JP3860161B2 - Packet flooding relay collision prevention system - Google Patents

Description

  The present invention belongs to the technical field of a collision prevention system that prevents vehicle collision in advance by transmitting vehicle information such as the position, speed, and time of all vehicles existing within a certain range to all vehicles as much as possible.

  Currently, the number of deaths due to vehicle accidents has reached over 8,000 people a year. Vehicle location information and speed information are regularly communicated wirelessly to neighboring vehicles, and the vehicle's collision can be prevented by notifying the driver of the mutual positional relationship. Anti-collision prevention systems are attracting attention. In this vehicle collision prevention system, it is important to reliably transmit the position information and speed information of the host vehicle to surrounding vehicles in real time. However, due to the nature of wireless communication, there are problems that there are places where it is difficult to receive packets due to shadowing by buildings in urban areas, and packet loss due to packet collisions occurs in an environment where the vehicle density is high. Therefore, when the collision prevention system is put into practical use, there is a lot of obstacles such as urban areas, and a method for reliably transmitting packets to surrounding vehicles even in an environment with a high vehicle density is necessary.

  As a means to increase the packet transmission rate of inter-vehicle communication, a method using radio wave diffraction using 5.8 GHz instead of millimeter waves as a radio frequency band (see Non-Patent Document 1) and an ad hoc network between vehicles are constructed. A method using packet relay processing has been proposed. Paying attention to a method using an ad hoc network, it is known that flooding of a packet presses down on a radio band, and particularly when the station density is high, the transmission rate of the packet is significantly lowered due to a broadcast storm problem. For this reason, when performing packet flooding by an ad hoc network in a high vehicle density environment such as an urban area, a flooding relay control method that efficiently propagates packets becomes an important issue.

  As a flooding relay control method for vehicle-to-vehicle communication, ACK confirmation from a vehicle that has successfully received a packet is performed, and if ACK is not confirmed, a relay request is made to the vehicle nearest to the vehicle, and the packet is retransmitted. There has been proposed a method for autonomously determining packet relay if the received power of a packet or the ratio of desired wave power to interference wave power is within a certain range from a threshold (see Non-Patent Document 2).

Further, a method has been proposed in which the traveling directions of the host vehicle and other vehicles are treated as vectors, and the vehicle is classified into a vehicle traveling on the same road as the host vehicle and other vehicles (see Non-Patent Document 3).
Yuichi Morioka, Toshihiro Hamada, Masao Nakagawa, “A Collision Prevention System Using DGPS and Inter-Vehicle Communication at Out-of-Line Intersection”, IEICE Technical Report ITS2000-4, May 2000, p. 19-24 Yoshitsugu Shimazu, Eiichi Murata, Susumu Yoshida, “Autonomous Packet Relay Control Method in ITS Inter-Vehicle Communication”, IEICE Transactions B, November 1999, Vol. J82-B No. 11, p. 2018-2025 Kentaro Yamada, Min-Te Sun, Wuchi Feng, Ten H Lai, Hiromi Okada, “Broadcasting Protocol Using GPS for In-Vehicle Communication”, IEICE Technical Report DSP99-161, SAT99-116, RCS99-166 , January 2000, p. 61-68

  However, in an environment where a large number of roads intersect with each other as in an urban area and the vehicle density is high, a large number of packet relay vehicles can exist regardless of which method is used. As in the collision prevention system, for example, when all vehicles transmit packets including position information at a cycle of about 100 ms, a decrease in packet transmission rate due to compression of the radio band becomes an unavoidable problem.

An object of the present invention is to solve such a problem.
The present invention is a relayed packet flooding system for a collision prevention system that is particularly effective in an environment with a high vehicle density such as an urban area.
In the system of the present invention, each vehicle calculates a plurality of relay points based on position information, speed information, traveling direction, and time information, and specifies the vehicle closest to the relay point to perform packet relay processing. Is. According to the system of the present invention, the number of packet relay vehicles can be suppressed below the set number of relay points regardless of the vehicle density, so that packet flooding can be performed effectively.

