KR100429009B1 - Apparatus and Method for Synchronization of remotely located clock by common-view measurement of satellite time - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a remote clock synchronizing apparatus and method for synchronizing a clock of an entire remote clock unit with a clock of a reference clock unit. The present invention relates to a rubidium oscillator 21, a divider 22, a first GPS receiver 23, and a first clock receiver. A remote clock unit 20 including a computer 24, a digital analog converter 25, and a phase adjuster 26; A reference clock section 30 including a cesium atomic clock 31, a second GPS receiver 32, and a second computer 33; A GPS clock output from the GPS satellite 10 and simultaneously received by the first and second GPS receivers 23 and 32 of the remote clock unit 20 and the reference station clock unit 30 to receive the first GPS receiver. At 23, the time interval between the remote clock and the GPS clock is measured, and at the second GPS receiver, the time interval between the reference clock and the GPS clock is measured to measure the measured data of the first and second GPS receivers 23 and 32 through the network. The first computer 24 receives and synchronizes the remote clock with the reference clock through a predetermined operation to increase the accuracy of the clock synchronization and to maintain the uniform clock synchronization quality of the entire remote clock.

Description

Apparatus and Method for Synchronization of remotely located clock by common-view measurement of satellite time}

The present invention relates to a remote clock synchronizer and method for synchronizing each remote clock to a reference clock.

Recently, the necessity of precise visual synchronization device is required due to the rapid development of communication system related equipment, and as part of such a request, a synchronization network is established to match the clocks of communication network related devices including a remote switch with a special reference signal. Efforts have been made.

6 is a schematic block diagram showing an embodiment of a conventional clock synchronization apparatus. As shown, when the external reference signal output from the cesium or rubidium atomic clock and the reference clock output from the oscillator are detected by the phase detector and output to the microcomputer, the microcomputer compares the two clocks and returns an error value to the oscillator. By adjusting the frequency of the oscillator, the reference clock is synchronized with the external reference signal. When the external reference signal cannot be received, the oscillator frequency is adjusted by providing error tolerance by returning the measured and predicted value to the oscillator. The reference clock output from the conventional clock synchronizing apparatus is output through the dedicated communication lines E1 and T1 to synchronize other oscillators on the communication network.

However, when synchronizing the communication network using the conventional clock synchronization device, the synchronization quality is affected by the good and bad state of the dedicated communication line, and the reference clock is hierarchical structure (tree structure) to reduce noise caused by the dedicated communication line. Since the synchronization quality is deteriorated toward lower layers, the reliability of the clock synchronization device is low, the synchronization quality of the entire remote clock is not uniform, and the fee for using the dedicated communication line used as the synchronous communication network is expensive.

The present invention has been invented to solve the above problems, by measuring the difference between the remote clock and the reference station clock in real time using a GPS (Global Positioning System) satellite to correct and synchronize the difference so that a separate dedicated communication line An object of the present invention is to provide a remote clock synchronizing apparatus by satellite time simultaneous measurement, which is not necessary and can keep the synchronizing quality of all remote clocks uniform in the same order.

Another object of the present invention is to provide a remote clock synchronization apparatus by simultaneous satellite time measurement that can be monitored by receiving the measurement data of the GPS receiver from the entire remote clock unit over the network.

1 is a block diagram showing an embodiment of a remote clock synchronizing apparatus by simultaneous satellite time measurement according to the present invention;

2 is an operation flowchart of a remote clock synchronizing apparatus using simultaneous satellite time measurement according to the present invention.

