JP2017016681A - Roadside communication apparatus and communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a road-to-road communication period during a road-to-vehicle communication period.SOLUTION: A road-side communication apparatus 2 includes a control unit for controlling to transmit downlink data to a vehicle in a road-to-vehicle communication period allocated to the own apparatus. The downlink data may include static information and dynamic information. In a first road-to-vehicle communication period, the dynamic information and the static information are transmitted as the downlink data. In a second road-to-vehicle communication period, the dynamic information is transmitted as the downlink data without transmission of the static information. A portion of a period in the second road-to-vehicle communication period in which a temporal margin is produced because of not transmitting the static information is secured as a period for other purposes to be used for road-to-road communication or the like.SELECTED DRAWING: Figure 5

Description

  The present invention relates to, for example, a roadside communication device used for an intelligent transport system (ITS).

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, vehicle safety has been achieved by receiving information from infrastructure devices installed on roads or exchanging information between vehicles and utilizing these information. An intelligent road traffic system that improves the above has been studied (for example, see Patent Document 1). Moreover, the specification of the radio | wireless communication which assumed the above intelligent road traffic systems is drawn up (for example, refer nonpatent literature 1).
Such an intelligent road traffic system is mainly composed of a plurality of roadside communication devices which are wireless communication devices on the infrastructure side and a plurality of in-vehicle communication devices which are wireless communication devices mounted on each vehicle.

  In this case, the combination of communication performed between each communication subject includes road-to-vehicle (or vehicle-road) communication performed by a roadside communication device and a vehicle-mounted communication device, and vehicle-to-vehicle communication performed between vehicle-mounted communication devices, roadside communication Inter-road communication performed by communication devices is included.

Japanese Patent No. 2806801

The Japan Radio Industry Association, "700MHz band Intelligent Transport System ARIB-STD T109 1.0 Edition", [online], February 14, 2012, [Search May 8, 2012], Internet <http : //www.arib.or.jp/tyosakenkyu/kikaku_tushin/tsushin_kikaku_number.html>

  However, since the usable frequency band (for example, about 10 MHz) is limited in the above-described intelligent road traffic system, it cannot be said that the band is sufficient only by sharing road-to-vehicle communication and inter-vehicle communication. It is very difficult to secure a bandwidth for roadside communication.

  In addition to road-to-road communication, communication between pedestrian communication devices and roadside communication devices that pedestrians have, communication between pedestrian communication devices and in-vehicle communication devices. Communication such as certain inter-vehicle communication is also assumed.

  Therefore, an object of the present invention is to make it possible to perform communication other than road-to-vehicle communication (such as road-to-road communication) using a road-to-vehicle communication period.

(1) The present invention is a roadside communication device including a control unit that performs control to transmit downlink data to a vehicle in a road-to-vehicle communication period allocated to the own device, wherein the downlink data includes static information And the dynamic information, the dynamic information is information whose information content fluctuates with the passage of time is higher than the static information, and the control unit In the assigned first road-to-vehicle communication period, the dynamic information and the static information are controlled to be transmitted as the downlink data, and the other road-to-vehicle communication period assigned to the own device is the first road-to-vehicle communication period. In a second road-to-vehicle communication period that is different from the road-to-vehicle communication period, the dynamic information is controlled to be transmitted without transmitting the static information as the downlink data. Department period And a roadside communication device, characterized by controlling so as to secure another object period to be used for other communication purposes than the road-vehicle communication.

  According to the present invention, dynamic information and static information are transmitted in the first road-to-vehicle communication period, but static information is not transmitted in the second road-to-vehicle communication period. There is a time margin. By securing the other purpose period in the second road-to-vehicle communication period with sufficient time, communication for other purposes than the road-to-vehicle communication (for example, road-to-road communication) can be performed.

(2) The control unit may control to perform communication other than the road-to-vehicle communication using the other purpose period secured in the road-to-vehicle communication period allocated to another roadside communication device. it can. In this case, communication other than road-to-vehicle communication (for example, road-to-road communication) can be performed using the other purpose period secured in the road-to-vehicle communication period assigned to other roadside communication devices.

(3) The occurrence frequency of the second road-to-vehicle communication period is preferably lower than the occurrence frequency of the first road-to-vehicle communication period. Since the occurrence frequency of the second road-to-vehicle communication period is low, it is possible to suppress a decrease in the transmission frequency of static information.