In order to solve the above problems, the first configuration of the packet flooding relay collision prevention system of the present invention is characterized by comprising the following means to be mounted on each vehicle.
(B) A collision prevention packet is transmitted every time the vehicle travels a predetermined distance, and a collision prevention packet transmitted by another vehicle is received, and the received vehicle collision prevention packet includes the own vehicle address. In addition, when the number of relays of the packet is less than the limit number, transmission / reception means that immediately relays the packet. (B) Location information, speed information, traveling direction, time information of the vehicle, and (f) Collision prevention packet generation means that generates a transmission packet (collision prevention packet) including the first relay vehicle address for each relay point in the relay vehicle candidate storage table and a relay number counter and sends the packet to the transmission / reception unit. Set multiple relay points that serve as reference points for selecting a relay vehicle that relays the collision prevention packet transmitted by the vehicle within the effective radio wave distance range centered on the next transmission point of the car (D) From the position information, speed information, traveling direction, and time information of one or more other vehicles that directly received the collision prevention packet by the transmission / reception means, Other vehicle position calculation means for calculating the position of the vehicle (e) Distance calculation means for calculating the distance between each relay point and each other vehicle position (f) For each relay point, the relay point and each other vehicle position Relay vehicle candidate storage table that stores vehicle addresses from the first rank to a predetermined rank in order of increasing distance between them.

In the second configuration, instead of the transmission / reception means (a) of the first configuration, a collision prevention packet is transmitted every time a predetermined time elapses, and a collision prevention packet transmitted by another vehicle is transmitted. In addition to receiving, when the own vehicle address is included in the received collision prevention packet and the number of relays of the packet is less than the limit number, a transmission / reception unit that immediately relays the packet is used. This is a feature of a packet flooding relay collision prevention system.
FIG. 1 is a block diagram showing the configuration of the above means.

  By providing each of the above means, each vehicle sets a plurality of relay points within the effective radio wave distance range centered on the next transmission point of the own vehicle by the relay point setting means 3. By the vehicle position calculation means 4, the position of the other vehicle at the next transmission time of the own vehicle is determined from the position information, speed information, traveling direction, and time information of one or more other vehicles from which the transmission / reception unit 1 directly received the collision prevention packet Calculated by the vehicle position calculation means 4, and the distance between the other vehicle position and the relay point is calculated by the distance calculation means 5, and for each relay point, the distance between the relay point and each other vehicle position is increased in advance in advance. The vehicle addresses up to a predetermined order are stored in a table.

And at the time of collision prevention packet transmission, a relay vehicle is determined in a fixed order about each relay point. When a first relay vehicle candidate at a certain relay point overlaps with a relay vehicle at another relay point, a relay station is selected from the second and lower relay vehicle candidates. This vehicle address is designated as a relay vehicle by putting it in the collision prevention packet by the collision prevention packet generation means 2.
Therefore, the number of relay vehicles is not only limited to a predetermined number of relay points, but also the vehicle designated as a relay station differs for each vehicle, so it is possible to avoid load concentration.

  Also, if the vehicle address is included in the collision prevention packet received by the vehicle, the vehicle is designated as a relay vehicle, so if the number of relays of the packet is less than the limit The received collision prevention packet is immediately relayed by the relay processing means 13.

  In this relay process, the received collision prevention packet is immediately transmitted as it is, separately from the transmission timing transmitted every time the vehicle travels a certain distance or every certain period of time. At this time, the relay hop count counter in the packet is incremented by one. Thus, the vehicle that has received the collision prevention packet knows how many times the packet has been relayed. Therefore, a packet relayed a predetermined number of times can be prevented from being relayed thereafter.

