Patent Publication Number: US-2023136285-A1

Title: Wireless communication device, wireless communication system, and wireless communication method

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national stage of PCT/JP2020/046080 filed on Dec. 10, 2020, which claims priority of Japanese Patent Application No. JP 2019-233530 filed on Dec. 24, 2019, the contents of which are incorporated herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a wireless communication device, a wireless communication system, and a wireless communication method for performing road-vehicle wireless communication. 
     BACKGROUND 
     Conventionally, a road-vehicle wireless communication system that provides various types of information by wireless signals from a roadside wireless communication device installed on a road to an in-vehicle wireless communication device mounted in a vehicle has been put into practical use. The information transmitted from the roadside wireless communication device to the in-vehicle wireless communication device can be, for example, information such as the lighting state of a traffic signal and traffic information in the surrounding area, and in a vehicle that has received these pieces of information, for example, it is possible to perform processing such as alerting the driver of the vehicle or performing driving assistance control of the vehicle. 
     JP 2019-28000A proposes a travel assistance device that acquires position information of vehicles in the surrounding area through wireless communication with an infrastructure unit and other vehicles, and detects traffic congestion of the road caused by branching of the road, based on the acquired position information and the shape of the road. 
     In recent years, services provided by vehicles have become more sophisticated and diversified, and the amount of data that is handled in order to provide the services has increased. In the future, it is expected that various services using road-vehicle wireless communication will start to be provided, and thus there is a risk that the amount of data transmitted and received on a network inside the vehicle and the amount of data transmitted and received between the road and vehicles will increase. 
     The present disclosure has been made in view of such circumstances, and an object thereof is to provide a wireless communication device, a wireless communication system, and a wireless communication method that can be expected to suppress an increase in the amount of data transmitted and received through road-vehicle wireless communication. 
     SUMMARY 
     The wireless communication device according to this aspect is a wireless communication device including a wireless communication unit configured to perform wireless communication with a vehicle and a processing unit configured to perform processing relating to communication, in which the processing unit determines a communication amount in wireless communication performed between one or a plurality of vehicles by the wireless communication unit, transmits communication amount information relating to the determined communication amount to the vehicle by the wireless communication unit, and receives data transmitted from the vehicle at a size corresponding to the transmitted communication amount information by the wireless communication unit. 
     The present application can be realized not only as a device such as a wireless communication device including such a characteristic processing unit, but can also be realized as a method of performing the characteristic processing as a step, or can be realized as a computer program for causing a computer to execute the step. It can be realized as a semiconductor integrated circuit that realizes some or all of these devices, or can be realized as another device or system including these devices. 
     Advantageous Effects of Disclosure 
     According to the description above, it can be expected that an increase in the amount of data transmitted and received through road-vehicle wireless communication will be suppressed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG.  1    is a schematic diagram for illustrating an overview of a wireless communication system according to the present embodiment. 
         FIG.  2    is a schematic diagram showing a configuration example of a vehicle of the wireless communication system according to the present embodiment. 
         FIG.  3    is a schematic diagram showing a configuration of an in-vehicle wireless communication device according to the present embodiment. 
         FIG.  4    is a block diagram showing a configuration of a roadside wireless communication device according to the present embodiment. 
         FIG.  5    is a schematic diagram for illustrating data transmission processing performed in the wireless communication system according to the present embodiment. 
         FIG.  6    is a schematic diagram for illustrating data transmission processing performed in the wireless communication system according to the present embodiment. 
         FIG.  7    is a flowchart showing a procedure of data reception processing performed by an in-vehicle wireless communication device according to the present embodiment. 
         FIG.  8    is a flowchart showing a procedure of data transmission processing performed by the roadside wireless communication device according to the present embodiment. 
         FIG.  9    is a flowchart showing a procedure of data reception processing performed by the roadside wireless communication device according to the present embodiment. 
         FIG.  10    is a flowchart showing a procedure of data transmission processing performed by the in-vehicle wireless communication device according to the present embodiment. 
         FIG.  11    is a schematic diagram for illustrating data transmission processing performed in a wireless communication system according to a modified example. 
         FIG.  12    is a schematic diagram for illustrating data transmission processing performed in a wireless communication system according to a modified example. 
         FIG.  13    is a schematic diagram for illustrating data transmission stop processing performed in the wireless communication system according to the present embodiment. 
         FIG.  14    is a flowchart showing a procedure of data transmission stop processing performed by the in-vehicle wireless communication device according to the present embodiment. 
         FIG.  15    is a flowchart showing a procedure of data transmission stop processing performed by the roadside wireless communication device according to the present embodiment. 
         FIG.  16    is a schematic diagram for illustrating data transmission stop processing performed in the wireless communication system according to the present embodiment. 
         FIG.  17    is a flowchart showing a procedure of data transmission stop processing performed by the in-vehicle wireless communication device according to the present embodiment. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     First, embodiments of the present disclosure will be listed and described. At least some of the embodiments described below may be combined as appropriate. 
     First Aspect 
     The wireless communication device according to a first aspect is a wireless communication device installed on a road, the wireless communication device including a wireless communication unit for performing wireless communication with a vehicle and a processing unit for performing processing relating to communication, in which the processing unit determines a communication amount in wireless communication performed with one or a plurality of vehicles by the wireless communication unit, transmits communication amount information relating to the determined communication amount in the wireless communication to the vehicle by the wireless communication unit, and receives data transmitted from the vehicle at a size corresponding to the transmitted communication amount information, by the wireless communication unit. 
     In the first aspect, a wireless communication device provided outside the vehicle determines the communication amount of wireless communication performed with one or more vehicles. The wireless communication device transmits information regarding the determined communication amount to the vehicle as the communication amount information. As a result, the vehicle can keep track of and predict the status of wireless communication based on the communication amount information from the wireless communication device, and the like, and for example, the information can be transmitted to the wireless communication device with the data size compressed to a size suitable for the free capacity of wireless communication or the like. The wireless communication device can receive data transmitted from the vehicle at a size corresponding to the transmitted communication amount information and use it for its own processing. Due to the wireless communication device transmitting the communication amount information, the vehicle can transmit data of a size suitable for the wireless communication device, and it can be expected that an increase in the amount of data transmitted and received between the road and vehicles will be suppressed. 
     Second Aspect 
     In a second aspect, it is preferable that the processing unit receives communication amount information relating to a communication amount in an in-vehicle network provided inside of the vehicle from the vehicle, adjusts the size of data to be transmitted to the vehicle according to the received communication amount information, and transmits the data with the adjusted size to the vehicle by the wireless communication unit. 
     In the second aspect, the vehicle transmits the communication amount information relating to the communication amount in the in-vehicle network provided inside the vehicle to the wireless communication device. The wireless communication device that received the communication amount information from the vehicle adjusts the data size by, for example, compressing the data size to a size suitable for the free capacity of the in-vehicle network or the like, and transmits the data with the adjusted size to the vehicle. Due to the size of the data transmitted by the wireless communication device being adjusted according to the communication amount information received from the vehicle, the vehicle can receive data of a size suitable for the communication amount of the in-vehicle network. 
     Third Aspect 
     In a third aspect, it is preferable that the processing unit receives a request for data from the vehicle by the wireless communication unit, adjusts the size of the data corresponding to the received request, and transmits image data with an adjusted size to the vehicle by the wireless communication unit. 
     In the third aspect, a request for acquisition or transmission of data is given from the vehicle to the wireless communication device, and the wireless communication device transmits the requested data to the vehicle in response to this request. At this time, the wireless communication device adjusts the size of the data corresponding to the request and transmits the data with the adjusted size to the vehicle. Accordingly, it can be expected that the data requested by the vehicle will be prevented from being discarded or the like based on the size of the data being large. 
     Fourth Aspect 
     In a fourth aspect, the processing unit stops transmission of data to a vehicle according to the determined communication amount in the wireless communication. 
     In the fourth aspect, the wireless communication device stops transmitting data to the vehicle if, for example, there is no leeway in the communication amount that can be transmitted and received wirelessly to and from the vehicle according to the determined communication amount. This makes it possible to suppress an increase in the amount of communication between the vehicle and the wireless communication device in a situation where, for example, many vehicles perform wireless communication with the wireless communication device. 
     Fifth Aspect 
     In a fifth aspect, if there are a plurality of vehicles with which the wireless communication unit can communicate, the processing unit determines priority levels of the plurality of vehicles, and stops transmission of data to the vehicle determined to have a low priority level. 
