JPH0681120B2 - Confidential communication method - Google Patents

Description

DETAILED DESCRIPTION [Overview] In order to solve deterioration of decoding quality and loss of synchronization due to frequency deviation on a confidential communication line, a transmitter side inserts a plurality of pilot signals, and a receiver side receives these pilot signals. The frequency deviation is eliminated by detecting and multiplying appropriately and extracting the difference frequency signal.

[Industrial application field]

The present invention relates to a confidential communication system, and more particularly to a frequency deviation correction system.

Conventionally, to prevent eavesdropping on narrow-band lines such as telephones,
A scrambling technique as shown in FIG. 7 has been studied as a voice encryption technique. In this type of system, on the transmission side, voice is input to the analog / digital converter 210 of the scrambler 200, encrypted via the scrambler 220, re-analogized by the digital / analog converter 230, and transferred to the communication channel. In general, the method of sending out and receiving side converts this analog signal into a digital signal by the analog / digital converter 250 of the descrambler 240, decodes it by the descrambler 260, and receives it as voice through the digital / analog converter 270. Is considered to be. Then, analog elements such as a filter bank and a delay element were used for the scramble processing.

However, in recent years, development of digital signal processing technology and high-speed LSI specialized in digital signal processing have become available at relatively low cost, and by using these, the hardware scale is smaller and more sophisticated than those using conventional analog components. It has become possible to realize a scramble method that can obtain excellent confidential performance.

What is important in the scrambler using these digital signal processing techniques is synchronization of the sampling clock of the A / D converter. In particular, a voice as shown in FIG. 8 ((1) in FIG. 8) is divided into frames every predetermined sampling, and each frame is time-frequency converted. (Eighth
Figure (2)). Then, scrambling processing (transposition) is performed with each generated frame as one unit (FIG. 8 (3)). This transposed information is reconverted into frequency-time on a frame-by-frame basis and sent out on the transmission path (Fig. 8 (4)). In this type of encryption, the transmission / reception frame length is defined by the number of samplings. If clock synchronization cannot be achieved, the transmission / reception frame length will be different, and the frame synchronization will be lost and correct decoding will not be possible. Therefore, a scrambler using digital signal processing requires a stable clock synchronization system even with a line failure.

[Conventional technology]

FIG. 9 is a block diagram showing a confidential communication system by the clock synchronization system. In the figure, an A / D converter 90 on the transmitting side converts a voice input into a digital signal. The clock signal for this conversion is given from the clock oscillator 91. The voice converted into a digital signal is scrambled (encrypted) by a scrambler 92 and converted again into an analog signal by a D / A converter 93. Further, in order to reproduce the clock signal of the transmitting side on the receiving side, the clock signal is frequency-divided by the frequency divider 94 and the adder is added.
At 95, it is added to the secret voice and output as a pilot carrier signal.

On the receiving side, the bandpass filter 96 extracts the clock signal, and the multiplier 97 multiplies it to reproduce the clock signal on the transmitting side, which is used as the clock signal of the A / D converter 98. And this A
The confidential voice input by the / D converter 98 becomes a digital signal and is decoded by the descrambler 99, and the D / A converter 100 obtains a voice output as an analog signal.

[Problems to be solved by the invention]

In such a conventional confidential communication system, Δf is used in the communication line.
If there is a frequency deviation of (Hz), the frequency of the received pilot clock signal similarly shifts by Δf (Hz) and the sampling clock on the receiving side has a frequency that is twice Δf, so the frame on the receiving side is transmitted. The length is different from that on the side and the frame synchronization shift occurs.

For example, when switching on the frequency, 8KHz on the transmitting side
Assume that 256 points of the sampling clock of 1 are set as 1 frame length and the replacement method is converted. 2KHz on the transmitting side
Is sent to the receiving side as a pilot signal, and 2 KHz at the receiving side
It is assumed that the sampling clock is synchronized by multiplying 4 by 8 KHz. At this time, if there is a frequency deviation of ΔfHz on the communication line, the received pilot signal is 2K.
Hz + ΔfHz, and the sampling clock on the receiving side is 8KH
Since it becomes z + 4ΔfHz, the length of the frame on the receiving side is different from that on the transmitting side, causing a frame synchronization shift.

