Communication device, base station, and communication method

Abstract

A communication device (100) according to one embodiment of the present invention comprises: a reception unit (112) that receives, from a base station (200), retransmission parameters which are random access parameters used to control the retransmission of an RA preamble in a physical random access channel (PRACH) occasion of a random access (RA) procedure; and a control unit (120) that controls the retransmission of the RA preamble on the basis of the retransmission parameters. The retransmission parameters include a specific retransmission parameter used exclusively when changing the period of the PRACH occasion through signalling in a layer lower than a radio resource control (RRC) layer.

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. 2023-187080, 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, from a base station, retransmission parameters that are random access parameters used for controlling retransmission of RA preambles on Physical Random Access Channel (PRACH) opportunities in a random access (RA) procedure, and a controller that controls retransmission of the RA preamble based on the retransmission parameters, wherein the retransmission parameters include specific retransmission parameters that are exclusively used when a periodicity of the PRACH opportunities is changed by signaling in a layer lower than a Radio Resource Control (RRC) layer.

[0007] A base station according to a second aspect includes a transmitter configured to transmit, to a communication device, retransmission parameters, which are random access parameters used for controlling retransmission of RA preambles on Physical Random Access Channel (PRACH) opportunities in a random access (RA) procedure, the retransmission parameters including specific retransmission parameters used exclusively when a periodicity of the PRACH opportunities is changed by signaling in a layer lower than a Radio Resource Control (RRC) layer.

[0008] A communication method according to a third aspect is a communication method executed by a communication device, the communication method comprising the steps of receiving, from a base station, retransmission parameters that are random access parameters used for controlling retransmission of RA preambles on Physical Random Access Channel (PRACH) opportunities in a random access (RA) procedure, and controlling retransmission of the RA preamble based on the retransmission parameters, wherein the retransmission parameters include specific retransmission parameters that are used exclusively when the periodicity of the PRACH opportunities is changed by signaling in a layer lower than a Radio Resource Control (RRC) layer.

[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 illustrating an example operation according to the first embodiment. FIG. 6 is a diagram illustrating the first embodiment. FIG. 7 is a flowchart (part 1) illustrating an example operation according to the second embodiment. FIG. 8 is a flowchart (part 2) illustrating 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 executing a random access procedure when dynamic adaptation of PRACH opportunities is performed.

[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 request 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 receiving unit 112 receives retransmission parameters from the base station 200, which are random access parameters used to control the retransmission of RA preambles at PRACH opportunities in the RA procedure. The control unit 120 controls the retransmission of RA preambles based on the retransmission parameters. The retransmission parameters include specific retransmission parameters that are used exclusively when changing the periodicity of PRACH opportunities by signaling in layers lower than the RRC layer. This enables the UE 100 to use the specific retransmission parameters when controlling the retransmission of RA preambles. Since the specific retransmission parameters can be set separately from the values ​​of normal retransmission parameters, it is possible to flexibly control the random access procedure when dynamic adaptation of PRACH opportunities is performed. As a result, it is possible to appropriately perform the random access procedure when dynamic adaptation of PRACH opportunities is performed.

[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 the base station 200 configured in this manner, the transmitter 211 transmits to the UE 100 retransmission parameters, which are random access parameters used to control the retransmission of RA preambles at PRACH opportunities in the RA procedure. The retransmission parameters include specific retransmission parameters that are used exclusively when changing the periodicity of PRACH opportunities by signaling in a layer lower than the RRC layer. This enables the UE 100 to use the specific retransmission parameters when controlling the retransmission of RA preambles. Since the specific retransmission parameters can be set separately from the values ​​of normal retransmission parameters, it is possible to flexibly control the random access procedure when dynamic adaptation of PRACH opportunities is performed. As a result, it is possible to appropriately perform the random access procedure when dynamic adaptation of PRACH opportunities is performed.

[0048] First Embodiment A first embodiment will be described with reference to Figures 5 and 6. Previous descriptions may be omitted.

[0049] In order to save energy in the network, it is assumed that, for example, in a certain base station 200, the PRACH period is frequently changed by lower layer signaling such as downlink control information (DCI). Since a longer PRACH period reduces opportunities for PRACH transmission, multiple UEs 100 that perform PRACH transmission (i.e., transmission of random access (RA) preambles) may temporarily concentrate on a small number of PRACH transmission opportunities. This may make congestion more likely to occur in the base station 200, raising concerns that the random access procedure in which PRACH transmission is performed may not be properly performed. Therefore, an operation for enabling the random access procedure to be properly performed when dynamic adaptation of PRACH opportunities is performed will be described.

[0050] In FIG. 5 , UE 100 may be in an RRC idle state or an RRC inactive state with a cell managed by base station 200. Also, UE 100 may be in an RRC connected state with the cell. The cell may be a cell on which UE 100 is camped, or may be a cell that UE 100 has (re)selected. The cell may be a cell to which UE 100 has established an RRC connection. In this operation example, the description will proceed assuming that UE 100 is in an RRC idle state.

