JPS6377233A - Voice communication system - Google Patents

Abstract

PURPOSE:To contrive to improve the noise caused in an FM demodulation circuit by using an equivalent circuit to process in advance a voice signal to be fed to the EM demodulation circuit so as to have a flat spectrum. CONSTITUTION:The voice signal from an input terminal 1 of a transmission section A is subject to scramble processing, the result goes to a pseudo PM wave by the FM modulation circuit 5 and radiated from an output terminal 6. The frequency is detected by an FM demodulation circuit 5 via an input terminal 7 of a reception circuit B. The signal subject to frequency detection is decoded for scrambling processing at the scramble circuit 4 by means of a descrambling circuit 9, the spectrum is changed from (e) to (f) and the frequency axis is decoded correctly. Then the signal subject to release of scrambling processing is restored from a flat spectrum into an original curved spectrum by an inverse equivalent circuit 10. That is, the inverse equivalent circuit 10 has a characteristic interpolating the spectrum with the equivalent circuit 2.

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to a voice communication system, and in particular, even when the reception level of a frequency-modulated voice communication signal decreases, there is little noise and the deterioration of communication quality is minimized as much as possible. related to voice communication methods.

(Prior Art) There have been various types of confidential voice communication systems, and FIG. 8 is a block diagram of a conventional confidential voice communication system.
In the figure, A is a transmitter and B is a receiver.

In the transmitter A, 21 is an input terminal for an audio signal, 22 is a differentiation circuit, 23 is a scramble circuit for secret speech processing, and 24
is an FM modulation circuit, 25 is an output terminal, and input terminal 21
to the output terminal 25 are serially connected in numerical order. In the receiving section B, 26 is an input terminal, 27 is an FM demodulation circuit, 28 is a descrambling circuit for restoring confidential speech processing, 29 is an integration circuit, and 30 is an output terminal for audio signals, from the input terminal 26 to the output terminal 30. are connected serially in numerical order.

The operation of such a conventional voice communication system will be explained. The waveform inside the mouth in FIG. 8 shows the signal spectrum a to ri at each part. H in the illustration on the edge of this subekdrum indicates the lowest and highest frequency positions of the audio spectrum, for example, L is 0.3 kHz, H is 3'Hz.
It is. In general, the spectrum of an audio signal is as shown in Figure 2 (quoted from Speech and Hearing, edited by the Institute of Electronics and Communication Engineers).
a, b.

C is a foreign language and d is Japanese, but in the case of Japanese it is 1
It has a characteristic of being inversely proportional to the cube of the frequency f above kHz (1-3).

The audio signal with such characteristics is differentiated by the differentiating circuit 22, so that the tendency of the spectrum above 1 kl-12 becomes f2, and the tendency of the spectrum below 1 kHz becomes (°1. This differentiated signal is After the scrambled signal 23 is subjected to well-known scrambling processing such as frequency inversion, it is FM modulated in an FM modulation circuit 24, and is radiated from a not-shown transmitting antenna via an output terminal 25 and a not-shown transmitting circuit.

This radiated signal is demodulated by an FM demodulation circuit 27 via a receiving antenna, a receiving circuit, and an input terminal 26 (not shown), and then deprived of the deprivation processed by the scrambling circuit 23 by a descrambling circuit 28.

This de-confidential signal is still a spectrum differentiated by the differentiating circuit 22, so in order to restore it to its original state,
An audio signal integrated by the integrating circuit 29 and returned to the original audio spectrum is obtained at the output terminal 30.

(Problems to be Solved by the Invention) In the conventional voice communication system as described above, when the level of the received signal decreases due to fading, etc., the noise level increases and flattens due to the triangular noise (f2) unique to FM modulation. Because it becomes noise, at f2 in the low frequency band of the audio spectrum,
Since the level of the high frequency band decreases at f-', an important part of the voice spectrum is masked by noise, and there is a problem in that the quality of the call cannot be improved much.

