Road-to-vehicle communication system, road-to-vehicle communication method, roadside communication device, roadside communication program, in-vehicle communication device, and in-vehicle communication program

Abstract

When transmitting a wireless signal between an in-vehicle communication device and a roadside communication device, the possibility of successful signal transmission is increased while suppressing radio wave interference with other systems. [Solution] The present invention relates to a road-to-vehicle communication system including an in-vehicle communication device and a roadside communication device. The in-vehicle communication device of the present invention performs an obstruction determination process to determine whether or not there is obstruction between the vehicle and the roadside communication device, adjusts the amount of power attenuation of radio waves due to obstruction when obstructed, adjusts the amount of power attenuation of radio waves to be transmitted to the roadside communication device when obstructed based on the estimated amount of power attenuation, and transmits information including the result of the obstruction estimation process and the amount of power attenuation to the roadside communication device. When obstructed, the roadside communication device adjusts the amount of power attenuation of radio waves to be transmitted to the in-vehicle communication device based on the amount of power attenuation acquired from the in-vehicle communication device.

Description

[Technical Field]

[0001] The present invention relates to a road-to-vehicle communication system, a road-to-vehicle communication method, a roadside communication device, a roadside communication program, an in-vehicle communication device, and an in-vehicle communication program, and can be applied, for example, to a system for wireless communication between a roadside communication device installed in roadside infrastructure and an in-vehicle communication device installed in a vehicle. [Background technology]

[0002] Conventionally, there is a system described in Patent Document 1 as a road-to-vehicle communication system that performs wireless communication between a roadside communication device installed in roadside infrastructure on a road and an in-vehicle communication device installed in a vehicle moving on the road.

[0003] The system described in Patent Document 1 proposes a technology for increasing the possibility of successful information transmission from roadside infrastructure (roadside communication device) to a vehicle (on-board communication device). Specifically, Patent Document 1 is configured to determine whether a vehicle in a service area is shielded from radio waves by another vehicle, and transmit information to the vehicle individually after controlling one or more of the directivity, output intensity, and modulation method. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-282562 Summary of the Invention [Problem to be solved by the invention]

[0005] In a road-to-vehicle communication system, if there is an obstruction between a vehicle (on-board communication device) and roadside infrastructure (roadside communication device), obstruction occurs not only to radio wave transmission from the roadside infrastructure (roadside communication device), but also to radio wave transmission from the vehicle (on-board communication device).

[0006] In such cases, in conventional road-to-vehicle communication systems such as those described in Patent Document 1, the transmission power for radio wave transmission from a vehicle (on-board communication device) is designed in advance assuming that radio wave shielding will occur due to an obstruction (for example, a transmission power greater than that in the case where no shielding occurs), but there is a concern that if the shielding no longer occurs, radio waves will travel too far and cause radio wave interference with other systems.On the other hand, in conventional road-to-vehicle communication systems, if the transmission power for radio wave transmission from a vehicle (on-board communication device) is designed assuming that no shielding will occur, if shielding occurs contrary to the assumption, the power will be attenuated by the shielding, and communication may not be established.

[0007] Furthermore, in wireless communication between a vehicle (on-board communication device) and roadside infrastructure (roadside communication device), the appropriate design value of transmission power varies depending on surrounding features. Therefore, when a new structure is erected or when a vehicle (on-board communication device) is in mobile operation, it is difficult to achieve sufficient adjustment by simply adjusting the transmission power depending on whether or not there is obstruction, as in the method of Patent Document 1.

[0008] In view of the above problems, there is a need for a road-to-vehicle communication system that can increase the likelihood of successful signal transmission while suppressing radio wave interference with other systems when transmitting wireless signals between an in-vehicle communication device and a roadside communication device. [Means for solving the problem]

[0009] The first invention of the present invention is a road-to-vehicle communication system including an on-board communication device mounted on a vehicle on a road, and a roadside communication device arranged on the road and communicating wirelessly with the on-board communication device, wherein the on-board communication device comprises: an information holding means for holding surrounding vehicle information including position information of surrounding vehicles located around the on-board communication device and information regarding the shapes of the surrounding vehicles, host vehicle information including position information of the on-board communication device, and roadside information including position information of the roadside communication device; an obstruction determination means for performing an obstruction determination process based on the surrounding vehicle information, the host vehicle information, and the roadside information to determine whether the wireless communication between the on-board communication device and the roadside communication device is obstructed by the surrounding vehicle, or whether the wireless communication between the on-board communication device and the roadside communication device is not obstructed by the surrounding vehicle; and a vehicle-side transmission power adjusting means for estimating the amount of power attenuation of radio waves transmitted and received between the vehicle-mounted communication device and the roadside communication device by a blocking vehicle that blocks wireless communication between the vehicle-mounted communication device and the roadside communication device based on vehicle information, the vehicle information, and the roadside information, and adjusting the amount of power of the radio waves to be transmitted to the roadside communication device based on the amount of power attenuation while the result of the blocking determination process indicates a blocking state; and a vehicle-side packet transmitting means for generating an vehicle-mounted transmission packet containing information including at least the amount of power attenuation and the result of the blocking determination process, and transmitting the vehicle-mounted transmission packet to the roadside communication device, wherein the roadside communication device has a roadside transmission power adjusting means for adjusting the amount of power of the radio waves to be transmitted to the vehicle-mounted communication device based on the amount of power attenuation while the result of the blocking determination process indicates a blocking state while the result of the blocking determination process indicates a blocking state.

[0010] The second aspect of the present invention is a road-to-vehicle communication system including an on-board communication device mounted on a vehicle on a road and a roadside communication device arranged on the road and communicating wirelessly with the on-board communication device, wherein the on-board communication device has an information holding means, a shielding determination means, an on-board transmission power adjustment means, and an on-board packet transmission means, and the roadside communication device has the roadside transmission power adjustment means, and the information holding means holds surrounding vehicle information including position information of surrounding vehicles located around the on-board communication device and information regarding the shapes of the surrounding vehicles, host vehicle information including position information of the on-board communication device, and roadside information including position information of the roadside communication device, and the shielding determination means determines, based on the surrounding vehicle information, the host vehicle information, and the roadside information, whether a shielding state occurs in which wireless communication between the on-board communication device and the roadside communication device is shielded by the surrounding vehicle, or a non-shielding state in which wireless communication between the on-board communication device and the roadside communication device is not shielded by the surrounding vehicle. a vehicle-side transmission power adjusting means for adjusting a power level of radio waves transmitted between the vehicle-mounted communication device and the roadside communication device based on the power attenuation amount of radio waves transmitted between the vehicle-mounted communication device and the roadside communication device, the vehicle-side transmission power adjusting means performing an obstruction determination process when the obstruction determination process determines that obstruction exists, the vehicle-side transmission power adjusting means estimating an amount of power attenuation of radio waves transmitted and received between the vehicle-mounted communication device and the roadside communication device due to a obstructing vehicle that obstructs wireless communication between the vehicle-mounted communication device and the roadside communication device based on the surrounding vehicle information, the vehicle information, and the roadside information, and adjusting an amount of power of radio waves to be transmitted to the roadside communication device while the result of the obstruction determination process indicates that obstruction exists, the vehicle-side packet transmitting means generating an in-vehicle transmission packet containing information including at least the amount of power attenuation and the result of the obstruction determination process, and transmitting the in-vehicle transmission packet to the roadside communication device, the roadside transmission power adjusting means adjusting an amount of power of radio waves to be transmitted to the vehicle-mounted communication device based on the power attenuation amount set in the in-vehicle transmission packet while the result of the obstruction determination process indicates that obstruction exists.

