JPS6313441A - Privacy communicating system - Google Patents

Abstract

PURPOSE:To eliminate a frequency deviation by inserting plural pilot signals at a transmitting side, detecting these pilot signals at a receiving side, multiplying it suitably and extracting a difference frequency signal. CONSTITUTION:The system is composed of a transmitting side to sample, scrambling-process and make the sound into a privacy and a receiving side to sample, descramblingprocess and decode the privacy sound into the sound signal. At the transmitting side, a pilot inserting means 1 to frequency divide a sampling clock signal to the first and second pilot frequency signals and add it to a privacy sound is provided, and at the receiving side, a pilot detecting means 2 to detect the first and second pilot frequency signals and a clock reproducing means 3 to generate the frequency signal of the difference from the first and second pilot frequency signals and reproduce the sampling clock signal of the privacy sound are provided. Thus, a clock synchronizing dislocation at the transmitting receiving side due to a channel frequency deviation and the deterioration of the privacy decode can be cancelled.

Description

[Detailed Description of the Invention] [Summary] In order to solve deterioration of decoding quality and loss of synchronization due to frequency deviation on a confidential communication line, a plurality of pilot signals are inserted on the transmitting side, and these pilot signals are inserted on the receiving side. The frequency deviation is eliminated by detecting, multiplying as appropriate, and extracting the difference frequency signal.

[Industrial application field]

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

Traditionally, in order to prevent eavesdropping on narrowband lines such as telephones,
A scrambling technique as shown in FIG. 7 is being researched as a voice encryption technique. In this type of system, on the transmitting side, audio is input to an analog/digital converter 210 of a scrambler 200, encrypted via a scrambler 220, and then input to a digital/analog converter 230.
On the receiving side, this analog signal is converted into a digital signal by the analog/digital converter 250 of the descrambling device 240, decoded by the descrambler 260, and then sent to the digital/analog converter 270. Generally speaking, a method is considered in which the audio is received as audio via the Internet. Analog elements such as filter banks and delay elements were used for the scrambling process.

However, in recent years, with the development of digital signal processing technology, high-speed LSIs dedicated to digital signal processing have become available at relatively low prices. It has now become possible to realize a scrambling method that provides excellent confidential communication performance.

What is important in scramblers using these digital signal processing techniques is synchronization of the sampling clock of the A/D converter. In particular, the audio as shown in FIG. 1 and FIG. 8 (FIG. 8 (1)) is divided into frames by dividing it into frames at predetermined sampling intervals, and each frame is subjected to time-frequency conversion (FIG. 8 (2)).

Then, scrambling processing (transposition) is performed for each generated frame as one unit (FIG. 8 (3)). This transposed information is reconverted into a frequency of one frame in units of frames and sent out on the transmission path (Figure 8 (4)). In this type of encryption, the frame length for transmission and reception is defined by the number of samples, so the clock is synchronized. If this cannot be achieved, the frame lengths for transmission and reception will be different, resulting in frame synchronization and incorrect decoding. Therefore, a scrambler using digital signal processing requires a clock synchronization system that is stable even against line failures.

[Conventional technology]

FIG. 9 is a block diagram showing a confidential communication system using a clock synchronization system. In the figure, on the transmitting side, an A/D converter 90 converts audio input into a digital signal. A clock signal for this conversion is provided by a clock oscillator 91.

The audio converted to digital signal is scrambler 92
The signal is scrambled (polarized) and converted back into an analog signal by the D/A converter 93. Further, in order to reproduce the clock signal of the transmitting side on the receiving side, the frequency of the clock signal is divided by a frequency divider 94 and added to the secret speech sound by an adder 95, and the resulting signal is output as a pilot carrier signal.

On the receiving side, a band pass filter 96 extracts the clock signal, and a multiplier 97 multiplies it to reproduce the transmitting side clock signal, which is used as a clock signal for the A/D converter 98. The input confidential voice is converted into a digital signal by this A/D converter 98, decoded by a descrambler 99, and then D/A
The converter 100 obtains audio output as an analog signal.

