JP2011199738A - Wireless communication system and roadside communication instrument used for the same, and method of assigning time slot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively ensure a transmission opportunity of a mobile communication instrument by reducing the number of required slots in assignment of time slots for wireless communication of a plurality of roadside communication instruments.SOLUTION: A wireless communication system includes: the plurality of roadside communication instruments 2A, 2B for performing wireless transmission by at least one of a plurality of time slots T1 repeated in a prescribed cycle; and the mobile communication instrument 3 for allowing wireless transmission in a time zone except a time slot T1. In the wireless communication system, transmission time of the plurality of roadside communication instruments 2A, 2B in a position relationship for generating a direct interference, where downlink signals simultaneously reach one mobile communication instrument 3, or the other radio wave interferences, is assigned by time sharing within the same time slot T1.

Description

  The present invention relates to a radio communication system suitable for, for example, an intelligent transport system (ITS) and a roadside communication device as a component of the system. More specifically, the present invention relates to a time slot allocation method for the roadside communication device.

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).
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, a combination of communication performed between communication subjects includes road-to-road communication between road-side communication devices, road-to-vehicle (or vehicle-road) communication between road-side communication devices and vehicle-mounted communication devices, and vehicle-mounted communication. Vehicle-to-vehicle communication performed between aircraft.

Japanese Patent No. 2806801

  In the above-mentioned intelligent road traffic system, including communication between vehicles, road-to-vehicle communication, road-to-road communication, and road-to-step communication, in order to coexist these communications, what kind of communication is used by effectively utilizing the bandwidth. The issue is whether to perform control. In view of this, it has been studied that multiple access is used to perform communication between roads, road vehicles, and vehicles within a limited frequency band.

  As this multi-access method, there are frequency division multiplexing (FDMA) and code division multiple access (CDMA), but communication with only a small number of in-vehicle communication devices is assumed in mountainous areas. As a multi-access method for inter-vehicle communication, it is preferable to adopt an autonomous random access method represented by CSMA (Carrier Sense Multiple Access), for example.

However, road-to-vehicle communication, road-to-road communication, and vehicle-to-vehicle communication coexist in an area where roadside communication devices exist. In this case, since the priority of the information handled by the roadside communicator that is the infrastructure side is generally high, a mechanism that gives priority to road-to-vehicle communication and road-to-road communication over vehicle-to-vehicle communication is required. .
Therefore, in order to preferentially transmit information of the roadside communication device, a time division multiplexing (TDMA) time division multiple (TDMA) time division in which a time for communication is divided and a time slot dedicated to transmission of the roadside communication device is provided. Access is enabled.

Therefore, for example, assuming a wireless communication system composed of a group of roadside communication devices installed at a plurality of intersections, a time slot transmitted by each roadside communication device is assigned by the TDMA method, and the remaining time slot is assigned to a vehicle by the CSMA method. It is considered to be a rational communication system to be used for inter-vehicle communication.
In this case, in order to control the transmission timing from each roadside communication device, each roadside communication device needs to have a time synchronization function with other roadside communication devices.

In an intelligent road traffic system in which the TDMA system for roadside transmission control as described above and the CSMA system for multi-access between vehicles are mixed, if the transmission time preferentially assigned to the roadside communication device is too long, There is a concern that the transmission time of the in-vehicle communication device becomes too short, or the inter-vehicle packet arrival rate is lowered, which adversely affects the inter-vehicle communication.
In particular, as a communication band for ITS, a standard of approximately 10 MHz in the 700 MHz band has been studied. In the case of such a relatively narrow bandwidth, the vehicle is mounted in the downlink area where the transmission signal of the roadside communication device reaches. The problem is how to ensure the transmission time of the communication device effectively.

On the other hand, if the installation of roadside communicators becomes widespread, it is assumed that many roadside communicators are concentrated and installed at adjacent intersections in a relatively small area in urban areas.
When roadside communication devices are installed at a plurality of intersections as described above, radio wave interference (hereinafter sometimes referred to as “direct interference”) with respect to in-vehicle communication devices in the range where the downlink areas overlap is prevented. It is reasonable to assign the transmission times of the roadside communication devices in the positional relationship where the direct interference occurs to different time slots.

However, as described above, in the method in which the transmission times of a plurality of roadside communication devices that may cause direct interference are assigned to different time slots, the number of slots to be defined increases as the number of roadside communication devices is increased. There is a high possibility that it will be unavoidable, and there is a problem that the transmission time to open to the vehicle side is shortened accordingly. This problem also applies to the case where the transmission times of a plurality of roadside communication devices that may cause indirect interference described later are assigned to different time slots.
In the present invention, in view of such conventional problems, when a plurality of roadside communication devices allocate time slots for performing wireless communication, the number of necessary slots is reduced to effectively secure transmission opportunities of mobile communication devices. This is the first purpose.

On the other hand, roadside communication devices that are in a positional relationship where direct interference does not occur can be basically assigned to time slots with the same slot number, assuming only the collision of transmission signals of the roadside communication devices. is there.
However, even for a plurality of roadside communication devices that are in a positional relationship where direct interference does not occur, if the slot length of the time slot of each roadside communication device is not aligned, The downlink signal and the transmission signal from another in-vehicle communication device may cause radio wave interference (hereinafter, also referred to as “indirect interference”). May not be properly received.

  A second object of the present invention is to provide a wireless communication system and the like that can effectively prevent indirect interference via wireless communication by a mobile communication device in view of such conventional problems.

(1) In the wireless communication system of the present invention, a plurality of roadside communication devices that wirelessly transmit in at least one of a plurality of time slots repeated in a predetermined cycle, and wireless transmission is permitted in a time zone other than the time slots A wireless communication system including a mobile communication device, wherein a plurality of the roadside communication are in a positional relationship in which direct interference defined in the following (a) or indirect interference defined in the following (b) may occur. The transmission times of the machines are allocated in a time division within the same time slot.
(A) Direct interference in which downlink signals from a plurality of roadside communication devices reach one mobile communication device at the same time

  (B) The downlink area of the second roadside communication device that has the first mobile communication device in the downlink area of the first roadside communication device and has a positional relationship that does not cause direct interference with the first roadside communication device. In addition, when there is a second mobile communication device, the downlink signal of the first roadside communication device, the transmission signal of the second mobile communication device, or another mobile communication device wirelessly transmitted using this transmission signal as a trigger Indirect interference that simultaneously arrives at the first mobile communication device

According to the wireless communication system of the present invention, since the transmission times of a plurality of roadside communication devices in a positional relationship in which direct interference or indirect interference can occur are allocated in a time division within the same time slot, direct interference Or, compared with the case where roadside communication devices that may cause indirect interference are uniformly assigned to different time slots, the number of necessary slots can be reduced, and the transmission time that is open to the mobile communication device can be set as long as possible. it can.
For this reason, the transmission opportunity of a mobile communication apparatus can be ensured more effectively, and the first object is achieved.