[0011] The third aspect of the present invention is a road-to-vehicle communication system including an on-vehicle communication device mounted on a vehicle on a road and a roadside communication device arranged on the road and communicating wirelessly with the on-vehicle communication device, the on-vehicle communication device comprising: information holding means for holding peripheral vehicle information including position information of peripheral vehicles located around the on-vehicle communication device and information regarding the shapes of the peripheral vehicles; host vehicle information including position information of the on-vehicle communication device; and roadside information including position information of the roadside communication device; and information holding means for holding, based on the peripheral vehicle information, the host vehicle information, and the roadside information, a shielded state in which wireless communication between the on-vehicle communication device and the roadside communication device is shielded by the peripheral vehicles, or a state in which wireless communication between the on-vehicle communication device and the roadside communication device is not shielded by the peripheral vehicles. an in-vehicle communication device comprising: an obstruction determination means for performing an obstruction determination process to determine whether the obstruction state is present or not; an in-vehicle transmission power adjustment means for, when the obstruction determination process determines that there is obstruction, estimating the amount of power attenuation of radio waves transmitted and received between the in-vehicle communication device and the roadside communication device due to a blocking vehicle that blocks wireless communication between the in-vehicle communication device and the roadside communication device based on the surrounding vehicle information, the vehicle information, and the roadside information, and adjusting the amount of power attenuation of radio waves to be transmitted to the roadside communication device while the result of the obstruction determination process is a blocked state; and an in-vehicle packet transmission means for generating an in-vehicle transmission packet containing information including at least the amount of power attenuation and the result of the obstruction determination process and transmitting the packet to the roadside communication device.

[0012] The fourth aspect of the present invention is a road-to-vehicle communication system including an on-vehicle communication device mounted on a vehicle on a road and a roadside communication device arranged on the road and communicating wirelessly with the on-vehicle communication device, the road-to-vehicle communication system including a computer mounted on the on-vehicle communication device, the computer comprising: information holding means for holding peripheral vehicle information including position information of peripheral vehicles located around the on-vehicle communication device and information regarding the shapes of the peripheral vehicles, host vehicle information including position information of the on-vehicle communication device, and roadside information including position information of the roadside communication device; and information holding means for holding, based on the peripheral vehicle information, the host vehicle information, and the roadside information, a shielding state in which wireless communication between the on-vehicle communication device and the roadside communication device is shielded by the peripheral vehicle, or a state in which wireless communication between the on-vehicle communication device and the roadside communication device is shielded by the peripheral vehicle. and an in-vehicle communication program that causes the in-vehicle communication device to function as an obstruction determination means that performs an obstruction determination process to determine whether the vehicle is obstructed or not; an in-vehicle transmission power adjustment means that, when the obstruction determination process determines that there is obstruction, estimates the amount of power attenuation of radio waves transmitted and received between the in-vehicle communication device and the roadside communication device by a blocking vehicle that blocks wireless communication between the in-vehicle communication device and the roadside communication device based on the amount of power attenuation; and an in-vehicle packet transmission means that generates an in-vehicle transmission packet containing information including at least the amount of power attenuation and the result of the obstruction determination process and transmits the packet to the roadside communication device.

[0013] A fifth aspect of the present invention is a roadside communication device that constitutes a road-to-vehicle communication system including an on-board communication device mounted on a vehicle on a road and a roadside communication device that is placed on the road and communicates wirelessly with the on-board communication device, wherein the roadside communication device comprises a roadside transmission power adjustment means that, while a result of a shielding determination process set in an on-board transmission packet transmitted from the on-board communication device to the on-board communication device determines whether the wireless communication between the on-board communication device and the on-board communication device is a shielded state by another surrounding vehicle, or an unshielded state by which the wireless communication between the on-board communication device and the on-board communication device is not shielded by the surrounding vehicle, adjusts the power amount of radio waves to be transmitted to the on-board communication device based on the amount of power attenuation of radio waves transmitted and received between the on-board communication device and the on-board communication device by a shielding vehicle that shields the wireless communication between the on-board communication device and the on-board communication device, as set in the on-board transmission packet.

[0014] A sixth aspect of the present invention is a roadside communication program characterized in that the roadside communication device, which constitutes a road-to-vehicle communication system comprising an onboard communication device mounted on a vehicle on a road and a roadside communication device arranged on the road and communicating wirelessly with the onboard communication device, is made to function as a roadside transmission power adjustment means for adjusting the amount of power of radio waves to be transmitted to the onboard communication device based on the amount of power attenuation of radio waves transmitted and received between the onboard communication device and the onboard communication device by a blocking vehicle that blocks the wireless communication between the onboard communication device and the onboard communication device, as set in the onboard transmission packet, while the result of a blocking determination process set in the onboard transmission packet sent from the onboard communication device to the onboard communication device determines whether the result is a blocked state, in which wireless communication between the onboard communication device and the onboard communication device is blocked by another surrounding vehicle, or an unblocked state, in which wireless communication between the onboard communication device and the onboard communication device is not blocked by the surrounding vehicle. [Effects of the Invention]

[0015] According to the present invention, when transmitting wireless signals between an in-vehicle communication device and a roadside communication device, it is possible to increase the possibility of successful signal transmission while suppressing radio wave interference with other systems. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a block diagram showing the functional configuration of a roadside communication device and an in-vehicle communication device according to an embodiment. [Figure 2] 1 is a diagram illustrating an overall configuration of a road-to-vehicle communication system according to an embodiment. [Figure 3] 4 is a flowchart showing an operation of the roadside communication device according to the embodiment. [Figure 4] 4 is a flowchart showing the operation of the in-vehicle communication device according to the embodiment. [Figure 5] 10A and 10B are diagrams illustrating an example of an occlusion determination process performed by an occlusion determination unit according to an embodiment. [Figure 6] 1 is an explanatory diagram (part 1) showing the configuration of a knife-edge diffraction model that an in-vehicle communication device (transmission power adjustment value calculation unit) according to an embodiment applies to a screen (a shielded vehicle). FIG. [Figure 7] FIG. 10 is an explanatory diagram (part 2) showing the configuration of a knife-edge diffraction model that the in-vehicle communication device (transmission power adjustment value calculation unit) according to the embodiment applies to a screen (a shielded vehicle). DETAILED DESCRIPTION OF THE INVENTION

[0017] (A) Main embodiment Hereinafter, an embodiment of a road-to-vehicle communication system, a road-to-vehicle communication method, a roadside communication device, a roadside communication program, an in-vehicle communication device, and an in-vehicle communication program according to the present invention will be described in detail with reference to the drawings.

[0018] (A-1) Configuration of the embodiment FIG. 2 shows the overall configuration of a road-to-vehicle communication system 1 according to this embodiment.

[0019] The road-to-vehicle communication system 1 includes a roadside communication device 10 mounted on a roadside infrastructure 40, which is an infrastructure facility located on the road side, and in-vehicle communication devices 20 (20-0, 20-1, 20-2, ...) mounted on each of the vehicles 30 (30-1, 30-2, ...) on the road.

