JPS60236527A - Alternating system of reference station for tdma satellite communication system - Google Patents

Abstract

PURPOSE:To attain an alternating system of reference station which can be applied concentrically by selecting one of earth stations as a spare reference station excluding the reference station to transmit a synchronizing burst that can be easily discriminated from those of other earth stations and at the same time securing a function that transmits a spare reference burst which can substitute the function of a reference burst when no reference burst is transmitted. CONSTITUTION:A spare reference station discontinues the burst synchronization that is so far carried out subordination to a reference burst in case the reference burst is lost and the prescribed conditions are satisfied. Then the spare reference station transmits the burst of own station with the timing of its own. Thus a spare reference burst is transmitted only when a fact is confirmed that at least one of synchronizing bursts of stations exculding the reference station and own station is received normally.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical field of the invention)
e Division Multiple Accesses
s (hereinafter referred to as TDMA) relates to a reference station alternation method for satellite communication systems.

(Technical background) A TDMA satellite communication system is a system in which multiple earth stations communicate with each other by using carrier waves of the same frequency and sharing the corresponding frequency bands of satellite repeaters (transponders) in a time-sharing manner. It is.

FIG. 1 is an explanatory diagram of such a TDMA system. It is assumed that four earth stations A, B%C, and D participate in Jin's system.

Each station transmits traffic data of 1.2
．． As shown in 3 and 4, one frame structure called a TDMA frame is created by transmitting in the form of a temporally compressed burst, and this is periodically repeated. These bursts must be controlled so that they do not overlap each other on the transponder. For this reason, each burst contains a synchronization signal jumped on 10.20.30 and 40, which is used to identify the position of each burst, and also to indicate the starting point of the data contained in each burst. used.

One of these synchronization signals, for example synchronization signal 10, is identified as different from the synchronization signals of the other bursts and is used as the frame synchronization signal.

The station transmitting the burst containing the frame synchronization signal, station A, is called the reference station.

The bursts transmitted from each station are received by each station via a transponder. Each station first establishes frame synchronization using the received frame synchronization signal. That is,
Establish a time reference for receiving each burst within a TDMA frame. Furthermore, it receives the burst transmitted by its own station, detects the seven synchronization signals, compares this with a predetermined position on the time standard of the above-mentioned receiving station, measures the difference, and uses this result. The transmission timing of the own station's burst is corrected, and burst synchronization is performed to maintain the own station's burst at a predetermined position within the TDMA frame.

In such a TDMA system, each station can receive all the signals in the TDMA 7 frames with one receiver, so the communication capacity of each station can be easily changed by changing the width of the corresponding burst. Therefore, the TDMA system has the advantage of being able to construct a very flexible network, and has recently been widely used not only in the field of international communication but also in the field of domestic communication or so-called business communication.

(Prior art and problems) Now, one of the most important functions to maintain a TDMA system is
The first is "synchronization." This synchronization includes the frame synchronization and burst synchronization described above.

Returning to FIG. 1, this synchronization problem will be discussed.

In the figure, station A is the reference station and the frame synchronization signal lO
Each station sends a burst containing
．． ) If a failure occurs in station A and it is no longer able to send bursts, the entire system will collapse. One possible solution to this problem would be for station B to act as a reference station if a failure occurs in station A. This is called reference station switching. For example, if station A has a failure, station B changes the synchronization signal 20 included in burst 2 transmitted by itself to a frame synchronization signal, and each station resynchronizes with this new frame synchronization signal. This kind of technical failure
in a TDMA System.

However, this method has the drawback that the position of the frame synchronization signal changes every time the reference station is replaced.

To improve this shortcoming, the reference station can send a special burst containing a 7-rem synchronization signal but no traffic data at the beginning of the TDMA frame, as indicated by the dashed line 11 in Figure 1. --7'' The arm 911 with Koenshun is also drowning in par 1, it is called S-strike, and the no(-strike that includes other traffic data is called data burst.This is 19
U.S. Patent No. 3,838, issued September 24, 1974;
No. 211 (W, G, Sehmidt et at
'TDMA SatelliteCommunicat
ion System having 5special
Reference Burst') is a prototype TDM planned by IN SAT to investigate the possibility of adapting the TDMA system to international communications.
A system specifications BG-1-18E (Rev, 2) 2
0March 1974'SYSTEM 5PECIF
ICATION OF THE IN SAT PROT
It was also adopted by "OTYPE TDMA STEM".

