JP4940451B2 - Synchronization device and synchronization method - Google Patents

Description

  The present invention relates to time-division communication synchronization, and in particular, based on the transmission timing of the local station and the local station within a predetermined time in the past from the transmission timing of the local station this time. The present invention relates to a synchronization device and a synchronization method.

Currently, a system (AIS) in which a ship automatic identification device that automatically transmits and receives ship-specific data such as an identification code, ship name, position, course, ship speed, destination, etc. is installed in each ship (for example, , See Patent Document 1). In AIS, a time division communication system is used for communication between ships, and synchronization is performed according to different standards for each class. For example, since a CLASS A ship is equipped with a GPS device according to the standard, synchronization is performed with reference to a GPS 1PPS signal, and when a GPS signal cannot be received, another ship that can receive the GPS signal. Synchronization is performed on the basis of the transmission timing. On the other hand, in a CLASS B'CS ship, the transmission timing of the other ship and the own ship is acquired for one minute, and the average value of the transmission timing is calculated from the transmission timings of the plurality of other ships and the own ship that have been continuously acquired for one minute. . And it synchronizes by correct | amending the transmission timing of this own ship using the average value of this transmission timing.
Japanese Patent No. 3882025

  In the transmission timing determination method in CLASS B'CS described above, synchronization is performed without any problem if the transmission timing of the ship is not included in one minute immediately before the timing at which the ship is going to transmit. However, if the ship's transmission timing is included in this one minute, the transmission timing of the ship before the previous time in this one minute is already corrected.

6 and 7 are diagrams for explaining the occurrence of a synchronization shift due to the transmission timing of the ship. Here, FIG. 6 shows a case where the transmission cycle of the ship is equal to or longer than a predetermined time τ (1 minute in the above case), and FIG. 7 shows a case where the transmission cycle of the ship is shorter than the predetermined time τ.
As shown in FIG. 6, if the transmission cycle of the ship is longer than a predetermined time τ for obtaining a sample for calculating the average value, the transmission timing of the ship is not included in the sampled transmission timing. There is no sync gap. On the other hand, as shown in FIG. 7, if the transmission cycle of the ship is shorter than a predetermined time τ for obtaining a sample for calculating the average value, the transmission timing of the ship is included in the sampled transmission timing. Since the sampled transmission timing of the ship has already been added with a correction value for synchronization at that time, the correction value is included in the calculation value for calculating the current transmission timing. End up. For this reason, since the correction is based on the calculation value including the previous correction value, a synchronization shift occurs as a result.

  FIG. 8 is a diagram showing the influence of correction at the transmission timing of the ship before the previous time. In this figure, (A) shows the case where the ship's transmission cycle is 60 seconds, that is, if there is no ship's transmission timing within 1 minute of acquiring the transmission timing, (B) shows that the ship's transmission cycle is 30 seconds, C) shows a case where the transmission cycle of the ship is 10 seconds.

  As shown in FIG. 8A, when the transmission timing of the ship does not fall within the one minute, the original delay unit time “30” is corrected and converges to “0”. On the other hand, as shown in FIG. 8B, when the ship's transmission timing is included once or twice in the above minute, the original delay unit time “30” tends to converge. Although it does not converge completely, it does not approach “0”. Further, as shown in FIG. 8C, if the transmission timing of the ship is included about 5 or 6 times per minute, the delay unit time will diverge without converging. In other words, if the transmission timing of the ship enters the above-mentioned 1 minute, accurate synchronization cannot be performed.

  Therefore, an object of the present invention is to provide a synchronization device that can accurately synchronize even if the transmission timing group used for correcting the transmission timing of this ship includes the transmission timing corrected by the ship before. And to realize a synchronization method.

  The synchronization device of the present invention includes transmission timing acquisition means, reference timing generation means, and transmission timing determination means. The transmission timing acquisition means receives the communication data from the other station and acquires the transmission timing of the communication data from the other station, and acquires the transmission timing of the own station at the time of transmission of the own station. The reference timing generation unit generates a reference timing having a fixed time interval. The transmission timing determining means calculates a timing difference between the transmission timing of the local station using the reference timing and the transmission timing of each station for each transmission timing of each station, and is earlier than the timing at which the current local station intends to transmit. The timing difference is calculated by calculating the average value by adding the common accumulated timing difference based on the timing correction value determined at the previous transmission timing to the timing difference. An average value is calculated, and a timing correction value at a timing at which the current local station intends to transmit is determined by subtracting a preset accumulated timing difference from the average timing difference value.

