Terminal device, base station device, and wireless communication system

Abstract

A terminal device for executing a non-contention-type random access procedure, wherein the device includes: a reception unit for receiving, from a base station device, threshold information including a threshold related to the received electric power of a signal from the base station device, candidate information indicating a plurality of candidates for a preamble used for transmission of a PRACH in a random access procedure, and first transmission timing indicating the beginning of the transmission timing of the PRACH; a control unit for determining the number of transmission times of the PRACH in accordance with the received electric power and the threshold information, referring to the candidate information, selecting a preamble corresponding to the number of transmission times from the plurality of candidates of the candidate information, and determining a second transmission timing of each PRACH to be transmitted after the first transmission timing in accordance with the first transmission timing and the number of transmission times; and a transmission unit for transmitting the PRACH to the base station device at each of the first transmission timing and the second transmission timing by using the selected preamble.

Description

Terminal device, base station device, and wireless communication system

[0001] The present disclosure relates to a terminal device, a base station device, and a wireless communication system.

[0002] In today's networks, traffic from mobile devices (smartphones and feature phones) accounts for the majority of network resources, and this trend is expected to continue. In addition to traffic from mobile devices, IoT (Internet of Things) services (e.g., transportation systems, smart meters, and monitoring systems for devices) are also being developed. Therefore, these networks are being required to support services with diverse requirements.

[0003] In order to accommodate such diverse services, communication standards for fifth-generation mobile communications (5G or NR (New Radio)) (for example, Non-Patent Documents 11 to 27) include, for example, 4G (fourth-generation mobile communications) standard technologies (for example, Non-Patent Documents 1 to 10), as well as eMBB (Enhanced Mobile Broadband), Massive MTC (Machine Type Communications), and URLLC (Ultra-Reliable and Low Latency Communications). Standards have been developed that assume support for many use cases.

[0004] The 3rd Generation Partnership Project (3GPP), an international standardization project, is currently continuously studying and standardizing technologies to extend the above communication standards.

[0005] In a wireless communication system, for example, a random access procedure (RACH: Random Access CHannel procedure) is performed to perform data communication between a terminal device and a base station device. The random access procedure includes, for example, a two-step random access procedure and a four-step random access procedure. Furthermore, the random access procedure includes, for example, a contention-based random access procedure (CBRA: Contention Based Random Access) and a contention-free random access procedure (CFRA: Contention Free Random Access) (Non-Patent Documents 6 and 21).

[0006] A 3GPP working group is currently studying the introduction of a technology called PRACH Multiple Transmission, which is a physical channel used in random access procedures (PRACH Multiple Transmission) (Non-Patent Document 28). This technology enables the coverage to be expanded by transmitting multiple PRACHs.

[0007] 3GPP TS 36.133 V17.10.03GPP TS 36.211 V17.3.03GPP TS 36.212 V17.1.03GPP TS 36.213 V17.5.03GPP TS 36.214 V17.0.03GPP TS 36.300 V17.4.03GPP TS 36.321 V17.5.03GPP TS 36.322 V17.0.03GPP TS 36.323 V17.2.03GPP TS 36.331 V17.4.03GPP TS 37.324 V17.0.03GPP TS 37.340 V17.5.03GPP TS 38.133 V17.10.03GPP TS 38.201 V17.0.03GPP TS 38.202 V17.3.03GPP TS 38.211 V17.5.03GPP TS 38.212 V17.5.03GPP TS 38.213 V17.6.03GPP TS 38.214 V17.6.03GPP TS 38.215 V17.3.03GPP TS 38.300 V17.5.03GPP TS 38.321 V17.5.03GPP TS 38.322 V17.3.03GPP TS 38.323 V17.5.03GPP TS 38.331 V17.5.03GPP TS 38.420 V17.2.03GPP TS 38.423 V17.5.0R1-2306069

[0008] Here, the continuous transmission of the PRACH as described above is linked to a random access preamble (hereinafter also simply referred to as a preamble) used for transmitting the PRACH. Therefore, when multiple transmissions of the PRACH are performed in CBRA, the terminal device determines the number of multiple transmissions of the PRACH (hereinafter also simply referred to as the number of multiple transmissions) by using a measurement result of RSRP (Reference Signal Received Power), and then selects a preamble according to the determined number of multiple transmissions.

[0009] However, when CFRA is performed, the base station device selects a preamble, and therefore, in this case, the base station device cannot determine the number of multiple transmissions using the RSRP measurement results in the terminal device, and therefore cannot select a preamble.

[0010] Therefore, in a wireless communication system, for example, when CFRA is performed, multiple transmissions of PRACH cannot be performed.

[0011] Therefore, one disclosure provides a terminal device, a base station device, and a communication system that enable multiple transmissions of PRACH when CFRA is performed.

