Communication method, terminal, and communication program

Abstract

To improve reliability of communication between vehicles.SOLUTION: A communication method contains a step (S11) of preserving a transmission resource and a relay resource group from a plurality of communication resources by a first terminal (20A); a step (S12) of selecting a second terminal (20B) from terminals (20) that can be directly communicated with the first terminal as the relay terminal (20B); a step (S13) of transmitting a transmission signal containing transmission terminal information expressing an identification number and a position of the first terminal, relay terminal information expressing the identification number of the relay terminal, and relay resource information expressing a relay resource contained in the relay resource group in side link communication by using the transmission resource; a step (S23) of transmitting the relay signal containing the transmission terminal information by the second terminal receiving the transmission signal in the side link communication by using the relay resource; and a step (S31) of performing decoding processing of the transmission terminal information on the basis of the reception signal containing at least one of the transmission signal and the relay signal by a third terminal (20C).SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a communication method, a terminal, and a communication program, which can be suitably used, for example, for sidelink communication between terminals mounted in vehicles. [Background technology]

[0002] Among the accidents that have occurred at intersections with poor visibility, there are some that could have been prevented if vehicles entering the intersection or vehicles traveling around the intersection had detected each other's presence. However, even if a sensor device that detects other vehicles using electromagnetic waves or light, such as a radar or a camera, is used as a means of detecting other vehicles, it is not possible to detect another vehicle located outside the line of sight of the vehicle equipped with the sensor device. In addition, by using V2V (Vehicle-to-Vehicle) communication that wirelessly communicates between vehicles, a vehicle can notify another vehicle located outside the line of sight of the vehicle of its own location, but wireless signals can be blocked by obstacles such as buildings that limit visibility, causing packet loss, which can result in a decrease in the reliability of wireless communication.

[0003] In relation to the above, non-patent document 1 (G. Ghatak, “Cooperative Relaying for URLLC in V2X Networks”, IEEE Wireless Communications Letters, vol. 10, no. 1, pp. 97-101, January 2021) discloses a technology in which, in delivering URLLC (Ultra-Reliable Low Latency Communications) messages, the delivery time period is divided into two parts, the delivery vehicle transmits via broadcast communication, and a terminal that fails to receive the message requests an adjacent terminal to resend the message. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] G. Ghatak, “Cooperative Relaying for URLLC in V2X Networks”, IEEE Wireless Communications Letters, vol. 10, no. 1, pp.97-101, January 2021. Summary of the Invention [Problem to be solved by the invention]

[0005] However, in Non-Patent Document 1, it is unclear which adjacent terminal a terminal that has failed to receive a message should request, and it is also unclear how multiple terminals that have failed to receive a message should cooperate to request a retransmission of the message.

[0006] In view of the above, an object of the present disclosure is to provide a vehicle-to-vehicle communication method with improved reliability, a terminal using the communication method, and a communication program for the terminal to realize the communication method. Other objects and novel features will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0007] The means for solving the problems will be described below using the numbers and symbols used in the description of the embodiment of the invention. These numbers and symbols are added in parentheses for reference purposes to show an example of the correspondence between the description of the claims and the description of the embodiment of the invention. Therefore, the description in parentheses should not be interpreted as limiting the scope of the claims.

[0008] According to an embodiment, the communication method includes a first terminal (20A) reserving a transmission resource and a relay resource group from among a plurality of communication resources that combine a plurality of time subframes and a plurality of frequency subchannels (S11). The communication method further includes the first terminal (20A) selecting a second terminal (20B) as a relay terminal (20B) from a candidate terminal group that is a set of terminals (20) that can directly communicate with the first terminal (20A) (S12). The communication method further includes the first terminal (20A) transmitting a transmission signal including transmission terminal information indicating the identification number and position of the first terminal (20A), relay terminal information indicating the identification number of the relay terminal (20B), and relay resource information indicating the relay resource included in the relay resource group by side link communication using the transmission resource (S13). The communication method further includes a step of transmitting a relay signal including the transmitting terminal information by the side link communication using the relay resource by the second terminal (20B) that has received the transmitting signal (S23). The communication method further includes a step of decoding the transmitting terminal information by the third terminal (20C) based on the receiving signal including at least one of the transmitting signal and the relay signal (S31).

[0009] According to an embodiment, the terminal (20) is a terminal (20) that performs wireless communication and includes a resource reservation unit (221), a relay terminal selection unit (222), a transmission unit (223), a relay unit (225), and a reception unit (224). When the terminal (20) operates as a transmitting terminal (20A), the resource reservation unit (221) reserves a transmission resource and a relay resource group from among a plurality of communication resources that combine a plurality of time subframes and a plurality of frequency subchannels. When the terminal (20) operates as a transmitting terminal (20A), the relay terminal selection unit (222) selects a predetermined terminal (20) as a relay terminal (20B) from a candidate terminal group that is a set of other terminals (20) that can directly communicate with the transmitting terminal (20A). When the terminal (20) operates as a transmitting terminal (20A), the transmitting unit (223) transmits a transmission signal including transmitting terminal information indicating the identification number and position of the transmitting terminal (20A), relay terminal information indicating the identification number of the relay terminal (20B), and relay resource information indicating the relay resource included in the relay resource group, by side link communication using the transmitting resource. When the terminal (20) operates as a relay terminal (20B), the relay unit (225) transmits a relay signal including the transmitting terminal information by side link communication using the relay resource. When the terminal (20) operates as a receiving terminal (20C), the receiving unit (224) performs a decoding process of the transmitting terminal information based on a receiving signal including at least one of the transmitting signal and the relay signal (S31).

