JP5477743B2 - Communication apparatus and communication method - Google Patents

Description

The present invention relates to a communication device suitable for communication between vehicles such as automobiles, and a communication method applied to the communication device.

  In recent years, wireless communication (hereinafter referred to as inter-vehicle communication) between vehicles such as automobiles has been performed, and data such as the driving state of each vehicle is transmitted to nearby vehicles to prevent traffic accidents. A safe driving support system has been proposed and various experiments have been conducted.

  As a communication method when performing vehicle-to-vehicle communication, for example, a CSMA (Carrier Sense Multiple Access) method applied to a wireless LAN or the like may be applied. In this CSMA method, the state of the prepared transmission channel is monitored for a certain period by the communication device of each vehicle, and when it is determined that communication is in progress, transmission is not performed and communication is determined not being performed. Is a method for transmitting packets. When this CSMA method is applied to inter-vehicle communication, relatively good communication is possible because the number of nearby vehicles is limited when driving on a relatively congested road. .

  However, the CSMA method has a problem of a hidden terminal that cannot directly wirelessly communicate with its own communication device, and a problem of a decrease in communication quality due to an increase in traffic due to transmission of a control message. For this reason, in the inter-vehicle communication, an autonomous distributed TDMA (Time Division Multiple Access) method has attracted attention. In this autonomous distributed TDMA system, a frame period is determined, and a packet is transmitted using one slot in the frame period. However, in the case of inter-vehicle communication, basically there is no base station that transmits a control signal or the like, so there is a problem how to synchronize the frame period with the communication device of another vehicle.

  FIG. 11 is an example of a state in which this inter-vehicle communication is performed. In this example, a terminal is mounted on a vehicle that is a mobile body, and vehicle-to-vehicle communication in four groups of terminal groups A, B, C, and D that are communicating with a plurality of terminals is not The state being performed at the position is shown. Within each terminal group, a frame period is determined by the autonomous distributed TDMA system, and wireless communication is performed in slot units within the frame period.

Here, a configuration example of a terminal device that performs communication by the conventional autonomous distributed TDMA scheme will be described.
FIG. 12 is a diagram illustrating a configuration example of a communication apparatus to which a conventional autonomous distributed timing synchronization technique is applied.
The configuration will be described with reference to FIG. 12. In this example, the transmission / reception antenna 101 is provided, and the transmission / reception antenna 101 is selectively connected to the radio reception unit 103 and the radio transmission unit 104 via the changeover switch 102. It is as. The wireless transmission unit 104 transmits the transmission packet supplied from the data generation unit 112 in synchronization with the clock generated by the clock generation unit 111. The wireless reception unit 103 supplies the received packet to the shift amount acquisition unit 105 and also supplies it to the phase difference detection unit 106.

  The shift amount acquisition unit 105 acquires shift amount information that is information included in the packet received by the reception unit 103. This shift amount is information given by the transmission source of the packet, and is acquired by all receivable communication devices. The acquired shift amount information is supplied to the adder 107.

  The phase difference detection unit 106 detects a phase difference between the timing of the clock pulse supplied from the clock generation unit 111 and the timing at which the reception unit 103 receives a packet. Information on the detected phase difference is supplied to the adder 107.

The adder 107 adds the shift amount information acquired by the shift amount acquisition unit 105 and the phase difference information acquired by the phase difference detection unit 106 to obtain timing error information, and supplies the timing error information to the memory 108. And memorize it. The memory 108 stores timing error information obtained by adding the phase difference detected by the phase difference detection unit 106 and the shift amount for each packet transmitted from each of a plurality of terminals (communication devices). .
The timing error information here is the difference between the timing of the pulse output from the clock generator 111 and the timing at which each communication device capable of receiving a signal close to the local station is expected to transmit a packet next time. Information.

  The timing error information stored in the memory 108 is sent to the average calculation unit 109. The average calculation unit 109 calculates an average value of timing errors calculated for each of the plurality of communication apparatuses accumulated in the memory 108.

  The average value of the timing errors calculated by the average calculation unit 109 is sent to the calibration unit 110. The calibration unit 110 generates a calibration output based on the average value of timing errors, and supplies the calibration output to the clock generation unit 111 and the data generation unit 112.

  The data generation unit 112 generates a transmission packet including the instructed calibration output as timing information, supplies the generated transmission packet to the wireless transmission unit 104, and the transmission / reception antenna 101 connected to the wireless transmission unit 104. Wirelessly transmit to nearby communication devices. The clock generation unit 111 also instructs the timing for wireless transmission.

