JPH0454745A - Time synchronization system - Google Patents

Abstract

PURPOSE:To allow the system to synchronize a time of a slave set with a time of a master set accurately even in the case of changeover of transmission lines by correcting a delay time of a transmission line interconnecting the master set and the slave set so as to synchronize the time of the slave set with the time of the master set. CONSTITUTION:A reference time signal 6 from a reference time generating section 3 of a master set 1 is sent to a slave set 2. The slave set 2 returns the received signal 6 to the master set 1. A time interval measuring device 5 of the master set 1 measures a time difference between the sent signal 6 and the returned signal 6 and sends a half of the difference to the slave set 2 as time information A. A time interval measuring device 14 of the slave set 1 measures a time difference between the signal 6 from the master set 1 and a reference time signal 17 outputted from a reference oscillator 13 in the slave set 2 and uses the result as time information B. A time information arithmetic section 15 obtains a difference between the time information sets A and B and sends the result as time information C to a time information correction section 16. The correction section 16 subtracts a correction value from the information C as control information 21 and sends it to a phase control section 12. The control section 12 applies phase control of the signal 17 based on the information 21 to generate a synchronizing time signal 28 synchronously with the time of the master set 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention is applied to a time synchronization method for establishing time synchronization between geographically distant devices in a digital communication network.

[Conventional technology]

Conventionally, as a method of synchronizing the time of devices between geographically distant points, as shown in FIG.
The slave device 2 transmits the reference time signal 6 to the outgoing transmission line 8.
A method is used to generate a time signal 28 that is always synchronized with the reference time of the main device 10 by correcting the transmission delay time and its fluctuations.

In this method, the reference time signal 6 sent to the slave device 2 is returned, the main device 1 side measures the sum of the delay times of the outgoing transmission path 8 and the incoming transmission path 9, and the sum of the delay times of the outgoing transmission path 8 and The time information 7 is sent to the slave device 2 as the delay time, and the slave device 2
The phase control unit 12 controls the phase of the reference time signal 6.

In this method, the difference between the outbound delay time and the return delay time becomes a time synchronization error.

Generally, when opposing transmission lines are used, the difference between the outbound and inbound delays is several hundred n5ec, so for highly accurate time synchronization, it is necessary to measure and correct the initial delay difference between the outbound and inbound routes. be. To measure the initial delay difference between the outbound and return trips,
How to transport the atomic clock from the main device 1 to the slave device 2,
PS (global positroning system)
A time comparison method using radio waves such as Stem) or Loran-C is used.

[Problem to be solved by the invention]

In actual transmission lines, switching is performed to recover from failures in transmission equipment or lines.

There is no guarantee that the difference between the forward delay and the return delay in the transmission path after switching is the same as before switching. In particular, when only one of the outbound and inbound routes is switched, the difference between the outbound delay and the inbound delay becomes large.

With the conventional time synchronization method, it was not possible to know the difference between the forward delay and the return delay after switching the transmission path. Therefore,
In order to maintain high-precision time synchronization, each time the transmission line was switched, the difference between the forward and return delays had to be remeasured using atomic clock transport or radio wave comparison methods.

An object of the present invention is to provide a time synchronization system that can accurately synchronize the time of the slave device with the time of the master device even after switching the transmission path by eliminating the above-mentioned drawbacks.

[Means to solve the problem]

The present invention includes a main device and a slave device that are connected to each other via an outbound transmission path, a return transmission path, and a time information transmission path,
The main device includes means for generating a reference time signal, transmitting the generated reference time signal to the slave device via the outward transmission path, and transmitting the transmitted reference time signal and the slave device from the slave device via the return transmission path. the slave device receives the reference time signal sent from the main device, sends it back to the main device, and receives the reference time signal from the main device. A time synchronization method comprising: a synchronization means for controlling the phase of a reference time signal received from the device using the time information (A) sent from the main device and outputting a synchronized time signal synchronized with the time of the main device. In the above, the synchronization means includes means for generating a reference time signal within the device, and measures a time difference between the generated reference time signal within the device and the reference time signal received from the main device, and generates time information (B). means for calculating the difference between this time information (B) and the time information (A) sent from the main device and outputting it as time information (C); time information correction means for outputting control information obtained by subtracting a correction value that is a percentage of the difference between the delay time of the outward transmission line and the delay time of the return transmission line; and a reference time signal in the apparatus based on this control information. and means for controlling the phase of the synchronized time signal and outputting the synchronized time signal.

