JPH04135333A - Speech privacy telephone set - Google Patents

Abstract

PURPOSE:To increase the number of keys for decoding privacy talk and to improve strength for privacy talk by generating a signal adding the respective plural noise signals of a transmission noise generating circuit and a reference noise generating circuit. CONSTITUTION:A transmission noise generating circuit 102 generates noise, and an adder circuit 103 adds the output of the transmission noise generating circuit 102 to a transmitted voice signal. Then, a reference noise generating circuit 113 generates the practically same noise signal as that of the transmission noise generating circuit 102, and an adaptive echo canceler 112 extracts the transmitted voice signal from a received secret talk signal while referring to the output signal from the reference noise generating circuit 113. The signal adding the respective plural noise signals of these transmission noise generating circuit 102 and reference noise generating circuit 113 is outputted. Thus, the number of keys for decoding the secret talk can be increased, and the strength for the secret talk can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a voice signal polarization device, and particularly to a periodic noise signal whose power spectrum is approximately flat within the entire frequency band of the transmitted voice signal on the transmitting side. This invention relates to an improvement in a voice secret speech device that transmits a secret speech signal on which a transmitted speech signal is superimposed, and on the receiving side uses an adaptive echo canceller to refer to a reference noise signal and extracts a transmitted speech signal from the received secret speech signal. .

2. Description of the Related Art Conventional confidential communication devices transmit a confidential signal 3 in which the transmitted audio signal is superimposed on a noise signal whose power spectrum is approximately flat over the entire frequency band of the transmitted audio signal on the transmitting side, and transmit an adaptive signal to the receiving side. For example, a method for extracting a voice signal from a confidential signal received using an echo canceller.
6012) was proposed.

Problems to be Solved by the Invention This type of voice privacy device adds a periodic noise signal whose power spectrum is approximately flat within the entire frequency band of the transmitted signal to the transmitted voice signal on the transmitting side. A confidential signal is created by masking it with a noise signal, and this is sent to the receiving side.The receiving side refers to the reference noise signal and uses an adaptive echo canceller to cancel the transmission noise component of the confidential signal, and then transmits the transmitted voice. This is for extracting signals. The key to deciphering these confidential messages is the coincidence of the noise signals used in the transmission noise generation circuit and the reference noise generation circuit on the receiving side. Therefore,
If the noise signals used on the transmitting and receiving sides are different in nature, it is desirable that the secret message cannot be deciphered at all. However, if the noise signals used for both are similar despite their inherent differences, some of the noise signals contained in the secret signal may be affected by the adaptive echo canceler depending on the degree of similarity between the noise signals. The disadvantage is that the transmitted audio signal is extracted to the extent that it can be recognized, or in other words, the number of keys for decoding the secret message is reduced.

The present invention has been made in order to eliminate the above-mentioned drawbacks inherent in the conventional technology, and therefore, an object of the present invention is to provide a novel audio confidential communication device with higher privacy strength.

Means for Solving the Problems According to the present invention, on the transmitting side, there is provided a transmission noise generation circuit that generates noise using several PN patterns, and an addition that adds the output of this transmission noise generation circuit and a transmission audio signal. A reference noise generation circuit that can generate substantially the same noise signal as the transmission noise generation circuit on the reception side using the same number of PN patterns as on the transmission side; Using an adaptive echo canceller that extracts the transmitted audio signal from the received confidential signal by referring to the output signal,
It is characterized in that the number of keys for deciphering secret messages is extremely increased by utilizing an increase in the number of combinations of the types of P'N patterns and time differences on the transmitter and receiver sides, thereby further increasing the strength of secret messages. A voice secret device is obtained.

Embodiment Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram showing the present invention.

Referring to FIG. 1, reference numeral 101 is a transmitting side input terminal for inputting a transmitted voice signal to the voice privacy device, and 102 is a transmitting side input terminal for inputting a transmitted voice signal into the voice privacy device, and 102 is a transmitting side input terminal that has a substantially flat power spectrum and periodically the same waveform within the entire frequency band of the transmitted voice signal. A transmission noise generation circuit that generates a noise signal is shown in each figure. This noise signal is
In terms of the secret strength of the transmitted audio signal, it is effective to make it close to white noise.