[0051] Note that, for UE 100, communication with base station 200 may be communication with a cell. Therefore, for UE 100, receiving information / messages, etc. from base station 200 may be receiving information / messages, etc. from a cell, and transmitting information / messages, etc. to base station 200 may be transmitting information / messages, etc. to a cell.

[0052] Step S101: The transmitter 211 of the base station 200 transmits a system information block type 1 (SIB1) message to the UE 100. The transmitter 211 of the base station 200 transmits the SIB1 message by broadcast. The receiver 112 of the UE 100 receives the SIB1 message from the base station 200 (cell).

[0053] The SIB1 message may be a message that includes information relevant to the UE 100 when evaluating whether it is allowed to access the cell, or a message that specifies the scheduling of other system information.

[0054] The SIB1 message includes information used to specify random access parameters (hereinafter referred to as RACH configuration common information). The RACH configuration common information may be, for example, "RACH-ConfigCommon" or "RACH-ConfigCommonTwoStepRA". The random access parameters may include so-called cell-specific four-step random access type parameters or cell-specific two-step random access type parameters.

[0055] The RACH configuration common information may be included in information used to configure common parameters of the uplink bandwidth portion (BWP) (hereinafter referred to as BWP uplink common information (e.g., BWP-UplinkCommon)). The BWP uplink common information may be included in information providing common uplink parameters of the cell (hereinafter referred to as uplink configuration common SIB information (e.g., UplinkConfigCommonSIB)). Note that the BWP uplink common information may be included in information used to configure an additional uplink bandwidth portion (not for the initial BWP) (hereinafter referred to as BWP uplink information (e.g., BWP-Uplink)). The uplink configuration common SIB information may be included in information used in SIB1 to configure cell-specific parameters of the serving cell of UE100 (hereinafter referred to as serving cell configuration common SIB information (e.g., ServingCellConfigCommonSIB)).

[0056] The RACH configuration common information may include information used to identify random access parameters for both regular random access and beam failure recovery (hereinafter referred to as RACH configuration general information (e.g., RACH-ConfigGeneric)).

[0057] The RACH configuration general information includes, for example, a PRACH configuration index (e.g., prach-ConfigurationIndex, msgA-PRACH-ConfigurationIndex), information on the number of PRACH transmission opportunities (e.g., msg1-FDM, msgA-RO-FDM), information on the maximum number of RA preambles (e.g., preambleTransMax), and information on power control of PRACH transmission. The information may include information on the RA response reception window length (e.g., ra-ResponseWindow, msgB-ResponseWindow), information on the RA response reception window length (e.g., powerRampingStep, preambleReceivedTargetPower, msgA-PreamblePowerRampingStep, msgA-PreambleReceivedTargetPower), and information on the RA response reception window length (e.g., ra-ResponseWindow, msgB-ResponseWindow).

[0058] The information regarding the maximum number of RA preambles may indicate, for example, the maximum number of RA preamble transmissions performed before declaring failure. The information regarding power control of PRACH transmissions may indicate RA parameters for controlling the transmission power of RA preambles. The information regarding power control of PRACH transmissions may include, for example, information indicating a power ramping step for PRACH (e.g., powerRampingStep, msgA-PreamblePowerRampingStep) and information indicating a target power level at the network receiving side (e.g., preambleReceivedTargetPower, msgA-PreambleReceivedTargetPower). The information on the receiving window length of the RA response may include information indicating the receiving window length of message 2 (e.g., ra-ResponseWindow), or may include information indicating the receiving (monitoring) window length of message B (e.g., msgB-ResponseWindow). The information on the receiving window length may be indicated, for example, by the number of slots.

[0059] In addition, the RACH configuration common information may include information indicating (a value for) a contention resolution timer (hereinafter referred to as second timer information or contention resolution timer information (for example, ra-ContentionResolutionTimer)). The value may be an initial value.

[0060] Here, the SIB1 message may include retransmission parameters, which are RA parameters used to control retransmission of RA preambles on PRACH opportunities in the RA procedure. The retransmission parameters may include, for example, the maximum number of RA preambles, the receive window length, and (a 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 necessarily include RA parameters for controlling the transmission power of the RA preamble.

[0061] The retransmission parameters may include normal retransmission parameters (hereinafter referred to as first retransmission parameters) used when changing the periodicity of PRACH opportunities by RRC signaling. The first retransmission parameters may include, for example, parameters included in the RACH configuration common information specified in 3GPP technical specifications prior to Release 19.

[0062] Furthermore, the control unit 230 of the base station 200 may include configuration information related to dynamic adaptation (hereinafter referred to as DA configuration information) in the SIB1 message. Note that, if the cell supports dynamic adaptation, the control unit 230 may include the DA configuration information in the SIB1 message. On the other hand, if the cell does not support dynamic adaptation, the control unit 230 does not need to include the DA configuration information in the SIB1 message.

[0063] Here, the dynamic adaptation may be referred to as, for example, dynamic RACH adaptation. The dynamic adaptation may be, for example, at least one of the following actions (or definitions):

[0064] 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, an RNTI by which a CRC added to the downlink control information including information used to switch the RA configuration is scrambled may be specified. 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.

