JPH10285140A - Time synchronization system and time synchronization method in time synchronization system - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To accurately synchronize time between a master station and a slave station even if the distance between the master station and the slave station is long. SOLUTION: In a master station 1, when a transmitter 15 transmits a trigger signal S4 for measuring a signal propagation delay time T to a slave station 2, the slave station 2 receives the trigger signal S4 and returns a trigger signal. A reply is sent to the main station 1 as S4. Then, based on the trigger signal S4 and the turned-back trigger signal S4, the delay time calculator 18 calculates the master station 1 and the slave station 2 based on the trigger signal S4.
, And calculates a signal propagation delay time T according to a distance or the like to the time signal correction circuit 13. Time signal correction circuit 1
3 is a time advanced by the signal propagation delay time T based on the time correction information, which is a signal propagation delay time T according to the distance between the master station 1 and the slave station 2 from the delay time calculator 18, and the like. The transmission information is transmitted, and the clock 12 of the master station 1 is synchronized with the clock 23 of the slave station 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a time synchronization system for synchronizing time between a master station and a slave station, and to a time synchronization method in the time synchronization system.

[0002]

2. Description of the Related Art As a conventional time synchronization system, for example, a spread spectrum communication system and a GPS (Global
Positioning System) is known.

FIG. 11 shows a configuration of a time synchronization system based on a conventional spread spectrum communication system described in Japanese Patent Application Laid-Open No. 7-38529. In the figure, 41 is a time management unit, 42 is a weak radio wave transmission unit for transmitting time information, 43 is an antenna, 44 is an FH controller, 45
Is a carrier generator, 46 is a primary modulator for modulating data to be transmitted, 47 and 48 are frequency converters, 49 is an antenna,
50 is an input terminal for inputting data, 51 is an IF signal, 5
2 is an RF signal. 53 and 58 are antennas, 5
4 is a weak radio wave receiving unit for receiving time information, 55 is a time information demodulator, 56 is an FH controller, 57 is a local oscillator, 58 is an antenna, 59 and 60 are frequency converters,
61 is a primary demodulator, 62 is an RF signal, 63 is an IF signal,
64 is an output terminal, 65 is a master station for performing time management of each slave station, and 66 is a slave station.

Next, the operation will be described. First, the time management unit 4
When 1 gives the time information data to the weak radio wave transmission unit 42, the weak radio wave transmission unit 42 transmits this time information via the antenna 43. The time management unit 41 also provides time information to the FH controller 44. The FH controller 44 calculates a hopping pattern based on the provided time information, and provides the hopping pattern to the carrier generation unit 45. On the other hand, data as information is provided from the input terminal 50 to the primary modulator 46. On the other hand, the primary modulator 46 performs FSK modulation or PS modulation.
The data is primarily modulated by K modulation or the like, and is provided to the first frequency converter 47. The first frequency conversion unit 47 mixes the primary modulated data with the carrier wave supplied from the carrier wave generation unit 45, generates an IF signal 51, and supplies the IF signal 51 to the second frequency conversion unit 48 to convert the data into an RF signal 52. , Antenna 49
Send from.

On the other hand, the slave station 66 receives and demodulates at the weak radio wave receiving unit 54 and the time information demodulation unit 55 via the antenna 53 to demodulate the original time information. The demodulated time information is given to the FH controller 57,
The controller 57 calculates a hopping pattern based on the given time information signal, provides a pattern signal to the local generator 57, generates a local signal based on the pattern, and provides the second frequency converter 60.

[0006] The signal radiated from the antenna 49 is received by the antenna 58 and the first frequency converter 59 to obtain an IF signal 63. The IF signal 63 is frequency-converted by the second frequency converter 60 using the local signal generated by the local oscillator 57. At this time, the local signal is hopping based on the time information. As a result, the hopping component in the received signal can be removed and despread by changing the frequency in the frequency converter 60, and the primary demodulator 61 And the data is output to the output terminal 64.

Further, Japanese Patent Application Laid-Open No. 7-18328 discloses that
A time synchronization system that uses a GPS time signal to synchronize in a spread spectrum communication system is described. The GPS system is a satellite navigation system, and usually obtains a three-dimensional position (x, y, z) and time of a receiver by receiving different radio waves transmitted from four or more satellites on the ground. This system has been developed for military use, and recently C / A (Coarse / Acq)
uisition) Only the code is released.

