JP5581771B2 - Roadside communication device and position accuracy estimation method - Google Patents

Description

  The present invention relates to, for example, a roadside communication device suitable as a component of an intelligent transport system (ITS) and a position accuracy estimation method for position information acquired by the roadside communication device from an in-vehicle communication device.

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, advanced road traffic systems that improve the safety of vehicles by receiving information from infrastructure devices installed on the road and utilizing this information have been studied. (For example, refer to Patent Document 1).
Such an intelligent road traffic system is mainly composed of a plurality of roadside communication devices which are wireless communication devices on the infrastructure side and a plurality of in-vehicle communication devices which are wireless communication devices mounted on each vehicle.

  In this case, a combination of communication performed between communication subjects includes road-to-road communication between road-side communication devices, road-to-vehicle (or vehicle-road) communication between road-side communication devices and vehicle-mounted communication devices, and vehicle-mounted communication. Vehicle-to-vehicle communication performed between aircraft. Thus, in a communication system in which a plurality of types of communication are performed, the transmission timing is divided between the roadside communication device and the vehicle-mounted communication device, thereby preventing mutual signals from colliding with each other. In addition, since roadside communication devices transmit at the same timing, the communication areas are devised so that the communication areas do not overlap as much as possible.

  The in-vehicle communication device has a function of broadcasting its own position information and the like, and the roadside communication device detects the presence of the vehicle and its position based on this position information. Further, based on this position information, the roadside communication device can grasp (or estimate) the communication area with the in-vehicle communication device.

Japanese Patent No. 2806801

  In the conventional roadside communication device as described above, in order to accurately grasp the communication area, the position information on which it is based must be accurate. However, in reality, there are cases where the accuracy of the position information varies and the accuracy is poor. However, since the roadside communication device that receives the position information does not know whether the position information is accurate or not, it may detect a position with a large amount of error based on the position information that is not accurate.

  In view of such conventional problems, an object of the present invention is to enable the roadside communication device side to grasp the accuracy of position information transmitted from an in-vehicle communication device.

(1) The present invention is a roadside communication device that detects a position of an in-vehicle communication device based on position information included in an uplink signal of the in-vehicle communication device, and receives a signal transmitted from a GPS satellite and performs GPS. A GPS receiver that acquires GPS information related to positioning accuracy, a control unit that estimates the accuracy of the position information based on the acquired GPS information, and selects the position information according to the quality of the estimated position information ; It is equipped with.
In the roadside communication device configured as described above, the accuracy of the position information included in the uplink signal is estimated based on the GPS information related to the GPS positioning accuracy. Thereby, the quality of the positional information transmitted from the vehicle-mounted communication device can be grasped on the roadside communication device side.

(2) In the roadside communication device of the above (1), the GPS information may include the number of GPS satellites captured.
In this case, the accuracy of the position information can be improved by adopting the position information only when the number of captures is equal to or greater than the threshold.

(3) In the roadside communication device of (1), the GPS information may include a DOP value.
In this case, the accuracy of the position information can be improved by adopting the position information only when the DOP value is equal to or less than the threshold value.

(4) In the roadside communication device of the above (1), the GPS information may include at least one of the signal reception intensity from the GPS satellite and the signal-to-noise ratio.
In this case, the accuracy of the position information can be improved by adopting the position information only when the signal reception intensity is equal to or higher than the threshold and / or the signal-to-noise ratio is equal to or higher than the threshold.

(5) In the roadside communication device according to any one of (1) to (4), the communication area in which the uplink signal can be received is estimated based on the position information and the estimated accuracy of the position information. Also good.
In this case, the communication area can be estimated more accurately based only on highly accurate position information.

(6) In the roadside communication device according to any one of (1) to (5), the roadside communication device includes a transmission unit that transmits downlink information that can be received by the in-vehicle communication device to a predetermined downlink area. The transmission unit may determine the content of the downlink information provided wirelessly by the roadside communication device based on the position information and the estimated accuracy of the position information.
In this case, it is possible to provide downlink information with appropriate contents according to the accuracy of the position information.

(7) In the roadside communication device of any one of (1) to (6) above, the downlink information can include safe driving support information for the in-vehicle communication device to support safe driving of the vehicle. The transmission unit may include the safe driving support information in the downlink information only when the accuracy of the position information and the estimated position information is determined to be equal to or higher than a predetermined level.
In this case, since the safe driving support information can be provided only when the accuracy of the position information is equal to or higher than a predetermined level, the advanced safe driving support information is provided but the safety is deteriorated although the accuracy is not good. This can be prevented.

