Terminal device, wireless communication system, and retransmission control method

Abstract

A terminal device (100) comprises: a wireless communication unit (110) which transmits and receives signals between a first terminal device and a second terminal device; and a processor (120) connected to the wireless communication unit, wherein the processor (120) detects, on the basis of the signals received by the wireless communication unit (110), that simultaneous transmission by the first terminal device and the second terminal device occurs, when simultaneous transmission is detected, and executes a process for generating a retransmission request for at least one of the first terminal device and the second terminal device, and transmitting the generated retransmission request from the wireless communication unit (110).

Description

[Technical field]

[0001] The present invention relates to a terminal device, a wireless communication system, and a retransmission control method. [Background technology]

[0002] In today's networks, traffic from mobile devices (smartphones and feature phones) accounts for the majority of network resources, and the traffic used by mobile devices is expected to continue to expand in the future.

[0003] On the other hand, there is a demand to support services with diverse requirements in line with the development of IoT (Internet of Things) services (e.g., transportation systems, smart meters, and monitoring systems for devices, etc.). Therefore, in addition to the standard technologies of 4G (4th generation mobile communications), the communication standards for 5th generation mobile communications (5G or NR (New Radio)) require technologies that achieve even higher data rates, larger capacities, and lower latency.

[0004] Regarding the fifth-generation communication standard, technical studies are being conducted in working groups of the Third Generation Partnership Project (3GPP) (e.g., TSG-RAN WG1, TSG-RAN WG2, etc.), and the standard specifications have been updated since December 2017 (Non-Patent Documents 2 to 28).

[0005] As mentioned above, in order to accommodate a wide variety of services, 5G is expected to support many use cases classified into eMBB (Enhanced Mobile Broadband), Massive MTC (Machine Type Communications), and URLLC (Ultra-Reliable and Low Latency Communication).

[0006] In addition, the 3GPP working group is also discussing NR-V2X (New Radio Vehicle to Everything) communication. NR-V2X is a general term for V2V (Vehicle to Vehicle), which performs communication between vehicles, V2P (Vehicle to Pedestrian), which performs communication between vehicles and pedestrians, V2I (Vehicle to Infrastructure), which performs communication between vehicles and road infrastructure such as signs, and V2N (Vehicle to Network), which performs communication between vehicles and networks, using, for example, a side link channel. Provisions regarding V2X are described in, for example, Non-Patent Document 1.

[0007] Regarding resource allocation in NR-V2X, there is an allocation method in which a control channel (PSCCH: Physical Sidelink Control CHannel) and a data channel (PSSCH: Physical Sidelink Shared CHannle) are multiplexed by TDM (Time Division Multiplexing) or FDM (Frequency Division Multiplexing). Note that, for example, SCI (Sidelink Control Information) including information on the modulation method and coding rate of the corresponding PSSCH data is mapped to the PSCCH resource.

[0008] Also, in order to improve the channel quality of the sidelink, a feedback channel (PSFCH: Physical Sidelink Feedback CHannel) has been introduced. The PSFCH is used for data retransmission control. That is, the receiving terminal device transmits information indicating whether or not data retransmission is necessary using the PSFCH, thereby making it possible to control retransmission by the transmitting terminal device. For example, in the case of groupcast in which a terminal device transmits data to multiple terminal devices belonging to the same group, there are the following two types of retransmission control using the PSFCH.

[0009] In the first retransmission control, when control information such as SCI is received but the corresponding data is not received correctly, each terminal device in the group transmits a NACK indicating that the data needs to be retransmitted in the PSFCH. Also, when the control information and the data are received correctly, each terminal device does not transmit anything in the PSFCH. Therefore, the terminal device that is the data transmission source retransmits the data when a NACK is received in the PSFCH.

[0010] On the other hand, in the second retransmission control, when the control information is received but the corresponding data is not received correctly, each terminal device in the group transmits a NACK in the PSFCH in the same manner as in the first retransmission control. Also, when the control information and the data are received correctly, each terminal device transmits an ACK indicating that the data does not need to be retransmitted in the PSFCH. Therefore, the terminal device that is the data transmission source retransmits the data when an ACK is not received in the PSFCH, that is, when a NACK is received or nothing is received. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] International Publication No. 2015 / 115505 [Non-patent literature]

[0012] [Non-Patent Document 1] 3GPP TS 22.186 V16.2.0(2019-06) [Non-Patent Document 2] 3GPP TS 37.340 V16.2.0(2020-07) [Non-Patent Document 3] 3GPP TS 38.201 V16.0.0(2019-12) [Non-Patent Document 4] 3GPP TS 38.202 V16.1.0(2020-06)

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Non-licensed literature 9

Non-licensed literature 10

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Non-licensed Document 13

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Non-licensed Document 15

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Non-licensed Document 20

[0013] Incidentally, a terminal device implementing V2X may perform half-duplex communication in which transmission and reception are not performed simultaneously, for example, to reduce costs, etc. A terminal device performing half-duplex communication does not receive control information and data transmitted from other terminal devices during a transmission process.

