JP2013102541A - Roadside communication apparatus, computer program, and transmission timing synchronization method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the time accuracy of an apparatus (roadside communication apparatus) by selecting a synchronization target of air synchronization in consideration of the time accuracy of another apparatus (roadside communication apparatus) as a transmission source.SOLUTION: A roadside communication apparatus 2 makes radio transmission at the transmission timing generated so as to synchronize with another apparatus in a time zone (first slot T1) assigned to its own apparatus in time division. The roadside communication apparatus 2 comprises: synchronization means 23C which generates the transmission timing of its own apparatus BS3 using as a reference any one of the reception times of reception signals received from the plurality of other apparatuses BM, BS1, BS2; and selection means 23C which selects one of the other apparatuses BM, BS1, BS2 so as to make synchronization with the reception time of the selected apparatus, on the basis of the time accuracy of the other apparatuses BM, BS1, BS2 contained in the transmission signals of the other apparatuses BM, BS1, BS2.

Description

  The present invention relates to a roadside communication device suitable as a component of an intelligent transport system (ITS), for example. More specifically, it relates to transmission timing synchronization performed by the roadside 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.

Japanese Patent No. 2806801

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

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

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

Therefore, for example, assuming a communication system composed of a plurality of roadside communication device groups installed at each intersection, a time slot transmitted by each roadside communication device is assigned by the TDMA method, and the remaining time slot is assigned to a vehicle by the CSMA method. It is considered to be a rational communication system to be used for inter-vehicle communication.
In such an intelligent road traffic system, for example, a time slot used by a roadside communication device is notified to an in-vehicle communication device, and the in-vehicle communication device transmits using the CSMA method at times other than the time slot. Conceivable. In that case, if each roadside communication device does not perform wireless transmission at the correct transmission timing, a gap occurs between the time slot notified to the in-vehicle communication device and the time slot actually transmitted by the roadside communication device, and transmission from the roadside communication device Interference will occur between the signal and the transmission signal from the in-vehicle communication device.

  As a method of time synchronization between the roadside communication devices, for example, a GPS synchronization that adjusts its own clock to a GPS (Global Positioning System) time, a network that matches a network time acquired from a network line that conforms to IEEE 1588, IEEE802.1AS, or the like. Synchronization and air synchronization for adjusting its own clock to a transmission signal from another roadside communication device are conceivable.

Among these, when performing the air synchronization described above, there is not necessarily one other roadside communication device (other device) that is adjacent to the extent that a received signal can be obtained when viewed from a certain roadside communication device (own device), and there are multiple there's a possibility that.
In this way, when there are multiple adjacent devices, the reception status of the device changes due to various factors such as changes in the installation location and environment. It is difficult to keep.

Therefore, if the accuracy of the reception time is determined for each of the other devices based on the quality of the received signal obtained from a plurality of other devices, and the one with the highest accuracy is selected, the synchronization target It is possible to autonomously determine other devices to be used.
However, even if the accuracy of the reception time that can be measured on the own device side is good, the time accuracy itself at the other device that is the synchronization target may be poor. If selected as a target, the time accuracy of the own device may deteriorate as a result.

  In view of such conventional problems, the present invention selects a synchronization target for air synchronization in consideration of the time accuracy of another device that is a transmission source, thereby improving the time accuracy of the device itself. The purpose is to provide.

  A roadside communication device according to the present invention (Claim 1) is a roadside communication device that performs wireless transmission at a transmission timing generated so as to synchronize with another device in a time zone assigned to the device in a time division manner. Synchronizing means for generating the transmission timing of the own apparatus with reference to any one of the reception times of the received signals received from the other apparatus, and the other apparatus included in the transmission signal of the other apparatus Selection means for selecting whether to synchronize with the reception time corresponding to which other device based on the time accuracy.

  In addition, in this specification, when referring to its own device among a plurality of roadside communication devices installed at intersections of roads, the roadside communication device is referred to as “own device”, and other than this When referring to a device, the roadside communication device is referred to as “another device”.

  According to the roadside communication device of the present invention, the selection unit determines which other device is synchronized with the reception time in consideration of the time accuracy of the other device included in the transmission signal of the other device. Therefore, for example, it is possible to prevent other devices with poor time accuracy from being selected as synchronization targets compared to the case of selecting a synchronization destination based only on the accuracy of the reception time that can be measured by the device itself. And the time accuracy of the device itself can be improved.

In the roadside communication device of the present invention, specifically, the selection unit includes an error for each other device in consideration of the accuracy of the reception time that can be measured by the own device with respect to the time accuracy of the other device. An expected value may be obtained, and the other device having the smallest expected error value may be selected as a synchronization target (claim 2).
According to the selection process based on the expected error value, a very simple selection logic of selecting the one with the smallest expected error value, both the time accuracy of the other device and the accuracy of the reception time at the own device are good. The device can be selected, and the synchronization target selection process is simplified.

