JPH03216028A - Satellite transmission system - Google Patents

Abstract

PURPOSE:To allow plural transmission stations to take synchronization at all times stably without use of a reference burst by controlling a transmission timing so that a deviation between a reference station synchronization code detection timing and its own station synchronization code detection timing reaches a prescribed value. CONSTITUTION:A synchronization code in a signal (A channel) outputted from a reference station 10 included in a signal sent from a communication satellite 14 and a synchronization code in a signal (loopback signal: B channel) sent by itself are detected respectively at a slave station 11. A timewise deviation TAB between a detection timing of a reference synchronization code and a detection timing of its own station synchronization code is detected this time by a deviation detection means 11d and its own transmission timing is controlled by a slave station transmission timing control means 11e so that the deviation TAB reaches a prescribed time. Thus, plural transmission stations always take synchronization stably without use of a reference burst and without being affected by temperature and level fluctuation.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a satellite transmission system in which a plurality of transmitting stations time-divisionally transmit signals via a communication satellite.

(Prior Art) In recent years, various communication services using communication satellites have been considered, and among them is video time-division transmission. For example, as shown in FIG. 3, a system implementing this type of service consists of a plurality of video transmitting stations 1, a communication satellite 2, and a large number of receiving stations 3 on the side receiving the service. One allocated channel (if the communication satellite 2 is of the frequency division multiple access type, normally only one continuous signal is transmitted) is divided into multiple channels (
In the figure, the four channels A to D are time-divided and allocated to each video transmitting station 1. Each video transmitting station inserts a video signal and an audio signal into the channel to which it is assigned among the plurality of channels. On the other hand, the receiving station 3 on the side receiving the service selectively receives a signal of an arbitrary channel among the signals of the above-mentioned channels arriving via the communication satellite M2, and reproduces the video and audio. In this system, if the communication satellite 2 is of the frequency division multiple access (FDMA) type, the modulation method of the video signal and audio signal in this system is FM modulation method for the video signal, and QPSK of the subcarrier after the audio signal is digitized. Use a method.

Here, a signal obtained by thinning out, for example, an NTSC video signal is inserted into each channel. That is, if the time is divided into four channels as shown in FIG. 4, for example, the length of one transmission frame is two frames of the NTSC video signal. Then, 1 channel is 2/2 of the NTSC video signal.
This is 4 frames, that is, 1 field of the NTSC video signal, so 1 field from the NTSC video signal of 2 frames.
Extract the field and insert it into one channel. Therefore, the transmission speed of the video signal is 60 frames per second.

When configuring such a system, each transmitting station 1 needs to transmit a signal in a time slot corresponding to the channel to which it is assigned, and it is necessary to synchronize each transmitting station.

Here, as a method for synchronizing each transmitting station, for example, in a conventional general time division multiple access (TDMA) system, a base station is provided and a reference burst is transmitted from this base station. Each transmitting station 1 receives this reference burst and controls transmission timing using this reference burst as a time reference.

As a result, each transmitting station 1 is synchronized.

However, with this method, it is necessary to provide a time slot for inserting the reference burst, but in the video time division transmission with the above configuration, there is no room in the video signal to provide a time slot for inserting the prefix word. The above method is difficult to apply.

Therefore, it is conceivable to add a synchronization signal to the vertical blanking period, etc., in the video signal and transmit it. The detection timing of the synchronization signal may shift due to the influence of temperature, level fluctuation, etc., and each transmitting station may become unable to synchronize. To solve this problem, it is necessary to add a temperature compensation circuit, a level control circuit, etc., which increases the circuit scale.

(Problems to be Solved by the Invention) As described above, in a system such as a video time-division transmission system, it is difficult to provide a time slot for a reference burst in order to time-divisionally transmit an analog signal. “Also, if a synchronization signal is added to the video signal and transmitted in order to synchronize each transmitting station, the detection timing of this synchronization signal will shift due to the effects of temperature and level fluctuations, resulting in loss of synchronization. There was a problem.