[0065] - UE100 supports multiple PRACH configurations.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] Change of PRACH configuration based on signaling in layers lower than the RRC layer

[0071] The PRACH settings are settings related to the control of PRACH transmission. The PRACH settings may include, for example, RA settings. The PRACH settings may include parameters related to the control of PRACH transmission. The PRACH settings 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 periodicity of PRACH opportunities. The PRACH settings may include, for example, RA parameters related to the control of PRACH transmission.

[0072] The DA configuration information may include a specific PDCCH configuration for dedicated monitoring of a PDCCH (or DCI) that triggers a change in the RA configuration. The specific PDCCH configuration may be information for configuring a search space (common search space) dedicated to dynamic adaptation and / or a CORESET. Note that the control unit 230 may include the specific PDCCH configuration in another system information block (e.g., SIBx) or in an individual RRC message.

[0073] 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.

[0074] 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.

[0075] As shown in Fig. 6, for example, a RACH adaptation configuration list (e.g., RACHAdaptation-ConfigList(-r19)) may be included in the BWP uplink common information. The BWP uplink common information may include the RACH adaptation configuration list separately from the RACH configuration common information including the first RA parameters described below (see E1 in Fig. 6). A 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 described below (see E2 in Fig. 6).

[0076] 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.

[0077] The specific RA configuration may be a dynamic adaptation-dedicated RA configuration. The specific RA configuration may include, for example, a dynamic adaptation-dedicated PRACH preamble format and a dynamic adaptation-dedicated time domain allocation configuration of PRACH opportunities. The specific RA configuration may include a dynamic adaptation-dedicated PRACH configuration index as the index.

[0078] Furthermore, (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 association 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 configuration of 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 ｆmod 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”.

[0079] Furthermore, the DA configuration information may include dedicated RA parameters (hereinafter sometimes referred to as second RA parameters) that are applied (used) only while dynamic adaptation is being performed. The second RA parameters may be RA parameters that are changed by lower layer signaling. The second RA parameters may be specific RA parameters that are used exclusively when the periodicity of PRACH opportunities is 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.

[0080] The second retransmission parameter may be included in at least one of, for example, (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), or (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 may be information newly specified in a technical specification released after the release in which dynamic adaptation was introduced.

[0081] 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.

[0082] 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. 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.

[0083] In this way, the transmitter 211 of the base station 200 can transmit the retransmission parameter (for example, the second retransmission parameter) to the UE 100 by using the SIB1 message. The receiver 112 of the UE 100 can receive the retransmission parameter (for example, the second retransmission parameter) from the base station 200.

[0084] Step S102: The transmitter 211 of the base station 200 transmits signaling of a layer lower than the RRC layer to the UE 100. The receiver 112 of the UE 100 receives the signaling of the lower layer from the base station 200. The signaling of the lower layer may be DCI. The signaling of the lower layer may be a PDCCH carrying DCI. The signaling of the lower layer may be signaling in the MAC layer (e.g., MAC CE). In this operation example, the description will proceed assuming that the signaling of the lower layer is DCI.

[0085] For example, when changing the PRACH period of UE 100, transmission unit 211 of base station 200 may transmit DCI (hereinafter referred to as specific DCI) that includes a specific field for changing the PRACH period (or in which a specific field is set). Note that when not changing the PRACH period of UE 100, transmission unit 211 may transmit DCI (hereinafter sometimes referred to as normal DCI) that does not include a specific field (or in which a specific field is not set). The specific DCI may be information that triggers a change in the PRACH period of UE 100 and / or a change in the RA setting. On the other hand, the normal DCI may be information that does not trigger a change in the PRACH period of UE 100 and / or a change in the RA setting.

[0086] The specific field may be a field for changing the PRACH period. Furthermore, the specific field may be, for example, a field for changing the RA setting. The specific field may include specific field information. The specific field information may be information for changing the PRACH period. Furthermore, the specific field information may be information for changing the random access setting. Details of the specific field information will be described later.

[0087] When a specific PDCCH configuration is configured for UE 100, transmitter 211 of base station 200 may transmit the specific DCI in a search space and / or CORESET dedicated to dynamic adaptation. Note that transmitter 211 may transmit the normal DCI in a search space and / or CORESET configured by a normal PDCCH configuration.

[0088] The specific DCI may be a DCI to which a CRC (also referred to as a CRC parity bit) scrambled with a predetermined Radio Network Temporary Identifier (RNTI) is added. The specific DCI may be information that triggers a change in RA configuration. A PDCCH including a specific DCI may be referred to as a PDCCH with a predetermined RNTI or as a PDCCH addressed to a predetermined RNTI. The predetermined RNTI may be an SI-RNTI, a P-RNTI, an RA-RNTI, and / or an RNTI dedicated to dynamic adaptation.

[0089] Note that the search space and CORESET for monitoring a specific DCI may be configured for each of one or more DL BWPs in the UE 100. In this case, the control unit 120 of the UE 100 may perform control to perform dynamic adaptation (PRACH transmission based on the dynamic adaptation) in an uplink bandwidth portion (UL BWP) corresponding to the DL BWP in which the DCI is received.