  And in the synchronizing method of this invention, it synchronizes by the following processes. The communication data from the other station is received, the transmission timing of the communication data from the other station is acquired, and the transmission timing of the own station is acquired at the time of transmission of the own station. Further, a timing difference between the transmission timing of the own station and the transmission timing of each station using a reference timing consisting of a fixed time interval is calculated for each transmission timing of each station. Then, the timing difference calculated within a predetermined time in the past from the timing at which the current station intends to transmit is acquired. Further, the timing difference average value is calculated by adding the common accumulated timing difference based on the timing correction value determined at the previous transmission timing to the plurality of timing differences and calculating the average value. Then, by subtracting a preset cumulative timing difference from this timing difference average value, a timing correction value at a timing at which the current station intends to transmit is determined, and based on this determined timing correction value, Correct the transmission timing of your station.

  In such a configuration and method, a timing difference in which the timing correction value in the transmission timing of the previous station is offset by the common accumulated timing difference based on the timing correction value of the transmission timing of the previous station is calculated. Averaged. Thereby, even if the transmission timing of the local station exists within a predetermined time in the past, it is not affected by this.

Also, the transmission timing determining means of the synchronization device of the present invention calculates the accumulated timing difference and the timing correction value immediately before the transmission timing of the own station. At this time, the transmission timing determination means sets the current timing difference average value to D (n), the previous timing difference average value to D (n−1), the current timing difference to C (n), and a predetermined time. The timing difference at this time is C (n−p), and the number of data within the predetermined time at each timing is T (n−1) and T (n). n)
D (n) = {D (n-1) * T (n-1) + C (n) -C (n-p)} / T (n)
This is calculated using the following formula.

  By performing such processing, the current timing difference average value can be calculated by performing addition, subtraction, multiplication, and division once each with respect to the previous timing difference average value except for the initial state. Can do. Thereby, it is possible to reduce the amount of processing calculation, rather than reading out the timing difference within a predetermined time each time and adding the accumulated timing difference to calculate the average value. In particular, when the amount of data is large, that is, in a situation where transmission is performed in most slots, the amount of processing computation can be greatly reduced.

  The transmission timing determining means of the synchronization device of the present invention calculates at least three or more arithmetic timing differences obtained by adding different offset values in advance when calculating the timing difference average value. The transmission timing determination means calculates a difference value of each of the at least three calculation timing differences for each preset offset determination timing. The transmission timing determination means calculates a timing difference average value using a calculation timing difference that is not related to a difference value that is discontinuous over time.

  In the synchronization method of the present invention, at least three or more arithmetic timing differences obtained by adding different offset values in advance are calculated when calculating the average timing difference value. Then, the difference values of at least three or more calculation timing differences are calculated for each preset offset determination timing. Then, a timing difference average value is calculated using a calculation timing difference that is not related to a difference value that is discontinuous over time.

  With this configuration and method, if there is a potential error in the reference clock of the local station, even if the above-described synchronization is performed, a complete synchronization cannot be performed potentially. In such a case, the calculated timing difference uniformly increases or decreases with time. If such processing is repeated, the arithmetic unit that performs the processing operation overflows or underflows. FIG. 9 is a diagram showing a problem that occurs when the calculated value overflows. As shown in FIG. 9, for example, when an overflow is about to occur, the arithmetic unit shifts the operation value from the + side maximum value to the − side maximum value so as to prevent this overflow. In such a case, the timing difference average value including the overflow time or the underflow time becomes a value UNF different from the original accurate value COR. For this reason, the timing correction amount becomes incorrect and cannot be accurately synchronized. In order to solve this, three or more timing differences each having different offset values are calculated as calculation timing differences, and a difference value of these calculation timing differences is calculated. These difference values do not change unless any calculation timing difference overflows or underflows. However, if one calculation timing difference changes, the difference value based on this calculation timing difference changes. By using this principle, if the difference value continues to be observed, and the difference value changes, the timing difference average value is calculated using the timing difference for calculation not related to the difference value. The timing correction amount can be calculated without being affected by the above. That is, accurate synchronization can be performed without being affected by the upper and lower limits of the processing calculation values of the calculator.

