JPH07110002B2 - Receiver for confidential communication - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a confidential communication device, and more particularly to a confidential communication receiver capable of increasing the confidential communication intensity of a confidential communication system using rotational folding of a frequency spectrum.

[0002]

2. Description of the Related Art Conventionally, various secret communication systems have been known in order to keep secrets of telephone calls. Among them, the method using the spectrum turn-back is characterized by good sound quality and considerably easy circuit implementation. However, the secret story device using this method has a problem that the secret story strength is not sufficient.

Therefore, for example, US Pat.
8,840 (Name: Dynamic frequency)
and time voice encryptio
nsystem and method, 1981, 7
As shown in (14th of the month), etc., it is often used in combination with a secret system on the time axis, but it has a drawback that the structure becomes complicated.

An object of the present invention is to eliminate the above drawbacks and to provide a receiver for confidential communication using a spectrum rotation folding method in which the confidential strength is increased.

The receiver for confidential communication according to the present invention uses as input signal a signal transmitted from a secret transmitter using a spectrum rotation exchange method in which a band-limited input voice signal is input and a delay time difference is given. bifurcated, and means for providing said delay time difference of synchronization with time varying or fixed to the transmitter branched one signal, the one
The spectrum of the signal on top of the spectrum of the other signal
Means for frequency conversion so that they are adjacent to each other, means for adding the output of the means for giving the delay time difference and the output of the means for frequency conversion, and the output signal of the adding means as an input,
Of this input frequency band, the frequency that changes in time in synchronism with the transmitter is used as the center frequency, and only the portion corresponding to the spectrum of the band-limited input audio signal of the transmitter is passed through and obtained from this. It is characterized by comprising means for frequency-converting the received signal into a band of the voice input signal of the transmitter, and means for making the output the received voice output.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A detailed description will be given below with reference to the drawings. FIG. 1 is a spectrum diagram for explaining the operation principle of the spectrum rotation loopback confidential speech method used in the present invention.
Consider a band-limited audio signal as shown in FIG.

The frequency of this signal is moved so that it becomes the frequency f _L shown by the broken line fs, and the portion protruding to the lower frequency side is moved to the higher frequency side, as shown in FIG. A spectrum that is rotated and folded is obtained.

Here, by changing the frequency fs irregularly, the shape of the spectrum changes and a confidential signal can be obtained.

FIG. 2 is a block diagram showing a conventional embodiment. As shown in FIG. 5A, the band-limited input audio signal is applied from the input terminal 210, and the first path 25
It branches into first and second passages 252. The signal in the first path becomes one input of the adder circuit 214. The signal in the second path is frequency-converted by the frequency converter 212 using the fixed frequency oscillator 211 having the frequency f ₁ as a local oscillation signal, and only the upper sideband is extracted by the high-pass filter 213, and the other one of the adder circuit 214 is supplied. It becomes an input.

Here, if the frequency f ₁ of the fixed frequency oscillator is appropriately selected, the outputs of the first and second paths, that is, the two inputs of the adder circuit 214 can be made to have adjacent spectra. As a result, a signal having a spectrum as shown in FIG. 5B is obtained at the output of the adder circuit 214. In the same figure, the signal spectrum with hatching shows the signal input from the first passage.

In this way, the first and second lines are shaded.
The distinction of the signals in the passages in FIG. 1 facilitates the understanding of the operation of an embodiment of the present invention, as will be shown later. Adder circuit 21
The output of No. 4 is frequency-converted by the frequency converter 216 using the oscillator 216 whose oscillation frequency changes according to the control signal generated by the confidential code generator 215 as a local oscillation signal, and as shown in FIG. A wide spectrum is obtained. Here, the frequency of the oscillator 216 is assumed to be f ₂ .
The output of the frequency converter 217 is passed through a bandpass filter 218 to cut off a part of the band, as shown in FIG. Here, if the bandwidth of the bandpass filter is made the same as the bandwidth of the input audio signal,
As described above with reference to (a) and (b), the spectrum is rotated to obtain the folded back confidential signal. By changing the frequency f ₂ of the variable frequency oscillator, the shape of the spectrum cut by the bandpass filter 218 can be any shape obtained by spectrum rotation folding.

The output of the band-pass filter 218 can be transmitted as it is, or the output of the fixed frequency oscillator 220 is used as a local oscillation signal for frequency conversion by the frequency converter 219, and the spectrum as shown in FIG. After that, it is also possible to extract only the lower sideband by the low-pass filter 221, frequency-convert to the original voice band, and then transmit.

What is essential in the above-mentioned circuit implementation method for performing spectrum rotation folding is that (a) first, the voice signal is branched into two paths and frequency conversion operation is performed, so that the signals of the two paths are converted into spectra. This is a combination of an operation of adding the signals so that they are adjacent to each other, and then (b) an operation of cutting a part of the spectrum of the added signals by the original voice bandwidth. Therefore, various other circuit realizing means for realizing the above operation can be devised. The spectrum rotation loopback secret story system has a problem that the secret story strength is weak because the band is essentially divided and replaced.

FIG. 3 is a block diagram of a confidential communication transmitter related to the present invention, and FIG. 4 is a block diagram showing an embodiment of a confidential communication receiver of the present invention. As can be seen from FIGS. 3 and 4, the transmitter and the receiver have the same configuration.

Further, as compared with the conventional embodiment, the first
The delay circuit 230 is newly added to the path of the.

