Communication system, communication method, roadside device, and on-board equipment

Abstract

This communication system comprises: a roadside device that transmits a response request signal and receives a response signal; and on-board equipment that transmits the response signal in response to the response request signal received from the roadside device. The roadside device transmits, as the response request signal, a first response request signal including information defining a plurality of regions set in the communication area, an existing vehicle list recording, as existing vehicles for each region, vehicles identified in terms of located region from the received response signal, information indicating a communicable time for each region of the existing vehicles, and information indicating a communicable time for each region of newly entered vehicles newly entering the communication area. The on-board equipment, if a host vehicle is included in the existing vehicle list, transmits the response signal within the communicable time of the existing vehicles allocated to the region in which the host vehicle is located and, if the host vehicle is not included in the existing vehicle list, transmits the response signal within the communicable time of the newly entered vehicles allocated to the region in which the host vehicle is located.

Description

Communication systems, communication methods, roadside units, and in-vehicle units

[0001] This disclosure relates to a communication system, a communication method, a roadside unit, and an in-vehicle unit.

[0002] Patent Document 1 describes a communication system that uses the same carrier frequency for both vehicle-to-vehicle communication and vehicle-to-infrastructure communication, and employs a carrier-sensing multiplex access / collision avoidance method as the access method, and provides a configuration to prevent vehicle-to-infrastructure communication from being hindered by vehicle-to-vehicle communication. In the communication system described in Patent Document 1, if an in-vehicle communication terminal (hereinafter referred to as an in-vehicle device) is located within the transmission prohibition area of ​​a roadside unit, the transmission of data for vehicle-to-vehicle communication is stopped. In this case, the determination of whether or not an in-vehicle device is located within the transmission prohibition area is made by the in-vehicle device based on the reception level of the signal received from the roadside unit, or based on the device's own location information and area information indicating the range in which the transmission prohibition area is set. The transmission prohibition area is, for example, within a certain distance centered on the installation location of the roadside unit, and is set according to the distance over which the signal transmitted by the in-vehicle device can reach while maintaining a decodeable level (or carrier sense level). In addition, in vehicle-to-infrastructure communication, broadcast communication or unicast communication is performed between the in-vehicle device and the in-vehicle device. Furthermore, in broadcast communication, for example, response request data is transmitted to all in-vehicle devices within the wireless communication area (the range to which the transmitted signal can reach).

[0003] Japanese Patent Publication No. 2015-207940

[0004] In the communication system described in Patent Document 1, when the range in which vehicle-to-roadside communication is performed is set such that, for example, the radius centered on the installation position of the roadside unit is equal to the distance at which the signal transmitted by the in-vehicle device reaches while maintaining a detectable level, there is a problem that a hidden terminal problem may occur. The hidden terminal problem is a problem in wireless communication where two transmitting terminals (in-vehicle devices) simultaneously transmit signals to a receiving terminal (roadside unit) located between them, causing signal collisions and the receiving terminal (roadside unit) being unable to receive the signals. This occurs because the transmitting terminals (in-vehicle devices) cannot detect each other's transmitted signals.

[0005] The present disclosure has been made to solve the above problems, and an object thereof is to provide a communication system, a communication method, a roadside unit, and an in-vehicle device capable of reducing collisions between signals transmitted by a plurality of in-vehicle devices.

[0006] According to one aspect of the present disclosure, a communication system includes a roadside unit that transmits a response request signal toward a communication area and receives a response signal to the response request signal, and an in-vehicle device that transmits the response signal including the position information of the host vehicle on which the device is mounted in response to the response request signal received from the roadside unit. The roadside unit transmits, as the response request signal, a first response request signal including information defining a plurality of areas set in the communication area, an existing vehicle list in which vehicles identified as being located in which area are recorded for each area as existing vehicles from the received response signals, information indicating the communication available time for each area of the existing vehicles, and information indicating the communication available time for each area of newly entered vehicles that have newly entered the communication area. The in-vehicle device transmits the response signal within the communication available time of the existing vehicle assigned to the area where the host vehicle is located when the host vehicle is included in the existing vehicle list, and transmits the response signal within the communication available time of the newly entered vehicle assigned to the area where the host vehicle is located when the host vehicle is not included in the existing vehicle list.

[0007] According to one aspect of the present disclosure, a communication method comprising the steps of: a roadside unit transmitting a response request signal toward a communication area; an in-vehicle unit transmitting a response signal including location information of the vehicle on which the unit is mounted in response to the response request signal received from the roadside unit; and the roadside unit receiving a response signal for the response request signal, wherein in the step of transmitting the response request signal, the roadside unit includes, as the response request signal, information defining a plurality of regions set within the communication area, and a vehicle identified from the received response signal as being located in one of those regions. The in-vehicle unit transmits a first response request signal that includes an existing vehicle list recorded for each area as an existing vehicle, information indicating the communication time available for each area of ​​the existing vehicle, and information indicating the communication time available for each area of ​​a newly entering vehicle that has just entered the communication area. In the step of transmitting the response signal, the in-vehicle unit transmits the response signal within the communication time available for the existing vehicle allocated to the area where the vehicle is located if the vehicle is included in the existing vehicle list, and transmits the response signal within the communication time available for the newly entering vehicle allocated to the area where the vehicle is located if the vehicle is not included in the existing vehicle list.

[0008] According to one aspect of the present disclosure, a roadside unit transmits a response request signal to a communication area and receives a response signal to the response request signal, the roadside unit transmits a first response request signal which includes, as the response request signal, information defining a plurality of areas set up within the communication area, an existing vehicle list recording each vehicle as an existing vehicle based on the received response signal, information indicating the communication time for each area of ​​the existing vehicles, and information indicating the communication time for each area of ​​a newly entering vehicle that has just entered the communication area.

[0009] According to one aspect of the present disclosure, an in-vehicle unit transmits a response signal including location information of the vehicle on which the unit is installed in response to a response request signal received from a roadside unit, and receives a first response request signal which includes information defining a plurality of areas set within the communication area of ​​the roadside unit, an existing vehicle list recording each area as an existing vehicle where the vehicle identified as being located in each area from the received response signal, information indicating the communication time available for each area of ​​the existing vehicle, and information indicating the communication time available for each area of ​​a newly entering vehicle that has newly entered the communication area, and transmits the response signal within the communication time available for the existing vehicle allocated to the area where the vehicle is located if the vehicle is included in the existing vehicle list, and transmits the response signal within the communication time available for the newly entering vehicle allocated to the area where the vehicle is located if the vehicle is not included in the existing vehicle list.

[0010] According to the above embodiment, collisions between signals transmitted by multiple in-vehicle devices can be reduced.

[0011] This is a block diagram showing an example configuration of the communication system according to the first embodiment. This is a schematic plan view showing an example installation of the communication system according to the first embodiment. This is a schematic plan view showing an example installation of the communication system according to the first embodiment. This is a timing chart showing an example operation of the communication system according to the first embodiment. This is a schematic diagram showing an example configuration of the response request signal according to the first embodiment. This is a schematic diagram showing an example configuration of the response signal according to the first embodiment. This is a timing chart showing an example operation of the communication system according to the first embodiment. This is a flowchart showing an example operation of the roadside unit according to the first embodiment. This is a flowchart showing an example operation of the roadside unit according to the first embodiment. This is a flowchart showing an example operation of the in-vehicle unit according to the first embodiment. This is a diagram showing an example of the division of the communication time of the communication system according to the second embodiment. This is a timing chart showing an example operation of the communication system according to the second embodiment. This is a schematic diagram showing an example configuration of the response request signal according to the second embodiment. This is a first flowchart showing an example operation of the roadside unit according to the second embodiment. This is a second flowchart showing an example operation of the roadside unit according to the second embodiment. This is a third flowchart showing an example operation of the roadside unit according to the second embodiment. This is a fourth flowchart showing an example operation of the roadside unit according to the second embodiment. This is a fifth flowchart showing an example of operation of a roadside unit according to the second embodiment. This is a flowchart showing an example of operation of an in-vehicle unit according to the second embodiment. This is a schematic block diagram showing the configuration of a computer according to at least one embodiment.

[0012] <First Embodiment> Hereinafter, a communication system, communication method, roadside unit, and in-vehicle unit according to the first embodiment of this disclosure will be described with reference to Figures 1 to 10. Figure 1 is a block diagram showing an example configuration of the communication system according to the first embodiment. Figures 2 and 3 are schematic plan views showing an example installation of the communication system according to the first embodiment. Figures 4 and 7 are timing charts showing an example operation of the communication system according to the first embodiment. Figure 5 is a schematic diagram showing an example configuration of a response request signal according to the first embodiment. Figure 6 is a schematic diagram showing an example configuration of a response signal according to the first embodiment. Figures 8 and 9 are flowcharts showing an example operation of a roadside unit according to the first embodiment. Figure 10 is a flowchart showing an example operation of an in-vehicle unit according to the first embodiment. In each figure, the same or corresponding components are used with the same reference numerals and explanations are omitted as appropriate.

[0013] (Configuration of the communication system) As shown in Figure 1, the communication system 1 according to the embodiment of this disclosure comprises, for example, one roadside unit 2 and a plurality of on-board units 3. The roadside unit 2 transmits and receives predetermined information, for example, by DSRC (Dedicated Short-Range Communications), between itself and each on-board unit 3 mounted on a plurality of vehicles 4a to 4m located on roads 10a or 10b intersecting at the intersection 11, as shown in Figure 2. Vehicles 4a to 4m are collectively referred to as vehicle 4. There may also be multiple roadside units 2 for a single intersection 11. Furthermore, the roadside unit 2 may be installed to communicate wirelessly with each on-board unit 3 mounted on one or more vehicles 4 located outside the vicinity (surroundings) of the intersection 11 (for example, on a single road).

[0014] As shown in Figure 1, the roadside unit 2 comprises a control unit 21, a communication unit 22, and a storage unit 23 as a functional block composed of hardware, a combination of hardware and software, etc. The control unit 21 controls each part within the roadside unit 2 and, for example, transmits and receives predetermined information with a plurality of in-vehicle units 3 via the communication unit 22, or transmits and receives predetermined information with an external server (not shown) using a wide-area communication network, etc. The communication unit 22 is equipped with an antenna 221 and performs wireless communication with a plurality of in-vehicle units 3. The storage unit 23 stores identification information of the roadside unit 2 (hereinafter also referred to as the unit itself), location information of the roadside unit 2, information indicating an area described later, etc., and stores information received from the in-vehicle units 3, for example, in response to instructions from the control unit 21.

[0015] The on-board unit 3 is a device mounted on the vehicle 4 that has at least the function of performing vehicle-to-infrastructure wireless communication with the roadside unit 2. The on-board unit 3 may also have the function of performing vehicle-to-vehicle wireless communication with other on-board units 3. Furthermore, the on-board unit 3 may be configured as part of other electronic control devices mounted on the vehicle 4, or may function by utilizing a part of the configuration of other electronic control devices.

[0016] As shown in Figure 1, the in-vehicle unit 3 comprises a control unit 31, a location information acquisition unit 32, a communication unit 33, and a storage unit 34 as functional blocks consisting of hardware, a combination of hardware and software, etc. The control unit 31 controls each part within the in-vehicle unit 3, and for example, transmits and receives predetermined information with the roadside unit 2 via the communication unit 33.

