JP2006039762A - Vehicle speed measuring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a system capable of measuring a vehicle speed without setting special equipment. <P>SOLUTION: This system comprises a plurality of access points 11 set on a road and a radio terminal 13 mounted on a vehicle 12 traveling on the road. When the vehicle 12 passes through the vicinity of the set point of the access point 11, a receiving signal intensity RSSI gradually increases as the vehicle 12 gets close to the access point 11, reaches a peak at the point of time when it gets closest to the access point 11, and gradually reduced as it leaves the access point 11. If the speed v [m/s] of the vehicle is high, the curve of a graph showing RSSI is shape, and if the speed v [m/s] is low, the graph curve is gentle. Therefore, the vehicle speed can be calculated from the degree of such a change in RSSI. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vehicle speed measurement system, and more particularly to a vehicle speed measurement system using a wireless network.

As a conventional method for measuring vehicle speed, for example, two sensors are embedded in a road surface at a predetermined distance and a vehicle speed is calculated by measuring a time difference when the vehicle passes through the two sensors. It has been known. In addition, an ultrasonic Doppler system ground speed meter that measures the vehicle speed using the ultrasonic Doppler effect is also known (see Patent Document 1).
JP-A-5-080152

  However, in the conventional vehicle speed measurement system described above, a dedicated device having a sensor must be installed at a predetermined position on the road. Moreover, a total of two such dedicated devices must be installed, one on the upstream side and one on the downstream side of the road. In the case where vehicle speed measurement is performed simultaneously at a plurality of points, more dedicated devices are required. Thus, in the conventional vehicle speed measurement system, it is necessary to install many dedicated devices, so that there is a problem that it takes much time and cost to measure the vehicle speed. In order to solve this problem, it is considered desirable to perform vehicle speed measurement using a general-purpose device used for other purposes, not a special device for vehicle speed measurement.

  Accordingly, an object of the present invention is to provide a system capable of measuring the vehicle speed without installing special equipment.

  The object of the present invention includes an access point for connecting to the Internet installed near the road and a wireless terminal mounted on a vehicle, the access point including means for connecting the wireless terminal to the Internet, and the wireless And a means for calculating a vehicle speed of the vehicle passing on the road based on a change in received signal strength of a signal from a terminal. According to the present invention, since the vehicle speed is measured using an Internet connection access point that will be installed on the road in the near future, the vehicle speed can be measured without using a special device. it can. The “means” herein includes both those realized by hardware and those realized by software, and single hardware and single software are realized by the above two means. It does not matter even if it has the function to be.

  The object of the present invention also includes at least one access point for internet connection installed near the road, the access point comprising means for connecting a wireless terminal mounted on a vehicle to the internet, and the wireless terminal And a means for calculating a vehicle speed of the vehicle passing on the road based on a change in received signal strength of the signal.

  In a preferred embodiment of the present invention, the access point comprises a directional antenna, and the means for calculating the vehicle speed is a received signal strength of a signal from the wireless terminal mounted on the vehicle approaching the access point. The vehicle speed of the vehicle passing on the road is calculated based on the degree of change or the degree of change in the received signal strength of the signal from the in-vehicle wireless terminal mounted on the vehicle moving away from the access point, or both. . According to this, it is possible to reliably determine the vehicle speed of the vehicle, and it is not necessary to install two dedicated devices, one on the upside and one on the downside of the road.・ Descent can be judged.

  Also, in a preferred embodiment of the present invention, the vehicle speed of the vehicle passing through the road is determined based on the distance between the access points and the time when the wireless terminal connects to each access point. to decide. According to this, it is possible to reliably determine the vehicle speed and the traveling direction of the vehicle.

  In a further preferred embodiment of the present invention, the access point is a wireless LAN access point. According to this, a vehicle speed measurement system can be constructed using a highly versatile system.

  The object of the present invention is also provided with an access point for Internet connection installed near the road, a wireless terminal mounted on a vehicle, and a server connected to the access point via the Internet. The point includes means for connecting the wireless terminal to the Internet, and means for transferring information related to a change in received signal strength of a signal from the wireless terminal to the server, wherein the server passes the road. It is also achieved by a vehicle speed measurement system characterized by comprising means for calculating the vehicle speed. According to this, according to this, the processing load of the access point can be reduced.

  According to the present invention, the vehicle speed can be measured without using a special device. In addition, it is possible to determine whether the vehicle travels in the upward or downward direction using a single access point.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a schematic diagram for explaining an outline of a vehicle speed measurement system according to a preferred embodiment of the present invention.

  The vehicle speed measurement system according to the present invention measures the vehicle speed using an access point for Internet connection, and as shown in FIG. 1, an access point (AP) 11 installed on a road serving as a survey point. And a wireless terminal 13 mounted on the vehicle 12.