[0012] a control unit that determines a number of transmissions of the PRACH according to the received power and the threshold information, selects the preamble corresponding to the number of transmissions from the plurality of candidates by referring to the candidate information, and determines a second transmission timing of each of the PRACHs to be transmitted after the first transmission timing according to the first transmission timing and the number of transmissions; and a transmission unit that transmits the PRACH to the base station device at the first transmission timing and the second transmission timing by using the selected preamble.

[0013] One disclosure enables multiple transmissions of PRACH when CFRA is performed.

[0014] FIG. 1 is a diagram illustrating an example of the configuration of a wireless communication system 10. FIG. 2 is a diagram illustrating an example of the configuration of a terminal device 100. FIG. 3 is a diagram illustrating an example of the configuration of a base station device 200. FIG. 4 is a diagram illustrating an example of a sequence of terminal transmission processing and base station transmission control processing in the first embodiment. FIG. 5 is a diagram illustrating a specific example of threshold information DT1. FIG. 6 is a diagram illustrating a specific example of candidate information DT2. FIG. 7 is a diagram illustrating terminal transmission processing and base station transmission control processing in the first embodiment. FIG. 8 is a diagram illustrating an example of a sequence in the second embodiment.

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. However, such descriptions should not be interpreted in a limiting sense, and do not limit the subject matter described in the claims. Furthermore, various changes, substitutions, and modifications can be made without departing from the spirit and scope of the present disclosure. Furthermore, different embodiments can be combined as appropriate.

[0016] [First embodiment] (Regarding wireless communication system 10) Fig. 1 is a diagram showing an example of the configuration of a wireless communication system 10. The wireless communication system 10 includes, for example, a terminal device 100, a base station device 200a, and a base station device 200b. Hereinafter, the base station device 200a and the base station device 200b will also be collectively referred to simply as the base station device 200.

[0017] The terminal device 100 is, for example, a communication device that wirelessly connects to the base station device 200 and transmits and receives data. Specifically, the terminal device 100 is, for example, a smartphone or a tablet terminal.

[0018] The base station device 200 is, for example, a device that is wirelessly connected to the terminal device 100 and transmits and receives data. Specifically, the base station device 200 is, for example, an eNodeB or a gNodeB. Note that the base station device 200 may be compatible with various communication generations (for example, 4G, 5G, or Beyond 5G, etc.). The base station device 200 may be, for example, a single device, or may be composed of multiple devices such as a CU (Central Unit) and a DU (Distributed Unit).

[0019] The terminal device 100 performs a radio connection procedure (e.g., a random access procedure (RACH procedure)) when communicating with the base station device 200. The random access procedure is a procedure performed by the terminal device 100 to synchronize with the base station device 200, for example.

[0020] 2 is a diagram showing an example of the configuration of the terminal device 100. The terminal device 100 includes, for example, a CPU (Central Processing Unit) 110, a storage 120, a memory 130, and a wireless communication circuit 150.

[0021] The storage 120 is, for example, an auxiliary storage device that stores programs and data, and is a flash memory, a hard disk drive (HDD), a solid state drive (SSD), etc. The storage 120 stores, for example, a terminal communication program 121 and a terminal transmission program 122.

[0022] The memory 130 is, for example, an area into which programs stored in the storage 120 are loaded. Note that the memory 130 may also be used as an area in which programs store data.

[0023] The wireless communication circuit 150 is, for example, a circuit that performs wireless communication with the base station device 200. The wireless communication circuit 150 has, for example, an antenna 151. The antenna 151 includes, for example, a directional antenna that can control the direction of transmission and reception of radio waves.

[0024] The CPU 110 is a processor that, for example, loads a program stored in the storage 120 into the memory 130 and executes it to configure each unit and realize each process.

[0025] The CPU 110 executes the terminal communication program 121 to configure a receiving unit and a transmitting unit and perform terminal communication processing. The terminal communication processing is processing for establishing a wireless connection with the base station device 200 and performing wireless communication, for example.

[0026] The CPU 110 executes, for example, the terminal transmission program 122 to construct a terminal transmitter (hereinafter also simply referred to as a controller) and perform terminal transmission processing. The terminal transmission processing is, for example, processing to transmit multiple PRACHs to the base station device 200. Hereinafter, the PRACH is also referred to as message 1. Specifically, the terminal transmission processing is processing to transmit multiple PRACHs when, for example, CFRA is performed. Note that CFRA is performed, for example, in conjunction with Handover, a PDCCH (Physical Downlink Control Channel) order, or Beam Failure Recovery.

[0027] 3 is a diagram showing an example of the configuration of the base station device 200. The base station device 200 includes a CPU 210, a storage 220, a memory 230, and a wireless communication circuit 250, for example.

[0028] The storage 220 is, for example, an auxiliary storage device that stores programs and data, and is a flash memory, HDD, SSD, etc. The storage 220 stores, for example, a base station communication program 221 and a base station transmission control program 222.

[0029] The memory 230 is, for example, an area into which programs stored in the storage 220 are loaded. Note that the memory 230 may also be used as an area in which programs store data.

