JP6988866B2 - Communication system and transmission period allocation method - Google Patents

Description

The present invention relates to, for example, a communication system that can be suitably used as a component of an intelligent transport system (ITS).

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, moving objects (vehicles, etc.) receive information from infrastructure devices installed on the road, or exchange information between vehicles and utilize this information. An advanced road traffic system that improves the safety of vehicle driving by doing so has been studied (see, for example, Patent Document 1).
The wireless communication systems used in such intelligent transportation systems are mainly a plurality of roadside communication devices that are wireless communication devices on the infrastructure side and a plurality of in-vehicle communication devices (mobile communication devices) that are wireless communication devices mounted on each vehicle. ) And.

In this case, the combination of communication performed between the communication subjects includes roadside communication between the roadside communication device and the in-vehicle communication device, vehicle-to-vehicle communication between the in-vehicle communication devices, and roadside communication. This includes road-to-road communication performed between communication devices (see, for example, Patent Document 2).

Japanese Patent No. 2806801 Japanese Unexamined Patent Publication No. 2011-114647

In the above-mentioned advanced road traffic system, in order to coexist with each of these communications including vehicle-to-vehicle communication, road-to-vehicle communication, road-to-road communication, and road-to-step communication, road-to-road communication within a limited frequency band Time Division Multiple Access (TDMA), which divides radio resources into time regions and provides a time slot, which is a time zone dedicated to transmission of roadside communication equipment, in order to perform communication between road vehicles and vehicles. The multi-access method is adopted.

In the above-mentioned multi-access method by TDMA, a plurality of time slots dedicated to transmission of the roadside communication device are usually arranged in one wireless frame. That is, one radio frame includes a plurality of time slots set in different time zones. These plurality of time slots are allocated as transmission resources to each roadside communication device.

Roadside communicators are usually installed at intersections on the road, but the transmittable areas (service areas) of the roadside communicators installed at the intersections may overlap with each other. When the service areas overlap, the in-vehicle communication device existing in the overlapping portion receives the transmission signal of the two-way side communication device. That is, interference occurs between the two roadside communication devices.
Therefore, different time slots set in different time zones are assigned at least between the roadside communication devices having a positional relationship in which interference occurs. This makes it possible to avoid interference in road-to-vehicle communication.

At this time, the plurality of roadside communication devices can be divided into a group of roadside communication devices that can share one or more time slots because the roadside communication devices do not interfere with each other in the road-to-vehicle communication. Even if the roadside communicators belonging to the same group transmit using the same time slot (group), interference does not occur, so that a different time slot (group) is assigned to each of these groups. The transmission period assigned to each group is also referred to as a time channel.
If a different time channel (time slot group) is assigned to each group and a time channel assigned to each roadside communication device is assigned to the group to which the own device belongs, interference can be avoided in the road-to-vehicle communication.

In the above, the case where only the interference of the road-to-vehicle communication is considered is shown, but when the roadside communication device performs the road-to-road communication using the time slot assigned considering only the road-to-vehicle communication, the radio wave interference occurs. May occur.
The communication area may differ between road-to-vehicle communication and road-to-vehicle communication, and radio wave interference does not occur in road-to-vehicle communication, but radio wave interference occurs in road-to-road communication. This is because the interference relationship may be different.

Therefore, when the roadside communication device performs road-to-road communication, the time is required for each roadside communication device after considering the interference relationship between the two communications so that interference does not occur in both the road-to-vehicle communication and the road-to-road communication. It is conceivable to allocate slots.
Here, the roadside communication devices are grouped in consideration of both road-to-vehicle communication and road-to-road communication, and the number of time channels to which time slots should be allocated is specified.

FIG. 10 is a graph showing an example of the relationship between the number of time channels required for each of a plurality of roadside communication devices arranged in a predetermined area and the intersection interval.
In the figure, the vertical axis shows the required number of required time channels, and the horizontal axis shows the intersection interval. Further, the solid line shows the case where the interference of both the road-to-vehicle communication and the road-to-road communication is taken into consideration, and the broken line shows the case where the interference of only the road-to-vehicle communication is taken into consideration.

As shown in FIG. 10, as the distance between intersections increases, the required number of time channels is relatively larger when the road-to-vehicle communication and the road-to-vehicle communication are considered than when only the road-to-vehicle communication is considered. It tends to increase.

Then, more transmission time must be given to the road-to-vehicle communication, which is the communication between the in-vehicle communication devices existing more than the roadside communication devices, and as described above, the road-to-vehicle communication and the road-to-vehicle communication and If the allocation that considers the interference of both road-to-road communication is adopted, the time slot (transmission time) must be allocated to the increased time channel in order to avoid the interference of the road-to-road communication, and the time slot must be allocated. Many will be wasted.

The present invention has been made in view of such circumstances, even when subjected to allocation of time considering interference avoidance of road-road communication slot, you suppress time the slot is wasted an object of the present invention and this.

In the present invention, each of the plurality of roadside communication devices performs wireless transmission using the first slot assigned to each roadside communication device among the plurality of first slots and second slots arranged in a periodic wireless frame. This is a communication system in which the in-vehicle communication device performs wireless transmission by a carrier sense method using the second slot.
The plurality of first slots are a plurality of road-to-vehicle communication time slots used in road-to-vehicle communication performed between a roadside communication device and an in-vehicle communication device, and a time slot different from the road-to-vehicle communication time slot. It includes a plurality of road-to-road communication time slots used in road-to-road communication performed between roadside communication devices.
Each roadside communication device is assigned to the road-to-vehicle communication time slot according to the first grouping that does not interfere with the road-to-vehicle communication, and the road-to-vehicle communication time slot is assigned to the first grouping. Are assigned according to a second grouping that is different and does not interfere with the road-to-road communication.
Further, in the roadside communication device assigned to the roadside communication time slot of the first frame in the periodic radio frame and the roadside communication time slot of the second frame following the first frame. It is different from the assigned roadside communication device.
Another invention is a method of allocating a transmission period, which is performed for the above-mentioned communication system.
The allocation method includes a step of allocating each roadside communication device to the road-to-vehicle communication time slot according to a first grouping that does not interfere with the road-to-vehicle communication, and each roadside communication device for the road-to-road communication. The time slot includes a step that is different from the first grouping and is assigned according to the second grouping that does not interfere with the road-to-road communication.

