Patent Publication Number: US-2021168803-A1

Title: Communication device and communication system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of International Application Number PCT/JP2018/030713 filed on Aug. 20, 2018 and designated the U.S., the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The present invention relates to a communication device and a communication system. 
     BACKGROUND 
     In current networks, traffic from mobile terminals (smartphones and feature phones) takes up the majority of network resources. Moreover, traffic used by mobile terminals is expected to expand further in the future. 
     Meanwhile, with the development of IoT (Internet of things) services (for instance, transportation systems, smart meters, and systems for monitoring devices and so on), there is a need to deal with services that have to meet various needed conditions. Therefore, in the communication standard for fifth generation mobile communication (5G or NR (New Radio)), in addition to the standard technology (NPL 2 to 12, for instance) of 4G (fourth generation mobile communication), techniques for realizing further increases in data rate and capacity and further reductions in latency are desired. 
     Note that with regard to the fifth generation communication standard, technical examinations are being undertaken by working groups (TSG-RAN WG1, TSG-RAN WG2, and so on, for instance) of the 3GPP (Third Generation Partnership Project) (NPL 13 to 40). 
     As described above, in order to deal with diverse services, in 5G, support for a great number of use cases classified into eMBB (Enhanced Mobile Broad Band), Massive MTC (Machine Type Communications), and URLLC (Ultra-Reliable and Low Latency Communication) is envisaged. 
     Further, the working groups of the 3GPP have also discussed V2X (Vehicle to Everything) communication. V2X is the generic name for V2V (Vehicle to Vehicle) communication, i.e. communication between automobiles, V2P (Vehicle to Pedestrian) communication, i.e. communication between an automobile and a pedestrian, V2I (Vehicle to Infrastructure) communication, i.e. communication between an automobile and road infrastructure, e.g., a road sign, and so on, using sidelink channels, for instance. Definitions relating to V2X are described in NPL 1, for instance. 
     With regard to resource arrangements in V2X, an arrangement method in which a control channel and a data channel are adjacent and an arrangement method in which the control channel and the data channel are not adjacent are being examined. 
       FIG. 23  is a view illustrating an example of a resource arrangement in a case where a PSCCH (Physical Sidelink Control CHannel) serving as a control channel and a PSSCH serving as a data channel are adjacent. In  FIG. 23 , the horizontal axis represents a time axis direction, and the vertical axis represents a frequency axis direction. In the example of  FIG. 23 , the frequency axis direction has four subchannels. In each subchannel, a PSCCH of two RBs (Resource Blocks) and a PSSCH of n (where n is an integer of three or more) RBs are disposed adjacent to each other. As illustrated in  FIG. 23 , the PSCCH resources indicated by diagonal lines and PSSCH resources indicated by horizontal lines are used for actual transmission. SCI (Sidelink Control Information) is mapped onto the PSCCH resources, the SCI including information such as the data modulation method and the code rate of the corresponding PSSCH. 
       FIG. 24  is a view illustrating an example of a resource arrangement in a case where the PSCCH and the PSSCH are not adjacent. Likewise in  FIG. 24 , PSCCH resources indicated by diagonal lines and PSSCH resources indicated by horizontal lines are used for actual transmission. As illustrated in  FIG. 24 , the respective resources of the PSCCH and the PSSCH are not adjacent. SCI relating to the corresponding PSSCH is mapped onto the PSCCH resources. 
     As a method for allocating these resources, a method in which a mobile communication system performs intensive control or a method in which respective terminal devices implementing V2X perform autonomous control, for instance, may be used. The method in which the mobile communication system performs intensive control can be applied when the terminal devices implementing V2X are within the coverage range of the mobile communication system, and is also known as mode  3 . The method in which the respective terminal devices perform autonomous control, on the other hand, can be applied even when the terminal devices are not within the coverage range of the mobile communication system, and is also known as mode  4 . In mode  4 , communication is not performed between the terminal device used to allocate the resources and the mobile communication system, and therefore transmission delays occurring when transmission data are generated in the terminal device can be shortened, with the result that strict latency necessity can be satisfied. 
     In mode  4 , each terminal device senses the frequency band used for V2X, and when transmission data are generated, the terminal device selects a resource to be used for to transmit the data on the basis of the sensing result by excluding resources that are highly likely to be in use by another terminal device. 
       FIG. 25  is a view illustrating an example of resource selection. As illustrated in  FIG. 25 , when transmission data from a certain terminal device is generated at a time T, the terminal device sets a selected window of a time width corresponding to an allowable latency deadline of the transmission data. Then, on the basis of sensing results acquired up to the time T, the terminal device excludes resources that are highly likely to be in use by other terminal devices from the selected window. In  FIG. 25 , for instance, resources indicated by diagonal lines and horizontal lines are excluded. The terminal device then selects any of the remaining resources not excluded from the selected window and transmits the transmission data by mapping the data onto the selected resource. 
     CITATION LIST 
     Non-Patent Literature 
       
     
       
         
           
               
               
               
               
             
               
                   
               
             
            
               
                 NPL 1: 3GPP 
                 TS 
                 22.186 
                 V15.2.0(2017 September) 
               
               
                 NPL 2: 3GPP 
                 TS 
                 36.211 
                 V15.1.0(2018 March) 
               
               
                 NPL 3: 3GPP 
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                 36.212 
                 V15.1.0(2018 March) 
               
               
                 NPL 4: 3GPP 
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                 36.213 
                 V15.1.0(2018 March) 
               
               
                 NPL 5: 3GPP 
                 TS 
                 36.300 
                 V15.1.0(2018 March) 
               
               
                 NPL 6: 3GPP 
                 TS 
                 36.321 
                 V15.1.0(2018 March) 
               
               
                 NPL 7: 3GPP 
                 TS 
                 36.322 
                 V15.0.1(2018 April) 
               
               
                 NPL 8: 3GPP 
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                 36.323 
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                 NPL 9: 3GPP 
                 TS 
                 36.331 
                 V15.1.0(2018 March) 
               
               
                 NPL 10: 3GPP 
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                 36.413 
                 V15.1.0(2018 March) 
               
               
                 NPL 11: 3GPP 
                 TS 
                 36.423 
                 V15.1.0(2018 March) 
               
               
                 NPL 12: 3GPP 
                 TS 
                 36.425 
                 V14.1.0(2018 March) 
               
               
                 NPL 13: 3GPP 
                 TS 
                 37.340 
                 V15.1.0(2018 March) 
               
               
                 NPL 14: 3GPP 
                 TS 
                 38.201 
                 V15.0.0(2017 December) 
               
               
                 NPL 15: 3GPP 
                 TS 
                 38.202 
                 V15.1.0(2018 March) 
               
               
                 NPL 16: 3GPP 
                 TS 
                 38.211 
                 V15.1.0(2018 March) 
               
               
                 NPL 17: 3GPP 
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                 38.212 
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                 NPL 18: 3GPP 
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                 38.213 
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                 NPL 19: 3GPP 
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                 38.214 
                 V15.1.0(2018 March) 
               
               
                 NPL 20: 3GPP 
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                 38.215 
                 V15.1.0(2018 March) 
               
               
                 NPL 21: 3GPP 
                 TS 
                 38.300 
                 V15.1.0(2018 March) 
               
               
                 NPL 22: 3GPP 
                 TS 
                 38.321 
                 V15.1.0(2018 March) 
               
               
                 NPL 23: 3GPP 
                 TS 
                 38.322 
                 V15.1.0(2018 March) 
               
               
                 NPL 24: 3GPP 
                 TS 
                 38.323 
                 V15.1.0(2018 March) 
               
               
                 NPL 25: 3GPP 
                 TS 
                 38.331 
                 V15.1.0(2018 March) 
               
               
                 NPL 26: 3GPP 
                 TS 
                 38.401 
                 V15.1.0(2018 March) 
               
               
                 NPL 27: 3GPP 
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                 38.410 
                 V0.9.0(2018 April) 
               
               
                 NPL 28: 3GPP 
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                 38.413 
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                 NPL 29: 3GPP 
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                 38.420 
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                 NPL 30: 3GPP 
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                 38.423 
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                 NPL 31: 3GPP 
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                 38.470 
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                 38.803 
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                 NPL 36: 3GPP 
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                 38.804 
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                 NPL 37: 3GPP 
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                 38.900 
                 V14.3.1(2017 July) 
               
               
                 NPL 38: 3GPP 
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                 38.912 
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                 NPL 39: 3GPP 
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                 38.913 
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                 NPL 40: 3GPP 
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                 37.885 
                 V15.0.0 (2018 June) 
               
               
                 NPL 41: 3GPP 
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                 22.886 
                 V15.1.0 (2017 March) 
               
            
           
           
               
            
               
                 NPL 42: 3GPP TSG RAN #80, RP-180602, “Status Report for RAN WG1 to TSG-RAN 
               
               
                 #80”, La Jolla, USA 11h-14th Jun. 2018. 
               
               
                 NPL 43: 3GPP TSG RAN #80, RP-181429, “New SID: Study on NR V2X”, La Jolla, 
               
               
                 USA 11h-14th Jun. 2018. 
               