When base station switching is performed using this method, a predetermined backup base station is placed in the same TDMA frame position where the base station was previously transmitting the reference burst.
A new reference burst will be sent.

Next, we will discuss burst synchronization. When multiple stations share one carrier, jri
Multiple synchronous bursts will be included.

Figure 2 shows a synchronized parse of stations using the same carrier as the reference berth (11) mentioned above.
The structure of an A frame is shown.

This method makes it possible to separate the parts related to synchronization and the parts related to traffic data transmission.
The flexible nature of the system can be fully utilized. This method is described in Japanese Patent Publication No. 55-47781 (Watanabe et al., "Time Division Multiple Access Communication System", Japanese Patent Application Laid-open No. 51-5914) published on December 2, 1980.

In addition, in this case, since the synchronization burst 21 of the backup reference station (for example, station B) is also transmitted, if the reference parse) 11 is lost due to a failure, the other stations will immediately receive the synchronization signal in the burst of the backup reference station. can be used as a frame synchronization signal to maintain synchronization. The advantage of this method over the reference station replacement method described above is that first, the position on the frame of the synchronization burst (or preliminary reference burst) of the backup reference station is determined in advance, and each station uses the seven receiving devices to perform frame synchronization. It is possible to design the circuit according to this frame configuration, that is, it is possible to configure it so that frame synchronization can be established and maintained using either the reference burst or the preliminary reference burst. The next advantage is that in the above-mentioned method in which there is only one reference burst 11 at the beginning of the frame, it takes only a few seconds for the backup base station to send out a replacement base burst after the loss of the regular base burst. The problem with this scheme is that such problems do not exist at all, whereas other stations have to operate without reference bursts.

This method was adopted at the 3rd International Conference held in Kyoto from November 11th to 13th, 1975.
e-rence on Digital 5atell
Watanabe and others will discuss A New TDMA System for Do ite Communications.
mestic 5service 5Lnd its H
lgh 5peed PSKModem", and is currently being used as Japan's practical communication satellite [Sakura 2+ (
C8-2) is in practical use on the lines of Nippon Telegraph and Telephone Public Corporation.

A method of arranging the reference burst and the preliminary reference burst on the same frame is described in US Pat. No. 4,054,753 (p. 18, 1977).

Kaul et, al'Double 5yns B
urat TDMA System).

However, as shown in Figure 2, the method in which all related earth stations transmit a synchronized burst every frame increases the frame efficiency, that is, the proportion of the TDMA frame width that can be used for transmitting traffic data, as the number of stations increases. The problem is that it reduces the amount of Also, as a recent trend, the role of reference stations in communication systems is becoming more important, and they do not only provide a time reference for frame synchronization, but also transmit control commands for remote control of each earth station, The length of the reference burst is also becoming longer due to the transmission of download data for the control computer used in each earth station. It is uneconomical to arrange them on the same frame.

(Objective of the Invention) The object of the present invention is to solve the above-mentioned problems and to transform the TDMA system using a single carrier wave into a TDMA system using multiple carrier waves by adding appropriate equipment and functions to the TDMA system.
The present invention aims to provide a standard station replacement method that can be uniformly applied to systems that are gradually expanded to the A system.

(Structure and operation of the invention) In order to achieve the above object, the present invention has the following structure. That is, the reference station replacement method of the present invention is a system including one satellite and a plurality of earth stations, one of the earth stations is selected as a reference station, and TDM in the system is achieved by periodically transmitting a reference burst.
Define the A frame, and then multiply the frame by n (where n>
2) defining a multi-frame by transmitting a reference burst that is distinguishable from others in the TDMA frame period, each of said earth stations transmitting at least one data burst containing data to be transmitted in said TDMA frame period; , and in a TDMA satellite communication system in which one synchronization burst is transmitted in the multi-frame period, one of the earth stations other than the reference station is selected as a preliminary reference station and transmits a synchronization burst that can be easily distinguished from that of other earth stations. transmitting, and transmitting a preliminary reference burst capable of substituting the function of the reference burst at a time position on the TDMA frame at which the reference burst should be transmitted, when the reference burst is not being transmitted; each of the earth stations establishes and maintains a time reference in the reception of the TDMA frame and the multiframe by receiving bursts of either the reference burst or the preliminary reference burst; Or, a reference station changeover in a TDMA satellite communication system, in which the synchronization burst of the backup base station is received and the time reference is maintained in the reception, after the backup reference burst ceases to exist until the other burst is present. Method In the present invention, the reference station defines the TDMA frame of the system by periodically transmitting a reference burst, and also defines the TDMA frame of the system by transmitting a reference burst that can be distinguished from others at a frame period of 11(n,)2). Define the frame.

