JPH0250663B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a composite digital communication system that inserts and transmits another digital meeting line into main communication using a time division method.

Conventionally, in wireless communication of various digital signals, the signals have been processed as follows. That is, the information signals to be transmitted are multiplexed at the digital signal level as so-called time division multiplexed (TDM) signals. That multiplexed signal can be modulated using only one modulation method, e.g.
It is modulated and transmitted using the FSK (Frequency Shift Keying) modulation method. On the receiving side, demodulation is performed using a corresponding demodulator, such as an FSK demodulator, and the transmitted digital signal is reproduced using the demodulated signal. A demultiplexing circuit separates and extracts the necessary information signal from the reproduced digital signal.

On the other hand, in digital communication systems, there are auxiliary signals, such as signals for meeting lines, which are small in terms of information but must be transmitted. In order to transmit signals for such meeting lines using conventional communication methods, as mentioned earlier, a multiplexing device on the transmitting side, a demultiplexing circuit on the receiving side, and a signal to operate them are required. For example, even in a case where only a signal for a meeting line is required, such as in a relay station, the device becomes complicated.

FIG. 1 shows such a conventional communication system; for example, the first input from terminal 11 is a main signal;
The second input from terminal 12 is a meeting signal.
Both of these signals are time-division multiplexed by a multiplexing circuit 13, and the time-division multiplexed signal is applied to a modulator 14. In the modulator 14, the time-division multiplexed input signal is uniformly modulated according to a fixed modulation method and is sent out. On the receiving side, the received signal is demodulated using a demodulator 15 corresponding to the modulation method on the transmitting side, and the demodulated signal is separated from the original signal by a synchronization separation circuit 16, and the main signal is sent to a terminal 17 for meeting purposes. The signals are sent to terminals 18, respectively.

It is clear that in such a configuration, the multiplexing circuit 13 synchronous separation circuit 16, modulation circuit 14, and demodulation circuit 15 are all required even if it is desired to input/output only the meeting line, such as in a relay station. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a composite digital communication system in which an auxiliary signal such as a meeting signal can be easily transmitted together with a main signal and can be easily retrieved on the receiving side.

In contrast to conventional communication systems, this invention divides multiple input signals to be transmitted into groups on the time axis, modulates each group using a different digital modulation method, and time-division multiplexes each group. On the receiving side, the difference in modulation methods is used to detect the position of the signal to be demodulated, and the received signal is demodulated using a demodulation method that corresponds to the modulation method of the signal to be demodulated. A necessary signal is extracted from the demodulated signal using the detected position signal. With such a configuration, only the necessary signal groups can be reproduced by a simple demodulator.

The principle of this invention will be explained in more detail with reference to FIG. In FIG. 2, for the sake of simplicity, two input signals are used and one of these input signals is demodulated. The main signals (hereinafter referred to as "first input signals") and auxiliary signals (hereinafter referred to as "second input signals") from the input terminals 11 and 12 are applied to the multiplexing circuit 13. The signal and the second input signal are grouped into time-sharing groups, and both signals are transformed to occupy different positions on the time axis, that is, a first position and a second position. The resulting signals are applied to a modulator 21 and a modulator 22, respectively.The modulators 21 and 22 use different digital modulation methods, for example, the modulator 21 is an FSK modulator, and the modulator 22 is an FSK modulator. This is a two-phase phase modulator.These modulator output signals are time-division multiplexed in a combining circuit 23 to become a series of signals.

When demodulating only the signal corresponding to the second input signal on the receiving side (or relay station), the input signal is demodulated by the demodulator 24 corresponding to the modulation method of the modulator 22, and the input signal is demodulated by the synchronization circuit 2.
5. In the synchronization circuit 25, the position of the group corresponding to the second input signal is detected using the difference in the modulation method of the input signal. For example, in the above example, the input signal is doubled and the carrier wave is
It is sufficient to detect twice the frequency. Because, F.S.K.
Even if the signal is doubled, it does not have a bright line spectrum at twice the frequency of the carrier wave, but in the case of a two-phase phase modulated wave, it becomes a bright line spectrum, so the position of the second input signal, that is, the second position, depends on the presence or absence of the bright line spectrum. can be detected. The demodulated signal is applied to the reproducing circuit 26 where the code is regenerated, and only the necessary signals are selected by the signal from the synchronizing circuit 25 and outputted to the terminal 27. In this way, only the auxiliary signal can be extracted by simple processing without demodulating or separating the main signal.