3 is an operation flowchart of a first computer of a remote clutter unit of a remote clock synchronizing apparatus using simultaneous satellite time measurement according to the present invention;

4 is a characteristic diagram of frequency synchronization of a remote clock synchronized by a remote clock synchronizer by simultaneous satellite time measurement according to the present invention;

5 is a comparison result table of the maximum time interval error according to the observation time of the rubidium oscillator and the rubidium oscillator which is not synchronized by the remote clock synchronizer by simultaneous satellite time measurement according to the present invention

6 is a schematic configuration diagram showing an embodiment of a conventional clock synchronizing apparatus;

<Short description of drawing symbols>

10: GPS satellites

20: first remote location clock unit

21: rubidium oscillator 22: frequency divider

23: GPS receiver 24: first computer

25: digital-to-analog converter 26: phase adjuster

30: reference clock portion

31: cesium atomic clock 32: GPS receiver

33: second computer

According to an aspect of the remote clock synchronizing apparatus by satellite time simultaneous measurement according to the present invention for achieving the above object, a rubidium oscillator 21 for outputting a remote clock; A divider 22 for dividing the remote clock output from the rubidium oscillator 21 at 1pps; A first GPS receiver 23 for receiving a 1pps remote clock divided by the divider 22 and a 1pps GPS clock output from the GPS satellite 10 to measure a time interval between the two clocks; The measurement data of the first GPS receiver 23 and the measurement data of the second GPS receiver 32 are input from the second computer 33 of the reference station clock unit 30 via a network, and the clock of the remote station is converted into the reference station clock. A first computer (24) for obtaining time and frequency correction data for synchronizing with the data and outputting the time and frequency correction data; A digital analog converter (25) for converting the digital signal corresponding to the frequency corrected relative frequency output from the first computer (24) into an analog signal and outputting the analog signal to the rubidium oscillator (21); A remote clock including; a phase fine adjuster 26 which receives the time correction data output from the first computer 24 and corrects the clock phase of the rubidium oscillator 21 output from the divider 22; Characterized in that it comprises a portion (20).

According to an additional aspect of the present invention, there is provided a cesium atomic clock 31 for outputting a reference clock; A second GPS receiver 32 which receives a reference clock output from the cesium atomic clock 31 and a GPS clock output from the GPS satellite 10 and measures a time interval between the two clocks; A reference station clock unit 30 including a second computer 33 which receives the measurement data of the second GPS receiver 32 and outputs it to the first computer 24 of the remote clock unit 20 through a network. It characterized by including).

According to an aspect of the method for synchronizing a remote clock by satellite time simultaneous measurement according to the present invention for achieving the above object, outputting a remote clock from the rubidium oscillator (21) to the frequency divider (22); Dividing and outputting a remote clock at 1pps in the divider (22); Receiving a 1pps remote clock output from the frequency divider (22) and a GPS clock of the GPS satellite (10) by the first GPS receiver (23) to measure a time interval between the two clocks; Downloading data of the first and second GPS receivers (23, 32) of the reference clock section (30) and the remote clock section (20); After selecting and sorting the data of the first and second GPS receivers 23 and 32 of the downloaded reference clock unit 30 and the first remote clock unit 20 by the same time data at the same satellite, the alignment is performed. Obtaining a time difference data string between the reference station and the remote location from the classified data; Determining an initial relative frequency from the time difference data sequence; Setting a time of time difference data corresponding to the initial relative frequency as a reference time; Inputting a current time; Determining an expected relative frequency and time and frequency correction data at a current time; outputting the frequency correction data to a D / A converter 25 and outputting the time correction data to a phase fine adjuster 26; And converting the digital signal corresponding to the frequency correction data from the D / A converter 25 into an analog signal and outputting the analog signal to the rubidium oscillator 21.

Hereinafter, with reference to the accompanying drawings will be described in detail so that those skilled in the art can easily understand and reproduce.

1 is a block diagram showing an embodiment of a synchronization device of a remote clock by simultaneous satellite time measurement according to the present invention.

As shown, the synchronous device of the remote clock by simultaneous satellite time measurement according to the present invention includes a rubidium oscillator 21, a divider 22, a first GPS receiver 23, a first computer 24, and a digital analog converter. 25 and a remote clock unit 20 including a phase adjuster 26.

The rubidium oscillator 21 outputs a 10 MHz remote clock.

