the control unit 120 may omit the process of step S123 and execute the process of step S124. If the CBRA procedure is to be executed, the control unit 120 may omit the process of step S124 and execute the process of step S125. On the other hand, if the CBRA procedure is not to be executed, i.e., if the CFRA procedure is to be executed, the control unit 120 may execute the process of step S126.

[0093] In this way, the control unit 120 may determine whether to use the second RA configuration based on the type of random access procedure executed by the UE 100 in the target cell. Similarly, the control unit 120 may determine whether to use the second RA parameters based on the type of random access procedure.

[0094] Note that the control unit 120 determines to execute the CFRA procedure when the synchronization reconfiguration information (including the RACH setting common information) associated with the identifier of the target cell includes CFRA information, i.e., when a CFRA information field exists in the synchronization reconfiguration information (including the RACH setting common information). On the other hand, the control unit 120 determines to execute the CBRA procedure when the synchronization reconfiguration information (including the RACH setting common information) does not include CFRA information, i.e., when a CFRA information field does not exist in the synchronization reconfiguration information (including the RACH setting common information).

[0095] Step S123: The control unit 120 may determine whether or not the second RA configuration and / or the second RA parameters of the target cell are indicated to be used. The control unit 120 may make this determination based on, for example, availability information. Note that, for example, if the synchronization reconfiguration information does not include availability information, the control unit 120 may omit the processing of step S123.

[0096] When the availability information indicates that the second RA setting is used (or permitted), the control unit 120 may execute the process of step S124 for the second RA setting. On the other hand, when the availability information indicates that the second RA setting is not used (or not permitted), the control unit 120 may execute the process of step S126 for the second RA setting.

[0097] As with the second RA setting, when the availability information indicates that the second RA parameters are to be used, the control unit 120 may execute the process of step S124 for the second RA parameters. On the other hand, when the availability information indicates that the second RA parameters are not to be used, the control unit 120 may execute the process of step S126 for the second RA parameters.

[0098] If the availability information indicates that dynamic adaptation is permitted, the control unit 120 may execute the process of step S124. On the other hand, if the availability information indicates that dynamic adaptation is not permitted, the control unit 120 may execute the process of step S126.

[0099] Step S124: The control unit 120 may determine whether the execution timing is within the validity period of the second RA configuration and / or the second RA parameters of the target cell. The control unit 120 may make this determination based on, for example, period information. Note that, for example, if the synchronization reconfiguration information does not include period information, the control unit 120 may omit the processing of step S124.

[0100] The execution timing may be, for example, at least one of the timing of executing the RA procedure in the target cell, the timing of transmitting a PRACH in the target cell, and the timing of transmitting an RA preamble in the target cell.

[0101] The control unit 120 may execute the process of step S125 for the second RA setting if the execution timing is within the validity period of the second RA setting. On the other hand, the control unit 120 may execute the process of step S126 for the second RA setting if the execution timing is outside the validity period of the second RA setting.

[0102] As with the second RA setting, the control unit 120 may execute the process of step S125 for the second RA parameter if the execution timing is within the validity period of the second RA parameter. On the other hand, the control unit 120 may execute the process of step S126 for the second RA parameter if the execution timing is outside the validity period of the second RA parameter.

[0103] The control unit 120 may execute the process of step S125 when the execution timing is a timing at which dynamic adaptation is to be executed, or may execute the process of step S126 when the execution timing is not a timing at which dynamic adaptation is to be executed.

[0104] Step S125: The control unit 120 uses the second RA setting and / or the second RA parameters. Therefore, in the case of the CBRA procedure, the control unit 120 can determine to use the second RA setting and / or the second RA parameters. Note that even when the control unit 120 uses the second RA setting and / or the second RA parameters, it may use the first RA setting and / or the first RA parameters for RA parameters that are not included in the second RA setting and / or the second RA parameters.

[0105] Step S126: The control unit 120 uses the first RA setting and / or the first RA parameters. Therefore, in the case of the CFRA procedure, the control unit 120 can determine to use the first RA setting and / or the first RA parameters.

[0106] Note that, when the CFRA information includes opportunity information, i.e., when an opportunity information field exists in the CFRA information, the control unit 120 may use the (contention-free) RA opportunity setting for the CFRA procedure included in the opportunity information. Therefore, when a contention-free RA opportunity for the CFRA procedure is provided, the control unit 120 may determine to use the RA setting based on the contention-free RA opportunity for the CFRA procedure (i.e., the first RA setting) rather than the second RA setting. On the other hand, when the CFRA information does not include opportunity information, i.e., when the opportunity information field does not exist in the CFRA information, the control unit 120 may use the RA opportunity set in the RACH configuration shared information of the first active uplink BWP. The RA opportunity is determined based on the first RA setting and the first RA parameters. Note that the first active uplink BWP may be, for example, an uplink BWP used when executing a handover.

