Patent Publication Number: US-2021168763-A1

Title: Communication device that supports d2d communication, base station device, and communication method

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation application of International Application PCT/JP2018/029980 filed on Aug. 9, 2018 and designated the U.S., the entire contents of which are incorporated herein by reference. 
    
    
     FIELD 
     The embodiments discussed herein are related to a communication device that supports D2D communication, a base station device, a communication system that includes the communication device and the base station device, and a method for communication between the communication device and the base station device. 
     BACKGROUND 
     Recently, many network resources are occupied by traffic used by mobile terminals (including smartphones or feature phones). Traffic to be used by mobile terminals is considered to increase in the future as well. 
     Meanwhile, with the development of Internet-of-things (IoT) services (e.g., traffic systems, smart meters, monitoring services for devices and the like), services with various required conditions need to be addressed. Accordingly, communication standards for the fifth-generation mobile communication (5G (NR: New Radio)) need to attain techniques for implementing the standard techniques of the fourth-generation mobile communication (4G (LTE: Long Term Evolution)) (e.g., documents 1-12) as well as higher data rates, larger capacities, and lower latencies. The 3GPP working groups (e.g., TSG-RAN WG1, TSG-RAN WG2) have studied standards for the fifth-generation communication (e.g., documents 13-38). 
     With respect to 5G, supports have been considered for use cases classified as Enhanced Mobile BroadBand (eMBB), Machine Type Communications (Massive MTC), and Ultra-Reliable and Low Latency Communication (URLLC) in order to address a wide variety of services. 
     The 3GPP working groups have also discussed device-to-device (D2D) communication. D2D communication may also be referred to as sidelink communication. V2X has been studied as an example of D2D communication. V2X includes V2V, V2P, and V2I. V2V indicates vehicle-to-vehicle communication. V2P indicates communication between vehicles and pedestrians. V2I indicates communication between vehicles and roadside infrastructures such as signs. Regulations pertaining to V2X are described in, for example, document 39. In the meantime, concentrated resource allocation (In-coverage RRC_CONNECTED UEs) and distributed resource allocation (In-coverage RRC_IDLE UEs or out-of-coverage UEs) are defined for the V2X of 4G. 
     Prior Art Documents 
     Document 1: 3GPP TS 36.211 V15.1.0 (2018-03) 
     Document 2: 3GPP TS 36.212 V15.1.0 (2018-03) 
     Document 3: 3GPP TS 36.213 V15.1.0 (2018-03) 
     Document 4: 3GPP TS 36.300 V15.1.0 (2018-03) 
     Document 5: 3GPP TS 36.321 V15.1.0 (2018-03) 
     Document 6: 3GPP TS 36.322 V15.0.1 (2018-04) 
     Document 7: 3GPP TS 36.323 V14.5.0 (2017-12) 
     Document 8: 3GPP TS 36.331 V15.1.0 (2018-03) 
     Document 9: 3GPP TS 36.413 V15.1.0 (2018-03) 
     Document 10: 3GPP TS 36.423 V15.1.0 (2018-03) 
     Document 11: 3GPP TS 36.425 V14.1.0 (2018-03) 
     Document 12: 3GPP TS 37.340 V15.1.0 (2018-03) 
     Document 13: 3GPP TS 38.201 V15.0.0 (2017-12) 
     Document 14: 3GPP TS 38.202 V15.1.0 (2018-03) 
     Document 15: 3GPP TS 38.211 V15.1.0 (2018-03) 
     Document 16: 3GPP TS 38.212 V15.1.1 (2018-04) 
     Document 17: 3GPP TS 38.213 V15.1.0 (2018-03) 
     Document 18: 3GPP TS 38.214 V15.1.0 (2018-03) 
     Document 19: 3GPP TS 38.215 V15.1.0 (2018-03) 
     Document 20: 3GPP TS 38.300 V15.1.0 (2018-03) 
     Document 21: 3GPP TS 38.321 V15.1.0 (2018-03) 
     Document 22: 3GPP TS 38.322 V15.1.0 (2018-03) 
     Document 23: 3GPP TS 38.323 V15.1.0 (2018-03) 
     Document 24: 3GPP TS 38.331 V15.1.0 (2018-03) 
     Document 25: 3GPP TS 38.401 V15.1.0 (2018-03) 
     Document 26: 3GPP TS 38.410 V0.9.0 (2018-04) 
     Document 27: 3GPP TS 38.413 V0.8.0 (2018-04) 
     Document 28: 3GPP TS 38.420 V0.8.0 (2018-04) 
     Document 29: 3GPP TS 38.423 V0.8.0 (2018-04) 
     Document 30: 3GPP TS 38.470 V15.1.0 (2018-03) 
     Document 31: 3GPP TS 38.473 V15.1.1 (2018-04) 
     Document 32: 3GPP TR 38.801 V14.0.0 (2017-04) 
     Document 33: 3GPP TR 38.802 V14.2.0 (2017-09) 
     Document 34: 3GPP TR 38.803 V14.2.0 (2017-09) 
     Document 35: 3GPP TR 38.804 V14.0.0 (2017-03) 
     Document 36: 3GPP TR 38.900 V14.3.1 (2017-07) 
     Document 37: 3GPP TR 38.912 V14.1.0 (2017-06) 
     Document 38: 3GPP TR 38.913 V14.3.0 (2017-06) 
     Document 39: 3GPP TS 22.186 V15.2.0 (2017-09) 
     In 5G system, low-latency D2D communication may be requested depending on a use case. However, no procedures have been determined for implementing low-latency D2D communication. For example, no procedures for resource allocation for V2X communication have been determined. 