The flowchart in FIG. 13 shows the communication operation in this communication apparatus. This flowchart is an operation for each communication device to ensure the communication timing with the surrounding communication devices and maintain the synchronization.
First, the communication device observes the communication timing of the peripheral device based on beacons, data packets, and the like transmitted from the peripheral communication device for one period which is the minimum unit of communication of each device (step S1). The observation of the communication timing of the peripheral device corresponds to the processing in the average calculation unit 109. Then, the communication timing of itself is corrected based on statistical values such as the distribution and average of the communication timings of the peripheral communication devices (step S2). This correction process corresponds to the process in the calibration unit 110. Then, the communication timing information corrected in step S2 is added to the transmission packet, and notification is made to surrounding communication devices (step S3). Then, the process returns to step S1.

Each communication device performs the processing shown in the flowchart of FIG. 13 so that communication timing can be synchronized with neighboring communication devices, and communication can be satisfactorily performed at the synchronized timing.
Patent Document 1 describes an example of communication technology that performs such synchronization processing.

JP 2008-22307 A

In the communication apparatus having the configuration shown in FIG. 12, timing information is notified and synchronized as shown in FIG. Can be synchronized. However, assuming a state in which vehicle-to-vehicle communication is actually performed, for example, when driving on a congested road, it is assumed that a large number of communication devices exist in the vicinity. In this case, it is difficult to completely synchronize all the communication apparatuses due to various factors only by performing the processing shown in the flowchart of FIG.
That is, when the number of communication devices is too large, there is a problem that timing synchronization of the entire network is not completed and convergence to an asynchronous state occurs only by timing information notification as described in FIG.

  As another synchronization process for solving this problem, for example, a GPS (Global Positioning System) signal, which is a positioning time information signal transmitted from a satellite, is received and a communication timing set by a communication device is set. May be set to a timing synchronized with the time obtained from the received positioning signal.

  However, in the real environment, the accuracy of the time obtained from the GPS signal is degraded due to various factors. One of them is a decrease in the positioning rate due to shielding such as buildings, forests, and tunnels. In general, the accuracy of an internal clock mounted on a GPS receiver is not high, and when positioning cannot be performed for several tens of seconds, the accuracy is greatly deviated from the synchronization accuracy required for inter-vehicle communication. In addition, the accuracy of GPS signals is not always guaranteed, and the positioning and weather of GPS satellites, and in the case of vehicle-to-vehicle communication, are affected by fading, and are therefore subject to significant time accuracy. Degradation can occur.

Also, those that perform synchronization processing by notifying timing information are designed to improve performance on the premise that “data packets can be received without errors”. In situations where data packets cannot be received correctly, other terminals It is difficult to synchronize with. That is, in order to realize smooth timing synchronization with the configuration of FIG. 12, it is essential to be able to acquire the “shift amount” included in the data packet. However, in an environment where timing synchronization is not sufficiently performed, such as immediately after the start of the network, collision between data packets is inevitable, and therefore various improvements based on these known techniques may not function effectively.
Furthermore, as another problem, it is known that an error that depends on individual differences or environment occurs in an oscillator that manages the time possessed by each terminal (for example, the oscillator included in the clock generation unit 111 in FIG. 12). ing. When the time advance based on the oscillator differs depending on the terminal, a synchronization error occurs, and the autonomous distributed TDMA may not function.

  The present invention has been made in view of the above points, and when performing autonomous distributed synchronous communication applicable to inter-vehicle communication or the like, each communication device regardless of whether the wireless communication state with other communication devices is good or bad. The purpose of this is to make it possible to quickly synchronize communication timing.

The present invention is applied to a communication apparatus that transmits and receives a wireless signal bidirectionally with other communication apparatuses in the vicinity. Based on the received signal of the radio signal transmitted from the other communication device, the communication timing managed by the own communication device is set. Then, an OFDM digital broadcast signal is received, and a guard interval is detected from the received digital broadcast signal. Further, the positioning signal is received, and the positioning time information or timing information included in the received positioning signal is detected. Then, based on the detection timing of the guard interval, to correct the communication timing to be set. Here, when the positioning signal can be received, the time information or timing information included in the received positioning signal is included in the wireless signal to be transmitted for a certain period after the positioning signal can be received, and the positioning signal is transmitted. When reception of the signal is not successful, processing for correcting the communication timing is executed based on the detection timing of the guard interval.

  According to the present invention, a high-speed and stable synchronization state can be realized in a communication system that requires timing synchronization such as the autonomous distributed TDMA system. In particular, the present invention is expected to have a stable effect even in an environment where the movement of a vehicle equipped with a communication device such as inter-vehicle communication is remarkable. The present invention is particularly expected to be used in a safe driving support system in ITS.

It is a block diagram which shows the structural example of the communication apparatus by the 1st Embodiment of this invention. It is explanatory drawing which showed the example of 1 symbol of an OFDM signal. It is the flowchart which showed the example of a correction process by the 1st Embodiment of this invention. It is explanatory drawing which showed the example of each signal by the 1st Embodiment of this invention. It is explanatory drawing which shows the example of the frame structure by the 1st Embodiment of this invention. It is a flowchart which shows the example of a synchronous process with the other terminal by the 1st Embodiment of this invention. It is a characteristic view which shows the change of the synchronous state by the 1st Embodiment of this invention. It is a block diagram which shows the structural example of the communication apparatus by the 2nd Embodiment of this invention. It is a block diagram which shows the structural example of the communication apparatus by the 3rd Embodiment of this invention. It is the flowchart which showed the example of a timing notification process by the 3rd Embodiment of this invention. It is explanatory drawing which shows an example of a mobile body network. It is a block diagram which shows the structural example of the conventional communication apparatus. It is the flowchart which showed the example of the conventional timing notification process.

