JP2699718B2 - Audio transmission device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voice transmission device,
In particular, it relates to a voice transmission device in a mobile satellite communication system.

[0002]

2. Description of the Related Art A mobile satellite communication system includes a small number of central stations and a very large number of slave stations communicating with the central stations. A major feature is that the number of slave stations accommodated in the system is much larger than that of a conventional satellite communication system.

[0003] When transmitting voice in a mobile satellite communication system, the time rate at which voice is actually transmitted as voice data is very low. It is common practice to adopt a so-called voice activation method that does not output a transmission signal to the network, thereby increasing the number of participating stations.

FIG. 3 shows an example of a voice data burst in a conventional mobile satellite communication system. As shown in FIG. 3, while there is audio data to be transmitted, the audio data and the unique word signal are transmitted, and when there is no audio data to be transmitted, the transmission is completely stopped.

[0005] Next, when voice is generated, a preamble pattern signal is placed at the head, followed by a unique word signal, and the unique word signal is inserted at a cycle of a frame length, and voice data is transmitted during that time. The preamble pattern signal is installed in order to improve the synchronization pull-in characteristic in the receiving side demodulator, and the unique word signal determines the start timing of the audio data and removes the phase uncertainty generated at the time of demodulation based on the detection pattern. Therefore, it is installed with a fixed period frame length.

In the conventional voice transmission system having the above-described configuration, a voice data burst signal is transmitted only when voice to be transmitted exists, and voice communication can be performed without any problem if the pause period is relatively short. Can be performed.

[0007]

However, in the above conventional example, if the listener only listens for a long time and does not emit any voice, the mobile station changes its traveling direction and speed. In this case, in the demodulator on the partner station side, the received signal frequency changes due to the Doppler effect, so that there is a disadvantage that the demodulation cannot be performed correctly or the demodulation takes time and the sound is interrupted.

[0008]

SUMMARY OF THE INVENTION It is an object of the present invention to improve the disadvantages of the prior art, and in particular to a mobile satellite communication system capable of preventing loss of voice data even when there is no voice data to be transmitted. A transmission device is provided.

[0009]

Therefore, according to the present invention, audio data is input, a preamble pattern signal and a unique word signal are inserted at the head position of the audio data in a cycle of one frame length, and when an end signal is detected, an end-of-end signal is input. A transmission data generator for adding and outputting a pattern after voice data, and a voice detection for inputting the voice data and determining the presence or absence of voice data to be transmitted, and outputting an end signal to the transmission data generator when there is no voice data A unique word burst generator that generates a unique word signal of a fixed period in synchronization with a frame timing signal from the transmission data generator based on an instruction of the voice detector, and an output signal of the transmission data generator. A modulator for combining and modulating the output signal of the unique word generator. It has taken. This aims to achieve the above-mentioned object.

[0010]

When voice data is input to the transmission data generator and the voice detector, the transmission data generator inserts a unique word signal at the head position of the voice data for each frame, modulates the data with the modulator, and outputs the modulated data. You. When the voice detector detects that the voice data has disappeared, an end signal is transmitted from the voice detector to the transmission data generator, and the transmission data generator inserts an end-of-pattern signal after the voice data. The transmission data from the transmission data generator is modulated by the modulator and output.

When the receiving side detects the end-of-pattern signal, it recognizes the unique word reception timing based on the frame synchronization established during the normal voice transmission period, and performs a burst operation on a carrier recovery circuit for reproducing the carrier. In this case, the sampling of the reception frequency is performed only at the time of receiving the unique word, thereby preventing adverse effects on the reproduced carrier signal due to noise in a section where no transmission signal exists.

When the voice data is exhausted, on the transmitting side, a start signal is output from the voice detector to the unique word burst generator at a constant period. In the unique word burst generator, when a start signal is input, a unique word signal is generated in synchronization with a frame timing pulse from the transmission data generator, and the output signal of the transmission data generator and the unique word burst are generated by the modulator. The output signals of the generator are combined, that is, the transmission data of only the unique word signal is modulated and output.

On the receiving side, frame synchronization is maintained by the unique word signal input for each frame. Also, in preparation for the next input of audio data, the received signal is demodulated using the reproduced carrier frequency reproduced by sampling.

In this state, when audio data is generated,
On the transmitting side, the transmission data generator inserts a preamble pattern at the head position. Further, the unique word signal is inserted before the audio data following the preamble pattern signal. Then, the transmission data from the transmission data generator 1 is modulated by the modulator 2 and output.

On the receiving side, upon detecting the preamble pattern, the demodulator is returned from the burst mode to the continuous mode.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

In the embodiment shown in FIG. 1, a unique word signal and a preamble pattern signal are inserted into input audio data, converted into a transmission burst format, and an end-of-pattern is inserted into transmission data when an end signal is received. Unit 1, a unique word burst generator 4 for generating a unique word in synchronization with the frame timing pulse from the transmission data generator 1, and a unique word burst generator 4 for monitoring the audio data and when there is no audio, the unique word burst generator 4 And a sound detector 3 for outputting a start signal to generate a unique word signal and outputting an end signal indicating the end of the sound to the transmission data generator 1 when there is no sound data, and an output of the transmission data generator 1. The signal is combined with the output signal of the unique word burst generator 4 and modulated. And a modulator 2 for outputting Te.