(2) In the wireless communication system of the present invention, the roadside communication device that performs wireless transmission after the second in the same time slot can receive downlink signals of other roadside communication devices that wirelessly transmit in advance. In addition, it is preferable to start wireless transmission after detecting the completion of transmission of the downlink signal.
In this case, even if the end of the transmission time is delayed due to inaccurate time of the roadside communication device that performs wireless transmission in advance, direct interference due to overlap with the subsequent transmission time can be prevented in advance. There are advantages.

  (3) Further, in the wireless communication system of the present invention, if the transmission times of the plurality of roadside communication devices assigned to the same time slot by time division are densely allocated with a predetermined guard time in between. As many transmission times of roadside communication devices as possible can be assigned to one time slot, and an increase in the number of slots can be prevented more effectively.

(4) In the wireless communication system of the present invention, the plurality of roadside communication devices assigned in time division to the same time slot are installed at a medium-scale or small-scale intersection connected to at least one side road. It is preferable that it is a machine.
The reason for this is that medium-sized or small-scale intersections have fewer road lanes than the large-scale intersections, and the amount of information of downlink signals is reduced accordingly, so the transmission time is short. This is because the transmission time of as many roadside communication devices as possible can be assigned to the slot.

(5) However, the radio communication system of the present invention may further include the roadside communication device installed at a large intersection where only the main road flows, and the transmission time of the roadside communication device is the same. It is preferable that the time slot is assigned independently.
The reason for this is that, in the case of a large intersection, the amount of downlink signal transmission data is large and the transmission time is long, so if it is assigned in the same time slot along with the transmission time of other roadside communication devices in time division, the time slot This is because the slot length is too large.

(6) On the other hand, in the wireless communication system of the present invention, for the transmission times of the plurality of roadside communication devices in a positional relationship where indirect interference can occur, the same start time and slot length are the same. You may decide to allocate to a time slot.
In this case, with respect to a plurality of roadside communication devices to which the same time slot is assigned because direct interference does not occur, wireless communication between mobile communication devices occurs when the start time and slot length of the time slot are not uniform. The indirect interference can be effectively prevented, and the second object is achieved.

(7) The roadside communication device of the present invention is a time-division method in a time slot in which the transmission time of its own device and the transmission time of other roadside communication devices are the same among the roadside communication devices constituting the wireless communication system of the present invention. This relates to the assigned roadside communication device related to the device.
Therefore, according to the roadside communication device of the present invention, the first object can be achieved as in the wireless communication system of the present invention.

(8) The time slot allocation method of the present invention is an allocation method for the roadside communication device constituting the wireless communication system of the present invention, and is defined by direct interference defined in (a) or defined in (b). Extracting a plurality of roadside communication devices in a positional relationship where indirect interference can occur, and assigning transmission times of the extracted plurality of roadside communication devices in a time division within the same time slot; It is characterized by including.
Therefore, according to this allocation method, the first object can be achieved as in the radio communication system of the present invention.

(9) Further, in the time slot allocation method of the present invention, the transmission times of the plurality of roadside communication devices extracted as being in a positional relationship where the indirect interference can occur are substantially the same in start time and slot length. And assigning to the same time slot aligned.
Therefore, according to this allocation method, the second object can be achieved as in the radio communication system of the present invention.

As described above, according to the present invention, the number of slots required for slot assignment of a plurality of roadside communication devices can be reduced, so that it is possible to effectively secure transmission opportunities for mobile communication devices.
Further, according to the present invention, since indirect interference via wireless communication by the mobile communication device can be prevented, it is possible to more reliably prevent a downlink signal reception failure.

It is a schematic perspective view which shows the whole structure of an intelligent road traffic system. It is a road top view which shows a part of jurisdiction area of an intelligent road traffic system. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a conceptual diagram which shows an example of the time slot of road-to-vehicle communication. It is a figure which shows an example of the data format which a vehicle-mounted communication apparatus transmits. (A) is explanatory drawing of direct interference, (b) (c) is a time chart which shows slot allocation which avoids direct interference. (A) is explanatory drawing of indirect interference, (b) is a time chart which shows slot allocation which can generate indirect interference, (c) is a time chart which shows slot allocation which avoids indirect interference. It is a road figure which shows the example of arrangement | positioning of a roadside communication apparatus. It is a table | surface which shows the amount of transmission data and transmission time required in each intersection, (a) is the case of A series, (b) is the case of B series, (c) is the case of C, D series. (A) is a time chart which shows the time slot of an initial stage (A series), (b) and (c) are the allocation tables of the slot number of B series, C series, and D series, respectively. It is a time chart which shows slot allocation of the time division of a C and D series. It is a time chart which shows the time slot of all the series AD after the slot allocation of a tertiary stage is complete | finished. It is a top view of the road for showing the modification of this invention.

[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 is equipped with a traffic signal 1, a roadside communication device 2, an in-vehicle communication device 3 (see FIGS. 2 and 3), a central device 4, and an in-vehicle communication device 3. A vehicle 5 and a roadside sensor 6 including a vehicle detector and a monitoring camera are included.

The traffic signal 1 and the roadside communication device 2 are installed at each of a plurality of intersections Ji (i = 1 to 12 in the example), and are connected to the router 8 via a communication line 7 such as a telephone line. . 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 at each intersection Ji included in the area under its control. Therefore, the central device 4 can perform bidirectional communication with each traffic signal 1 and each roadside communication device 2. The central device 4 may be installed on the road instead of the traffic control center.

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 Ji. The roadside sensor 6 includes a vehicle sensor that ultrasonically senses the vehicle 5 that passes underneath, or a monitoring camera that shoots traffic conditions on the road in time series. The sensing information S4 and the image data S5 are transmitted via the communication line 7. Is transmitted to the central device 4 via
In FIG. 1 and FIG. 2, only one signal lamp is depicted at each intersection Ji for the sake of simplicity of illustration, but each actual intersection Ji is used for ascending and descending roads that intersect each other. At least four signal lamps are installed.