The divider 22 divides and outputs a 10 MHz remote clock output from the rubidium oscillator 21 to a remote clock of 1 pps (PPS: Pulse per Second). .

The first GPS receiver 23 receives a 1pps GPS clock output from the GPS satellite 10 and a 1pps remote clock output from the remote clock unit 20, rather than the position measurement or clock supply that is generally used. GPS receiver for measuring the time interval between two clocks through the time interval counter of. Input the time comparison schedule of the Far East Asia region from the International Metropolitan Metropolitan Bureau. It stores 150 data, 3 days' worth of data, about 50 times each day. The GPS receiver is connected to the computer via an RS-232C cable so that each remote clock unit can exchange data for the last three days to each computer connected to a telephone network or Ethernet, if necessary.

The first computer 24 downloads data measured by the first and second GPS receivers 23 and 32 and calculates time and frequency correction data for synchronizing a remote clock with a reference clock. A control program for downloading data measured by the first GPS receiver 23, a communication program for importing the data file of the second GPS receiver 32, and a correction program for synchronizing the remote clock with the reference station clock.

The D / A converter 25 converts the digital signal corresponding to the correction relative frequency of the remote clock with respect to the reference clock output from the first computer 24 into an analog signal and outputs the analog signal to the rubidium oscillator 21.

The phase adjuster 26 adjusts the phase of the 1pps remote clock output from the divider 22 according to the time correction data calculated by the first computer 24.

In addition, the apparatus for synchronizing a remote clock by simultaneous satellite time measurement according to the present invention includes a reference clock unit 30 including a cesium atomic clock 31, a second GPS receiver 32, and a second computer 33. have.

The cesium atomic clock 31 outputs a reference clock.

Like the first GPS receiver, the second GPS receiver receives a 1pps GPS clock output from the GPS satellite 10 and a reference clock of 1pps output from the reference station clock unit 30, and then receives a second clock signal through an internal time interval counter. Measure the time interval between clocks.

The second computer 33 receives the measurement data of the second GPS receiver 32 and outputs the measured data to the first computer 24 via a network, and each of the remote clocks synchronized with the reference clock from the entire remote clock unit. By receiving and monitoring the measured data of the GPS receiver through the network, the synchronization quality of the remote clock by the simultaneous satellite time measurement according to the present invention and the operation state of the GPS receiver of each remote clock unit and the reference station clock unit 20 are monitored. You can check it.

It will be described below with reference to the drawings showing the effect of the synchronization device of the remote clock by the satellite time simultaneous measurement according to the present invention having the above configuration.

2 is a flowchart illustrating an operation of a remote clock synchronizer using simultaneous satellite time measurement according to the present invention.

As shown, when the remote clock is output from the rubidium oscillator 21 of the remote clock unit 20 to the divider 22 (s401), the divider 22 divides and outputs the remote clock at 1pps (s402). . The first GPS receiver 23 receives the 1pps remote clock output from the frequency divider 22 and the GPS clock received from the GPS satellite 10, and measures the time interval between the two clocks (s403). 24 receives the measurement data of the first and second GPS receivers 23 and 32 of the reference clock unit 30 and the remote clock unit 20 (s404) and the downloaded reference clock unit 30 and After selecting and sorting the data of the first and second GPS receivers 23 and 32 of the first remote clock unit 20 by the same time data at the same satellite, the time difference between the reference station and the remote site from the sorted data. Obtain a data sequence (s405), determine the initial relative frequency from the time difference data sequence (s406), set the time of the time difference data corresponding to the initial relative frequency as a reference time (s407), enter the current time (s408) Expected relative frequency and time and frequency in time After determining the information data (s409) the frequency correction data is the time correction data to the D / A converter and outputs as a phase fine adjuster (26) (s410). Thereafter, the digital signal corresponding to the frequency correction data is converted from the D / A converter 25 into an analog signal and output to the rubidium oscillator 21 (s411).

