JPH0648795B2 - Burst synchronization method for SS-TDMA satellite communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention uses a satellite having a plurality of spot beam antennas and switches a TDMA signal transmitted from an earth station corresponding to each beam by a switch matrix on the satellite. SS-TDMA method (Satellite Switched-Time)
Division Multiple Access) for the transmission burst synchronization method of the earth station.

[Conventional technology]

FIG. 3 is a configuration diagram for realizing the burst synchronization method used in the conventional SS-TDMA method. 1, 2 are spot beam antennas, 3 and 4 are circulators, 5 and 6 are receivers, 7 is a switch matrix, 8 and 9 are transmitters, 10 satellites, 11 are reference stations, 12 is a transmission frame counter, 13
Is a reference station synchronization burst generator, 14 is a multiplexing circuit, 15 is a modulator, 16 is a demodulator, 17 is a station identifier, 18 is a bit phase error measuring circuit, 19 is a received frame counter, 20
Is a slave station burst position error detection circuit, 21 is a slave station transmission synchronization control circuit, 22 is a slave station, 23 is a slave station synchronization burst generator, 24 is a modulator, 25 is a demodulator, 26 is a transmission synchronization error control circuit, and 27 is It is a transmission frame counter. Fourth
The figure shows a time chart of the burst synchronization error according to the conventional method, and shows the relationship between the reference station synchronization window, the reference station synchronization burst signal, and the slave station synchronization burst signal. This reference station synchronization window is the time when the switch matrix on the satellite is setting the switch path so that it is folded back to the reference station, and the signal transmitted from the reference station to the satellite is this synchronization window. Only while it is turned on, the data can be returned on the satellite and received by the reference station. The operation of the burst synchronization method used in the conventional SS-TDMA method is divided into an operation of a reference station and an operation of a slave station, and the outline thereof is as follows.

In the steady state, the reference station 11 can almost estimate the time when the reference station synchronization window is turned on, and therefore the reference station synchronization burst is transmitted during this period. The reference station synchronization burst is a signal generated by the reference station synchronization burst generator 13 operating under the control of the transmission frame counter 12 and modulated by the modulator 15. The transmitted reference station synchronization burst is received by the spot beam antenna 1 on the satellite 10,
Switch matrix 7 because the reference station synchronization window is on
Thus, the beam corresponding to the reference station 11 is transmitted again. In the reference station 11, the demodulator 16 demodulates the reference station synchronization burst, and the station identifier 17 distinguishes it from other bursts and selectively inputs the reference station synchronization burst to the bit phase error measuring circuit 18. A fixed pattern indicating the beginning of the burst is provided at the beginning of the reference station synchronization burst, and the reception frame counter 19 is reset using the synchronization word detection pulse generated when this pattern is received. The reference station synchronization burst, which is returned by the satellite 10 and received by the reference station 11, cannot be received when the reference station synchronization window is turned off. Therefore, the bit length error measurement circuit 18 measures the bit length cut at the trailing edge of the reference station synchronization window. Then, the error from the expected regular bit length is obtained. The transmission time of the reference station synchronization burst, that is, the transmission frame counter 12 is corrected so that this error becomes smaller. By this correction, the time error between the reference station synchronization burst and the reference station synchronization window corresponding to the frame on the satellite 10 can be suppressed within a certain range. In Figure 4, this is ±
Expressed as a bit.