As described above, the position information, speed information, traveling direction, and time information (collectively referred to as vehicle information) of one vehicle are allowed to be relayed up to a predetermined number of relay times by a designated relay vehicle. From the car, the vehicle information of the vehicle is delivered to a vehicle that is far away from where the radio waves do not reach, or a vehicle that is nearby but does not reach the radio waves due to an obstacle in the building. In other words, information on a vehicle that is far away or does not receive radio waves due to obstacles reaches the vehicle through a vehicle that receives radio waves.
Thus, a collision can be prevented by knowing the position information, speed information, and time information of other vehicles around the own vehicle.

  As described above, in the system of the present invention, a vehicle that has received a collision prevention packet of another vehicle does not perform unlimited relay processing, but the same number of designated vehicles as a predetermined relay point at the time of collision prevention packet transmission. Only the relay processing is performed and the relay points are not specified redundantly, and the number of relays for the same collision prevention packet is limited to a predetermined number. There is an advantage that a high packet arrival rate (also referred to as a packet transmission rate) can be realized while avoiding the broadcast storm problem even in a high environment.

In practicing the present invention, how to set the number and position of relay points, how many relay times a certain collision prevention packet is allowed, and how to configure the system configuration of the system It will be taken into consideration.
First, as to how to position the relay point, the problem of the system of the present invention is that it is in an environment where the vehicle density is high and a high packet transmission rate is achieved by avoiding broadcast storm. As an urban area. In the case of an urban area, in many cases, a vehicle generally travels on a road network that is orthogonal (intersect) with buildings.

That is, in the vicinity of the intersection, the vehicles existing in the vicinity are present in the direction close to the front-rear direction and the left-right direction of the own vehicle. Therefore, one typical example would be to set the relay points in the front and rear direction and the left and right direction in the traveling direction of the vehicle. As for how many relay points in each direction are used, it is desirable to select a number that can achieve a packet transmission rate that can achieve the effect of sufficient collision prevention by a simulation in which various conditions are set.
As for the limit of the number of relays, it is desirable to find an appropriate number of times by the same simulation as described above.

  Next, the devices constituting the system are classified according to functional blocks in the claims, but the specific hardware configuration does not have to be according to this division. It is considered to be the best mode that each function is realized by one computer and software sequentially or in parallel.

FIG. 2 shows an example of relay point setting.
Every time the vehicle 11 travels a predetermined distance (for example, 2.5 m), or when the speed is 2.5 m / s or less, a collision prevention packet is transmitted every second.
Assume that the vehicle 11 in progress is at point O at the next transmission. A relay point is set by the relay point setting means 3 within a circle centered on the point O and having a radio wave effective distance r as a radius. There are 6 points in total: 2 points Pf1 and Pf2 on the front, 2 points Pb1 and Pb2 on the rear, 1 point on the left and 1 point on the right and Pr on the right. The distance from the point O to each relay point is r / 3 for each point of Pf2, Pb2, and 2r / 3 for each point of Pf1, Pb1, Pl, Pr.

At the next collision prevention packet transmission scheduled time, a vehicle that is predicted to be present at the nearest position from each of Pf1, Pf2, Pb1, Pb2, Pr, and Pl is selected as the next collision prevention packet relay vehicle. For each relay point, vehicle information is stored in a table up to the top six candidates in order of increasing distance between the vehicle and the relay point. When transmitting a collision prevention packet, relay vehicles are determined in the order of Pf1, Pb1, Pf2, Pb2, Pr, and Pl. When a first relay vehicle candidate at a certain relay point overlaps with a relay vehicle at another relay point, a relay station is selected from the second to sixth relay vehicle candidates.
According to the system of the present invention, not only the number of packet relay vehicles is limited to 6 or less, but also the vehicle designated as a relay station is different for each vehicle, so it is possible to avoid load concentration.

