JP6512343B2 - Wireless communication system and mobile communication device and transmission control method used therefor - Google Patents

Description

  The present invention relates to, for example, a wireless communication system suitable for Intelligent Transport System (ITS), and a mobile communication device which is a component of this system. More specifically, the present invention relates to a transmission control method for the mobile communication device.

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, information from infrastructure equipment installed on roads is received, or information exchanged between vehicles and information security is achieved by utilizing these information. An intelligent transportation system is being studied to improve the (see, for example, Patent Document 1).
The intelligent transportation system is mainly configured by a plurality of roadside communication devices, which are wireless communication devices on the infrastructure side, and a plurality of in-vehicle communication devices, which are wireless communication devices mounted on each vehicle.

  In this case, the combination of communication performed between the communication entities includes inter-road communication performed by the roadside communication devices, road-vehicle (or roadway) communication performed by the roadside communication device and the in-vehicle communication device, and in-vehicle communication. The inter-vehicle communication performed by the aircraft is included.

Patent No. 2806801 gazette

In the above-mentioned intelligent transportation system, including communication between vehicles, road-to-vehicle communication, road-to-road communication, road-to-road communication, and road-to-walk communication, any communication can be performed by effectively utilizing the bandwidth in coexistence of these respective communications. The issue is whether to control.
Therefore, it is considered that multiple access (Multiple Access) is used to perform communication between roads, between vehicles and between vehicles within a limited frequency band.

As this multi-access method, there are Frequency Division Multiple Access (FDMA) and Code Division Multiple Access (CDMA), but communication with only a few in-vehicle communication devices is also assumed in mountain areas etc. For example, 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).
However, in the area where the roadside communication device exists, road-to-vehicle communication, road-to-road communication, and inter-vehicle communication coexist.

In this case, since it is general that the information handled by the roadside communication equipment on the infrastructure side has a high priority, it is necessary to have a mechanism in which road-to-vehicle communication and road-to-road communication are prioritized over inter-vehicle communication. is there.
As described above, in order to give priority to information transmission by the roadside communication device, time division multiple access (TDMA: Time Division Multiple Access) is provided by dividing the time for communication and providing a time slot dedicated to the transmission of the roadside communication device. Multi-access by is effective.

Therefore, for example, assuming a communication system including a plurality of roadside communication groups installed at each intersection, the timeside dedicated to wireless transmission from the roadside to which the roadside communication apparatus wirelessly transmits is allocated by the TDMA method, and remains Using a time slot for inter-vehicle communication according to the CSMA scheme is considered to be a rational communication system.
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 transportation system in which the TDMA method for roadside transmission control as described above and the CSMA method for multi-access between vehicles are mixed, slot information on the transmission timing of each roadside communication device (start of time slot It is necessary to notify the on-vehicle communication device of the time, slot length, etc.).
As one of the notification methods, a method in which the roadside communication device broadcasts slot information by including slot information in the downlink signal can be considered. In this case, the in-vehicle communication device separately receives slot information in the downlink area of each roadside communication device. You will get.

On the other hand, when roadside communication devices are installed at a plurality of adjacent intersections, radio wave interference (hereinafter sometimes referred to as "direct interference") to vehicle communication devices in the overlapping range of the downlink area may not occur. It is necessary to assign the transmission time to different time slots for roadside communication devices in a positional relationship in which the direct interference occurs.
On the other hand, for roadside communication devices that are not in direct interference with each other, the number of slots is reduced to secure the transmission time zone of the in-vehicle communication devices as much as possible. It is preferable to assign and overlap transmission timing.

However, the amount of transmission data required varies depending on the size of the intersection where the roadside communication device is installed, so the slot lengths for a plurality of roadside communication devices allocated redundantly to the time slot of the same start time are not uniform. There is a possibility.
In this case, for a specific in-vehicle communication device according to the longer slot length, the downlink signal of the roadside communication device adopting that slot length and the transmission signal from the other in-vehicle communication device according to the shorter slot length Radio wave interference (hereinafter sometimes referred to as “indirect interference”) may occur, and the particular on-vehicle communication device may not properly receive the downlink signal.

  In view of such circumstances, the present invention is a wireless communication system in which time slots for roadside communication devices are allocated in a time division manner and the mobile communication devices transmit wirelessly in time zones other than the time slots. The purpose is to effectively prevent indirect interference through transmission.

(1) The wireless communication system of the present invention is a wireless communication in which a time slot dedicated to wireless transmission from the roadside communication device is allocated by time division, and the mobile communication device wirelessly transmits only in a time zone other than that time slot. A system,
The mobile communication device stores the slot number representing which of the plurality of periodically repeated time slots, and the slot number of the time slot of the different roadside communication device having the same slot number. And transmitting control means for setting the longest slot length as a time zone in which transmission of the own is not permitted when the lengths are not aligned .