Each earth station participating in the system transmits a data burst in a TDMA frame period, and also transmits a synchronization burst in a multi-frame period.

A first feature of the invention is that the preliminary reference station transmits synchronization bursts that are easily distinguishable from those of other stations. Of course, the preliminary reference station is another earth station, and the L-Kaiku Itsudo is subordinated to the station, performs the I-frame M period, and performs burst synchronization using the synchronization burst of its own station.

A second feature of the present invention is that the reference station that is transmitting the reference burst also transmits synchronization bursts like other stations. The purpose of this synchronization burst will be discussed later.

A third feature of the invention is that the preliminary reference station has the ability to transmit a preliminary reference burst that is isomorphic to the reference burst at the same time position as the reference burst on the TDMA frame. Of course, this feature is not used while the reference burst is normally present on the frame.

A fourth feature of the invention is that each earth station has the ability to maintain frame synchronization using synchronization bursts of a preliminary reference station.

Based on the above characteristics, the reference station change of the present invention is performed as follows.

First, in a situation where the reference burst cannot be normally received or used, each station maintains frame synchronization by receiving the synchronization burst from the preliminary reference station and maintains the time reference in reception.

The backup reference station controls its own station independently from the reference station, and after confirming that the Kiji burst has been lost, transmits a backup reference burst with the same shape as the reference burst to the same frame position as the reference burst, It takes over the role of network control on behalf of the reference station.

Each earth station is subject to the preliminary base burst once it is received.

When the reference station recovers from a failure and joins the network, it first establishes burst synchronization using synchronization bursts like other general stations.

When the preliminary reference station confirms that the synchronization burst of the reference station is being transmitted normally, it stops transmitting the preliminary reference burst, and the reference station stops transmitting the preliminary reference burst and controls its own station independently from the preliminary reference station, and starts transmitting the reference burst. Start sending.

(Embodiment of the Invention) FIG. 3 is a configuration diagram of a network assumed by the present invention. As shown in the figure, this system consists of one satellite ioo and a number of earth stations 102, 104, 106, 108, . . . . Each earth station has a terrestrial line 152.154.
156, 158,..., and satellite 1
They exchange traffic data with each other via 00.

Each station is basically an unmanned station, and the operating status of each station, alarm signals, etc. are sent to the reference station via a satellite using a preset channel.

The earth station 102 is a reference station, and the earth station 104 is a backup reference station, and has a station configuration similar to other stations, but it is manned and has network control devices 112 and 114, and can monitor the operating status and alarm signals sent from each station. It monitors and displays the information, and sends command signals to remotely control each station as necessary.

In a large system, a central network control facility 120 is placed at a reference station or in a city near the reference station to integrally monitor and control the network instead of or in parallel with the network controllers 112 and 114.

The central network control facility 120 is connected to the reference station and backup reference station by terrestrial lines 162 and 164, and can directly monitor the status of both stations and, if necessary, communicate with any station in the network through either station. You can send commands.

Furthermore, it is also possible to monitor and control the operating status of any station using the terrestrial public communication network 170 at the time of start-up or failure of the satellite line.

FIG. 4 shows an example of the configuration of an earth station using the present invention.

The traffic power 150 from the terrestrial line is connected to the multiplex control circuit 2.
02 into a time-division multiplexed format, output in a burst form in response to a timing signal 254 sent from the transmission timing control circuit 204, and applied to the modulator 206. In TDMA system, modulation is usually 4-phase PSK (Qu
adruturePhase 5hift Keyin
g: QPSK) is used.