As described above, there is the first problem that if the transmission / reception frame synchronization is lost, the decoding cannot be performed correctly and the decoding quality is deteriorated. In this case, using a high-precision oscillator independently for transmission and reception has a drawback that the scale of the oscillator becomes large and the cost becomes high.

Further, even if the problem of frame synchronization is solved, there remains a problem that a good decoding quality cannot be obtained unless the synchronization process is corrected because the secret speech itself includes frequency deviation.

Therefore, in order to solve these problems, an object of the present invention is to provide a confidential communication system capable of correcting frequency deviation with high accuracy and with a small amount of hardware.

[Means for solving problems]

FIG. 1 is a diagram showing the principle of the confidential communication system of the first invention for solving the above-mentioned problems. It is a transmitting side that samples voice and scrambles it to make confidential voice, and samples confidential voice. This is an improvement of the confidential communication system composed of a receiver that descrambles and decodes it into an audio signal.

In the first aspect of the invention, the transmitting side is provided with the pilot inserting means 1 for dividing the sampling clock signal into the first and second pilot frequency signals and adding it to the confidential voice, and the receiving side is provided with the first and second pilot inserting means 1. And a clock reproducing means 3 for generating a frequency signal of the difference between the first and second pilot frequency signals to reproduce the sampling clock signal of the secret voice. There is.

FIG. 2 is a diagram showing the principle of the confidential communication system of the second invention in order to solve the above problems. In the second invention, the sampling clock signal is supplied to the first and second pilots on the transmitting side. In addition to the frequency signal, pilot inserting means 4 is provided for dividing the third pilot frequency signal having a predetermined relationship with both pilot frequency signals and adding it to the secret voice. In addition, on the receiving side, the pilot detecting means 5 for detecting the first, second and third pilot frequency signals f1, f2 and f3 and the frequency signal of the difference between the first and second pilot frequency signals are received. Generated difference frequency generation means 6 and carrier frequency generation means 7 for generating a carrier frequency signal from the difference frequency signal and the third pilot frequency signal.
And a correction means 8 for extracting the difference frequency signal from the carrier frequency signal and the secret voice and using it for the sampling.
And are provided.

[Work]

In FIG. 1 showing the first aspect of the present invention, on the transmission side, pilot inserting means 1 divides the frequency of a sampling clock signal into first and second pilot frequencies and adds them to the scrambled secret voice. On the receiving side, the pilot detecting means 2 detects the first and second pilot frequencies f.
1, 1 and f2 are detected, and the clock reproduction means 3 reproduces the sampling clock signal of the secret voice by generating the difference between the first and second pilot frequency signals.

In FIG. 2 showing the second invention, on the transmission side, the pilot inserting means 4 adds a sampling clock signal to the first and second pilot frequency signals and adds a third pilot having a predetermined relationship with both pilot frequency signals. It is divided into frequency signals and added to secret voice. On the receiving side, the pilot detection means 5 detects the first, second, and third pilot frequency signals f1, f2, f3, and the difference frequency generation means 6
Generates a difference frequency signal from the first and second pilot frequency signals, and the carrier frequency generating means 7 generates a carrier frequency signal from the difference frequency signal and the third pilot frequency signal. Then, the correction means 8 extracts the difference frequency signal from the carrier frequency signal and the secret voice and uses it for the sampling.

〔Example〕

 Examples of the present invention will be described below.

FIG. 3 shows an embodiment of the secret communication system of the first invention conceptually shown in FIG. 1, in which the transmitting side is an A / D converter 51 for sampling a voice input, and a sampled signal. The scrambler 52 scrambles the digital signal to make it secret, the D / A converter 53 for converting the secret digital signal to secret voice, and the pilot insertion means 1. The pilot inserting means 1 divides the sampling clocks of the converters 51 and 53 generated by the clock oscillator 11 into first and second pilot frequencies f1 and f2, respectively, and the pilot signals thereof. Of the D / A converter 53, and an adder 14 for inserting the D / A converter 53 into the secret voice.