The present invention has been made in consideration of these circumstances, and its purpose is to
Another object of the present invention is to provide a satellite transmission system in which a plurality of transmitting stations can always be stably synchronized without being affected by temperature or level fluctuations.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides synchronization code adding means for adding a synchronization code for transmission timing synchronization to a digital signal to be transmitted, to each of a plurality of transmitting stations, and One of the plurality of transmitting stations, which is determined as a reference station, is provided with a first transmission timing control means for transmitting a transmission signal at every predetermined period set in advance; a reference station synchronization code detection means for detecting the synchronization code in a transmission signal transmitted from the reference station and transmitted via the communication satellite to a transmitting station other than the reference station; A self-station synchronization code detection means for detecting the synchronization code in the returned transmission signal, and an amount of deviation between the synchronization code detection timing by the reference station synchronization code detection means and the synchronization code detection timing according to the self-station synchronization code detection means timing. and a shift amount detection means for detecting the synchronization code detection timing in the signal sent from the reference station and transmitted via the communication satellite based on the detection result of the shift amount detection means. The transmission timing is controlled so that the amount of deviation from the synchronization code detection timing in the signal returned via the communication satellite becomes a predetermined value.

(Function) By taking such measures, digital signals are added to the transmission signal sent out at predetermined intervals from one transmitting station designated as a reference station among multiple transmitting stations. The amount of deviation in detection timing between the synchronization code added by itself as a digital signal to the transmission signal is detected, and based on this detection result, the synchronization code is sent from the reference station and transmitted via the communication satellite. The transmission timing is controlled so that the amount of deviation between the synchronization code detection timing in the signal transmitted by the communication satellite and the synchronization code detection timing in the signal transmitted by itself and returned via the communication satellite becomes a predetermined value.

Therefore, the transmission signal of the reference station can be used as a time reference and no reference burst is required. Furthermore, since the synchronization code is a digital signal, its detection is easy.

(Embodiment) Hereinafter, a satellite transmission system according to an embodiment of the present invention will be described with reference to the drawings. Here, a system will be exemplified and explained in which one channel allocated by a communication satellite is time-divided into four channels A to D, as shown in FIG. 4, and a video signal is transmitted.

FIG. 1 is a diagram showing a schematic configuration of the satellite transmission system. In the figure, 10, 11, 12, and 13 are transmitting stations, and channels A, B, C, and D are assigned to them, respectively. Further, the transmitting station 10 serves as a reference station, and the transmitting station 11 .
12 and 13 are set as slave stations.

The reference station 10 has a reference station transmission timing control means 10b as a first transmission timing control means, and sends out a signal (burst signal) every period T, L, which is the same as the period of the transmission frame. The signal sent out by the reference station 10 is a video signal superimposed with audio data, and a predetermined synchronization code is added to the audio data by the synchronization code adding means 10a.

On the other hand, the slave station 11 includes a synchronization code adding means 1181, a reference station synchronization code detection means 1lb, an own station synchronization code detection means 11C1, a deviation amount detection means lid, and a slave station transmission timing control means 11e. This slave station 11 adds a predetermined synchronization code to the audio data in the burst signal sent out by the synchronization code adding means 11H. Then, the synchronization code (base station synchronization code) in the signal (A channel) output by the reference station 10, which is included in the signal transmitted from the communication satellite 14.
and the synchronization code (local station synchronization code) in the signal sent by itself (return signal 2B channel) are detected by the reference station synchronization code detection means 1lb and the local station synchronization code detection means 11c, respectively. At this time, the time difference TAB between the detection timing of the reference station synchronization code and the detection timing of the own station synchronization code is detected by the difference detection means lid, and this difference TAB is determined for a predetermined time ( Here, since the time difference is between the A channel and the B channel, the slave station transmission timing control means lie as the second transmission timing control means controls its own transmission timing so that the time difference is one time slot period of the A channel).

Although not shown, the slave stations 12 and 13 are also equipped with synchronization code adding means, reference station synchronization code detection means, own station synchronization code detection means, deviation amount detection means, and slave station transmission timing control means, like the slave station 11. Then, the slave station 12 calculates the time difference 41 T AC between the A channel and the C channel by a predetermined time determined by the division form of each channel (here, it is the time difference between the A channel and the C channel, so one time slot of the A channel period and one time slot period of the B channel), and the slave station 13
is the time shift amount T A between the A channel and the D channel
D is a predetermined time determined by the division form of each channel (here, it is the time difference between the A channel and the D channel, so
The time is the sum of one time slot period of the A channel, one time slot period of the B channel, and one time slot period of the C channel).

As a result, each slave station 11, 12, 13 uses the output signal (A channel) of the reference station 10 as a time reference, and each channel B,
Signals will be sent to C and D, and the signals sent from the communication satellite 14 can be as shown in FIG.

Figure 2 shows slave stations 11 and 12 in the above system.
．． 13 is a block diagram showing a specific configuration example of No. 13. FIG. In the figure,
21 is an FM demodulator, 22 is a low-pass filter, 23 is a Takagi filter, 24 is a QPSK demodulator, 25.26 is a synchronization code detector, 27 is a timing comparison unit, 28 is a frame generator, 29 is a frame delay unit, 30 is a video synchronization section, 31 is a synchronization code addition section, 32 is an output switch, 33 is a synthesizer,
34 is a QPSK modulation section, and 35 is an FM modulation section.