     SUMMARY 
     According to an aspect of the present invention, a communication device supports device-to-device (D2D) communication. The communication device includes: a processor configured to generate control information that pertains to D2D data and requests a resource for transmitting the D2D data; a transmitter configured to transmit the control information to a base station; and a receiver configured to receive, from the base station, information indicating resource allocation for transmitting the D2D data via D2D communication. The transmitter transmits the D2D data to a destination device via D2D communication according to the information indicating the resource allocation. 
     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. 1A  illustrates an example of a wireless communication system; 
         FIG. 1B  illustrates an example of resource allocation for sidelink communication; 
         FIG. 2  illustrates an example of resource allocation according to 4G (LTE); 
         FIG. 3  indicates latency in a procedure depicted in  FIG. 2 ; 
         FIG. 4  illustrates an example of a case in which 4G resource allocation is performed in a 5G wireless communication system; 
         FIG. 5  indicates latency in a procedure depicted in  FIG. 4 ; 
         FIG. 6  illustrates an example of the configuration of a base station; 
         FIG. 7A  illustrates an example of a wireless communication device; 
         FIG. 7B  illustrates another example of a wireless communication device; 
         FIG. 8  illustrates an example of a sequence of V2X communication; 
         FIG. 9  illustrates an example of relations between sidelink control information and attributes of V2X traffic/services; 
         FIG. 10  is a flowchart illustrating an example of processes performed by a VUE; 
         FIG. 11  is a flowchart illustrating an example of processes performed by a base station; 
         FIG. 12  illustrates an example of resource allocation in a first embodiment; 
         FIG. 13  indicates latency in a procedure depicted in  FIG. 12 ; 
         FIGS. 14A, 14B, 15A, and 15B  illustrate examples of cases in which a plurality of VUEs each request sidelink communication; 
         FIG. 16  is a flowchart illustrating an example of processes performed by a VUE in a second embodiment; 
         FIG. 17  is a flowchart illustrating an example of processes performed by a base station in a second embodiment; 
         FIG. 18  illustrates an example of resource allocation in a third embodiment; and 
         FIG. 19  indicates latency in a procedure depicted in  FIG. 18 . 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1A  illustrates an example of a wireless communication system in accordance with embodiments of the invention. As depicted in  FIG. 1A , a wireless communication system  100  includes a base station  10  and a plurality of wireless communication devices  20 . In this example, each of the wireless communication devices  20  is equipped in a vehicle. 
     The base station  10  controls cellular communication performed by the wireless communication devices  20  (uplink/downlink communication performed via Uu interfaces). Thus, the base station  10  receives uplink signals (control signals and data signals) from the wireless communication devices  20 . Meanwhile, the base station  10  transmits downlink signals (control signals and data signals) to the wireless communication devices  20 . 
     The wireless communication device  20  can communicate with another communication device via the base station  10 . The wireless communication device  20  can also communicate with another wireless communication device without the intervention of the base station  10 . That is, the wireless communication device  20  supports Device-to-Device (D2D) communication. In D2D communication, a signal may be transmitted via a PC5 interface. D2D communication may also be referred to as “sidelink communication.” The wireless communication device  20  may also be referred to as a “user equipment (UE)” or “vehicle UE (VUE).” 
     As described above, the wireless communication devices  20  are each equipped in a vehicle. Thus, in this example, the wireless communication devices  20  can perform V2X communication. V2X includes V2V, V2P, and V2I. V2V indicates vehicle-to-vehicle communication. V2P indicates communication between vehicles and pedestrians. V2I indicates communication between vehicles and roadside infrastructures such as signs. 
     In this example, the base station  10  controls allocation of resources for sidelink communication. The following descriptions are based on the assumption that resource allocation for sidelink communication is controlled in accordance with the scheduled resource allocation mode (sidelink transmission mode 3 ). In this case, a wireless communication device  20  makes a request for the base station  10  to provide this device with resources for sidelink communication. The base station  10  performs the requested resource allocation for implementing sidelink communication. In the example depicted in  FIG. 1B , a time slot # 4  is allocated to V2X communication. The resources allocated to V2X communication include resources for transmitting V2X data and resources for transmitting control information SCI for V2X data. Control information SCI indicates subcarriers, symbols, modulation scheme, code, and the like for transmitting V2X data. This resource allocation implements a sidelink communication for the in-coverage RRC_CONNECTED V-UEs. Resource allocation methods for sidelink communication are described in, for example, 3GPP TS 36.300 and 3GPP TS 36.213. 
       FIG. 2  illustrates an example of resource allocation according to 4G (LTE). In this example, a wireless communication device  20  makes a request for the base station  10  to provide this device with resources for transmitting V2X data via sidelink communication. The resource allocation is performed in the scheduled resource allocation mode (sidelink transmission mode 3 ). Note that the length of each subframe in 4G is 1 millisecond. 
     At a subframe s 1 , V2X data is generated by an application of the wireless communication device  20 . In this case, at a subframe s 2 , the wireless communication device  20  transmits a scheduling request (SR) to the base station  10 . The scheduling request SR requests resources for uplink. 