[1] Another invention of the present invention is a communication system in which a plurality of roadside communication devices transmit using a plurality of time slots arranged in a wireless frame, and the wireless frame includes the roadside communication device and a vehicle. A time slot used for road-to-vehicle communication performed with a communication device and a time slot used for road-to-road communication performed between the plurality of roadside communication devices are provided, and the plurality of roadside communication devices are provided. , The road-to-vehicle communication is divided into a plurality of first group groups, and the transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of first groups so as to be different, and the roadside communication is performed. Communication is divided into a plurality of second group groups, and the transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of second groups so as to be different.
The number of the first group is _CRV ,
The number of the second group is _CRR ,
The number of time slots for the road-to-vehicle communication included in one radio frame is _SRV ,
The number of time slots for inter-road communication included in one radio frame is _SRR ,
When, the _CRV and the _CRR satisfy the following equation (1).
The plurality of roadside communicators are characterized in that they include a control unit that performs transmission satisfying the following equation (2) by sharing the time slot for inter-road communication with the plurality of second groups. ..
_{C RV <C RR ··· (1} )
S _RV > S _RR ... (2)
According to the communication system having the above configuration, even when the number C _{RR of the second group is larger than the number C RV} of the first group, the time slot for road-to-road communication is shared by the second group. the number S _RR time slot road-road communication, which is included in the radio frame, not be set larger than the number S _RV time slots for road-to-vehicle communication.
Therefore, by allocating the time slot in consideration of the interference avoidance of the road-to-vehicle communication in addition to the interference avoidance of the road-to-vehicle communication, the number _CRR of the second group is larger than _{the number CRV of} the first group. Even if it does, it is possible to prevent the time slot from being wasted.

[2] Further, the present invention is a communication system in which a plurality of roadside communication devices transmit using a plurality of time slots arranged in a wireless frame, and the wireless frame includes the roadside communication device and a vehicle. A time slot used for road-to-vehicle communication performed with a communication device and a time slot used for road-to-road communication performed between the plurality of roadside communication devices are provided, and the plurality of roadside communication devices are provided. In the road-to-vehicle communication, _{the transmission period is divided into a plurality of (CRV} ) first group groups, and the transmission period for simultaneous use by the roadside communication devices in the same group is assigned to each of the plurality of first groups so as to be different. , The roadside communication is divided into a plurality of ( _CRR pieces) second group groups, and the transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of second groups so as to be different. And
The number of the first group is _CRV ,
The number of the second group is _CRR ,
The number of time slots for the road-to-vehicle communication included in one radio frame is _SRV ,
The number of time slots for inter-road communication included in one radio frame is _SRR ,
When, the _CRV and the _CRR satisfy the following equation (3).
The plurality of roadside communicators are characterized in that they include a control unit that performs transmission satisfying the following equation (4) by sharing the time slot for inter-road communication with the plurality of second groups. ..
_CRV < _CRR ... (3)
(S _{RV- CRV} ) + C _RR ≧ S _RV + S _RR ... (4)

The above equation the left-hand side of the _{(3) (S RV - C} RV) indicates the number of time slots allocated to a plurality of first group, the difference between the number of the first group. This is a positive value when there is a first group to which two or more time slots are assigned among the plurality of first groups. In other words, the first group shows that an extra ( _{SRV- CRV} ) time slots are needed.

Therefore, the left side of the above equation (3) indicates at least the number of time slots required for road-to-vehicle communication when the interference of both road-to-vehicle communication and road-to-road communication is taken into consideration.
_{On the other hand, the right side is the number of time slots (SRV} ) required for road-to-vehicle communication and the time slot required for road-to-road communication when considering the interference of only road-to-vehicle communication. The total value of the number ( _{SRR) is shown.}

That is, the above equation (4) is the total of the number of time slots ( _{SRV ) for road-to-vehicle communication and the number of time slots (SRR} ) for road-to-road communication, which are required when the interference of only road-to-vehicle communication is taken into consideration. It is shown that the value is at least the number of time slots (the left side of the equation (4)) required for the road-to-vehicle communication in consideration of the interference of both the road-to-vehicle communication and the road-to-road communication.
By sharing the time slot for the previous road-to-road communication in an environment where only the interference of the road-to-vehicle communication is considered so as to satisfy the above equation (4), the interference of both the road-to-vehicle communication and the road-to-road communication can be prevented. The total number of time slots can be reduced to the same or less than when both road-to-vehicle communication and road-to-road communication are performed under the environment considered.
As a result, it is possible to suppress wasteful consumption of the time slot as compared with the case where the time slot is allocated in consideration of the interference of both the road-to-vehicle communication and the road-to-road communication.

[3] The control unit allocates the transmission period of the plurality of second groups to the time slots for inter-road communication included in each of a predetermined number of wireless frames arranged adjacent to each other. It is preferable that the transmission period of the plurality of second groups is distributed and allocated to each of the predetermined number of radio frames.
In this case, a transmission period can be allocated to a plurality of second groups over each of a predetermined number of radio frames arranged adjacent to each other. Even if the time slots for inter-road communication included in each of the adjacent wireless frames have the same position in the wireless frame, the transmission timing as the wireless frame is different, so they are assigned to each second group. be able to. Therefore, the transmission period can be allocated to a larger number of second groups.

[4] Further, the control unit can allocate a transmission period to each of the plurality of second groups by dividing and using the time slots for inter-road communication included in the wireless frame.

[5] It is considered that the transmission data in the road-to-road communication is smaller than the transmission data in the road-to-vehicle communication that communicates with the in-vehicle communication device that exists more than the roadside communication device.
Therefore, the transmission data by the road-to-vehicle communication is regarded as the data that needs to be transmitted for each wireless frame and requires a high transmission frequency, and the transmission data by the road-to-vehicle communication is the transmission data by the road-to-vehicle communication. It can be transmitted as data with a lower transmission frequency than.