The output of modulator 206 is 70 MHz or 140 MHz
It is a signal in the intermediate frequency (IF) band of Z and is supplied to the p1 up converter-41919. The RF ratio output of upconverter 212 is provided to high power amplifier 216 . The output of the high power amplifier 216 is transmitted from the antenna 242 to the satellite as an RF multiplied signal of frequency f.

The signal received from the satellite undergoes frequency conversion on the satellite, so it becomes a signal with frequency F multiplied by RF. ' This signal is supplied to the down converter 232 via the low noise amplifier 236, converted into an IF band signal, and then supplied to the Enoki modulator 226.

The output of the demodulator 226 is sent to the separation control circuit 222 as a timing signal 264 from the reception timing control circuit 224.
A necessary output signal 151 is separated by control and output to the terrestrial line.

The aforementioned reception timing control circuit 224 normally establishes the time reference for TDMA frames and multiframes by receiving a reference burst sent from a reference station and performing frame synchronization. That is, it is possible to generate timing signals for identifying various signals received arranged on a TDMA frame.

The synchronization control circuit 240 is supplied with a signal identifying the reception position of the synchronization burst transmitted by its own station from the reception timing control circuit 224, compares this with the position of the actually received burst, and determines the difference, that is, the transmission timing. detecting the error and controlling the operation of the transmission timing control circuit 204;
Establish and maintain burst synchronization.

Frame synchronization and burst synchronization are well known techniques and are described in detail in, for example, the aforementioned US Pat. No. 3,838,221.

FIG. 5 shows the upper apparatus and structure of various burst frames used in the TDMA system. Figure (a) shows an example of the frame structure used in the present invention, in which there is a reference burst 11 sent by the reference station at the beginning of the frame, and a frame 1-1.
system synchronization signal 10.

Next, there is a synchronized pulse (ml) in which m stations transmitting signals using this carrier wave sequentially. Synchronization bursts are transmitted in a multi-frame period with a period of n frames, so if m ) n, two or more synchronization bursts will be transmitted for the same frame, as shown in Figure 2. Arranged in parallel.

Next, each station sends data bursts 1.2 for each frame.
．． 3... are arranged in pre-assigned time slots.

FIG. 5(b) is an enlarged view of an example of the configuration of the reference perspective) 11, and FIG. 5(e) is an enlarged view of an example of the configuration of the synchronization burst ml. d) is a diagram showing an enlarged example of the configuration of data bursts 1, 2, 3, and so on.

Reference berth) 11 is a C/BTR at the beginning to facilitate recovery of the carrier wave and bit timing of the reception demodulator.
(Carrier and Bit Tlming R
) pattern, and then there is a frame synchronization signal. This synchronization signal is called a unique word (UW) in the sense that it can be uniquely found even in a random code string.

Next is the identification code (ID) for the transmitting station and operational status, and then there is the control data channel (CDC) used by the reference station to control each station. After that, an order wire channel and various network control data channels are arranged depending on the case.

When arranging bursts on a TDMA frame, it is necessary to leave a space between the bursts to avoid mutual overlap, and in the figure, a guard time GT is reserved in front of each burst.

The synchronous parse) ml is similar to the reference berth) 11, but instead of the CDC there is a service channel used for reporting the station status and responding to commands from the reference station. Synchronous bursts do not send commands, but by displaying the status of the own station using an ID or the like, it is possible to make the other station perform the expected operation.

Data parsing) 1, 2, 3, ... are the same length as the other bursts six times in the front (this is called the preamble part), but after that there is a sub-burst for transmitting traffic data. You can add as much as you like.

Although the frame synchronization signal and other synchronization signals are all shown as UWs in the figure, in reality, several UWs are created and allocated depending on the purpose. For example, create four types of UWs, and define them as: (1) UWl (base fl1M multiframe marker), which is transmitted once every n frames in a reference burst and defines a multiframe;
) UW2 used for synchronization bursts transmitted by the preliminary reference station,
(31) UW3 (-crotch multiframe marker) indicating that other bursts are synchronized with the multiframe, and (4) UWOL indicating other synchronization signals).