On the other hand, the following feedback loop method is used for slave station burst synchronization. The slave station 22 modulates the slave station synchronization burst generated by the slave station synchronization burst generator 23 operating under the control of the transmission frame counter 27 by the modulator 24 and transmits it to the satellite 10. The slave station synchronization burst returned by the beam corresponding to the reference station 11 to the switch matrix 7 of the satellite 10 is demodulated by the demodulator 16 of the reference station 11.
After demodulated by the station identifier 17 and identified by the station identifier 17, the slave station burst position error detection circuit 20 receives the received frame counter 1
The arrival time, that is, t ₁ in FIG. 4 is measured with reference to 9 to detect an error from the expected normal burst position.
The burst position error is format-converted by the slave station transmission synchronization control circuit 21, modulated by the modulator 15, and then transmitted again to the slave station 22 via the satellite 10. In the slave station 22, the demodulator 25 demodulates the signal, and the transmission synchronization error control circuit 2
In step 6, the transmission frame counter 27 is corrected so as to reduce the above error. Here, in the configuration of the slave station 22 of FIG. 3, the description is omitted because it is described by paying attention to the time position error detection of the burst to be transmitted and the correction function of the error, but the TDMA device in a normal earth station is omitted. In the composition of, for example, Kenichi Miya, “Satellite Communication Technology” published by the Institute of Electronics and Communication Engineers, November 10, 1980, Chapter 7, Section 7.4, Section 7.7.1 T
As shown in the basics of the DMA method (pp216-218),
The demodulator 25 of the slave station 22 also has a circuit corresponding to the station discriminator 17 and the reception frame counter 19 in the same stage as the reference station 11, and the reception timing of the reference station synchronization burst signal obtained thereby is used as a reference. The reception timing is controlled so that the data can be obtained from the burst to be received at the proper timing. However, the slave station 22 does not have a function of detecting a temporal position error of the slave station synchronization burst signal.
Also in the transmission, the transmission frame counter 27 is set to the slave station transmission synchronization control circuit 26 in consideration of the propagation delay time between the satellite and the earth station, which will be described later, with reference to the reception timing of the reference station synchronization burst signal. Then, the transmission time of the slave station synchronization burst signal is set by correction. By the above operation, the burst synchronization of the slave station 22 is maintained.
However, as in the case of the reference station described above, it is difficult to reduce this synchronization error to zero, and the slave station synchronization burst fluctuates ± b bits with respect to the reference station synchronization burst, as shown in FIG.

[Problems to be solved by the invention]

Conventionally, the reference station synchronization burst fluctuates ± a bits and the slave station synchronization burst fluctuates ± b bits with respect to the reference station synchronization burst. To cover these fluctuations, a guard of ± (a + b) bits is applied to the frame on the satellite. It is necessary to set time, and there is a drawback that high transmission efficiency cannot be achieved.

The present invention was devised to solve the above drawbacks, and an object of the present invention is to provide a burst synchronization method that reduces burst synchronization error and reduces the required guard time to achieve high transmission efficiency.

[Means for solving problems]

The present invention is characterized in that a signal as a reference for synchronization is generated on a satellite and burst synchronization between a reference station and a slave station is established based on the signal.

〔Example〕

 The details will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the present invention, in which 28 is a satellite reference burst generator, 29 is a burst position error detection circuit,
The same numbers are given to the parts having the same functions as those in FIG. FIG. 2 is a time chart of the burst synchronization error according to the embodiment of the present invention, showing the relationship between the satellite reference burst signal, the reference station synchronization burst signal and the slave station synchronization burst signal. The operations of the reference station and the slave stations will be described below.

In the steady state, the reference station 11 receives the satellite reference burst transmitted from the satellite 10 to the earth station and receives the demodulator 16
Demodulate with. The station discriminator 17 detects a sync word detection pulse provided at the head of the satellite reference burst, and upon detection, the reception frame counter 19 is reset. The received frame counter 19 of the reference station 11 is always reset by the satellite reference burst. That is, conventionally, the counter 19 is reset by the reference station synchronization burst, and the burst synchronization of the slave station is performed based on this burst, but in the present invention, the satellite reference burst is used as the synchronization reference. On the transmitting side, the reference station synchronization burst generated by the reference station synchronization burst generator 13 operating under the control of the transmission frame counter 12 is modulated by the modulator 15 and sent to the satellite 10. Satellite 10
The reference station synchronization burst returned by the upper switch matrix 7 is again received by the reference station 11 and demodulated by the demodulator 16. After that, the burst position error detection circuit 29 detects the error from the normal position based on the coefficient value of the reception frame counter 19 which is identified by the station identification device 17. That is, since the reception frame counter 19 is reset by the satellite reference burst, the time t ₂ shown in FIG. ₂ can be measured by the above operation. Based on this error,
The transmission frame counter 12 is corrected to synchronize the transmission frame of the reference station 11 with the frame of the satellite reference burst. Thereby, the time error of the reference station synchronization burst with respect to the satellite reference burst can be suppressed within a certain range.
In FIG. 2, this variation is represented as ± a ′ bit.

