JPH04150534A - Privacy telephone set - Google Patents

Abstract

PURPOSE:To make tapping on a communication channel impossible by privacy- processing an input signal after spectrum-conversion-processing it at a transmitting part, and executing spectrum inverse conversion after removing a noise from the privacy-processed privacy signal at a receiving part. CONSTITUTION:The signal inputted to the input terminal 10 of a transmitting side is converted in its spectrum distribution by a spectrum conversion circuit 11, and is added simply with a noise signal having amplitude sufficiently larger than the amplitude of the input signal and generated from a transmission noise generation circuit 13 by an addition circuit 12. The signal is inputted to a privacy telephone set 2 through the communication channel 3, and a noise component is removed from the privacy signal by an adaptive type echo canceler 16 by referring to a reference noise generated from a reference noise generation circuit 17. Then, by passing it through a spectrum inverse conversion circuit 18 having a spectrum distribution conversion characteristic opposite to the spectrum conversion circuit 11, the same signal as the signal inputted from the input terminal 10 of the transmitting side of the privacy telephone set 1 is outputted from the output terminal 19 of a receiving side of the privacy telephone set 2. Thus, since the privacy signal on the communication channel becomes incapable of being discriminated, it is never tapped.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a secret communication device that makes it impossible to eavesdrop on signals on a communication channel during communication transmission.

[Conventional technology]

Conventionally, this type of secret communication device has performed noise superimposition processing and noise suppression processing on the input signal, but has not performed conversion or inverse conversion processing on the spectrum of the input signal.

This conventional confidential communication device will be explained with reference to the drawings. FIG. 2 is a block diagram of a conventional confidential communication device. In FIG. 2, 51.52 is a private communication device, and 53.54 is a communication path. The confidential communication device 51 and the confidential communication device 52 are connected to the communication path 53.5.
4, the respective transmission side output terminals 63.74 and reception side input terminals 64.73 are connected. 60.77
are the respective transmission side input terminals of the secret communication devices 51 and 52, 6
3.74 is a transmitting side output terminal, 64.73 is a receiving side input terminal, and 67.70 is a receiving side output terminal.

Also, 61.75 is an adder circuit that simply adds signals;
2.76 is a transmission noise generation circuit capable of generating noise whose power spectrum is approximately flat within the signal transmission frequency band; 65.71 is an adaptive echo canceller; 66.
72 is a reference noise generation circuit having the same function as the transmission noise generation circuits 62 and 76.

First, from the transmission side input terminal 60 of the confidential communication device 51 to the communication path 5
The operation of the signal going to the receiving side output terminal 67 of the confidential communication device 52 via the communication terminal 3 will be explained. The signal input from the transmission side input terminal 60 is simply added to the noise signal by the adder circuit 61 so that the power spectrum is approximately flat within the transmission frequency band that is the output of the transmission noise generation circuit 62, and is output as a secret signal. It is output from the transmission side output terminal 63.

This secret signal is transmitted to the receiving side input terminal 6 via the communication path 53.
4 and generated by a reference noise generation circuit 66, the adaptive echo canceller 65 removes the noise component to restore the input signal, and the input signal is output from the receiving side output terminal 67.

In this way, the confidential communication device 51 degrades the S/N of the signal on the communication H53, that is, the confidential communication signal by adding transmission noise, making it difficult to distinguish the signal, and realizing the confidential communication function. It becomes possible.

Next, from the transmission side input terminal 77 of the confidential communication device 52 to the communication path 54
This operation is exactly the same as the operation described above.

[Problem to be solved by the invention]

However, in conventional confidential communication devices, although the confidential signal is difficult to eavesdrop on from the normal communication channel, it becomes possible to distinguish a portion of the signal when the amplitude of the input signal suddenly increases. Furthermore, if it is desired to make it impossible to distinguish the signal due to eavesdropping even when the amplitude of the input signal is maximum, it is necessary to further deteriorate the S/N between the input signal and the noise signal added by the adding circuit. This results in the need for the adaptive echo canceller to have a high noise removal ability, which has the disadvantage of increasing the circuit scale of the privacy device.

[Means to solve the problem]

The encrypted speech device of the present invention includes a spectrum conversion circuit that performs spectrum conversion on an input signal, a transmission noise generation circuit that outputs a noise signal, and an encrypted speech signal that adds the noise signal and the input signal subjected to the spectrum conversion processing. a transmitting section having an addition circuit that outputs a signal to a communication channel; a reference noise generation circuit that outputs a reference noise signal; and converting the spectrum from the confidential signal received from the communication channel with reference to the reference noise signal. It is composed of an adaptive echo canceller that extracts a processed input signal, and a receiving section that has a spectrum inversion circuit that performs spectrum inversion on the extracted signal. After spectrum conversion processing, confidential speech processing is performed, and the receiving section performs spectral inverse transformation after noise removal from the confidential speech signal subjected to the privacy processing.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