Therefore, if each station transmits the synchronization burst of the preliminary reference station in the first TDMA frame of the multi-frame frame in which each station transmits the map signal, UWI, UW2 , UW3O
The synchronization signals are lined up, and UWO is used for all other frames, including the frame synchronization signals.

The various bursts shown in FIG. 5, including the generation of UW, are generated or formed by the multiplex control circuit 202 of FIG. 4 by a known method.

FIG. 6 shows the process of changing the reference station from the perspective of the frame structure of the system to which the present invention is applied.

The configuration of the (alti TDMA frame and multiframe) in the figure is shown.

Frame l indicates the first TDMA frame of the multiframe, and the reference parse) 11 transmitted from the reference station is located at the light end of the frame and contains the multiframe marker UWI. Next, there is an area where synchronization bursts of each station are arranged, and then data bursts 1, 2, 3, . . . are arranged.

Now, let the multi-frame period be i-frame, and the participating station is 0.
Equation 1 is 2n≧m) n. Therefore, synchronization bursts are sent in pairs to the ITDMA.

In FIG. 6(a), it is assumed that 12 is the synchronization burst of the reference station and 21 is the synchronization burst of the preliminary reference station.

In frame 1, all bursts include multiframe markers, so the reference station synchronization burst and data bar are U.
W3, preliminary reference station synchronization burst includes UW2.

Frame 2, frame 3, etc. have a similar format to frame 1, but with a synchronous burst of 31°41.51
．． 61,... are transmitted from different earth stations, and the synchronization signals included in each burst are all from U.
It is WO.

Frame (n+1) has exactly the same frame configuration as frame 1, and corresponds to the first frame of the next multiframe.

In such a situation, all stations use the standard perspective) 11.
11'..., frame synchronization is performed, and a reception time standard is established.

Figure (b) shows 7 frames when a failure occurs at the base station.
The reference burst 11, synchronization burst 12, and data burst 1 that were sent from the reference station have disappeared. At this stage, each station performs preliminary reference station synchronization burst 2.
1 to maintain frame synchronization.

(e) of the figure shows a state in which the preliminary reference station has transmitted the preliminary reference burst 22. The preliminary reference burst is transmitted every TDMA frame like the reference burst, and since frame l includes the multi-frame marker UW1, all stations transmit this preliminary reference burst 2 in the same way as in the case of reference burst 2.
2 to maintain frame synchronization and follow the instructions of the control commands contained in the preliminary reference burst 22.

FIG. 7 shows a circuit that maintains υ frame synchronization using the preliminary reference station synchronization burst 21, which is one of the features of the present invention, ie, the main part of the reception timing control circuit 224 of FIG. 4.

It is stated in The circuit used in the present invention differs from known systems in that preliminary reference station synchronization burst and knee frame synchronization maintenance is performed by control for each multi-frame.

In the figure, a binary stage counter 3.02 counts symbol clocks 350, while the contents of the bits of the counter are monitored by a decoder 1304, and when the contents match, a reset signal 352 is generated and the counter 302 is Reset the contents to 'ooo...000#. As a result,
Counter 302 has a period that is equal to decoder I 304. This period is chosen as the period of the TDMA frame.

On the other hand, when the reference burst is received, the frame synchronization signal contained therein is detected and applied as a detection pulse 354 to the preset terminal of the counter 302; (DATAI) to counter 3
Load into 02. This data corresponds to the frame position of the reference burst. Frame ll [4 to #-1: UW appearing in the first frame of multi-frame
There are I and UWO that appear in other frames, but any detection pulse can preset the counter 302. That is, the counter 302 operates in TDMA frame cycles and in synchronization with the received frame synchronization signal. This is a state in which 7-rem synchronization is established, and the contents of the counter 302 can be compared one-to-one with the phase within the TDMA frame. The phase here means a relative position on the time axis in each TDMA frame.

That is, counter 302 can provide a time reference for received TDMA frames.

In order to process various received signals according to the phase on the TDMA frame, information regarding a large number of events is stored in a random access memory circuit (hereinafter referred to as RAM) 30.
It is recorded in 8.

These event information consists of two types of information: control information indicating the content of the control and timing information indicating the phase on the frame to be controlled.
The address counter 310 is a collection of words consisting of two elements, arranged in timing order, and appears on the output in accordance with control from the address counter 310.