[0017] The position information acquisition unit 32 is equipped with, for example, a GNSS (Global Navigation Satellite System) receiver and acquires position information (latitude, longitude, altitude, etc.) using GNSS. However, the position information acquisition unit 32 may acquire position based on detection signals from a vehicle speed sensor, an angular velocity sensor, or received signals from a wide-area communication network, instead of (or in addition to) using GNSS.

[0018] The communication unit 33 is equipped with an antenna 331 and performs wireless communication with the roadside unit 2, etc. The communication unit 33 also has a wireless signal collision avoidance function 332. Here, the collision avoidance function 332 is a function that detects signals transmitted by other in-vehicle units 3 and avoids collisions between response signals transmitted by the in-vehicle unit 3 to the roadside unit 2, which will be described later. The collision avoidance function 332 can be implemented, for example, by the well-known CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) protocol. CSMA / CA is used as a protocol for the data link layer (or the MAC (Medium Access Control) layer, which is part of the data link layer) of the OSI (Open Systems Interconnection) reference model. In CSMA / CA, to avoid collisions of radio signals (frames, packets, etc.), when attempting to transmit a radio signal, the carrier (carrier wave) usage is monitored in advance. Transmission begins after a predetermined frame interval and a random amount of time, which vary depending on priority, if the medium is unused. On the other hand, if the medium is in use, it enters a waiting state and transmission is postponed until it becomes available.

[0019] The memory unit 23 stores identification information of the in-vehicle unit 3 (hereinafter also referred to as the unit itself), information such as the type of vehicle 4 on which the in-vehicle unit 3 is installed, location information for a predetermined period of time, and also stores information received from, for example, the roadside unit 2, other in-vehicle units 3, or an external server, in response to instructions from the control unit 31.

[0020] (Example of area setting for the communication system) In the communication system 1 of this embodiment, as shown in Figure 2, multiple areas 1 (CPA1) to 5 (CPA5) are set within the communication area 2CA of the roadside unit 2 (hereinafter also referred to as areas CPA1 to CPA5), and the roadside unit 2 performs wireless communication with the on-board units 3 located within each of areas CPA1 to CPA5 in a time-division manner. The communication area 2CA is the range in which the roadside unit 2 can perform wireless communication with the on-board units 3, the roadside unit 2 can receive wireless signals transmitted by each on-board unit 3 located within the communication area 2CA, and each on-board unit 3 located within the communication area 2CA can receive wireless signals transmitted by the roadside unit 2. In the example shown in Figure 2, the antenna 221 of the roadside unit 2 (or the entire roadside unit 2, etc.) is installed in the center (above) of the intersection 11.

[0021] Furthermore, the area CPA1, indicated by the downward-sloping diagonal shading, is a rectangular area centered on the antenna 211. Within this area CPA1, a vehicle 4l is located traveling on the road 10b from bottom to top.

[0022] Furthermore, the area CPA2, indicated by the upward-sloping diagonal shading, is a rectangular area set above the intersection 11 of road 10b. A vehicle 4m traveling from bottom to top on road 10b is located within this area CPA2.

[0023] Furthermore, the area CPA3, indicated by the upward-sloping diagonal shading, is a rectangular area set to the right of the intersection 11 on road 10a. Within this area CPA3 are vehicles 4a, 4b, 4c, and 4d traveling on road 10a from right to left, and vehicles 4e and 4f traveling on road 10a from left to right.

[0024] Furthermore, the area CPA4, indicated by the upward-sloping diagonal shading, is a rectangular area set below the intersection 11 of road 10b. Within this area CPA4, there are vehicles 4j traveling on road 10b from bottom to top and vehicles 4k traveling on road 10b from top to bottom.

[0025] Furthermore, the area CPA5, indicated by the upward-sloping diagonal shading, is a rectangular area set to the left of intersection 11 on road 10a. Within this area CPA5 are vehicle 4g ​​traveling from right to left on road 10a, and vehicles 4h and 4i traveling from left to right on road 10a.

[0026] In this embodiment, each region CPA1 to CPA5 is configured to detect signals transmitted by other in-vehicle units 3 within each region CPA1 to CPA5. For example, for an in-vehicle unit 3 of vehicle 4d located within region CPA3, all of the other in-vehicle units 3 of vehicles 4a to 4c and 4e to 4f located within region CPA3 are included within the communication area 4dCA of the in-vehicle unit 3 of vehicle 4d. Here, the communication area 4dCA is the range in which the in-vehicle unit 3 of vehicle 4d can communicate wirelessly with roadside units 2 or other in-vehicle units 3 located within the communication area 4dCA (or the range in which it can detect the carrier of a wireless signal transmitted by roadside units 2 or other in-vehicle units 3). Therefore, the in-vehicle unit 3 of vehicle 4d can detect wireless signals transmitted by the other in-vehicle units 3 of vehicles 4a to 4c and 4e to 4f located within region CPA3, and the collision avoidance function 332 can avoid collisions between wireless signals. On the other hand, for example, the onboard unit 3 of vehicle 4l located within area CPA1 is located outside communication area 4dCA, so the onboard unit 3 of vehicle 4d cannot detect the radio signal transmitted by the onboard unit 3 of vehicle 4l. If the onboard unit 3 of vehicle 4 located within area CPA1 and the onboard unit 3 of vehicle 4 located within area CPA3 were to transmit at the same time, there is a possibility of a collision between the transmitted signals. However, in this embodiment, since the time for transmission is set in time division for each area CPA1 to CPA5, the onboard unit 3 of vehicle 4 located within area CPA1 and the onboard unit 3 of vehicle 4 located within area CPA3 will not transmit radio signals at the same time. Therefore, for example, the possibility of a collision between a radio signal transmitted by the onboard unit 3 of vehicle 4 located within area CPA1 and a radio signal transmitted by the onboard unit 3 of vehicle 4 located within area CPA3 can be kept low.

[0027] Furthermore, it is desirable that each region CPA1 to CPA5 be configured to detect signals transmitted by other in-vehicle units 3 within a predetermined range from other regions CPA1 to CPA5 (excluding its own region) within each region CPA1 to CPA5. For example, as shown in Figure 3, the in-vehicle unit 3 of vehicle 4a is correctly located within region CPA3, but may be mistakenly identified as being located in region CPA1 due to errors in acquiring location information or the influence of driving speed. In this case, the in-vehicle unit 3 of vehicle 4a will transmit a radio signal within the communication time allocated to region CPA1. In this case, if the communication area 4aCA of the in-vehicle unit 3 of vehicle 4a does not include the entire region CPA1, there is a risk of collision between the radio signal transmitted by the in-vehicle unit 3 of vehicle 4a and the radio signal transmitted by another in-vehicle unit 3 located outside the communication area 4aCA within region CPA1. Therefore, in this embodiment, for example, within region CPA3, within a predetermined range CPA1A (in this example, a rectangular area where the length of each side is extended vertically and horizontally by a distance LA from region CPA1), it is set to be possible to detect signals transmitted by other in-vehicle devices 3 (for example, an in-vehicle device 3 in vehicle 4l) within other region CPA1. In this example, region CPA1 is set so that the communication area 4aCA of the in-vehicle device 3 of vehicle 4a located within range CPA1A in region CPA3 covers the entirety of region CPA1. However, unlike the examples shown in Figures 2 and 3, if a sufficient interval is set between each region to avoid the effects of false detection of location information, for example, it is not necessary to consider collisions of wireless signals with other regions.

[0028] (Example of wireless signals in a communication system) In this embodiment, as described above, for example, five regions CPA1 to CPA5 are set within the communication area 2CA of the roadside unit 2, and the roadside unit 2 performs wireless communication with the in-vehicle units 3 located within each region CPA1 to CPA5 in a time-division manner for each region CPA1 to CPA5. Figure 4 shows an example of the correspondence between the response request signal transmitted by the roadside unit 2 and the respective communication time T1a to T5a allocated to each region CPA1 to CPA5. The horizontal axis is the time axis. The in-vehicle units 3 located in each region CPA1 to CPA5 transmit a response signal to the response request signal within the respective communication time T1a to T5a allocated to each region CPA1 to CPA5.

[0029] The response request signal is a radio signal transmitted by the roadside unit 2 at a predetermined period T1, and is a broadcast signal that requests each on-board unit 3 to transmit a response signal. As shown in Figure 5, for example, the response request signal 50 includes information 51 that defines area 5 (CPA5) from area 1 (CPA1), information 52 that indicates the communication available time T1a of area 1 (CPA1), information 53 that indicates the communication available time T2a of area 2 (CPA2), information 54 that indicates the communication available time T3a of area 3 (CPA3), information 55 that indicates the communication available time T4a of area 4 (CPA4), and information 56 that indicates the communication available time T5a of area 5 (CPA5).

[0030] The information 51 defining areas 1 (CPA1) to 5 (CPA5) can be, for example, information indicating the latitude and longitude of multiple vertices of a rectangular area. Alternatively, if information (coordinate information, etc.) regarding each area of ​​the roadside unit 2 around the driving position is transmitted in advance to each on-board unit 3 using, for example, broadband communication, and stored, then the information 51 defining areas 1 (CPA1) to 5 (CPA5) can consist only of the identification information of the roadside unit 2.

[0031] The information 52 to 56 indicating the communication available time T1a to T5a for regions 1 (CPA1) to 5 (CPA5) can be as shown in Figure 4, with the end time of the response request signal at time T2 as the reference time, and the information indicating the time from the start time (hereinafter referred to as start time) T1s to T5s and the time from the end time (hereinafter referred to as end time) T1e to T5e for each communication available time T1a to T5a. In the example shown in Figure 4, a gap time Tg is provided between each communication available time T1a to T5a. The start time and end time for each communication available time T1a to T5a become the reference time plus the start times T1s to T5s and the end times T1e to T5e.

[0032] Figure 6 shows an example of a response signal transmitted by the in-vehicle unit 3 to the roadside unit 2. In the example shown in Figure 6, the response signal 60 includes in-vehicle unit identification information 61 and location information 62. However, Figure 6 shows only one example of the configuration of the response signal 60, and the response signal 60 may also include information indicating the vehicle type, direction of travel, and speed, in addition to (or omitting) the location information.

[0033] In the example shown in Figure 4, the lengths of the communication available time T1a to T5a are equal, but the lengths of the communication available time T1a to T5a may be different. The communication available time T1a to T5a may be varied, for example, according to the measured or estimated values ​​of the communication volume for each area CPA1 to CPA5. Figure 7 shows an example in which the lengths of the communication available time T1a to T5a are different. In the example shown in Figure 7, compared to the example shown in Figure 4, the lengths of the communication available time T1a, T2a, and T4a are set to two-thirds, the length of the communication available time T3a is doubled, and the length of the communication available time T5a is the same. The measured value of the communication volume can be, for example, the number of response signals received from each area CPA1 to CPA5 during a predetermined time (one or more times T1). The estimated value of the communication volume can be calculated (predicted), for example, based on the traffic volume expected based on past performance, and based on whether it is a day of the week or a public holiday, time of day, etc.

[0034] (Example of operation of roadside unit and on-board unit) Figure 8 shows the flow of processing performed by the roadside unit 2 in a period T1. In the processing shown in Figure 8, the roadside unit 2 (for example, the control unit 21) determines whether or not it is necessary to adjust the communication available time T1a to T5a (step S11). Here, if adjustment is necessary, for example, if the measured or estimated value of the communication volume has changed by a predetermined amount or more since the last adjustment was made. If adjustment is necessary (step S11: YES), the roadside unit 2 adjusts the communication available time T1a to T5a according to the amount of change in the communication volume, for example (step S12). If adjustment is not necessary (step S11: NO), or if adjustment has been made (step S12), the roadside unit 2 transmits a response request signal 50 that includes information defining a plurality of areas CPA1 to CPA5 set within its own communication area 2CA, and information indicating each communication available time T1a to T5a assigned to each area CPA1 to CPA5 (step S13), and terminates the processing shown in Figure 8.

