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

Abstract

This communication system comprises: a roadside device that transmits, at a prescribed cycle, a response request signal including information for specifying a plurality of areas set within the communication area of the own device and information indicating communicable time allocated to each of the areas, and receives a response signal in reply to the response request signal; and a plurality of pieces of on-board equipment that each receive a response request signal, recognize the area where the own equipment is located, and transmit a response signal within the communicable time allocated to the recognized area.

Description

Communication system, communication method, roadside device, and vehicle-mounted device

[0001] The present disclosure relates to a communication system, a communication method, a roadside device, and an in-vehicle device.

[0002] Patent Document 1 describes a communication system in which vehicle-to-vehicle communication and road-to-vehicle communication are performed using carrier waves with the same carrier frequency and employs carrier sense multiple access / collision avoidance as an access method, and in which road-to-vehicle communication is less likely to be disrupted 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 present within a transmission-prohibited area of ​​a roadside device, transmission of data for vehicle-to-vehicle communication is stopped. The in-vehicle device determines whether the in-vehicle device is present within the transmission-prohibited area based on the reception level of a signal received from the roadside device or based on its own location information and area information indicating the range of the transmission-prohibited area. The transmission-prohibited area is, for example, within a certain distance from the installation location of the roadside device, and is set based on, for example, the distance that the signal transmitted by the in-vehicle device can reach while maintaining a decodable level (or carrier sense level). In road-to-vehicle communication, communication between the in-vehicle device and the roadside device is performed using a broadcast method or a unicast method. In broadcast communication, response request data and the like are transmitted to all vehicle-mounted devices present within a wireless communication area (a range within which a transmitted signal can be received).

[0003] JP 2015-207940 A

[0004] The communication system described in Patent Document 1 has a problem in that a hidden terminal problem may occur if the range for road-to-vehicle communication is set, for example, so that the radius of the roadside unit centered on the installation location is equal to the distance that the signal transmitted from the vehicle-mounted unit can reach while maintaining a detectable level. The hidden terminal problem occurs in wireless communication when two transmitting terminals (vehicle-mounted units) simultaneously transmit signals to a receiving terminal (roadside unit) located, for example, between them, causing a signal collision and making it impossible for the receiving terminal (roadside unit) to receive the signal. This problem occurs because the transmitting terminals (vehicle-mounted units) cannot detect each other's transmitted signals.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a communication system, a communication method, a roadside unit, and an on-board device that can reduce collisions between signals transmitted by multiple on-board devices.

[0006] In order to solve the above problem, the communication system of the present disclosure includes a roadside unit that transmits a response request signal at a predetermined period, the response request signal including information defining a plurality of areas set within the communication area of ​​the roadside unit and information indicating each communication available time allocated to each of the areas, and receives a response signal to the response request signal; and a plurality of vehicle-mounted units that receive the response request signal, recognize the area in which the vehicle-mounted unit is located, and transmit the response signal within the communication available time allocated to the recognized area.

[0007] The communication method according to the present disclosure includes the steps of: a roadside device transmitting, at a predetermined interval, a response request signal including information defining a plurality of areas set within the communication area of ​​the roadside device and information indicating each communication available time allocated to each of the areas; a vehicle-mounted device receiving the response request signal, recognizing the area in which the vehicle-mounted device is located, and transmitting a response signal within the communication available time allocated to the recognized area; and a step of the roadside device receiving the response signal.

[0008] The roadside device according to the present disclosure transmits a response request signal at a predetermined period, the response request signal including information defining multiple areas set within the communication area of ​​the roadside device and information indicating the communication time allocated to each of the areas, and receives the response request signal, recognizes the area in which the roadside device is located, and receives each response signal transmitted by one or more vehicle-mounted devices within the communication time allocated to the recognized area.

[0009] The vehicle-mounted device according to the present disclosure receives a response request signal transmitted by a roadside device at a predetermined period, the response request signal including information defining multiple areas set within the vehicle's communication area and information indicating the communication time allocated to each of the areas, recognizes the area in which the vehicle-mounted device is located, and transmits a response signal within the communication time allocated to the recognized area.

[0010] According to the communication system, communication method, roadside device, and vehicle-mounted device of the present disclosure, collisions between signals transmitted from a plurality of vehicle-mounted devices can be reduced.