[0030] The wireless communication circuit 250 is, for example, a device that performs wireless communication with the terminal device 100. The wireless communication circuit 250 has, for example, an antenna 251. The antenna 251 includes, for example, a directional antenna that can control the direction of transmission and reception of radio waves.

[0031] The CPU 210 is a processor that, for example, loads a program stored in the storage 220 into the memory 230 and executes it to configure each unit and realize each process.

[0032] The CPU 210 executes, for example, the base station communication program 221 to configure a receiving unit and a transmitting unit and perform base station communication processing. The base station communication processing is, for example, processing to perform wireless communication with the terminal device 100. Specifically, in the base station communication processing, for example, the base station device 200 establishes a wireless connection with the terminal device 100, transmits data to the terminal device 100, and receives data from the terminal device 100. Note that the base station communication processing includes, for example, processing associated with a random access procedure between the terminal device 100 and the base station device 200.

[0033] The CPU 210 executes, for example, the base station transmission control program 222 to construct a base station transmission control unit (hereinafter also simply referred to as a control unit) and perform base station transmission control processing. The base station transmission control processing is, for example, processing to control multiple transmissions of the PRACH from the terminal device 100 to the base station device 200. Specifically, the base station transmission control processing is, for example, processing to control multiple transmissions of the PRACH when CFRA is performed.

[0034] [First embodiment] Next, terminal transmission processing and base station transmission control processing in the first embodiment will be described. Fig. 4 is a diagram showing an example of the sequence of terminal transmission processing and base station transmission control processing in the first embodiment. Figs. 5 to 7 are diagrams explaining the terminal transmission processing and base station transmission control processing in the first embodiment. Specifically, Fig. 4 is a diagram showing an example of the sequence of terminal transmission processing and base station transmission control processing when CFRA is performed in conjunction with Handover.

[0035] The terminal device 100 measures the RSRP of one or more SSBs (Synchronization Signal Blocks) broadcast from the base station device 200a, for example. Then, the terminal device 100 selects, for example, the SSB with the highest measured RSRP from among the one or more SSBs broadcast from the base station device 200a. The terminal device 100 also measures the RSRP of one or more SSBs broadcast from the base station device 200b, for example. Then, the terminal device 100 selects, for example, the SSB with the highest measured RSRP from among the one or more SSBs broadcast from the base station device 200b. Note that the terminal device 100 may select multiple SSBs instead of selecting the SSB with the highest measured RSRP. Thereafter, the terminal device 100 transmits to the base station device 200a a measurement report including information (hereinafter also referred to as information about the measurement result) about the result of measurement (for example, RSRP) using at least one of the CSI-RS (Channel State Information-Reference Signal) and the SSB transmitted from each of the base station device 200a and the base station device 200b (S11). Note that the terminal device 100 may include, for example, information indicating the SSB used to obtain the measurement result in the measurement report.

[0036] For example, when the base station device 200a receives a measurement report transmitted from the terminal device 100, the base station device 200a refers to information on the measurement results included in the received measurement report and determines whether or not to perform a handover from the base station device 200a to the base station device 200b (S12).

[0037] As a result, if it is determined that the base station device 200a should perform a handover to the base station device 200b, the base station device 200a transmits, for example, a handover request to the base station device 200b (S13).

[0038] Specifically, the base station device 200a transmits, to the base station device 200b, a HANDOVER REQUEST including information on the measurement result included in the measurement report received from the terminal device 100 (for example, the RSRP for the base station device 200b).

[0039] Note that, although the following description will be given of a case in which terminal device 100 measures RSRP for base station device 200a and base station device 200b, terminal device 100 may measure RSRP for three or more base station devices 200. Furthermore, the following description will be given of a case in which base station device 200a performs a handover to base station device 200b, but base station device 200a may also perform a handover to a base station device 200 other than base station device 200.

[0040] Returning to FIG. 4, for example, when the base station device 200b receives a HANDOVER REQUEST transmitted from the base station device 200a, the base station device 200b determines whether or not to permit the Handover from the base station device 200a (S14).

[0041] As a result, if it is determined that the Handover from the base station device 200a is permitted, the base station device 200b transmits, for example, a HANDOVER REQUEST ACKNOWLEDGE to the base station device 200a (S15).

[0042] Specifically, base station device 200b transmits to base station device 200a a HANDOVER REQUEST ACKNOWLEDGE message including, for example, information including a threshold value for RSRP (hereinafter also referred to as threshold information DT1) and information including multiple candidates for preambles to be used in PRACH transmissions (hereinafter also referred to as candidate information DT2). Threshold information DT1 is, for example, information generated by base station device 200b, which associates one or more RSRP threshold values ​​with multiple transmission counts corresponding to ranges defined by each threshold. Furthermore, candidate information DT2 is, for example, information generated by base station device 200b, which associates multiple candidates for preambles to be used in PRACH transmissions with multiple transmission counts corresponding to each candidate.