     In the fifth aspect, if the wireless communication device is in a situation where it can communicate with a plurality of vehicles, the wireless communication device determines the priority levels of the plurality of vehicles. The wireless communication device stops transmitting data to a vehicle determined to have a low priority level. Accordingly, it can be expected that the wireless communication device will reliably perform wireless communication with a vehicle having a high priority level. 
     Sixth Aspect 
     The wireless communication system according to a sixth aspect is a wireless communication system by which an in-vehicle wireless communication device and a wireless communication device perform wireless communication with each other, the in-vehicle wireless communication device being mounted in a vehicle and including a wireless communication unit for performing wireless communication with the outside of the vehicle and a processing unit for performing processing relating to communication, and the wireless communication device being installed outside of the vehicle and including a wireless communication unit for performing wireless communication with the vehicle and a processing unit for performing processing relating to communication, in which the processing unit of the wireless communication device determines a communication amount in wireless communication performed with one or a plurality of vehicles and transmits communication amount information relating to the determined communication amount to the vehicle, the processing unit of the in-vehicle wireless communication device receives the communication amount information transmitted by the wireless communication device, adjusts the size of data to be transmitted to the wireless communication device according to the received communication amount information, and transmits the data with the adjusted size to the wireless communication device, and the processing unit of the wireless communication device receives the data transmitted by the in-vehicle wireless communication device at a size corresponding to the communication amount information. 
     In the sixth aspect, similarly to the first aspect, it can be expected that an increase in the amount of data transmitted and received between the road and vehicles will be suppressed. 
     Seventh Aspect 
     The wireless communication method according to the seventh aspect is a wireless communication method in which an in-vehicle wireless communication device mounted in a vehicle and a wireless communication device installed outside of the vehicle perform wireless communication with each other, in which the wireless communication device determines a communication amount in wireless communication performed with one or a plurality of vehicles and transmits communication amount information relating to the determined communication amount to the vehicle, the in-vehicle wireless communication device receives the communication amount information transmitted by the wireless communication device, adjusts the size of data to be transmitted to the wireless communication device according to the received communication amount information, and transmits the data with the adjusted size to the wireless communication device, and the wireless communication device receives the data transmitted by the in-vehicle wireless communication device at a size corresponding to the communication amount information. 
     In the seventh aspect, similarly to the first aspect, it can be expected that an increase in the amount of data transmitted and received between the road and vehicles will be suppressed. 
     The following will describe specific examples of the wireless communication system according to the embodiment with reference to the drawings. The present disclosure is not limited to these examples but is defined by the claims, and all modifications within the meaning and scope equivalent to the claims are intended to be included. 
     System Configuration 
       FIG.  1    is a schematic diagram for illustrating an overview of a wireless communication system according to the present embodiment. The wireless communication system according to the present embodiment is a system in which an in-vehicle wireless communication device  1  mounted in a vehicle  101  and a roadside wireless communication device  2  provided on a traffic signal  102  installed at an intersection of roads or the like perform wireless communication with each other. Note that in the present embodiment, it is assumed that the roadside wireless communication device  2  is provided on the traffic signal  102 , but there is no limitation to this, and for example, the roadside wireless communication device  2  may be provided in various facilities or equipment such as street lights, signposts, pedestrian bridges, and guardrails installed on a road. The in-vehicle wireless communication device  1  can perform wireless communication with one or more roadside wireless communication devices  2  present within a predetermined range (a range in which radio waves reach) from the vehicle  101 . Similarly, the roadside wireless communication device  2  can perform wireless communication with one or a plurality of in-vehicle wireless communication devices  1  present within a predetermined range from the installation position of the traffic signal  102 . 
     The wireless communication system according to the present embodiment can be applied to a system in which, for example, the roadside wireless communication device  2  transmits image data of an intersection imaged by a camera provided in a traffic signal  102  or the like to the vehicle-mounted wireless communication device  1  of the vehicle  101 , and the driver is notified of the status of the intersection, which is a blind spot of the vehicle  101 , due to it being displayed as an image. Also, in the wireless communication system, for example, the in-vehicle wireless communication device  1  can transmit image data imaged by a camera mounted on the vehicle  101  to the roadside wireless communication device  2 , and due to the roadside wireless communication device  2  transmitting this image data to the in-vehicle wireless communication device  1  of another vehicle  101 , the driver can be notified of the status of the intersection due to it being displayed as an image. In the wireless communication system, data can be transmitted and received in both directions from the in-vehicle wireless communication device  1  to the roadside wireless communication device  2  and from the roadside wireless communication device  2  to the in-vehicle wireless communication device  1 . 
     Also, the data transmitted and received by the wireless communication system is not limited to the image data imaged by the above-mentioned camera, and may be various types of data. The data transmitted from the in-vehicle wireless communication device  1  to the roadside wireless communication device  2  can include, for example, various types of data such as detection results by various sensors mounted in the vehicle  101 , position information of the vehicle  101 , or information on an operation plan relating to automatic driving of the vehicle  101 . The data transmitted from the roadside wireless communication device  2  to the in-vehicle wireless communication device  1  can include, for example, various types of data such as position information of one or more vehicles  101  present around the intersection, an urgent stop command to the vehicle  101 , or data for updating an application program executed in the vehicle  101 . These pieces of data transmitted and received by the in-vehicle wireless communication device  1  and the roadside wireless communication device  2  are examples, and there is no limitation to this. 
     As described above, various types of data are transmitted and received between the in-vehicle wireless communication device  1  and the roadside wireless communication device  2 . Also, the vehicle  101  is equipped with multiple in-vehicle devices such as an ECU (Electronic Control Unit), and these multiple in-vehicle devices transmit and receive data via an in-vehicle network. The data transmitted by the roadside wireless communication device  2  is received by the in-vehicle wireless communication device  1 , and the in-vehicle wireless communication device  1  transmits this data to the in-vehicle devices via the in-vehicle network. There is a limit to the amount of data that can be sent and received on the in-vehicle network, and if the amount of communication due to data transmission and reception between in-vehicle devices inside the vehicle  101  increases, a situation can occur in which the data received from outside the vehicle cannot be handled by the in-vehicle network. In view of this, in the wireless communication system according to the present embodiment, the in-vehicle wireless communication device  1  determines the communication amount of the in-vehicle network of the vehicle  101  and transmits it to the roadside wireless communication device  2 , and the roadside wireless communication device  2  compresses the data according to the communication amount and transmits the compressed data to the in-vehicle wireless communication device  1 . As a result, the in-vehicle wireless communication device  1  can receive data of a size that can be handled by the in-vehicle network from the roadside wireless communication device  2 . 
     Note that in the present embodiment, the amount of data that can be transmitted and received in the communication between the devices is referred to as the communication capacity, and the amount of data being transmitted and received at a certain point in time is referred to as the communication amount. Also, the difference between the communication capacity and the communication amount at a certain point in time is called the free capacity. The communication capacity can also be generally referred to as the communication band. The communication capacity, the communication amount, and the free capacity are, for example, amounts expressed in units such as bits/second and packets/second. 
     Similarly, the roadside wireless communication device  2  transmits and receives data to and from a plurality of in-vehicle wireless communication devices  1 . For example, if a large number of vehicles  101  are present around an intersection where a traffic signal  102  is installed, a situation can occur in which the communication amount of data transmitted and received through wireless communication between the roadside wireless communication device  2  and a large number of in-vehicle wireless communication devices  1  increases, and it will not be possible to handle this with the communication capacity of the wireless communication of the roadside wireless communication device  2 . In view of this, in the wireless communication system according to the present embodiment, the roadside wireless communication device  2  determines the communication amount of wireless communication performed with one or a plurality of in-vehicle wireless communication devices  1  and transmits the determined communication amount to the in-vehicle wireless communication device  1 , and the in-vehicle wireless communication device  1  compresses the data according to this communication amount and transmits the compressed data to the roadside wireless communication device  2 . As a result, the roadside wireless communication device  2  can receive data of a size that can be handled by the communication capacity of its own wireless communication from the in-vehicle wireless communication device  1 . 
       FIG.  2    is a schematic diagram showing a configuration example of the vehicle  101  of the wireless communication system according to the present embodiment. The vehicle  101  according to the present embodiment is equipped with the above-mentioned in-vehicle wireless communication device  1  and various in-vehicle devices such as a camera  5 , an ECU  6 , and a display device  7 . The in-vehicle wireless communication device  1 , the camera  5 , the ECU  6 , the display device  7 , and the like are connected to each other via the in-vehicle network  4  provided in the vehicle  101 , and can transmit and receive data to and from each other. Note that in  FIG.  2   , the in-vehicle network  4  is shown as a bus-type network, but there is no limitation to this, and other network configurations such as a star-type or a ring-type may be adopted. Also,  FIG.  2    shows a camera  5 , an ECU  6 , and a display device  7  as in-vehicle devices mounted in the vehicle  101 , but this is an example, and any kind of device may be mounted in the vehicle  101 . 