FIG. 3 shows a state where the vehicle 11 directly receives the collision prevention packet transmitted by the vehicle 12 within the radio wave effective distance.
When the vehicle 11 receives the collision prevention packet (time T1), the other vehicle position calculation means 4 determines where the vehicle 12 is located at the scheduled time T2 when the own vehicle (vehicle 11) transmits the collision prevention packet next time. Calculated by

As a result, it is assumed that the vehicle 12 exists at point P at the next scheduled transmission time T2 of the vehicle 11. Therefore, the distances from the point P to the relay points Pf1, Pf2, Pb1, Pb2, Pr, Pl are calculated by the distance calculation means 5, and this is the top 6 stored in the relay vehicle candidate existence table 6 for each relay point. If it is within the candidates, the relay vehicle candidate storage table 6 is updated. At the next transmission, the relay vehicle is designated by the updated storage table.
The above collision prevention reception processing is performed only for packets received directly without being relayed.

  If the number of times that a packet has propagated on a radio wave is defined as the number of relays (or the number of relays), the collision prevention reception process is performed only for packets with one relay number. If it is assumed that the number of relays is allowed up to 5, if the number of relays of the received collision prevention packet is 1 to 4 and the own vehicle address is included, the received collision prevention packet is relayed immediately. Process. If the number of relays of the received collision prevention packet is already 5, the relay process is not performed and the packet is discarded.

  In addition, for vehicles stored in the relay vehicle candidate storage table 6, the next collision prevention packet reception deadline is set, and when the collision prevention packet is not received from the vehicle even after the deadline has passed. Is deleted from the relay vehicle candidate.

Next, evaluation by simulation of the system of the present invention will be described.
NS2 is used as a simulation, and a Manhattan model shown in FIG. 4 is assumed as a simulation model. In a 412m square area, a two-lane road with a lane of 6m extends east-west and north-south at 100m intervals. Vehicles are placed on this road with random numbers.
Vehicles arranged on even-numbered roads in the figure travel at 40 km / h, and vehicles arranged on odd-numbered roads travel at 80 km / h. A vehicle that has approached the intersection turns right or left with a certain probability.

An enlarged view of the intersection of the simulation model is shown in FIG.
If it is a sufficient condition for the collision prevention system that vehicles 100 m away from the intersection can recognize each other, a vehicle located within a radius of 140 m from the packet transmission vehicle is a collision prevention target vehicle. It is assumed that an area 14 meters or more away from the road (obstacle in FIG. 5) is a complete absorber of radio waves, and radio waves that touch the obstacle do not reach vehicles ahead.

  The value of 14 m was determined based on a measurement result in which communication between vehicles 40 m away from an intersection in a radio wave propagation experiment in an urban area was almost 100% successful. When the radio wave effective distance is 80 m, in order to transmit a packet to a vehicle located 140 m away, it cannot be reached unless at least two vehicles are relayed.

A simulation is performed for cases of 200 and 800 vehicles.
FIG. 6 shows the specifications of the simulation model. It is assumed that a wireless LAN of IEEE802.11b is used as wireless communication.

For such a simulation model, the packet reception rate was obtained for all collision prevention packets transmitted by each vehicle within the simulation period. The average value of the obtained results is shown in FIG.
The figure shows what percentage of the vehicles that existed within a certain distance range from the transmitting station at the time of transmitting the collision prevention packet could receive the packet. Pure flooding is taken up as a comparison object of the system of the present invention. The values at the number of vehicles 200 and the number of vehicles 800 in FIG. 7 are shown as graphs in FIGS. 8 and 9, respectively.

  FIG. 8 shows that the system of the present invention shows a high packet reception rate up to 80 m, which is an effective radio wave distance, but the packet reception rate has dropped from the effective radio wave distance. This is because a vehicle designated as a relay station failed to receive due to a packet collision, or a vehicle existing near the center of an intersection could not be selected as a relay station. Since the number of relay vehicles is limited to 6 or less, if the relay vehicle fails to receive a packet, it becomes difficult for the packet to reach a vehicle located farther away.

