Communication device and communication method

Abstract

A communication device (100, 100B), which is a second communication device (100B) having reduced communication capability compared to a first communication device (100A) having prescribed communication capability, comprises a control unit (140) that performs a random access procedure in a radio resource control (RRC) idle state or an RRC inactive state by using a specific initial bandwidth part (BWP) which is a BWP forming a portion of the bandwidth for a cell of a base station (200) and which is for the second communication device (100B). When a cell-defining synchronization signal and physical broadcast channel block (CD-SSB) do not exist in the specific initial BWP, the control unit (140) switches, on the basis of the failure of the random access procedure, from the specific initial BWP to an initial BWP where the CD-SSB exists.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims the benefit of priority from Patent Application No. 2022-019075, filed February 9, 2022, the entire contents of which are incorporated herein by reference. [Technical Field]

[0002] The present disclosure relates to a communication device and a communication method used in a mobile communication system. [Background technology]

[0003] In recent years, 3GPP (registered trademark, the same applies hereinafter) (3rd Generation Partnership Project) has been considering introducing a second communication device having reduced communication capabilities compared to a general communication device (hereinafter referred to as a first communication device) into a 5G system. The second communication device is a communication device with mid-range performance and price for IoT (Internet of Things), and, for example, compared to the first communication device, the second communication device has a narrower maximum bandwidth for the bandwidth part (BWP) used for wireless communication and a smaller number of receivers.

[0004] Here, when introducing the initial BWP for the second communication device in a 3GPP mobile communication system, it has been agreed that the initial BWP for the second communication device (hereinafter referred to as a specific initial BWP) will be set independently from the initial BWP for the first communication device (hereinafter referred to as a default initial BWP).

[0005] It is agreed that the second communication device, when in an RRC (Radio Resource Control) idle state or an RRC inactive state, monitors paging in an initial BWP in which a cell-defining-synchronization signal and a physical broadcast channel block (Cell Defining-Synchronization Signal Block: CD-SSB) exist, and performs cell (re)selection and measurement in the CD-SSB. Also, it is agreed that the second communication device, when a specific initial BWP is configured, performs a random access procedure in the specific initial BWP (see, for example, Non-Patent Document 1). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] 3GPP contribution: R2-2201662 Summary of the Invention

[0007] A communication device according to a first aspect is a second communication device having reduced communication capability compared to a first communication device having a predetermined communication capability. The communication device includes a control unit configured to execute a random access procedure using a specific initial BWP for the second communication device, the specific initial BWP being a bandwidth portion (BWP) that is a part of the bandwidth of a cell of a base station, in a Radio Resource Control (RRC) idle state or an RRC inactive state. If a Cell-Defined Synchronization Signal and Physical Broadcast Channel Block (CD-SSB) is not present in the specific initial BWP, the control unit switches from the specific initial BWP to an initial BWP in which the CD-SSB is present, based on a failure of the random access procedure.

[0008] A second aspect of the present invention relates to a second communication device having reduced communication capabilities compared to a first communication device having predetermined communication capabilities. The communication device includes: a control unit that performs a random access procedure in a Radio Resource Control (RRC) idle state or an RRC inactive state using a specific initial BWP, which is a bandwidth portion (BWP) of a cell of a base station and is intended for the second communication device; and a transmission unit that transmits an RRC connection establishment or RRC connection resumption request message to the base station during the random access procedure. When a Cell Definition Synchronization Signal and Physical Broadcast Channel Block (CD-SSB) is not present in the specific initial BWP, the control unit switches from the specific initial BWP to the initial BWP based on receiving an RRC rejection message from the base station in response to the request message.

[0009] A communication device according to a third aspect is a second communication device having reduced communication capabilities compared to a first communication device having predetermined communication capabilities. The communication device includes: a control unit that performs a random access procedure in a Radio Resource Control (RRC) idle state or an RRC inactive state using a specific initial BWP, which is a bandwidth portion (BWP) that is a part of the bandwidth of a cell of a base station and is intended for the second communication device; and a transmission unit that transmits an RRC connection establishment or RRC connection resumption request message to the base station during the random access procedure. When a Cell Definition Synchronization Signal and Physical Broadcast Channel Block (CD-SSB) is not present in the specific initial BWP, the control unit switches from the specific initial BWP to the initial BWP based on not receiving a response to the request message from the base station within a predetermined time after transmitting the request message.

[0010] A fourth aspect of the present invention relates to a second communication device having reduced communication capabilities compared to a first communication device having predetermined communication capabilities. The communication device includes: a control unit that executes a random access procedure in a Radio Resource Control (RRC) idle state or an RRC inactive state using a specific initial BWP, which is a portion of the bandwidth of a cell of a base station and is intended for the second communication device; and a transmission unit that transmits an RRC connection resumption request message to the base station during the random access procedure. When a cell-defined synchronization signal and physical broadcast channel block (CD-SSB) is not present in the specific initial BWP, the control unit switches from the specific initial BWP to the initial BWP based on an integrity check failure indicator indicating an integrity check failure being sent from a lower layer to an RRC layer within a predetermined time after receiving the request message.

[0011] A communication method according to a fifth aspect is a communication method executed by a communication device that is a second communication device having reduced communication capability compared to a first communication device having a predetermined communication capability, the communication method comprising: performing a random access procedure in a Radio Resource Control (RRC) idle state or an RRC inactive state using a specific initial BWP that is a part of a bandwidth of a cell of a base station and is intended for the second communication device; and, if a Cell Defined Synchronization Signal and Physical Broadcast Channel Block (CD-SSB) is not present in the specific initial BWP, switching from the specific initial BWP to an initial BWP in which the CD-SSB is present based on a failure of the random access procedure. [Brief explanation of the drawings]

[0012] The objects, features, advantages, and other features of the present disclosure will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. [Figure 1] FIG. 1 is a diagram showing a configuration of a mobile communication system according to an embodiment. [Figure 2]FIG. 2 is a diagram illustrating an example of the configuration of a protocol stack according to the embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example of a relationship between an SSB and an initial BWP according to the embodiment. [Figure 4] FIG. 4 is a sequence diagram for explaining an example of the operation of a UE in an RRC idle state or an RRC inactive state. [Figure 5] FIG. 5 is a diagram illustrating a configuration of a UE according to the embodiment. [Figure 6] FIG. 6 is a diagram illustrating a configuration of a base station according to the embodiment. [Figure 7] FIG. 7 is a flowchart illustrating an example of the operation of the UE according to the embodiment. [Figure 8] FIG. 8 is a diagram (part 1) for explaining an example of the operation of the UE according to the embodiment. [Figure 9] FIG. 9 is a diagram (part 2) for explaining an example of the operation of the UE according to the embodiment. [Figure 10] FIG. 10 is a diagram (part 3) for explaining an example of the operation of the UE according to the embodiment. [Figure 11] FIG. 11 is a diagram (part 4) for explaining an example of the operation of the UE according to the embodiment. [Figure 12] FIG. 12 is a diagram (part 5) for explaining an example of the operation of the UE according to the embodiment. [Figure 13] FIG. 13 is a diagram (part 6) for explaining an example of the operation of the UE according to the embodiment. [Figure 14] FIG. 14 is a diagram for explaining an example of the operation of a UE according to another embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] 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.

[0014] Assume that a second communication device in an RRC idle state or an RRC inactive state attempts to establish an RRC connection, for example, by a random access procedure, in a specific initial BWP in which no CD-SSB exists, but the RRC connection establishment fails. In this case, since no CD-SSB exists in the specific initial BWP, the second communication device cannot perform paging monitoring, cell (re)selection, and measurements, and may not be able to perform appropriate communication.

[0015] Therefore, one object of the present disclosure is to provide a communication device and a communication method that are capable of performing appropriate communication even when CD-SSB does not exist in the initial BWP for the second communication device.

[0016] (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, that is, a mobile communication system based on NR (New Radio Radio Access).

[0017] The mobile communication system 1 includes a network 10 and user equipment (UE) 100 that communicates with the network 10. The network 10 includes a next generation radio access network (NG-RAN) 20 that is a 5G radio access network, and a 5G core network (5GC) 30 that is a 5G core network.