Embodiments of the present invention will be described in the following order.
1. 1st Embodiment (FIGS. 1-7)
2. Second embodiment (FIG. 8)
3. Third embodiment (FIGS. 9 and 10)
4). Modified example

[1. First Embodiment]
An example of the first embodiment of the present invention will be described with reference to FIGS. 1 to 7, parts corresponding to those in FIGS. 12 and 13 described as the prior art are denoted by the same reference numerals.
In the embodiment described below, an example applied to what performs so-called vehicle-to-vehicle communication that performs communication between communication devices mounted on a vehicle such as an automobile will be described. The present invention is not limited to this, and can be applied to communication systems using various types of communication devices.
In the present embodiment, the communication device is mounted on a vehicle (mobile body) such as an automobile. And each communication apparatus communicates in the mobile communication environment which cannot use a base station. Specifically, it is a communication system that does not have a base station, and performs two-way communication with other communication devices within a range of, for example, a radius of about several hundred meters centered on its own (own) communication device. . The communicable distance is an example, and a configuration for communicating with a communication device farther away may be used. As a wireless method in which a communication device performs wireless communication with other communication devices, an autonomous distributed TDMA method is applied, and a communication device autonomously performs synchronization processing without providing a so-called base station.

FIG. 1 is a diagram illustrating a configuration example of a communication apparatus according to the present embodiment.
The communication apparatus according to the present embodiment includes a transmission / reception antenna 101, and the transmission / reception antenna 101 is selectively connected to the wireless reception unit 103 and the wireless transmission unit 104 via a changeover switch 102. The wireless transmission unit 104 is a wireless signal transmission unit that performs processing for transmitting the transmission packet supplied from the data generation unit 112 in synchronization with the clock generated by the clock generation unit 111. The wireless reception unit 103 is a wireless signal reception unit that performs processing of supplying the received packet to the shift amount acquisition unit 105 and supplying the received packet to the phase difference detection unit 106. The clock generation unit 111 functions as a communication timing setting unit that sets communication timings such as transmission and reception with clock pulses for time management supplied to each unit.

  The shift amount acquisition unit 105 acquires shift amount information that is information included in the packet (or beacon) received by the reception unit 103. This shift amount or time information is information given by the packet transmission source, and is acquired only when the packet can be received without error. The acquired shift amount information or time information is supplied to the adder 107.

  The phase difference detection unit 106 detects a phase difference between the timing of the clock pulse supplied from the clock generation unit 111 and the timing at which the reception unit 103 receives a packet. This phase difference information is information detected by each communication device at the start of packet reception, and is acquired by all communication devices that detected the start of reception regardless of whether or not the packet was received without error. The Information on the detected phase difference is supplied to the adder 107. The clock generator 111 includes a clock generator 111a, which is an oscillator, and a counter 111b that generates a clock pulse by counting the oscillation clock output from the clock generator 111a, and outputs a pulse as a count output of the counter 111b. , And supplied to each unit as a fixed-period clock pulse for controlling communication.

The adder 107 adds the shift amount or time information information acquired by the shift amount acquisition unit 105 and the phase difference information acquired by the phase difference detection unit 106 to obtain timing error information, and the timing error information is stored in the memory. It supplies to 108 and memorize | stores it. The memory 108 stores a timing error obtained by adding the phase difference detected by the phase difference detection unit 106 and the information of the shift amount or time information for each packet transmitted from each of a plurality of terminals (communication devices). Information is stored.
The timing error information here is the difference between the timing of the pulse output from the clock generator 111 and the timing at which each communication device capable of receiving a signal close to the local station is expected to transmit a packet next time. Information.

  The timing error information stored in the memory 108 is sent to the average calculation unit 109. The average calculation unit 109 calculates an average value of timing errors calculated for each of the plurality of communication apparatuses accumulated in the memory 108.

The average value of the timing errors calculated by the average calculation unit 109 is sent to the calibration unit 110. The calibration unit 110 generates a calibration output based on an average value of timing errors and an output of a difference detector 127 described later, and supplies the calibration output to the counter 111b in the clock generation unit 111, and also generates a data generation unit. 112. The shift amount acquisition unit 105, the phase difference detection unit 106, the adder 107, the memory 108, the average calculation unit 109, and the calibration unit 110 function as a timing correction unit and are managed by a clock generation unit 111 that is a timing management unit. Processing for correcting the timing of (pulse) is performed.
The calibration output generated by the calibration unit 110 is supplied to the data generation unit 112. The data generation unit 112 generates a transmission packet including the instructed calibration output as timing information, supplies the generated transmission packet to the wireless transmission unit 104, and the transmission / reception antenna 101 connected to the wireless transmission unit 104. Wirelessly transmit to nearby communication devices. The clock generation unit 111 also instructs the timing for wireless transmission.
The basic configuration so far is the same as the configuration shown in FIG. 12 as a conventional example.