Further, the roadside communication device of the present invention preferably includes a communication control unit that includes the minimum expected error value selected by the selection unit as a time accuracy of the own device in a transmission signal from the own device. (Claim 3).
In this case, the communication control unit includes the minimum expected error value in the transmission signal as the time accuracy of the own device. Therefore, when the own device becomes the air synchronization information providing side (source side), the information acquisition side (slave More accurate accuracy information can be provided to other devices.

By the way, in the roadside communication device of the present invention, in consideration of the time error due to propagation delay, the influence of multipath, etc., the accuracy of the reception time is improved when a transmission signal is received from another device at an installation position as close as possible to the device itself Can be estimated to be higher.
Therefore, the selection unit may determine the accuracy of the reception time based on the installation position of the other device.

However, if there is a high-rise building or other obstacle between the own device and another device, even if both are relatively close, the received signal at the own device weakens and an accurate reception time is obtained. Most likely not. On the other hand, since it can be considered that there is no obstacle between the two devices with good visibility from the own device, such other devices have a correct reception time and are suitable for synchronization.
Therefore, it is preferable that the selection unit obtains the accuracy of the reception time based on information relating to the prospect to the other device.

In addition, it can be estimated that the other device of the transmission source of the received signal having a higher reception strength has a smaller distance from the own device and is less affected by a time error and multipath due to propagation delay.
Therefore, the selection means may determine the accuracy of the reception time based on the reception intensity of the reception signal.

  As described above, according to the present invention, since the synchronization target of the air synchronization is selected in consideration of the time accuracy of the other device that is the transmission source, the time accuracy of the own device can be improved.

It is a schematic perspective view which shows the whole structure of an intelligent road traffic system. It is a road top view which shows a part of jurisdiction area of an intelligent road traffic system. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a conceptual diagram which shows an example of the time slot contained in allocation information. It is a figure which shows an example of the data format which a vehicle-mounted communication apparatus transmits. It is a flowchart which shows an example of the processing content of synchronous mode. It is a conceptual diagram which shows an example of the electromagnetic wave reception state of a some roadside communication apparatus. It is a table | surface which shows an example of the precision data obtained with the roadside communication apparatus (slave BS3 of FIG. 7) which is performing slave mode. It is a top view of the road for showing the modification of this invention.

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

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

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

[Central equipment]
The central device 4 has a control unit composed of a workstation (WS), a personal computer (PC), etc., and this control unit collects and processes various traffic information from the roadside communication device 2 and the roadside sensor 6. (Calculation)-Performs recording, signal control and information provision in an integrated manner.
Specifically, the control unit of the central device 4 performs system control for adjusting the traffic signal group 1 on the same road for the traffic signal 1 at the intersection 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 A (range in which the transmission signal of the roadside communication device 2 can sufficiently reach) spreading around the roadside communication device 2 and the vehicle-mounted communication device 3 of the vehicle 5 traveling in its communication area A. Wireless communication is possible. Each roadside communication device 2 can also perform wireless communication with other roadside communication devices 2 in which the communication area A overlaps (partially overlaps or all overlaps).

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 (first slot T1 in FIG. 4) for wireless transmission by its own device by the TDMA method, and a time slot other than this time slot (second slot T2 in FIG. 4). Does not perform wireless transmission. 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 for adjusting its own clock to the GPS time, air synchronization for adjusting its own clock to a transmission signal from another roadside communication device 2, and the like. Will be described later.

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

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 extracts a reference time (first reference time: hereinafter referred to as “GPS time”) CL1 included in GPS signals received from a plurality of GPS satellites (not shown). Can do. The first reference time CL1 is an absolute time made up of, for example, a pulse signal (1PPS signal) every second, and is sent to the control unit 23 (first synchronization means 23B) through the wired communication unit 22.

The GPS signal includes a 10 MHz reference clock signal. This reference clock signal is input to the wireless communication unit 21, multiplied by the PLL method, and used for a wireless signal amplification operation or the like.
The storage unit 24 of the roadside communication device 2 stores a computer program for communication control executed by the control unit 23, communication device IDs of the communication devices 2 and 3, and the like.