[Problem that the invention seeks to solve]

In such a conventional confidential communication system, Δf is
(Hz), the frequency of the received pilot clock signal will similarly shift by Δf (Hz), and the sampling clock on the receiving side will have a frequency multiple of Δr, so the frame on the receiving side will be transmitted The length is different compared to the side, causing frame synchronization.

For example, when exchanging frequencies, the transmitting side uses 8K
Assume that 256 points of the Hz sampling clock are used as one frame length, and the replacement method is changed. It is also assumed that the transmitting side sends 2 KHz as a pilot signal to the receiving side, and the receiving side multiplies 2 KHz by 4 to obtain 8 KHz and synchronizes the sampling clock. At this time, if there is a frequency deviation of ΔfHz in the communication line, the received pilot signal will be 2KHz + ΔfHz, and the sampling clock on the receiving side will be 8KHz + 4ΔfHz, so the frame on the receiving side will have a different length compared to the transmitting side, and frame synchronization will occur. cause misalignment.

The first problem is that when the transmission and reception frames are out of synchronization, correct decoding is not possible and decoding quality is degraded. In this case, using high-precision oscillators independently for transmission and reception has the disadvantage that the scale of the oscillator becomes large and the cost increases.

Furthermore, even if the problem of frame synchronization is solved, there remains the problem that the secret speech itself contains frequency deviations and good decoding quality cannot be obtained unless the synchronization process is corrected.

Therefore, in order to solve these problems, an object of the present invention is to provide a confidential communication system that can correct frequency deviations with high precision and with a small amount of hardware.

[Means for solving problems]

Figure 1 is a diagram showing the principle of the first invention's confidential communication method to solve the above problems, and shows the transmitting side that samples and scrambles audio to convert it into confidential audio, and the transmitter that samples and scrambles audio to create confidential audio. This is an improved version of the confidential communication system, which consists of a receiving side that descrambles and decodes the audio signal.

In this first invention, the transmitting side is provided with the pilot insertion means 1 which divides the sampling clock signal into the first and second pilot frequency signals and adds them to the confidential voice, and the receiving side is provided with the pilot inserting means 1 which divides the sampling clock signal into the first and second pilot frequency signals and adds them to the confidential voice. a pilot detection means 2 for detecting a pilot frequency signal of the first and second pilot frequency signals; and a clock regeneration means 3 for generating a difference frequency signal from the first and second pilot frequency signals and reproducing a sampling clock signal of the secret speech. 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 addition to the frequency signal, a pilot insertion means 4 is provided which divides the frequency into a third pilot frequency signal having a predetermined relationship with both pilot frequency signals and adds it to the secret voice. Further, on the receiving side, there is a pilot detection means 5 for detecting first, second, and third pilot frequency signals f1, f2, and f3, and a frequency signal of the difference from the first and second pilot frequency signals. a difference frequency generating means 6 to generate;
a carrier frequency generating means 7 that generates a carrier frequency signal from the difference frequency signal and the third pilot frequency signal; a correction means 8 that extracts the difference frequency signal from the carrier frequency signal and the secret speech and provides it for the sampling; has been established.

[For production]

In FIG. 1 showing the first invention, on the transmitting side, pilot insertion means 1 divides the frequency of the sampling clock signal into first and second pilot frequencies and adds them to the scrambled secret speech. On the receiving side, the pilot detection means 2 detects the first and second pilot frequencies f
1, f2 is detected, and the clock reproducing means 3 detects the first and second clocks.
The difference between the pilot frequency signals is generated to reproduce the sampling clock signal of the confidential voice.

In FIG. 2 showing the second invention, on the transmitting side, pilot insertion 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. Divide the frequency signal and add it to the secret voice. Furthermore, on the receiving side, the pilot detection means 5 detects the first, second, and third pilot frequency signals f1, f2, and f3, and the difference frequency generation means 6 detects the first, second, and third pilot frequency signals f1, f2, and f3. A carrier frequency generating means 7 generates a carrier frequency signal from the difference frequency signal and the third pilot frequency signal. And the correction means 8
A difference frequency signal is extracted from the carrier frequency signal and the confidential voice and is used for the sampling.

