JP2013055582A - Wireless apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of synchronization.SOLUTION: A wireless apparatus 2 which counts a value of a timer 22b on the basis of a clock signal outputted from a clock oscillator 25 comprises: a receiver 23 for outputting a reference signal which periodically occurs on the basis of a signal received from the outside; an error detector 22c which detects an error of the value of the timer 22b on the basis of the reference signal outputted from the receiver 23; and a timer corrector 22d which corrects the value of the timer 22b on the basis of the error detected by the error detector 22c. The timer corrector 22d corrects the value of the timer at intervals shorter than a cycle of the occurence of the reference signal.

Description

  The present invention relates to a wireless device suitably used as a roadside communication device for an intelligent transport system (ITS), for example.

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, vehicle safety has been achieved by receiving information from infrastructure devices installed on roads or exchanging information between vehicles and utilizing these information. An intelligent road traffic system that improves the above has been studied (for example, see 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 JP 2010-206354 A

In the above-mentioned intelligent road traffic system, road-to-vehicle communication, road-to-road communication, road-to-road communication, and road-to-step communication, including road-to-vehicle communication, can be carried out between roads within a limited frequency band. In order to perform each communication between road vehicles and between vehicles, a multi-access method by time division multiple access (TDMA) that divides the time for communication and provides a time slot dedicated to transmission of the roadside communication device. Adopted.
In the multi-access scheme based on TDMA, transmission time slots are normally set periodically for each communication device. For this reason, each roadside communication device performs transmission using its own transmission time slot that is set periodically, and at other times it receives transmission signals from other roadside devices or in-vehicle communication devices. Do.

  When the above system adopts the multi-access method by TDMA, if the time is not accurately synchronized between roadside communication devices and between the roadside communication device and the in-vehicle communication device, the time slot that each roadside communication device and the in-vehicle communication device grasps There is a possibility that a difference occurs in the start time of the communication, causing interference between the communication devices.

  Therefore, the moving in-vehicle communication device is synchronized with the roadside communication device by correcting the time of the own device based on the transmission signal from the nearby roadside communication device, and the roadside communication device corrects the time of the own device. It is possible to synchronize with other roadside communication devices. If each roadside communication device is synchronized, the in-vehicle communication device can be synchronized with other roadside communication devices by synchronizing with a nearby roadside communication device.

  Here, in order to synchronize each roadside communication device with each other, it is conceivable to use a signal of GNSS (Global Navigation Satellite Systems) such as GPS (Global Positioning System).

  For example, a 1PPS signal generated by a GPS receiver is a pulse signal that becomes High once every second. Since this 1PPS signal is based on a signal sent from a GPS satellite equipped with a transmitter such as rubidium, it is a highly accurate signal of 1 ppm level.

  Here, Non-Patent Document 2 discloses a method of generating a high-accuracy 10 MHz reference clock by taking a 1 PPS signal generated by a GPS receiver into a PLL circuit. If a high-accuracy clock can be generated inside the roadside communication device, each roadside communication device performs time correction with the 1PPS signal, and also during each 1PPS signal generation cycle (1 second), A high-accuracy clock can suppress time errors between the roadside communication devices.

  However, if the clock accuracy of the clock signal itself is to be increased by the method described in Patent Document 2, a PLL circuit or the like is separately required, leading to an increase in cost.

  Therefore, the present invention aims to improve the accuracy by correcting the timer (time) of the wireless device (roadside communication device) instead of increasing the clock accuracy itself.

(1) The present invention is a radio that counts the value of a timer based on a clock signal output from a clock oscillator, and outputs a reference signal that is periodically generated based on a signal received from the outside. And an error detection unit for detecting an error in the timer value based on the reference signal output from the receiver, and a correction for the timer value based on the error detected by the error detection unit. A timer correction unit, wherein the timer correction unit corrects the value of the timer at an interval shorter than a cycle in which the reference signal is generated.

  According to the present invention, even if the accuracy of the clock oscillator is low, the timer error is reduced by correcting the timer, and the timer value can be increased even if the accuracy of the clock oscillator remains low.

(2) A correction table that defines correction amounts at a plurality of correction timings for each error level is provided, and the timer correction unit determines an error level based on an error detected by the error detection unit. It is preferable that the correction amount is obtained at each correction timing by referring to the correction table based on the error level, and the timer is subjected to correction for the obtained correction amount at each correction timing. In this case, correction can be performed with simple hardware.