Further, in the present invention, the time information correction means includes a memory that stores the input time information (C), and a memory that stores the time information (C) before switching that is stored in the memory when the transmission path is switched. and a comparison unit that updates a correction value to be subtracted from the time information (C) by comparing the time information (C) with the time information (C) after switching, and a calculation unit that subtracts the correction value from the time information (C) to obtain control information. can be included.

[Effect]

A reference time signal is transmitted from the master device to the slave device, and this signal is sent back from the slave device to the master device. At this time, the main device calculates the time difference between the transmitted reference time signal and the returned reference time signal, and transmits the second one to the slave device as time information (A). The time information (A) is 2, which is the sum of the outbound delay time and the return delay time. In the slave device, the time difference between the output signal of the reference oscillator in the slave device and the reference time signal transmitted from the main device is determined and used as time information (B). The time information (B) is the sum of the time difference between the main device and the slave device and the outward delay time.

Therefore, if the outbound delay time and the inbound delay time are equal, time information A becomes the outbound delay time, so time information (C), which is the difference between time information (B) and time information (A>), is the main device. This is the time difference between the slave devices, and by controlling the phase of the reference oscillator output signal of the slave device using time information (C), the time of the slave device can be synchronized with the time of the main device. In some cases, accurate delay correction can be achieved by setting the percentage of the difference as a correction value and using that correction value from the time information (C) to perform phase control.Also, when transmission path switching is performed, In the slave device, the increment of the time information (C) at the time of switching is added to the correction value before switching to obtain a new correction value, and the new correction value is subtracted from the time information (C) to obtain control information. The increment of the time information (C) is the increment of the difference between the outbound delay time and the inbound delay time, so even after switching the transmission path, the delay difference between the outbound transmission path and the inbound transmission path can be corrected. , it becomes possible to accurately synchronize the time of the slave device with the time of the main device.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of a time information correction section thereof.

According to FIG. 1, the present embodiment includes a main device 1 and a slave device 2 that are connected to each other via an outgoing transmission path 8, an incoming transmission path 9, and a time information transmission path 10, and the main device 1 is capable of transmitting signals. A transmission device 4 that transmits and receives a reference time signal 6, a reference time signal generator 3 as a means for generating a reference time signal 6, and a reference time signal generator 3 that transmits the generated reference time signal 6 to a slave device 2 via an outgoing transmission line 8. Time information (
A) The slave device 2 includes a time interval measuring device 5 as a means for determining 7, and the slave device 2 receives the reference time signal 6 transmitted from the main device 1 and the transmission device 11 that transmits and receives signals.
A time synchronization method includes a synchronization means for outputting a synchronized time signal 28 synchronized with the time of the main device 1 by controlling the phase of the reference time signal 6 received from the main device 1 using time information (A) 7. A feature of the present invention is that the synchronization means includes a reference oscillator 13 as a means for generating a reference time signal 17 within the device, and a reference time signal 17 received from the main device 1 and the generated reference time signal 17 within the device. A time interval measuring device 14 serves as a means for measuring the time difference with the reference time signal 6 and outputting it as time information (B) 18, and this time information (B) 18 and the time information (
A) A time information calculation unit 15 as a means for calculating the difference between the time information and the time information (C) 19 and outputting it as time information (C) 19;
Control information 2 obtained by subtracting a correction value that is 1/2 of the difference between the delay time of the outbound transmission line 8 and the delay time of the return transmission line 9 from N9
1, and a phase control section 12 that controls the phase of the reference time signal 17 using control information 21 and outputs a synchronized time signal 28.