3 is a flowchart illustrating an operation of a first computer of a remote clock unit, which is a remote clock synchronization device using simultaneous satellite time measurement according to the present invention.

As illustrated in FIG. 1, when the clock of the GPS satellite 10 is simultaneously received by the reference clock unit 30 and the first and second GPS receivers 23 and 32 of the remote clock unit 20, the reference clock unit 30 may be used. In the second GPS receiver 32, the time interval between the clock (GPS clock) output from the GPS satellite 10 and the master clock output from the cesium atomic clock 31 (Master clock-GPS clock) And at the same time, the time interval between the GPS clock output from the GPS satellite 10 and the local clock output from the rubidium oscillator 21 in the first GPS receiver 23 Local clock—GPS clock is measured. The data measured by the first and second GPS receivers 23 and 32 are respectively output to the first and second computers 24 and 33 and the second GPS receiver 32 to the second computer 33. The measurement data is output to the first computer 24 of the remote clock unit 20 via the network.

The first computer 24 downloads data measured by the first and second GPS receivers 23 and 32 and calculates time and frequency correction data for synchronizing a remote clock with a reference clock.

First, the principle of calculating the time and frequency correction data for synchronizing the remote clock with the reference clock is as follows.

As shown in FIG. 1, since the GPS satellite 10 is located far away from the distance between the reference clock unit 30 and the remote clock unit 20, the GPS satellites 10 receive the first and second GPS receivers 23 and 32, respectively. It can be seen that the error factors due to the arrival of the GPS clock are the same. Therefore, when the clocks of the reference clock unit 30 and the remote clock unit 20 are measured at the same time using the same GPS satellite 10, the equation ⑴ As such, the time interval between the remote clock and the reference clock can be obtained in real time.

Formula (1)

Where τ ₁ is the remote clock _, τ ₂ is the reference clock, and τ _g is the GPS clock. Comparative measurements using this method are possible not only for navigation satellites but also for communication satellites such as Mugunghwa.

However, the oscillator there is itself a change does not hold the initial time interval (χ ₀₎ because over time as changes constantly the frequency value due to the aging can not be avoided in accordance with the accumulated time error, χ (t) over time of the oscillator is formula It can be expressed as

Formula (2)

Where χ ₀ represents an initial time interval, y ₀ is the accuracy of the general remote clock frequency to an initial relative frequency, which is defined as a value obtained by dividing the frequency difference between the reference clock and the remote clock of the first time with the frequency of the reference clock K is the relative It is a secular change rate indicating the rate of change of frequency, which means long term stability of the oscillator. While these three items can be improved by being caused by environmental causes, ε (t) is an irregular deviation that is difficult to improve. This equation can generally be used to predict the oscillator's time error, except when the oscillator's signal is frequency-modulated or its secular variation is nonlinear. If the remaining terms except ε (t) in Equation 적절히 are appropriately binomially divided by elapsed time, it can be transformed into Equation 에 by the relationship of ｙ = δχ / t .

Formula (3)

As indicated in Equation VII, we can know the expected relative frequency at any time by knowing the initial relative frequency ( xy ₀ ) and the oscillator long-term stability ( K ). In order to synchronize the relative frequency of the remote clock at a given time to a value close to the reference clock, the correction data to be applied inversely is as follows.

Formula (4)

Here, since the relative frequency is zero, the state closest to the reference oscillator, the value subtracted from zero is time and frequency data to be corrected to synchronize the remote clock with the reference clock. The frequency correction data thus obtained may be output from the first computer 24 to the rubidium oscillator 21 of the remote clock to synchronize the remote clock output from the rubidium oscillator 21 to the reference clock.

As shown in FIG. 3, the first computer performs a predetermined calculation process for obtaining time and frequency correction data for synchronizing a remote clock with a reference station clock.