[0018] UE100 is an example of a communication device. UE100 may be a mobile wireless communication device. UE100 may be a communication device that communicates via base station 200. UE100 may be a device used by a user. UE100 is 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. UE100 may be a vehicle (e.g., a car, a train, etc.) or a device provided therein (e.g., Vehicle UE). UE100 may be a transport vehicle other than a vehicle (e.g., a ship, an airplane, etc.) or a device provided therein (e.g., Aerial UE). UE100 may be a sensor or a device provided therein. Note that UE 100 may be referred to by other names such as terminal, terminal device, mobile station, mobile terminal, mobile device, mobile unit, subscriber station, subscriber terminal, subscriber device, subscriber unit, wireless station, wireless terminal, wireless device, wireless unit, remote station, remote terminal, remote device, or remote unit. Also, UE 100 is an example of a terminal, and terminals may include factory equipment, etc.

[0019] In this embodiment, two types of UEs are assumed as the NR UE 100: a general UE (general user equipment: general UE) 100A and a specific UE 100B having a communication capability reduced compared to the general UE 100A. The general UE 100A may have a predetermined communication capability. The specific UE 100B may have a communication capability reduced below the predetermined communication capability. The predetermined communication capability may be a capability based on at least one of a maximum bandwidth used for wireless communication and the number of receivers. The predetermined communication capability may be a capability defined by the maximum bandwidth and / or the number of receivers. The specific UE 100B may be a device having a narrower maximum bandwidth and / or a smaller number of receivers than the general UE 100A. The general UE 100A is a first communication device, and the specific UE 100B is a second communication device. The general UE 100A may be referred to as a general communication device, and the specific UE 100B may be referred to as a specific communication device. Furthermore, the specific UE 100B may be referred to as a RedCap user equipment (RedCap UE). The general UE 100A has advanced communication capabilities such as enhanced Mobile Broadband (eMBB) and Ultra-Reliable and Low Latency Communications (URLLC), which are features of NR. Therefore, the general UE 100A has higher communication capabilities than the specific UE 100B. The general UE 100A may also be referred to as a non-RedCap UE. The general UE 100A may be an existing UE, i.e., a UE prior to Release 16 (so-called legacy UE).

[0020] The specific UE 100B is a UE with reduced device cost and complexity compared to the general UE 100A. The specific UE 100B is a UE 100 with mid-range performance and price for IoT, and, for example, compared to the general UE 100A, the maximum bandwidth used for wireless communication is set narrower and the number of receivers is smaller. Note that the receivers are sometimes referred to as receiving branches. The specific UE 100B is sometimes referred to as a Reduced capability NR device.

[0021] Specifically, the specific UE 100B may be capable of communication at a communication speed equal to or greater than the communication speed specified in an LPWA (Low Power Wide Area) standard, for example, LTE Cat. (Long Term Evolution UE Category) 1 / 1bis, LTE Cat. M1 (LTE-M), or LTE Cat. NB1 (NB-IoT). The specific UE 100B may be capable of communication at a bandwidth equal to or greater than the bandwidth specified in the LPWA standard. The specific UE 100B may have a limited bandwidth used for communication compared to a Rel-15 or Rel-16 UE. For example, for FR1 (Frequency Range 1), the maximum bandwidth (also referred to as UE maximum bandwidth) supported by the specific UE 100B may be 20 MHz. Furthermore, for FR2 (Frequency Range 2), the maximum bandwidth supported by the specific UE 100B may be 100 MHz. The specific UE 100B may have only one receiver for receiving wireless signals. The specific UE 100B may be, for example, a wearable device or a sensor device.

[0022] The NG-RAN 20 includes multiple base stations 200. Each base station 200 manages at least one cell. A cell constitutes the smallest unit of a communication area. One cell belongs to one frequency (carrier frequency). The term "cell" may refer to wireless communication resources or to 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. 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. 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).

[0023] The 5GC 30 includes a core network device 300. The core network device 300 includes, for example, an Access and Mobility Management Function (AMF) and / or a User Plane Function (UPF). 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.

[0024] (Example of protocol stack configuration) Next, an example of the configuration of a protocol stack according to this embodiment will be described with reference to FIG.

[0025] The protocol for the wireless section between the UE 100 and the 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 an RRC layer.

[0026] 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.

[0027] The MAC layer performs data priority control, retransmission processing using Hybrid Automatic Repeat reQuest (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.

[0028] The RLC layer transmits data to the RLC layer on the receiving side using the functions of the MAC layer and 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.

[0029] The PDCP layer performs header compression / decompression and encryption / decryption.

[0030] An SDAP (Service Data Adaptation Protocol) layer may be provided above the PDCP layer, which maps IP flows, which are units for QoS control by the core network, to radio bearers, which are units for QoS control by the AS (Access Stratum).

[0031] 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 there is an RRC connection 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.

[0032] 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.

[0033] The UE 100 has an application layer and the like in addition to the radio interface protocol.

[0034] (Radio frame structure) 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 configured with 10 subframes. For example, one subframe may be 1 ms long. Furthermore, one subframe may be configured with one or more slots. For example, the number of symbols constituting one slot is 14 for a normal CP (Cyclic Prefix) and 12 for an extended CP. Furthermore, the number of slots constituting one subframe varies depending on the set subcarrier spacing. For example, for a normal CP, if the subcarrier spacing is set to 15 kHz, the number of slots per subframe is 1 (i.e., 14 symbols); if the subcarrier spacing is set to 30 kHz, the number of slots per subframe is 2 (i.e., 28 symbols); if the subcarrier spacing is set to 60 kHz, the number of slots per subframe is 4 (i.e., 56 symbols); and if the subcarrier spacing is set to 120 kHz, the number of slots per subframe is 8 (i.e., 128 symbols). Furthermore, when the subcarrier spacing is set to 60 kHz for the 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 base station 200. Also, the number of symbols constituting one subframe is determined based on the subcarrier spacing set by base station 200. That is, the number of symbols constituting a 1 ms subframe is determined based on the subcarrier spacing set by base station 200, and the length of each symbol (length in the time direction) changes.

[0035] (BWP) Bandwidth parts (hereinafter referred to as BWPs) are defined to reduce the power consumption of UE 100 and to effectively utilize wideband carriers. BWPs include initial BWPs (initial DL BWPs and initial UL BWPs) and dedicated BWPs (dedicated DL BWPs and dedicated UL BWPs). Up to four DL BWPs and up to four UL BWPs are configured in a serving cell for UE 100 according to its capabilities. In the following, when there is no need to distinguish between DL BWPs and UL BWPs, they are simply referred to as BWPs.

[0036] The initial BWP is a BWP used at least for initial access and is used in common by multiple UEs 100. The initial DL BWP and the initial UL BWP each have a BWP identifier, bwp-id, specified as "0". There are two types of initial BWPs: an initial BWP derived and set by a Master Information Block (MIB) transmitted on the PBCH, and an initial BWP set by a System Information Block (SIB), specifically, a System Information Block Type 1 (SIB1). The initial BWP set by the MIB has a bandwidth according to CORESET#0, which is set using parameters included in the MIB. The initial BWP set by SIB1 is set by various parameters (locationAndBandwidth, subcarrierSpacing, cyclicPrefix) included in a ServingCellConfigCommonSIB, which is an information element in SIB1.

[0037] During initial access to a cell, UE 100 receives a synchronization signal and a physical broadcast channel block (hereinafter, SSB) of the cell and acquires the bandwidth (24, 48, or 96 RBs) of the Type-0 PDCCH CSS set from the setting value of controlResourceSetZero (an integer value between 0 and 15) in pdcch-ConfigSIB1, which is an information element included in the PBCH (MIB). UE 100 then monitors the Type-0 PDCCH CSS set to acquire SIB1, and acquires locationAndBandwidth, a parameter indicating the frequency location and / or bandwidth of the initial BWP, from SIB1. Until receiving message 4 (Msg.4) during the random access procedure during initial access, UE 100 uses the initial BWP set by the MIB, i.e., the bandwidth based on CORESET #0, for the initial BWP. After receiving Msg.4, UE 100 uses the bandwidth set in locationAndBandwidth in SIB1 for the initial BWP. Note that Msg.4 may be an RRC Setup message, an RRC Resume message, or an RRC Reestablishment message. The UE 100 transitions, for example, from an RRC idle state to an RRC connected state by such initial access (random access procedure).