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

In FIG. 1, numerals 1 and 2 are private communication devices provided by the present invention, and they have exactly the same configuration. 3 and 4 are communication paths connecting the private communication devices 1.2, respectively, and have respective transmitting side output terminals 14.25 and receiving side input terminals 15.
．． 24 are connected. In addition, 10.29 is a transmission side input terminal, 11.28 is a spectrum conversion circuit that converts the spectral distribution within the transmission band for input signals, 1226 is an addition circuit that simply adds signals, and 13 and 27 are transmission frequencies. 16.22 is an adaptive echo canceller; 17.23 is a transmission noise generation circuit 13.27 capable of generating noise whose power spectrum is approximately flat within the band;
18.21 is a spectral inverse conversion circuit that inversely converts the spectral distribution converted by spectral conversion circuit 11.28 into the spectral distribution of the original input signal, 19.20 is a receiving side output It is a terminal. The constituent elements indicated by the symbols shown earlier are included in the secret communication device 1, and the constituent elements indicated by the symbols shown later are included in the secret communication device 2.

Next, the operation of this confidential communication device 1.2 will be explained. First, we will explain the operation of the signal from the transmitting side input terminal 10 of the confidential communication device 1 via the communication path 3 to the receiving side output terminal 19 of the confidential communication device 2.9 The signal input to the transmitting side input terminal 10 is as follows. The spectrum distribution is converted in the spectrum conversion circuit 11, and further added to the noise signal generated from the transmission noise generation circuit 13, which has an amplitude sufficiently larger than the amplitude of the input signal, in the addition circuit 12. The signal is then output from the transmitting side output terminal 14 to the communication path 3 as a secret signal that cannot be distinguished from the input signal on the communication path 3. This confidential communication signal is transmitted to the receiving side input terminal 15 of the confidential communication device 2.
The adaptive echo canceller 16 removes noise components from the confidential signal by referring to the reference noise input from the reference noise generating circuit 17. At this time, the transmitting side noise generating circuit 13. If the noise generated from each of the reference noise generation circuits 17 is the same, the noise output from the transmission side noise signal generation circuit 13 can be removed from the confidential signal by the adaptive echo canceller 16. This adaptive echo canceller 16
By passing the signal after noise removal by the spectrum conversion circuit 11 and the spectrum inverse conversion circuit 18 having spectrum distribution conversion characteristics opposite to that of the spectrum conversion circuit 11, the same signal as the signal inputted from the transmission side input terminal 10 of the confidential communication device l is It is output from the receiving side output terminal 19 of the confidential communication device 2. Here, communication path 3
Even if the amplitude of the input signal from the transmission side input terminal 10 is somewhat larger than the noise output from the transmission noise generation circuit 13, the above signal cannot be distinguished because the spectrum distribution has been converted by the spectrum conversion circuit 11. Furthermore, even if the noise level from the transmission noise generation circuit 13 that is added to the input signal is reduced and the S/N of the signal output from the transmission side output terminal 14 is improved to some extent, the secret signal on the communication path 3 is It becomes impossible to distinguish. Since the amount of added noise is reduced, the noise removal ability of the adaptive echo canceller 16 can be reduced, and the circuit scale of the confidential communication device 2 can be reduced.

Next, the operation of the signal from the transmitting side input terminal 29 of the confidential communication device 2 to the receiving side output terminal 2o of the confidential communication device 1 via the communication path 4 is exactly the same as the above-mentioned operation.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to easily create a confidential communication device that prevents signals and voices from being intercepted and is less susceptible to the secrecy of confidential signals on a communication path due to large fluctuations in the amplitude of input signals. can be realized.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIG. 2 is a block diagram of a conventional example. 1.2, 51.52... Secret device, 3, 4, 53.5
4... Communication path, 10.29, 60.77... Transmission side input terminal, 11.28... Spectrum conversion circuit, 12
, 26, 61.75...addition circuit, 1327.62.
76... Transmission noise generation circuit, 14, 25. 63, 74
．． ...Sending side output terminal, 15, 24.64.73...
- Receiving side input terminal, 16.2265.71...Adaptive echo canceller, 173.66.72...Reference noise generation circuit, 18.2...Spectral inverse conversion circuit, 19
, 20, 670... Receiving side output terminal.

Claims (1)

[Claims] A spectrum conversion circuit performs spectrum conversion on an input signal, a transmission noise generation circuit outputs a noise signal, and adds the noise signal and the input signal subjected to the spectrum conversion processing and outputs the result to a communication channel as a confidential signal. a transmitter having an adder circuit; a reference noise generation circuit that outputs a reference noise signal; and an input on which the spectrum conversion processing is performed from the confidential signal received from the communication channel with reference to the reference noise signal. The transmitter includes an adaptive echo canceller that extracts a signal, and a spectrum inversion circuit that performs spectrum inversion on the extracted signal, and the transmitter performs a spectral transformation process on the input signal and then performs confidential speech processing. A confidential communication device, wherein the receiver performs spectral inverse transformation after noise removal from the confidential communication signal subjected to the confidential communication processing.