[0014] Therefore, for example, when multiple terminal devices in the same group perform transmission processing at the same time, the control information and data transmitted from the terminal device are not received by the other terminal devices that are performing transmission processing. In other words, each terminal device that performs transmission processing at the same time does not detect that control information and data have been transmitted from the other terminal devices during transmission processing. As a result, these terminal devices do not transmit ACK or NACK in PSFCH.

[0015] However, in the wireless communication system in which the above-mentioned first retransmission control is performed, there is a problem that the reliability of communication may be reduced because ACK and NACK are not transmitted and appropriate retransmission is not performed. Specifically, when a terminal device performs half-duplex communication in a wireless communication system in which the first retransmission control is performed, data may not be retransmitted even though there is a terminal device in the group that has not correctly received data. That is, a terminal device that does not detect control information and data transmitted from another terminal device because it is in the middle of transmission processing does not transmit ACK or NACK, so that data retransmission does not occur when the first retransmission control is performed. As a result, there is a risk that the reliability required for the wireless communication system will not be satisfied. For example, in a wireless communication system for automatic driving, although a high reliability of 99.99 to 99.999% is required, appropriate data retransmission is not performed when the terminal device performs half-duplex communication, making it difficult to satisfy the required reliability.

[0016] The disclosed technology has been made in consideration of the above points, and aims to provide a terminal device, a wireless communication system, and a retransmission control method that can improve the reliability of communications. [Means for solving the problem]

[0017] In one aspect, a terminal device disclosed in the present application has a wireless communication unit that transmits and receives signals between a first terminal device and a second terminal device, and a processor connected to the wireless communication unit, and the processor detects that simultaneous transmission by the first terminal device and the second terminal device is occurring based on a signal received by the wireless communication unit, and when simultaneous transmission is detected, generates a retransmission request for at least one of the first terminal device and the second terminal device, and executes a process of transmitting the generated retransmission request from the wireless communication unit. Effect of the Invention

[0018] According to one aspect of the terminal device, the wireless communication system, and the retransmission control method disclosed in the present application, it is possible to achieve an effect of improving the reliability of communication. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram showing a configuration of a wireless communication system according to the first embodiment. [Diagram 2] FIG. 2 is a block diagram showing a configuration of a terminal device according to the first embodiment. [Diagram 3] FIG. 3 is a flow diagram showing a retransmission control method according to the first embodiment. [Figure 4] FIG. 4 is a diagram showing a specific example of transmission and reception timing of the terminal device. [Diagram 5] FIG. 5 is a diagram for comparing specific examples of reception rates. [Figure 6] FIG. 6 is a block diagram showing a configuration of a terminal device according to the second embodiment. [Figure 7] FIG. 7 is a flow diagram showing a retransmission control method according to the second embodiment. [Figure 8] FIG. 8 is a diagram showing a specific example of transmission and reception timing of the terminal device. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, embodiments of a terminal device, a wireless communication system, and a retransmission control method disclosed in the present application will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

[0021] (Embodiment 1) Fig. 1 is a diagram showing a configuration of a wireless communication system according to the first embodiment. As shown in Fig. 1, for example, a plurality of terminal devices 100 mounted on an automobile form a group with other terminal devices 100 located within a communication range CR from the respective terminal devices, and execute groupcast within the group. That is, the terminal devices 100 transmit signals to the other terminal devices 100 within their respective communication ranges CR, and receive signals from the other terminal devices 100 within their respective communication ranges CR.

[0022] However, since the terminal device 100 performs signal transmission and reception by half-duplex communication, it does not receive signals from other terminal devices 100 during transmission processing, and does not transmit signals to other terminal devices 100 during reception processing. In addition, the terminal device 100 performs retransmission control such as HARQ (Hybrid Automatic Repeat reQuest). That is, when control information such as SCI is received but the corresponding data is not received correctly, the terminal device 100 requests retransmission of the data. Specifically, when the data is not received correctly, the terminal device 100 transmits a NACK in the PSFCH indicating that the data needs to be retransmitted.

