JPH06104792A - Voice transmission system - Google Patents

Abstract

PURPOSE:To attain the voice transmission of a high quality whose speech head is not cut off by transmitting a voice signal and a unique word signal inserted in one frame length period when the voice signal to be transmitted is present on a transmission side, and continuously transmitting the unique word and a continuous wave signal while decreasing a transmission level than a normal level when the voice signal to be transmitted is absent on the transmission side. CONSTITUTION:A unique word pattern is inserted into the voice signal, the voice signal is converted into a transmission frame format by a transmission data generator 1, and inputted to a modulator 2. The output signal of the generator 1 is modulated by the modulator 2, adjusted by a transmission level adjuster 4, and outputted to an outside. At that time, a voice signal detector 3 monitors the voice signal, and outputs a level control signal as '1' to the adjuster 4 so that the transmission output level can be the normal level when the voice signal is present. However, the voice signal detector 3 outputs the level control signal as '0' to the adjuster 4 so that the transmission output level can be decreased when the voice signal is absent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice transmission system in a mobile satellite communication system, and more particularly to a voice transmission system adopting a voice activation system to effectively utilize the power of a communication satellite.

[0002]

2. Description of the Related Art In general, a mobile satellite communication system is composed of a small number of central stations and a large number of mobile stations, which are mobile stations. A major feature of this system is that the number of slave stations accommodated in this system is much larger than in conventional satellite communication systems. In such a mobile satellite communication system, when a large number of speakers transmit voice, the time rate in which the voice data normally emitted by the speakers exists is low. Therefore, in order to effectively utilize the limited power of the communication satellite, a so-called voice activation system is adopted in which a transmission signal is not output when there is no voice. By adopting this method, the number of carrier waves input to the communication satellite is reduced and the number of participating stations is increased.

Conventionally, the signal format of a voice data burst in this type of mobile satellite communication system is shown in FIG.
As shown in, the voice signal and the unique word signal are transmitted while there is a voice signal to be transmitted, and the transmission is completely stopped when there is no voice signal to be transmitted. That is,
When voice is generated, preamble word at the beginning,
Next, a unique word pattern is arranged, the unique word pattern is inserted at a frame length cycle, and an audio signal is transmitted during that period. The preamble word is present to improve the synchronization pull-in characteristic when the voice burst signal transmitted in burst mode is demodulated by the demodulator on the receiving side.
The unique word is set with a frame length of a fixed period in order to determine the start timing of the audio data and remove the phase uncertainty generated at the time of demodulation according to the detection pattern.

In such a conventional voice transmission system,
Since the voice data burst signal is transmitted only when there is voice to be transmitted, voice communication can be executed without any problems if the pause period of transmission without voice signal is relatively short. When the length becomes longer, the preamble word and the unique word are not demodulated, so that it took time to pull in the synchronization.

[0005]

According to this conventional voice transmission system, when the mobile station on the listener's side listens for a long time and produces no voice, the mobile station is May change speed. Therefore, even if the mobile station emits voice after a certain period of time, the demodulator on the partner station side changes the received signal frequency due to the Doppler effect, etc. There is a drawback that the so-called head disconnection, which is interrupted, is likely to occur and the voice quality is extremely deteriorated.

[0006]

A voice transmission system of the present invention is a voice transmission system used in a mobile communication system, in which a voice signal is inputted, and a voice data and a unique word signal are combined and outputted. A voice signal detector for determining the presence or absence of a voice signal to be transmitted by the input voice signal, an output signal of the transmission data generator and an output signal of the voice signal detector, When there is no voice, when there is no voice, a modulator that modulates a part other than the unique word portion as a continuous wave and the output signal of the modulator and the output signal of the voice detection signal are input. And a transmission level adjuster that lowers the transmission output level from the normal level when it has.

[0007]

The present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a voice transmission system according to the present invention, and FIG. 2 is a timing diagram for explaining a transmission signal and a transmission level of this embodiment in comparison.

