JPH11344583A - Time synchronizing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a time synchronizing method with high accuracy which is not affected by the length of an optical fiber or the difference in wavelength. SOLUTION: The optical signal is transmitted from an optical transmitter 2 of the main node, the optical signal is allowed to reach the sub-node through an optical fiber 6, the reached optical signal is returned to the main node through the optical fiber 6, the optical signal is received by an optical receiver 3 of the main node, the delay time for the reciprocation of the optical signal is measured, the time difference between the transmission time of the optical signal of the main node and the reception time of the optical signal of the sub-node is obtained from the value, the time difference and the clock time of the main node are transmitted, and the clock time of the sub-node is synchronized with the time of the clock of the main node.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time synchronization method in an optical communication network.

[0002]

2. Description of the Related Art High precision time synchronization is required in various fields. When trying to synchronize the time between two geographically distant points, the delay time when transmitting the reference time signal becomes a considerable amount of time.

When an optical fiber is used as a transmission medium,
There is a time synchronization method shown in FIG. In this case, the delay measuring signal generated by the clock 1 at the node A is converted into an optical signal by the optical transmitter 2, and the signal is transmitted to the node B using the optical fiber 6.
Send to In the node B, the delay measuring signal received by the optical receiver 8 is converted into an optical signal by the optical transmitter 9, and the optical fiber 6 '
And send it back to node A. In the node A, the returned delay measuring signal is received by the optical receiver 3, and the difference between the transmission time and the receiving time of the delay measuring signal is measured by the counter 5.

The delay time from node A to node B is Δ
Assuming that T1 is the delay time from the node B to the node A is ΔT2, the counter 5 of the node A can measure the round trip delay time ΔT = ΔT1 + ΔT2. Optical fiber 6
If the lengths of と and 6 'are approximately equal, it can be assumed that ΔT1 仮 定 ΔT2, so that the one-way delay time from node A to node B can be estimated as ΔT1 ≒ ΔT2. Based on this result,
If the reference time T0 and the delay time ΔT held by the clock 1 are transmitted from the node A to the node B, and the time of the clock 10 at the node B is set to T0 + ΔT / 2, the time synchronization between the nodes A and B is established. To establish.

Up to this point, it has been assumed that ΔT11ΔT2,
In practice, the length of the optical fiber 6 used for transmission from the node A to the node B and the length of the optical fiber 6 'used for transmission from the node B to the node A are completely the same. Because of the difficulty, a delay time error occurs. As a method for improving this point, there is a time synchronization method using wavelength multiplexing shown in FIG.

In this case, the delay measuring signal generated by the clock 1 at the node A is converted into an optical signal at the wavelength λa by the optical transmitter 2 and transmitted to the node B using the optical fiber 6. In the node B, the delay measuring signal received by the optical receiver 8 is converted into an optical signal by the optical transmitter 9 at the wavelength λb (λa ≠ λb), and sent back to the node A using the same optical fiber 6. 4
And 7 are wavelength multiplexing devices. In the node A, the returned delay measuring signal is received by the optical receiver 3, and the difference between the transmission time and the receiving time of the delay measuring signal is measured by the counter 5.

In this method, since the same optical fiber 6 is used, there is no delay time error due to the difference in the length of the optical fiber. However, since the optical wavelength λa used for transmission from the node A to the node B and the optical wavelength λb used for transmission from the node B to the node A are different, the error of the delay time due to the dispersion of the optical fiber is reduced. Remains. For example, 15
When using an optical fiber whose dispersion becomes 0 at 50 nm,
Since the dispersion gradient is about 0.07 ps / nm ² / km, the wavelength λa =
The delay time error when using 1550 nm and λb = 1310 nm is 1
4 ns per km.

However, for example, in a positioning system that determines a position based on the arrival time of a radio wave from a reference station,
In the case where the clock of the reference station is time-synchronized, it is necessary to keep the clock synchronization accuracy within 1 ns in order to keep the positioning accuracy within 30 cm.

Similarly, there has been proposed a method of measuring the round-trip phase difference of a delay measurement signal using one transmission line and using half of the phase difference time as the delay time of the transmission line. JP
7-162344 "Transmission delay measurement method"), this method also
It is difficult to be practical in a high frequency light region.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly accurate time synchronization method which is not affected by differences in the length and wavelength of an optical fiber in view of the above-mentioned problems. .

[0011]

In order to achieve the above object, the time synchronization method of the present invention transmits an optical signal from an optical transmitter of a master node and transmits the optical signal to a slave node via an optical fiber. The reflected optical signal is reflected by the optical signal reflecting means of the slave node, the reflected optical signal is returned to the main node via the optical fiber, and the optical signal is received by the optical receiver of the main node. Then, the delay time of the reciprocation of the optical signal is measured, and the time difference between the transmission time of the optical signal of the main node and the reception time of the optical signal of the slave node is obtained from the measured value. Is sent to the slave node, and the clock time of the slave node is synchronized with the clock time of the master node.

According to the time synchronization method of the present invention, the round-trip delay time of the optical signal is measured using the optical fiber of the same round trip and the optical signal of the same wavelength. Alternatively, highly accurate measurement can be performed without including an error in delay time due to a difference in wavelength.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1] FIGS. 3 to 5 are conceptual diagrams of an example of an optical communication system for implementing the time synchronization method of the present invention.
In the normal communication mode, the connections of the optical switches 11 and 12 are as shown in FIG. When measuring the delay time, a switching signal is sent from node A to node B in advance,
The connection of the optical switch 12 is switched as shown in FIG. After such switching, a signal for delay measurement is generated by the clock 1 of the node A, the signal is converted into an optical signal by the optical transmitter 2, and transmitted to the node B using the optical fiber 6.