     The base station  10  generates an uplink grant in response to the scheduling request. The uplink grant includes information indicating resources for a physical uplink shared channel (PUSCH). At a subframe s 3 , the base station  10  transmits the uplink grant to the wireless communication device  20 . 
     The wireless communication device  20  transmits a sidelink buffer status report (sidelink BSR) to the base station  10  by using resources reported by the uplink grant. In this example, at a subframe s 4 , the sidelink buffer status report BSR is transmitted using the PUSCH. The sidelink buffer status report BSR indicates the amount of V2X data stored in a buffer memory of the wireless communication device  20 . 
     The base station  10  determines resources for V2X communication according to the sidelink buffer status report BSR. In particular, resources for a physical sidelink control channel (PSCCH) and resources for a physical sidelink shared channel (PSSCH) are determined. The resources for the PSCCH are allocated to a control signal for controlling V2X communication. The resources for the PSSCH are allocated to V2X data. At a subframe s 5 , the base station  10  transmits a sidelink grant to the wireless communication device  20 . The sidelink grant includes information indicating the PSCCH resources and the PSSCH resources. 
     The wireless communication device  20  transmits V2X data to a destination device by using the resources reported by the sidelink grant. In this example, V2X data is transmitted at a subframe s 6 . 
     In the procedure depicted in  FIG. 2 , the time period from the moment at which V2X data is generated to the moment at which the V2X data is transmitted (i.e., latency or delay) corresponds to the sum of t 1 -t 4  and t s1 -t s6  depicted in  FIG. 3 . Thus, in 4G (LTE) system, a latency pertaining to the transmission of V2X data may be about 17.5 milliseconds. 
     Various use cases pertaining to V2X communication are defined for 5G (NR: New Radio). In particular, V2X services include the following four types of use. 
     (1) Vehicle platooning
 
(2) Advanced driving
 
(3) Extended sensors
 
(4) Remote driving
 
The vehicle platooning allows a plurality of vehicles to travel in a column. The advanced driving allows for semi-automatic driving or full automatic driving. The extended sensors allow for exchange of data output from sensors equipped in vehicles, roadside units (RSUs), or devices held by a pedestrians or exchange of live video data of V2X application servers. The remote driving allows a vehicle to be driven by a driver in a remote location or to be driven according to V2X applications.
 
     Depending on a use case, a very small latency may be needed. For example, in some applications for the advanced driving or the extended sensors, a maximum end-to-end latency of 3 milliseconds may be needed. 
     However, 5G has no procedures determined yet for resource allocation in V2X communication. Accordingly, consideration is given to a case in which the procedures for 4G depicted in  FIG. 2  are applied to the V2X communication according to 5G. 
       FIG. 4  illustrates an example of a case in which 4G resource allocation is performed in a 5G wireless communication system. In this example, the resource allocation is performed in the scheduled resource allocation mode (mode 3 ). 
     The length of each slot is 0.5 milliseconds. The time domain of each slot is formed from 14 symbols. In the example depicted in  FIG. 4 , three symbols are allocated to a downlink (data and control information). Eight symbols are allocated to an uplink (data). Two symbols are allocated to an uplink (control information). Furthermore, one symbol of guard section is provided. 
     In this case, the time period from the moment at which V2X data is generated to the moment at which the V2X data is transmitted (i.e., latency) corresponds to the sum of t 1 -t 5  and t s1 -t s5  depicted in  FIG. 5 . Thus, a latency pertaining to the transmission of V2X data is estimated to be 3.32-3.82 milliseconds. Accordingly, when the 4G (LTE) resource allocation procedure is simply applied to the 5G (NR) wireless communication system, requirements pertaining to a latency in 5G V2X services are not always satisfied. 
     First Embodiment 
       FIG. 6  illustrates an example of the configuration of a base station. For example, a base station  10  may be a next generation base station device (gNB: Next generation Node B). As depicted in  FIG. 6 , the base station  10  includes a controller  11 , a storage  12 , a network interface  13 , a radio transmitter  14 , and a radio receiver  15 . Note that the base station  10  may include other circuits or functions that are not depicted in  FIG. 6 . 
     The controller  11  controls cellular communication provided by the base station  10 . The controller  11  can allocate resources to D2D communication (i.e., sidelink communication) performed by wireless communication devices  20 . In this example, the controller  11  is implemented by a processor. In this case, the controller  11  executes a software program stored in the storage so as to provide a function for controlling cellular communication and a function for allocating resources to D2D communication. However, some of the functions of the controller  11  may be implemented by a hardware circuit. 
     The storage  12  stores a software program to be executed by a processor. The storage  12  also stores data needed to control operations of the base station  10 . For example, the storage  12  may be implemented by a semiconductor memory. The network interface  13  provides an interface for connecting to a core network. Accordingly, the base station  10  can be connected via the network interface  13  to another base station  10  or a network management system for controlling the base station  10 . 
     The radio transmitter  14  transmits radio signals for cellular communication in accordance with an instruction from the controller  11 . Thus, the radio transmitter  14  transmits downlink signals to the wireless communication devices  20  within the cell. The radio receiver  15  receives radio signals for cellular communication in accordance with an instruction from the controller  11 . Thus, the radio receiver  15  receives uplink signals transmitted from the wireless communication devices  20  within the cell. For example, cellular communication may be provided using a 2.4 GHz band and/or 4 GHz band. 