According to the wireless communication system of the present invention, the storage means stores a slot number indicating which one of the plurality of periodically repeated time slots, and the transmission control means uses the same slot number. When the slot lengths of the time slots of different roadside communication devices are not equal, the longest slot length is set as a time zone in which transmission of the own is not permitted . Even if the slot length differs for each roadside communication device, it is possible to effectively prevent indirect interference via radio transmission by the mobile communication device due to the fact that the slot lengths are not uniform.

( 2 ) The mobile communication device of the present invention is a mobile communication device which is a component of the wireless communication system of the present invention, and has the same technical features as the wireless communication system of the present invention. Therefore, the mobile communication device of the present invention exhibits the same effects as the wireless communication system of the present invention.
( 3 ) The transmission control method of the present invention is the transmission control method for the mobile communication device of the present invention, and has the same technical features as the mobile communication device of the present invention. Therefore, the transmission control method of the present invention has the same effects as the mobile communication device and the wireless communication system of the present invention.

  As described above, according to the present invention, it is possible to effectively prevent indirect interference through wireless transmission by the mobile communication device, so that the mobile communication device can receive the downlink signal from the roadside communication device more reliably. become.

FIG. 1 is a schematic perspective view showing an overall configuration of an intelligent transportation system. It is a road top view showing a part of jurisdiction area of an intelligent transportation 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 format of the transmission frame of a vehicle-mounted communication apparatus. (A) is an explanatory view of direct interference, (b) is an explanatory view of indirect interference, and (c) is a time chart showing slot allocation in which indirect interference may occur. (A) is a road top view which shows the positional relationship of a roadside communication apparatus and a vehicle-mounted communication apparatus, (b) is explanatory drawing which shows the specific example of the setting process of the transmission possible time by a vehicle-mounted communication apparatus.

[Whole system configuration]
FIG. 1 is a schematic perspective view showing the overall configuration of an intelligent transportation system (ITS) according to an embodiment of the present invention. In this embodiment, a grid structure in which a plurality of roads in the north-south direction and in the east-west direction cross each other is assumed as an example of the road structure.
As shown in FIG. 1, the intelligent traffic system according to the present embodiment includes a traffic signal 1, a roadside communication device 2, an in-vehicle communication device 3 (see FIGS. 2 and 3), a central unit 4 and an in-vehicle communication device 3. The vehicle 5 and the roadside sensor 6 which consists of a vehicle sensor, a surveillance camera, etc. 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 illustrated example), and are connected to the router 8 via the communication line 7 such as a telephone line. . The router 8 is connected to the central unit 4 in the traffic control center.
The central unit 4 constitutes a LAN (Local Area Network) with the traffic signal 1 and the roadside communication unit 2 at each intersection Ji included in the area under its control. Therefore, the central unit 4 can perform two-way communication with each traffic signal 1 and each roadside communication device 2. The central apparatus 4 may be installed on the road instead of the traffic control center.

The roadside sensor 6 is installed at each place of 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 ultrasonically sensing a vehicle 5 passing immediately below, or a monitoring camera imaging the traffic condition of the road in time series, and the sensing information S4 and the image data S5 are transmitted through the communication line 7 Is sent to the central unit 4 via
In addition, in FIG.1 and FIG.2, in order to simplify illustration, although only one signal lamp apparatus is described by each intersection Ji, it is for the going up and down of the road which mutually cross | intersects in each actual intersection Ji. At least four signal lights are installed.

[Central unit]
The central unit 4 has a control unit including 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 (Operation) · Comprehensive control of recording, signal control and information provision.
Specifically, the control unit of the central unit 4 controls the traffic signal 1 on the same road with respect to the traffic signal 1 at the intersection Ji belonging to its own network, or performs this system control on the road network. Extended wide area control (surface control) can be performed.

Further, the central unit 4 has a communication unit which is a communication interface connected to the LAN side via the communication line 7. This communication unit is a signal control command S1 regarding the light color switching timing of the signal light, Traffic information S2 including traffic congestion information and the like is transmitted to the traffic signal 1 and the roadside communication device 2 at predetermined time intervals (see FIG. 1).
The signal control command S1 is transmitted every calculation cycle (for example, 1.0 to 2.5 minutes) of the signal control parameter when the system control or the wide area control is performed, and the traffic information S2 is transmitted every 5 minutes, for example. Be done.

  In addition, the communication unit of the central unit 4 generates from the roadside communication device 2 corresponding to each intersection Ji 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, etc. The control information of the vehicle sensor (not shown) consisting of pulse signals and image data S5 consisting of digital information of the road taken by the monitoring camera etc. are received, and the control unit of the central unit 4 The system control and the wide area control are executed based on various information.