According to FIG. 2, the time information correction unit 16 has a memory 22 that stores the input time information (C) 19, and pre-switch time information that is stored in the memory 22 when the transmission path is switched. Correction value 27 to be subtracted from time information (C) 19 by comparing (C) 25 and post-switching time information (C) 26
, and an arithmetic unit 24 that subtracts a correction value 27 from the time information (C) 19 to obtain control information 21.

Next, the operation of this embodiment will be explained.

A reference time signal 6 is transmitted from the reference time generator 3 of the main device 1 to the slave device 2 via the transmission device 4 and the outward transmission path 8.

The slave device 2 transmits the transmitted reference time signal 6 to the transmission device 11.
and is sent back to the main device 1 via the return transmission line 9. Main device 1
The time interval measuring device 5 measures the time difference between the transmitted reference time signal 6 and the returned reference time signal 6, and uses the percentage as time information (A) 7 to transmit the time difference to the slave device 2 via the time information transmission line 10. Send to.

The time interval measuring device 14 of the slave device 2 measures the time difference between the reference time signal 6 transmitted from the main device 1 and the reference time signal 17 output from the reference oscillator 13 in the slave device, and obtains time information (B). 18. The time information calculation unit 15 calculates the difference between the time information (A) and the time information (B).
It is sent to the time information correction section 16 as N3. The time information correction section 16 subtracts the correction value 27 from the time information (C) 19 to obtain control information 21, which is sent to the phase control section 12. The correction value 27 is the difference between the outbound delay time and the return delay time, which is 2.
This correction value 27 is updated only when a switching signal 20 indicating that the transmission path has been switched arrives from the transmission device 11.

The phase control unit 12 controls the phase of the reference time signal 17 output from the reference oscillator 13 in the slave device based on the control information 21, and generates a synchronized time signal 2 synchronized with the time of the main device 1.
Names that generate 8.

In FIG. 2, the memory 22 stores time information (C) 19, and the comparator 23 uses the pre-switching time information (C) stored in the memory 22 only when the switching signal 20 from the transmission device 11 is input. ) 25 and the post-switching time information (C) 26, it is added to the pre-switching correction value 27, and sent to the calculation unit 24 as a new correction value 27. In the calculation section 24,
The new correction value 27 is subtracted from the time information (C) 19 and the control information 21 is sent to the phase control section 12 .

The operation at the time of transmission line switching in this embodiment will be explained using an example. The table shows the delay time of the transmission line immediately before switching and immediately after switching, and the values of each time information.

(The following is the margin of this page) In this example, immediately before switching, the outbound delay time is Δτ + Δτ, the return delay time is ΔT - Δτ, and the time information (A) is ΔT
It shows a state where . At this time, if the time information (B) is Δt, Δt is the time difference Become something.

Therefore, time information (C) 19 (=Δt−ΔT), which is the difference between time information (B) 18 and time information (A) 17, becomes X+Δτ. If Δτ is measured by atomic clock transport or time comparison using radio waves and given as a correction value, correct control information (=X) can be obtained by subtracting this correction value from time information (CN3. are the reference time generator 3 of the main device 1 and the reference oscillator 13 in the slave device 2.
Since there is a time difference between the slave device 2 and
By controlling the phase of the time signal 17 output from the reference oscillator 13, a synchronized time signal 28 synchronized with the time of the main device 1 is obtained.