〔Example〕

The present invention will be described in detail below.

FIG. 3 shows an embodiment of the confidential communication system of the first invention conceptually shown in FIG. It is composed of a scrambler 52 that scrambles a digital signal to make it private, a D/A converter 53 that converts the private voice into a private voice, and a pilot insertion means 1. The pilot insertion means 1 includes frequency dividers 12 and 13 that divide 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 these pilot signals. and an adder 14 for inserting the signal into the secret voice of the D/A converter 53.

The receiving side includes an A/D converter 55 that samples the confidential speech that has passed through the communication path 54, a descrambler 56 that descrambles the digitized confidential speech, and a D that converts the confidential speech into audio. It is comprised of a /A converter 57, a pilot detecting means 2 for detecting a pilot signal from a confidential voice, and a black reproducing means 3 for reproducing a sampling clock from the detected pilot signal. The pilot detection means 2 includes first and second bandpass filters 21 and 22, and the clock recovery means 3 includes the first and second bandpass filters detected by the filters 21 and 22.
a multiplier 31 that multiplies the pilot signal of , 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.
and a multiplier 33, such as a PLL, which multiplies this difference frequency to generate a clock frequency signal equal to the sampling frequency of the clock oscillator 11.

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 the case where communication is performed through the communication path 54 in the voice band of 300 to 3.4 KH2.

On the transmitting side, audio is sampled at 8 KHz, which is divided into 8 by a frequency divider 12 and 3/8 by a frequency divider 13.

As a result, f 1 = IKHz and f 2 = 3KHz become transmitter side pilot signals. Then, it is added to the scrambled confidential voice and sent to the communication channel 54.

On the receiving side, pilot signals are extracted by filters 21 and 22 for each pilot signal, and multiplied by a multiplier 31.

Here, consider the case where the pilot frequencies fl and f2 are multiplied. Now, Fl wave, F2 wave, Fl(t) = A1s
in2πf1・LF2(t) = A25in 2πf
2-t (ignoring the phase component), the multiplication result is F4 = A1sin2 fffl-t X A25in
2 πf2 ・t=AIA2/2 (cos2 tt
(f2-fl) t-cos 2 fc (f2+fl
) becomes tl. Therefore, the high center frequency f3=
The F3 wave can be extracted by using a bandpass filter of f2-rt, and even if there is a frequency deviation of Δf in the communication channel, at r3, AlA2/2 (cos2 ft (f2-fl) t
The component of l does not include Δf, so if it is extracted with a filter, there will be no frequency deviation.

Therefore, the filter 32 is fc = f 2 - r 1 (=
31) A clock signal with a center frequency of 2 KHz is used, and then multiplier 33 multiplies it by 4 to reproduce the same clock signal as on the transmitting side.

In this case, if the multiplier can be multiplied by α(f2
If f2 and rl are selected so that -fl)=clock frequency, it can be realized at any frequency. This frequency is f
1. It is determined by the line characteristics of the F2 wave, the scrambling method of the scrambler, and the elements used.

Figure 4 shows the relationship between the confidential voice and the pilot signal, with Figure 4 (A) at the time of transmission, Figure 4 (B) at the time of reception,
C) is a waveform diagram after multiplication, and the filter 32 extracts the 2 KHz signal of FIG. 4(C).

According to the first invention, the problem of clock synchronization and frame synchronization becoming out of sync is solved.

However, there is a deviation (Δf) in the frequency itself before the secret conversation.
If there is a shift in the boundaries of the divided frames as described above, decoding quality may deteriorate or synchronization signals such as frame synchronization or cryptographic synchronization (synchronization of the start of cryptographic processing)
Since the frequencies of the signals are shifted, a problem arises in that synchronization processing must be corrected.