(4) It is preferable that the said other purpose period is ensured as the range of the predetermined period from the end of the 2nd road-vehicle communication period. In this case, the range of the predetermined period from the end of the second road-to-vehicle communication period is the other purpose period.

(5) The second road-to-vehicle communication period is constituted by a plurality of road-to-vehicle communication time slots that are separated in time, and the other purpose period is the plurality of roads constituting the second road-to-vehicle communication period. Of the inter-vehicle communication time slots, it is preferable that the predetermined time period is secured from the end of the last road-to-vehicle communication time slot. In this case, the range of the predetermined period from the end of the last road-to-vehicle communication time slot among the plurality of road-to-vehicle communication time slots is the other purpose period.

(6) Preferably, the one other purpose period is used for a plurality of communication purposes other than the road-to-vehicle communication. In this case, one other purpose period can be used for a plurality of communication purposes.

(7) The plurality of other communication purposes includes a plurality of road-to-road communication that is communication between roadside communication devices, and the plurality of road-to-road communication is road-to-road communication with different transmission sources. Is preferred. In this case, one other purpose period can be used for a plurality of road-to-road communication by a plurality of roadside communication devices.

(8) The present invention viewed from another viewpoint is a communication system including a plurality of roadside communication devices according to any one of (1) to (7).

  According to the present invention, it is possible to ensure the other purpose period during the road-to-vehicle communication period.

It is a schematic perspective view which shows one Embodiment of an intelligent road traffic system. It is a block diagram of a roadside communication apparatus. (A) shows a frame, and (b) is a diagram showing the structure (partial) of slots in the frame and how to assign them. It is a figure which shows the slot allocation of each intersection. It is a figure which shows the example of the method of utilization of the road-vehicle communication period.

[Overall system configuration]
FIG. 1 is a schematic perspective view showing an overall configuration of an intelligent road traffic system (ITS) according to an embodiment of the present invention. In this embodiment, as an example of the road structure, a grid structure in which a plurality of roads in the north-south direction and the east-west direction intersect with each other is assumed.
As shown in FIG. 1, the intelligent transportation system of this embodiment includes a traffic signal 1, a roadside communication device (radio device) 2, an in-vehicle communication device (radio device) 3 (see FIG. 2), a central device 4, and in-vehicle communication. A vehicle 5 on which the machine 3 is mounted, and a roadside sensor 6 including a vehicle detector, a monitoring camera, and the like are included.

The traffic signal 1 and the roadside communication device 2 are installed at each of a plurality of intersections A1 to A5, B1 to B5, C1 to C5, and D1 to D5, and are connected to the router 8 via a wired communication line 7 such as a telephone line. It is connected. This router 8 is connected to the central device 4 in the traffic control center.
The central device 4 constitutes a local area network (LAN) with the traffic signal device 1 and the roadside communication device 2 in the area that it is in charge of. The central device 4 may be installed on the road instead of the traffic control center.

The traffic signal device 1 and the roadside communication device 2 (online roadside communication device) connected to the central device 4 via the wired communication line 7 are a part of all the roadside communication devices 2 included in the area controlled by the central device 4. There is also a roadside communication device 2 (stand-alone roadside communication device) that is not connected to the central device 4 via the wired communication line 7.
In FIG. 1, the roadside communication devices 2 installed at the intersections A1 to A5 are online roadside communication devices, and the roadside communication devices 2 installed at the other intersections B1 to B5, C1 to C5, and D1 to D are stands. Alone roadside communication device. Thus, the installation / maintenance cost of the wired communication line 7 can be reduced by not using all the roadside communication devices 2 as online roadside communication devices.

The roadside sensor 6 is installed in various places on the road in the jurisdiction area for the purpose of counting the number of vehicles flowing into each intersection. The roadside sensor 6 is composed of a vehicle sensor for ultrasonically sensing the vehicle 5 passing underneath, or a monitoring camera for photographing road traffic conditions in time series, and the sensing information and image data are transmitted via the communication line 7. To the central device 4.
In FIG. 1, for simplification of illustration, only one signal lamp is depicted at each intersection. However, at each actual intersection, at least four signal lamps are used for ascending and descending roads that intersect each other. Is installed.

