JPH0618338B2 - Synchronous burst transmission phase control method for SS-TDMA satellite communication - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a synchronous burst transmission phase control system, and in particular, SS-TDMA (Satellite Swing) via a communication satellite.
It relates to a synchronous burst transmission phase control method for establishing and maintaining a TDMA frame between a plurality of earth stations, which performs communication by the itched-Time Division Multiple Access (satellite exchange time division multiple access) method.

(Prior Art) Recently, as one of satellite communication systems formed between a plurality of earth stations using a large-capacity communication satellite, SS-TD
The MA system is expected as a future form of the satellite communication system. First, SS-TDMA will be briefly described with reference to the drawings.

FIG. 3 is a principle diagram of the SS-TDMA system and shows the configuration of a repeater inside a communication satellite and the relationship between the earth stations corresponding thereto. In the figure, reference numeral 300 denotes a spot beam antenna mounted on a communication satellite, and as an example, a case having four transmission / reception shared antennas is shown. Each antenna produces a narrow spot beam 301, which illuminates a limited ground spot area 302 (A, B, C and D).

On the contrary, each antenna has a spot area 302A, B, C.
And the radio waves radiated from the earth station 303 in D are respectively received.

The SS-TDMA system increases the gain of the satellite antenna by using the spot beam in this way, and can significantly increase the effective radiated power, and the frequency can be increased by using the same frequency for the well separated spot areas. In terms of reuse, the major feature is that an ideal communication system can be constructed.

The route from the earth station to the satellite is called the uplink, and vice versa is called the downlink, but it is also possible to make the antenna 300 independent for the uplink and downlink and to combine one with a narrow spot beam and the other with a wider beam. is there.

Here, for the sake of simplicity, the description will be continued by taking the configuration shown in FIG. 3 as an example.

In the figure, only one earth station is shown in each spot area 302, but it is possible that each area actually includes a plurality of earth stations. Each spot area 302A,
Radio waves radiated from the earth stations 303 in B, C, and D are received by the corresponding antennas 300, RA,
Amplified by receiver 304, shown as RB, RC, RD.

On the other hand, from the antenna 300 to each spot area 302A,
Electric power to be applied to B, C, D is TA, TB, TC, TD
Are respectively supplied from the transmitter 305 shown as.

A matrix switch 306 is provided to connect the uplink and the downlink, and is controlled by the matrix switch control circuit 307.

The function of the matrix switch is defined by a connection mode indicating a combination of which uplink and which downlink are connected, and by switching some connection modes according to a defined time schedule, an arbitrary uplink and downlink can be obtained. The link will be periodically combined.

Among these connection modes, there is also a broadcast mode in which one uplink signal is generally connected to all downlinks. Table 1 shows examples of connection mode combinations.

The table shows a case where five connection modes I, II, III, IV and V are periodically repeated. B) shows which region the signal from each region is connected to the downlink corresponding to the receivers RA, RB, RC, RD of the uplink, and B) changes the viewpoint and the downlink is changed. Of the transmitters TA, TB, TC, TD, the signals to be radiated in the respective regions are shown from which uplink the corresponding signals are supplied.

Therefore, the respective areas are connected periodically and intermittently. The communication method performed via such a communication satellite is limited to TDMA, that is, the time division multiple access method. The repetition period of the frame corresponds to the frame period of TDMA.

Generally, in the TDMA communication system, one of the participating earth stations serves as a reference station, and the reference station transmits a signal called a reference burst in a TDMA frame cycle according to its own timing reference, and each participating station receives it to form a communication system. Establish timing reference.

However, in the case of SS-TDMA, the connection mode switching described above is performed by the matrix switch control circuit 3 shown in FIG.
Since it is performed in accordance with the timing reference built in 07, the reference station must first synchronize its own timing reference with the timing reference on the satellite. Of course, since the distance between the satellite and the reference station fluctuates from moment to moment even when using a geostationary satellite, the meaning of the above "synchronization" means that the signal transmitted by the reference station according to its own timing reference is On the satellite, it means controlling the timing reference of the own station so as to be synchronized with the timing reference of the satellite.

As a countermeasure, TDM in SS-TDMA system
As a means for establishing and maintaining the A frame, the synchronous burst transmission phase control method is considered. Among the connection modes shown in Table 1, in order for the reference station to synchronize its own timing reference with that of the satellite, a connection mode in which the synchronization burst transmitted by the own station can be received in its own area is used. .