[0038] A dedicated BWP is a BWP that is set exclusively for a certain UE 100 (specific to the UE). A bwp-id other than "0" may be set for the dedicated BWP. For example, a dedicated DL BWP and a dedicated UL BWP are set based on BWP-Downlink and BWP-Uplink, which are information elements included in SavingcellConfig in an RRC message that is dedicated signaling transmitted from base station 200 to UE 100. For example, each of BWP-Downlink and BWP-Uplink may include various parameters (locationAndBandwidth, subcarrierSpacing, cyclicPrefix) for setting the BWP.

[0039] The base station 200 can notify the UE 100 of a BWP to be used for communication with the base station 200 (i.e., an active BWP) from among one or more configured BWPs. For example, the base station 200 can transmit to the UE 100 a BWP identifier indicating a BWP to be activated when the configuration is performed, i.e., a BWP to be used first for communication with the base station 200. Furthermore, for controlling switching from an active BWP to a BWP that is not an active BWP (hereinafter, an inactive BWP) and switching from an inactive BWP to an active BWP, for example, switching by a PDCCH (DCI), RRC signaling, a MAC control element (MAC CE), or a timer is used.

[0040] In addition, communication in an active BWP may include at least one of transmission on an uplink shared channel (UL-SCH) in the BWP, transmission on a random access channel (RACH) in the BWP (if a physical random access channel (PRACH) opportunity is configured), monitoring of a physical downlink control channel (PDCCH) in the BWP, transmission on a physical uplink control channel (PUCCH) in the BWP (if a PUCCH resource is configured), reporting of channel state information (CSI) for the BWP, and reception of a downlink shared channel (DL-SCH) in the BWP.

[0041] Here, the UL-SCH is a transport channel and is mapped to a physical uplink shared channel (PUSCH), which is a physical channel. Data transmitted on the UL-SCH is also referred to as UL-SCH data. For example, the UL-SCH data may correspond to uplink user data. The DL-SCH is a transport channel and is mapped to a physical downlink shared channel (PDSCH), which is a physical channel. Data transmitted on the DL-SCH is also referred to as DL-SCH data. For example, the DL-SCH data may correspond to downlink user data.

[0042] The PUCCH is used to transmit uplink control information (UCI). For example, the uplink control information includes a Hybrid Automatic Repeat Request (HARQ-ACK), CSI, and / or a Scheduling Request (SR). The HARQ-ACK includes a positive acknowledgment or a negative acknowledgment. For example, the PUCCH is used to transmit a HARQ-ACK for a PDSCH (i.e., DL-SCH (DL-SCH data, downlink user data)). Here, the DL-SCH data and / or the downlink user data are also referred to as a downlink transport block.

[0043] For example, in an active DL BWP, UE 100 monitors a set of PDCCH candidates in one or more control resource sets (CORESET(s)). Monitoring the PDCCH may include decoding each of the PDCCH candidates according to a monitored downlink control information (DCI) format. Here, UE 100 may monitor a DCI format to which a CRC (Cyclic Redundancy Check, also referred to as a CRC parity bit) scrambled by an RNTI (Radio Network Temporary Identifier) ​​set by base station 200 is added. Here, the RNTI may include a System Information-RNTI (SI-RNTI), a Random Access RNTI (RA-RNTI), a Temporary C-RNTI (TC-RNTI), a Paging RNTI (P-RNTI), and / or a Cell-RNTI (C-RNTI). The set of PDCCH candidates monitored by UE 100 may be defined as a PDCCH search space set. The search space set may include common search space set(s) (CSS set(s)) and / or UE specific search space set(s) (USS set(s)). Thus, base station 200 may configure CORESET and / or search space set for UE 100, and UE 100 may monitor the PDCCH in the configured CORESET and / or search space set.

[0044] (SSB) Base station 200 transmits a synchronization signal and a physical broadcast channel block (hereinafter, SSB) in the initial DL BWP. For example, an SSB consists of four consecutive OFDM symbols, and includes a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a PBCH (MIB), and a demodulation reference signal (DMRS) for the PBCH. The locations of the resource elements (time resources and frequency resources) to which the SSBs are mapped are specified in 3GPP technical specifications, such as "section 7.4.3.1" of "TS38.211 v16.2.0" and "section 4.1" of "TS38.213 v16.2.0." The bandwidth of the SSB is, for example, 240 consecutive subcarriers, i.e., a bandwidth of 20 RBs.

[0045] An SSB associated with SIB1 is referred to as a cell-defined SSB (CD-SSB). From the perspective of a certain UE 100, one serving cell is associated with one CD-SSB. SIB1 is also referred to as RMSI (Remaining Minimum System Information). One CD-SSB corresponds to one cell having a unique NCGI (NR Cell Global Identifier). An SSB not associated with SIB1 (RMSI) is referred to as a non-cell-defined SSB (Non-CD-SSB).

[0046] Base station 200 notifies UE 100 of the SSBs being transmitted using parameters (ssb-PositionsInBurst, ssb-periodicityServingCell) included in ServingCellConfigCommonSIB, an information element in SIB1. ssb-PositionsInBurst indicates the time position of the SSBs being transmitted within a half-frame (5 ms) SS burst. ssb-periodicityServingCell indicates the transmission period of the SSBs.

[0047] Based on ssb-PositionsInBurst, UE 100 can determine which SSB index an SSB is being transmitted. Specifically, the maximum number of SSBs in a half frame (up to 64) is determined based on the subcarrier spacing and frequency band, and UE 100 can identify candidate SSB positions in the time domain based on the SSB index. UE 100 determines whether an SSB is actually being transmitted at the candidate position based on ssb-PositionsInBurst.

[0048] (Specific initial BWP) In 3GPP, it has been agreed that, assuming a specific UE 100B (RedCap UE), an initial BWP (second initial BWP) for the specific UE 100B (RedCap UE) will be set independently of the conventional initial BWP. The newly introduced initial BWP is referred to as a specific initial BWP. Note that the specific initial BWP may be referred to as a separate initial BWP or a RedCap-specific initial BWP. The specific initial BWP may be an initial BWP specific to the specific UE 100B.

[0049] The conventional initial BWP is a first initial BWP for a general UE 100 (Non-RedCap UE). The first initial BWP may be used not only for the general UE 100A but also for the specific UE 100B. Therefore, the first initial BWP may be an initial BWP used for communication between the general UE 100A and the base station 200 and communication between the specific UE 100B and the base station 200.

[0050] On the other hand, the specific initial BWP is a second initial BWP different from the first initial BWP. The specific initial BWP may be used exclusively for the specific UE 100B. The specific initial BWP may be an initial BWP that is not used for communication between the general UE 100A and the base station 200, but is used for communication between the specific UE 100B and the base station 200. When a specific initial BWP is configured for the specific UE 100B (for example, when the specific UE 100 receives configuration information for specifying the specific initial BWP from the base station 200), the specific UE 100B may perform the random access procedure in the specific initial BWP, which is the second initial BWP, instead of the first initial BWP. When (only) a specific initial BWP is not configured for the specific UE 100B, the specific UE 100B may perform the random access procedure in the first initial BWP.

[0051] The bandwidth of the specific initial BWP may be equal to or less than the maximum bandwidth of the specific UE 100B (RedCap UE). The frequency band of the specific initial BWP may be set so as not to overlap with the frequency band of the conventional initial BWP so as not to adversely affect UL transmission of the general UE 100 (Non-RedCap UE).

[0052] For example, base station 200 transmits, via SIB1, parameters (e.g., locationAndBandwidth) indicating the frequency location and / or bandwidth for each of a specific initial DL BWP and / or a specific initial UL BWP. Note that subcarrier spacing and cyclic prefix parameters (e.g., subcarrierSpacing, cyclicPrefix) for each of a specific initial DL BWP and / or a specific initial UL BWP may or may not be configured. CORESET#0 may not be configured in a specific initial DL BWP. Also, SIB1 may not be transmitted in a specific initial DL BWP.

