JPH0316334A - Privacy telephone set - Google Patents

Abstract

PURPOSE:To enhance the privacy by applying amplitude scramble to a signal subjected to band split and applying amplitude scramble independent of each split band. CONSTITUTION:The band split section 1 of a transmission section 7 splits the band of an input voice signal, a multiplier section 4 multiplies the band split signal with a pseudo random amplitude signal to apply the amplitude scramble. Moreover, a 2nd modulation section 5 modulates a carrier signal to output a lower side band component and the frequency of a carrier signal is selected to apply frequency scramble, thereby forming a privacy call signal. Then the voice signal is decoded by applying inverse processing in a reception section 17. Thus, the privacy is enhanced.

Description

[Detailed Description of the Invention] [Summary] The purpose of this invention is to combine an amplitude scrambling method and a frequency scrambling method to improve speech privacy with a communication device that can improve communication privacy with a relatively simple structure. The section includes a band division section that divides the input audio signal into a plurality of bands, a first modulation section that modulates the divided signal, and a multiplication section that multiplies the output signal of the first modulation section by a pseudorandom amplitude signal. a second modulation section for modulating the output signal of the multiplication section to perform band division permutation; and an addition section for adding the output signals of the second modulation section corresponding to the division bands to obtain a secret signal. The receiving section includes a band dividing section that divides the received confidential signal into a plurality of bands, a third modulating section that modulates the divided signal, and an output signal of the third modulating section with a pseudo-random amplitude. A division section that divides by the signal, a fourth modulation section that modulates the output signal of the division section and restores the band division permutation, and an output signal of the fourth modulation section corresponding to the division band are added together. The configuration includes an addition section that restores the audio signal.

[Industrial application field]

The present invention relates to a confidential communication device that can improve communication confidentiality with a relatively simple configuration.

The number of users of wireless voice communication such as car phones and cordless phones is increasing because it has the advantage of not being subject to location restrictions like wired communication. However, on the other hand, problems such as interception and eavesdropping have arisen, and a confidential communication device has been proposed that converts the audio signal into a confidential signal and transmits the confidential signal so that the content of the call cannot be understood by a third party. It is desired that such a privacy device has a simple configuration, is inexpensive, has excellent privacy, and does not degrade the quality of the decoded audio signal.

[Conventional technology]

Various configurations of secret speech devices have already been proposed, and the secret speech methods can be broadly classified into (a) time scrambling method, fbl amplitude scrambling method, and (C) frequency scrambling method. In the above-mentioned (a) time scrambling method, on the transmitting side, a block of audio signals of a certain length of time is temporarily stored in memory, and the audio signal waveform over that time is divided into a plurality of small pieces. A secret signal is created by randomly rearranging the
On the receiving side, a block of a secret signal of a certain length of time is temporarily stored in a memory, and the pieces within one block that make up the secret signal are rearranged to their original order to restore the audio signal.

In addition, the above-mentioned (bl amplitude scrambling method) samples the audio signal at fixed time intervals on the transmitting side, indexes the table using the amplitude value of the audio signal as an address signal, and converts it to another amplitude value, thereby generating random On the receiving side, a table for inverse conversion is provided to restore the voice signal from the secret signal.

In addition, in the frequency scrambling method (C) mentioned above, on the transmitting side, the audio signal is divided into multiple bands, and the divided band signals are randomly rearranged to create a confidential signal. The method divides a secret speech signal into a plurality of bands, rearranges the divided band signals in the original order, and restores the audio signal.

[Problem to be solved by the invention]

In the fa) time scrambling method described above, by increasing the time length of one block, the number of pieces to be rearranged on the time axis can be increased, and the types of pieces to be rearranged can be increased, thereby improving confidentiality. This results in a delay of at least one block length, and such a delay is a major disadvantage in making real-time calls. In addition, there is a drawback that echoes occur in the sidetone and sound quality deteriorates due to waveform discontinuity between blocks of the decoded audio signal.