       FIG. 7A  illustrates an example of a wireless communication device. A wireless communication device  20  supports cellular communication and D2D communication. D2D communication is implemented using a different frequency band from cellular communication. For example, D2D communication may be provided using a 6 GHz band. However, D2D communication may use the same frequency band as the uplink in cellular communication. The wireless communication device  20  includes a controller  21 , a storage  22 , a radio transmitter  23 , a radio receiver  24 , a radio transmitter  25 , and a radio receiver  26 . Note that the wireless communication device  20  may include other circuits or functions that are not depicted in  FIG. 7A . 
     In the example depicted in  FIG. 7A , the radio communication unit for cellular communication and the radio communication unit for D2D communication are provided separately from each other. However, the wireless communication device  20  is not limited to this configuration. For example, as depicted in  FIG. 7B , one radio communication unit may be shared by cellular communication and D2D communication. In this case, the radio transmitter  23  transmits cellular signals and D2D signals, and the radio receiver  24  receives cellular signals and D2D signals. 
     The controller  21  controls cellular communication and D2D communication provided by the wireless communication device  20 . In this example, the controller  21  is implemented by a processor. In this case, the controller  21  executes a software program stored in the storage  22  so as to provide a function for controlling cellular communication and D2D communication. However, some of the functions of the controller  21  may be implemented by a hardware circuit. 
     The storage  22  stores a software program to be executed by a processor. The storage  22  also stores data and information needed to control operations of the wireless communication device  20 . For example, the storage  22  may be implemented by a semiconductor memory. 
     The radio transmitter  23  transmits a radio signal for cellular communication in accordance with an instruction from the controller  21 . Thus, the radio transmitter  23  transmits an uplink signal to the base station  10 . The radio receiver  24  receives a radio signal for cellular communication in accordance with an instruction from the controller  21 . Thus, the radio receiver  24  receives a downlink signal transmitted from the base station  10 . 
     The radio transmitter  25  transmits a radio signal for D2D communication in accordance with an instruction from the controller  21 . Thus, the radio transmitter  25  transmits a D2D signal to another wireless communication device by using resources allocated by the base station  10 . The radio receiver  26  receives a radio signal for D2D communication in accordance with an instruction from the controller  21 . Thus, the radio receiver  26  receives a D2D signal transmitted from another wireless communication device. In this example, a D2D signal includes V2X data and V2X data control information. 
       FIG. 8  illustrates an example of a sequence of V2X communication. In this example, a wireless communication system includes a base station (gNB)  10  and a plurality of wireless communication devices (VUEs)  20 . A VUE  20   a  transmits data to a VUE  20   b  via V2X communication. Alternatively, the VUE  20   a  may transmit data to a plurality of VUEs  20 , including the VUE  20   b , via V2X communication. At least the VUE  20   a  of the plurality of VUEs  20  is located within a cell covered by the base station  10 . The VUE  20   a  is implemented in a vehicle. The other VUEs  20   a  may be implemented in vehicles, held by pedestrians, or incorporated into roadside infrastructures. 
     Although not indicated in  FIG. 8 , the VUE  20   a  transmits, to the base station  10 , information indicating that the VUE  20   a  is a terminal that performs V2X communication. In response to this, the base station  10  transmits system information pertaining to V2X communication to the VUE  20   a . For example, the system information may include the mapping information depicted in  FIG. 9 . 
     The mapping information indicates relations between sidelink control information SL_UCI and attributes of V2X traffic/services. In this example, sidelink control information SL_UCI is expressed by four bits. In this example, the attributes of the V2X traffic/services include communication type, payload size, reliability, minimum communication distance, and latency. Communication type identifies broadcast, groupcast, and unicast. Payload size indicates the size of data transmitted in V2X communication. Reliability indicates a reliability required by the V2X traffic/services. Minimum communication distance indicates a transmission distance required by the V2X traffic/services. Latency (or delay) indicates a permissible value for the time period from the moment at which V2X data is generated to the moment at which the V2X data is received (i.e., end-to-end latency). Other elements that are not indicated in  FIG. 9  may be used as attributes for the V2X traffic/services. For example, sidelink control information SL_UCI may be associated with the service quality (QoS) of the V2X traffic/services. 
     When the VUE  20   a  has mapping information in advance, the base station  10  does not need to transmit mapping information to the VUE  20   a . Mapping information is not limited to the example depicted in  FIG. 9 , and another piece of information may be allocated to sidelink control information SL_UCI. For example, sidelink control information SL_UCI may indicate a use case of V2X communication (vehicle platooning, advanced driving, extended sensors, remote driving). Alternatively, sidelink control information SL_UCI may indicate scenarios described in 3GPP TS 22.186 V15.2.0 (Table 5.2-1, Table 5.3-1, Table 5.4-1). 
     When transmitting data via V2X communication, the VUE  20   a  determines the attributes of the data (i.e., V2X data). For example, the attributes of V2X data may be reported from an application that has generated the V2X data to the controller  21  of the VUE  20   a . Meanwhile, the VUE  20   a  generates sidelink control information SL_UCI based on the attributes of V2X data. In a case where the mapping information depicted in  FIG. 9  is used, the VUE  20   a  determines a value of SL_UCI corresponding to the attributes of V2X data. Then, the VUE  20   a  transmits sidelink control information SL_UCI to the base station  10 . For example, the sidelink control information SL_UCI may be transmitted from the VUE  20   a  to the base station  10  by using specified resources in a PUCCH. Note that the resource for transmitting sidelink control information SL_UCI is indicated by control information broadcast from the base station to UEs or individual control information (e.g., RRC_DEDICATED). 
