JPS62175032A - Network synchronizing system - Google Patents

Abstract

PURPOSE:To execute the absorption of the difference of an interface and to execute the absorption of the frequency deviation due to a Doppler effect by a satellite position change by supplying the transmitting/receiving timing of a ground communicating system with the local clock of a satellite communicating system for a satellite communication network system. CONSTITUTION:When a ground communication system transmits the data, the receiving data from a satellite communication system are inputted to an X.21 adapter 2 corresponding to the clock of a signal line RT from a receiving data RD signal line. At such a time, the clock of a signal line RT is also inputted from the satellite communication system. For a receiving clock RT inputted to an X.21 adapter 2, the frequency drifts by a Doppler shift due to the change of the satellite position. Since the receiving clock RT is extracted from the receiving data by a clock extracting circuit in the satellite communication system, the synchronization between the receiving clock and the receiving data is established.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a network system such as satellite communication, and particularly to a communication system having two separate transmission/reception data timing lines and a communication system having only one common transmission/reception data timing line. The present invention relates to a highly reliable network synchronization method suitable for establishing synchronization.

(Background of the Invention) Conventionally, when connecting different types of communication systems, Triketsubs' [Multimedia Network Communication Processing Technology J]
(PL54-P167), gateways that perform proto-Turkish transformations involving higher logic levels are commonly used. If only lower physical level protocol conversion is to be performed, there is no need to use a gateway, and it is sufficient to install a dedicated conversion according to the system. In this case, multiple communication systems have individual clocks, and it is difficult to match the frequency and phase of each clock, and it is often impossible to establish synchronization (system synchronization) between the systems.

In that case, a grid synchronization method is adopted in which the clock of one communication system is supplied to the other connected communication system. ) cannot be used for satellite communication network systems connected to This is because the distance variation to one communication satellite is ±74 km per day even for a geostationary satellite (medium distance increase, - decrease)
8 degrees, and a relative change in the received bit rate, that is, a frequency shift (hereinafter referred to as Doppler shift) due to the Doppler effect due to positional fluctuation, occurs on the order of 10-6.

Therefore, if a timing clock reproduced from a received signal with this Doppler shift is used, the reception timing clock in the satellite communication system will inevitably vary.

Therefore, as described above, for example, it is not possible to use a method of supplying the clock of the terrestrial communication system with a clock having fluctuations reproduced from the received signal of the satellite communication system. As prior art for compensating for synchronization deviation due to satellite position fluctuation in a satellite communication system, for example, Japanese Patent Application Laid-Open No. 57-125538 and Japanese Patent Application Laid-open No. 57-125539
There is a publication. These are Time Division Multiple Access (TDMA)
The 5atellite 5w1tched T is equipped with a dynamic switch that synchronizes with the TDMA frame and quickly switches beam connections on the satellite.
This is known as a DMA (SS/TDMA) satellite tower repeater system. However, while the application of the TDMA method is economical for large-capacity satellite communication systems such as international communications and domestic public communications, for small-capacity satellite communication systems, the 5CPC (Single Charre) method, which allocates a separate carrier wave for each channel, is (Per C
arrier) method is the lowest and has been adopted. In the 5CPC system, the satellite-mounted relay only performs direct relay, so when digital communication is applied to the 5CPC system line, the shift in transmission and reception timing clocks due to Doppler shift is not resolved.

(Objective of the Invention) The object of the present invention is to establish a system synchronization system between a communication system having separate transmitting and receiving data timing lines and a communication system having only one common transmitting and receiving data timing line. The purpose of this invention is to provide a method that absorbs the frequency deviation of the received recovered clock due to the Doppler effect, realizes reliable network synchronization, and at the same time provides scalability to the system.

[Summary of the invention]

Specifically regarding a satellite communication system, which is a typical application field of the present invention, in order to achieve the above object, the present invention supplies the transmission/reception timing of a terrestrial communication system using a local clock of the satellite communication system. For this purpose, an interface conversion device is placed between the two systems.
Eliminate interface differences and absorb frequency shifts due to the Doppler effect. We also devised a connection method that allows the interface between terrestrial communication systems and satellite communication systems to be expandable.

[Embodiments of the invention]

A first embodiment of the present invention will be described below with reference to FIG.

FIG. 1 is an overall configuration diagram of a first embodiment of a satellite communication network system according to the present invention. As shown in FIG. 1, the satellite communication network system is a satellite communication system 1. Interface conversion device 2 (in this embodiment, an adapter for converting the interface between CCI Recommendations Fi
rst-in First out) buffer 5a
, 5b Local clock installed in the satellite communication system 6, NRZ (Non Return to Zero
) to CMI code (CodedMark Inv6rs
Timing clock extraction device 7 for code conversion to ion)
．． The interface device of the satellite communication network system shown in FIG.
, 21 adapter), constitutes an integrated satellite communication network system in which a main station with a local clock connected to the ground communication system via an optical module and a slave station without a local clock are connected by a satellite link. are doing. An example of connection with a terrestrial communication system is the CCITT recommended interface, and an example of connection with a satellite communication system is an EIA regulation R8-422 interface.