In an intelligent road traffic system, a plurality of roadside communication devices (radio devices) 2 installed at each of a plurality of intersections constituting a wireless communication system are wirelessly communicated with an in-vehicle communication device 3 of a vehicle traveling around the roadside communication device. (Road-to-vehicle communication) is possible.
Each roadside communication device 2 is also capable of wireless communication (inter-road communication) with other roadside communication devices 2 that are located within a predetermined range within which their transmission waves reach.
An in-vehicle communication device (radio device) 3 that also constitutes a wireless communication system performs wireless communication with the roadside communication device 2 and also wirelessly communicates with other in-vehicle communication devices 3 using a carrier sense method (inter-vehicle communication). Is possible.

  As shown in FIG. 2, the roadside communication device 2 includes a wireless communication unit (transmission / reception unit) 21 to which an antenna 20 for wireless communication is connected, a control unit 23 that performs processing such as communication control, and necessary information. And a storage unit 24 for storing. The online roadside communication device 2 connected to the central device 4 via the wired communication line 7 further includes a wired communication unit 22 for communicating with the central device 4 via the wired communication line 7.

[Wireless communication systems, etc.]
FIG. 3A shows a radio frame used in the radio communication system. This radio frame has a time axis length (frame length) set to 100 milliseconds. That is, 10 frames are generated per second.
The frame is generated based on, for example, 1 PPS (signal with a period of 1 second) included in a GPS signal received by a GPS receiver (not shown) included in the roadside communication device 2.

FIG. 3B shows a structure (a part) inside one radio frame. As shown in FIG. 3B, one radio frame includes a first slot SL1 and a second slot SL2.
The first slot SL1 is a time slot for road-to-vehicle communication (road-to-vehicle communication period) assigned to the roadside communication device 2, and wireless transmission by the roadside communication device 2 is permitted in this time zone.
On the other hand, the second slot SL2 is a time slot (vehicle communication period) for the in-vehicle communication device 3, and since this time zone is opened for wireless transmission by the in-vehicle communication device 3, the road side communication device 2 is in the second slot. In SL2, wireless transmission is not performed.

The first slots SL1 and the second slots SL2 included in the radio frame are alternately arranged in the time axis direction.
Each first slot SL1 is assigned a slot number i.

One or more slots among a plurality of first slots SL1 (for example, 16 first slots) included in the radio frame are allocated to the roadside communication device 2. The roadside communication device 2 recognizes which slot is assigned to itself by the slot number i.
When one slot among the plurality of first slots SL1 included in the radio frame is allocated to one roadside communication device 2, for example, the intersection of the first slot SL1 with i = 1 included in the radio frame Assigned to the roadside communication devices 2 of A2, B5, C3, D1, and assigned to the roadside communication device 2 of the intersections A3, B1, C4, D2 to the first slot SL1 of i = 2 and the first of i = 3 The slot SL1 is assigned to the roadside communication devices 2 at the intersections A4, B2, C5, D3, the i = 4 first slot SL1 is assigned to the roadside communication devices 2 at the intersections A5, B3, C1, D4, The first slot SL1 with i = 5 is assigned to the roadside communication device 2 at the intersections A1, B4, C2, and D5.

  FIG. 4 shows how to assign the first slot SL1 according to FIG. 3 to the plurality of roadside communication devices 2 shown in FIG. In FIG. 4, the numbers in the circles at the respective intersections indicate the slot numbers i. Each roadside communication device 2 performs road-to-vehicle communication in the first slot SL1 of the slot number i assigned to the own device 2.

  When the same first slot SL1 is assigned to the roadside communication device 2 at the adjacent intersection, the vehicle 5 between the adjacent intersections receives radio waves of road-to-vehicle communication from both roadside communication devices 2, Interference occurs. However, as shown in FIG. 3, by distributing and assigning the same first slots SL <b> 1, interference during road-to-vehicle communication by each roadside communication device 2 can be prevented.

[Examination of number of slots]
The slot assignment as shown in FIG. 4 is appropriate when only road-to-vehicle communication is considered, but is not appropriate when road-to-vehicle communication is also considered, and radio wave interference may occur in road-to-road communication.

  For example, the first slot with slot number i = 5 is assigned to both the roadside communication device 2 at the intersection C2 and the roadside communication device 2 at the intersection D5 in FIG. And if the building of parts other than a road is considered between the intersections C2 and D5, it will be in the state where an electromagnetic wave cannot reach directly. Therefore, vehicles near the intersection C2 (vehicles in the service area of the roadside communication device 2 at the intersection C2) are almost subject to interference from the roadside communication device 2 at the intersection D5 that transmits radio waves for road-to-vehicle communication at the same timing. It is possible to receive the packet of the roadside communication device 2 at the intersection C2.