[0011] FIG. 1 is a block diagram showing a configuration example of a communication system according to an embodiment of the present disclosure. FIG. 2 is a plan view schematically showing an installation example of a communication system according to an embodiment of the present disclosure. FIG. 3 is a plan view schematically showing an installation example of a communication system according to an embodiment of the present disclosure. FIG. 4 is a timing chart showing an operation example of a communication system according to an embodiment of the present disclosure. FIG. 5 is a schematic diagram showing a configuration example of a response request signal according to an embodiment of the present disclosure. FIG. 6 is a schematic diagram showing a configuration example of a response signal according to an embodiment of the present disclosure. FIG. 7 is a timing chart showing an operation example of a communication system according to an embodiment of the present disclosure. FIG. 8 is a flowchart showing an operation example of a roadside device according to an embodiment of the present disclosure. FIG. 9 is a flowchart showing an operation example of a roadside device according to an embodiment of the present disclosure. FIG. 10 is a flowchart showing an operation example of an in-vehicle device according to an embodiment of the present disclosure. FIG. 11 is a schematic block diagram showing the configuration of a computer according to an embodiment of the present disclosure.

[0012] A communication system, a communication method, a roadside device, and an in-vehicle device according to embodiments of the present disclosure will be described below with reference to FIGS. 1 to 11 . FIG. 1 is a block diagram showing an example configuration of a communication system according to an embodiment of the present disclosure. FIGS. 2 and 3 are plan views schematically showing an example installation of a communication system according to an embodiment of the present disclosure. FIGS. 4 and 7 are timing charts showing an example operation of a communication system according to an embodiment of the present disclosure. FIG. 5 is a schematic diagram showing an example configuration of a response request signal according to an embodiment of the present disclosure. FIG. 6 is a schematic diagram showing an example configuration of a response signal according to an embodiment of the present disclosure. FIGS. 8 and 9 are flowcharts showing an example operation of a roadside device according to an embodiment of the present disclosure. FIG. 10 is a flowchart showing an example operation of an in-vehicle device according to an embodiment of the present disclosure. FIG. 11 is a schematic block diagram showing the configuration of a computer according to an embodiment of the present disclosure. Note that the same or corresponding components in each drawing are designated by the same reference numerals, and descriptions thereof will be omitted as appropriate.

[0013] (Configuration of Communication System) As shown in FIG. 1, a communication system 1 according to an embodiment of the present disclosure includes, for example, one roadside device 2 and multiple vehicle-mounted devices 3. As shown in FIG. 2, for example, the roadside device 2 transmits and receives predetermined information to and from each of the vehicle-mounted devices 3 mounted on multiple vehicles 4a to 4m located on a road 10a or 10b intersecting at an intersection 11, for example, via DSRC (Dedicated Short-Range Communications). Note that the vehicles 4a to 4m are collectively referred to as vehicles 4. There may be multiple roadside devices 2 for one intersection 11. The roadside device 2 may also be installed to wirelessly communicate with each of the vehicle-mounted devices 3 mounted on one or more vehicles 4 located outside the vicinity (surrounding area) of the intersection 11 (for example, on one road).

[0014] 1 , the roadside unit 2 includes a control unit 21, a communication unit 22, and a storage unit 23 as functional blocks configured from hardware, a combination of hardware and software, etc. The control unit 21 controls each unit within the roadside unit 2, and, for example, transmits and receives predetermined information to and from multiple in-vehicle units 3 via the communication unit 22, and transmits and receives predetermined information to and from an external server (not shown) using, for example, a wide area communication network, etc. The communication unit 22 includes an antenna 221 and performs wireless communication with the multiple in-vehicle units 3. The storage unit 23 stores identification information of the roadside unit 2 (hereinafter also referred to as its own unit), location information of the roadside unit 2, information indicating the area described below, etc., and stores information received from the in-vehicle units 3, for example, in response to instructions from the control unit 21.

[0015] The in-vehicle device 3 is a device that has at least the function of performing road-to-vehicle wireless communication with the roadside device 2, and is a device that is mounted on the vehicle 4. Note that the in-vehicle device 3 may also have the function of performing vehicle-to-vehicle wireless communication with another in-vehicle device 3. Furthermore, the in-vehicle device 3 may be configured as a part of another electronic control device mounted on the vehicle 4, or may function by using part of the configuration of the other electronic control device.