  The access point 11 calculates the speed of the vehicle passing through the survey point by measuring the degree of change in the received signal strength (RSSI) of the signal transmitted from the wireless terminal 13 mounted on the vehicle 12, It is also determined whether the vehicle travels, that is, whether the vehicle is an ascending vehicle or a descending vehicle. Hereinafter, a method for measuring the vehicle speed will be described.

  First, the access point 11 includes a directional antenna, has an output of f [dBm] in one direction of the road (for example, the upward direction), and is larger in the reverse direction (downward direction) b. It has an output of [dBm]. FIG. 2 is a graph showing an example of the horizontal characteristic of such a directional antenna. As shown in FIG. 2, the gain of this directional antenna is maximum in the 0 ° direction and minimum in the 180 ° direction.

  When a signal with an output A [dBm] is transmitted from the wireless terminal 13 to the access point 11 having such a directional antenna, the access point 11 receives a signal from the wireless terminal 13, but FIG. Thus, when the vehicle 12 is located on the upstream side of the access point 11, the reception gain of the transmission signal is (A + f) [dBm], and when the vehicle 12 is located on the downstream side of the access point 11, (A + b ) [DBm].

As shown in the figure, when the vehicle 12 travels in the downward direction at a speed v [m / s] and gradually approaches the access point 11, a signal transmitted from the vehicle 12 at a distance L from the access point 11. The received signal strength (RSSI) can be expressed as follows.
RSSI∝ (A + f) / (L−vt) (1)

On the other hand, when the vehicle 12 traveling in the downward direction at the speed v [m / s] passes the installation point of the access point 11 and gradually moves away from the access point 11, the vehicle 12 at a position away from the access point 11 by the distance L. The received signal strength (RSSI) of the signal transmitted from can be expressed as follows.
RSSI∝ (A + b) / (L−vt) (2)

  3 and 4 are graphs showing changes in received signal strength (RSSI).

  As shown in FIG. 1, when the vehicle 12 traveling at a speed v [m / s] passes near the installation point of the access point 11, the received signal strength (RSSI) increases as the vehicle 12 approaches the access point 11. It gradually increases, reaches a peak when it is closest to the access point 11, and gradually decreases as it moves away from the access point 11. Here, when the vehicle 12 travels in the downward direction, the change in RSSI becomes a graph as shown in FIG. 3 based on the above formulas (1) and (2), and the vehicle 12 travels in the upward direction. In this case, the RSSI changes as shown in FIG. When the speed v [m / s] of the vehicle 12 is high, the curve of the graph becomes steep, and when the speed v [m / s] is low, the curve of the graph becomes gentle. Therefore, the vehicle speed can be calculated from the degree of the RSSI change, and further, the up / down of the vehicle can be determined from the difference in the RSSI pattern.

  FIG. 5 is a block diagram schematically showing the configuration of a vehicle speed measurement system according to a preferred embodiment of the present invention.

  As shown in FIG. 5, the vehicle speed measurement system 10 includes a plurality of access points 11 installed on the road, a wireless terminal 13 mounted on a vehicle 12 traveling on the road, and each access point via the Internet 14. 11 is connected to the server 15.

  The access point 11 is a relay device for connecting the wireless terminal 13 to the Internet 14, and relays packets from a node on the wireless network to a node on the wired network and from a node on the wired network to a node on the wireless network. To do. The access point 11 is installed at predetermined intervals along the road so that a plurality of wireless terminals can be simultaneously connected and an Internet connection can be provided as a roaming service. As the access point 11, for example, a wireless LAN access point based on the IEEE802.11 standard can be used, but other network devices can also be used. When a wireless LAN access point based on the IEEE802.11 standard is used, a vehicle speed measurement system based on a highly versatile system can be constructed. As a result, the user can connect to the Internet 14 from the wireless terminal 13 via the access point 11 while the vehicle 12 is traveling, and receive services such as a navigation system and traffic jam information. In addition, the access point 11 has the connection node counting function described above, and thereby has a function of measuring the speed of the vehicle passing on the road.

  The wireless terminal 13 is a vehicle-mounted wireless device for connecting to the Internet 14 via the access point 11 and is a node connected to the network. The wireless terminal 13 has hardware necessary for realizing a navigation system and a traffic jam information providing system. For example, a personal computer or PDA equipped with a network device corresponding to the access point 11 can be used. Other network devices can also be used. The wireless terminal 13 is preferably mounted on all vehicles traveling on the road, but may be mounted only on a specific vehicle to be investigated. If all vehicles are equipped with wireless terminals, complete vehicle speed measurement can be performed.