     The data transmitted by the roadside wireless communication device  2  is received by the in-vehicle wireless communication device  1  of the vehicle  101 . The in-vehicle wireless communication device  1  transmits the data received from the roadside wireless communication device  2  to, for example, the ECU  6 , the display device  7 , or the like that requires the data via the in-vehicle network  4 . Also, the in-vehicle wireless communication device  1  acquires data to be transmitted to the outside of the vehicle from the camera  5 , the ECU  6 , or the like via the in-vehicle network  4 , and transmits the acquired data to the roadside wireless communication device  2 . 
       FIG.  3    is a schematic diagram showing the configuration of the in-vehicle wireless communication device  1  according to the present embodiment. The in-vehicle wireless communication device  1  according to the present embodiment includes a processing unit (processor)  11 , a storage unit (storage)  12 , a wireless communication unit (transceiver)  13 , an in-vehicle communication unit (transceiver)  14 , and the like. The processing unit  11  is constituted using, for example, an arithmetic processing device such as a CPU (Central Processing Unit) or an MPU (Micro-Processing Unit). The processing unit  11  can perform various types of processing by reading out and executing a program stored in the storage unit  12 . In the present embodiment, by reading out and executing a program  12   a  stored in the storage unit  12 , the processing unit  11  performs various types of processing such as processing for transmitting and receiving data wirelessly with the roadside wireless communication device  2  provided outside of the vehicle  101  and processing for controlling wireless transmission and reception of data according to the communication amount of the in-vehicle network  4 . 
     The storage unit  12  is constituted by using, for example, a non-volatile memory element such as a flash memory or an EEPROM (Electrically Erasable Programmable Read Only Memory). The storage unit  12  stores various programs to be executed by the processing unit  11  and various types of data required for processing performed by the processing unit  11 . In the present embodiment, the storage unit  12  stores the program  12   a  to be executed by the processing unit  11 . 
     Note that the program  12   a  may be written in the storage unit  12 , for example, at the manufacturing stage of the in-vehicle wireless communication device  1 , a program distributed by a remote server device or the like, for example, may be acquired by the in-vehicle wireless communication device  1  through communication, a program recorded on a recording medium  99  such as a memory card or an optical disk, for example, may be read out by the in-vehicle wireless communication device  1  and stored in the storage unit  12 , and a program recorded on the recording medium  99 , for example, may be read out and written in the storage unit  12  of the in-vehicle wireless communication device  1  by a writing device. The program  12   a  may be provided in a form of distribution via the network, or may be provided in a form recorded on the recording medium  99 . 
     The wireless communication unit  13  performs wireless communication with the roadside wireless communication device  2  provided outside the vehicle  101 . The wireless communication unit  13  transmits data to the roadside wireless communication device  2  by outputting a signal obtained by modulating the data for transmission provided from the processing unit  11  from an antenna (not shown), receives the data from the roadside wireless communication device  2  by demodulating the signal received by the antenna, and provides the received data to the processing unit  11 . 
     The in-vehicle communication unit  14  is connected to the in-vehicle network  4  and performs transmission and reception of data to and from in-vehicle devices such as the camera  5 , the ECU  6 , and the display device  7  via the in-vehicle network  4 . In the present embodiment, the in-vehicle communication unit  14  transmits and receives data according to, for example, a CAN (Controller Area Network) communication standard. The in-vehicle communication unit  14  can be constituted by using, for example, an IC of a CAN controller. However, the communication standard used by the in-vehicle communication unit  14  is not limited to CAN, and the in-vehicle communication unit  14  may perform communication using a communication standard other than CAN, for example, a communication standard such as Ethernet (registered trademark). The in-vehicle communication unit  14  transmits data by outputting the message provided by the processing unit  11  as an electric signal to the communication line constituting the in-vehicle network  4 . Also, the in-vehicle communication unit  14  converts the electric signal of the communication line into digital data by sampling and acquiring the potential of the communication line, and provides the converted data to the processing unit  11  as reception data. 
     Also, in the in-vehicle wireless communication device  1  according to the present embodiment, due to the processing unit  11  reading out and executing the program  12   a  stored in the storage unit  12 , a communication amount determination unit  11   a , a wireless communication processing unit  11   b , an in-vehicle communication processing unit  11   c , a data size adjustment unit  11   d , a priority level determination unit  11   e , a stop request unit  11   f , and the like are realized in the processing unit  11  as software-like functional units. 
     The communication amount determination unit  11   a  performs processing for determining the communication amount of data transmitted and received via the in-vehicle network  4 . The communication amount determination unit  11   a  can monitor the data transmitted and received via the in-vehicle network  4 , measure the amount of data transmitted and received via the in-vehicle network  4  in a predetermined period such as one second, and set the measured amount of data as the communication amount. Also, the communication amount determination unit  11   a  may, for example, perform the measurement for the predetermined period a plurality of times and set the average value as the communication amount. Also, the communication amount determination unit  11   a  may predict the future communication amount based on the measured past and present amounts of data, and may set the predicted amount of data as the communication amount. In this case, any method may be adopted as the method for predicting the communication amount. 
     The wireless communication processing unit  11   b  performs processing relating to wireless communication with the roadside wireless communication device  2  by the wireless communication unit  13 . The wireless communication processing unit  11   b  wirelessly transmits data to the roadside wireless communication device  2  by generating data to be transmitted to the roadside wireless communication device  2  and providing the data to the wireless communication unit  13 . The wireless communication processing unit  11   b  receives the data wirelessly transmitted from the roadside wireless communication device  2  by the wireless communication unit  13 . 
     Also, in the present embodiment, the wireless communication processing unit  11   b  performs processing for transmitting information relating to the communication amount determined by the communication amount determination unit  11   a  to the roadside wireless communication device  2  as communication amount information. The information included in the communication amount information may be, for example, the communication amount determined by the communication amount determination unit  11   a , or may be, for example, the free capacity of the in-vehicle network  4  calculated based on the communication amount determined by the communication amount determination unit  11   a . However, if the communication amount determined by the communication amount determination unit  11   a  is transmitted as the communication amount information, it is preferable to include the communication capacity of the in-vehicle network  4  in the communication amount information. The free capacity of the in-vehicle network  4  can be calculated as the difference between the communication capacity of the in-vehicle network  4  and the communication amount determined by the communication amount determination unit  11   a . The communication amount information transmitted by the wireless communication processing unit  11   b  need only include information according to which the roadside wireless communication device  2  can keep track of the free capacity of the in-vehicle network  4 . The communication capacity of the in-vehicle network  4  is determined at the design stage of the vehicle  101  or the like, and the value thereof is stored in the storage unit  12  or the like. 
     Also, in the present embodiment, the wireless communication processing unit  11   b  receives the communication amount information transmitted by the roadside wireless communication device  2 . The communication amount information transmitted by the roadside wireless communication device  2  is information relating to the communication amount of wireless communication performed by the roadside wireless communication device  2 . The wireless communication processing unit  11   b  provides the received communication amount information to the data size adjustment unit  11   d . 
     The in-vehicle communication processing unit  11   c  performs processing relating to communication performed via the in-vehicle network  4  by the in-vehicle communication unit  14 . The in-vehicle communication unit  14  performs data transmission to the in-vehicle devices such as the camera  5 , the ECU  6 , and the display device  7  mounted in the vehicle  101  by generating data to be transmitted to the in-vehicle devices and providing the generated data to the in-vehicle communication unit  14 . The in-vehicle communication processing unit  11   c  receives the data transmitted by the in-vehicle device in the in-vehicle communication unit  14 . 
     The wireless communication processing unit  11   b  and the in-vehicle communication processing unit  11   c  relay data between the roadside wireless communication device  2  and the in-vehicle device in the vehicle  101  by the in-vehicle wireless communication device  1 . The wireless communication processing unit  11   b  receives the data from the roadside wireless communication device  2  and provides the received data to the in-vehicle communication processing unit  11   c , and the in-vehicle communication processing unit  11   c  transmits this data to the in-vehicle device via the in-vehicle network  4 . The in-vehicle communication processing unit  11   c  receives data from the in-vehicle device via the in-vehicle network  4  and provides the received data to the wireless communication processing unit  11   b , and the wireless communication processing unit  11   b  transmits this data to the roadside wireless communication device  2 . 