[0016] 1, the vehicle-mounted device 3 includes, as functional blocks configured from hardware, a combination of hardware and software, a control unit 31, a location information acquisition unit 32, a communication unit 33, and a storage unit 34. The control unit 31 controls each unit in the vehicle-mounted device 3, and transmits and receives predetermined information to and from the roadside device 2 via the communication unit 33, for example.

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

[0018] The communication unit 33 includes an antenna 331 and performs wireless communication with the roadside unit 2 and the like. The communication unit 33 also has a wireless signal collision avoidance function 332. The collision avoidance function 332 is a function for detecting signals transmitted from other in-vehicle devices 3 and thereby avoiding collisions between response signals (described later) transmitted from the in-vehicle devices 3 to the roadside devices 2. The collision avoidance function 332 can be realized, for example, by the well-known CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance). 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 wireless signals (frames, packets, etc.), when attempting to transmit a wireless signal, the carrier (carrier wave) usage status is monitored in advance, and if the medium is unused for a predetermined frame interval and a random time that differs depending on the priority, transmission begins.On the other hand, if the medium is in use, transmission is postponed until it becomes unused and the medium enters a standby state.

[0019] The memory unit 23 stores identification information of the vehicle-mounted device 3 (hereinafter also referred to as its own device), information such as the type of vehicle 4 in which the vehicle-mounted device 3 is installed, location information for a specified period of time, etc., and also stores information received, for example, from the roadside unit 2, other vehicle-mounted devices 3, external servers, etc. in response to instructions from the control unit 31.

[0020] (Example of Area Setting in Communication System) In the communication system 1 of this embodiment, as shown in FIG. 2, a plurality of areas 1 (CPA1) to 5 (CPA5) are set within a 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 vehicle-mounted units 3 located within each of the areas CPA1 to CPA5 in a time-sharing manner for each of the areas CPA1 to CPA5. The communication area 2CA is the range within which the roadside unit 2 can perform wireless communication with the vehicle-mounted units 3, and the roadside unit 2 can receive wireless signals transmitted by each vehicle-mounted unit 3 located within the communication area 2CA, and each vehicle-mounted unit 3 located within the communication area 2CA can receive wireless signals transmitted by the roadside unit 2. In the example shown in FIG. 2, the antenna 221 of the roadside unit 2 (or the entire roadside unit 2, etc.) is installed at the center (above) of the intersection 11.

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

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

[0023] Area CPA3, which is indicated by hatching with diagonal lines sloping upward to the right, is a rectangular area set on road 10a to the right of intersection 11. Within area CPA3, vehicles 4a, 4b, 4c, and 4d traveling from right to left on road 10a, and vehicles 4e and 4f traveling from left to right on road 10a are located.

[0024] An area CPA4 indicated by hatching with diagonal lines sloping upward to the right is a rectangular area set below the intersection 11 of the road 10b. Within this area CPA4, a vehicle 4j traveling from bottom to top on the road 10b and a vehicle 4k traveling from top to bottom on the road 10b are located.

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

[0026] In this embodiment, each of the areas CPA1 to CPA5 is configured to detect signals transmitted by other on-board devices 3 within each of the areas CPA1 to CPA5. For example, for the on-board device 3 of vehicle 4d located within area CPA3, the on-board devices 3 of the other vehicles 4a to 4c and 4e to 4f located within area CPA3 are all included within the communication area 4dCA of the on-board device 3 of vehicle 4d. Here, the communication area 4dCA is the range within which the on-board device 3 of vehicle 4d can communicate wirelessly with the roadside device 2 or other on-board devices 3 located within the communication area 4dCA (or the range within which the carriers of the wireless signals transmitted by the roadside device 2 or other on-board devices 3 can be detected). Therefore, the on-board device 3 of vehicle 4d can detect wireless signals transmitted by the on-board devices 3 of the other vehicles 4a to 4c and 4e to 4f located within area CPA3, and collision avoidance function 332 can avoid collisions between the wireless signals. On the other hand, for example, the on-board device 3 of vehicle 4l located within area CPA1 is located outside communication area 4dCA, so the on-board device 3 of vehicle 4d cannot detect the wireless signal transmitted by the on-board device 3 of vehicle 4l. If the on-board device 3 of a vehicle 4 located within area CPA1 and the on-board device 3 of a vehicle 4 located within area CPA3 were to transmit in the same time period, there is a possibility of collision between the transmitted signals. However, in this embodiment, the time during which transmission can be performed in a time-division manner is set for each of areas CPA1 to CPA5, so that the on-board device 3 of a vehicle 4 located within area CPA1 and the on-board device 3 of a vehicle 4 located within area CPA3 will not transmit wireless signals in the same time period. Therefore, for example, the possibility of collision between the wireless signal transmitted by the on-board device 3 of a vehicle 4 located within area CPA1 and the wireless signal transmitted by the on-board device 3 of a vehicle 4 located within area CPA3 can be reduced.