               
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                 Communications”, IEEE Vehicular Technology Magazine, Pages: 30-39, Volume-2, 
               
               
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     In NPL 40, noted above, a PRR (Packet reception ratio) is defined. In the case of Type 1, for instance, the PRR is expressed by X/Y in relation to a transmission packet, where Y is the number of terminal devices (or vehicles) positioned within a range having a distance (a, b) from the transmission packet and X is the number of terminal devices (or vehicles), among Y, that successfully receive the transmission packet. Alternatively, in the case of Type 2, for instance, the PRR is expressed by S/Z, where Z is the number of receiving terminal devices and S is the number of terminal devices, among Z, that achieve reception successfully. The PRR expresses the number of terminal devices that achieve reception successfully among receiving terminal devices, for instance. 
       FIG. 26  is a view illustrating an example of communication performed between vehicles h 1  to h 8  having terminal devices.  FIG. 26  depicts an example in which the vehicle h 2  transmits packet data (also referred to hereafter as a “packet”) #1 to the other vehicles h 1  and h 3  to h 8 , and the vehicle h 4  also transmits a packet #2 to the other vehicles h 1  to h 3  and h 5  to h 8 . In this case, due to Half Duplex limitations, the vehicle h 2  is in a transmission mode and the vehicle h 4  is also in the transmission mode, and therefore the packet #1 transmitted from the vehicle h 2  is not able to be received normally by the vehicle h 4 . Likewise, the packet #2 transmitted from the vehicle h 4  is not able to be received normally by the vehicle h 2 . In this case, PRR=6/7. 
     As also described in NPL 1, in 5G, low latency and ultra-high reliability are needed with respect to V2X communication. In the example of  FIG. 26 , the PRR is 6/7, but when the PRR takes this numerical value, it may be impossible to satisfy these necessities. 
     SUMMARY 
     A communication device includes, a subgroup manager which, among a total of N×N T  resources of a control channel, the N×N T  resources having N (where N is an integer of 1 or more) resources in a frequency axis direction and N T  (where N T  is an integer of 2 or more) resources in a time axis direction, allocates N frequency axis direction resources in first place in the time axis direction to respective communication devices as resources of a first control channel, allocates second to N T -th time axis direction resources in first place in the frequency axis direction to the respective communication devices as resources of a second control channel, allocates second to N-th frequency axis direction resources in second place in the time axis direction to respective other communication devices as resources of the first control channel, and allocates third to N T -th time axis direction resources in second place in the frequency axis direction to the respective other communication devices as resources of the second control channel, and by repeating this operation, allocates the resources of the first and second control channels to a plurality of communication devices, and a transmission controller that transmits a control signal by using a resource of the first control channel and resends the control signal by using a resource of the second control channel. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating an example configuration of a wireless communication system. 
         FIG. 2  is a view illustrating an example configuration of the terminal  100 . 
         FIG. 3  is a view illustrating an example of PSCCH allocation. 
         FIG. 4  is a view illustrating an example of a correspondence relationship between the PSCCH and the PSSCH. 
         FIG. 5A  is a view illustrating an example of PSCCH resource allocation in a case where N=2. 
         FIG. 5B  is a view illustrating an example of PSCCH allocation in a case where N=3. 
         FIG. 6  is a view illustrating an example of PSCCH resource allocation in a case where N=4. 
         FIGS. 7A and 7B  are views respectively illustrating an example of PSCCH resource allocation and an example of randomization. 
         FIGS. 8A and 8B  are views illustrating examples of randomization. 
         FIG. 9  is a view illustrating an example of resource allocation in a case where high-priority data are transmitted. 
         FIG. 10  is a view illustrating an example of resource allocation in a case where high-priority data are transmitted. 
         FIG. 11  is a view illustrating an example of resource allocation in a case where high-priority data are transmitted. 
         FIG. 12  is a view illustrating an example of resource allocation in a case where high-priority data are transmitted. 
         FIG. 13  is a view illustrating an example of resource allocation in a case where high-priority data are transmitted. 
         FIG. 14  is a view illustrating an example of resource allocation in a case where high-priority data are transmitted. 
         FIGS. 15A and 15B  are views respectively illustrating an example of an arrangement of a PCRLICH and an example of information transmitted using the PCRLICH. 
         FIG. 16  is a view illustrating an example of allocation to a resource pool of terminals included in a V2X group. 
         FIGS. 17A and 17B  are views illustrating examples of PSCCH allocation in the evenly allocation manner. 
         FIGS. 18A and 18B  are views illustrating examples of PSCCH allocation in the non-uniform spacing allocation manner. 
         FIG. 19  is a flowchart illustrating an example operation of PSCCH resource allocation. 
         FIG. 20  is a flowchart illustrating an example operation performed to transmit high-priority data. 
         FIG. 21  is a view illustrating an example of PRR simulation results. 
         FIG. 22  is a view illustrating an example of PRR simulation results. 
         FIG. 23  is a view illustrating an example of an arrangement of PSCCH and PSSCH resources. 
         FIG. 24  is a view illustrating an example of an arrangement of PSCCH and PSSCH resources. 
         FIG. 25  is a view illustrating an example of resource selection according to mode  4 . 
         FIG. 26  is a view illustrating an example of vehicle to vehicle communication. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Embodiments will be described in detail below with reference to the figures. The problems and embodiments described in this description are examples and do not limit the scope of rights of this application. More specifically, even when different expressions are used in the description, as long as the expressions are technically equivalent, the technology of the present application can be applied even to these different expressions, and the scope of rights is not limited thereby. Moreover, the embodiments can be combined as appropriate within a scope that does not contradict the processing content. 
     Furthermore, as regards the terminology used in this description and the technical content described therein, the terminology and technical content described in specifications and contributed articles as communication-related standards by the 3GPP and so on may be used as appropriate. Examples of such specifications include 3GPP TS 38.211 V15.1.0 (2018 March) and so on. 
     Note that 3GPP specifications are updated as needed. Therefore, the latest specifications at the time of filing of this application may be used as the aforesaid specifications. The terminology and technical content described in the latest specifications may be used as appropriate in this description. 
     Embodiments of the communication device and the communication system disclosed in this application will be described in detail below on the basis of the figures. Note that the embodiments described below do not limit the technology disclosed herein. 
     First Embodiment 
     &lt;1. Example Configuration of Wireless Communication System&gt; 
       FIG. 1  is a view illustrating an example configuration of a wireless communication system  10  according to a first embodiment. 
     The wireless communication system (or the communication system; also referred to hereafter as “the wireless communication system”)  10  includes a plurality of terminal devices  100 - 1  to  100 - 4 . The terminal devices  100 - 1  to  100 - 4  are respectively provided in vehicles  100 - v   1  to  100 - v   4 . 
     The terminal devices (or the communication devices; also referred to hereafter as “the terminals”)  100 - 1  to  100 - 4  are communication devices that are capable of wireless communication, e.g., as feature phones, smartphones, personal computers, tablet terminals, or game devices, for instance. 
     Further, the terminals  100 - 1  to  100 - 4  are capable of performing wireless communication through V2X communication, for instance. As noted above, for instance, V2X is the generic name for V2V, V2P, V2I, and so on. Therefore, in  FIG. 1 , for instance, when the terminal  100 - 1  is provided in the vehicle  100 - v   1 , the terminal  100 - 2  serving as the communication partner may be carried by a pedestrian or provided on a road sign rather than being installed in the vehicle  100 - v   2 . Note, however, that in the following description, it is assumed that the terminals  100 - 1  to  100 - 4  are provided in the vehicles  100 - v   1  to  100 - v   4 . 
     Furthermore, the terminals  100 - 1  to  100 - 4  are capable of performing wireless communication using mode  4  of V2X communication, for instance. As noted above, for instance, mode  4  is a method with which the terminals  100 - 1  to  100 - 4  can control wireless communication autonomously even when the terminals  100 - 1  to  100 - 4  are not within the coverage range of a mobile communication system. 
     Note that when the terminals  100 - 1  to  100 - 4  transmit data or the like, the terminals  100 - 1  to  100 - 4  cannot receive data or the like transmitted from another terminal, and when the terminals  100 - 1  to  100 - 4  receive data or the like from another terminal, the terminals  100 - 1  to  100 - 4  cannot transmit data or the like to another terminal. In other words, the terminals  100 - 1  to  100 - 4  cannot enter a reception mode while in the transmission mode and cannot enter the transmission mode while in the reception mode. These terminals  100 - 1  to  100 - 4  may be referred to as Half-duplex (mode) terminals, for instance. 
     Note that  FIG. 1  depicts an example in which the four terminals  100 - 1  to  100 - 4  are included in the wireless communication system  10 . The number of terminals  100 - 1  to  100 - 4  included in the wireless communication system  10  may be two, three, five, or more. 
     Unless specified otherwise, the terminals  100 - 1  to  100 - 4  will be referred to hereafter as the terminal  100  or the terminals  100 . 
     &lt;2. Example Configuration of Terminal Device&gt; 
       FIG. 2  is a view illustrating an example configuration of the terminal  100 . 
     The terminal  100  includes a processor  110 , a memory  120 , a wireless communication unit (communicator)  130 , and an antenna  140 . 
     The processor  110  is a CPU (Central Processing Unit), a DSP (Digital Signal Processor), an FPGA (Field Programmable Gate Array), or the like, for instance, and performs overall control of the terminal  100 . The processor  110  includes a group management unit (manager)  111 , a used resource control unit (controller)  112 , a transmission control unit (controller)  113 , and a reception control unit (controller)  114 . 
     The group management unit  111  manages a group to which the terminals  100  belong. More specifically, the group management unit  111  controls admission to and withdrawal from the group of the terminals  100  and manages identification information and used resources of the terminals  100  belonging to the same group. Note that the group managed by the group management unit  111  may also be referred to as a V2X group, for instance. 