[0010] According to one embodiment, the communication program is a communication program for realizing a predetermined process by executing it on the arithmetic device (22) of the terminal (20), and the process includes reserving (S11) a transmission resource and a relay resource group from among a plurality of communication resources combining a plurality of time subframes and a plurality of frequency subchannels by the first terminal (20A). The process further includes (S12) the first terminal (20A) selecting as a relay terminal (20B) from among a candidate terminal group which is a set of terminals (20) capable of direct communication with the first terminal (20A). The process further includes (S13) the first terminal (20A) transmitting, by side link communication, a transmission signal including transmission terminal information indicating the identification number and position of the first terminal (20A), relay terminal information indicating the identification number of the relay terminal (20B), and relay resource information indicating the relay resource included in the relay resource group, using the transmission resource. This process further includes a step (S23) in which the second terminal (20B) that has received the transmission signal transmits a relay signal including the transmission terminal information by using the relay resource through sidelink communication. This process further includes a step (S31) in which the third terminal (20C) performs a decoding process of the transmission terminal information based on a received signal including at least one of the transmission signal and the relay signal. Effect of the Invention

[0011] According to one embodiment, it is possible to improve the reliability of communication between vehicles. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram illustrating an example of a configuration of a communication system according to an embodiment. [Diagram 2] FIG. 2 is a block circuit diagram showing a configuration example of a terminal according to an embodiment. [Diagram 3] FIG. 3 is a diagram illustrating communication resources according to an embodiment. [Figure 4] FIG. 4 is a sequence diagram showing an example of a process of a communication method according to an embodiment. [Diagram 5] FIG. 5 is a diagram for explaining a process of reserving a group of communication resources according to an embodiment. [Figure 6] FIG. 6 is a diagram for explaining a process of selecting a relay terminal according to an embodiment. [Figure 7] FIG. 7 is a diagram for explaining a transmission signal and a relay signal according to an embodiment. [Figure 8] FIG. 8 is a diagram for explaining the conditions of a computer simulation performed on the communication method according to an embodiment. [Figure 9] FIG. 9 is a graph showing the results of a computer simulation performed on a communication method according to one embodiment. [Figure 10] FIG. 10 is a diagram for explaining the conditions of a computer simulation performed on the communication method according to an embodiment. [Figure 11] FIG. 11 is a graph showing the results of a computer simulation performed on a communication method according to one embodiment. [Figure 12] FIG. 12 is a graph showing the results of a computer simulation performed on a communication method according to one embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] A communication method, a terminal, and a communication program according to the present disclosure will be described below with reference to the accompanying drawings. In addition, in order to better understand the subject of the present disclosure, a semi-persistent scheduling (SPS) method will also be described.

[0014] (First embodiment) As shown in Fig. 1, a communication system 1 according to an embodiment includes a plurality of terminals 20A, 20B, 20C, and 20D. The terminals 20A, 20B, 20C, and 20D are mounted on vehicles 2A, 2B, 2C, and 2D, respectively. Hereinafter, when the terminals 20A, 20B, 20C, and 20D are not distinguished from each other, they may be collectively referred to as terminals 20. In addition, when the vehicles 2A, 2B, 2C, and 2D are not distinguished from each other, they may be collectively referred to as vehicles 2. Note that the total number of terminals 20 and vehicles 2 is merely an example and does not limit the present embodiment.

[0015] The terminals 20 mounted on the vehicles 2 transmit and receive wireless signals to each other through sidelink communication, and transmit the position of the vehicle 2 on which the terminals 20 are mounted to other terminals 20 mounted on other vehicles 2. In sidelink communication, wireless signals are transmitted and received between the terminals 20 without going through other communication devices such as base stations. In sidelink communication, the SPS method is adopted in order to prevent deterioration of reliability due to packet collision. In the SPS method, multiple in-vehicle devices mounted on multiple vehicles 2 respectively select wireless communication resources by autonomous distributed control in order to prevent deterioration of reliability due to packet collision. The wireless communication resource is a combination of the timing at which an in-vehicle device transmits data to another in-vehicle device and the frequency subchannel used for transmission. Details of the wireless communication resource and the SPS method will be described later.

[0016] In the example of FIG. 1, the wireless signal transmitted from the terminal 20A mounted on the vehicle 2A is received by the terminal 20B mounted on the vehicle 2B. As a result, the terminal 20A as a transmitting terminal can transmit vehicle information including the identification number, current position, moving speed, moving direction, etc. of the vehicle 2A to the terminal 20B as a receiving terminal, and the vehicle 2B mounted with the terminal 20B can obtain information for suppressing an accident that may occur between the vehicle 2B mounted with the terminal 20A and the vehicle 2A mounted with the terminal 20A. Similarly, the wireless signal transmitted from the terminal 20B mounted on the vehicle 2B is also received by the terminal 20C mounted on the vehicle 2C and the terminal 20D mounted on the vehicle 2D. As a result, each of the vehicles 2C and 2D can obtain information for suppressing an accident that may occur between the vehicle 2B and the vehicle 2B.

[0017] However, depending on the relative positions of the transmitting vehicle 2 and the receiving vehicle 2, the wireless signal may be blocked by obstacles such as buildings, which may result in packet loss. In that case, even if the distance between the two vehicles 2 is relatively short, the two vehicles 2 may not be able to obtain information from each other, and the probability of an accident occurring may not be reduced.