FIG. 4 is a system conceptual diagram showing only relevant main parts in the conventional system. In FIG. 4, a synchronization burst generating means 500, a modulation transmission system 501, a reference transmission station on the earth,
A reception demodulation system 502, a phase error detection means 503, and a metric pattern phase control means 504 are provided, and a communication means 505 is provided with a gate means 506. Also, in the figure, 507 indicates an uplink propagation path, and 508 indicates a downlink propagation path.

In FIG. 4, from the synchronous burst generating means 500,
A predetermined synchronization burst signal generated based on the reference time signal in the reference station is output, and the modulation transmission system 501,
And via the uplink propagation path 507 to the gate means 506. In the gating means 506, the synchronization burst signal is gated by the synchronization window which is generated and inputted on the basis of the reference time signal in the communication satellite, and the downlink propagation path 508.
Returned to the base station via.

The synchronous burst signal is a PSK (Phase Shift Ke) that is normally used, as shown in FIG.
corresponding to the case where a modulation method or the like is applied as a modulation method for a carrier wave,
An unmodulated carrier wave portion (abbreviated as CW) which acts as a carrier wave extraction on the receiving side, and a predetermined code time series signal (Bi
t Timing Recovery: abbreviated as BTR) and a preamble consisting of
A metric pattern (Metric Pattern: a pattern modulated by a predetermined sync signal (Unique Word: UW)) and a predetermined code time-series signal used for measuring a time phase error with respect to a time reference in a communication satellite. ME
(Abbreviated as TRIC) followed by a modulation part.

When the synchronous burst transmission phase control method is in a normal operation state, as described above, the downlink propagation path 5
The sync burst signal returned to the predetermined reference station via 08 is bounded by the trailing edge 600 of the sync window generated based on the time reference in the communication satellite shown in FIG. 5 (b). , The latter half of the metric pattern is input to the reception demodulation system 502 in a gate-off form. This synchronization burst signal is demodulated in the reception demodulation system 502 through a two-phase, four-phase, or multi-phase PSK position demodulation action, and a unique word (UW) shown by a solid line in FIG. 5 (c). And the second half is time position 60
1 gated off metric pattern (METR
IC) is generated and sent to the phase error detecting means 503. In the phase error detecting means 503, the metric pattern (METRIC) of the synchronization burst signal shown in FIG. 5 (c) corresponding to the trailing edge portion 600 of the synchronization window in FIG. 5 (b).
Of the gated-off trailing edge of the metric pattern (METRIC) is detected by measuring the correctly received symbol length in the code string of the metric pattern (METRIC). The time difference from the reference time position set at the central time position and represented by the reference symbol length is extracted and output as a phase error signal in the synchronous burst transmission phase control method. This phase error signal is used as the metric pattern phase control means 50.
4 to the synchronous burst generating means 500 and controls the phase of the synchronous burst generated in the synchronous burst generating means 500. With respect to the subsequent operation, as already described above, the phase error signal outputted from the phase error detecting means 503 becomes zero by the synchronous burst transmission phase control method formed by the closed loop shown in FIG. , The phase of the sync burst signal is controlled and adjusted,
A TDMA frame synchronized with the synchronization window in the communication satellite is established and maintained. As the phase control method in the synchronous burst generation means 500, for example, a voltage controlled oscillator may be used or a frequency divider may be used.

For details of the above-mentioned synchronous burst transmission phase control method, see RARAPUANO, AND N.SHIMASAKI, “SYNCH.
RONIZATION OF EARTH STATIONS TO SATELLITE-SWITCHED
SEQUENCES, ”AIAA 4TH COMMUNICATIONS SATELLITE SYS
As described in detail in TEMS CONFERENCE, APRIL 1972., the symbol length of the metric pattern (METRIC) correctly received according to the code string that transmitted the time position 601 of the gate-off trailing edge in the measurement metric pattern (METRIC). Is detected by measuring, the error factor is caused by the signal-to-noise ratio in the transmission system including the uplink and the downlink and the waveform characteristics in the trailing edge portion 600 (FIG. 5 (b)) of the synchronization window. , The metric pattern (ME
(TRIC) An uncertain time domain is generated at the time position of the trailing edge.