[0020] In the road-to-vehicle communication system 1, wireless communication (hereinafter referred to as "road-to-vehicle communication") is performed at least between the roadside communication device 10 and each of the in-vehicle communication devices 20 (20-1, 20-2, ...). Note that in the road-to-vehicle communication system 1, wireless communication (hereinafter referred to as "vehicle-to-vehicle communication") may also be performed between each of the in-vehicle communication devices 20 (20-1, 20-2, ...).

[0021] Hereinafter, the vehicle 30 equipped with the in-vehicle communication device 20 will be referred to as the "own vehicle," and other vehicles present around the in-vehicle communication device 20 will be referred to as the "surrounding vehicles." Also, hereinafter, a surrounding vehicle that is blocking communication between the in-vehicle communication device 20 and the roadside communication device 10 (i.e., a surrounding vehicle determined to be blocking communication between the in-vehicle and the roadside communication device 10) will be referred to as the "blocking vehicle." For example, a surrounding vehicle that is present between the position of the in-vehicle and the position of the roadside communication device 10 is highly likely to be a blocking vehicle. Also, hereinafter, information about the in-vehicle vehicle (including the in-vehicle communication device 20) collected by each in-vehicle communication device 20 will be referred to as the "own vehicle information," and information about surrounding vehicles collected by each in-vehicle communication device 20 will be referred to as the "surrounding vehicle information." Also, hereinafter, information about blocking vehicles (information of the same items as the surrounding vehicle information) will be referred to as the "blocking vehicle information" by each in-vehicle communication device 20. In the following, information relating to the roadside communication device 10 collected by each in-vehicle communication device 20 will also be referred to as "roadside information." The subject vehicle information, surrounding vehicle information (obstructed vehicle information), and roadside information will be described in detail later.

[0022] Next, the internal configuration of the roadside communication device 10 and each of the vehicle-mounted communication devices 20 (20-1, 20-2, . . . ) will be described with reference to FIG.

[0023] FIG. 1 is a block diagram showing the functional configuration of a roadside communication device 10 and each of the in-vehicle communication devices 20 (20-1, 20-2, . . . ).

[0024] In this embodiment, the internal configuration of each vehicle-mounted communication device 20 is the same and can be shown in a block diagram such as FIG.

[0025] First, the internal configuration of the roadside communication device 10 will be described.

[0026] The roadside communication device 10 includes a wireless communication unit 110 and a communication control unit 120 .

[0027] The wireless communication unit 110 communicates with each in-vehicle communication device 20 (road-to-vehicle communication) using a wireless antenna 111. In addition to the wireless antenna 111, the wireless communication unit 110 includes various components (not shown) required for transmitting and receiving wireless signals (packets). When receiving a transmission instruction from the communication control unit 120, the wireless communication unit 110 transmits a packet (wireless signal) storing specified information. When the wireless communication unit 110 receives a packet via wireless communication, it supplies the packet information to the communication control unit 120. Basically, the packet received by the wireless communication unit 110 via wireless communication is a packet transmitted from one of the in-vehicle communication devices 20 (hereinafter also referred to as a "vehicle-transmitted packet").

[0028] The roadside communication device 10 may be configured as hardware including a computer having a memory and a processor, and a wireless communication unit 110. In this case, the roadside communication device 10 may be configured by installing a program (including the roadside communication program according to the embodiment) in the hardware including the computer or the like.

[0029] The communication control unit 120 generates packets storing necessary information based on the information obtained from the wireless communication unit 110, and transmits the information by controlling the transmission power of the wireless communication unit 110. The communication control unit 120 may be configured to control the directivity and modulation method of the wireless communication unit 110 in addition to the transmission power.

[0030] Next, a specific configuration of the communication control unit 120 will be described. The communication control unit 120 includes a vehicle transmission packet storage unit 121, a transmission power adjustment value calculation unit 122, and a roadside transmission packet generation unit 123.

[0031] The vehicle-transmitted packet storage unit 121 records information about vehicle-transmitted packets (information for a plurality of packets) acquired from the wireless communication unit 110. The vehicle-transmitted packet storage unit 121 may manage the recorded information about vehicle-transmitted packets for each vehicle (for each in-vehicle communication device 20) and for each time series (for example, for each reception time).

[0032] The transmission power adjustment value calculation unit 122 performs a process (hereinafter also referred to as a "power adjustment amount update process") of updating the amount of power adjustment (e.g., constants and coefficients related to power adjustment) when communicating wirelessly with the on-board communication device 20 so as to improve the communication quality of wireless communication with the on-board communication device 20 in an area covered by the transmission power adjustment value calculation unit 122 (hereinafter also referred to as a "service area"). The transmission power adjustment value calculation unit 122 performs the power adjustment amount update process based on information about the vehicle transmission packet obtained from the vehicle transmission packet storage unit 121. The transmission power adjustment value calculation unit 122 provides the updated power adjustment amount to the roadside transmission packet generation unit 123 and the wireless communication unit 110. The transmission power adjustment value calculation unit 122 also supplies information about the transmission power adjustment value calculation unit 122 (roadside information) related to the transmission power adjustment value calculation unit 122 (roadside information) to the vehicle transmission packet generation unit 112. The roadside information may include at least information defining the range (area) of the service area covered by the device (hereinafter referred to as "service area information") and location information of the device (location information of the device's radio antenna 111).

[0033] The roadside transmission packet generation unit 123 generates a packet (hereinafter referred to as a "roadside transmission packet") that stores information including each piece of information (e.g., updated power adjustment amount, roadside information, etc.) supplied from the transmission power adjustment value calculation unit 122, and instructs the wireless communication unit 110 to transmit the packet. Note that if the roadside information is set in advance in each in-vehicle communication device 20, it is not necessary to set the roadside information in the vehicle transmission packet.

[0034] Next, the internal configuration of the on-board communication device 20 mounted on the vehicle 30 will be described.

[0035] The in-vehicle communication device 20 includes a wireless communication unit 210, a communication control unit 220, a surrounding vehicle detection unit 230, and a host vehicle information collection unit 240.

[0036] The wireless communication unit 210 performs road-to-vehicle communication and has a function of transmitting and receiving packets as appropriate. The wireless communication unit 210 performs communication (road-to-vehicle communication) with the roadside communication device 10 using a wireless antenna 211. In addition to the wireless antenna 211, the wireless communication unit 210 has various components (not shown) necessary for transmitting and receiving wireless signals (packets). When receiving a transmission instruction from the communication control unit 220, the wireless communication unit 210 transmits a packet (wireless signal) storing specified information. Furthermore, when the wireless communication unit 210 receives a packet via wireless communication, it supplies the packet information to the communication control unit 220.

[0037] The in-vehicle communication device 20 may be configured as hardware including a computer having a memory and a processor, and a wireless communication unit 210. In this case, the roadside communication device 10 may be configured by installing a program (including the in-vehicle communication program according to the embodiment) in the hardware including the computer or the like.

[0038] The surrounding vehicle detection unit 230 executes a process (hereinafter referred to as a "surrounding vehicle information collection process") to retain surrounding vehicle information about vehicles (surrounding vehicles) present around the host device (host vehicle). The surrounding vehicle information may include, for example, the distance from the host vehicle to the surrounding vehicle and information about the shape of the surrounding vehicle (hereinafter referred to as "surrounding vehicle shape information"). The surrounding vehicle shape information may also include, for example, information about the vehicle height, width, length, etc., of the surrounding vehicle. Furthermore, the surrounding vehicle information may also include information about the vehicle type of the surrounding vehicle. The specific means by which the surrounding vehicle detection unit 230 collects surrounding vehicle information is not limited. For example, if the host vehicle is equipped with autonomous sensors (e.g., a compound eye camera, radar, LIDAR (Light Detection and Ranging) sensor, etc.) used to realize driving assistance and autonomous driving (not shown), the surrounding vehicle detection unit 230 may perform the surrounding vehicle information collection process using the autonomous sensors.