  In the model with 200 vehicles, the average vehicle interval is 41.2 m, so each vehicle is designated as a relay vehicle at a location away from the ideal relay point, and an obstacle is wrapped around. The probability of failing to propagate a packet is high.

As shown in FIG. 9, the packet reception rate declines when the number of vehicles is 800 as well as the number of vehicles is 200. However, the reception rate is higher than that of pure flooding. I understand that. In the model with 800 vehicles, the average vehicle distance is 10.3 m, and there is a high probability that the vehicle is present at a position near the ideal relay point. However, the vehicle density is higher than that of the model with 200 vehicles, and the probability that the relay station fails to receive a packet due to packet collision increases. Therefore, the reception rate for vehicles after the radio wave effective distance decreases.

  In the case of pure flooding, the vehicle density has a great influence on the packet reception rate, whereas the system of the present invention does not have a great influence on the vehicle density, especially for vehicles within 80 m. Is shown. This is effective for use in an urban collision prevention system.

It is a block diagram which shows the structure of this invention system, and each vehicle information acquisition means. It is explanatory drawing of the Example of the relay point setting in this invention system. In this invention system, it is explanatory drawing for calculating the position of the other party vehicle at the time of the next transmission of the own vehicle received directly from the radio wave effective distance. It is a Hattan model which is a street model used in evaluation simulation of the system of the present invention. It is an enlarged view of the intersection of the Manhattan model of FIG. It is a figure which shows the specification of the simulation model at the time of performing the evaluation simulation of this invention system. It is a figure which shows the average value of the packet reception rate calculated | required about all the collision prevention packets which each vehicle transmits within the simulation period of this invention system. The number of vehicles is 200 and 800. It is the figure which compared the data in the case of 200 vehicles of FIG. 7 with the data in the case of pure flooding, and was made into the graph. It is the figure which compared the data in the case of the number of vehicles of FIG. 7 with the data in the case of pure flooding, and was made into the graph.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transmission / reception part 2 Collision prevention packet generation means 3 Relay point setting means 4 Other vehicle position calculation means 5 Distance calculation means 6 Relay vehicle candidate preservation | save table 7 Position information acquisition means 8 Speed information acquisition means 9 Traveling direction information acquisition means 10 Time information acquisition Means 11 Vehicle 12 Vehicle 13 Relay processing means 14 Antenna

Claims (2)

A packet flooding relay collision prevention system comprising the following means to be mounted on each vehicle:
(B) A collision prevention packet is transmitted every time the vehicle travels a predetermined distance, and a collision prevention packet transmitted by another vehicle is received, and the received vehicle collision prevention packet includes the own vehicle address. In addition, when the number of relays of the packet is less than the limit number, transmission / reception means that immediately relays the packet. (B) Location information, speed information, traveling direction, time information of the vehicle, and (f) Collision prevention packet generation means that generates a transmission packet (collision prevention packet) including the first relay vehicle address for each relay point in the relay vehicle candidate storage table and a relay number counter and sends the packet to the transmission / reception unit. Set multiple relay points that serve as reference points for selecting a relay vehicle that relays the collision prevention packet transmitted by the vehicle within the effective radio wave distance range centered on the next transmission point of the car (D) From the position information, speed information, traveling direction, and time information of one or more other vehicles that directly received the collision prevention packet by the transmission / reception means, Other vehicle position calculation means for calculating the position of the vehicle (e) Distance calculation means for calculating the distance between each relay point and each other vehicle position (f) For each relay point, the relay point and each other vehicle position Relay vehicle candidate storage table that stores vehicle addresses from the first rank to a predetermined rank in order of increasing distance between them. In place of the transmission / reception means of (a) of claim 1, a collision prevention packet is transmitted every time a predetermined time elapses, and a collision prevention packet transmitted by another vehicle is received and the received collision prevention Packet flooding relay collision prevention, characterized in that when the address of the vehicle is included in the packet and the number of relays of the packet is less than the limit number, a transmission / reception means that immediately relays the packet system.

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