JPH0446026B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a transmission device for a confidential audio signal.

In general, in wireless communication, the recipient cannot be restricted in principle, so for communications that require secrecy or communications established under a specific contract between the sender and receiver, confidential communication methods using encryption are used. It is valid.

The confidential communication method can be roughly divided into two types: a method in which scrambling is performed on the frequency axis, and a method in which scrambling is performed on the time axis.

The former method includes (1) inverting the frequency, and (2) dividing the audio signal into multiple frequency slots on the frequency axis and replacing these slots according to predetermined rules. , a method of inverting the frequency within one slot, a method of (3), a method of changing the switching rule of the above (2) over time, etc.

Also, as belonging to the latter method, (4), a method of changing the polarity of the sample value of an audio signal according to a certain rule, and (5), a method of dividing the audio signal into frames temporally and changing the sample value within one frame. Method (6): Divide the audio signal into frames as in (5) above, but do not change the order of sample values within one frame, but change the order of frames within several frames. There are methods etc.

However, all of the conventional methods described above have various drawbacks as described below. In other words, in method (1), secrecy is very low in that it can be decoded if the receiver has the same demodulator, and in method (2), the number of slots is not too large in terms of circuit scale. Since it is not possible, confidentiality is low. In method (3), as in method (2) above, the number of bandpass filters for dividing into multiple frequency slots is included as many as the number of slots, but the narrower the slot bandwidth, the lower the time response. You will end up subtracting . Therefore,
If the slot replacement order is changed, a large amount of noise will be introduced near the end of the frame because the effect of the order replacement in the previous frame remains in the descrambling process. In addition, in methods (4) and (5), the scrambled signal becomes close to white noise and has a wider band than the original audio signal, so if it passes through a band-limited transmission path, distortion may occur in the descrambled audio. There are some drawbacks. Furthermore, in the method (6), the sample value within one frame does not change, so the bandwidth is less widened, and the distortion during descrambling is smaller than in the method (5) above. If you try to improve the confidentiality of the conversation, it is necessary to increase the number of frames to be replaced, which increases the delay during communication.

This invention was made in view of the above points, and has a method of frequency shifting the sound, which has higher confidentiality than the above-mentioned conventional method, and also improves the quality of the sound because it is not divided into slots and there is no joint. To provide a transmission device for a voice confidential signal, which further improves voice privacy without impairing the communication quality.

Hereinafter, one embodiment of the present invention will be described in detail based on FIGS. 1 and 2.

FIG. 1 shows an example of the encoder side of the transmission device used in the present invention.
2 is an input terminal to which an audio signal is supplied; 2 is a phase shift circuit network to which the audio signal is supplied from the input terminal 1; Output signal e.g. 0° output signal and -
A 90° output signal is taken out. Reference numerals 3 and 4 are balanced mixers, and one input terminal is supplied with the above-mentioned 0° output signal and -90° output signal, and the other input terminal is supplied with a frequency of ₀ and a phase of Two SSB carrier signals different from each other (0° and -90°) are supplied. These ₀ (0°), ₀ (−90°)
The SSB carrier signal is obtained by dividing the clock frequency _C from the clock generator 5 to 1/N0 by the frequency divider 6 to obtain a frequency of ₄₀ , and then dividing the _clock frequency C from the clock generator 5 to 1/4 by the frequency divider 7.
It is created by dividing the frequency into Therefore, the frequency divider 6 has a frequency division ratio 1/N ₀ set in advance to a predetermined value so that a frequency of ₄₀ is obtained on its output side.

8 is an adder that adds the output signals of the mixers 3 and 4, and 9 is a band waver to which the output signal of the adder 8 is supplied. signal components are removed, and only the LSB wave signal components are extracted at the output side. This LSB wave signal is supplied to one input end of the balanced mixer 10, and the other input end of this mixer 10 is supplied with a frequency shifting carrier signal having a frequency of ₁ or ₂ , which will be described later.

The carrier signals ₁ and ₂ , which are FSK waves, are created as follows. That is, the clock frequency _C from the clock generator 5 is divided to 1/N ₁ by the frequency divider 11 to obtain a signal with a frequency of 2 ₁ on the output side, and the frequency is divided to 1/N ₂ by the frequency divider 12. After dividing the frequency into 2 to obtain a signal with a frequency of 2 ₂ on the output side, these signals are switched by a switching circuit 13 to obtain an FSK wave.
This FSK wave is further supplied to a frequency divider 14, where the frequency is divided into 1/2. Therefore, carrier signals ₁ and ₂ , which are FSK waves, are obtained at the output side of the frequency divider 14, and these signals are supplied to the other input terminal of the mixer 10.