[0107] From the above, the control unit 120 may determine the RA parameters to be used based on whether the second RA setting and / or the second RA parameters are provided. The control unit 120 may perform the following operations, for example.

[0108] (A1) When CFRA information is not provided, if the synchronization reconfiguration information includes a second RA setting and / or second RA parameters, the control unit 120 performs a CBRA procedure using the second RA setting and / or second RA parameters.

[0109] (A2) When CFRA information is not provided and the synchronization reconfiguration information does not include the second RA setting and / or the second RA parameters, the control unit 120 performs the CBRA procedure using the first RA setting and / or the first RA parameters.

[0110] (B1) When CFRA information is provided but opportunity information is not provided, if the synchronization reconfiguration information includes a second RA setting and / or a second RA parameter, the control unit 120 performs a CFRA procedure using the second RA setting and / or the second RA parameter.

[0111] (B2) When CFRA information is provided but opportunity information is not provided, if the synchronization reconfiguration information does not include the second RA setting and / or the second RA parameters, the control unit 120 performs the CFRA procedure using the first RA setting and / or the first RA parameters.

[0112] (C) When CFRA information and opportunity information are provided, the control unit 120 executes the CFRA procedure using first RA parameters included in the RACH configuration general information in the opportunity information. Here, the control unit 120 may ignore some of the first RA parameter fields included in the RACH configuration general information. The control unit 120 may use RA parameters (e.g., powerRampingStep, preambleReceivedTargetPower) for controlling the transmission power of the RA preamble included in the RACH configuration shared information.

[0113] (C1) When the synchronization reconfiguration information includes at least one of information regarding the maximum number of RA preambles (e.g., preambleTransMax) and information regarding the receiving window length of the RA response (e.g., ra-ResponseWindow) as the second RA parameter, the control unit 120 may use at least one of the information regarding the maximum number of RA preambles and information regarding the receiving window length of the RA response.

[0114] (C2) When the synchronization reconfiguration information does not include at least one of information regarding the maximum number of RA preambles and information regarding the reception window length of an RA response as the second RA parameter, the control unit 120 may use at least one of information regarding the maximum number of RA preambles and information regarding the reception window length of an RA response as the first RA parameter included in the RACH setting shared information.

[0115] Step S112: The control unit 120 determines a PRACH opportunity based on the determined RA configuration and / or RA parameters. Based on the determined RA configuration, the control unit 120 determines a radio frame to which the PRACH opportunity is allocated, a slot to which the PRACH opportunity is allocated, and a symbol to which the PRACH opportunity is allocated.

[0116] The control unit 120 may determine the PRACH opportunity, for example, based on the RA setting (first RA setting or second RA setting) associated with the PRACH setting index, which is the determined RA parameter (first RA parameter or second RA parameter).

[0117] For example, when multiple RA configurations are configured in the UE 100, the control unit 120 may determine the PRACH opportunity based on an RA configuration indicated by an index among the configured multiple RA configurations. For example, the control unit 120 may select a second RA configuration associated with an index among multiple second RA configurations in the RACH adaptation configuration list. The index may be a second RA parameter.

[0118] For example, when multiple RA settings are configured in UE 100, the control unit 120 may determine the PRACH opportunity based on the second RA setting of the order indicated by the second RA parameter among the multiple RA settings configured.

[0119] The control unit 120 may determine the PRACH period based on the determined RA setting and / or RA parameters. The control unit 120 may determine the PRACH period based on the determined RA setting. The control unit 120 may also determine the changed PRACH period based on a setting value for adjusting the PRACH period as an RA parameter. The control unit 120 may, for example, calculate a different PRACH period based on a setting value for the PRACH period based on the determined RA setting. The control unit 120 may determine the calculated PRACH period as the changed PRACH period.

[0120] The control unit 120 executes the RA procedure using the determined RA parameters. In this operation example, the RA procedure will be described using the CBRA procedure as an example. Note that, in the RA procedure, the control unit 120 may control the retransmission of the RA preamble based on the retransmission parameters.

[0121] Note that even when using the second RA parameters, the control unit 120 may use the first RA parameters for some of the RA parameters. For example, even when using at least one of the maximum number of RA preambles, the receive window length, and the contention resolution timer (value for the timer) included in the second RA parameters, the control unit 120 may use information indicating a power ramping step for the PRACH and information indicating a target power level on the network receiving side included in the first RA parameters as RA parameters for controlling the transmission power of the RA preambles. For example, the control unit 120 may use the maximum number of RA preambles, the receive window length, and the contention resolution timer (value for the timer) included in the DA configuration information, and may use information indicating a power ramping step for the PRACH and information indicating a target power level on the network receiving side included in the RACH configuration common information including the first RA parameters. In this way, the control unit 120 may use, as an RA parameter for controlling the transmission power of the RA preamble, a parameter used when changing the periodicity of PRACH opportunities by signaling in the RRC layer, i.e., the first RA parameter, even when the periodicity of PRACH opportunities is changed by signaling in a lower layer.