(3) In the timer correction unit, it is preferable that a correction amount for correcting the timer value is a value equal to or less than half of a maximum allowable error of the timer value. In this case, the correction amount at one time becomes relatively small, and the error of the timer value immediately before the correction is difficult to increase.

(4) It is preferable that the timer correction unit corrects the value of the timer based on a plurality of errors detected by the error detection unit. In this case, more appropriate correction can be performed.

(5) The receiver is preferably a GNSS receiver. In this case, a highly accurate signal from the GNSS satellite can be used.

(6) The clock generator has a clock accuracy that is low enough to cause the timer to generate an error exceeding the maximum allowable error of the timer value during one cycle in which the reference signal is generated. Is preferred. Even if the clock generator has a clock accuracy that is low enough to cause the timer to generate an error that exceeds the maximum allowable error of the timer value during one cycle in which the reference signal is generated, the timer correction is performed. Thus, the error of the timer can be suppressed below the maximum allowable error.

(7) It is preferable to include a communication control unit that includes time information based on the value of the timer in a transmission signal for transmission. In this case, the receiving side of the time information can obtain highly accurate time information, and can synchronize the time with the wireless device that transmitted the time information with high accuracy.

  According to the present invention, even if the accuracy of the clock oscillator is low, it is possible to increase the accuracy of the timer value.

It is a schematic perspective view which shows the whole structure of the intelligent transport system (ITS) which concerns on one Embodiment of this 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 explanatory drawing of the error which arises in a timer. It is explanatory drawing of the correction method of the error of a timer. It is explanatory drawing of the correction method of the error of a timer. It is a figure which shows a correction table.

[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 (radio device) 2, an in-vehicle communication device (radio device) 3 (see FIG. 3), a central device 4, and in-vehicle communication. A vehicle 5 on which the machine 3 is mounted, and a roadside sensor 6 including a vehicle detector, a monitoring camera, and the like 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 is composed of a vehicle sensor for ultrasonically sensing the vehicle 5 passing underneath, or a monitoring camera for photographing road traffic conditions in time series, and the sensing information and image data are transmitted via the communication line 7. To the central device 4.
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.

[Wireless communication systems, etc.]
In an intelligent road traffic system, a plurality of roadside communication devices (radio devices) 2 installed at each of a plurality of intersections constituting a wireless communication system are wirelessly communicated with an in-vehicle communication device 3 of a vehicle traveling around the roadside communication device. (Communication between road vehicles (vehicle roads)) 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.
An in-vehicle communication device (radio device) 3 that also constitutes a wireless communication system performs wireless communication with the roadside communication device 2 and also wirelessly communicates with other in-vehicle communication devices 3 using a carrier sense method (inter-vehicle communication). Is possible.

  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”.

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 assigned 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 radio frames of the two roadside communication devices 2A and 2B. The roadside communication device 2A has a first slot SL1 with slot number 2 indicated by hatching in the roadside communication device 2B. The first slot SL1 of slot number 1 indicated by hatching is assigned.

  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, a plurality of roadside communication devices 2 set their own local time (time indicated by their own timer) based on a signal from a GNSS satellite such as a GPS satellite, so that each roadside communication device 2 The timer (local time) is set to the correct state (GPS (GNSS) synchronization). Thereby, the timing of the radio frame of each roadside communication device 2 matches. This GPS (GNSS) 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 control unit 22 that performs processing such as communication control, and a GPS (GSNN) receiver 23. ing.
The in-vehicle communication device 3 includes a wireless communication unit 31 to which an antenna 30 for wireless communication is connected, a control unit 32 that performs processing such as communication control, a storage unit 33 that stores information necessary for communication, It has.

  The control unit 23 of the roadside communication device 2 includes a communication control unit 22a, a timer 22b, an error detection unit 22c, a timer correction unit 22d, a correction table 22e, and the like.

  The communication control unit 22a executes processing related to communication control in the wireless communication unit 21, and controls, for example, timing of wireless transmission (transmission in SL1) by the wireless communication unit 21. The communication control unit 22a determines the timing of wireless transmission (transmission in SL1) by the wireless communication unit 21 based on the value (local time) indicated by the timer 22b.