[Method of wireless communication etc.]
FIG. 2 is a road plan view showing a part of the jurisdictional area of the above-mentioned intelligent transportation system.
In FIG. 2, each of the two intersecting roads is illustrated as going up and down with one lane on each side, but the road structure is not limited to this.
As also shown in FIG. 2, in the intelligent traffic system according to the present embodiment, 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 in a carrier sense system. It also functions as a wireless communication system equipped with an on-vehicle communication device 3 which is a type of mobile wireless transceiver that performs wireless communication with the wireless communication system.

In the example of FIG. 1 and FIG. 2, the plurality of roadside communication devices 2 are installed at each of the roadside intersections Ji and attached to the support of the traffic signal 1. On the other hand, the in-vehicle communication device 3 is mounted on 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, which is the reach of the downlink signal from the roadside communication device 2.

Further, in the present embodiment, it is assumed that the arrival distance of the transmission signal of the in-vehicle communication device 3 is equal to or less than the arrival distance of the downlink signal of the roadside communication device 2. Therefore, each roadside communication device 2 can perform wireless communication with the in-vehicle communication device 3 traveling in the range of the downlink area A of the own device.
Thus, in the present embodiment ITS, communication between on-vehicle communication devices 3 (inter-vehicle communication), between roadside communication device 2 and on-vehicle communication device 3 (road-to-vehicle communication from “road” to “vehicle” Wireless communication is used for the communication of "car" to "road", including both of the inter-vehicle communication.

In addition, when the installation positions of the adjacent roadside communication devices 2 are relatively close to each other, and the downlink areas A of each other overlap (may overlap partially or entirely), the wireless communication between the roadside communication devices 2 is performed. Communication (inter-path communication) is possible.
As described above, the central unit 4 provided in the traffic control center can perform two-way communication with each roadside communication device 2 by wire, but wireless communication may be performed between them.

The roadside communication device 2 allocates a dedicated time slot (first slot T1 in FIG. 4) for wireless transmission by itself according to the TDMA method, and a time zone other than this time slot (second slot T2 in FIG. 4). Does not transmit wirelessly.
That is, the time zone other than the time slot for the roadside communication device 2 is opened as the transmission time according to the CSMA method for the in-vehicle communication device 3.

Also, 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 which synchronizes its own clock with the time acquired from the GPS satellite, or air synchronization which synchronizes its own clock with a transmission signal from another roadside communication device 2 .

[Roadside communication device]
FIG. 3 is a block diagram showing an 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 performing bidirectional communication with the central apparatus 4, and a processor (CPU And a storage unit 24 including a storage device such as a ROM or a RAM connected to the control unit 23.

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

The data relay unit 23B of the roadside communication device 2 temporarily stores temporarily the traffic information S2 and the like from the central apparatus 4 received by the wired communication unit 22 in the storage unit 24, and causes the wireless communication unit 21 to broadcast.
Further, the data relay unit 23 B temporarily stores the vehicle information S 3 received by the wireless communication unit 21 in the storage unit 24 temporarily, and transfers the vehicle information S 3 to the central apparatus 4 via the wired communication unit 22.

The transmission control unit 23A of the roadside communication device 2 synchronizes the transmission timing with another device, and at the same time, transmits a time slot T1 of a predetermined slot number i assigned to the own device (see FIG. 4: “slot i” hereinafter) Wireless transmission within a predetermined transmission time.
That is, the storage unit 24 of the roadside communication unit 2 stores, for example, slot information S6 including the following information a) and b). The slot information S6 is set individually for each roadside communication device 2.
a) Slot number i used by own device (see Fig. 4)
b) Start time and duration of the first slot T1 (see FIG. 4) of slot number i

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

The transmission time of the roadside communication device 2 may be set to the maximum of the duration time (slot length) of the time slot T1 assigned to the own device, but the synchronization deviation with other communication devices 2 and 3 or the receiving side In consideration of the information processing time, etc., it is preferable to set the length slightly shorter than the slot length with a predetermined margin (for example, a guard time on the order of 10 μs).
In addition, the transmission time of the roadside communication device 2 can be set to an arbitrary time length within the range of the slot length allocated to the own apparatus, and the time significantly shorter than the slot length (for example, 1⁄3 or It can also be set to 1/2).

Of the transmission start time and the transmission time of the downlink signal, the transmission control unit 23A of each roadside communication apparatus 2 determines the transmission start time based on the start time of the slot i included in the slot information S6 of the own apparatus. It may be generated 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 slot 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 slot information S6 and the time stamp, a time other than the first slot T1 of the slot number i described in the slot information S6 is used with reference to the current time of the time stamp. The wireless transmission is performed in the band (the second slot T2 in FIG. 4).
If the main cycle Cm to be described later is included in the slot information S6, the start time of the slot i and the current time of the time stamp can be expressed as a relative time within the main cycle Cm. In this case, the number of bits of the slot information S6 can be reduced as compared to the case where those times are represented by absolute times.