     Upon receipt of the sidelink control information SL_UCI, the base station  10  determines, according to the value of SL_UCI, resources to be allocated to the V2X communication requested by the VUE  20   a . In this case, the base station  10  determines resources to be allocated to the requested V2X communication in accordance with, for example, the mapping information depicted in  FIG. 9 . In particular, resources for the V2X communication are determined so as to satisfy a data size and a maximum latency corresponding to the value of SL_UCI. In this way, sidelink control information SL_UCI is used as resource request information requesting resources for V2X communication. 
     Subsequently, the base station  10  generates sidelink grant information indicating the resources allocated to the requested V2X communication and transmits the sidelink grant information to the VUE  20   a . The sidelink grant information includes information indicating PSSCH resources for transmitting V2X data and information indicating PSCCH resources for transmitting control information for the V2X data. Note that sidelink grant information is an example of resource allocation information indicating resources granted by the base station  10  for D2D communication or sidelink communication. For example, sidelink grant information may be incorporated into downlink control information DCI so as to be transmitted from the base station  10  to the VUE  20   a . 
     The VUE  20   a  generates a sidelink transport block and control information SCI. The sidelink transport block is generated according to the sidelink grant information. For example, symbols and subcarriers for transmitting the sidelink transport block may be determined according to the sidelink grant information. The V2X data is stored in the sidelink transport block. The control information SCI indicates the arrangement in V2X data (symbols and subcarriers), a modulation scheme, code, and the like. Control information SCI is used when a wireless communication device that has received V2X data decodes the V2X data. 
     The VUE  20   a  transmits the V2X data to the VUE  20   b  by using the resources reported by the sidelink grant information. In this case, the control information SCI is transmitted using the PSCCH designated by the sidelink grant information. Meanwhile, the V2X data is transmitted using the PSSCH designated by the sidelink grant information. 
     As described above, the wireless communication system in the first embodiment is such that when a VUE  20  transmits sidelink control information SL_UCI to the base station  10 , the base station performs resource allocation for V2X communication and transmits sidelink grant information to the VUE  20 . Thus, sidelink grant information indicating resources for V2X communication is reported from the base station  10  to the VUE  20  without transmitting a buffer status report BSR from the VUE  20  to the base station  10  via a PUSCH. Accordingly, the first embodiment reduces a latency in transmitting V2X data in comparison with the procedure depicted in  FIG. 4 . 
       FIG. 10  is a flowchart illustrating an example of processes performed by a VUE. The processes of this flowchart are performed when V2X data from an application arrives at a VUE  20 . 
     In S 1 , the controller  21  acquires V2X data generated by an application for V2X communication. 
     In S 2 , the controller  21  determines values of SL_UCI based on the attributes of the acquired V2X data. For example, when the mapping information depicted in  FIG. 9  has been configured for the VUE  20 , four bits of SL_UCI may be generated according to the attributes of V2X data. Then, the controller  21  generates sidelink control information SL_UCI including the SL_UCI. 
     In S 3 , the radio transmitter  23  transmits the sidelink control information SL_UCI to the base station  10 . The sidelink control information SL_UCI is transmitted from the VUE  20  to the base station  10  by using a PUCCH. For example, resources (symbols and subcarriers) for transmitting the sidelink control information SL_UCI may be determined in advance between the base station  10  and the VUE  20 . Upon receipt of the sidelink control information SL_UCI, the base station  10  performs resource allocation for V2X communication so as to generate sidelink grant information. The sidelink grant information includes information indicating PSSCH resources for transmitting the V2X data and information indicating PSCCH resources for transmitting control information SCI for the V2X data. 
     In S 4 , the radio receiver  24  receives the sidelink grant information transmitted from the base station  10 . The sidelink grant information is transmitted from the base station  10  to the VUE  20  by using a PDCCH. For example, resources (symbols and subcarriers) for transmitting the sidelink grant information may be determined in advance between the base station  10  and the VUE  20 . 
     In S 5 , the radio transmitter  25  transmits the V2X data in accordance with the sidelink grant information. In this case, together with the V2X data, the control information SCI for decoding the V2X data is transmitted. The V2X data is transmitted using the PSSCH resources designated by the sidelink grant information. The control information SCI is transmitted using the PSCCH resources designated by the sidelink grant information. Note that the control information SCI is generated by the controller  21  according to the sidelink grant information. 
       FIG. 11  is a flowchart illustrating an example of processes performed by a base station. The processes of this flowchart are performed by the base station  10  depicted in  FIG. 6 . 
     In S 11 , the radio receiver  15  receives sidelink control information SL_UCI transmitted from a VUE  20 . As described above, the sidelink control information SL_UCI is transmitted from the VUE  20  to the base station  10  by using a PUCCH. For example, resources (symbols and subcarriers) for transmitting the sidelink control information SL_UCI may be determined in advance between the base station  10  and the VUE  20 . 
