JP2014023090A - Receiver and radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a receiver and a radio communication system that can accurately and appropriately execute time synchronization.SOLUTION: A receiver 51 according to the invention comprises: an acquisition unit 53a for acquiring a time-stamp Ts stored at a prescribed position in a PDU received from a transmitter 41; a time correction unit 23b for correcting a local time of the receiver on the basis of the time-stamp Ts; and an error determination unit 53b for conducting error determination of a communication frame. When the time correction unit 23b acquires the time-stamp Ts, it obtains a synchronization error relative to the local time of the receiver on the basis of the time-stamp Ts by the time when the error determination unit 53b finishes the error determination of the communication frame, and further corrects the local time of the receiver using the synchronization error if the error determination unit 53b has determined the communication frame does not have any error.

Description

  The present invention relates to a receiver used in, for example, an intelligent transport system (ITS) and a wireless communication system.

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, the use of a CSMA (Carrier Sense Multiple Access) method as a multiple access method has been studied in order to perform communication between roads, road vehicles, and vehicles within a limited frequency band.

However, in the above system, road-to-vehicle communication, road-to-road communication, and vehicle-to-vehicle communication will coexist, and it is common that the priority of information handled by the roadside communication device on the infrastructure side is high, A mechanism for preferentially performing road-to-vehicle communication and road-to-road communication over vehicle-to-vehicle communication is required.
For this reason, as a mechanism for preferentially performing information transmission of roadside communication devices, time division multiplexing (TDMA) in which a frequency band used for communication is time-divided at regular intervals to provide time slots dedicated to transmission of roadside communication devices. : Time Division Multiple Access) is effective.

For example, assuming a communication system composed of a plurality of roadside communication device groups installed at each intersection, a time slot dedicated to wireless transmission from the roadside that is wirelessly transmitted by the roadside communication device is allocated by the TDMA method, and the remaining time slots It can be considered that it is a rational communication system to use the system for inter-vehicle communication by the CSMA method.
In such an intelligent road traffic system, slot information related to the time slot used by each roadside communication device is notified to the in-vehicle communication device by a downlink signal, and the in-vehicle communication device wirelessly uses the CSMA method in a time zone other than the time slot. It is conceivable to perform transmission.

  In this case, if accurate time synchronization is not established between the roadside communication devices and between the roadside communication device and the in-vehicle communication device, the time slot start time and end time grasped by each roadside communication device and the in-vehicle communication device Deviation occurs, and radio wave interference occurs between the downlink signal of the roadside communication device and the transmission signal of the in-vehicle communication device.

On the other hand, as a method of time synchronization between roadside communication devices, GPS synchronization for adjusting its own local time to GPS (Global Positioning System) time, or time information (time) notified from other roadside communication devices of its own local time. Air synchronization to match the stamp) can be considered.
Among these, in GPS synchronization, synchronization is possible autonomously, while in air synchronization, the time stamp needs to be acquired from a device other than its own device.
The time stamp generally includes information on the local time when the time stamp is generated. For this reason, when the time stamp of another communication apparatus is acquired, it is preferable to synchronize the local time of the own apparatus based on the time stamp as soon as possible. This is because when the local time of the own device is synchronized, it is necessary to perform correction for the elapsed time with respect to the time indicated by the time stamp.

  The time stamp is stored and transmitted at a predetermined position in the communication frame of the roadside communication device. Therefore, in order to synchronize the time as soon as possible after acquiring the time stamp, it is conceivable to synchronize the local time of the own apparatus using the acquired time stamp as soon as the time stamp is acquired.

  However, in this case, since the time stamp is stored at a predetermined position in the communication frame, before reading the FCS data necessary for executing the error determination of the communication frame stored at the end of the normal communication frame, That is, time synchronization is performed before error determination is performed for the time stamp. For this reason, there is a possibility that the time synchronization is executed with a time stamp including an error. In such a case, there is a possibility that the time synchronization cannot be performed appropriately.

  On the other hand, if an attempt is made to synchronize the time based on the time stamp after executing the error determination by FCS, an error occurs in the time information indicated by the time stamp after the time stamp is acquired until the error determination is performed and the process is terminated. As a result, the accuracy of time synchronization may be reduced.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a receiver and a wireless communication system that can perform time synchronization with high accuracy and appropriateness.

(1) The present invention provides a wireless communication system in which at least one roadside communication device allocates a first time zone in which radio transmission is performed in a time-sharing manner and opens the other second time zone for radio transmission by a mobile communication device. A receiver that is used for each of the communication devices and performs time synchronization with another communication device, and is stored in a predetermined position of a communication frame received from the other communication device. An acquisition unit that acquires time information indicating the local time of the communication device, a correction unit that corrects the local time of the own device based on the time information, and stored behind the time information in the communication frame, A determination unit that performs error determination using error determination data necessary for performing error determination of the communication frame, and when the acquisition unit acquires the time information, the correction unit Until the error determination of the communication frame is completed, a synchronization error with respect to the local time of the own device is obtained based on the time information, and the correction unit further includes an error in the error determination of the communication frame. After determining that it is not, the local time of the own device is corrected using the synchronization error.

According to the receiver of the present invention, when the acquisition unit acquires the time information, the correction unit synchronizes with the local time of the own device based on the time information until the determination unit finishes the error determination of the communication frame. Since the error is calculated, the synchronization error immediately after the acquisition unit acquires the time information can be obtained. Even if the time synchronization is performed using this synchronization error later, it occurs at least when the time information is acquired. The synchronization error can be eliminated with high accuracy. Furthermore, since the correction unit performs time synchronization of the own device using the synchronization error immediately after acquiring the time information after the determination unit determines that there is no error in the communication frame, the time information includes an error. After confirming that there is no such device, it is possible to synchronize the time of its own device.
As a result, it is possible to perform time synchronization appropriately without performing time synchronization of the own device with accurate and time information including an error.