103 is an addition circuit that adds two input signals;
Adding the transmission audio signal guided to the transmission side input terminal 101 and the noise signal output from the transmission noise generation circuit 102,
The output is sent out as a confidential signal to the transmission line 110 via the transmission side output terminal 104.

The level relationship between the voice signal and the noise signal included in this secret message signal is extremely important and is one of the factors that determines the strength of the secret message. Normally, in order to cope with overhearing on the transmission path 110, the level of the noise signal is set higher than that of the voice signal.

111 is a receiving side input terminal, and a transmission line 11 is connected from the transmitting side.
A confidential signal is conducted via 0. 112 is an adaptive echo canceller, and 113 is a reference noise generation circuit that can generate substantially the same noise as the transmission noise generation circuit 102. The adaptive echo canceller 113 generally includes a transversal filter with variable tap coefficients and a subtractor, and synthesizes similar echoes by passing a reference signal through the transversal filter.

A residual error is obtained from the pseudo echo and the actual echo using a subtractor, and the tap coefficients of the transversal filter are adaptively modified so that this residual error is minimized.

Comparing the signals of each part of the -a adaptive echo canceller and the present invention, the reference signal of the transversal filter is the output signal of the reference noise generation circuit 113 of the present invention, and the actual echo is the received secret signal. The residual signal corresponds to the output of the adaptive echo canceller 112 in the components of the transmission noise signal included.

Then, in the output of the adaptive echo canceller 112, similar echo synthesis error signals, the transmitter's voice signal, and noise mixed in the transmission line 110 appear. In this way, in order to remove the transmission noise component included in the confidential signal using the adaptive echo canceller, the transmission noise generation circuit 10
It is desirable that the output signal of No. 2 is the same as the output signal of the reference noise generating circuit 113, but is given linear distortion (attenuation distortion, phase distortion). If nonlinear distortion exists, the distortion component appears at the output of adaptive echo canceller 112 as a residual signal. On the other hand, if the output signals of the transmission noise generation circuit 102 and the reference noise generation circuit 113 are similar even though they are originally different signals, some of the noise signals included in the secret message are erased to generate the secret message. It reduces functionality.

A feature of the present invention is that the transmission noise generation circuit 102 and the reference noise generation circuit 113 each have a plurality of noise signal sources, and output a signal obtained by adding the output signals of these noise signal sources. It is in. In the present invention, since the transmission noise generation circuit 102 and the reference noise generation circuit 113 have similar circuit configurations, only the configuration of the transmission noise generation circuit 102 will be described.

FIG. 2 is a block diagram showing one embodiment of the transmission noise generation circuit 102.

In FIG. 2, reference numeral 201 indicates a PN pattern generation circuit 1, and 202 indicates a PN pattern generation circuit 2, each of which generates a different PN pattern at the same period. P
The N pattern is generally well known as a pattern that can generate random signals at a constant period. 204 is a PN beat addition circuit that adds the outputs of these PNN pattern generation circuits; 205 is a D/A conversion circuit that includes a filter that band-limits the output of the PN pattern addition circuit 204 to a signal within the audio frequency band; Outputs an analog noise signal in the voice band.

206 is an output terminal, which corresponds to the output terminal of the transmission noise generation circuit 102 in FIG. 203 is a control circuit that initializes the plurality of PN pattern generation circuits 201 and 202. The initial settings are for each PN button generation circuit 2.
It is used to select the type of pattern of 01.202 and select which part of the pattern to use, and corresponds to the key to deciphering the secret story.