[0008]

However, in the conventional time synchronization system based on the spread spectrum communication system, the master station 65 and the slave station 66 are simply transmitted from the master station 65 to the slave station 66. Time synchronization between the master station 65 and the slave station 6
When the distance between the master station 65 and the slave station 6 becomes large, there is a problem that time synchronization cannot be performed with high accuracy between the master station 65 and the slave station 66 due to the influence of signal transmission delay. .

Further, the conventional GPS time synchronization system has a problem that only a C / A code can be used as a time signal, and it is difficult to obtain a signal having an accuracy of 100 ns or less due to ionospheric delay.

Therefore, the present invention has been made to solve such a problem. Even when the distance between the master station and the slave station is long, the time between the master station and the slave station can be accurately determined. An object of the present invention is to provide a time synchronization system capable of achieving synchronization and a time synchronization method in the time synchronization system.

[0011]

According to the present invention, there is provided a time synchronization system for synchronizing time between a master station and a slave station. , A reference signal generating means for generating a reference signal for measuring a signal propagation delay time from the master station to the slave station, and correcting the time signal generated by the time signal generating means. Time signal correction means, and transmission means for transmitting the time signal corrected by the time signal correction means and the reference signal generated by the reference signal generation means toward the slave station, while the slave station is the master station Receiving means for receiving the time signal and the reference signal transmitted by the transmitting means, clocking means for measuring the time on the slave station side based on the time signal received by the receiving means, and a reference signal received by the receiving means Reply means for replying to the master station, wherein the master station further includes a receiving means for receiving a reference signal returned by the reply means of the slave station, and a receiving means for receiving the reference signal. Delay time calculating means for calculating a signal propagation delay time from the master station to the slave station based on a time difference between a reference signal from a slave station and a reference signal generated by the reference signal generating means; The means corrects the time signal generated by the time signal generating means so as to be advanced by the delay time calculated by the delay time calculating means.

In the present invention, the transmitting means of the main station is a direct spread transmitter for transmitting by direct spreading modulation, and the receiving means of the main station is a direct spreading receiver for receiving by direct spreading demodulation. The return means of the slave station is a direct spread transmitter for returning by direct spreading modulation, and the receiving means of the slave station is a direct spread receiver for receiving by direct spread demodulation.

In the present invention, the transmitting means of the master station is a digital transmitter for transmitting by digital modulation, and the receiving means of the master station is a digital receiver for receiving by digital demodulation, while the reply means of the slave station is provided. Is
A digital transmitter for returning by digital modulation, and the receiving means of the slave station is a digital receiver for receiving by digital demodulation.

In the present invention, the transmitting means of the main station is a frequency hopping transmitter for transmitting by frequency hopping modulation, and the receiving means of the main station is a frequency hopping receiver for receiving by frequency hopping demodulation. The return means of the slave station is a frequency hopping transmitter for returning by frequency hopping modulation, and the receiving means of the slave station is a frequency hopping receiver for receiving by frequency hopping demodulation.

In the present invention, the transmitting means of the main station is a laser wave transmitter for transmitting by laser wave modulation, and the receiving means of the main station is a laser wave receiver for receiving by laser wave demodulation. The return means of the slave station is a laser wave transmitter for returning by laser wave modulation, and the receiving means of the slave station is a laser wave receiver for receiving by laser wave demodulation.

In the present invention, the transmitting means of the main station is a visible light transmitter for transmitting by visible light modulation, and the receiving means of the main station is a visible light receiver for receiving by visible light demodulation. The return means of the slave station is a visible light transmitter for returning by visible light modulation, and the receiving means of the slave station is a visible light receiver for receiving by visible light demodulation.