(2) When it is known at which position in the communication frame the time information is stored, the time required from the start of receiving the communication frame to the end of acquiring the time information can be grasped in advance. . Therefore, in this case, it is preferable that the correction unit obtains the synchronization error using the time information and a time required from the start of reception of the communication frame to the acquisition of the time information. The delay time generated in the time information can be corrected according to the time, and the synchronization error can be obtained with higher accuracy.

(3) When the determination unit determines that there is an error in the error determination of the plurality of transmission signals, the correction unit may stop the correction based on the time information stored in the communication frame. In this case, it is possible to prevent time synchronization of the own device from time information including an error.

(4) Furthermore, if the own device has performed time synchronization with other communication devices in the past and the synchronization error is not large with respect to the local time of the own device when the time information is acquired, a plurality of transmissions It can be estimated that the accuracy of time information is maintained regardless of signal error determination.
Therefore, even when the determination unit determines that there is an error in determining the error of the communication frame, the correction unit automatically uses the synchronization error if the synchronization error is within a predetermined value. The time correction of the machine may be executed.

(5) The receiver further includes a storage unit that stores the synchronization error, and the correction unit calculates the synchronization error stored in the storage unit every time a new synchronization error is obtained. The synchronization error may be updated, and in this case, the latest synchronization error can always be provided.

(6) Further, the present invention provides a roadside communication device in which a first time zone in which radio transmission is performed is allocated in a time division manner, and a mobile communication device in which radio transmission is performed in a second time zone other than the first time zone. In the wireless communication system provided, each of the communication devices includes the receiver described in the above (1) to (6). According to the wireless communication system of the present invention, the same operational effects as those of the above-described receiver can be obtained.

  As described above, according to the present invention, time synchronization can be performed accurately and appropriately.

1 is a schematic perspective view showing an overall configuration of an intelligent road traffic system according to an embodiment of the present invention. It is a conceptual diagram which shows an example of the time slot of road-to-vehicle communication. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a block diagram which shows the structure of the transmitter and receiver of a radio | wireless communications system in a protocol stack format. (A) is a time chart which shows the event which arises in transmission / reception of time stamp Ts, (b) is a table | surface which shows the content of the delay time between the events. It is explanatory drawing of an acquisition delay time, (a) is a figure which shows an example of the format of a communication frame, (b) is a table | surface which shows the required time of the frame reproduction | regeneration according to a modulation method and a transmission rate. It is a flowchart which shows the process sequence regarding the delay time correction | amendment and the correction | amendment of local time which the time correction part of a roadside communication apparatus performs for the time synchronization of local time. It is a flowchart which shows the process sequence regarding correction | amendment of local time when memorize | storing synchronous error (DELTA) T in a memory | storage part and updating. It is a flowchart which shows the process sequence regarding the delay time correction | amendment and correction | amendment of local time which the time correction part of a vehicle-mounted communication apparatus performs for the time synchronization of local time.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
[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 includes a traffic signal 1, a roadside communication device 2, an in-vehicle communication device 3 (see FIG. 3), a central device 4, a vehicle 5 equipped with the in-vehicle communication device 3, And the roadside sensor 6 which consists of a vehicle sensor, a surveillance camera, etc. is 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, for simplification of illustration, only one signal lamp is depicted at each intersection Ji, but at each actual intersection Ji, there are at least four for ascending and descending roads intersecting each other. A signal lamp is 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 Ji 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.]
In an intelligent road traffic system, a plurality of roadside communication devices 2 installed at each of a plurality of intersections constituting a wireless communication system communicate wirelessly with a vehicle-mounted communication device 3 of a vehicle traveling around the roadside vehicle (road vehicle ( Inter-roadway communication) is possible. Each roadside communication device 2 is also capable of wireless communication (inter-road communication) with other roadside communication devices 2 that are located within a predetermined range within which their transmission waves reach.
The in-vehicle communication device 3 that also constitutes a wireless communication system can perform wireless communication with the roadside communication device 2 and can perform wireless communication (vehicle-to-vehicle communication) with other in-vehicle communication devices 3 using a carrier sense method. is there.

As described above, in the ITS of this embodiment, communication between the vehicle-mounted communication devices 3 (vehicle-to-vehicle communication) and communication between the road-side communication device 2 and the vehicle-mounted communication device 3 (from “road” to “car”). Wireless communication is used for the communication between the vehicle and the “road” from the “car” to the “road”.
In addition, although the central apparatus 4 provided in the traffic control center can perform bidirectional communication with each roadside communication device 2 by wire, wireless communication may be performed between these devices.

The roadside communication device 2 is assigned a dedicated time slot (first slot SL1 in FIG. 2) for wireless transmission by itself in the TDMA system, and a time slot other than this time slot (second slot in FIG. 2). No wireless transmission is performed for SL2). That is, the time zone other than the time slot for the roadside communication device 2 is open as a transmission time by the CSMA method for the in-vehicle communication device 3.
Although the roadside communication device 2 and the vehicle-mounted communication device 3 use the same frequency band for communication, the transmission time zones of the roadside communication device 2 and the vehicle-mounted communication device 3 are distinguished as described above. A collision between the transmission signal and the transmission signal by the in-vehicle communication device 3 can be avoided.

  The roadside communication device 2 and the in-vehicle communication device 3 are not particularly limited with respect to reception of transmission signals. Accordingly, the roadside communication device 2 can receive transmission signals from the in-vehicle communication device 3 and can also receive transmission signals from other roadside communication devices 2. The in-vehicle communication device 3 can receive transmission signals from the roadside communication device 2 and other in-vehicle communication devices 3.

[Contents of time slot]
FIG. 2 is a conceptual diagram showing an example of a time slot for road-to-vehicle communication in the present embodiment. As shown in FIG. 2, in the road-to-vehicle communication, radio frames arranged side by side in the time axis direction are used.
This radio frame has a length in the time axis direction set to 100 milliseconds, and includes a first slot SL1 and a second slot SL2.
The first slot SL1 is a time slot assigned to the roadside communication device 2, and wireless transmission by the roadside communication device 2 is permitted in this time zone. On the other hand, the second slot SL2 is a time slot for the in-vehicle communication device 3, and since this time zone is opened for wireless transmission by the in-vehicle communication device 3, the roadside communication device 2 performs wireless transmission in the second slot SL2. Absent.