[0090] The control unit 120 of the UE 100 may determine whether the received DCI is a normal DCI or a specific DCI. The control unit 120 may make this determination based on, for example, whether the received DCI includes a specific field (and / or specific field information). The control unit 120 may make this determination by, for example, any of the following methods.

[0091] First, the control unit 120 may determine the received DCI as a specific DCI when, for example, decoding of the PDCCH using a predetermined RNTI (e.g., an RNTI dedicated to dynamic adaptation) is successful. On the other hand, the control unit 120 may determine the received DCI as a normal DCI when decoding of the PDCCH using a predetermined RNTI (e.g., an RNTI dedicated to dynamic adaptation) is unsuccessful.

[0092] Second, when a dedicated PDCCH configuration is configured, the control unit 120 may determine that DCI received in a search space and / or CORESET dedicated to dynamic adaptation is a specific DCI, whereas the control unit 120 may determine that DCI received in a search space and / or CORESET configured by a normal PDCCH configuration is a normal DCI.

[0093] Third, when the control unit 120 receives DCI determination information for determining a specific DCI from the base station 200, the control unit 120 may make a determination based on the DCI determination. Note that the transmission unit 211 of the base station 200 transmits the DCI determination information to the UE 100. The reception unit 112 of the UE 100 receives the DCI determination information from the base station 200. The DCI determination information may be included in the DA setting information, for example.

[0094] The DCI determination information may be, for example, information indicating whether or not the DCI includes a specific field and / or specific field information. When the DCI determination information indicates that the DCI includes a specific field and / or specific field information, the control unit 120 may determine that the received DCI is a specific DCI. On the other hand, when the DCI determination information indicates that the DCI does not include a specific field and / or specific field information, the control unit 120 may determine that the received DCI is a normal DCI.

[0095] In this operation example, the explanation will proceed on the assumption that the control unit 120 of the UE 100 determines that the received DCI is a specific DCI.

[0096] Note that, for example, when the control unit 120 of the UE 100 has not received second RA parameters that are changed by lower layer signaling, the control unit 120 may ignore the specific DCI even if the specific DCI is received. For example, when the SIB1 message does not include RACH adaptation configuration information, the control unit 120 may ignore the specific DCI. When ignoring the specific DCI, the control unit 120 may perform PRACH transmission that is not based on dynamic adaptation and / or a random access procedure that is not based on dynamic adaptation. When ignoring the specific DCI, the control unit 120 may not perform the random access procedure. Therefore, the control unit 120 may regard the specific DCI itself as invalid.

[0097] Step S103: The control unit 120 of the UE 100 determines a PRACH opportunity. The control unit 120 may also specify a PRACH period. The control unit 120 may perform at least one of the following methods, for example.

[0098] In a first method, the control unit 120 may change (select) the RA setting used to determine a PRACH opportunity based on a specific DCI. The control unit 120 selects the changed RA setting as the RA setting to be used in the RA procedure. The control unit 120 may determine a PRACH opportunity and a PRACH period based on the changed RA setting (selected RA setting). The control unit 120 may determine the PRACH opportunity and the PRACH period based on specific field information included in a specific field.

[0099] The specific field information may include, for example, information indicating an index. The control unit 120 may change to the RA configuration indicated by the index. When multiple RA configurations are configured in the UE 100, the control unit 120 of the UE 100 may change to the RA configuration indicated by the index among the multiple configured RA configurations. The control unit 120 may, for example, select a specific RA configuration associated with the index from among multiple specific RA configurations in the RACH adaptation configuration list. This allows the control unit 120 to select a specific RA configuration to be used in the RA procedure based on lower layer signaling.

[0100] Furthermore, the specific field information may include information indicating the order in which a specific RA configuration is entered in the RACH adaptation configuration list. The control unit 120 may select a specific RA configuration in the order indicated by the information and change to the selected RA configuration. In this way, the control unit 120 can select a specific RA configuration to be used in the RA procedure.

[0101] The control unit 120 determines the radio frame to which the PRACH opportunity is allocated, the slot to which the PRACH opportunity is allocated, and the symbol to which the PRACH opportunity is allocated based on the changed RA configuration, thereby determining the PRACH opportunity and the PRACH period.

[0102] In a second method, the control unit 120 may specify a changed PRACH period based on a setting value for adjusting the PRACH period. For example, the control unit 120 may calculate a different PRACH period based on a setting value for a PRACH period based on an already set RA setting. The control unit 120 may specify the calculated PRACH period as the changed PRACH period. Furthermore, the control unit 120 may calculate a different PRACH period based on a setting value for a PRACH period based on an RA setting (or a specific RA setting) determined by the first method.

[0103] The configuration value may be a scaling factor for changing the periodicity. The scaling factor may be a scaling factor that extends the periodicity of a baseline RA configuration (or a specific RA configuration). The control unit 230 of the base station 200 may include the configuration value in a specific DCI, for example. The receiving unit 112 of the UE 100 may receive the configuration value from the base station 200.

[0104] In the second method, the control unit 120 may use either the first RA setting or the second RA setting as the RA setting to determine the PRACH opportunity.