The control unit 23 of the roadside communication device 2 generates monitoring information S7 regarding a time lag with other adjacent devices every predetermined period (for example, 1 day to several days), and the generated monitoring information Communication control for transmitting the information S7 to the wireless communication unit 21 can be executed.
In addition, the control unit 23 of the roadside communication device 2 includes the accuracy information S8 describing the time accuracy (expected value of time error) stored in the storage unit 24 in the transmission device, and transmits the accuracy information S8 to the wireless communication unit 21. It is also possible to execute communication control. When the time accuracy is updated with the correction accuracy (expected error value) obtained by the second synchronization means 23C described later, the updated time accuracy is newly stored in the storage unit 24.

  Furthermore, the control unit 23 of the roadside communication device 2 includes a data transfer unit 23A, a first synchronization unit 23B, and a second synchronization unit 23C as functional units achieved by executing the computer program. .

[Data transfer means]
Among them, the data transfer means 23A of the control unit 23 temporarily stores the traffic information S2 and the like received from the central device 4 received by the wired communication unit 22 in the storage unit 24, and automatically transmits it via the wireless communication unit 21. Broadcast transmission to the communication area A of the device.
Further, the data transfer unit 23A 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.

Further, the data transfer unit 23A broadcasts the time slot allocation information S6 stored in the storage unit 24 to the communication area A of the own apparatus 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, and includes, for example, the following contents (1) and (2).

(1) Slot number i (see FIG. 4) in use by its own device and other devices
(2) Start time and duration of the first slot T1 (see FIG. 4) of the slot number i When the in-vehicle communication device 3 of the vehicle 5 traveling in the communication area A receives the allocation information S6 from the roadside communication device 2 In addition to the time zone originally allocated for inter-vehicle communication, the time zone other than the first slot T1 described in the allocation information S6 (second slot T2 in FIG. 4) is also used to perform wireless communication using the carrier sense method. Send.

[Time slot allocation information]
FIG. 4 is a conceptual diagram showing an example of the time slot included in the allocation information S6.
As shown in FIG. 4, the time slots T1 and T2 include a first slot T1 and a second slot T2, and the total period of these times is repeated at a constant period C.
The first slot T1 is a time slot for the roadside communication device 2, and wireless transmission by the roadside communication device 2 is permitted in this time zone. A slot number i is assigned to the first slot T1, and the slot number i is periodically incremented or decremented.

The second slot T2 is a time slot for the in-vehicle communication device 3. Since this time zone is opened for wireless transmission by the in-vehicle communication device 3, the roadside communication device 2 does not perform wireless transmission in the second slot T2.
In the time slot shown in FIG. 4, the dots ● marked in the first slot T1 of each slot number i = 1 to 3 indicate that the transmission times of the plurality of roadside communication devices 2 are assigned to the first slot T1. Show.

  That is, in the example shown in FIG. 4, the transmission times of the two roadside communication devices 2 at the intersections J1 and J5 (see FIG. 1) are allocated to the first slot T1 of the slot number (1), and the slot number (2 ) Is assigned to the transmission times of the three roadside communication devices 2 at the intersections J2, J6 and J8, and the first slot T1 of the slot number (3) is assigned to one roadside at the intersection J3. The transmission time of the communication device 2 is assigned.

Thus, the transmission time of each roadside communication device 2 is not assigned to the first slot T1 in a one-to-one correspondence, but is installed at the intersection Ji (i = 1 to 12) where no radio wave interference occurs. The roadside communication devices 2 can be assigned to the same slot number i.
Such slot allocation can be performed autonomously by each roadside communication device 2 using the installation position and slot information acquired from other devices, or one parent device is selected in advance from a plurality of roadside communication devices 2 In addition, it is possible to perform this operation collectively for the slave unit so that the master unit has a transmission timing at which radio interference does not occur between the slave units managed by itself.

[First synchronization means]
The first synchronization means 23B of the control unit 23 uses the GPS time CL1 acquired from the GPS receiver 25 to execute GPS synchronization for generating the transmission timing of the own device.
Specifically, the first synchronization means 23B of the present embodiment determines whether the GPS time CL1 is normal based on the quality of the GPS signal and the monitoring information S7 collected from a plurality of other devices, and this GPS time Only when the CL1 is normal, the transmission timing of the wireless communication unit 21 is generated with the GPS time CL1 as a reference.
Details of the synchronization mode (GPS synchronization) executed by the first synchronization means 23B will be described later.

[Second synchronization means]
On the other hand, the second synchronization unit 23C of the control unit 23 receives the transmission signal from the other device by the wireless communication unit 21 of the own device (second reference time: hereinafter simply referred to as “reception time”) CL2. As a reference, air synchronization is performed to generate the transmission timing of the own device.
Specifically, the storage unit 24 of the roadside communication device 2 stores in advance a preamble pattern used by another device as a known pattern, and the second synchronization unit 23C of the present embodiment uses the known pattern and the received wave. Based on this correlation, the type of preamble, the reception strength (RSSI) of the preamble, and the reception timing (reception time) are detected, and the transmission timing of the radio communication unit 21 is generated based on this reception timing.