  The server 15 performs overall management of each access point 11 and performs totalization and management of vehicle speed. The server 15 can be configured using a general computer and is connected to each access point 11 via the Internet 14.

  FIG. 6 is a block diagram schematically showing the configuration of the access point 11.

  As shown in FIG. 6, the access point 11 includes a wireless network interface unit 21, a wired network interface unit 22, a system controller 23, and a memory 24. The wireless network interface unit 21 is an interface for connecting to a wireless network, and realizes network connection with the wireless terminal 13. The wireless network interface unit 21 includes a directional antenna 21X. The wired network interface unit 22 is an interface for connecting to a wired network, and realizes Internet connection. The system controller 23 controls the wireless network interface unit 21 and the wired network interface unit 22 to control packet relay processing. The memory 24 serves as a normal memory and a buffer memory, and records software and various data.

  The access point 11 realizes a bridge function for connecting the wireless terminal 13 to the Internet 14 in cooperation with the hardware and software described above, as well as a function for measuring the vehicle speed and a function for counting the number of connection nodes. As described in detail below, monitoring / recording of received signal strength (RSSI), node connection processing, counting of the number of nodes, recording of the count value, and the like are performed.

  FIG. 7 is a flowchart showing a procedure for measuring the vehicle speed by the access point 11.

  As shown in FIG. 7, the access point 11 broadcasts a beacon (S71), and when the wireless terminal 13 detects a beacon when the vehicle 12 enters the communication area of the access point 11 (S72Y), the wireless terminal An RTS (Request To Send) signal is transmitted from 13 (S73). When the access point 11 receives the RTS signal from the wireless terminal 13 (S74) and transmits a CTS (Clear To Send) signal in response (S75), the wireless terminal 13 that has received the CTS signal receives an ACK (Acknowledge). A signal is transmitted (S76Y, S77). Then, when the access point 11 receives the ACK signal, a network connection is established and communication is started (S78Y, S79). At this time, the access point 11 constantly monitors the RSSI during communication, and records the RSSI from the start to the end of the network connection in the memory (S80).

  Thereafter, when the vehicle 12 moves out of the communication area and the RSSI becomes weak and communication becomes difficult, the access point 11 disconnects the network connection of the wireless terminal 13 and ends the communication (S81). Then, the access point 11 reads the RSSI pattern from the start to the end of the network connection by the wireless terminal 13 from the memory, and calculates the vehicle speed from the degree of change of the RSSI (S82). Further, the change in RSSI is compared with the patterns of ascending vehicles and descending vehicles (S83). When the pattern is an ascending vehicle, the count value of the ascending vehicle is counted up (S84), and when the pattern is a descending vehicle Counts up the count value of the descending vehicle (S85). The vehicle speed and the count values of the ascending vehicle and descending vehicle are transferred to the server 15 in response to a request from the server 15 or periodically (S86).

  As described above, according to the present embodiment, the vehicle speed can be measured using an access point for connecting to the Internet, and only one access point equipped with a directional antenna can be used. Since it is possible to determine the passing of the vehicle, there is no need to prepare two dedicated devices, one on the upstream side and one on the downstream side as in the past, and vehicle speed measurement can be performed with a small number of facilities. it can.

  In the above embodiment, only one access point is used, and the directional antenna is used as the access point antenna to determine whether it is up or down, but two or more access points are used. Up / down discrimination may be performed.

  FIG. 8 is a schematic diagram for explaining an outline of a vehicle speed measurement system according to another preferred embodiment of the present invention.

  As shown in FIG. 8, in this system, two access points including a first access point 11X and a second access point 11Y installed on the road are used. Access points 11X and 11Y are arranged at a certain distance along the road so that their communication areas do not overlap each other.

  As shown in the figure, when the vehicle 12 is traveling in the downward direction, the wireless terminal 13 mounted on the vehicle 12 is first connected to the first access point 11X, and then connected to the second access point 11Y. Thus, it can be determined that the vehicle 12 is traveling in the downward direction, and the vehicle speed at that time is determined from the distance between the access points 11X and 11Y and the time when the access points 11X and 11Y are connected. Can be calculated. On the other hand, when the vehicle 12 is traveling in the upward direction, the vehicle is traveling in the upward direction because it is first connected to the second access point 11Y and then to the first access point 11X. The vehicle speed at that time can be calculated from the distance between the access points 11X and 11Y and the time of connection to each access point 11X and 11Y. As described above, the connection status of the wireless terminal 13 and the data of the time are transferred from the access points 11X and 11Y to the server 15 and processed by the server 15, and the vehicle of the vehicle at the installation point of the access point 11X or the access point 11Y. Speed and up / down are determined.