[0053] In the embodiment, it is assumed that a CD-SSB does not exist (i.e., is not transmitted) in a specific initial DL BWP. FIG. 3 shows an example of the relationship between SSBs and initial BWPs. In the example shown in FIG. 3, base station 200 (cell) transmits a CD-SSB in the frequency band of a first initial BWP, but does not transmit a CD-SSB in the frequency band of a second initial BWP. Note that a non-CD-SSB may be transmitted in the frequency band of the second initial BWP.

[0054] (Assumed scenario) An assumed scenario in the mobile communication system 1 according to the embodiment will be described with reference to Fig. 3 and Fig. 4. Fig. 4 shows an example of operation of a UE in an RRC idle state or an RRC inactive state. The description will proceed assuming that the UE is a specific UE 100B. Note that, as shown in Fig. 3, CD-SSB exists in the first initial BWP, and CD-SSB does not exist in the second initial BWP.

[0055] Step S11: Base station 200 transmits a CD-SSB in the first initial BWP. Specific UE 100B receives the CD-SSB in the first initial BWP from base station 200. Specific UE 100B receives (i.e., detects) the CD-SSB transmitted from base station 200 and can synchronize the time and / or frequency.

[0056] Furthermore, the specific UE 100B acquires the MIB by receiving the CD-SSB. The specific UE 100B configures an initial BWP based on CORESET#0, which is configured based on the MIB. The initial BWP configured based on CORESET#0 (initial downlink BWP) may be referred to as a "MIB Configured Initial DL BWP" or an "Initial DL BWP derived by MIB." Hereinafter, this initial BWP may be referred to as an MIB initial BWP. The specific UE 100B specifies a type-0 PDCCH CSS set (e.g., a bandwidth (24, 48, or 96 RBs)) based on, for example, a configuration value indicated by controlResourceSetZero in the MIB. As a result, the type-0 PDCCH CSS set is configured for the specific UE 100B. The specific UE 100B monitors a system information block (specifically, SIB1) in the type-0 PDCCH CSS set using the MIB initial BWP.

[0057] Step S12: The base station 200 transmits the SIB1. The specific UE 100B receives the SIB1 from the base station 200. The SIB1 includes first setting information for setting a first initial BWP and second setting information for setting a second initial BWP.

[0058] As will be described below, the specific UE 100B communicates with the base station 200 in the first initial BWP based on the first setting information, and communicates with the base station 200 in the second initial BWP based on the second setting information.

[0059] Step S13: The base station 200 and the specific UE 100B may perform paging. The base station 200 transmits a PDCCH (a DCI format (paging DCI) to which a CRC scrambled by the P-RNTI is added) in a corresponding CORESET and / or search space set (type 2-PDCCH CSS set).

[0060] The specific UE 100B may monitor a PDCCH (paging DCI) in the first initial BWP. The specific UE 100B may receive a paging message based on scheduling information included in the paging DCI. The specific UE 100B determines whether or not its own unique identifier is included in the paging message. If its own identifier is included in the paging message, the specific UE 100B may consider that a call has been made, and may perform an operation of transitioning to an RRC connected state, for example.

[0061] Step S14: The specific UE 100B performs cell reselection and measurement using CD-SSB. Specifically, the specific UE 100B performs measurement by detecting CD-SSB, measuring the radio quality of the detected CD-SSB, and evaluating the measurement results. If the evaluation process satisfies the conditions for cell reselection, the specific UE 100B performs cell reselection.

[0062] Step S15: When the specific UE 100B executes a random access (RA) procedure, the specific initial BWP is set, and therefore the specific UE 100B switches from the first initial BWP to the second initial BWP.

[0063] After that, a random access (RA) procedure is executed between the specific UE 100B and the base station 200.

[0064] Step S16: The specific UE 100B uses a specific initial BWP to transmit a message 1 (hereinafter, MSG1) to the base station 200. The specific UE 100B transmits MSG1 including a random access (RA) preamble on a physical random access channel (PRACH) in the specific initial BWP. The base station 200 (receiving unit 221) receives MSG1 from the specific UE 100B.

[0065] Step S17: The base station 200 transmits a message 2 (hereinafter, MSG2) to the specific UE 100B. The MSG2 is a random access (RA) response. The specific UE 100B (receiving unit 121) receives the MSG2 from the base station 200.

[0066] The MSG2 includes, for example, preamble information indicating an RA preamble received from a specific UE 100B, an uplink grant (UL grant) indicating a time-frequency resource used by the UE 100 to transmit the message 3, etc. The time-frequency resource may be located at a frequency within a specific initial BWP.

[0067] When the RA preamble transmitted by the specific UE 100B that has received the RA response matches the RA preamble indicated by the preamble information received from the base station 200 in step S17, the specific UE 100B executes the process of step S18.

[0068] Step S18: The specific UE 100B (transmitter 122) transmits a message 3 (hereinafter, MSG3) to the base station 200. The specific UE 100B (transmitter 122) transmits MSG3 to the base station 200 in the time-frequency resource allocated by the uplink grant. The base station 200 (receiver 221) receives MSG3 from the specific UE 100B.

[0069] MSG3 may include an RRC connection establishment or RRC connection resumption request message. The RRC connection establishment request message may be an RRC Setup Request (RRCSetupRequest) message sent by a UE in an RRC idle state. The RRC connection resumption request message may be an RRC Resume Request (RRCResumeRequest or RRCResumeRequest1) message sent by a UE in an RRC inactive state.

[0070] Step S19: The base station 200 transmits a message 4 (hereinafter, MSG4) to the specific UE 100B. The base station 200 (transmitting unit 222) transmits MSG4 by using the specific initial BWP. The specific UE 100B receives MSG4 from the base station 200 by using the specific initial BWP.

[0071] MSG4 is a response to a request message. MSG4 may be an RRC setup message for an RRC setup request, an RRC resume message for an RRC resume request message, or an RRC rejection message for rejecting an RRC connection establishment or RRC connection resumption.

[0072] If the random access procedure is successful, the specific UE 100B transitions from the RRC idle state or the RRC inactive state to the RRC connected state. After that, the specific UE 100B in the RRC connected state can communicate with the base station 200 by using the dedicated BWP.

[0073] Here, assume a case where a specific UE 100B in an RRC idle state or an RRC inactive state attempts to establish or resume an RRC connection, for example, by a random access procedure, in a specific initial BWP in which no CD-SSB exists, but the establishment or resumption of the RRC connection fails. In this case, since no CD-SSB exists in the specific initial BWP, the specific UE 100B cannot perform paging monitoring, cell (re)selection, and measurement, and may not be able to perform appropriate operations. In one embodiment described later, an operation for enabling appropriate operations to be performed even when no CD-SSB exists in the specific initial BWP will be described.

[0074] Furthermore, a specific UE 100B in an RRC idle state or an RRC inactive state continues measurement processing and evaluation processing for cell reselection even after transmitting a request message for RRC connection establishment or RRC connection resumption. Therefore, in a specific initial BWP in which no CD-SSB exists, the specific UE 100B may perform a useless operation of attempting measurement and evaluation for cell reselection even though no CD-SSB exists in the specific initial BWP after transmitting a request message for RRC connection establishment or RRC connection resumption. In one embodiment described later, an operation for suppressing useless operations even when no CD-SSB exists in the specific initial BWP will be described.

[0075] (Configuration of user device) Next, the configuration of the UE 100 according to this embodiment will be described with reference to Fig. 5. The UE 100 includes a communication unit 120 and a control unit 140.

[0076] The communication unit 120 performs wireless communication with the base station 200 by transmitting and receiving radio signals to and from the base station 200. The communication unit 120 has at least one receiving unit 121 and at least one transmitting unit 122. The receiving unit 121 and the transmitting unit 122 may be configured to include an antenna and an RF circuit. 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.

[0077] The receiving unit 121 may be referred to as a receiver (RX). The transmitting unit 122 may be referred to as a transmitter (TX). When the UE 100 is a general UE 100A, the number of receivers included in the communication unit 120 may be two to four. When the UE 100 is a specific UE 100B, the number of receivers included in the communication unit 120 may be one or two.