     If the wireless communication processing unit  11   b  receives a predetermined data acquisition request from the roadside wireless communication device  2 , the wireless communication processing unit  11   b  provides the received acquisition request to the in-vehicle communication processing unit  11   c . The in-vehicle communication processing unit  11   c  acquires the data requested in the acquisition request from the data transmitted and received via the in-vehicle network  4 , and provides the acquired data to the wireless communication processing unit  11   b . The wireless communication processing unit  11   b  transmits the data provided from the in-vehicle communication processing unit  11   c  to the roadside wireless communication device  2  as data relating to the acquisition request. Also, the wireless communication processing unit  11   b  may transmit an acquisition request for predetermined data to the roadside wireless communication device  2 . 
     The data size adjustment unit  11   d  performs processing for adjusting the size of data to be transmitted to the roadside wireless communication device  2  based on the communication amount information received from the roadside wireless communication device  2 . The data size adjustment unit  11   d  determines the free capacity of the wireless communication of the roadside wireless communication device  2  based on the communication amount information. If the size of the data to be transmitted to the roadside wireless communication device  2  exceeds the free capacity obtained based on the communication amount information, the data size adjusting unit  11   d  performs processing for reducing (compressing) the size of this data. For example, if the data to be transmitted is the image data imaged by the camera  5 , the data size adjustment unit  11   d  reduces the data size through a method such as reducing the resolution of the image data, reducing the frame rate, or changing from a color image to a monochrome image. Also, for example, the data size adjustment unit  11   d  may compress the data size using a coding technique that changes the information to be represented by a smaller number of bits than the original representation. The compression of the data size performed by the data size adjustment unit  11   d  may be either lossless compression or lossy compression. Also, the degree to which the data size adjusting unit  11   d  compresses the data size may be determined in advance such that it is, for example, 80% or less of the free capacity, or the like, and the compression rate may be variable based on, for example, a prediction of a future communication volume, or the like. 
     The priority level determination unit  11   e  performs processing for determining which roadside wireless communication device  2  is prioritized when the in-vehicle wireless communication device  1  can perform wireless communication with a plurality of roadside wireless communication devices  2 . The priority level determination unit  11   e  may determine the priority level according to, for example, the type of data transmitted by each roadside wireless communication device  2 , may determine the priority level according to, for example, the positional relationship, the distance, or the like between the vehicle  101  and the roadside wireless communication device  2 , and may determine the priority level using a reference other than these. Any method may be adopted as the method for determining the priority levels of the plurality of roadside wireless communication devices  2  by the priority level determination unit  11   e . 
     The stop request unit  11   f  performs processing for requesting the roadside wireless communication device  2  having a low priority level determined by the priority level determination unit  11   e  to stop transmitting data in a situation where the in-vehicle wireless communication device  1  can perform wireless communication with a plurality of roadside wireless communication devices  2 . The stop request unit  11   f  calculates the free capacity of the in-vehicle network  4  based on the communication amount determined by the communication amount determination unit  11   a , and gives a request to stop data transmission to the roadside wireless communication device  2  determined to have a low priority level if the free capacity becomes less than a predetermined threshold value. 
       FIG.  4    is a block diagram showing a configuration of the roadside wireless communication device  2  according to the present embodiment. The roadside wireless communication device  2  according to the present embodiment includes a processing unit (processor)  21 , a storage unit (storage)  22 , a wireless communication unit (transceiver)  23 , a wired communication unit (transceiver)  24 , and the like. The processing unit  21  is constituted by using an arithmetic processing device such as a CPU or an MPU. The processing unit  21  can perform various processes by reading and executing the program stored in the storage unit  22 . In the present embodiment, the processing unit  21  performs various types of processing such as processing for transmitting and receiving data wirelessly with the in-vehicle wireless communication device  1  mounted in the vehicle  101  by reading and executing the program  22   a  stored in the storage unit  22 . 
     The storage unit  22  is constituted by using, for example, a non-volatile memory element such as a flash memory or an EEPROM. The storage unit  22  stores various programs to be executed by the processing unit  21  and various types of data required for processing performed by the processing unit  21 . In the present embodiment, the storage unit  22  stores the program  22   a  to be executed by the processing unit  21 . 
     Note that the program  22   a  may be written in the storage unit  22  at the manufacturing stage of the roadside wireless communication device  2 , for example, a program distributed by a remote server or the like, for example, may be acquired by the roadside wireless communication device  2  through communication, the roadside wireless communication device  2  may read out a program recorded in the recording medium  98  such as a memory card or an optical disk, for example, and store the program in the storage unit  22 , and a writing device may read out a program recorded in the recording medium  98  and write it in the storage unit  22  of the roadside wireless communication device  2 . The program  22   a  may be provided in a mode of distribution via a network, or may be provided in a mode recorded in the recording medium  98 . 
     The wireless communication unit  23  performs wireless communication with the in-vehicle wireless communication device  1  provided in the vehicle  101 . The wireless communication unit  23  transmits data to the in-vehicle wireless communication device  1  by outputting a signal obtained by modulating the data for transmission provided from the processing unit  21  from an antenna (not shown), and receives the data from the in-vehicle wireless communication device  1  by demodulating the signal received by the antenna, and provides the received data to the processing unit  21 . 
     The roadside wireless communication device  2  according to the present embodiment is connected to various sensors  8  installed around the intersection where the traffic signal  102  is installed, via a communication line, a signal line, or the like. As the sensor  8 , for example, various things can be adopted, such as a camera that images an intersection, or a sensor that detects a vehicle, a pedestrian, or the like present near the intersection. The wired communication unit  24  transmits and receives data to and from these sensors  8  via a communication line, a signal line, or the like. The wired communication unit  24  receives the data transmitted from the sensor  8 , provides it to the processing unit  21 , and transmits the data provided from the processing unit  21  to the sensor  8 . The wired communication unit  24  may transmit and receive data to and from the sensor  8  based on any kind of communication standard. Also, the wired communication unit  24  may communicate with the sensor  8  via, for example, a wide area network such as the Internet, and may communicate with another roadside wireless communication device  2  provided in another traffic signal  102 . Note that in the present embodiment, it is assumed that the roadside wireless communication device  2  performs wired communication with the sensor  8 , but there is no limitation to this, and the roadside wireless communication device  2  may perform wireless communication with the sensor  8 . 
     Also, in the roadside wireless communication device  2  according to the present embodiment, due to the processing unit  21  reading out and executing the program  22   a  stored in the storage unit  22 , a communication amount determination unit  21   a , a wireless communication processing unit  21   b , a sensor information acquisition unit  21   c , a data size adjustment unit  21   d , and the like are realized in the processing unit  21  as software-like functional units. 
     The communication amount determination unit  21   a  performs processing for determining the communication amount of data transmitted and received wirelessly by the wireless communication unit  23 . The communication amount determination unit  21   a  can monitor the data transmitted and received by the wireless communication unit  23 , measure the amount of data transmitted and received in a predetermined period such as one second, and set the measured amount of data as the communication amount. Also, the communication amount determination unit  21   a  may, for example, perform the measurement for the predetermined period a plurality of times and set the average value as the communication amount. Also, the communication amount determination unit  21   a  may predict the future communication amount based on the measured past and present amounts of data, and may set the predicted amount of data as the communication amount. In this case, any kind of method may be adopted as the method for predicting the communication amount. 
     The wireless communication processing unit  21   b  performs processing relating to wireless communication with the in-vehicle wireless communication device  1  by the wireless communication unit  23 . The wireless communication processing unit  21   b  wirelessly transmits data to the in-vehicle wireless communication device  1  by generating data to be transmitted to the in-vehicle wireless communication device  1  and providing the data to the wireless communication unit  23 . The wireless communication processing unit  21   b  receives the data wirelessly transmitted from the in-vehicle wireless communication device  1  in the wireless communication unit  23 . 
     Also, in the present embodiment, the wireless communication processing unit  21   b  performs processing for transmitting information relating to the communication amount determined by the communication amount determination unit  21   a  to the in-vehicle wireless communication device  1  as communication amount information. The information included in the communication amount information may be, for example, the communication amount determined by the communication amount determination unit  21   a , or may be, for example, the free capacity of wireless communication calculated based on the communication amount determined by the communication amount determination unit  21   a . However, if the communication amount determined by the communication amount determination unit  21   a  is transmitted as the communication amount information, it is preferable to include the communication capacity of the wireless communication in the communication amount information. The free capacity of wireless communication can be calculated as the difference between the communication capacity of wireless communication and the communication amount determined by the communication amount determination unit  21   a . The communication amount information transmitted by the wireless communication processing unit  21   b  need only include information according to which the in-vehicle wireless communication device  1  can keep track of the free capacity of wireless communication. The communication capacity of wireless communication is determined at the design stage of the roadside wireless communication device  2 , and the value thereof is stored in the storage unit  22  or the like. 