Further, in the next invention, there is provided a time synchronization method in a time synchronization system in which time is synchronized between a master station and a slave station, wherein the master station generates a time signal and A reference signal for measuring a signal propagation delay time from the master station to the slave station is generated, the time signal is corrected, and the corrected time signal and the reference signal are transmitted toward the slave station. The slave station receives the time signal and the reference signal transmitted by the master station, outputs a time signal based on the received time signal, and returns a reference signal to the master station. Further, receiving the reference signal returned by the slave station, the signal propagation delay time from the master station to the slave station based on the received time difference between the reference signal from the slave station and the generated reference signal. Calculation , It is corrected to advance by the delay time which is the calculated time signal as described above occurred.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. FIG. 1 shows a configuration of a time synchronization system according to a first embodiment of the present invention. In the figure, 1 is a master station,
2 is a slave station. First, the configuration in the master station 1 will be described. Reference numeral 11 denotes a high-precision oscillator for generating a reference clock signal S1, and 12 denotes a reference clock signal S from the high-precision oscillator 11.
The clock 13 outputs the reference time signal S2 based on the reference time signal 1. The reference time signal S2 output from the clock 23 is corrected based on the signal propagation delay time T between the master station 1 and the slave station 2 as described later. A time signal correction circuit for outputting a correction time signal S3; a trigger signal generator 14 for outputting a trigger signal S4 as a reference signal for measuring a signal propagation delay time T from the master station 1 to the slave station 2; Clock signal S
1. A direct spreading transmitter having a direct spreading modulator (not shown) for directly spreading and transmitting the corrected time signal S3 and the trigger signal S4, and 16a and 16b are transmitting and receiving antennas, respectively. Is a direct-spread receiver having a direct-spread demodulator (not shown) for directly spreading and demodulating and receiving the trigger signal S4 returned from the slave station 18;
Is a delay time calculator for calculating a signal propagation delay time T between the master station 1 and the slave station 2.

The configuration in the slave station 2 includes 21a and 21b.
Is a transmitting and receiving antenna, 22 is a direct spread receiver having a direct spread demodulator for receiving a reference clock signal S1, a corrected time signal S3, and a trigger signal S4 from the main station 1, and 23 is a received corrected time signal A clock for measuring the time based on S3 and the reference clock signal S1, and a direct spread transmitter 24 having a direct spread modulator for returning the received trigger signal S4 to the main station 1 and the like.

Next, the operation of the time synchronization system according to the first embodiment will be described. First, on the master station 1 side, the reference clock signal S serving as a reference when counting the time at which the high-precision oscillator 11 synchronizes with the master station 1 and this system is used.
1 and the clock 12 has its reference clock signal S
1, the current time is counted, and a reference time signal S2 indicating the current time is output to a time display unit (not shown) composed of an LED, an LCD, etc., to display the current time on the main station 1 side. , To the time signal correction circuit 13.

Then, the time signal correction circuit 13 operates the clock 1
The reference time signal S2 input from the second base station 2 is corrected by advancing the time by the signal propagation delay time T from the master station 1 to the slave station 2 calculated by the delay time calculator 18 as described later, and is directly converted into a corrected time signal S3. Output to the spread transmitter 15.

The trigger signal generator 14 generates a trigger signal S4 generated by a code having a low probability of erroneous detection, such as a gold code, based on the reference clock signal S1 generated by the high-precision oscillator 11. 15 is output.

Then, the direct spread transmitter 15 receives the reference clock signal S 1 from the high precision oscillator 11, the corrected time signal S 3 obtained by correcting the reference time signal S 2 by the time signal correction circuit 13, and the signal from the trigger signal generator 14. Trigger signal S
4 is subjected to time division multiplexing and direct spread modulation, and is transmitted to the slave station 2 via the transmitting antenna 16a.

In the slave station 2, the time division multiplexed and directly spread modulated reference clock signal S1, the corrected time signal S3 and the trigger signal S4 from the master station 1 are directly spread-received via the receiving antenna 21b. Machine 22 receives the
The received signal is directly spread-spectrum demodulated and time-division multiplexed to output a reference clock signal S1, a corrected time signal S3, and a trigger signal S4.

Then, in the slave station 2, the clock 23 continuously outputs the reference clock signal S 1,
And the reference time signal S2 by the time signal correction circuit 13.
The time is counted based on the corrected time signal S3 advanced by the signal propagation delay time T between the master station 1 and the slave station 2.

Therefore, the clock 23 of the slave station 2 uses the reference clock signal S1 and the time signal correction circuit 1 of the master station 1.
3, the time is counted based on the corrected time signal S3 advanced by the signal propagation delay time T between the master station 1 and the slave station 2 with respect to the reference time signal S2. Therefore, even if the signal arrives at the slave station 2 after being delayed by the signal propagation delay time T, the time synchronized with the clock 12 of the master station 1 can always be measured.

Next, the operation for correcting the signal propagation delay time T from the master station 1 to the slave station 2 will be described.

First, in the slave station 2, the direct spread receiver 22
Directly transmits the trigger signal S4 received by the
4 and the direct spread transmitter 24 transmits the antenna 21 for transmission.
The data is returned to the master station 1 via a.

Then, the main station 1 receives the antenna 16 for reception.
The direct spread receiver 17 receives the trigger signal S4 turned back from the slave station 2 via b, and outputs it to the delay time calculator 18.