     The group management unit  111  also manages which terminal  100  is to serve as a cluster header (CH), this being determined dynamically for each subframe within the group. The CH is a representative terminal (or a representative communication device) for each subframe and reorders the resources in each subframe as needed. Hereafter, the terminal serving as the CH may also be referred to as the representative terminal, for instance. When a packet (a sporadic packet) to be transmitted with high priority (or transmitted suddenly) is generated, the terminal  100  can transmit the packet quickly by using a resource reordered by the representative terminal. This will be described in detail in an example operation. 
     Furthermore, when the terminal  100  is not the CH and a packet to be transmitted with high priority is generated, the group management unit  111  generates a transmission request for high-priority transmission and instructs the used resource control unit  112  to transmit the generated transmission request. When, on the other hand, the terminal  100  is the CH and the terminal  100  receives a transmission request from another terminal  100  via the reception control unit  114 , the group management unit  111  reorders the resources that are used by the respective terminals  100  as a control channel (a PSCCH). The group management unit  111  then generates reordering information indicating the reordered resources and instructs the used resource control unit  112  to transmit the generated reordering information. 
     The group management unit  111  includes a subgroup management unit (manager)  1110 . 
     The subgroup management unit  1110  manages a subgroup to which the terminals  100  belong. More specifically, for instance, the subgroup management unit  1110  controls admission to and withdrawal from the subgroup of the terminals  100  and manages identification information and used resources of the terminals  100  belonging to the same subgroup. 
     Note that the subgroup managed by the subgroup management unit  1110  is a subgroup included in the V2X group, for instance. In other words, the subgroup management unit  1110  manages the resources of the terminals  100  included in the subgroup and allocates a control channel (a PSCCH) and a data channel (a PSSCH) to the terminals  100  included in the subgroup, for instance. 
       FIG. 3  is a view illustrating an example of PSCCH allocation. As illustrated in  FIG. 3 , identification information from v 1  to v(N×(N+1)/2) (where N, for instance, expresses a number of PSCCH subchannels in the frequency axis direction and is an integer of 1 or more) is allocated to the PSCCH resources. The identification information represents the identification information of each of the terminals  100 , for instance. For instance, v 1  is a resource of the terminal  100 - 1 , v 2  is a resource of the terminal  100 - 2 , and so on. The subgroup management unit  1110  allocates the PSCCH resources depicted in  FIG. 3  to the terminals  100  included in the subgroup using the identification information of each of the terminals  100 . Further, the subgroup management unit  1110  allocates a resource in the same subframe as the PSCCH resource allocated to the terminal  100  as a PSSCH resource for the terminal  100 . The subchannel to which the data of each terminal  100  are to be mapped is indicated by SCI (Sidelink Control Information) included in a control signal. For instance, the subgroup management unit  1110  may generate the SCI, generate a control signal including the SCI, and output the generated control signal to the used resource control unit  112 . 
       FIG. 4  is a view illustrating an example of a correspondence relationship between the PSCCH and the PSSCH. As illustrated in  FIG. 4 , for instance, the subgroup management unit  1110 , when allocating the resource indicated by v 1  to the terminal  100 - 1  as a PSCCH resource, allocates one of the resources of the PSCCH (in the example of  FIG. 4 , SC 1  (subchannel  1 )) belonging to the same subframe as v 1  as a PSSCH resource. Note that  FIGS. 3 and 4  will be described in detail below. 
     Returning to  FIG. 2 , the subgroup management unit  1110  outputs an allocation result to the used resource control unit  112  and instructs the used resource control unit  112  to transmit a control signal using the control channel or to transmit data using the data channel. 
     The used resource control unit  112  controls the resources used by the terminal  100  to transmit control signals and data. More specifically, the used resource control unit  112  executes control so that in response to an instruction relating to a packet transmission request or a reordering request output from the group management unit  111 , the transmission request or the reordering request is transmitted using a resource of a PSCRLICH (Physical Control Resource Location Indication CHannel) provided in a predetermined frequency band. The PSCRLICH is a different channel to the PSCCH and the PSSCH, for instance, and  FIG. 15A , for instance, illustrates an example of a channel arrangement. This will be described in detail below. 
     Returning to  FIG. 2 , the used resource control unit  112  also controls the control channel resources and data channel resources in accordance with the allocation result output from the subgroup management unit  1110 . More specifically, for instance, the used resource control unit  112  receives the allocation result illustrated in  FIGS. 3 and 4  and, in accordance with the allocation result, controls transmission of a control signal using a predetermined PSCCH resource (v 1 , v 2 , or the like) and transmission of data using a predetermined PSSCH resource. 
     The transmission control unit  113  controls the wireless communication unit  130  so that control signals and data are transmitted using the resources controlled by the used resource control unit  112 . More specifically, the transmission control unit  113  performs the following processing. The transmission control unit  113  receives data from an application processing unit or the like provided in the processor  110  and implements error correction and encoding processing (also referred to hereafter as “encoding processing”), modulation processing, and the like on the received data. Further, the transmission control unit  113  implements encoding processing, modulation processing, and the like on a control signal received from the subgroup management unit  1110  or a transmission request, reordering information, or the like received from the group management unit  111  via the used resource control unit  112 . The transmission control unit  113  maps the control signal onto a PSCCH resource, the data onto a PSSCH resource, and the transmission request, the reordering information, or the like onto a PSCRLICH resource. The transmission control unit  113  then transmits a transmission signal acquired as a result of the mapping by multicasting (or grouping) via the wireless communication unit  130 . 
     The reception control unit  114  implements demodulation processing, error correction and decoding processing (also referred to hereafter as “decoding processing”), and the like on a reception signal received from another terminal  100 . More specifically, the reception control unit  114  extracts the control signal by implementing demodulation processing and the like on a reception signal mapped onto the PSCCH. Further, the reception control unit  114  extracts the data by implementing demodulation processing and the like on a reception signal mapped onto the PSSCH. Furthermore, the reception control unit  114  extracts the transmission request, reordering information, or the like by implementing demodulation processing, and so on, on a reception signal mapped onto the PSCRLICH. The reception control unit  114  outputs the extracted data or control signal to the application processing unit or the like provided in the processor  110 . Further, having extracted a transmission request, the reception control unit  114  outputs the extracted transmission request to the group management unit  111  in order to request reordering of the resources in accordance with the transmission request. 
     The memory  120  is a ROM (Read Only Memory), a RAM (Random Access Memory), or the like, for instance. The memory  120  stores a program, for instance, and the program is read by the processor  110  and executed in the processor  110 . The functions of the group management unit  111 , the subgroup management unit  1110 , the used resource control unit  112 , the transmission control unit  113 , and the reception control unit  114  can be realized by executing the program, for instance. The memory  120  also stores information used when the processor  110  executes processing, and so on, for instance. 
     The wireless communication unit  130  implements D/A (Digital to Analog) conversion processing, frequency conversion processing (up-conversion) from a base band to a wireless band, and the like on the transmission signal output from the transmission control unit  113 . The wireless communication unit  130  outputs the wireless signal converted to the wireless band to the antenna  140 . 
     Further, the wireless communication unit  130  implements frequency conversion processing (down-conversion) to the base band, A/D (Analog to Digital) conversion processing, and the like on the wireless signal output from the antenna  140 . The wireless communication unit  130  outputs a reception signal to the reception control unit  114 . 
     The antenna  140  transmits the wireless signal output from the wireless communication unit  130  to another terminal  100 . Further, the antenna  140  receives a wireless signal transmitted from another terminal  100  and outputs the received wireless signal to the reception control unit  114 . 
     &lt;3. Example of PSCCH Resource Allocation&gt; 
       FIG. 3  is a view illustrating an example of PSCCH resource allocation. 
     In  FIG. 3 , the horizontal axis represents the time axis direction, and the vertical axis represents the frequency axis direction. In  FIG. 3 , N PSCCH resources, N being the number of subchannels, are provided in the frequency axis direction. Further, N T  (where N T  is an integer of 2 or more) PSCCH resources, which are resources corresponding to the subchannels in the frequency axis direction, are provided in the time axis direction. Hence, the number of PSCCH resources in  FIG. 3  is N×N T . For instance, one resource (or resource region; also referred to hereafter as a “resource”) serves as one subchannel in the frequency axis direction and a time period corresponding to one subchannel in the time axis direction. 
     Note that in the example of  FIG. 3 , the unit of a single resource in the time axis direction is one subframe. The time axis direction unit may also be one slot or one symbol, for instance. Hereafter, one subframe will be described as the time axis direction unit of a single resource. Further,  FIG. 3  depicts an example in which N T =N+1. An example in which N T =N+1 will be described below. 
     The resources illustrated in  FIG. 3  respectively serve as transmission resources of the PSCCH, which are allocated to the respective terminals  100 . Further, v 1  to v(N×(N+1)/2), depicted on the respective resources, serve as the identification information of the terminals  100 , for instance. As described above, the terminal  100 - 1  is v 1 , the terminal  100 - 2  is v 2 , and so on, for instance. 
     Hereafter, the terminal  100  to which the identification information v 1  is applied may be referred to as a terminal v 1 , and the terminal  100  to which the identification information v 2  is applied may be referred to as a terminal v 2 . Accordingly, the terminal  100  to which the identification information v(N×(N+1)/2) is applied may be referred to as a terminal v(N×(N+1)/2). 