[0027] It is desirable that each of the areas CPA1-CPA5 be configured so that signals transmitted by other on-board devices 3 within the other areas CPA1-CPA5 (excluding the area itself) can be detected within a predetermined range from each of the other areas CPA1-CPA5 (excluding the area itself). For example, as shown in FIG. 3, the on-board device 3 of vehicle 4a may be correctly located within area CPA3 but may be mistakenly recognized as being located within area CPA1 due to location information acquisition errors, driving speed, etc. In this case, the on-board device 3 of vehicle 4a transmits wireless signals within the communication time allocated to area CPA1. In this case, if the communication area 4aCA of the on-board device 3 of vehicle 4a does not include the entire area of ​​area CPA1, there is a risk of collision between the wireless signals transmitted by the on-board device 3 of vehicle 4a and the wireless signals transmitted by other on-board devices 3 located within area CPA1 but outside the communication area 4aCA. Therefore, in this embodiment, for example, within the area CPA3, within a predetermined range CPA1A (in this example, a rectangular range whose sides are extended vertically and horizontally by a distance LA from the area CPA1) from the other area CPA1, a signal transmitted by another on-board device 3 (e.g., the on-board device 3 of vehicle 41) within the other area CPA1 can be detected. In this example, the area CPA1 is set so that the communication area 4aCA of the on-board device 3 of vehicle 4a located within the range CPA1A within the area CPA3 covers the entire area CPA1. However, unlike the examples shown in Figures 2 and 3, for example, if a sufficient gap is set between each area to avoid the effects of erroneous detection of location information, it is not necessary to consider collision of wireless signals with other areas.

[0028] (Example of Wireless Signals in a Communication System) In this embodiment, as described above, for example, five areas CPA1 to CPA5 are set within the communication area 2CA of the roadside device 2, and the roadside device 2 performs wireless communication with the in-vehicle devices 3 located within each of the areas CPA1 to CPA5 in a time-sharing manner for each of the areas CPA1 to CPA5. Figure 4 shows an example of the correspondence between the response request signal transmitted by the roadside device 2 and the available communication times T1a to T5a assigned to each of the areas CPA1 to CPA5. The horizontal axis represents the time axis. The in-vehicle devices 3 located in each of the areas CPA1 to CPA5 transmit response signals in response to the response request signals within the available communication times T1a to T5a assigned to each of the areas CPA1 to CPA5.

[0029] The response request signal is a radio signal transmitted by the roadside device 2 at a predetermined period T1, and is a broadcast signal requesting the transmission of a response signal from each vehicle-mounted device 3. As shown in Fig. 5 , for example, the response request signal 50 includes information 51 defining areas 1 (CPA1) to 5 (CPA5), information 52 indicating a communication available time T1a in area 1 (CPA1), information 53 indicating a communication available time T2a in area 2 (CPA2), information 54 indicating a communication available time T3a in area 3 (CPA3), information 55 indicating a communication available time T4a in area 4 (CPA4), and information 56 indicating a communication available time T5a in area 5 (CPA5).

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

[0031] As shown in FIG. 4, information 52-56 indicating communication times T1a-T5a for areas 1 (CPA1)-5 (CPA5) can be information indicating the time until the start of each communication time T1a-T5a (hereinafter referred to as the start time) T1s-T5s and the time until the end of each communication time T1a-T5a (hereinafter referred to as the end time) T1e-T5e, with the end time of the response request signal at time T2 as the reference time. Note that in the example shown in FIG. 4, a gap time Tg is provided between each communication time T1a-T5a. The start time and end time of each communication time T1a-T5a are calculated by adding the start time T1s-T5s and the end time T1e-T5e to the reference time.

[0032] Fig. 6 shows an example of a response signal transmitted from the vehicle-mounted device 3 to the roadside device 2. In the example shown in Fig. 6, the response signal 60 includes vehicle-mounted device identification information 61 and location information 62. However, Fig. 6 shows only one example of the configuration of the response signal 60, and the response signal 60 may include, for example, information indicating the vehicle type, driving direction, driving speed, etc. in addition to the location information (or without including the location information).