[0023] Furthermore, when the terminal device 100 detects that multiple terminal devices 100 in a group are transmitting data simultaneously based on control information such as SCI, the terminal device 100 transmits a NACK on the PSFCH even if the terminal device 100 itself correctly receives the data. That is, when multiple terminal devices 100 in a group are simultaneously performing transmission processing, the terminal device 100 transmits a NACK on behalf of these terminal devices 100.

[0024] Fig. 2 is a block diagram showing a configuration of the terminal device 100 according to the embodiment 1. The terminal device 100 shown in Fig. 2 includes a radio communication unit 110, a processor 120, and a memory .

[0025] The wireless communication unit 110 executes wireless communication with the other terminal devices 100. That is, the wireless communication unit 110 performs a predetermined wireless transmission process on a transmission signal output from the processor 120, and transmits the signal to the other terminal devices 100 via an antenna. The wireless communication unit 110 also receives a signal from the other terminal devices 100 via the antenna, performs a predetermined wireless reception process on the received signal, and outputs the received signal to the processor 120.

[0026] The processor 120 includes, for example, a CPU (Central Processing Unit), an FPGA (Field Programmable Gate Array), or a DSP (Digital Signal Processor), and generally controls the entire terminal device 100. Specifically, the processor 120 includes a reception control unit 121, a simultaneous transmission detection unit 122, a retransmission control unit 123, a control information generation unit 124, a transmission data generation unit 125, and a transmission control unit 126.

[0027] The reception control unit 121 demodulates and decodes the received signal in the wireless communication unit 110, acquires control information such as SCI from a control channel such as PSCCH, and acquires data from a data channel such as PSSCH. At this time, the reception control unit 121 identifies a radio resource to be used as the data channel based on the result of decoding the control information such as SCI, and executes demodulation and decoding of the data channel.

[0028] The simultaneous transmission detection unit 122 detects, based on the decoded result of the control channel, that there is a terminal device 100 in the group that is simultaneously executing a transmission process. Specifically, the simultaneous transmission detection unit 122 acquires information specifying a radio resource used as a data channel from the control information, and determines whether or not the data channels of the multiple terminal devices 100 overlap in time. Then, when the data channels of the multiple terminal devices 100 overlap in time, the simultaneous transmission detection unit 122 detects that simultaneous transmission by these terminal devices 100 occurs.

[0029] When the reception control unit 121 does not obtain a correct data decoding result, the retransmission control unit 123 generates a NACK indicating that the data needs to be retransmitted, and outputs the NACK to the transmission control unit 126. That is, when the decoding accuracy of the data channel in the reception control unit 121 does not satisfy a predetermined standard, the retransmission control unit 123 generates a retransmission request to the terminal device 100 that is the data transmission source.

[0030] Furthermore, when the simultaneous transmission detection unit 122 detects the occurrence of simultaneous transmission by multiple terminal devices 100, the retransmission control unit 123 generates a NACK indicating that data retransmission is necessary, and outputs it to the transmission control unit 126. That is, when the retransmission control unit 123 detects that the data channels of multiple terminal devices 100 overlap in time, it generates a retransmission request for these terminal devices 100.

[0031] Furthermore, after the control information and transmission data are transmitted by the transmission control unit 126, the retransmission control unit 123 monitors the feedback channel corresponding to the transmission data, and performs retransmission control of the transmitted transmission data when a NACK is received on the feedback channel. That is, when a NACK is received, the retransmission control unit 123 instructs the transmission control unit 126 to retransmit the transmitted transmission data.

[0032] The control information generator 124 generates control information related to data to be transmitted to other terminal devices 100. Specifically, the control information generator 124 generates an SCI including, for example, information specifying a radio resource used as a data channel.

[0033] The transmission data generation unit 125 generates data to be transmitted to other terminal devices 100 .

[0034] The transmission control unit 126 transmits the control information and the transmission data through physical channels such as the PSCCH and the PSSCH. That is, the transmission control unit 126 transmits the control information through a control channel such as the PSCCH, and transmits the transmission data through a data channel such as the PSSCH.