     As illustrated in  FIG. 3 , the terminal  100  allocates the N resources from the first to the N-th frequency axis direction resources in first place in the time axis direction respectively to the terminals  100  from the terminal v 1  to the terminal vN. Further, the terminal  100  allocates the N resources from the second to the (N+1)th time axis direction resources in first place in the frequency axis direction respectively to the terminals  100  from the terminal v 1  to the terminal vN. 
     Furthermore, the terminal  100  allocates the (N−1) resources from the second to the N-th frequency axis direction resources in second place in the time axis direction respectively to the terminals  100  from a terminal v(N+1) to a terminal v(2N−1). Moreover, the terminal  100  allocates the (N−1) resources from the third to the (N+1)th time axis direction resources in second place in the frequency axis direction respectively to the terminals from the terminal v(N+1) to the terminal v(2N−1). 
     Thereafter, the terminal  100  repeats this operation with respect to the remaining resources. Finally, the terminal  100  allocates the N-th frequency axis direction resource in N-th place in the time axis direction and the N-th frequency axis direction resource in (N+1)th place in the time axis direction to the terminal v(N×(N+1)/2). 
     As illustrated in  FIG. 3 , two PSCCH resources are allocated to each terminal v 1  to v(N×(N+1)/2). For instance, the N PSCCH resources from the first to the N-th frequency axis direction resources in first place in the time axis direction are initial resources for the control signal, while the second to the (N+1)th time axis direction PSCCH resources in first place in the frequency axis direction are repetition resources for the control signal. Further, for instance, the second to the N-th frequency axis direction resources in second place in the time axis direction are initial resources for the control signal, while the PSCCH resources from the third to the (N+1)th time axis direction resources in second place in the frequency axis direction are repetition resources for the control signal. 
     Hence, the terminal v 1  transmits the control signal using the first frequency axis direction resource in first place in the time axis direction, and resends the control signal using the first frequency axis direction resource in second place in the time axis direction. Since there are two opportunities to transmit the control signal, the probability that the reception-side terminal  100  will receive the data transmitted from the transmission-side terminal  100 , for instance, can be improved in comparison with a case where there is only one transmission opportunity. 
     Note that  FIG. 3  depicts an example arrangement of PSCCH resources according to the method ( FIG. 24 , for instance) in which the PSCCH and the PSSCH are not adjacent. However, this arrangement can also be applied to the method ( FIG. 23 , for instance) in which the PSCCH and the PSSCH are adjacent. In the latter case, it may be assumed that  FIG. 3  illustrates a grouping of PSCCHs, for instance. Alternatively, for instance, it may be assumed that PSSCH resources are inserted respectively between the PSCCH resources, but that the PSSCH resources are not depicted in  FIG. 3 . 
     Further, the example illustrated in  FIG. 3  is a method according to mode  4  of V2X communication, for instance. Therefore, the PSCCH resources depicted in  FIG. 3  may be considered as a grouping of the remaining resources that have not been excluded from the selected window as a result of sensing, for instance. 
       FIG. 4  is a view illustrating an example of a relationship between the PSCCH and the PSSCH. The control signal includes SCI, and the SCI includes information indicating which subchannel of the same subframe has been used to allocate the corresponding PSSCH. As a result, the reception-side terminal  100  can ascertain the resource of the PSSCH corresponding to the PSCCH from the SCI. In the example of  FIG. 4 , information indicating SC 1  (a subcarrier  1 ) as the PSSCH is included in the SCI transmitted using the PSCCH resource allocated to the terminal v 1 . The terminal v 1  can transmit data using this subcarrier. 
     Next, an example of PSCCH resource allocation in a case where N=2 to 4 will be described. 
       FIG. 5A  is a view illustrating an example of PSCCH resource allocation in a case where N=2. 
     As illustrated in  FIG. 5A , when N=2, the PSCCH can be allocated to three terminals, namely the terminals v 1  to v 3 . The allocation method is identical to that of  FIG. 3 . As a result, a resource in SF 1  in the time axis direction and in first place in the frequency axis direction and a resource in SF 2  in the time axis direction and in first place in the frequency axis direction are allocated to the terminal v 1  as PSCCH resources. Further, a resource in SF 1  in the time axis direction and in second place in the frequency axis direction and a resource in SF 3  in the time axis direction and in first place in the frequency axis direction are allocated to the terminal v 2  as PSCCH resources. Furthermore, a resource in SF 2  in the time axis direction and in second place in the frequency axis direction and a resource in SF 3  in the time axis direction and in second place in the frequency axis direction are allocated to the terminal v 3  as PSCCH resources. 
     Here, focusing on SF 1 , in the period of SF 1 , PSCCH resources are allocated to the terminal v 1  and the terminal v 2 . PSCCH resources are not allocated to the terminal v 3  in the period of SF 1 . During the period of SF 1 , therefore, the terminal v 3  serves as a reception mode terminal, for instance. Hence, during the period of SF 1 , the terminal v 3  can receive data transmitted from the terminal v 1  and the terminal v 2 . 
     Further, focusing on SF 2 , in the period of SF 2 , PSCCH resources are allocated to the terminal v 1  and the terminal v 3 . PSCCH resources are not allocated to the terminal v 2  in the period of SF 2 . During the period of SF 2 , therefore, the terminal v 2  serves as a reception mode terminal, for instance. Hence, during the period of SF 2 , the terminal v 2  can receive data transmitted from the terminal v 1  and the terminal v 3 . 
     Furthermore, focusing on SF 3 , in the period of SF 3 , PSCCH resources are allocated to the terminal v 2  and the terminal v 3 , but PSCCH resources are not allocated to the terminal v 1 . During the period of SF 3 , therefore, the terminal v 1  can receive data transmitted from the terminal v 2  and the terminal v 3 . 
     In other words, the terminal v 3  can receive data during the period of SF 1 , the terminal v 2  can receive data during the period of SF 2 , and the terminal v 1  can receive data during the period of SF 3 , and as a result, all of the terminals v 1  to v 3  can receive data during the period from SF 1  to SF 3 . 
     When PSCCH resources are allocated to the terminal v 1  and the terminal v 2 , for instance, during the entire period from SF 1  to SF 3 , the terminal v 1  and the terminal v 2  remain in the transmission mode for the entire period from SF 1  to SF 3 . In this case, the terminal v 1  and the terminal v 2  cannot receive data transmitted from the other terminals v 2  and v 1  for the entire period from SF 1  to SF 3 . As a result, as illustrated in  FIG. 26 , packets collide, leading to a reduction in the PRR. 
     When the PSCCHs are allocated as illustrated in  FIG. 5A , however, a period in which each of the terminals v 1  to v 3  is in the reception mode exists within the period from SF 1  to SF 3 , and therefore the data that are transmitted over the period from SF 1  to SF 3  can be received in one of these periods. As a result, an improvement in the PRR can be achieved in comparison with a case where PSCCH resources are allocated to the terminal v 1  and the terminal v 2  over the entire period from SF 1  to SF 3 . 
       FIG. 5B  is a view illustrating an example of PSCCH allocation in a case where N=3. 
     The allocation method of  FIG. 5B  is also identical to that of  FIG. 3 . Likewise in this case, focusing on the period of SF 1 , PSCCH resources are allocated to the terminals v 1  to v 3 , but PSCCH resources are not allocated to the other terminals v 4  to v 6 . During the period of SF 1 , the terminals v 4  to v 6  are in the reception mode and are therefore capable of receiving data transmitted from the terminals v 1  to v 3 . 
     Further, during the period of SF 2 , the terminals v 2 , v 3 , and v 6  are in the reception mode and are therefore capable of receiving data transmitted from the terminals v 1 , v 4 , and v 5 . Furthermore, during the period of SF 3 , the terminals v 1 , v 3 , and v 5  can enter the reception mode, and during the period of SF 4 , the terminals v 1 , v 2 , and v 4  can enter the reception mode. 
     In other words, when N=3, all of the terminals v 1  to v 6  are in the reception mode at least once between SF 1  and SF 3 . When, for instance, PSCCH resources are allocated to the terminals v 1  to v 3  over the entire period from SF 1  to SF 4 , the terminals v 1  to v 3  do not enter the reception mode and are therefore incapable of receiving data transmitted from the terminals v 1  to v 3 . In the example of  FIG. 5B , the terminals v 1  to v 6  enter the reception mode at least once over the period from SF 1  to SF 3 , and therefore the PRR can be improved in comparison with a case where PSCCH resources are allocated to the terminals v 1  to v 3  over the entire period from SF 1  to SF 4 . 
     Furthermore, in the example of  FIG. 5B , focusing on the terminal v 4 , the terminal v 4  can enter the reception mode in two subframe periods, namely SF 1  and SF 4 . Moreover, focusing on the terminal v 6 , the terminal v 6  can enter the reception mode in two subframe periods, namely SF 1  and SF 2 . In the example of  FIG. 5A , the respective terminals v 1  to v 3  can enter the reception mode in a single subframe period, i.e. one of SF 1  to SF 3 , whereas in the example of  FIG. 5B , each of the terminals v 1  to v 6  can enter the reception mode in a plurality of subframe periods from SF 1  to SF 4 . Hence, with the example of  FIG. 5B , the reception efficiency of the terminal in the reception mode can be improved in comparison with the example of  FIG. 5A . 
       FIG. 6  is a view illustrating an example of PSCCH resource allocation in a case where N=4. 
     The allocation method of  FIG. 6  is also identical to that of  FIG. 3 . Likewise in the example depicted in  FIG. 6 , all of the terminals v 1  to v 10  enter the reception mode for at least one subframe period among the periods from SF 1  to SF 5 . 
     Further, focusing on the terminal v 1 , the terminal v 1  can enter the reception mode in three subframe periods, namely SF 3  to SF 5 . Furthermore, focusing on the terminal v 2 , the terminal v 2  can enter the reception mode in three subframe periods, namely SF 2 , SF 4 , and SF 5 . Moreover, focusing on the terminal v 8 , the terminal v 8  can enter the reception mode in three subframe periods, namely SF 1 , SF 2 , and SF 5 . 
     In other words, in the example depicted in  FIG. 6 , the periods in which the respective terminals  100  can enter the reception mode are even longer than those of the example depicted in  FIG. 5B . Therefore, with the example depicted in  FIG. 6 , the reception efficiency can be improved over the example depicted in  FIG. 5B . 
     The number of terminals  100  installed in a vehicle may reach several tens. When PSCCH resources are allocated to this number of terminals  100  using the allocation method illustrated in  FIG. 3 , each terminal  100  enters the reception mode in an even great number of subframe periods than the case illustrated in  FIG. 6 , and as a result, a further improvement can be achieved in the reception efficiency. 
     The examples of PSCCH resource allocation illustrated in  FIG. 3  and  FIGS. 5A to 6  are implemented in a subgroup included in the V2X group, for instance. When, for instance, the number of PSCCHs (in the above examples, the number of PSCCH subchannels) included in the frequency axis direction is set as N and the number of terminals  100  included in one V2X group is set as M (where M is an integer of 1 or more), a number L of subgroups can be calculated using the following formula. 
     