[0033] In the example shown in FIG. 4, the communication times T1a to T5a are all equal in length, but the communication times T1a to T5a may be different in length. The communication times T1a to T5a may be varied, for example, depending on the actual or estimated communication volume for each of the areas CPA1 to CPA5. FIG. 7 shows an example in which the communication times T1a to T5a are different in length. In the example shown in FIG. 7, the communication times T1a, T2a, and T4a are two-thirds the length of the communication time T3a, twice as long as the communication time T3a, and the communication time T5a is the same in length. The actual communication volume may be, for example, the number of response signals received from each of the areas CPA1 to CPA5 during a predetermined period (one or more periods T1). The estimated communication volume may be calculated (predicted) based on, for example, expected traffic volume based on past traffic data, the day of the week, whether it is a public holiday, the time of day, etc.

[0034] (Example of Operation of Roadside Device and Vehicle-Mounted Device) FIG. 8 shows the flow of processing executed by the roadside device 2 at a period T1. In the processing shown in FIG. 8, the roadside device 2 (e.g., the control unit 21) determines whether adjustment of the available communication times T1a to T5a is necessary (step S11). Here, adjustment is necessary when, for example, the actual or estimated communication volume has changed by a predetermined amount or more since the previous adjustment. If adjustment is necessary (step S11: YES), the roadside device 2 adjusts the available communication times T1a to T5a, for example, in accordance with the change in communication volume (step S12). If adjustment is not necessary (step S11: NO), or if adjustment has been performed (step S12), the roadside device 2 transmits a response request signal 50 including information defining multiple areas CPA1 to CPA5 set within its own communication area 2CA and information indicating each available communication time T1a to T5a assigned to each area CPA1 to CPA5 (step S13), and then terminates the processing shown in FIG. 8.

[0035] 9 shows the flow of processing that the roadside unit 2 starts when the roadside unit 2 receives a response signal 60 from the vehicle-mounted unit 3. In the processing shown in Fig. 9, the roadside unit 2 (e.g., the control unit 21) executes processing in response to the response signal (step S21) and then ends the processing shown in Fig. 9. The processing in response to the response signal can be, for example, processing to accumulate information included in the response signal for a predetermined period in the storage unit 23, processing to calculate traffic volume (the number of vehicles per unit time) for each predetermined period and processing to transmit the calculated traffic volume to an external server or the like, etc.

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

[0037] If the vehicle-mounted device 3 is located in any of the areas CPA1 to CPA5 (step S32: YES), the vehicle-mounted device 3 repeatedly determines whether or not the communication time set for that area is within the available time (step S33: YES) until the communication time set for that area is within the available time (step S33: NO is repeated). If the communication time set for that area is within the available time (step S33: YES), the vehicle-mounted device 3 determines whether or not the communication time for that area has ended (step S34). If the communication time for that area has ended (step S34: YES), the vehicle-mounted device 3 ends the process shown in FIG. 10 (however, the initial determination result of step S34 is NO). If the communication time for that area has not ended (step S34: NO), the vehicle-mounted device 3 transmits a response signal via the communication unit 33 (step S35). In step S35, the communication unit 33 monitors whether the other in-vehicle device 3 is transmitting a response signal using the collision avoidance function 332. If the other in-vehicle device 3 is transmitting a response signal, the communication unit 33 waits until the other in-vehicle device 3 has finished transmitting the response signal and a predetermined time has elapsed since the end of transmission. If no other response signal is detected, the communication unit 33 transmits the response signal. Therefore, after starting the process for transmitting the response signal in step S35, the communication unit 33 determines, at predetermined time intervals, whether the transmission of the response signal has been completed or whether the standby state continues (step S36). If the standby state continues (step S36: standby), the communication unit 33 again determines in step S34 whether the communication available time for the area has ended (step S34). On the other hand, if the transmission of the response signal has been completed (e.g., if an ACK (ACKnowledgement; positive response) in response to the response signal has been sent from the roadside device 2) (step S36: completed), the in-vehicle device 3 ends the process shown in FIG. 10.