[Central equipment]
The central device 4 has a control unit composed of a workstation (WS), a personal computer (PC), etc., and this control unit collects and processes various traffic information from the roadside communication device 2 and the roadside sensor 6. (Calculation)-Performs recording, signal control and information provision in an integrated manner.
Specifically, the control unit of the central device 4 performs system control for adjusting the traffic signal group 1 on the same road for the traffic signal 1 at the intersection Ji belonging to its own network, and this system control is applied to the road network. Extended wide area control (surface control) can be performed.

In addition, the central device 4 has a communication unit that is a communication interface connected to the LAN side via the communication line 7, and this communication unit includes a signal control command S1 relating to the lamp color switching timing of the signal lamp, Traffic information S2 including traffic jam information and the like is transmitted to the traffic signal device 1 and the roadside communication device 2 every predetermined time (see FIG. 1).
The signal control command S1 is transmitted every calculation period (for example, 1.0 to 2.5 minutes) of the signal control parameter when performing the system control and the wide area control, and the traffic information S2 is transmitted every 5 minutes, for example. Is done.

  Further, the communication unit of the central device 4 is generated when the vehicle passes through the vehicle information S3 including the current position of the vehicle 5 received by the communication device 2 from the in-vehicle communication device 3 from the roadside communication device 2 corresponding to each intersection Ji. Sensing information S4 of a vehicle sensor (not shown) consisting of a pulse signal and image data S5 consisting of digital information of a road photographed by a surveillance camera are received, and the control unit of the central device 4 Based on various information, the system control and the wide area control are executed.

[Wireless communication systems, etc.]
FIG. 2 is a road plan view showing a part of the jurisdiction area of the above intelligent road traffic system.
In FIG. 2, each of two roads intersecting each other is illustrated as one lane on one side in the up and down directions, but the road structure is not limited to this.
As shown also in FIG. 2, the intelligent transportation system of this embodiment includes a plurality of roadside communication devices 2 capable of wireless communication with the in-vehicle communication device 3, and other communication devices 2 and 3 using a carrier sense method. It also functions as a wireless communication system provided with the in-vehicle communication device 3 that is a kind of mobile wireless transceiver that performs wireless communication.

In the example of FIG. 1 and FIG. 2, the plurality of roadside communication devices 2 are installed at each roadside intersection Ji, and are attached to the pillars of the traffic signal device 1. On the other hand, the in-vehicle communication device 3 is mounted on a part or all of the vehicle 5 traveling on the road.
Each in-vehicle communication device 3 mounted on the vehicle 5 can receive the downlink signal in the downlink area A that is the reach range of the downlink signal from the roadside communication device 2.

In the present embodiment, it is assumed that the reach of the transmission signal of the in-vehicle communication device 3 is equal to or less than the reach of the downlink signal of the roadside communication device 2. Accordingly, each roadside communication device 2 can perform wireless communication with the in-vehicle communication device 3 that travels within the range of the downlink area A of the own device.
Thus, in the present embodiment ITS, communication between the vehicle-mounted communication devices 3 (vehicle-to-vehicle communication) and between the roadside communication device 2 and the vehicle-mounted communication device 3 (road-to-vehicle communication from “road” to “car”) (Including both inter-vehicle communication from “car” to “road”), wireless communication is used.

Further, when the installation positions of the adjacent roadside communication devices 2 are relatively close to each other and the downlink areas A overlap (may be partially overlapped or all overlapped), the wireless communication between the roadside communication devices 2 is performed. Communication (inter-road communication) is possible.
As described above, the central device 4 provided in the traffic control center is capable of two-way communication with each roadside communication device 2 by wire, but wireless communication may be performed between these devices.

The roadside communication device 2 assigns a time slot (first slot T1 in FIG. 4) for wireless transmission by the TDMA method, and in a time slot other than this time slot (second slot T2 in FIG. 4). Does not perform wireless transmission.
That is, the time zone other than the time slot for the roadside communication device 2 is open as a transmission time by the CSMA method for the in-vehicle communication device 3.

The roadside communication device 2 has a time synchronization function with other roadside communication devices 2 in order to control its own transmission timing.
The time synchronization of the roadside communication device 2 is performed by, for example, GPS synchronization for adjusting its own clock to the time acquired from the GPS satellite, air synchronization for adjusting its own clock to a transmission signal from another roadside communication device 2, or the like. .

[Roadside communication device]
FIG. 3 is a block diagram showing the internal configuration of the roadside communication device 2 and the in-vehicle communication device 3.
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 wired communication unit 22 that performs bidirectional communication with the central device 4, and a processor (CPU) that performs communication control thereof. A central processing unit) and a storage unit 24 connected to the control unit 23, such as a ROM or a RAM.

The storage unit 24 of the roadside communication device 2 stores a computer program for communication control executed by the control unit 23, communication device IDs of the communication devices 2 and 3, and the like.
The control unit 23 of the roadside communication device 2 includes a transmission control unit 23A that controls the transmission timing of the wireless communication unit 21 and received data of each of the communication units 21 and 22 as functional units that are achieved by executing the computer program. And a data relay unit 23B for performing the relay process.

The data relay unit 23B of the roadside communication device 2 temporarily stores the traffic information S2 and the like from the central device 4 received by the wired communication unit 22 in the storage unit 24 and causes the wireless communication unit 21 to perform broadcast transmission.
In addition, the data relay unit 23B temporarily stores the vehicle information S3 received by the wireless communication unit 21 in the storage unit 24 and transfers the vehicle information S3 to the central device 4 via the wired communication unit 22.

The transmission control unit 23A of the roadside communication device 2 synchronizes the transmission timing with the other device, and the time slot T1 of the predetermined slot number i assigned to the own device (see FIG. 4; hereinafter, “slot i”). In this case, wireless transmission is performed for a predetermined transmission time.
That is, the storage unit 24 of the roadside communication device 2 stores allocation information S6 including the following information a) and b), for example. This allocation information S6 is individually set for each roadside communication device 2.
a) Slot number i being used by the own device (see FIG. 4)
b) Start time and duration of the first slot T1 (see FIG. 4) with slot number i

Further, the storage unit 24 of the roadside communication device 2 stores a transmission time corresponding to the amount of information (transmission data amount) to be downlink transmitted from the own device and the transmission start time. The transmission start time and transmission time are individually set for each roadside communication device 2 so as to be within the time slot T1 assigned to the own device.
The transmission control unit 23A generates a downlink signal having the set transmission time length, and causes the radio communication unit 21 to transmit the downlink signal at the set transmission start time.