  The timer 22 b counts up (increments) based on a clock signal generated by a clock oscillator (crystal oscillator) 25 connected to the control unit 23. Therefore, the accuracy of the timer 22b depends on the accuracy of the clock signal of the oscillator 25.

  As shown in FIG. 4, the value of the timer 22b is reset to 0 in a 1-second cycle. After the reset, the timer 22b is ideally based on the clock signal generated by the oscillator 25 until the next reset (ideally, ) One count up (increment) every 1 μs. The 1-second cycle is reset by a pulse rising edge (generated every second) of the 1PPS signal generated by the GPS receiver 23 based on a signal received from a GPS satellite.

The period of the 1PPS signal has a high accuracy of 1 ppm level. Therefore, when each roadside communication device 2 is reset by the 1PPS signal, time synchronization is achieved with very high accuracy. However, when the accuracy of the oscillator 25 is low, for example, when the accuracy of the oscillator 25 is ± 20 ppm, an error of ± 20 μs at maximum occurs in one second.
Therefore, a difference of 40 μs at maximum occurs between the timers 22b of the two roadside communication devices 2 immediately before the 1PPS signal is obtained.

  For example, as shown in FIG. 4, when there is no error in the clock signal of the oscillator 25, immediately after the timer 22b acquires the 1PPS signal (for example, after 50 nanoseconds), the timer value becomes 1,000,000. Should be. On the other hand, if the clock signal of the oscillator 25 has an error delayed by about 3 ppm, the timer value becomes 999,997 immediately after the timer 22b acquires the 1PPS signal. Conversely, if there is an error that is as early as 2 ppm in the clock signal of the oscillator 25, the timer value becomes 1,000,002 immediately before the timer 22b acquires the 1PPS signal.

  Thus, if the accuracy of the oscillator 25 is ± 20 ppm, the timer value can take a value in the range of 999,980 to 1,000,020 immediately before the timer 22b acquires the 1PPS signal.

However, when the value required as the synchronization accuracy between the roadside communication devices 2 is higher than the error (40 μs) (for example, when the maximum allowable synchronization error between the roadside communication devices is 16 μs), A low-precision oscillator 25 that causes a difference of up to 40 μs in the timer 22b cannot be used.
That is, in the plurality of roadside communication devices 2, when a difference of up to 40 μs occurs in the respective timers 22, the difference in radio frame timing (transmission timing) determined by the timer 22 also occurs up to 40 μs. The synchronization error between the machines 2 exceeds the maximum allowable synchronization error (16 μs).
However, increasing the accuracy of the clock signal output from the oscillator 25 causes a significant cost increase.

  Therefore, the control unit 22 detects the error of the timer 22b by the error detection unit 22 and corrects the error of the timer 22b by the timer correction unit 22d while using the oscillator 25 having a relatively low accuracy. To ensure accuracy. Thereby, the synchronization precision between the some roadside communication apparatuses 2 is raised.

The error detector 22 detects an error in the value of the timer 22b based on a value immediately before the timer 22b is reset by the 1PPS signal (reference signal). If there is no error immediately before the timer 22b is reset by the 1PPS signal, the timer value should be 1,000,000 (theoretical value). Therefore, by taking the difference between the actual value and the theoretical value of the timer at this time, it is possible to detect a timer error generated in one second due to a clock signal accuracy error.
That is, the timer error can be detected based on the 1PPS signal that is the reference signal.

  Since timer correction described later is performed, the timer correction value + the detected timer error becomes the timer error actually generated in one second.

The error detection unit 22c calculates the average of the “timer correction value + detected timer error” obtained as described above or the “timer correction value + detected timer error” for the past multiple times as the next 1PPS signal. It is determined as an error amount (error level) to be corrected until it occurs (until 1 second later), and is given to the timer correction unit 22d.
A more appropriate error amount (error level) can be obtained by averaging the past multiple times as the error amount to be corrected.

  The timer correction unit 22d divides the correction for the error amount (error level) received from the error generation unit 22c into small or small increments until the next 1PPS signal is generated (after 1 second). To do. That is, the timer 22b is corrected at an interval shorter than 1 second, which is a cycle in which the 1PPS signal that is the reference signal is generated.