The receiving side samples the confidential voice that has passed through the communication path 54.
An A / D converter 55, a descrambler 56 that descrambles the digitized secret story, a D / A converter 57 that converts the unsecreted digital signal into voice, and a pilot signal is detected from the secret voice. Pilot detecting means 2,
The clock reproducing means 3 for reproducing a sampling clock from the detected pilot signal. The pilot detection means 2 comprises first and second bandpass filters 21 and 22, and the clock recovery means 3 comprises a filter 21.
A multiplier 31 that multiplies the first and second pilot signals detected in steps 22 and 22, and a bandpass filter 32 that extracts the frequency component of the difference between the first and second pilot frequencies from the frequency component obtained as a result of the multiplication. , The frequency difference is multiplied to generate a clock frequency signal that is the same as the sampling frequency of the clock oscillator 11, for example, a multiplier 33 such as a PLL.
And are equipped with.

Next, the operation of the embodiment of the confidential communication system of the first invention shown in FIG. 3 will be described as a specific example in which communication is performed on the communication path 54 in the voice band of 300 to 3.4 KHz.

On the transmitting side, the voice is sampled at 8 KHz, and the frequency divider 12 divides this by 8 and the frequency divider 13 divides it by 3/8. This gives f
1 = 1KHz and f2 = 3KHz are the transmitter pilot signals. Then, it is added to the scrambled secret voice and the communication path 54
Sent to.

On the receiving side, a filter 21 for each pilot signal and
The pilot signal is extracted at 22 and multiplied by the multiplier 31.

Here, consider the case where the pilot frequencies f1 and f2 are multiplied. Now, assuming that F1 wave and F2 wave are F1 (t) = A1sin2πf1 ・ t F2 (t) = A2sin2πf2 ・ t (however, the phase component is ignored), the multiplication result is F4 = A1sin2πf1 ・ t × A2sin2πf2 ・ t ＝ A1A2 / 2 {cos2π (f2-f1) t-cos2π (f2 + f1)
t}. Therefore, the f3 wave can be extracted by using a bandpass filter with a high Q center frequency f3 = f2−f1, and even if there is a frequency deviation of Δf in the communication path, f3 wave can be extracted.
Then, Δf is not included in the component of A1A2 / 2 {cos2π (f2-f1) t}. Therefore, if this is taken out by the filter, there will be no frequency deviation.

Therefore, the filter 32 uses a filter having a center frequency of fc = f2-f1 (= 3-1) = 2 KHz. After that, the multiplier 32 multiplies by 4 to reproduce the same clock signal as on the transmitting side.

In this case, if the multiplier can multiply by α, then α (f2−
If f2 and f1 are selected so that f1) = clock frequency, it can be realized at any frequency. This frequency is determined by the line characteristics of f1 and f2 waves, the scrambler scramble system, and the elements used.

FIG. 4 shows the relationship between the secret voice and the pilot signal. FIG. 4 (A) is a waveform diagram at the time of transmission, FIG. 4 (B) is at the time of reception, and FIG. 4 (C) is a waveform diagram after multiplication. At 32, the 2 KHz signal of FIG. 4 (C) is taken out.

The first invention solves the problem that the clocks are synchronized and the frame synchronization is deviated. However,
If there is a deviation (Δf) in the frequency of the secret sound itself, a deviation will occur in the boundary of the divided frames described above,
Since the decoding quality is deteriorated and the frequency of the synchronization signal, for example, frame synchronization or encryption synchronization (synchronization at the start of encryption processing) is shifted, there is a problem that the synchronization processing must be corrected.

Therefore, in the second invention of the present application, such a problem is solved.