[0122] Note that, when changing the RA configuration (or PRACH period), the control unit 120 of the UE 100 may remap the SSB (SSB index) to the PRACH opportunity. The control unit 120 may map the SSB (SSB index) to the PRACH opportunity taking into consideration the period of the PRACH opportunity, the PRACH configuration period, the association period, and / or the association pattern period.

[0123] The SSB may be a cell-defining SSB (CD-SSB) in the target cell. Information about the SSB may be included in the synchronization reconfiguration information. Based on the information about the SSB, the control unit 120 can map the SSB (SSB index) to a PRACH opportunity.

[0124] Step S113: The transmitter 111 of the UE 100 performs PRACH transmission at the determined PRACH opportunity. The transmitter 111 transmits an RA preamble (message 1) on the PRACH to the base station 202. The receiver 212 of the base station 202 receives the RA preamble (message 1) from the UE 100.

[0125] After transmitting the PRACH, the control unit 120 starts a receive window. In this operation example, the control unit 120 may start a receive window with the receive window length of the second retransmission parameter. In addition, in this operation example, the control unit 120 may perform the following control using the maximum number of RA preambles of the second retransmission parameter.

[0126] If the control unit 120 does not receive an RA response within the reception window, the control unit 120 determines that the RA response has not been received successfully. The control unit 120 increments a preamble transmission counter (e.g., PREAMBLE_TRANSMISSION_COUNTER) by one each time the control unit 120 determines that the RA response has not been received successfully.

[0127] If the value of the preamble transmission counter is equal to "the maximum number of RA preambles + 1" and the PRACH is transmitted in the Sp cell, the control unit 120 indicates a random access problem to a layer higher than the MAC layer. Furthermore, if the value of the preamble transmission counter is equal to "the maximum number of RA preambles + 1" and the PRACH is transmitted in the S cell, the control unit 120 determines that the random access procedure has not been completed successfully. If the random access procedure has not been completed, the control unit 120 retransmits the PRACH, i.e., retransmits the RA preamble. In this way, the control unit 120 controls the retransmission of the RA preamble based on the maximum number of RA preambles and the reception window. The control unit 120 may perform the process of step S105 again.

[0128] Step S114: The transmitting unit 211 of the base station 202 transmits an RA response (RAR: message 2) to the UE 100. The receiving unit 112 of the UE 100 receives the RA response from the base station 202.

[0129] Step S115: The transmitter 111 of the UE 100 transmits the message 3 to the base station 202. The receiver 212 of the base station 202 receives the message 3 from the UE 100.

[0130] The control unit 120 may start a contention resolution timer after transmitting message 3. In this operation example, the control unit 120 may start a contention resolution timer for the second retransmission parameters.

[0131] If the control unit 120 does not receive message 4 before the contention resolution timer expires, the control unit 120 determines that contention resolution has not been successful. The control unit 120 increments a preamble transmission counter (e.g., PREAMBLE_TRANSMISSION_COUNTER) by one each time the control unit 120 determines that contention resolution has not been successful.

[0132] When the value of the preamble transmission counter becomes equal to "the maximum number of RA preambles + 1," this indicates a random access problem to a layer higher than the MAC layer. If contention resolution is not completed, the control unit 120 retransmits the PRACH, i.e., retransmits the RA preamble. In this way, the control unit 120 controls the retransmission of the RA preamble based on the maximum number of RA preambles and the reception window. The control unit 120 may perform the process of step S112 again.

[0133] Step S116: The transmitting unit 211 of the base station 202 transmits the message 4 to the UE 100. The receiving unit 112 of the UE 100 receives the message 4 from the base station 202.

[0134] Thereafter, the control unit 120 of the UE 100 may determine a PRACH opportunity and / or a periodicity of the PRACH opportunity based on the control information. For example, when the second RA configuration based on the DA configuration information is configured, the control unit 120 of the UE 100 may change the periodicity of the PRACH opportunity by lower layer signaling from the base station 202. On the other hand, when the first RA configuration is configured, the control unit 120 of the UE 100 may change the periodicity of the PRACH opportunity by RRC layer signaling until the second RA configuration based on the DA configuration information is configured.

[0135] As described above, the transmitter 211 of the base station 201 transmits an RRC message to the UE 100 that triggers a handover to the target cell. The receiver 112 of the UE 100 receives a radio resource control (RRC) message from the base station 200 that triggers a handover to the target cell. The controller 120 of the UE 100 determines a PRACH opportunity in the RA procedure in the target cell based on the RRC message. The RRC message includes control information for controlling a change in the periodicity of the PRACH opportunity by signaling in a layer lower than the RRC layer in the target cell. The controller 120 determines the PRACH opportunity based on the control information. Note that the control information may be used to change the periodicity of the PRACH opportunity using lower layer signaling as a trigger after execution of a handover to the target cell. When executing a handover, the control information does not need to be triggered by lower layer signaling to change (determine / select) the PRACH opportunity and / or the PRACH periodicity.