     In S 12 , the controller  11  performs resource allocation based on the sidelink control information SL_UCI. In this example, the controller  11  manages one or more data resource pools for V2X data and one or more control resource pools for control information SCI for V2X data. Each data resource pool is associated with a respective one of the control resource pools. The controller  11  detects the attributes of V2X data according to the values of SL_UCI so as to estimate the size of the V2X data. The controller  11  selects one resource pool D from the data resource pools in accordance with the attributes of the V2X data and the estimated data size and selects resources for the V2X data from the resource pool D. Meanwhile, the controller  11  selects a control resource pool C corresponding to the resource pool D from the control resource pools and selects resources for the control information SCI from the control resource pool C. 
     As a result, sidelink grant information is generated. The sidelink grant information includes information indicating PSSCH resources for transmitting the V2X data and information indicating PSCCH resources for transmitting control information SCI for the V2X data. 
     In S 13 , the radio transmitter  14  transmits the sidelink grant information to the VUE  20 . As described above, the sidelink grant information is transmitted from the base station  10  to the VUE  20  by using a PDCCH. For example, resources (symbols and subcarriers) for transmitting the sidelink grant information may be determined in advance between the base station  10  and the VUE  20 . 
       FIG. 12  illustrates an example of the resource allocation in the first embodiment. In this example, the length of each slot is 0.5 milliseconds, as in the example depicted in  FIG. 4 . Thus, the time domain of each slot is formed from 14 symbols. Three symbols are allocated to a downlink D (data and control information). Eight symbols are allocated to an uplink U (data). Two symbols are allocated to an uplink U (control information). Furthermore, one symbol of guard section G is provided. 
     Upon V2X data from an application for V2X communication arriving at a VUE  20 , the VUE  20  transmits sidelink control information SL_UCI to the base station  10  by using an uplink (PUCCH). In this example, the waiting time for the PUCCH corresponds to the time period from the moment at which the V2X data arrives at the VUE  20  to the moment at which the PUCCH is obtained for the first time after arrival of the V2X data. Thus, an average waiting time t 1  for obtaining PUCCH is ½ of the slot period. Each slot has two symbols allocated to the PUCCH. Thus, a time t s1  needed to transmit the sidelink control information SL_UCI to the base station  10  corresponds to a time needed to transmit two symbols. 
     The base station  10  performs resource allocation for V2X communication according to the sidelink control information SL_UCI and transmits sidelink grant information to the VUE  20 . The sidelink grant information is transmitted from the base station  10  to the VUE  20  by using a downlink (e.g., PDCCH). In this example, three symbols are allocated to the downlink. Thus, a time t s2  needed to receive the sidelink grant information from the base station  10  corresponds to a time needed to transmit three symbols. A period t 2  from the moment at which the sidelink control information SL_UCI is transmitted to the moment at which the sidelink grant information is received is substantially the same as the slot period. During the period t 2 , the base station  10  performs resource allocation based on the sidelink control information SL_UCI and generates sidelink grant information. 
     After receiving the sidelink grant information from the base station  10 , the VUE  20  transmits the V2X data at slot s 3 . Thus, a time t s3  needed to transmit the V2X data is substantially the same as the slot period. Meanwhile, the VUE  20  decodes the sidelink grant information within the period from the moment at which the sidelink grant information is received via the downlink to the time of start of a new slot. Thus, a period t 3  needed to decode the sidelink grant information from the base station  10  corresponds to a time needed to transmit 11 symbols. However, depending on the processing capacity of the VUE  20 , one additional slot period may be needed to decode sidelink grant information. 
     Accordingly, in the example depicted in  FIG. 12 , the time period from the moment at which V2X data is generated to the moment at which the V2X data is transmitted (i.e., a latency) corresponds to the sum of t 1 -t 3  and t s1 -t s3  depicted in  FIG. 13 . In this case, the latency is 1.82-2.32 milliseconds. Thus, the first embodiment reduces the latency in V2X communication to less than 3 milliseconds. Hence, the requirements pertaining to the types of use of 5G V2X services can be satisfied. 
     In the first embodiment, sidelink control information SL_UCI, not a scheduling request SR, is transmitted from a VUE  20  to the base station  10 , in comparison with the procedure depicted in  FIG. 4 . Meanwhile, the first embodiment does not need the procedure for transmitting a buffer status report BSR. In this regard, the time pertaining to a transmission of a scheduling request SR is substantially the same as a time pertaining to a transmission of sidelink control information SL_UCI. Thus, in comparison with the procedure depicted in  FIG. 4 , the first embodiment has a reduced time pertaining to a transmission of a buffer status report BSR (including the time needed to determine PUSCH resources for transmitting the buffer status report BSR). 
     In the example depicted in  FIGS. 9-10 , sidelink control information SL_UCI expresses the attributes of V2X data with a plurality of bits. However, embodiments of the invention are not limited to this configuration. For example, in a case where V2X data is generated by an application pertaining to services determined in advance or a case in which the size or the like of V2X data to be transmitted is fixed in advance, a VUE  20  does not need to report the attributes of the V2X data to the base station  10 . Thus, in these cases, the VUE  20  may request resources for V2X communication by using one bit of sidelink control information SL_UCI. In this case, upon receipt of the sidelink control information SL_UCI, the base station  10  performs resource allocation in accordance with the services determined in advance or the data size determined in advance. Note that parameters pertaining to resource allocation (e.g., data size) may be configured in advance for the base station  10  or reported to the base station  10  from the network management system. 