[0035] Figure 9 shows the processing flow initiated by the roadside unit 2 when it receives a response signal 60 from the on-board unit 3. In the processing shown in Figure 9, the roadside unit 2 (for example, the control unit 21) executes processing for the response signal (step S21) and then terminates the processing shown in Figure 9. The processing for the response signal can include, for example, storing the information contained in the response signal in the storage unit 23 for a predetermined period, or calculating the traffic volume (number of vehicles per unit time) at predetermined intervals and transmitting it to an external server or the like.

[0036] Figure 10 also shows the processing flow that is initiated when the in-vehicle unit 3 receives a response request signal from the roadside unit 2. In the processing shown in Figure 10, the in-vehicle unit 3 (for example, the control unit 31) acquires the location information of the in-vehicle unit 3 using the location information acquisition unit 32 (step S31). Next, the in-vehicle unit 3 determines whether or not it is located in any of the regions (any of regions CPA1 to CPA5) based on the response request signal (step S32). If it is not located in any of the regions CPA1 to CPA5 (step S32: NO), the in-vehicle unit 3 terminates the processing shown in Figure 10.

[0037] If the in-vehicle unit 3 is located in any of the areas CPA1 to CPA5 (step S32: YES), the in-vehicle unit 3 repeatedly determines whether it is within the communication time set for that area (step S33: YES) until it is within the communication time set for that area (step S33: NO repeated). If it is within the communication time set for that area (step S33: YES), the in-vehicle unit 3 determines whether the communication time for that area has ended (step S34). If the communication time for that area has ended (step S34: YES), the in-vehicle unit 3 terminates the process shown in Figure 10 (however, the initial determination result in step S34 is NO). If the communication time for that area has not ended (step S34: NO), the in-vehicle unit 3 transmits a response signal via the communication unit 33 (step S35). In step S35, the communication unit 33 monitors whether other in-vehicle units 3 are transmitting a response signal using the collision avoidance function 332. If other in-vehicle units 3 are transmitting a response signal, the other in-vehicle units 3 terminate their transmission and wait for a predetermined time to elapse. If no other response signals are detected, the communication unit 33 transmits a response signal. Therefore, after starting the process for transmitting a response signal in step S35, the communication unit 33 determines at predetermined intervals whether the transmission of the response signal is complete or whether the standby state continues (step S36). If the standby state continues (step S36: standby), it determines again in step S34 whether the communication time for that area has ended (step S34). On the other hand, when the transmission of the response signal is complete (for example, when an ACK (ACKknowledgment; affirmative response) is sent from the roadside unit 2 to the response signal) (step S36: completion), the in-vehicle unit 3 terminates the process shown in Figure 10.

[0038] (Effects) The communication system 1 according to this embodiment includes a roadside unit 2 that transmits a response request signal at a predetermined interval, which includes information defining a plurality of areas set within the communication area of ​​the unit itself and information indicating each communication time allocated to each area, and also receives a response signal to the response request signal, and a plurality of in-vehicle units 3 that receive the response request signal, recognize the area where the unit is located, and transmit a response signal within the communication time allocated to the recognized area. The communication method according to this embodiment includes the steps of: the roadside unit 2 transmitting a response request signal at a predetermined interval, which includes information defining a plurality of areas set within the communication area of ​​the unit itself and information indicating each communication time allocated to each area; the in-vehicle unit 3 receiving the response request signal, recognizing the area where the unit is located, and transmitting a response signal within the communication time allocated to the recognized area; and the roadside unit 2 receiving the response signal. Furthermore, the roadside unit 2 according to this embodiment transmits a response request signal at a predetermined interval that includes information defining a plurality of areas set within its own communication area and information indicating the communication time allocated to each area. It also receives the response request signal, recognizes the area where it is located, and receives the response signals transmitted by one or more in-vehicle units within the communication time allocated to the recognized area. Furthermore, the in-vehicle unit 3 according to this embodiment receives a response request signal transmitted by a roadside unit that transmits a response request signal at a predetermined interval that includes information defining a plurality of areas set within its own communication area and information indicating the communication time allocated to each area. It recognizes the area where it is located and transmits a response signal within the communication time allocated to the recognized area.

[0039] Therefore, according to the communication system, communication method, roadside unit, and in-vehicle unit of this embodiment, collisions between signals transmitted by multiple in-vehicle units can be reduced.

[0040] In the above example, a configuration was described in which the roadside unit 2 adjusts the communication time T1a to T5a according to the change in communication volume, but this is not the only configuration. In other embodiments, the roadside unit 2 may dynamically change the distribution of the communication time T1a to T5a according to the maximum traffic volume of each area 1 to 5 (CPA1 to CPA5). For example, the length of the communication time Tia for area i (i=1 to 5) is proportional to the sum of the number of existing vehicles xi in area i and the maximum number of new vehicles yi (xi + yi). The number of existing vehicles xi in area i can be measured from the response signal received from the on-board unit 3. The maximum number of new vehicles yi is determined by assuming the case with the highest traffic volume and finding the maximum number of vehicles that can newly enter area i during the cycle T1. Specifically, the maximum number of new vehicles yi is calculated by multiplying the number of lanes Li in area i by a predetermined coefficient α (yi = α × Li). The coefficient α is set based on the traffic capacity per lane in region i. Traffic capacity is generally expressed as the number of passenger cars that can pass through per hour (e.g., 2200 cars / h). However, if there are many motorcycles, which occupy less lane space than passenger cars, the traffic capacity of region i is expected to be even larger. For this reason, the traffic capacity may be corrected by assuming that a certain proportion of passing vehicles are motorcycles, and the coefficient α may be set based on the corrected traffic capacity. For example, if the corrected traffic capacity is 2750 cars / h and the period T1 is 1 second, the coefficient α is 0.76.

[0041] <Second Embodiment> Next, a communication system, communication method, roadside unit, and in-vehicle unit according to the second embodiment of this disclosure will be described with reference to Figures 11 to 16. Components common to the first embodiment are denoted by the same reference numerals and their detailed descriptions are omitted.

[0042] Figure 11 is a diagram showing an example of the division of the communication time available for the communication system according to the second embodiment. Figure 12 is a timing chart showing an example of the operation of the communication system according to the second embodiment. Figure 13 is a schematic diagram showing an example of the configuration of a response request signal according to the second embodiment. Figures 14 and 15 are flowcharts showing an example of the operation of a roadside unit according to the second embodiment. Figure 16 is a flowchart showing an example of the operation of an in-vehicle unit according to the second embodiment.

[0043] (Example of a wireless signal in a communication system) As shown in FIG. 11, the roadside unit 2 of the present embodiment divides the communication cycle T1 into three parts: time I, time II, and time III, and further divides each of time I, time II, and time III into regions.

[0044] Time I is the communication available time allocated to "existing vehicles". An existing vehicle is a vehicle 4 equipped with an in-vehicle device 3 that exists within the communication area 2CA and has already established communication (transmission and reception of a response signal 60) with the roadside unit 2. Time I is further divided into the communication available times T11 to T15 of each of regions 1 to 5 (CPA1 to CPA5). The in-vehicle devices 3 of the existing vehicles located in regions 1 to 5 transmit the response signal 60 within the communication available times T11 to T15 allocated to each of regions 1 to 5.

[0045] Time II is the communication available time allocated to "newly entered vehicles". A newly entered vehicle is a vehicle 4 equipped with an in-vehicle device 3 that has newly entered the communication area 2CA and has not established communication with the roadside unit 2. Time II is further divided into the communication available times T22 to T25 of each of regions 2 to 5 (CPA2 to CPA5). The in-vehicle devices 3 of the newly entered vehicles located in regions 2 to 5 (CPA2 to CPA5) transmit the response signal 60 within the communication available times T22 to T25 allocated to each of regions 2 to 5.

[0046] Time III is the communication available time for vehicles that have failed to communicate during time I and time II among the existing vehicles and newly entered vehicles in each region to perform re-communication (re-transmission of the response signal 60). Time III is further divided into the communication available times T31 to T35 of each of regions 1 to 5 (CPA1 to CPA5). The existing vehicles and newly entered vehicles that have failed to communicate transmit the response signal 60 within the communication available times T31 to T35 allocated to each of regions 1 to 5.

[0047] Thus, in this embodiment, by dividing time I and time II according to whether the vehicle is an existing vehicle or a new vehicle, and further dividing each of the times I to II for each area, it is possible to more reliably suppress the collision of the response signal 60 due to the hidden terminal problem. Further, in this embodiment, when the roadside unit 2 fails to receive the response signal 60, a time III for the in-vehicle unit 3 to retransmit the response signal 60 is provided. Thereby, even if a collision of the response signal 60 occurs by chance, the in-vehicle unit 3 can be given an opportunity to retransmit, so that the reception omission of the response signal 60 by the roadside unit 2 can be more reliably suppressed.

[0048] Further, the roadside unit 2 may further specify the communication start time of each existing vehicle for the communicable times T11 to T15 of the existing vehicles. For example, the roadside unit 2 provides a plurality of communication slots SL within each of the communicable times T11 to T15. The length of each communication slot SL is set to be at least as long as the time required for transmission and reception of the response signal 60. The roadside unit 2 assigns different communication slots SL to each of the existing vehicles in each of the areas 1 to 5. FIG. 12 shows an example in which a plurality of communication slots SL11a, SL11b, SL11c,... are provided in the communicable time T11 of the existing vehicle in area 1. Each of the existing vehicles in area 1 is assigned one of these communication slots SL. The same applies to the existing vehicles in the other areas 2 to 5. The communication start time of each existing vehicle is the start time of the assigned communication slot SL. Each existing vehicle transmits the response signal 60 in the designated communication slot SL. By doing so, the possibility that the existing vehicles transmit the response signal 60 at the same time can be reduced. Further, if the clocks of the in-vehicle units of each existing vehicle are accurately synchronized, the existing vehicles will not transmit the response signal 60 at the same time. Therefore, the collision of communication between existing vehicles can be more reliably suppressed.

[0049] In this embodiment, the area set within communication area 2CA includes a first area including the intersection and multiple second areas which are the connection points between each of the multiple roads connected to the intersection. In the example in Figure 2, the area including intersection 11 (area 1) is the first area, and the connection points between each of the roads 10a to 10b and intersection 11 (areas 2 to 5) are each the second area. Vehicles 4 passing through intersection 11 enter intersection 11 (first area) from each of the roads 10a to 10b (second area), and then exit from intersection 11 to each of the roads 10a to 10b (second area). In other words, new vehicles entering communication area 2CA first communicate with the roadside unit 2 in the second area, and thereafter continue to communicate with the roadside unit 2 as existing vehicles, so only existing vehicles exist in the first area. For this reason, in this embodiment, as shown in Figures 11 to 12, in the time II for new vehicles, communication time is allocated only to the second area (areas 2 to 5).