[0018] 1, a wireless signal transmitted from terminal 20A mounted on vehicle 2A is not received by terminal 20C mounted on vehicle 2C and terminal 20D mounted on vehicle 2D because the signal is blocked by obstacle 92. As a result, each of vehicle 2C and vehicle 2D may not be able to obtain information for preventing an accident that may occur between vehicle 2A and vehicle 2C.

[0019] Here, since terminal 20B is capable of communicating with terminal 20A, terminal 20C, and terminal 20D, if terminal 20B relays a wireless signal transmitted by terminal 20A, terminal 20C and terminal 20D can receive the wireless signal. In this embodiment, a description will be given of control of a process of relaying a wireless signal when a transmitting terminal transmits a wireless signal by broadcast communication in which a receiving terminal is not specified.

[0020] 2, each terminal 20 may be configured as a so-called computer. That is, the terminal 20 includes a bus 21, a calculation device 22, a storage device 23, a communication device 24, a monitor device 25, and an input / output device 26. The bus 21 is configured to connect the calculation device 22, the storage device 23, the communication device 24, the monitor device 25, and the input / output device 26 so that they can communicate with each other.

[0021] The arithmetic device 22 includes a resource reservation unit 221, a relay terminal selection unit 222, a transmission unit 223, a reception unit 224, and a relay unit 225. The storage device includes a program storage unit 231 that stores a communication program, and a data storage unit 232 that stores an identification number of the terminal 20. The arithmetic device 22 executes the communication program to realize the processing of the resource reservation unit 221, the relay terminal selection unit 222, the transmission unit 223, the reception unit 224, and the relay unit 225. The resource reservation unit 221, the relay terminal selection unit 222, the transmission unit 223, the reception unit 224, and the relay unit 225 are virtual functional blocks that realize the processing by the arithmetic device 22 and the storage device 23 working together. The resource reservation unit 221 reserves a part of a plurality of communication resources that are used jointly by a plurality of terminals 20. When the terminal 20 operates as a transmitting terminal, the relay terminal selection unit 222 selects, from among the other terminals 20, a terminal 20 to be requested to operate as a relay terminal. When the terminal 20 operates as a transmitting terminal, the transmission unit 223 transmits a wireless signal to the other terminals 20 including the relay terminal. When the terminal 20 operates as a receiving terminal, the reception unit 224 decodes the received wireless signal and reads out information contained in the wireless signal. When the terminal 20 operates as a relay terminal, the relay unit 225 receives a wireless signal transmitted from the transmitting terminal and relays it to the other terminals 20. Details of the processes realized by the resource reservation unit 221, the relay terminal selection unit 222, the transmission unit 223, the reception unit 224, and the relay unit 225 will be described later.

[0022] The communication program may be read from the recording medium 230 and stored in the program storage unit 231. The recording medium 230 may be a non-transitory and tangible medium.

[0023] The communication device 24 performs sidelink communication with another terminal 20 using the antenna device 240. The communication device 24 may further perform communication with an external device such as a base station. A communication program may be stored in the program storage unit 231 from the external device via the communication device 24.

[0024] The monitor device 25 observes the state of the vehicle 2 on which the terminal 20 is mounted. More specifically, the monitor device 25 acquires and outputs vehicle information representing the state of the vehicle 2 by receiving various signals from the vehicle 2. The vehicle information may include position information representing the position of the vehicle 2, speed information representing the moving speed of the vehicle 2, status information representing the state of the vehicle 2, attribute information representing the attributes of the vehicle 2, and the like. The position information is obtained by a positioning means such as a Global Navigation Satellite System (GNSS). The monitor device 25 may be equipped with a positioning means, or may receive the position information of the vehicle 2 from an external positioning means. The status information represents the orientation of the vehicle 2, and the like. The vehicle attribute information represents the vehicle size, the purpose of use, the vehicle width, and the like. The monitor device 25 may continue to acquire the vehicle information at predetermined intervals. The vehicle information acquired by the monitor device 25 is associated with time information representing the time of acquisition and stored in the data storage unit 232 of the storage device 23.

[0025] The input / output device 26 outputs information to a user and accepts operations input by the user. As an example, the input / output device 26 includes a display device that outputs images, a speaker that outputs sound, a microphone that accepts sound input, a button that accepts a press operation, a keyboard that accepts key input operations, a touch panel that accepts touch operations and outputs images, and the like.

[0026] (Wireless Communications Resources) An example of a configuration of a wireless communication resource according to an embodiment will be described with reference to Fig. 3. A wireless communication resource is a combination of any one of a plurality of time subframes, which are transmission timings obtained by dividing a time frame, and any one of a plurality of frequency subchannels, which are frequency bands obtained by dividing a frequency channel. For example, from time T0 to time T n The time frame up to is divided into n time subframes, and the time T i-1 From time T i and the i-th time subframe from frequency F0 to frequency F m Of the frequency channels divided into m frequency subchannels,j-1 from frequency F j The j-th frequency subchannel is combined with the j-th frequency subchannel to form a wireless communication resource R i,j is identified. A set of multiple wireless communication resources, each of which is a combination of multiple time subframes included in a certain time frame and multiple frequency subchannels included in a certain frequency channel, is called a resource set for convenience. In the above example, the resource set includes a total of m×n wireless communication resources. Hereinafter, the wireless communication resource may be simply referred to as a communication resource or a resource.