If the latter half of the metric pattern (METRIC) is lost due to the synchronization window, the demodulator output will ideally have a random pattern, such as 000 ... or 111 ..., depending on the demodulator tuning state. The pattern appears. Therefore, it is necessary to use a pattern that can be easily distinguished from the above pattern as the specific pattern of the metric area.

Usually, this metric pattern is uniquely selected by experiments or the like. In order to remove the position uncertainty in the time position determination of the synchronization window trailing edge portion 600 (FIG. 5 (b)) by measuring the symbol length of the metric pattern correctly received according to the transmitted code string, the synchronization is performed. A predetermined metric pattern forming a part of the burst signal is accumulated for a predetermined number of n times of measurement, and is compared and collated with a predetermined metric pattern for each symbol, and the comparison and collation result is simply integrated or transmitted for each symbol. After converting to a predetermined weighting coefficient to correct the error occurrence characteristic of the road, the weight is integrated, and the integrated value for each symbol is compared and collated with a predetermined reference level value to determine the symbol length of the correctly received metric pattern. The method of seeking is taken.

(Problems to be Solved by the Invention) In the above-mentioned conventional method, since the metric pattern in the synchronization burst is uniquely selected, there is a drawback that the metric pattern is not the optimum one depending on the adjustment state of the demodulator. . Particularly, in a device requiring particularly high reliability such as a reference station of the SS-TDMA satellite communication system, a duplex configuration is generally adopted, and in that case, a demodulator of each device is used. It is unlikely that the adjustment state will be the same, and even if the demodulator is replaced for maintenance, there is no guarantee that the optimal adjustment state is set for the metric pattern used, and it will not be possible for actual operation. There is a serious drawback in that a mechanism is needed to reduce the inadequacy of the metric pattern due to external factors such as the adjustment state of the demodulator, which is overcome by the SS-TDMA satellite communication system. It was the biggest technical issue that should be addressed.

In view of the above problems of the prior art, an object of the present invention is to provide an intermediate frequency (Intermediate Frequency) in a satellite communication reference station.
ency: IF) Burst signal returned at the signal stage is used to constantly monitor the demodulator operating characteristics and select the metric pattern that achieves the highest synchronization accuracy according to the demodulator operating characteristics at that time. To provide a synchronous burst transmission phase control method.

(Means for Solving the Problem) The present invention has the following means configuration in order to achieve the above object.

That is, the synchronous burst transmission phase control method of SS-TDMA satellite communication according to the present invention includes a plurality of spot beams in one or both of the uplink and the downlink, and connects the uplink and the downlink with a satellite switch. A communication satellite having a function of sequentially switching in accordance with a predetermined connection mode and repeating this at a constant frame cycle according to a timing reference on the satellite, and a plurality of earths performing communication by a time division multiple access method via the communication satellite. In a predetermined satellite communication reference station that establishes and maintains TDMA frames between earth stations in a plurality of different spot areas in the satellite communication system by the SS-TDMA system configured with the station, the TDMA frame is supported by the communication satellite to the TDMA frame. Is transmitted based on the cycle of TD, which is generating a time as the base
Receives and detects a predetermined synchronization burst which is returned by being gated off by the synchronization window for defining the MA frame,
By controlling the transmission reference time of the synchronization burst so that the detection state of the synchronization burst is constantly in a predetermined state, T between the earth stations in a plurality of different spot areas is controlled.
The TD specified by the DAM frame in the communication satellite
In a synchronous burst transmission phase control system for synchronizing with an AM frame; in addition to the synchronous burst transmitted from a satellite communication reference station to a communication satellite, the same structure as the synchronous burst at a time position different from the synchronous burst in a TDMA frame A means for generating a burst signal having the same content; the burst signal is folded back at an intermediate frequency signal stage in the satellite communication reference station, and the satellite communication reference station is gated off by a window generated on the basis of the TDMA frame in the satellite communication reference station. Means for inputting to the demodulator in the device; means for detecting the burst signal after demodulation and steadily monitoring the operating characteristics of the demodulator; and a metric pattern included in the synchronization burst obtained by the monitoring means. And means for selecting the optimum one according to the operating characteristics of the demodulator, It is characterized in.

(Operation) The use of the present invention having the above-mentioned means configuration will be described below.