Download the measurement data of the reference clock unit 30 and the first and second GPS receivers 23 and 32 of the remote clock unit 20 and select and sort the data by the same time data in the same satellite; Obtaining a time difference data string of a remote clock and a reference station clock from the sorted identical time data; From the time difference data sequence, the relative frequency defined as the value obtained by dividing the frequency difference between the reference clock and the remote clock at each time by the frequency of the reference clock is obtained through the slope of the change of time in the time difference data sequence, and one of the values is obtained. Determine the initial relative frequency; Setting a time of time difference data corresponding to the initial relative frequency value as a reference time and inputting a current time; Expected relative time at the present time by calculating the product of adding the relative value of the initial relative frequency and the long-term stability K of the rubidium oscillator 21 of the remote clock unit 20 times the elapsed time from the reference time to the present time. Obtain a frequency and determine time and frequency correction data from the expected relative frequency; The frequency correction data is output to a D / A converter 25 and the time correction data is output to a phase fine adjuster 26; Check whether data of the first and second GPS receivers 23 and 32 of the reference clock unit 30 and the remote clock unit 20 has been updated, and when the data is not updated, the current time is again after a predetermined waiting time. Repeating a loop for outputting the estimated relative frequency, time and frequency correction data at that time, and outputting the frequency correction data to the D / A converter 25 and the time correction data to the phase adjuster 26; When the data update is confirmed, the loop returns to the beginning of downloading the measurement data of the first and second GPS receivers.

4 is a characteristic diagram of frequency synchronization of a remote clock corrected by a remote clock synchronizer by simultaneous satellite time measurement according to the present invention.

As shown in Fig. 1, the synchronization quality of the remote clock phase synchronizing device using the satellite clock simultaneous measurement according to the present invention was measured. It can be seen that it is approaching -4 × 10 ^-12 from 1.2 × 10 ^-10 before synchronization.

FIG. 5 shows the maximum time interval error (MTIE) at each observation time for the remote clock and the reference clock output from the rubidium oscillator 21. The rubidium oscillator is obtained. (21) If it is used without synchronization, it greatly exceeds the MTIE recommended value of the reference clock for network synchronizer recommended by G.811, the best standard of ITU-T standard, but it is remote clock by simultaneous satellite time measurement according to the present invention. The remote clock output from the rubidium oscillator 21 synchronized with the synchronization device of the apparatus is satisfied.

As described in detail above, a remote clock synchronizer using simultaneous satellite time measurement according to the present invention uses a GPS receiver and a GPS satellite for clock signal comparison measurement in real time to clock the oscillator operating in the entire remote clock unit. When synchronizing with the clock of stable cesium oscillator of the reference station, it is possible to obtain a synchronous output so that the synchronization quality of the entire remote area is uniform and the frequency accuracy is continuously maintained at the level of 10 ^-12 . Demonstrates an alternative to clock synchronization.

In addition, the reference clock unit receives the measurement data of the corresponding GPS receiver from the entire remote clock unit through the network and monitors each remote clock synchronized with the reference clock through time difference data operation from the same time data sequence measured at the same satellite. According to the present invention, the synchronization quality of the remote clock by the simultaneous satellite time measurement and the performance of the GPS receiver of each remote clock unit and the reference station clock unit have a useful effect of real time checking.

Although the invention has been described in terms of preferred embodiments with reference to the accompanying drawings, it will be apparent to those skilled in the art that various modifications are possible without departing from the scope of the invention, which is covered by the following claims.