FIG. 3 shows an embodiment in which the present invention is applied to a repeater, and the received signal input to the terminal 28 is, for example, a signal obtained by the transmitting side of FIG. 2. The received signal is divided into two parts, one of which is input to the demodulation circuit 24 and the synchronization circuit 25, and the other to the switch 32. Demodulation circuit 24, synchronization circuit 2
5. In the reproduction circuit 26, the processing as explained in FIG. 2 is performed, and the auxiliary signal which is time-division multiplexed at the second position on the time axis can be obtained at the terminal 27.

Further, a new auxiliary signal input to the terminal 29, that is, a auxiliary signal to be transmitted to the subsequent repeater or receiving side, is applied to the modulator 31, where the second auxiliary signal on the time axis obtained in the synchronization circuit 25 is applied to the modulator 31. A second modulation is performed on the auxiliary signal in accordance with the application timing of the detection signal indicating the position of the auxiliary signal, and the auxiliary signal is supplied to the switch 32. The switch 32 eliminates the second input signal from the received signal based on the detection signal indicating the second position on the time axis, and replaces the second input signal with the modulated signal from the modulator 31. It is time division multiplexed with the first input signal and transmitted to a subsequent repeater or receiver.

Note that if the auxiliary signal obtained at the terminal 27 includes one that should be transmitted to a subsequent repeater or receiving side, the auxiliary signal is discriminated and transmitted together with the auxiliary signal generated by this repeater. terminal 27
Enter. Since this invention is configured as described above, if the signal group you need has a relatively simple modulation method, even if other signals have complex modulation methods, it can be used independently of the simple modulation method. Using a modulator, a demodulator, and a synchronization circuit for grouping, it is possible to demodulate and separate or modulate and insert the signal groups that you need.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional composite digital communication system, FIG. 2 is a block diagram showing an embodiment of the composite digital communication system according to the present invention, and FIG.
The figure is a block diagram showing another example. 11, 12... Input terminal, 13... Multiplexing circuit, 21... First digital modulator, 22...
Second digital modulator, 23... Signal synthesis circuit, 24... Digital demodulator, 25... Synchronization circuit, 26... Reproduction circuit, 27... Output terminal, 29
...Insert signal input terminal, 31...Digital modulator.

Claims (1)

[Claims] 1. A main signal that is transmitted to the receiving side via one or more relay stations, and a main signal that has a smaller amount of information than the main signal, is always transmitted, and does not necessarily reach the receiving side. In a composite digital communication system in which auxiliary signals that do not need to be transmitted are time-division multiplexed and transmitted at different positions on the time axis, on the transmitting side, the main signal and auxiliary signals are transmitted at different first and second positions, respectively. After modulating the auxiliary signal using the second modulation method, the auxiliary signal is time-division multiplexed and transmitted to different first and second positions on the time axis, and in the relay station that should receive the auxiliary signal,
dividing the received signal into two, demodulating one of the received signals in accordance with the second modulation method to obtain a composite signal including the demodulated auxiliary signal;
A detection signal indicating the second position is obtained by utilizing the difference in modulation method in the received signal, and this detection signal is used to extract only the auxiliary signal from the composite signal, and further, to extract another auxiliary signal. A second modulation is performed at the presence timing of the detection signal, and the modulated signal thus obtained is time-division multiplexed to the other second position of the received signal to obtain a transmission signal, and this transmission signal is transmitted to the next repeater. or a composite digital communication method characterized by transmitting to the receiving side.