     Also, in the present embodiment, the wireless communication processing unit  21   b  receives the communication amount information transmitted by the in-vehicle wireless communication device  1 . The communication amount information transmitted by the in-vehicle wireless communication device  1  is information relating to the communication amount of data transmission and reception via the in-vehicle network  4  in the vehicle  101 . The wireless communication processing unit  21   b  provides the received communication amount information to the data size adjustment unit  21   d . 
     The sensor information acquisition unit  21   c  performs processing for acquiring various types of information detected by the sensors  8  by performing communication by the wired communication unit  24  via a communication line, a signal line, or the like. The sensors  8  transmit, for example, an image obtained by imaging, or data on information relating to a vehicle or a pedestrian whose presence is detected, and the sensor information acquisition unit  21   c  acquires the information from the sensors  8  by receiving these pieces of data transmitted by the sensors  8  by the wired communication unit  24 . 
     The sensor information acquisition unit  21   c  provides the acquired information of the sensor  8  to the wireless communication processing unit  21   b , and the wireless communication processing unit  21   b  wirelessly transmits data including the provided information to the in-vehicle wireless communication device  1  mounted in the vehicle  101 . Also, if the wireless communication processing unit  21   b  receives a predetermined data acquisition request from the in-vehicle wireless communication device  1 , the wireless communication processing unit  21   b  provides the received acquisition request to the sensor information acquisition unit  21   c . The sensor information acquisition unit  21   c  acquires the information relating to the requested data from the sensor  8  and provides the acquired information to the wireless communication processing unit  21   b , and the wireless communication processing unit  21   b  wirelessly transmits the provided information of the sensor  8  to the in-vehicle wireless communication device  1  that is the request source. 
     Also, the wireless communication processing unit  21   b  transmits a request to acquire predetermined data to the in-vehicle wireless communication device  1 . For example, regarding a location that is a blind spot that cannot be imaged with a camera installed as a sensor  8  in the intersection, the roadside wireless communication device  2  may request transmission of image data imaged by the camera  5  to the in-vehicle wireless communication device  1  of the vehicle  101  that can carry out imaging of this blind spot. Also, for example, the roadside wireless communication device  2  may request the in-vehicle wireless communication device  1  to transmit various types of data such as the position information of the vehicle  101 , destination information set in a car navigation device, or the vehicle speed of the vehicle  101 . 
     The data size adjustment unit  21   d  performs processing for adjusting the size of data to be transmitted to the in-vehicle wireless communication device  1  based on the communication amount information received from the in-vehicle wireless communication device  1 . The data size adjustment unit  21   d  determines the free capacity of the in-vehicle network  4  of the vehicle  101  in which the in-vehicle wireless communication device  1  is mounted based on the communication amount information. If the size of the data to be transmitted to the in-vehicle wireless communication device  1  exceeds the free capacity based on the communication amount information, the data size adjustment unit  21   d  performs processing for reducing (compressing) the size of this data. For example, if the data to be transmitted is image data imaged by a camera, the data size adjustment unit  21   d  reduces the data size through a method such as reducing the resolution of the image data, reducing the frame rate, and changing from a color image to a monochrome image. Also, for example, the data size adjusting unit  21   d  may compress the data size using a coding technique that changes the information such that it is expressed with a smaller number of bits than the original expression. The data size compression performed by the data size adjustment unit  21   d  may be either lossless compression or lossy compression. The extent to which the data size adjustment unit  21   d  compresses the data size may be predetermined, for example, 80% or less of the free capacity, or the like, or the compression rate may be made variable based on, for example, a prediction of a future communication amount or the like. 
     Data Transmission Processing 
       FIG.  5    is a schematic diagram for describing data transmission processing performed in the wireless communication system according to the present embodiment. Note that in the following description, the device on the data transmitting side will be referred to as a “roadside wireless communication device  2 ”, and the device on the data receiving side will be referred to as an “in-vehicle wireless communication device 1”, but the same applies even if the reverse is true. In the example shown in the drawing, the transmission-side roadside wireless communication device  2  includes transmission data  1  with a small data size (a small data amount) and transmission data  2  with a large data size (a large data amount) as data to be transmitted to the in-vehicle wireless communication device  1  on the receiving side. Note that in  FIG.  5   , each piece of transmission data is shown with different hatching as a block having a size corresponding to the data amount. 
     The in-vehicle wireless communication device  1  on the receiving side determines the communication amount of the in-vehicle network  4  of the vehicle  101 , and calculates the free capacity based on the difference between the determined communication amount and the communication capacity of the in-vehicle network  4 . The in-vehicle wireless communication device  1  transmits the communication amount information including the information on the calculated free capacity (or communication capacity and communication amount) to the roadside wireless communication device  2 . Note that the determination of the communication amount and the transmission of the communication amount information by the in-vehicle wireless communication device  1  are repeatedly performed at a predetermined period. 
     In the illustrated example, if the roadside wireless communication device  2  transmits the transmission data  1  and the transmission data  2  to the in-vehicle wireless communication device  1 , the data size of the transmission data  2  is large and exceeds the free capacity of the in-vehicle network  4 . The roadside wireless communication device  2  that has received the communication amount information from the in-vehicle wireless communication device  1  keeps track of the communication status of the in-vehicle network  4  of the vehicle  101  to which the data is transmitted, and compresses the transmission data  2  having a large data size. At this time, the roadside wireless communication device  2  determines the compression rate of the transmission data  2  based on the received communication amount information so as to fit in the free capacity of the in-vehicle network  4 . The roadside wireless communication device  2  transmits the transmission data  1  and transmits the compressed transmission data  2  to the in-vehicle wireless communication device  1 . The in-vehicle wireless communication device  1  receives the transmission data  1  and the transmission data  2  transmitted from the roadside wireless communication device  2 , and transmits these pieces of data to the in-vehicle device in the vehicle  101  via the in-vehicle network  4 . 
     Note that the same also applies to the case where the device on the data transmitting side is the in-vehicle wireless communication device  1  and the device on the data receiving side is the roadside wireless communication device  2 . The roadside wireless communication device  2  repeatedly determines the communication amount related to wireless communication and transmits the communication amount information at a predetermined period. The in-vehicle wireless communication device  1  that has received the communication amount information from the roadside wireless communication device  2  compresses the transmission data according to the free capacity of the roadside wireless communication device  2  and transmits the compressed transmission data. 
       FIG.  6    is a schematic diagram for illustrating data transmission processing performed in the wireless communication system according to the present embodiment. The in-vehicle wireless communication device  1 , which is a device on the data receiving side, determines the communication amount of the in-vehicle network  4  of the vehicle  101 , and transmits the communication amount information including information such as the determined communication amount or the free capacity calculated based on the determined communication amount to the roadside wireless communication device  2 , which is the device on the data transmitting side. 
     The roadside wireless communication device  2  generates data to be transmitted to the in-vehicle wireless communication device  1 , and receives communication amount information transmitted from the in-vehicle wireless communication device  1 . The roadside wireless communication device  2  determines whether or not the transmission data needs to be compressed by, for example, comparing the free capacity of the in-vehicle network  4  and the data size of the transmission data based on the received communication amount information. At this time, the roadside wireless communication device  2  may determine the compression rate of the transmission data. If the roadside wireless communication device  2  determines that the transmission data needs to be compressed, the roadside wireless communication device  2  compresses the transmission data to adjust the data size, and transmits the compressed data to the in-vehicle wireless communication device  1 . Note that if it is determined that compression is not needed, the roadside wireless communication device  2  may transmit the data to the in-vehicle wireless communication device  1  without compressing the data. The in-vehicle wireless communication device  1  receives the data transmitted from the roadside wireless communication device  2 . 
       FIG.  7    is a flowchart showing a procedure of data reception processing performed by the in-vehicle wireless communication device  1  according to the present embodiment. The communication amount determination unit  11   a  of the processing unit  11  of the in-vehicle wireless communication device  1  according to the present embodiment determines the communication amount of the in-vehicle network  4  by monitoring the transmission and reception of data in the in-vehicle network  4  of the vehicle  101  (step S 1 ). The wireless communication processing unit  11   b  of the processing unit  11  generates communication amount information including information such as the communication amount determined in step S 1  or the free capacity calculated based on this communication amount, and wirelessly transmits the generated communication amount information to the roadside wireless communication device  2  (step S 2 ). 