       FIGS. 14A-14B and 15A-15B  illustrate examples of cases in which a plurality of VUEs each request sidelink communication. Note that when starting sidelink communication, the VUE transmits sidelink control information SL_UCI to the base station  10  by using a PUCCH, as described above. 
     In the examples depicted in  FIGS. 14A and 14B , a plurality of VUEs are multiplexed in a time domain (time division multiplexing). In the example depicted in  FIG. 14A , a Short PUCCH format may be used. In the Short PUCCH format, each slot has one or two symbols allocated to a PUCCH. The sidelink control information SL_UCI of VUE # 1  is transmitted using the PUCCH in slot # 1 , and the sidelink control information SL_UCI of VUE # 2  is transmitted using the PUCCH in slot # 2 . 
     In the example depicted in  FIG. 14B , a Long PUCCH format is used. In the Long PUCCH format, each slot has four to fourteen symbols allocated to a PUCCH. In this example, the first to fourteenth symbols in each symbol may be used as a PUCCH. The first to seventh PUCCH symbols are transmitted using a different frequency (i.e., different subcarriers) from the eighth to fourteenth PUCCH symbols. The sidelink control information SL_UCI of VUE # 1  is transmitted using the first, third, eighth, and tenth PUCCH symbols in slot # 1 . Other PUCCH symbols may transmit, for example, demodulation reference signals (DMRSs) or other pieces of uplink control information of VUE # 1 . For example, DMRSs may be transmitted using the second, fourth, sixth, ninth, eleventh, and thirteenth PUCCH symbols, and SR may be transmitted using the fifth, seventh, twelfth, and fourteenth PUCCH symbols. The sidelink control information SL_UCI of VUE # 2  is transmitted using the first, third, eighth, and tenth PUCCH symbols in slot # 2 . For example, other PUCCH symbols may transmit DMRSs or other pieces of uplink control information of VUE # 2 . 
     In the examples depicted in  FIGS. 15A and 15B , a plurality of VUEs are multiplexed in a frequency domain (frequency division multiplexing). In the example depicted in  FIG. 15A , the Short PUCCH format is used. The sidelink control information SL_UCI of VUE # 1  is transmitted using a different frequency (i.e., different subcarriers) from the sidelink control information SL_UCI of VUE # 2 . 
     In the example depicted in  FIG. 15B , the Long PUCCH format is used. The sidelink control information SL_UCI of VUE # 1  is transmitted using a different frequency from the sidelink control information SL_UCI of VUE # 2 . 
     With respect to the time division multiplexing and the frequency division multiplexing depicted in  FIGS. 14A-14B and 15A-15B , a plurality of VUEs may each transmit corresponding sidelink control information SL_UCI by using a different base sequence of DMRSs. 
     Second Embodiment 
     In the first embodiment, a VUE transmits sidelink control information SL_UCI to the base station immediately after acquiring V2X data. By contrast, in the second embodiment, a VUE selects a sequence for requesting sidelink resources in accordance with a maximum latency required by V2X data. 
       FIG. 16  is a flowchart illustrating an example of processes performed by a VUE in the second embodiment. As in the method depicted in  FIG. 10 , V2X data from an application for V2X communication arrives at a VUE  20  at S 1 . 
     In S 21 , the controller  21  decides whether a latency required by the V2X data is less than or equal to a threshold. For example, the required latency may be reported from an application. Alternatively, the required latency may be determined in advance for the application for generating V2X data. The threshold may be autonomously determined by the VUE. Meanwhile, the threshold may be indicated by control information broadcast from the base station or individual control information (e.g., RRC_DEDICATED). 
     When the required latency is less than or equal to the threshold, the controller  21  generates and transmits sidelink control information SL_UCI to the base station  10  in S 22 . The process of S 22  corresponds to S 2 -S 3  depicted in  FIG. 10 . Thus, upon the VUE  20  performing the process of S 22 , the base station  10  performs resource allocation in accordance with the sidelink control information SL_UCI and transmits sidelink grant information to the VUE  20 . 
     When the required latency is greater than the threshold, the controller  21  performs the processes of S 23 -S 25 . The processes of S 23 -S 25  are realized using a similar procedure to the existing resource allocation method depicted in  FIG. 2 . In particular, the radio transmitter  23  transmits a scheduling request SR to the base station  10  in S 23 . In this case, the base station  10  transmits an uplink grant indicating resources for an available uplink in return to the VUE  20 . In S 24 , the VUE  20  receives the uplink grant. Then, the radio transmitter  23  transmits, in S 25 , a buffer status report BSR to the base station  10  by using the resources designated by the uplink grant. Note that the buffer status report is generated by the controller  21  according to the size or the like of the V2X data. 
     In this way, the VUE  20  transmits sidelink control information SL_UCI or a buffer status report BSR to the base station  10  according to the maximum latency required by V2X data. In this example, irrespective of which of sidelink control information SL_UCI or a buffer status report BSR is received, the base station  10  can perform resource allocation so as to generate sidelink grant information. The sidelink grant information is transmitted from the base station  10  to the VUE  20 . Thus, in S 4 -S 5 , the VUE  20  transmits V2X data in accordance with the sidelink grant information. 