(8) On the other hand, the present invention provides a positional accuracy estimation method accuracy roadside communication device location information included in the uplink signal of the in-vehicle communication device estimates, the roadside communication device a signal transmitted from a GPS satellite Receives GPS information related to GPS positioning accuracy, and based on the acquired GPS information, the roadside communication device estimates the accuracy of the location information, and according to the accuracy of the estimated location information , The roadside communication device selects the position information.
In the position accuracy estimation method as described above, the roadside communication device estimates the accuracy of the position information included in the uplink based on the GPS information related to the GPS positioning accuracy. Thereby, the quality of the positional information transmitted from the vehicle-mounted communication device can be grasped on the roadside communication device side.

  According to the roadside communication device / position accuracy estimation method of the present invention, whether the accuracy of the position information is good can be grasped on the roadside communication device side. Moreover, if the position information is selected based on such estimation, the accuracy of the position information can be improved.

It is a schematic perspective view which shows the whole structure of the intelligent transport system (ITS) including the roadside communication apparatus which concerns on embodiment of this invention. It is a road top view which shows a part of jurisdiction area of the intelligent transport system shown in FIG. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a figure which shows an example of the data format which a vehicle-mounted communication apparatus transmits. It is the schematic which shows the communication area seen from the roadside communication apparatus, (a) has shown the positional relationship of the roadside communication apparatus and the vehicle carrying a vehicle-mounted communication apparatus. (B) is the figure which planarly represented the shape image of the communication area expanded to one direction on a road among all the communication areas seen from the roadside communication apparatus. It is a figure which shows notionally the GPS satellite which a roadside communication apparatus can acquire as an example. It is a flowchart regarding position accuracy estimation (first embodiment) by a roadside communication device. It is a flowchart regarding position accuracy estimation (second embodiment) by a roadside communication device. It is a flowchart regarding position accuracy estimation (third embodiment) by a roadside communication device. It is a figure which shows the state from which the communication area changed from the state shown in FIG.

[Overall system configuration]
FIG. 1 is a schematic perspective view showing an overall configuration of an intelligent road traffic system (ITS) including a roadside communication device according to an embodiment of the present invention. In this embodiment, as an example of the road structure, a grid structure in which a plurality of roads in the north-south direction and the east-west direction intersect with each other is assumed.
As shown in FIG. 1, the intelligent transportation system of this embodiment is equipped with a traffic signal 1, a roadside communication device 2, an in-vehicle communication device 3 (see FIGS. 2 and 3), a central device 4, and an in-vehicle communication device 3. A vehicle 5 and a roadside sensor 6 including a vehicle detector and a monitoring camera are included.

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

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

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

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

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

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

The plurality of roadside communication devices 2 are installed at each roadside intersection Ji, and are attached to the pillars of the traffic signal 1 in the examples of FIGS. 1 and 2. On the other hand, the in-vehicle communication device 3 is mounted on each vehicle 5 traveling on the road.
Each roadside communication device 2 has a communication area (range in which the transmission signal of the roadside communication device 2 can sufficiently reach) spreading around it, and wireless communication with the in-vehicle communication device 3 of the vehicle 5 traveling in its communication area. Is possible. Each roadside communication device 2 can also communicate with other roadside communication devices 2.

In the intelligent transport system of this embodiment, wireless communication is used between the roadside communication devices 2 (roadside communication), and between the roadside communication device 2 and the vehicle-mounted communication device 3 (from “road” to “car” Wireless communication is also used for both vehicle-to-vehicle communication and vehicle-mounted communication devices 3 (vehicle-to-vehicle communication).
As described above, the central device 4 provided in the traffic control center is capable of two-way communication with each roadside communication device 2 by wire, but wireless communication may be performed between these devices.

Each roadside communication device 2 assigns a time slot for wireless transmission by its own device by the TDMA method, and does not perform wireless transmission in a time zone other than this time slot. Therefore, the time zone other than the time slot for the roadside communication device 2 is opened as a transmission time by the CSMA method for the in-vehicle communication device 3.
The roadside communication device 2 has a time synchronization function with other roadside communication devices 2 in order to control its own transmission timing. The time synchronization of the roadside communication device 2 is performed by, for example, GPS synchronization that adjusts its own clock to the GPS time, air synchronization that adjusts its own clock to a transmission signal from another roadside communication device 2, or the like.