According to the present invention, in addition to the synchronization burst actually sent from the satellite communication reference station to the communication satellite,
A burst signal having the same structure and content as the sync burst (hereinafter referred to as a (demodulator) monitoring burst) is generated at a position different from the sync burst in the TDMA frame,
Without sending out the monitoring burst to the communication satellite, it is returned at the IF level in the satellite communication reference station, gated off by the window generated based on the TDMA frame in the satellite communication reference station, and then actually transmitted from the communication satellite. It is input to the demodulator in combination with the system of the synchronous burst returned to, and the demodulated monitor burst is detected (especially, the pattern state of the metric pattern in the monitor burst after being gated off by the window) The demodulator operating characteristics (especially the demodulation pattern characteristics when there is no signal input) are monitored, and the metric pattern included in the synchronization burst is selected to obtain the highest synchronization accuracy according to the operating characteristics of the demodulator. To do.

(Example) Next, the Example of this invention is described with reference to drawings.

FIG. 1 shows a functional block diagram of a synchronization control unit in a satellite communication reference station as one embodiment of the present invention. The transmission frame counter 100 counts the TDMA frame with the system clock 1 as a clock input, and uses the phase correction information 15 output from the position error detection circuit 108 to define the TDMA frame in the communication satellite. It has a function of synchronizing with a TDMA frame.

Further, the transmission frame counter 100 transmits the synchronization burst / monitoring burst generation timing signal 2 to the synchronization burst / monitoring burst generation circuit 101 to the transmission IF signal switching circuit 103 based on the TDMA frame generated by itself. The IF signal switching timing signal 5 and the monitoring burst window generation timing signal 8 are output to the monitoring burst window generation circuit 104. Synchronous burst / monitoring burst generation circuit 101
Is a synchronization burst / monitoring burst generation timing signal 2
Is used as a start signal, and each burst signal of a synchronization burst and a monitoring burst is generated and supplied to the modulator 102 as a transmission synchronization burst / monitoring burst signal 3. At this time,
The metric pattern information signal 19 after being selected by the metric pattern selection selector 110 is inserted into the metric pattern portion of the synchronization burst / monitoring burst,
Generate each burst signal. The modulator 102 transmits a transmission synchronization burst / monitoring burst signal 3 which is a baseband signal.
Input, and after modulation, transmit sync burst / IF signal
The monitor burst IF signal 4 is supplied to the transmission IF signal switching circuit 103.

The transmission IF signal switching circuit 103 divides the input transmission synchronization burst / monitoring burst IF signal 4 into a transmission synchronization burst IF signal 6 and a transmission monitoring burst IF signal 7 based on the transmission IF signal switching timing signal 5. . The transmission synchronization burst IF signal 6 divided here is
Since it is sent out to the communication satellite and is frequency-converted, the up-converter of the satellite communication reference station, RF (Radi
o Frequency) is supplied to the equipment and the transmission monitoring burst IF
The signal 7 is input to the IF signal gate circuit 105. By this operation, only the synchronization burst is transmitted to the actual communication satellite, and the monitoring burst is not output to the outside.

The IF signal gate circuit 105 uses the input monitoring supervisory burst IF signal 7 by using the supervisory burst window signal 9 generated by the supervisory burst window generating circuit 104 with the supervisory burst window generation timing signal 8 as a start signal. Gating is performed and the reception monitoring burst IF signal 10 is output to the reception IF signal switching circuit 106. Reception IF signal switching circuit 1
06 is received monitoring burst IF signal 10 and is returned after being gated off in the communication satellite, and is returned by R of the satellite communication reference station.
The F device and the reception synchronization burst IF signal 11 whose frequency is converted by the down converter are input, and are combined as a reception synchronization burst / monitoring burst IF signal 13 based on the reception IF signal switching timing signal 12, and the demodulator 10
Output to 7. The demodulator 107 inputs the reception synchronization burst / monitoring burst IF signal 13 which is an IF signal, demodulates it, and outputs it as a reception synchronization burst / monitoring burst signal 14 which is a base bad signal.