[0027] (SPS method) In the SPS scheme, a frequency channel used in sidelink communication performed by a terminal 20 and a plurality of frequency subchannels obtained by dividing this frequency channel are shared by a plurality of terminals 20 performing sidelink communication. Similarly, a length of a time frame used in sidelink communication performed by a terminal 20 and a plurality of time subframes obtained by dividing this time frame are shared by a plurality of terminals 20 performing sidelink communication. In addition, these terminals 20 are synchronized so as to share the time subframe and the start time of each of the time subframes.

[0028] In the SPS method, during one time subframe, a terminal 20 transmits a packet using any one of the communication resources included in the resource set of this time subframe. The packet may be transmitted by broadcast communication that does not specify the terminal 20 to receive the packet. Here, each terminal 20 schedules the communication resources by autonomous distributed control. At this time, each terminal 20 reserves the communication resources to be used for transmitting the packet so as to avoid resources reserved by other terminals 20, thereby suppressing the occurrence of packet collisions.

[0029] An example of the process of the communication method according to an embodiment will be described with reference to the sequence diagram of Fig. 4. When the terminal 20 is started, the process of the sequence diagram of Fig. 4 starts. When the terminal 20 operates as a transmitting terminal, step S11 of Fig. 4 is executed. When the terminal 20 operates as a relay terminal other than the transmitting terminal or a receiving terminal, step S21 of Fig. 4 is executed. Hereinafter, for the sake of distinction, the terminal 20 operating as a transmitting terminal will be referred to as a transmitting terminal 20A, the terminal 20 operating as a relay terminal will be referred to as a relay terminal 20B, and the terminal 20 operating as a receiving terminal will be referred to as a receiving terminal 20C.

[0030] In step S11 in Fig. 4, the resource reservation unit 221 in Fig. 2 of the transmitting terminal 20A reserves a transmission resource and a relay resource group from among a plurality of communication resources. The relay resource group includes one or more communication resources. In this embodiment, a case will be described in which the relay resource group includes a total of two relay resources, a first relay resource and a second relay resource, but this is merely an example and does not limit this embodiment. After step S11 in FIG. 4, the process of the transmitting terminal 20A proceeds to step S12.

[0031] In step S12 in Fig. 4, the relay terminal selection unit 222 in Fig. 2 of the transmitting terminal 20A selects one terminal 20 as the relay terminal 20B from a candidate terminal group which is a set of terminals 20 that can directly communicate with the transmitting terminal 20A among the other terminals 20. Here, the candidate terminal group may be a set of terminals 20 that have transmitted a signal previously received by the transmitting terminal 20A. After step S12, the processing of the transmitting terminal 20A proceeds to step S13.

[0032] In step S13 in Fig. 4, the transmitter 223 in Fig. 2 of the transmitting terminal 20A transmits a transmission signal by broadcast communication of the sidelink communication using a transmission resource. Here, the transmission signal includes transmitting terminal information indicating the identification number and position of the transmitting terminal 20A, relay terminal information indicating the identification number of the relay terminal 20B, and relay resource information indicating each relay resource included in the relay resource group. After step S13, the processing of the transmitting terminal 20A returns to step S11, and starts processing for transmitting the next transmission signal.

[0033] In step S21 of Fig. 4, the receiver 224 of Fig. 2 of a terminal 20 other than the transmitting terminal 20A, i.e., a terminal 20 as the relay terminal 20B or the receiving terminal 20C, judges whether or not it has received the transmission signal transmitted by the transmitting terminal 20A in step S13. If the result of the judgment is that the transmission signal has not been received (NO), the process of the relay terminal 20B and the receiving terminal 20C returns to step S21, and repeats step S21 until the transmission signal is received. If the result of the judgment is that the transmission signal has been received (YES), the process of the relay terminal 20B or the receiving terminal 20C proceeds to step S22. At this time, the receiver 224 may store the received transmission signal in the data storage unit 232.

[0034] In step S22 of Fig. 4, the receiver 224 of Fig. 2 of the terminal 20 operating as the relay terminal 20B or the receiving terminal 20C determines whether or not the identification number indicated by the relay terminal information included in the transmission signal received in step S21 of Fig. 4 matches the identification number of the terminal 20 equipped with the receiver 224. If the determination result shows that the identification numbers do not match (NO), the processing of the terminal 20 proceeds to step S31 of Fig. 4, and thereafter the terminal 20 operates as the receiving terminal 20C. If the determination result shows that the identification numbers match (YES), the processing of the terminal 20 proceeds to step S23 of Fig. 4.

[0035] In step S23 in Fig. 4, among the terminals 20 operating as the relay terminal 20B, the relay unit 225 in Fig. 2 transmits a relay signal by broadcast communication of the sidelink communication using unused relay resources included in the relay resource group represented by the relay resource information included in the transmission signal, in ascending order of time subframes. Here, the relay signal includes at least the transmission terminal information of the received transmission signal. After step S23 in Fig. 4, the process of the relay terminal 20B proceeds to step S24.

[0036] In step S31 of FIG. 4, the receiver 224 of FIG. 2 among the terminals 20 operating as the receiving terminal 20C receives the relay signal transmitted by the relay terminal 20B in step S23, and performs a decoding process of the transmitting terminal information contained in the received relay signal. Here, the receiver 224 may perform a decoding process of the transmitting terminal information using the transmitting signal received in step S21 of FIG. 4 and the relay signal received in step S31. At this time, if multiple relay signals including the same transmitting terminal information are received as described later, the receiver 224 may perform a decoding process of the transmitting terminal information using the transmitting signal and the multiple relay signals. In this way, even if the receiving state of the transmitting signal and / or the relay signal is incomplete, the probability of successfully decoding the transmitting terminal information is improved by compensating for the missing parts of the transmitting signal and the relay signal. After step S31 of FIG. 4, the process of the receiving terminal 20C proceeds to step S32.