[6] Further, the present invention is a transmission method for performing transmission using a plurality of time slots arranged in a wireless frame, and the wireless frame is used between a roadside communication device and an in-vehicle communication device. A time slot used for road-to-vehicle communication performed and a time slot used for road-to-road communication performed between the plurality of roadside communication devices are provided, and the plurality of roadside communication devices are provided in the roadside communication. It is divided into a plurality of first group groups, and the transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of first groups so as to be different, and a plurality of second groups in the roadside communication. It is divided into group groups, and the transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of second groups so as to be different.
The number of the first group is _CRV ,
The number of the second group is _CRR ,
The number of time slots for the road-to-vehicle communication included in one radio frame is _SRV ,
The number of time slots for inter-road communication included in one radio frame is _SRR ,
When, the _CRV and the _CRR satisfy the following equation (5).
By sharing the time slot for inter-road communication among the plurality of second groups, transmission satisfying the following equation (6) is performed.
_CRV < _CRR ... (5)
S _RV > S _RR ... (6)

[7] Further, the present invention is a computer program for causing a computer to execute a transmission process of transmitting using a plurality of time slots arranged in a wireless frame, and the wireless frame includes a roadside communication device. A time slot used for road-to-vehicle communication performed with an in-vehicle communication device and a time slot used for road-to-road communication performed between the plurality of roadside communication devices are provided, and the plurality of roadside communication devices are provided. Is divided into a plurality of first group groups in the road-to-vehicle communication, and the transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of first groups so as to be different, and the roadside communication device is used. It is divided into a plurality of second group groups in inter-communication, and the transmission period for simultaneous use by roadside communicators in the same group is assigned to each of the plurality of second groups so as to be different.
The number of the first group is _CRV ,
The number of the second group is _CRR ,
The number of time slots for the road-to-vehicle communication included in one radio frame is _SRV ,
The number of time slots for inter-road communication included in one radio frame is _SRR ,
When, the _CRV and the _CRR satisfy the following equation (7).
It is a computer program that causes a computer to execute a transmission process that satisfies the following equation (8) by sharing the time slot for road-to-road communication among the plurality of second groups.
_CRV < _CRR ... (7)
S _RV > S _RR ... (8)

[8] The present invention is a transmission method for performing transmission using a plurality of time slots arranged in a wireless frame, and the wireless frame is performed between a roadside communication device and an in-vehicle communication device. A time slot used for road-to-vehicle communication and a time slot used for road-to-road communication performed between the plurality of roadside communication devices are provided, and the plurality of roadside communication devices may be used in a plurality of roadside communication devices. It is divided into first group groups, and the transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of first groups so as to be different, and a plurality of second group groups in the roadside communication. The transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of second groups so as to be different.
The number of the first group is _CRV ,
The number of the second group is _CRR ,
The number of time slots for the road-to-vehicle communication included in one radio frame is _SRV ,
The number of time slots for inter-road communication included in one radio frame is _SRR ,
When, the _CRV and the _CRR satisfy the following equation (9).
By sharing the time slot for inter-road communication among the plurality of second groups, transmission satisfying the following equation (10) is performed.
_CRV < _CRR ... (9)
(S _{RV- CRV} ) + C _RR ≧ S _RV + S _RR ... (10)

[9] Further, the present invention is a computer program for causing a computer to execute a transmission process of transmitting using a plurality of time slots arranged in a wireless frame, and the wireless frame includes a roadside communication device. A time slot used for road-to-vehicle communication performed with an in-vehicle communication device and a time slot used for road-to-road communication performed between the plurality of roadside communication devices are provided, and the plurality of roadside communication devices are provided. Is divided into a plurality of first group groups in the road-to-vehicle communication, and the transmission period for simultaneous use by roadside communication devices in the same group is assigned to each of the plurality of first groups so as to be different, and the roadside communication device is used. It is divided into a plurality of second group groups in inter-communication, and the transmission period for simultaneous use by roadside communicators in the same group is assigned to each of the plurality of second groups so as to be different.
The number of the first group is _CRV ,
The number of the second group is _CRR ,
The number of time slots for the road-to-vehicle communication included in one radio frame is _SRV ,
The number of time slots for inter-road communication included in one radio frame is _SRR ,
When, the _CRV and the _CRR satisfy the following equation (11).
It is a computer program that causes a computer to execute a transmission process that satisfies the following equation (12) by sharing the time slot for inter-road communication among the plurality of second groups.
_CRV < _CRR ... (11)
(S _{RV- CRV} ) + C _RR ≧ S _RV + S _RR ... (12)

According to the above [6], [7], [8], and [9], in addition to avoiding interference of road-to-vehicle communication, even if time slots are allocated in consideration of avoiding interference of road-to-road communication. It is possible to prevent the time slot from being wasted.

According to the present invention, in addition to avoiding interference of road-to-vehicle communication, even if time slots are allocated in consideration of avoiding interference of road-to-road communication, it is possible to suppress wasteful consumption of time slots. Can be done.

It is a schematic perspective view which shows one embodiment of the intelligent transportation system. It is a block diagram of a roadside communication device. (A) is a diagram showing a frame, and (b) is a diagram showing the structure (part) of slots in the frame and how to allocate them. It is a figure which shows the allocation of the time channel of each intersection. It is a figure which shows an example of the arrangement model of a roadside communication device. It is a figure which shows an example of the whole structure of the wireless frame used in the communication system of this embodiment. It is a figure which shows the relationship between the slot for exclusive use of road-to-road communication included in a 1st radio frame, and the slot for exclusive use of road-to-road communication included in a 2nd radio frame. It is a figure which shows the extended area of the IVC-RVC layer of the transmission packet described in "Association of Radio Industries and Businesses," 700MHz band intelligent transportation system ARIB-STD T109 1.0 version "". It is a figure which shows an example of the radio frame when there is no important intersection. An example of the relationship between the minimum number of time channels required when allocating time channels to prevent radio wave interference for each of a plurality of roadside communication devices arranged in a predetermined area and the intersection interval is shown. It is a graph.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[Overall system configuration]
FIG. 1 is a schematic perspective view showing an overall configuration of an intelligent transportation 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 each other is assumed.
As shown in FIG. 1, the intelligent transportation system of the present 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. The vehicle 5 equipped with the machine 3 and a roadside sensor 6 including a vehicle detector, a surveillance 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, 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 LAN (Local Area Network) with a traffic signal 1 and a roadside communication device 2 in an area under its jurisdiction. The central device 4 may be installed on the road instead of the traffic control center.

Roadside sensors 6 are installed at 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 comprises a vehicle detector that ultrasonically detects a vehicle 5 passing directly underneath, a surveillance camera that captures the traffic condition of the road in chronological order, and the like, and the detection information and image data are transmitted via the communication line 7. Is transmitted to the central device 4.
In addition, in FIG. 1, for simplification of the illustration, only one signal lamp is drawn at each intersection, but at each actual intersection, at least four signal lamps are used for going up and down roads that intersect each other. Is installed.