Next, the operation of the slave station configured as above will be explained. First, the signal received by the receiving section (not shown) is FM demodulated.
1, FM1n:A is performed. Here, the received signal subjected to FM demodulation is input to a low-pass filter 22 and a Takagi filter 23, respectively. The low-pass filter 22 extracts an analog signal, that is, a video signal, from the FM demodulated received signal. This extracted video signal is output from the video signal output terminal. Furthermore, the high-pass filter 23 extracts digital signals from the FM demodulated received signal, that is, data including audio data. This extracted data is QP
The signal is input to the SK demodulation section 24, where it is QPSK demodulated and reproduced into the original data.

This reproduced data is output from the data output terminal.

On the other hand, the data reproduced by the QPSKijt tuning section 24 is
It is also input to the synchronization code detection units 25 and 26.

Here, the synchronization code detection section 25 detects the synchronization code of the reference station 10 from the input data. That is, this synchronization code detection section 25 functions as a reference station synchronization code detection means 1lb. Furthermore, the synchronization code detection section 26 detects the synchronization code of its own station from the input data. That is, this synchronization code detection section 26 functions as local synchronization code detection means 11C. The synchronization code detection units 25 and 26 output a detection signal when detecting a corresponding synchronization code. These detection signals are input to the timing comparator 27, respectively. The detection signal output from the synchronization code detection section 25 is also input to the frame generation section 28.

The timing comparison unit 27 compares the detection timing of the synchronization code of the reference station 10 by the synchronization code detection unit 25 and the detection timing of the own station's synchronization code by the synchronization code detection unit 26, and outputs information on the time difference between the two detection timings. . That is, this timing comparison section 27 detects the amount of deviation lid
Work as.

The time difference information output from the timing comparison section 27 is input to the frame delay section 29.

On the other hand, the frame generator 28 generates a frame signal in synchronization with the detection signal output from the synchronization code detector 25. This frame signal is output over one time slot period.

This frame signal is then input to the frame delay section 29, and in a state where the transmission signal of the own station has not yet arrived and the time difference information has not been output from the timing comparison section 27, the frame division form (this slave station channels allocated and time allocated to each channel)
A predetermined time determined by (for example, if the B channel is assigned to the transmitting station,
(time corresponding to the time obtained by subtracting the signal transmission time from B)
output with a delay of 1 minute.

The frame signal delayed by the frame delay section 29 is input to a video synchronization section 30, a synchronization code addition section 31, and an output switch 32, respectively.

The video synchronization unit 30 outputs the video signal input from the video signal input terminal in synchronization with the input frame signal. Here, the video signal synchronized with the frame signal is input to the synthesizer 33.

The synchronization code adding section 31 adds a predetermined synchronization code to data input from the data input terminal in synchronization with the frame signal. That is, this synchronization code addition section 31 functions as synchronization code addition means 11a. The data to which this synchronization code has been added is converted into QPSK by the QPSK modulator 34.
After being modulated, it is input to the synthesizer 33 and superimposed on the video signal. The output signal of the synthesizer 33 is then transmitted to the FM modulator 35.
After being subjected to FM modulation, the signal is applied to a transmitter (not shown) via an output switch 32 and sent out toward the communication satellite 14. At this time, the output switch 32 is turned on/off by the frame signal.

In this way, the transmission signal is sent out after a predetermined time period determined by the frame division format has elapsed from the timing at which the reference station 10 detects the synchronization code.

By the way, when the signal sent by the local station is returned from the communication satellite 14 and arrives, time difference information is output from the timing comparator 27 and input to the frame delay circuit 29. The frame delay circuit 29 increases or decreases the delay time based on this input time difference information. Specifically, for example, the difference between the time indicated by the time difference information and a predetermined time determined by the frame division format is increased or decreased from the predetermined time determined by the frame division format. In other words, if the time indicated by the time difference information is longer than the predetermined time determined by the frame division format, the delay time in the frame delay circuit 29 is determined by the time indicated by the time difference information and the frame division at the predetermined time determined by the frame division format. This is the time obtained by adding the difference from the predetermined time determined depending on the form.

For example, if the time indicated by the time difference information is shorter than the predetermined time determined by the frame division method, the difference between the time indicated by the time difference information and the predetermined time determined by the frame division method is calculated from the predetermined time determined by the frame division format. It is the time obtained by subtracting .