[0037] In step S24 in FIG. 4, the relay unit 225 in FIG. 2 among the terminals 20 operating as the relay terminal 20B judges whether or not an unused relay resource remains in the relay resource group represented by the relay resource information included in the transmission signal received in step S21 in FIG. 4. If the result of the judgment is that an unused relay resource remains (YES), the process of the relay terminal 20B returns to step S23, and the process of transmitting a relay signal is repeated until all the relay resources are used. As a result, step S23 in FIG. 4, in which the relay unit 225 in FIG. 2 transmits a relay signal, is executed a number of times equal to the total number of relay resources included in the relay resource group. This is because, in the case of broadcast communication, the relay terminal 20B does not acquire a reception success signal and / or a reception failure signal from the receiving terminal 20C. If the result of the judgment is that an unused relay resource does not remain (NO), the process of the relay terminal 20B returns to step S21 in FIG. 4, and waits for the next transmission signal.

[0038] In step S32 in Fig. 4, the receiver 224 in Fig. 2 of the terminal 20 operating as the receiving terminal 20C judges whether the decryption process performed in step S31 was successful. If the result of the judgment is that the decryption process was not successful (NO), the process of the receiving terminal 20C returns to step S31, and the next relay signal received is further used to perform the decryption process. If the result of the judgment is that the decryption process was successful (YES), the process of the receiving terminal 20C returns to step S21, and waits for the next transmission signal to be transmitted.

[0039] In the example of the process shown in Fig. 4, the terminal 20 operating as the transmitting terminal 20A, the terminal 20 operating as the relay terminal 20B, and the terminal 20 operating as the receiving terminal 20C have been described as performing separate processes, but in reality, one and the same terminal 20 can operate as the transmitting terminal 20A, the relay terminal 20B, and the receiving terminal 20C. Also, one and the same terminal 20 can simultaneously operate as the transmitting terminal 20A, the relay terminal 20B, and the receiving terminal 20C. As an example, while a certain terminal 20 is operating as the transmitting terminal 20A, it may perform a process of relaying a transmission signal transmitted from another terminal 20, and may further perform a process of receiving a relay signal relayed from another terminal 20.

[0040] The process of reserving the communication resource group in step S11 in Fig. 4 will be described in more detail with reference to Fig. 5. In step S11 in Fig. 4, the resource reservation unit 221 of the terminal 20 shown in Fig. 2 reserves a transmission resource used by the transmitting terminal 20A to transmit a transmission signal and a relay resource group used by the relay terminal 20B to transmit a relay signal after the transmitting terminal 20A transmits the transmission signal, before the transmitting terminal 20A transmits the transmission signal. The relay resource group includes one or more relay resources.

[0041] As an example, communication resources including transmission resources and relay resources may be managed by the SPS method as shown in Fig. 5. In the SPS method, information on communication resources reserved by any one of terminals 20 that perform sidelink communication by sharing communication resources is shared among multiple terminals 20, and the other terminals 20 reserve communication resources to be used in the future from among candidates of communication resources that have not yet been reserved. The terminal 20 may calculate an average RSSI, which is an average value across a sensing window of RSSI (Received Signal Strength Indicator) of communication resources used in past communications. As an example, when the period of communication using the communication resources is 100 ms (milliseconds), the average RSSI of communication resources used in the past 10 communications in the t-th time subframe of the fourth frequency subchannel is calculated as shown in the following formula 1.

number

[0042] The resource reservation unit 221 of the terminal 20 shown in FIG. 2 reserves communication resources whose calculated average RSSI is equal to or less than a predetermined threshold and which have not yet been reserved by other terminals 20 as transmission resources and relay resource groups across multiple future windows.

[0043] The process of selecting a relay terminal in step S12 in Fig. 4 will be described in more detail with reference to Fig. 6. Fig. 6 shows a plurality of terminals including transmitting terminal N as transmitting terminal 20A, relay terminal R as relay terminal 20B, receiving terminal I as receiving terminal 20C, and other adjacent terminals as a plurality of circles, and shows wireless communication that may be performed between each terminal as straight lines connecting the circles corresponding to each terminal. Here, the adjacent terminals include candidate terminals that are capable of direct communication with transmitting terminal N and are candidates for relay terminal R, and target terminals that are capable of direct communication with any of the candidate terminals and can receive a transmission signal transmitted by transmitting terminal N by relaying it through one relay terminal R.

[0044] The indirect transmission success rate when communication from a transmitting terminal N to a receiving terminal I is relayed by a relay terminal R can be calculated using the following formula 2.

number

[0045] The average delivery success rate from a sending terminal N to all adjacent terminals is calculated using the following formula 3.

number

number

[0046] As an example, in this embodiment, the relay terminal selected in step S12 in FIG. 4 is the one that is the average value p n r may be the relay terminal R for which the

[0047] With reference to Fig. 7, the transmission signal 80 transmitted in step S13 in Fig. 4 and the relay signals 81, 8K transmitted in step S23 will be described in more detail. The transmission signal 80 transmitted by the transmitting unit 223 in Fig. 2 in step S13 in Fig. 4 includes a header 80a and a payload 80b. Moreover, the i-th relay signal 8i (81, 8K, etc.) transmitted by the relay unit 225 in Fig. 2 in step S23 in Fig. 4 includes a header 8ia (81a, 8Ka, etc.) and a payload 8ib (81b, 8Kb, etc.). Here, "i" is a natural number representing the number of the relay signal, and its value is included in the range from 1 to K. Here, "K" represents the total number of relay signals.