In addition, the second synchronization unit 23C of the present embodiment selects one reception time CL2 to be used as a reference for the transmission timing of the own device based on the accuracy of a plurality of reception times CL2 from which other devices of the transmission source are different. It is also possible to execute processing, that is, selection processing of another device to be followed that is a synchronization target of air synchronization.
The details of the synchronization mode (air synchronization) executed by the second synchronization means 23C including this selection process will also be described later.

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

The control unit 32 of the in-vehicle communication device 3 causes the communication unit 31 to perform wireless communication 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.

In addition, the control part 32 of the vehicle-mounted communication apparatus 3 carries out the radio transmission of the vehicle information S3 including the present position, direction, speed, etc. of the vehicle 5 (vehicle-mounted communication apparatus 3) via the communication part 31 by radio. Yes.
In addition, the control unit 32 of the in-vehicle communication device 3 has the position, speed, and direction included in the vehicle information S3 received directly from the other vehicle 5 or the vehicle information S3 of the other vehicle 5 received from the roadside communication device 2. Based on this, it is possible to perform safe driving support control for avoiding a right-handed collision or a head-on collision.

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

[Synchronous mode of roadside communication device]
FIG. 6 is a flowchart showing the processing content of the synchronous mode executed by the control unit 23 of the roadside communication device 2.
In FIG. 6, the “master mode” (steps ST1 to ST6) does not depend on the transmission timing of other devices, and the device itself is an external signal (in this embodiment, the GPS time CL1 included in the GPS signal). This is a synchronous mode that autonomously generates transmission timing based on the above.

On the other hand, the “slave mode” (steps ST7 to ST10) in FIG. 6 is based on the transmission timing of the other device (specifically, the reception time CL2 at which the own device received the transmission signal from the other device). This means a synchronization mode (air synchronization) for generating the transmission timing of the own device.
In the present embodiment, it is assumed that the device itself is connected to the GPS receiver 25. Therefore, as shown in FIG. 6, the control unit 23 of the own apparatus first executes the master mode by the first synchronization means 23B (step ST1 in FIG. 6).

[Master mode]
In this master mode, the first synchronization means 23B of the control unit 23 self-measures the accuracy of the GPS time CL1 (step ST2 in FIG. 6) and determines whether the GPS time CL1 is normal (step ST3 in FIG. 6). ).
The accuracy of the GPS time CL1 is, for example, the number of satellites from which the GPS signal is transmitted, the reception intensity (RSSI) of each GPS signal, and the S / N ratio of the GPS signal. (Value) σ is determined in advance by a numerical experiment or the like, and the number of satellites, reception intensity, and S / N ratio are substituted for the influence function.

The first synchronization means 23B of the control unit 23 compares the accuracy σ of the GPS time CL1 obtained by the influence function with a predetermined threshold, and determines that the GPS time CL1 is normal if the accuracy σ is equal to or less than the threshold. If the threshold value is exceeded, it is determined that the GPS time CL1 is abnormal.
When the first synchronization means 23B determines that the GPS time CL1 is abnormal based on the accuracy determination (No in step ST3 in FIG. 6), the first synchronization means 23B does not execute the master mode using the GPS time CL1, and sets the synchronization mode. Shift to the slave mode described later.

Conversely, when the first synchronization means 23B determines that the GPS time CL1 is normal by the accuracy determination (Yes in step ST3 in FIG. 6), the first synchronization means 23B further stores the monitoring information S7 acquired from a plurality of other devices. Based on this, it is determined whether or not the GPS time CL1 is normal (steps ST4 and ST5 in FIG. 6).
For example, when a time lag (a time difference greater than or equal to a predetermined value) is detected in the majority of monitoring information S7 from among the monitoring information S7 received from a plurality of adjacent other devices, a so-called majority logic Thus, it can be estimated that the GPS time CL1 of the own device is abnormal.

If the first synchronization means 23B determines that the GPS time CL1 is abnormal based on the monitoring information S7 (No in step ST5 in FIG. 6), the master mode using the GPS time CL1 is not executed, and the synchronization mode Is shifted to the slave mode described later.
Conversely, if the first synchronization means 23B determines that the GPS time CL1 is normal based on the monitoring information S7 (Yes in step ST5 in FIG. 6), the first synchronization means 23B uses its own GPS communication unit as a reference. 21 is generated (step ST6 in FIG. 6).