Also, although the fb) amplitude scrambling method has less delay than the above-mentioned time scrambling method, it has the disadvantage that the band of the confidential signal is expanded. For this reason, a method has been adopted to prevent band expansion by adding a certain weight to the random step signal, but the use of this method has the drawback of reducing confidentiality.

In addition, (the Cl frequency scrambling method uses a secret signal obtained by dividing and replacing the band of the audio signal, and based on the spectral distribution of this secret signal, the secret key is determined from the statistical properties of the spectral distribution of the audio signal. There are drawbacks that can be found.

The present invention aims to improve confidentiality by combining an amplitude scrambling method and a frequency scrambling method.

[Means to solve the problem]

The confidential communication device of the present invention divides the band of an audio signal, performs amplitude scrambling for each divided band, and performs divided band replacement, and will be explained with reference to FIG.

A band dividing section l consisting of a bandpass filter etc. that divides a human voice signal into a plurality of bands, a first modulating section 2 that modulates the divided band signal divided by this band dividing section l, and this first modulating section a multiplier 4 that multiplies the lower sideband signal of the output signal of No. 2 by a pseudorandom amplitude signal from the IM pseudorandom generator 3; A second modulation section 5 using an SSB modulator or the like that outputs a lower sideband signal, and an addition section 6 that combines the output signals of each second modulation section 5 of the divided band corresponding section to generate a secret signal.
The transmitting section 7 is configured by the following.

Also, a band division section 1l such as a bandpass filter that receives the confidential signal and divides it into a plurality of bands, and a third modulation section 12 that modulates the divided band signal divided by the band division section 11.
a division unit 14 that divides the lower sideband signal of the output signal of the third modulation unit l2 by a pseudorandom amplitude signal from the pseudorandom generation unit l3 synchronized with the pseudorandom generation unit on the transmitting side; A fourth modulating section 15 that outputs a lower sideband signal by modulating the output signal of the subband and outputting the lower sideband signal so as to return to the base band division permutation, and the output signal of each fourth modulating section 15 of the division band corresponding section are combined or The receiving section 17 is constituted by the adding section 16 which reproduces the audio signal.

[Effect]

The band dividing sections 1 and 11 are each composed of a plurality of band filters having different passbands, and divide an input audio signal or a received confidential speech signal into a plurality of predetermined bands. The divided band signals divided by the band dividing unit l in the transmitting unit 7 are modulated by the first modulating unit 2, and the lower sideband is extracted using a low-pass filter or the like to obtain a divided signal that is shifted to a lower frequency band. converted into a band signal.

The pseudo-random generator 3 can be composed of a digital pseudo-random generator and a DA converter, and the digital pseudo-random signal is converted into an analog pseudo-random amplitude signal.

In this case, the pseudo-random amplitude signal is selected such that its period and bounce are different for each subband corresponding section. A multiplier 4 multiplies this pseudo-random amplitude signal by the output signal of the first modulator 2 . If the audio signal is multiplied by a pseudo-random amplitude signal without band division, the band will be expanded, but since each divided band signal is multiplied by a pseudo-random amplitude signal, the narrow divided band The expansion will also be slight.

The output signal of this multiplier 4 is modulated by a carrier signal of a different frequency for each divided band corresponding part in the second modulation part 5, and only the lower sideband is extracted, thereby performing divided band replacement. It is.

Then, by adding the output signals of the respective division corresponding parts in the adder 6, the divided band signal is multiplied by the pseudo-random amplitude signal, and a confidential signal is obtained which has been subjected to the divided band replacement.