[0050] As shown in Figures 11 and 12, the roadside unit 2 of this embodiment transmits multiple response request signals within a predetermined cycle T1. In this embodiment, the roadside unit 2 transmits four response request signals 70A to 70D. The roadside unit 2 divides the communication time T11 to T35 within one cycle T1 into the response request signals 70A to 70D and transmits this to the on-board unit 3 of each vehicle. Figure 13 also shows an example of each response request signal 70A to 70D.

[0051] The response request signal 70A (second response request signal) includes roadside unit identification information 71, a list of vehicles whose tracking has ended 72, a list of existing vehicles in area 1 (area CPA1) 73a, and information 74a indicating the communication slot of each existing vehicle in area 1.

[0052] The roadside unit identification information 71 is information that can identify the roadside unit 2, which is the source of the transmission, and is information common to each response request signal.

[0053] The tracking completion list 72 records existing vehicles that the roadside unit 2 will stop tracking (receiving response signals 60) from the next cycle onward. For example, the roadside unit 2 only needs to track the direction in which each vehicle 4 enters and exits the intersection 11 (i.e., which road it entered the intersection 11 from and which road it exited onto). Therefore, the roadside unit 2 records the identification information (onboard unit identification information) of existing vehicles that have exited from area 1 to other areas 2 to 5 in the tracking completion list 72. If the onboard unit 3 finds its own vehicle (onboard unit identification information) recorded in the tracking completion list 72, it records the roadside unit identification information 71 as the identification information of the roadside unit that has stopped tracking. The onboard unit 3 does not transmit a response signal 60 to a response request signal 70 that contains the same roadside unit identification information 71 as the roadside unit that has stopped tracking.

[0054] The existing vehicle list 73a in area 1 records the identification information (in-vehicle device identification information) of existing vehicles located in area 1.

[0055] The information 74a indicating the communication slot for each existing vehicle in area 1 is information that specifies the assignment of a different communication slot SL to each existing vehicle as the communication available time for each existing vehicle in area 1. The information 74a indicating the communication slot includes information that associates the start time of the communication slot SL (communication start time) in the communication available time T11 of the existing vehicle in area 1 with the identification information of the existing vehicle (in-vehicle device identification information). The start time of the communication slot SL is expressed, for example, as time from the reference time which is the end time of the response request signal 70A.

[0056] The response request signal 70B (first response request signal) includes roadside unit identification information 71, information 75 defining areas 1 to 5, a list of existing vehicles in areas 2 to 5 73b, information 74b indicating the communication slots of each existing vehicle in areas 2 to 5, and information 76 indicating the available communication time for each area for newly arriving vehicles.

[0057] The information 75 defining regions 1 to 5 is the same as the information 51 defining regions 1 to 5 included in the response request signal 50 of the first embodiment.

[0058] The existing vehicle list 73b for areas 2 to 5 records the identification information (in-vehicle device identification information) of existing vehicles located in each of areas 2 to 5, for each area.

[0059] The information 74b indicating the communication slots of each existing vehicle in regions 2 to 5 is information that specifies the assignment of a different communication slot SL to each existing vehicle as the communication available time for each existing vehicle in regions 2 to 5. The information 74b indicating the communication slots includes information that associates the start time of the communication slot SL (communication start time) during the communication available time T12 to T15 of each existing vehicle in regions 2 to 5 with the identification information of the existing vehicle (in-vehicle device identification information). The start time of the communication slot SL is expressed, for example, as time from the reference time which is the end time of the response request signal 70B.

[0060] The information 76 indicating the communication availability time for each area of ​​newly arrived vehicles includes the start times of the communication availability times T22 to T25 for each of the newly arrived vehicles in areas 2 to 5. The start times of each communication availability time T22 to T25 are expressed, for example, as time from a reference time which is the end time of the response request signal 70B.

[0061] The response request signal 70C (third response request signal) includes roadside unit identification information 71, a list of existing vehicles that failed to communicate in areas 1 to 3 77c, a list of newly arrived vehicles that succeeded in communicating in areas 2 to 3 78c, and information 79c indicating the time available for recommunication in areas 1 to 3.

[0062] The existing vehicle list 77c (communication failure list) for areas 1 to 3 records the identification information (on-board unit identification information) of existing vehicles that were recorded in the existing vehicle lists 73a and 73b of the response request signals 70A and 70B, and for which the roadside unit 2 was unable to receive the response signal 60 within the allocated communication time T11 to T13, T22 to T23 (or within the communication slot SL), categorized by area.

[0063] The new vehicle list 78c (communication success list) for which communication was successful in areas 2-3 records the identification information (on-board unit identification information) of new vehicles for which the roadside unit 2 was able to receive a response signal 60 within the new vehicle's communication time T22-T23, categorized by area.

[0064] The information 79c indicating the recommunication availability time for areas 1 to 3 includes the start times of the recommunication availability time T31 to T33, during which existing vehicles included in the existing vehicle list 77c (which failed to communicate) and new vehicles not included in the new vehicle list 78c (which succeeded in communicating) can retransmit the response signal 60. The start times of the recommunication availability time T31 to T33 are expressed, for example, as time from a reference time which is the end time of the response request signal 70C.

[0065] The response request signal 70D (third response request signal) includes roadside unit identification information 71, a list of existing vehicles 77d that failed to communicate in areas 4-5, a list of newly arrived vehicles 78d that succeeded in communicating in areas 4-5, and information 79d indicating the time available for recommunication in areas 4-5.

[0066] The existing vehicle list 77d, which shows the results of communication failures in areas 4-5, records the identification information (on-board unit identification information) of existing vehicles that were recorded in the existing vehicle lists 73a and 73b of the response request signals 70A and 70B, and for which the roadside unit 2 was unable to receive the response signal 60 within the allocated communication time T14-T15 and T24-T25 (or within the communication slot SL), categorized by area.

[0067] The new vehicle list 78d, which successfully communicated in areas 4-5, records the identification information (on-board unit identification information) of new vehicles that the roadside unit 2 was able to receive a response signal 60 from within the new vehicle's communication time T24-T25, categorized by area.

[0068] The information 79d indicating the recommunication availability time for regions 4-5 includes the start times of the recommunication availability time T34-T35, during which existing vehicles included in the existing vehicle list 77d (which failed to communicate) and new vehicles not included in the new vehicle list 78d (which succeeded in communicating) can retransmit the response signal 60. The start times of the recommunication availability time T34-T35 are expressed, for example, as time from a reference time which is the end time of the response request signal 70D.

[0069] The response request signals 70A to 70D are transmitted at a timing prior to the start time of the communication time (or communication slot) allocated within each signal. In the examples in Figures 11 to 13, the response request signal 70A includes the allocation of communication time T11, so it is transmitted at a time prior to this. For example, the response request signal 70A is transmitted during the communication time T32 of the previous cycle. Similarly, the response request signal 70B is transmitted during communication time T11. The response request signal 70C is transmitted during communication time T31. The response request signal 70D is transmitted during communication time T32. In this way, the onboard unit 3 of each vehicle 4 can receive the response request signal containing the information of its allocated communication time before the start of that time.

[0070] (Example of roadside unit operation) Figure 14 shows the processing flow initiated by the roadside unit 2 when it receives a response signal 60 from the on-board unit 3. The content of the response signal 60 is the same as in the first embodiment.

[0071] The roadside unit 2 (for example, the control unit 21) waits until it receives a response signal 60 from the in-vehicle unit 3 (step S401).

[0072] When the roadside unit 2 receives a response signal 60 from the in-vehicle unit 3, it acquires the vehicle identification information (in-vehicle unit identification information) and location information of the vehicle 4 included in the response signal 60 (step S402).

[0073] Next, the roadside unit 2 determines the area where the vehicle 4 (onboard unit 3) is located based on the acquired location information (step S403). The roadside unit 2 stores the vehicle 4 in association with the area where the vehicle 4 is located. The storage unit 23 stores the time history of the association data between each vehicle 4 and its area.

[0074] Each time the roadside unit 2 receives a response signal 60 from the on-board unit 3, it executes the series of processes shown in Figure 14, sequentially updating the correspondence between each vehicle 4 and the area. In this way, because the roadside unit 2 determines the area where each vehicle 4 is located based on the response signal 60, the on-board unit 3 does not need to perform the process of determining the area itself after communication with the roadside unit 2 (sending and receiving the response signal 60) is established. In other words, the processing load on the on-board unit 3 can be reduced, and as a result, the on-board unit 3 can be made cheaper and simpler in configuration.

[0075] Furthermore, the roadside unit 2 may perform the same processing as in the first embodiment (step S21 in Figure 9) on the received response signal 60. For example, the traffic volume and traffic flow (such as whether vehicles 4 are accumulating) on ​​each road can be detected from data that tracks the location of each vehicle 4 at each time. The detection of traffic volume and traffic flow may be performed by the roadside unit 2 and the detection results sent to an external server, or it may be performed by the external server based on the tracking data accumulated by the roadside unit 2.

[0076] Furthermore, Figures 15A to 15D show the processing flow of the roadside unit 2 generating and transmitting a response request signal. Each of the processes in Figures 15A to 15D is executed repeatedly in parallel while the roadside unit 2 is operating. In addition, the roadside unit 2 executes the process in Figure 14 and the processes in Figures 15A to 15D in parallel.

[0077] First, an example of the process of generating and transmitting a response request signal 70C will be explained with reference to Figure 15A. The roadside unit 2 (for example, the control unit 21) determines whether it has finished receiving the response signals 60 for time I to II (communication available time T11 to T13, T22 to T23) in regions 1 to 3 (step S501). If it has not finished receiving the target response signals 60 (step S501; NO), it proceeds to the process in step S505. If it has finished receiving the target response signals 60 (step S501; YES), it generates a response request signal 70C based on the received response signals 60 (step S501).

[0078] For example, suppose that in the communication time T11 of an existing vehicle in region 1 (CPA1) in Figure 2, a response signal 60 is received from the on-board unit 3 of vehicle 4l; in the communication time T13 of an existing vehicle in region 3 (CPA3), a response signal 60 is received from the on-board units 3 of vehicles 4a and 4c; and in the communication time T23 of a newly arrived vehicle in region 3 (CPA3), a response signal 60 is received from the on-board unit 3 of vehicle 4d. At this time, if the roadside unit 2 does not receive a response signal 60 from vehicle 4b in the current cycle's communication time T13 (specified communication slot SL), even though the information of vehicle 4b is included in the existing vehicle list 73b and the information 74b indicating the communication slot of the previous response request signal 70B, the roadside unit 2 determines that communication for the existing vehicle 4b has failed. Therefore, the roadside unit 2 records the identification information of vehicle 4b in the existing vehicle list 77c of the response request signal 70C that has failed to communicate.

[0079] Furthermore, if the roadside unit 2 receives a response signal 60 from the on-board unit 3 of vehicle 4d during the communication time T23 for new vehicles entering area 3, it records the identification information of vehicle 4d in the list of successful new vehicles 78c of the response request signal 70C.

[0080] In step S502, the roadside unit 2 generates a response request signal 70C that includes these lists 77c and 78c, roadside unit identification information 71, and information 79c indicating the recommunication available time (T31 to T33) for areas 1 to 3.

[0081] The roadside unit 2 distributes (transmits) the generated response request signal 70C to the communication area 2CA. In the example in Figure 11, the roadside unit 2 transmits the response request signal 70C at the timing when it has finished receiving the target response signal 60 (communication available time T23), i.e., during the communication available time T24. At this time, if it is in the process of transmitting another response request signal, it waits until it is finished (step S503). Once the transmission of the previous response request signal is complete, the roadside unit 2 transmits the generated response request signal 70C (step S504).