In an intelligent transportation system, a plurality of roadside communication devices (radio devices) 2 installed at each of a plurality of intersections constituting a wireless communication system communicate wirelessly with an in-vehicle communication device 3 of a vehicle traveling around the roadside communication device (radio device) 2. (Road-to-vehicle communication) is possible.
Further, each roadside communication device 2 is capable of wireless communication (roadside communication) with other roadside communication devices 2 located within a predetermined range reached by its own transmission wave.
Further, the in-vehicle communication device (radio) 3 that also constitutes the wireless communication system performs wireless communication with the roadside communication device 2 and also wirelessly communicates with another in-vehicle communication device 3 (vehicle-to-vehicle communication) by a carrier sense method. ) Is possible.

As shown in FIG. 2, the roadside communication device 2 is wired to communicate with a central device 4 via a wireless communication unit (transmission / reception unit) 21 to which an antenna 20 for wireless communication is connected and a wired communication line 7. It includes a communication unit 22 and a communication processing device 25 that performs communication control processing.
The communication processing device 25 includes a control unit 23 and a storage unit 24 for storing necessary information. The control unit 23 performs communication control processing for wireless communication and wired communication. The storage unit 24 stores information necessary for wireless communication and priority communication.

The communication processing device 25 may have a part or all of its functions configured by a hardware circuit, or a part or all of its functions may be realized by a computer program. When a part or all of the functions of the communication processing device 25 are realized by a computer program, the communication processing device 25 (control unit 23) includes a computer, and the computer program executed by the computer is stored in the storage unit 24. To.

[Wireless communication method, etc.]
FIG. 3A shows a wireless frame used in a wireless communication system. The length (frame length) of this wireless frame in the time axis direction is set to 100 milliseconds. That is, 10 frames are generated per second.
The frame is generated based on, for example, 1PPS (a signal having 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 (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 (time slot) is a time slot (road-to-vehicle communication period) for transmission of the roadside communication device 2 assigned to the roadside communication device 2, and in this time zone, wireless transmission by the roadside communication device 2 is performed. Is acceptable.
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 roadside communication device 2 is the second slot. Wireless transmission is not performed in SL2.

The first slot SL1 and the second slot SL2 included in the wireless frame are alternately arranged in the time axis direction.
A slot number i is attached to each of the first slots SL1.

The roadside communication device 2 is assigned one or a plurality of first slot SL1s among the plurality of first slots SL1 (for example, 16 first slots) included in the wireless frame. The roadside communication device 2 recognizes which first slot SL1 is assigned to the own device by the slot number i.
When allocating one of the plurality of first slots SL1 included in the wireless frame to one roadside communication device 2, for example, the first slot SL1 with i = 1 included in the wireless frame has an intersection. It is assigned to the roadside communication device 2 of A2, B5, C3, D1, and is assigned to the roadside communication device 2 of the intersections A3, B1, C4, D2 in the first slot SL1 of i = 2, and the first of i = 3. Slot SL1 is assigned to the roadside communication device 2 at the intersections A4, B2, C5, D3, and the first slot SL1 at i = 4 is assigned to the roadside communication device 2 at the intersections A5, B3, C1, D4. The first slot SL1 at i = 5 is assigned to the roadside communication device 2 at the intersections A1, B4, C2, and D5.

The plurality of roadside communication devices 2 can be divided into groups of roadside communication devices 2 that can use the same slot (transmission period) at the same time because the roadside communication devices 2 do not interfere with each other in the road-to-vehicle communication. .. In FIG. 3B, the roadside communication device 2 at the intersections A2, B5, C3, D1, the roadside communication device 2 at the intersections A3, B1, C4, D2, the roadside communication device 2 at the intersections A4, B2, C5, D3, and the intersection. It is divided into five groups: roadside communication equipment 2 at A5, B3, C1 and D4, and roadside communication equipment 2 at intersections A1, B4, C2 and D5.
Even if the roadside communication devices 2 belonging to the same group transmit using the same transmission period, interference does not occur. Therefore, by allocating different transmission periods to each of these groups, interference can be prevented.

The transmission period that is assigned differently to each of these groups is also referred to as a time channel. The number of time channels is the same as the number of groups of roadside communicators 2 that can try the same transmission period.
In FIG. 3B, different first slots SL1 (i = 1 to 5) are assigned to each time channel (time channel numbers Ch1 to Ch5).

FIG. 4 shows how to allocate a time channel according to FIG. 3 to the plurality of roadside communication devices 2 shown in FIG. In FIG. 4, the numbers in the circles at each intersection indicate the time channel numbers. Each roadside communication device 2 performs road-to-vehicle communication in the first slot SL1 of the time channel number assigned to the own device 2.

When the same first slot SL1 is assigned to the roadside communication device 2 at an adjacent intersection, the vehicle 5 between the adjacent intersections receives radio waves for road-to-vehicle communication from both roadside communication devices 2. Interference occurs. However, as shown in FIG. 3, by distributing and allocating the same first slot SL1, it is possible to prevent interference during road-to-vehicle communication by each roadside communication device 2.

[Examination of the number of time channels]
The slot allocation as shown in FIG. 4 is appropriate when only the road-to-vehicle communication is taken into consideration, but is not appropriate when the road-to-road communication is also taken into consideration, and radio wave interference may occur in the road-to-road communication.
That is, if a slot allocated in consideration of only road-to-vehicle communication is to be used in road-to-road communication, radio wave interference may occur.

For example, the roadside communication device 2 at the intersection C2 and the roadside communication device 2 at the intersection D5 in FIG. 4 are both assigned the first slot SL1 having the time channel number Ch5. Then, between the intersections C2 and D5, it is difficult for radio waves to reach directly, considering the buildings other than the road. Therefore, the vehicle near the intersection C2 (the vehicle in the service area of the roadside communication device 2 at the intersection C2) receives almost all the 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 road-to-vehicle communication data of the roadside communication device 2 at the intersection C2 without any problem.