[0136] As a result, even if, for example, the synchronization reconfiguration information for the target cell includes the first RA parameter (or the first RA setting) and the second RA parameter (or the second RA setting), the UE 100 can appropriately determine the PRACH opportunity based on the control information and perform dynamic adaptation of the PRACH opportunity.

[0137] The control information may also include a second RA configuration that is used to set the periodicity of the PRACH opportunity and is used exclusively when the periodicity of the PRACH opportunity is changed by lower layer signaling. The control unit 120 may determine the PRACH opportunity using the second RA configuration. This allows the control unit 120 to acquire the second RA configuration before performing handover to the target cell. The control unit 120 can perform dynamic adaptation from the RA procedure in the target cell.

[0138] Furthermore, the control unit 120 may determine whether to use the second RA configuration based on the type of RA procedure executed by the UE 100 in the target cell. This allows the UE 100 to use the second RA configuration differently depending on the type of RA procedure.

[0139] Furthermore, the control unit 120 may determine to use the second RA configuration when the RA procedure executed by the UE 100 is the CBRA procedure. By using the second RA configuration, it is possible to ensure flexibility in handover.

[0140] In addition, when the RA procedure executed by the UE 100 is a CFRA procedure and a random access opportunity for the CFRA procedure is provided by an RRC message, the control unit 120 may determine to use an RA configuration based on an RA opportunity for the CFRA procedure instead of the second RA configuration. By using the RA opportunity for the CFRA procedure, the UE 100 can increase the success of the RA procedure without RA preamble collision.

[0141] Furthermore, the control information may include at least one of a value indicating the maximum number of RA preambles and a reception window length of an RA response, which is a response to an RA preamble, as a second RA parameter used exclusively when changing the periodicity of PRACH opportunities by lower layer signaling in the target cell. Even when using RA configuration based on random access opportunities for the CFRA procedure, the control unit 120 may use at least one of the value indicating the maximum number of times and the reception window length as the second RA parameter. Use of such second RA parameters can ensure handover flexibility.

[0142] Furthermore, the control information includes information indicating whether to use a second RA configuration that is used to set a periodicity of the PRACH opportunity and is used exclusively when the periodicity of the PRACH opportunity is changed by signaling of a lower layer. As a result, whether to use the second RA configuration or not is explicitly indicated to the UE 100 based on the information, and therefore the UE 100 can use an appropriate RA configuration.

[0143] Furthermore, the control information may include information indicating a validity period of the second RA configuration that is used to set the period of the PRACH opportunity and is used exclusively when the period of the PRACH opportunity is changed by signaling of a lower layer. This allows the UE 100 to determine whether the second RA configuration is valid or not, based on the information indicating the validity period. The UE 100 can use an appropriate RA configuration.

[0144] Furthermore, the control information may include second RA parameters that are used exclusively when the periodicity of the PRACH opportunities is changed by lower layer signaling in the target cell. The control unit 120 may use the second RA parameters in the RA procedure in the target cell. This allows the control unit 120 to acquire the second RA parameters before executing handover to the target cell. The control unit 120 can perform dynamic adaptation from the RA procedure in the target cell.

[0145] Furthermore, the control unit 120 may determine whether to use the second RA parameter based on the type of random access procedure executed by the UE 100 in the target cell. Thereby, the UE 100 can use the second RA parameter depending on the type of RA procedure.

[0146] Furthermore, the control information may include information indicating whether to use a second RA parameter that is used exclusively when changing the periodicity of the PRACH opportunity by signaling of a lower layer in the target cell. This explicitly indicates to the UE 100 whether to use the second RA parameter based on the information, so that the UE 100 can use an appropriate RA parameter.

[0147] Furthermore, the control information may include information indicating a validity period of a second RA parameter that is used exclusively when the period of the PRACH opportunity is changed by signaling of a lower layer in the target cell. As a result, the UE 100 can determine whether the second RA parameter is valid or not by the information indicating the validity period. The UE 100 can use an appropriate RA parameter.

[0148] Second Embodiment A second embodiment will be described with reference to Figures 9 and 10. Previous descriptions may be omitted.

[0149] It is proposed to prohibit UEs 100 that do not have the capability to perform NES-related operations (hereinafter referred to as NES capability) from accessing NES cells, thereby enabling the NES to save energy in the network 10.

[0150] However, for example, there is a concern that the UE 100 that does not have the NES capability cannot access the NES cell, and therefore a necessary service cannot be provided to the UE 100. Therefore, an operation for enabling a necessary service to be provided to the UE 100 that does not have the NES capability will be described.

[0151] A UE 100 that does not have NES capability (referred to as a non-NES capable UE 100) may be, for example, a UE 100 that does not support NES-related operations. A non-NES capable UE 100 may be, for example, a UE 100 that does not support the dynamic adaptation described above. A non-NES capable UE 100 may be a so-called legacy UE. A non-NES capable UE 100 may be a UE that is temporarily unable to perform NES-related operations.