[0043] In this case, the base station device 200b, for example, refers to information on the measurement result included in the HANDOVER REQUEST received from the base station device 200a, and identifies an RO (Rach Occasion) linked to the index of the SSB corresponding to the SSB used by the terminal device 100 for the measurement according to the information on the measurement result. The RO is, for example, a PRACH transmission opportunity. That is, the RO corresponds to, for example, a resource available for transmitting the PRACH. Then, the base station device 200b includes, for example, the identified RO in the HANDOVER REQUEST ACKNOWLEDGE. Specific examples of the threshold information DT1 and the candidate information DT2 will be described below.

[0044] (Specific Example of Threshold Information DT1) First, a specific example of threshold information DT1 will be described. Fig. 5 is a diagram illustrating a specific example of threshold information DT1. In the following examples, "-" indicates that no information is set.

[0045] In the first line of the threshold information DT1 shown in Fig. 5, for example, "a" is set as the "threshold" and "1 (time)" is set as the "number of multiple transmissions." In addition, in the second line of the threshold information DT1 shown in Fig. 5, for example, "b" is set as the "threshold" and "2 (times)" is set as the "number of multiple transmissions." In addition, in the third line of the threshold information DT1 shown in Fig. 5, for example, "c" is set as the "threshold" and "4 (times)" is set as the "number of multiple transmissions." Furthermore, in the fourth line of the threshold information DT1 shown in Fig. 5, for example, "-" is set as the "threshold" and "8 (times)" is set as the "number of multiple transmissions."

[0046] That is, the threshold information DT1 shown in Figure 5 indicates that, for example, the number of multiple transmissions corresponding to when RSRP is a or greater is 1 (times), the number of multiple transmissions corresponding to when RSRP is b or greater but less than a is 2 (times), the number of multiple transmissions corresponding to when RSRP is c or greater but less than b is 4 (times), and the number of multiple transmissions corresponding to when RSRP is less than c is 8 (times).

[0047] (Specific Example of Candidate Information DT2) Next, a specific example of the candidate information DT2 will be described. Fig. 6 is a diagram for explaining a specific example of the candidate information DT2.

[0048] In the first line of the candidate information DT2 shown in FIG. 6, for example, "Preamble #A" is set as the "preamble" and "1 (time)" is set as the "number of multiple transmissions." Furthermore, in the second line of the candidate information DT2 shown in FIG. 6, for example, "Preamble #B" is set as the "preamble" and "2 (times)" is set as the "number of multiple transmissions." Furthermore, in the third line of the candidate information DT2 shown in FIG. 6, for example, "Preamble #C" is set as the "preamble" and "4 (times)" is set as the "number of multiple transmissions." Furthermore, in the fourth line of the candidate information DT2 shown in FIG. 6, for example, "Preamble #D" is set as the "preamble" and "8 (times)" is set as the "number of multiple transmissions."

[0049] That is, the candidate information DT2 shown in FIG. 6 indicates that, for example, the preamble corresponding to the number of multiple transmissions being 1 is Preamble #A, the preamble corresponding to the number of multiple transmissions being 2 is Preamble #B, the preamble corresponding to the number of multiple transmissions being 4 is Preamble #C, and the preamble corresponding to the number of multiple transmissions being 8 is Preamble #D.

[0050] Returning to FIG. 4, for example, when the base station device 200a receives a HANDOVER REQUEST ACKNOWLEDGE transmitted from the base station device 200b, the base station device 200a transmits an RRC Reconfiguration to the terminal device 100 (S16).

[0051] Specifically, the base station device 200a transmits to the terminal device 100, for example, an RRC Reconfiguration in which an RO (the RO included in the HANDOVER REQUEST ACKNOWLEDGE) is specified in the ra-ssb-occasionMakingIndex or the ssb-SharedRO-MaskIndex in the RACH-ConfigDedicated.

[0052] In this case, the base station device 200a also includes, for example, the threshold information DT1 and candidate information DT2 included in the HANDOVER REQUEST ACKNOWLEDGE transmitted from the base station device 200b in the RRC Reconfiguration.

[0053] For example, when the terminal device 100 receives an RRC Reconfiguration transmitted from the base station device 200a, the terminal device 100 transmits a PRACH to the base station device 200b (S17).

[0054] Specifically, the terminal device 100 transmits the PRACH in a plurality of ROs including the RO indicated by the ra-ssb-occasionMakIndex or the ssb-SharedRO-MaskIndex in the RRC Reconfiguration received from the base station device 200a. Details of the process of S17 will be described below.

[0055] (Details of the Process in S17) The terminal device 100, for example, refers to threshold information DT1 included in the RRC Reconfiguration transmitted from the base station device 200a, and identifies the number of multiple transmissions corresponding to the RSRP measured in the terminal device 100.