  According to the present invention, when other station synchronization such as CLASS B'CS is performed, the transmission timing group acquired over the past predetermined time includes the transmission timing of the local station that has been corrected by the local station before. Can also be accurately synchronized. Furthermore, at this time, synchronization can be reliably performed without being affected by overflow or underflow of the arithmetic unit.

A synchronization device according to an embodiment of the present invention will be described with reference to the drawings. In the following description, a synchronizer mounted on a ship automatic identification device will be described as an example.
FIG. 1 is a block diagram showing a main configuration of a synchronization device 1 of the present embodiment and a ship automatic identification device equipped with the same.
The ship automatic identification device includes a synchronization device 1, a transmission signal generation unit 3, a reception antenna 20, and a transmission antenna 30, and includes a ship-specific data processing unit, a display unit, an operation unit, and the like (not shown). The synchronization device 1 includes a received signal demodulator 11, a reference timing signal generator 12, and a transmission timing determiner 13.

  The reception signal demodulator 11 is connected to the reception antenna 20 and demodulates the AIS communication signal received by the reception antenna 20 to detect each slot timing, that is, the transmission slot timing Tr (x) of another ship and Get the data. The reception signal demodulator 11 sequentially outputs the transmission timing Tr (x) of the other ship to the transmission timing determination unit 13. The reception signal demodulator 11 outputs the vessel specific data to a subsequent vessel specific data processing unit (not shown).

  The reference timing signal generator 12 is composed of, for example, an oscillation circuit including a crystal resonator, and outputs a reference timing Tst (x) in advance at a timing interval according to the slot length of the AIS. The output reference timing Tst (x) is input to the transmission timing determination unit 13.

  When the transmission timing Trm (x) of the own ship using the reference timing Tst (x) and the transmission timing Tr (x) of the other ship are input, the transmission timing determination unit 13 receives a time difference between these timings (hereinafter, referred to as “transmission timing Trm (x)”). A (x) (= Tr (x) −Trm (x)), which is referred to as “timing difference”, is calculated. The transmission timing determination unit 13 calculates a timing difference A (x) and stores it in the memory 130 every time transmission timing Tr (x) of another ship is input. Further, the transmission timing determination unit 13 corrects the transmission timing of the own ship by a method described later when the transmission timing of the own ship comes. The timing difference A (x) calculated in this way is sequentially stored in the memory 130 in time series. At this time, the transmission timing determination unit 13 stores an average value D of timing differences calculated at the previous transmission timing in the memory 130 as the accumulated timing correction amount B. For example, if the timing difference average value of the current transmission timing is D (n), the timing difference average value D (n−1) of the previous transmission timing is stored as the current cumulative timing correction amount B (n). .

When receiving the transmission start instruction by carrier sense, the transmission timing determination unit 13 reads the timing difference A (x) for the past one minute with reference to the time point at which own ship transmission is performed.
The transmission timing determination unit 13 calculates an accumulated correction added timing difference C (x) obtained by adding the current accumulated timing correction amount B (n) to each read timing difference A (x). The transmission timing determination unit 13 calculates a timing difference average value D (n) that is an average value of the calculated cumulative correction added timing differences C (x).

  The transmission timing determination unit 13 calculates the current timing correction amount F (n) by subtracting the current cumulative timing correction amount B (n) from the timing difference average value D (n) calculated in this way. .

  The transmission timing determination unit 13 corrects the current transmission timing based on the calculated timing correction amount F (n), and provides the transmission signal generation unit 3 with the current transmission timing. At this time, the transmission timing determination unit 13 updates and stores the current timing difference average value D (n) in the memory 130 as a new cumulative timing correction amount B (n + 1).

  The transmission signal generator 3 modulates the ship-specific data of the ship with a predetermined modulation method to generate an AIS communication signal. Then, the transmission signal generation unit 3 outputs a communication signal at the transmission timing given from the transmission timing determination unit 13. The output communication signal is transmitted to the outside via the transmission antenna 30.

Next, the transmission timing correction method will be described more specifically with reference to FIG.
FIG. 2 is a diagram illustrating a transmission timing correction method according to the present embodiment, and is a diagram illustrating a correction method at timings Tm and Tn. In this case, the case where the sampling time τ which is a problem in the past is longer than the transmission cycle (τ> Tn−Tm) is shown.