The first slots SL1 and the second slots SL2 included in the radio frame are alternately arranged in the time axis direction.
Slot numbers i (i = 1 to 10 in FIG. 2) are assigned to the first slots SL1, respectively. This slot number i is incremented or decremented within the radio frame.
One of the plurality of first slots SL1 included in the radio frame is allocated to the roadside communication device 2. The roadside communication device 2 can recognize which slot is assigned to itself by the slot number i.
Since a plurality of radio frames are arranged side by side in the time axis direction as described above, the first slot SL1 for each slot number assigned to any roadside communication device 2 has a radio frame length of 1 respectively. It is periodically arranged with a period, that is, 100 milliseconds as one period. Therefore, the roadside communication device 2 performs transmission using the first slot SL1 every 100 milliseconds.

A plurality of roadside communication devices 2 can also be assigned to the same slot. In this case, it is necessary that the positional relationship between the roadside communication devices 2 to which slots are assigned redundantly be sufficiently far enough to determine that the possibility of causing interference by mutual transmission signals is extremely low.
As in the present embodiment, when the positional relationship between the roadside communication devices 2 is close in distance, different slots are assigned. This is to prevent interference between the transmission signals of each other.

  FIG. 2 shows an example of a radio frame of each of the roadside communication devices 2A and 2B that are close to each other in distance, and the roadside communication device 2A has a first slot SL1 with slot number 2 indicated by hatching. The roadside communication device 2B is assigned with the first slot SL1 with slot number 1 indicated by hatching.

  In FIG. 2, the radio frame of the roadside communication device 2 </ b> B is delayed in the time axis direction with respect to the radio frame of the roadside communication device 2 </ b> A. Is shown. Since the roadside communication devices 2A and 2B are assigned different first slots SL1, mutual transmission signals do not overlap and cause interference, but the first slot SL1 assigned to one is not It overlaps with the other second slot SL2, and there is a possibility that interference occurs between the transmission signal of the roadside communication device 2 and the transmission signal of the in-vehicle communication device 3 in this overlapping portion. For this reason, between the roadside communication devices 2 (particularly, between the roadside communication devices 2 that are close to each other in distance), it is necessary to synchronize the local times of each other so that the timings of the radio frames coincide with each other.

Therefore, the roadside communication device 2 has a synchronization function for synchronizing with the time of another roadside communication device 2 in order to control its transmission timing. The time synchronization of the roadside communication device 2 is corrected based on, for example, GPS synchronization for adjusting the local time of the own device to the GPS time, or the local time of the own device based on information included in a transmission signal from another roadside communication device 2. This is done by air synchronization or the like.
The roadside communication device 2 of the present embodiment is configured to perform synchronization between the roadside communication devices 2 by air synchronization. This air synchronization will be described in detail 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.

The storage unit 24 of the roadside communication device 2 stores a computer program for realizing communication control executed by the control unit 23, communication device IDs of the communication devices 2 and 3, slot information S6 described later, and the like.
The control unit 23 of the roadside communication device 2 includes a transmission control unit 23a that controls the transmission timing of the wireless communication unit 21 as a functional unit achieved by executing the computer program, and a time stamp that corrects its own local time. And a time correction unit 23b that generates Ts and corrects the local time of the own device based on the time stamp Ts included in the transmission signal from the synchronization destination of the time synchronization.

The transmission control unit 23a performs radio transmission for a predetermined transmission time in the first slot SL1 (FIG. 2) of the slot number i assigned to the own device. The storage unit 24 stores, for example, slot information S6 including information on the following a) and b). The slot information S6 is individually set for each roadside communication device 2.
a) Slot number i of the first slot SL1 assigned to the own device
b) Start time and transmission time of the slot number i of the first slot SL1 assigned to the radio frame or the own device

The control unit 23 of the roadside communication device 2 has a function of counting the local time based on the operation clock of the own device, and the transmission control unit 23a uses the local time counted by the own device as a reference to the slot information S6. Wireless transmission is performed in accordance with the start time of the included wireless frame.
Further, the transmission control unit 23a has a function of broadcasting by including a time stamp Ts as time information used for time synchronization with other communication devices in a transmission signal (downlink signal) of the own device. Yes.
This time stamp Ts indicates a time value obtained by adding a delay time described later to the current time value at the local time of the own device.

  The time correction unit 23b has a function of generating a time stamp Ts indicating the local time of the own device by correcting the delay time with respect to the current time value at the local time of the own device. Further, the time correction unit 23b obtains a synchronization error ΔT that is a difference between the time stamp Ts acquired by receiving a transmission signal from another roadside communication device 2 and the local time of the own device, and uses the synchronization error ΔT. Thus, the local time of the own device is corrected, and the time synchronization is performed using the other roadside communication device 2 as the synchronization source.

  That is, the roadside communication device 2 exchanges the time stamp Ts of its own device or the time stamp Ts of another communication device with another roadside communication device 2 or the in-vehicle communication device 3 via wireless communication. It has a function of performing air synchronization that synchronizes each other's local time.

Further, the control unit 23 of the roadside communication device 2 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 broadcasts it via the wireless communication unit 21. It has a function to do.
In addition, 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, and the wireless communication unit 21 It also has a function of broadcast transmission via the network.

Further, the control unit 23 has a function of including the slot information S6 of its own device in a transmission signal (downlink signal) and performing broadcast transmission.
Upon receiving the slot information S6 from the roadside communication device 2, the in-vehicle communication device 3 receives a time slot (FIG. 2) other than the time slot (first slot SL1 in FIG. 2) dedicated to the roadside communication device 2 described in the slot information S6. The second slot SL2) is used to perform wireless transmission by the carrier sense method.