  As described above, according to the present embodiment, the traveling direction of the vehicle is determined from the difference in timing at which the wireless terminal is connected to the plurality of access points installed on the road, so the traveling direction of the vehicle is reliably determined. In addition, it is not always necessary to employ a directional antenna as in the above embodiment.

  The present invention is not limited to the embodiments described above, and various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

  For example, in the above embodiment, the vehicle speed is calculated from the degree of change in the received signal strength (RSSI) of the signal transmitted from the vehicle traveling at the speed v [m / s]. It is also possible to calculate the vehicle speed of the vehicle passing through the access point using the time of connection to the vehicle and the travel distance of the vehicle in the communication area covered by the access point. That is, a time t1 when a vehicle traveling on the road enters the communication area of the access point and the network connection is started, a time t2 when the vehicle travels further and reaches the outside of the communication area and the network connection is disconnected, and the vehicle The vehicle speed V can be obtained as V = Lx / (t2−t1) from the total length Lx of the range covered by the access point communication area in the road on which the vehicle travels.

  In the above embodiment, the case where the access point is installed on the road has been described. However, the present invention is not limited to this. For example, the access point is located near the road such as a roadside (roadside) or a median. It only has to be installed.

  In the above embodiment, the case where the access point includes means for measuring the vehicle speed and means for determining the traveling direction of the vehicle has been described. However, such a function may be provided on the server side. . That is, the server calculates the vehicle speed of the ascending vehicle and the descending vehicle by sending necessary information from the access point to the server. As information to be sent from the access point to the server at this time, for example, information related to a change in the received signal strength of the signal from the wireless terminal such as received electric field strength (RSSI) data over time is transmitted. In this way, since the main processing relating to vehicle speed measurement is performed on the server side, the access point only needs to perform processing relating to the Internet connection of the wireless terminal, and the processing load on the access point can be reduced.

FIG. 1 is a schematic diagram for explaining an outline of a vehicle speed measurement system according to a preferred embodiment of the present invention. FIG. 2 is a graph showing an example of the horizontal characteristic of such a directional antenna. FIG. 3 is a graph showing changes in received signal strength (RSSI). FIG. 4 is a graph showing changes in received signal strength (RSSI). FIG. 5 is a block diagram schematically showing the configuration of a vehicle speed measurement system according to a preferred embodiment of the present invention. FIG. 6 is a block diagram schematically showing the configuration of the access point 11. FIG. 7 is a flowchart showing a vehicle counting procedure by the access point 11. FIG. 8 is a schematic diagram for explaining an outline of a vehicle speed measurement system according to another preferred embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Vehicle speed measurement system 11 Access point 11X Access point 11Y Access point 12 Vehicle 13 Wireless terminal 14 Internet 15 Server 21 Wireless network interface part 21X Directional antenna 22 Wired network interface part 23 System controller 24 Memory

Claims (6)

An access point for Internet connection installed near the street,
With a wireless terminal mounted on the vehicle,
The access point is
Means for connecting the wireless terminal to the Internet;
A vehicle speed measurement system comprising: means for calculating a vehicle speed of the vehicle passing on the road based on a change in received signal strength of a signal from the wireless terminal. Including at least one access point for internet connection installed near the road,
The access point is
Means for connecting a wireless terminal mounted on a vehicle to the Internet;
A vehicle speed measurement system comprising: means for calculating a vehicle speed of the vehicle passing on the road based on a change in received signal strength of a signal from the wireless terminal. The access point comprises a directional antenna;
The means for calculating the vehicle speed is:
Degree of change in received signal strength of a signal from the wireless terminal mounted on the vehicle approaching the access point or change in received signal strength of a signal from the wireless terminal mounted on the vehicle moving away from the access point The vehicle speed measurement system according to claim 1 or 2, wherein the vehicle speed of the vehicle passing on the road is calculated based on the degree or both.   2. The vehicle according to claim 1, wherein a plurality of the access points are provided, and the vehicle speed of the vehicle passing on the road is determined based on a distance between the access points and a time when the wireless terminal is connected to each access point. 2. The vehicle speed measurement system according to 2.   The vehicle speed measurement system according to any one of claims 1 to 4, wherein the access point is a wireless LAN access point. An access point for Internet connection installed near the street,
A wireless terminal mounted on the vehicle;
A server connected to the access point via the Internet,
The access point is
Means for connecting the wireless terminal to the Internet;
Means for transferring information relating to a change in received signal strength of a signal from the wireless terminal to the server,
The server
A vehicle speed measurement system comprising means for calculating a vehicle speed of the vehicle passing on the road based on a change in the received signal strength.

Images