[0152] An NES cell may be, for example, a cell managed by base station 200 that follows certain behaviors related to NES capabilities.

[0153] As shown in FIG. 9, the control unit 120 of the non-NES capable UE 100 may perform the following operations when attempting to access an NES cell.

[0154] Step S1010: The control unit 120 determines whether the NES cell to which access is being attempted is an NES cell that supports emergency calls (hereinafter referred to as a supporting NES cell). If the NES cell is a supporting NES cell, the control unit 120 executes the process of step S1020. On the other hand, if the NES cell is not a supporting NES cell, the control unit 120 executes the process of step S1040.

[0155] The control unit 120 may determine whether the NES cell is a supporting NES cell, for example, based on an SIB message received from the NES cell. For example, if the SIB message includes NES cell information indicating whether the cell is a supporting NES cell, the control unit 120 may determine whether the cell is a supporting NES cell based on the NES cell information. The NES cell information may be, for example, eCallOverIMS-Support included in the SIB1 message. eCallOverIMS-Support indicates whether the cell supports eCalls over IMS (Internet Protocol Multimedia Subsystem (IP)) services. The SIB message may be a SIB1 message or another SIB message.

[0156] If the NES cell information indicates that the NES cell is a supporting NES cell, the control unit 120 may execute the process of step S1020. If the NES cell information indicates that the NES cell is a supporting NES cell, the control unit 120 may execute the process of step S1020. If the NES cell information indicates that the NES cell is not a supporting NES cell, the control unit 120 may execute the process of step S1040.

[0157] Furthermore, if the SIB message does not include NES cell information indicating that the NES cell is not a supported NES cell, the control unit 120 may execute the process of step S1020. On the other hand, if the SIB message does not include NES cell information indicating that the NES cell is a supported NES cell, the control unit 120 may execute the process of step S1040.

[0158] The control unit 120 may perform the following determination instead of the above determination: Alternatively, the control unit 120 may perform the following determination in addition to the above determination: The control unit 120 may perform the following determination when the NES cell is a supporting NES cell.

[0159] The control unit 120 may determine, for example, based on an SIB message received from the NES cell, whether the NES cell prohibits or permits access (Camp) and / or cell selection / reselection from the non-NES capable UE 100. For example, when the SIB message includes NES cell access information indicating whether the non-NES capable UE 100 is prohibited from accessing the cell or permitted to access the cell, the control unit 120 may determine, based on the NES cell access information, whether to access the cell and / or perform cell selection / reselection. The NES cell access information may be information (e.g., intraFreqReselectionNonNES) dedicated to the non-NES capable UE 100 included in the SIB1 message. When the SIB message does not include intraFreqReselectionNonNES, the control unit 120 may consider that access to the cell and / or cell selection / reselection is prohibited. When the SIB message includes intraFreqReselectionNonNES and the intraFreqReselectionNonNES indicates permission, the control unit 120 may determine that access to the cell and / or cell selection / reselection is permitted. When the SIB message includes intraFreqReselectionNonNES and the intraFreqReselectionNonNES indicates prohibition, the control unit 120 may determine that access to the cell and / or cell selection / reselection is prohibited. The SIB message may be a SIB1 message or another SIB message.

[0160] If the control unit 120 considers (determines) that access to the cell and / or cell selection / cell reselection is permitted, the control unit 120 may execute the process of step S1020. On the other hand, if the control unit 120 considers (determines) that access to the cell and / or cell selection / cell reselection is prohibited, the control unit 120 may execute the process of step S1040.

[0161] Step S1020: The control unit 120 determines whether or not an emergency call has been detected. If an emergency call has been detected, the control unit 120 executes the process of step S1030. If an emergency call has not been detected, the control unit 120 executes the process of step S1040.

[0162] Step S1030: The control unit 120 does not access the NES cell, and may search for other cells.

[0163] Step S1040: The control unit 120 accesses the NES cell. When accessing the NES cell, the control unit 120 may perform PRACH transmission. The control unit 120 may perform the following operations as shown in FIG. 10 .

[0164] Step S1041: The control unit 120 may determine whether to execute PRACH transmission for making an emergency call. If the PRACH transmission is to be executed with the emergency call as a trigger, the control unit 120 may execute the process of step S1042. On the other hand, if the PRACH transmission is to be executed without the emergency call as a trigger, the control unit 120 may execute the process of step S1044.

[0165] For example, when UE 100 supports dynamic adaptation, that is, when UE 100 has capability for dynamic adaptation, control unit 120 may execute the process of step S1042. For example, when UE 100 does not support dynamic adaptation, that is, when UE 100 does not have capability for dynamic adaptation, control unit 120 may omit the process of step S1042 and execute the process of step S1043.

[0166] Note that the use of the normal RA setting when placing an emergency call may be specified in advance in the technical specifications. In this case, the control unit 120 may omit the process of step S1042 and execute the process of step S1043.