Although the transmission time of the roadside communication device 2 may be set to the maximum of the slot length assigned to the own device, in this embodiment, synchronization deviation with other communication devices 2 and 3 and information processing on the reception side In consideration of time and the like, it is set slightly shorter than the slot length with a predetermined margin (for example, a guard time of the order of 10 μs).
Further, the transmission time of the roadside communication device 2 can be set to an arbitrary time length within the range of the slot length assigned to the own device, and is significantly shorter than the slot length (for example, 1/3 or 1/2) can also be set.

Of the transmission start time and transmission time of the downlink signal, the transmission start time is determined by the transmission control unit 23A of each roadside communication device 2 based on the start time of slot i included in the allocation information S6 of the own device. You may make it produce | generate autonomously.
The transmission control unit 23A of the roadside communication device 2 adds a time stamp of the current time to the downlink signal including the allocation information S6, and causes the wireless communication unit 21 to perform broadcast transmission.

When the in-vehicle communication device 3 receives the downlink signal including the allocation information S6 and the time stamp, a time other than the first slot T1 of the slot number i indicated in the allocation information S6 with reference to the current time of the time stamp. Radio transmission is performed in the band (second slot T2 in FIG. 4).
If the main period Cm described later is included in the allocation information S6, the start time of the slot i and the current time of the time stamp can be expressed by relative time within the main period Cm. In this case, the number of bits of the allocation information S6 can be reduced compared to the case where those times are expressed in absolute time.

The allocation information S6 only needs to include at least the time of the slot i used by the own device. However, the allocation information S6 of another roadside communication device 2 is obtained by inter-road communication or communication with the central device 4. If it is known, the allocation information S6 of the other device may be transmitted from the own device.
Details of the allocation information S6 and the transmission time setting method (time slot allocation method) for each roadside communication device 2 will be described later.

[Contents of time slot]
FIG. 4 is a conceptual diagram illustrating an example of a time slot for road-to-vehicle communication.
As shown in FIG. 4, the time slot of road-to-vehicle communication includes a first slot T1 and a second slot T2, and the total period of these is repeated at a constant slot period Cs. The first slot T1 of each slot cycle Cs is a time slot for the roadside communication device 2, and wireless transmission by the roadside communication device 2 is permitted in this time zone.

A slot number i is assigned to the first slot T1, and the slot number i is periodically incremented (may be decremented).
The second slot T2 is a time slot for the in-vehicle communication device 3, and since this time period is opened for wireless transmission by the in-vehicle communication device 3, the transmission control unit 23A of the roadside communication device 2 has the second slot T2. Then, wireless transmission is not performed.

When the slot number i reaches a predetermined number n, it returns to the initial number (i = 1 in the figure). Therefore, if the slot period Cs for n times is the main period Cm, the first slot T1 of each slot number i to n is generated once for each main period Cm.
The system operator can appropriately set the time length of each cycle Cs, Cm and the total number n of slot cycles Cs. In this embodiment, as an example, Cs = 10 ms, Cm = 100 ms, and n = 10 is assumed.

In FIG. 4, the dot ● marked in the first slot T1 of the slot number i = 1 to 3 indicates that the transmission times of the plurality of roadside communication devices 2 are allocated to the first slots T1 of the slot number i. Show.
That is, in the example of FIG. 4, the transmission time of the two roadside communication devices 2 installed at the intersection J1 and the intersection J11 is allocated to the slot 1, and the slot 2 is installed at the intersection J2, the intersection J9, and the intersection J10. The transmission times of the two roadside communication devices 2 are allocated.

  The reason is that, for example, as shown in the intersection J1 and the intersection J11 in FIG. 1, the roadside communication devices 2 that are separated from each other do not overlap the downlink area A, and one in-vehicle communication device 3 is connected to each roadside communication device 2. Since direct interference (see FIG. 6 (a)) that simultaneously receives a downlink signal from the mobile station does not occur or the possibility thereof is extremely low, the same slot i is set for them and the transmission time of each roadside communication device 2 is set. This is because the in-vehicle communication device 3 can appropriately receive the downlink signal from each roadside communication device 2 even if they overlap.

On the other hand, in the case of roadside communication devices 2 having a relatively close positional relationship in which the above-described direct interference can occur with respect to one in-vehicle communication device 3, it is not possible to set the same slot number i and overlap the transmission time .
Of course, even the roadside communication devices 2 that may cause direct interference can be set to the same slot number i if the transmission time is scheduled in the first slot T1 in a time division manner, which will be described later. In addition, indirect interference shown in FIG. 7B may occur between the roadside communication devices 2 of the same slot number i where no direct interference occurs. This point will also be described later.

[In-vehicle communication device]
Returning to FIG. 3, the in-vehicle communication device 3 includes a communication unit (transmission / reception unit) 31 connected to the antenna 30 for wireless communication, a control unit 32 including a processor that performs communication control on the communication unit 31, and the like. And a storage unit 33 including a storage device such as a ROM or a RAM connected to the control unit 32.
The storage unit 33 stores a computer program for communication control executed by the control unit 32, communication device IDs of the communication devices 2 and 3, and the like.

The control unit 32 of the in-vehicle communication device 3 causes the communication unit 31 to perform wireless communication based on the carrier sense method for inter-vehicle communication, and the communication control function in the time division multiplexing method like the roadside communication device 2 is I don't have it.
Accordingly, the communication unit 31 of the in-vehicle communication device 3 always senses the reception level of a predetermined carrier frequency, and when the value is equal to or greater than a certain threshold, wireless transmission is not performed, and when the value is less than the threshold Only intended to perform wireless transmission.

In addition, when the communication unit 31 receives a downlink signal from a certain roadside communication device 2, the control unit 32 of the in-vehicle communication device 3 extracts the allocation information S6 and the time stamp of the roadside communication device 2 from the downlink signal.
Then, the control unit 32 uses the carrier sense method only in the time zone (second slot T2 in FIG. 4) other than the time slot T1 of the slot number i written in the assignment signal S6 with reference to the time of the time stamp. The communication unit 31 performs wireless transmission.

Furthermore, the control unit 32 of the in-vehicle communication device 3 causes the vehicle information S3 including the current position, direction, speed, and the like of the vehicle 5 (in-vehicle communication device 3) to be broadcast and wirelessly transmitted to the outside via the communication unit 31. Yes.
In addition, the control unit 32 of the in-vehicle communication device 3 has the position, speed, and direction included in the vehicle information S3 received directly from the other vehicle 5 or the vehicle information S3 of the other vehicle 5 received from the roadside communication device 2. Based on this, it is possible to perform safe driving support control that avoids a right-handed collision or a head-on collision.

