JP5092115B2 - COMMUNICATION DEVICE, MOBILE COMMUNICATION SYSTEM, AND COMMUNICATION METHOD - Google Patents

Description

  The present invention relates to a communication device, a mobile communication system, and a communication method that can synchronize communication between a plurality of communication devices without having a base station serving as a communication synchronization reference.

  In an ad hoc sensor network, synchronizing the local time of each terminal with each other and maintaining one common timing at the network level is called timing synchronization. In particular, when TDMA (Time Division Multiple Access) is used in the network, or when each terminal performs on / off control simultaneously using the power save mode, this timing synchronization is essential.

  As a research trend of such timing synchronization, a synchronization algorithm as described in Non-Patent Document 1 has been proposed. This synchronization algorithm is mainly intended for timing synchronization between a plurality of vehicle groups in inter-vehicle communication. According to this timing synchronization process, a stable synchronization state between a plurality of vehicle groups is maintained. ing.

  FIG. 6 shows a state in which a large number of cars pass on one road. Each vehicle shown in FIG. 6 has a communication function, and is a communication terminal that can communicate with other vehicles existing within a certain communication range.

  Here, when one or more communication terminals that can communicate with a certain terminal are viewed as one set, terminals that can communicate with one or more communication terminals belonging to the set are included in the set. Here, this set is defined as a terminal group. For example, in FIG. 6, there are four terminal groups A, B, C, and D. In such an environment, in order to construct a communication system that performs communication by the TDMA (Time Division Multiple Access) method, each terminal group needs a communication synchronization method that synchronizes all communication terminals belonging to the own terminal group. is there.

  Further, in the environment as shown in FIG. 6, since the terminal is moving, it is expected that the terminal or the terminal group is frequently fused and separated. For example, in the case of FIG. 6, it can be imagined that the terminal groups B and C are immediately after being separated, and then the terminal group B merges with the terminal group A and the terminal group C merges with the terminal group D. For this reason, it is necessary to use a communication synchronization method in which the synchronization state is not easily lost.

Each terminal of the terminal groups A to D shown in FIG. 6 receives transmission data of a plurality of other communication terminals for one frame after data transmission, and obtains the next transmission timing by observing the transmission timing. Then, the next transmission timing of the own terminal is adjusted by using an arithmetic average of transmission data from a plurality of communication terminals. As a result, the terminal group can be synchronized without causing a communication collision between the communication terminals without requiring a reference station. Patent Document 1 discloses the above-described communication synchronization method.
JP 2008-22307 A Imai, Suzuki “Study on Independent Distributed Control of Timing Synchronization”, IEICE Technical, USN2007-13, pp67-71, May 2007

  However, in the techniques disclosed in Patent Document 1 and Non-Patent Document 1, there is a “local solution” called a mode-locked state in which the timing of each terminal is stably maintained while causing a certain shift on the plane like a traveling wave. It has been found to occur. FIG. 7 conceptually shows a terminal group in which this mode lock state occurs. The mode lock state is a state in which the synchronization timing of terminals located around a specific small number of terminals proceeds like a rotating wave while maintaining a uniform gradient, and has a very strong structure. It is known that there is. For this reason, a method for avoiding the occurrence of the mode lock state has been proposed (see, for example, Non-Patent Document 1). However, in the proposal described in Non-Patent Document 1, the mode lock state disappears at a certain rate and, as a result, desired May be obtained, but the state has been found to be uncertain.

  This invention is made | formed in view of this point, and it aims at providing the communication apparatus, the mobile communication system, and the communication method which suppress generation | occurrence | production of a mode lock state more effectively, and eliminate reliably.