[0167] Furthermore, the transmitting unit 211 of the base station 200 may transmit information for determining an RA setting to be used when an emergency call is executed (hereinafter, RA setting determination information) to the UE 100. The receiving unit 112 of the UE 100 may receive the RA setting determination information from the base station 200. The RA setting determination information may be included in, for example, an SIB message.

[0168] The RA setting determination information may indicate, for example, which RA setting should be preferentially used between a normal RA setting and a specific RA setting when an emergency call is executed. The RA setting determination information may indicate that the normal RA setting is to be used (preferentially) when an emergency call is executed. The RA setting determination information may also indicate that a specific RA setting is to be used (preferentially) when an emergency call is executed. Furthermore, the RA setting determination information may indicate that either the normal RA setting or the specific RA setting may be used when an emergency call is executed.

[0169] The control unit 120 may determine which RA setting to use based on the RA setting determination information. When the RA setting determination information indicates that the normal RA setting should be used when an emergency call is executed, the control unit 120 may execute the process of step S1043.

[0170] When the RA setting determination information indicates that a specific RA setting is to be used when an emergency call is executed, the control unit 120 may execute the process of step S1044. Note that, for example, when the control unit 120 cannot recognize a change to a specific RA setting, the control unit 120 may execute the process of step S1043 even if the RA setting determination information indicates that a specific RA setting is to be used (preferentially).

[0171] If the RA setting determination information indicates that either RA setting may be used, the control unit 120 may execute the processing of step S1042, or may select either step S1043 or S1044 (e.g., depending on the implementation).

[0172] Step S1042: The control unit 120 may determine whether or not a PRACH period based on a normal RA setting (hereinafter, normal PRACH period) is shorter than a PRACH period based on a specific RA setting (hereinafter, specific PRACH period). For example, the control unit 120 may determine whether or not a normal PRACH period based on RACH setting common information including a first RA parameter is shorter than a specific PRACH period based on RACH setting common information including a second RA parameter.

[0173] If the normal PRACH period is shorter than the specific PRACH period, the control unit 120 may execute the process of step S1043. On the other hand, if the normal PRACH period is longer than the specific PRACH period, the control unit 120 may execute the process of step S1044.

[0174] Step S1043: The control unit 120 performs PRACH transmission using the normal RA setting.

[0175] Step S1044: The control unit 120 performs PRACH transmission using a specific RA setting. Note that, if the control unit 120 cannot recognize a change to the specific RA setting, it may perform PRACH transmission using a normal RA setting. The case in which the control unit 120 cannot recognize a change to the specific RA setting may be, for example, at least one of the following: failure to receive a specific DCI; not receiving a specific RA setting; or the UE 100 not supporting dynamic adaptation.

[0176] Thereafter, the control unit 120 accesses the NES cell by executing PRACH transmission. After accessing the NES cell, the control unit 120 executes the outgoing emergency call. When the outgoing emergency call is completed, the control unit 120 may terminate the access to the NES cell.

[0177] As described above, when the UE 100 having the emergency call capability attempts to access a cell for the purpose of making an emergency call, and the NES cell supports emergency calls even if the NES cell prohibits access, the UE 100 can execute the access. This makes it possible to provide the necessary service of making an emergency call even to the UE 100 not having the NES capability.

[0178] Furthermore, when UE 100 originates an emergency call, for example, it can perform PRACH transmission using a normal RA setting regardless of setting information related to dynamic adaptation. This allows UE 100 to reliably perform PRACH transmission when executing an emergency call. For example, if UE 100 fails to receive a specific DCI, it may not be able to recognize the selection of a specific RA setting (or a change to a specific RA setting), and PRACH transmission may fail. Therefore, by UE 100 using a normal RA setting, it is possible to prevent failure of PRACH transmission based on the specific DCI and realize a robust emergency call.

[0179] Furthermore, the UE 100 may compare a normal PRACH period with a specific PRACH period and perform PRACH transmission at a shorter PRACH period. This allows the UE 100 to perform PRACH transmission at a shorter PRACH period. As a result, the UE 100 can originate an emergency call more quickly.

[0180] Note that, in order to prioritize delay suppression of emergency calls, the control unit 230 of the base station 200 may include, for example, in an SIB message, a second RA setting for setting a specific PRACH period that is shorter than a normal PRACH period in the UE 100. The control unit 120 of the UE 100 may use the second RA setting, for example, when transmitting an emergency call. On the other hand, in order to save energy in the network 10, the control unit 230 of the base station 200 may include, for example, in an SIB message, a second RA setting for setting a specific PRACH period that is longer than a normal PRACH period in the UE 100.

[0181] (Other Embodiments) In the above-described embodiments, when executing the CFRA procedure, the UE 100 may use the first RA parameters for the CFRA procedure or the second RA parameters. Therefore, the base station 200 may be able to configure the UE 100 with the second RA parameters as the RA parameters for the CFRA procedure, and may be able to configure the UE 100 with the second RA configuration as the RA configuration for the CFRA procedure. For example, the RACH configuration-specific information included in the synchronization reconfiguration information may include the second RA parameters and / or the second RA configuration.