[0056] Specifically, the information in the second row of the threshold information DT1 described in Fig. 5 indicates, for example, that the number of multiple transmissions corresponding to the range in which the RSRP is equal to or greater than b but less than a is 2. Therefore, for example, when the RSRP measured in the terminal device 100 is equal to or greater than b but less than a, the terminal device 100 specifies 2 as the number of multiple transmissions.

[0057] Furthermore, the terminal device 100 identifies an RO group including ROs included in the RRC Reconfiguration transmitted from the base station device 200 a. The RO group is a group of ROs used in multiple PRACH transmissions and associated with the same SSB.

[0058] 7, for example, an RO group including RO4, RO16, RO28, and RO40 is an RO group associated with SSB4. Therefore, for example, when the RO included in the RRC Reconfiguration transmitted from the base station device 200a is RO4, the terminal device 100 identifies the RO group corresponding to SSB4 as the RO group to be used in multiple transmissions of the PRACH.

[0059] Then, the terminal device 100 selects, for example, from the ROs corresponding to the identified RO group, a number of ROs corresponding to the number of transmissions in order from the top, and transmits the PRACH in each of the selected ROs.

[0060] Specifically, in the examples of each RO shown in FIG. 7 , for example, if the RO included in the RRC Reconfiguration transmitted from the base station device 200a is RO4 and the number of multiple transmissions is 2 (times), the terminal device 100 transmits the PRACH in each of RO4 and RO16.

[0061] 4, for example, when the base station device 200b receives a PRACH transmitted from the terminal device 100, the base station device 200b transmits an RAR (Random Access Response) corresponding to the received PRACH to the base station device 200a (S18). Hereinafter, the RAR is also referred to as message 2.

[0062] For example, when the terminal device 100 receives an RAR transmitted from the base station device 200b, the terminal device 100 transmits an RRC Reconfiguration Complete to the base station device 200b (S19).

[0063] In this way, the base station device 200b in this embodiment transmits to the terminal device 100, for example, threshold information DT1 including a threshold related to the received power of the signal from the base station device 200b (hereinafter also referred to as the first received power), candidate information DT2 indicating multiple candidates for the preamble to be used for transmitting the PRACH, and an RO indicating the start of the transmission timing of the PRACH (hereinafter also referred to as the first RO or the first transmission timing).

[0064] Then, the terminal device 100 in this embodiment determines the number of times of transmission of the PRACH (hereinafter also referred to as the first number of times of transmission) in accordance with, for example, the first received power and threshold information DT1, selects a preamble (hereinafter also referred to as the first preamble) corresponding to the first number of times of transmission from among the plurality of candidates by referring to the candidate information DT2, and determines each RO of the PRACH to be transmitted after the first RO (hereinafter also referred to as the second RO or the second transmission timing) in accordance with the first RO and the first number of times of transmission. Thereafter, the terminal device 100 in this embodiment transmits the PRACH to the base station device 200b in each of the first RO and the second RO by using, for example, the selected first preamble.

[0065] That is, for example, for each number of times that the terminal device 100 may calculate as the number of multiple transmissions, the base station device 200b assigns to the terminal device 100 a preamble to be used for transmitting the PRACH corresponding to that number. Specifically, if the number of times that the terminal device 100 may calculate as the number of multiple transmissions is 2, 4, or 8, the base station device 200b assigns to the terminal device 100, for example, a preamble corresponding to 2, 4, or 8, respectively. Then, the base station device 200a generates candidate information DT2 that associates the multiple preambles assigned to the terminal device 100 with the number of multiple transmissions corresponding to each preamble, and transmits this candidate information to the terminal device 100. Furthermore, the base station device 200b transmits, for example, threshold information DT1 that the terminal device 100 uses when identifying the number of multiple transmissions to the terminal device 100.

[0066] Thereafter, the terminal device 100 specifies the first plurality of transmission counts, for example, from threshold information DT1 transmitted from the base station device 200b and the first received power at the terminal device 100. Then, the terminal device 100 selects a first preamble corresponding to the first plurality of transmission counts, from among a plurality of preamble candidates indicated in candidate information DT2 received from the base station device 200b, for example. Furthermore, the terminal device 100 specifies one or more second ROs from the first RO specified by the base station device 200b, for example. Then, the terminal device 100 repeatedly transmits the PRACH for the first plurality of transmission counts in each of the first RO and the one or more second ROs, for example.

[0067] As a result, even when CFRA is performed, for example, the terminal device 100 in this embodiment can specify the number of times the PRACH is transmitted multiple times and the ROs for transmitting each of the PRACHs corresponding to the number of times the PRACH is transmitted. Therefore, even when CFRA is performed, for example, the wireless communication system 10 in this embodiment can perform multiple transmissions of the PRACH from the terminal device 100 to the base station device 200b.