[0105] Step S104: The control unit 120 of the UE 100 determines RA parameters to be used in the random access procedure. The control unit 120 may determine, for example, either the first RA parameters or the second RA parameters as the RA parameters to be used in the RA procedure.

[0106] For example, when the PRACH period or RA settings have been changed by RRC signaling, the control unit 120 may determine the first RA parameters as the RA parameters to be used in the RA procedure.

[0107] On the other hand, the control unit 120 may determine the second RA parameters as the RA parameters to be used in the RA procedure, for example, in at least one of the following cases: - When the PRACH cycle or the RA setting has been changed based on dynamic adaptation - When the PRACH cycle or the RA setting has been changed based on a specific DCI - When the second RA setting has been selected or changed to the second RA setting as the setting to be used in the random access procedure

[0108] For example, when each of the multiple second RA configurations is associated with a second RA parameter, the control unit 120 may use the second RA parameter associated with the selected second RA configuration (i.e., the changed RA configuration). Therefore, the control unit 120 may use the second retransmission parameter associated with the selected second RA configuration in the RA procedure. The control unit 120 may use the second retransmission parameter when receiving a specific DCI.

[0109] The control unit 120 executes the RA procedure using the determined RA parameters, and controls the retransmission of the RA preamble based on the retransmission parameters.

[0110] 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 PRACH period by signaling in the RRC layer, i.e., the first RA parameter, even when the PRACH period is changed by signaling in a lower layer.

[0111] Note that, when changing the RA configuration (and / or the 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 PRACH period, the PRACH configuration period, the association period, and / or the association pattern period.

[0112] The SSB may be a cell-defining SSB (CD-SSB) and / or a non-cell defining SSB (NCD). The UE 100 may always perform dynamic adaptation based on the CD-SSB. The control unit 120 of the UE 100 may include information for setting the subcarrier spacing for the SSB in the serving cell and / or the downlink bandwidth portion (DL BWP) in the SIB or in an RRC message.

[0113] Furthermore, information for setting subcarrier spacing for the PRACH may be included in RACH configuration information (e.g., RACH-config common). This information may be included in predetermined configuration information (e.g., BWP-UplinkCommon) within the RACH configuration information. "BWP-UplinkCommon" may be information used to set common parameters for uplink BWPs. The subcarrier spacing may be set for each of one or more DL BWPs (e.g., initial DL BWP and / or dedicated DL BWP) and one or more UL BWPs (e.g., initial UL BWP and / or dedicated UL BWP).

[0114] Step S105: 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 200. The receiver 212 of the base station 200 receives the RA preamble (message 1) from the UE 100.

[0115] 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.

[0116] 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.

[0117] 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.

[0118] Step S106: The transmitting unit 211 of the base station 200 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 200.

[0119] Step S107: The transmitter 111 of the UE 100 transmits the message 3 to the base station 200. The receiver 212 of the base station 200 receives the message 3 from the UE 100.

[0120] 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.

[0121] 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.

[0122] 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 S105 again.

[0123] Step S108: The transmitter 211 of the base station 200 transmits the message 4 to the UE 100. The receiver 112 of the UE 100 receives the message 4 from the base station 200.

[0124] As described above, the transmitter 211 of the base station 200 transmits retransmission parameters, which are random access parameters used to control the retransmission of RA preambles at PRACH opportunities in the RA procedure, to the UE 100. The receiver 112 of the UE 100 receives the retransmission parameters from the base station 200. The controller 120 controls the retransmission of the RA preamble based on the retransmission parameters. The retransmission parameters include specific retransmission parameters that are used exclusively when changing the periodicity of PRACH opportunities by signaling in a layer lower than the RRC layer. This enables the UE 100 to use the specific retransmission parameters when controlling the retransmission of RA preambles. Since the specific retransmission parameters can be set separately from the values ​​of normal retransmission parameters, it is possible to flexibly control the random access procedure when dynamic adaptation of PRACH opportunities is performed. As a result, it is possible to appropriately perform the random access procedure when dynamic adaptation of PRACH opportunities is performed. Furthermore, the base station 200 can flexibly control the RA procedure by setting appropriate retransmission parameters to the UE 100 according to the state of the PRACH transmission load of the plurality of UEs 100, for example. Furthermore, by setting appropriate retransmission parameters, the base station 200 makes it difficult for the RA procedure to fail, and can suppress a delay until the RA procedure is completed.

[0125] Additionally, the specific retransmission parameters may be included in the SIB1 message, which allows the base station 200 to save energy in the network 10, since it does not need to notify each UE 100 individually of the specific retransmission parameters.

[0126] The specific retransmission parameters may include at least one of a value indicating a reception window length for an RA response that is a response to an RA preamble, a value of a contention resolution timer that triggers retransmission of the RA preamble, and a value indicating a maximum number of times the RA preamble is transmitted, thereby enabling flexible control of the random access procedure when dynamic adaptation of PRACH opportunities is performed.