  In order to solve the above problems, a communication apparatus according to the present invention includes an antenna, a receiving unit that receives radio waves from a plurality of terminals that are in a communicable range via the antenna, and a plurality of communication units that are also in a communicable range via the antenna. A transmitter that transmits radio waves to the terminal of the terminal, a phase detector that detects a phase difference between a received radio wave received by the receiver and a transmitted radio wave transmitted from the transmitter, and stores a phase difference obtained from the phase detector A memory, an average calculating unit that calculates an average of a plurality of phase differences stored in the memory, a variance calculating unit that calculates a variance of a plurality of phase differences stored in the memory, and an average obtained from the average calculating unit A control unit that stops the radio wave transmission operation of the transmission unit when it is detected that the value is equal to or less than a predetermined first threshold value and the variance value obtained from the variance calculation unit is equal to or greater than a predetermined second threshold value. Yes.

Further, as a preferred form of the present invention, the above-mentioned control unit is obtained from the variance calculation unit when the average value obtained from the average calculation unit is larger than a predetermined first threshold when the radio wave transmission operation of the transmission unit is stopped. When it is detected that the variance value is less than the predetermined second threshold, the radio wave transmission operation is stopped after a predetermined time.
Furthermore, as a preferred embodiment of the present invention, a group setting unit for grouping a plurality of terminals according to a plurality of phase differences stored in the memory is provided, and the number of groups divided by the group setting unit is set. calculate. The control unit is configured such that the average value obtained from the average calculation unit is equal to or less than a predetermined first threshold value, and the variance value obtained from the variance calculation unit is equal to or greater than a predetermined second threshold value or the number of calculated groups is a predetermined value. The radio wave transmission operation of the transmission unit is stopped by detecting that it is equal to or greater than the third threshold value.

  The communication method of the present invention includes a step of receiving radio waves from a plurality of terminals in a communicable range via an antenna, and a step of transmitting radio waves to the plurality of terminals in the communicable range via an antenna; Detecting a phase difference between the received received radio wave and the transmitted transmitted radio wave, storing the detected phase difference, calculating an average value of a plurality of stored phase differences, and Calculating a variance of a plurality of phase differences, detecting that the calculated average value is equal to or less than a predetermined first threshold value, and that the calculated variance value is equal to or greater than a predetermined second threshold value; Stopping the transmission operation.

  In the communication device, the mobile communication system, and the communication method described above, transmission of radio waves is prohibited when becoming a mode-locked core, and transmission of radio waves is performed after a predetermined period of time when the mode-locked core is removed. It can be extinguished.

  According to the present invention, it is possible to provide a communication device, a mobile communication system, and a communication method capable of obtaining a complete synchronization state even from a mode lock state.

  Hereinafter, examples of embodiments of the present invention will be described with reference to the accompanying drawings.

The communication apparatus of the present invention and the mechanism of the communication synchronization method using this communication apparatus will be described with reference to the block diagram of FIG. 1 and the flowcharts of FIGS.
FIG. 1 is a block diagram of a communication apparatus according to this embodiment. As shown in FIG. 1, the communication apparatus 100 of this example includes a wireless antenna 101, and this antenna 101 is connected to a reception unit 103 and a transmission unit 104 via a changeover switch 102. The receiving unit 103 receives radio waves from a plurality of terminals within the communicable range, and the transmission unit 104 transmits radio waves to the plurality of terminals within the communicable range.

  The reception unit 103 and the transmission unit 104 are connected to the phase detection unit 105 and the shift amount acquisition unit 120.

  The phase difference detection unit 105 detects a difference between the timing of the pulse output from the clock generator 108 and the timing at which the reception unit 103 receives the transmission radio wave as a phase difference. The clock generator 108 is an oscillator that oscillates a clock according to a calibration output from the calibration unit 106 described later, and an oscillator that oscillates a clock synchronized with the timing at which the communication apparatus 100 performs radio wave transmission. Specifically, the phase detection unit 105 detects the phase difference between the timing at which radio waves are transmitted from a receivable terminal close to the own station and the clock synchronized with the timing at which the communication device 100 performs radio wave transmission. . Such a phase difference is detected for each of all receivable terminals.

  The shift amount acquisition unit 120 acquires a shift amount, which will be described later, which is information included in the radio wave packet received by the reception unit 103. This shift amount is acquired for each of the receivable terminals.