  At timing Tm, the own ship's transmission timing determination unit 13 stores the accumulated timing correction amount B (m) determined at the time of the previous own ship's transmission timing Tk. Further, the transmission timing determination unit 13 sequentially stores the timing difference A (x) between the sampling times τ before the timing Tm.

  When transmission at the timing Tm is set, the transmission timing determination unit 13 reads out the timing difference A (x) corresponding to the sampling time τ before the timing Tm from the memory 130, and accumulates a common accumulation in the timing difference A (x). The timing correction amount B (m) is added to calculate the accumulated correction added timing difference C (x) = A (x) + B (m). The transmission timing determination unit 13 calculates a timing difference average value D (m) that is an average value of the calculated cumulative correction added timing differences C (x). That is, in the case of AIS, since there are 2250 slots per minute, if the number of data per minute is Em, the timing difference average value D (m) at the timing Tm is

Is calculated using

  The transmission timing determination unit 13 subtracts the current accumulated timing correction amount B (m) from the timing difference average value D (m) calculated in this manner, thereby obtaining the timing correction amount F (m) = timing at the timing Tm. D (m) -B (m) is calculated. This calculation timing is set, for example, at least one slot before the timing at which the ship intends to transmit.

  The transmission timing determination unit 13 corrects the transmission timing of the ship based on the calculated timing correction amount F (m) and performs transmission. Further, the transmission timing determination unit 13 stores the calculated timing difference average value D (m) in the memory 130 as the accumulated timing correction amount B (n) at the next transmission timing Tn.

  Next, when transmission at the timing Tn is set, the transmission timing determination unit 13 reads the timing difference A (x) corresponding to the sampling time τ before the timing Tn from the memory 130, and at the timing difference A (x), The common accumulated timing correction amount B (n) is added to calculate the accumulated correction added timing difference C (x) = A (x) + B (n). That is, after the synchronization at timing Tm, until the timing Tn, the average value calculation is performed assuming that the acquired transmission timing includes the accumulated timing correction amount B (n) according to the actual timing shift amount.

  Then, the transmission timing determination unit 13 calculates a timing difference average value D (n) that is an average value of the calculated cumulative correction added timing differences C (x). That is, in the case of AIS, since there are 2250 slots per minute, assuming that the number of data per minute is En, the timing difference average value D (n) at the timing Tn is in accordance with equation (1). ,

Is calculated using

  The transmission timing determination unit 13 subtracts the current accumulated timing correction amount B (n) from the timing difference average value D (n) calculated in this manner, thereby obtaining the timing correction amount F (n) = timing at the timing Tn. D (n) -B (n) is calculated.

  The transmission timing determination unit 13 corrects the transmission timing of the ship based on the calculated timing correction amount F (n) and performs transmission. Further, the transmission timing determination unit 13 stores the calculated timing difference average value D (n) in the memory 130 as the accumulated timing correction amount B (n ′) at the next transmission timing Tn ′.

  By performing such processing, since the average value and the correction amount are calculated in a state where the transmission timing included in the sampling time τ is corrected by the cumulative timing correction amount B, it is not affected by the previous correction, The current correction amount can be accurately calculated. That is, even when the own ship's transmission timing is included in the sampling time τ, synchronization can be performed accurately.

FIG. 3 is a diagram showing a transmission timing correction result when this embodiment is used. In this figure, (A) shows the case where the ship's transmission cycle is 60 seconds, that is, if there is no ship's transmission timing within one minute of acquiring the transmission timing, (B) shows the case where the ship's transmission cycle is 30 seconds, C) shows a case where the transmission cycle of the ship is 10 seconds.
As shown in FIG. 3, by performing the transmission timing correction of this embodiment, synchronization can be performed reliably and accurately.

  FIG. 4 is a diagram showing a state of synchronization return when the ship moves to a different broadcast area after being synchronized. In this figure, (A) shows the case where the ship's transmission cycle is 60 seconds, that is, if there is no ship's transmission timing within one minute of acquiring the transmission timing, (B) shows the case where the ship's transmission cycle is 30 seconds, C) shows a case where the transmission cycle of the ship is 10 seconds.

  As shown in FIG. 4, even if the synchronization timing is changed due to a change in the broadcast area or the like, reliable and accurate synchronization can be performed again by using the configuration and processing of this embodiment. At this time, the shorter the transmission cycle, the more affected by the configuration and processing of this embodiment, and the quicker synchronization can be achieved.