The communication apparatus according to the present embodiment has a configuration for receiving a digital broadcast signal, and also supplies the calibration component 110 with the detection status of the synchronization component obtained by receiving the digital broadcast signal.
That is, an antenna 121 for receiving a terrestrial digital television broadcast signal is provided, and the antenna 121 is connected to the wireless reception unit 122. Then, the wireless reception unit 121 performs reception processing of the frequency at which the digital television broadcast signal is transmitted. The digital television broadcast signal received by the wireless reception unit 121 is a wireless signal transmitted as an OFDM (Orthogonal Frequency Division Multiplexing) signal that transmits data while being distributed to a plurality of subcarriers, for example, in the UHF band.

  The OFDM signal received by the wireless receiver 121, which is an OFDM signal receiver, is directly supplied to the complex correlation calculator 123 and is also supplied to the complex correlation calculator 123 via the delay circuit 124. The guard interval periodically included in is detected.

An OFDM signal is formed by continuously connecting signals of a predetermined length called symbols, and includes guard intervals (guard symbols) at a constant period. That is, as shown in FIG. 2, one symbol of the OFDM signal is composed of a combination of an effective symbol containing data and a guard symbol for interference suppression, and one symbol is 1.134 ms. The effective symbol length and the guard symbol length are standardized by the standard. The guard symbol is determined as a signal obtained by copying a part of the end of the effective symbol.
For this reason, if the signal in the guard symbol interval is cut out and the signal is overlapped with the interval at the end of the effective symbol, the signal is completely matched.

  The complex correlation calculator 123 shown in FIG. 1 performs processing equivalent to cutting out the signal in the guard symbol period and superimposing the signal at the end of the effective symbol, and the delay circuit 124 performs delay processing therefor. Is done. The detection signal from the complex correlation calculator 123 is supplied to the detector 126 via the low-pass filter 125 and subjected to detection processing to obtain period information at 1.134 ms intervals. The detector 126 detects the peak position of the output subjected to the complex correlation calculation by the complex correlation calculator 123.

  The acquired period information is supplied to the difference detector 127 and also supplied to the memory 128 for storage. The memory 128 stores the count value of the clock pulse at the peak position, and the difference detector 127 compares the stored count value with the count value of the clock pulse at the current peak position output from the detector 126. Detect differences. The difference count value information is supplied from the difference detector 127 to the calibration unit 110.

The calibration unit 110 generates a calibration output from the detection information of the guard interval component of the digital broadcast signal and the average timing error calculated by the average calculation unit 109, and supplies the calibration output to the clock generation unit 111. The pulse output timing is corrected. In the example of FIG. 1, the calibration output of the calibration unit 110 is supplied to the counter 111b in the clock generation unit 111 to correct the generation timing of the clock pulse obtained by counting the clock.
In addition, the calibration output supplied from the calibration unit 110 to the data generation unit 112 is also a calibration output using detection information of the guard interval component, and the timing information included in the transmission packet corresponds to the timing output included in the neighboring communication device. For wireless transmission.

FIG. 3 is a flowchart showing the execution state of the correction process of the clock pulse generated by the clock generation unit 111 based on the calibration output output from the calibration unit 110.
The calibration unit 110 (or its control unit) determines whether or not the wireless reception unit 122 is currently ready to receive a digital broadcast signal (step S11). When the digital broadcast signal can be received, the detection information of the guard interval component is received from the difference detector 127 (step S12), and the timing information of the guard interval information and the average calculation unit 109 calculate it. A calibration output is generated from the average value of the timing errors, and a clock pulse correction process generated by the clock generation unit 111 using the generated calibration output is performed (step S13).

FIG. 4 is a diagram showing an outline of the relationship between a received digital broadcast signal, a detection state of a guard interval component from the broadcast signal, and a corrected clock pulse.
The digital broadcast signal waveform shown in FIG. 4A is received, and the detection signal of the peak position of the guard interval component shown in FIG. 4B is obtained from the received signal of the digital broadcast signal. The peak position of this guard interval is exactly 1.134 ms in synchronization with the broadcast signal. The detection timing of the peak position received and detected is an error of about 10 μs or less from the position of the guard interval indicated by the actual broadcast signal.

Based on the detection timing of the guard interval of 1.134 ms shown in FIG. 4B, a clock pulse which is a clock in the device (inside the station) output from the clock generator 111 shown in FIG. 4C. A process for correcting the generation timing is performed.
By correcting the timing of the clock pulse, the frame period for performing communication in the autonomous distributed TDMA system, which is the timing for transmitting and receiving radio signals in this communication device, is corrected and notified to other communication devices The timing information to be corrected is also corrected.