[0078] The control unit 140 performs various controls in the UE 100. The control unit 140 controls communication with the base station 200 via the communication unit 120. The operation of the UE 100, described below, may be controlled by the control unit 140. The control unit 140 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 operation of the control unit 140. The control unit 140 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. The memory may include at least one of a read-only memory (ROM), an erasable programmable read-only memory (EPROM), an electrically erasable programmable read-only memory (EEPROM), a random access memory (RAM), and a flash memory. All or a part of the memory may be included in the processor.

[0079] The UE 100 configured in this way is a specific UE 100B having reduced communication capability compared to a general UE 100A. The control unit 140 controls a specific UE 100B to transmit a bandwidth portion (BWP) that is a part of the bandwidth of the cell of the base station 200 in a radio resource control (RRC) idle state or an RRC inactive state. 1 The specific UE 100B executes the random access procedure using a specific initial BWP for UE 100B. If CD-SSB does not exist in the specific initial BWP, the control unit 140 switches from the specific initial BWP to an initial BWP in which CD-SSB exists, based on the failure of the random access procedure. As a result, the specific UE 100B performs paging monitoring, cell (re)selection, and measurement in the initial BWP in which CD-SSB exists, rather than in the specific initial BWP in which CD-SSB does not exist, thereby enabling the specific UE 100B to perform appropriate communication.

[0080] The random access procedure may include a process of transmitting a random access preamble to the base station 200 and a process of receiving a response to the random access preamble from the base station. The control unit 140 may switch from the specific initial BWP to the initial BWP based on the fact that the number of times a response cannot be received from the base station 200 reaches a predetermined number, which is regarded as a failure of the random access procedure.

[0081] The random access procedure may include a process of transmitting an RRC connection establishment or RRC connection resumption request message to the base station 200 and a process of receiving a response to the request message from the base station. The control unit 140 may switch from the specific initial BWP to the initial BWP based on receiving an RRC rejection message from the base station 200 as a response to the request message.

[0082] Furthermore, the transmitting unit 122 may transmit a request message for establishing an RRC connection to the base station 200. The control unit 140 may switch from the specific initial BWP to the initial BWP based on the fact that a response to the request message is not received from the base station within a predetermined time after transmitting the request message.

[0083] Furthermore, the transmitting unit 122 may transmit an RRC connection resumption request message to the base station 200. The control unit 140 may switch from the specific initial BWP to the initial BWP on the basis of not receiving a response to the request message from the base station 200 within a predetermined time period after transmitting the request message.

[0084] Furthermore, the transmitting unit 122 may transmit an RRC connection resumption request message to the base station 200. The control unit 140 may switch from the specific initial BWP to the initial BWP based on the fact that an integrity check failure indicator indicating a failure of the integrity check is sent from a lower layer to the RRC layer within a predetermined time after receiving the request message.

[0085] In addition, when CD-SSB exists in a specific initial BWP, the control unit 140 may perform control to perform at least one of paging monitoring, cell selection, cell reselection, and measurement in the specific initial BWP after the random access procedure fails.

[0086] The specific initial BWP may be an initial BWP that is not used for communication between the general UE 100A and the base station 200, but is used for communication between the specific UE 100B and the base station 200.

[0087] The specific initial BWP may be an initial BWP used for communication between the general UE 100A and the base station 200 and communication between the specific UE 100B and the base station 200.

[0088] Furthermore, in the RRC idle state or the RRC inactive state, the control unit 140 executes a random access procedure using a specific initial BWP for the specific UE 100B, which is a bandwidth portion (BWP) that is a part of the bandwidth of the cell of the base station 200. The transmission unit 122 transmits an RRC connection establishment or RRC connection resumption request message to the base station 200 during the random access procedure. When CD-SSB does not exist in the specific initial BWP, the control unit 140 switches from the specific initial BWP to the initial BWP based on receiving an RRC rejection message from the base station 200 as a response to the request message. As a result, when the specific UE 100B receives the RRC rejection message, it performs paging monitoring, cell (re)selection, and measurement in the initial BWP where CD-SSB exists, rather than in the specific initial BWP where CD-SSB does not exist, thereby enabling the specific UE 100B to perform appropriate communication.

[0089] Furthermore, in the RRC idle state or the RRC inactive state, the control unit 140 executes a random access procedure using a specific initial BWP intended for the second communication device, which is a BWP that is part of the bandwidth of the cell of the base station 200. The transmission unit 122 transmits a request message for RRC connection establishment or RRC connection resumption to the base station (200) in the random access procedure. When CD-SSB is not present in the specific initial BWP, the control unit 140 switches from the specific initial BWP to the initial BWP based on the fact that a response to the request message is not received from the base station 200 within a predetermined time after transmitting the request message. As a result, when the specific UE 100B does not receive a response to the request message from the base station 200 within a predetermined time, the specific UE 100B performs paging monitoring, cell (re)selection, and measurement in the initial BWP that includes CD-SSB, instead of the specific initial BWP that does not include CD-SSB, thereby enabling the specific UE 100B to perform appropriate communication.

[0090] Furthermore, in the RRC idle state or the RRC inactive state, the control unit 140 executes a random access procedure using a specific initial BWP for the second communication device, which is a bandwidth portion (BWP) that is a part of the bandwidth of the cell of the base station 200. The transmission unit 122 transmits an RRC connection resumption request message to the base station (200) during the random access procedure. When the CD-SSB does not exist in the specific initial BWP, the control unit 140 switches from the specific initial BWP to the initial BWP based on an integrity check failure indicator indicating an integrity check failure being sent from a lower layer to the RRC layer within a predetermined time after receiving the request message. As a result, when the integrity check failure indicator is sent from a lower layer to the RRC layer, the specific UE 100B performs paging monitoring, cell (re)selection, and measurement in the initial BWP where the CD-SSB exists, rather than in the specific initial BWP where the CD-SSB does not exist, thereby enabling the specific UE 100B to perform appropriate communication.

[0091] The predetermined communication capability may be a capability based on at least one of a maximum bandwidth used for wireless communication and a number of receivers, and the second communication device may be at least one of a device with a narrower maximum bandwidth and a device with a smaller number of receivers than the first communication device.

[0092] The second communication device may also be a reduced capability NR device in a fifth generation system of the 3rd Generation Partnership Project standard.

[0093] Furthermore, the transmitter 122 transmits a request message for RRC connection establishment or RRC connection resumption to the base station 200 in the specific initial BWP. The controller 140 executes measurement processing and evaluation processing for cell reselection after transmitting the request message. If CD-SSB does not exist in the specific initial BWP, the controller controls to suspend at least one of the measurement processing and the evaluation processing after transmitting the request message. This makes it possible for the specific UE 100B to suppress useless operations such as attempting measurement and evaluation for cell reselection even when CD-SSB does not exist in the specific initial BWP. Furthermore, it is possible for the specific UE 100B to suppress useless operations such as switching the BWP to the initial BWP for cell reselection and attempting measurement and evaluation even when attempting to establish or resume an RRC connection in the specific initial BWP.

[0094] Furthermore, the control unit 140 may perform control to suspend at least one of the measurement process and the evaluation process during the period from when the request message is transmitted until the transition to the RRC connected state.

[0095] Furthermore, the receiving unit 121 may receive a response to the request message from the base station 200. Based on receiving an RRC rejection message from the base station 200 as a response, the control unit 140 may perform control to switch from the specific initial BWP to the initial BWP and execute the measurement process and the evaluation process in the initial BWP.

[0096] Furthermore, the transmitting unit 122 may transmit a request message for establishing an RRC connection to the base station 200. The control unit 140 may perform control to switch from the specific initial BWP to the initial BWP and execute the measurement process and the evaluation process in the initial BWP, based on the fact that a response to the request message is not received from the base station 200 within a predetermined time after transmitting the request message.

[0097] Furthermore, the transmitting unit 122 may transmit a request message for resuming the RRC connection to the base station 200. The control unit 140 may perform control to switch from the specific initial BWP to the initial BWP and execute the measurement process and the evaluation process in the initial BWP, based on the fact that a response to the request message is not received from the base station 200 within a predetermined time after transmitting the request message.

[0098] Furthermore, the transmitting unit 122 may transmit a request message for resuming the RRC connection to the base station 200. The control unit 140 may perform control to switch from the specific initial BWP to the initial BWP and execute the measurement process and the evaluation process in the initial BWP, based on the fact that an integrity check failure indicator indicating a failure of the integrity check is sent from a lower layer to the RRC layer within a predetermined time after transmitting the request message.