FIG. 5 is a diagram illustrating an example of a data format transmitted by the in-vehicle communication device 3.
As shown in FIG. 5, the transmission signal of the in-vehicle communication device 3 includes a preamble, a header, data, and a CRC (Cyclic Redundancy Check).
Among these, the data includes the position, direction (traveling direction), and speed of the vehicle 5, but can also include a reception level when a transmission signal from the roadside communication device 2 is received. The position and direction of the vehicle 5 are usually information autonomously measured by sensors on the vehicle 5 side such as GPS, but may be acquired from the infrastructure side such as an optical beacon. The speed is information based on a speed sensor of the vehicle 5.

[Slot allocation method to avoid direct interference]
FIG. 6A is an explanatory diagram of direct interference, and FIGS. 6B and 6C are time charts showing slot assignment for avoiding direct interference.
Here, “direct interference” means that downlink signals from a plurality of roadside communication devices 2 reach one in-vehicle communication device 3 simultaneously. In this case, since a plurality of downlink signals collide and cause radio wave interference, there is a high possibility that the in-vehicle communication device 3 cannot receive the downlink signals properly.

As shown in FIG. 6A, such direct interference is caused by the roadside communication devices 2A and 2B being in contact with the vehicle 5 in the range where the downlink areas A and A of the two roadside communication devices 2A and 2B overlap. Occurs when transmitting downlink simultaneously.
In order to avoid such direct interference, for example, as shown in FIG. 6B, the transmission time Ta of one roadside communication device 2A is set to slot k (first slot T1 with slot number i = k). Both the transmission times Ta and Tb may be assigned to different slot numbers such that the transmission time Tb of the other roadside communication device 2B is assigned to the slot k + 1.

However, in the method in which the transmission times Ta and Tb of the roadside communication devices 2A and 2B are uniformly assigned to different slots k and k + 1, the number of slots i to be defined must be increased as the number of roadside communication devices 2 is increased. Therefore, there is a high possibility that the transmission time for opening to the in-vehicle communication device 3 will be shortened accordingly.
Therefore, as shown in FIG. 6C, the transmission times Ta and Tb necessary for downlink transmission are set to the times of the same slot number k even between the roadside communication devices 2A and 2B in a positional relationship where direct interference can occur. The slot T1 may be allocated in a time division manner.

  In this way, if a plurality of roadside communication devices 2A, 2B transmission times Ta, Tb are allocated in time division to the time slot T1 of the same slot number k, the transmission times Ta, Tb of the roadside communication devices 2A, 2B are always different times. Compared with the method of allocating to the slot T1 (in the case of FIG. 6B), the number of required slots can be reduced, and the transmission time opened to the in-vehicle communication device 3 may be set as long as possible.

In the present embodiment, the transmission times Ta and Tb of the roadside communication devices 2A and 2B allocated in the time division manner to the same time slot T1 (slot k) are densely allocated with a predetermined guard time G in between.
In FIG. 6C, the transmission times Ta and Tb of the two roadside communication devices 2A and 2B are assigned to one slot k. However, the transmission time of the roadside communication device 2 assigned to one slot k is 3 In this case, three or more transmission times are densely allocated inside the slot k with the guard time G interposed therebetween.

In this way, if a plurality of transmission times are densely allocated with a predetermined guard time G interposed therebetween, as many transmission times of the roadside communication device 2 as possible can be allocated to one slot k, and the number of slots increases. Can be prevented more effectively.
On the other hand, in FIG. 6C, for example, when the time of the roadside communication device 2A that wirelessly transmits in advance is inaccurate, if the end of the transmission time Ta is delayed beyond the guard time G, It may overlap with the transmission time Tb of the roadside communication device 2B that performs wireless transmission, which may cause direct interference.

Therefore, when the roadside communication device 2B that performs radio transmission later in the slot k can receive the downlink signal of the roadside communication device 2A that performs radio transmission in advance, the roadside communication device 2B It is preferable to start the wireless transmission after detecting the completion of the transmission of the downlink signal of the roadside communication device 2A that performs wireless transmission.
In this way, even when the transmission time Ta of the roadside communication device 2B is delayed beyond the guard time G, duplication with the transmission time Tb of the roadside communication device 2B can be avoided, and duplication of the transmission times Ta and Tb. It is possible to prevent the direct interference associated with.

[Slot allocation method to avoid indirect interference]
FIG. 7A is an explanatory diagram of indirect interference, and FIG. 7B is a time chart showing slot allocation in which indirect interference can occur. FIG. 7C is a time chart showing slot assignment for avoiding indirect interference.
Here, as shown to Fig.7 (a), there exists the 1st vehicle-mounted communication apparatus 3A in the downlink area A of the 1st roadside communication apparatus 2A, and the position which does not produce direct interference with the 1st roadside communication apparatus 2A A case is assumed where the second in-vehicle communication device 3B is present in the downlink area A of the second roadside communication device 2B in the relationship.

  In the above case, “indirect interference” means that the downlink signal of the first roadside communication device 2A and the transmission signal Sb of the second in-vehicle communication device 3B or the transmission signal Sb is transmitted wirelessly as a trigger It means that the transmission signal Sc of the other in-vehicle communication device 3C reaches the first in-vehicle communication device 3A at the same time.

Such indirect interference is a problem that may occur when the durations (slot lengths) of the time slots T1 of the roadside communication devices 2A and 2B are different, as shown in FIG. 7B. Hereinafter, this point will be described.
That is, as shown in FIG. 7B, the transmission times Ta and Tb of the roadside communication devices 2A and 2B are all assigned to the time slot T1 of the same slot number k, but are assigned to the roadside communication device 2A. Assume that the slot length La is longer than the slot length Lb assigned to the roadside communication device 2B.

In this case, the first in-vehicle communication device 3A that has acquired the allocation information S6 of the roadside communication device 2A in the downlink area A of the roadside communication device 2A is restricted from wireless transmission within the range of the longer slot length La.
On the other hand, in the downlink area A of the roadside communication device 2B, the second in-vehicle communication device 3B that has acquired the allocation information S6 of the roadside communication device 2B is restricted in radio transmission only within the shorter slot length Lb. Instead, radio transmission can be performed after the elapse of the slot length Lb and before the elapse of the slot length La (the time period La-Lb in FIG. 6B).