[0038] (Effects) A communication system 1 according to this embodiment includes a roadside unit 2 that transmits, at a predetermined cycle, a response request signal including information defining a plurality of regions set within its own communication area and information indicating each available communication time allocated to each region, and receives a response signal in response to the response request signal, and a plurality of vehicle-mounted units 3 that receive the response request signal, recognize the region in which the vehicle-mounted unit 3 is located, and transmit the response signal within the available communication time allocated to the recognized region. A communication method according to this embodiment includes: a step in which the roadside unit 2 transmits, at a predetermined cycle, a response request signal including information defining a plurality of regions set within its own communication area and information indicating each available communication time allocated to each region, a step in which the vehicle-mounted unit 3 receives the response request signal, recognizes the region in which the vehicle-mounted unit 3 is located, and transmits the response signal within the available communication time allocated to the recognized region, and a step in which the roadside unit 2 receives the response signal. Furthermore, the roadside device 2 according to this embodiment transmits a response request signal at a predetermined cycle, the response request signal including information defining a plurality of regions set within its own communication area and information indicating the available communication times allocated to each region, and receives the response request signal, recognizes the region in which the roadside device 2 is located, and receives each response signal transmitted by one or more vehicle-mounted devices within the available communication times allocated to the recognized region. Furthermore, the vehicle-mounted device 3 according to this embodiment receives a response request signal transmitted by a roadside device that transmits a response request signal at a predetermined cycle, the response request signal including information defining a plurality of regions set within its own communication area and information indicating the available communication times allocated to each region, recognizes the region in which the vehicle-mounted device 3 is located, and transmits a response signal within the available communication times allocated to the recognized region.

[0039] Therefore, according to the communication system, communication method, roadside device, and vehicle-mounted device of the present embodiment, it is possible to reduce collisions between signals transmitted from a plurality of vehicle-mounted devices.

[0040] Other Embodiments Although the embodiments of the present disclosure have been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and design modifications within the scope of the present disclosure are also encompassed. While the above embodiment illustrates an example in which the intersection 11 is a crossroads, the intersection where the roadside unit 2 is installed may be a four-way intersection other than a crossroads, or a three-way intersection, five-way intersection, or more than five-way intersection. For example, in the case of a five-way intersection, a new area may be set on the third road, or the ranges covered by each area may be changed so that one of the five areas shown in FIG. 2 covers the third road. In the example shown in FIG. 2, two areas are set on each of the roads 10a and 10b, sandwiching the area CPA1. However, three or more areas may be set. In the above embodiment, the shape of the areas is rectangular, but is not limited to rectangular. For example, if the shape of the areas is circular, the information defining the areas may include, for example, information indicating the center coordinates and the radius. Furthermore, the areas may overlap with each other. In this case, determining which area the overlapping portion is to be, can be handled by, for example, including information indicating the priority between areas in the response request signal, or by defining in advance how to determine which area it is to be.

[0041] <Computer Configuration> Fig. 11 is a schematic block diagram showing the configuration of a computer according to this embodiment. The computer 90 includes a processor 91, a main memory 92, a storage 93, and an interface 94. The roadside device 2 and the vehicle-mounted device 3 described above are implemented in the computer 90. The operations of the above-described processing units are stored in the storage 93 in the form of a program. The processor 91 reads the program from the storage 93, loads it into the main memory 92, and executes the above-described processing in accordance with the program. The processor 91 also allocates storage areas in the main memory 92 corresponding to the above-described storage units in accordance with the program.

[0042] The program may be for realizing some of the functions to be performed by the computer 90. For example, the program may be combined with other programs already stored in storage or implemented in other devices to perform the functions. In other embodiments, the computer may include 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), and FPGA (Field Programmable Gate Array). In this case, some or all of the functions realized by the processor may be realized by the integrated circuit.

[0043] Examples of storage 93 include a hard disk drive (HDD), a solid state drive (SSD), a magnetic disk, a magneto-optical disk, a compact disc read-only memory (CD-ROM), a digital versatile disc read-only memory (DVD-ROM), and a semiconductor memory. Storage 93 may be an internal medium directly connected to the bus of computer 90, or an external medium connected to computer 90 via interface 94 or a communication line. Furthermore, if this program is distributed to computer 90 via a communication line, computer 90 that receives the program may load the program into main memory 92 and execute the above-described processing. In at least one embodiment, storage 93 is a non-transitory tangible storage medium.

[0044] <Additional Notes> The communication system 1 described in each embodiment can be understood, for example, as follows.