Here, when transmitting the reference station synchronization burst, the own station burst is delayed by a certain time from the reception timing of the satellite reference burst signal so that the satellite reference burst signal and the burst signals from each earth station do not overlap on the satellite. It is necessary to send out the message and adjust the transmission timing.
Such a method is described in, for example, Kenichi Miya, "Satellite Communication Technology," IEICE, November 7, 1980, Chapter 7, Section 7.4, Section 7.4.4, Burst synchronization (pp227-228). Is also generally performed as described in "It is based on the fact that the local station burst is transmitted at a time delayed by an appropriate time from the reception timing of the reference burst." An example of the specific transmission timing setting is shown below. FIG. 5 shows a frame configuration example showing the transmission timing of the reference station synchronization burst signal in the reference station. In the reference station, the propagation delay time T between the satellite and the reference station is transmitted after the satellite reference burst signal of the nth frame on the satellite is transmitted.
After _d , the satellite reference burst signal is received. Therefore, (n
The timing of transmitting the reference station synchronization burst signal of the +1) th frame is determined by the satellite reference in consideration of the time difference T ₂ between the satellite reference burst signal and the reference station synchronization burst signal and the propagation delay time T _d from the reference station to the satellite. It is necessary to transmit the reference station synchronization burst signal after a predetermined time (Tf−2Td + T ₂ ) [where Tf is a frame period] after receiving the burst signal. However, in the present invention, in addition to the function of transmitting the satellite reference burst signal for a certain period of time after reception and transmitting the reference station synchronous burst, as described above, a function of detecting an error in the transmission time and a function of correcting the transmission time are provided. Has been added. As a result, as described above, the relative time positional relationship between the satellite reference burst signal and the reference station synchronization burst signal can be kept below the fluctuation amount of ± a ′ bits.

On the other hand, the slave station 22 modulates the slave station synchronization burst generated by the slave station synchronization burst generator 23 operating under the control of the transmission frame counter 27 by the modulator 24 and transmits it to the satellite 10. The slave station synchronization burst returned to the reference station by the switch matrix 7 of the satellite 10 is demodulated by the demodulator 16 of the reference station 11 and identified by the station identifier 17, and then the burst position error detection circuit based on the count value of the reception frame counter 19 The error from the normal burst position is measured by 29, that is, t ₃ in FIG. The information on the burst position error is format-converted by the slave station transmission synchronization control circuit 21, modulated by the modulator 15, and then transmitted again to the slave station 22 via the satellite 10. In the slave station 22, after demodulating by the demodulator 25, the transmission synchronization error control circuit 26 corrects the transmission frame counter 27. That is, the transmission time of the slave station synchronization burst signal is reset based on the satellite reference burst signal. Here, as in the prior art of FIG. 3, description is made focusing on the temporal position error detection of the burst to be transmitted and the error correction function thereof in the configuration of the slave station 22 in FIG. However, the demodulator 25 of the slave station 22 has a circuit corresponding to the station identifier 17 and the reception frame counter 19 in the latter stage of the demodulator 25, and a satellite reference burst signal (reference station synchronization burst in the prior art) obtained by this is provided. With reference to the reception timing of (signal), the reception timing is controlled so that data can be obtained from the burst to be received at the timing to be received. However, the slave station 22 also does not have the function of detecting the temporal position error of the slave station synchronization burst signal. Also in the transmission, the transmission frame counter 27 is set to the slave station transmission synchronization control circuit 26 in consideration of the propagation delay time between the satellite and the earth station, which will be described later, with reference to the reception timing of the satellite reference burst signal. Then, the transmission time of the slave station synchronization burst signal is set by correction. By the above operation, the burst synchronization of the slave station is maintained. However, the transmission time of the slave transmission burst cannot be completely fixed with respect to the satellite reference burst, and fluctuation within a certain range cannot be avoided. This is represented as ± b 'bit in FIG.

Here, as for the timing of transmitting the slave station synchronization burst signal, the transmission timing is adjusted so that the satellite reference burst signal and the burst signals from each earth station do not overlap on the satellite, as in the case of transmitting the reference station synchronization burst signal. There is a need. FIG. 6 shows an example of the frame structure showing the transmission timing of the slave station synchronization burst signal in the slave station. The slave station receives the satellite reference burst signal after the propagation delay time Td 'between the satellite and the slave station after the satellite reference burst signal of the nth frame on the satellite is transmitted. Therefore, the timing of transmitting the slave station synchronization burst signal of the (n + 1) th frame is based on the time difference T ₃ between the satellite reference burst signal and the slave station synchronization burst signal and the propagation delay time Td ′ from the slave station to the satellite. , A fixed time (Tf-2Td '+) after receiving the satellite reference burst signal
It is necessary to transmit the slave station synchronization burst signal after T ₃ ) [where Tf is a frame period]. However, in the present invention, in addition to the function of transmitting the satellite reference burst signal for a fixed time after receiving the satellite reference burst signal to transmit the slave station synchronization burst signal, as described above, the time position error information of the slave station synchronization burst signal is the reference station synchronization. A function for correcting the transmission time obtained from the burst signal is added. As a result, as described above, the relative time positional relationship between the satellite reference burst signal and the slave synchronization burst signal can be kept below the fluctuation amount of ± b ′ bits.