  Information on the phase difference and the shift amount obtained from the phase difference detection unit 105 and the shift amount acquisition unit 120 is added by the adder 121 and then supplied to the memory 107. The memory 107 is a value obtained by adding the phase difference detected for each of the plurality of terminals by the phase difference detection unit 105 and the shift amount acquired for each of the plurality of terminals by the shift amount acquisition unit 120. A so-called timing error is stored. The timing error is a difference between the timing of the pulse output from the clock generator 108 and the timing at which each receivable terminal close to the local station is predicted to perform radio wave transmission next time.

  The memory 107 is connected to the average calculation unit 109, the variance calculation unit 110, and the group setting unit 111. First, the average calculation unit 109 calculates an average value of timing errors calculated for each of a plurality of terminals stored in the memory 107. The average value of the timing errors is compared with a predetermined threshold value a by the comparator 112. The threshold value a is 8% of the period of the received radio wave. That is, the comparator 112 generates an output when it detects an error of 8% or more of one period of the received radio wave.

  The average calculation unit 109 is connected to the calibration unit 106. The calibration unit 106 generates a calibration output based on the average value of timing errors output from the average calculation unit 109 and supplies the calibration output to the clock generator 108.

  Further, the variance calculation unit 110 calculates variances of a plurality of timing errors stored in the memory 107. The variance is compared with a predetermined threshold value b by the second comparator 113, and when the threshold value b is exceeded, the second comparator 113 generates an output. An equation for calculating the threshold value b is shown below.

  Further, the memory 107 is connected to the group setting unit 111, where a plurality of terminals are grouped according to a plurality of phase differences stored in the memory 107. Then, the group setting unit 111 performs grouping, and the group number calculation unit 114 calculates the number of groups.

The group number calculation unit 114 is compared with a predetermined threshold value (for example, the group number 100) by the third comparator 115, and an output is obtained from the third comparator 115 when the threshold value is 100 or more.
Further, the outputs of the second comparator 113 and the third comparator 115 are applied to an OR circuit 116, and the output of the OR circuit 116 is applied to an AND circuit 117. The AND circuit 117 performs a logical product with the output of the first comparator 112, and sends this output to the control unit 118.
The control unit 118 controls the transmission / reception changeover switch 102 and the transmission control 119 of the transmission unit 104. That is, the control unit 118 has an average value obtained from the average calculation unit 109 equal to or smaller than a predetermined first threshold a, and a variance value obtained from the variance calculation unit 110 is equal to or greater than a predetermined second threshold σ or a group number calculation unit 114. When the number of groups obtained from is equal to or greater than a predetermined third threshold (for example, 100), the transmission control switch 119 is turned off to stop the radio wave transmission operation from the transmission unit 104.

  Further, the control unit 118 controls the transmission / reception selector switch 102 based on the output switching timing of the AND circuit 117, thereby changing the timing for receiving the transmission radio wave from each receivable terminal.

  2 is a flowchart relating to a method in which a communication terminal (hereinafter referred to as communication terminal X) that has not yet started communication with another communication terminal joins a group in which a plurality of communication terminals are communicating, These are the flowcharts regarding the method of synchronizing communication, when the communication terminal X has already participated in communication of several other communication terminals.

First, a method for newly joining a communication terminal (hereinafter referred to as communication terminal X) will be described based on the flowchart of FIG.
The communication terminal X that wants to participate in communication receives the transmission data of all other communication terminals that can be received for one frame from a certain point in time, and measures their transmission timing and shift amount Δ (step S10). .
Next, the transmission timing is corrected using this shift amount Δ, and the transmission timings of all other communication terminals that can be received after one frame are predicted (step S12).

Then, from the predicted transmission timing, an empty slot (a section where the transmission interval is longer than one slot length) is specified (step S14), and data is transmitted in the specified empty slot, that is, participates in communication. At this time, information indicating that the shift amount Δ ₀ = 0 is included in the transmission data (step S16). Thereafter, the process proceeds to step S20 (A) in FIG.