[0035] Furthermore, the transmission control unit 126 transmits the NACK generated by the retransmission control unit 123 through a feedback channel corresponding to the data channel. That is, when the decoding of the data channel fails and a NACK is generated, the transmission control unit 126 transmits the NACK through the feedback channel corresponding to the data channel whose decoding has failed. Furthermore, when simultaneous transmission by a plurality of terminal devices 100 is detected and a NACK is generated, the transmission control unit 126 transmits the NACK through the feedback channel corresponding to the data channels that overlap in time.

[0036] Furthermore, the transmission control unit 126 retransmits the already transmitted transmission data in accordance with an instruction from the retransmission control unit 123 .

[0037] The memory 130 includes, for example, a random access memory (RAM) or a read only memory (ROM), and stores information used in processing by the processor 120.

[0038] Next, a retransmission control method by the terminal device 100 configured as above will be described with reference to a flow diagram shown in FIG.

[0039] Groupcast is performed in the group to which the terminal device 100 belongs, and other terminal devices 100 in the group transmit control information and data. Specifically, the control information is transmitted in a control channel such as the PSCCH, and the data is transmitted in a data channel such as the PSSCH.

[0040] When a control channel signal is received by the wireless communication unit 110 (step S101), the reception control unit 121 demodulates and decodes the control channel to obtain control information. The control information includes information specifying a radio resource to be used as a data channel, and so the data channel signal is received using this information (step S102), and the reception control unit 121 demodulates and decodes the data channel.

[0041] Then, the retransmission control unit 123 judges whether the decoding of the data channel has been successful (step S103), and if it is judged that the decoding of the data channel has failed and retransmission of the data is necessary (step S103 No), a NACK is generated to request retransmission of the data. The generated NACK is transmitted by the transmission control unit 126 using a feedback channel corresponding to the data channel for which decoding has failed. In other words, a retransmission request is made for the data that has not been correctly received (step S105).

[0042] On the other hand, if the decoding of the data channel is successful (step S103 Yes), the simultaneous transmission detection unit 122 judges whether or not multiple terminal devices 100 have executed the transmission process simultaneously (step S104). Specifically, information specifying the radio resource used as the data channel is acquired from the control information, and it is judged whether or not the data channels of the multiple terminal devices 100 overlap in time. If the result of this judgment is that the data channels do not overlap in time, there is no simultaneous transmission by the multiple terminal devices 100 (step S104 No), and the process ends without transmitting a retransmission request.

[0043] If the determination result in step S104 is that the data channels overlap in time, it means that simultaneous transmission by multiple terminal devices 100 has been detected (Yes in step S104), and therefore the retransmission control unit 123 generates a NACK requesting a retransmission of the simultaneously transmitted data. The generated NACK is transmitted by the transmission control unit 126 using a feedback channel corresponding to the data channels that overlap in time. In other words, a retransmission request is made for the data that the multiple terminal devices 100 transmitted simultaneously (step S105).

[0044] In this way, when multiple terminal devices 100 in a group transmit simultaneously, the terminal devices 100 that do not transmit simultaneously detect the simultaneous transmission based on the control information and request a retransmission of the simultaneously transmitted data. Therefore, even if the terminal device 100 that transmits simultaneously does not request a retransmission despite not receiving data because it is in the process of transmitting, the other terminal devices 100 that received the data will request a retransmission instead. As a result, the simultaneously transmitted data is retransmitted, and the terminal devices 100 that transmitted simultaneously can receive data retransmitted at different times from the other terminal devices 100. Therefore, even when the terminal devices 100 communicate in half-duplex communication, appropriate data retransmission is performed, and the reliability of communication can be improved.

[0045] Next, a specific example of retransmission control will be described with reference to Fig. 4. Fig. 4 is a diagram showing a specific example of transmission and reception timing of terminal devices UE#1 to #3. These terminal devices UE#1 to #3 belong to the same group and transmit and receive signals by groupcast.

[0046] As shown in Fig. 4, terminal devices UE#1 and #2 transmit data 201 and 202, respectively, using radio resources that overlap in time. That is, terminal devices UE#1 and #2 execute transmission processing at the same time. Therefore, terminal device UE#1 does not detect that data 202 is transmitted from terminal device UE#2, and terminal device UE#2 does not detect that data 201 is transmitted from terminal device UE#1.