[0048] As an example, the header 80a of the transmission signal 80 includes at least information for transmission to the relay terminal 20B, and the payload 80b of the transmission signal 80 includes information for transmission to the relay terminal 20B and the receiving terminal 20C. At this time, it is preferable that the payload 8ib of the relay signal 8i is the same as the payload 80b of the transmission signal 80, but the header 8ia of the relay signal 8i does not necessarily have to be the same as the header 80a of the transmission signal 80. The header 80a of the transmission signal 80 includes, for example, relay terminal information indicating the identification number of the relay terminal 20B and relay resource information indicating a relay resource group. In addition, the payload 80b of the transmission signal 80 and the payload 8ib of the relay signal 8i include, for example, transmitting terminal information indicating the identification number and position of the transmitting terminal 20A.

[0049] As described above, according to the communication method, terminal, and communication program of one embodiment, in broadcast communication of side link communication, by introducing a relay terminal 20B that relays communication from a transmitting terminal 20A to a receiving terminal 20C that is located in a position where direct communication from the transmitting terminal 20A may be obstructed by an obstacle or the like, it is possible to improve the reliability of communication between vehicles.

[0050] (Computer Simulation, Part 1) The inventors performed a computer simulation under the conditions shown in Fig. 8 to confirm the effectiveness of the communication method, terminal, and communication program according to the embodiment. In Fig. 8, among a total of 20 vehicles 301-320 traveling on roads 91A-91D and an intersection 90 surrounded by obstacles 92A-92D, the terminal 20 mounted on the first vehicle operates as the transmitting terminal 20A, the terminal 20 mounted on the second vehicle operates as the relay terminal 20B, and the terminal 20 mounted on the third vehicle operates as the receiving terminal 20C. Here, each of the roads 91A-91D is connected to the intersection 90. More specifically, the first road 91A and the second road 91B are connected in a straight line, and the third road 91C and the fourth road 91D are connected in a straight line, and the first road 91A and the second road 91B intersect with the third road 91C and the fourth road 91D at the intersection 90. Here, a first road 91A on which vehicles 301, 302, 303, 304, and 305 are traveling is sandwiched between two obstacles 92A and 92B. A second road 91B on which vehicles 306, 307, 308, 309, and 310 are traveling is sandwiched between two obstacles 92C and 92D. A third road 91C on which vehicles 311, 312, 313, 314, and 315 are traveling is sandwiched between two obstacles 92A and 92C. A second road 91B on which vehicles 317, 318, 319, and 320 are traveling is sandwiched between two obstacles 92C and 92D. A vehicle 316 is traveling through an intersection 90.

[0051] 8 described above, when two terminals 20 mounted on any of the vehicles 301-320 operate as the transmitting terminal 20A and the receiving terminal 20C, respectively, the terminal 20 mounted on the vehicle 316 located at the intersection 90 is most likely to be selected as the relay terminal 20B. This is because there are no obstacles 92A-92D that impede wireless communication between the vehicles 301-315 and 317-320 and the vehicle 316.

[0052] FIG. 9 shows the results of a simulation under the conditions of FIG. 8. FIG. 9 includes two graphs G11 and G12 in total, and in both graphs G11 and G12, the horizontal axis represents the average PDR (Packet Delivery Rate) and the vertical axis represents the CDF (Cumulative Distribution Function). The first graph G11 represents the relationship between the average PDR and its CDF when direct communication is performed from the transmitting terminal 20A to the receiving terminal 20C without using the relay terminal 20B, as a comparison target of this embodiment. The second graph G12 represents the relationship between the average PDR and its CDF when communication is relayed from the transmitting terminal 20A to the receiving terminal 20C using the relay terminal 20B according to the communication method, terminal, and communication program of this embodiment. As shown in FIG. 9, it was confirmed that a higher average PDR can be obtained with this embodiment represented by the second graph G12 than with the direct communication represented by the first graph G11.

[0053] (Computer Simulation, Part 2) The inventors performed a computer simulation under the conditions shown in Fig. 10 to confirm the effectiveness of the communication method, terminal, and communication program according to an embodiment. The conditions in Fig. 10 can be obtained by making the following changes to the conditions in Fig. 8 described above. That is, the vehicle 316 is traveling on the fourth road 91D, and no vehicles are present at the intersection 90.

[0054] FIG. 11 shows the results of a simulation under the conditions of FIG. 10. FIG. 11 includes two graphs G21 and G22 in total, and the horizontal axis indicates the average PDR and the vertical axis indicates the CDF in both graphs G21 and G22. The first graph G21 shows the relationship between the average PDR and its CDF when direct communication is performed from the transmitting terminal 20A to the receiving terminal 20C without using the relay terminal 20B, as a comparison target of this embodiment. The second graph G22 shows the relationship between the average PDR and its CDF when communication is relayed from the transmitting terminal 20A to the receiving terminal 20C using the relay terminal 20B according to the communication method, terminal, and communication program of this embodiment. As shown in FIG. 11, it was confirmed that a higher average PDR can be obtained with this embodiment shown by the second graph G22 than with the direct communication shown by the first graph G21.