[0127] For example, the control unit 230 of the base station 200 can set the maximum number of RA preambles of the second retransmission parameter to a value different from the maximum number of RA preambles of the first retransmission parameter. Furthermore, the control unit 230 of the base station 200 can set the receive window length of the second retransmission parameter to a value different from the receive window length of the first retransmission parameter. Furthermore, the base station 200 can set the contention resolution timer (value for) of the second retransmission parameter to a value different from the contention resolution timer (value for) of the first retransmission parameter. This enables flexible control of the random access procedure when dynamic adaptation of PRACH opportunities is performed.

[0128] Note that the control unit 230 of the base station 200 may set the maximum number of RA preambles of the second retransmission parameter used when changing the PRACH period to a longer period by lower layer signaling, for example, to a value greater than the maximum number of RA preambles of the first retransmission parameter. Here, a longer PRACH period reduces opportunities for PRACH transmission, making it more likely that RA preambles from multiple UEs 100 will collide, making it more difficult to successfully transmit the RA preambles. However, a larger value for the maximum number of RA preambles increases the number of times PRACH transmission is retransmitted before the random access procedure is deemed to have been successfully completed, making it less likely that the random access procedure will fail.

[0129] On the other hand, the control unit 230 of the base station 200 may set the maximum number of RA preambles of the second retransmission parameter used when changing the PRACH period to a shorter period by lower layer signaling to a value smaller than the maximum number of RA preambles of the first retransmission parameter. Here, shortening the PRACH period increases the opportunities for PRACH transmission, making it less likely that RA preambles from multiple UEs 100 will collide, and making it easier to successfully transmit the RA preambles. In such a case, a small value for the maximum number of RA preambles reduces, for example, the number of times the PRACH transmission is retransmitted before the random access procedure is deemed to have been successfully completed. Even in such a case, if the random access procedure fails, it becomes easier for the UE 100 to select another resource as the PRACH resource to be used for the random access procedure.

[0130] Furthermore, the control unit 230 of the base station 200 may set the receive window length of the second retransmission parameter, which is used when changing the PRACH period to a longer period by lower layer signaling, to a value greater than the receive window length of the first retransmission parameter. Here, it is assumed that multiple UEs 100 temporarily concentrate on a small number of PRACH transmission opportunities to transmit RA preambles via the PRACH. When resources within a certain period are limited, the base station 200 that has received many RA preambles may run out of resources for transmitting message 2 within the certain period and must use resources later than the certain period as resources for transmitting part of message 2. As a result, the receive window of the first retransmission parameter may expire by the time the UE 100 receives message 2, which may cause the UE 100 to retransmit the RA preamble even though the base station 200 is attempting to transmit message 2. Therefore, by setting the receive window length of the second retransmission parameter to a value greater than the receive window length of the first retransmission parameter, the UE 100 is more likely to receive the message 2 before the receive window of the second retransmission parameter expires, even in a case where resources later than a certain period must be used as resources for transmitting part of the message 2. As a result, the UE 100 can be prevented from retransmitting the RA preamble even when the base station 200 is about to transmit the message 2, and the random access procedure can be appropriately performed.

[0131] Furthermore, the control unit 230 of the base station 200 may set the contention resolution timer (value for) of the second retransmission parameter, which is used when changing the PRACH period to a longer period by lower layer signaling, to a value greater than the contention resolution timer (value for) of the first retransmission parameter. As with message 2, the contention resolution timer of the first retransmission parameter may expire by the time the UE 100 receives message 4, which may cause the UE 100 to retransmit the RA preamble despite the base station 200 attempting to transmit message 4. Therefore, by setting the contention resolution timer (value for) of the second retransmission parameter to a value greater than the contention resolution timer (value for) of the first retransmission parameter, the UE 100 is more likely to receive message 4 before the contention resolution timer of the second retransmission parameter expires. As a result, it is possible to prevent the UE 100 from retransmitting the RA preamble despite the base station 200 attempting to transmit message 4, and it is possible to appropriately execute the random access procedure.

[0132] Furthermore, the control unit 120 may use the specific retransmission parameter when receiving lower layer signaling for changing the periodicity of the PRACH opportunity. As a result, when the control unit 120 changes the PRACH periodicity by the conventional method, i.e., by RRC layer signaling, the specific retransmission parameter is not used (i.e., normal retransmission parameter is used), thereby making it possible to appropriately use the normal retransmission parameter and the specific retransmission parameter.

[0133] Furthermore, when the control unit 120 has not received the random access parameters changed by the signaling of the lower layer, even if the control unit 120 has received the signaling of the lower layer for changing the period of the PRACH opportunity, the control unit 120 may ignore the signaling of the lower layer. This prevents the UE 100 from using an incorrect random access parameter, and therefore allows the UE 100 to properly execute the random access procedure.

[0134] Furthermore, the receiving unit 112 may receive a list configured of multiple specific RA configurations used to set the periodicity of PRACH opportunities and changed by lower layer signaling from the base station 200. The control unit 120 may select a specific RA configuration to be used in the RA procedure based on the lower layer signaling from the base station 200. This allows the base station 200 to set multiple RA configurations for the UE 100, thereby enabling flexible control of PRACH transmission.

[0135] Furthermore, the lower layer signaling may include information indicating the order in which a specific RA configuration is entered in the RACH adaptation configuration list. The control unit 120 may select the specific RA configuration in the order indicated by the information. This makes it possible to specify a specific RA configuration without including an index in the RACH adaptation configuration list, thereby saving radio resources.