However, when the roadside communication device 2 at the intersection C2 and the roadside communication device 2 at the intersection D5 perform road-to-road communication at the same timing, the roadside communication device 2 at the intersection D5 is connected to the roadside communication device 2 at the intersection C5. When the road-to-road communication packet is transmitted, the road-to-road communication packet transmitted by the roadside communication device 2 at the intersection C2 becomes an interference wave and directly reaches the intersection C5.
For this reason, there is a possibility that the roadside communication device 2 at the intersection C5 cannot correctly receive the roadside communication packet from the roadside communication device 2 at the intersection D5.

  As described above, the road-to-vehicle communication and the road-to-road communication have different communication areas. Therefore, the road-to-vehicle communication and the road-to-road communication require different numbers of slots, and the road-to-road communication requires more slots. May increase. For example, road-to-vehicle communication may require 10 slots for road-to-road communication in a road structure in which allocation is possible with avoiding interference with 5 slots. That is, the road-to-road communication requires about twice as many slots as the road-to-vehicle communication.

[Transmission control by roadside communication device]
The control unit 23 of the roadside communication device 2 wirelessly transmits downlink data from the wireless communication unit 21 to the vehicle 5 (vehicle-mounted communication device 3) in the first slot SL1 (road-to-vehicle communication period) assigned to the own device 2. Control to send.

Downlink data includes static information and dynamic information.
Static information refers to information whose information content does not change in a short time, such as road alignment information indicating a road structure or the like, or restriction information indicating the content / period of traffic regulation.
The dynamic information refers to information whose information content can change from moment to moment, such as signal information indicating traffic signal information or sensor information indicating detection by the roadside sensor 6. In other words, the dynamic information is information whose information content varies with time as compared to static information.

  As a result of the study by the present inventor, if only one first slot SL1 is allocated to one roadside communication device 2 in one radio frame, both static information and dynamic information are sent. It turns out that it can be difficult. That is, the period of one first slot SL1 may be too short to send both static information and dynamic information.

Therefore, in the present embodiment, as shown in FIG. 5, a plurality (2 to 3) of adjacent first slots SL <b> 1 are allocated to one roadside communication device 2. Hereinafter, a group of a plurality of first slots SL1 assigned to the same roadside communication device 2 is referred to as a “channel”. In FIG. 5, 16 first slots SL1 are included in one radio frame, and there are seven channels (first channel to seventh channel). In FIG. 5, the first channel to the fifth channel are composed of two first slots SL1, and the sixth channel and the seventh channel are composed of three first slots SL1.
Each channel is a communicable period assigned to each roadside communication device 2 within one radio frame.

  FIG. 5 shows a first frame (first radio frame) and a second frame (second radio frame). For example, as shown in FIG. 3, the first frame is an odd-numbered frame (odd frame) among 10 frames (frame numbers: 1 to 10) generated per second, and the second frame is 1 Of the 10 frames (frame numbers: 1 to 10) generated per second, the frames are even-numbered frames (even frames). Therefore, the first frame and the second frame occur alternately. When the first frame and the second frame occur alternately, the frequency of occurrence of the first frame is equal to the frequency of occurrence of the second frame, but the frequency of occurrence of both frames may be different.

  The method of assigning each channel to the roadside communication device 2 is common to the first frame and the second frame. That is, the roadside communication device 2 assigned as the period in which the first channel can communicate in the first frame is assigned as the period in which the first channel can communicate in the second frame, and the same applies to the other channels.

In the first frame, the control unit 23 of the roadside communication device 2 transmits both dynamic information and static information as downlink data in the channel assigned to the own device 2 (first road-to-vehicle communication period). Control.
Further, in the second frame, the control unit 23 controls to transmit only dynamic information as downlink data in the channel (second road-to-vehicle communication period) allocated to the own device 2. Accordingly, in each channel, dynamic information is transmitted at a 100 ms period and static information is transmitted at a 200 ms period.

  That is, the dynamic information is transmitted in both the first frame and the second frame, but the static information is transmitted only in the first frame, and the transmission period of the static information is the transmission period of the dynamic information. Longer than Moreover, the fall of the transmission frequency of static information can be suppressed by making the occurrence frequency of a 2nd frame lower than the occurrence frequency of a 1st frame.