[Roadside communication device]
FIG. 3 is a block diagram showing the internal configuration of the roadside communication device 2 and the in-vehicle communication device 3.
The roadside communication device 2 includes a wireless communication unit (transmission / reception unit) 21 to which an antenna 20 for wireless communication is connected, a wired communication unit 22 that performs bidirectional communication with the central device 4, and a CPU that performs communication control thereof. A control unit 23, a storage unit 24 including a storage device such as a ROM and a RAM connected to the control unit 23, and a GPS receiver 25. The storage unit 24 stores a communication control program executed by the control unit 23, communication device IDs of the communication devices 2 and 3, and the like.

  In addition to the central device 4, a GPS receiver 25 is connected to the wired communication unit 22 of the roadside communication device 2. The GPS receiver 25 receives GPS signals from a plurality of GPS satellites (not shown) by a GPS antenna 26. The GPS receiver 25 obtains radio wave arrival time and GPS satellite position information and performs GPS positioning, as well as GPS information related to GPS positioning accuracy (for example, the number of captured GPS satellites, DOP (Dilution Of Precision) value, reception) Intensity (RSSI), signal-to-noise ratio (S / N ratio)).

  The control unit 23 temporarily stores the traffic information S2 and the like from the central device 4 received by the wired communication unit 22 in the storage unit 24, and broadcasts it to its own communication area via the wireless communication unit 21. Further, the control unit 23 temporarily stores the vehicle information S3 received by the wireless communication unit 21 in the storage unit 24 and transfers the vehicle information S3 to the central device 4 via the wired communication unit 22.

  In addition, the control unit 23 broadcasts the time slot allocation information S6 stored in the storage unit 24 to its own communication area via the wireless communication unit 21. This allocation information S6 is for notifying the in-vehicle communication device 3 of the transmission time of the roadside communication device 2. The in-vehicle communication device 3 of the vehicle 5 traveling in the communication area performs wireless transmission by the carrier sense method in a time zone when the roadside communication device 2 does not transmit.

[In-vehicle communication device]
On the other hand, the in-vehicle communication device 3 includes a communication unit (transmission / reception unit) 31 connected to an antenna 30 for wireless communication, a control unit 32 including a CPU that performs communication control on the communication unit 31, and the control unit 32. A storage unit 33 including a storage device such as a ROM or a RAM connected to the communication unit 31 and a GPS receiver 34 connected to the communication unit 31. The storage unit 33 stores a communication control program executed by the control unit 32, communication device IDs of the communication devices 2 and 3, and the like. The GPS receiver 34 receives GPS signals from a plurality of GPS satellites (not shown) by the GPS antenna 35. A speed sensor 36 is connected to the communication unit 31.

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

The control unit 32 of the in-vehicle communication device 3 broadcasts and wirelessly transmits vehicle information S3 including the current position, direction, speed, vehicle type, etc. of the vehicle 5 (in-vehicle communication device 3) to the outside via the communication unit 31. I am letting.
In addition, the control unit 32 of the in-vehicle communication device 3 has the position, speed, and direction included in the vehicle information S3 received directly from the other vehicle 5 or the vehicle information S3 of the other vehicle 5 received from the roadside communication device 2. Based on this, it is possible to perform safe driving support control for avoiding a right-handed collision or a head-on collision.

FIG. 4 is a diagram illustrating an example of a data format transmitted by the in-vehicle communication device 3.
As shown in FIG. 4, the transmission signal of the in-vehicle communication device 3 includes a preamble, a header, data, and a CRC (Cyclic Redundancy Check).
Among these, the data includes the position, direction (traveling direction), speed, and vehicle type of the vehicle 5, but can also include a reception level when a transmission signal from the roadside communication device 2 is received. Information on the position and direction of the vehicle 5 can be acquired by the GPS receiver 34. The speed is information based on the speed sensor 36 of the vehicle 5.

[Position accuracy estimation by roadside communication device: first embodiment]
Next, position accuracy estimation by the roadside communication device according to the first embodiment as a main part of the present invention will be described.
FIG. 5 is a schematic diagram showing a communication area viewed from the roadside communication device 2, and (a) shows the positional relationship between the roadside communication device 2 and the vehicles 51, 52, and 54 in which the in-vehicle communication device 3 is mounted. . (B) is the figure which represented planarly the shape image of the communication area A extended to one direction on a road among all the communication areas seen from the roadside communication apparatus 2. FIG.