[0045] (1) A communication system 1 according to a first aspect includes a roadside device 2 that transmits a response request signal 50 at a predetermined period T1, the response request signal 50 including information 51 defining a plurality of areas CPA1 to CPA5 set within a communication area 2CA of the roadside device 2 (the roadside device 2) and information 52 to 56 indicating available communication times T1a to T5a allocated to each of the areas, and receives a response signal 60 in response to the response request signal 50, and a plurality of in-vehicle devices 3 that receive the response request signal 50, recognize the area in which the roadside device 2 (the in-vehicle device 3) is located, and transmit the response signal 60 within the available communication time allocated to the recognized area. According to this aspect and each of the following aspects, it is possible to reduce collisions between signals transmitted by a plurality of in-vehicle devices.

[0046] (2) A communication system 1 according to a second aspect is the communication system of (1), in which each of the vehicle-mounted devices has a function (collision avoidance function 332) for avoiding collisions between the response signals by detecting signals transmitted by other vehicle-mounted devices, and each of the areas is configured to be able to detect signals transmitted by other vehicle-mounted devices within the area, and each of the areas is configured to be able to detect signals transmitted by other vehicle-mounted devices within a predetermined range CPA1A from the other areas. According to this aspect, it is possible to improve the degree of freedom in setting the intervals between the multiple areas CPA1 to CPA5, for example.

[0047] (3) A communication system 1 according to a third aspect is the communication system of (1) or (2), in which the length of each of the available communication times varies depending on an actual or estimated value of the communication volume for each of the areas. According to this aspect, the length of the available communication time can be appropriately set depending on the communication volume.

[0048] (4) A communication system 1 according to a fourth aspect is the communication system of any one of (1) to (3), wherein the communication area includes an intersection where multiple roads intersect. According to this aspect, it is possible to reduce collisions between signals transmitted from multiple in-vehicle devices at an intersection where multiple roads intersect.

[0049] According to each aspect of the present invention, it is possible to reduce collisions between signals transmitted from a plurality of vehicle-mounted devices.

[0050] 1...Communication system 2...Roadside unit 3...In-vehicle unit 4...Vehicle 2CP...Communication area CPA1 to CPA5...Area (Area 1 to 5) T1a to T5a...Communicable time

Claims

1. A communication system comprising: a roadside unit that transmits, at a predetermined interval, a response request signal including information defining a plurality of regions set within the communication area of ​​the roadside unit and information indicating each communication available time allocated to each of the regions, and receives a response signal in response to the response request signal; and a plurality of vehicle-mounted units that receive the response request signal, recognize the region in which the roadside unit is located, and transmit the response signal within the communication available time allocated to the recognized region.

2. The communication system described in claim 1, wherein each of the vehicle-mounted devices has a function for avoiding collisions between the response signals by detecting signals transmitted by other vehicle-mounted devices, and each of the areas is configured to be able to detect signals transmitted by other vehicle-mounted devices within the area, and each of the areas is configured to be able to detect signals transmitted by other vehicle-mounted devices within the other areas within a predetermined range from the other areas.

3. The communication system according to claim 2, wherein the length of each of the communication available times varies depending on an actual measurement or an estimated value of the traffic volume for each of the areas.

4. The communication system according to claim 3, wherein the communication area includes an intersection where a plurality of roads intersect.

5. A communication method comprising: a step in which a roadside device transmits, at a predetermined interval, a response request signal including information defining a plurality of areas set within the communication area of ​​the device itself and information indicating each communication available time allocated to each of the areas; a step in which an in-vehicle device receives the response request signal, recognizes the area in which the device itself is located, and transmits a response signal within the communication available time allocated to the recognized area; and a step in which the roadside device receives the response signal.

6. A roadside device that transmits, at a predetermined interval, a response request signal including information defining a plurality of regions set within its own communication area and information indicating each communication available time allocated to each of said regions, receives said response request signal, recognizes the region in which it is located, and receives each response signal transmitted by one or more vehicle-mounted devices within the communication available time allocated to the recognized region.

7. An on-board device that receives a response request signal transmitted from a roadside device at a predetermined interval, the response request signal including information defining a plurality of regions set within the communication area of ​​the on-board device and information indicating each communication available time allocated to each of the regions, recognizes the region in which the on-board device is located, and transmits a response signal within the communication available time allocated to the recognized region.

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