Next, the configuration and operation outline of this embodiment will be described with reference to FIG. The transmission data generator 1 inserts a unique word pattern into the voice signal, converts the voice signal into a transmission frame format, and then inputs the voice signal to the modulator 2. The modulator 2 modulates the output signal of the transmission data generator 1, and the modulated output signal is adjusted in transmission output level by the transmission level adjuster 4 and output to the outside. The voice signal detector 3 monitors the voice signal, and if there is voice, the transmission level adjuster 4
For example, a level control signal is output at a logical "1" level so that the transmission output level becomes a normal level, but if there is no audio signal, the transmission level adjuster 4 lowers the transmission output level. Thus, the level control signal is output at the reverse logic "0" level.

Next, the operation of this embodiment will be described with reference to FIG. In FIG. 2, section (A) when there is a voice signal
Sets the transmission output level to the normal level, and lowers the transmission output level in the period (B) when there is no sound, but the transmission data continues to be transmitted in the normal frame format. Therefore, since the receiving side sends the frame synchronization established in the normal voice transmission section (A) and the carrier signal (CW) also in the section without voice (B), the pattern of the unique word (UW) input in each frame is used. Continue to maintain frame synchronization. Here, if the transmission output level when there is no voice is reduced by X dB from the normal level, the input level at the receiving side demodulator will also be reduced, but at the same time, synchronization by the unique word is prevented so that the demodulation operation does not become unstable. Reserved.

In the present invention, the portion except the unique word signal in the output signal in the section (B) where there is no voice has a CW pattern which can be easily detected by the receiving side. This is performed by the modulator 2 receiving the voice detection signal from the voice signal detector 3. As a result, the demodulator on the receiving side can surely execute the demodulation operation even if the reception level decreases.

According to the present invention, even in the section (B) where there is no audio signal, the transmitter does not completely turn off the transmitter by the control signal of the audio signal detector 3 and outputs power to some extent.
However, this does not impair the characteristic of the conventional voice activation method, that is, the efficient use of the power of the communication satellite. That is, for example, it is assumed that there are 1000 carriers in communication. Assuming that the speaker speaks only about 40% of the time rate, at a certain moment, only 400 waves are transmitted at the normal level. Assuming that the output of the earth station is 10 dBW per wave, it becomes about 36 dBW for 400 waves. On the other hand, in the audio transmission method according to the present invention, the amount X of decrease from the normal level is, for example, 10d.
Assuming that the frequency is B, 600 dB is 29 dBW, which is 36.6 dBW even when combined with the normal level wave, which is an increase of only about 0.6 dB. If all 1000 waves are transmitted at the normal level, it is 40 dBW, which means that the power of the communication satellite is saved by 3.4 dB.

[0012]

As described above, in the voice transmission system of the present invention, the voice signal is detected by the voice signal detector, and the transmission at the low level is continued while keeping the feature of saving the communication satellite power. , It is possible to facilitate demodulation on the receiving side and maintain frame synchronization. Therefore, it is possible to provide a high-quality voice transmission system without disconnecting the talk head even when voice is generated.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram (b) of a signal format (a) transmission output level for explaining the operation of the present embodiment.

FIG. 3 is an explanatory diagram of a conventional example.

[Explanation of symbols]

 1 Transmission data generator 2 Modulator 3 Voice signal detector 4 Transmission level detector

Claims (1)

[Claims] 1. A transmission data generator used in a mobile communication system, which receives a voice signal, synthesizes a voice signal and a unique word signal, and outputs the synthesized data.
An audio signal detector that determines the presence or absence of an audio signal to be transmitted based on the input audio signal, an output signal of the transmission data generator and an output signal of the audio signal detector are input, and when there is audio, it is left as it is. When there is no voice, a modulator that modulates a part other than the unique word portion as a continuous wave, and the output signal of the modulator and the output signal of the voice detection signal are input, and when there is no voice, when the voice has A voice transmission system comprising: a transmission level adjuster that lowers the transmission output level from a normal level.