[In-vehicle communication device]
The in-vehicle communication device 3 is connected to a communication unit (transmission / reception unit) 31 connected to an antenna 30 for wireless communication, a control unit 32 including a processor that performs communication control on the communication unit 31, and the control unit 32. And a storage unit 33 including a storage device such as a ROM or a RAM.
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 based on the carrier sense method for inter-vehicle communication, and the communication control function in the time division multiplexing method like the roadside communication device 2 is I don't have it.
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 includes a transmission control unit 32a that controls the wireless transmission timing of the communication unit 31 as a functional unit achieved by executing the computer program, and a transmission signal from a synchronization destination of time synchronization. And a time correction unit 32b that corrects the local time of the own device based on the time stamp Ts included in.

The transmission control unit 32a of the in-vehicle communication device 3 sets the wireless transmission time zone allowed by itself according to the start time of the slot information S6 acquired from the roadside communication device 2 and the slot information S6, and the communication unit only in this time zone. 31 is made to perform wireless transmission.
That is, the transmission control unit 32a extracts the slot information S6 of the roadside communication device 2 from the downlink signal from the roadside or the received frame from the vehicle side, and the first slot SL1 of the slot number i indicated in the slot information S6. The communication unit 31 is caused to perform wireless transmission by the carrier sense method only in a time zone other than the above.
In addition, the transmission control unit 32a wirelessly transmits the vehicle information S3 including the current position, direction, speed, and the like of the vehicle 5 (vehicle communication device 3) to the outside via the communication unit 31 by broadcast.

  The time correction unit 32b has the same function as the time correction unit 23b of the roadside communication device 2. Therefore, the time correction unit 32b has a function of correcting the delay time with respect to the current time value at the local time of the own device and generating a time stamp Ts indicating the local time of the own device, and other communication. A synchronization error ΔT, which is the difference between the time stamp Ts obtained by receiving the transmission signal from the machine and the local time of the own machine, is obtained, and the local time of the own machine is corrected using the synchronization error ΔT. It has a function of performing time synchronization using a communication device as a synchronization source.

  That is, the in-vehicle communication device 3 exchanges the time stamp Ts of its own device or the time stamp Ts of another communication device with the roadside communication device 2 or other in-vehicle communication device 3 via wireless communication, It has a function of performing air synchronization that synchronizes each other's local time.

  The control unit 32 receives the traffic information S2 and the vehicle information S3 transmitted from the roadside communication device 2, and also receives the vehicle information S3 transmitted from the other vehicle 5 (the in-vehicle communication device 3). Based on these pieces of information, it also has a function of performing safe driving support control that avoids a right-handed collision or a head-on collision.

[About giving and receiving time stamp Ts]
As described above, in the wireless communication system according to the present embodiment, the communication devices 2 and 3 that have acquired the time stamp Ts generated by the other communication devices 2 and 3 that are the synchronization source of the time synchronization include the time stamp Ts. Use to correct the local time, and perform air synchronization between roads, roads, and vehicles.

FIG. 4 is a block diagram showing the configuration of the transmitter 41 and the receiver 51 of the wireless communication system in a protocol stack format, and exchange of the time stamp Ts accompanying air synchronization between the transmitter 41 and the receiver 51. Show.
In FIG. 4, when the transmitter 41 is the roadside communication device 2 as another communication device as a synchronization source, and the receiver 51 is the roadside communication device 2 as a communication device that performs time synchronization with another communication device. Is illustrated. When the transmitter 41 is the roadside communication device 2 and the receiver 51 is the in-vehicle communication device 3, the transmitter 41 is the in-vehicle communication device 3 as another communication device, and the receiver 51 is between the other communication devices. The case of the in-vehicle communication device 3 as a communication device that performs time synchronization is almost the same as that in FIG.

As shown in FIG. 4, the transmitter 41 has an upper layer 42, a MAC (Media Access Control) unit 43, a PHY (Physical) unit 44, and an RF (Radio Frequency) unit 45 in order from the upper side. A transmission antenna 46 is connected to the RF unit 45. Protocol control of the layers 42 to 44 is performed by the control unit 23 of the roadside communication device 2 on the transmission side.
The receiver 51 includes an upper layer 52, a MAC (Media Access Control) unit 53, a PHY (Physical) unit 54, and an RF (Radio Frequency) unit 55 in order from the upper side. The transmission antenna 56 is connected. The control of the layers 52 to 54 is performed by the control unit 23 of the roadside communication device 2 on the receiving side.

When the MAC unit 43 of the transmitter 41 is given a SDU (Servise Data Unit) from the upper layer 42, the time correction unit 23b1 on the transmitter 41 side obtains the PDU (Protocol Data Unit) from the SDU. The time stamp Ts (time information) is stored in a predetermined position of the PDU, and the PDU is given to the lower PHY unit 44. In the present embodiment, the PDU corresponds to a communication frame described later.
The PHY unit 44 modulates the generated PDU and supplies this modulated signal to the lower RF unit 45. The RF unit 45 converts the modulated signal into an analog signal, amplifies it, and transmits the radio wave from the transmitting antenna 46 to the outside.

  In the present embodiment, the modulation of the PHY unit 44 of the transmitter 41 includes an OFDM (Orthogonal Frequency-Division Multiplexing) modulation process. Therefore, demodulation of the PHY unit 54 of the receiver 51 includes demodulation processing using the OFDM method.

  On the other hand, when the transmission radio wave reaches the receiving antenna 56, the RF unit 55 of the receiver 51 amplifies the received signal and converts it into a digital signal, and gives this signal to the PHY unit 54. The PHY unit 54 demodulates the digital signal, extracts the PDU from the carrier wave, and gives it to the MAC unit 53.

The MAC unit 53 of the receiver 51 reproduces the SDU from the given PDU, and gives this SDU to the upper layer 52.
The MAC unit 53 includes an acquisition unit 53a that acquires a time stamp Ts stored at a predetermined position of the PDU. The acquisition unit 53a gives the acquired time stamp Ts to the time correction unit 23b2 on the receiver 51 side.

