JPH0355062B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to an improvement in a secret communication device, and in particular to an improvement in a Spestre reversal rotary type communication device.

(Prior Art) Various methods have been proposed to maintain the confidentiality of communication contents, one of which is dividing the frequency spectrum of the signal to be transmitted into a required number of sections and rearranging or inverting the frequency spectrum. Some are transmitted as rotating spectra.

This spectrum inversion/rotation method has superior demodulated sound quality and is easy to implement as a circuit compared to other methods, but on the other hand, the simple inversion/rotation method has the disadvantage that the secrecy strength is somewhat low, and the device that implements this method requires a band filter that is difficult to operate. There was a problem that required .

For this reason, conventionally, for example, Japanese Patent Application No. 21148 of 1982 (Secret Communication Device) or Japanese Patent Application No. 1983-44141) Secret Communication Method and Device)
As shown in Figure 2, by arbitrarily changing the inversion frequency position or rotation combination of the spectrum and by replacing the bandpass filter with a relatively easy-to-manufacture low-pass filter, it is possible to improve confidentiality and reduce costs. A wide range of methods have been proposed.

In order to facilitate understanding of the present invention, the conventional method will be briefly explained below.

FIGS. 2a and 2b are a block diagram showing a conventional reversing rotary type private communication device and a signal spectrum diagram illustrating its operation.

First, to briefly explain the device configuration shown in Fig. 2a, as shown in Fig. 2b A, from _L to _M (f _L < f _M )
The band-limited audio signal 1 is branched into two, one is directly connected to one input terminal of the adder 2, and the other is connected to the frequency conversion circuit 3 which sets the local frequency to ₁ and outputs only the sum of the two out of the mixed output. The audio signal 1 is then inputted to the other input terminal of the adder 2, and the frequency of the audio signal 1 is shifted as shown in FIG.

Furthermore, this signal is split into two, and two multipliers are used.
A first series circuit route in which a low frequency filter LPF ₁ is inserted between MULT ₁ and MULT ₂ , and a second low frequency filter LPF ₂ is similarly inserted between two multipliers MULT ₃ and MULT ₄ . is input to the second adder 4 through each of the second series circuit routes in which the The output of the second adder 4 is directly applied to the root multiplier by commonly applying the oscillator OSC ₁ and OSC ₂ outputs as local frequencies to the respective pre-multipliers and post-multipliers. The system is constructed to obtain an inverted and rotated audio spectrum as shown in Figure 2b and c.

With this configuration, it is possible to eliminate the need for a bandpass generator that is difficult to manufacture, but it is also possible to add a code generator to either the local oscillator OSC ₁ or OSC ₂ to generate the local frequency according to a predetermined rule. If the information is changed and then transmitted via a desired communication line, confidentiality can be further improved. When receiving this signal, the original audio signal can be restored by controlling the local oscillator and demodulating it in synchronization with the code margin rule.

However, although such spectrum inversion circuit processing is possible with analog signals as they are,
The circuit elements used for this are generally large and complex, so one step is analog/digital conversion (AD conversion).
It is normal to perform digital processing afterward, and by doing so, the device itself can be simplified.

However, the conventional secret communication device mentioned above is a wave device 3.
Since a total of 10 arithmetic elements, including 5 multipliers and 2 adders/subtractors, are required at least, various problems occur when these are digitized.

That is, since the bit length for representing data in digital calculations is generally finite, rounding errors and truncation errors (also called rounding errors and truncation errors) occur in inverse proportion to the bit length, acting as if noise had been mixed in. This problem is significant in fixed-point arithmetic, so it is desirable to use as few arithmetic elements as possible.

(Object of the Invention) The present invention has been made in order to solve the problems of the conventional spectrum inversion rotation type confidential communication device as described above. The purpose of the present invention is to provide a confidential communication device suitable for performing digital processing.

(Summary of the Invention) For this purpose, in the present invention, the audio spectrum signal subjected to the required band restriction is split into two, one of which is split into two.
A first frequency conversion circuit configured to have a local frequency fm and extract a low frequency component from the mixed output, and a second frequency conversion circuit configured to have a local frequency _fK and extract a high frequency component from the mixed output. The frequency conversion circuit and the mixing circuit with the local frequency as fm are input to one input terminal of the adder circuit via a serially connected route, and the other of the two branched audio spectrum components is input as the local frequency f _K +
A desired inverted rotating spectrum signal is inputted to the other input terminal of the adder circuit through a series circuit consisting of a mixing circuit set as fm and a predetermined delay circuit, and the output of the adder circuit is further passed through a low-band filter as a desired inverted rotation spectrum signal. Configure it to get .

(Example) The present invention will be described in detail below based on an illustrated example.

FIG. 1 is a block diagram showing an embodiment of the secret communication device of the present invention.

In the figure, 4 is an audio signal input terminal,
This is branched into two parts, one of which is input to a multiplier 6 whose input is the output of an oscillator 5 with an oscillation frequency fm, and a low-frequency component of the mixed components generated in this section is extracted via a low-frequency filter 7. The second multiplier 8
The output of a second oscillator 9 that outputs a frequency f K is input to one input terminal of the multiplier 8, and the output of a second oscillator 9 that outputs a frequency f _K is input to one input terminal of the multiplier 8. is extracted by a high frequency generator 10, and then extracted by a third oscillator 11 whose oscillation frequency is fm.
is input to one terminal of an adder 13 via a third multiplier 12 which has one input as the output. Further, the oscillation frequency of the other of the two-branched audio signal is f _K +
The output of the fourth oscillator 14, fm, is input to the multiplier 15, which has one input, and the output of the multiplier 15 is sent to the adder 15 through a delay circuit 16 having a required delay time.
3, and its output is passed through a low frequency filter 17 to obtain a desired inverted rotation spectrum.