Therefore, when the second in-vehicle communication device 3B performs wireless transmission in the time zone (La-Lb), if the distance between the in-vehicle communication devices 3A and 3B is less than or equal to the radio wave reachable distance of the in-vehicle communication device 3, The transmission signal Sb of the second in-vehicle communication device 3B transmitted in the time zone (La-Lb) reaches the first in-vehicle communication device 3A.
Further, even when the distance between the in-vehicle communication devices 3A and 3B exceeds the radio wave arrival distance, the transmission signal of the third in-vehicle communication device 3C that receives the transmission signal Sb of the second in-vehicle communication device 3B and relays the vehicle information S3. Sc may reach the first in-vehicle communication device 3A.

  As described above, since the positional relationship is such that no direct interference occurs, even when the transmission times Ta and Tb of the roadside communication devices 2A and 2B are assigned to the same slot k, the slot lengths La and Lb are different from each other. In this case, for the first in-vehicle communication device 3A according to the roadside communication device 2A having the longer slot length La, the second in-vehicle communication according to the downlink signal from the roadside communication device 2A and the shorter slot length Lb. There is a case where the transmission signal Sb from the communication device 3B or another transmission signal Sc triggered by this transmission signal Sb arrives at the same time (indirect interference). There is a possibility that the communication device 3A cannot properly receive the downlink signal of the roadside communication device 2A.

  In the example of FIG. 7B, the case where the slot lengths La and Lb are different on the assumption that the start times of the slots k of the roadside communication devices 2A and 2B are the same is illustrated. , Lb, not only when the start times of the slots k of the roadside communication devices 2A, 2B are set different from each other, or when both the start time and the slot length of the slot k are different. The indirect interference can occur.

Therefore, in order to avoid such indirect interference, in this embodiment, as shown in FIG. 7C, the transmission times Ta and Tb of the roadside communication devices 2A and 2B in which direct interference does not occur are set to the same slot k (slot When assigning to the first slot T1) of number i = k, the time slot T1 is assigned to the roadside communication devices 2A and 2B with the start time of each slot k and the slot lengths La and Lb being substantially the same. ing.
In this way, for roadside communication devices 2A and 2B to which the same slot k is assigned because no direct interference occurs, in-vehicle communication that occurs because the start time of the slot k and the slot lengths La and Lb are not aligned. Indirect interference via wireless communication of the machines 3A to 3C can be effectively prevented.

Note that the indirect interference is radio wave interference between the downlink signal of the first roadside communication device 2A and the transmission signal Sb of the other onboard communication devices 3B and 3C with respect to the first onboard communication device 3A. Assuming only the transmission signal Sb from the vehicle-mounted communication device 3B, the roadside communication devices 2A and 2B whose ends of the downlink area A are farther than the radio wave reachable distance of the vehicle-mounted communication device 3 have the problem of indirect interference. Can be handled as not.
Further, when the transmission signal Sc of the third in-vehicle communication device 3C is also assumed, the distance between the ends of the downlink area A multiplied by the radio wave reachable distance of the in-vehicle communication device 3 by the number of times that the inter-vehicle communication can be relayed What is necessary is just to handle the roadside communication apparatuses 2A and 2B farther than each other as having no problem of indirect interference.

  Therefore, in order to extract the roadside communication devices 2A and 2B in a positional relationship that may cause indirect interference, the ends of the downlink area A are connected to the in-vehicle communication device from among the plurality of roadside communication devices 2 that do not cause direct interference. The roadside communication devices 2A and 2B having a positive determination result may be employed to determine whether the distance is equal to or shorter than the radio wave reachable distance 3 or the distance obtained by multiplying the distance by the relayable number of times.

  Furthermore, in the case where the start time and the slot length of the slot k of the roadside communication devices 2A and 2B that are in the positional relationship of indirect interference are aligned, it is convenient to simply set the time and time to exactly the same value. Considering the delay time until the transmission signals Sb and Sc reach the first in-vehicle communication device 3A due to the signal processing time of the transmission signals Sb and Sc by the other in-vehicle communication devices 3B and 3C. The time and time may be slightly different.

Note that the transmission times Ta and Tb of the roadside communication devices 2A and 2B that are in a positional relationship that can cause indirect interference shown in FIG. 7A are also the times of the same slot number k as shown in FIG. 6C. You may decide to allocate to slot T1 by a time division.
In this case, since the transmission times Ta and Tb of the roadside communication devices 2A and 2B are different, it is possible to prevent reception failure of the in-vehicle communication device 3 due to indirect interference, and at the same time reduce the number of necessary slots as much as possible. it can.

[Specific example of slot allocation method]
Hereinafter, a specific example of the slot allocation method according to the present embodiment will be described with reference to FIGS. Here, FIG. 8 is a road diagram showing an arrangement example of the roadside communication device 2.
In FIG. 8, of the six roads R1 to R6 in the north-south direction, two roads R2 and R4 are trunk roads (for example, a road having a total of four or more lanes), and the other roads R1, R3, R5, and R6 are trunk roads. Suppose that the road is smaller than the road.

In addition, it is assumed that two roads Ra and Rb are main roads and the other roads Rc and Rd are side roads among the four Ra to Rd in the east-west direction.
Further, in the road area shown in FIG. 8, at the initial stage of starting the operation of the roadside communication device 2, the roadside communication device 2 is installed at the intersections A1 to A6 (A series) of the main road Ra, and the next secondary stage. The roadside communication devices 2 are installed at the intersections B1 to B6 (B series) of the main road Rb, and the intersections C1 to C6, D1 to D6 (the C series and the intersections) of the side roads Rc and Rd are installed at the tertiary stage where the installation is progressing. It is assumed that the roadside communication device 6 is installed in the D series).

In addition, in the A-series intersections A1 to A6 along the road Ra in the east-west direction shown in FIG. The same applies to the other series B to D.
Further, at the intersections A1, B1, C1, and D1 along the north-south road R1 shown in FIG. 8, the distance between adjacent intersections is a direct interference, but the intersections C1, D1 and the intersection A1 cause a direct interference. Suppose there is no distance. The same applies to the intersections Aj, Bj, Cj, Dj (j = 2 to 6) along the other north-south roads R2 to R6.