  The slot information S6 only needs to include at least the time of the slot i used by the own device, but the slot information S6 of the other roadside communication device 2 is obtained by inter-path communication or communication with the central device 4. If known, the slot information S6 of the other device may be transmitted from the own device.

[Contents of time slot]
FIG. 4 is a conceptual view showing an example of a time slot for road-to-vehicle communication.
As shown in FIG. 4, the time slot of the 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. In this time zone, wireless transmission by the roadside communication device 2 is permitted.

The first slot T1 is assigned a slot number i, and this slot number i is periodically incremented (may be decremented).
The second slot T2 is a time slot for the in-vehicle communication device 3. Since the time slot is opened for wireless transmission by the in-vehicle communication device 3, the transmission control unit 23A of the roadside communication device 2 performs the second slot T2. Does not transmit wirelessly.

The slot number i returns to the initial number (i = 1 in the illustrated example) when the number n becomes a predetermined number. Therefore, assuming that a slot cycle Cs for n times is a main cycle Cm, the first slots T1 of each slot number i to n occur once for each main cycle Cm.
The time length of each cycle Cs, Cm and the total number n of slot cycles Cs can be set as appropriate by the system operator, but in this embodiment, Cs = 10 ms, Cm = 100 ms and n = as an example. And 10

In FIG. 4, the dots ● in the first slot T1 of slot numbers i = 1 to 3 indicate the roadside communication device 2 that performs wireless transmission to the first slot T1 of the slot number i. , 2 indicate that the transmission timings of the plurality of roadside communication devices 2 overlap, and the plurality of roadside communication devices 2 share the slot number i.
That is, in the example of FIG. 4, the slot 1 is shared by the two roadside communication devices 2 installed at the intersection J1 and the intersection J11, and the slot 2 is installed at the intersection J2, the intersection J9, and the intersection J10. Two roadside communication devices 2 are shared.

  The reason is that, for example, as in the intersection J1 and the intersection J11 in FIG. 1, the downlink areas A do not overlap in the roadside communication devices 2 with a long distance, and one in-vehicle communication device 3 has a plurality of roadside communication devices Since the direct interference (see FIG. 6 (a)) which receives the downlink signal simultaneously from 2 does not occur or its possibility is extremely low, the same slot i is set to these and the transmission time of each roadside communication device 2 Even if the vehicle-mounted communication device 3 overlaps, the in-vehicle communication device 3 can properly receive the downlink signal from each roadside communication device 2.

On the other hand, in the case of roadside communicators 2 in a relatively close positional relationship in which the direct interference can occur with respect to one in-vehicle communicator 3, the slot numbers i can not be set to be the same and transmission times can not be overlapped. .
However, even the roadside communication devices 2 where direct interference may occur can share the same slot number i if the transmission time is scheduled by time division in the first slot T1. In addition, although indirect interference shown in FIG.6 (b) may arise also by the roadside communication apparatuses 2 comrades which use the same slot number i, since direct interference does not arise, this point is mentioned later.

[Vehicle communication device]
Returning to FIG. 3, the in-vehicle communication device 3 includes a communication unit (transmission / reception unit) 31 connected to an antenna 30 for wireless communication, and a control unit 32 including a processor that performs communication control for the communication unit 31. A storage unit 33 connected to the control unit 32 and configured of a storage device such as a ROM or a RAM is provided.
The storage unit 33 stores a computer program for communication control executed by the control unit 32, a communication device ID of each 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 by the carrier sense system for inter-vehicle communication, and the communication control function in the time division multiplex system such as the roadside communication device 2 I do not have it.
Therefore, the communication unit 31 of the in-vehicle communication device 3 constantly senses the reception level of the predetermined carrier frequency, and when the value is equal to or higher than a threshold, wireless transmission is not performed and becomes lower than the threshold. Only wireless transmission is to be performed.

The control unit 32 of the in-vehicle communication device 3 performs, as a functional unit achieved by executing the computer program, a transmission control unit 32A that controls wireless transmission timing of the communication unit 31, and relay processing of reception data of the communication unit 31. And a data relay unit 32B that
Transmission control unit 32A of in-vehicle communication device 3 sets a time zone of wireless transmission permitted by itself according to the start time of slot information S6 acquired from roadside communication device 2 and slot information S6, and the communication unit only for this time period. Make 31 wireless transmission.

That is, the transmission control unit 32A extracts the slot information S6 of the roadside communication device 2 from the downlink signal from the roadside and the reception frame from the vehicle side, and the slot based on the time stamp included in the downlink signal. Only in the time slot (the second slot T2 in FIG. 4) other than the time slot T1 of the slot number i described in the information S6, the communication unit 31 is caused to perform wireless transmission by the carrier sense scheme.
The transmission control unit 32A of the in-vehicle communication device 3 avoids the indirect interference based on the plurality of slot information S6 in the case of the slot i to which the transmission timings of the plurality of roadside communication devices 2 are allocated in duplicate. The process of setting the transmittable time is executed, the details of which will be described later.