[0082] Next, an example of the process of generating and transmitting a response request signal 70D will be described with reference to Figure 15B. The roadside unit 2 determines whether it has finished receiving the response signals 60 for time I to II (communication available time T14 to T15, T24 to T25) in region 4 to 5 (step S505). If it has not finished receiving the target response signals 60 (step S505; NO), it proceeds to the process in step S509. If it has finished receiving the target response signals 60 (step S505; YES), it generates a response request signal 70D based on the received response signals 60 (step S506).

[0083] The roadside unit 2 generates a response request signal 70D using the same procedure as the response request signal 70C, which includes a list of existing vehicles that failed to communicate 77d and a list of newly arrived vehicles that succeeded in communicating 78d, roadside unit identification information 71, and information 79d indicating the recommunication time (T34 to T35) for areas 4 to 5.

[0084] Furthermore, the roadside unit 2 distributes (transmits) the generated response request signal 70D to the communication area 2CA. In the example shown in Figure 11, the roadside unit 2 transmits the response request signal 70C at the timing when it has finished receiving the target response signal 60 (communication time T25), i.e., during the communication time T31. At this time, if it is in the process of transmitting another response request signal, it waits until it is finished (step S507). Once the transmission of the previous response request signal is complete, the roadside unit 2 transmits the generated response request signal 70D (step S508).

[0085] Next, an example of the process of generating and transmitting a response request signal 70A will be described with reference to Figure 15C. The roadside unit 2 determines whether it has finished receiving the response signals 60 for time I and time III (communication available time T11, T31) in area 1 (step S509). If it has not finished receiving the target response signal 60 (step S509; NO), it proceeds to the process in step S513. If it has finished receiving the target response signal 60 (step S509; YES), it generates a response request signal 70A based on the received response signal 60 (step S510).

[0086] For example, the roadside unit 2 refers to the correspondence between each vehicle and the area in the processing shown in Figure 14 and records the identification information of the vehicle determined to be located in area 1 based on the latest location information (for example, vehicles 4a and 4l in Figure 2) in the existing vehicle list 73a for area 1. Once the existing vehicle list 73a for area 1 is complete, the roadside unit 2 determines the communication slot SL (communication start time) in which the onboard unit 3 of vehicle 4l should send a response signal 60 during the next available communication time T11, and records it in the information 74a indicating the communication slot.

[0087] Furthermore, assume that response signals 60 are received from the on-board units 3 of vehicles 4k and 4l during the existing vehicle's communication time T11 and recommunication time T31. On the other hand, assume that in the correspondence between each vehicle and area in the processing of Figure 14, it is determined that vehicles 4a and 4l are located in area 1. In this case, the roadside unit 2 detects that between the previous communication and the current communication, vehicle 4a moved from another area (area 3 in the example of Figure 2) to area 1, and vehicle 4k moved from area 1 to another area (area 4 in the example of Figure 2). Alternatively, the movement of each vehicle 4 between areas may be detected from the time history of the correspondence data between each vehicle 4 and area. The roadside unit 2 may update the existing vehicle list 73a in area 1 after detecting such movement of vehicle 4. The roadside unit 2 may also terminate tracking of vehicle 4k whose exit destination (area 4) from area 1 has been identified based on this information. When tracking is terminated, the roadside unit 2 records the identification information of this vehicle 4k in the tracked vehicle list 72.

[0088] In step S510, the roadside unit 2 generates a response request signal 70A that includes the list of vehicles whose tracking has ended 72, the list of existing vehicles 73a, information 74a indicating a communication slot, and roadside unit identification information 71.

[0089] Furthermore, the roadside unit 2 distributes (transmits) the generated response request signal 70A to the communication area 2CA. In the example shown in Figure 11, the roadside unit 2 transmits the response request signal 70A at the timing when it has finished receiving the target response signal 60 (communication available time T31), i.e., during the communication available time T32. At this time, if it is in the process of transmitting another response request signal, it waits until that is finished (step S511). Once the transmission of the previous response request signal is complete, the roadside unit 2 transmits the generated response request signal 70A (step S512).

[0090] Next, an example of the process of generating and transmitting a response request signal 70B will be described with reference to Figure 15D. The roadside unit 2 determines whether it has finished receiving the response signals 60 for time I, time II, and time III (communication available time T12-T15, T22-T25, T32-T35) in regions 2-5 (step S513). If it has not finished receiving the target response signals 60 (step S513; NO), it proceeds to the process in step S501. If it has finished receiving the target response signals 60 (step S513; YES), it generates a response request signal 70B based on the received response signals 60 (step S514).

[0091] In step S514, the roadside unit 2 creates a list of existing vehicles 73b in areas 2 to 5 and information 74b indicating the communication slots for each existing vehicle in areas 2 to 5, using the same procedure as for the response request signal 70A. The roadside unit 2 also generates a response request signal 70B that includes the created information 73b and 74b, roadside unit identification information 71, information 75 defining areas 1 to 5, and information 76 indicating the area-specific communication availability time for newly arriving vehicles.

[0092] After generating the response request signal 70B, the roadside unit 2 waits until it has finished transmitting another response request signal (step S515). Once the transmission of the previous response request signal is complete, the roadside unit 2 transmits the generated response request signal 70B (step S516).

[0093] Furthermore, the roadside unit 2 distributes (transmits) the generated response request signal 70B to the communication area 2CA. In the example shown in Figure 11, the roadside unit 2 transmits the response request signal 70B at the timing when it has finished receiving the target response signal 60 (communication available time T35), that is, in the next cycle's communication available time T11. At this time, if the transmission of the previous response request signal is still in progress, it waits until it is finished (step S515). Once the transmission of the previous response request signal is complete, the roadside unit 2 transmits the generated response request signal 70B (step S516).

[0094] (Example of distribution of available communication time) As shown in the example in Figure 12, the roadside unit 2 may dynamically adjust the distribution of the length of time I for communication with existing vehicles, time II for communication with newly arriving vehicles, and time III for recommunication in a predetermined cycle T1, according to the amount of communication and traffic volume. Here, we will explain an example in which the available communication time T11 to T35 is dynamically changed according to the maximum traffic volume of each area 1 to 5 (CPA1 to CPA5).

[0095] For example, in steps S510 and S514 of Figure 15, the roadside unit 2 sets the length of time I for communication with existing vehicles. The communication time T1i for each region i (i = 1 to 5) in time I is proportional to the number of existing vehicles xi in each region i. For example, T1i = a1 × xi, where a1 is the time obtained by adding a certain margin to the time required to send and receive the response signal 60. In step S510, the communication time T11 for region 1 is set, and in step S514, the communication times T12 to T15 for regions 2 to 5 are set respectively. The length of time I is the sum of the communication times T1i for each region i.

[0096] Furthermore, in step S514 of Figure 15, the roadside unit 2 sets the length of time II for communication with incoming vehicles. The communication time T2i for each region i (i = 2 to 5) in time II is proportional to the maximum number of incoming vehicles yi for each region i. For example, T2i = b2 × yi + c2, where b2 is an arbitrary coefficient and c2 is the minimum time allocated to each region i. The coefficient and minimum time are set in advance by the operator of the roadside unit 2 based on simulations, etc. The length of time II is the sum of the communication times T2i for each region i.

[0097] Furthermore, in steps S502 and S506 of Figure 15, the roadside unit 2 sets the length of time III for recommunication. The communication time T3i for each region i (i = 1 to 5) in time III is proportional to the sum of the value obtained by multiplying the number of existing vehicles xi in region i by a coefficient and the value obtained by multiplying the maximum number of new vehicles yi by a coefficient. For example, T3i = a3 × xi + b3 × yi + c3, where a3 and b3 are arbitrary coefficients, and c3 is the minimum time to be allocated to each region i, which is set in advance by the operator of the roadside unit 2 based on simulations, etc. In step S502, the communication times T31 to T33 for each region 1 to 3 are set, and in step S514, the communication times T34 to T35 for each region 4 to 5 are set. The length of time III is the sum of the communication times T3i for each region i.

[0098] If the total time of T11 to T35 is excessive or insufficient compared to the period T1, it will be adjusted in time III. For example, in steps S502 and S506, a value proportional to xi + b4 × yi is added to or subtracted from the length of the communicationable time T3i in each region i of time III. b4 is an arbitrary coefficient and is set in advance by the operator of the roadside unit 2 based on simulations, etc.

[0099] In this way, by dynamically adjusting the communication time allocated to each time region I to III according to the maximum traffic volume, it is possible to suppress the occurrence of collisions of response signals 60 due to an increase in traffic volume in a particular region.

[0100] (Example of operation of the in-vehicle unit) Figure 16 shows the process flow in which the in-vehicle unit 3 transmits a response signal 60 in response to a response request signal 70. The process in Figure 16 is repeatedly executed while the in-vehicle unit 3 is operating.

[0101] The on-board unit 3 (for example, the control unit 31) waits until it receives a response request signal 70A (step S601). When the on-board unit 3 receives the response request signal 70A, it determines whether the signal is from the roadside unit 2 that has finished tracking (step S602). If the roadside unit identification information 71 of the response request signal 70A is the same as the identification information of the roadside unit that has finished tracking recorded in the on-board unit 3, the on-board unit 3 determines that the signal is from the roadside unit 2 that has finished tracking (step S602; YES). In this case, the on-board unit 3 terminates communication with the roadside unit 2 without transmitting a response signal 60 for this response request signal 70A (step S603) and returns to the beginning of the flow (step S601).

[0102] If the roadside unit identification information 71 of the response request signal 70A is different from the identification information of the roadside unit that has finished tracking, or if the roadside unit that has finished tracking is not recorded (step S602; NO), the onboard unit 3 determines whether it has been notified by the roadside unit 2 that tracking has ended (step S604). If the onboard unit 3 finds that its own vehicle (the onboard unit identification information of its own unit) is included in the list of vehicles that have finished tracking 72 of the response request signal 70A, i.e., it has been notified that tracking has ended (step S604; YES), it registers the roadside unit identification information 71 of the response request signal 70A as the identification information of the roadside unit that has finished tracking, and notifies the roadside unit 2 that it has received a tracking end notification (response request signal 70A including the list of vehicles that have finished tracking 72) (step S605). For example, the roadside unit 2 may reserve the communication slot SL of vehicle 4 until it receives a notification (response signal 60) from the onboard unit 3 of vehicle 4 that it has received a tracking end notification. The on-board unit 3 transmits a response signal 60 indicating that it has received a tracking completion notification in the communication slot SL assigned to its vehicle. After step S605, the on-board unit 3 terminates communication with the roadside unit 2 (step S606) and returns to the beginning of the flow (S601).

[0103] If the roadside unit 2 has notified the end of tracking (step S604; NO), the on-board unit 3 determines whether its own vehicle (on-board unit identification information) is included in the existing vehicle list 73a in area 1 of the response request signal 70A (step S607). If its own vehicle is included in the existing vehicle list 73a in area 1 (step S607; YES), the on-board unit 3 refers to the information 74a indicating the communication slot of the response request signal 70A and transmits the response signal 60 in the communication slot SL assigned to its own vehicle at time I (communication available time T11 for existing vehicles in area 1) (step S610). At this time, the on-board unit 3 may, taking into consideration the possibility of errors in the clocks of each on-board unit 3, monitor the communication of other on-board units 3 using the collision avoidance function 332, as in the first embodiment, and avoid collisions in the transmission of the response signal 60 with other on-board units 3.