The MAC unit 53 further includes an error determination unit 53b. The error determination unit 53b has a function of performing error determination for a given PDU. The error determination unit 53b reads FCS data for executing an FCS (Flame Check Sequence) stored at the end of the PDU, and determines whether there is an error with respect to the PDU in which the FCS data is stored.
The time stamp Ts is stored at a predetermined position of the PDU, while the FCS data is stored behind the time stamp Ts by being stored at the end of the PDU (see FIG. 6). Therefore, the error determination unit 53b performs error determination after the acquisition unit 53a acquires the time stamp Ts.

When the determination result indicates that there is no error, the error determination unit 53b reproduces the PDU in which the FCS data has been stored into the SDU, and gives it to the upper layer 52. On the other hand, when there is an error in the determination result, processing for requesting the transmitter 41 to retransmit the corresponding PDU is performed.
The error determination unit 53b also has a function of giving a determination result of error determination to the time correction unit 23b2.

Here, the time correction unit 23b1 on the transmitter 41 side obtains a time stamp Ts obtained by correcting the delay time by adding a predetermined delay time to be corrected on the transmission side to its own local time, and uses this time stamp Ts as the MAC unit. 43.
The time correction unit 23b2 on the receiver 51 side corrects the delay time by adding a predetermined delay time to be corrected on the reception side to the time stamp Ts obtained from the MAC unit 53 and transmitted from the transmitter 41 side. To do. The time correction unit 23b2 on the receiver 51 side obtains a synchronization error ΔT that is a difference between the time stamp Ts whose delay time has been corrected and the local time of the own device.
Further, the time correction unit 23b2 on the receiver 51 side corrects the local time of the own device using the synchronization error ΔT in order to perform time synchronization with other roadside communication devices 2.

  In this case, if the delay time to be added on the transmission side and the reception side is appropriately set in the transmitter 41 and the receiver 51, the receiver 51 determines its own (reception) based on the time stamp Ts. The local time of the machine 51) can be matched with the local time of the transmitter 41 with high accuracy.

[Contents of delay time and correction]
Next, the contents of the delay time that occurs during transmission / reception of the communication frame (transfer of the time stamp Ts) will be described.
FIG. 5A is a time chart showing events that occur in transmission / reception of the time stamp Ts, and FIG. 5B is a table showing contents of delay times between the events. As shown in FIG. 5A, the events during the transmission / reception of the time stamp Ts include the following.

1) Time A when the transmitter MAC sets the time stamp Ts
2) Time B when the transmitting antenna 46 transmits radio waves
3) Time C when the receiving antenna 56 receives radio waves
4) Time point D when the preamble reaches the receiver MAC
5) Time E when the receiver MAC acquires the time stamp Ts
6) Time F when receiver MAC acquires FCS data
7) Time G when the receiver MAC finishes determining whether there is an error

  Among these, the “transmission delay time” from the time point A to the time point B is generated by the digital signal processing in the MAC unit 43 and the PHY unit 44 of the transmitter 41 and the delay characteristic of the analog filter in the RF unit 45 of the transmitter 41. On the transmitter 41 side, prediction can be made by calculation based on circuit characteristics or by performing measurement in advance. This time is, for example, about 5 μsec in an actual machine.

The “transmission delay time” from time point B to time point C depends on the distance between the transmitter 41 and the receiver 51, and cannot be predicted independently on either side of transmission and reception, but can be calculated if the distance is known. is there.
Therefore, if the position information including the coordinates (latitude / longitude) of the transmitter 41 is included in the SDU or PDU, the receiver 51 can detect the position of the transmitter 41 and the position of its own device (receiver 51). Based on the distance, the transmission delay time can be calculated.

Since this transmission delay time increases by about 1 μsec every 300 m, for example, when the communication distance in ITS is 600 m, it becomes about 2 μsec at the maximum.
Further, the information for specifying the position of the transmitter 41 is not limited to information for directly specifying the position such as the coordinates, but may be identification information such as a communication device ID of the roadside communication device 2, for example. In this case, if the receiver 51 stores position information corresponding to the communication device ID, the position of the transmitter 41 can be obtained from the communication device ID.

  The “reception delay time” from the time point C to the time point D is generated by the delay characteristics of the analog filter in the RF unit 55 of the receiver 51 and the digital signal processing in the MAC unit 53 and the PHY unit 54 of the receiver 51. On the 51st side, prediction can be made by performing calculation based on circuit characteristics or performing measurement in advance. Moreover, this time is 5 microseconds in an actual machine, for example.

The “acquisition delay time” from the time point D to the time point E is the time from the arrival of the preamble to the MAC unit 53 to the time of acquisition of the time stamp Ts in the receiver 51. This time varies depending on which part of the communication frame stores the time stamp Ts and the communication speed.
FIG. 6 is an explanatory diagram of the acquisition delay time, FIG. 6 (a) is a diagram showing an example of the format of the communication frame, and FIG. 6 (b) is the time required for frame reproduction according to the modulation method and transmission rate. It is a table | surface which shows.

As shown in FIG. 6A, in the frame format conforming to IEEE 802.11, the playback time of the preamble and the signal has a fixed length, and the data amount of the header is 30 bytes. In the illustrated example, time information (time stamp Ts) is stored in a 30-byte portion from the beginning of the data area.
Also, in the communication frame, the modulation method (BPSK, QPSK or 16QAM) of the frame is described in the signal in the part before the header (and hence the part before the storage part of the time stamp Ts). Based on this, the transmission rate can be calculated.

Therefore, as shown in the table of FIG. 6B, the reproduction time t1 from the beginning of the header part to the beginning of the time stamp Ts and the reproduction time t2 from the beginning of the preamble to the beginning of the time stamp Ts Can be determined in response to
Accordingly, the storage location of the time stamp Ts (the number of bytes from the beginning of the data, etc.) is determined in advance, and a reference table as shown in FIG. 6B is stored in the memory of the receiver 51, thereby modulating the signal. The acquisition delay time can be obtained from the speed.