The switching circuit 13 is switched by a switching control signal K from a code generator 15. For example, K is 0
When K is 1, the switching circuit 13 is connected to the contact a side and outputs a 2 ₁ signal to its output side, while when K is 1, the switching circuit 13 is switched to the contact b side and outputs a 2 ₂ signal to its output side. It is designed to output a signal of. On the input side of the code generator 15, a frequency divider 16 divides the clock frequency _C of the clock generator 5 into 1/1.
A clock signal of _K divided by N _K is supplied.
On the other hand, the code key 17 is configured to set the switching control signal K to the code generator 15 in advance, so that when the clock signal from the frequency divider 16 is input, the code set by the code key 17 is set. Accordingly, a switching control signal K is supplied to the switching circuit 13,
A switching operation as described above is performed.

By mixing the carrier signals ₁ and ₂ , which are the FSK waves obtained in this way, with the output signal from the bandpass filter 9, that is, the LSB wave, in the mixer 10,
Substantially, the LSB wave is modulated by carrier signals ₁ and ₂ , and by passing the output of this mixer 10 through a low frequency filter 18, an audio scramble signal _S0 is extracted at its output side. This audio scramble signal is supplied to one input terminal of an adder 19, and the other input terminal of this adder 19 is supplied with a frequency _P
A synchronization carrier signal is supplied. This synchronization carrier signal is created as follows. That is, the clock frequency _C of the clock generator 5 is divided by 1/N _P by the frequency divider 20 to generate a synchronizing carrier signal of _P. This _P synchronization carrier signal is supplied to one input terminal of the AND circuit 21, and the synchronization signal generator 22 generates the synchronization signal S in synchronization with the clock of the clock generator 5. is supplied to the other input terminal of the AND circuit 21, the synchronization carrier signal is switched at _P using this synchronization signal S, and _P is supplied to the output side of the AND circuit 21.
The synchronizing carrier signal is taken out and supplied to the other input terminal of the adder 19. In addition, the synchronization signal generator 2
The synchronization signal S from 2 is also supplied to the code generator 15 for reset purposes. Therefore, output terminal 2
3, a scrambled audio signal S' ₀ to which _{a P} synchronization carrier signal is added is output.
This scrambled audio signal is transmitted using any transmission method. Furthermore, the frequency divider 11,1
2, 16 and 20 frequency division ratios 1/N ₁ , 1/N ₂ ,
1/N _K and 1/N _P are set in advance so that predetermined frequencies are respectively extracted corresponding to the clock frequency _C of the clock generator 5.

Next, the operation of this embodiment will be explained. Now, when the audio signal E _A(t) =Acosat is input to the input terminal 1, this signal is supplied to the phase shift network 2, and the phase shift network 2
Signals expressed by the following equations are taken out from the output side of each.

E _AI(t) = Acosat...(1) E _AQ(t) = Asinat...(2) In other words, equation (1) is the output signal with a phase of 0°, and equation (2) is the output signal with a phase of -90°. It's a signal.

On the other hand, the clock frequency _C is divided into 1/ _4N0 and supplied to mixers 3 and 4, respectively, ₀ (0°) and ₀ (-
90°) SSB carrier signal is expressed by the following formula.

E _CI(t) = cosω ₀ t ...(3) E _CQ(t) = sinω ₀ t ...(4) Therefore, mixer 3 receives the signals expressed by equations (1) and (3) above. Meanwhile, the mixer 4 is supplied with the signals expressed by the above equations (2) and (4), respectively.
Then, a signal expressed by the following equation is taken out at the output side of the mixers 3 and 4.

E _AI(t)・E _CI(t) = A/2 {cos(ω ₀ +a)t+cos(ω ₀
−a)t}……(5) E _AQ(t)・E _CQ(t) =−A/2{cos(ω ₀ +
a) t + cos (ω ₀ - a) t}...(6) The signals expressed by equations (5) and (6) are supplied to the adder 8 and added, and then passed through the band waver 9. On the output side, there is an LSB as expressed by the following formula.
You get waves.

[LSB]=Acos(ω ₀ −a)t (7) This LSB wave is supplied to one input end of the mixer 10.