Next, a method of synchronizing communication when a new communication terminal X participates in communication of a plurality of communication terminals will be described based on the flowchart shown in FIG.
First, after transmitting data, the communication terminal X receives transmission data of all other communication terminals that can be received for one frame, and measures their transmission timing and shift amount Δ (step S20). .

Thereafter, the transmission timing is corrected using the shift amount Δ and the shift amount Δ _i of the communication terminal X itself, and the transmission timings of all the other receivable communication terminals after one frame are predicted (steps). S22).

Next, the shift amount Δ _{i + 1} of the communication terminal X itself is obtained from the predicted transmission timing (step S24). Then, it is determined from the distribution of the transmission timing predicted in step S22 whether the network is in a mode lock state (step S26).

If it is determined in step S26 that the mode is locked, the transmission timing is shifted by [Delta] _i, but its own transmission timing is not notified to the surroundings (step S30). On the other hand, if it is determined in step S26 that the mode is not locked, the data is transmitted with the shift amount Δ _i shifted.
At this time, information of the shift amount Δ _{i + 1} is included in the transmission data (step S28). Subsequently, i + 1 is substituted into _i , Δi _{+ 1} is substituted into Δi (step S32), and the process returns to step S20.

  Next, the correction of the transmission timing in step S12 and step S22 and how to obtain the shift amount in step S24 will be described in detail.

  First, from the transmission timing measurement data at step S10 and step S20, the distribution of the timing at which the other communication terminal has transmitted one slot length is examined with reference to the one slot length of the communication terminal for which the shift amount is obtained, and the self The transmission timing is corrected from the shift amount and the shift amount of other communication terminals. For example, if the transmission timing of a certain communication terminal Y is 0.4 slot length and the shift amount of the communication terminal Y is 0.1 slot length, the corrected transmission timing is 0.5 slot length.

  Next, a histogram is created from the corrected transmission timing, with the horizontal axis representing time and the vertical axis representing frequency. The most frequent timing in this histogram is set as the shift amount. If the shift amount is selected in this way, the sum of the shift amounts of the communication terminals becomes small, so that synchronization can be performed efficiently. If there are a plurality of timings with the highest frequency, the one with the shortest shift amount is selected. If the shift amount is 1/2 slot length or less, the transmission timing is delayed by the shift amount, and if the shift amount is greater than 1/2 slot length, the transmission timing is advanced by a value obtained by subtracting the shift amount from 1 slot length. Shall.

Next, the method for determining the mode lock state in step S26 will be described in detail. If the shift amount Δ _{i + 1} obtained in step S24 is smaller than an appropriate threshold value, and the degree of variation in all the predicted transmission timings obtained in step S22 is greater than an appropriate threshold value, the terminal X determines that the network in which it is participating is in the mode lock state. If the above condition is not satisfied, it is determined that the mode is not locked. As the degree of variation here, dispersion may be used, or information such as how many pieces of data are received from terminals whose synchronization degree and transmission timing are greatly separated may be used.

  Each terminal holds information indicating whether or not the network in which it participates is in the mode lock state. If it is determined that the network is in the mode lock state, it continues to determine that the terminal is in the mode lock state for a certain frame time.

  As a method of not reporting its own transmission timing in step S30, a method of canceling data transmission in the frame, or information including that the transmission timing of this data is not included in the calculation of the shift amount in step S24 is transmitted. Possible ways to do this.

  According to the method shown in the flowcharts of FIG. 2 and FIG. 3, communication can be started without causing a collision, a network can be constructed, and communication can be synchronized.

  Next, simulation was performed in order to evaluate the performance of the communication apparatus 100 according to the embodiment of the present invention and the communication synchronization method using the same. 4 and 5 both show the simulation results of the present embodiment and the simulation results of the prior art in comparison.