When the roadside communication device 2 at the intersection C2 and the roadside communication device 2 at the intersection D5 perform roadside communication at the same timing, the roadside communication device 2 at the intersection D5 is between the roadside communication devices 2 at the intersection C5. When the communication data is transmitted, the road-to-road communication or the road-to-vehicle communication data transmitted by the roadside communication device 2 at the intersection C2 may become an interference wave and reach the intersection C5 directly.
Therefore, the roadside communication device 2 at the intersection C5 may not be able to correctly receive the downlink data of the roadside communication from the roadside communication device 2 at the intersection D5.

In this way, since the communication area is different between the road-to-vehicle communication and the road-to-road communication, if the time channel allocated considering only the road-to-vehicle communication is used for the road-to-road communication, the road-to-road communication can be performed. Radio interference may occur.
Therefore, as described above, when the roadside communication device 2 performs both road-to-vehicle communication and road-to-road communication using the same time channel, interference caused by both road-to-vehicle communication and road-to-road communication is avoided. It is conceivable to allocate a time channel to each roadside communicator 2 in consideration of both interference relationships so that it can be performed.

However, when a time channel is assigned to each roadside communication device 2 in consideration of both interference relationships, as shown in FIG. 10, road-to-vehicle communication and road-to-road communication are considered as the intersection interval increases. In this case, the required number of slots tends to be relatively larger than when only the road-to-vehicle communication is considered.
In FIG. 10, when only the road-to-vehicle communication is considered and the intersection interval is 300 m, the road-to-vehicle communication and the road-to-road communication can be assigned in a road structure in which interference can be avoided in five time channels. When the above is taken into consideration, nine time channels are required. That is, when considering road-to-road communication and road-to-vehicle communication, if one first slot SL1 is simply assigned to one time channel, it is about twice as much as when only road-to-vehicle communication is considered. First slot SL1 may be required.

As a result, a larger number of first slots SL1 must be provided for road-to-vehicle communication, which is communication with in-vehicle communication devices that originally exist in a larger number than the roadside communication device 2, as described above. , If the allocation considering the interference of both road-to-vehicle communication and the road-to-road communication is adopted, many first slots SL1 must be allocated to the increased time channel to avoid the interference of the road-to-road communication. Instead, much of the first slot SL1 will be wasted.

On the other hand, in the present embodiment, by providing the first slot SL1 for road-to-road communication described later, even if the first slot SL1 is allocated in consideration of avoiding interference in road-to-road communication, the first slot SL1 is assigned. It is possible to prevent the 1-slot SL1 from being wasted.

[Transmission control of roadside communication device 2]
The communication control device 25 of the roadside communication device 2 controls the vehicle 5 (vehicle-mounted communication device 3) to wirelessly transmit road-to-vehicle communication data from the wireless communication unit 21 in the first slot SL1 assigned to the own device 2. conduct.
That is, the communication control device 25 of each roadside communication device 2 controls to perform transmission using the plurality of first slots SL1 arranged in the wireless frame.

For example, consider an arrangement model of the roadside communication device 2 as shown in FIG. In FIG. 5, 13 roadside communication devices 2 are arranged so that the arrangement area becomes a rhombus at an intersection where each road intersects with each other.
The intersection located in the center of this area is an important intersection that has a great influence on the improvement of traffic flow and accident prevention, such as the intersection with the highest traffic volume at the intersection of arterial roads. In order to give more communication resources to the roadside communication device 2 arranged at the important intersection than to the roadside communication device 2 arranged at the other intersection, the roadside communication device 2 arranged at the other intersection is provided with the communication resource. While one first slot SL1 is assigned, two first slot SL1s are assigned to the roadside communication device 2 arranged at the important intersection.

In the road-to-vehicle communication of the arrangement model shown in FIG. 5, a plurality of (13) roadside communication devices 2 are grouped by the roadside communication devices 2 that can be assigned a transmission period that can be used at the same time, and a plurality of groups (first). When divided into groups), it is assumed that the number of these first groups (= _CRV ), that is, the number of required time channels is 5.
In this case, if five different transmission periods are prepared and assigned to each group, interference in road-to-vehicle communication can be avoided.

Further, in the roadside communication of the arrangement model, a plurality of (13) roadside communication devices 2 are grouped by the roadside communication devices 2 that can be assigned a transmission period that can be used at the same time, and a plurality of groups (second). When divided into groups), it is assumed that the number of these second groups (= _CRR ), that is, the number of required time channels is nine.
In this case, if nine different transmission periods are prepared and assigned to each group, interference in inter-road communication can be avoided.

FIG. 6 is a diagram showing an example of the overall configuration of the wireless frame used in the communication system of the present embodiment. The wireless frame of the communication system of the present embodiment has 16th number in accordance with "Association of Radio Industries and Businesses," 700MHz band intelligent transportation system ARIB-STD T109 1.0 version "" which is a regulation regarding the roadside communication device 2. One slot SL1 is arranged.

In FIG. 6, the first wireless frame in the upper row is, for example, an even-numbered frame (even-numbered frame) among the 10 wireless frames (frame numbers: 0 to 9) generated in one second as shown in FIG. The second radio frame is an odd-numbered frame (odd-numbered frame) out of 10 radio frames (frame numbers: 0 to 9) generated in one second. Therefore, the first radio frame and the second radio frame are alternately and periodically generated.
The allocation of the first slot SL1 to each roadside communication device 2 in the first wireless frame and the allocation of the first slot SL1 to each roadside communication device 2 in the second wireless frame are the first slots for roadside communication described later. It is common except for SL1.
The radio frame shown in FIG. 6 shows a case where it is applied to the arrangement model shown in FIG.

In FIG. 6, the wireless frame is provided with a first slot SL1 (group) for road-to-vehicle communication and a first slot SL1 (group) for road-to-road communication. In this wireless frame, six first slots SL1 (= S _RV ) are used for road-to-vehicle communication, and three first slots SL1 (= S _RR ) are used for road-to-road communication. There is. The remaining seven first slots SL1 are unused.

In the model shown in FIG. 5, as described above, the number of time channels required for road-to-vehicle communication is five. Therefore, when one first slot SL1 is assigned to these time channels, the first slot SL1 group for road-to-vehicle communication may include at least five first slot SL1s.

In the model shown in FIG. 5, among the plurality of roadside communication devices 2, the roadside communication device 2 installed at an important intersection exists. Two first slot SL1s are assigned to the roadside communication device 2 arranged at the important intersection, and one first slot SL1 is assigned to the other roadside communication devices 2. Therefore, in the present embodiment, the first slot SL1 group for road-to-vehicle communication is composed of a total of six, including the minimum number of five and one for the roadside communication device 2 arranged at the important intersection. ing.