[0047] On the other hand, terminal device UE#3, which does not execute transmission processing at this timing, receives data 201, 202 from terminal devices UE#1, UE#2. Furthermore, terminal device UE#3 detects that data 201, 202 are transmitted simultaneously based on control information from terminal devices UE#1, #2. Therefore, terminal device UE#3 transmits NACK203 in the feedback channel corresponding to data 201, 202. That is, terminal device UE#3 requests retransmission of data 201, 202 instead of terminal devices UE#1, UE#2, which do not request retransmission despite not correctly receiving data 201, 202.

[0048] The terminal devices UE#1 and UE#2 receive NACK 203 on the feedback channels to monitor the feedback channels corresponding to the data 201 and 202, respectively. Then, the terminal devices UE#1 and UE#2 execute retransmission processing of the data 201 and 202 using predetermined radio resources for retransmission. Specifically, the terminal device UE#1 transmits retransmission data 211, and the terminal device UE#2 transmits retransmission data 212.

[0049] At this time, since the retransmission timings of the terminal devices UE#1 and UE#2 are different, the retransmission data 211 is received by the terminal devices UE#2 and #3 that are not executing the transmission process. Also, the retransmission data 212 is received by the terminal devices UE#1 and UE#3 that are not executing the transmission process. As a result, the terminal devices UE#1 and UE#2 that did not receive each other's data 201 and 202 can receive the retransmission data 211 and 212, respectively. In this way, the terminal device UE#3 makes a retransmission request on behalf of the terminal devices #1 and #2, so that the terminal devices #1 and #2 can receive the retransmission data 211 and 212 transmitted from each other, thereby improving the reliability of communication.

[0050] Fig. 5 is a diagram showing a specific example of the relationship between the distance between terminal devices and the packet reception ratio (PRR) indicating the reliability of communication. In Fig. 5, the communication range is assumed to be 100 m, and each terminal device does not make a retransmission request for data transmitted from a terminal device outside the communication range. Moreover, the solid line in Fig. 5 indicates the PRR when a retransmission request is made for data transmitted simultaneously, and the dashed line in Fig. 5 indicates the PRR when a retransmission request is not made for data transmitted simultaneously.

[0051] As is clear from Fig. 5, between terminal devices within a communication range of 100 m, the PRR can be maintained at a high level of 99.9% or more by having the other terminal device that receives both pieces of simultaneously transmitted data make a retransmission request. On the other hand, even between terminal devices within a communication range of 100 m, if a retransmission request is not made for simultaneously transmitted data, the PRR drops to about 98.8%. In this way, by making a retransmission request for simultaneously transmitted data as well, the reliability of communication can be improved.

[0052] As described above, according to this embodiment, when multiple terminal devices in a group transmit data simultaneously, other terminal devices that receive the data execute a retransmission request for the simultaneously transmitted data. Therefore, the terminal devices that transmit data simultaneously can each receive the retransmitted data, thereby improving the reliability of communication.

[0053] (Embodiment 2) The feature of the second embodiment is that when the radio resources for retransmission of simultaneously transmitted data overlap in time, a retransmission request is made to one of the terminal devices, thereby preventing the retransmission data from being transmitted simultaneously.

[0054] Fig. 6 is a block diagram showing a configuration of terminal device 100 according to embodiment 2. In Fig. 6, the same components as those in Fig. 2 are given the same reference numerals, and their description will be omitted. Terminal device 100 shown in Fig. 6 has retransmission resource determination section 301 and retransmission control section 302 instead of retransmission control section 123 of terminal device 100 shown in Fig. 2.

[0055] When the simultaneous transmission detection unit 122 detects the occurrence of simultaneous transmission by multiple terminal devices 100, the retransmission resource determination unit 301 determines whether or not the radio resources for retransmission of simultaneously transmitted data overlap in time. That is, the retransmission resource determination unit 301 acquires information for identifying the radio resources used for retransmitting data from the control information, and determines whether or not the radio resources for retransmission corresponding to the multiple pieces of simultaneously transmitted data overlap in time. Then, the retransmission resource determination unit 301 notifies the retransmission control unit 302 of the determination result.

[0056] When the reception control unit 121 does not obtain a correct decoded result of the data, the retransmission control unit 302 generates a NACK indicating that the data needs to be retransmitted, and outputs the NACK to the transmission control unit 126. That is, when the decoding accuracy of the data channel in the reception control unit 121 does not satisfy a predetermined standard, the retransmission control unit 302 generates a retransmission request to the terminal device 100 that is the data transmission source.