Next, the operation when the transmission path is switched will be explained. Assume that the increment in the outbound delay time due to switching of the transmission path is δ1, and the increment in the inbound delay time is δ2. At this time, the time information (A) 7 changes from ΔT to ΔT+ (δ1+δ2)/2 due to switching. In addition, in the short time required for switching, the reference oscillator 13 in the slave device 2 is stable, so X does not change, so the time information (B) 18 is changed from Δt to Δt+δ1
Changes to

Therefore, time information (C) 19 is obtained from Δt-ΔT, Δt-
It changes to ΔT+ (δ1−δ2)/2. This time information (CN3 increment, (δ1−
The new correction value obtained by adding the correction value Δτ before switching to δ2)/2 is % of the difference in delay time between the outbound transmission line 8 and the return transmission line 9 after switching, so from the time information (C) 19 By subtracting this amount and setting it as the control information 21, it is possible to accurately correct the delay time. The error during this switching is the memory 22
It is determined by the stability of the reference oscillator 13 in the slave device 2 during the accumulation time. Generally, switching is completed in several tens of seconds, so if a highly stable crystal oscillator or rubidium oscillator is used, the time error during switching will be sufficiently small.

In the above embodiment, the time information transmission path 10 and the outgoing transmission path 9
Although shown as separate transmission paths, the present invention can be implemented in the same way even if the same transmission path is used.

Furthermore, in this embodiment, the determination as to whether or not the transmission path has been switched is based on the switching signal 20 from the transmission device 11;
The present invention can be implemented in the same way by using a method of determining based on the interruption of the input of the reference time signal 6 from the main device 1 or a method of determining that a sudden change in time information (CN3) indicates a transmission line switching.

〔Effect of the invention〕

As explained above, the present invention is capable of synchronizing the time of the slave device with the time of the master device by correcting the delay time of the transmission path connecting the master device and the slave device, and also when switching the transmission path, the forward transmission This has the effect of correcting the delay difference between the transmission line and the return transmission line, and accurately synchronizing the time of the slave device with the time of the main device.

Therefore, according to the present invention, it is possible to supply highly accurate time by using the current digital communication network where transmission paths are frequently switched due to failures, etc., and the effect is great. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 2 is a block diagram showing an example of the time information correction section. FIG. 3 is a block diagram showing a conventional example. DESCRIPTION OF SYMBOLS 1... Main device, 2... Slave device, 3... Reference time signal generator, 4.11... Transmission device, 5.14... Time interval measuring device, 6.17... Reference time signal, 7...
Time information (A), outbound transmission line, 9 return transmission line, 10 time information transmission line, 12 phase control unit, 13 reference oscillator, 15 time information calculation section,
16... Time information correction section, Engineering 8... Time information (B)
, 19... Time information (C), 20... Switching signal, 21... Control information, 22... Memory, 23...
Comparison unit, 24... Calculation unit, 25... Pre-switching time information (C), 26... Post-switching time information (C), 27...
- Correction value, 28...Synchronized time signal.

Claims (1)

[Scope of Claims] 1. A main device and a slave device are connected to each other via an outgoing transmission path, a backward transmission path, and a time information transmission path, and the main device includes means for generating a reference time signal; The generated reference time signal is transmitted to the slave device via the outward transmission path, and time information ( A), the slave device receives a reference time signal transmitted from the master device and returns it to the master device, and receives the reference time signal received from the master device and returns it to the master device. and a synchronizing means for outputting a synchronized time signal synchronized with the time of the main device by controlling a phase based on the time information (A) that has been received, the synchronizing means outputs a reference time signal in the device. means for measuring the time difference between the generated reference time signal in the device and the reference time signal received from the main device and outputting it as time information (B); means for determining the difference from the time information (A) sent from the main device and outputting it as time information (C); and determining the delay time of the outgoing transmission path and the delay of the incoming transmission path from this time information (C). time information correction means for outputting control information obtained by subtracting a correction value that is 1/2 of the time difference; and based on this control information, phase control is performed on a reference time signal in the device to output the synchronized time signal. A time synchronization method characterized by comprising means. 2. The time information correction means input time information (C
), and compare the time information (C) before switching and the time information (C) after switching, which were accumulated in the memory when the transmission path switching was performed, from the time information (C). 2. The time synchronization system according to claim 1, comprising: a comparison section that updates the correction value to be subtracted; and a calculation section that subtracts the correction value from the time information (C) and uses it as control information.