As shown in FIG. 6, in the first slot SL1 group for road-to-vehicle communication, two first slot SL1s having slot numbers i = 0 and 1 are assigned to roadside communication devices at important intersections.
_{The time channel Ch RV} 1 in road-to-vehicle communication is assigned to the two first slots SL1 having slot numbers i = 0 and 1, and the first slot SL1 (slot number i = 2) for road-to-vehicle communication is sequentially assigned. _{~ 5) Time channels Ch RV} 2 to 5 in road-to-vehicle communication are assigned to each.

As described above, a transmission period is assigned to _{each time channel Ch RV} 1 to 5 of the road-to-vehicle communication. In other words, a transmission period is assigned to each of the plurality (five) first groups grouped in the road-to-vehicle communication.

Road-to-vehicle communication data generated by each roadside communication device 2 is arranged in each slot for road-to-vehicle communication.
There are static information and dynamic information in the road-to-vehicle communication data.
Static information refers to information whose information content does not change in a short period of time, such as road alignment information indicating a road structure or regulation information indicating the content / period of traffic regulation.
The dynamic information refers to information whose information content may change from moment to moment, such as signal information indicating information of a traffic signal or sensor information indicating detection by a roadside sensor 6. That is, the dynamic information is information in which the frequency of the information content fluctuating with the passage of time is higher than that of the static information.

The roadside communication device 2 installed at an important intersection allocates static information and dynamic information to each of the two assigned first slot SL1s, and transmits both information to each one first slot SL1. do.
The roadside communication device 2 other than the roadside communication device 2 installed at the important intersection transmits both static information and dynamic information by using one assigned first slot SL1.

On the other hand, the first slot SL1 group for road-to-road communication includes three first slots SL1 (slot numbers i = 6, 7, 8).
In the model shown in FIG. 5, as described above, the number of time channels required for inter-road communication is nine. Therefore, when one first slot SL1 is assigned to these time channels, the first slot SL1 group for road-to-road communication may include at least nine first slot SL1s.

In the present embodiment, there are three first slots SL1 for inter-road communication in one wireless frame. Therefore, one first slot SL1 cannot be assigned to each time channel.
Therefore, in the present embodiment, the first slot SL1 for road-to-road communication is configured to be shared by each time channel (a plurality of second groups).
In the present embodiment, of the three first slot SL1s constituting the slots for road-to-road communication, the two first slots SL1 (slot numbers i = 7, 8) are divided into two subs. A slot SS is provided. By allocating the first slot SL1 and the subslot SS to the time channel as the transmission period, it is possible to secure five transmission periods that can be allocated to the time channel in one radio frame.

Further, by using the first slot SL1 for inter-road communication included in the first wireless frame and the first slot SL1 for inter-road communication included in the second wireless frame, the above nine roads are used. Set to allocate a transmission period for each communication time channel.
In this case, the transmission period of the time channel for inter-road communication is distributed and allocated to each of the first and second radio frames.
That is, the transmission period of nine road-to-road communication time channels is used as one unit for the first slot SL1 for six-way communication included in each of the two adjacent radio frames. To assign.
As a result, the transmission period of the time channel of the road-to-road communication is allocated to each of the two adjacent radio frames.

By setting in this way, since each of the first and second radio frames includes five transmission periods, a total of ten transmission periods that can be assigned to the time channel of inter-road communication are secured. can do.
As described above, in the present embodiment, the transmission period corresponding to the number of time channels of the road-to-road communication is secured by sharing the first slot SL1 for the road-to-road communication.

_{In FIG. 6, the time channel Ch RR} 1 in the road-to-road communication is assigned to the first slot SL1 having the slot number i = 6 of the first radio frame. _{The time channels Ch RR} 2 to 5 in the road-to-road communication are assigned to the sub-slot SS included in each of the first slots SL1 of the slot numbers i = 7 and 8 of the first radio frame.
_{Further, the time channel Ch RR} 6 in the inter-road communication is assigned to the first slot SL1 of the slot number i = 6 of the second radio frame. _{The time channels Ch RR} 7 to 9 in the road-to-road communication are assigned to the sub-slot SS included in each of the first slots SL1 of the slot numbers i = 7 and 8 of the second radio frame. One of the two subslot SSs included in the first slot SL1 having slot number i = 8 of the second radio frame is not assigned a time channel.

In this way, a transmission period is assigned to each time channel Ch _{RR 1 to 9 for inter-road communication.} In other words, a transmission period is assigned to each of the plurality (9) second groups grouped in the road-to-road communication.

As described above, a transmission period is assigned to each of the five time channels (plural first groups) in the road-to-vehicle communication and the nine time channels (plural second groups) in the road-to-road communication. ..

FIG. 7 is a diagram showing the relationship between the first slot SL1 for road-to-road communication included in the first radio frame and the first slot SL1 for road-to-road communication included in the second radio frame. In the figure (a), the first slot SL1 (for example, the first slot SL1 having the slot number i = 6) for inter-road communication included in the first wireless frame is shown, and in the figure (b), the second slot SL1 is shown. The first slot SL1 for inter-road communication included in the wireless frame (for example, the first slot SL1 having slot number i = 6) is shown.

Since the length of one radio frame is 100 ms, the first radio frame and the second radio frame are switched at a cycle of 100 ms.
Therefore, as shown in the figure, the first slot SL1 for inter-road communication included in both radio frames appears with a transmission cycle of 200 ms. The first slot SL1 of the first radio frame and the first slot SL1 of the second radio frame are shifted by 100 ms, and the transmission timings are different from each other.

Therefore, since each roadside communication device 2 can surely obtain a transmission opportunity of roadside communication every 200 ms, it is possible to surely perform roadside communication when each roadside communication device 2 is required.

Each roadside communication device 2 uses 1PPS to specify a frame number, and transmits roadside communication data at the timing of the first slot SL1 for roadside communication assigned to each roadside communication device 2. conduct.