Next, the connection operation between the terrestrial communication system, the satellite communication system, and the interface device will be briefly explained.

The interface converter [(X, 21 adapter) 2 has transmission data SD, reception data RD, reception clock RT, and local clock timing LT in the master station (transmission clock ST in the slave station) as signal lines. Note that a control signal line is provided separately from these signal lines. This is a plurality of signal lines consisting of a control line for sending control data and a status signal line for knowing the state of the other party. In the description of the present invention, there is no need to explain the control line on one communication interface, so this will be omitted. The optical module 4 has signal lines for transmission data SD, reception data RD, and transmission common lock S/RT for the terrestrial communication system.

Now, a case will be described in which the main station on the right side of FIG. 1 transmits data from the satellite communication system to the terrestrial communication system via the interface device. Received data from the satellite communication system is received from the received data RD signal line.
It is input to the X, 21 adapter 2 in response to the clock on the signal line RT.

At this time, the clock on the signal line RT is also input from the satellite communication system. However, as mentioned earlier, X,
The reception clock RT input to the X.21 adapter has a frequency drift due to Doppler shift due to satellite position fluctuations. However, since this reception clock RT is extracted from the reception data by a clock extraction circuit within the satellite communication system, synchronization between the reception clock and the reception data is established.

From the local clock 6 in the satellite communication system to ensure that this frequency drift does not affect the transmitting and receiving clocks of the terrestrial communication system, thereby causing a synchronization shift in the timing of the transmission of data from the terrestrial communication system to the satellite communication system. The supplied tally signal LT is used separately.

Note that this LT signal line is also connected to the optical module.

Therefore, the timing extraction clock necessary for converting from NRZ to CMI code is also supplied.

In other words, the data sent from the satellite communication system to the terrestrial communication system is input into the X, 21 adapter, and then FIFO
The signal is put into a buffer 5a, taken out from there at the timing of an independent clock LT that does not include frequency drift, and sent to the optical module.

In the optical module, a double-frequency clock necessary for converting the LT timing to a CMI code is created using a timing clock extraction device 7 for code conversion, and this is added to the data and sent to the terrestrial communication system via an optical cable. It will be done. By performing the connection operation as described above, the frequency drift as described above will not affect the transmission/reception clock of the terrestrial communication system.

If the terrestrial communication system is installed at a distance of, for example, several tens of kilometers, from the satellite communication system, the data sent to the terrestrial communication system via the above-mentioned optical cable enters the optical module 4 in the terrestrial communication system example with a transmission delay. . There, in contrast to the optical module on the satellite communication system side, the data sent to the terrestrial communication system and the tarot received by the terrestrial communication system are extracted from the data sent from the optical cable. The data sent to the ground communication system is sent to the ground communication system by the RD, and the clock is sent to the ground communication system by the S/RT. R.D.
and S/RT signal line connections are shown in FIG.

Next, a case in which data is transmitted from the terrestrial communication system to the satellite communication system via the interface device in the main station of FIG. 1 will be described.

Data sent from the terrestrial communication system to the satellite communication system is transmitted from the satellite communication system as described above in the case of an interface that has only one common transmission/reception timing signal line, such as the X, 21 interface used in this embodiment. The provided clock will be used by the terrestrial communication system for both data transmission and reception timing. In other words, as mentioned above, the satellite communication system transmits data to the transmitted data SD using the clock supplied from the S/RT signal line.
Give it to the signal line. This data is sent to the optical module 4 in the opposite way to when the ground communication system receives the data.
There, the code is converted from NRZ to CMI code and then sent to the optical module on the satellite communication system side via an optical cable. At this time, in addition to the data, the clock supplied to the optical cable Sl) is originally supplied all the way from the local clock of the satellite communication system through the optical cable using the code conversion timing clock extraction device 7. Therefore, the clock supplied to the satellite communication system through the SD signal line has a transmission delay corresponding to the round trip of the optical cable with respect to the original local clock. Therefore, in order for the satellite communication system to faithfully receive data sent from the terrestrial communication system to the satellite communication system and transmit it to the satellite link, it is necessary to synchronize the data transmission lock S/RT in the terrestrial communication system with the clock of the satellite communication system. Therefore, before inputting the data to the satellite communication system, it is input into the FIFO buffer 5b of the - and After extracting the S
Sent through D. And the satellite communication system is SD
It receives data from the local clock and transmits it to the satellite link 8.

On the other hand, a case will be described in which the slave station on the left side of FIG. 1 transmits data from the satellite communication system to the terrestrial communication system t1 via the interface device X, 21 adapter. After the data is received by the satellite communication system 1 through the satellite ring 8, it is supplied to the RT line and 5Tli from which the reception clock is extracted from the reception data. in this case,
Synchronization between the reception clock and the reception data has been established. Therefore, the received data is sent through the RD line to S/R,T
It is synchronized with the clock and received by the ground communication system.

When transmitting data from the terrestrial communications system to the terrestrial communications system via the be done. In order for the satellite communication system to receive this data, the S
Receives input data from D. For that purpose, PIFO
It is necessary to provide 5c.