  The above-described method performs addition calculation between each timing difference and the accumulated timing correction amount, average value calculation based on the added value, and difference calculation between the average value and the accumulated timing correction amount at each transmission timing. The calculation processing load becomes enormous as the number of transmission timings increases. For this reason, if the timing difference average value is calculated in each slot, it can be calculated by the following equation (2).

At this time, for example, at the timing Tn described above, the average timing difference value is D (n), the average timing difference value at the previous timing Tm is D (m), and the current timing difference is C (n). The timing difference average value D (n) at this time is represented by C (n-2250) when the timing difference is traced back by the sampling time τ and the number of data within the sampling time τ is Em.
D (n) = {D (m) * Em + C (n) -C (n-2250)} / En
This is calculated using the following formula.

  In this method, the timing difference average value D is stored and used, but the sum of the timing differences C before calculating the average value may be used. That is, D (m) * Em in the above formula may be stored and used at the next timing.

  By using such a method, the timing difference average value in each slot can be calculated once for each addition, subtraction, multiplication and division, and the amount of processing calculation can be reduced. This is particularly effective when the number of transmission timings is large, and the processing calculation load can be greatly reduced when transmission timings are set in a sea area where there are many other ships.

  Such timing difference average value D and timing difference C may be calculated for each slot or for each predetermined time interval.

  In the above description, the case where a plurality of timings have occurred in the past one minute has been described, but the above configuration and processing can be applied even if there is only one.

  By the way, when the above-described method is used, various processes such as the generation of the reference timing signal are based on the reference clock generated by the crystal oscillator in the synchronization device 1, and this reference clock is also generated by the crystal oscillator. There are variations due to individual differences. Since this variation has a uniform characteristic with respect to the true timing interval, the timing difference C (x) also increases or decreases uniformly when the above processing is continuously performed. For this reason, for example, if the calculated value of the timing difference C (x) increases uniformly, it reaches the maximum positive calculated value of the calculator in the transmission timing determination unit 13 and overflows. In such a case, the arithmetic value shifts from the + side maximum value to the − side maximum value so that the arithmetic unit does not overflow. In such a case, as shown in FIG. 9 described above, the timing difference average value including the overflow time or the underflow time becomes a value UNF that is different from the original accurate value COR. For this reason, the timing correction amount becomes incorrect and cannot be accurately synchronized.

In order to prevent this, the transmission timing determination unit 13 performs the process shown in FIG. FIG. 5 is a diagram for explaining a process for solving the problem caused by the overflow.
The transmission timing determination unit 13 calculates timing differences Ca (x), Cb (x), and Cc (Cc (x) obtained by adding different offset values (Offset1, Offset2, Offset3) to the timing difference C (x). x) is calculated. Further, the transmission timing determination unit 13 calculates difference values Ddab, Ddbc, and Ddca of the timing differences for calculation Ca (x), Cb (x), and Cc (x). Here, the difference values Ddb = ABS (Ca (x) −Cb (x)), Ddbc = ABS (Cb (x) −Cc (x)), Ddca = ABS (Cc (x) −Ca (x)) Calculated. Note that ABS () is an operator that returns an absolute value.

  By using such a difference value, as shown in FIG. 5, when an offset is related to any of the arithmetic timing differences Ca (x), Cb (x), Cc (x), the offset is related. The difference value using the timing difference for calculation becomes discontinuous. For example, when the calculation timing difference Ca (x) overflows at the timing T1 as shown in FIG. 5A, the difference value Ddb, as shown in FIGS. Ddca becomes discontinuous. When the calculation timing difference Cb (x) overflows at the timing T2 as shown in FIG. 5A, the difference value Ddb, as shown in FIGS. 5B and 5C at the timing T2. Ddbc becomes discontinuous. Further, when the calculation timing difference Cc (x) overflows at the timing T3 as shown in FIG. 5A, the difference value Ddbc, as shown in FIGS. 5C and 5D at the timing T3. Ddca becomes discontinuous.

  Using this state change, the transmission timing determination unit 13 periodically observes the difference values Ddab, Ddbc, Ddca (for example, every slot timing), and selects a calculation timing difference that is not related to the discontinuous difference value. Then, the timing difference average value is calculated. At this time, the transmission timing determination unit 13 subtracts the offset value used for the selected calculation timing difference from the timing difference average value. Thereby, an accurate timing difference average value can be calculated. Then, the transmission timing determination unit 13 calculates a timing correction amount using the timing difference average value calculated in this way.