     The wireless communication processing unit  11   b  determines whether or not data transmitted wirelessly from the roadside wireless communication device  2  has been received (step S 3 ). If the data has been received (S 3 : YES), the wireless communication processing unit  11   b  provides the received data to the in-vehicle communication processing unit  11   c , and the in-vehicle communication processing unit  11   c  relays this data to the in-vehicle devices of the vehicle  101  (step S 4 ) and returns the processing to step S 1 . If no data has been received (S 3 : NO), the processing unit  11  returns the processing to step S 1 . 
       FIG.  8    is a flowchart showing a procedure of data transmission processing performed by the roadside wireless communication device  2  according to the present embodiment. The processing unit  21  of the roadside wireless communication device  2  according to the present embodiment generates data to be transmitted to the in-vehicle wireless communication device  1  based on, for example, the detection result of the sensor  8  acquired by the sensor information acquisition unit  21   c  (step S 11 ). The wireless communication processing unit  21   b  of the processing unit  21  determines whether or not the communication amount information transmitted by the in-vehicle wireless communication device  1  has been received (step S 12 ). 
     If the communication amount information has been received (S 12 : YES), the wireless communication processing unit  21   b  determines whether or not the data size of the data generated in step S 1  exceeds the free capacity based on the communication amount information (step S 13 ). If the data size exceeds the free capacity (S 13 : YES), the data size adjustment unit  21   d  of the processing unit  21  adjusts the size of the data by compressing the data to be transmitted (step S 14 ). The wireless communication processing unit  21   b  transmits the size-adjusted data to the in-vehicle wireless communication device  1  (step S 15 ), and returns the processing to step S 11 . 
     If the communication amount information has not been received from the in-vehicle wireless communication device  1  (S 12 : NO), or if the data size of the data to be transmitted does not exceed the free capacity (S 13 : NO), the wireless communication processing unit  21   b  transmits the data generated in step S 11  to the in-vehicle wireless communication device  1  (step S 15 ) without adjusting the size, and returns the processing to step S 11 . 
       FIG.  9    is a flowchart showing a procedure of data reception processing performed by the roadside wireless communication device  2  according to the present embodiment. The communication amount determination unit  21   a  of the processing unit  21  of the roadside wireless communication device  2  according to the present embodiment determines the communication amount of the wireless communication by monitoring the wireless communication of the wireless communication unit  23  (step S 21 ). The wireless communication processing unit  21   b  of the processing unit  21  generates communication amount information including information such as the communication amount determined in step S 21  or the free capacity calculated based on this communication amount, and wirelessly transmits the generated communication amount information to the in-vehicle wireless communication device  1  (step S 22 ). 
     The wireless communication processing unit  21   b  determines whether or not the data transmitted wirelessly from the in-vehicle wireless communication device  1  has been received (step S 23 ). If the data has been received (S 23 : YES), the processing unit  21  performs data processing according to the received data (step S 24 ), and returns the processing to step S 21 . If no data has been received (S 23 : NO), the processing unit  21  returns the processing to step S 21 . 
       FIG.  10    is a flowchart showing a procedure of data transmission processing performed by the in-vehicle wireless communication device  1  according to the present embodiment. The processing unit  11  of the in-vehicle wireless communication device  1  according to the present embodiment generates data to be transmitted to the roadside wireless communication device  2  based on, for example, an image captured by the camera  5 , a processing result of the ECU  6 , or the like (step S 31 ). The wireless communication processing unit  11   b  of the processing unit  11  determines whether or not the communication amount information transmitted by the roadside wireless communication device  2  has been received (step S 32 ). 
     If the communication amount information has been received (S 32 : YES), the wireless communication processing unit  11   b  determines whether or not the data size of the data generated in step S 31  exceeds the free capacity based on the communication amount information (step S 33 ). If the data size exceeds the free capacity (S 33 : YES), the data size adjustment unit  11   d  of the processing unit  11  adjusts the size of the data by compressing the data to be transmitted (step S 34 ). The wireless communication processing unit  11   b  transmits the size-adjusted data to the roadside wireless communication device  2  (step S 35 ), and returns the processing to step S 31 . 
     If the traffic information has not been received from the roadside wireless communication device  2  (S 32 : NO), or if the data size of the data to be transmitted does not exceed the free capacity (S 33 : NO), the wireless communication processing unit  11   b  transmits the data generated in S 31  to the roadside wireless communication device  2  (step S 35 ) without adjusting the size, and returns the processing to step S 31 . 
     Modified Examples 
       FIG.  11    is a schematic diagram for illustrating data transmission processing performed in the wireless communication system according to a modified example. In the wireless communication system according to the modified example, the device on the data transmitting side compresses the data to be transmitted according to its own communication amount. Note that in Modified Example  1 , the device on the data transmitting side is referred to as the in-vehicle wireless communication device  1 , and the device on the data receiving side is referred to as the roadside wireless communication device  2 , but the same applies even if the reverse is true. The roadside wireless communication device  2 , which is a device on the data receiving side, specifies the type and the like of data required for its own processing, and transmits a request for this data to the in-vehicle wireless communication device  1 . The in-vehicle wireless communication device  1 , which is a device on the data transmitting side, attempts to generate data corresponding to a request from the roadside wireless communication device  2 . 
     For example, if the roadside wireless communication device  2  requests transmission of image data captured by the camera  5  by designating a resolution or frame rate and there is not enough free capacity left in the vehicle network  4  to transmit and receive this image data, there is a risk that image data cannot be transmitted from the camera  5  to the in-vehicle wireless communication device  1  via the in-vehicle network  4 . In view of this, the in-vehicle wireless communication device  1  according to the modified example controls the operation of the camera  5  so as to compress the size of the image data by reducing the resolution or the frame rate. The in-vehicle wireless communication device  1  acquires the compressed image data from the camera  5  via the in-vehicle network  4 , and transmits this image data to the roadside wireless communication device  2 . 
       FIG.  12    is a schematic diagram for illustrating data transmission processing performed in the wireless communication system according to the modified example. The roadside wireless communication device  2 , which is a device on the data receiving side, requests the in-vehicle wireless communication device  1  for the data needed for its own processing. The in-vehicle wireless communication device  1 , which is a device on the data transmitting side, attempts to generate data corresponding to the request from the roadside wireless communication device  2 . Here, the in-vehicle wireless communication device  1  determines the communication amount of the in-vehicle network  4 , compares the determined communication amount and the data size of the requested data, and determines whether or not the requested data needs to be compressed. 
     If it is determined that data compression is needed, in the example shown in  FIG.  12   , the in-vehicle wireless communication device  1  performs arbitration processing with the roadside wireless communication device  2  to obtain approval for compressing the data. In the arbitration processing, for example, the in-vehicle wireless communication device  1  transmits information such as the communication amount information and the data compression rate to the roadside wireless communication device  2 , and the roadside wireless communication device  2  notifies the in-vehicle wireless communication device  1  that the data compression is approved. Note that if approval is not obtained, the in-vehicle wireless communication device  1  does not compress the data, but the data cannot be transmitted due to this, and there is a possibility that there will be a lack of data transmitted from the in-vehicle wireless communication device  1  to the roadside wireless communication device  2  or the like. 
     If the approval of data compression is obtained through the arbitration processing, the in-vehicle wireless communication device  1  compresses the requested data and transmits the compressed data to the roadside wireless communication device  2 . The roadside wireless communication device  2  receives the data compressed by the in-vehicle wireless communication device  1  and uses it for its own processing. 
     Data Transmission Stop Processing 
       FIG.  13    is a schematic diagram for illustrating data transmission stop processing performed in the wireless communication system according to the present embodiment. Note that in the following description, the device on the data transmitting side will be referred to as a “roadside wireless communication device  2 ”, and the device on the data receiving side will be referred to as an “in-vehicle wireless communication device  1 ”, but the same applies even if the reverse is true. In the wireless communication system according to the present embodiment, one in-vehicle wireless communication device  1  can communicate wirelessly with a plurality of roadside wireless communication devices  2  in some cases, depending on the position of the vehicle  101 , the position of the traffic signal  102 , the radio wave condition of the surrounding area, and the like. In such a situation, if data is transmitted from a plurality of roadside wireless communication devices  2  to one in-vehicle wireless communication device  1 , the amount of data received by the in-vehicle wireless communication device  1  increases, and there is a risk that the received data cannot be handled in the in-vehicle network  4 . 