       FIG. 17  is a flowchart illustrating an example of processes performed by a base station in the second embodiment. In the processes of this flowchart, sidelink control information SL_UCI or a scheduling request SR is transmitted from a VUE  20  using the method depicted in  FIG. 16 . 
     When the radio receiver  15  receives sidelink control information SL_UCI from the VUE  20  (S 31 : Yes), the base station  10  performs the processes of S 12 -S 13 . Thus, in S 12 , the controller performs resource allocation based on the sidelink control information SL_UCI and generates sidelink grant information. In S 13 , the radio transmitter  14  transmits the sidelink grant information to the VUE  20 . 
     When the radio receiver  15  receives a scheduling request SR from the VUE  20  (S 32 : Yes), the radio transmitter  14  transmits an uplink grant to the VUE  20  in S 33 . In this case, the VUE  20  transmits a buffer status report BSR by using resources designated by the uplink grant. In S 34 , the radio receiver  15  receives the buffer status report BSR. In S 35 , the controller  11  performs resource allocation based on the buffer status report BSR and generates sidelink grant information. Then, in S 13 , the sidelink grant information generated in S 35  is transmitted to the VUE  20 . 
     Accordingly, in the second embodiment, when V2X communication with a small maximum latency is requested, sidelink control information SL_UCI is transmitted; otherwise, a scheduling request SR is transmitted. In this regard, both sidelink control information SL_UCI and a scheduling request SR are transmitted via a PUCCH. Thus, assuming that the bit length of sidelink control information SL_UCI is greater than the bit length of scheduling requests SR, overheads on PUCCHs will be larger if sidelink control information SL_UCI is transmitted for all V2X communication. Accordingly, the second embodiment is such that scheduling requests SR are transmitted only for V2X communication that is not accompanied by a strict requirement in terms of latency, thereby reducing overhead on PUCCHs. In the example depicted in  FIG. 9 , SL_UCI is constituted by four bits. Meanwhile, a scheduling request SR may be constituted by one bit. 
     In the second embodiment, both sidelink control information SL_UCI and a scheduling request SR may be transmitted from a VUE  20  to the base station  10  by using a PUCCH. Thus, both the sidelink control information SL_UCI and the scheduling request SR may be transmitted using the resources represented by hatched regions indicated in  FIGS. 14A, 14B, 15A , or  15 B. 
     Third Embodiment 
     5G allows a slot configuration to be dynamically changed. For example, a base station can select a desired slot among a slot of 1 millisecond, a slot of 0.5 milliseconds, and a slot of 0.25 milliseconds. The base station can also select a “mini-slot” having 2-13 symbols. A “mini-slot” may also be referred to as “non-slot based transmission/scheduling.” 
     In the third embodiment, the slot configuration is dynamically changed in the procedure for allocating resources to V2X communication. Thus, a latency in the procedure for resource allocation for V2X communication can be reduced. 
       FIG. 18  illustrates an example of the resource allocation in the third embodiment. In the third embodiment, when V2X data is generated, a VUE  20  transmits a scheduling request SR to the base station  10 . The scheduling request SR requests resources for uplink through a procedure similar to the procedure for 4G depicted in  FIG. 2 . 
     Upon receipt of the scheduling request SR, the base station  10  generates an uplink grant, as in the procedure for 4G depicted in  FIG. 2 . However, in the third embodiment, configuration change information is generated in addition to the uplink grant. The configuration change information includes an instruction to decrease the slot length. In this example, the configuration change information includes the following information. 
     Slot length: Slot of 0.5 milliseconds is changed to Mini-slot of 0.125 milliseconds with 7 symbols 
     SCS: 60 kHz 
     Downlink: 7 Symbols 
     Guard section: 1 symbol
 
Uplink (data): 6 Symbols
 
Uplink (control information): 1 Symbol
 
The uplink grant and the configuration change information are reported from the base station  10  to the VUE  20  via a PDCCH.
 
     Upon receipt of the configuration change information from the base station  10 , the VUE  20  changes the configurations of the subsequent slots. Then, the VUE  20  transmits a buffer status report BSR to the base station  10  by using mini-slot s 3 . Note that the uplink resources for transmitting the buffer status report BSR to the base station  10  are designated by the above uplink grant. 
     The base station  10  allocates resources to the requested V2X communication in accordance with the buffer status report BSR. In this case, PSSCH resources for transmitting the V2X data and PSCCH resources for transmitting control information SCI are determined. Subsequently, the base station  10  transmits, to the VUE  20 , sidelink grant information indicating the resource allocation. 
     The VUE  20  receives the sidelink grant information at mini-slot s 4 . Then, the VUE  20  transmits the V2X data and the control information SCI according to the sidelink grant information. In the example depicted in  FIG. 18 , V2X data is transmitted via the sidelink at mini-slot s 5 . 
     In the third embodiment, the time period from the moment at which V2X data is generated to the moment at which the V2X data is transmitted (i.e., a latency) corresponds to the sum of t 1 -t 5  and t s1 -t s5  depicted in  FIG. 19 . In this example, the latency pertaining to the transmission of V2X data is 2.68-2.93 milliseconds. 
     As described above, the third embodiment is such that the slot configuration is dynamically changed in the procedure for allocating resources to V2X communication. As a result, the third embodiment allows a latency pertaining to resource allocation for V2X communication to be reduced in comparison with the procedure depicted in  FIG. 4 . 
     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 inventions 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.