[0039] The host vehicle information collection unit 240 executes a process (hereinafter referred to as a "host vehicle information collection process") for retaining information about the host vehicle (hereinafter referred to as "host vehicle information"). The host vehicle information includes at least the location information of the host vehicle. The host vehicle information may include information about the speed of the host vehicle and the distance to a merging point in addition to the location information of the host vehicle. The specific means by which the host vehicle information collection unit 240 collects the host vehicle information is not limited. Incidentally, a typical vehicle is equipped with devices (hereinafter also referred to as a "navigation device") such as a vehicle speed pulse generator and inertial sensors (acceleration sensor, gyroscope), a map information processing system used in car navigation systems, and a GNSS (Global Navigation Satellite System) that are commonly installed in the vehicle. Therefore, if the host vehicle is equipped with the above-mentioned navigation device, the host vehicle information collection unit 240 can retain the host vehicle information by using the above-mentioned navigation device.

[0040] The communication control unit 220 generates a packet (vehicle transmission packet) storing necessary information based on the information obtained from the wireless communication unit 210, the surrounding vehicle detection unit 230, and the host vehicle information collection unit 240, and transmits the information by controlling the transmission power of the wireless communication unit 210. The communication control unit 220 may control the directivity and modulation method in addition to the transmission power.

[0041] Next, a specific configuration of the communication control unit 220 will be described. The communication control unit 220 has a roadside transmission packet storage unit 221, an obstruction determination unit 222, a transmission power adjustment value calculation unit 223, and a vehicle transmission packet generation unit 224.

[0042] The roadside transmission packet storage unit 221 records a plurality of packets of information (roadside transmission packet information) acquired from the wireless communication unit 210. The roadside transmission packet storage unit 221 may manage the recorded roadside transmission packet information in chronological order (for example, by reception time).

[0043] The occlusion determination unit 222 performs a process (hereinafter referred to as the "occlusion determination process") to determine whether occlusion will occur when communicating with the roadside communication device 10, based on the roadside information of the roadside communication device 10 obtained from the roadside transmission packet storage unit 221, the surrounding vehicle information obtained from the surrounding vehicle detection unit 230, and the host vehicle information obtained from the host vehicle information collection unit 240, and supplies the determination result of the occlusion determination process (hereinafter also referred to as the "occlusion determination process result") and information including the roadside information, the host vehicle information, and the surrounding vehicle information used in the determination to the transmission power adjustment value calculation unit 223. The occlusion determination process result is either "occlusion present," indicating that occlusion by a surrounding vehicle has occurred, or "no occlusion," indicating that occlusion by a surrounding vehicle has not occurred. Here, a surrounding vehicle determined to be the cause of occlusion by the occlusion determination process is also referred to as a "occlusion vehicle." In addition, hereinafter, the surrounding vehicle information of the occlusion vehicle is also referred to as "occlusion vehicle information."

[0044] When the result of the obstruction determination process obtained from the obstruction determination unit 222 is "obstructed," the transmission power adjustment value calculation unit 223 estimates the amount of power attenuation due to obstruction (hereinafter referred to as "power attenuation") from roadside information, vehicle information, and surrounding vehicle information (obstructed vehicle information), and adjusts the amount of power of the radio waves transmitted by the wireless communication unit 210 (wireless antenna 211) when obstruction is present based on the estimated power attenuation.

[0045] Here, the basic characteristics of the amount of power adjustment processed in the road-to-vehicle communication system 1 (the roadside communication device 10 and the in-vehicle communication device 20) will be described.

[0046] Here, in the road-to-vehicle communication system 1, a constant (hereinafter also referred to as a "power adjustment constant") for dealing with the radio wave propagation characteristics specific to the service area covered by the roadside communication device 10, regardless of whether or not it is blocked by a vehicle, is set as G c In the road-to-vehicle communication system 1, this power adjustment constant G c By updating, it is possible to adjust the transmission power to an appropriate level even when the radio wave propagation characteristics change due to, for example, the construction of a new building around the service area. Here, the amount of power attenuation (power attenuated by the shielding of a shielding vehicle in wireless communication between the roadside communication device 10 and the in-vehicle communication device 20; mainly taking into consideration the influence of diffracted waves) that varies depending on the size and distance of the shielding object is represented by L. Furthermore, assuming that the influence of reflected waves when shielding occurs between the roadside communication device 10 and the in-vehicle communication device 20 cannot be ignored, a coefficient (hereinafter referred to as "power adjustment coefficient") to deal with this variation is set as G. i In addition, when a general diffraction model (for example, a knife-edge diffraction model) is applied as a method for calculating the attenuation amount L, the diffraction loss is calculated by simulating an obstruction with a simple structure such as a screen (one plane), so it is difficult to reproduce the difference in attenuation amount due to differences in complex structures such as vehicle types. i It is also possible to manage this for each vehicle model and absorb differences in the amount of attenuation in this section.

[0047] In this embodiment, the total amount of power adjustment of transmission power (hereinafter referred to as "total power adjustment amount") is set to G. In this case, the total amount of power adjustment G when there is shielding (i.e., when a shielding vehicle exists between the roadside communication device 10 and the in-vehicle communication device 20) is expressed by the following formula (1), and the total amount of power adjustment G when there is no shielding (i.e., when no shielding vehicle exists between the roadside communication device 10 and the in-vehicle communication device 20) is expressed by the following formula (2). G=G c +G i L...(1) G=G c …(2)

[0048] The in-vehicle communication device 20 (transmission power adjustment value calculation unit 223) adjusts the power when the wireless communication unit 210 transmits radio waves based on the total power adjustment amount G. Similarly, the roadside communication device 10 (transmission power adjustment value calculation unit 122) also adjusts the power when the wireless communication unit 110 transmits radio waves based on the total power adjustment amount G. Furthermore, the power adjustment amount (power adjustment constant G c and power adjustment coefficient G i ) is managed on the roadside communication device 10 (transmission power adjustment value calculation unit 122) side, and is added to the roadside transmission packet as a power adjustment amount (power adjustment constant G c and power adjustment coefficient G i ) and thus can be notified to the in-vehicle communication device 20. Furthermore, the estimation process of the amount of power attenuation L and the shadowing estimation process are calculated by the in-vehicle communication device 20 (transmission power adjustment value calculation unit 223), and the calculated amount of power attenuation L and the result of the shadowing estimation process can be included in the vehicle transmission packet and thus can be notified to the roadside communication device 10.

[0049] As described above, parameters such as the amount of power adjustment are processed in the road-to-vehicle communication system 1 (the roadside communication device 10 and the in-vehicle communication device 20).

[0050] The transmission power adjustment value calculation unit 223 supplies information including at least the result of the obstruction determination process and the amount of power attenuation L to the vehicle transmission packet generation unit 224. At this time, the transmission power adjustment value calculation unit 223 also supplies the vehicle information (including at least the position information), the obstructed vehicle information (none if there is no obstruction), and the most recently used power adjustment amount (power adjustment constant G c and power adjustment coefficient G i ) may also be supplied to the vehicle transmission packet generator 224.