  The roadside communication device 2 receives an uplink signal (vehicle information S3) transmitted by any on-vehicle communication device 3 by broadcast. For example, the received power from the in-vehicle communication device 3 of the vehicle 54 at the position P4 (distance 200 m) is −80 dBm. The received powers from the in-vehicle communication devices 3 of the vehicles 51 and 52 at the positions P1 (distance 50 m from the roadside communication device 2) and P2 (distance 100 m) are −70 dBm and −75 dBm, respectively. Further, an uplink signal from a position far from the position P4 cannot be received. That is, the uplink area in which the uplink signal reaches is the area A in FIG.

  Here, in order to accurately obtain the uplink area, it is important that the position information transmitted from the in-vehicle communication device 3 is accurate. Therefore, the accuracy of position information is examined using GPS information. GPS satellites are orbiting at an altitude of about 20000 km, and the number of GPS satellites is about 30 including 24 spare units. These are quasi-synchronous satellites that orbit around the earth in about 12 hours. Therefore, the number and direction of GPS satellites that can be captured from one point on the earth change with time.

  Here, the GPS receiver 34 (FIG. 3) of the in-vehicle communication device 3 and the GPS receiver 25 (FIG. 3) of the in-vehicle communication device 3 within the range of a distance of about 200 m (that is, about 1 / 100,000 of the distance to the satellite). In 3), it is understood that the conditions are the same with respect to GPS information (capture number, DOP value, etc.) related to GPS positioning accuracy. Therefore, the accuracy of the position information of the in-vehicle communication device 3 can be estimated based on the GPS information obtained by the GPS receiver 25 of the roadside communication device 2 (hereinafter simply referred to as the roadside communication device 2).

  FIG. 6 is a diagram conceptually showing GPS satellites that can be captured by the roadside communication device 2 as an example. In this state, the roadside communication device 2 captures five GPS satellites S1 to S5, that is, receives signals transmitted from the five GPS satellites S1 to S5. The GPS positioning calculates three distances by multiplying the difference (arrival time) between the transmission time and the reception time respectively transmitted from three GPS satellites by the speed of light, and calculates these distances as the position of the roadside communication device 2. The position (x, y, z) is obtained by solving the three simultaneous equations represented by (x, y, z). Also, to correct the time error, an equation for another GPS satellite is required, and therefore it is necessary to acquire at least four GPS satellites. Furthermore, since the position accuracy can be improved by capturing more GPS satellites at 4 or more, for example, 5 or 6 can be set as a threshold for the number of captured GPS satellites.

  FIG. 7 is a flowchart regarding position accuracy estimation. This process is periodically executed in the control unit (FIG. 3) of the roadside communication device 2. In the figure, the roadside communication device 2 first acquires the number of captured GPS satellites (step S1). Here, if the number of captures is equal to or greater than the threshold, it is determined that the accuracy of the position information is good (step S2), and the position information included in the uplink signal from the in-vehicle communication device 3 is acquired (step S3). . In addition, it is preferable to collect positional information from as many in-vehicle communication devices 3 as possible over a certain period of time.

  On the other hand, when the number of captures is less than the threshold value in step S2, the roadside communication device 2 determines that there is no guarantee that position information with good accuracy can be obtained, and avoids acquisition of position information. Therefore, the roadside communication device 2 does not acquire the position information from the in-vehicle communication device 3 when it is determined that the number of GPS satellites captured does not reach the threshold value and the accuracy of the position information is not good. As a result, the position information is acquired only when the position information with good accuracy is obtained, and the position accuracy acquired with respect to the in-vehicle communication device 3 can be improved.

  In this way, the uplink area shown in FIG. 5B can be estimated based on highly accurate position information. In addition, the roadside communication device 2 confirms the uplink area as its own downlink area if, for example, a part of the information transmitted by itself is sent back to the in-vehicle communication device 3, and communication from both sides can be performed. Possible communication area A.

[Position accuracy estimation by roadside communication device: second embodiment]
Next, position accuracy estimation by the roadside communication device according to the second embodiment will be described. FIG. 8 is a flowchart regarding this position accuracy estimation. The difference from FIG. 7 is that the DOP value is used instead of the number of GPS satellites captured. The DOP value is one piece of GPS information related to GPS positioning accuracy. The larger the volume of the polygonal pyramid formed by connecting a GPS satellite that can be captured and a GPS receiver with a straight line, the smaller the DOP value, and the better the GPS positioning accuracy. Conversely, the smaller the volume of the polygonal pyramid, the larger the DOP value and the worse the GPS positioning accuracy.