  In the second frame, only dynamic information is transmitted as downlink data, and a part of the remaining time in each channel is set as the other purpose period P. In this case, in a frame in which no static information is transmitted, a transmission period equal to or less than the data amount of the static information can be used for communication for other purposes.

  Static information such as road alignment information has a lower frequency of change in information content than dynamic information, so even if the transmission cycle is longer than that of dynamic information, the receiving side (in-vehicle communication device 3) There are few problems.

In this way, the control unit 23 performs processing for making the contents of the downlink data different between the first frame and the second frame based on the transmission cycle required for the downlink data (dynamic information and static information). Thus, it is possible to set the other target period P corresponding to the remaining time acquired by reducing the transmission frequency of the static information.
In addition, in the road-to-vehicle communication period in which static information is not transmitted, by preferentially securing the other purpose period P such as road-to-road communication, as compared with the case of securing the other purpose communication period exclusively, Reduction of the period during which vehicle-to-vehicle communication can be performed can also be suppressed.

In the second frame, the control unit 23 secures a range of a predetermined period from the end of the channel (second road-to-vehicle communication period) allocated to the own device 2 as the other purpose period P. The other purpose period P is a period used for communication purposes other than the road-to-vehicle communication by the own device 2 (for example, road-to-road communication).
The other purpose period P is a period secured according to a time (referred to as a surplus time) obtained by subtracting a time required for transmitting road-to-vehicle communication data from a road-to-vehicle communication period.
All or a part of the remaining time that is not allocated data is used as the other purpose period P. Since the surplus time can change, the length of the other purpose period can be changed according to the length of the surplus time.

  In view of the maximum amount of information when only dynamic information is transmitted as downlink data, the control unit 23, in the second frame, out of the channels (second road-to-vehicle communication period) allocated to the own device 2 A period (actual use period) that can actually be used in the road-to-vehicle communication period is secured, and the remaining period is secured as another purpose period P.

Here, the communication method shown in FIG. 3 conforms to a standard defined in Non-Patent Document 2 (hereinafter referred to as “current standard”). A new standard that increases the communication period dedicated to road-to-road communication in addition to the road-to-vehicle communication period, or a new standard that increases the number of road-to-vehicle communication periods as a period in which either road-to-vehicle communication or road-to-road communication can be performed When the standard is established, the in-vehicle communication device that conforms to the current standard cannot recognize the dedicated period for road-to-road communication or the added road-to-vehicle communication period. Interference or road-to-vehicle communication may cause interference.
On the other hand, according to this embodiment, since the other purpose period P is provided within the road-to-vehicle communication period, other systems such as road-to-road communication are maintained while maintaining the system of road-to-vehicle communication and vehicle-to-vehicle communication according to the current standard. You can add the desired communication.

  In addition, when a system with a new standard is introduced, for the in-vehicle communication device 3 that supports only the current standard, the roadside communication device 2 that conforms to the new standard communicates with each other in the destination address area of the MAC layer. Since the in-vehicle communication device 3 is considered to discard other-purpose communication data upon reception by performing communication for other purposes in a format that is not stipulated by the current standard, such as entering a destination, the in-vehicle communication device of the current standard There is no need to update the equipment and programs.

  In FIG. 5, the other purpose period P is secured as a range of a predetermined period from the end of the last slot among a plurality of slots constituting each channel. The other purpose period P may be secured in each of the plurality of slots constituting each channel, but one channel can be obtained by providing the other purpose period P at the end of the last slot of the plurality of slots constituting each channel. However, it can be prevented from being divided by the other purpose period P, which is advantageous. If one channel is divided, road-to-vehicle communication is interrupted accordingly, and the in-vehicle communication device 3 that is the reception side of road-to-vehicle communication can resume reception processing after interruption, It is necessary to retain the information before the interruption during the interruption. As a result, an extra memory amount is required, but an increase in the necessary memory amount can be suppressed by providing the other purpose period P at the end.