[0099] Note that the operation of the functional units (specifically, at least one of communication unit 120 and control unit 140) included in UE 100 may be described as the operation of UE 100.

[0100] (Base station configuration) Next, the configuration of the base station 200 according to this embodiment will be described with reference to Fig. 6. The base station 200 has a radio communication unit 220, a network communication unit 230, and a control unit 240.

[0101] The wireless communication unit 220 communicates with the UE 100 via an antenna under the control of the control unit 240. The wireless communication unit 220 has a receiving unit 221 and a transmitting unit 222. The receiving unit 221 converts a wireless signal received by the antenna into a received signal, which is a baseband signal, performs signal processing on the received signal, and outputs the received signal to the control unit 240. The transmitting unit 222 performs signal processing on a transmission signal, which is a baseband signal output by the control unit 240, converts the transmission signal into a wireless signal, and transmits the wireless signal from the antenna.

[0102] The network communication unit 230 transmits and receives signals to and from the network. For example, the network communication unit 230 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 230 also receives signals from the core network device 300 connected via an NG interface, and transmits the signals to the core network device 300.

[0103] The control unit 240 performs various controls in the base station 200. The control unit 240 controls, for example, communication with the UE 100 via the radio communication unit 220. The control unit 240 also controls, for example, communication with a node (for example, an adjacent base station or the core network device 300) via the network communication unit 230. The operation of the base station 200 described below may be an operation controlled by the control unit 240.

[0104] The control unit 240 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 240. The control unit 240 may include a digital signal processor that performs digital processing of signals transmitted and received via the antenna and RF circuitry. 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. All or a part of the memory may be included in the processor.

[0105] The operation of the functional units (specifically, at least one of the wireless communication unit 220 (receiving unit 221 and / or transmitting unit 222), the network communication unit 230, and the control unit 240) provided in the base station 200 may be described as the operation of the base station 200.

[0106] (Example of operation) An example of the operation of the UE 100 (specifically, the specific UE 100B) will be described with reference to Fig. 7 to Fig. 14. This example of the operation is based on the above-described configuration and operation. Therefore, the previous description may be omitted.

[0107] The specific UE 100B is in an RRC idle state or an RRC inactive state. The specific UE 100B can execute the following process when the BWP used for communication with the base station 200 is switched from the first initial BWP to the second initial BWP (i.e., a specific initial BWP) and a CD-SSB does not exist in the second initial BWP. Furthermore, the specific UE 100B may execute the following process when a specific initial BWP in which a CD-SSB does not exist is configured for the specific UE 100B and the current BWP (specifically, a downlink BWP) is a specific initial BWP (specifically, a specific initial downlink BWP).

[0108] The specific UE 100B (control unit 140) can identify the center frequency at which CD-SSB exists by cell search. The specific UE 100B (control unit 140) determines that CD-SSB exists in the second initial BWP when the frequency of the second initial BWP at the switching destination includes the center frequency at which CD-SSB exists. On the other hand, the specific UE 100B (control unit 140) determines that CD-SSB does not exist in the second initial BWP when the frequency of the second initial BWP at the switching destination does not include the center frequency at which CD-SSB exists.

[0109] Step S101: The control unit 140 starts a random access (RA) procedure. Specifically, in FIG. 7, the control unit 140 starts a random access (RA) procedure in step S1 01 It controls the execution of the process.

[0110] Step S102: The control unit 140 determines whether or not a request message for RRC connection establishment or RRC connection resumption has been transmitted. If the request message has been transmitted, the control unit 140 executes the process of step S103. If the request message has not been transmitted, the control unit 140 executes the process of step S104.

[0111] Step S103: The control unit 140 performs control to suspend at least one of the measurement process and the evaluation process for cell reselection, or the control unit 140 performs control to suspend both the measurement process and the evaluation process.

[0112] After transmitting the RRC setup request message, the control unit 140 may perform control to suspend both the measurement process and the evaluation process (see F8A in FIG. 8). Also, after transmitting the RRC resume request message or the RRC resume request message 1, the control unit 140 may perform control to suspend both the measurement process and the evaluation process (see F8B in FIG. 8).

[0113] The control unit 140 may perform control to suspend at least one of the measurement process and the evaluation process during the period from when the request message is transmitted until the transition to the RRC connected state.

[0114] If the control unit 140 can receive CD-SSB transmitted from a neighboring cell in the second initial BWP, the control unit 140 may perform measurement processing and evaluation processing on the CD-SSB transmitted from the neighboring cell.

[0115] In this way, the control unit 140 continues to use the second initial BWP as the active BWP without switching the BWP from the second initial BWP. The control unit 140 performs control to suspend at least one of the measurement process and the evaluation process while using the second initial BWP.

[0116] Step S104: The control unit 140 determines whether the switching condition is satisfied. If the switching condition is satisfied, the control unit 140 executes the process of step S105. If the switching condition is not satisfied, the control unit 140 executes the process of step S102. Note that if the RA procedure is successful, the control unit 140 may end the process of this operation example.

[0117] The control unit 140 determines that the switching condition is satisfied in at least one of the following cases, for example.

[0118] First, the control unit 140 may determine that the RA procedure has failed based on the fact that the number of times a response from the base station 200 has not been received reaches a predetermined number. When the control unit 140 determines that the RA procedure has failed, the control unit 140 may determine that a switching condition has been satisfied. As shown in FIG. 9, for example, when the control unit 140 determines that reception of a random access response has failed, the control unit 140 increments the preamble transmission counter by 1. Furthermore, as shown in FIG. 10, for example, when the control unit 140 determines that contention resolution has not been successful, the control unit 140 increments the preamble transmission counter by 1. When the preamble transmission counter exceeds an upper limit value (i.e., preambleTransMax), the control unit 140 may determine that the RA procedure has failed.

[0119] Second, the control unit 140 may determine that the switching condition is satisfied based on the fact that the random access problem has been indicated to a higher layer in the MAC layer. As shown in Figures 9 and 10, the control unit 140, for example, controls the transmission of a random access preamble in the Sp cell. The control unit 140 may determine that the switching condition is satisfied when the random access problem has been indicated to a higher layer in the MAC layer based on the transmission of the random access preamble.

[0120] Third, the control unit 140 may determine that the switching condition is satisfied based on the fact that a response to the request message for RRC connection establishment is not received from the base station 200 within a predetermined time after transmitting a request message for RRC connection establishment. Specifically, the control unit 140 may start a first timer (specifically, timer T300) that measures a predetermined time after transmitting an RRC setup request (RRCSetupRequest) message. The control unit 140 stops the first timer if an RRC setup message or an RRC rejection message is received before the first timer expires, or if cell reselection and connection establishment are aborted in a layer higher than the MAC layer. The control unit 140 may determine that the switching condition is satisfied based on the fact that the first timer expires.

[0121] Fourth, the control unit 140 may determine that the switching condition is satisfied based on the fact that a response to the request message for RRC connection resumption is not received from the base station 200 within a predetermined time after transmitting an RRC connection resumption request message. Specifically, after transmitting an RRC resume request (RRCResumeRequest or RRCResumeRequest1) message, the control unit 140 may start a second timer (specifically, timer T319) that measures a predetermined time. The control unit 140 stops the second timer when an RRC resume message, an RRC setup message, an RRC release message, an RRC release message with suspend configuration (suspendConfig), or an RRC rejection message is received before the second timer expires, or when cell reselection and connection establishment are aborted in a layer higher than the MAC layer. The control unit 140 may determine that the switching condition is satisfied based on the fact that the second timer expires.

[0122] Fifth, the control unit 140 may determine that the switching condition is satisfied based on the fact that an integrity check failure indication indicating a failure of an integrity check is sent from a lower layer to the RRC layer within a predetermined time after the transmission of the RRC connection resumption request message. Specifically, the control unit 140 may determine that the switching condition is satisfied when the integrity check failure indication is sent from a lower layer to the RRC layer while the second timer is running. Note that the integrity check failure indication is sent from a lower layer to the RRC layer based on a failure of an integrity check in the security and decryption process on an SRB (Signaling Radio Bearer), which is a bearer that transmits RRC messages and NAS messages.