Claims (5)

In the remote clock synchronizer for synchronizing the remote clock to the reference station clock using a GPS satellite, A rubidium oscillator for outputting a remote clock; A divider for dividing the remote clock output from the rubidium oscillator at 1pps; A first GPS receiver for measuring a time interval between a 1pps remote clock divided by the frequency divider and a 1pps GPS clock input from a GPS satellite; Time and frequency correction for synchronizing the remote clock to the reference station clock by receiving the time interval measurement data t ₁ input from the first GPS receiver and the time interval measurement data t ₂ from the reference station connected through the Internet. A first computer for obtaining data; A digital analog converter for converting a digital signal corresponding to the frequency correction data input from the first computer into an analog signal and outputting the analog signal to the rubidium oscillator; A phase fine adjuster which receives the time correction data output from the first computer and corrects and outputs a clock phase of 1 pps output from the divider; Remote clock synchronizing device by a satellite time simultaneous measurement, characterized in that it comprises a remote clock unit comprising a. The method of claim 1, The remote clock synchronizer by simultaneous satellite time measurement is: A cesium atomic clock 31 for outputting a reference clock; A second GPS receiver 32 receiving a reference clock output from the cesium atomic clock 31 and a GPS clock of 1pps output from the GPS satellite 10 and measuring a time interval between the two clocks; A second computer 33 which receives the measurement data of the second GPS receiver 32 and outputs the measured data of the second GPS receiver 32 to the first computer 24 of the remote clock unit 20; Remote clock synchronizing apparatus by a satellite time simultaneous measurement, comprising a reference station clock unit comprising a. The method according to claim 1 or 2, The first computer 24 of the remote clock unit is: Download the measurement data of the reference clock unit 30 and the first and second GPS receivers 23 and 32 of the remote clock unit 20 and select and sort the data by the same time data in the same satellite; Obtaining a time difference data sequence of a remote clock and a reference station clock from the aligned same-time data string; Obtaining a slope of a change over time of the time difference data sequence from the time difference data sequence and determining one of the values as an initial relative frequency; Setting a time of time difference data corresponding to the initial relative frequency value as a reference time and inputting a current time; Expected relative time at the present time by calculating the product of adding the relative value of the initial relative frequency and the long-term stability K of the rubidium oscillator 21 of the remote clock unit 20 times the elapsed time from the reference time to the present time. Obtain a frequency and determine time and frequency correction data from the expected relative frequency; Outputting the frequency correction data to a D / A converter 25 and the time correction data to a phase fine adjuster 26; Check whether the data of the first and second GPS receivers 23 and 32 of the reference clock unit 30 and the remote clock unit 20 has been updated, and present again after a predetermined waiting time when confirming that the data has not been updated. Inputting time, obtaining the expected relative frequency, time and frequency correction data at that time, and repeating the loop for outputting the frequency correction data to the D / A converter 25 and the time correction data to the phase adjuster 26; And the time and frequency correction data are obtained by repeating the loop by returning to the beginning of downloading the measurement data of the first and second GPS receivers when confirming the data update. The method according to claim 1 or 2, The second computer 32 of the reference station clock section 30 A remote clock synchronizing apparatus by simultaneous measurement of satellite time, characterized by receiving and monitoring each remote clock synchronized with a reference station clock from a total of remote clock units through a network. Outputting a remote clock from the rubidium oscillator 21 to the divider 22; Dividing and outputting a remote clock at 1pps in the divider (22); Receiving a 1pps remote clock output from the frequency divider (22) and a GPS clock of the GPS satellite (10) by the first GPS receiver (23) to measure a time interval between the two clocks; Downloading data of the first and second GPS receivers (23, 32) of the reference clock section (30) and the remote clock section (20); After selecting and sorting the same-time data strings in the same satellite among the data of the downloaded reference clock unit 30 and the first and second GPS receivers 23 and 32 of the first remote clock unit 20, the alignment is performed. Obtaining a time difference data string between the reference station and the remote location from the received same time data string; Determining an initial relative frequency from the time difference data sequence; Setting a time of time difference data corresponding to the initial relative frequency as a reference time; Inputting a current time; Determining an expected relative frequency and time and frequency correction data at a current time; Outputting the frequency correction data to a D / A converter (26) and outputting the time correction data to a phase fine adjuster (26); And converting the digital signal corresponding to the frequency correction data from the D / A converter (26) into an analog signal and outputting the analog signal to the rubidium oscillator (21).