       
         
           
             
               
                 
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     Note that M expresses the total number of terminals  100 , including a host terminal  100  and other terminals, for instance. 
     The relationship between the subgroups and the V2X group and randomization within the V2X group will now be described. 
     Note that the resource allocation illustrated in  FIGS. 3 to 6  is performed by the subgroup management unit  1110 , for instance, while the calculation of formula (1) is performed by the group management unit  111 , for instance. 
     &lt;4. Relationship Between Subgroups and V2X Group&gt; 
       FIG. 7A  is a view illustrating an example of PSCCH resource allocation in a case where N=2 (the number of PSCCHs in the frequency axis direction=2) and M=7 (the number of terminals  100  included in the V2X group=7). 
     When the number L of subgroups included in the V2X group is calculated using formula (1) in a case where N=2 and M=7, L=3. Hence, as illustrated in  FIG. 7A , the V2X group can be divided into three subgroups. 
     The terminal  100  then allocates the PSCCH resources to the respective terminals  100  in each subgroup using the PSCCH allocation method illustrated in  FIG. 3 . In the example of  FIG. 7A , the terminal  100  allocates PSCCH resources to the terminals v 1  to v 3  in a subgroup #1. Further, the terminal  100  allocates PSCCH resources to the terminals v 4  and v 5  in a subgroup #2. Furthermore, the terminal  100  allocates PSCCH resources to the terminals v 6  and v 7  in a subgroup #3. 
     In accordance with L and M, the terminal  100  calculates the number L of subgroups using formula (1) and allocate PSCCH resources to the respective terminals  100  in each subgroup using the PSCCH allocation method illustrated in  FIG. 3  and so on. 
     In this case, as illustrated in  FIG. 7A , for instance, resources to which PSCCH resources are not allocated exist. In the first embodiment, such empty resources are permitted. For instance, when the PSCCHs of the terminals  100  are allocated to all of the PSCCH resources, and a packet delay occurs in one resource, for instance, the packet may be delayed in the other resources. In anticipation of such a situation occurring, empty resources may be left as is. Note that in the first embodiment, the empty resources are used when high-priority data are transmitted. This will be described in detail below. 
     &lt;5. Randomization&gt; 
     In the first embodiment, after the PSCCH resources have been allocated to the respective terminals  100  in the respective subgroups using the allocation method illustrated in  FIG. 3 , the resources can be randomized within the V2X group. In  FIG. 7A , for instance, the terminal v 6  and the terminal v 7  take a longer time to transmit the PSCCH than the other terminals v 1  to v 5 . By performing randomization, the time taken by the respective terminals v 1  to v 7  to transmit the PSCCH can be made uniform, for instance, and as a result, the resources can be allocated fairly. 
     As a randomization procedure, randomization is performed in the frequency axis direction first and then in the time axis direction. 
       FIG. 7B  is a view illustrating an example of PSCCH resource allocation after PSCCH resource allocation has been performed in accordance with  FIG. 7A  and randomization has been performed in the frequency axis direction. 
     In the example of  FIG. 7B , in SF 2 , the resource allocated to the terminal v 3  and the resource allocated to the terminal v 1  are switched in the frequency axis direction. Further, in SF 7 , the resource allocated to the terminal v 6  and the resource allocated to the terminal v 7  are switched in the frequency axis direction. The resources are also switched in the frequency axis direction in SF 8  and SF 9 . 
     For instance, randomization in the frequency axis direction may be realized by switching any resources within the range of the frequency axis direction resources allocated to the respective subframe periods, as long as one resource is switched for another resource. In the example of  FIG. 7B , N=2, and therefore two resources are switched in the frequency axis direction, but when N=3 such that PSCCH resources are allocated in sequence to the terminals v 1  to v 3  in SF 1 , the resource of the terminal v 1  may be switched with the resource of the terminal v 2  or the resource of the terminal v 1  may be switched with the resource of the terminal v 3 . Alternatively, the resource of the terminal v 1  and the resource of the terminal v 2  may be switched alone without switching the resource of the terminal v 3 , or the resources of all of the terminals v 1  to v 3  may be switched. 
     Further, in the example of  FIG. 7B , the resources of SF 2  and SF 7  to SF 9  are subjected to switching, but the resources of the other SFs may also be subjected to switching. For instance, the resources of SF 1  (the resources of the terminal v 1  and the terminal v 2 ) may be subjected to switching, or the resources of SF 5  (the resource of the terminal v 4 ) may be subjected to switching. 
     Thus, randomization in the frequency axis direction is performed by switching the PSCCH resources allocated to the respective terminals  100  in the frequency axis direction. 
       FIGS. 8A and 8B  are views illustrating examples of PSCCH allocation in a case where randomization is performed in the time direction.  FIG. 8A  illustrates an example of PSCCH allocation prior to randomization in the time direction (the same allocation example as  FIG. 7B ), and  FIG. 8B  illustrates an example of PSCCH allocation following randomization in the time direction. 
     In the example of  FIG. 8B , the resources of SF 2  are disposed in SF 6 , and the resources of SF 3  are disposed in SF 4 . Further, in the example of  FIG. 8B , the resources of SF 4  are disposed in SF 9 , the resources of SF 5  are disposed in SF 7 , the resources of SF 6  are disposed in SF 2 , the resources of SF 7  are disposed in SF 3 , the resources of SF 8  are disposed in SF 5 , and the resources of SF 9  are disposed in SF 8 . Note, however, that the resources of SF 1  are not moved. 
     Randomization in the time axis direction is performed by grouping the resources in each subframe in the frequency axis direction into one and disposing each grouping in a different subframe. Alternatively, randomization in the time direction is performed by performing switching in units of the frequency axis direction resources allocated to each subframe period. In this case, as long as switching is not performed so that one grouping and another grouping overlap in the same subframe period, the resources may be disposed in any subframe. 
     Hence, randomization involves switching the PSCCH resources at random in the frequency axis direction and the time axis direction, for instance. Further, the PSSCH is also switched in accordance with switching of the PSCCH resources. 
     However, in  FIG. 8A , for instance, switching of the resources of the terminal v 1  allocated to the SF 1  period and the terminal v 3  allocated to SF 2  is not permitted. In other words, switching the resources of a certain terminal  100  in a subframe period and another terminal  100  in another subframe period across subframe periods is not permitted. When randomization is to be performed across subframe periods, for instance, it is permitted to form the PSCCH resources of the two terminals v 1  and v 2  allocated to SF 1  into a single grouping, form the PSCCH resources of the two terminals v 3  and v 1  allocated to SF 2  into a single grouping, and switch the resources between the groupings. 
     &lt;5.1 Randomization&gt; 
     Next, formularization of the randomization described above will be described. 
     A matrix formula of N×(N+1)L, as illustrated below, will be considered. 
     
       
         
           
             
               
                 
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     In formula (2), V k,j  represents an index of the terminals  100  in an i-th V2X group. The object of randomization is to randomize the indices of the terminals  100  within the i-th V2X group, for instance. In other words, the object of randomization is to randomize V k,j , for instance. 
     First, for instance, randomization is performed individually on each of the columns illustrated in  FIG. 3  on the basis of a predetermined N×(N+1)L matrix including a series R (c) . 
     Here, the series R (c)  is expressed by 
       [Math. 3] 
         R   (c) =[ R   1   (c)   R   2   (c)    . . . R   (N+1)L   (c) ]  (3).
 
     Note that R in the determinant of formula (3) is a pseudo-random number sequence expressed by a vector illustrated below. 
       [Math. 4] 
         R   l   (c) =[ r   l,1   (c)   r   l,2   (c)    . . . r   l,N   (c) ] T   (4)
 
     Note that r in the determinant of formula (4) is an integer satisfying the following. 
       [Math. 5] 
         r   l,k   (c)   ≠r   l,j   (c)  if  k≠j , and  r   l,k   (c)   ≤N   (5)
 
     Here, randomization is executed continuously on the column on the basis of a predetermined 1×(N+1)L vector including a pseudo-random number sequence V) illustrated below. 
       [Math. 6] 
         R   (r) =[ r   1   (r)   r   2   (r)    . . . r   (N+1)L   (r) ]  (6)
 
     In formula (6), r is an integer satisfying the following. 
       [Math. 7] 
         r   l   (r)   ≠r   j   (r)  if  l≠j , and  r   l   (r) ≤( N+ 1) L   (7)
 
     The manner in which the matrix R (c)  and the vector R (r)  are used can be ascertained easily by using the example of N=2, L=3 illustrated in  FIGS. 8A and 8B . 
     In other words, a matrix V of the terminals  100  is expressed as follows. 
     