The receiving section 17 decodes the audio signal by performing the opposite processing to that of the transmitting section 7, and the band dividing section 11 divides the received confidential signal into a plurality of bands, each of which is divided into a plurality of bands by the division corresponding section. It is modulated by the third modulation section 12 and shifted to the lower frequency side, divided by the pseudorandom amplitude signal from the pseudorandom generation section 13 in the division section 14, and modulated by the fourth modulation section 15 for band division replacement. Perform the replacement process to return to the base,
The audio signal is decoded by adding the output signals of the divided band corresponding sections in the adding section 16.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention, and shows the case where the audio band is divided into three. In the same figure, 20-
1 to 20-3 are divided band corresponding parts of the transmitting section, 2l is a bandpass filter forming a part of the band dividing section 1, 22 is a balanced modulator forming the second modulation section 2, and 23 is a band corresponding to an unnecessary band. 24 is a multiplication 2L 25 is a pseudo-random generator, 26 is a DA converter, 27 is a low-pass filter for removing unnecessary bands, 28 is an SSB modulator constituting the second modulation section 5, 29 is a This is an adder corresponding to the adding section 6.

Further, 30-1 to 30-3 are divided band corresponding parts of the receiving section, 3l
32 is a bandpass filter that constitutes a part of the band division section 11;
3 is a balanced modulator constituting the third modulation section 12; 33 is a low-pass filter for removing unnecessary bands; 34 is a divider; 35 is a pseudo-random generator; 36 is a DA converter; 37 is for removing unnecessary bands. A low-pass filter, 38 an SSB modulator constituting the fourth modulator 15, and 39 an adder corresponding to the adder l6.

The band of the input audio signal is 0. 3 KHz ~3.
In the case of 0 KHz, the division band support units 20-1 to 20
-3, the bandpass filters 21 are, for example, each 0
．． 3=1.2KHz, 1.2~2.1KHz, 2.1~
It is configured to have a passband of 3.0 KHz. Therefore, as shown in FIG. 3(a), 0. 3KH
The input audio signals of z ~3, QKHz are A, B. It is divided into three bands of C.

The divided band signals divided by the bandpass filter 2l are modulated by carrier signals corresponding to the divided bands in the balanced modulator 22. Therefore, the signal of subband A is (
bl, and the low-pass filter 23 shown as 23A.
Due to the characteristics of
added to.

The pseudo-random generator 25 is configured to output a digital pseudo-random signal so as to obtain a pseudo-random amplitude signal having a frequency at least twice the frequency of the divided band signal. Although it is desirable that the corresponding parts 20-1 to 20-13 have different periods and patterns, they can also be the same.

This digital pseudo-random signal is converted into an analog pseudo-random amplitude signal (random step signal) by the DA converter 26 and is applied to the multiplier 24 . Therefore,
The output signal of the multiplier 24 in the divided band corresponding section 20-1 is obtained by replacing the amplitude of the divided band signal with a random amplitude, as shown in FIG. 3(C).

The unnecessary band of the output signal of this multiplier 24 is expressed as (C
) is removed by a low-pass filter 27 having the characteristics shown at 27A and input to the SSB modulator l8.

The SSB modulator 18 transmits the carrier signal to the divided band corresponding section 2.
0-1 to 20-3, the output signal of the low-pass filter 27 is modulated, and only the lower sideband signal is output. When the subband signals are replaced and added to the adder 29, for example, as shown in (d+) in FIG. It becomes a secret signal with high confidentiality.

In the receiving section, the received confidential signal is transmitted to the divided band corresponding section 30.
-1 to 30-3 bandpass filters 31 each divide the signal by a pass band similar to that of the bandpass filter 2l of the transmitting section. The band-divided received confidential signal is sent to a balanced modulator 32.
The modulated output signal is modulated by a carrier signal corresponding to the divided band, and the lower sideband component of the modulated output signal is extracted by a low-pass filter 33 and applied to a divider 34.

Further, the pseudo-random generator 35 has a structure corresponding to the pseudo-random generator 25 of the transmitting section, and is synchronized with the pseudo-random generator 25 of the transmitting section by a control path (not shown). Therefore, the analog pseudo-random amplitude signal (random step signal) obtained by converting the output digital pseudo-random signal by the DA converter 36 is as follows:
This is the same as the pseudo-random amplitude signal output from the DA converter 26 of the transmitter.