In FIG. 7, each roadside communication device 2 synchronizes with each other by GPS synchronization using 1PPS, identifies the first radio frame and the second radio frame, and specifies the first slot SL1 for road-to-road communication. Although the case has been shown, the first radio frame and the second radio frame can be specified even in the case of synchronizing with each other by so-called air synchronization, in which synchronization is performed by road-to-road communication between the roadside communication devices 2.
In this case, since it is necessary to share the timing of the wireless frame with a specific frame number among the roadside communication devices 2, for example, the roadside communication device 2 that recognizes the timing of the wireless frame transmits. It can be configured to store the frame number of the current wireless frame in the header of the packet or the like and notify the other roadside communication device 2.
FIG. 8 is a diagram showing an extended region of the IVC-RVC layer of the transmission packet described in "Association of Radio Industries and Businesses," 700MHz band intelligent transportation system ARIB-STD T109 1.0 version "". As shown in the figure, the frame number of the above-mentioned radio frame can be stored in the extended area of the IVC-RVC layer, and the timing of the frame number can be notified to the other roadside communication device 2.
Further, the synchronization is not limited to GPS synchronization and air synchronization, and synchronization may be performed using a radio clock, or a synchronization signal capable of specifying a frame number of a wireless frame may be transmitted from the central device 4.

As described above, in this system, the first slot SL1 for road-to-road communication assigned to each roadside communication device 2 is included in the first radio frame and the second radio frame having different transmission timings, respectively. It is set.

Here, in the case of the present embodiment, since the timing of transmission of the road-to-road communication by each roadside communication device 2 is every 200 ms, it may be less than the communication resource allocated for the road-to-vehicle communication.

In this respect, the road-to-vehicle communication generally requires more communication resources than the road-to-road communication because the communication is performed with the in-vehicle communication device 3 which exists more than the roadside communication device 2.
The present inventor conducted an experiment on this system, estimated the amount of transmitted data per unit time actually required for road-to-vehicle communication and road-to-road communication, and compared the two.
As a result, it has been confirmed that it is sufficient to secure about half the amount of transmitted data per unit time required for road-to-road communication as compared with road-to-vehicle communication.

In the present embodiment, based on the above comparison result, between roads including a predetermined number (three in this embodiment) of the first slots SL1 so that the communication resources required for the road-to-road communication are secured. A first slot SL1 group for communication is provided.
Therefore, it is permissible even if the communication resource allocated to the road-to-road communication is set to be smaller than the communication resource allocated to the road-to-vehicle communication.

[About the effect]
In the present embodiment, the wireless frame includes a first slot SL1 (time slot for road-to-vehicle communication) for road-to-vehicle communication and a first slot SL1 (time slot for road-to-road communication) for road-to-road communication. Is provided.
The number of the first group is included in _CRV (= the number of time channels in road-to-vehicle communication), the number of the second group is included in _CRR (= the number of time channels in road-to-road communication), and one wireless frame. When the number of the first slot SL1 for the road-to-vehicle communication is S _RV and the number of the first slot SL1 for the road-to-road communication included in one wireless frame is S _RR , these numerical values are calculated. It is as follows.

_CRV = 5
_CRR = 9
S _RV = 6
S _RR = 3

Each of the above numerical values satisfies the following equations (21) and (22).
_CRV < _CRR ... (21)
S _RV > S _RR ... (22)

According to the communication system having the above configuration, each roadside communication device 2 is a communication control device that performs transmission satisfying the above equation (22) by sharing the first slot SL1 for road-to-road communication with a plurality of second groups. It has 25.
_{Therefore, even when the number C RR} of the second group _{is larger than the number C RV} of the first group, the first slot SL1 for road-to-road communication is shared by the second group and is included in the wireless frame. The first slot SL1 for road-to-road communication is not set more than the first slot SL1 for road-to-vehicle communication. Therefore, even if the slots are allocated in consideration of the interference avoidance of the road-to-vehicle communication in addition to the interference avoidance of the road-to-vehicle communication, it is possible to suppress the wasteful consumption of the first slot SL1.

Further, each of the above numerical values satisfies the following formula (23).
(S _{RV- CRV} ) + C _RR ≧ S _RV + S _RR ... (23)

The left side of equation of _{(23) (S RV - C} RV) indicates the number of the first slot SL1 assigned to the plurality of first group, the difference between the number of the first group. This is a positive value when there is a first group to which two or more time slots are assigned among the plurality of first groups. In other words, the number of duplicates of the first slot SL1 when the first slot SL1 is duplicatedly assigned to one first group among the plurality of first groups is shown. In the case of the above embodiment, ( _{SRV- CRV} ) is "1", corresponding to the fact that one extra first slot SL1 is assigned to the roadside communication device 2 arranged at the important intersection. There is.

Further, the number _CRR of the second group is the same as the number of groups (the number of required time channels) that can be divided when the interference of both road-to-vehicle communication and road-to-road communication is taken into consideration. Therefore, the left side of the above equation (23) is the number of first slots SL1 required for (at least) road-to-vehicle communication in consideration of interference between road-to-vehicle communication and road-to-road communication.

Therefore, the left side of the above equation (23) is the number of time channels in the plurality of first groups and the plurality of second groups (both) when considering the interference of both road-to-vehicle communication and road-to-road communication. The number of first slots SL1 required for road-to-vehicle communication with the method of allocating the time channel having the larger number of groups) is shown. _{On the other hand, the right side of the above equation (23) is the number of first slots SL1 (SRV} ) required for road-to-vehicle communication and road-to-road communication when considering the interference of only road-to-vehicle communication. _{The total value of the number (SRR} ) of the first slot SL1 required for this is shown.

_{That is, the above equation (23) is the number of the first slot SL1 (SRV} ) for the road-to-vehicle communication and the number of the first slot SL1 for the road-to-vehicle communication, which are required when the interference of only the road-to-vehicle communication is considered. the sum of (S _RR) is, (the left-hand side of equation (23)) the number of the first slot SL1 required when performing at least road-vehicle communication in consideration of the interference of both the road-vehicle communication and road-road communication below It shows that it becomes.
By sharing the first slot SL1 for the previous term road-to-road communication in an environment where only the interference of the road-to-vehicle communication is considered so as to satisfy the above equation (23), both the road-to-vehicle communication and the road-to-road communication are satisfied. Compared with the case where both road-to-vehicle communication and road-to-road communication are performed in an environment considering interference, the total number of the first slot SL1 can be reduced to the same or less.
As a result, it is possible to suppress the wasteful consumption of the first slot SL1 as compared with the case where the first slot SL1 is assigned in consideration of the interference of both the road-to-vehicle communication and the road-to-road communication.