With the above configuration, the major difference from the conventional device is the problem of control to make the output signal of the transmitting side noise generating circuit 102 and the output one word of the receiving side reference noise generating circuit 113 substantially the same. It is. In other words, it is necessary that the superimposition relationship of the patterns generated by each of the PN bang generation circuits 201 and 202 is maintained in the same relationship on the transmitting side and the receiving side. However, it is easily understood that this can be controlled so as to initialize the time relationship between the pond and the P-bang generating circuit 202 based on the bi-soto pattern related to the pattern period of the PN-bang generating circuit 201.

In the above description, the periods of the PN pattern generation circuits 201 and 202 are the same, but it is also possible to control the periods of the respective PN pattern generation circuits to be different. When the respective periods are made different, it is possible not only to increase the types and combinations of noise signals by simply using a plurality of PN pattern generation circuits, but also to have the following effects. The adaptive echo canceller 112 on the receiving side refers to the reference noise signal and cancels the echo included in the received confidential signal to extract the transmitted audio signal, or the noise signal that should originally be received as an echo is replaced with the reference noise. The signal is received with linear distortion such as delay, attenuation distortion, phase distortion, etc., and components caused by nonlinear distortion are adaptively processed as residual signals of the adaptive echo canceller 112 like external noise. It appears in the output of the echo canceller 112. Here, the outputs of the PN pattern generation circuits 201 and 202 that generate the PN patterns of different cycles mentioned above are added, and this is added to the outputs of the transmission noise generation circuit 102 and the reference noise generation circuit 113. When applied as a signal, assume that the period of the PN pattern generation circuit 202 of either the transmission side or the reception side is changed by a minimum time (for example, 1 bit length).At this time, Assuming that the impulse response of the echo path already generated in the transversal filter of the adaptive echo canceller 112 is not disturbed, the output signal of the PN bang generation circuit 202 is not canceled by the adaptive echo canceller 112 and becomes a residual signal. Similarly, the output signal of the PN pattern generation circuit (same as 202) of the reference noise generation circuit 113 prepared on the reception side also appears at the reception side output terminal 114 as a replica of the echo. Send 1i11
And received 1! ! The difference between the 11 PN patterns is 1 as described above.
Despite the difference in the pattern due to the time difference in bit length,
This results in a completely different signal being output. Therefore, the power addition of these noise signals will be large compared to the level of the transmitted audio signal to be extracted from the confidential signal, and the signal-to-noise ratio (S/N) of the input audio signal to be extracted will be extremely small, making it difficult to hear. It becomes difficult to recognize the above. In the above, it is assumed that the impulse response already generated in the transversal filter is not disturbed, but if this impulse response is disturbed, the transmitted audio signal extracted based on the above assumption will be further distorted. This makes recognition of the reproduced sound even more difficult.

Effects of the Invention As is clear from the above explanation, according to the present invention, it is possible to increase the number of keys for deciphering secret messages, and to increase the strength of secret messages while also using similar PN patterns.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention. 101... Transmission side input terminal, 102... Transmission noise generation circuit, 1θ3... Addition circuit, 104... Transmission side output terminal, 110... F transmission path, 111... Receiving side input Terminal, 112...Adaptive echo canceller, 113
. . . Reference noise generation circuit, 114 . . . Reception side output terminal FIG. 2 is a block diagram showing a specific embodiment of the transmission noise generation circuit 102 and the reference noise generation circuit 113 of the present invention.

Claims (2)

[Claims] (1) On the transmitting side, a transmission noise generation circuit that generates a noise signal and an addition circuit that adds the output signal of the transmission noise generation circuit and the transmission audio signal and sends a confidential signal to the transmission path are provided, and the reception side comprises a reference noise generation circuit that generates a reference noise signal substantially the same as the transmission noise generation circuit, and an adaptive echo canceller that extracts a voice signal from the received confidential signal with reference to the reference noise signal. 1. A voice confidential communication device characterized in that said transmission noise generation circuit and said reference noise generation circuit are each configured to generate a signal obtained by adding a plurality of noise signals. (2) A plurality of PNs are used as signal sources of the plurality of noise signals.
Claim further characterized in that a pattern generation circuit is used, and the periods of the plurality of PN patterns are made different from each other.
1) The audio secret communication device described in 1).