[0104] If the vehicle is not included in the existing vehicle list 73a in area 1 (step S607; NO), the vehicle waits until it receives the next response request signal 70B (step S608). Upon receiving the response request signal 70B, the vehicle unit 3 determines whether its vehicle (the vehicle unit's identification information) is included in the existing vehicle list 73b in areas 2 to 5 of the response request signal 70B (step S609). If the vehicle is included in the existing vehicle list 73a (step S609; YES), the vehicle unit 3 refers to the information 74b indicating the communication slot in the response request signal 70B and transmits a response signal 60 in the communication slot SL assigned to the vehicle during time I (the communication time T12 to T15 for existing vehicles in areas 2 to 5) (step S610). In this case, the in-vehicle unit 3 may, taking into consideration the possibility of errors in the clocks of each in-vehicle unit 3, monitor the communication of other in-vehicle units 3 using the collision avoidance function 332, similar to the first embodiment, and avoid collisions in the transmission of response signals 60 with other in-vehicle units 3.

[0105] Furthermore, if the vehicle is not included in the existing vehicle list 73b (step S609; NO), the in-vehicle unit 3 determines whether the vehicle is located in areas 2 to 5 (step S611). Based on the vehicle's location information obtained from the location information acquisition unit 32 and the information 75 that defines areas 1 to 5 included in the response request signal 70B, the in-vehicle unit 3 determines whether the vehicle is located in any of areas 2 to 5. If the vehicle is not located in any of areas 2 to 5 (step S611; NO), the in-vehicle unit 3 determines that the vehicle is located outside the communication area 2CA, terminates communication with the roadside unit 2 (step S613), and returns to the beginning of the flow (S601).

[0106] If the vehicle is located in any of areas 2 to 5 (step S611; YES), the vehicle is a new vehicle that has just entered communication area 2CA. In this case, the on-board unit 3 resets the information of the tracking-completed roadside unit (clears the roadside unit identification information) and transmits a response signal 60 (step S612). At this time, the on-board unit 3 refers to the information 76 indicating the communication available time for each area of ​​the new vehicle in the response request signal 70B, and transmits the response signal 60 at a random time within the communication available time T22 to T25 assigned to the area where the vehicle is located at time II. At this time, similar to the first embodiment, the on-board unit 3 monitors the communication of other on-board units 3 using the collision avoidance function 332 and avoids collisions in the transmission of the response signal 60 with other on-board units 3.

[0107] The onboard unit 3 of an existing vehicle transmits a response signal 60 at time I (T11 to T15) and then waits until it receives a response request signal 70C or a response request signal 70D (step S614). The onboard units 3 of existing vehicles located in regions 1 to 3 wait until they receive a response request signal 70C. The onboard units 3 of existing vehicles located in regions 4 to 5 wait until they receive a response request signal 70D.

[0108] When the onboard unit 3 of an existing vehicle receives a response request signal 70C or a response request signal 70D, it determines whether its own vehicle (the onboard unit identification information of its own unit) is included in the list of existing vehicles that failed to communicate, 77c or 77d, for the received response request signals 70C or 70D (step S615). If the vehicle is not included in the list of existing vehicles that failed to communicate, 77c or 77d (step S615; NO), the response signal 60 transmitted in the previous time I was correctly received by the roadside unit 2. In this case, the onboard unit 3 terminates communication with the roadside unit 2 (step S618) and returns to the beginning of the flow (S601). On the other hand, if the vehicle is included in the list of existing vehicles that failed to communicate, 77c or 77d (step S615; YES), the response signal 60 transmitted in the previous time I was not received by the roadside unit 2 due to a collision or the like. Then, the in-vehicle unit 3 refers to the information 79c and 79d indicating the re-communication time for the received response request signals 70C and 70D, and retransmits the response signal 60 at a random time within the communication time T31 to T35 allocated to the area where its vehicle is located at time III (step S619). At this time, similar to the first embodiment, the in-vehicle unit 3 monitors the communication of other in-vehicle units 3 using the collision avoidance function 332 to avoid a collision in the transmission of the response signal 60 with that of other in-vehicle units 3. After retransmitting the response signal 60, the in-vehicle unit 3 terminates communication with the roadside unit 2 (step S620) and returns to the beginning of the flow (S601).

[0109] The onboard unit 3 of a newly arrived vehicle transmits a response signal 60 during time II (T22-T25) and then waits until it receives a response request signal 70C or a response request signal 70D (step S616). The onboard unit 3 of newly arrived vehicles located in areas 2-3 waits until it receives a response request signal 70C. The onboard unit 3 of newly arrived vehicles located in areas 4-5 waits until it receives a response request signal 70D.

[0110] When the onboard unit 3 of a newly arrived vehicle receives a response request signal 70C or 70D, it determines whether its own vehicle (the onboard unit's identification information) is included in the list of newly arrived vehicles 78c and 78d that successfully communicated with the received response request signals 70C and 70D (step S617). If the vehicle is included in the list of newly arrived vehicles 78c or 78d that successfully communicated (step S617; YES), the response signal 60 transmitted during the previous time II (T22-T25) for the new vehicle was correctly received by the roadside unit 2. In this case, the onboard unit 3 terminates communication with the roadside unit 2 (step S618) and returns to the beginning of the flow (S601). From this point onward, this vehicle becomes an existing vehicle. On the other hand, if the vehicle is not included in the list of newly arrived vehicles 78c and 78d that successfully communicated (step S615; NO), the response signal 60 transmitted during the previous time II was not received by the roadside unit 2 due to a collision or the like. Then, the in-vehicle unit 3 refers to the information 79c and 79d indicating the re-communication time for the received response request signals 70C and 70D, and retransmits the response signal 60 at a random time within the communication time T31 to T35 allocated to the area where the vehicle is located at time III (step S619). After retransmitting the response signal 60, the in-vehicle unit 3 terminates communication with the roadside unit 2 (step S620) and returns to the beginning of the flow (S601).

[0111] (Effects) The communication system 1 according to this embodiment includes a roadside unit 2 that transmits a response request signal 70 toward the communication area 2CA and receives a response signal 60 in response to the response request signal 70, and an on-board unit 3 that transmits a response signal 60 including location information of the vehicle on which the unit is installed, based on the response request signal 70 received from the roadside unit 2. The roadside unit 2 transmits a response request signal 70B (first response request signal) which includes, as the response request signal 70, information 75 that defines a plurality of areas 1 to 5 (areas CPA1 to CPA5) set within the communication area 2CA, an existing vehicle list 73b that records vehicles identified as existing vehicles for each area based on the received response signal 60, information 74b that indicates the communication available time for each area of ​​existing vehicles (time I, T12 to T15), and information 76 that indicates the communication available time for each area of ​​newly entering vehicles (time II, T22 to T25). If the vehicle is included in the existing vehicle list 73b, the in-vehicle unit 3 transmits a response signal 60 during the communication time T12 to T15 allocated to the area where the vehicle is located for existing vehicles. If the vehicle is not included in the existing vehicle list 73b, the in-vehicle unit 3 transmits a response signal 60 during the communication time T22 to T25 allocated to the area where the vehicle is located for newly arrived vehicles.

[0112] Communication system 1 divides the communication time (Time I or Time II) according to whether it is an existing vehicle or a newly arrived vehicle, and further divides this time into communication available times T11-T15 and T22-T25 for each region, thereby more reliably suppressing communication collisions caused by the hidden terminal problem.

[0113] Furthermore, regions 1 to 5 include a first region (region 1) which includes an intersection where multiple roads intersect, and multiple second regions (regions 2 to 5) which are the connection points between each road and its respective intersection. The roadside unit 2 transmits a response request signal 70, which includes a tracking completion vehicle list 72, recording existing vehicles that have exited from the first region (region 1) to any of the second regions (regions 2 to 5) based on the received response signal, as tracking completion vehicles that have ended the tracking of the response signal 60. If the in-vehicle unit 3 finds that its own vehicle is included in the tracking completion vehicle list 72, it registers the roadside unit 2 that transmitted the response request signal 70A including the tracking completion vehicle list 72 as a tracking completion roadside unit, and also notifies the roadside unit 2 that it has received a tracking completion notification. Furthermore, the in-vehicle unit 3 does not transmit a response signal 60 to the response request signal 70 of the roadside unit 2 thereafter.

[0114] In this way, the communication system 1 can reduce the number of vehicles 4 that it tracks (communicates with), so even if there is heavy traffic in the communication area 2CA or if there is congestion (logging) of vehicles 4, communication collisions can be suppressed.

[0115] Furthermore, the roadside unit 2 transmits, at different timings, a response request signal 70B (first response request signal) which includes an existing vehicle list 73b recording existing vehicles located in any of the second areas (areas 2 to 5) and information 74b indicating the communication available time T12 to T15 for each of the existing vehicles assigned to the second area (areas 2 to 5), and a response request signal 70A (second response request signal) which further includes an existing vehicle list 73a recording existing vehicles located in the first area (area 1) and information 74a indicating the communication available time T11 for the existing vehicle assigned to the first area (area 1).

[0116] If the system attempts to transmit a list of existing vehicles in all regions and their available communication time with a single response request signal, it must wait until it has finished receiving the response signal from each existing vehicle. This increases the communication cycle and potentially reduces the frequency of communication with the in-vehicle unit (tracking accuracy). On the other hand, the communication system 1 of this embodiment, by splitting the response request signal 70 into two signals 70A and 70B as described above, can notify existing vehicles in the first region (region 1) and the second region (regions 2 to 5) of the existing vehicle list and their available communication time in stages without waiting until it has finished receiving information (response signals) from all regions. As a result, it is possible to suppress the lengthening of the communication cycle and the decrease in the tracking accuracy of the in-vehicle unit 3.

[0117] Furthermore, the communication time (time I) of existing vehicles includes information 74a and 74b that specifies the assignment of a different communication slot SL to each existing vehicle within the communication time T11 to T15 allocated for each region. If the vehicle itself is included in the existing vehicle list 73a and 73b, the in-vehicle unit 3 transmits a response signal 60 using the communication slot SL assigned to its vehicle.

[0118] In this way, the communication system 1 can prevent existing vehicles within the communication area 2CA from transmitting response signals 60 at the same time, thereby more reliably suppressing communication collisions between existing vehicles.

[0119] Furthermore, the roadside unit 2 transmits response request signals 70C and 70D (third response request signals) as response request signals 70, which include communication failure lists 77c and 77d that record existing vehicles that did not receive the response signal 60 within the existing vehicle communication time T11 to T15 for each area, and information 79c and 79d indicating the re-communication time (T31 to T35 of time III) for the response signal 60 for each area. If the vehicle itself is included in the communication failure lists 77c and 77d, the onboard unit 3 retransmits the response signal 60 within the re-communication time T31 to T35 allocated to the area where the vehicle is located.

[0120] In this way, even if a communication collision occurs between existing vehicles, the communication system 1 can give the in-vehicle unit 3 an opportunity to retransmit, thereby more reliably suppressing the loss of reception of the response signal 60.

[0121] Furthermore, the response request signals 70C and 70D (third response request signals) further include communication success lists 78c and 78d, which record new vehicles that received the response signal 60 during the new vehicle communication availability time T22 to T25, for each area. The in-vehicle unit 3 transmits the response signal 60 during the new vehicle communication availability time T22 to T25, and if its own vehicle is not included in the communication success lists 78c and 78d, it retransmits the response signal 60 during the re-communication availability time T31 to T35 allocated to the area where its own vehicle is located.