Further, the transmission control unit 32A of the in-vehicle communication device 3 stores vehicle information S3 including the current position, direction, speed and the like of the vehicle 5 (in-vehicle communication device 3) in a transmission frame. Radio transmission via broadcast to the outside.
The data relay unit 32B of the in-vehicle communication device 3 can perform a relay process of extracting predetermined data from the reception frame received by the communication unit 31, and transmitting the extracted data to the communication unit 31 by including it in the transmission frame. .

For example, the data relay unit 32B extracts traffic information S3 and vehicle information S3 of the other vehicle 5 from the downlink signal of the roadside communication device 2, generates a transmission frame including the extracted data, and transmits the transmission frame to the communication unit 31 .
In addition, when slot information S6 is included in the downlink signal of the roadside communication device 2 or the received frame received from the other vehicle 5, the data relay unit 32B extracts the slot information S6 and stores the slot information S6. , And stores the slot information S6 in a transmission frame for transmission to the communication unit 31.

In the present embodiment, the field of the number of relays is defined in the transmission frame of the in-vehicle communication device 3, and when the data relay unit 32B stores the slot information S6 in the transmission frame transmitted by itself, A transmission frame is generated by incrementing the field value by one, and the communication unit 31 is caused to transmit this frame.
Therefore, when the slot information S6 directly received from the roadside communication device 2 is included in the transmission frame transmitted by itself, the field value of the number of times of relaying is "1". When the slot information S6 extracted from the reception frame of which the number of relays received from the other vehicle 5 is “1” is included in the transmission frame transmitted by itself, the field value of the number of relays becomes “2”.

Further, when the transmission control unit 32A of the in-vehicle communication device 3 receives the downlink signal including the slot information S6 and the reception frame from the other vehicle 5, the transmission control unit 32A counts an elapsed time from the reception time.
In the present embodiment, the control unit 32 of the in-vehicle communication device 3 receives the vehicle information S3 directly received from the other vehicle 5 (in-vehicle communication device 3) and the vehicle information of the other vehicle 5 received from the roadside communication device 2. Based on the position, speed, and direction included in S3, safe driving support control can be performed to avoid a right-hand collision, a head-on collision, and the like.

[Transmission frame of in-vehicle communication device]
FIG. 5 is a view showing an example of the format of a transmission frame of the in-vehicle communication device 3.
As shown in FIG. 5, the transmission frame of the in-vehicle communication device 3 includes a preamble, a header, data, and a cyclic redundancy check (CRC).
Among these, in the header, an extended MAC header in which the MAC header is extended is defined, and the slot information S6 and the number of relays thereof are stored in the extended header.

The data also includes the position, direction (traveling direction), and speed of the vehicle 5, but may include the reception level when the downlink 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 side of the vehicle 5 such as GPS, but may be obtainable from the infrastructure side such as a light beacon. The speed is information based on the speed sensor of the vehicle 5.

[Direct interference and indirect interference]
FIG. 6 (a) is an explanatory view of direct interference, and FIG. 6 (b) is an explanatory view of indirect interference. FIG. 6C is a time chart showing slot allocation in which indirect interference can occur.
Hereinafter, with reference to FIG. 6, the contents of the two types of radio wave interference that become problems in the wireless communication system of the present embodiment and a transmission control method in the on-vehicle communication device 3 for avoiding indirect interference will be described.

First, “direct interference” means that downlink signals from a plurality of roadside communicators 2 simultaneously reach one in-vehicle communicator 3. In this case, there is a high possibility that the in-vehicle communication device 3 can not properly receive the downlink signal because a plurality of downlink signals collide and cause radio wave interference.
As shown in FIG. 6A, the direct interference is caused by the roadside communication devices 2X and 2Y with respect to the vehicle 5 in which the downlink areas A and A of the two roadside communication devices 2X and 2Y overlap. Occurs when downlink transmission is performed simultaneously.

In order to avoid the direct interference, for example, the transmission time of one roadside communication device 2X is allocated to slot k (the first slot T1 of slot number i = k), and the transmission time of the other roadside communication device 2Y is slot k It is sufficient to assign to other slots and shift the transmission time of the two.
Conversely, for the roadside communication devices 2X and 2Y in the positional relationship shown in FIG. 6 (b) where the direct interference does not occur, only direct collision of the transmission signals from the roadside communication devices 2X and 2Y is assumed. If so, basically it is efficient to assign to the same slot k.