[0057] Furthermore, the retransmission control unit 302 generates a NACK indicating that data retransmission is necessary according to the determination result by the retransmission resource determination unit 301, and outputs the NACK to the transmission control unit 126. Specifically, when the occurrence of simultaneous transmission by multiple terminal devices 100 is detected and the radio resources for retransmission of the simultaneously transmitted data do not overlap in time, the retransmission control unit 302 generates a NACK for all data to be simultaneously transmitted. Furthermore, when the occurrence of simultaneous transmission by multiple terminal devices 100 is detected and the radio resources for retransmission of the simultaneously transmitted data overlap in time, the retransmission control unit 302 compares the priorities of the simultaneously transmitted data. Then, the retransmission control unit 302 generates a NACK for the data with the highest priority among the data whose radio resources for retransmission overlap in time.

[0058] In addition, when radio resources for retransmission are provided for each data at multiple timings, the retransmission control unit 302 may generate a NACK for each data so that the radio resources for retransmission of data transmitted simultaneously do not overlap in time. That is, when radio resources for retransmission that overlap in time are provided for data transmitted simultaneously from two terminal devices 100, for example, a retransmission request may be made so that data is retransmitted from the two terminal devices 100 using the radio resources for retransmission. That is, the retransmission control unit 302 may make a retransmission request so that data is retransmitted from one terminal device 100 with a higher priority in the radio resources for the first retransmission, and may make a retransmission request so that data is retransmitted from the other terminal device 100 in the radio resources for the second retransmission.

[0059] Furthermore, after the control information and transmission data are transmitted by the transmission control unit 126, the retransmission control unit 302 monitors the feedback channel corresponding to the transmission data, and performs retransmission control of the transmitted transmission data when a NACK is received on the feedback channel. That is, when a NACK is received, the retransmission control unit 302 instructs the transmission control unit 126 to retransmit the transmitted transmission data.

[0060] Next, a retransmission control method by the terminal device 100 configured as above will be described with reference to the flow diagram shown in Fig. 7. In Fig. 7, the same parts as in Fig. 3 are given the same reference numerals, and detailed description thereof will be omitted.

[0061] When a control channel signal is received by the wireless communication unit 110 (step S101), the reception control unit 121 demodulates and decodes the control channel to obtain control information. The control information includes information specifying a radio resource to be used as a data channel, and so the data channel signal is received using this information (step S102), and the reception control unit 121 demodulates and decodes the data channel.

[0062] Then, the retransmission control unit 302 judges whether the decoding of the data channel has been successful (step S103), and if it is judged that the decoding of the data channel has failed and retransmission of the data is necessary (step S103 No), a NACK is generated to request retransmission of the data. The generated NACK is transmitted by the transmission control unit 126 using a feedback channel corresponding to the data channel for which decoding has failed. In other words, a retransmission request is made for the data that was not correctly received (step S202).

[0063] On the other hand, if the decoding of the data channel is successful (step S103 Yes), the simultaneous transmission detection unit 122 judges whether or not multiple terminal devices 100 have performed the transmission process simultaneously (step S104). If the result of this judgment is that multiple terminal devices 100 have not performed simultaneous transmission (step S104 No), the process ends without transmitting a retransmission request.

[0064] As a result of the determination in step S104, when simultaneous transmission by a plurality of terminal devices 100 is detected (step S104 Yes), the retransmission resource determination unit 301 determines whether or not the radio resources for retransmitting the simultaneously transmitted data overlap in time (step S201). Specifically, since the control information includes information for identifying the radio resources used for retransmitting the data, the retransmission resource determination unit 301 acquires information for identifying the radio resources for retransmitting the simultaneously transmitted data, and determines whether or not the radio resources for retransmission overlap in time.

[0065] If the determination result indicates that the radio resources for retransmission do not overlap in time, the retransmission control unit 302 generates a NACK for requesting retransmission of the simultaneously transmitted data. The generated NACK is transmitted by the transmission control unit 126 using a feedback channel corresponding to the data channels that overlap in time. In other words, a retransmission request is made for the data that is simultaneously transmitted by the multiple terminal devices 100 (step S202).

[0066] Furthermore, when the radio resources for retransmission overlap in time, the retransmission control unit 302 compares the priorities of the data to be simultaneously transmitted. The comparison of priorities may be a comparison of the priorities of the data based on QoS (Quality of Service) information included in the control information, or a comparison of the priorities of the terminal device 100 that is the data transmission source. Then, a NACK is generated for the data with the highest priority among the data with the radio resources for retransmission overlapping in time. The generated NACK is transmitted by the transmission control unit 126 using a feedback channel corresponding to the data with the highest priority. In other words, a retransmission request is made for the data with the highest priority among the data simultaneously transmitted by the multiple terminal devices 100 (step S202).