FIG. 5 is a diagram showing an example of a frame period set by this communication apparatus, and a frame configuration when communication is performed by the autonomous distributed TDMA method will be described.
In the autonomous distributed TDMA system, as shown in FIG. 5A, one frame period is defined, and a predetermined number of slots are arranged within the one frame period. In FIG. 5A, among the plurality of slots, slots used for wireless communication are indicated by hatching, and the other slots are vacant slots. Here, for example, each communication device transmits a packet every frame using one slot at a predetermined slot position in one frame. Here, the length of one slot is 1 ms. The timing for setting the frame position and the slot is set at the timing obtained by counting the clock pulses in the communication apparatus. When the period of the clock pulse for communication coincides with the period of 1 slot (1 ms), the period of the clock pulse becomes the slot period as it is.

  In the packet transmitted by each communication device, for example, as shown in FIG. 5B, the data portion is arranged following the preamble of the head portion. In the case of inter-vehicle communication, traveling state information such as the current position, current speed, traveling direction, and brake of the host vehicle is added to the data portion. Furthermore, the timing information described above is added as information for communication synchronization processing. This timing information may be arranged in either the preamble part or the data part.

FIG. 6 shows a synchronization process performed by causing the other communication device to receive timing information transmitted from the communication device.
First, the communication device receives transmission data of a plurality of other communication devices located in the vicinity of itself for one frame, and detects their transmission timing and shift amount Δ (step S21). Then, the transmission timing is corrected using the detected shift amount Δ and the shift amount Δi of the communication device X itself, and the transmission timings of all the other receivable communication terminals after one frame are predicted. To do. From the predicted transmission timing, a shift amount Δi + 1 in the next period of the communication device is obtained (step S22).

Then, information of the shift amount Δi + 1 is included in the data packet for transmission to be generated (step S23). Thereafter, the transmission timing is shifted by Δi, and the data generated in step S23 is transmitted. Further, the value of Δi + 1 is substituted for the transmission timing Δi, and i + 1 is substituted for the value i (step S25). Then, it returns to step S21.
By performing the processing shown in the flowchart of FIG. 6, the frame period is determined autonomously among a plurality of communication apparatuses using the same frame period, and wireless communication using the autonomous distributed TDMA method can be performed appropriately. .
In the example of the present embodiment, by receiving a digital broadcast signal and correcting the clock timing with a guard interval detected from the digital broadcast signal, wireless communication in the autonomous distributed TDMA system is performed. When performing, each communication apparatus has a clock with less error, and it is possible to perform synchronization processing with other communication apparatuses more favorably by the autonomous distributed TDMA system.

Here, a specific example of processing for correcting the communication timing in the guard interval of the OFDM signal (digital broadcast signal) received by the wireless reception unit 121 in the communication apparatus will be described.
The guard symbol of the terrestrial digital broadcast signal can be detected every fixed period T _PM = 1.134 ms. That is, if the nth guard timing detection time is t _PM (n),
t _PM (n + 1) −t _PM (n) = T _PM (1)
Holds. This equation can be expressed as follows:
t _PM (n) = t _PM (0) + n · T _PM (2)
Here, in order to simplify the description, it is assumed that t _PM (0) = 0.

Next, the time at which the communication device i detects the terrestrial digital broadcast signal for the nth time is defined as t ^α _i (n). Based on this t ^α _i (n), the error of the period of the terrestrial digital broadcast signal and the time management clock in its own communication device is corrected. The period T ^* _i of the terrestrial digital broadcast signal viewed from the communication device i is set as follows.
T ^* _i = [delta] (t [ ^alpha] _i (n) -t [ ^alpha] _i (n-1)) + (1- [delta]) T [ ^alpha] _i (3)
Here, δ is a constant of 0 ≦ δ ≦ 1 representing the degree of dependence on the terrestrial digital broadcast signal.
T ^α _i is a value T ^α _i = T _PM + ΔT _{i obtained} by adding a communication device-specific offset time ΔT _i caused by a frequency offset of a clock for managing the time of the communication device i to the period t _PM of the terrestrial digital broadcast signal. Represents.

An error occurs in the process of receiving a terrestrial digital broadcast signal. Assuming that an error occurring in the guard timing received by the communication device i for the nth time is ξ _i (n), the following is obtained.
t ^α _i (n) = t _PM (n) + ξ _i (n) (4)
According to the equation (2), ξ _i (n) has a normal distribution and is a value of about 10 μs at the maximum as an actually assumed value.

Next, consider the frame period of inter-vehicle communication.
A frame period T ITS = 100 ms, the cycle obtained from the terrestrial digital broadcasting signal, T * i ≡t α i and (n) -t α i (n -1), the head timing of the n-th frame t beta i ( If n), each communication apparatus updates its own timing of the (n + 1) th frame based on the following formulas (1), (2), and (3). k is an arbitrary step size of 0 ≦ k ≦ 1.