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

FIG. 5 shows an embodiment of the confidential communication system of the second invention conceptually shown in FIG.
and a frequency divider 41 that divides the frequency into third frequencies f1, f2, and f3, and an adder 42 that inserts these frequency-divided pilot signals into the confidential voice. The relationship between these three frequencies is, for example, f3=f2-fl, but any relationship may be used as long as a constant relationship is maintained on the transmitting and receiving sides.

The pilot detecting means 5 on the receiving side includes first, second, and third pilot detecting means 5.
includes filters FLI, FL2, and Fl3 for detecting pilot frequencies f1, f2, and r3, respectively. The difference frequency generating means 6 includes 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.
It consists of The carrier frequency generation means 7 includes a circuit 71 that multiplies 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, and a circuit 71 that multiplies or divides the difference frequency, and Third
It is comprised of a multiplier 72 that multiplies the bi-low/ The correction means 8 includes a multiplier 81 that multiplies the carrier frequency signal and the confidential voice, a low-pass filter 82 that extracts a difference frequency signal resulting from the multiplication, and a spectrum inversion circuit 83 that inverts the output of this filter 82. It is configured.

Next, we will explain the operation of the embodiment of the second invention using specific numerical values as an example.
This will be explained with reference to the waveform diagram in the figure.

8KHz which is the audio input sampling clock on the transmitting side
Divide the clock signal to IKHz, 2KHz, 3KH
A pilot signal of z is generated by a frequency divider 41, added to the confidential voice by an adder 42, and sent to a communication path 54 (FIGS. 5 and 6).

On the receiving side, both the pilot signal and the secret voice should be input in the form shifted by the frequency deviation (Δf) (Figures 5 and 6 ■)
, IKHz+Δf for filters FLI and FL2, respectively.
After extracting the 3KHz+Δf pilot signal, it is multiplied by a multiplier 61 and passed through a filter 62, as in the first invention.
Extract the difference frequency signal of 2KHz between the two (Figures 5 and 6)
Figure ■).

At the same time, the output of the filter 62 is multiplied by the frequency of 2KHz+Δf extracted from the filter FL3 (Fig.
This is a signal corresponding to the carrier frequency, and the secret speech is added to it by the multiplier 8.
Multiplication (that is, modulation) by 1, a broken line section containing 2Δf created by multiplication of 1 and 2 in FIG. 6 and a solid line section that is its inverse are created. A low-pass filter 82 extracts the difference frequency signal and performs frequency correction (FIGS. 5 and 6). However, since the spectrum is inverted, it is inverted by the spectrum inversion circuit 83. By sampling this and inputting it to the descrambler 56, the frequency deviation can be removed.

Incidentally, in the second invention, as in the first invention, the sampling clock of the A/D converter 55 is outputted from the filter 62 at 2KHz (■ in FIG. 8) or divided/divided. The output multiplied by 4 by the multiplier 71 can be used. Alternatively, this clock may be extracted from the corrected secret signal.

〔Effect of the invention〕

As described above, according to the confidential communication system of the first invention, two pyro signals obtained by dividing the audio sampling frequency are used, a difference frequency signal with no frequency deviation is obtained from these signals, and a difference frequency signal with no frequency deviation is obtained from these signals. Since the sampling signal on the receiving side is used as a sampling signal on the receiving side, it is possible to eliminate clock synchronization deviation and decoding deterioration on the transmitting and receiving sides due to channel frequency deviation, which are problems in confidential communication.Furthermore, in the confidential communication method of the second invention, three By using a pilot frequency signal and using a difference frequency signal with no frequency deviation and another signal containing a frequency deviation on the receiving side, it is possible to remove the frequency deviation of the secret voice itself.