The trigger signal S4 generated by the trigger signal generator 14 and the trigger signal S4 returned from the slave station 2 are input to the delay time calculator 18, and the delay time calculator 18 The trigger signal S4 generated by the signal generator 14 and the trigger signal S returned from the slave station 2
4, the signal propagation delay time T corresponding to the distance between the master station 1 and the slave station 2 is calculated, and is output to the time signal correction circuit 13 as the correction amount signal S5.

Here, an example of a method of calculating the signal propagation delay time T in the delay time calculator 18 will be described. The time difference between the trigger signal S4 in the master station 1 and the slave station 2 and the folded trigger signal S4 is determined by However, since each device is provided in the master station 1 and the slave station 2,
The master station 1 or the slave station 2 can be regarded as a predetermined value which is substantially zero or very close to zero.

For this reason, the delay time correction circuit 18 obtains the time difference between the trigger signal S4 and the trigger signal S4 that are folded back based on the reference clock signal S1, and calculates the signal propagation delay time in the master station 1 and the slave station 2. If it is regarded as 0, the obtained time difference is not corrected, and if the signal propagation delay time T in the master station 1 or the slave station 2 is taken into consideration, the obtained time difference is further corrected by the predetermined value, and 1 /
By doubling, the signal propagation delay time T between master station 1 and slave station 2 can be determined.

That is, the trigger signal S4 transmitted from the master station 1 to the slave station 2 and the trigger signal S4 received by the slave station 2 from the slave station 2
The time difference from the trigger signal S4 returned to the main station 1
Is twice as long as the signal propagation delay time T between the master station 1 and the slave station 2 including the signal propagation delay time T from the slave station 2 to the slave station 2 and the signal propagation delay time T from the slave station 2 to the master station 1. The signal propagation delay time T between the master station 1 and the slave station 2 is obtained by halving the time difference.

FIG. 2 shows the relationship between the trigger signal S4 and the folded trigger signal S4 and the signal propagation delay time T between the master station 1 and the slave station 2. FIG. 2A shows a reference pulse signal S1 generated by the high-precision oscillator 11 of the main station 1.
(B) shows the timing of the direct spread transmitter 15 of the main station 1.
3 shows the timing of the correction time signal S3 and the timing of the trigger signal S4 to be transmitted. (C) shows the timing of the trigger signal S4 received by the direct spreading receiver 22 in the slave station 2 and delayed by the signal propagation delay time T between the master station 1 and the slave station 2; d) shows the timing of the trigger signal S4 which is turned back from the slave station 2 to the master station 1 and received by the direct-sequence receiver 17 of the master station 1, respectively.

Therefore, the transmission timing of the trigger signal S4 transmitted from the master station 1 to the slave station 2 shown in FIG. 2B and the return timing from the slave station 2 to the master station 1 shown in FIG. The time difference between the reception timing of the received trigger signal S4 and the reception timing is twice as long as the signal propagation delay time T between the master station 1 and the slave station 2. It can be seen that the signal propagation delay time T with the slave station 2 can be obtained.

The delay time calculator 18 calculates the signal propagation delay time T between the master station 1 and the slave station 2 in this way, and instructs the advance of the time by the signal propagation delay time T in advance. Is transmitted to the time signal correction circuit 13.

In the time signal correction circuit 13, based on the correction amount signal S5 from the delay time calculator 18, the clock 12
The reference time signal S2 input from the
Is advanced by the signal propagation delay time T corresponding to the distance between the master station 1 and the slave station 2 calculated as described above to obtain a corrected time signal S3, and the corrected time signal S3 thus corrected is directly transmitted to the direct spread transmitter 15 and The data is transmitted to the slave station 2 via the antenna 16a.

Therefore, even if the corrected time signal S3 arrives from the master station 1 to the slave station 2 with a delay of the signal propagation delay time T, the corrected time signal S3 is previously stored in the master station 1 as described above. Since the time signal S2 is corrected to a value advanced by the signal propagation delay time T between the master station 1 and the slave station 2, there is a signal propagation delay time T between the master station 1 and the slave station 2. However, the clock 23 of the slave station 2 measures the current time based on the corrected time signal S3, so that the time based on the time signal output from the clock 23 of the master station 1 and the time measured by the clock 23 of the slave station 2 Will be synchronized.