In the roadside communication device 2 of the present embodiment, since the transmission signal from the other device can always be received except when the own device is transmitting, whether or not the own device is transmitting at the correct transmission timing as described above. Such monitoring can be easily performed using the monitoring information S7 from other devices (mutual monitoring).
In this case, if it is determined by the monitoring information S7 from the other device that the transmission timing of the own device is deviated, for example, it can be estimated that the GPS receiver 25 is defective. Switch to mode (air synchronization).

In the case of the roadside communication device 2 that cannot execute the slave mode, if it is determined by the monitoring information S7 that the GPS receiver 25 is defective, the operation of the roadside communication device 2 is stopped.
In this case, if other roadside communication devices 2 in the vicinity, for example, broadcast information to the vehicle-mounted communication device 3 that “the roadside communication device in the XX area is stopped” is transmitted to the vehicle 5 side. The operation stop of the roadside communication device 2 can be notified in advance.

[Slave mode]
Next, the slave mode (step ST7 in FIG. 6) by the second synchronization means 23C will be described.
In this slave mode, the second synchronization means 23C first collects reception times CL2 from reception signals received from a plurality of other devices (step ST8 in FIG. 6).
The reception time CL2 is detected by scanning the preamble included in the transmission signal when the wireless communication unit 21 receives a transmission signal from another device, and the scanned pattern (reception wave) is the highest of the known patterns. This is performed by setting the time point indicating the correlation value as the reception timing (reception time CL2).

In the present embodiment, each roadside communication device 2 performs signal transmission by including the ID corresponding to itself in the data following the preamble pattern. For this reason, even if the device itself receives a plurality of received waves, the received intensity, the reception time CL2, and the like in each received wave can be distinguished and detected for each received wave.
As described above, when each reception time CL2 corresponding to the transmission signal transmitted by a plurality of other devices is collected, the second synchronization unit 23C further performs a selection process of selecting another device to be tracked to match the transmission timing. This is executed (step ST9 in FIG. 6).

[Synchronization target selection process in slave mode]
Specifically, the selection process evaluates the accuracy of the reception time CL2 based on the collected quality of each received signal, and uses the accuracy information S8 included in the transmission data of the other device that is the transmission source to determine the accuracy of the other device. Collects time accuracy and selects one reception time CL2 to be used as a reference for the transmission timing of the own device based on both the accuracy of the reception time CL2 evaluated by the own device and the time accuracy of the other device acquired from the other device. Is done by doing.

  Of the two above-mentioned accuracies that serve as a selection criterion for synchronization, the accuracy of the reception time CL2 is, for example, the reception strength (RSSI) of the received signal, the S / N ratio, and the correlation coefficient with the known pattern. An influence function affecting the accuracy (expected value of time error) σ is determined in advance by a numerical experiment or the like, and the reception intensity, S / N ratio, and correlation coefficient are substituted into the influence function.

However, it is not always necessary to comprehensively evaluate the influence of each parameter indicating the quality of the received signal to obtain the accuracy of the reception time CL2, and simply determine the accuracy of the reception time CL2 based on the installation position of other devices. It can also be evaluated.
The reason is that the closer to the device, the smaller the time error due to propagation delay, the influence of multipath, etc., and the accuracy of the reception time CL2 can be evaluated only by the distance from the device.

In this case, it is preferable that the second synchronization means 23C also sets the selection condition for the identification information of the road passing through the installation position of the other device.
The reason is that when there is a high-rise building or other obstacle between the own device and another device, even if both are relatively close, the received signal at the own device is weakened and the accurate reception time CL2 This is because there is a possibility that cannot be obtained.
Thus, when there is no line of sight between the own device and the other device, it can be determined that the accuracy of the reception time obtained from the received signal is low. For example, in FIG. 7 described later, the accuracy of the signal received by the slave BS 3 from the master BM is about 20 μs.
On the other hand, since it can be considered that there is no obstacle between the two devices on the same road as the own device, it can be determined that the accuracy of the reception time obtained from the reception signal is high. For example, in FIG. 7 described later, the accuracy of the signal received by the slave BS 3 from the slave BS 1 is about 5 μs.

Note that the installation position of the other apparatus and the road identification information passing through the installation position may be stored in advance in the storage unit 24 of the own apparatus as advance setting information, or transmitted to the transmission data of the roadside communication device 2. A rule including such information may be adopted to receive a transmission signal from another device and acquire the information.
Further, whether or not there is an obstacle between the own device and the other device is determined by the degree of visibility from the own device to the other device, and therefore can be determined not only by road identification information but also by map information.
For example, if there is no obstacle between your device and the other device, you can score 100 points, and if you decide in advance on the map an index that will be deducted depending on the size and number of buildings between them, The magnitude of the value of the index can be used as a selection condition for other devices to be followed.