     In view of this, in the wireless communication system according to the present embodiment, it is possible to give a command to stop data transmission from the device on the data receiving side to the device on the data transmitting side. The example shown in  FIG.  13    is a case where one in-vehicle wireless communication device  1  receives data from two roadside wireless communication devices  2 . The in-vehicle wireless communication device  1  determines the communication amount of the in-vehicle network  4 , and determines whether or not to give a stop command for data transmission, for example, depending on whether or not the communication amount exceeds a predetermined threshold value. 
     If it is determined that the communication amount exceeds the threshold value and the data transmission stop command is given, the in-vehicle wireless communication device  1  determines the priority level of the plurality of roadside wireless communication devices  2  capable of wireless communication. The in-vehicle wireless communication device  1  gives a data transmission stop command to the roadside wireless communication device  2  determined to have a low priority level. The low-priority-level roadside wireless communication device  2  stops the transmission of data to the in-vehicle wireless communication device  1  if a stop command has been given from the in-vehicle wireless communication device  1 . The high-priority-level roadside wireless communication device  2  to which the stop command has not been given continuously transmits data to the in-vehicle wireless communication device  1 . 
     Note that the in-vehicle wireless communication device  1  may determine the priority levels of the plurality of roadside wireless communication devices  2  according to, for example, the type of data transmitted by each roadside wireless communication device  2 , may determine the priority levels of the plurality of roadside wireless communication devices  2  according to, for example, the positional relationship, the distance, and the like between the vehicle  101  and the roadside wireless communication device  2 , or may determine the priority level by a criterion other than these. The in-vehicle wireless communication device  1  may determine the priority levels of the plurality of roadside wireless communication devices  2  through any method. 
     Also, in this example, two roadside wireless communication devices  2  transmit data to one in-vehicle wireless communication device  1 , but three or more roadside wireless communication devices  2  may also transmit data to one in-vehicle wireless communication device  1 . In this case, the in-vehicle wireless communication device  1  assigns priority levels from first priority to third priority to the three or more roadside wireless communication devices  2 , and for example, gives a data transmission stop command to the one roadside wireless communication device  2  having the lowest priority level, or gives data transmission stop commands to the two roadside wireless communication devices  2  with the lower priority levels. The in-vehicle wireless communication device  1  may determine how many of the plurality of roadside wireless communication devices  2  are to be given a stop command according to, for example, the communication amount of the in-vehicle network  4 , or based on other factors. Also, the in-vehicle wireless communication device  1  may have a configuration capable of giving a command to cancel the transmission stop and resume the data transmission to the roadside wireless communication device  2  to which the data transmission stop command has been given. 
     Also, similarly to the case where one roadside wireless communication device  2  is capable of wireless communication with a plurality of in-vehicle wireless communication devices  1 , the roadside wireless communication device  2  can determine the amount of communication and the priority levels, and can give a data transmission stop command to the in-vehicle wireless communication device  1 . 
     Also, regarding a case where one roadside wireless communication device  2  is capable of wireless communication with a plurality of in-vehicle wireless communication devices  1 , the roadside wireless communication device  2  may determine the communication amount and the priority levels, and may stop data transmission to the in-vehicle wireless communication devices  1 . For example, the closer an in-vehicle wireless communication device  1  of a vehicle is located to the center of the intersection where the roadside wireless communication device  2  is installed, the higher its priority level is. By stopping the data transmission to the in-vehicle wireless communication device  1  of a low-priority-level vehicle located far from the intersection, the increase in the amount of data transmitted and received between the road and the vehicle is suppressed, and it is possible to continue the data transmission from the roadside wireless communication device  2  to the in-vehicle wireless communication device of the vehicle entering the intersection. Also, as another method for setting the priority levels, the priority level may be set higher for an in-vehicle wireless communication device  1  of a vehicle having a higher vehicle speed. By stopping the data transmission to the in-vehicle wireless communication device  1  of the low-speed vehicle, the increase in the amount of data transmitted and received between the road and the vehicle can be suppressed, and it is possible to continue data transmission from the roadside wireless communication device  2  to the in-vehicle wireless communication device of the high-speed vehicle. 
     Also, both the above-mentioned data transmission processing and the data transmission stop processing may be performed by one device. For example, the in-vehicle wireless communication device  1  can give a data transmission stop command to the roadside wireless communication device  2  having a low priority level, can transmit communication amount information to the roadside wireless communication device  2  having a high priority level, and can receive data with a compressed data size. 
       FIG.  14    is a flowchart showing a procedure of data transmission stop processing performed by the in-vehicle wireless communication device  1  according to the present embodiment. The communication amount determination unit  11   a  of the processing unit  11  of the in-vehicle wireless communication device  1  according to the present embodiment determines the communication amount of the in-vehicle network  4  (step S 41 ). The processing unit  11  determines whether or not the communication amount determined in step S 41  exceeds a predetermined threshold value (step S 42 ). If the communication amount does not exceed the threshold value (S 42 : NO), the processing unit  11  proceeds to step S 45 . 
     If the communication amount exceeds the threshold value (S 42 : YES), the priority level determination unit  11   e  of the processing unit  11  determines the priority levels of the plurality of roadside wireless communication devices  2  capable of wireless communication at that time (step S 43 ). The stop request unit  11   f  of the processing unit  11  gives a data transmission stop command to the roadside wireless communication device  2  having a low priority level based on the priority levels determined in step S 43  (step S 44 ), and advances the processing to step S 45 . 
     The wireless communication processing unit  11   b  of the processing unit  11  determines whether or not the data transmitted wirelessly from the roadside wireless communication device  2  has been received (step S 45 ). If the data has been received (S 45 : YES), the wireless communication processing unit  11   b  performs data processing such as relaying the received data to the in-vehicle device (step S 46 ), and returns the processing to step S 41 . If no data has been received (S 45 : NO), the processing unit  11  returns the processing to step S 41 . 
       FIG.  15    is a flowchart showing a procedure of data transmission stop processing performed by the roadside wireless communication device  2  according to the present embodiment. The wireless communication processing unit  21   b  of the processing unit  21  of the roadside wireless communication device  2  according to the present embodiment determines whether or not a data transmission stop command has been received from the in-vehicle wireless communication device  1  (step S 51 ). If the stop command has not been received (S 51 : NO), the wireless communication processing unit  21   b  transmits data to the in-vehicle wireless communication device  1  (step S 52 ), and returns the processing to step S 51 . If the stop command has been received (S 51 : YES), the wireless communication processing unit  21   b  stops the data transmission to the in-vehicle wireless communication device  1 , which is the transmission source of the stop command (step S 53 ), and ends the processing. 
     Note that the processing performed in the case where the command to stop the data transmission from the in-vehicle wireless communication device  1  to the roadside wireless communication device  2  is given from the roadside wireless communication device  2  to the in-vehicle wireless communication device  1  is not shown in the illustration of the flowchart. 
       FIG.  16    is a schematic diagram for illustrating the data transmission stop processing performed in the wireless communication system according to the present embodiment.  FIG.  16    shows an example of a case in which, if one in-vehicle wireless communication device  1  transmits data to a plurality of roadside wireless communication devices  2 , the in-vehicle wireless communication device  1  itself stops data transmission to a low-priority-level roadside wireless communication device  2 . Note that in the following, the device on the data transmitting side will be referred to as an in-vehicle wireless communication device  1 , and the device on the data receiving side will be referred to as a roadside wireless communication device  2 , but the same applies even if the reverse is true. In the wireless communication system according to the present embodiment, one in-vehicle wireless communication device  1  can communicate wirelessly with a plurality of roadside wireless communication devices  2  in some cases, depending on the position of the vehicle  101 , the position of the traffic signal  102 , the radio wave condition of the surrounding area, and the like. In such a situation, if a request for data transmission from a plurality of roadside wireless communication devices  2  to one in-vehicle wireless communication device  1  is given, there is a risk that the requested data cannot be handled in the in-vehicle network  4  of the vehicle  101  in which the in-vehicle wireless communication device  1  is mounted. 