Further, in this system, as described above, the transmission period of the plurality of second groups is allocated to the time slots for inter-road communication included in each of a predetermined number of wireless frames arranged adjacent to each other. The transmission period of the plurality of second groups is distributed and allocated to each of the predetermined number of radio frames.
In this case, the transmission period of the time channel of the road-to-road communication can be assigned to each of the two adjacent radio frames. Further, even if the first slots SL1 for inter-road communication included in the wireless frames having different transmission timings have the same position in the wireless frame, the transmission timings as the wireless frames are different. It can be assigned to the second group. Therefore, the transmission period can be allocated to a larger number of second groups.

Further, in this system, of the three first slot SL1s constituting the slots for road-to-road communication, the subslot SS configured by dividing the first slot SL1 into two first slots SL1 is provided. include.
That is, if the amount of communication in the road-to-road communication is relatively small, the first slot SL1 for the road-to-road communication can be divided and used.

As described above, in the present embodiment, by time-dividing the first slot SL1 for road-to-road communication, a plurality of sub-slot SS can be provided, and the time channel for road-to-road communication (a plurality of second groups) can be provided. ) Can be secured for a longer transmission period.

[About other embodiments]
The present invention is not limited to the above embodiment. In the above embodiment, the description is based on the arrangement model (FIG. 5) including the roadside communication device 2 arranged at the important intersection, but for example, even if the same model does not have the important intersection, the above-mentioned numerical values are obtained. ( _CRV , _CR R, S _RV , S _RR ) satisfies the above equations (21), (22), and (23).

FIG. 9 is a diagram showing an example of a radio frame when there is no important intersection. When there is no important intersection, one first slot SL1 is assigned to each roadside communication device 2 as a time channel for road-to-vehicle communication, so that the first slot SL1 group for road-to-vehicle communication is the first. It is configured to include five 1-slot SL1s.

Therefore, each of the above numerical values in this case is as follows.

_CRV = 5
_CRR = 9
S _RV = 5
S _RR = 3

Each of the above numerical values satisfies the above equations (21), (22), and (23).
Therefore, even when there is no important intersection, it is possible to obtain the effect of suppressing the wasteful consumption of the first slot SL1 as in the above embodiment.

Further, in the wireless frame shown in FIG. 9, a case is shown in which the first slot SL1 for three road-to-road communication includes three subslot SSs, respectively.
In this case, each subslot SS can be used as a transmission period that can be assigned to the time channel (plural second groups) of inter-road communication.
Therefore, as shown in FIG. 9, nine time channels Ch _RR 1 to 9 for inter-road communication are assigned to each subslot SS.

As described above, the first slot SL1 for inter-road communication can be appropriately divided into a plurality of transmission periods (sub-slot SS) according to the number of time channels for inter-road communication and the amount of communication.

Further, in the above embodiment, the case where the setting is made so as to satisfy all of the above equations (21), (22), and (23) is shown, but each of the above numerical values does not satisfy the equation (23). Also, it is sufficient that both the equation (21) and the equation (22) are satisfied, and even if the equation (22) is not satisfied, both the equation (21) and the equation (23) may be satisfied. ..

It should be noted that the embodiments disclosed this time are exemplary in all respects and are not restrictive. The scope of the present invention is shown by the scope of claims, not the above-mentioned meaning, and is intended to include the meaning equivalent to the scope of claims and all modifications within the scope.

2 Roadside communication device 3 In-vehicle communication device 5 Vehicle 20 Antenna 21 Wireless communication unit 23 Control unit SL1 1st slot (time slot)

Claims (2)

Each of the plurality of roadside communication devices performs wireless transmission using the first slot assigned to each roadside communication device among the plurality of first slots and the second slots arranged in the periodic wireless frame, and performs in-vehicle communication. The machine is a communication system that performs wireless transmission by a carrier sense method using the second slot.
The plurality of first slots are
A plurality of road-to-vehicle communication time slots used in road-to-vehicle communication performed between a roadside communication device and an in-vehicle communication device, and
A time slot different from the road-to-vehicle communication time slot, including a plurality of road-to-road communication time slots used in road-to-road communication performed between roadside communication devices.
Each roadside communication device is assigned to the road-to-vehicle communication time slot according to the first grouping that does not interfere with the road-to-vehicle communication, and the road-to-vehicle communication time slot is assigned to the first grouping. Are assigned according to a second grouping that is different and does not interfere with the road-to-road communication.
It is assigned to the roadside communication device assigned to the roadside communication time slot of the first frame in the periodic radio frame and to the roadside communication time slot of the second frame following the first frame. It said the Do different and roadside communication equipment was Ri,
The first grouping is a grouping in which the roadside communication devices that interfere with the road-to-vehicle communication are assigned to different time slots for road-to-vehicle communication in the same wireless frame.
The second grouping is a communication system in which the roadside communication equipment that interferes with the roadside communication is assigned to the roadside communication time slots of the same radio frame and different radio frames . Each of the plurality of roadside communication devices performs wireless transmission using the first slot assigned to each roadside communication device among the plurality of first slots and the second slots arranged in the periodic wireless frame, and performs in-vehicle communication. A method of allocating a transmission period, which is executed for a communication system in which the machine performs wireless transmission by a carrier sense method using the second slot.
The plurality of first slots are
A plurality of road-to-vehicle communication time slots used in road-to-vehicle communication performed between a roadside communication device and an in-vehicle communication device, and
A time slot different from the road-to-vehicle communication time slot, including a plurality of road-to-road communication time slots used in road-to-road communication performed between roadside communication devices.
The allocation method is
A step of allocating each roadside communication device to the road-to-vehicle communication time slot according to a first grouping that does not interfere with the road-to-vehicle communication.
Each roadside communication device includes a step of allocating each roadside communication device to the roadside communication time slot according to a second grouping which is different from the first grouping and does not interfere with the roadside communication.
It is assigned to the roadside communication device assigned to the roadside communication time slot of the first frame in the periodic radio frame and to the roadside communication time slot of the second frame following the first frame. Different from the roadside communication device
The first grouping is a grouping in which the roadside communication devices that interfere with the road-to-vehicle communication are assigned to different time slots for road-to-vehicle communication in the same wireless frame.
The second grouping is a method of allocating a transmission period, which is a grouping in which the roadside communication devices that interfere with the roadside communication are assigned to the roadside communication time slots of the same radio frame and different radio frames.

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