[0068] Note that, when CFRA is performed in association with a PDCCH order or Beam Failure Recovery, the base station device 200a transmits, for example, the RO transmitted from the base station device 200b to the terminal device 100 by Random Access Preamble Assignment (hereinafter also referred to as message 0). In this case, the base station device 200a also broadcasts, for example, threshold information DT1 and candidate information DT2 by SIB1 (System Information Block Type 1).

[0069] In the above example, the base station device 200a and the base station device 200b are different base station devices 200. However, this is not limiting. Specifically, the base station device 200a and the base station device 200b may be the same base station device 200, and CFRA may be performed in conjunction with inter-cell handover in multiple cells corresponding to the base station device 200.

[0070] [Second embodiment] Next, terminal transmission processing and base station transmission control processing in a second embodiment will be described. Fig. 8 is a diagram showing an example of a sequence in the second embodiment. Specifically, Fig. 8 is a diagram showing an example of a sequence of terminal transmission processing and base station transmission control processing when CFRA is performed in conjunction with Handover. Note that, as in the case described in Fig. 4, the following description will be given of a case where Handover is performed from base station device 200a to base station device 200b.

[0071] 4, the terminal device 100 transmits to the base station device 200a a measurement report including information (information about the measurement result) about the result of measurement using at least one of the CSI-RS and the SSB transmitted from each of the base station device 200a and the base station device 200b (S21). Note that the terminal device 100 may include, for example, information indicating the SSB used to obtain the measurement result in the measurement report.

[0072] As in the case described with reference to FIG. 4, when the base station device 200a receives, for example, a measurement report transmitted from the terminal device 100, the base station device 200a refers to information on the measurement result included in the received measurement and determines whether or not to perform a handover from the base station device 200a to the base station device 200b (S22).

[0073] As a result, if it is determined that the base station device 200a should perform a handover to the base station device 200b, the base station device 200a transmits, for example, a HANDOVER REQUEST to the base station device 200b, as in the case described with reference to FIG. 4 (S23).

[0074] As in the case described with reference to FIG. 4, when the base station device 200b receives a HANDOVER REQUEST transmitted from the base station device 200a, the base station device 200b determines whether or not to permit the Handover from the base station device 200a (S24).

[0075] As a result, if it is determined that the Handover from the base station device 200a is permitted, the base station device 200b transmits, for example, a HANDOVER REQUEST ACKNOWLEDGE to the base station device 200a (S25).

[0076] Specifically, unlike the case described in Fig. 4, base station device 200b specifies the number of times that the PRACH will be transmitted from terminal device 100 to base station device 200b, for example, from the RSRP included in base station device 200a (RSRP for base station device 200b) and threshold information DT1. Then, base station device 200b transmits, for example, a HANDOVER REQUEST ACKNOWLEDGE including the specified number of times of transmission to base station device 200a.

[0077] That is, in the wireless communication system 10 in the example shown in Fig. 8, unlike the case described in Fig. 4, for example, the number of times that the PRACH is transmitted from the terminal device 100 to the base station device 200b is determined by the base station device 200b. Therefore, in the wireless communication system 10 in the example shown in Fig. 8, unlike the case described in Fig. 4, for example, threshold information DT1 and candidate information DT2 are not transmitted from the terminal device 100 to the base station device 200b.

[0078] In this case, the base station device 200b, for example, refers to information on the measurement result included in the HANDOVER REQUEST received from the base station device 200a, and, according to the information on the measurement result, identifies an RO linked to the index of the SSB corresponding to the SSB used for the measurement by the terminal device 100. Then, the base station device 200b includes, for example, the identified RO in the HANDOVER REQUEST ACKNOWLEDGE.

[0079] For example, when the base station device 200a receives a HANDOVER REQUEST ACKNOWLEDGE transmitted from the base station device 200b, the base station device 200a transmits an RRC Reconfiguration to the terminal device 100 (S26).

[0080] Specifically, as in the case described with reference to FIG. 4, the base station device 200a transmits to the terminal device 100 an RRC Reconfiguration in which the RO (the RO included in the HANDOVER REQUEST ACKNOWLEDGE) is specified in, for example, the ra-ssb-occasionMakingIndex or the ssb-SharedRO-MaskIndex in the RACH-ConfigDedicated.

[0081] Also, unlike the case described with reference to FIG. 4, the base station device 200a includes, for example, the number of multiple transmissions included in the HANDOVER REQUEST ACKNOWLEDGE transmitted from the base station device 200b in the RRC Reconfiguration.

[0082] For example, when the terminal device 100 receives an RRC Reconfiguration transmitted from the base station device 200a, the terminal device 100 transmits a PRACH to the base station device 200b (S27).

[0083] Specifically, the terminal device 100 transmits the PRACH in a plurality of ROs including the RO indicated by the ra-ssb-occasionMakIndex or the ssb-SharedRO-MaskIndex in the RRC Reconfiguration received from the base station device 200a, for example.