[0182] In the above-described embodiment, a four-step random access procedure has been described as an example, but the present invention is not limited to this. The above-described operations may also be performed in a two-step random access procedure. In this case, for example, message 1 may be replaced with message A, and message 2 may be replaced with message B. Furthermore, in the above-described embodiment, "PRACH" may be replaced with "RACH."

[0183] Furthermore, the above-described embodiments may be combined with each other. For example, when PRACH transmission is performed to make an emergency call in the first embodiment, the operation of the second embodiment may be performed.

[0184] In the second embodiment described above, the control unit 120 of the UE 100 executes the process of step S1020 when it considers (determines) that access to the NES cell and / or cell selection / cell reselection is permitted, but this is not limiting. The control unit 120 may execute step S1040 when it considers (determines) that access to the NES cell and / or cell selection / cell reselection is permitted.

[0185] 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.

[0186] 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.

[0187] 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.

[0188] 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)).

[0189] 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.

[0190] 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.

[0191] (Additional Notes) Additional notes will be given regarding the features of the above-described embodiment.

[0192] (Supplementary Note 1) A communication device comprising: a receiver unit that receives, from a base station, a radio resource control (RRC) message that triggers a handover to a target cell; and a controller that determines a physical random access channel (PRACH) opportunity in a random access procedure in the target cell based on the RRC message, wherein the RRC message includes control information for controlling a change in a periodicity of the PRACH opportunity by signaling in a layer lower than the RRC layer in the target cell, and the controller determines the PRACH opportunity based on the control information.

[0193] (Supplementary Note 2) The communication device according to Supplementary Note 1, wherein the control information includes a specific random access (RA) configuration that is used to set a periodicity of the PRACH opportunity and is used exclusively when the periodicity of the PRACH opportunity is changed by signaling of the lower layer, and the controller determines the PRACH opportunity using the specific RA configuration.

[0194] (Supplementary Note 3) The communication device according to Supplementary Note 2, wherein the control unit determines whether to use the specific RA configuration based on a type of random access procedure executed by the communication device in the target cell.

[0195] (Supplementary Note 4) The communication device according to Supplementary Note 3, wherein the control unit determines to use the specific RA setting when the random access procedure executed by the communication device is a contention-based random access (CBRA) procedure.

[0196] (Supplementary Note 5) The communication device according to Supplementary Note 3 or 4, wherein, when the random access procedure executed by the communication device is a contention-free random access (CFRA) procedure and a random access opportunity for the CFRA procedure is provided by the RRC message, the control unit determines to use an RA configuration based on a random access opportunity for the CFRA procedure instead of the specific RA configuration.

[0197] (Supplementary Note 6) The communication device according to Supplementary Note 5, wherein the control information includes at least one of a value indicating a maximum number of RA preambles and a reception window length of an RA response that is a response to the RA preamble, as a specific random access (RA) parameter exclusively used when changing a periodicity of the PRACH opportunity by the lower layer signaling in the target cell, and the control unit uses at least one of the value indicating the maximum number of times and the reception window length even when using RA configuration based on a random access opportunity for the CFRA procedure.

[0198] (Supplementary Note 7) The communication device according to any one of Supplementary Notes 1 to 6, wherein the control information includes information indicating whether to use a specific random access (RA) configuration that is used to set a periodicity of the PRACH opportunity and is used exclusively when the periodicity of the PRACH opportunity is changed by the lower layer signaling.

[0199] (Supplementary Note 8) The communication device according to any one of Supplementary Notes 1 to 7, wherein the control information includes information indicating a validity period of a specific random access (RA) configuration that is used to set a periodicity of the PRACH opportunity and is used exclusively when the periodicity of the PRACH opportunity is changed by signaling of the lower layer.

[0200] (Supplementary Note 9) The communication device according to any one of Supplementary Notes 1 to 8, wherein the control information includes a specific random access (RA) parameter that is exclusively used when changing a periodicity of the PRACH opportunity by the lower layer signaling in the target cell, and the controller uses the specific RA parameter in the RA procedure in the target cell.

[0201] (Supplementary Note 10) The communication device according to Supplementary Note 9, wherein the control unit determines whether to use the specific RA parameters based on a type of random access procedure executed by the communication device in the target cell.

[0202] (Supplementary Note 11) The communication device according to Supplementary Note 9 or 10, wherein the control information includes information indicating whether to use specific random access (RA) parameters that are exclusively used when changing a periodicity of the PRACH opportunity by the lower layer signaling in the target cell.

[0203] (Supplementary Note 12) The communication device according to any one of Supplementary Notes 9 to 11, wherein the control information includes information indicating a validity period of a specific random access (RA) parameter that is exclusively used when changing a periodicity of the PRACH opportunity in the target cell by the lower layer signaling.