     In view of this, in the wireless communication system according to the present embodiment, if a data request is given from a plurality of devices on the data receiving side to the device on the data transmitting side, the device on the transmitting side can stop transmission of the data according to the priority level of the device on the receiving side. In the example shown in  FIG.  16   , a data request is first given from one roadside wireless communication device  2  to the in-vehicle wireless communication device  1 . Upon receiving the data request, the in-vehicle wireless communication device  1  generates the requested data and transmits the generated data to the roadside wireless communication device  2  that is the request source. The roadside wireless communication device  2  that is the request source can receive the data transmitted by the in-vehicle wireless communication device  1  in response to the request. 
     Thereafter, if a data request is given from another roadside wireless communication device  2  to the in-vehicle wireless communication device  1 , the in-vehicle wireless communication device  1  is given a data request from a plurality of roadside wireless communication devices  2 , and therefore the in-vehicle wireless communication device  1  determines the communication amount of the in-vehicle network  4 . The in-vehicle wireless communication device  1  determines whether or not to stop data transmission, for example, depending on whether or not the communication amount of the in-vehicle network  4  exceeds the threshold value. If it has been determined that the communication amount exceeds the threshold value and the data transmission is to be stopped, the in-vehicle wireless communication device  1  determines the priority levels of the plurality of roadside wireless communication devices  2  that requested the data. The in-vehicle wireless communication device  1  stops data transmission to the roadside wireless communication device  2  determined to have a low priority level. As a result, the low-priority-level roadside wireless communication device  2  cannot receive the data from the in-vehicle wireless communication device  1 . The in-vehicle wireless communication device  1  generates the requested data and transmits the generated data to the roadside wireless communication device  2  determined to have a high priority level. The high-priority-level roadside wireless communication device  2  can receive data transmitted from the in-vehicle wireless communication device  1 . 
     The in-vehicle wireless communication device  1  may determine the priority levels of the plurality of roadside wireless communication devices  2  according to, for example, the type of data to be transmitted to each roadside wireless communication device  2 , may determine the priority levels according to, for example, the positional relationship, the distance, or the like between the vehicle  101  and the roadside wireless communication device  2 , and may determine the priority levels according to a criterion other than these. The in-vehicle wireless communication device  1  may determine the priority levels of the plurality of roadside wireless communication devices  2  through any method. 
     Also, in this example, although it was assumed that one in-vehicle wireless communication device  1  transmits data to two roadside wireless communication devices  2 , one in-vehicle wireless communication device  1  may also transmit data to three or more roadside wireless communication devices  2 . In this case, the in-vehicle wireless communication device  1  assigns priority levels from first priority to third priority to the three or more roadside wireless communication devices  2 , and for example, stops data transmission to the one roadside wireless communication device  2  having the lowest priority level, or stops data transmission to the two roadside wireless communication devices  2  with the lower priority levels. The in-vehicle wireless communication device  1  may also determine how many of the plurality of roadside wireless communication devices  2  to stop data transmission for according to, for example, the communication amount of the in-vehicle network  4 , or based on other factors. Also, the in-vehicle wireless communication device  1  may have a configuration capable of canceling the transmission stop and resuming the data transmission with respect to the roadside wireless communication device  2  that has stopped the data transmission. 
     Also, similarly to the case where one roadside wireless communication device  2  transmits data to a plurality of in-vehicle wireless communication devices  1 , the roadside wireless communication device  2  can determine the communication amount and the priority levels, and stop data transmission to the in-vehicle wireless communication device  1 . 
       FIG.  17    is a flowchart showing a procedure of data transmission stop processing performed by the in-vehicle wireless communication device  1  according to the present embodiment. The wireless communication processing unit  11   b  of the processing unit  11  of the in-vehicle wireless communication device  1  according to the present embodiment determines whether or not a data request has been given from the roadside wireless communication device  2  (step S 61 ). If no data request has been given (S 61 : NO), the wireless communication processing unit  11   b  waits until the data request is given. 
     If a data request has been given from the roadside wireless communication device  2  (S 61 : YES), the communication amount determination unit  11   a  of the processing unit  11  determines the communication amount of the in-vehicle network  4  (step S 62 ). The processing unit  11  determines whether or not the communication amount determined in step S 62  exceeds a predetermined threshold value (step S 63 ). If the communication amount does not exceed the threshold value (S 63 : NO), the processing unit  11  advances the processing to step S 66 . 
     If the communication amount exceeds the threshold value (S 63 : YES), the priority level determination unit  11   e  of the processing unit  11  determines the priority level of the plurality of roadside wireless communication devices  2  that are data request sources at that time (step S 64 ). Based on the priority levels determined in step S 64 , the processing unit  11  stops data transmission to the roadside wireless communication device  2  having a lower priority level (step S 65 ), and advances the processing to step S 66 . 
     Thereafter, the wireless communication processing unit  11   b  of the processing unit  11  transmits the data requested from the roadside wireless communication device  2  to the roadside wireless communication device  2  that is the request source (step S 66 ), and returns the processing to step S 61 . 
     Summary 
     The in-vehicle wireless communication device  1  according to the present embodiment having the above configuration determines the communication amount in the in-vehicle network  4  of the vehicle  101 . The in-vehicle wireless communication device  1  wirelessly transmits information relating to the determined communication amount to the roadside wireless communication device  2  provided outside the vehicle  101  as communication amount information. As a result, the roadside wireless communication device  2  can keep track of and predict the communication status in the in-vehicle network  4  of the vehicle  101  to which data is to be transmitted based on the communication amount information from the in-vehicle wireless communication device  1  and the like, and can compress the data size to, for example, a size suitable for the free capacity of the communication of the in-vehicle network  4  or the like, and transmit the result to the in-vehicle wireless communication device  1 . The in-vehicle wireless communication device  1  can receive data transmitted from the roadside wireless communication device  2  at a size corresponding to the transmitted communication amount information, and can be used for processing in the vehicle  101 . Due to the in-vehicle wireless communication device  1  transmitting the communication amount information, the roadside wireless communication device  2  can transmit data of an appropriate size. 
     Also, the roadside wireless communication device  2  determines the communication amount of wireless communication performed with one or a plurality of vehicles  101 , and transmits the communication amount information relating to the determined communication amount to the in-vehicle wireless communication device  1 . The in-vehicle wireless communication device  1  that has received the communication amount information from the roadside wireless communication device  2  adjusts the data size by, for example, compressing the data size to a size suitable for the free capacity of the wireless communication of the roadside wireless communication device  2 , and transmits the data with the adjusted size to the roadside wireless communication device  2 . The roadside wireless communication device  2  can receive the data transmitted from the in-vehicle wireless communication device  1  at a size corresponding to the transmitted communication amount information and use the data for its own processing. Due to the roadside wireless communication device  2  transmitting the communication amount information, the in-vehicle wireless communication device  1  can transmit data of an appropriate size. 
     Also, the in-vehicle wireless communication device  1  receives a data request from the roadside wireless communication device  2 , adjusts the size of the data according to the request, and transmits the resulting data to the roadside wireless communication device  2 . As a result, the roadside wireless communication device  2  can request the in-vehicle wireless communication device  1  for the data necessary for its own processing, and can receive the data corresponding to the request at an appropriate data size. 
     Also, the in-vehicle wireless communication device  1  requests the stop of data transmission to the roadside wireless communication device  2  according to the determined communication amount of the in-vehicle network  4 . As a result, the in-vehicle wireless communication device  1  can be expected to prevent data of an amount that cannot be handled in the in-vehicle network  4  from being transmitted from the roadside wireless communication device  2 . 
     Also, if there are a plurality of roadside wireless communication device  2  that can perform wireless communication, the in-vehicle wireless communication device  1  determines the priority levels of the plurality of roadside wireless communication devices  2 , and requests stopping of data transmission to the roadside wireless communication device  2  that was determined to have a low priority level. As a result, it can be expected that the in-vehicle wireless communication device  1  will reliably receive the data transmitted by the high-priority-level roadside wireless communication device  2 , and suppress an increase in the communication amount due to the data transmitted by the low-priority-level roadside wireless communication device  2 . 
     Each device in a wireless communication system includes a computer including a microprocessor, ROM, RAM, and the like. The computation processing devices such as microprocessors may respectively read out and execute computer programs including some or all of the steps of the sequence charts or flowcharts, such as  FIGS.  6  to  10  and  12  to  17   , from storage units such as a ROM and RAM. The computer programs of this plurality of devices can be respectively installed from an external server device or the like. Also, the computer programs of this plurality of devices are respectively distributed in a state of being stored in a recording medium such as a CD-ROM, a DVD-ROM, or a semiconductor memory. 
     The embodiments disclosed herein are to be considered exemplary in all respects and not limiting. The scope of the present disclosure is expressed not by the above-described meaning but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.