[0136] Furthermore, each of the multiple specific RA configurations may be associated with an index. Lower layer signaling may include information indicating the index. The control unit 120 may select the specific RA configuration associated with the index. This enables the base station 200 to associate, for example, information not included in the RACH adaptation configuration list with the specific RA configuration via the index. As a result, the base station 200 can specify other information along with the specific RA configuration to the UE 100, thereby enabling flexible control of PRACH transmission.

[0137] Furthermore, each of the multiple specific RA configurations may be associated with specific retransmission parameters. The control unit 120 may use the specific retransmission parameters associated with the selected specific RA configuration in the RA procedure. This allows the base station 200 to specify the specific RA configuration and the specific retransmission parameters to the UE 100, thereby enabling flexible control of PRACH transmission.

[0138] The control unit 120 may use, as the RA parameter for controlling the transmission power of the RA preamble, a parameter used when changing the period of the PRACH opportunity by signaling in the RRC layer, even when the period of the PRACH opportunity is changed by signaling in a lower layer. The transmission power of the RA preamble is less likely to be affected by a failure of the random access procedure due to a change in the PRACH period, compared to, for example, the receive window and the contention resolution timer. Therefore, the base station 200 can omit transmitting a parameter for controlling the transmission power of the preamble that is used exclusively when changing the period of the PRACH opportunity by signaling in a lower layer, thereby saving radio resources.

[0139] Second Embodiment A second embodiment will be described with reference to Figures 7 and 8. Previous descriptions may be omitted.

[0140] 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.

[0141] 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.

[0142] 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.

[0143] An NES cell may be, for example, a cell managed by base station 200 that follows certain behaviors related to NES capabilities.

[0144] As shown in FIG. 7, the control unit 120 of the non-NES capable UE 100 may perform the following operations when attempting to access an NES cell.

[0145] 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.

[0146] 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.

[0147] 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.

[0148] 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.

[0149] 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.

[0150] 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.

[0151] 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.

[0152] 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.

[0153] Step S1030: The control unit 120 does not access the NES cell, and may search for other cells.

[0154] 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. 8 .

[0155] 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.

[0156] 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.

[0157] 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.

[0158] 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.

[0159] 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.

[0160] 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.

[0161] 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).

[0162] 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).

[0163] 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.

[0164] 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.

[0165] Step S1043: The control unit 120 performs PRACH transmission using the normal RA setting.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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.

[0171] 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.

[0172] (Other Embodiments) 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. Message 2 may be replaced with message B. Furthermore, in the above-described embodiment, "PRACH" may be replaced with "RACH".

[0173] 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.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] 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.

[0178] 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)).

[0179] 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.

[0180] 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.

[0181] (Additional Notes) Additional notes will be given regarding the features of the above-described embodiment.

[0182] (Supplementary Note 1) A communication device comprising: a receiving unit that receives retransmission parameters from a base station, the retransmission parameters being random access parameters used for controlling retransmission of RA preambles on physical random access channel (PRACH) opportunities in a random access (RA) procedure; and a control unit that controls retransmission of the RA preamble based on the retransmission parameters, wherein the retransmission parameters include specific retransmission parameters that are exclusively used when a periodicity of the PRACH opportunities is changed by signaling in a layer lower than a radio resource control (RRC) layer.

[0183] (Supplementary Note 2) The communications device according to Supplementary Note 1, wherein the specific retransmission parameters are included in a System Information Block Type 1 message.

[0184] (Supplementary Note 3) The communication device according to Supplementary Note 1 or 2, wherein the specific retransmission parameters include at least one of a value indicating a receive window length of an RA response that is a response to the RA preamble, a value of a contention resolution timer that triggers retransmission of the RA preamble, and a value indicating a maximum number of times the RA preamble is transmitted.

[0185] (Supplementary Note 4) The communication device according to any one of Supplementary Notes 1 to 3, wherein the control unit uses the specific retransmission parameter when receiving signaling from the lower layer for changing a periodicity of the PRACH opportunity.

[0186] (Supplementary Note 5) The communication device according to any one of Supplementary Notes 1 to 4, wherein the control unit, when not receiving a random access parameter changed by signaling from the lower layer, ignores the signaling from the lower layer even if the control unit receives signaling from the lower layer for changing a periodicity of the PRACH opportunity.

[0187] (Supplementary Note 6) The communication device according to any one of Supplementary Notes 1 to 5, wherein the receiver receives from the base station a list consisting of a plurality of specific random access (RA) configurations used to set a periodicity of the PRACH opportunity and changed by the lower layer signaling, and the controller selects a specific RA configuration to be used in the RA procedure based on the lower layer signaling from the base station.

[0188] (Supplementary Note 7) The communication device according to Supplementary Note 6, wherein the lower layer signaling includes information indicating an order in which the specific RA configuration is entered in the list, and the control unit selects the specific RA configuration in the order indicated by the information.