Further, the second synchronization means 23C can evaluate the accuracy of the reception time CL2 based on the reception intensity of the reception signal from the other device.
The reason is that it can be estimated that the other device of the transmission source of the received signal having a higher reception strength has a smaller distance from the own device and a smaller time error and multipath effect due to propagation delay. Therefore, in this case, the accuracy of the reception time CL2 is obtained using only the reception strengths of the collected reception signals as variables.

[Selection processing using both precisions]
As described above, in addition to the accuracy of the reception time CL2 measured from the quality of reception signals from a plurality of other devices, the second synchronization means 23C of the present embodiment includes the other devices included in the transmission signal of each other device. In consideration of the accuracy information S8, another device to be synchronized is selected.
Hereinafter, a specific example of the selection process using both the precisions will be described with reference to FIGS.

FIG. 7 is a conceptual diagram showing an example of radio wave reception states of a plurality of roadside communication devices, and FIG. 8 is an example of accuracy data obtained by a roadside communication device (slave BS3 in FIG. 7) executing the slave mode. It is a table | surface which shows.
In FIG. 7, “Master” (one in the example) is the roadside communication device 2 that is executing the master mode (GPS synchronization in this embodiment), and “Slave” (three in the example) is the slave. The roadside communication device 2 that is executing the mode (air synchronization) is shown.

As shown in FIG. 7, the master BM and the slave BS3 are located on one diagonal of the building, and the slave BS1 and the slave BS2 are located on another diagonal of the building.
Furthermore, the selection process performed by the slave BS 3 is assumed here. Therefore, among the radio signals Ra to Re indicated by arrows in FIG. 7, the radio signal Re from the master BM to the slave BS 3 has an intervening building between them, so that it is much more difficult than the other radio signals Ra to Rd. It will be weak. In addition, about each radio signal Ra-Rd, it has shown that the quality of a received signal is so good that the line of the arrow which shows the direction of the said signal is thick.

In the accuracy data of the slave BS 3 shown in FIG. 8, the master BS is highly accurate because it performs GPS synchronization, and its time accuracy is 0 μs. On the other hand, the time accuracy of the slave BS1 and the slave BS3 is 1 μs and 5 μs, respectively.
On the other hand, the accuracy of the reception time obtained from the quality of the received signal received by the slave BS3 from other neighboring devices BM, BS1 and BS2 is 20 μs for the master BM, 5 μs for the slave BS1, and 3 μs for the slave BS2, respectively.

In general, since the time accuracy in the master BM is high (σ = 0 μs), there is no problem if the radio signal Re from the master BM can be received with high quality.
However, in the situation where there is a building between them as shown in FIG. 7, the radio signal Re from the master BM is considerably deteriorated and reaches the slave BS 3, so the reception time accuracy (σ = 20 μs) is inferior. Will end up.

Further, when paying attention to the slave BS1, the time accuracy σ of itself is 1 μs, which can be said to be quite high accuracy, but the time accuracy σ of the reception time based on the reception quality measured by the slave BS3 is 5 μs. It cannot be said that it is highly accurate.
On the other hand, when paying attention to the slave BS2, the time accuracy σ of itself is 5 μs, which is not very high accuracy, but the time accuracy σ of the reception time based on the reception quality measured by the slave BS3 is 3 μs, which is considerably high accuracy.

  Accordingly, if another device to be synchronized is determined based on the time accuracy of the reception time (second column in the table of FIG. 8) based on the reception quality measured by the slave BS 3 (self device), the slave BS 2 In the case of the slave BS 2, the time accuracy (σ = 5 μs) of the slave BS 2 is not so high, so if this time accuracy is taken into consideration, the slave BS 2 is synchronized. However, the time accuracy of the slave BS 3 (own device) cannot be improved much.

Therefore, in the second synchronization means 23C of the present embodiment, the reception time based on the reception quality of the slave BS3 which is the own device with respect to the time accuracy of the other devices BM, BS1 and BS2 (first column in the table of FIG. 8). Is taken into consideration (second column in the table of FIG. 8), and the correction accuracy (third column of the table of FIG. 8: expected error value) for each of the other devices BM, BS1, BS2 is obtained.
Then, the second synchronization means 23C selects the other device BS1 having the smallest correction accuracy (expected error value) as a synchronization target.

  As described above, according to the roadside communication device 2 of the present embodiment, the second synchronization unit 23C of the control unit 23 not only has the accuracy of the reception time that can be measured by the own device (slave BS3 in FIG. 7) but also other devices. The reception time corresponding to any other device based on the correction accuracy (expected error value) that also takes into account the time accuracy of the other device included in its transmission signal (master BM and slave BS1, BS2 in FIG. 7). Therefore, it is possible to prevent the other device (slave BS2 in FIG. 7), which is actually poor in time accuracy, from being selected as a synchronization target, and the time of the own device (slave BS3 in FIG. 7). Accuracy can be improved.