As described above, according to the present embodiment, the detection timing, that is, the reception timing, of the synchronization code transmitted from the reference station 10 by adding it to the data and the synchronization code sent back by the own station by adding it to the data is compared. However, in order to control the transmission timing so that the time difference between the reception timings of both synchronization codes becomes a predetermined value, the signal transmitted by itself is set at a predetermined time position with respect to the signal (A channel signal) output by the reference station 10. Therefore, synchronization can be achieved based on a normal transmission signal that is not a reference burst sent out by the reference station 10. This eliminates the need to provide a time slot for the reference burst. Furthermore, since the synchronization code is transmitted in addition to the data, which is a digital signal, its detection can be performed with high precision and stability without being affected by temperature changes or level fluctuations.

Note that the present invention is not limited to the above embodiments. For example, although the above embodiment exemplifies a satellite transmission system that performs video time-division transmission, the transmission target is not limited to video signals, but can be transmitted by superimposing a digital signal on an analog signal. Applicable. Further, in the above embodiment, the number of transmitting stations is four, but the number of transmitting stations may be any number. In addition, various modifications can be made without departing from the gist of the present invention.

[Effects of the Invention] According to the present invention, each of a plurality of transmitting stations is provided with a synchronization code adding means for adding a synchronization code for transmission timing synchronization into a digital signal to be transmitted, and one of the plurality of transmitting stations One transmitting station determined as a reference station is provided with a first transmission timing control means for transmitting a transmission signal at every preset predetermined period, and among the plurality of transmitting stations other than the reference station, a reference station synchronization code detection means for detecting the synchronization code in a transmission signal sent from the reference station and transmitted via the communication satellite; Local station synchronization code detection means for detecting the synchronization code, and deviation amount detection means for detecting the amount of deviation between the synchronization code detection timing by the reference station synchronization code detection means and the synchronization code detection timing by the local station synchronization code detection means timing. Based on the detection result of the deviation amount detection means, the synchronization code detection timing in the signal sent from the reference station and transmitted via the communication satellite, and the synchronization code detection timing in the signal sent by the reference station and transmitted via the communication satellite. Since the transmission timing is controlled so that the amount of deviation from the synchronization code detection timing in the returned signal is a predetermined value, the transmission timing can be controlled without using a reference burst and without being affected by temperature or level fluctuations. , resulting in a satellite transmission system in which multiple transmitting stations can always be stably synchronized.

[Brief explanation of drawings]

1 and 2 are diagrams explaining a satellite transmission system according to an embodiment of the present invention, in which FIG. 1 is a diagram showing a schematic configuration, and FIG. 2 is a block diagram showing a specific example of the configuration of a slave station. , FIG. 3, and FIG. 4 are diagrams each explaining the prior art. 10... Reference station, 10a... Synchronization code adding means, 1
0b...Reference station transmission timing control means, 11.12
．． 13...Slave station, 11a...Synchronization code addition means, 1
lb... Base station synchronization code detection means, 11c... Local station synchronization code detection means, lid... Displacement amount detection means, 11
e...Slave station transmission timing control means, 14...Communication satellite.

Claims (1)

[Claims] One channel of communication line allocated by a communication satellite is time-divided into a plurality of channels so that the transmission frame has a predetermined length, and a transmitting station transmits an analog signal to each of the plurality of channels. In a satellite transmission system in which a digital signal is superimposed on the analog signal inserted into each channel and transmitted as a transmission signal, each of the plurality of transmitting stations is provided with a signal for transmission timing synchronization in the digital signal to be transmitted. a synchronization code adding means for adding a synchronization code, and a first transmission timing control for transmitting a transmission signal to one transmitting station determined as a reference station among the plurality of transmitting stations at predetermined intervals set in advance; means, to a transmitting station other than the reference station among the plurality of transmitting stations,
a reference station synchronization code detection means for detecting the synchronization code in a transmission signal sent from the reference station and transmitted via the communication satellite; Local station synchronization code detection means for detecting the synchronization code; and deviation amount detection means for detecting the amount of deviation between the synchronization code detection timing by the reference station synchronization code detection means and the synchronization code detection timing by the local station synchronization code detection means timing. Based on the detection result of the deviation amount detection means, the synchronization code detection timing in the signal sent from the reference station and transmitted via the communication satellite and the synchronization code detection timing in the signal sent by the reference station and transmitted back via the communication satellite are determined. a second transmission timing control means for controlling the transmission timing so that the amount of deviation from the synchronization code detection timing in the transmitted signal becomes a predetermined value.