In the present invention, the slave station synchronization burst signal is not based on the reference station synchronization burst as in the conventional case but is based on the satellite reference burst. Therefore, the error is not the accumulation of the errors of both bursts as in the conventional case, whichever is larger. The guard time is determined according to the larger of ± a 'and ± b' for the frame on the satellite. That is, assuming that the guard time of the conventional system is α bits and that of the present invention is β bits, α = ± (a + b) and β = max (a ′, b ′) can be expressed. However, max (a ', b') refers to the larger of a'and b '.

First, consider the magnitude relationship between a and a '. Since a is conventionally measured by the metric bit method or the like, the estimation error of the synchronization window cannot be avoided, and a> a '.
Further, b is affected by the fluctuation of the reference station synchronization burst, but b> b ′ because b ′ is based on the satellite reference burst having no fluctuation.

As described above, according to the present invention, the guard time β can be made smaller than that of the conventional method, and when a '<a≤b'<b, the guard time is 1/2 that of the conventional method.

〔The invention's effect〕

As described above, according to the present invention, the guard time required for the TDMA signal frame can be reduced, and thus there is an advantage of improving the frame utilization efficiency.

[Brief description of drawings]

FIG. 1 is a configuration diagram of the present invention, FIG. 2 is a time chart showing a burst synchronization error, FIG. 3 is a configuration diagram of a conventional method, and FIG. 4 is a time chart showing a burst synchronization error of the conventional method. FIG. 6 is a diagram showing the transmission timing of the reference station synchronization burst signal in the reference station, and FIG. 6 is a diagram showing the transmission timing of the slave station synchronization burst signal in the slave station. 1, 2 ... Spot beam antenna, 5, 6 ... Receiver, 7 ... Switch matrix, 8, 9 ... Transmitter, 1
0 ... Satellite, 11 ... Reference station, 12 ... Transmission frame counter, 13 ... Reference station synchronous burst generator, 14 ...
Multiplexer circuit, 15, 24 ... Modulator, 16, 25 ... Demodulator, 17 ... Station discriminator, 18 ... Bit phase error detection circuit, 19 ... Received frame counter, 20 ... Slave station position error Measurement circuit, 21 ... Slave station transmission synchronization control circuit, 22 ... Slave station, 23 ... Slave station synchronization burst generator, 26 ... Transmission synchronization error control circuit, 27 ... Transmission frame counter, 28 ... Satellite reference burst generation Bowl, 29
... Burst position error detection circuit.

Claims (1)

[Claims] 1. A communication satellite and an earth station, the earth station comprising a reference station and a slave station for performing communication by the TDMA method via the satellite, the satellite having a plurality of spot beam antennas,
In SS-TDMA satellite communication, the satellite switches the connection between the uplink and the downlink according to a predetermined format by the switch matrix provided in the satellite and repeats this switching at a fixed frame cycle according to the timing reference on the satellite. Has a function of generating a satellite reference burst signal serving as a time reference of SS-TDMA synchronized with and transmitting the satellite reference burst signal to the corresponding earth station through the switch matrix, and the slave station receives the satellite reference burst signal and then It has a function of transmitting a slave station synchronization burst signal after a fixed time determined by a cycle, a propagation delay time between a satellite and an earth station, and a time difference within a frame between a satellite reference burst signal and a slave station synchronization burst signal. The reference station, after receiving the satellite reference burst, has a frame period, a propagation delay time between the satellite and the earth station, A function of transmitting the reference station synchronization burst signal after a fixed time determined by the time difference within the frame between the star reference burst signal and the reference station synchronization burst signal, and the satellite reference burst signal of the reference station synchronization burst signal folded back by the satellite. A function of detecting an error in transmission time, a function of correcting the transmission time of the reference station synchronization burst signal based on the error, and a function of detecting an error in transmission time of the slave station synchronization burst signal and transmitting the error information to the slave station. SS-TDMA, characterized in that the slave station has a function of correcting the transmission time of the slave station synchronization burst signal based on the error information.
Burst synchronization method for satellite communication.