FIGS. 9A to 9C are tables showing the amount of transmission data and transmission time required at each intersection. FIG. 9A shows the case of the A series, and FIG. 9B shows the case of the B series. FIG. 9C shows the case of the C and D series. The transmission data amount is assumed to be digital modulation with 16QAM.
In the A series, the intersections A2 and A4 are large-scale intersections where the east-west trunk road Ra and the north-south trunk roads R2 and R4 intersect, and as shown in the table of FIG. It is assumed that the amount of transmission data is large (5000 bytes in the example) and the transmission time required corresponding to this is long (3540 μs in the example).

In the A series, the intersections A1, A3, A5, and A6 are medium-scale intersections where the east-west main road Ra and the north-south side roads R1, R3, R5, and R6 intersect. The amount is also medium (3000 bytes in the example), and the transmission time required corresponding to this is also medium (2140 microseconds in the example).
The same applies to the B-sequence, and the transmission time required for the downlink signal of the roadside communication device 2 is determined as shown in the table of FIG. 9B according to the transmission data amount corresponding to the scale of the intersections B1 to B6. Shall.

Further, in the C series and the D series, the transmission time required for the downlink signal of the roadside communication device 2 according to the transmission data amount corresponding to the scale of the intersections C1 to C6 is as shown in the table of FIG. It shall be determined by
As will be described later, the transmission times of the roadside communication devices 2 installed in the C-sequence and the D-sequence are allocated to the same slot k in a time-sharing manner, so that the rightmost column in the table of FIG. And the total transmission time of the D series.

FIG. 10A is a time chart showing time slots in the initial stage (A series).
Since this initial stage is the first stage in which the roadside communication device 2 is newly installed in the A series (intersections A1 to A6) of the road area shown in FIG. 8, the roadside communication devices 2 installed at the respective intersections A1 to A6. The transmission time is assigned to slots 1 to 6 in order.

FIG. 10B is a B-sequence slot number assignment table.
Here, as described above, the intersection B1 is close to the A-series intersection A1 passing through the road R1 in the north-south direction, and has a positional relationship in which direct interference occurs with the intersection A1. Similarly, the other intersections B2 to B6 of the B series are in a positional relationship in which direct interference occurs with the intersections A2 to A6, respectively.
Therefore, in the example shown in FIG. 10B, for the roadside communication device 2 installed at the B series intersection Bj (j = 1 to 6), the roadside installed at the A series intersection Aj (j = 1 to 6). In order to avoid direct interference with the communication device 2, the slot number is changed from that in the case of the A series.

In this case, the reason why the time division allocation (allocation in FIG. 6C) in the same slot is not adopted between the A series and the B series is as follows.
That is, the A series and the B series include large-scale intersections A2, A4, B2, and B4 into which only the main roads Ra, Rb, R2, and R4 flow (see FIG. 8). In the case of A2, A4, B2, and B4, the transmission data amount of the roadside communication device 2 is large and the required transmission time (3540 μsec) is very long.

Therefore, if such large-scale intersections A2, A4, B2, and B4 are allocated to the same slot in a time-sharing manner together with the transmission time of the other roadside communication devices 2, the slot length of the slot becomes too large. .
For example, the transmission time of the intersection A2 and the intersection B2 is 3540 μs, and if this transmission time is assigned to one slot, the slot length exceeds 7000 μs. 3, wireless transmission becomes impossible in more than 70% within the slot period Cs (= 10 milliseconds).
Furthermore, even in the in-vehicle communication device 3 positioned between the roadside communication device 2 at the intersection A2 or the intersection B2 and the roadside communication device 2 in a positional relationship that may cause indirect interference, the wireless communication is performed at over 70% within the slot period Cs. Cannot send.

On the other hand, when the same slot number as the roadside communication device 2 already installed at the A series intersection Bj (j = 1 to 6) is assigned to the roadside communication device 2 installed at the B series intersection Bj (j = 1 to 6). If the slot lengths of the newly established B series and the existing A series are not equal, the indirect interference (see FIG. 7C) may occur.
Therefore, in the B-sequence slot allocation shown in the table of FIG. 10B, the slot numbers are changed so that the slot length of the newly installed B-sequence roadside communication device 2 is the same as the slot length of the existing A-sequence. Yes.

For example, since the transmission time (2140 μsec) at the intersection B1 is the same as the transmission time (2140 μsec) at the intersection A5 (see FIG. 9), the slot 5 of the intersection A5 is used as the slot of the roadside communication device 2 installed at the intersection B1. (Slot length = 2.2 milliseconds) is adopted as it is.
Further, since the transmission time (3540 μsec) of the intersection B2 is the same as the transmission time (3540 μsec) of the intersection A4 (see FIG. 9), the slot 4 of the intersection A4 is used as the slot of the roadside communication device 2 installed at the intersection B2. (Slot length = 3.6 msec) is adopted as it is.

FIG. 10C is an allocation table of slot numbers of C and D series.
As described above, the C series intersection Cj (j = 1 to 6) and the D series intersection Dj (j = 1 to 6) are both the A series intersection Aj (j = 1 to 6) of the same number j. And in a positional relationship where no direct interference occurs.
Therefore, as shown in FIG. 10C, the existing A-sequence slots 1 to 6 are employed as they are for the C-sequence and D-sequence.

FIG. 11 is a time chart showing time-division slot allocation of the C and D sequences.
Here, as described above, the intersection Cj (j = 1 to 6) of the C series and the intersection Dj (j = 1 to 6) of the D series are in a positional relationship that directly interfere with each other with respect to the same number j. .
Further, as shown in FIG. 9C, the total transmission time of the intersection C1 and the intersection D1 is substantially equal to the transmission time of the intersection A1, and can be accommodated in the slot length of the slot 1.

Therefore, in the present embodiment, as shown in FIG. 11, the transmission time of the roadside communication device 2 installed at the intersection C1 and the transmission time of the roadside communication device 2 installed at the intersection D1 correspond to the existing intersection A1. The slots 1 are allocated in a time division manner.
Similarly, the transmission time of the roadside communication device 2 installed at the intersection Cj (j = 2-6) and the transmission time of the roadside communication device 2 installed at the intersection Dj (j = 2-6) are the same as the existing intersection Aj. Time slots are assigned to slots 2 to 6 corresponding to (j = 2 to 6).

FIG. 12 is a time chart showing the time slots of all series A to D after the third-stage slot allocation is completed.
In the tertiary stage in which roadside communication devices 2 are widely used, it is necessary to assign slots to the roadside communication devices 2 installed at the intersections Cj and Dj (j = 1 to 6) of medium or small scale. In the case of a small intersection, since the necessary transmission time is relatively small, it is often considered that the transmission time can be allocated in a time-sharing manner within the range of the already determined slots 1 to 6. It is done.