On the other hand, as shown in FIG. 6 (b), the first in-vehicle communication device 3X is in the downlink area A of the first roadside communication device 2X, and direct interference occurs with the first roadside communication device 2X. It is assumed that there is a second on-vehicle communication device 3Y in the downlink area A of the second roadside communication device 2X in a non-positional relationship.
In this case, “indirect interference” refers to the downlink signal of the first roadside communication device 2X, the transmission signal Sy of the second on-vehicle communication device 3Y, or other radio transmission triggered by this transmission signal Sy. The transmission signal Sz of the in-vehicle communication device 3Z simultaneously arrives at the first in-vehicle communication device 3X.

Such indirect interference is a problem that can occur when the durations (slot lengths) of the time slots T1 of the roadside communication devices 2X and 2Y are different as shown in FIG. 6 (c).
That is, as shown in FIG. 6C, the transmission times Tx and Ty of the roadside communication devices 2X and 2Y are assigned to the slot k (the first slot T1 of the slot number i = k) having the same start time, It is assumed that the slot length Lx assigned to the roadside communication device 2X is longer than the slot length Ly assigned to the roadside communication device 2Y.

In this case, if it is assumed that the roadside communication devices 2X and 2Y broadcast only their own slot information without knowing the slot length of the other party, the first vehicle that received the slot information in the downlink area A of the roadside communication device 2X In the case of the communication device 3X, wireless transmission is restricted within the range of the longer slot length Lx.
On the other hand, in the case of the second on-vehicle communication device 3Y that received the slot information in the downlink area A of the roadside communication device 2Y, the wireless transmission is restricted within the range of the shorter slot length Ly, so the slot length It is possible to perform wireless transmission in a time zone (time zone of (Lx-Ly) in FIG. 6C) after lapse of Ly and before lapse of the slot length Lx.

When the second in-vehicle communication device 3Y performs wireless transmission in the above time zone (Lx-Ly), when the distance between the in-vehicle communication devices 3X and 3Y is equal to or less than the radio wave reach distance of the in-vehicle communication device 3, The transmission signal Sy of the second in-vehicle communication device 3Y transmitted in the time zone (Lx-Ly) reaches the first in-vehicle communication device 3X.
In addition, even when the distance between the in-vehicle communication devices 3X and 3Y exceeds the radio wave arrival distance, the transmission signal Sz of the third in-vehicle communication device 3Z that receives the transmission signal Sy of the second in-vehicle communication device 3Y and relays data is , And may reach the first on-vehicle communication device 3X.

  Thus, even if the transmission times Tx and Ty of the roadside communication devices 2X and 2Y are allocated to the slot k at the same start time because of the positional relationship in which direct interference does not occur, the slot length Lx of each roadside communication devices 2X and 2Y , Ly are different, the first in-vehicle communication device 3X according to the roadside communication device 2X according to the longer slot length Lx, the downlink signal from the roadside communication device 2X, and the shorter slot length Indirect interference may occur, in which the transmission signal Sy from the second in-vehicle communication device 3Y according to the roadside communication device 2Y according to Ly (or another transmission signal Sz triggered by the transmission signal Sy) arrives simultaneously. If indirect interference occurs, there is a risk that the first on-vehicle communication device 3X can not properly receive the downlink signal of the roadside communication device 2X.

  In the above description, in FIG. 6B, the in-vehicle communication device 3X directly receives the slot information from the roadside communication device 2X, and the in-vehicle communication device 3Y directly receives the slot information from the roadside communication device 2Y. In the case where the in-vehicle communication device 3Y indirectly acquires not only the slot information of the roadside communication device 2Y but also the slot information of the roadside communication device 2X by relay from the in-vehicle communication device 3X or the in-vehicle communication device 3Z. However, depending on the slot information selection method, the problem of indirect interference may occur.

  That is, for example, when the on-vehicle communication device 3Y acquires a plurality of slot information directly or indirectly, it is possible to set a possible transmission time of itself based on the slot information with the smallest number of relays from among them. In this method, the on-vehicle communication device 3Y always sets the transmittable time (in this case, the time period in which the roadside communication device 2Y does not transmit) based on the slot information received directly from the roadside communication device 2Y. Eventually, wireless transmission is restricted only in the range of slot length Ly, and indirect interference may still occur.

Transmission Control Method to Avoid Indirect Interference (Principle)
Therefore, in the present embodiment, the transmission control unit 32A of the mobile communication device 3Y uses the slot k of the same slot number k based on the received plurality of slot information S6, and each roadside communication device 2X has an overlapping transmission timing. The above indirect interference is avoided by setting the time zone permitted by any of the above and 2Y to its own transmittable time.