In this embodiment, since each delay time is shared and corrected between the transmission side and the reception side, the time correction unit 23b1 of the transmitter 41 adds the following transmission delay time (a) to its own local time. Then, a time stamp Ts corrected to substantially coincide with the local time of the own device (transmitter 41) at time B is obtained.
(A) Transmission delay time from the time stamp Ts is set to the time of radio wave transmission (time from time A to time B in FIG. 5)

In addition, the time correction unit 23b2 of the receiver 51 sets the sum of the following reception delay time (b), acquisition delay time (c), and transmission delay time (d) to the time given from the transmitter 41. By adding to the stamp Ts, the time stamp Ts corrected so as to substantially coincide with the local time of the transmitter 41 at the time point E is obtained.
(B) Reception delay time from the time of reception of radio waves to the arrival of the preamble to the MAC unit 53 (time from time point C to time point D in FIG. 5)
(C) Acquisition delay time from the arrival of the preamble to the MAC unit 53 to the acquisition of the time stamp Ts (time from time D to time E in FIG. 5)
(D) Transmission delay time according to the distance between the position of the transmitter 41 determined from the position specifying information and the position of the receiver 51 which is its own device (time from time B to time C in FIG. 5)

As described above, according to the wireless communication system of the present embodiment, the time correction unit 23b1 of the transmitter 41 adds the transmission delay time in its own device to its own local time to obtain the time stamp Ts. The time stamp Ts of the machine 41 substantially coincides with the time B at which a carrier wave obtained by modulating a communication frame (PDU) including the time stamp Ts is transmitted from the transmission antenna 46.
On the other hand, the time correction unit 23b2 of the receiver 51 acquires the corrected time stamp Ts by adding the reception delay time, the acquisition delay time, and the transmission delay time to the time stamp Ts. Therefore, the time stamp Ts corrected by the time correction unit 23b2 substantially matches the local time of the transmitter 41 at the time point E when the MAC unit 53 acquires the time stamp Ts.

As described above, at each time point, the time stamp Ts is corrected for the delay time caused by transmission and reception.
For this reason, the time correction unit 23b2 on the receiver 51 side corrects the delay time in its own device to the time stamp Ts acquired by receiving the transmission signal from the transmitter 41 side at the time point E, and after the delay time correction If the local time of the own device is corrected at a time point closer to the time point E based on the time stamp Ts, time synchronization with other roadside communication devices 2 can be performed with high accuracy.

Returning to FIG. 5, after obtaining the time stamp Ts, the receiver 51 reads and obtains FCS data stored at the end of the communication frame (time point F), and then determines an error for the communication frame based on the FCS data. (Error check) is performed and the determination result is output (time point G). Therefore, the MAC unit 53 performs error determination in the period from the time point F to the time point G (determination time).
In parallel with the above processing, the time correction unit 23b2 of the receiver 51 corrects the delay time (time point H) after acquiring the time stamp Ts, acquires the synchronization error ΔT, and, if necessary, the local time of its own device. Time correction (time point J) is performed.

[Regarding correction of local time]
Since the time stamp Ts acquired by the MAC unit 53 is acquired before the error determination by the error determination unit 53b is performed, an error may be included.
Therefore, even when the time correction unit 23b2 of this embodiment acquires the time stamp Ts and corrects the delay time, the time correction unit 23b2 does not immediately correct the local time of the own device, and the error determination unit 53b determines the error determination result. Based on this, it is configured to determine whether or not to correct the local time.

FIG. 7 is a flowchart showing a processing procedure related to delay time correction and local time correction performed by the time correction unit 23b2 for time synchronization of the local time.
First, when the time correction unit 23b2 acquires the time stamp Ts from the MAC unit 53 (step S1, time E in FIG. 5), the time correction unit 23b2 performs the above-described delay time correction on the time stamp Ts (step S2, FIG. 5). Medium, time point H).
Next, the time correction unit 23b2 acquires a synchronization error ΔT that is the difference between the time stamp Ts whose delay time has been corrected and the local time of the own device (step S3, time point I in FIG. 5).
As shown in FIG. 5, the synchronization error ΔT indicates a time lag between the local time of the own device at the time point I and the time stamp Ts, and the time of the local time of the own device is corrected using this value. Then, time synchronization can be performed with high accuracy.

  The correction of the delay time performed at the time point H includes the delay time from the time point E at which the time stamp Ts is acquired to the time point I at which the synchronization error ΔT is acquired in addition to the delay time up to the time point E described above. Can do. Thereby, time synchronization can be performed with higher accuracy. The delay time from time point E to time point I can be grasped by measuring in advance.

  Returning to FIG. 7, when the synchronization error ΔT is acquired in step S3, the time correction unit 23b2 refers to the result of the error determination regarding the data of the communication frame in which the time stamp Ts is stored by the error determination unit 53b, and the determination result It is determined whether or not there is no error (step S4).

Here, the error determination unit 53b determines the presence or absence of an error using the FCS data stored at the end of the communication frame.
Therefore, referring to FIG. 5, the result of the error determination regarding the data of the communication frame is obtained at time point G, which is a later timing than time point F at which the MAC unit 53 finishes reading the last FCS data of the communication frame. .

Since the time stamp Ts is arranged at a predetermined position in the data area in the communication frame, the time stamp Ts is arranged at a position (in time) before the FCS data area. Is acquired at time point E located within the frame reading time. Therefore, the time correction unit 23b2 of this embodiment is configured to finish acquisition of the synchronization error ΔT at a time point I before the time point F at which the reading of the communication frame is completed by reading the FCS data.
As a result, it is possible to obtain a synchronization error ΔT that can accurately eliminate at least the synchronization error occurring at the time point I regardless of the error determination result.

Returning to FIG. 7, when the determination result of the error determination is that there is no error in step S4, the time correction unit 23b2 corrects the local time of the own device (step S5) and ends the process.
The time correction unit 23b2 performs correction by adding the synchronization error ΔT to the local time of the own device. Since the synchronization error ΔT is a value obtained with high accuracy at the time point E, by correcting the local time of the own device by the synchronization error ΔT, the local time of the own device can at least include the synchronization error generated at the time point I. The time can be synchronized with the transmitter 41 side.