At the node B, the above-mentioned signal for delay measurement is reflected by the high reflection coating section 13 and sent back to the node A using the same optical fiber 6. In the node A, the connection of the optical switch 11 after the transmission of the delay measurement signal is switched as shown in FIG. 5, and the returned delay measurement signal is received by the optical receiver 14, and the delay measurement signal is transmitted. The difference between the transmission time and the reception time is measured by the counter 5.

The delay time from node A to node B is Δ
Assuming that T1 is the delay time from the node B to the node A is ΔT2, the counter 5 of the node A can measure the round trip delay time ΔT = ΔT1 + ΔT2. Since the same optical fiber and the same light wavelength λa are used, ΔT1 = Δ
T2 holds, and the one-way delay time from the node A to the node B is ΔT1 = ΔT2 = ΔT / 2. Based on the result, the reference time T0 and the delay time ΔT / 2 held by the clock 1 are transmitted from the node A to the node B, and the node B
If the time of clock 10 at is T0 + ΔT / 2,
High-precision time synchronization is established between the nodes A and B.

[Embodiment 2] FIGS. 6 to 8 are conceptual diagrams of an example of a wavelength division multiplexing optical communication system for implementing the time synchronization method of the present invention. In the normal communication mode, the connections of the optical switches 11 and 12 are as shown in FIG. When measuring the delay time, a switching signal is sent from node A to node B in advance.
To switch the connection of the optical switch 12 as shown in FIG. After such switching, a signal for delay measurement is generated at clock 1 of the node A, and this signal is transmitted to the optical transmitter (wavelength λ).
a) The optical signal is converted into an optical signal in 2 and transmitted to the node B using the optical fiber 6.

At the node B, the above-mentioned signal for delay measurement is reflected by the high reflection coating section 13 and sent back to the node A using the same optical fiber 6. In the node A, the connection of the optical switch 11 after the transmission of the delay measurement signal is switched as shown in FIG. 8, the returned delay measurement signal is received by the optical receiver 14, and the delay measurement signal is transmitted. The difference between the transmission time and the reception time is measured by the counter 5.

The delay time from node A to node B is Δ
Assuming that T1 is the delay time from the node B to the node A is ΔT2, the counter 5 of the node A can measure the round trip delay time ΔT = ΔT1 + ΔT2. Since the same optical fiber and the same light wavelength λa are used, ΔT1 = Δ
T2 holds, and the one-way delay time from the node A to the node B is ΔT1 = ΔT2 = ΔT / 2. Based on the result, the reference time T0 and the delay time ΔT / 2 held by the clock 1 are transmitted from the node A to the node B, and the node B
If the time of clock 10 at is T0 + ΔT / 2,
High-precision time synchronization is established between the nodes A and B.

[0020]

As described above, according to the time synchronization method of the present invention, it is possible to realize highly accurate time synchronization which is not affected by the difference between the length of the optical fiber and the measurement wavelength. Since this method of the present invention can be applied to a passive double-star type optical subscriber transmission network using wavelength division multiplexing, highly accurate time synchronization including the terminal system becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a conventional time synchronization method.

FIG. 2 is a diagram for explaining another conventional time synchronization method.

FIG. 3 is a diagram for explaining a normal communication mode of the system to which the embodiment of the time synchronization method of the present invention is applied.

FIG. 4 is a diagram for explaining a delay time measurement signal transmission mode of the system to which the embodiment of the time synchronization method of the present invention is applied;

FIG. 5 is a diagram for explaining a delay time measurement signal reception mode of the system to which the embodiment of the time synchronization method of the present invention is applied.

FIG. 6 is a diagram for explaining a normal communication mode of a system to which another embodiment of the time synchronization method of the present invention is applied.

FIG. 7 is a diagram for explaining a delay time measurement signal transmission mode of a system to which another embodiment of the time synchronization method of the present invention is applied.

FIG. 8 is a diagram for explaining a delay time measurement signal reception mode of a system to which another embodiment of the time synchronization method of the present invention is applied.

[Explanation of symbols]

 Reference Signs List 1 clock 2 optical transmitter 3 optical receiver 4, 7 wavelength multiplexing device 5 counter 6 optical fiber 8 optical receiver 9 optical transmitter 10 clock 11, 12 optical switch 13 high reflection coating section 14 optical receiver A, B node

Claims (1)

[Claims] 1. A time synchronization method between a master node and a slave node in an optical communication network comprising a master node, a slave node, and an optical fiber coupling between the master node and the slave node, comprising: A signal is transmitted, the optical signal reaches the slave node via the optical fiber, the reached optical signal is reflected by the optical signal reflecting means of the slave node, and the reflected optical signal is mainly transmitted through the optical fiber. The optical signal is returned to the node, the optical signal is received by the optical receiver of the main node, the delay time of the optical signal going round trip is measured, and the transmission time of the optical signal of the main node and the optical signal A time synchronization method comprising: obtaining a time difference from a reception time; transmitting the time difference and a clock time of a master node to a slave node; and synchronizing a clock time of the slave node with a clock time of the master node.