  Specifically, the transmission control unit 32A of the in-vehicle communication device 3Y transmits the slot information S6 of the roadside communication device 2X to the other in-vehicle communication with respect to the slot k to which the transmission times of the plurality of roadside communication devices 2X and 2Y are allocated in duplicate. When the slot information S6 of the roadside communication device 2Y is directly received by the downlink signal of the communication device 2Y obtained from the on-vehicle communication device 3Z (for example, in FIG. 6B), the slot length included in each slot information S6 Lx and Ly are extracted respectively, and the maximum value of this slot length Lx and Ly (in this case, slot Lx) is regarded as the slot length of slot k related to duplicate allocation, and the time slot other than the maximum slot length Lx is transmitted by itself. Set to possible time.

  In other words, the transmission control unit 32A of the in-vehicle communication device 3Y uses the same slot number k, and among the plurality of roadside communication devices 2X and 2Y whose transmission timings overlap, the roadside communication device 2X having the longest transmission time. The time zone (a time zone other than the slot Lx) which is allowed is set as its own transmittable time.

In this way, the in-vehicle communication device 3Y does not transmit wirelessly in the time zone (Lx-Ly) of the difference between the slot length Lx and the slot length Ly, and the slots of the plurality of roadside communication devices 2X and 2Y to which the same slot k is assigned It is possible to effectively prevent the indirect interference through the wireless communication of the in-vehicle communication devices 3X to 3Z, which occurs because the lengths Lx and Ly are not aligned.
6B and 6C illustrate two roadside communication devices 2X and 2Y, the same slot k may be allocated to three or more roadside communication devices 2 in an overlapping manner. It is similar. That is, in this case, the transmission control unit 32A sets a time zone other than the maximum value of each slot length for three or more roadside communication devices 2 as its own transmittable time.

In the example of FIG. 6C, it is assumed that the start time of slot k is common to each roadside communication device 2, but the start time may differ depending on the roadside communication devices 2X and 2Y even with the same slot number k. . Therefore, transmission control unit 32A of in-vehicle communication device 3Y sets the roadside communication devices 2X and 2Y sharing time slot T1 of the same slot number k other than the maximum time from the earliest slot start time to the latest slot end time among them. The time zone of may be set to its own transmittable time.
In this case, the indirect interference can be effectively prevented even when the slot start times are not aligned as well as the slot length of the slot k where the transmission timings of the plurality of roadside communication devices 2 overlap.

[Specific example of setting process of possible transmission time]
FIG. 7A is a plan view showing the positional relationship between the roadside communication devices 2X to 2Z and the in-vehicle communication devices 3X and 3Y. FIG. 7B is a process for setting the transmission available time by the in-vehicle communication device 3Y. It is explanatory drawing which shows a specific example.
Hereinafter, the setting process of the transmission possible time which the transmission control part 32A of the vehicle-mounted communication apparatus 3Y performs is demonstrated, referring FIG.

  In FIG. 7A, of the two roads R1 and R2 in the north-south direction, the road R1 on the left is a main road (for example, a road with a total of 4 lanes or more), and the road R2 on the right is larger in size than the main road Of the three roads Ra to Rc in the east-west direction, which is a small side road, the north-most road Ra is a main road, and the other roads Rb and Rc are side roads.

In addition, the first roadside communication device 2X is installed at a large-scale intersection where the main roads R1 and Ra intersect, and the second roadside communication device 2Y is installed at a small-sized intersection where the side roads R2 and Rc intersect. It is assumed that the third roadside communication device 2Z is installed at an intersection (for example, 2 km or more) far away from the in-vehicle communication device 3Y.
Furthermore, since the roadside communication devices 2X to 2Z are not in the positional relationship of direct interference, as shown in FIG. 7B, they use the slot k of the same start time (t = 10 ms).

Further, in the first roadside communication device 2X at a large-scale intersection with a large amount of transmission data, the slot information SLx is longer slot length (= 5 ms), and the first roadside communication device 2X The roadside communication device 2Y of 2 has the slot information SLy of a short slot length (= 3 msec).
Assuming that the third roadside communication device 2Z is installed at an intersection larger than the roadside communication device 2X, the longest slot length (= 7 ms) among the three parties 2X to 2Z. It is slot information SLz.

Also, the two in-vehicle communication devices 3X and 3Y are mounted on a vehicle traveling on the road R2, and the first in-vehicle communication device 3X can receive the downlink signal of the first roadside communication device 2X. There is a positional relationship in which the in-vehicle communication device 3Y can receive the downlink signal of the second roadside communication device 3X.
Under such circumstances, the transmission control unit 32A of the in-vehicle communication device 3Y first performs each slot based on the number of times of relaying each slot information SLx to SLz acquired by itself and the elapsed time from the time of reception to the current time. The validity of the information SLx to SLz is determined.