[0204] (Supplementary Note 13) A base station comprising: a transmitter unit that transmits, to a communication device, a radio resource control (RRC) message that triggers a handover to a target cell; the RRC message is used in the communication device to determine a physical random access channel (PRACH) opportunity in a random access procedure in the target cell; and the RRC message includes control information for controlling a change in a periodicity of the PRACH opportunity by signaling in a layer lower than an RRC layer in the target cell.

[0205] (Supplementary Note 14) A communication method executed by a communication device, comprising: receiving, from a base station, a Radio Resource Control (RRC) message that triggers a handover to a target cell; and determining, based on the RRC message, a Physical Random Access Channel (PRACH) opportunity in a random access procedure in the target cell, wherein the RRC message includes control information for controlling a change in a periodicity of the PRACH opportunity by signaling in a layer lower than the RRC layer in the target cell; and wherein, in the determining, the PRACH opportunity is determined based on the control information.

Claims

1. A communications device (100) comprising: a receiver (112) that receives a radio resource control (RRC) message from a base station (200, 201) that triggers a handover to a target cell; and a control unit (120) that determines a physical random access channel (PRACH) opportunity in a random access procedure in the target cell based on the RRC message, wherein the RRC message includes control information for controlling a change in a period of the PRACH opportunity by signaling of a layer lower than the RRC layer in the target cell, and the control unit determines the PRACH opportunity based on the control information.

2. The communication device described in claim 1, wherein the control information includes a specific random access (RA) setting that is used to set a periodicity of the PRACH opportunity and is used exclusively when the periodicity of the PRACH opportunity is changed by signaling of the lower layer, and the control unit determines the PRACH opportunity using the specific RA setting.

3. The communication device according to claim 2, wherein the control unit determines whether or not to use the specific RA setting based on a type of random access procedure executed by the communication device in the target cell.

4. The communication device according to claim 3, wherein the control unit determines to use the specific RA setting when the random access procedure executed by the communication device is a contention-based random access (CBRA) procedure.

5. The communication device described in claim 3 or 4, wherein the control unit determines that when the random access procedure executed by the communication device is a contention-free random access (CFRA) procedure and a random access opportunity for the CFRA procedure is provided by the RRC message, to use an RA setting based on a random access opportunity for the CFRA procedure rather than the specific RA setting.

6. The communication device described in claim 5, wherein the control information includes at least one of a value indicating the maximum number of RA preambles and a receiving window length of an RA response, which is a response to the RA preamble, as specific random access (RA) parameters used exclusively when changing the periodicity of the PRACH opportunities in the target cell by signaling of the lower layer, and the control unit uses at least one of the value indicating the maximum number of times and the receiving window length even when using an RA setting based on a random access opportunity for the CFRA procedure.

7. The communication device according to claim 1 or 2, wherein the control information includes information indicating whether or not to use a specific random access (RA) setting that is used to set the periodicity of the PRACH opportunities and is used exclusively when the periodicity of the PRACH opportunities is changed by signaling of the lower layer.

8. The communication device according to claim 1 or 2, wherein the control information includes information indicating a validity period of a specific random access (RA) setting that is used to set the period of the PRACH opportunity and is used exclusively when the period of the PRACH opportunity is changed by signaling of the lower layer.

9. The communication device according to claim 1 or 2, wherein the control information includes a specific random access (RA) parameter that is used exclusively when changing the periodicity of the PRACH opportunity in the target cell by signaling of the lower layer, and the control unit uses the specific RA parameter in the RA procedure in the target cell.

10. The communication device according to claim 9, wherein the control unit determines whether or not to use the specific RA parameters based on a type of random access procedure executed by the communication device in the target cell.

11. The communication device according to claim 9, wherein the control information includes information indicating whether or not to use a specific random access (RA) parameter that is used exclusively when changing the periodicity of the PRACH opportunity in the target cell by the lower layer signaling.

12. The communication device according to claim 9, wherein the control information includes information indicating a validity period of a specific random access (RA) parameter that is used exclusively when changing the periodicity of the PRACH opportunity in the target cell by the lower layer signaling.

13. A base station (200, 201), comprising: a transmission unit (211) that transmits a radio resource control (RRC) message to a communication device (100) that triggers a handover to a target cell, the RRC message being used in the communication device to determine a physical random access channel (PRACH) opportunity in a random access procedure in the target cell, and the RRC message including control information for controlling a change in a periodicity of the PRACH opportunity by signaling in a layer lower than the RRC layer in the target cell.

14. A communication method executed by a communication device (100), comprising: a step of receiving a radio resource control (RRC) message from a base station (200, 201) that triggers a handover to a target cell; and a step of determining a physical random access channel (PRACH) opportunity in a random access procedure in the target cell based on the RRC message, wherein the RRC message includes control information for controlling a change in a periodicity of the PRACH opportunity by signaling of a layer lower than the RRC layer in the target cell, and in the determining step, the PRACH opportunity is determined based on the control information.

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