In this way, the clock timing of the communication device itself is corrected at a cycle obtained from the received terrestrial digital broadcast signal. When correcting the period obtained from the clock of the communication device itself with the period obtained from the terrestrial digital broadcast signal, it is not immediately corrected to match the period obtained from the terrestrial digital broadcast signal. The period obtained from the digital broadcast signal is weighted and reflected at a certain rate (for example, about 20%) to correct the timing, and gradually adjusted to the period obtained from the received digital terrestrial broadcast signal. Is preferred.
By correcting in this way, the oscillation error of the clock generator included in the communication device is corrected, and synchronization processing more accurate than the conventional one can be performed.

FIG. 7 shows a change in the timing synchronization state when wireless communication is performed by an autonomous distributed TDMA system with a plurality of communication apparatuses (four in this example), and the vertical axis indicates the standard deviation. The horizontal axis indicates the passage of time. A characteristic a indicated by a solid line is a characteristic when the timing is synchronized by the communication apparatus having the configuration of the present embodiment, and a characteristic b indicated by a broken line is a characteristic that does not receive a terrestrial digital broadcast signal, This is an example in which timing synchronization is performed simply by transmitting and receiving timing information.
In the case of the characteristic b of the conventional example, after the standard deviation has once become a small value, the standard deviation becomes a large value to some extent because there is an error in the accuracy of the clock of each terminal device. On the other hand, in the case of the characteristic “a” of the present embodiment, the standard deviation gradually decreases with the passage of time, and the synchronization timing can be matched well with other communication devices.

[2. Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG.
In FIG. 8, parts corresponding to those in FIG. 1 described as the first embodiment are denoted by the same reference numerals.
In the present embodiment, the communication device mounted on a vehicle (mobile body) such as an automobile is the same as the communication device shown in FIG. 1 in the first embodiment, and is an autonomous distributed TDMA. The point of applying the system and the basic configuration of the communication device are also the same as those described in FIG. 1, and in addition to the configuration for transmitting and receiving radio signals to and from the other communication device, terrestrial digital television broadcast signals The same is true in that a receiving configuration is provided and the clock error is corrected at the detection timing of the guard interval of the OFDM signal received as the broadcast signal.

In the second embodiment, as shown in FIG. 8, the configuration for controlling the oscillation output of the clock generator 111 by the calibration output of the calibration unit 110 is different from that of the first embodiment.
That is, the communication apparatus according to the second embodiment shown in FIG. 8 includes a clock generator 111a that is an oscillator and a counter 111b that counts the oscillation clock output from the clock generator 111a and generates a clock pulse. The configuration of the clock generator 111 is the same as that of the first embodiment shown in FIG.

Here, in the case of the configuration of the first embodiment shown in FIG. 1, the clock pulse error is corrected by correcting the count timing of the counter 111b with the calibration output of the calibration unit 110. It was.
On the other hand, in the case of the configuration of the second embodiment shown in FIG. 8, the calibration output of the calibration unit 110 is supplied to the clock generator 111a which is an oscillator in the clock generation unit 111, and the basic The clock itself is directly corrected. The clock generator 111a is configured such that the oscillation frequency changes corresponding to the voltage value of the control voltage, for example, and the control voltage supplied to the clock generator 111a is corrected with the calibration output.

Other parts are configured in the same manner as the communication apparatus of the example of the first embodiment described with reference to FIGS.
According to the configuration of the second embodiment, the oscillation error of the clock generator 111 can be corrected by directly controlling the clock generator 111a, and other communication is performed as in the configuration of the first embodiment. There is an effect that the synchronization processing with the apparatus can be performed well.

[3. Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIGS.
9, parts corresponding to those in FIGS. 1 and 8 described as the first and second embodiments are denoted by the same reference numerals.
In the present embodiment, the communication device mounted on a vehicle (mobile body) such as an automobile is the same as the communication device shown in FIGS. 1 and 8 in the first and second embodiments. Yes, the application of the autonomous distributed TDMA system and the basic configuration of the communication device are the same as those described with reference to FIGS. 1 and 8, and other than the configuration for transmitting and receiving radio signals to and from the other communication device. The same is true in that a configuration for receiving a terrestrial digital television broadcast signal is provided, and the clock error is corrected at the detection timing of the guard interval of the OFDM signal received as the broadcast signal.

  In the present embodiment, in addition to the configuration for receiving a terrestrial digital television broadcast signal, an external signal receiving unit for receiving a GPS signal transmitted from an artificial satellite as a positioning signal is provided, and the GPS at the start of communication is provided. Time information obtained by receiving a signal is transmitted.

