JP2670283B2 - Auxiliary transmission line transmission method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Industrial Application) The present invention relates to a signal transmission system of an auxiliary transmission line laid between radio devices of a PCM radio communication system, for example.

(Prior Art) In general, an auxiliary transmission line is laid separately from a main transmission line between wireless devices of a PCM wireless communication system. This auxiliary transmission line is used for, for example, order wire communication or low-speed data transmission, and its transmission speed is generally set to 64 kbps.

By the way, when an audio signal for a meeting is to be transmitted using such an auxiliary transmission line, for example, when the audio signal is converted into a digital signal by a normal PCM codec, the signal speed is equal to the transmission speed of the auxiliary transmission line. Same 64kbps
become. For this reason, it is impossible to transmit a synchronizing signal that is indispensable for transmitting an audio signal. Therefore,
Conventionally, for example, an audio signal is converted to a digital signal by a codec that adopts the ADPCM method or ΔM method, and the speed converter converts the speed to a signal with a bit rate lower than 64 kbps. Is inserted to transmit the audio signal and the synchronization signal. However, such a system requires the ADPCM, which has a complicated circuit configuration to convert the audio signal into a digital signal.
Method or ΔM method codec must be used,
Further, since a speed converter is required, the configuration of the transmission / reception circuit for the auxiliary transmission line is complicated and large, and the apparatus becomes expensive.

(Problems to be Solved by the Invention) As described above, in the conventional auxiliary transmission line transmission method, when an analog signal in a voice band is converted into a digital signal and transmitted, a digital signal is transmitted to transmit a synchronization signal. It is necessary to reduce the bit rate of the signal, which causes a problem that the transmission and reception circuit becomes complicated and large.Therefore, the present invention pays attention to this point and adjusts the bit rate of the digitized audio band signal. To provide an auxiliary transmission path transmission system that can transmit a synchronization signal without lowering the quality and without causing significant quality deterioration in reproduced sound, thereby simplifying and reducing the size of a transmission / reception circuit and reducing the cost of an apparatus. It is what

[Configuration of the Invention] (Means for Solving the Problems) The present invention provides a method for re-converting the digital signal into an analog signal for each predetermined unit bit of a digitized voice band signal. A specific lower bit which does not have great importance is selected, and a synchronizing signal is inserted and transmitted instead of the selected lower bit.

(Operation) As a result, a part of the bits of the digitized voice band signal is diverted to the bit for transmitting the synchronization signal, so that the bit rate of the digitized voice band signal needs to be reduced in order to transmit the synchronization signal. Thus, an analog signal in the voice band can be converted into a digital signal by a normal codec. Therefore, as compared with the case where a special codec or speed converter is used, the structure of the transmission / reception circuit can be simplified and downsized, and the device can be reduced in cost accordingly.

Also, since the synchronizing signal is inserted in place of a specific lower-order bit that does not have a significant importance when re-converting a digital signal into an analog signal among the unit bits, a large deterioration in sound quality occurs on the receiving side. , The audio band signal can be reproduced. In general, in a meeting call using the auxiliary transmission path, it is sufficient that the contents of the talk of the other party can be understood, and the sound quality does not matter. Therefore, even if the synchronization signal is inserted in place of the specific lower bits of the digitized audio signal as described above, there is no concern that the call will be disturbed.

(Embodiment) FIGS. 2 and 3 are schematic configuration diagrams of a transmission circuit and a reception circuit to which an auxiliary transmission line system according to an embodiment of the present invention is applied. First, the transmission circuit is composed of a PCM coder 11 for converting a voice signal for inter-office meeting supplied from a voice signal input circuit (not shown) into a digital signal, and a sync signal insertion circuit 12. The PCM coder 11 is of a normal type that converts an audio signal into an 8-bit digital signal for each sample.
A 4kbps digitized audio signal is output. The synchronization signal insertion circuit 12 inserts a synchronization signal into the least significant LSB bit for each unit bit of the digitized audio signal output from the PCM coder 11, that is, for every 8 bits.

On the other hand, the receiving circuit includes a synchronization circuit 21 and a PCM coder 22. First, the synchronization circuit 21 detects a synchronization signal inserted every eight bits from the digitized audio signal arriving via the auxiliary transmission path. Also PCM decoder 22
Is for converting a digitized voice signal that has arrived via the auxiliary transmission line into an analog signal in synchronization with the timing of the synchronization signal detected by the synchronization circuit 21.