[0123] Sixth, the control unit 140 may determine that the switching condition is satisfied based on receiving an RRC rejection message from the base station 200 in response to the RRC connection establishment or RRC connection resumption request message.

[0124] Step S105: The control unit 140 performs control to switch from a specific initial BWP (i.e., the second initial BWP) to an initial BWP (i.e., the first initial BWP). Specifically, the control unit 140 performs control to switch from a specific initial BWP to an initial BWP based on the satisfaction of a switching condition, for example, based on a failure of the RA procedure. The control unit 140 may switch from a specific initial BWP to an initial BWP, for example, in at least one of the following cases:

[0125] First, the control unit 140 may switch from the specific initial BWP to the initial BWP when the number of times that a response cannot be received from the base station 200 reaches a predetermined number (see F9 in FIG. 9 and F10 in FIG. 10).

[0126] Second, the control unit 140 may switch from a specific initial BWP to an initial BWP based on the MAC layer indicating a random access problem to a higher layer (see F9 in FIG. 9 and F10 in FIG. 10).

[0127] Third, the control unit 140 may switch from a specific initial BWP to an initial BWP based on not receiving a response to the request message from the base station 200 within a predetermined time after sending the request message for RRC connection establishment (see F11 in FIG. 11).

[0128] Fourth, the control unit 140 may switch from the specific initial BWP to the initial BWP based on not receiving a response to the request message from the base station 200 within a predetermined time after sending the request message for RRC connection resumption (see F12A in FIG. 12).

[0129] Fifth, the control unit 140 may switch from a specific initial BWP to the initial BWP based on the fact that an integrity check failure indicator indicating an integrity check failure is sent from a lower layer to the RRC layer within a predetermined time period after sending the RRC connection resumption request message (see F12B in FIG. 12).

[0130] Sixth, the control unit 140 may switch from a specific initial BWP to the initial BWP based on receiving an RRC rejection message from the base station 200 in response to a request message for RRC connection establishment or RRC connection resumption (see F13A and F13B in FIG. 13).

[0131] The control unit 140 may switch from the specific initial BWP to the initial BWP based on a trigger different from the above trigger, when the switching condition is satisfied.

[0132] After switching to the initial BWP, the control unit 140 controls the execution of measurement processing and evaluation processing in the first initial BWP. Therefore, after switching to the initial BWP, the control unit 140 may control the restart of measurement processing and evaluation processing. Furthermore, after switching to the initial BWP, the control unit 140 may execute cell (re)selection and paging monitoring (see Figures 9-12).

[0133] As described above, the control unit 140 executes the random access procedure using a specific initial BWP in the RRC idle state or the RRC inactive state. When the CD-SSB is not present in the specific initial BWP, the control unit 140 switches from the specific initial BWP to an initial BWP including the CD-SSB based on the failure of the random access procedure. Furthermore, the control unit 140 switches from the specific initial BWP to the initial BWP based on receiving an RRC rejection message from the base station 200. Furthermore, when the CD-SSB is not present in the specific initial BWP, the control unit 140 switches from the specific initial BWP to the initial BWP based on not receiving a response to the request message from the base station 200 within a predetermined time after transmitting the request message. Furthermore, when the CD-SSB is not present in the specific initial BWP, the control unit 140 switches from the specific initial BWP to the initial BWP based on an integrity check failure indicator being sent from a lower layer to the RRC layer within a predetermined time after receiving the request message. This allows the specific UE 100B to perform paging monitoring, cell (re)selection and measurements in the initial BWP where CD-SSB is present, rather than in the specific initial BWP where CD-SSB is not present, thereby enabling the specific UE 100B to perform appropriate communication.

[0134] Furthermore, the transmitter 122 transmits a request message for RRC connection establishment or RRC connection resumption to the base station 200 in the specific initial BWP. After transmitting the request message, the controller 140 executes measurement processing and evaluation processing for cell reselection. If CD-SSB does not exist in the specific initial BWP, the controller 140 performs control to suspend at least one of the measurement processing and the evaluation processing after transmitting the request message. This makes it possible for the specific UE 100B to suppress useless operations such as attempting measurement and evaluation for cell reselection even though CD-SSB does not exist in the specific initial BWP. Furthermore, it is possible for the specific UE 100B to suppress useless operations such as switching the BWP to the initial BWP for cell reselection and attempting measurement and evaluation even though the specific UE 100B is attempting to establish or resume an RRC connection in the specific initial BWP.

[0135] (Other embodiments) In the above-described embodiment, the case where the RA procedure is a four-step random access (RA) type has been described, but this is not limiting. For example, the above-described operations may be performed in the case where the RA procedure is a two-step RA type. For example, after transmitting a preamble and a payload (i.e., transmitting an MSGA) in the two-step RA type RA procedure, the control unit 140 may switch from a specific initial BWP to an initial BWP based on the satisfaction of a switching condition, for example, a failure of the RA procedure (see F14 in FIG. 14). After switching from the specific initial BWP to the initial BWP, the control unit 140 may perform cell (re)selection and paging monitoring.

[0136] In the above-described embodiment, a case where a CD-SSB does not exist in a specific initial BWP has been described. When a CD-SSB exists in a specific initial BWP, the specific UE 100B may perform control to perform at least one of paging monitoring, cell selection, cell reselection, and measurement in the specific initial BWP after a failure of the RA procedure, without switching from the specific initial BWP to the initial BWP (i.e., the first initial BWP). Furthermore, when a CD-SSB exists in a specific initial BWP, the specific UE 100B may perform the RA procedure again in the specific initial BWP after a failure of the RA procedure, without switching from the specific initial BWP to the initial BWP (i.e., the first initial BWP).

[0137] 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 a TS of any of LTE (Long Term Evolution) or other generation systems (e.g., 6th generation) of the 3GPP standard. The base station 200 may be an eNB that provides E-UTRA (Evolved Universal Terrestrial Radio Access) user plane and control plane protocol termination for the UE 100 in LTE. The mobile communication system 1 may be a system compliant with a 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.

[0138] 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 a 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 compliant with a TS of a standard other than the 3GPP standard.

[0139] 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.

[0140] A program may be provided that causes a computer to execute each process performed by UE 100 or base station 200. The program may be recorded in a computer-readable medium. Using the computer-readable medium, the program can be installed in 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 Disk Read Only Memory). Furthermore, circuits that execute each process performed by UE 100 or base station 200 may be integrated, and at least a part of UE 100 or base station 200 may be configured as a semiconductor integrated circuit (chip set, SoC (System On Chip)).

[0141] In the above embodiments, "transmit" may mean 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 processing at least one layer and physically transmitting a signal wirelessly or via a wired connection. Similarly, "receive" may mean 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 information. Similarly, the terms "based on" and "depending on / in response to" do not mean "based only on" or "depending only on," unless otherwise specified. The phrase "based on" means both "based only on" and "based at least in part on." Similarly, the phrase "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 does mean 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.

[0142] 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.

[0143] (Addendum) The following additional notes are about the features of the above-described embodiment.

[0144] (Appendix 1) A communication device (100, 100B) is a second communication device (100B) having a reduced communication capability compared to a first communication device (100A) having a predetermined communication capability, A control unit (120) is provided that executes a random access procedure using a bandwidth portion (BWP) that is a part of the bandwidth of a cell of a base station (200) and is a specific initial BWP for the second communication device (100B) in a radio resource control (RRC) idle state or an RRC inactive state, The control unit (140) switches from the specific initial BWP to an initial BWP in which the CD-SSB exists based on a failure of the random access procedure when the cell-defined synchronization signal and physical broadcast channel block (CD-SSB) does not exist in the specific initial BWP. Communication equipment.

[0145] (Appendix 2) The random access procedure includes a process of transmitting a random access preamble to the base station (200) and a process of receiving a response to the random access preamble from the base station (200); The control unit (140) switches from the specific initial BWP to the initial BWP based on the fact that the number of times the response cannot be received from the base station (200) reaches a predetermined number as a failure of the random access procedure. 2. The communication device of claim 1.