[0122] In this way, even if a communication collision occurs between newly arrived vehicles, the communication system 1 can give the in-vehicle unit 3 an opportunity to retransmit, thereby more reliably suppressing the loss of reception of the response signal 60.

[0123] Furthermore, the roadside unit 2 transmits, at different timings, a response request signal 70C containing a communication failure list 77c, a communication success list 78c, and information 79c indicating the time available for recommunication for some of the multiple areas 1 to 5 (areas 1 to 3), and a response request signal 70D containing a communication failure list 77d, a communication success list 78d, and information 79d indicating the time available for recommunication for the other areas 4 to 5.

[0124] By splitting the response request signal 70 into two signals 70C and 70D, the communication system 1 can notify existing and newly arrived vehicles in areas 1-3 and areas 4-5 of the lists 77c, 77d, 78c, 78d and the recommunication availability times 79c, 79d in stages, without having to wait until all information (response signals) from all areas has been received. As a result, it is possible to suppress the lengthening of the communication cycle and the decrease in the tracking accuracy of the in-vehicle device 3.

[0125] <Other Embodiments> Although embodiments of the present disclosure have been described in detail above with reference to the drawings, the specific configuration is not limited to these embodiments and may include design changes, etc., that do not depart from the gist of the present disclosure. In the above embodiments, the case where the intersection 11 is a crossroads was shown as an example, but the intersection where the roadside unit 2 is installed may be a four-way intersection other than a crossroads, or a three-way intersection or an intersection with five or more intersections. For example, in the case of a five-way intersection, a new area may be set on the third road, or the setting of the coverage area of ​​each area may be changed so that one of the five areas shown in Figure 2 covers the third road. In the example shown in Figure 2, two areas are set on each of the roads 10a and 10b with area CPA1 in between, but three or more areas may be set. Also, in the above embodiments, the shape of the area is rectangular, but it is not limited to a rectangle. For example, if the shape of the area is circular, the information that defines the area can consist of, for example, information indicating the center coordinates and the length of the radius. In addition, each area may include overlapping parts. In this case, determining which region to classify the overlapping area as can be addressed by, for example, including information indicating the priority between regions in the response request signal, or by pre-defining the method for determining which region to classify it as.

[0126] <Computer Configuration> Figure 17 is a schematic block diagram showing the configuration of a computer according to at least one embodiment. The computer 90 comprises a processor 91, main memory 92, storage 93, and interface 94. The roadside unit 2 and in-vehicle unit 3 described above are implemented in the computer 90. The operation of each processing unit described above is stored in the storage 93 in the form of a program. The processor 91 reads the program from the storage 93 and loads it into the main memory 92, and executes the above processing according to the program. The processor 91 also allocates storage areas in the main memory 92 corresponding to each of the storage units described above according to the program.

[0127] The program may be for implementing a part of the functions to be performed by the computer 90. For example, the program may perform functions in combination with other programs already stored in storage, or in combination with other programs implemented in other devices. In other embodiments, the computer may be equipped with a custom LSI (Large Scale Integrated Circuit) such as a PLD (Programmable Logic Device) in addition to or instead of the above configuration. Examples of PLDs include PAL (Programmable Array Logic), GAL (Generic Array Logic), CPLD (Complex Programmable Logic Device), FPGA (Field Programmable Gate Array), etc. In this case, some or all of the functions implemented by the processor may be implemented by the integrated circuit.

[0128] Examples of storage 93 include HDDs (Hard Disk Drives), SSDs (Solid State Drives), magnetic disks, magneto-optical disks, CD-ROMs (Compact Disc Read Only Memory), DVD-ROMs (Digital Versatile Disc Read Only Memory), and semiconductor memory. Storage 93 may be an internal medium directly connected to the bus of the computer 90, or an external medium connected to the computer 90 via an interface 94 or a communication line. Furthermore, if this program is distributed to the computer 90 via a communication line, the computer 90 that receives the distribution may expand the program into the main memory 92 and execute the above processing. In at least one embodiment, storage 93 is a tangible storage medium that is not temporary.

[0129] <Note> The communication system 1 described in each embodiment can be understood, for example, as follows.

[0130] (1) According to the first embodiment, the communication system 1 comprises a roadside unit 2 that transmits a response request signal 70 toward the communication area 2CA and receives a response signal 60 in response to the response request signal 70, and an on-board unit 3 that transmits a response signal 60 including location information of the vehicle on which the unit is installed in response to the response request signal 70 received from the roadside unit 2, wherein the roadside unit 2 records as an existing vehicle for each area the vehicle 4 identified as being located in each area from the received response signal 60, as the response request signal 70 The in-vehicle unit 3 transmits a first response request signal (response request signal 70B) which includes an existing vehicle list 73b, information 74b indicating the communication available time T12 to T15 for each area of ​​existing vehicles, and information 76 indicating the communication available time for each area of ​​newly entering vehicles that have newly entered the communication area 2CA. If the in-vehicle unit 3 is included in the existing vehicle list 73b, it transmits a response signal 60 within the communication available time T12 to T15 for existing vehicles assigned to the area where the in-vehicle unit 3 is located. If the in-vehicle unit 3 is not included in the existing vehicle list, it transmits a response signal 60 within the communication available time T22 to T25 for newly entering vehicles assigned to the area where the in-vehicle unit 3 is located.

[0131] Communication system 1 divides the communication time according to whether it is an existing vehicle or a newly arrived vehicle, and further divides this time into communication time zones T11-T15 and T22-T25 for each zone, thereby more reliably suppressing communication collisions caused by the hidden terminal problem.

[0132] (2) According to the second embodiment, in the communication system 1 according to the first embodiment, the area includes a first area (area 1) including an intersection where multiple roads intersect, and a plurality of second areas (areas 2 to 5) which are connection parts between each road and an intersection, the response request signal 70 includes roadside unit identification information 71 that can identify the roadside unit 2, the roadside unit 2 transmits a second response request signal (response request signal 70A) as a response request signal 70, which includes a list of vehicles that have finished tracking, in which existing vehicles that have left the first area to one of the second areas based on the received response signal 60 are recorded as vehicles that have finished tracking the response signal 60, and the in-vehicle unit 3, if its own vehicle is included in the list of vehicles that have finished tracking, registers the roadside unit identification information 71 of the roadside unit 2 that transmitted the second response request signal including the list of vehicles that have finished tracking as the identification information of a roadside unit that has finished tracking, and does not transmit a response signal 60 to the response request signal 70 which includes the same roadside unit identification information 71 as the identification information of a roadside unit that has finished tracking.

[0133] In this way, the communication system 1 can reduce the number of vehicles 4 that it tracks (communicates with), so even if there is heavy traffic in the communication area 2CA or if there is congestion (logging) of vehicles 4, communication collisions can be suppressed.

[0134] (3) According to the third embodiment, in the communication system 1 according to the second embodiment, if the vehicle is not included in the existing vehicle list 73b included in the response request signal 70 and the vehicle is located in the second area (areas 2 to 5), the in-vehicle unit 3 deletes the identification information of the tracking completion roadside unit and transmits a response signal to the response request signal.

[0135] In this way, even after the in-vehicle unit 3 has been notified by the roadside unit 2 that tracking has ended and has stopped transmitting the response signal 60, if it receives a response request signal 70 from a roadside unit 2 having different roadside unit identification information, it can erase the identification information of the roadside unit that has ended tracking and start transmitting a new response signal 60.

[0136] (4) According to the fourth embodiment, in the communication system 1 according to the second embodiment, the roadside unit 2 transmits, at different timings, a first response request signal (response request signal 70B) which includes an existing vehicle list 73b recording existing vehicles located in any of the second areas (areas 2 to 5) and information indicating the communication available time T12 to T15 for each of the existing vehicles assigned to the second area, and a second response request signal (response request signal 70A) which further includes an existing vehicle list 73a recording existing vehicles located in the first area (area 1) and information indicating the communication available time T11 for the existing vehicles assigned to the first area.

[0137] (5) According to the fifth embodiment, in the communication system 1 according to the third embodiment, the roadside unit 2 transmits, at different timings, a first response request signal (response request signal 70B) which includes an existing vehicle list 73b recording existing vehicles located in any of the second areas (areas 2 to 5) and information indicating the communication available time T12 to T15 for each of the existing vehicles assigned to the second area, and a second response request signal (response request signal 70A) which further includes an existing vehicle list 73a recording existing vehicles located in the first area (area 1) and information indicating the communication available time T11 for the existing vehicles assigned to the first area.

[0138] As described above, the communication system 1 notifies the response request signal 70 by dividing it into two signals 70A and 70B, allowing it to notify existing vehicles in the first region (region 1) and second region (regions 2-5) in stages, along with the existing vehicle list and communication availability time, without having to wait until all information (response signals) from all regions has been received. As a result, it is possible to suppress the lengthening of the communication cycle and the decrease in the tracking accuracy of the in-vehicle device 3.

[0139] (6) According to the sixth embodiment, in the communication system 1 according to any one of the first to fifth embodiments, the communication time of the existing vehicle includes information specifying the assignment of a different communication slot SL to each existing vehicle within the communication time T11 to T15 allocated for each region, and the in-vehicle unit 3 transmits a response signal 60 in the communication slot SL assigned to its vehicle when its own vehicle is included in the existing vehicle lists 73a and 73b.

[0140] In this way, the communication system 1 can prevent existing vehicles within the communication area 2CA from transmitting response signals 60 at the same time, thereby more reliably suppressing communication collisions between existing vehicles.

[0141] (7) According to the seventh embodiment, in a communication system 1 according to any one of the first to sixth embodiments, the roadside unit 2 further transmits a third response request signal (response request signals 70C, 70D) as a response request signal 70, which includes a communication failure list 77c, 77d recording for each region any existing vehicle that did not receive a response signal 60 within the existing vehicle communication time T11 to T15, and information indicating the re-communication time T31 to T35 for the response signal 60 for each region. The in-vehicle unit 3, if its own vehicle is included in the communication failure list 77c, 77d, retransmits the response signal 60 within the re-communication time T31 to T35 allocated to the region where its own vehicle is located.

[0142] In this way, even if a communication collision occurs between existing vehicles, the communication system 1 can give the in-vehicle unit 3 an opportunity to retransmit, thereby more reliably suppressing the loss of reception of the response signal 60.

[0143] (8) According to the eighth aspect, in the communication system 1 according to the seventh aspect, the third response request signal (response request signals 70C, 70D) further includes communication success lists 78c, 78d which record new vehicles that received the response signal 60 within the new vehicle communication time T22 to T25 for each area, and the in-vehicle unit 3 transmits the response signal 60 within the new vehicle communication time T22 to T25, and if its own vehicle is not included in the communication success lists 78c, 78d, it retransmits the response signal 60 within the re-communication time T31 to T35 allocated to the area where its own vehicle is located.

[0144] In this way, even if a communication collision occurs between newly arrived vehicles, the communication system 1 can give the in-vehicle unit 3 an opportunity to retransmit, thereby more reliably suppressing the loss of reception of the response signal 60.

[0145] (9) According to the ninth aspect, in the communication system 1 according to the seventh aspect, the roadside unit 2 transmits a third response request signal (response request signal 70C) containing information indicating a communication failure list 77c and a recommunication available time 79c for some of the multiple areas 1 to 5, and a third response request signal (response request signal 70D) containing information indicating a communication failure list 77d and a recommunication available time 79d for the other areas 4 to 5, at different timings.