Since previous simulations have shown that the mode-locked state persists even when there is terminal movement, here the time scale of terminal movement is sufficiently longer than the time scale of convergence of timing synchronization (ie timing synchronization) In this case, the process of canceling the mode lock state is verified.
Here, even if the movement of the terminal is taken into consideration, it is difficult to suppress the mode lock state even if it is promoted, so the above assumptions make sense for verifying the operation of the mode lock state cancellation method. It is thought that.

Therefore, first, the terminals were arranged in a 32 × 32 grid, and the number of terminals was 1024. Further, following the simulation of Non-Patent Document 1, all terminals do not perform any communication in the initial state, but are randomly activated within 100 frame time and participate in communication.
Here, the initial communication timing of each terminal is set at random, and each terminal performs the operation described in the flowcharts of FIGS. Also, for simplicity, it is assumed that the effect of collision between timing beacons can be ignored, and each terminal can always transmit timing information to all terminals in the communication range once every frame time. As the communication range of each terminal, two types of peripheral terminals with 20 or 24 terminals around the terminal are assumed. In other words, when performing time division multiple access, the number of slots set in one frame is sufficient for the number of peripheral terminals.

  For simplicity, the data packet lengths are all equal, and the guard time is 8% of the slot length. 4 and 5 show the performance evaluation of the proposed method under the above conditions. FIG. 4 shows the results when the communication range is 20, and FIG. An expression for calculating the degree of synchronization as an evaluation index is shown below.

  σ = 1 represents complete synchronization, and conversely, σ = 0 represents a state in which the timings of all terminals are uniformly distributed (N represents the number of terminals constituting the terminal group). In general, in the mode lock state, since timing is widely distributed, σ has a value close to 0.

In both FIG. 4 and FIG. 5, when 500 frames have elapsed after 1000 trials, the horizontal axis represents the degree of synchronization, and the ratio of trials corresponding to the degree of synchronization, that is, the percentage that synchronization cannot be achieved is the frequency (%). It showed in. As a comparison target, the results of (i) the synchronization method that does not cancel the mode lock state (conventional 2), and (ii) the communication synchronization method (conventional 1) using the ideas of Non-Patent Document 1 and Patent Document 1 It is shown at the same time.
4 and 5, the portion surrounded by a small frame in the figure shows the maximum value of the frequency scale shown on the vertical axis enlarged to 10%.

As can be seen from FIGS. 4 and 5, the communication device of the present invention achieves perfect synchronization with a probability close to 100%, whereas the two conventional methods cannot achieve synchronization with a certain probability. It is confirmed that it occurs.
In the case of FIG. 4 (20 communication ranges), it was observed that even in the proposal of this example, some synchronization was not achieved, but in the case of FIG. 5 (24 communication ranges), synchronization was not achieved. The state became zero. In other words, it can be said that complete synchronization is realized.

  In addition, the mobile communication between vehicles can always be comfortably performed by mounting the communication apparatus of this embodiment in a vehicle. In other words, the driver can accurately know the distance from the vehicle adjacent to the vehicle that the driver drives, for example. Thereby, there is an effect that the safety when driving the vehicle is reliably improved.

  As mentioned above, although the example of embodiment of this invention was demonstrated, this invention is not limited to the said embodiment example, Unless it deviates from the summary of this invention described in the claim, other modifications Needless to say, application examples are included.