  In FIG. 5, the other purpose period P in each channel is divided into a plurality of (three in FIG. 5) divided periods D1, D2, and D3 so that a plurality of other purpose communications can be performed. In FIG. 5, there are only 7 channels for road-to-vehicle communication in one radio frame, but the other purpose period P in each channel is divided into three, so that the other purpose is 21 times in total. Communication opportunities are secured. That is, the other-purpose communication period is provided during the road-to-vehicle communication period, but for other-purpose communication, 21 channels, which are larger than the number of channels in the road-to-vehicle communication period (7 channels), are secured (note that Here, one divided period is regarded as one channel. However, when a plurality of (for example, two) divided periods are regarded as one channel, for example, the number is 14 channels, which is smaller than 21 channels.

  As described above, when trying to avoid interference appropriately, road-to-road communication requires more slots (channels) than road-to-vehicle communication. However, in the present embodiment, by dividing the other purpose period P, it is possible to secure a larger number of channels than the number of road-vehicle communication channels. Since a large number of channels (the number of division periods; the number of slots) can be ensured, assignment with avoiding interference becomes possible by assigning such division periods D1, D2, and D3 to roadside communication.

The other purpose period P in a certain channel (road-to-vehicle communication channel) may be used for transmission for road-to-road communication by the roadside communication device 2 to which the channel is assigned as the road-to-vehicle communication period. It may be used for transmission for road-to-road communication by a roadside communication device (a roadside communication device to which another channel is assigned as a road-to-vehicle communication period) 2.
When one other purpose period P is divided into a plurality of divided periods D1, D2 and D3, one other purpose period P can be used for a plurality of communication purposes. For example, each of the plurality of divided periods D1, D2, and D3 included in one other target period P can be used by the plurality of roadside communication devices 2 for road-to-road communication.

  Therefore, the control unit 23 of the roadside communication device 2 transmits downlink data in the road-to-vehicle communication using the channel assigned to the own device 2 (one or more road-to-vehicle communication period group). The other purpose period P in the given channel is released to other purpose communication such as roadside communication of the other roadside communication device 2 and is assigned to the other roadside communication device 2 (road-to-vehicle communication channel). The secured other purpose period P may be controlled to be used for other purpose communication (such as communication between roads) by the own device 2.

  The other purpose period P may be used not only for road-to-road communication but also for road-to-step communication or vehicle-to-vehicle communication. The other purpose period P may not be divided.

  With respect to the present invention, the embodiments disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not meant to be described above, but is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Traffic signal device 2 Roadside communication device 3 Car-mounted communication device 4 Central apparatus 5 Vehicle 6 Roadside sensor 7 Wired communication line 23 Control part 24 Storage part

Claims (8)

A roadside communication device including a control unit that performs control to transmit downlink data to a vehicle in a road-to-vehicle communication period allocated to the own device,
The downlink data may include static information and dynamic information, and the dynamic information is information that has a higher frequency of information content with time than the static information. ,
The controller is
In the first road-to-vehicle communication period assigned to the aircraft, control is performed to transmit the dynamic information and the static information as the downlink data,
In a second road-to-vehicle communication period other than the first road-to-vehicle communication period assigned to the own aircraft, the dynamic information is transmitted without transmitting the static information as the downlink data. Control to send specific information,
A roadside communicator, wherein a part of the second road-to-vehicle communication period is controlled to be secured as another purpose period used for other communication purposes than road-to-vehicle communication. The said control part controls to perform communication other than the said road-to-vehicle communication using the said other purpose period ensured in the road-to-vehicle communication period allocated to the other roadside communication apparatus. Roadside communication device. The roadside communication device according to claim 1 or 2, wherein an occurrence frequency of the second road-to-vehicle communication period is lower than an occurrence frequency of the first road-to-vehicle communication period. The roadside communication device according to any one of claims 1 to 3, wherein the other purpose period is secured as a range of a predetermined period from the end of the second road-vehicle communication period. The second road-to-vehicle communication period is constituted by a plurality of road-to-vehicle communication time slots that are separated in time,
The other purpose period is secured as a range of a predetermined period from the end of the last road-to-vehicle communication time slot among the plurality of road-to-vehicle communication time slots constituting the second road-to-vehicle communication period. Item 5. The roadside communication device according to any one of Items 1 to 4. The roadside communication device according to any one of claims 1 to 5, wherein the one other purpose period is used for a plurality of communication purposes other than the road-to-vehicle communication. The other plurality of communication purposes includes a plurality of road-to-road communication that is communication between roadside communication devices,
The roadside communication device according to claim 6, wherein the plurality of roadside communication are roadside communication having different transmission sources.   A communication system comprising a plurality of the roadside communication devices according to any one of claims 1 to 7.