[0084] More specifically, unlike the case described in Fig. 4, the terminal device 100 identifies, for example, the number of multiple transmissions included in the RRC Reconfiguration transmitted from the base station device 200a. Furthermore, the terminal device 100 identifies, for example, an RO group including an RO included in the RRC Reconfiguration transmitted from the base station device 200a. Then, the terminal device 100 selects, from the RO group corresponding to the identified RO group, a number of ROs corresponding to the number of multiple transmissions, sequentially from the top, and transmits the ROs to the base station device 200a for each of the selected ROs.

[0085] For example, when the base station device 200b receives a PRACH transmitted from the terminal device 100, the base station device 200b transmits an RAR corresponding to the received PRACH to the base station device 200a (S28).

[0086] For example, when the terminal device 100 receives an RAR transmitted from the base station device 200b, the terminal device 100 transmits an RRC Reconfiguration Complete to the base station device 200b (S29).

[0087] In this way, the terminal device 100 in this embodiment transmits, for example, the received power of the signal from the base station device 200b (hereinafter also referred to as second received power) to the base station device 200b.

[0088] Then, base station device 200b in this embodiment calculates a plurality of transmission times of the PRACH (hereinafter also referred to as a second plurality of transmission times) in accordance with, for example, the second received power and threshold information including a threshold related to the second received power. Furthermore, base station device 200b in this embodiment transmits, to terminal device 100, for example, the second plurality of transmission times and transmission timing indicating the start of the transmission timing of the PRACH (hereinafter also referred to as a third RO or third transmission timing).

[0089] Thereafter, the terminal device 100 in this embodiment determines, for example, each RO of the PRACH to be transmitted after the third RO (hereinafter also referred to as a fourth RO or a fourth transmission timing) in accordance with the second plurality of transmission times and the third transmission timing. Then, the terminal device 100 in this embodiment transmits the PRACH to the base station device 200b in each of the third RO and the fourth RO, for example.

[0090] 4 , the base station device 200b calculates the second plurality of transmission times by using, for example, the second received power received from the terminal device 100. Then, the base station device 200b transmits the calculated second plurality of transmission times to the terminal device 100, for example.

[0091] Thereafter, the terminal device 100 identifies one or more fourth ROs from the third RO specified by the base station device 200b, for example. Then, the terminal device 100 repeatedly transmits the PRACH a third plurality of times in each of the third RO and the one or more fourth ROs, for example.

[0092] As a result, the terminal device 100 in this embodiment can specify the number of times to transmit the PRACH multiple times and the ROs for transmitting each of the PRACHs corresponding to the number of times to transmit the PRACH, even when, for example, CFRA is performed, as in the case described with reference to Fig. 4. Therefore, the wireless communication system 10 in this embodiment can perform multiple transmissions of the PRACH from the terminal device 100 to the base station device 200b, even when, for example, CFRA is performed.

[0093] When CFRA is performed in association with a PDCCH order, the base station device 200a may notify the terminal device 100 of the number of multiple transmissions by using, for example, the reserved bits-2 bit of DCI format1_0.

[0094] Furthermore, the base station device 200a may notify the terminal device 100 of the number of multiple transmissions by using reserved bits of the PRACH Mask Index, for example.

[0095] Furthermore, the base station device 200a may notify the terminal device 100 of the number of multiple transmissions by using a preamble index associated with the number of multiple transmissions, for example. That is, each preamble corresponds to each of the multiple transmission numbers. Therefore, the base station device 200a can notify the terminal device 100 of the number of multiple transmissions by notifying the preamble index, for example.

[0096] In the above example, the case where the number of transmissions is determined by using RSRP has been described, but this is not limiting. Specifically, the base station device 200b may determine the number of transmissions by using, for example, SINR (Signal to Interference Noise Ratio).

[0097] In the above example, the case where the number of multiple transmissions is determined using the threshold information DT1 has been described, but this is not limiting. Specifically, the base station device 200b may determine the number of multiple transmissions using, for example, power class information or information such as the number of terminal devices subordinate to the base station device 200b.

[0098] In the above example, the base station device 200a and the base station device 200b are different base station devices 200. However, this is not limiting. Specifically, the base station device 200a and the base station device 200b may be the same base station device 200, and CFRA may be performed in conjunction with inter-cell handover in multiple cells corresponding to the base station device 200.

[0099] 10: Wireless communication system 100: Terminal device 110: CPU 120: Storage 121: Terminal communication program 122: Terminal transmission program 130: Memory 150: Wireless communication circuit 151: Antenna 200: Base station device 210: CPU 220: Storage 221: Base station communication program 222: Base station transmission control program 230: Memory 250: Wireless communication circuit 251: Antenna

Claims

1. A terminal device that executes a non-contention type random access procedure, comprising: a receiver that receives from the base station device threshold information including a threshold related to the received power of a signal from a base station device, candidate information indicating multiple candidates for a preamble used in transmitting a PRACH (Physical Random Access CHannel) in the random access procedure, and a first transmission timing indicating the beginning of the transmission timing of the PRACH; a control unit that determines the number of transmissions of the PRACH in accordance with the received power and the threshold information, refers to the candidate information to select the preamble corresponding to the number of transmissions from the multiple candidates, and determines a second transmission timing of each of the PRACHs to be transmitted after the first transmission timing in accordance with the first transmission timing and the number of transmissions; and a transmitter that transmits the PRACH to the base station device at each of the first transmission timing and the second transmission timing by using the selected preamble.