  As described above, when the other device BM1 to be synchronized with is selected from the plurality of other devices BM, BS1 and BS2, the second synchronization means 23C of the own device (slave BS3) By adding a fixed time with reference to the reception time CL2 detected from the reception signal from BM1, the transmission timing in its own wireless communication unit 21 is generated (step ST10 in FIG. 6).

Further, in this case, the second control means 23C updates the accuracy information S8 with the selected minimum correction accuracy (correction accuracy (= 6 μs) of the slave BS1 in FIG. 8) as the time accuracy of its own device, and this accuracy The information S8 is included in the transmission signal from the own device.
For this reason, when the own device (slave BS3) becomes the information providing side (source side) of air synchronization by another device, more accurate accuracy information is provided to the other device on the information acquisition side (slave side). It will be.

Note that, as described above, the roadside communication device 2 of the present embodiment selects which of the transmission timings of its own device is to be generated based on the accuracy of the GPS time CL1 and the reception time CL2. It is possible to determine the transmission timing of the own device by selecting a highly accurate one from the times CL1 and CL2.
For this reason, even if one of the GPS time CL1 and the reception time CL2 is inaccurate for some reason, the transmission timing can be generated using the other more accurate reference times CL1 and CL2. There is also an advantage that time synchronization with the apparatus can be performed accurately.

[Modification: Roadside communication device with directivity]
FIG. 9 is a plan view of a road for showing a modification of the present invention.
Each roadside communication device 2 according to this modification is equipped with a wireless communication unit capable of wireless communication using a plurality of antennas having different directivities.
As shown by arrows in FIG. 9, each antenna of the wireless communication unit has directivity along the traveling direction of each road flowing into the intersection, and the wireless communication unit sets transmission / reception timing for each antenna. Can be set.

In the case of the roadside communication device 2 as described above, it can be considered that a single roadside communication device 2 has a plurality of independent communication areas for each antenna.
Therefore, in the case of the roadside communication device 2 capable of wireless communication for each directional antenna, assuming that there is a communication device for each antenna instead of for each roadside communication device 2 and performing slot assignment and reference time selection. Also, the present invention can be applied.

[Other variations]
Each embodiment disclosed this time is an illustration of the present invention and is not restrictive. The scope of the present invention is shown not by the above-described embodiment but by the scope of claims for patent, and includes all modifications within the scope and meaning equivalent to the scope of claims for patent.
For example, in the above embodiment, the absolute time (GPS time) CL1 is extracted from the GPS signal received by the GPS receiver 25, but the slave device or other external device connected to the network line conforming to IEEE 1588, IEEE 802.1AS or the like. Thus, the absolute time CL1 can also be acquired.

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

DESCRIPTION OF SYMBOLS 1 Traffic signal device 2 Roadside communication device 3 In-vehicle communication device (mobile communication device)
4 Central device 5 Vehicle 6 Roadside sensor 7 Communication line 8 Router 20 Antenna 21 Wireless communication unit (second acquisition means)
22 Wired communication unit (first acquisition means)
23 Control unit (communication control unit)
23A Data transfer means 23B First synchronization means 23C Second synchronization means (selection means)
24 storage unit 25 GPS receiver 30 antenna 31 communication unit 32 control unit 33 storage unit S1 signal control information S2 traffic information S3 vehicle information S4 sensing information S5 image data S6 allocation information S7 monitoring information S8 accuracy information CL1 GPS time CL2 reception time T1 1st slot (time slot)
T2 Second slot (Time slot)

The present invention relates to, for example, a roadside communication device suitable as a component of an intelligent transport system (ITS) and a computer program for operating the roadside communication device . More specifically, the present invention relates to a transmission timing synchronization method performed by the roadside communication device.

In view of such conventional problems, the present invention selects a synchronization target for air synchronization in consideration of the time accuracy of another device that is a transmission source, thereby improving the time accuracy of the device itself. The purpose is to provide.

In the roadside communication device of the present invention, specifically, the selection unit adds the accuracy of the reception time that can be measured by the own device to the time accuracy of the other device to correct each other device. The accuracy may be obtained, and the other device having the best correction accuracy may be selected as a synchronization target (claim 1 ).
According to the selection process based on such correction accuracy, a very simple selection logic of selecting the one with the best correction accuracy , and the other device having both the time accuracy of the other device and the accuracy of the reception time of the own device can be obtained. It is possible to select, and the selection process of the synchronization target becomes simple.