Figure 1b shows the operation of the confidential communication device configured as described above.
This will be explained in detail with reference to the spectrum diagrams of each part shown in .

First, it is assumed that an audio spectrum signal having the configuration shown in FIG. 4B is input to the input terminal 4. Although this spectrum differs in appearance from the original speech spectrum in the conventional example described above, it is generally shown in FIG.

The above-mentioned branched original audio signal is mixed with the same frequency component as the highest frequency fm of the original audio signal in the first frequency conversion circuit, resulting in a mixed component shown by the broken line in b and b of the same figure. fm frequency
Only the low frequency spectrum shown by the solid line in the figure is obtained by the low frequency converter 7, and this signal is further converted to the local frequency f _K in the next stage frequency conversion circuit.
(0 < f _K < fm), producing a spectrum like the dotted line in b c of the same figure, of which the cutoff frequency of the next stage is
Only the spectrum between fm and fm+ _fK is extracted by the high-frequency wave generator 10 with fm as shown by the solid line in the figure. Since this component is mixed with the local frequency fm by the frequency conversion circuit in the next stage, one input terminal of the adder 13 has f=
Spectra are input in which the high-frequency spectrum from f K to fm of the original audio spectrum is arranged from =0 to f _K and from f = 2fm to 2fm + _{f K} at symmetrical positions with respect to 0 as the base axis.

On the other hand, the other of the two-branched original speech spectrum is frequency-converted by the oscillator 14 and the multiplier 15 to a local frequency of fm+f _K , and as a result, as shown in b-e of the same figure, a spectrum obtained by shifting the original speech spectrum by fm+f _K is obtained. This signal is injected into the other input terminal of the adder 13 via the next-stage delay circuit 16, where it is added and mixed with the signal input via the other route mentioned above. .

The reason for the existence of the delay circuit is that the two routes through which the two divided original audio signals pass have different circuit configurations and therefore have different phase delays. Therefore, this is corrected so that both signals reach the adder 13. Since this is to match the times, the delay time of this section is determined by taking into account the time difference between the two routes.

In this way, when the two signals N and F that arrive at the same time with their respective phases adjusted are added in the adder 13, a signal which is the sum of both signals is obtained. If the input signal is input to , an inverted and rotated spectral signal can be obtained as the output as shown in FIG.

As is clear from the above explanation, according to the confidential communication device of the present invention, only 8 arithmetic units are required, including 4 multipliers, 3 waveform units, and 1 adder, so the conventional device described above can be used for a total of 10 arithmetic units. This can be reduced by two compared to the number needed.

Furthermore, in the above-described embodiment, the frequency f _K of the second oscillator 9 may be changed depending on a required coded signal in order to improve the privacy.

At this time, it is sufficient to add a code oscillator CG to the oscillator, and by changing the local frequency f _K in this way, the final output of the low frequency converter 17, that is, the frequency of the inverted rotation in b in the same figure. Since the position changes, secrecy can be ensured as long as the coded signal is not known.

Also, in this way, the range of change of the inversion rotation frequency position f _K of the spectrum is set from 0 to the highest frequency fm of the original voice.
It has been experimentally confirmed that if the sample frequency (sampling frequency) at this time is set to about 4 fm, the fidelity of the demodulation frequency on the receiving side can be maintained at the desired level, and real-time processing is sufficient. Since this is possible, it is suitable as a confidential communication device for telephone lines, etc., for example.

It should be noted that among the oscillators in the above-mentioned embodiment, those having the same frequency can share the same oscillator, and the oscillator 14 with the sum frequency of fm + f _K
It is unnecessary to explain that this may be omitted by injecting the outputs of the oscillators 5 and 9 that oscillate fm and _fK through a separately provided mixing circuit and wave generator.

However, since the oscillation frequency of the oscillator 11 determines the low range of the audio spectrum to be transmitted, it should be set appropriately depending on the desired frequency range, and it is preferable that it be set separately from the oscillator 5. would be convenient.

(Effects of the Invention) Since the present invention is constructed as described above and obtains the same secret speech characteristics with fewer arithmetic elements when the sampling frequency is the same, the present invention provides a secret speech device that reduces rounding errors and increases the calculation speed. It is effective in bringing about

[Brief explanation of drawings]

FIGS. 1a and b are a block diagram showing an embodiment of the present invention and a spectrum diagram for explaining its operation. FIGS. 2a and b are a block diagram showing a conventional confidential communication device and a spectrum diagram showing its operation. It is. 4...Audio signal input board, 5, 9, 11 and 14
... oscillator, 6, 8, 12 and 15 ... multiplier,
7 and 17...Low frequency unit, 10...High band unit, 13...Adder.

Claims (1)

[Claims] 1. A first frequency conversion circuit that makes a frequency signal ₁ local and extracts a low frequency component, a second frequency conversion circuit that makes a frequency signal ₂ local and extracts a high frequency component, and ₃ . A first route is connected in series with a local mixing circuit, and a second route is made up of a mixing circuit with a local frequency of ₁ + ₂ and a delay circuit having a predetermined delay time. What is claimed is: 1. A secret speech device characterized in that the voice signals are passed through, the two are added together, and only the high-frequency or low-frequency components of the added components are extracted and transmitted. 2. The secret communication device according to claim 1, wherein the local frequencies ₁ and ₃ are made to match the highest frequency m of the audio signal. 3. The secret communication device according to claim 1, wherein the local frequency ₃ is determined according to a cutoff frequency of a high frequency or a low frequency of an audio signal to be transmitted. 4. The confidential communication device according to claims 1, 2, and 3, characterized in that communication confidentiality is enhanced by varying the local frequency ₂ by a predetermined control signal.