On the other hand, in step S4, (if there is an error) the results of error judgment may not be without error, the time correction unit 23b2, the synchronization error ΔT is within a range from the lower limit value T _min a predetermined upper limit T _max It is determined whether or not there is (step S6).
If the own device has performed time synchronization with other communication devices in the past, and the synchronization error is not large with respect to the local time of the own device when the time stamp Ts is acquired, the time is not affected regardless of the error determination. It can be estimated that the accuracy of the stamp Ts is maintained.
Therefore, even if the time correction unit 23b2 of the present embodiment determines that the error determination unit 53b has an error, the time correction unit 23b2 determines that the synchronization error ΔT is within a predetermined value. The own time is corrected using the synchronization error ΔT.

Here, the lower limit value T _min and the lower limit value T _min are set to the minimum value and the maximum value of the time lag value that normally occurs when the own device has performed time synchronization with other communication devices in the past. When the value is out of the numerical range, it is determined that the time synchronization has not been performed in the past, or that the time stamp Ts includes an error. More specifically, the lower limit value T _min is set to “−16 μs”, and the upper limit value T _max is set to “16 μs”.

When it is determined in step S6 that the synchronization error ΔT is within the range from the lower limit value T _min to the upper limit value T _max , the time correction unit 23b2 proceeds to step S5 and corrects the local time using the synchronization error ΔT. (Step S5), the process ends.
In this case, even if it is determined that the error determination result includes an error in the entire communication frame, since the synchronization error ΔT is within the above range, the time stamp Ts may not include an error. High nature. Therefore, in this case, the time correction unit 23b2 corrects the local time using the synchronization error ΔT.

In step S6, when it is determined that the synchronization error ΔT is not within the range from the lower limit value T _min to the upper limit value T _max , the time correction unit 23b2 stops the correction of the local time of the own device and performs the process without performing the correction. Finish.
In this case, since it is determined that the error determination result includes an error in the entire communication frame, and the value of the synchronization error ΔT can be determined to include an error, the time correction unit 23b2 The correction using ΔT is stopped, and the process ends without performing the correction.
In this case, it is possible to prevent time synchronization of the own device based on the time stamp Ts including an error.

In the above description, in step S6, it is determined whether or not to correct the local time depending on whether or not the synchronization error ΔT is within the range from the lower limit value T _min to the upper limit value T _max. In step S4, when the error determination result is not error-free, the correction using the synchronization error ΔT may be stopped regardless of the value of the synchronization error ΔT, and the process may be terminated without performing the correction. . This is because there is a possibility that an error is included in the time stamp Ts when the error determination result is not error-free.

  In the above embodiment, the time correction unit 23b2 acquires the synchronization error ΔT using the corrected time stamp Ts when the delay time correction of the time stamp Ts is performed in step S2 in FIG. The case where the local time of the own device is corrected using the synchronization error ΔT is illustrated, but the time correction unit 23b2 stores the synchronization error ΔT in the storage unit 24 and acquires a new synchronization error ΔT. The synchronization error ΔT stored in the storage unit 24 may be updated to the new synchronization error ΔT each time it is performed.

FIG. 8 is a flowchart showing a processing procedure relating to correction of local time when the synchronization error ΔT is stored in the storage unit 24 and updated.
8 is the same as the flowchart shown in FIG. 7 except for step S31 provided after step S3.
In step S3 in FIG. 8, when the synchronization error ΔT, which is the difference between the time stamp Ts corrected for the delay time and the local time of its own device, is acquired, the time correction unit 23b2 acquires the past stored in the storage unit 24. Instead of the synchronization error ΔT, the newly acquired synchronization error ΔT is stored. As described above, the time correction unit 23b2 updates the synchronization error ΔT stored in the storage unit 24 every time a new synchronization error ΔT is acquired (step S31).

Thereafter, the time correction unit 23b2 performs error determination by reading the FCS data (step S4). When the determination result indicates that there is no error, the time correction unit 23b2 corrects the local time of the own device using the synchronization error ΔT stored in the storage unit 24 (step S5), and ends the process.
On the other hand, in step S4, (if there is an error) determination result may not be without error, the time correction unit 23b2, the synchronization error ΔT stored in the storage unit 24, the upper limit value T from the lower limit value T _min predetermined It is determined whether it is within the range of _max (step S6).
Since the following processing is as described above, the description thereof is omitted.

  In the above case, since the synchronization error ΔT is stored in the storage unit 24 and updated every time a new synchronization error ΔT is acquired, the latest synchronization error ΔT can always be provided. Therefore, if the correction of the local time is allowed, the local time can be corrected quickly with the latest synchronization error ΔT.

[Effect]
According to the receiver 51 configured as described above, when the MAC unit 53 (the acquisition unit 53a) acquires the time stamp Ts, the time correction unit 23b2 continues until the error determination unit 53b finishes the error determination of the communication frame. During this period, the synchronization error ΔT with respect to the local time of the own device is obtained based on the time stamp Ts. Therefore, the synchronization error ΔT immediately after the MAC unit 53 obtains the time stamp Ts can be obtained. Even if time synchronization is performed using ΔT, at least a synchronization error that has occurred when the time stamp Ts is acquired can be eliminated with high accuracy. Further, the time correction unit 23b2 uses the synchronization error ΔT immediately after acquiring the time stamp Ts after the error determination unit 53b determines that there is no error in the communication frame (PDU) including the time stamp Ts. Since synchronization is performed, it is possible to perform time synchronization of the own device after confirming that no error is included in the time stamp Ts.
As a result, it is possible to perform time synchronization appropriately without performing time synchronization of the own device with the time stamp Ts including the error with accuracy.

[Regarding correction of local time by in-vehicle communication device]
In the said embodiment, although the communication apparatus which performs time synchronization (air synchronization) between the other communication apparatus which is a synchronization origin, and another communication apparatus was shown, it is the roadside communication apparatus 2, but in-vehicle communication Also in the device 3, since it is necessary to perform wireless transmission using the second slot SL2 (FIG. 2), it is necessary to synchronize the time with the time of another communication device located in the vicinity. In this case, the in-vehicle communication device 3 performs time synchronization (air synchronization) by receiving the time stamp Ts included in the downlink signal of the roadside communication device 2 around the own device.