Specifically, the transmission control unit 32A determines whether the number of relays of the slot information SLx to SLz is equal to or less than a predetermined threshold (for example, five times). The transmission control unit 32A also determines whether the elapsed time of the slot information SLx to SLz is less than or equal to a predetermined threshold (for example, 10 minutes).
Then, the transmission control unit 32A validates the slot information whose determination results are all positive and the slot information whose one of the determination results is negative is the target of the setting process of the transmission available time as being invalid. Exclude from

In the example of FIG. 7B, since the first and second slot information SLx and SLy both clear each determination, they are determined as valid slot information, and the third slot information Sz is determined as each determination. It is determined that the slot information is invalid because none of them is cleared.
Next, the transmission control unit 32A of the in-vehicle communication device 3Y extracts the slot length from the slot information SLx and SLy determined to be valid, and the maximum value (= 5 ms) among them is determined by the roadside communication devices 2X and 2Y. Assuming that the transmission timing of T is the slot length of the overlapping slot k, a time zone other than the maximum value is set to its own transmittable time (hatched portion in FIG. 7B).

As a result, since the in-vehicle communication device 3Y does not wirelessly transmit in the time slot of 13 to 15 ms in the slot k, the downlink signal of the roadside communication device 2X and the transmission signal from the in-vehicle communication device 3Y become the in-vehicle communication device 3X. It does not reach at the same time, and the above-mentioned indirect interference is prevented.
Further, in the present embodiment, the transmission control unit 32A of the in-vehicle communication device 3Y determines the validity based on the number of relays and the elapsed time of the slot information SLx to SLz. The slot information SLz of the communication device 2Z is excluded.

Therefore, it is possible to prevent unnecessary shortening of the transmittable time accompanying the inclusion of the slot information SLz of the third roadside communication device 2Z in the target of the process of setting the transmittable time.
That is, in the example of FIG. 7B, since the slot length of the third roadside communication device 3Z is actually 7 msec (= maximum length), the roadside communication device 3Z located at a distance is not excluded unless the slot information SLz is excluded. However, in the present embodiment, the slot information SLz of the third roadside communication device 2Z is excluded as invalid. It can be prevented in advance.

Further, in the present embodiment, the roadside communication relayed from the other in-vehicle communication devices 3X and 3Z is effective for the received slot information SLx to SLz of the transmission control unit 32A of the in-vehicle communication device 3Y. Even the slot information SLx of the device 2X is included in the setting object of the transmittable time.
For this reason, it is possible to effectively prevent the indirect interference accompanying the on-vehicle communication device 3Y setting the transmission available time based on the slot information SLy of the minimum number of times of relaying.

  In the above example, the transmission control unit 32A of the in-vehicle communication device 3Y determines the validity based on both the number of times of relaying the slot information SLx to SLz and the elapsed time, but only one of them determines the validity. The validity may be determined.

[Other Modifications]
Each embodiment disclosed this time is an illustration of the present invention and is not restrictive. The scope of the present invention is indicated not by the embodiments described above but by the claims, and includes all modifications within the scope of the claims and their equivalents.

  In the intelligent transportation system of the above embodiment, a communication device (portable 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, as in the case of the on-vehicle communication device 3 of the above embodiment, the mobile communication terminal does not perform wireless transmission during the transmission time (first slot T1) of the roadside communication device 2. You need to follow.

1 Traffic Signal 2 Roadside Communication Device 3 Vehicle Communication Device (Mobile Communication Device)
REFERENCE SIGNS LIST 4 central apparatus 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 (reception means)
32 control unit 32A transmission control unit (transmission control means)
32B Data relay unit 33 Memory unit S1 Signal control command S2 Traffic information S3 Vehicle information S4 Sensing information S5 Image data S6 Slot information T1 First slot (time slot)
T2 second slot (time slot)

Claims (3)

A wireless communication system in which a time slot dedicated to wireless transmission from a roadside communication device is allocated by time division, and a mobile communication device is allowed to perform wireless transmission only in a time zone other than the time slot,
The mobile communication device is
Storage means for storing a slot number representing which one of the plurality of periodically repeated time slots ;
Transmission control means for setting the longest slot length as a time zone in which transmission of the same is not permitted when the slot lengths of the time slots of different roadside communication devices having the same slot number are not uniform A wireless communication system characterized by A mobile communication device permitted to transmit wirelessly during a time zone other than a time slot assigned in time division for wireless transmission of a roadside communication device,
Storage means for storing a slot number representing which one of the plurality of periodically repeated time slots ;
Transmission control means for setting the longest slot length as a time zone in which transmission of the same is not permitted when the slot lengths of the time slots of the different roadside communication devices having the same slot number are not uniform A mobile communication device characterized by A transmission control method of a mobile communication device, wherein it is permitted to perform wireless transmission in a time zone other than the time slot assigned in time division for wireless transmission of the roadside communication device,
Storing a slot number representing which one of the plurality of periodically repeated time slots ;
And, if the slot lengths of the time slots of the different roadside communication devices having the same slot number are not uniform, setting the longest slot length to a time zone in which transmission of the same is not permitted. Transmission control method of mobile communication device.

Images