       
         
           
             
               
                 
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                           4 
                         
                         
                           4 
                         
                         
                           5 
                         
                         
                           6 
                         
                         
                           6 
                         
                         
                           7 
                         
                       
                       
                         
                           2 
                         
                         
                           3 
                         
                         
                           3 
                         
                         
                           5 
                         
                         
                           ϰ 
                         
                         
                           ϰ 
                         
                         
                           7 
                         
                         
                           ϰ 
                         
                         
                           x 
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   8 
                   ) 
                 
               
             
           
         
       
     
     In formula (8), x represents an idle channel (or an empty resource), for instance, and indicates non-allocation to a terminal  100 . 
     Hence, R (c)  and R (r)  determined in advance are expressed as follows. 
                   [     Math   .              9     ]                             R     (   c   )       =     [         1       2       1       1       1       1       2       2       2           2       1       2       2       2       2       1       1       1         ]             (   9   )               [Math. 10] 
         R   (r) =[1 6 7 3 8 2 5 9 4]  (10)
 
     Randomization is executed first on R (c)  and then on R (r) , and as a result, a random matrix V illustrated below is acquired. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     11 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     V 
                     i 
                     
                       ( 
                       
                         g 
                         ′ 
                       
                       ) 
                     
                   
                   = 
                   
                     [ 
                     
                       
                         
                           1 
                         
                         
                           5 
                         
                         
                           7 
                         
                         
                           2 
                         
                         
                           ϰ 
                         
                         
                           3 
                         
                         
                           4 
                         
                         
                           ϰ 
                         
                         
                           4 
                         
                       
                       
                         
                           2 
                         
                         
                           ϰ 
                         
                         
                           6 
                         
                         
                           3 
                         
                         
                           6 
                         
                         
                           1 
                         
                         
                           ϰ 
                         
                         
                           7 
                         
                         
                           5 
                         
                       
                     
                     ] 
                   
                 
               
               
                 
                   ( 
                   11 
                   ) 
                 
               
             
           
         
       
     
     &lt;6. Transmission of High-Priority Data&gt; 
     The terminal  100  allocates the PSCCH to the respective terminals within the subgroup, as illustrated in  FIG. 3 , for instance, randomizes the PSCCH resources in the V2X group, and uses the result of randomized PSCCH resource allocation to transmit a control signal and data. At this time, the terminal  100  may transmit data with high priority. An example of high-priority data transmission will be described below using  FIGS. 9 to 14 . 
     It is assumed, for instance, that the terminal  100  has acquired the PSCCH allocation result depicted in  FIG. 8B  following randomization. 
       FIG. 9  is a view illustrating an example of resource allocation. The examples of PSCCH resource allocation illustrated in  FIGS. 9 and 8B  are identical. 
     As depicted in  FIG. 9 , a case in which the terminal v 1  has the occasion to transmit high-priority data (or a sporadic packet; also referred to hereafter as high-priority data) during the SF 1  period may occur (S 10 ). In this case, as illustrated in  FIG. 10 , the terminal v 1  generates a transmission request and transmits the generated transmission request (S 11 ). The terminal v 1  transmits the transmission request using the PCRLICH. 
       FIG. 15A  is a view illustrating an example of PCRLICH resource allocation. The PCRLICH exists in a different frequency domain to the PSCCH and the PSSCH. The PCRLICH may also be referred to as a reordering control channel, for instance. 
       FIG. 15B  is a view illustrating an example of information transmitted using the PCRLICH. 
     The PCRLICH is divided into two regions, namely a slot #1 and a slot #2. The slot #1 is provided with an AGC (Automatic Gain Control) region, a DMRS (Demodulation Reference Signal) region, a guard interval region, and a transmission request region. Each region represents a single symbol period, for instance. 
     The AGC region is a region for automatically controlling the gain, for instance. The DMRS region is a region for transmitting a reference signal that serves as a reference signal during demodulation, for instance. The guard interval region is a region used to prevent interference with the adjacent slot, for instance. 
     The transmission request region is a region for transmitting the transmission request, for instance. The terminal  100  that generates the high-priority data transmits the transmission request using the symbol of the transmission request region in the slot #1. 
     The slot #2 is provided with an AGC region, a DMRS region, a guard interval region, and a reordering information region. The reordering information region is a region in which, for instance, the representative terminal (the terminal  100 - 6 , for instance), having received the transmission request, transmits information on the reordered resources. The representative terminal  100 , having received the transmission request using the symbol of the transmission request region of the slot #1, transmits reordering information using the symbol of the reordering information region of the slot #2. Meanwhile, the terminal  100  that transmitted the transmission request receives the reordering information transmitted from the representative terminal using the symbol of the reordering information region of the slot #2. 
     Returning to  FIG. 10 , when transmitting the transmission request, the terminal v 1  transmits the transmission request using the symbol of the transmission request region in the slot (the slot #1) in the first half of the period of SF 2  (S 11 ). 
     Then, as illustrated in  FIG. 11 , the terminal v 1  receives the reordering information from the representative terminal (the terminal  100 - 6 , for instance) on the PCRLICH using the symbol of the reordering information region in the slot (the slot #2) in the second half of SF 2  (S 12 ). 
     As illustrated in  FIG. 11 , the reordering information (“Re-order”) is information indicating that the resources of SF 3  and the resources of SF 5  are to be switched and that the resources of SF 4  and the resources of SF 7  are to be switched. 
     As illustrated in  FIG. 12 , the terminal v 1  reorders the resources again in accordance with the reordering information from the randomized PSCCH resource allocation result (S 13 , S 14 ). 
     Following reordering, as illustrated in  FIG. 13 , the terminal v 1  allocates the “Idle” resource in SF 3  as a high-priority data transmission resource (S 15 ). Further, the terminal v 1  allocates the “Idle” resource in SF 4  as a high-priority data transmission resource (S 16 ). As a result, the terminal v 1  becomes capable of two transmissions, namely initial transmission and repetition transmission, as the PSCCH for high-priority data transmission, and also becomes capable of two transmissions, namely initial transmission and repetition transmission, of the high-priority data. The terminal v 1  transmits the high-priority data using the PSSCH resource indicated by the PSCCH. 
     As illustrated in  FIG. 14 , having completed transmission of the high-priority data, the terminal v 1  returns to the state prior to high-priority data allocation of the PSCCH and PSSCH resources allocated to transmission of the high-priority data. In other words, the terminal v 1  returns the resource allocated as the high-priority data PSCCH of SF 3  to an “Idle” resource (S 17 ). Further, the terminal v 1  returns the resource allocated as the high-priority data PSCCH of SF 4  to an “Idle” resource (S 18 ). 
     Thus, the terminal v 1  switches the PSCCH resources in accordance with the reordering information generated by the representative terminal. The switching itself is identical to the switching performed in the time axis direction during randomization, for instance ( FIGS. 8A and 8B , for instance). In other words, the terminal v 1  groups the frequency axis direction resources in one subframe period and switches the grouping with the resources in another subframe period. At this time, the terminal v 1  switches the resources so as to ensure that a plurality of resources do not overlap in the same subframe period. 
     Further, the terminal v 1  transmits the high-priority data using a resource in an “Idle” state. In this case, the terminal v 1  transmits the transmission request to the representative terminal in the slot in the first half of the subframe period and receives the reordering information from the representative terminal in the slot in the second half of the subframe period. Therefore, the terminal v 1  can secure the PSCCH and PSSCH resources for transmitting the high-priority data within a subframe period, and as a result, resources can be secured and the high-priority data can be transmitted quickly. 
     &lt;7. V2X Grouping Based on Reuse of Resource Pool&gt; 
       FIG. 16  is a view illustrating an example in which a plurality of V2X groups are formed and each V2X group is allocated to two resource pools. 
     In the example depicted in  FIG. 16 , a V2X group #1 includes two subgroups SG 1 , SG 2 , and a V2X group #2 includes two subgroups SG 3 , SG 4 . When the number of subgroups is set as P, the number of V2X groups is up to P/2, and a V2X group #(P/2) includes two subgroups SG P-1 , SG P . 
     Further, in the example depicted in  FIG. 16 , two resource pools, namely a resource pool #1 and a resource pool #2, are provided. The two resource pools are disposed in different frequency bands. 
     The terminal  100  allocates the PSCCHs of the terminals included in the V2X group #1 to the resource pool #1 and allocates the PSCCHs of the terminals included in the V2X group #2 to the resource pool #2. Further, the terminal  100  allocates the PSCCHs of the terminals included in a V2X group #3 to the resource pool #1 and allocates the PSCCHs of the terminals included in a V2X group #4 to the resource pool #2. Thereafter, the terminal  100  repeats this operation so as to allocate the PSCCHs of the terminals included in the V2X group #(P/2) to the resource pool #1. 
     The terminals  100  included in the subgroup SG 2  and the terminals  100  included in the subgroup SG 3 , for instance, are closer in distance than two terminals  100  included in the other subgroups. Therefore, interference is more likely to occur between the terminals  100  of the subgroups SG 2  and SG 3  than with the other terminals  100 . 
     In the first embodiment, however, the terminals  100  of the subgroup SG 2  and the terminals  100  of the subgroup SG 3  belong to different V2X groups and allocate the PSCCH resources to different resource pools. Therefore, with the PSCCH allocation method according to the first embodiment, the effects of interference occurring when the distance between terminals  100  is short can be reduced. Moreover, in the first embodiment, by reducing the effects of interference, the rate at which packets are received in the reception terminal can be increased, leading to an improvement in the PRR. 
       FIG. 16  depicts an example in which the PSCCH resources are allocated to two resource pools in each V2X group. Instead, for instance, the PSCCH resources may be allocated to a single resource pool in V2X group units, or the PSCCH resources may be allocated to three or more resource pools in V2X group units. A single resource pool may be shared by a plurality of V2X groups, for instance. 
     Note that allocation of the V2X groups to the resource pools is performed by the subgroup management unit  1110  or the group management unit  111 , for instance. 
     Here, an attempt will be made to formularize  FIG. 16 . 
     The terminals  100  are divided into P subgroups, namely SG 1 , SG 2 , . . . , SG P . Here, when the number of terminals  100  included in a p-th subgroup is set as Mp, Mp is expressed as follows. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     12 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     M 
                     p 
                   