[0055] FIG. 12 shows another result of the simulation under the conditions of FIG. 10. FIG. 12 includes two graphs G31 and G32 in total, and in both graphs G31 and G32, the horizontal axis represents the vehicle numbers 301 to 320, and the vertical axis represents the average PDR. The first graph G31 represents the average PDR of the terminal 20 mounted on each vehicle when direct communication is performed from the transmitting terminal 20A to the receiving terminal 20C without using the relay terminal 20B, as a comparison target of this embodiment. The second graph G32 represents the average PDR of the terminal 20 mounted on each vehicle when communication is relayed from the transmitting terminal 20A to the receiving terminal 20C using the relay terminal 20B by the communication method, terminal, and communication program according to this embodiment. As shown in FIG. 12, it was confirmed that for all vehicles, the present embodiment represented by the second graph G12 can obtain a higher average PDR than the direct communication represented by the first graph G11.

[0056] Second embodiment In the above-described first embodiment, a configuration has been described in which a transmitting terminal performs broadcast communication without designating a receiving terminal when multiple terminals 20 perform sidelink communication not via a base station, etc. In the present embodiment, as a modification of this configuration, a case will be described in which a transmitting terminal performs unicast communication designating one receiving terminal.

[0057] The terminal 20 according to this embodiment is configured similarly to the terminal 20 according to the first embodiment shown in FIG.

[0058] The communication method and processing of the communication program according to this embodiment can be obtained by making the following changes to the processing of the sequence diagram according to the first embodiment shown in FIG.

[0059] In step S12 of FIG. 4, the relay terminal selection unit 222 of FIG. 2 selects a transmission success rate P n,r,i The terminal 20 with the highest transmission success rate P may be selected as the relay terminal 20B. n,r,i is calculated as in the above formula 2.

[0060] In step S13 in Fig. 4, the transmitter 223 shown in Fig. 2 of the terminal 20 operating as the transmitting terminal 20A transmits a transmission signal by unicast communication of the sidelink communication using a transmission resource. Here, the transmission signal further includes receiving terminal information representing the terminal 20 operating as the receiving terminal 20C, in addition to the transmitting terminal information, relay terminal information, and relay resource information. The receiving terminal information may include identification information representing the terminal 20 operating as the receiving terminal 20C.

[0061] In step S23 of FIG. 4, among the terminals 20 operating as the relay terminal 20B, the relay unit 225 shown in FIG. 2 transmits a relay signal by unicast communication of the sidelink communication using unused relay resources included in the relay resource group represented by the relay resource information included in the transmission signal, in ascending order of time subframes.

[0062] In step S31 of FIG. 4, among the terminals 20C operating as the receiving terminal 20C, the receiving unit 224 shown in FIG. 2 performs a decoding process when the receiving terminal information included in the transmission signal includes identification information representing the receiving terminal 20C, and does not perform a decoding process in other cases.

[0063] In step S32 of Fig. 4, if the reception unit 224 shown in Fig. 2 of the terminal 20 operating as the receiving terminal 20C determines that the decoding process is not successful (NO), the process of the receiving terminal 20C returns to step S31 and transmits a reception failure signal indicating that reception of the transmission signal and / or relay signal has failed. If the determination determines that the decoding process is successful (YES), the process of the receiving terminal 20C returns to step S21 and transmits a reception success signal indicating that reception of the transmission signal and / or relay signal has been successful.

[0064] In step S24 of FIG. 4, the relay unit 225 shown in FIG. 2 among the terminals 20 operating as the relay terminal 20B judges whether or not an unused relay resource remains in the relay resource group represented by the relay resource information included in the transmission signal received in step S21 of FIG. 4, and judges whether or not a reception failure signal or a reception success signal has been received. If the result of the judgment shows that the relay resource remains (YES) and the reception success signal has been received, the relay unit 225 of the relay terminal 20B releases the unused relay resource, and the process of the relay terminal 20B returns to step S21 and waits for the next transmission signal. If the result of the judgment shows that the relay resource remains (YES) and the reception failure signal has been received, the process of the relay terminal 20B returns to step S23 and repeats the process of transmitting the relay signal until all the relay resources are used or until the reception success signal is received. If the result of the judgment shows that the unused relay resource does not remain (NO), the process of the relay terminal 20B returns to step S21 of FIG. 4 and waits for the next transmission signal.

[0065] As described above, according to the communication method, terminal, and communication program of one embodiment, even when unicast communication of side link communication is used, the relay terminal 20B can relay a transmission signal to the receiving terminal 20C that is located at a position where direct communication from the transmitting terminal 20A may be obstructed by an obstacle or the like, and unused relay resources can be released in response to a reception success signal, enabling even more effective use of communication resources.

[0066] (Modification) In each of the above-described embodiments, a configuration has been described in which terminals 20 as mobile terminals mounted on vehicles 2 that are moving bodies perform side link communication with each other. As a variation of this configuration, some of the terminals 20 may be fixed terminals provided on fixed roadside units. In this case, by disposing the roadside unit at an intersection 90, it can be effectively used as a relay terminal 20B that performs direct communication with terminals 20 mounted on vehicles 2 traveling on roads connected to the intersection 90.