The timing information is YakevK beat, and the comparator 312
It is compared with the contents of counter 302 at step . Also, the control information of the same word is applied to the decoder 314, and the content of the control is output.

Timing information of output of RAM 308 and counter 302
When the contents of the comparator 312 match, the comparator 312 generates a match pulse 356 which is applied to the AND gates 316, 316'...
The gate timing signal 358 or 358' that matches the output of the decoder 11314 is then supplied to necessary circuits.

Match pulse 356 is '17'c address counter 310
It is also used as a clock signal for address counter 3.
Since the contents of 10 are advanced by one, the next word appears in the output of RAM 308 as a result. address counter 31
0 is reset to %6N of the reset signal output 352 of the decoder I 304, so as the contents of the counter 302 progresses, the AND gates 316, 316'...
As a result, timing signals necessary for processing the received signal on the TDMA frame are successively obtained from the output of the TDMA frame.

Counter 302 if reference burst is no longer received
The preset signal will disappear, but the reset signal 352 will be used for a while! It can continue to move at the IITDMA frame period, and the timing signal 358.358'...
・Can also be output normally. However, symbol clock 35
If it is free-running at 0, phase errors will accumulate, and in particular, the various bursts that each station is transmitting due to errors in burst synchronization that operate and operate based on the time standard created by this circuit. starts to slip from its normal position on the TDMA frame,
If they overlap with each other, the TDMA system will no longer work. Therefore, normally, when a reference burst is not received for a period of time, it is determined that the frame is out of synchronization, and it is necessary to stop the transmission of that station.

That is, the objective of the present invention is to provide a backup reference station to replace the reference burst before it is determined that the frame is out of synchronization.

In the present invention, this reference station change has two phases. That is, the first phase is a phase in which the detection pulse 360 of the synchronization signal UW2 of the synchronization burst of the preliminary reference station is used instead of the detection pulse 354 of the frame synchronization signal. The second phase is the phase in which the preliminary reference station transmits preliminary reference bursts and uses the detection pulse 354 of the frame synchronization signal, which is now detectable again.

Of these, the first phase is controlled by the frame synchronization signal loss indication signal 362. That is, when the frame synchronization signal is lost and a predetermined condition is satisfied, for example, "the frame synchronization signal could not be detected continuously over P frames or more", the frame synchronization signal loss indication signal 362 is generated and the switching is performed. A register or manual digital controller that controls the logic switch 318 and the data selector 320 and guides the detection pulse signal 360 of the synchronization signal UW2 of the preliminary reference station synchronous burst to the counter 302 as a preset signal, and at the same time sets data corresponding to the position of the preliminary reference station synchronous burst. The contents of the bit (DATA2) of switch 322 are loaded into counter 302.

If the frame synchronization signal detection pulse 354 is obtained again due to the reappearance of the reference burst or the appearance of the preliminary burst, other conditions, such as "the frame synchronization signal was detected continuously over Q frames", are satisfied. , the frame synchronization signal loss indication signal 362 disappears, and the switching logic switch 318 and data selector 320
returns to the normal state and enters the normal state or phase 2.

In exactly the same way, when the backup reference station stops transmitting backup reference bursts because the reference station has recovered from a failure, and the reference station sends out reference bursts, phase 2 is first transmitted to phase 1.
state, and then returns to the normal state.

The difference between the normal or phase 2 state using the frame synchronization signal detection pulse 354 and the phase 1 state using the preliminary reference station synchronization burst synchronization signal detection pulse 360 is that the former is a signal with a TDMA frame period of 9; , the latter is a multi-frame signal, that is, a signal with an n-frame period.

Now, suppose the symbol clock frequency is 3500 MH
Assume that the frequency error with respect to the time base obtained from the reference burst received from the reference station via satellite is 1xio-'. In this case, if the counter 302 were to run free without a preset signal, there would be an error of 3 symbols per second.

The preset signal corrects this error, but since it cannot correct an error smaller than l symbol, a kind of jitter occurs between each frame in the timing output 358.358'. Considering the TDMA frame period in the range of 2 m5ec to 3 Q m5ec, the frequency of the preset signal using the frame synchronization signal detection pulse 354 is sufficiently high, and the above-mentioned jitter can be considered to be one symbol at most.