The position error detection circuit 108 compares the metric pattern of the synchronization burst part of the reception synchronization burst / monitoring burst signal 14 with the metric pattern information signal 19 to define the TDMA frame in the satellite communication reference station and the communication satellite. A position error between the TDMA frame and the TDMA frame is detected, and the detected information is supplied as position correction information 15 for correcting the counting operation of the transmission frame counter 100. The demodulator operating characteristic monitoring circuit 109 uses the reception synchronization burst / monitoring burst signal 14
The metric pattern selection information 16 for determining the operation characteristic of the demodulator 107 at that point in time and observing the metric pattern of the monitoring burst part of the metric pattern selection information 16 for selecting the optimum metric pattern at that point Output to the selector 110. Based on the metric pattern selection information 16, the metric pattern selection selector 110 outputs a predetermined metric pattern 1 information 17 or metric pattern 2 information 18 as the metric pattern information signal 19 that is the most suitable at that time. Here, the predetermined metric pattern information is
Although it is possible to prepare a plurality of types, two types are used here for the sake of clarity.

FIG. 2 is an example of a time chart showing a typical time relationship of main signals in the functional block diagram shown in FIG. However, in FIG. 2, the time relationship between the signal on the transmitting side of the synchronous burst and the signal on the receiving side of the synchronous burst is neglected for the sake of clarity in ignoring the propagation delay time of the synchronous burst via the communication satellite. There is.

Next, the operation of this embodiment will be described with reference to FIGS. 1 and 2. The transmission and reception of the synchronization burst and the operation of detecting the position error are the same as the operations in the conventional example, and therefore are omitted here, and mainly the transmission of the monitoring burst,
The operation of reception and its processing will be described.

The supervisory burst (FIG. 2) having the same burst structure as the synchronous burst and containing the same contents and generated by the same path is transmitted by the transmission IF signal switching circuit 103 to the system of the supervisory burst alone (transmission supervisory burst IF). Signal 7) (Fig. 2). By applying the monitor burst window signal 9 (FIG. 9) generated by the monitor burst window generation circuit 104 to the transmission monitor burst IF signal 7 in the IF signal gate circuit 105, Gate off a part of the metric pattern of FIG. However, in this case, unlike the gate-off in the communication satellite, both the generation timing of the monitoring burst and the generation timing of the window signal 9 for monitoring burst are based on the output of the transmission frame counter 100. The gate is always turned off at a fixed timing. The monitoring burst after being gated off is received by the reception IF signal switching circuit 106 in combination with a system of a synchronization burst which is gated off and returned in the communication satellite (reception synchronization burst IF signal 11 (FIG. 2)). The synchronization burst / monitoring burst IF signal 13 (FIG. 2) is supplied to the demodulator 107. The demodulator operating characteristic monitoring circuit 109 causes the demodulator 107 to operate the baseband signal (reception synchronization burst / monitoring burst signal 1).
Of the signals demodulated as 4), the metric pattern of the monitoring burst portion is input, and the state of the pattern after being gated off by the monitoring burst window signal 9 in the metric pattern is monitored. As a result of this monitoring, the demodulation characteristics of the reception synchronization burst / monitoring burst IF signal 13 when no signal is input to the demodulator 107 can be determined, and the demodulation characteristics are expected to be applied to the metric pattern of the synchronization burst portion. To be done. As a result, the optimum metric pattern for the characteristics of the demodulator 107 at that time can be selected, and the metric pattern is also applied to the synchronization burst, so that the optimum synchronization accuracy at that time can be obtained.

(Effects of the Invention) As described above, according to the present invention, the metric pattern included in the synchronization burst is changed according to the operation characteristics of the demodulator.
By selecting the optimum one, it is possible to eliminate the inadequacy of the metric pattern due to the demodulator adjustment state, which is the main factor of the demodulator operation characteristics, and realize the optimum synchronization accuracy at that time. The effect is that the metric pattern can be selected. Especially, by constantly monitoring the operating characteristics of the demodulator, the optimum metric pattern is always selected, so that the optimum synchronization accuracy is maintained even when switching duplication or replacing the demodulator during maintenance. There is an effect that can be done.