Below, the effects of the addition of this delay circuit and the fact that the reception is correctly performed in this way are shown in FIGS. 5 (a) to 5 (e) and 6 (a) to 6 (e). This will be described with reference to the spectrum diagram. The operation of the transmitter related to the present invention is such that, in the operation of the conventional embodiment, the signal obtained from the signal of the first path passes through the second path as shown by the shaded spectrum in FIG. It is delayed relative to the signal obtained by the time τ. By making the delay time τ large enough, the rhythm of the voice also changes, the residual intelligibility is significantly reduced, and Also has the effect of becoming stronger.

The operation of the receiver of the present invention will be described with reference to FIG. FIG. 7A shows a received input signal, that is, a confidential transmission signal. Similar to the operation of the transmitter shown in FIG. 2, the adder circuit 214 obtains a signal spectrum as shown in FIG. 6B.

Here, the delay time of the delay circuit 230 is set to be the same as that of the transmitter.

Therefore, the spectrum is divided into three regions having different delay times. That is, the hatched portion with a high hatch density has a delay time of 2τ and the hatched portion with a low hatch density has τ, and the unhatched portion has a delay time of zero. The lower density of the hatch corresponds to the spectrum of the input audio signal of the transmitter. The spectrum of the output of the frequency converter 217 is as shown in FIG. Here, as the oscillation frequency f ₂ of the variable frequency oscillator 216 in the transmitter changes, the folding frequency of the received signal spectrum changes, and accordingly, among the spectra shown in FIG. 6B, The spectrum of the hatched portion with low density shifts in frequency up and down.

By changing the oscillation frequency f ₂ 'of the variable frequency oscillator 216 of the receiver in synchronization with f ₂ , the spectrum of the output signal of the frequency converter 217 ((c) in the figure) It is possible to keep the low density hatch portion included in at least one of the upper side wave and the lower side wave constant on the frequency axis, and adjust the center frequency thereof to the center frequency of the band pass filter 218. it can. In the same figure, the case of cutting out the lower sideband is shown in FIG.
In the output of the band-pass filter 218, a signal obtained by inverting the spectrum of the transmitter voice input signal has a delay time τ (where transmission and reception delay times are not taken into consideration). Will be obtained. Frequency converter 219
By performing frequency conversion in (1), a transmission voice signal is obtained as shown in FIG. As mentioned above, it is shown that the transmitted signal can be correctly obtained from the received confidential signal with the delay, although it is accompanied by the time delay.

A block diagram of the transmitter associated with the present invention is shown in FIG.

Here, the delay circuit 2 provided in the first passage is used.
It is the same as FIG. 3 except that the delay time of 30 is changed according to the output of the second confidential code generator 270. Here, of the output of the adder circuit 216, a means for passing only the audio bandwidth at an arbitrary center frequency is a band pass circuit 260.
Is shown as a representative. By changing the delay time in this manner, the confidential story strength is further increased. The configuration and operation of the receiver of the present invention are also the same as those of FIGS. 4 and 7 except that the delay time τ changes with time in synchronization with the transmitter, and therefore description thereof is omitted here.

In the embodiment of the present invention, the delay circuit is provided in the first passage. However, in practice, any structure may be used as long as it provides a delay time difference between the first and second passages. Absent.

Further, since the receiver of the present invention can be realized with a circuit configuration almost the same as that of the transmitter, it is possible to provide one circuit like the conventional one by providing a switch and switch between transmission and reception for use.

[0025]

As described above, according to the present invention,
It is possible to realize the method of adding the time delay to the conventional spectrum rotation loopback confidential communication method with a simple circuit configuration and increasing the confidential communication strength.

[Brief description of drawings]

FIG. 1 is a spectrum diagram for explaining an operation principle of a spectrum rotation loopback confidential system.

FIG. 2 is a block diagram showing a conventional embodiment.

FIG. 3 is a block diagram of a transmitter associated with the present invention.

FIG. 4 is a block diagram of a receiver showing the first embodiment of the present invention.

FIG. 5 is a spectrum diagram illustrating the operation of the transmitter associated with the present invention.

FIG. 6 is a spectrum diagram illustrating the operation of the receiver of the present invention.

FIG. 7 is a block diagram related to the present invention.

[Explanation of symbols]

 210 Input terminal 211, 220 Fixed frequency oscillator 212, 217, 219 Frequency converter 213 High pass filter 214 Adder circuit 215, 270 Confidential code generator 216 Variable frequency oscillator 218 Band pass filter 221 Low pass filter 222 Output terminal

Claims (1)

[Claims] 1. An input signal is a signal transmitted from a secret-speech transmitter using a spectrum rotation interchange method in which a band-limited input voice signal is input and a delay time difference is given, and this signal is branched into two and branched. Means for providing one signal with a time delay that varies in synchronism with the transmitter or with a fixed delay time difference; and the spectrum of the one signal for the other signal.
Frequency conversion so that it is adjacent to the upper part of the No. spectrum
Means, means for adding the output of the means for giving the delay time difference and the output of the means for frequency conversion, and an output signal of the adding means as an input, in the frequency band of this input, in synchronization with the transmitter. With a frequency that changes with time as the center frequency, only a portion corresponding to the spectrum of the band-limited input voice signal of the transmitter is passed, and a signal obtained from this is passed to the band of the voice input signal of the transmitter. A receiver for confidential communication, comprising means for converting and means for converting the output to a received voice output.