Next, the operation of this embodiment will be described with reference to FIG.

Voice data is input to a transmission data generator 1 and a voice detector 3. Then, in the transmission data generator 1,
A unique word signal is inserted at the head position of audio data for each frame. Transmission data from the transmission data generator 1 is modulated by the modulator 2 and output. When the voice detector 3 detects that the voice data is gone, the voice detector 3
Sends an end signal to the transmission data generator 1. When the transmission data generator 1 receives the end signal, the end of pattern signal is inserted after the audio data. Transmission data from the transmission data generator 1 is modulated by the modulator 2 and output. Here, as an end-of-pattern, a pattern having strong autocorrelation is selected and transmitted several times repeatedly in order to correctly notify the receiving side. (Section (A) in FIG. 2)

Upon detecting the end-of-pattern signal, the receiving side recognizes the unique word reception timing based on the frame synchronization established during the normal voice transmission period (section (A) in FIG. 2), and reproduces the carrier. The carrier recovery circuit performs a burst operation to sample the reception frequency only when the unique word is received, thereby preventing adverse effects on the reproduced carrier signal due to noise in a section where there is no transmission signal.

When there is no more voice data, on the transmitting side, a start signal is output from the voice detector 3 to the unique word burst generator 4 at a constant period. When a start signal is input, the unique word burst generator 4 generates a unique word signal in synchronization with a frame timing pulse from the transmission data generator 1. In the modulator 2, the output signal of the transmission data generator 1 and the unique word burst generator 4
Are synthesized, that is, the transmission data of only the unique word signal is modulated and output. (Section (B) in FIG. 2)

On the receiving side, during the interval (B), the frame synchronization is maintained by the unique word signal input for each frame. Also, in preparation for the next input of audio data, the received signal is demodulated using the reproduced carrier frequency reproduced by sampling. However, the reproduced carrier frequency used for this demodulation is held until the next unique word signal is input.

In this state, when audio data is generated,
On the transmission side, the transmission data generator 1 inserts an audio data transmission start signal at the head position. For this signal, a pattern containing many carrier frequency components, that is, a normal burst mode preamble pattern is used to facilitate the reproduction of the carrier. Further, the unique word signal is inserted before the audio data following the preamble pattern signal. This is to clarify the head position of the audio data to the receiving side and to prevent the delay of the audio data from occurring on the receiving side and to prevent the deterioration of the voice line quality. Here, the transmission timing of the unique word signal deviates from the fixed cycle up to that time. Regarding the insertion of the unique word signal, the characteristics of voice activation are not impaired for the following reasons. That is, in general, the unique word length is extremely short with respect to one frame time length, and 1/1
In many cases, the transmission is set to about 00 or less, and even if the transmission is performed at this ratio, the power consumption of the communication satellite is hardly reduced by the voice activation. Therefore, there is no problem in inserting the unique word signal. Then, the transmission data from the transmission data generator 1 is modulated by the modulator 2 and output.

On the receiving side, upon detecting the preamble pattern, the demodulator returns to the normal mode, that is, from the burst mode to the continuous mode.

As described above, according to the present invention, even when there is no audio data to be transmitted, only a unique word signal having a very short time length is transmitted at a constant frame period, and synchronization at the receiving side demodulator is maintained. By continuing to do so, the next time audio data is received, demodulation can be performed immediately, and loss of audio data is prevented.

[0026]

Since the present invention is constructed and functions as described above, according to the present invention, it is possible to save the power of the communication satellite by utilizing the voice activation,
Demodulation on the receiving side can be facilitated, which
Unprecedented superior voice that can sufficiently cope with changes in the received signal frequency due to the movement of the mobile station and can build a mobile satellite communication system without increasing the delay in voice transmission leading to loss of voice data. A transmission device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a transmitting side of the present invention.

FIG. 2 is a diagram showing an example of an audio data burst according to the present invention.

FIG. 3 is a diagram showing an example of an audio data burst according to a conventional audio data transmission method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmission data generator 2 Modulator 3 Voice detector 4 Unique word burst generator

Claims (1)

(57) [Claims] 1. An audio data is inputted, a preamble pattern signal and a unique word signal are inserted at a head position of the audio data in a cycle of one frame length, and when an end signal is present, an end-of-pattern is added after the audio data and output. A transmission data generator, a voice detector that inputs the voice data, determines whether or not there is voice data to be transmitted, and outputs an end signal to the transmission data generator when there is no voice data; A unique word burst generator that generates a unique word signal having a fixed period in synchronization with a frame timing signal from the transmission data generator, and combines an output signal of the transmission data generator and an output signal of the unique word generator. And a modulator for performing modulation. System voice transmission device.