JPH04241000A - Digital exchange synchronization system and digital exchange independent synchronization system - Google Patents

Abstract

PURPOSE:To obtain digital exchange processing with high reliability by obtaining a clock signal with high accuracy without use of a highly stable oscillator which is expensive and has a problem on maintenance. CONSTITUTION:A satellite radio wave receiver 34 extracts a synchronizing signal 32 from a satellite radio wave received from a NAVSTAR satellite 26 and gives it to a phase comparator circuit 36. The phase comparator circuit 36 compares the phase of the synchronizing signal 32 with the phase of a clock 33 outputted from a voltage controlled crystal oscillator 37 and gives a control signal 38 to the voltage controlled crystal oscillator 37. The voltage controlled crystal oscillator 37 generates a clock signal 39 synchronized with the synchronizing signal 32 based on the control signal 38 and gives the signal 39 to a digital exchange 11. Digital exchanges 11, 16 are respectively activated according to clock signals 39, 49 fed from respective digital exchange synchronization systems 31, 41.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital switching system, and more particularly to a digital switching synchronization system and a digital switching network independent synchronization system that synchronizes a digital switching network using radio waves from a satellite as a clock source.

0002

2. Description of the Related Art Generally, in a digital communication system, it is necessary to synchronize the clock frequencies of the transmitting side and the receiving side in order for the receiving side to receive a signal without error. In digital integrated networks in which transmission and switching are performed through only one digital modulation/demodulation process, network synchronization in which the entire network is one synchronization system is particularly important, and various synchronization methods have been proposed.

One such method is slave network synchronization, in which the clock is distributed from one master oscillator to each station,
Based on this, each station uses a phase controlled oscillator to regenerate the clock.

Another synchronization method is independent network synchronization, which is a method in which a highly stable clock source is provided at each station and incoming pulses are read out using this clock source.

[0005] These conventional synchronization methods will be explained below.

FIG. 2 shows a conventional digital switching network dependent synchronization system. In this system, a digital exchange 11 serving as a main station is equipped with a master clock oscillator 12 for network synchronization, and digital transmission is performed based on the clock supplied from the master clock oscillator 12.

The master clock oscillator 12 is a highly stable atomic oscillator using cesium (Cs) or rubidium (Rb), and the rate of synchronization is 10-11 to 10-11.
It is about 10-12.

The main station digital exchange 11 receives a synchronous clock signal 17 supplied from a master clock oscillator 12.
In synchronization with , digital data is transmitted to the digital exchange 16 as a slave station via the digital transmission path 13 and the digital trunks 14 and 15 that monitor and control it.

A phase synchronized oscillator 18 is connected to the trunk 15 on the digital exchange 16 side, and extracts a synchronization signal from the bit string arriving from the digital exchange 11 via the digital transmission path 13 to generate a synchronization clock signal 19.
generate. The digital exchange 16 is a phase synchronized oscillator 1
The receiving operation and the like are performed in accordance with the synchronized clock signal 19 supplied from 8.

FIG. 3 shows a conventional digital switching network independent synchronization system. In this system, digital exchange 11 and digital exchange 16 are mutually independent. That is, each of these digital exchanges is equipped with highly stable master clock oscillators 21 and 22 similar to those described above, and is adapted to operate in accordance with synchronous clock signals 23 and 24 supplied individually from these.

For example, the digital exchange 11 transmits digital data to the digital exchange 16 via the digital trunk 14, the digital transmission path 13, and the digital trunk 15 in accordance with its own synchronous clock signal 23. The digital exchange 16 receives the transmitted digital data according to its own synchronous clock signal 24.

0012

[Problems to be Solved by the Invention] As described above, conventional digital switching network synchronization systems have used the dependent network synchronization method or the independent network synchronization method as described above, and have had the following problems. Ta.

First, in the dependent network synchronization method shown in FIG.
The reliability of the digital exchange 16, which is a slave station, depends on the reliability of the digital exchange 11, which is a master station, and the digital transmission line 13. Therefore, the reliability and independence of the digital exchange as a slave station may be weakened.

On the other hand, in the independent network synchronization system shown in FIG.
Although it is possible to ensure the independence of each digital exchange, each digital exchange must be equipped with a highly stable master clock oscillator, which has the disadvantage of increasing the cost of the entire system. Furthermore, even if a highly stable master clock oscillator is used, it is inevitable that digital exchanges will lose synchronization (slip) at a certain rate due to different clock sources, which poses a problem in terms of maintainability. was there.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to obtain a highly accurate clock signal without using a highly stable oscillator that is expensive and has maintenance problems, and thereby to perform highly reliable digital data transmission. The purpose of this invention is to provide a digital exchange synchronization system and a digital exchange network independent synchronization system that can perform the following tasks.

[0016]

[Means for Solving the Problems] The invention according to claim 1 includes (i) a receiving means for receiving radio waves from a satellite deployed in outer space; and (ii) synchronization from the radio waves received by the receiving means. synchronous signal extraction means for extracting a signal;
ii) The digital exchange synchronization system is equipped with a phase synchronization oscillator that uses the synchronization signal extracted by the synchronization signal extraction means as a clock source to generate a synchronization clock signal to be supplied to the digital exchange.