  FIG. 9 is a flowchart showing a processing procedure related to delay time correction and local time correction performed by the time correction unit 32b of the in-vehicle communication device 3 for time synchronization of the local time of the own device.

First, when the time correction unit 32b acquires the time stamp Ts included in the downlink signal from the roadside communication device 2 as another communication device (step S11), the time correction unit 32b receives the time stamp Ts in the same device as described above. The delay time generated by the process is corrected (step S12).
Next, the time correction unit 32b acquires a synchronization error ΔT that is a difference between the time stamp Ts with the delay time corrected and the local time of the own device when the time stamp Ts is acquired (step S13).

When acquiring the synchronization error ΔT in step S13, the time correction unit 32b, synchronization error ΔT is equal to or within the range from the lower limit value _{T min} a predetermined upper limit _{T max} (step S14).
Here, the lower limit value T _min and the lower limit value T _min are the minimum values of the time lag values that normally occur when the own device has performed time synchronization with other communication devices in the past, as in the above embodiment. The maximum value is set to a value that can be determined to be out of these numerical ranges, when time synchronization has not been performed in the past, or when the time stamp Ts includes an error. More specifically, the lower limit value T _min is set to “−16 μs”, and the upper limit value T _max is set to “16 μs”.

If it is determined in step S14 that the synchronization error ΔT is within the range from the lower limit value T _min to the upper limit value T _max , the time correction unit 32b proceeds to step S15 and corrects the local time using the synchronization error ΔT. (Step S15), the process ends.
In this case, since the synchronization error ΔT is within the above range, there is a high possibility that the time stamp Ts does not contain an error. Therefore, the time correction unit 32b corrects the local time using the synchronization error ΔT regardless of the error determination result.

The moving in-vehicle communication device 3 may have fewer opportunities for time synchronization than the roadside communication device 2 installed at a fixed position. In this regard, in this embodiment, when the synchronization error ΔT is within the range from the lower limit value T _min to the upper limit value T _max , the time correction unit 32b corrects the local time regardless of the error determination result. The opportunity for synchronization can be substantially increased.
In this case, the time correction unit 32b corrects the local time regardless of the error determination result. Therefore, if the time stamp Ts is acquired and the delay time is corrected, the FCS data at the end of the communication frame is acquired. The local time can be corrected quickly without waiting for the time point F (FIG. 5) or the time point G (FIG. 5) at which the determination result of the error determination is obtained.

On the other hand, when it is determined in step S14 that the synchronization error ΔT is not within the range from the lower limit value T _min to the upper limit value T _max , the time correction unit 32b determines an error regarding the data of the communication frame in which the time stamp Ts is stored. Referring to the result, it is determined whether or not the determination result has no error (step S16).

  In step S16, when the determination result of the error determination is that there is no error, the time correction unit 32b corrects the local time of the own device using the synchronization error ΔT (step S15) and ends the process. In this case, even if the synchronization error ΔT is outside the above range, it is determined that there is no error. Therefore, since the time stamp Ts does not include an error, the time correction unit 32b corrects the local time using the synchronization error ΔT.

  In step S16, when the determination result of the error determination is that there is no error, the time correction unit 32b stops the correction of the local time of the own device and ends the process without performing the correction. Thereby, it is possible to prevent time synchronization of the own device based on the time stamp Ts including an error.

[Other variations]
The present invention is not limited to the above embodiment. For example, in each of the above embodiments, the roadside communication device 2 is used as a synchronization source, and the roadside communication device 2 or the vehicle-mounted communication device 3 performs air synchronization with the synchronization source communication device. When there is no 2, the in-vehicle communication device 3 can also perform time synchronization using another in-vehicle communication device 3 as a synchronization source. Also in this case, time synchronization can be performed by the same processing as in the above embodiments.
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.

2 Roadside communication device 3 In-vehicle communication device 23b, 23b1, 23b2 Time correction unit 24 Storage unit 32b Time correction unit 41 Transmitter 51 Receiver 53a Acquisition unit 53b Judgment unit SL1 1st slot SL2 2nd slot

Claims (6)

Used for each communication device in a wireless communication system in which a first time zone in which at least one roadside communication device performs wireless transmission is allocated in a time-sharing manner and other second time zones are opened for wireless transmission by a mobile communication device And a receiver that performs time synchronization with other communication devices,
An acquisition unit that acquires time information indicating a local time of the other communication device, which is stored at a predetermined position of a communication frame received from the other communication device;
Based on the time information, a correction unit for correcting the local time of the own machine,
A determination unit configured to perform error determination using error determination data necessary for performing error determination of the communication frame stored behind the time information in the communication frame;
When the acquisition unit acquires the time information, the correction unit obtains a synchronization error with respect to the local time of the own device based on the time information until the determination unit finishes the error determination of the communication frame,
Further, the correction unit corrects the local time of the own device using the synchronization error after the determination unit determines that there is no error in the error determination of the communication frame.   The receiver according to claim 1, wherein the correction unit obtains the synchronization error using the time information and a time required from the start of reception of the communication frame to acquisition of the time information.   The reception according to claim 1 or 2, wherein when the determination unit determines that there is an error in determining an error in the communication frame, the correction unit stops correction based on time information stored in the communication frame. Machine.   When the determination unit determines that there is an error in the error determination of the plurality of communication signals, the correction unit uses the synchronization error to determine the time of the own device if the synchronization error is within a predetermined value. The receiver according to claim 1 or 2, wherein correction is performed. A storage unit for storing the synchronization error;
The receiver according to claim 1, wherein the correction unit updates the synchronization error stored in the storage unit to the new synchronization error every time a new synchronization error is obtained. In a wireless communication system comprising: a roadside communication device in which a first time zone for performing wireless transmission is assigned in a time division manner; and a mobile communication device for performing wireless transmission in a second time zone other than the first time zone.
Each said communication apparatus is provided with the receiver of Claims 1-5, The radio | wireless communications system characterized by the above-mentioned.

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