[0067] For data other than the highest priority data among data for which retransmission radio resources overlap in time, a NACK may be transmitted using a feedback channel with a later timing. In other words, when retransmission radio resources with multiple timings are provided for one data, the timing of feedback of the NACK may be shifted so that the simultaneously transmitted data is retransmitted using retransmission radio resources with different timings.

[0068] In this way, when multiple terminal devices 100 in a group transmit simultaneously, the terminal devices 100 that do not transmit simultaneously detect the simultaneous transmission based on the control information and then determine whether or not the radio resources for retransmission of the simultaneously transmitted data overlap in time. If the radio resources for retransmission overlap in time, a retransmission request is made so that data with a high priority among the simultaneously transmitted data is retransmitted preferentially. Therefore, when data is transmitted simultaneously from multiple terminal devices 100, the retransmission of the data is prevented from occurring simultaneously, and the retransmitted data can be reliably received.

[0069] Next, a specific example of retransmission control will be described with reference to Fig. 8. Fig. 8 is a diagram showing a specific example of transmission and reception timing of terminal devices UE#1 to #3. In Fig. 8, the same parts as in Fig. 4 are given the same reference numerals. The terminal devices UE#1 to #3 shown in Fig. 8 belong to the same group and transmit and receive signals by groupcast.

[0070] As shown in Fig. 8, terminal devices UE#1 and #2 transmit data 201 and 202, respectively, using radio resources that overlap in time. That is, terminal devices UE#1 and #2 execute transmission processing at the same time. Therefore, terminal device UE#1 does not detect that data 202 is transmitted from terminal device UE#2, and terminal device UE#2 does not detect that data 201 is transmitted from terminal device UE#1.

[0071] On the other hand, the terminal device UE#3, which does not execute the transmission process at this timing, receives the data 201, 202 from the terminal devices UE#1, UE#2. Also, the terminal device UE#3 detects that the data 201, 202 are simultaneously transmitted based on the control information from the terminal devices UE#1, #2. Then, the terminal device UE#3 specifies the radio resources for retransmission of the data 201, 202 from the control information, and judges whether the radio resources for retransmission overlap in time. Here, it is assumed that the radio resources for retransmission overlap in time, and that the data 201 has a higher priority among the data 201, 202. Therefore, the terminal device UE#3 transmits a NACK401 in the feedback channel corresponding to the data 201. That is, the terminal device UE#3 makes a retransmission request for the data 201, which has the highest priority among the data 201, 202 that are simultaneously transmitted.

[0072] Since the terminal devices UE#1 and UE#2 monitor the feedback channels corresponding to the data 201 and 202, respectively, the terminal device UE#1 receives a NACK 401 in the feedback channel corresponding to the data 201. On the other hand, the terminal device UE#2 does not receive a NACK in the feedback channel corresponding to the data 202. Therefore, the terminal device UE#1 executes a retransmission process of the data 201 using a predetermined radio resource for retransmission. Specifically, the terminal device UE#1 transmits the retransmission data 211.

[0073] At this time, even if the predetermined retransmission timings of terminal devices UE#1 and UE#2 overlap, only terminal device UE#1 transmits the retransmission data 211, and the retransmission data 211 is received by terminal devices #2 and #3 that are not executing the transmission process. As a result, terminal device UE#2 that did not receive data 201 can receive the retransmission data 211. In this way, terminal device UE#3 requests retransmission of data 201 with a higher priority among data 201 and 202 that are simultaneously transmitted and have overlapping retransmission timings, so that terminal device #2 can receive the retransmission data 211 of the data 201 with a higher priority, thereby improving the reliability of communication.

[0074] In addition, when radio resources for retransmission are provided at multiple timings for each of the data 201 and 202, the terminal device UE#3 transmits NACK401 in a feedback channel corresponding to the radio resource for the first retransmission so that the data 201 is retransmitted using this radio resource. Then, the terminal device UE#3 may transmit NACK402 in a feedback channel corresponding to the radio resource for the second retransmission so that the data 202 is retransmitted using this radio resource. This makes it possible to retransmit both data using radio resources with different timings even when the radio resources for retransmission of the data 201 and 202 that are simultaneously transmitted overlap in time.