FIG. 5 shows an embodiment of the confidential communication system of the second invention conceptually shown in FIG. 2, in which the pilot inserting means 4 on the transmitting side sets the sampling frequency of the voice input to the first, second,
And a frequency divider 41 that divides the frequency into third frequencies f1, f2, and f3.
And an adder 42 for inserting these divided pilot signals into the secret voice. The relationship between these three frequencies is, for example, f3 = f2-f1, but any relationship may be used as long as a certain relationship is maintained on the transmitting / receiving side.

The pilot detecting means 5 on the receiving side includes the first, second, and third
It includes filters FL1, FL2, and FL3 that detect pilot frequencies f1, f2, and f3, respectively. The difference frequency generation means 6 is composed of a multiplier 61 that multiplies the first and second pilot frequency signals, and a bandpass filter 62 that extracts the difference frequency component resulting from the multiplication.
The carrier frequency generation means 7 includes a circuit 71 that doubles or divides the difference frequency signal so as to generate the carrier frequency based on the predetermined relationship between the difference frequency signal and the third pilot signal, and the difference frequency signal. It is composed of a multiplier 72 that multiplies with the third pilot signal, and a bandpass filter 73 that extracts a carrier frequency signal that is a sum frequency component resulting from the multiplication. The correction means 8 includes a multiplier 81 that multiplies the carrier frequency signal and the confidential voice, and a low-pass filter 82 that extracts a difference frequency signal resulting from the multiplication.
Spectrum inversion circuit 83 for inverting the output of this filter 82
It consists of and.

Next, the operation of the embodiment of the second invention will be described with reference to a concrete numerical value.
Description will be made with reference to the waveform charts of the figures.

The 8KHz clock signal, which is the audio input sampling clock on the transmitting side, is divided to generate pilot signals of 1KHz, 2KHz, and 3KHz by the frequency divider 41, which is added to the confidential voice by the adder 42 and sent to the communication path 54. (FIGS. 5 and 6).

At the receiving side, both the pilot signal and the secret voice are input in the form of frequency deviation (Δf) shifted (Figs. 5 and 6), and the filters FL1 and FL2 respectively input 1KHz + Δf and 3KHz +.
After extracting the pilot signal of Δf, it is multiplied by the multiplier 61 and the difference frequency signal 2 KHz between them is taken out through the filter 62 as in the first invention (FIGS. 5 and 6). At the same time, the frequency of 2KHz + Δf extracted from the filter FL3 (Fig. 6)
Is multiplied by the output of the filter 62 by the multiplier 72, and 4KHz + Δf of the sum of the two is extracted via the filter 73 (see FIGS. 5 and 6).
Figure). This is the signal corresponding to the carrier frequency,
The secret voice is multiplied (ie, modulated) by the multiplier 81 to obtain the sixth voice.
A broken line portion including 2Δf and its inverted solid line portion are generated by multiplication with the figure. This is the low pass filter 82
The frequency signal of the difference is extracted with and the frequency is corrected (5th
(Fig. 6). However, since the spectrum is inverted, the spectrum is inverted by the spectrum inverting circuit 83. If this is sampled and input to the descrambler 56, the frequency deviation can be removed.

In the second invention as well, as in the first invention, the sampling clock of the A / D converter 55 outputs or divides / divides 2 KHz (FIG. 8) of the filter 62 as shown in the first invention. The output multiplied by 4 can be used by the multiplier 71. Further, this clock may be extracted from the corrected confidential signal.

〔The invention's effect〕

As described above, according to the confidential communication system of the first invention, two pilot signals obtained by dividing the sampling frequency of voice are used, a difference frequency signal having no frequency deviation is obtained from these pilot signals, and reception is performed based on the difference frequency signal. Since the sampling signal is used for the confidential communication, it is possible to eliminate the clock synchronization deviation on the transmitting and receiving side and the deterioration of decoding due to the channel frequency deviation which is a problem in the confidential communication. Furthermore, in the confidential communication system of the second invention, three pilot frequencies are used. By using the signal and using the difference frequency signal having no frequency deviation on the receiving side and the signal including another frequency deviation, it is possible to remove the frequency deviation of the confidential voice itself.