[0189] (Supplementary Note 8) The communication device according to Supplementary Note 6, wherein each of the plurality of specific RA configurations is associated with an index; the lower layer signaling includes information indicating the index; and the control unit selects the specific RA configuration associated with the index.

[0190] (Supplementary Note 9) The communication device according to any one of Supplementary Notes 6 to 8, wherein each of the plurality of specific RA settings is associated with the specific retransmission parameter, and the control unit uses the specific retransmission parameter associated with the selected specific RA setting in the RA procedure.

[0191] (Supplementary Note 10) The communication device according to any one or 2 of Supplementary Notes 1 to 9, wherein the control unit uses, as an RA parameter for controlling the transmission power of the RA preamble, a parameter used when changing a periodicity of the PRACH opportunities by signaling of the RRC layer, even when the periodicity of the PRACH opportunities is changed by signaling of the lower layer.

[0192] (Supplementary Note 11) A base station comprising: a transmitter that transmits, to a communication device, retransmission parameters, which are random access parameters used for retransmission control of RA preambles at physical random access channel (PRACH) opportunities in a random access (RA) procedure, wherein the retransmission parameters include a specific retransmission parameter that is exclusively used when a periodicity of the PRACH opportunities is changed by signaling in a layer lower than a radio resource control (RRC) layer.

[0193] (Supplementary Note 12) A communication method executed by a communication device, comprising: a step of receiving, from a base station, retransmission parameters, which are random access parameters used for controlling retransmission of RA preambles on physical random access channel (PRACH) opportunities in a random access (RA) procedure; and a step of controlling retransmission of the RA preamble based on the retransmission parameters, wherein the retransmission parameters include a specific retransmission parameter that is used exclusively when a periodicity of the PRACH opportunities is changed by signaling in a layer lower than a radio resource control (RRC) layer.

Claims

1. A communications device (100) comprising: a receiving unit (112) that receives retransmission parameters from a base station (200), the retransmission parameters being random access parameters used for controlling retransmission of an RA preamble on a physical random access channel (PRACH) opportunity in a random access (RA) procedure; and a control unit (120) that controls retransmission of the RA preamble based on the retransmission parameters, wherein the retransmission parameters include specific retransmission parameters that are used exclusively when the period of the PRACH opportunity is changed by signaling in a layer lower than a radio resource control (RRC) layer.

2. The communication device of claim 1, wherein the specific retransmission parameters are included in a System Information Block Type 1 message.

3. The communication device according to claim 1 or 2, wherein the specific retransmission parameters include at least one of a value indicating a receiving window length of an RA response which is a response to the RA preamble, a value of a contention resolution timer which triggers retransmission of the RA preamble, and a value indicating a maximum number of times the RA preamble is transmitted.

4. The communication device according to claim 1 or 2, wherein the control unit uses the specific retransmission parameter when receiving signaling from the lower layer for changing the periodicity of the PRACH opportunities.

5. The communication device according to claim 1 or 2, wherein the control unit, when not receiving random access parameters changed by signaling from the lower layer, ignores the lower layer signaling even if it receives signaling from the lower layer for changing the periodicity of the PRACH opportunities.

6. The communication device described in claim 1 or 2, wherein the receiving unit receives from the base station a list consisting of a plurality of specific random access (RA) settings used to set the periodicity of the PRACH opportunities and changed by the lower layer signaling, and the control unit selects a specific RA setting to be used in the RA procedure based on the lower layer signaling from the base station.

7. The communication device according to claim 6, wherein the lower layer signaling includes information indicating the order in which the specific RA setting is entered in the list, and the control unit selects the specific RA setting in the order indicated by the information.

8. The communication device according to claim 6, wherein each of the plurality of specific RA configurations is associated with an index, the lower layer signaling includes information indicating the index, and the control unit selects the specific RA configuration associated with the index.

9. The communication device according to claim 6, wherein each of the plurality of specific RA settings is associated with the specific retransmission parameter, and the control unit uses the specific retransmission parameter associated with the selected specific RA setting in the RA procedure.

10. The communication device described in claim 1 or 2, wherein the control unit uses, as an RA parameter for controlling the transmission power of the RA preamble, a parameter used when changing the periodicity of the PRACH opportunities by signaling of the RRC layer, even when the periodicity of the PRACH opportunities is changed by signaling of the lower layer.

11. A base station (200), comprising: a transmitting unit (211) that transmits retransmission parameters, which are random access parameters used for retransmission control of an RA preamble at a physical random access channel (PRACH) opportunity in a random access (RA) procedure, to a communication device, wherein the retransmission parameters include a specific retransmission parameter that is exclusively used when the period of the PRACH opportunity is changed by signaling of a layer lower than a radio resource control (RRC) layer.

12. A communication method executed by a communication device (100), comprising the steps of: receiving from a base station (200) a retransmission parameter, which is a random access parameter used for controlling retransmission of an RA preamble on a physical random access channel (PRACH) opportunity in a random access (RA) procedure; and controlling retransmission of the RA preamble based on the retransmission parameter, wherein the retransmission parameter includes a specific retransmission parameter used exclusively when changing the period of the PRACH opportunity by signaling of a layer lower than a radio resource control (RRC) layer.

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