[0051] The vehicle transmission packet generation unit 224 generates a vehicle transmission packet in which the information supplied from the transmission power adjustment value calculation unit 223 is set, and causes the wireless communication unit 210 to transmit the packet.

[0052] (A-2) Operation of the embodiment Next, the operation of the road-to-vehicle communication system 1 (roadside communication device 10 and in-vehicle communication device 20) of this embodiment (road-to-vehicle communication method according to the embodiment) will be described.

[0053] First, the operation of the roadside communication device 10 will be described with reference to Figures 3 and 4. In the following, for ease of explanation, the description will be focused on communication between the roadside communication device 10 and any one on-vehicle communication device 20 (hereinafter, this on-vehicle communication device 20 will also be referred to as a "target on-vehicle communication device"), but in reality, a plurality of on-vehicle communication devices 20 may be connected under the control of the roadside communication device 10.

[0054] FIG. 3 is a flowchart showing the operation of the roadside communication device 10.

[0055] First, it is assumed that the wireless communication unit 110 of the roadside communication device 10 receives a vehicle transmission packet transmitted by the in-vehicle communication device 20 (S101).

[0056] When the wireless communication unit 110 receives a vehicle-transmitted packet from the in-vehicle communication device 20, it supplies information set in the vehicle-transmitted packet (including, for example, host vehicle information, a result of the obstruction determination process, surrounding vehicle information, and the amount of power attenuation) to the vehicle-transmitted packet storage unit 121 for recording (S102). At this time, the wireless communication unit 110 may measure the communication quality (for example, the reception strength of radio waves when received) when the vehicle-transmitted packet is received, and supply the information on the communication quality together with the information on the vehicle-transmitted packet to the vehicle-transmitted packet storage unit 121. The vehicle-transmitted packet storage unit 121 stores the information on the vehicle-transmitted packet and the information on the communication quality in association with each other.

[0057] Next, the transmission power adjustment value calculation unit 122 acquires the information of the vehicle transmission packet stored in the vehicle transmission packet storage unit 121 (the information stored in step S101), checks the result of the obstruction determination process (S103), and if obstruction is present, proceeds to step S104 described below, and if obstruction is not present, proceeds to step S106 described below.

[0058] If the result of the obstruction determination process is that obstruction exists in the above-mentioned step S103, the transmission power adjustment value calculation unit 122 extracts information on vehicle-transmitted packets stored in the vehicle-transmitted packet memory unit 121 (information on vehicle-transmitted packets received from the target vehicle-mounted communication device) for which the result of the obstruction determination process is that obstruction exists for a certain period of time (for example, for the most recent certain period of time; including information on communication quality), and estimates the communication quality for each position of the target vehicle-mounted communication device (S104).

[0059] Next, the transmission power adjustment value calculation unit 122 compares the communication quality (hereinafter referred to as "reception communication quality") when receiving a vehicle-transmitted packet transmitted from a specific position (for example, a position within the service area that is expected to be the worst (for example, a position farthest from the roadside communication device 10)) for the target in-vehicle communication device with the target communication quality (hereinafter referred to as "target communication quality"), and calculates a power adjustment coefficient G i(S105), and the process proceeds to step S108, which will be described later. For example, if the reception communication quality does not satisfy the target communication quality, the transmission power adjustment value calculation unit 122 updates (adjusts) the power adjustment coefficient G i to a larger value, and if the received communication quality is higher than the target communication quality, the power adjustment coefficient G i In other words, the transmission power adjustment value calculation unit 122 may update the power adjustment coefficient G to a smaller value so that the reception communication quality approaches the target communication quality. i At this time, the transmission power adjustment value calculation unit 122 updates (adjusts) the power adjustment coefficient G i The adjustment amount (adjustment width) for adjusting the may be a constant value, or may be varied according to the value of the reception communication quality or the difference between the reception communication quality and the target communication quality.

[0060] If the result of the obstruction determination process is no obstruction in the above-mentioned step S103, the transmission power adjustment value calculation unit 122 extracts information on vehicle-transmitted packets stored in the vehicle-transmitted packet memory unit 121 (information on vehicle-transmitted packets received from the target vehicle-mounted communication device) for a certain period (the most recent certain period) that have been subject to the obstruction determination process, and estimates the communication quality for each position of the target vehicle-mounted communication device (S106).

[0061] Next, the transmission power adjustment value calculation unit 122 compares the reception communication quality of the vehicle-transmitted packet received from a specific position (for example, a position within the service area that is expected to be the worst (for example, a position farthest from the roadside communication device 10)) for the vehicle-mounted communication device of interest with the target communication quality, and calculates a power adjustment constant G c (S107), and the process proceeds to step S108, which will be described later. For example, if the reception communication quality does not satisfy the target communication quality, the transmission power adjustment value calculation unit 122 updates (adjusts) the power adjustment constant G c to a larger value, and if the received communication quality is greater than the target communication quality, the power adjustment constant G c In other words, the transmission power adjustment value calculation unit 122 may update the power adjustment constant G to a smaller value so that the reception communication quality approaches the target communication quality.c At this time, the transmission power adjustment value calculation unit 122 updates (adjusts) the power adjustment constant G c The amount of adjustment for adjusting the quality of received communication may be a constant value, or may be varied depending on the value of the received communication quality or the difference between the received communication quality and the target communication quality.

[0062] Furthermore, when calculating communication quality (e.g., received power), it is desirable for transmit power adjustment value calculation unit 122 to perform the calculation based on a large number of samples, but because power varies greatly with slight differences in position due to multipath fading, calculation by averaging or the like may result in insufficient estimation accuracy of the amount of power adjustment. Therefore, transmit power adjustment value calculation unit 122 may estimate the amount of power attenuation by assuming that the accumulated data follows a specific distribution, taking into account power fluctuations depending on the location within the service area, thereby improving communication success.

[0063] After the update process in steps S105 and S107, the transmission power adjustment value calculation unit 122 calculates at least the roadside information (including the service area information and the location information of the roadside communication device 10) and the updated power adjustment amount (power adjustment coefficient G i or power adjustment constant G c ) to the roadside transmission packet generator 123. The roadside transmission packet generator 123 controls the wireless communication unit 110 to transmit a roadside transmission packet in which the supplied information is set (S108).

[0064] Thereafter, when the roadside communication device 10 receives the next vehicle-transmitted packet, the process returns to step S101 and repeats the operation.

[0065] Next, the operation of the vehicle-mounted communication device 20 (target vehicle-mounted communication device) will be described with reference to FIG.

[0066] FIG. 4 is a flowchart showing the operation of the in-vehicle communication device 20 (the in-vehicle communication device of interest).

[0067] First, it is assumed that the wireless communication unit 210 of the in-vehicle communication device 20 receives the roadside transmission packet transmitted by the roadside communication device 10 (S201).

[0068] When the wireless communication unit 210 receives a roadside transmission packet from the in-vehicle communication device 20, it supplies the information set in the roadside transmission packet (e.g., power adjustment amount and roadside information, etc.) to the roadside transmission packet memory unit 221 and records it (S202).