[Modification: Roadside communication device with directivity]
FIG. 13 is a plan view of a road for showing a modification of the present invention.
Each roadside communication device 2 according to this modification is equipped with a wireless communication unit capable of wireless communication using a plurality of antennas having different directivities.
Each antenna of the wireless communication unit has directivity along the traveling direction of each road flowing into the intersection as indicated by an arrow in FIG. 11, and the wireless communication unit sets transmission / reception timing for each antenna. Can be set.

In the case of the roadside communication device 2 as described above, it can be considered that a single roadside communication device 2 has a plurality of independent communication areas for each antenna.
Therefore, if it is assumed that there is a communication device for each antenna instead of each roadside communication device 2, and determination of presence / absence of radio wave interference and slot allocation are performed, the roadside communication device 2 capable of wireless communication for each directional antenna. Also in this case, the present invention can be applied.

[Other variations]
Each embodiment disclosed this time is an illustration of the present invention and is not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims for patent, and includes all modifications within the scope and meaning equivalent to the scope of claims for patent.
For example, in the above-described embodiment, the central device 4 and other infrastructure-side control devices may automatically perform slot allocation for a plurality of roadside communication devices 2 in a predetermined area. Alternatively, one master unit may be selected in advance, and this master unit may perform overall slot allocation for the slave units.

  Furthermore, in the intelligent transportation system of the above embodiment, a communication device (mobile communication terminal) carried by a pedestrian or the like may be used instead of or in addition to the in-vehicle communication device 3. However, in this case, the mobile communication terminal does not perform wireless transmission during the transmission time (first slot T1) of the roadside communication device 2 as in the case of the in-vehicle communication device 3 of the above embodiment. Need to follow.

DESCRIPTION OF SYMBOLS 1 Traffic signal device 2 Roadside communication device 3 In-vehicle communication device (mobile communication device)
4 central device 5 vehicle 21 wireless communication unit 22 wired communication unit 23 control unit 23A transmission control unit 23B data relay unit 24 storage unit 30 antenna 31 communication unit 32 control unit 33 storage unit S1 signal control command S2 traffic information S3 vehicle information S4 sensing Information S5 Image data S6 Allocation information T1 First slot (time slot)
T2 Second slot (Time slot)

Claims (9)

A wireless communication system comprising a plurality of roadside communication devices that wirelessly transmit in at least one of a plurality of time slots repeated in a predetermined cycle, and a mobile communication device that is allowed to wirelessly transmit in a time zone other than the time slots. There,
The transmission times of the plurality of roadside communication devices in a positional relationship in which direct interference defined in the next (a) or indirect interference defined in the next (b) may occur are time-divided within the same time slot. A wireless communication system, characterized by being assigned by
(A) Direct interference in which downlink signals from a plurality of roadside communication devices reach one mobile communication device at the same time (b) There is a first mobile communication device in the downlink area of the first roadside communication device, When there is a second mobile communication device in the downlink area of the second roadside communication device in a positional relationship that does not cause direct interference with the first roadside communication device, the downlink signal of the first roadside communication device And indirect interference in which the transmission signal of the second mobile communication device or the transmission signal of another mobile communication device wirelessly transmitted in response to this transmission signal reaches the first mobile communication device at the same time   In the same time slot, the roadside communication device that performs wireless transmission for the second and subsequent times can receive downlink signals of other roadside communication devices that wirelessly transmit in advance, and transmit the downlink signal. The wireless communication system according to claim 1, wherein wireless transmission is started after completion is detected.   The radio communication system according to claim 1 or 2, wherein transmission times of the plurality of roadside communication devices assigned in time division to the same time slot are densely allocated with a predetermined guard time in between.   The plurality of roadside communication devices assigned in time division to the same time slot are the roadside communication devices installed at a medium-scale or small-scale intersection connected to at least one side road. The wireless communication system according to item 1. Further including the roadside communication device installed at a large intersection where only a main road flows in,
The radio communication system according to any one of claims 1 to 4, wherein a transmission time of the roadside communication device is independently assigned to one time slot.   The transmission time of the plurality of roadside communication devices in a positional relationship where the indirect interference can occur is assigned to the same time slot in which the start time and the slot length are substantially the same. A wireless communication system according to claim 1. A roadside communication device that wirelessly transmits in at least one of a plurality of time slots repeated in a predetermined cycle and opens a time zone other than the time slot for wireless transmission by a mobile communication device,
The transmission time of a specific roadside communication device and the transmission of another roadside communication device in a positional relationship where direct interference defined in (a) below or indirect interference defined in (b) below may occur. A roadside communication device characterized in that time is allocated in a time division within the same time slot.
(A) Direct interference in which downlink signals from a plurality of roadside communication devices reach one mobile communication device at the same time (b) There is a first mobile communication device in the downlink area of the first roadside communication device, When there is a second mobile communication device in the downlink area of the second roadside communication device in a positional relationship that does not cause direct interference with the first roadside communication device, the downlink signal of the first roadside communication device And indirect interference in which the transmission signal of the second mobile communication device or the transmission signal of another mobile communication device wirelessly transmitted in response to this transmission signal reaches the first mobile communication device at the same time A time slot allocation method for a roadside communication device that wirelessly transmits in at least one of a plurality of time slots repeated in a predetermined cycle and opens a time zone other than the time slot for wireless transmission by a mobile communication device. And
Extracting a plurality of the roadside communication devices in a positional relationship in which direct interference defined in the next (a) or indirect interference defined in the next (b) may occur;
Assigning transmission times of the extracted plurality of roadside communication devices in a time division within the same time slot;
A method for assigning a time slot, comprising:
(A) Direct interference in which downlink signals from a plurality of roadside communication devices reach one mobile communication device at the same time (b) There is a first mobile communication device in the downlink area of the first roadside communication device, When there is a second mobile communication device in the downlink area of the second roadside communication device in a positional relationship that does not cause direct interference with the first roadside communication device, the downlink signal of the first roadside communication device And indirect interference in which the transmission signal of the second mobile communication device or the transmission signal of another mobile communication device wirelessly transmitted in response to this transmission signal reaches the first mobile communication device at the same time Assigning the transmission times of the plurality of roadside communication devices extracted as being in a positional relationship in which the indirect interference can occur to the same time slot in which the start time and the slot length are substantially the same,
The time slot allocation method according to claim 8, further comprising:

Images