  That is, as shown in FIG. 9, a receiving antenna 113 that receives a GPS signal is provided, and the receiving antenna 113 is connected to an external signal receiving unit 114. The external signal receiving unit 114 receives and processes a GPS signal that is a positioning signal including time information transmitted from a GPS satellite. The external signal receiving unit 114 that receives and processes GPS signals is normally configured to receive signals of a plurality of channels, and captures GPS signals from a plurality of satellites. The GPS signal received by the external signal receiving unit 114 is supplied to the time reference unit 115.

  The time reference unit 115 calculates an accurate current time based on time information from a plurality of satellites received by the external signal reception unit 114, and performs time adjustment processing using the time of the internal clock as the calculated time. . Then, the time information obtained by the time reference unit 115 and the time of the acquired moment are stored in the memory 116.

  Then, the current time information obtained by the time reference unit 115 is supplied to the changeover switch 119. Further, the time instant at which an accurate time is acquired based on the received GPS signal stored in the memory 116 and the current time obtained by the time reference unit 115 are supplied to the comparator 118, and the 2-second setting unit 117. Compare whether the value is within the threshold set in. Here, the threshold is 2 seconds, and when the current time obtained by the time reference unit 115 is within 2 seconds from the time set based on the GPS signal, the changeover switch 119 is output from the memory 116. Let it be the side. When two seconds have elapsed from the time set based on the GPS signal, the changeover switch 119 is set to the output side of the calibration unit 110.

  The output selected by the changeover switch 119 is supplied to the data generation unit 112 and included in the transmission packet. For this reason, when it is within 2 seconds from the time when the time is adjusted based on the GPS signal, the timing information based on the current time information stored in the memory 116 is added to the transmission packet. Further, after 2 seconds have elapsed from the time when the time is adjusted based on the GPS signal, the changeover switch 119 is switched, and the timing information output from the calibration unit 110 is added to the transmission packet. As described above, the changeover switch 119, the 2-second setting unit 117 for performing the switching control, and the comparator 118 function as a control unit that selects timing information included in the transmission data. When the external signal receiving unit 114 cannot receive a GPS signal, the changeover switch 119 always selects the output of the calibration unit 110.

  The data generation unit 112 generates a transmission packet (or beacon) including any of the supplied timing information, supplies the generated transmission packet to the wireless transmission unit 104, and is connected to the wireless transmission unit 104. Wireless transmission from the transmitting / receiving antenna 101 to a nearby communication device. The timing for wireless transmission is instructed from the clock generator 111.

  Other parts are the same as the configuration of the communication apparatus according to the first embodiment shown in FIG. 1, and a clock is generated at a guard interval timing detected by receiving a digital broadcast signal, which is a feature of the present invention. The point of correcting the error of the output clock of the unit 111 is the same as in the first embodiment.

  As a configuration for correcting the error of the output clock of the clock generation unit 111, in the example of FIG. 9, the configuration of FIG. 1 is used as the configuration for supplying the calibration output of the calibration unit 110 to the counter 111b in the clock generation unit 111. As shown in FIG. 9 by connecting with a broken line, the calibration output of the calibration unit 110 is supplied to the clock generator 111a in the clock generation unit 111 to directly control the oscillation frequency of FIG. A configuration may be applied.

The flowchart of FIG. 10 shows the principle of the synchronous operation related to the reception of the GPS signal in the communication apparatus of the present embodiment.
First, the communication device observes the communication timing of the peripheral device based on beacons and data packets transmitted from the peripheral communication device for one period which is the minimum unit of communication of each device (step S31). The observation of the communication timing of the peripheral device corresponds to the processing in the average calculation unit 109. Then, the communication timing of itself is corrected based on statistical values such as the distribution and average of the communication timings of the peripheral communication devices (step S32). This correction process corresponds to the process in the calibration unit 110.

Next, it is determined whether or not an external signal (here, a GPS signal) is referred to at the latest timing (step S33). This determination corresponds to the comparison process in the comparator 118 in FIG. 9, and in the configuration example in FIG. 9, it is determined whether or not the current time is within 2 seconds from the GPS signal. Here, when the external signal is not referred to (that is, within 2 seconds after the current time is acquired), the communication timing information corrected in step S32 is added to the transmission packet, and peripheral communication is performed. Notification is made to the apparatus (step S34). Then, the process returns to step S31.
In step S33, when an external signal is referred to (that is, within 2 seconds after the current time can be acquired), the time information of the external signal is added to the transmission packet, and peripheral communication devices Is notified (step S35). Then, the process returns to step S31.

  As can be seen from the flowchart of FIG. 10, in this embodiment, for synchronization in the communication device, the external device (GPS signal) is not directly used but the timing is adjusted in the communication device. The received time information is transmitted to other peripheral communication devices and used indirectly. As a result, the instability of time information accuracy and reception accuracy of the external signal is greatly reduced.