With such a configuration, when an audio signal is input to the transmission circuit, the audio signal is first converted into a digital signal of 8 bits per sample by a PCM coder 11 using a normal PCM method, and a 64 kbps digital signal sequence is generated. Is output as. FIG. 1 (a) shows the signal structure. Then, the digitized audio signal output from the PCM coder 12 is next introduced into a synchronizing signal insertion circuit 12, where the least significant LSB bit is changed every 8 bits as shown in FIG. 1 (b). The synchronization signal F is inserted, and then transmitted to the auxiliary transmission path.

On the other hand, in the receiving circuit, when the digitized voice signal arrives via the auxiliary transmission line, the digitized voice signal is guided to the synchronizing circuit 21 and the PCM decoder 22, respectively. Then, the synchronizing circuit 21 detects the synchronizing signal F inserted in the least significant LSB bit for every 8 bits of the digitized audio signal. Further, the PCM decoder 22 converts the digitized audio signal into an analog signal in synchronization with the detection timing of the synchronization signal detected by the synchronization circuit 21. Then, the audio signal reproduced thereby is guided to an audio output circuit (not shown) and output from the speaker.

As described above, according to the present embodiment, the least significant LSB bit is set as a synchronization bit for every 8 bits of the digitized audio signal, and the synchronization signal F is inserted into the synchronization bit for transmission. It is not necessary to lower the bit rate of the encoded voice signal to separately provide a bit for inserting the synchronization signal, and as a result, it becomes possible to use a normal type PCM coder. Therefore, the configuration of the transmission circuit and the reception circuit can be made simpler and smaller than in the conventional case where it is necessary to perform encoding and speed conversion by the ADPCM system and the ΔM system in order to lower the bit rate of the digitized audio signal. Therefore, the terminal device can be provided at low cost. In this embodiment, the reproduced audio signal is slightly degraded because the LSB bit of every 8 bits of the digitized audio signal is used as a synchronization signal. Sound quality does not matter, as long as you understand the content of the story. Therefore, even if the LSB of the digitized audio signal is diverted to the synchronizing signal as described above, this does not hinder the call.

The present invention is not limited to the above embodiment.
For example, in the above embodiment, the synchronizing signal is inserted into the LSB every 8 bits, but the synchronizing signal may be inserted into every unit bit. In addition, as an application example of the present invention, a part of the synchronization signal insertion bits may be used for low-speed data insertion such as remote control data and signaling information. In addition, the insertion position of the synchronization signal, the configuration of the transmission / reception circuit, the type of the analog signal, and the like can be variously modified without departing from the gist of the present invention.

[Effects of the Invention] As described above in detail, according to the present invention, for each predetermined unit bit of a digitized audio band signal, a synchronization signal is inserted instead of a specific lower bit and transmitted. By doing so, it is possible to transmit the sync signal without lowering the bit rate of the digitized voice band signal and without causing a large quality deterioration in the reproduced voice,
As a result, it is possible to provide an auxiliary transmission line transmission system that can reduce the cost of the device by simplifying and downsizing the transmission / reception circuit.

[Brief description of the drawings]

FIG. 1 is a view for explaining an auxiliary transmission line transmission system in an embodiment of the present invention. FIG. 1 is a diagram showing a structure of transmission data according to the system, and FIG. 2 is a transmission circuit to which the transmission system is applied. FIG. 3 is a circuit block diagram showing a schematic configuration, and FIG. 3 is a circuit block diagram showing a schematic configuration of a receiving circuit to which the above transmission method is applied. 11 PCM coder, 12 synchronization signal insertion circuit, 21 synchronization circuit, 22 PCM decoder, F synchronization signal.

Claims (1)

(57) [Claims] 1. An auxiliary transmission line transmission system for converting an analog signal in a voice band into a digital signal and transmitting the digital signal through an auxiliary transmission line having a transmission speed equal to the signal speed thereof, wherein a predetermined unit bit of the digital signal. In each case, a specific lower bit that does not have a great significance when reconverting the digital signal into an analog signal among the unit bits is selected, and a synchronization signal is inserted in place of the selected lower bit. An auxiliary transmission line transmission method characterized by transmission.