  When the volume of the polygonal pyramid is large, the GPS satellites are scattered when viewed from the GPS receiver. Conversely, when the volume of the polygonal pyramid is small, the GPS satellites are near one position when viewed from the GPS receiver. It is in a state of being gathered so as to be crowded. More specifically, DOP includes HDOP (Horizontal DOP) in the horizontal direction and VDOP (Vertical DOP) in the vertical direction. The DOP referred to here is mainly HDOP.

  FIG. 8 is a flowchart regarding position accuracy estimation based on the DOP value. This process is periodically executed in the control unit (FIG. 3) of the roadside communication device 2. In the figure, the roadside communication device 2 first acquires the DOP value of the GPS satellite (step S1). Here, if the DOP value is equal to or smaller than the threshold value, it is determined that the accuracy of the position information is good (step S2), and the position information included in the uplink signal from the in-vehicle communication device 3 is acquired (step S3). .

  On the other hand, if the DOP value exceeds the threshold value in step S2, the roadside communication device 2 determines that there is no guarantee that position information with good accuracy can be obtained, and avoids acquisition of position information. Accordingly, when the DOP value of the GPS satellite exceeds the threshold and it is determined that the accuracy of the position information is not good, the roadside communication device 2 does not acquire the position information from the in-vehicle communication device 3. As a result, the position information is acquired only when the position information with good accuracy is obtained, and the accuracy of the position acquired with respect to the in-vehicle communication device 3 can be improved as a whole.

  Thus, as in the first embodiment, the uplink area shown in FIG. 5B can be estimated based on highly accurate position information. In addition, the roadside communication device 2 can confirm the uplink area as its own downlink area by communicating a part of the information transmitted by itself to the in-vehicle communication device 3, and communication from both sides is possible. Communication area A.

[Position accuracy estimation by roadside communication device: third embodiment]
Next, position accuracy estimation by the roadside communication device according to the third embodiment will be described. FIG. 9 is a flowchart regarding this position accuracy estimation. In this flowchart, the number of GPS satellites captured in the first embodiment and the DOP value in the second embodiment are both used as elements for position accuracy estimation. Further, an RSSI (Receive Signal Strength Indication) value indicating the reception intensity of a signal transmitted from a GPS satellite and an S / N ratio (signal-to-noise ratio) are used as elements of position accuracy estimation.

  In the figure, the roadside communication device 2 first acquires the number of captured GPS satellites (step S11), and determines whether or not the number of captured satellites is equal to or greater than a threshold (step S12). Here, if the number of captures is equal to or greater than the threshold value, the DOP value is acquired next (step S13). On the other hand, when the number of captures is less than the threshold value in step S12, the roadside communication device 2 determines that there is no guarantee that position information with good accuracy can be obtained, and avoids acquisition of position information.

  Next, the roadside communication device 2 determines whether or not the DOP value is equal to or less than a threshold value (step S14). Here, if the DOP value is equal to or smaller than the threshold value, the RSSI value is acquired (step S15). On the other hand, if the DOP value exceeds the threshold value in step S14, the roadside communication device 2 determines that there is no guarantee that position information with good accuracy can be obtained, and avoids acquisition of position information.

  Next, the roadside communication device 2 determines whether or not RSSI values related to signal reception of all GPS satellites are equal to or greater than a threshold value (step S16). Here, if the RSSI value is equal to or greater than the threshold value, the S / N ratio is acquired (step S17). On the other hand, if the RSSI value is less than the threshold value in step S16, the roadside communication device 2 determines that there is no guarantee that position information with good accuracy can be obtained because the reception strength is weak, and avoids acquisition of position information. .

  Next, the roadside communication device 2 determines whether or not the S / N ratio related to signal reception of all GPS satellites is equal to or greater than a threshold value (step S18). Here, if the S / N ratio is equal to or greater than the threshold value, it is determined that the accuracy of the position information is good, and the position information included in the uplink signal from the in-vehicle communication device 3 is acquired (step S19). On the other hand, when the S / N ratio is less than the threshold value in step S18, the roadside communication device 2 determines that there is no guarantee that position information with good accuracy can be obtained because there is relatively much noise. Avoid getting.