  While performing the synchronization processing for receiving the GPS signal shown in the flowchart of FIG. 10, the clock generation error correction of the clock generation unit 111, which is a feature of the present invention, is performed by receiving the digital broadcast signal. As compared with the communication apparatus described in the second embodiment, it is possible to further improve the synchronization accuracy when performing wireless communication by the autonomous distributed TDMA method.

[4. Modified example]
In each of the embodiments described so far, the communication device that performs vehicle-to-vehicle communication has been described as an example. However, the communication device may be applied to synchronization processing of a communication device for other purposes. Specifically, as long as the communication system does not have a base station, the communication system may be applied to a communication system in which some or all communication devices in the communication system perform communication at a fixed position. Further, for example, the present invention may be applied to synchronization between base stations in MIMO (Multiple Input Multiple Output).

In the above-described embodiment, the OFDM signal as the terrestrial digital television broadcast signal is received as the external signal received to correct the clock timing. Other broadcast signals may be received. Alternatively, as long as the signals are transmitted synchronously in a wide area, other OFDM signals may be received to correct the clock timing.
Further, in the third embodiment shown in FIGS. 8 and 9, a GPS signal that is a positioning signal is used as an external signal from which time information is obtained, but other time information or timing information is used. Also good.

  Furthermore, as a wireless communication system in which the communication apparatus of each embodiment autonomously performs synchronization processing, an autonomous distributed TDMA system in which time slots are set is applied. However, the communication apparatus autonomously determines a frame period and performs communication. Other communication methods may be applied as long as the wireless communication method is performed.

  DESCRIPTION OF SYMBOLS 101 ... Transmission / reception antenna, 102 ... Changeover switch, 103 ... Wireless reception part, 104 ... Wireless transmission part, 105 ... Shift amount acquisition part, 106 ... Phase difference detection part, 107 ... Adder, 108 ... Memory, 109 ... Average calculation part 110 ... calibration unit, 111 ... clock generation unit, 111a ... clock generator, 111b ... counter, 112 ... data generation unit, 113 ... reception antenna, 114 ... external signal reception unit, 115 ... time reference unit, 116 ... memory, 117: 2-second setting unit, 118: comparator, 119: changeover switch, 121 ... antenna, 122 ... wireless reception unit, 123 ... complex correlation calculator, 124 ... delay circuit, 125 ... low-pass filter, 126 ... detector, 127 ... Difference detector, 128 ... Memory

Claims (6)

In a communication device that performs transmission and reception of wireless signals bidirectionally with other communication devices in the vicinity,
A radio signal receiving unit for receiving the radio signal;
A wireless signal transmission unit for performing transmission processing of the wireless signal;
An OFDM signal receiver that receives the OFDM digital broadcast signal and detects a guard interval from the received digital broadcast signal;
A positioning signal receiver for receiving positioning time information or timing information;
The communication timing for performing transmission processing in the radio signal transmission unit is set based on the signal received by the radio signal reception unit, and the detection timing of the guard interval obtained by the OFDM signal reception unit Bei example a communication timing setting unit configured to correct the communication timing on the basis,
The communication timing setting unit causes the wireless signal transmission unit to transmit time information or timing information included in the received positioning signal when the positioning signal reception unit has received the positioning signal, and receives the positioning signal. If the communication signal is not successful, the communication apparatus executes processing for correcting the communication timing based on the detection timing of the guard interval received by the OFDM signal receiving unit . The communication device according to claim 1.
The positioning signal is a GPS signal, and the time signal or timing information included in the received GPS signal is transmitted from the radio signal transmission unit for a certain period after the GPS signal is received and time information is acquired. A communication device. The communication device according to claim 1 or 2,
The communication timing setting unit corrects the count value of a clock counter that determines communication timing based on a synchronization timing component received by the OFDM signal receiving unit. The communication device according to claim 1 or 2,
The communication timing setting unit corrects the oscillation frequency of an oscillator that generates a clock for determining communication timing based on a synchronization timing component received by the OFDM signal receiving unit. The communication apparatus according to any one of claims 1 to 4,
The communication timing setting unit acquires information on a shift amount of the transmission timing on the transmission partner side of the radio signal received by the radio signal receiving unit, and the acquired shift amount and a shift amount of its own communication timing A communication apparatus characterized in that the next transmission timing shift amount is obtained and information of the determined shift amount is included in transmission data at the next transmission timing. In a communication method for bidirectionally transmitting and receiving wireless signals between a plurality of communication devices,
Receives the OFDM broadcast digital broadcast signal, detects the guard interval from the received digital broadcast signal,
Receiving the positioning signal, detecting the positioning time information or timing information included in the received positioning signal,
The communication timing for performing the transmission process of the radio signal is set based on the reception signal obtained by the reception process of the radio signal, and the communication timing is corrected based on the detection timing of the guard interval,
Further, when the positioning signal can be received, the time information or the timing information included in the received positioning signal is included in the radio signal to be transmitted, and the guard signal is received when the positioning signal is not successfully received. A communication method, comprising: executing a process of correcting the communication timing based on an interval detection timing .

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