[0069] Next, the occlusion determination unit 222 acquires host vehicle information (information including host vehicle position information) from the host vehicle information collection unit 240 (S203), identifies the area (service area covered by the sender of the received roadside transmission packet) described in the roadside information (service area information) set in the roadside transmission packet received by the host vehicle, and determines whether the host device is located within the service area (S204). If the host device is located within the service area, the communication control unit 220 (occlusion determination unit 222) proceeds to step S205, which will be described later, and if not, ends the processing of this flowchart.

[0070] If the position of the own device is within the service area, the occlusion determination unit 222 acquires information on surrounding vehicles (surrounding vehicle information) from the surrounding vehicle detection unit 230 (S205). At this time, if the surrounding vehicle detection unit 230 acquires multiple pieces of surrounding vehicle information (information on multiple surrounding vehicles), all of the surrounding vehicle information may be held.

[0071] Next, the occlusion determination unit 222 performs occlusion determination processing to determine whether or not occlusion by a nearby vehicle (occlusion of communication between the device itself and the roadside communication device 10) occurs based on the acquired nearby vehicle information, the position information of the device itself, and the position information of the roadside communication device 10 (S206), and checks the result of the occlusion determination processing (S207). If the result of the occlusion determination processing indicates that occlusion occurs, the communication control unit 220 proceeds to step S208, which will be described later, and if not, proceeds to step S210, which will be described later.

[0072] At this time, the method of the occlusion determination process performed by the occlusion determination unit 222 is not limited, but the process shown in FIG. 5 may be performed.

[0073] FIG. 5 is a diagram showing an example of the occlusion determination process performed by the occlusion determination unit 222. In FIG.

[0074] Figure 5 shows an example of occlusion determination processing, in which the shape of each surrounding vehicle is simulated (modeled) as a rectangular parallelepiped specified based on the vehicle height, width, and length. In Figure 5, occlusion vehicle (surrounding vehicle) A is shown as a rectangular parallelepiped. In this case, the vehicle height, width, and length to be applied to the rectangular parallelepiped can be determined using the vehicle shape information included in the surrounding vehicle information. In Figure 5, the height, width, and length of occlusion vehicle A (rectangular parallelepiped) are h, w, and l, respectively.

[0075] In FIG. 5, the position of the vehicle (the position of the wireless antenna 211) is P0, and the position of the roadside communication device 10 (the position of the wireless antenna 111; information included in the roadside information) is P m Furthermore, in FIG. 5, the position P0 of the vehicle and the position P m Furthermore, in FIG. 5, the position where the line B intersects with one surface (the surface closest to the subject vehicle A) of the subject vehicle as viewed from the subject vehicle's position P0 is designated as P. k It states that:

[0076] For example, the occlusion determination unit 222 may determine that "occlusion exists" when there is a nearby vehicle (occluding vehicle) that exists in a position that blocks the straight line B connecting the local device and the roadside communication device 10, based on the position information of the local device and the position information of the roadside communication device 10, and may determine that "occlusion does not exist" when there is no nearby vehicle that blocks the straight line B. In the state of Fig. 5, there is nearby vehicle A (occluding vehicle) that blocks the straight line B, so it is determined that there is occlusion.

[0077] If the result of the obstruction determination process is confirmed to be "obstructed" in step S207 above, the transmission power adjustment value calculation unit 223 of the communication control unit 220 estimates the amount of power attenuation L due to obstruction (the amount of power attenuation during wireless communication between the device itself and the roadside communication device 10) (S208).

[0078] There is no limitation on the method for estimating the amount of power attenuation L, but for example, a knife-edge diffraction model or the like can be applied. As a method for estimating the amount of power attenuation L, in addition to the knife-edge diffraction model, a formula for calculating the amount of power attenuation based on the distance (and size) from the shielding object can also be applied.

[0079] As a method for estimating the power attenuation L using the knife-edge diffraction model, for example, the example in Reference 1 below can be applied. [References 1] ETSI (European Telecommunications Standards Institute), "3GPP TR 38. 901 V14.3.0 Blockage model B," 5G; Study on channel model for frequencies from 0.5 to 100 GHz (3GPP TR 38.901 version 14.3.0 Release 14) ”, pp. 58-60, [Online], INTERNET, [Retrieved August 12, 2024] <URL:https: / / www.etsi.org / deliver / etsi_tr / 138900_138999 / 138901 / 14.03.00_60 / tr_138901v140300p.pdf>

[0080] Next, the transmission power adjustment value calculation unit 223 calculates the calculated power attenuation amount L and the power adjustment amount (power adjustment constant G c and power adjustment coefficient G i ) and calculates the total power adjustment amount G according to equation (1) (S209), and then proceeds to step S211, which will be described later.

[0081] On the other hand, if the result of the occlusion determination process is confirmed to be "no occlusion" in step S207, the transmission power adjustment value calculation unit 223 calculates the power adjustment amount (power adjustment constant G c ) according to equation (2), the total power adjustment amount G is calculated (S210), and the process proceeds to step S211, which will be described later.

[0082] After calculating the total power adjustment amount G in step S209 or step S210, the transmission power adjustment value calculation unit 223 supplies the calculated total power adjustment amount G to the wireless communication unit 210 to be reflected in the wireless communication, and also supplies various information to the vehicle transmission packet generation unit 224. At this time, the transmission power adjustment value calculation unit 223 may supply information including the result of the obstruction determination process, the calculated total power adjustment amount G, host vehicle information, and obstructed vehicle information (which may be none if there is no obstruction) to the vehicle transmission packet generation unit 224. Then, the vehicle transmission packet generation unit 224 generates a vehicle transmission packet in which the information supplied from the transmission power adjustment value calculation unit 223 is set, and sends the packet to the wireless communication unit 210 (S211).

[0083] Next, details of the process by which transmission power adjustment value calculation section 223 calculates amount of power attenuation L will be described with reference to FIGS.

[0084] Here, the transmission power adjustment value calculation unit 223 calculates the amount of power attenuation L during wireless communication between the device itself and the roadside communication device 10 by processing using the knife-edge diffraction model described in the above-mentioned Reference 1.

[0085] First, the transmission power adjustment value calculation unit 223 selects one of the surfaces of the shielded vehicle A as a screen (shield) to be applied to the knife-edge diffraction model. The closer the screen is to the transmitting or receiving point of the radio wave, the larger the diffraction angle becomes, and the larger the diffraction loss tends to be. Therefore, the screen is selected from the position P0 of the vehicle itself or the position P of the roadside communication device 10. mThe surface closest to the position P0 of the subject vehicle is desirable. Note that the transmission power adjustment value calculation unit 223 may perform calculations for all surfaces (all eight surfaces) of the subject vehicle A, and adopt the surface with the largest diffraction loss as the screen. Here, the transmission power adjustment value calculation unit 223 selects the surface SC (the surface with diagonal lines in FIG. 5) that is closest to the position P0 of the subject vehicle as the screen. Hereinafter, this surface SC will also be referred to as the screen. Note that in FIG. 5, the surface SC is selected from the position P0 of the subject vehicle to the position P k The distance to is represented as "r'".

[0086] 6 and 7 are explanatory diagrams showing the configuration of the knife-edge diffraction model that transmission power adjustment value calculation unit 223 applies to screen SC.