Basic configuration diagrams of an optical modulator 9 and an optical demodulator 10 used in the embodiment of the present invention are shown in FIGS. 2 and 3, respectively. The optical modulation device 9 includes a kneader 11 that converts transmission data from NRZ to CMI code, a driver 12 for driving a light emitting diode, and a light emitting diode (LED) 13. After the transmitted data is converted into a CMI code by the kneader 11, the data is converted into a voltage by the driver 12 and the light emitting diode 13 is turned on.

The optical tI adjustment device 10 includes a PIN photodiode 14 and an AGC
(automatic gain control) amplifier 15, digital PLL circuit (P
has Locked 1 loop) 16 It is composed of an R-specific reproduction circuit 17, a decoder 18 that converts received data from CMI code to NRZ, and a code conversion rule error detection circuit 19. Receive data to PIN photodiode 1
4, the signal photocurrent is amplified by the AGC amplifier 15, the timing clock is extracted from it by the digital PLL circuit 16, and (1), (0'3) of the received signal is identified according to the obtained constant timing. Size 51 with reproduction circuit 17
j.

Furthermore, code conversion rules are monitored for the identified and reproduced CMI code, and when a code conversion violation due to a bit error is detected, an error pulse is output each time. It also has a code conversion rule error detection circuit 19 that performs this function.

The embodiment of the cylinder 1 has been described in detail above, and next, the second embodiment of the present invention will be explained with reference to FIG. 4.

In this embodiment, X, 21
A clock signal supplied from a local clock 6 placed within the adapter 2 is provided through signal lines LT and ST.

Note that this LT signal line is connected to the optical module.

Therefore, the timing extraction clock necessary for converting from NRZ to CM code is supplied.

In other words, the data sent from the satellite communication system to the terrestrial communication system is input into the X, 21 adapter, and then FIFO
The signal is put into the I buffer 5a, taken out from there at the timing of an independent local clock that does not include frequency drift, and sent to the optical module, but these points are the same as in the first embodiment.

Next, in the slave station on the left side of FIG. 4, data is transmitted from the satellite communication system to the terrestrial communication system via the interface equipment [X, 21 adapter], and the operation is as follows, similar to the first embodiment. After the data is received by the satellite communication system 1 through the satellite link 8, a reception clock is extracted from the reception jet and supplied to the RT line. In this case, the synchronization between the receiving clock and the receiving data is established. Therefore, the receiving data is received by the terrestrial communication system through RD line transmission in synchronization with the taro clock of the S/RT line connected to the RT6. When transmitting data from the terrestrial communication system to the terrestrial communication system via the be done. In order for the satellite communication system to receive this data, it is necessary to supply the satellite link extraction clock ST synchronized with the S/RT clock to the satellite communication system.
Receives input data from D.

The cylinder 1 and the second embodiment have been described above.

〔Effect of the invention〕

The satellite communication network system according to the present invention supplies the transmission and reception timing of the terrestrial communication system with the local clock of the satellite communication system, thereby absorbing differences in the interface between two systems and eliminating frequency deviations due to the Doppler effect due to satellite position fluctuations. allows absorption and also
By making it possible to provide expandability to network connections using optical modules and optical cables,
This has the effect of realizing highly reliable network synchronization of a satellite communication network system.

[Brief explanation of drawings]

FIG. 2 is a block diagram showing an optical modulation device according to an embodiment of the present invention, and FIG. 3 is a block diagram showing the basic configuration of an optical demodulation device according to an embodiment of the present invention. 1...Satellite communication system, 2...Interface conversion device, 3...Terrestrial communication system (computer system,
Including networks, etc. )4... Optical module. 5 a , 5 b , 5 c -FIFO (Fir
st-In First-Out) buffer, 6...
Local clock, 7...NRZ (Non Retu
rn to Zero) to CMI code (CodedM
ark Inversion); 8... Satellite link; 9... Optical modulator; 10... Optical demodulator; 11... Korg for converting transmission data from NRZ to CMI; 12... Driver for driving light emitting diode, 13... Light emitting diode (LED), 14-PIN photodiode, 15=-A
GC (automatic gain control) amplifier, 16...digital PL
L circuit (Phase Locked Loop), 17
---Identification/regeneration circuit, 18: Decoder for converting received data from CMI to NRZ, 19: Code conversion rule error detection circuit, 20: Optical cable, 21: Data, 22: Clock , 23...data, 24...
・Clock, 25...Error pulse, RD...Receive data line, RT...Receive data timing line, LT・
... Local clock timing line, SD... Transmission data line, S/RT... Receiving and transmitting timing line %ST...
- Transmission timing line.

Claims (1)

[Claims] 1. In a communication system having a configuration in which a plurality of communication systems are connected, there are devices in which the timing lines of the device interface are separate for transmission and reception, and devices that use a common timing line for transmission and reception. A network synchronization method characterized in that it has means for adjusting synchronization using a local clock and a buffer. 2. The network synchronization method of claim 1, wherein said local clock is in an adapter for said interface. 3. The network synchronization method according to item 1, wherein the buffer is a first-in, first-out type buffer. 4. The network synchronization method according to item 1, wherein the reception timing varies depending on radio waves received from a satellite.