On the other hand, the synchronization signal detection pulse 36 of the preliminary reference station synchronization burst
If 0 is used, the preset frequency will drop to -n, but if the multi-frame period is set to 300 m11se, the cumulative error during this period will be about 1 symbol, so the jitter mentioned above will slightly exceed 1 symbol. Even if there is 2
There is no more than a symbol.

This increase in jitter affects burst synchronization to the same extent, but it is actually absorbed by the existence of guard time between bursts and does not affect transmission quality.

When the present invention is applied, if the network shown in FIG. Since it is in a position to monitor and control, it is possible to control without contradiction the transmission of a backup reference burst from the backup reference station in the event of a failure of the reference station, the processing when the reference station is restored, etc.

However, if there is no central network control facility 120 and the reference station and backup reference station are functioning independently, reference station replacement must be performed with care. For example, if a backup reference station erroneously transmits a backup reference burst even though the reference station is normal, the system will collapse.

In the conventional method, if this base station switching was attempted to be done carefully, the entire system would have to operate for a long time without a reference burst, and each station equipment would be required to have extra functions. In the present invention, this limitation has been removed. Therefore, when the backup reference station sends out the reference burst, it can take sufficient time to confirm the loss of the reference burst. The following is a specific example of seven.

When a reference burst is lost, each station relies on the synchronization burst of a backup reference station to maintain frame synchronization, or time reference of reception. This also applies to preliminary reference stations. Therefore, if the reference burst is lost and a predetermined condition is met, for example, "the UW of the reference burst could not be detected for more than P frames", the backup reference station has not been able to follow the reference burst until now. Stop the burst synchronization that has occurred, and make your own station's burst transmission occur at its own timing. This corresponds to making the transmission timing control circuit 204 independent from the control from the synchronization control circuit 240 in FIG. 4 and allowing it to run freely. At this stage, not only the reference burst but also the synchronization burst from the reference station cannot be received, but if the synchronization burst from other stations cannot be received either, the system has already collapsed and all stations other than the own station are unable to receive the synchronization burst. Transmission may have stopped, or your station may have incorrectly synchronized to a completely different phase on the frame. Therefore, automatic transmission of preliminary reference bursts must be prohibited in such abnormal situations.

On the other hand, if even one synchronization burst from a station other than the reference station and the local station is received, this becomes objective evidence that the local station is subordinated by the other station.

In other words, the reference burst has been lost and this satisfies predetermined conditions, the synchronization burst of the own station is being received via satellite, the synchronization burst of the reference station has been lost, and the synchronization burst of the reference station and other stations than the own station has been lost. The pre-reference burst can only be transmitted after the condition that the synchronization burst of the station has been successfully received at least 1':) II'i is confirmed.

That the backup reference station is transmitting backup reference bursts and is operating in "base station mode" can be indicated by, for example, the ID of the backup reference station synchronization burst.

When the failure of the reference station is recovered, the reference station uses synchronization bursts to ensure burst synchronization in the same way as general stations. Once this process is completed, the reference station can transmit a data burst that transmits its own traffic data, and can indicate, for example, by the ID of the synchronization burst, that the base station can now operate "normally."

A preliminary reference station is a reference station whose synchronization burst causes the reference station to
When it learns that the state has returned to "normal", it stops transmitting the preliminary reference burst and changes the display of the synchronization burst ID from "base station mode" to "preliminary reference station mode."

The reference station transmits a reference burst after confirming that the synchronization burst of the preliminary reference station returns the preliminary reference station to the "preliminary reference station mode" and that the preliminary reference burst has disappeared.

Through the process described above, the reference station can be replaced without any contradiction to which the present invention is applied.

(Effects of the Invention) The first effect of the present invention is that frame efficiency can be improved because each station sends out various bursts at a frequency according to its purpose, and in particular does not send out extra reference bursts or synchronization bursts on the frame. It is.

A second advantage is that since the reference burst and the preliminary reference burst are received at the same location on the frame, the control data carried by these bursts is easier to handle and the apparatus is simplified.

The third effect is that as long as systems other than the reference station are normal,
In other words, if control from the reference station is not required, the system can be maintained without a reference burst, and the reference station changeover can be carried out in Shinto with sufficient time, which prevents erroneous operations related to the reference station changeover. Requirements are also reduced.