                   ≤ 
                   
                     
                       N 
                       × 
                       
                         ( 
                         
                           N 
                           + 
                           1 
                         
                         ) 
                       
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   12 
                   ) 
                 
               
             
           
         
       
     
     To reduce interference between the terminals  100 , V2X communication is assumed to include a resource pool having a reuse factor R. One resource pool is used exclusively for one V2X group, and as a result, the terminals  100  included in the V2X group are allocated to a resource pool that is reused by the factor R. 
     The number of subgroups included in the i-th V2X group is L, and therefore a number M i   (g)  of terminals  100  included in the i-th V2X group is expressed by the following formula. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     13 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       
                         M 
                         i 
                         
                           ( 
                           g 
                           ) 
                         
                       
                       = 
                       
                         
                           
                             ∑ 
                             
                               p 
                               = 
                               1 
                             
                             L 
                           
                            
                           
                             M 
                             
                               
                                 L 
                                  
                                 
                                   ( 
                                   
                                     i 
                                     - 
                                     1 
                                   
                                   ) 
                                 
                               
                               + 
                               p 
                             
                           
                         
                         ≤ 
                         
                           
                             L 
                              
                             N 
                             × 
                             
                               ( 
                               
                                 N 
                                 + 
                                 1 
                               
                               ) 
                             
                           
                           2 
                         
                       
                     
                     , 
                     
                         
                     
                      
                     for 
                   
                    
                   
                     
 
                   
                    
                   
                     1 
                     ≤ 
                     i 
                     ≤ 
                     
                       ⌈ 
                       
                         P 
                         L 
                       
                       ⌉ 
                     
                   
                 
               
               
                 
                   ( 
                   13 
                   ) 
                 
               
             
           
         
       
     
     A case in which two resource pools having equal reuse factors R=2 are provided and each V2X group has two subgroups (L=2), as illustrated in  FIG. 16 , will be considered. In this case, as described above, the two subgroups SG 1 , SG 2  form the V2X group #1, and the two subgroups SG 3 , SG 4  form the V2X group #2. Further, in accordance with the reuse factor R=2, the resource pool #1 and the resource pool #2 are allocated respectively to the terminals  100  included in the V2X group #1 and the terminals  100  included in the V2X group #2. Thereafter, the operation is repeated up to the final V2G group. 
     Note that likewise in the example depicted in  FIG. 16 , randomization processing ( FIGS. 8A and 8B , for instance) is performed individually on each V2X group. 
     &lt;8. Grouping of V2X Groups in Accordance with Various Packet Arrival Times&gt; 
     In the example described above, it is assumed that each terminal  100  sets a data arrival time at random and generates data periodically. When the data are generated periodically, the data arrival time may be 10 ms, 30 ms, 100 ms, or the like, but in the case of aperiodic traffic, the data arrival time is, on average, 10 ms or 50 ms. Considering various use cases, however, the arrival time is diverse. The most frequent data arrival time is 100 ms or less, but in several cases, the data arrival time may be 500 ms. Here, resource allocation to the terminals  100  in accordance with diverse data arrival times will be described. 
     When a maximum value of the data arrival time is set as T max , T max  is set at an identical length to the length of the V2X group, as indicated below. 
       [Math. 14] 
         T   max   =L ( N+ 1)· T   sf   (14)
 
     In formula (14), T sc  is the subframe interval, which is typically 1 ms, for instance, but depends on the sub-carrier space (SCS). Note, however, that slots, mini-slots, or symbols may be used instead of subframes. 
     Here, resource allocation to the terminals  100  is divided into two types. The first type is a case in which periodic traffic having an arrival time not exceeding T max  is generated. The second type is a case in which periodic traffic (or aperiodic traffic) having a longer time than T max  is generated. In the latter case, for instance, the terminal  100  can perform processing using the method described in &lt;6. Transmission of high-priority data&gt;. 
     Here, a great number of PSCCHs may be allocated to the terminals  100  in which the data arrival time does not exceed T max . Accordingly, the number of PSCCHs used exclusively by an m-th terminal  100  is expressed as follows. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     15 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     M 
                     m 
                     
                       ( 
                       
                         c 
                          
                         c 
                       
                       ) 
                     
                   
                   = 
                   
                     ⌈ 
                     
                       
                         T 
                         max 
                       
                       
                         T 
                         m 
                       
                     
                     ⌉ 
                   
                 
               
               
                 
                   ( 
                   15 
                   ) 
                 
               
             
           
         
       
     
     In formula (15), T m  represents the data arrival time in the m-th terminal  100 . 
     Accordingly, the maximum value M i   (g)  of the number of terminals  100  in the i-th V2X group satisfies the following formula. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Math 
                     . 
                     
                         
                     
                      
                     16 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   
                     
                       ∑ 
                       
                         m 
                         = 
                         1 
                       
                       
                         M 
                         i 
                         
                           ( 
                           g 
                           ) 
                         
                       
                     
                      
                     
                       M 
                       m 
                       
                         ( 
                         
                           c 
                            
                           c 
                         
                         ) 
                       
                     
                   
                   ≤ 
                   
                     
                       L 
                        
                       N 
                       × 
                       
                         ( 
                         
                           N 
                           + 
                           1 
                         
                         ) 
                       
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   16 
                   ) 
                 
               
             
           
         
       
     