For example, when the error amount to be corrected is a delay of 3 μs (3 counts of the timer 22b), as shown in FIG. 5, during the 1 second until the next pulse rising of the 1PPS signal, 3 It is sufficient to correct by performing two counts up (double increment).
Further, when the error amount to be corrected is advanced by 2 μs (2 counts of the timer 22b), as shown in FIG. 6, during the 1 second until the next pulse rise of the 1PPS signal, 2 It may be corrected by not counting up (incrementing) when counting up (incrementing) times.

  By correcting the error amount to be corrected little by little in a plurality of times during the 1 second until the next 1PPS signal (the period in which correction is performed), the correction amount for one time becomes small. Therefore, the fine correction is gradually added before the error of the value of the timer 22b becomes large.

  Further, by making the correction amount for one time very small, such as 1 count (or 2 counts) of the timer 22b, the error in the value of the timer 22b is 1 until the next 1PPS signal. Alternatively, even when only about 2 counts (1 or 2 μs) are generated and the oscillator 25 has low accuracy, the value of the timer 22b can be maintained with high accuracy. As a result, synchronization between the plurality of roadside communication devices 2 is also highly accurate.

Here, when the maximum allowable synchronization error between the roadside communication devices 2 is 16 μs, the maximum allowable error of the value of the timer 22b is also 16 μs. The amount of correction performed once by the timer correction unit 22d is preferably a value that is half or less of the maximum allowable error of the value of the timer 22b. In this case, correction is performed with a small correction value that is not more than half of the maximum allowable error of the value of the timer 22b, so that the timer error immediately before the correction is difficult to increase. Therefore, when the maximum allowable synchronization error between the roadside communication devices 2 is 16 μs, the correction amount for one time is preferably 8 μs or less, and more preferably 4 μs or less which is 1/4 or less. More preferably, the correction amount for one time is about 1 or 2 counts (1 or 2 μs) as described above.
It is preferable that the correction timing is substantially equally spaced until the next 1PPS signal.

  In order to easily perform the above correction, the timer correction unit 22d refers to the correction table 22e based on the error amount (error level) to be corrected, and the correction timing up to the next 1PPS signal and each correction timing. Get the correction amount at.

  As shown in FIG. 7, the correction table 22e has a plurality of correction timings in one second from a certain 1PPS signal to the next 1PPS for each error amount (error level) to be corrected (9 in every 100 ms in FIG. 7). The correction amount is defined for each. For example, in FIG. 7, if the error amount (error level) to be corrected is “−5” (5 μs delay), the respective correction amounts at 100 ms, 300 ms, 500 ms, 700 ms, and 900 ms after reset are as follows. “1” (1 μs; 1 count) is set, and the correction amount after 200 ms, 400 ms, 600 ms, and 800 ms after reset is set to “0”.

Therefore, if the error amount (error level) to be corrected is “−5”, the timer correction unit 22d refers to the column “−5” of the correction table 22e, and acquires the correction timing and the correction amount at each timing. To do.
Then, the timer correction unit 22 sets the normal count-up amount to 1 at the time of counting up after 100 ms, 300 ms, 500 ms, 700 ms, and 900 ms after reset according to the timing and correction amount acquired from the correction table 22. Then, 2 counts up (double increment) by adding the correction amount “1” is performed. In addition, at the time of count-up after 200 ms, 400 ms, 600 ms, and 800 ms after reset, one count up which is a normal count-up amount is performed.

  If the correction amount at one correction timing is “−1”, the correction is performed by not counting up at that timing. Further, if the correction amount at one correction timing is “−2”, correction is performed by decrementing (decrementing) by 1 when counting up at that timing.

Thus, by using the correction table 22b and correcting the timer by counting up / down the timer, an increase in circuit scale for correction can be suppressed.
For example, when there is a delay of 3 μs in the timer 22b, a division of 1,000,000 / 999,997 is performed to obtain an error per count, and an attempt is made to correct the error every count. In order to correct floating point errors when a floating point operation (real number operation) is required for this, or when the value of the timer 22b is set to a floating point number (real number) instead of an integer, The circuit scale tends to be large. However, if the correction table 22e is provided, floating point arithmetic is not necessary, and it is sufficient to secure a storage area for the correction table 22e, so that an increase in circuit scale can be suppressed.
Further, since the correction amount for one time is performed by adjusting the count-up amount at the normal count-up time of the timer (timing every 1 μs), the addition of hardware for correction can be reduced. Therefore, high accuracy can be achieved with a slight increase in cost.