[0087] In the knife-edge diffraction model shown in Figures 6 and 7, each position is shown in a three-dimensional coordinate system in which the screen SC is the XY plane and the direction perpendicular to the screen SC is the Z axis. Therefore, as shown in Figure 6, the dimension of the screen SC in the X direction is the vehicle width w, and the dimension in the Y direction is the height h. Also, here, as shown in Figures 5 to 7, the coordinates of the position P0 of the vehicle are (x0, y0, z0), and the position P where the line B intersects with the screen SC is (x0, y0, z0). k The coordinates of (x k ,y k ,z k ) Furthermore, as shown in FIG. 6, the upper edge (upper end) of the screen SC is EU, the lower edge (lower end) is ED, the right edge (right end) is ER, and the left edge (left end) is EL. Furthermore, in FIG. 6 and FIG. 7, the position P k The shortest distance from the upper edge EU to the position P k 6 and 7, the shortest distance from the position P k The shortest distance from the left edge EL to the position P k The shortest distance from the right edge ER to the right edge ER is w1. In this case, naturally, h1+h2=h and w1+w2=w.

[0088] FIG. 7(a) is a diagram of the screen SC and the position P0 of the vehicle as viewed from above, and FIG. 7(b) is a diagram of the screen SC and the position P0 of the vehicle as viewed from the left side.

[0089] Here, as shown in FIG. 7(a), the shortest distance from the position P0 of the vehicle to the right edge ER of the screen SC is D1. w1 , the shortest distance from the position P0 of the vehicle to the left edge EL of the screen SC is D1 w2 In addition, as shown in FIG. 7(b), the shortest distance from the position P0 of the vehicle to the upper edge EU of the screen SC is D1. h1 , the shortest distance from the position P0 of the vehicle to the lower edge ED of the screen SC is D1 h2 Let's say.

[0090] In this case, D1 h1 , D1 h2 , D1 w1 , D1 w2 , r' can be calculated by the following equations (3) to (7), respectively.

number

[0091] Then, based on the calculation results of the above equations (3) to (7), the power attenuation amount L [dB] (L dB ) can be calculated using the following formula (8). h1 , F h2 .F w1 , F w2 , can be calculated using equation (9). In other words, in this case, the diffraction loss in the knife-edge diffraction model shown in FIGS. 5 to 7 is the amount of power attenuation L due to the shielding by the shielded vehicle A.

number

[0092] (A-3) Effects of the embodiment In the road-to-vehicle communication system 1 of this embodiment, it is possible to transmit at an appropriate power depending on the presence or absence of shielding and the positional relationship with the shielded vehicle, compared to when the transmission power of the in-vehicle communication device 20 is set uniformly assuming that shielding will occur. As a result, the road-to-vehicle communication system 1 can maximize the possibility of successful information transmission (communication between the roadside communication device 10 and the in-vehicle communication device 20) while suppressing interference with other systems.

[0093] Furthermore, in the road-to-vehicle communication system 1 of this embodiment, when a new feature is installed in or around a service area, the radio wave propagation environment changes and the appropriate transmission power changes, but the amount of power attenuation can always be adjusted regardless of whether there is obstruction, which allows the road-to-vehicle communication system 1 of this embodiment to autonomously respond to environmental changes after installation.

[0094] (B) Other embodiments The present invention is not limited to the above-described embodiments, and may include modified embodiments such as those exemplified below.

[0095] (B-1) In the road-to-vehicle communication system 1 of the above embodiment, the power adjustment amount (power adjustment constant G c and power adjustment coefficient G i ) may be set to a fixed value, and the fixed value may be set in advance in the roadside communication device 10 and each in-vehicle communication device 20. In this case, there is no need to transmit and receive the amount of power adjustment between the roadside communication device 10 and each in-vehicle communication device 20. [Explanation of symbols]

[0096] 1... road-to-vehicle communication system, 10... roadside communication device, 110... wireless communication unit, 111... wireless antenna, 112... vehicle transmission packet generation unit, 120... communication control unit, 121... vehicle transmission packet storage unit, 122... transmission power adjustment value calculation unit, 123... roadside transmission packet generation unit, 20... vehicle-mounted communication device, 210... wireless communication unit, 211... wireless antenna, 220... communication control unit, 221... roadside transmission packet storage unit, 222... obstruction determination unit, 223... transmission power adjustment value calculation unit, 224... vehicle transmission packet generation unit, 230... surrounding vehicle detection unit, 240... host vehicle information collection unit, 30... vehicle, 40... roadside infrastructure

Claims

1. A road-to-vehicle communication system including an on-board communication device mounted on a vehicle on a road and a roadside communication device arranged on the road and wirelessly communicating with the on-board communication device, The in-vehicle communication device an information storage means for storing surrounding vehicle information including position information of surrounding vehicles located around the in-vehicle communication device and information regarding the shapes of the surrounding vehicles, host vehicle information including position information of the in-vehicle communication device, and roadside information including position information of the roadside communication device; an occlusion determination means for performing an occlusion determination process to determine whether the wireless communication between the in-vehicle communication device and the roadside communication device is in an occlusion state where the wireless communication between the in-vehicle communication device and the roadside communication device is occluded by the surrounding vehicle, or in an unoccluded state where the wireless communication between the in-vehicle communication device and the roadside communication device is not occluded by the surrounding vehicle, based on the surrounding vehicle information, the host vehicle information, and the roadside information; an in-vehicle transmission power adjustment means for estimating, when it is determined by the obstruction determination process that obstruction exists, an amount of power attenuation of radio waves transmitted and received between the in-vehicle communication device and the roadside communication device due to a obstructing vehicle that obstructs wireless communication between the in-vehicle communication device and the roadside communication device, based on the surrounding vehicle information, the host vehicle information, and the roadside information, and adjusting, based on the amount of power attenuation, an amount of power of radio waves to be transmitted to the roadside communication device while the result of the obstruction determination process indicates a state of obstruction; an in-vehicle packet transmitting means for generating an in-vehicle transmission packet in which information including at least the amount of power attenuation and the result of the obstruction determination process is set, and transmitting the in-vehicle transmission packet to the roadside communication device; The roadside communication device a roadside transmission power adjusting means for adjusting the amount of power of radio waves transmitted to the vehicle-mounted communication device based on the amount of power attenuation set in the vehicle-mounted transmission packet while the result of the obstruction determination process set in the vehicle-mounted transmission packet indicates obstruction; A road-to-vehicle communication system.

2. the roadside transmission power adjustment means adjusts the amount of power of radio waves to be transmitted to the in-vehicle communication device to a value obtained by multiplying the amount of power attenuation set in the in-vehicle transmission packet by a predetermined power adjustment coefficient while the result of the obstruction determination process set in the in-vehicle transmission packet indicates obstruction, and updates the power adjustment coefficient based on the reception strength of radio waves received from the in-vehicle communication device; the roadside communication device further includes a roadside packet transmitting means for generating a roadside transmission packet in which information including at least the power adjustment coefficient is set and transmitting the roadside transmission packet to the in-vehicle communication device; The vehicle-mounted transmission power adjusting means adjusts the amount of power of the radio waves to be transmitted to the roadside communication device while the result of the obstruction determination process indicates an obstruction state, to a value obtained by multiplying the power adjustment coefficient set in the roadside transmission packet by the amount of power attenuation.

2. The road-to-vehicle communication system according to claim 1.

3. the roadside transmission power adjusting means sets the amount of power of the radio waves to be transmitted to the in-vehicle communication device to a predetermined power adjustment constant while the result of the obstruction determination process set in the in-vehicle transmission packet indicates no obstruction; the roadside packet transmitting means further sets information of the power adjustment constant for the roadside transmission packet; The vehicle-mounted transmission power adjusting means adjusts the amount of power of the radio waves to be transmitted to the roadside communication device while the result of the obstruction determination process indicates that there is no obstruction, to the power adjustment constant set in the roadside transmission packet.