By dividing the band-split confidential signal by the pseudo-random amplitude signal by the divider 34, the reverse processing of the multiplier 24 in the transmitting section is performed, and the output signal is added to the low-pass filter 37. Unnecessary bandwidth restrictions are removed,
is applied to SSB modulator 38. This SSB strange #A device 3
8, the frequency of the carrier signal is selected so as to output only the lower sideband and to restore the original order of subband replacement in the transmitting section.

SSB modulator 3 of each divided band corresponding section 30-1 to 30-3
By adding the output signals of 8 by the adder 39,
The received confidential signal is amplitude descrambled corresponding to the divided bands, the divided bands are rearranged in the original order, and then decoded into an audio signal.

The present invention is not limited to the above-described embodiments. For example, it is possible to divide the input audio signal into a larger number, and the band dividing section may include band filters 21.3.
1, for example, an input audio signal and carrier signals of different frequencies may be multiplied by multipliers corresponding to the carrier signals, and passed through band filters with the same pass band, It is also possible to output signals of different subbands.

Further, the low-pass filters 27 and 33 can be Nyquist-type low-pass filters that remove high-order harmonics contained in the signal multiplied by the pseudo-random amplitude signal.

〔Effect of the invention〕

As explained above, the present invention divides the band of an input audio signal by the band dividing unit 1 in the transmitting unit 7, and multiplies the band divided signal by a pseudo-random amplitude signal in the multiplier 4. By doing so, amplitude scrambling is performed, and the second modulation section 5 modulates the signal using a carrier signal to output a lower sideband signal, and by selecting the frequency of the carrier signal, frequency scrambling is performed and the confidential message is transmitted. The receiving section 17 performs the reverse processing to decode the audio signal.

Therefore, since amplitude scrambling is applied to the band-divided signal, the spread of the band will be within each divided band, suppressing the spread of the band due to amplitude scrambling, and Since independent amplitude scrambling can be applied to each signal, the privacy is improved, and since band division permutation is performed, the privacy is further improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a prong diagram of an embodiment of the invention, and FIG. 3 is an explanatory diagram of the operation of the embodiment of the invention. 1.11 is a band division section, 2 is a first modulation section, 313 is a pseudorandom generation section, 4 is a multiplication section, 5 is a second modulation section, 6
．． 16 is an adder, 7 is a transmitter, 12 is a third modulator, 1
4 is a dividing section, 15 is a fourth modulating section, and 17 is a receiving section.

Claims (1)

[Claims] A band division unit (1
), a first modulating section (2) that modulates the divided band signal divided by the band dividing section (1), and a lower sideband signal of the output signal of the first modulating section (2), a multiplier (4) that multiplies the pseudorandom amplitude signal from the pseudorandom generator (3); and a multiplier (4) that modulates the output signal of the multiplier (4) and outputs a lower sideband signal to perform band division and replacement. a second modulating section (5) that performs the following: and an adding section (6) that combines the output signals of the second modulating section (5) with different subbands to generate a secret signal.
7), and a band dividing section (11) that divides the confidential signal into a plurality of bands.
), a third modulator (12) that modulates the divided band signal divided by the band divider (11), and a third modulator (12) that modulates the divided band signal divided by the band divider (11);
a dividing unit (14) that divides the lower sideband signal of the output signal of 2) by a pseudo-random amplitude signal from a pseudo-random generating unit (13) synchronized with the pseudo-random generating unit on the transmitting side; a fourth modulating section (15) that outputs a lower sideband signal by modulating the output signal of (14) and restoring the band division permutation; and the fourth modulating section (15) having different divided bands. A secret speech device characterized in that a receiving section (17) is constituted by an adding section (16) for synthesizing output signals and reproducing an audio signal.