In this way, position information is acquired only when the threshold condition is cleared in all of the number of GPS satellites captured, DOP value, RSSI value, and S / N ratio. If even one threshold condition cannot be cleared, the roadside The communication device 2 does not acquire position information from the in-vehicle communication device 3. As a result, the position information is acquired only when the position information with good accuracy is surely obtained, and the position accuracy acquired with respect to the in-vehicle communication device 3 can be increased.
Further, the roadside communication device 2 can estimate the uplink area shown in (b) of FIG. 5 based on the position information with higher accuracy than the first and second embodiments. Can be used as a communication area A in which communication from both sides is possible.

  Note that FIG. 9 is an example, and any combination of four GPS information such as the number of GPS satellites captured, DOP value, RSSI value, S / N ratio, or alone as in the first and second embodiments, Needless to say, it may be used to estimate the accuracy of the position information.

[Others]
Note that the communication area A can be estimated more accurately by selecting the position information according to each of the above embodiments and improving the accuracy of the position information as a whole. For example, the radio wave propagation environment changes under various conditions such as changes in buildings around roads, installation or removal of infrastructure on road traffic, and fallen leaves of street trees. Therefore, the communication area may change from A to A ′ as shown in FIG. 10, for example. That is, what is shown is an example in which the farthest end where the uplink signal arrives has changed from 200 m to 170 m. In this case, it is possible to return to the original area A by increasing the transmission power of the roadside communication device 2. On the contrary, when the area A is expanded, it can be returned to the original area A by reducing the transmission power of the roadside communication device 2.

  Further, by increasing the accuracy of the position information, the roadside communication device 2 associates the position information of the uplink signal with the reception intensity of the signal, and acquires a distribution map in which the position in the area and the reception intensity are mapped. It is also possible to do.

[Other applications]
As described above, the vehicle position information can also be used for estimation of the uplink area, but it can be used for safe driving support and provides information that contributes to safe driving to the vehicle. Can be used as basic data.

For example, if there is a vehicle that goes straight to the intersection at high speed, it is useful for preventing a right-handed accident if the vehicle turns right in the facing direction to inform the vehicle that the vehicle is approaching the intersection. In this case, in order to accurately predict the timing of entering the intersection, it is better that the positional accuracy from which the in-vehicle communication device transmits itself is high.
If an attempt is made to give a warning based on position information with insufficient accuracy, there is a possibility that the driver is warned in a scene where the warning is unnecessary, which may lead to a decrease in safety.

  As described above, if the accuracy of the position information transmitted from the in-vehicle communication device can be estimated, the level of the roadside service using the position information (for example, only providing it as reference information instead of a warning) or It is also possible to determine whether or not the service is executed (whether or not to provide information).

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

2 Roadside communication device 3 In-vehicle communication device 23 Control unit 25 GPS receivers S1 to S5 GPS satellites

Claims (8)

A roadside communication device that detects the position of the in-vehicle communication device based on the position information included in the uplink signal of the in-vehicle communication device,
A GPS receiver that receives signals transmitted from GPS satellites and obtains GPS information related to GPS positioning accuracy;
A roadside communication device comprising: a control unit that estimates accuracy of the position information based on the acquired GPS information and selects the position information according to whether the estimated accuracy of the position information is good or bad. .   The roadside communication device according to claim 1, wherein the GPS information includes the number of captured GPS satellites.   The roadside communication device according to claim 1, wherein the GPS information includes a DOP value.   The roadside communication device according to claim 1, wherein the GPS information includes at least one of a signal reception intensity from the GPS satellite and a signal-to-noise ratio.   The roadside communication device according to any one of claims 1 to 4, wherein a communication area where the uplink signal can be received is estimated based on the position information and the estimated accuracy of the position information. The roadside communication device includes a transmission unit that transmits downlink information that can be received by the in-vehicle communication device to a predetermined downlink area,
The said transmission part determines the content of the downlink information which the said roadside communication apparatus provides by radio | wireless based on the said positional infomation and the estimated precision of the said positional infomation. Roadside communication device. The downlink information is configured such that the in-vehicle communication device can include safe driving support information for supporting safe driving of the vehicle,
The transmission unit includes the safe driving support information in the downlink information only when the accuracy of the position information and the estimated position information is determined to be equal to or higher than a predetermined level. The roadside communication device described in 1. A position accuracy estimation method in which a roadside communication device estimates the accuracy of position information included in an uplink signal of an in-vehicle communication device,
Acquires GPS information about the GPS positioning accuracy signals transmitted from the GPS satellite received by the roadside communication equipment,
Based on the acquired GPS information, the roadside communication device estimates the accuracy of the position information,
The position accuracy estimation method , wherein the roadside communication device selects the position information in accordance with the accuracy of the estimated position information.

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