3. The road-to-vehicle communication system according to claim 2.

4. A road-to-vehicle communication system including an on-board communication device mounted on a vehicle on a road and a roadside communication device arranged on the road and wirelessly communicating with the on-board communication device, the in-vehicle communication device includes an information storage means, an obstruction determination means, an in-vehicle transmission power adjustment means, and an in-vehicle packet transmission means; the roadside communication device has roadside transmission power adjusting means, the information holding means holds nearby vehicle information including position information of nearby vehicles located around the in-vehicle communication device and information regarding the shapes of the nearby vehicles, host vehicle information including position information of the in-vehicle communication device, and roadside information including position information of the roadside communication device; the obstruction determination means performs obstruction determination processing to determine, based on the surrounding vehicle information, the host vehicle information, and the roadside information, whether the vehicle is in an obstructed state in which wireless communication between the in-vehicle communication device and the roadside communication device is obstructed by the surrounding vehicle, or whether the vehicle is in an unobstructed state in which wireless communication between the in-vehicle communication device and the roadside communication device is not obstructed by the surrounding vehicle; when it is determined by the obstruction determination process that obstruction exists, the in-vehicle transmission power adjustment means estimates an amount of power attenuation of radio waves transmitted and received between the in-vehicle communication device and the roadside communication device due to a obstructing vehicle that obstructs wireless communication between the in-vehicle communication device and the roadside communication device, based on the surrounding vehicle information, the host vehicle information, and the roadside information, and adjusts the amount of power of radio waves to be transmitted to the roadside communication device while the result of the obstruction determination process indicates a state of obstruction, based on the amount of power attenuation; the in-vehicle packet transmitting means generates an in-vehicle transmission packet in which information including at least the amount of power attenuation and a result of the obstruction determination process is set, and transmits the in-vehicle transmission packet to the roadside communication device; The roadside transmission power adjusting means adjusts the amount of power of the radio waves to be transmitted to the vehicle-mounted communication device based on the amount of power attenuation set in the vehicle-mounted transmission packet while the result of the obstruction determination process set in the vehicle-mounted transmission packet indicates that obstruction exists. A road-to-vehicle communication method.

5. In a road-to-vehicle communication system including an on-vehicle communication device mounted on a vehicle on a road and a roadside communication device disposed on the road and communicating wirelessly with the on-vehicle communication device, an information storage means for storing surrounding vehicle information including position information of surrounding vehicles located around the in-vehicle communication device and information regarding the shapes of the surrounding vehicles, host vehicle information including position information of the in-vehicle communication device, and roadside information including position information of the roadside communication device; an occlusion determination means for performing an occlusion determination process to determine whether the wireless communication between the in-vehicle communication device and the roadside communication device is in an occlusion state where the wireless communication between the in-vehicle communication device and the roadside communication device is occluded by the surrounding vehicle, or in an unoccluded state where the wireless communication between the in-vehicle communication device and the roadside communication device is not occluded by the surrounding vehicle, based on the surrounding vehicle information, the host vehicle information, and the roadside information; an in-vehicle transmission power adjustment means for estimating, when it is determined by the obstruction determination process that obstruction exists, an amount of power attenuation of radio waves transmitted and received between the in-vehicle communication device and the roadside communication device due to a obstructing vehicle that obstructs wireless communication between the in-vehicle communication device and the roadside communication device, based on the surrounding vehicle information, the host vehicle information, and the roadside information, and adjusting, based on the amount of power attenuation, an amount of power of radio waves to be transmitted to the roadside communication device while the result of the obstruction determination process indicates a state of obstruction; and an in-vehicle packet transmitting means for generating an in-vehicle transmission packet containing information including at least the amount of power attenuation and the result of the obstruction determination process and transmitting the packet to the roadside communication device. An in-vehicle communication device comprising:

6. a computer mounted on the vehicle-mounted communication device that constitutes a road-to-vehicle communication system, the computer being mounted on the vehicle-mounted communication device and a roadside communication device that is arranged on the road and that wirelessly communicates with the vehicle-mounted communication device; an information storage means for storing surrounding vehicle information including position information of surrounding vehicles located around the in-vehicle communication device and information regarding the shapes of the surrounding vehicles, host vehicle information including position information of the in-vehicle communication device, and roadside information including position information of the roadside communication device; an occlusion determination means for performing an occlusion determination process to determine whether the wireless communication between the in-vehicle communication device and the roadside communication device is in an occlusion state where the wireless communication between the in-vehicle communication device and the roadside communication device is occluded by the surrounding vehicle, or in an unoccluded state where the wireless communication between the in-vehicle communication device and the roadside communication device is not occluded by the surrounding vehicle, based on the surrounding vehicle information, the host vehicle information, and the roadside information; an in-vehicle transmission power adjustment means for estimating, when it is determined by the obstruction determination process that obstruction exists, an amount of power attenuation of radio waves transmitted and received between the in-vehicle communication device and the roadside communication device due to a obstructing vehicle that obstructs wireless communication between the in-vehicle communication device and the roadside communication device, based on the surrounding vehicle information, the host vehicle information, and the roadside information, and adjusting, based on the amount of power attenuation, an amount of power of radio waves to be transmitted to the roadside communication device while the result of the obstruction determination process indicates a state of obstruction; an in-vehicle packet transmitting means for generating an in-vehicle transmission packet in which information including at least the amount of power attenuation and the result of the obstruction determination process is set, and transmitting the in-vehicle transmission packet to the roadside communication device; and a vehicle-mounted communication program that functions as a communication device.

7. In the roadside communication device that constitutes a road-to-vehicle communication system comprising an onboard communication device mounted on a vehicle on a road and a roadside communication device that is placed on the road and communicates wirelessly with the onboard communication device, the roadside communication device is characterized in that, while the result of a shielding determination process set in an onboard transmission packet sent from the onboard communication device to the onboard communication device indicates a shielded state, in which wireless communication between the onboard communication device and the onboard communication device is shielded by another nearby vehicle, or an unshielded state, in which wireless communication between the onboard communication device and the onboard communication device is not shielded by the nearby vehicle, the roadside communication device has a roadside transmission power adjustment means that adjusts the amount of power of radio waves to be transmitted to the onboard communication device based on the amount of power attenuation of radio waves transmitted and received between the onboard communication device and the onboard communication device by a shielding vehicle that shields the wireless communication between the onboard communication device and the onboard communication device, as set in the onboard transmission packet.

8. A roadside communication program characterized by causing a computer mounted on a roadside communication device that constitutes a road-to-vehicle communication system comprising an onboard communication device mounted on a vehicle on a road and a roadside communication device that is positioned on the road and communicates wirelessly with the onboard communication device to function as a roadside transmission power adjustment means that, while the result of a shielding determination process set in an onboard transmission packet sent from the onboard communication device to the onboard communication device is a shielded state, in which wireless communication between the onboard communication device and the onboard communication device is a shielded state, adjusts the amount of power of radio waves to be transmitted to the onboard communication device based on the amount of power attenuation of radio waves transmitted and received between the onboard communication device and the onboard communication device by a shielding vehicle that shields the wireless communication between the onboard communication device and the onboard communication device, as set in the onboard transmission packet.

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