In the roadside communication device of the present invention, it is preferable that the roadside communication device includes a communication control unit that includes the best correction accuracy selected by the selection unit as a time accuracy of the own device in a transmission signal from the own device. Yes.
In this case, since the communication control unit includes the best correction accuracy as the time accuracy of the own device in the transmission signal, when the own device becomes the air synchronization information providing side (source side), the information acquisition side (slave side) ) More accurate accuracy information can be provided to other devices.

By the way, in the roadside communication device of the present invention, in consideration of the time error due to propagation delay, the influence of multipath, etc., the accuracy of the reception time is improved when a transmission signal is received from another device at an installation position as close as possible to the device itself Can be estimated to be higher.
Therefore, the selection means is based on the installation position of the other device, it may be decided to determine the accuracy of the reception time (Claim 2).

However, if there is a high-rise building or other obstacle between the own device and another device, even if both are relatively close, the received signal at the own device weakens and an accurate reception time is obtained. Most likely not. On the other hand, since it can be considered that there is no obstacle between the two devices with good visibility from the own device, such other devices have a correct reception time and are suitable for synchronization.
Therefore, the selection means, based on the information on sight to the other device, it is preferable to determine the accuracy of the reception time (claim 3).

In addition, it can be estimated that the other device of the transmission source of the received signal having a higher reception strength has a smaller distance from the own device and is less affected by a time error and multipath due to propagation delay.
Therefore, the selection means, based on the reception strength of the received signal may be to seek accuracy of the reception time (claim 4).
The computer program of the present invention (Claim 5) is for causing a computer to function as the above-mentioned roadside communication device, and has the same effects as the roadside communication device.
The synchronization method of the present invention (Claim 6) is a transmission timing synchronization method performed by the roadside communication device described above, and has the same effects as the roadside communication device.

Therefore, in the second synchronization means 23C of the present embodiment, the reception time based on the reception quality of the slave BS3 which is the own device with respect to the time accuracy of the other devices BM, BS1 and BS2 (first column in the table of FIG. 8). (The second column of the table of FIG. 8) is added to obtain the correction accuracy (third column of the table of FIG. 8: expected error value) for each of the other devices BM, BS1, BS2.
Then, the second synchronization means 23C selects the other device BS1 having the smallest correction accuracy value (error expected value) obtained as described above (that is, the best correction accuracy) as the synchronization target. It has become.

Also, in this case, the second control means 23C updates the accuracy information S8 with the selected best correction accuracy (correction accuracy (= 6 μs) of the slave BS1 in FIG. 8) as the time accuracy of its own device. The information S8 is included in the transmission signal from the own device.
For this reason, when the own device (slave BS3) becomes the information providing side (source side) of air synchronization by another device, more accurate accuracy information is provided to the other device on the information acquisition side (slave side). It will be.

Furthermore, in the intelligent transportation system of the above embodiment, a communication device (mobile communication terminal) carried by a pedestrian or the like can be used instead of or in addition to the in-vehicle communication device 3. However, in this case, the mobile communication terminal does not perform wireless transmission during the transmission time (first slot T1) of the roadside communication device 2 as in the case of the in-vehicle communication device 3 of the above embodiment. Need to follow.
In FIG. 7, as shown in parentheses under each variation value, the unit for expressing the time accuracy may be an accuracy index as well as the time value.

Claims (6)

A roadside communication device that performs wireless transmission at a transmission timing generated to synchronize with another device in a time zone assigned to the device in a time-sharing manner,
Synchronization means for generating the transmission timing of the own device based on any one of the reception times of the received signals received from the other devices;
Selection means for selecting which of the other devices to synchronize with the reception time based on the time accuracy of the other device included in the transmission signal of the other device;
Roadside communication device equipped with.   The selection means obtains an expected error value for each other device in consideration of the accuracy of the reception time that can be measured by the own device with respect to the time accuracy of the other device, and the expected error value is the smallest. The roadside communication device according to claim 1, wherein another device is selected as a synchronization target.   The roadside communication device according to claim 2, further comprising a communication control unit that includes the minimum expected error value selected by the selection unit as a time accuracy of the own device in a transmission signal from the own device.   The roadside communication device according to any one of claims 1 to 3, wherein the selection unit obtains the accuracy of the reception time based on an installation position of the other device.   5. The roadside communication device according to claim 4, wherein the selection unit obtains the accuracy of the reception time based on information regarding a prospect to the other device.   The roadside communication device according to any one of claims 1 to 5, wherein the selection unit obtains the accuracy of the reception time based on the reception intensity of the reception signal.

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