Therefore, according to the first embodiment, even if the distance between the master station 1 and the slave station 2 changes, the delay time calculator 18 determines whether the master station 1 and the slave station 2 correspond to the distance or the like. Since the signal propagation delay time T is obtained, and the time signal correction circuit 13 corrects the time signal based on the signal propagation delay time T and transmits the time signal, the master station 1 and the slave station 2 are separated from each other. Even in the case where a delay time occurs in signal propagation, the signal propagation delay time T can always be corrected.
And the slave station 2 can always synchronize the time quickly and with high accuracy.

That is, in the first embodiment, the master station 1 and the slave station 2 move, and the distance between the master station 1 and the slave station 2 and the signal propagation conditions change, and the master station 1 and the slave station 2 change. And the signal propagation delay time T changes, the trigger signal S
4 is always transmitted from the master station 1 to the slave station 2, and a trigger signal S4 that is folded back to the trigger signal S4 is returned to the master station 1 and a signal between the master station 1 and the slave station 2 is transmitted. The propagation delay time T is always calculated, and based on the signal propagation delay time T, the time signal correction circuit 13 advances the reference time signal S2 to be transmitted to the slave station 2 to advance the corrected time signal S3
Therefore, even if the signal propagation delay time T between the master station 1 and the slave station 2 changes, every time the signal propagation delay time T changes, the time between the master station 1 and the slave station 2 is changed. By synchronizing and correcting the synchronization based on the signal propagation delay time T therebetween, time synchronization in the present system can always be quickly and accurately performed.

In the first embodiment, time transmission by direct spreading modulation and demodulation by the direct spreading transmitter 15 and the direct spreading receiver 22 has been described. However, the present invention is not limited to these. For example, , GMSK modulation, DP
Transmitter using digital modulator such as SK modulation and G
Of course, a receiver using a digital demodulator such as MSK demodulation and DPSK demodulation, or a transmitter and a receiver using frequency hopping modulation and demodulation may be used.

In the first embodiment, the transmission of the time signal between the master station 1 and the slave station 2 has been described by using the radio, but in the present invention, a digital modulator such as DPSK modulation is used. A transmitter and a receiver using a digital demodulator such as DPSK demodulation may be used, and a transmission medium and a separate coaxial cable may be used as a transmission medium. Alternatively, one coaxial cable and one coaxial cable may be used. Of course, a duplexer may be provided at both ends.

Further, the direct spread transmitter 15 is used as an optical transmitter,
The direct spread receiver 4 may be an optical receiver, and transmission and reception optical cables may be provided instead of transmission and reception coaxial cables, or optical multiplexer / demultiplexers may be provided at both ends of one optical cable. Alternatively, the direct spread transmitter 15 may be used as a laser wave transmitter, the direct spread receiver 4 may be used as a laser wave receiver, or the direct spread transmitter 15 may be used as a visible light transmitter. May be a visible light receiver.

Also, in the time synchronization system of the first embodiment, only one slave station 2 is provided for one master station 1 for convenience. However, in the present invention, one slave station 1 is provided for one master station 1. A time synchronization system is constructed by providing a plurality of slave stations 2, and each slave station 2 receives a corrected time signal corrected in accordance with the signal propagation delay time T from the master station 1 so that one master station Of course, time synchronization may be established between the slave station and a plurality of slave stations. However, in this case, it is necessary to separately calculate the signal propagation delay time between the master station and each slave station. Therefore, for example, a trigger signal generator in the master station, a time signal correction circuit, a delay time calculation A trigger device or the like can be provided for each of the plurality of slave stations, or can be generated, corrected, calculated, etc., so that each trigger signal generator can receive signals corresponding to each slave station, that is, distinguishably among a plurality of slave stations. Trigger signals with different trigger patterns and frequency characteristics are sent to the slave stations, and the trigger signals that are turned back are received so that they can be distinguished from each slave station. By calculating the propagation delay time, each corresponding time signal correction circuit corrects the reference time signal based on the signal propagation delay time between each slave station and outputs a corrected time, Station and may be so take time synchronization between a plurality each slave station.

[0045]

As described above, according to the present invention, the master station generates a time signal, and also generates a reference signal for measuring a signal propagation delay time from the master station to the slave station. And transmits the corrected time signal and reference signal to the slave station, while the slave station receives the time signal and the reference signal transmitted by the master station, and generates a time signal based on the received time signal. Output, and returns a reference signal to the master station.The master station further receives the reference signal returned by the slave station, and obtains a time difference between the received reference signal from the slave station and the original reference signal. Based on the above, the signal propagation delay time from the master station to the slave station is calculated, and the generated time signal is corrected so as to be advanced by the calculated delay time. Cause delay time Even if it is possible to synchronize the time between the main station and the slave station always quickly and accurately.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a configuration of a time synchronization system according to the present invention.