[0017] In the invention as claimed in claim 1, a synchronization signal is extracted from radio waves received from a satellite, and using this synchronization signal as a clock source, a synchronization clock signal is generated by a phase synchronization oscillator, and the synchronization clock signal is supplied to a digital exchange. shall be.

In the invention as claimed in claim 2, a plurality of digital exchanges equipped with the digital exchange synchronization system as claimed in claim 1 are arranged, and these are interconnected by digital transmission lines to form a digital exchange network independent synchronization system. It will be configured.

According to the second aspect of the invention, each digital exchange in the system performs digital exchange processing based on clock signals independently generated based on satellite radio waves from a satellite.

[0020]

EXAMPLES The present invention will be explained in detail with reference to Examples below.

FIG. 1 shows a digital switching network independent synchronization system in one embodiment of the present invention. Here, the explanation will be given assuming that digital data is transmitted between two digital exchanges 11 and 16. In addition, the same parts as those in the conventional example (FIGS. 2 and 3) are given the same reference numerals, and description thereof will be omitted as appropriate.

In this figure, digital exchange 11 and digital exchange 16 are connected to digital exchange synchronization system 31 and digital exchange synchronization system 41, respectively.
Equipped with

The digital exchange synchronization system 31 is equipped with a satellite radio wave receiving device 34 and is configured to receive satellite radio waves from the Navstar satellite 26. This Navstar satellite is a satellite deployed in space for a position detection system on the earth, but the out-of-synchronization rate is 10-12
It has an oscillation source that outputs a highly stable synchronization signal, and transmits satellite radio waves toward the ground in accordance with this synchronization signal.

The satellite radio wave receiving device 34 is a phase synchronized oscillator 3
5, and further connected to a voltage controlled crystal oscillator 37 within this phase synchronized oscillator 35. This voltage controlled crystal oscillator 37 is connected to the digital exchange 11 and is also loopback connected to the phase comparator circuit 36.

The digital exchange synchronization system 41 has a similar configuration, and its explanation will be omitted here.

The digital exchange 11 and the digital exchange 16 are connected via a digital transmission line 13 and digital trunks 14 and 15 that monitor and control the digital transmission line 13.

The operation of the digital switching network independent synchronization system configured as above will be explained.

The satellite radio wave receiving device 34 of the digital exchange synchronization system 31 receives the satellite radio waves from the Navstar satellite 26, extracts the synchronization signal 32 from the received radio waves, and supplies it to the phase comparator circuit 36.

The phase comparator circuit 36 compares the synchronizing signal 32 with the clock 33 output from the voltage controlled crystal oscillator 37, and sends a control signal 38 to the voltage controlled crystal oscillator 37 to match their phases and frequencies. give.

The voltage controlled crystal oscillator 37 receives a control signal 38
Based on this, a clock signal 39 synchronized with the synchronization signal 32 from the Navstar satellite 26 is output, and
supply to.

Digital exchange 11 transmits digital data to digital exchange 16 via digital trunk 14, digital transmission line 13, and digital trunk 15 in accordance with clock signal 39 supplied from digital exchange synchronization system 31.

Similarly, in the digital exchange synchronization system 41 on the digital exchange 16 side, the Navstar satellite 26
A clock signal 49 is generated based on satellite radio waves from and supplied to the digital exchange 16.

The digital exchange 16 then receives the digital data transmitted from the digital exchange 11 in accordance with the clock signal 49.

[0034] In this way, the digital exchange 11 and the digital exchange 16 operate based on clock signals that are independently generated based on satellite radio waves from the Navstar satellite 26.

[0035]

As explained above, according to the present invention, a highly stable synchronized clock signal is extracted from satellite radio waves for each digital exchange, and digital exchange processing is performed based on this. This has the advantage that a highly accurate clock signal can be obtained without using a highly stable oscillator such as an atomic oscillator, which has problems in terms of economy and maintainability.

Furthermore, in the present invention, since the synchronization signal source of each digital exchange is the same satellite, each digital exchange forms an independent network with no mutual dependence, and there are no problems with the conventional independent network system. Another advantage is that it is possible to realize extremely reliable bit string transmission that does not cause out-of-synchronization.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a digital exchange synchronization system and a digital exchange network independent synchronization system in one embodiment of the present invention.

FIG. 2 is a block diagram illustrating a conventional digital switching network dependent synchronization system.

FIG. 3 is a block diagram showing a conventional digital switching network independent synchronization system.

[Explanation of symbols]

11 Digital exchange 13 Digital transmission line 26 Navstar satellite 31 Digital exchange synchronization system 34 Satellite radio wave receiver 35 Phase synchronized oscillator 36 Phase comparison circuit 37 Voltage controlled crystal oscillator 39 Clock signal

Claims (2)

[Claims] 1. A receiving means for receiving radio waves from a satellite deployed in outer space, a synchronizing signal extracting means for extracting a synchronizing signal from the radio waves received by the receiving means, and a synchronizing signal extracting means for extracting a synchronizing signal from the radio waves received by the receiving means. A digital exchange synchronization system comprising: a phase synchronization oscillator that uses a synchronization signal obtained as a clock source to generate a synchronization clock signal to be supplied to a digital exchange. 2. A digital exchange network independent synchronization system, characterized in that a plurality of digital exchanges equipped with the digital exchange synchronization system are arranged, and these are interconnected by digital transmission paths.