[0075] As described above, according to the present embodiment, when multiple terminal devices in a group transmit data simultaneously, other terminal devices receiving the data judge whether or not the radio resources for retransmission of the simultaneously transmitted data overlap in time. If the radio resources for retransmission overlap in time, a retransmission request is preferentially executed for data with a high priority. Therefore, even if the timing of the radio resources for retransmission of simultaneously transmitted data overlaps, the data with a high priority is retransmitted at a different timing from the other data, and the terminal device that transmits data simultaneously can receive the retransmitted data of the data with a high priority, thereby improving the reliability of communication. [Explanation of symbols]

[0076] 110 Wireless Communication Division 120 processors 121 Reception control section 122 Simultaneous transmission detector 123, 302 Retransmission control section 124 Control information generation unit 125 Transmission data generation unit 126 Transmission control section 130 Memory 301 Retransmission resource decision unit

Claims

1. a wireless communication unit for transmitting and receiving signals between a first terminal device and a second terminal device; A control unit that performs a process of detecting that simultaneous transmission by the first terminal device and the second terminal device occurs in a first resource based on control information received by the wireless communication unit and transmitted from the first terminal device and the second terminal device using a control channel, the control information including information specifying a wireless resource used as a data channel; The wireless communication unit includes: When the simultaneous transmission is detected, a first signal including information requesting that the first terminal device and / or the second terminal device transmit a signal using a second resource different from the first resource via a feedback channel is transmitted. A terminal device comprising:

2. The control unit is When the simultaneous transmission is detected, the first signal including a retransmission request is generated for at least one of the first terminal device and the second terminal device in response to the detection of the simultaneous transmission; The wireless communication unit includes: Transmitting the first signal over the feedback channel 2. The terminal device according to claim 1 .

3. The detecting process includes: Detecting an occurrence of simultaneous transmission by determining whether data channels corresponding to the first terminal device and the second terminal device overlap based on the control information.

2. The terminal device according to claim 1 .

4. The feedback channel: a feedback channel corresponding to the first terminal device and the second terminal device; 2. The terminal device according to claim 1 .

5. The detecting process includes: When the simultaneous transmission is detected, a process of determining whether or not radio resources used by the first terminal device and the second terminal device overlap is further performed; The wireless communication unit includes: When it is determined that the radio resources overlap, the first signal is transmitted to only one of the first terminal device and the second terminal device via a feedback channel.

2. The terminal device according to claim 1 .

6. The wireless communication unit includes: When it is determined that the wireless resources overlap, the first signal is transmitted via a feedback channel for data having a high priority among the data transmitted from the first terminal device and the second terminal device.

6. The terminal device according to claim 5,

7. The wireless communication unit includes: Half-duplex communication, which does not transmit and receive signals at the same time 2. The terminal device according to claim 1 .

8. The feedback channel:

2. The terminal device according to claim 1, wherein the channel is used when making a retransmission request.

9. A wireless communication system having a first terminal device that transmits a signal, a second terminal device that transmits a signal simultaneously with the first terminal device, and a third terminal device that receives signals from the first terminal device and the second terminal device, The third terminal device is a wireless communication unit for transmitting and receiving signals between the first terminal device and the second terminal device; a processor connected to the wireless communication unit; The processor, Detecting that simultaneous transmission by the first terminal device and the second terminal device will occur based on control information received by the wireless communication unit and transmitted from the first terminal device and the second terminal device using a control channel, the control information including information specifying a wireless resource used as a data channel; generating a retransmission request to at least one of the first terminal device and the second terminal device when simultaneous transmission is detected; Execute a process of transmitting the generated retransmission request from the wireless communication unit; Either the first terminal device or the second terminal device, When a retransmission request transmitted from the third terminal device is received, the retransmission of the signal is performed; The other of the first terminal device and the second terminal device, Receive a signal retransmitted from either the first terminal device or the second terminal device.

1. A wireless communication system comprising:

10. A retransmission control method executed by a terminal device receiving a signal from a first terminal device and a second terminal device, comprising: Detecting that simultaneous transmission by the first terminal device and the second terminal device occurs based on control information transmitted from the first terminal device and the second terminal device using a control channel, the control information including information specifying a radio resource used as a data channel; generating a retransmission request to at least one of the first terminal device and the second terminal device when simultaneous transmission is detected; Send the generated resend request 23. A retransmission control method comprising the steps of:

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