2. The terminal device according to claim 1, wherein the threshold information, the candidate information and the first transmission timing are included in an RRC Reconfiguration, and the receiving unit receives the RRC Reconfiguration transmitted from the base station device.

3. The terminal device according to claim 2, wherein the threshold information and the candidate information are included in SIB1 (System Information Block Type 1), the first transmission timing is included in message 0 in the random access procedure, and the receiving unit receives the SIB1 and the message 0 transmitted from the base station device.

4. The terminal device according to claim 1, wherein each of the first transmission timing and the second transmission timing is a RACH Occasion.

5. A terminal device according to claim 1, characterized in that the candidate information is information associating each of the multiple candidates with the number of transmissions corresponding to each of the multiple candidates, and the control unit selects, from the multiple candidates, the candidate corresponding to the number of transmissions as the preamble.

6. A terminal device that executes a non-contention type random access procedure, comprising: a transmitter that transmits the received power of a signal from a base station device to the base station device; a receiver that receives the number of PRACH transmissions in the random access procedure calculated in accordance with the received power and threshold information including a threshold related to the received power, and a third transmission timing indicating the beginning of the transmission timing of the PRACH; a control unit that determines a fourth transmission timing of each of the PRACHs that is transmitted after the third transmission timing in accordance with the number of transmissions and the third transmission timing; and the transmitter that transmits the PRACH to the base station device at each of the third transmission timing and the fourth transmission timing.

7. A base station device that executes a non-contention type random access procedure, comprising: a transmitting unit that transmits to a terminal device threshold information including a threshold related to the received power of a signal from the base station device, candidate information indicating a plurality of candidates for a preamble used in transmitting a PRACH in the random access procedure, and a first transmission timing indicating the beginning of the transmission timing of the PRACH, thereby determining the number of transmissions of the PRACH according to the received power and the threshold information, selecting the preamble corresponding to the number of transmissions from the plurality of candidates by referring to the candidate information, and causing the terminal device to perform a process of determining a second transmission timing for each of the PRACHs transmitted after the first transmission timing according to the first transmission timing and the number of transmissions; and a receiving unit that receives from the terminal device each of the PRACHs that is transmitted using the selected preamble and that is transmitted at the first transmission timing and the second transmission timing, respectively.

8. A base station device that executes a non-contention type random access procedure, comprising: a receiving unit that receives a signal from the base station device based on the received power in a terminal device; a control unit that calculates the number of transmissions of a PRACH in the random access procedure in accordance with the received power and threshold information including a threshold related to the received power; and a transmitting unit that transmits the number of transmissions and a third transmission timing indicating the beginning of the transmission timing of the PRACH to the terminal device, thereby causing the terminal device to determine a fourth transmission timing of each of the PRACHs that is transmitted after the third transmission timing in accordance with the number of transmissions and the third transmission timing, wherein the receiving unit receives from the terminal device each of the PRACHs that is transmitted at the third transmission timing and the fourth transmission timing and corresponds to the number of transmissions.

9. A wireless communication system having a terminal device and a base station device, and executing a non-contention type random access procedure between the terminal device and the base station device, wherein the base station device transmits to the terminal device threshold information including a threshold related to a received power of a signal from the base station device, candidate information indicating a plurality of candidates for a preamble to be used for transmitting a PRACH in the random access procedure, and a first transmission timing indicating the beginning of the transmission timing of the PRACH, the terminal device determines the number of transmissions of the PRACH according to the received power and the threshold information, selects the preamble corresponding to the number of transmissions from the plurality of candidates by referring to the candidate information, and determines a second transmission timing for each of the PRACHs to be transmitted after the first transmission timing according to the first transmission timing and the number of transmissions, and the terminal device transmits the PRACH to the base station device at each of the first transmission timing and the second transmission timing by using the selected preamble.

10. A wireless communication system having a terminal device and a base station device, and executing a non-contention type random access procedure between the terminal device and the base station device, wherein the terminal device transmits the received power of a signal from the base station device to the base station device, the base station device calculates the number of transmissions of PRACH in the random access procedure based on the received power and threshold information including a threshold related to the received power, the base station device transmits the number of transmissions and a third transmission timing indicating the beginning of the transmission timing of the PRACH to the terminal device, the terminal device determines a fourth transmission timing of each of the PRACHs to be transmitted after the third transmission timing based on the number of transmissions and the third transmission timing, and the terminal device transmits the PRACH to the base station device at each of the third transmission timing and the fourth transmission timing.

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