FIG. 2 is a configuration diagram illustrating a method of measuring a signal propagation delay time T between a master station and a slave station.

FIG. 3 is a configuration diagram showing a configuration of a conventional time synchronization system.

[Description of Signs] 1 master station, 2 slave stations, 11 high-precision oscillator, 12 clock (time signal generation means), 13 time signal correction circuit (time signal correction means), 14 trigger signal generator (reference signal generation means), 15 direct spreading transmitter (transmitting means), 16
a, 16b antenna, 17 direct spreading receiver (receiving means), 18 delay time calculator (delay time calculating means), 2
1a, 21b antenna, 22 direct spread receiver (receiver), 23 clock (timer), 24 transmitter (reply).

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04L 7/00 H04B 7/26 104A

Claims (7)

[Claims] 1. A time synchronization system in which time is synchronized between a master station and a slave station, the master station comprising: a time signal generating means for generating a time signal; Reference signal generating means for generating a reference signal for measuring a signal propagation delay time to the time signal; time signal correcting means for correcting the time signal generated by the time signal generating means; and time corrected by the time signal correcting means. Transmitting means for transmitting a signal and a reference signal generated by the reference signal generating means to the slave station, wherein the slave station receives a time signal and a reference signal transmitted by the transmitting means of the master station. And a timer means for measuring the time on the slave station side based on the time signal received by the receiving means, and a reply means for returning the reference signal received by the receiving means to the master station, The master station further includes a receiving means for receiving a reference signal returned by the reply means of the slave station, a reference signal from the slave station received by the receiving means of the master station, and a reference signal generated by the reference signal generating means. Delay time calculating means for calculating a signal propagation delay time from the master station to the slave station based on a time difference from the signal, and the time signal correcting means converts the time signal generated by the time signal generating means A time synchronization system, wherein correction is made to advance by the delay time calculated by the delay time calculation means. 2. The transmitting means of the master station is a direct spreading transmitter for transmitting by direct spreading modulation. The receiving means of the master station is a direct spreading receiver for receiving by direct spreading demodulation. 2. The time synchronization system according to claim 1, wherein is a direct-spread transmitter for returning by direct-spread modulation, and the receiving means of the slave station is a direct-spread receiver for receiving by direct-spread demodulation. 3. The transmitting means of the master station is a digital transmitter for transmitting by digital modulation. The receiving means of the master station is a digital receiver for receiving by digital demodulation. 2. A time synchronization system according to claim 1, wherein the digital signal is a digital transmitter which returns the digital signal by a digital demodulator. 4. The transmitting means of the master station is a frequency hopping transmitter for transmitting by frequency hopping modulation. The receiving means of the master station is a frequency hopping receiver for receiving by frequency hopping demodulation. 2. The time synchronization system according to claim 1, wherein is a frequency hopping transmitter returning by frequency hopping modulation, and the receiving means of the slave station is a frequency hopping receiver receiving by frequency hopping demodulation. 5. The transmitting means of the master station is a laser wave transmitter for transmitting by laser wave modulation, and the receiving means of the master station is a laser wave receiver for receiving by laser wave demodulation. 2. The time synchronization system according to claim 1, wherein: is a laser wave transmitter that replies by laser wave modulation; and the receiving means of the slave station is a laser wave receiver that receives by laser wave demodulation. 6. The transmitting means of the master station is a visible light transmitter for transmitting by visible light modulation, and the receiving means of the master station is a visible light receiver for receiving by visible light demodulation. 2. The time synchronization system according to claim 1, wherein is a visible light transmitter that replies by visible light modulation, and the receiving means of the slave station is a visible light receiver that receives by visible light demodulation. 7. A time synchronizing method in a time synchronizing system in which time is synchronized between a master station and a slave station, wherein the master station generates a time signal and transmits the time signal from the master station to the slave station. A reference signal for measuring a signal propagation delay time to the base station is generated, the time signal is corrected, and the corrected time signal and the reference signal are transmitted to the slave station. The time signal and the reference signal transmitted by the station are received, a time signal is output based on the received time signal, and a reference signal is returned to the master station. The master station further includes the slave station. Receives the returned reference signal, calculates a signal propagation delay time from the master station to the slave station based on a time difference between the received reference signal from the slave station and the generated reference signal, and did Time synchronization method in the time synchronization system and correcting to advance the time signal by a delay time amount obtained by the calculation.