[0146] (10) According to the tenth embodiment, in the communication system 1 according to the eighth embodiment, the roadside unit 2 transmits a third response request signal (response request signal 70C) containing information indicating a communication failure list 77c and a recommunication available time 79c for some of the multiple areas 1 to 5, and a third response request signal (response request signal 70D) containing information indicating a communication failure list 77d and a recommunication available time 79d for the other areas 4 to 5, at different timings.

[0147] By splitting the response request signal 70 into two signals 70C and 70D, the communication system 1 can notify existing and newly arrived vehicles in areas 1-3 and areas 4-5 of the lists 77c, 77d, 78c, 78d and the recommunication availability times 79c, 79d in stages, without having to wait until all information (response signals) from all areas has been received. As a result, it is possible to suppress the lengthening of the communication cycle and the decrease in the tracking accuracy of the in-vehicle device 3.

[0148] (11) According to the eleventh aspect, the communication method is a communication method comprising the steps of: a roadside unit 2 transmitting a response request signal 70 toward the communication area 2CA; an in-vehicle unit 3 transmitting a response signal 60 including location information of the vehicle on which the unit is installed in response to the response request signal 70 received from the roadside unit 2; and a roadside unit 2 receiving a response signal 60 for the response request signal 70, wherein in the step of transmitting the response request signal 70, the roadside unit 2 includes information 75 defining a plurality of areas 1 to 5 set within the communication area 2CA as the response request signal 70, and a vehicle 4 identified from the received response signal 60 as being located in one of the areas of an existing vehicle. In the step of transmitting a first response request signal (response request signal 70B) which includes an existing vehicle list 73b recorded for each area, information 74b indicating the communication time available for each area of ​​existing vehicles, and information 76 indicating the communication time available for each area of ​​newly entering vehicles that have newly entered the communication area 2CA, and transmitting a response signal 60, the in-vehicle unit 3 transmits the response signal 60 within the communication time T12 to T15 allocated to the area where the vehicle is located if the vehicle is included in the existing vehicle list 73b, and transmits the response signal 60 within the communication time T22 to T25 allocated to the area where the vehicle is located if the vehicle is not included in the existing vehicle list 73b.

[0149] By dividing the communication time according to whether the vehicle is an existing or newly acquired vehicle, and further dividing this time into communication time zones T11-T15 and T22-T25 for each region, communication collisions due to the hidden terminal problem can be suppressed more reliably.

[0150] (12) According to the twelfth embodiment, the roadside unit 2 transmits a response request signal 70 toward the communication area 2CA and receives a response signal 60 in response to the response request signal 70, and transmits a first response request signal (response request signal 70B) as the response request signal 70, which includes information 75 defining a plurality of areas 1 to 5 set within the communication area 2CA, an existing vehicle list 73b recording each vehicle 4 identified as existing vehicle in each area from the received response signal 60, information 74b indicating the communication time available for each area of ​​the existing vehicle, and information 76 indicating the communication time available for each area of ​​a newly entering vehicle that has newly entered the communication area 2CA.

[0151] The roadside unit 2 divides the communication time according to whether it is an existing vehicle or a newly arrived vehicle, further dividing this time into communication time zones T11-T15 and T22-T25 for each zone, and instructs each on-board unit 3 to transmit a response signal 60 during the time allocated to it, thereby more reliably suppressing communication collisions caused by the hidden terminal problem.

[0152] (13) According to the 13th embodiment, the on-board unit 3 is an on-board unit 3 that transmits a response signal 60 including location information of the vehicle on which the unit is installed in response to a response request signal 70 received from the roadside unit 2, the response request signal 70 includes information 75 defining a plurality of areas 1 to 5 set within the communication area 2CA of the roadside unit 2, an existing vehicle list 73b recording the vehicles identified as existing vehicles for each area based on the received response signal 60, and information 74b indicating the communication time for each area of ​​the existing vehicles. The system receives a first response request signal (response request signal 70B) which includes information 76 indicating the communication time available for each area of ​​a newly entering vehicle that has just entered communication area 2CA. If the vehicle is included in the existing vehicle list 73b, it transmits a response signal 60 within the existing vehicle communication time T12 to T15 allocated to the area where the vehicle is located. If the vehicle is not included in the existing vehicle list 73b, it transmits a response signal 60 within the new vehicle communication time T22 to T25 allocated to the area where the vehicle is located.

[0153] By transmitting a response signal 60 from the roadside unit 2 at the time allocated by the vehicle unit 3, the vehicle unit 3 can more reliably suppress communication collisions caused by the hidden terminal problem.

[0154] According to each aspect of the present invention, collisions between signals transmitted by multiple in-vehicle devices can be reduced.

[0155] 1...Communication system 2...Roadside unit 3...In-vehicle unit 4...Vehicle 2CA...Communication area CPA1-CPA5...Region (Region 1-5) T1a-T5a...Communication available time T11-T15...Communication available time for existing vehicles T22-T25...Communication available time for newly arrived vehicles T31-T35...Re-communication available time

Claims

1. A communication system comprising: a roadside unit that transmits a response request signal toward a communication area and receives a response signal to the response request signal; and an on-board unit that transmits a response signal including location information of the vehicle on which the unit is installed in response to the response request signal received from the roadside unit, wherein the roadside unit transmits a first response request signal that includes, as the response request signal, information defining a plurality of areas set within the communication area; an existing vehicle list recording each area as an existing vehicle where the vehicle identified as being located in each area from the received response signal; information indicating the communication time available for each area of ​​the existing vehicle; and information indicating the communication time available for each area of ​​a newly entering vehicle that has newly entered the communication area; and the on-board unit, if its own vehicle is included in the existing vehicle list, transmits the response signal within the communication time available for the existing vehicle allocated to the area where its own vehicle is located; and if its own vehicle is not included in the existing vehicle list, transmits the response signal within the communication time available for the newly entering vehicle allocated to the area where its own vehicle is located.

2. The communication system according to claim 1, wherein the area includes a first area including an intersection where a plurality of roads intersect, and a plurality of second areas which are the connection portions between each of the roads and the intersection, the response request signal includes roadside unit identification information that can identify the roadside unit, the roadside unit transmits a second response request signal as the response request signal, which includes a list of vehicles whose tracking has ended, recording existing vehicles that have left the first area to any of the second areas based on the received response signal as vehicles whose tracking of the response signal has ended, and the in-vehicle unit, if its own vehicle is included in the list of vehicles whose tracking has ended, registers the roadside unit identification information of the roadside unit that transmitted the second response request signal including the list of vehicles whose tracking has ended as the identification information of a roadside unit whose tracking has ended, and does not transmit a response signal to a response request signal that includes the same roadside unit identification information as the identification information of a roadside unit whose tracking has ended.

3. The communication system according to claim 2, wherein if the in-vehicle unit does not include its own vehicle in the existing vehicle list and its own vehicle is located in the second area, it erases the identification information of the tracking completion roadside unit and transmits a response signal to the response request signal.

4. The communication system according to claim 2, wherein the roadside unit transmits, at different timings, a first response request signal including the existing vehicle list recording existing vehicles located in any of the second areas and information indicating the communication available time for each of the existing vehicles assigned to each of the second areas, and a second response request signal further including the existing vehicle list recording existing vehicles located in the first area and information indicating the communication available time for each of the existing vehicles assigned to the first area.

5. The communication system according to claim 3, wherein the roadside unit transmits, at different timings, a first response request signal including the existing vehicle list recording existing vehicles located in any of the second areas and information indicating the communication available time for each of the existing vehicles assigned to each of the second areas, and a second response request signal further including the existing vehicle list recording existing vehicles located in the first area and information indicating the communication available time for each of the existing vehicles assigned to the first area.

6. The communication system according to any one of claims 1 to 5, wherein the communication time of the existing vehicles includes information specifying the assignment of a different communication slot to each of the existing vehicles within the communication time allocated for each region, and the in-vehicle unit transmits the response signal in the communication slot assigned to its vehicle when its own vehicle is included in the list of existing vehicles.

7. The communication system according to any one of claims 1 to 5, wherein the roadside unit further transmits a third response request signal as a response request signal, which includes a communication failure list recording for each region any existing vehicles that did not receive the response signal within the communication time of the existing vehicles, and information indicating the re-communication time for the response signal for each region, and the onboard unit, if its own vehicle is included in the communication failure list, retransmits the response signal within the re-communication time allocated to the region where its own vehicle is located.

8. The communication system according to claim 7, wherein the third response request signal further includes a communication success list for each region recording new vehicles that have received the response signal within the new vehicle's communication availability time, and the in-vehicle device transmits the response signal within the new vehicle's communication availability time, and if its own vehicle is not included in the communication success list, it retransmits the response signal within the re-communication availability time allocated to the region where its own vehicle is located.

9. The communication system according to claim 7, wherein the roadside unit transmits a third response request signal including a list of communication failures and information indicating the re-communication time for some of the plurality of regions, and a third response request signal including a list of communication failures and information indicating the re-communication time for other regions, at different timings.

10. The communication system according to claim 8, wherein the roadside unit transmits a third response request signal including a list of communication failures and information indicating the re-communication time for some of the plurality of regions, and a third response request signal including a list of communication failures and information indicating the re-communication time for other regions, at different timings.

11. A communication method comprising: a step of a roadside unit transmitting a response request signal toward a communication area; a step of an in-vehicle unit transmitting a response signal including location information of the vehicle on which the unit is mounted in response to the response request signal received from the roadside unit; and a step of the roadside unit receiving a response signal for the response request signal, wherein in the step of transmitting the response request signal, the roadside unit transmits a first response request signal which includes, as the response request signal, information defining a plurality of areas set within the communication area, an existing vehicle list recording each area as an existing vehicle whose location has been identified from the received response signal, information indicating the communication time available for each area of ​​the existing vehicles, and information indicating the communication time available for each area of ​​a newly entering vehicle that has newly entered the communication area. A communication method comprising the step of transmitting the response signal, wherein the in-vehicle device transmits the response signal within the communication time allocated to the area where the vehicle is located if the vehicle is included in the existing vehicle list, and transmits the response signal within the communication time allocated to the area where the vehicle is located if the vehicle is not included in the existing vehicle list.

12. A roadside unit that transmits a response request signal toward a communication area and receives a response signal to the response request signal, the roadside unit that transmits a first response request signal which includes, as the response request signal, information defining a plurality of areas set within the communication area, an existing vehicle list recording each vehicle located in each area as an existing vehicle based on the received response signal, information indicating the communication time available for each area of ​​the existing vehicles, and information indicating the communication time available for each area of ​​a newly entering vehicle that has just entered the communication area.

13. An on-board unit that transmits a response signal including location information of the vehicle on which the unit is installed in response to a response request signal received from a roadside unit, the on-board unit receives a first response request signal which includes information defining a plurality of areas set within the communication area of ​​the roadside unit, an existing vehicle list recording each area as an existing vehicle where the vehicle identified as being located in each area from the received response signal, information indicating the communication time available for each area of ​​the existing vehicle, and information indicating the communication time available for each area of ​​a newly entering vehicle that has newly entered the communication area, and transmits the response signal within the communication time available for the existing vehicle allocated to the area where the vehicle is located if the vehicle is included in the existing vehicle list, and transmits the response signal within the communication time available for the newly entering vehicle allocated to the area where the vehicle is located if the vehicle is not included in the existing vehicle list.

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