     Here, when determining the maximum value M i   (g)  of the number of terminals  100 , several “Idle” channels are preferably reserved for exclusive use with aperiodic and/or high-priority data. 
     PSCCH allocation within the V2X group is defined as being performed in evenly allocation manner or a non-uniform spacing allocation manner. When PSCCH randomization and reordering are performed as described above, the effects of the latency of each terminal  100  are to be considered. The manner in which to transfer data in consideration of the desired latency is to be considered as an implementation issue. 
       FIGS. 17A and 17B  are views illustrating examples of PSCCH allocation in the evenly allocation manner. The terminal  100  switches the resources in SF 2 , SF 3 , and SF 9  (randomization in the frequency axis direction), as illustrated in  FIG. 17A , and switches the resources of SF 1  to SF 9 , SF 3  to SF 1 , and so on (randomization in the time axis direction), as illustrated in  FIG. 17B . 
     In  FIG. 17B , focusing on the resources allocated to the terminal v 3 , in each subgroup, the PSCCHs are allocated in the same pattern. More specifically, in a subgroup #1, the PSCCH resources allocated to the terminal v 3  are SF 1  in first place in the frequency axis direction and SF 2  in first place in the frequency axis direction. Further, in a subgroup #2, the PSCCH resources of the terminal v 3  are allocated to SF 4  and SF 5  in first place in the frequency axis direction. In other words, in each subgroup, the PSCCHs of the terminal v 3  are allocated to the first subframe and the following subframe in the same position in the frequency axis direction. 
     By allocating the PSCCHs in the same pattern in each subgroup in this manner, the terminals  100  can handle reception of periodic traffic having an arrival time not exceeding T max , for instance. 
       FIGS. 18A and 18B  are views illustrating examples of PSCCH allocation in the non-uniform spacing allocation manner. 
     In the example of  FIG. 18A , the terminal  100  switches the resources in SF 2 , SF 3 , and SF 7  to SF 9  (randomization in the frequency axis direction). Further, as illustrated in  FIG. 18B , the terminal  100  switches the resources of SF 1  to SF 2 , SF 2  to SF 1 , and so on (randomization in the time axis direction), and so on. 
     In this case, as illustrated in  FIG. 18B , the positions of the PSCCH resources allocated to the terminal v 3  do not follow the same pattern in each group. Note, however, that with respect to the terminal v 3 , at least two subframe periods and PSCCH resources are allocated in every subgroup, and it is therefore possible to handle reception of periodic traffic having an arrival time not exceeding T max . 
     &lt;9. Example Operations&gt; 
     As example operations, first, an example operation of PSCCH resource allocation will be described. Next, an example operation in a case where high-priority data are transmitted will be described. 
     &lt;9.1 Example Operation of PSCCH Resource Allocation&gt; 
       FIG. 19  is a flowchart illustrating an example operation of PSCCH resource allocation. 
     At the start of the processing (S 30 ), the terminal  100  performs subgrouping of the plurality of terminals by determining the number L of subgroups from the number M of terminals in the V2X group and the number N of PSCCHs in the frequency axis direction (S 31 ). For instance, the subgroup management unit  1110  determines the number L of subgroups by reading the number M of terminals in the V2X group, the number N of PSCCHs in the frequency axis direction, and formula (1) from the memory  120  and inserting M and N into formula (1). The subgroup management unit  1110  allocates the respective terminals  100  to the subgroups in sequence in accordance with the number L of subgroups. 
     Next, the terminal  100  allocates the PSCCH resources within each subgroup (S 32 ). For instance, the subgroup management unit  1110  allocates the PSCCH resources to the respective terminals  100  in sequence within each subgroup, as illustrated in  FIG. 3 . 
     Next, the terminal  100  performs randomization within the V2X group (S 33 ). For instance, the subgroup management unit  1110  randomizes the PSCCH resources allocated to the respective terminals  100  in the frequency axis direction ( FIG. 7B , for instance) and then randomizes the PSCCH resources in the time axis direction ( FIG. 8B , for instance). 
     The terminal  100  then terminates PSCCH resource allocation (S 34 ). 
     Next, the subgroup management unit  1110  outputs the allocation result to the used resource control unit  112 . In accordance with the allocation result, the used resource control unit  112  instructs the transmission control unit  113  to transmit a control signal and data using the PSCCH and PSSCH resources allocated to the host terminal. In response to the instruction, the transmission control unit  113  transmits the control signal using the PSCCH and transmits the data using the PSSCH. In this case, as illustrated in  FIG. 3 , the transmission control unit  113  transmits the control signal using the initial PSCCH resource and then resends the control signal using the repetition PSCCH resource. In this case, the transmission control unit  113  transmits the data using the PSSCH resource specified by the SCI included in the initial control signal, and resends the data using the PSSCH resource specified by the SCI included in the resent control signal. 
     &lt;9.2 High-Priority Data Transmission&gt; 
       FIG. 20  is a flowchart illustrating an example operation performed to transmit high-priority data. 
     At the start of the processing (S 50 ), the terminal  100  performs grouping (S 51 ). The terminal  100  performs grouping by executing the processing illustrated in  FIG. 19 . 
     Returning to  FIG. 20 , next, the terminal  100  checks whether high-priority data have been generated (S 52 ). For instance, the group management unit  111  may perform this processing by checking whether or not high-priority data have been generated in the application processing unit of the processor  110 . 
     When high-priority data have been generated (Yes in S 53 ), the terminal  100  transmits a transmission request (S 53 ). For instance, the terminal  100  performs the following processing. 
     The group management unit  111  generates the transmission request and outputs the generated transmission request to the used resource control unit  112 . Upon receipt of the transmission request, the used resource control unit  112  instructs the transmission control unit  113  to transmit the transmission request using the symbol of the transmission request region in the first half slot of a predetermined subframe on the PCRLICH. The transmission control unit  113  transmits the transmission request using the specified symbol of the PCRLICH. The transmission request is transmitted to the representative terminal among the plurality of terminals  100 . 
     Next, the terminal  100  receives reordering information transmitted from the representative terminal (S 54 ). For instance, the group management unit  111  receives the reordering information via the reception control unit  114  using the symbol of the reordering information region in the second half slot of the predetermined subframe of the PCRLICH. 
     Next, the terminal  100  performs transmission using a switched resource (S 55 ). For instance, the terminal  100  executes the following processing. 
     The group management unit  111  switches the PSCCH resources in accordance with the reordering information and outputs the post-switching PSCCH allocation result to the used resource control unit  112 . In accordance with the allocation result, the used resource control unit  112  instructs the transmission control unit  113  to transmit a control signal and the high-priority data, whereupon the transmission control unit  113  transmits the control signal and the high-priority data in response to the instruction. Examples of switching can be found in  FIG. 12  and so on, for instance. 
     Returning to  FIG. 20 , next, the terminal  100  updates group information (S 56 ). Upon receipt of the reordering information, the terminal  100  switches parts of the PSCCH and PSSCH resources. Accordingly, the group management unit  111  updates group information in which the identification information of the respective terminals  100  is associated with the PSCCH resources. The group management unit  111  stores the updated group information in the memory  120 . 
     The terminal  100  then terminates the high-priority data transmission processing (S 57 ). 
     When, on the other hand, high-priority data are not generated (S 52 ), the terminal  100  transmits the control signal and data (S 58 ) using the PSCCH and PSSCH resources allocated thereto during grouping (S 51 ). The terminal  100  then terminates the high-priority data transmission processing (S 57 ). 
     Note that an example operation performed by the representative terminal  100  that transmits the reordering information upon receipt of a transmission request from the terminal that is to transmit high-priority data is as follows, for instance. 
     Upon receiving a transmission request via the reception control unit  114 , the group management unit  111  of the representative terminal  100  reads the reordering information, which is stored in the memory  120 , from the memory  120 . The group management unit  111  then instructs the used resource control unit  112  to transmit the read reordering information by groupcasting. The used resource control unit  112  instructs the transmission control unit  113  to transmit the reordering information using the symbol of the reordering information region in the second half slot of the same subframe of the PCRLICH as the subframe in which the transmission request was received. In response to the instruction, the transmission control unit  113  transmits the reordering information. 
     Example operations of the terminal  100  according to the first embodiment were described above. Hence, in the first embodiment, the terminal  100  allocates a total of N×N T  PSCCH resources, having N (where N is an integer of 2 or more) resources in the frequency axis direction and N T  (where N T  is an integer of 2 or more) resources in the time axis direction, to the terminals  100 . 
     In other words, the terminal  100  allocates the N frequency axis direction PSCCH resources in first place in the time axis direction to the terminals  100  (for instance, the terminals v 1  to vN) as initial PSCCHs. Further, the terminal  100  allocates the second to the N T -th time axis direction resources in first place in the frequency axis direction to the terminals  100  as repetition PSCCHs. 
     Furthermore, the terminal  100  allocates the second to the N-th frequency axis direction resources in second place in the time axis direction to the other terminals  100  (for instance, the terminals v(N+1) to v(2N−1)) as initial PSCCHs. Moreover, the terminal  100  allocates the third to the N T -th time axis direction resources in second place in the frequency axis direction to the other terminals  100  as repetition PSCCHs. 
     Thereafter, the terminal  100  repeats this operation so as to allocate PSCCH resources to the plurality of terminals  100  (the terminal v 1  to the terminal v(N×(N+1)/2), for instance). 
     The terminal  100  then transmits a control signal using the initial PSCCH allocated thereto and resends the control signal using the repetition PSCCH allocated thereto. 
     Thus, with the terminal  100  according to the first embodiment, all of the terminals  100  in a subgroup can enter the reception mode for at least one subframe period following the elapse of a predetermined period. 
     For instance, a control signal or data may be transmitted by selecting a resource at random from empty resources included in the selected window on the basis of the sensing result. 
       FIG. 21  illustrates a simulation result of the PRR in a case where this random resource selection method is used. 
     In  FIG. 21 , the vertical axis represents the PRR and the horizontal axis represents the distance (m) between terminals  100  (or vehicles). PRR=1 indicates that the reception-side terminal  100  was able to receive all of the transmitted packets, for instance. Further, in  FIG. 21 , the solid line indicates a case in which one subchannel of the PSSCH includes 40 RBs, while the dot-dash line indicates a case in which one subchannel of the PSSCH includes 20 RBs. 
     As illustrated in  FIG. 21 , even when the distance between the terminals was close to “0”, the PRR did not equal 1 with either 40 RBs or 20 RBs, and a result in which the PRR decreased to approximately “0.90” as the distance between the terminals lengthened was acquired. 
       FIG. 22  illustrates a simulation result of the PRR in a case where reordering is performed using the PCRLICH without allocating and randomizing the PSCCHs as illustrated in  FIG. 3 . 
     As illustrated in  FIG. 22 , in the case of 40 RBs, PRR=1 was attained when the distance between the terminals was no more than “200 m”, but beyond “200 m”, the PRR decreases. 
     According to the first embodiment, however, by allocating the PSCCHs as illustrated in  FIG. 3 , all of the terminals  100  in a subgroup can enter the reception mode for at least one subframe period following the elapse of a predetermined period. 
     For instance, even in the first embodiment, a situation as illustrated in  FIG. 26  may occur in a certain subframe period. In the following subframe period, however, the terminal  100  in the transmission mode may enter the reception mode so as to become capable of receiving data transmitted from another terminal  100 . Following the elapse of a predetermined period, all of the terminals  100  enter the reception mode for at least one subframe period so as to become capable of receiving data transmitted from another terminal  100 . 
     Following the elapse of a predetermined period, therefore, a situation in which the reception-side terminal  100  cannot receive data transmitted from another terminal can be avoided. As a result, the terminal  100  according to the first embodiment can prevent a reduction in the PRR. 
     Other Embodiments 
     In the first embodiment described above, the PSCCH resource allocation illustrated in  FIG. 3  is performed by a transmission-side terminal  100 , for instance. For instance, in the transmission-side terminal, following the PSCCH resource allocation and randomization illustrated in  FIG. 3 , a control signal and data are transmitted using the allocated resources. In this case, the reception-side terminal  100  ascertains the used resources by sensing and receives the control signal transmitted from the transmission-side terminal using the PSCCH resource allocated thereto by the transmission-side terminal. Further, the reception-side terminal  100  ascertains the PSSCH resource allocated thereto by the transmission-side terminal from the SCI included in the control signal, and receives the data transmitted from the transmission-side terminal using this resource. 
     Furthermore, in the first embodiment described above, an example in which randomization is performed in the frequency axis direction first and then in the time axis direction was described. Instead, for instance, randomization may be performed in the time axis direction first and then in the frequency axis direction. 
     The packet reception ratio can be improved. 
     All examples and conditional language provided herein are intended for the pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 
     REFERENCE SIGNS LIST 
     
         
           10 : wireless communication system 
           100  ( 100 - 1  to  100 - 4 ): terminal device (terminal) 
           110 : processor 
           111 : group management unit 
           112 : used resource control unit 
           113 : transmission control unit 
           114 : reception control unit 
           120 : memory 
           130 : wireless communication unit 
           140 : antenna 
         v 1  to vN: terminal device (terminal)