[Brief description of drawings]

FIG. 1 is a functional block diagram of a synchronization control unit in a satellite communication reference station which is an embodiment of a synchronous burst transmission phase control system for SS-TDMA satellite communication according to the present invention, and FIG. 2 is a functional block diagram shown in FIG. A time chart showing an example of a typical time relationship of main signals (however, the time relationship between a signal on the transmitting side of a synchronous burst and a signal on the receiving side of a synchronous burst is, for the sake of clarity, Propagation delay time via communication satellite is ignored), Fig. 3 shows S
4 is a principle diagram of the S-TDMA system, FIG. 4 is a system conceptual diagram of a conventional synchronous burst transmission phase control system, and FIG. 5 (a).
Is a synchronization burst at the time of transmission, FIG. 7B is a synchronization window, and FIG. 7C is a waveform conceptual diagram of the synchronization burst at reception demodulation. 1 ... System clock, 2 ... Synchronous burst / monitoring burst generation timing signal, 3 ... Transmission synchronous burst /
Monitoring burst signal, 4 ... Transmission synchronization burst / monitoring burst IF signal, 5 ... Transmission IF signal switching timing signal, 6 ... Transmission synchronization burst IF signal, 7 ... Transmission monitoring burst IF signal, 8 ... For monitoring burst Window generation timing signal, 9 ... Monitoring burst window signal, 10 ... Reception monitoring burst IF signal, 11 ... Reception synchronization burst IF signal, 12 ... Reception IF signal switching timing signal, 13 ... Reception synchronization burst / monitoring Burst IF signal, 14 ... Reception synchronous burst / monitoring burst signal, 15 ... Phase correction information, 16 ... Metric pattern selection information, 17 ... Metric pattern 1 information, 18 ... Metric pattern 2 information, 19 ... Metric Pattern information signal, 100 ... Transmission frame counter, 101 ... Same Burst / monitoring burst generator circuit, 102 ...... modulator, 103 ...... transmission IF signal switching circuit, 104 ...... monitor burst window generator circuit, 105 ...... IF signal gate circuit, 106 ...... reception I
F signal switching circuit, 107 ... Demodulator, 108 ... Position error detection circuit, 109 ... Demodulator operation characteristic monitoring circuit,
110 ... Selector for selecting metric pattern, 300
...... Spot beam antenna, 301 ...... Spot beam, 302 ...... Spot area, 303 ...... Earth station, 30
4 ... Receiver, 305 ... Transmitter, 306 ... Matrix switch, 307 ... Matrix switch control circuit,
500 ... Synchronous burst generation means, 501 ... Modulation transmission system, 502 ... Reception and demodulation system, 503 ... Phase error detection means, 504 ... Metric pattern phase control means, 50
5 ... Communication satellite, 506 ... Gate means, 507 ... Uplink propagation path, 508 ... Downlink propagation path, 600 ... Synchronous window trailing edge, 601 ... Time position.

Claims (1)

[Claims] 1. A plurality of spot beams are provided on one or both of an uplink and a downlink, and a connection between the uplink and the downlink is sequentially switched by a satellite switch according to a predetermined connection mode, which is a satellite. Satellite communication system by SS-TDMA system composed of a communication satellite having a function of repeating at a fixed frame cycle according to the above timing reference, and a plurality of earth stations performing communication by the time division multiple access system via the communication satellite In a predetermined satellite communication reference station that establishes and maintains TDMA frames between earth stations in a plurality of different spot areas in, the data is transmitted to the communication satellite on the basis of the period corresponding to the TDMA frame, and the predetermined in the communication satellite. Synchronization for TDMA frame definition generated based on the reference time of By receiving and detecting a predetermined synchronization burst that is gated off by the window and returned, and controlling the transmission reference time of the synchronization burst so that the detection state of the synchronization burst is constantly in a predetermined state, TDMA between earth stations in different spot areas
In a synchronous burst transmission phase control method for synchronizing a frame with a TDMA frame defined in the communication satellite; in addition to the synchronous burst transmitted from the satellite communication reference station to the communication satellite, the synchronous burst in the TDMA frame Means for generating burst signals having the same structure and contents as the synchronization burst at different time positions;
Means for returning the burst signal at an intermediate frequency signal stage in the satellite communication reference station, gate-off by a window generated based on the TDMA frame in the satellite communication reference station, and inputting the signal to a demodulator in the satellite communication reference station;
Means for detecting the burst signal after demodulation and steadily monitoring the operating characteristics of the demodulator; and optimizing the metric pattern included in the synchronization burst according to the operating characteristics of the demodulator obtained by the monitoring means. And a means for selecting any of the above, and a synchronous burst transmission phase control system for SS-TDMA satellite communication.