(Means for Solving the Problems) In order to solve the above problems, the present invention includes frequency-modulating and transmitting an audio signal in a transmitting section, and receiving and demodulating this transmitted signal in a receiving section. In the method of obtaining the original audio signal, the total depth of the audio signal to be transmitted is the frequency pair! i
A descrambling circuit that frequency-modulates and transmits the signal through a frequency-modulating circuit and a scrambling circuit to process the signal, and descrambles the frequency-demodulated signal at the receiving section that receives the signal. Furthermore, the present invention provides an audio communication system characterized in that an audio signal is obtained through an inverse equivalent circuit in which the equivalent circuit returns the frequency versus amplitude spectrum to the original spectrum with quick response.

(Embodiment) FIG. 1 is a block system diagram showing a first embodiment of the voice communication system of the present invention, in which A is a transmitting section and B is a receiving section.

In the transmitting section A, 1 is an input terminal for an audio signal, 2 is a spectrum equivalent circuit for flattening the audio spectrum, 3 is a limiter circuit, 4 is a scrambling circuit for confidential speech processing, and 5 is an FM modulation circuit for performing FM modulation. , 6 are output terminals, which are serially connected from the input terminal 1 to the output terminal 6. In the receiving section B, 7 is an input terminal, 8
is an FM demodulation circuit, 9 is a descrambling circuit for removing secret speech processing, 1o is an inverse equivalent circuit for returning a flat spectrum to an audio spectrum, 11 is an output terminal for audio signals,
The input terminal 7 and the output terminal 11 are serially connected.

The operation of the voice communication system of the present invention will be explained below.
The waveform inside the mouth in FIG. 1 shows the spectrum ag of the signal at each part. In this spectrum a-g diagram, H indicates the lowest and highest frequency positions of the audio spectrum, for example, L is 0.3k)-12%H is 3
k) lz.

In the case of Japanese, the spectrum of the audio signal supplied to the input terminal 1 is almost like the song md shown in Figure 2, so the equal circuit 2 has the same shape as the curve d shown in Figure 2 (spectrum a in Figure 1). It has the property of flattening the spectrum.

The output signal of the circuit 2 is subjected to amplitude limitation according to the communication standard in a limiter circuit 3, and then sent to a scramble circuit 4.
So, for example, frequency inversion? ! After dividing into a number of frequency bands, well-known scrambling processing such as inversion on the frequency axis is performed. Furthermore, a method of performing A/D conversion and performing scrambling processing as a digital signal can also be used.

The signal that has been scrambled as described above is FM
A pseudo PM wave is generated in the modulation circuit 5, and this signal is radiated as a radio wave signal from a transmitting circuit and a transmitting antenna (not shown) via an output terminal 6.

This radiated signal is received by a receiving antenna, a receiving circuit, etc. (not shown), and subjected to frequency detection by an FM demodulation circuit 8 via an input terminal 7. This frequency-detected signal is descrambled by the descrambling circuit 9, which removes the scrambling performed by the scrambling circuit 4, and the spectrum e shown in FIG. 1 becomes the spectrum f, meaning that the frequency axis is correctly restored.

The unscrambled signal is converted into a flat spectrum by the quick response circuit 10, which is the original curve d shown in the second figure.
It returns to the spectrum like .

That is, the quick response value circuit 10 and the equivalent circuit 2 have such characteristics that they mutually interpolate the spectrum.

FIG. 3 is a diagram showing the spectrum of a voice signal obtained by FM demodulating a received signal in the voice communication system. Curve N is the noise level when the S/N of the noise spectrum of the FM demodulation circuit is poor, and curve N is the noise level when the S/N is good.
Small shows. Spectrum a is the case of the voice communication system of the present invention when the voice spectrum is inverted, spectrum b is the case when the conventional voice signal is differentiated and then scrambled by frequency inversion, and spectrum C is the case when the voice signal is differentiated. This is a case where frequency inversion scrambling processing is performed without

Since the intelligibility of speech is controlled by the S/N of high frequency components,
When the noise gradually increases from N small to N large as shown in FIG. 3, the S/N ratio at high frequencies of spectrum C rapidly decreases, and the intelligibility deteriorates. Spectrum b has a lower S/N ratio at low and high frequencies, resulting in poor intelligibility, but spectrum a is flat, so good intelligibility can be obtained.