  By performing such processing, even if an overflow or underflow of the arithmetic unit based on a timing shift potentially included in the synchronization device 1 occurs, an accurate timing correction amount can be calculated without being affected by this. Can do.

  The offset detection may be performed for each slot, but the offset detection may be omitted during a period in which an overflow is unlikely to occur. For example, if overflow is detected several times, a period during which overflow does not occur can be estimated from the overflow interval, and offset detection can be omitted.

It is a block diagram which shows the main structures of the synchronizer 1 of this embodiment, and the ship automatic identification device provided with the same. It is a figure explaining the correction method of the transmission timing of this embodiment, and is a figure which shows the correction method in the time of timing Tm and Tn. It is the figure which showed the transmission timing correction result at the time of using this embodiment. It is the figure which showed the state of the synchronous return when the own ship transfers to a different broadcast area | region after being synchronized. It is a figure explaining the process for eliminating the problem by overflow. It is a figure explaining generation | occurrence | production of the synchronization shift by the transmission timing of the own ship. It is a figure explaining generation | occurrence | production of the synchronization shift by the transmission timing of the own ship. It is a figure which shows the influence by the correction | amendment by the transmission timing of the own ship before the last time. It is a figure which shows the problem which generate | occur | produces when a calculated value overflows.

Explanation of symbols

1-synchronizer, 11-received signal demodulator, 12-reference timing signal generator, 13-transmit timing determiner, 130-memory, 3-transmit signal generator, 20-receive antenna, 30-transmit antenna

Claims (5)

While receiving communication data from another station and obtaining the transmission timing of communication data from the other station, transmission timing obtaining means for obtaining the transmission timing of the own station at the time of transmission of the own station;
A reference timing generation means for generating a reference timing consisting of a fixed time interval;
The timing difference between the transmission timing of the own station using the reference timing and the transmission timing of each station is calculated for each transmission timing of each station, and is calculated at a predetermined time in the past from the timing at which the current station intends to transmit. The timing difference is obtained by calculating a mean value by obtaining a timing difference, adding a common cumulative timing difference based on the timing correction value determined at the previous transmission timing to the timing difference, and calculating an average value. And a transmission timing determination means for determining a timing correction value at a timing at which the current local station attempts to transmit by subtracting the preset cumulative timing difference from the average timing difference value. The transmission timing determining means includes
The cumulative timing difference and the timing correction value are calculated immediately before the transmission timing of the own station,
The current timing difference average value is D (n), the previous timing difference average value is D (n-1), the current timing difference is C (n), and the timing difference when the predetermined time is traced back. C (n−p), and T (n−1) and T (n) as the number of data in the predetermined time at each timing,
This timing difference average value D (n)
D (n) = {D (n-1) * T (n-1) + C (n) -C (n-p)} / T (n)
The synchronization device according to claim 1, wherein the synchronization device is calculated using the following formula. The transmission timing determining means includes
When calculating the timing difference average value,
Calculate at least three or more arithmetic timing differences obtained by adding different offset values in advance,
Each difference value of the at least three calculation timing differences is calculated for each preset offset determination timing,
3. The synchronization device according to claim 1, wherein the timing difference average value is calculated using an arithmetic timing difference that is not related to the difference value that is discontinuous over time. While receiving the communication data from the other station and obtaining the transmission timing of the communication data from the other station, obtaining the transmission timing of the own station at the time of transmission of the own station,
Calculate the timing difference between the transmission timing of the own station and the transmission timing of each station using a reference timing consisting of a fixed time interval for each transmission timing of each station,
Get the timing difference calculated within a predetermined time in the past than the timing this station is going to transmit,
The timing difference average value is calculated by adding the common cumulative timing difference based on the timing correction value determined at the previous transmission timing and calculating the average value with respect to the timing difference,
By subtracting the preset cumulative timing difference from the timing difference average value, a timing correction value at a timing at which the current station is going to transmit is determined,
Based on the determined timing correction value, the transmission timing of the current station is corrected.
Synchronization method. When calculating the timing difference average value,
Calculate at least three or more arithmetic timing differences obtained by adding different offset values in advance,
Each difference value of the at least three calculation timing differences is calculated for each preset offset determination timing,
The synchronization method according to claim 4, wherein the timing difference average value is calculated using an arithmetic timing difference that is not related to the difference value that is discontinuous over time.

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