It is a figure which shows the block configuration of the communication apparatus which concerns on one Embodiment of this invention. It is a flowchart for demonstrating the method for which the specific communication terminal which has not started communication newly joins based on one Embodiment of this invention. It is a flowchart for demonstrating the method to synchronize communication when the specific communication terminal in communication of the some other communication terminal has participated based on one Embodiment of this invention. It is the figure which compared and showed the simulation result (communication range is 20 units) of the example of 1 embodiment of this invention, and the simulation result of a prior art. It is the figure which compared and showed the simulation result (communication range is 24 units | sets) of the example of 1 embodiment of this invention, and the simulation result of a prior art. It is the figure which showed a mode that many motor vehicles passed on one road by making into a group the some terminal in the range which can communicate. It is the figure which showed notionally the terminal group in which the mode lock state in the prior art has arisen.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 ... Communication apparatus 101 ... Antenna 102 ... Transmission / reception changeover switch 103 ... Reception part 104 ... Transmission part 105 ... Phase detection part 106 ... Calibration part 107 ... Memory 108 ... Clock generator 109 ... Average calculation 110: dispersion calculation unit, 111 ... group setting unit, 112 ... first comparator, 113 ... second separator, 114 ... group calculation unit, 115 ... third comparator, 116 ... OR circuit, 117 ... AND circuit, 118 ... Control unit, 119 ... Transmission control switch, 120 ... Shift amount acquisition unit, 121 ... Adder

Claims (5)

An antenna,
A receiving unit that receives radio waves from a plurality of terminals in a communicable range via the antenna;
A transmitter for transmitting radio waves via the antenna to the plurality of terminals in the communicable range;
A phase detector that detects a phase difference between a received radio wave received by the receiver and a transmitted radio wave transmitted from the transmitter;
A memory for storing the phase difference obtained from the phase detector;
An average calculator that calculates an average of the plurality of phase differences stored in the memory;
A dispersion calculating unit that calculates dispersion of the plurality of phase differences stored in the memory;
When it is detected that the average value obtained from the average calculation unit is equal to or less than a predetermined first threshold value and the variance value obtained from the variance calculation unit is equal to or greater than a predetermined second threshold value, the radio wave of the transmission unit A control unit for stopping the transmission operation;
A communication device comprising:   The control unit, when the radio wave transmission operation of the transmission unit is stopped, the average value obtained from the average calculation unit is greater than a predetermined first threshold value and the variance value obtained from the variance calculation unit is a predetermined first value. The communication apparatus according to claim 1, wherein when the detection is less than two thresholds, the stop of the radio wave transmission operation is canceled after a predetermined time. A group setting unit for grouping the plurality of terminals according to the plurality of phase differences stored in the memory; and a group number calculating unit for calculating the number of groups divided by the group setting unit; With
The control unit is configured such that the average value obtained from the average calculation unit is equal to or less than a predetermined first threshold value and the variance value obtained from the variance calculation unit is equal to or greater than a predetermined second threshold value or obtained from the group number calculation unit. The communication apparatus according to claim 2, wherein it detects that the number of groups is a predetermined third threshold abnormality and stops the radio wave transmission operation of the transmission unit. An antenna, a receiving unit that receives radio waves from the plurality of terminals in the communicable range via the antenna, and a transmission unit that transmits radio waves to the plurality of terminals in the communicable range via the antenna; A phase detector that detects a phase difference between a received radio wave received by the receiver and a transmitted radio wave transmitted from the transmitter; a memory that stores the phase difference obtained from the phase detector; and the memory that is stored in the memory An average calculator that calculates an average of the plurality of phase differences, a variance calculator that calculates variances of the plurality of phase differences stored in the memory, and the average value obtained from the average calculator A control unit that stops a radio wave transmission operation of the transmission unit when it is detected that the variance value obtained from the variance calculation unit is equal to or less than a predetermined first threshold value and is equal to or greater than a predetermined second threshold value. A first vehicle comprising a first communication unit,
A mobile communication system comprising a second vehicle having the same configuration as the first communication unit and comprising a second communication unit that performs wireless communication with the first communication unit. Receiving radio waves from a plurality of terminals within a communicable range via an antenna;
Transmitting radio waves via the antenna to the plurality of terminals in the communicable range;
Detecting the phase difference between the received radio wave and the transmitted radio wave, and storing the detected phase difference;
Calculating an average value of a plurality of stored phase differences;
Calculating a variance of a plurality of stored phase differences;
And detecting that the calculated average value is equal to or less than a predetermined first threshold value and the calculated variance value is equal to or greater than a predetermined second threshold value, and stopping the radio wave transmission operation.

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