FIGS. 4 and 5 show examples of circuit diagrams of the equivalent circuit 2 and the quick-response circuit 10, which can be realized by constant circuits including resistors and capacitors before and after the amplifier circuit.

FIG. 6 is a block system diagram showing a second embodiment of the communication system of the present invention. It is similar to FIG. 1, and the same components will be described with the same reference numerals.

The configuration of the transmitter A is an audio input terminal 1 and a scrambling circuit 4.
, an equivalent circuit 12, a limiter circuit 3, an FM modulation circuit 5, and an output terminal 6 are connected in series. On the other hand, receiving section B
An input terminal 7, an FM demodulation circuit 8, a quick response circuit 13, a descrambling circuit 9, and an output terminal 11 are connected in series.

In this way, in the second embodiment, the audio signal supplied to the input terminal 1 is scrambled by the scramble circuit 4, and then the spectrum is flattened by the equivalent circuit 12, which is different from the first embodiment. The method is different. Therefore, the equivalent circuit 12 flattens the spectrum of the signal whose frequency band is scrambled on the time axis by the scrambling circuit 4, and its characteristics are different from those of the equivalent circuit 2.

Further, the characteristics of the quick response circuit 13 of the receiving circuit B are different from those of the quick response circuit 10 for the same reason. However, as in the case of the first embodiment, the equivalent circuit 12 and the quick-response circuit 13 have characteristics such that they mutually interpolate the spectrum.

FIG. 7 is a block system diagram showing a third embodiment of the voice communication system of the present invention, which is obtained by removing the scrambling circuit 4 and the descrambling circuit 9 from FIG. 1.

In FIGS. 6 and 7, as in the case of FIG. 1, illustrations of the transmitting circuit and transmitting antenna of the transmitting section A, and the receiving antenna and receiving circuit of the receiving section B are omitted.

Note that although the first to third embodiments have all been described with respect to wireless communication using an FM modulator, the present invention is not limited to this, and the present invention is also applicable to other modulation methods and transmission by wire or light. It is.

(Effects of the Invention) According to the present invention, even if the level of the received FM modulated signal decreases due to fading or the like, the audio signal is adjusted so that the spectrum of the signal supplied to the FM demodulation circuit is flat. Since it is processed in advance by an equivalent circuit, noise generated in the FM demodulation circuit can be improved and high quality voice communication can be performed.

[Brief explanation of the drawing]

Figure 1 is a block system diagram showing a first embodiment of the voice communication system of the present invention, Figure 2 is a diagram showing a voice spectrum, Figure 3 is a characteristic diagram for explanation, and Figure 4 is an equivalent circuit diagram. , FIG. 5 is a quick response circuit diagram, FIGS. 6 and 7 are block system diagrams showing second and third embodiments of the voice communication system of the present invention, and FIG.
The figure is a block system diagram showing a conventional communication system. 1.7...Input terminal, 2.12...Equivalent circuit, 3.
...Miritsuta circuit, 4...Scramble circuit, 5...
・FM modulation circuit, 6.11...output terminal, 8...-F
M demodulation circuit, 9... descrambling circuit, 10.13
...quick answer value circuit. Fig. 1j (K &) Fig. 2 (IL) (SL Shun CKHz) Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7

Claims (1)

[Claims] In a method in which the audio signal is frequency-modulated in the transmitter and transmitted, and the transmitted signal is received and demodulated in the receiver to obtain the original audio signal, the frequency versus amplitude spectrum is determined at the total depth of the audio signal to be transmitted. an equivalent circuit for flattening the signal, and a descrambling circuit for frequency-modulating and transmitting the signal through a scrambling circuit for decoding the signal, and descrambling the frequency-demodulated signal at a receiving section for receiving the signal, and a descrambling circuit for descrambling the signal, and the above-mentioned equivalent circuit. The circuit is an audio communication system characterized by the fact that the frequency versus amplitude spectrum is inversely equivalent and the audio signal is obtained through an inverse equivalent circuit to restore the original spectrum.