In FIG. 7, for the sake of convenience of description, the correction amount within the range of −10 μs to 10 μs for the error amount to be corrected is shown, but naturally the error amount to be corrected is set within the range of −20 μs to 20 μs. Good. The correction timing does not have to be every 100 ms, but may be another interval (for example, every 50 ms).
The correction table 22b does not need to specify the time of the correction timing, and only the correction amount corresponding to a plurality of correction timings (the first correction timing to the ninth correction timing) may be specified. . In this case, the correction timing time (100 ms, 200 ms) may be separately stored outside the table 22b, or the timing may be adaptively controlled.

  The communication control unit 22a performs radio transmission in the first slot SL1 assigned to the own device based on the local time indicated by the timer 22b whose accuracy is ensured by the timer correction. In other words, the communication control unit 22a causes the wireless communication unit 21 to perform wireless transmission when the value of the timer 22b (local time) is the timing for transmission using the time slot SL1 assigned to the own device.

  The timers 22 of the respective roadside communication devices 2 are simultaneously reset based on the 1PPS signal, and the timer 22b can be synchronized with high accuracy even during 1 second (self-running section) until the next 1PPS signal by the timer correction. Will be.

The communication control unit 22a of the roadside communication device 2 generates slot information including time information based on the value of the timer 22b, and transmits a transmission signal including the slot information from the wireless communication unit 21 (broadcast transmission).
The time information included in the slot information is a time shared between the roadside communication device 2 and the in-vehicle communication device 3. In addition to the time information, the slot information includes information for identifying the first slot SL1 used by the roadside communication device 2. Since the vehicle-mounted communication device 3 is time synchronized by sharing the time with the roadside communication device 2, the transmission timing of the first slot SL1 used by the roadside communication device 2 is grasped based on the slot information. can do.

  As described above, since the synchronization between the roadside communication device 2 and the vehicle-mounted communication device 3 is performed in a state where the synchronization is achieved with high accuracy in the plurality of roadside communication devices 2, the slot timing shift as shown in FIG. Therefore, interference between the transmission signal of the roadside communication device 2 and the transmission signal of the in-vehicle communication device 3 can be prevented.

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

  For example, the reference signal is not limited to a 1PPS signal based on a highly accurate GNSS signal, and may be another signal. That is, any signal can be adopted as long as the reference signal is an external signal that can be relied on as a reference.

2 roadside communication device 3 vehicle-mounted communication device 22 control unit 22a communication control unit 22b timer 22c error detection unit 22d timer correction unit 22e correction table 23 GPS receiver 25 clock oscillator

Claims (7)

A radio that counts a timer value based on a clock signal output from a clock oscillator,
A receiver that outputs a reference signal periodically generated based on a signal received from the outside;
An error detector for detecting an error in the value of the timer based on the reference signal output from the receiver;
A timer correction unit that corrects the value of the timer based on the error detected by the error detection unit;
With
The radio correction unit, wherein the timer correction unit corrects the value of the timer at an interval shorter than a cycle in which the reference signal is generated. With a correction table that specifies the correction amount at multiple correction timings for each error level,
The timer correction unit is
Based on the error detected by the error detector, an error level is determined,
Refer to the correction table based on the determined error level, obtain the correction amount at each correction timing,
The wireless device according to claim 1, wherein correction is performed for the acquired correction amount on the timer at each correction timing. The wireless device according to claim 1, wherein the timer correction unit corrects the timer value once by a value that is half or less of a maximum allowable error of the timer value. The wireless device according to any one of claims 1 to 3, wherein the timer correction unit corrects the value of the timer based on a plurality of errors detected by the error detection unit. The wireless device according to claim 1, wherein the receiver is a GNSS receiver. The clock generator has a clock accuracy that is low enough to cause the timer to generate an error that exceeds a maximum allowable error of the timer value during one period in which the reference signal is generated. The wireless device according to any one of 5. The wireless device according to any one of claims 1 to 6, further comprising a communication control unit configured to transmit time information based on the value of the timer in a transmission signal.