A fourth effect of the present invention is that the system constructed according to the present invention can be asymptotically extended to a large-scale network using multiple carrier waves, which has been separately filed.

As detailed above, the present invention is a TDM system using a single carrier wave.
In the A-satellite system, it solves all the conventional problems related to reference station replacement and provides a highly reliable network, and is highly effective when applied to domestic communication networks or business communication networks.

[Brief explanation of the drawing]

Figure 1 is an illustration of a TDMA system using a single carrier, Figure 2 is a TDMA system with a reference burst and a synchronization burst.
Figure 3 is a diagram showing the configuration of the network assumed by the present invention; Figure 4 is a diagram showing an example of the earth station configuration; Figure 5 is a diagram showing the configuration of various bursts used in the TDMA system. Figure 6 is a diagram showing the position and configuration on a frame; Figure 6 is a diagram showing the process of reference station replacement from the perspective of the frame configuration of a system to which the present invention is applied; Figure 7 is a circuit that maintains frame synchronization using preliminary reference station synchronization bursts. FIG. 1...Data burst from station A, 2...Data burst from station B, 3...Data burst from station 0, 4...Data burst from station D, 1O...A
Station synchronization signal (frame synchronization signal), 11.11'...
・Reference burst, 12... Reference station synchronization burst, 2
0...Synchronization signal of station B, 21...Synchronization burst of station B, 22...Preliminary reference burst, 30...Synchronization signal of station 0, 31...Synchronization burst of station 0, 40.・・D
station synchronization signal, 41...D station synchronization parse), 51.
61...Synchronized burst of other earth stations, 100...Satellite, 102.104,106,108...Earth station, 1
12.114...Network control device, 120...
・Central network control equipment, 150-...Traffic input, 151...Output signal, 152, 154, 156
,158,162.164...Terrestrial line, 202・
... multiplex control circuit, 204 ... transmission timing control circuit, 206 ... modulator, 212 ... up converter, 216 ... large power amplifier, 222 ... separation control circuit, 224 ... reception timing control circuit, 226
... Demodulator, 232 ... Down converter, 236
...Low noise amplifier, 240...Synchronization control circuit, 2
42... Antenna, 254, 264... Timing signal, 302... Counter, 304... Decoder 1
1306...Resistor or manual digital switch, 3
08...RAM, 310...Address counter, 3
12... Comparator, 314... Decoder ■, 316
．． 316'...AND gate, 318...Switching logic switch, 320...Data selector, 322...
Register or manual digital switch, 450... Symbol clock, 352... Reset signal, 354...
・7-rem synchronization signal detection pulse, 356... Coincidence pulse, 358, 358'... Timing signal, 360
... Synchronization signal detection pulse of preliminary reference station synchronization burst,
362... Frame synchronization signal loss display signal Agent Yoshihiro Yahata 411 Figure 18 8th 4th @ Gi, 5th temporary same

Claims (1)

[Claims] (1) A system including one satellite and a plurality of earth stations, wherein one of the earth stations is selected as a reference station and defines a TDMA frame in the system by periodically transmitting reference bursts, and A multiframe is defined by transmitting a distinguishable reference burst at a period n times that of the frame (where n>2), and each of said earth stations transmits at least one data burst containing data to be transmitted. In a TDMA satellite communication system that transmits at the TDMA frame period and transmits one synchronization burst at the multi-frame period, 3
the time at which said reference burst on said TDMA frame is to be transmitted when one of said earth stations other than said reference station is selected as a backup reference station and said reference burst is not being transmitted in common with that of other earth stations; each of the earth stations has a function of transmitting a preliminary reference burst capable of substituting the function of the reference burst to a location, and each of the earth stations performs the TDMA by receiving either the reference burst or the preliminary reference burst. Establishing and maintaining a time reference in the reception of frames and said multi-frames, said synchronization burst of said pre-reference station from the absence of the reference burst or pre-reference burst being received until the presence of the other burst; 1. A reference station switching system for a TDMA satellite communication system, characterized in that a reference station switching system for a TDMA satellite communication system is characterized in that the time reference in the reception is maintained by receiving the reference station.