[Brief explanation of drawings]

Fig. 1 is a principle block diagram of the secret communication method according to the first invention, Fig. 2 is a principle block diagram of the secret communication method according to the second invention, and Fig. 3 is an implementation of the secret communication method according to the first invention. A circuit diagram showing an example; FIG. 4 is a diagram showing the relationship between the confidential voice and pilot signal according to the first invention; FIG. 5 is a circuit diagram showing an embodiment of the confidential communication system according to the second invention; is a diagram showing the relationship between the confidential voice and the pilot signal according to the second invention, FIG. 7 is a diagram showing a general confidential communication system, FIG. 8 is a diagram explaining scrambling processing, and FIG. 9 is a diagram showing the conventional confidential communication method. FIG. 2 is a block diagram showing a communication method. 1 and 2, 1.4 is a pilot insertion means, 2.5 is a pilot detection means, 3 is a clock regeneration means, 6 is a difference frequency generation means, 7 is a carrier frequency generation means, 8 is a correction means, It is. In the drawings, the same reference numerals indicate the same or corresponding parts. Patent Applicant: Fujitsu Ltd. Representative Patent Attorney Mori 1) Hiroshi (and 1 other person) Invention 1 of a secret communication system based on Ray Buried 2nd invention L - Confidential communication system related to 0 Atsushi Atsube 6 0 Is the figure, ground, figure, figure, figure, figure, secret story sound shown by the first explanation of the first explanation? Figure 4 shows the relationship between the pilot signal and 5. Figure 5.

Claims (6)

[Claims] (1) A transmitting side that samples and scrambles the audio to convert it into a confidential audio; a receiving side that samples the confidential audio, performs a descrambling process, and decodes it into an audio signal;
In the confidential communication system, the transmitting side is provided with pilot insertion means (1) which divides the sampling clock signal into first and second pilot frequency signals and adds them to the confidential voice, and the receiving side a pilot detecting means (2) for detecting the first and second pilot frequency signals, and generating a frequency signal of the difference from the first and second pilot frequency signals (fl, f2) to detect the confidential message. A confidential communication system characterized by comprising a clock reproducing means (3) for reproducing an audio sampling clock signal. (2) The clock regeneration means (3) includes a multiplier (31) that multiplies the first and second pilot frequency signals, and a bandpass filter (32) that extracts a difference frequency component resulting from the multiplication; 2. The confidential communication system according to claim 1, further comprising a multiplier (33) that multiplies the difference frequency component to reproduce a clock signal having the sampling frequency on the transmitting side. (3) a transmitting side that samples and scrambles the audio to convert it into a confidential audio; a receiving side that samples the confidential audio, performs a descrambling process, and decodes it into an audio signal;
In the confidential communication system, the transmission side divides the sampling clock signal into first and second pilot frequency signals and a third pilot frequency signal having a predetermined relationship with both the pilot frequency signals. pilot insertion means (4) for adding to the secret speech using a pilot signal; and pilot detection means (5) for detecting the first, second, and third pilot frequency signals (f1, f2, f3) on the receiving side. ), a difference frequency generating means (6) for generating a frequency signal of the difference from the first and second pilot frequency signals, and a carrier frequency from the difference frequency signal and the third pilot frequency signal (f3). A secret story characterized by comprising a carrier frequency generating means (7) for generating a signal, and a correction means (8) for extracting a difference frequency signal from the carrier frequency signal and the secret speech voice and providing it for the sampling. Communication method. (4) The difference frequency generating means (6) includes a multiplier (61) that multiplies the first and second pilot frequency signals (f1, f2), and a bandpass filter that extracts the difference frequency component resulting from the multiplication. (62) The confidential communication system according to claim 3, comprising: (5) The carrier frequency generating means (7) multiplies or divides the difference frequency so as to generate a carrier frequency from a predetermined relationship between the difference frequency signal and the third pilot signal (f3). a circuit (71), a multiplier (72) that multiplies the difference frequency signal and the third pilot signal (f3), and a bandpass filter (73) that extracts a carrier frequency signal that is the sum frequency component of the multiplication result. ), and the confidential communication method according to claim 3 or 4. (6) The correction means (8) includes a multiplier (81) that multiplies the carrier frequency signal and the secret speech, and a low-pass filter (81) that extracts a difference frequency signal resulting from the multiplication.
2) and a spectrum inversion circuit (83) for inverting the output of the filter (82).