[Brief description of drawings]

1 is a block diagram showing the principle of the confidential communication system according to the first invention, FIG. 2 is a block diagram showing the principle of the confidential communication system according to the second invention, and FIG. 3 is an implementation of the confidential communication system according to the first invention. FIG. 4 is a circuit diagram showing an example, FIG. 4 is a diagram showing a relationship between a secret voice and a pilot signal according to the first invention, FIG. 5 is a circuit diagram showing an embodiment of a secret communication system of the second invention, and FIG. Is a diagram showing the relationship between the secret-speech voice and the pilot signal according to the second invention, FIG. 7 is a diagram showing a general secret-speech communication system, FIG. 8 is a diagram explaining the scramble processing, and FIG. 9 is a conventional secret-speech. It is a block diagram which shows a communication system. In FIG. 1 and FIG. 2, 1 and 4 are pilot inserting means, 2 and 5 are pilot detecting means, 3 is clock reproducing means, 6 is difference frequency generating means, 7 is carrier frequency generating means, 8 is correcting means, Is. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (6)

[Claims] 1. A confidential communication system comprising a transmitting side which samples voice and scrambles it to make a secret voice, and a receiving side which samples the secret voice, descrambles it and decodes it into a voice signal. The transmitting side is provided with pilot inserting means (1) for dividing the sampling clock signal into first and second pilot frequency signals and adding it to the secret voice, and the receiving side is provided with the first and second Pilot detecting means (2) for detecting the pilot frequency signal of the above, and a frequency signal of the difference between the first and second pilot frequency signals (f1, f2) is generated to reproduce the sampling clock signal of the secret voice. A secret communication system characterized by comprising a clock reproducing means (3). 2. The clock recovery means (3) comprises the first
And a multiplier (3
1), a bandpass filter (32) for extracting a difference frequency component resulting from the multiplication, and a multiplier (33) for multiplying the difference frequency component to reproduce a clock signal having the sampling frequency on the transmission side. The confidential communication system according to claim 1, which is configured by: 3. A confidential communication system comprising a transmitting side which samples voice and scrambles the voice to produce a secret voice, and a receiving side which samples the confidential voice, descrambles the voice to decode it into a voice signal. A pilot for dividing the sampling clock signal into first and second pilot frequency signals and a third pilot frequency signal having a predetermined relationship with both pilot frequency signals, and adding to the secret voice to the transmitting side, Inserting means (4) is provided, and pilot detecting means (5) for detecting the first, second and third pilot frequency signals (f1, f2, f3) on the receiving side, and the first and the second detecting means. Difference frequency generating means (6) for generating a difference frequency signal from the second pilot frequency signal, and the difference frequency signal and the third pilot frequency signal (f3 ) And a carrier frequency generating means (7) for generating a carrier frequency signal from the carrier frequency signal, and a correction means (8) for extracting the difference frequency signal from the carrier frequency signal and the secret voice and using the same for the sampling. A confidential communication method characterized by. 4. The difference frequency generating means (6) comprises:
And a multiplier (61) for multiplying the second pilot frequency signals (f1, f2), and a bandpass filter (62) for taking out a difference frequency component resulting from the multiplication, the claim 3. Confidential communication method described in paragraph. 5. The carrier frequency generating means (7) doubles or divides the difference frequency so as to generate a carrier frequency based on a predetermined relationship between the difference frequency signal and the third pilot signal (f3). Circuit (71), a multiplier (72) that multiplies the difference frequency signal and the third pilot signal (f3), and a bandpass filter that extracts a carrier frequency signal that is a sum frequency component resulting from the multiplication. (73) and the confidential communication system according to claim 3 or 4. 6. The correction means (8) comprises a multiplier (81) for multiplying the carrier frequency signal by the secret voice, a low-pass filter (82) for extracting a difference frequency signal resulting from the multiplication, The confidential communication system according to any one of claims 3 to 5, comprising a spectrum inverting circuit (83) for inverting the output of the filter (82).