[0146] (Appendix 3) The random access procedure includes a process of transmitting an RRC connection establishment or RRC connection resumption request message to the base station (200), and a process of receiving a response to the request message from the base station (200), The control unit (140) switches from the specific initial BWP to the initial BWP based on receiving an RRC rejection message from the base station (200) as the response. 3. The communication device according to claim 1 or 2.

[0147] (Appendix 4) A transmitter (122) for transmitting an RRC connection establishment request message to the base station (200), The control unit (140) switches from the specific initial BWP to the initial BWP based on the fact that a response to the request message is not received from the base station (200) within a predetermined time after the request message is transmitted. 4. A communication device according to any one of claims 1 to 3.

[0148] (Appendix 5) A transmitter (122) for transmitting an RRC connection resumption request message to the base station (200), The control unit (140) switches from the specific initial BWP to the initial BWP based on the fact that a response to the request message is not received from the base station (200) within a predetermined time after the request message is transmitted. 5. A communication device according to any one of claims 1 to 4.

[0149] (Appendix 6) A transmitter (111) for transmitting an RRC connection resumption request message to the base station (200), The control unit (140) switches from the specific initial BWP to the initial BWP based on the fact that an integrity check failure indicator indicating a failure of the integrity check is sent from a lower layer to an RRC layer within a predetermined time after receiving the request message. 6. A communication device according to any one of claims 1 to 5.

[0150] (Appendix 7) When CD-SSB exists in the specific initial BWP, the control unit (140) controls to perform at least one of paging monitoring, cell selection, cell reselection, and measurement in the specific initial BWP after the random access procedure fails. 7. A communication device according to any one of claims 1 to 6.

[0151] (Appendix 8) The specific initial BWP is an initial BWP that is not used for communication between the first communication device (100A) and the base station (200) but is used for communication between the second communication device (100B) and the base station (200). 8. A communication device according to any one of claims 1 to 7.

[0152] (Appendix 9) The specific initial BWP is an initial BWP used for communication between the first communication device (100A) and the base station (200) and for communication between the second communication device (100B) and the base station (200). 8. A communication device according to any one of claims 1 to 7.

[0153] (Appendix 10) A communication device (100, 100B) is a second communication device (100B) having a reduced communication capability compared to a first communication device (100A) having a predetermined communication capability, A control unit (140) that executes a random access procedure using a bandwidth portion (BWP) that is a part of the bandwidth of a cell of a base station (200) and is a specific initial BWP for the second communication device (100B) in a radio resource control (RRC) idle state or an RRC inactive state; a transmission unit (122) that transmits an RRC connection establishment or RRC connection resumption request message to the base station (200) in the random access procedure; When a cell-defined synchronization signal and physical broadcast channel block (CD-SSB) is not present in the specific initial BWP, the control unit (140) switches from the specific initial BWP to the initial BWP based on receiving an RRC rejection message from the base station (200) in response to the request message. Communication equipment.

[0154] (Appendix 11) A communication device (100, 100B) is a second communication device (100B) having a reduced communication capability compared to a first communication device (100A) having a predetermined communication capability, A control unit (140) that executes a random access procedure using a bandwidth portion (BWP) that is a part of the bandwidth of a cell of a base station (200) and is a specific initial BWP for the second communication device (100B) in a radio resource control (RRC) idle state or an RRC inactive state; a transmission unit (122) that transmits an RRC connection establishment or RRC connection resumption request message to the base station (200) in the random access procedure; When a cell-defined synchronization signal and a physical broadcast channel block (CD-SSB) are not present in the specific initial BWP, the control unit (140) switches from the specific initial BWP to the initial BWP based on the fact that a response to the request message is not received from the base station (200) within a predetermined time after transmitting the request message. Communication equipment.

[0155] (Appendix 12) A communication device (100, 100B) is a second communication device (100B) having a reduced communication capability compared to a first communication device (100A) having a predetermined communication capability, A control unit (140) that executes a random access procedure using a bandwidth portion (BWP) that is a part of the bandwidth of a cell of a base station (200) and is a specific initial BWP for the second communication device (100B) in a radio resource control (RRC) idle state or an RRC inactive state; a transmission unit (122) that transmits an RRC connection resumption request message to the base station (200) in the random access procedure; The control unit (140) switches from the specific initial BWP to the initial BWP based on the fact that an integrity check failure indicator indicating a failure of the integrity check is sent from a lower layer to an RRC layer within a predetermined time after receiving the request message when a cell-defined synchronization signal and a physical broadcast channel block (CD-SSB) are not present in the specific initial BWP. Communication equipment.

[0156] (Appendix 13) the predetermined communication capability is a capability based on at least one of a maximum bandwidth used for wireless communication and a number of receivers; The second communication device is at least one of a device having a narrower maximum bandwidth and a device having a smaller number of receivers than the first communication device. 13. A communication device according to any one of claims 1 to 12.

[0157] (Appendix 14) The second communication device is a reduced-capability new radio device in a fifth-generation system of the Third Generation Partnership Project standard. 14. A communication device according to any one of claims 1 to 13.

[0158] (Appendix 15) A communication method executed by a communication device (100, 100B), which is a second communication device (100B) having reduced communication capabilities compared to a first communication device (100A) having a predetermined communication capability, In a radio resource control (RRC) idle state or an RRC inactive state, a step of performing a random access procedure using a bandwidth portion (BWP) that is a part of the bandwidth of a cell of the base station (200), which is a specific initial BWP for the second communication device (100B); and if a cell-defined synchronization signal and physical broadcast channel block (CD-SSB) does not exist in the specific initial BWP, switching from the specific initial BWP to an initial BWP in which the CD-SSB exists based on a failure of the random access procedure. Communication method.

Claims

1. A communication device (100), a receiving unit (121) for receiving information for setting a first initial downlink bandwidth portion (BWP) and information for setting a second initial downlink BWP from a base station (200); a control unit (140) that executes a random access procedure in the second initial downlink BWP; a transmitter (122) for transmitting a radio resource control (RRC) connection resumption request message to the base station; The control unit Starting a predetermined timer based on the transmission of the RRC connection resumption request message; If the RRC layer receives an integrity check failure indicator indicating a failure of the integrity check from a lower layer while the predetermined timer is running, control is performed to operate in the first initial downlink BWP in which a cell-defined synchronization signal and physical broadcast channel block (CD-SSB) is transmitted. Communication equipment.

2. The control unit controls the operation to be performed in the first initial downlink BWP when the CD-SSB is not transmitted in the second initial downlink BWP. The communication device according to claim 1 .

3. The control unit controls the first initial downlink BWP to perform at least one of the following operations: monitoring downlink control information for paging, selecting a cell, reselecting the cell, measuring for selecting the cell, and measuring for reselecting the cell.

3. The communication device according to claim 1 or 2.

4. Information for setting the first initial downlink BWP and information for setting the second initial downlink BWP are included in system information.

3. The communication device according to claim 1 or 2.

5. The communication device is in an RRC idle state or an RRC inactive state.

3. The communication device according to claim 1 or 2.

6. A communication method executed by a communication device (100), comprising: receiving information for configuring a first initial downlink bandwidth portion (BWP) and information for configuring a second initial downlink BWP from a base station (200); performing a random access procedure in the second initial downlink BWP; sending a radio resource control (RRC) connection resumption request message to the base station; starting a predetermined timer based on the transmission of the RRC connection resumption request message; and when the RRC layer receives an integrity check failure indicator indicating a failure of an integrity check from a lower layer while the predetermined timer is running, controlling the RRC layer to operate in the first initial downlink BWP in which a cell-defined synchronization signal and physical broadcast channel block (CD-SSB) is transmitted. Communication method.

7. In the controlling step, when the CD-SSB is not transmitted in the second initial downlink BWP, the control is performed to operate in the first initial downlink BWP. The communication method according to claim 6.

8. In the controlling step, the first initial downlink BWP is controlled to perform at least one of the following operations: monitoring downlink control information for paging, selecting a cell, reselecting the cell, measuring for selecting the cell, and measuring for reselecting the cell. The communication method according to claim 6 or 7.

9. Information for setting the first initial downlink BWP and information for setting the second initial downlink BWP are included in system information. The communication method according to claim 6 or 7.

10. The communication device is in an RRC idle state or an RRC inactive state. The communication method according to claim 6 or 7.

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