[0067] Although the invention made by the inventor has been specifically described based on the embodiment, the present invention is not limited to the embodiment, and it goes without saying that various modifications can be made without departing from the gist of the invention. Furthermore, the respective features described in the embodiment can be freely combined within the scope of technical compatibility. [Explanation of symbols]

[0068] 1. Communication Systems 2, 2A, 2B, 2C, 2D vehicles 20 Terminals 20A Terminal (Transmitting Terminal) 20B terminal (relay terminal) 20C, 20D terminal (receiving terminal) 21 Bus 22 Arithmetic unit 221 Resource Reservation Department 222 Relay Terminal Selection Unit 223 Transmitter 224 Receiving section 225 Relay Section 23 Storage device 230 Recording media 231 Program Memory Unit 232 Data storage unit 24 Communication Equipment 240 Antenna Equipment 25 Monitor Device 26 Input / Output Devices 301~320 Cars 80 Transmitting Signal 80a Header 80b Payload 81 First relay signal 81a Header 81b Payload 8K Kth relay signal 8Ka Header 8Kb payload 90 Intersection 91, 91A, 91B, 91C, 91D Road 92, 92A, 92B, 92C, 92D Obstacles G11, G12 graphs G21, G22 graphs G31, G32 graphs

Claims

1. A first terminal reserves a transmission resource and a relay resource group from among a plurality of communication resources which are a combination of a plurality of time subframes and a plurality of frequency subchannels; The first terminal selects a second terminal as a relay terminal from a candidate terminal group which is a set of terminals capable of direct communication with the first terminal; The first terminal transmits a transmission signal including transmitting terminal information indicating an identification number and a position of the first terminal, relay terminal information indicating an identification number of the relay terminal, and relay resource information indicating a relay resource included in the relay resource group, by using the transmission resource through sidelink communication; The second terminal that has received the transmission signal transmits a relay signal including the transmission terminal information by side link communication using the relay resource; a third terminal performs a decoding process of the transmitting terminal information based on a received signal including at least one of the transmitting signal and the relay signal; Includes Communication methods.

2. 2. The communication method according to claim 1, Selecting the second terminal comprises: Calculating a probability that direct transmission from the first terminal to the candidate terminal in the past has been successful for each combination of the first terminal and a candidate terminal included in the candidate terminal group as a direct transmission success rate for each combination; Calculating, from the first terminal, for each combination of the candidate terminal included in the candidate terminal group and a target terminal included in the target terminal group, a probability that indirect transmission of a signal from the first terminal to the target terminal via the candidate terminal has been successful in the past as an indirect transmission success rate; selecting the second terminal as the relay terminal from the candidate terminal group based on the direct transmission success rate, the indirect transmission success rate, and a total number of the relay resources included in the relay resource group; Includes Communication methods.

3. 3. The communication method according to claim 1, The relay resource group includes at least one relay resource having a different time subframe; Transmitting the relay signal includes: Transmitting the relay signal by sidelink communication using each of the relay resources a number of times equal to the total number of relay resources included in the relay resource group. Including, The decoding process includes: performing the decoding process of the transmitting terminal information based on a received signal including the transmitting signal and at least one of the respective relay signals; Includes Communication methods.

4. 3. The communication method according to claim 1, The transmission signal further includes receiving terminal information representing an identification number of the third terminal; when the third terminal fails in the decoding process, transmitting a reception failure signal representing the failure of the decoding process; When the second terminal receives the reception failure signal, the second terminal retransmits the relay signal through side link communication using an unused relay resource among the relay resource group. Also includes Communication methods.

5. 5. The communication method according to claim 4, when the third terminal succeeds in the decoding process, transmitting a reception success signal representing the success of the decoding process; When the second terminal receives the reception success signal, releasing an unused relay resource from the relay resource group; Also includes Communication methods.

6. 3. The communication method according to claim 1, the first terminal and the third terminal are mounted on a moving object, The group of candidate terminals includes at least one of a mobile terminal mounted on a moving body or a fixed terminal fixed at a predetermined location. Communication methods.

7. A terminal for wireless communication, A resource reservation unit that reserves a transmission resource and a relay resource group from among a plurality of communication resources that combine a plurality of time subframes and a plurality of frequency subchannels when the terminal operates as a transmitting terminal; a relay terminal selection unit that, when the terminal operates as the transmitting terminal, selects a predetermined terminal as a relay terminal from a candidate terminal group that is a set of other terminals that can directly communicate with the transmitting terminal; a transmitting unit configured to transmit, when the terminal operates as the transmitting terminal, a transmission signal including transmitting terminal information indicating an identification number and a position of the transmitting terminal, relay terminal information indicating an identification number of the relay terminal, and relay resource information indicating a relay resource included in the relay resource group, by side link communication using the transmission resource; a relay unit that transmits a relay signal including the transmitting terminal information by side link communication using the relay resource when the terminal operates as the relay terminal; A receiving unit that performs a decoding process of the transmitting terminal information based on a received signal including at least one of the transmission signal and the relay signal when the terminal operates as a receiving terminal; Equipped Terminal.

8. A communication program for implementing a predetermined process by causing a computing device of a terminal to execute the program, The process comprises: reserving a transmission resource and a relay resource group from among a plurality of communication resources, which are a combination of a plurality of time subframes and a plurality of frequency subchannels, when the terminal operates as a transmitting terminal; When the terminal operates as the transmitting terminal, selecting a predetermined terminal as a relay terminal from a candidate terminal group which is a set of other terminals capable of direct communication with the transmitting terminal; When the terminal operates as the transmitting terminal, transmitting a transmission signal including transmitting terminal information indicating an identification number and a position of the transmitting terminal, relay terminal information indicating an identification number of the relay terminal, and relay resource information indicating a relay resource included in the relay resource group, by sidelink communication using the transmission resource; When the terminal operates as the relay terminal, transmitting a relay signal including the transmitting terminal information through sidelink communication using the relay resource; When the terminal operates as a receiving terminal, decoding processing of the transmitting terminal information based on a receiving signal including at least one of the transmitting signal and the relay signal; Includes Communications program.

Images