On the other hand, the clock frequency _C from the clock generator 5
The signals of frequencies 2 ₁ and 2 2 obtained by dividing the signal into 1/N ₁ and 1/N ₂ by frequency dividers 11 and ₁₂ , respectively, are switched by a switching circuit 13 to obtain an FSK wave. This switching circuit 1
3 is based on the clock frequency _C from the clock generator 5 divided by 1/N _K by the frequency divider 16, and the code signal K generated by the code generator 15 according to the key code is sent to the switching circuit. 13
Supply and switch. For example, when K=0, 2 ₁ signals are selected, and when K=1, 2 ₂ signals are selected.

Then, the frequency of the selected 2 ₁ and 2 ₂ signals is divided by 1/2 by a frequency divider 14 and supplied to one input terminal of the mixer 10 as a carrier signal for frequency shifting. If the carrier signal supplied to one input end of the mixer 10 at this time is E _CS(t) , then this
E _CS(t) is expressed by the following formula.

E _CS(t) = (1-K) cosω ₁ t + Kcosω ₂ t (8) However, in the above equation (8), the relationships among ω ₀ , ω ₁ , and ω ₂ are selected as follows.

Δω _S =ω ₁ +ω ₂ /2−ω ₀ , Δω _K =ω ₂ −ω ₁ /2, Δ
ω _S > Δω _K Therefore, the signal from the bandpass filter 9, i.e.
A signal expressed by the following equation is obtained at the output side of the mixer 10 to which the LSB wave and the frequency shift carrier signal from the frequency divider 14, that is, the FSK wave are supplied.

[LSB]・E _CS(t) = A/2 [(1-K) {cos(ω ₀ + ω ₁
−a)t+cos(ω ₁ −ω ₀ +a)t}+K{cos(ω ₀ +
ω ₂ −a)
t+cos(ω ₂ −ω ₀ +a)t}] ...(9) When this obtained signal is passed through the next-stage low-frequency wave generator 18, the output side is an audio scramble signal S as shown by the following equation. ₀ is obtained.

S ₀ =A/2{(1-K)cos(Δω _S −Δω _K +a)t+K
cos(Δω _S +Δω _K +a)t}...(10) Next, the clock frequency _C from the clock generator 5
is divided into 1/N _P by the frequency divider 20, and the synchronizing carrier signal _P obtained is switched and taken out by the synchronizing signal S from the synchronizing signal generator 22 in the AND circuit 21, and then sent to the other side of the adder 19. , and is added to the audio scramble signal S ₀ supplied from the low frequency converter 18 to one input terminal of the adder 19 . Therefore, at the output side of the adder 19, that is, at the output terminal 23, a scrambled audio signal _S'0 as expressed by the following equation is taken out.

S' ₀ = A/2 {(1-K)cos(Δω _S −Δω _K +a)t
+Kcos(Δω _S +Δω _P +a)t}+S・cosω _P t……(
11) Figure 2 shows an example of the decoder side of the transmission device used in this invention.
32 is an input terminal to which a scrambled audio signal is supplied; 32 is a sync separation circuit for separating a synchronization carrier signal added to the scrambled audio signal; 33 is a sync separation circuit 30 connected to one input terminal; This is a balanced mixer to which a scrambled audio signal is supplied and the other input terminal is supplied with _{an O} SSB carrier signal. _O 's SSB
The carrier signal for the encoder is created in the same way as in the encoder described above. That is, the clock frequency _C from the clock generator 34 is divided by the frequency divider 35 to 1/4N ₀ (substantially corresponding to the product of the division ratios of the frequency dividers 6 and 7) and is used for the SSB of _O. Obtain the carrier signal. still,
The clock frequency _C of the clock generator 34 is made to exactly match the clock frequency _C of the clock generator 5 of the encoder, for example.
The clock frequency accuracy is said to be around 50ppM. The output of the mixer 33 is supplied to a bandpass filter 36,
Only the USB component is taken out on the output side.

Incidentally, this SSB may be created using a phase shift circuit or the like as in the above-mentioned encoder.

The output of the band wave generator 36 is sent to the balanced mixer 3
7, and the other input terminal of this balanced mixer 37 is supplied with an encoder as well.
Frequency shifting carrier signals ₁ and ₂ , which are FSK waves, are supplied.

This frequency shift carrier signal is created in the same manner as the encoder. That is, the clock generator 34
_The clock _{frequency C} from
2 ₁ and 2 ₂ signals are taken out, these 2 ₁ and 2 ₂ signals are switched and taken out by the switching circuit 40, and the frequency is divided into 1/2 by the frequency divider 41, and ₁ or 2 is output on the output side.
_2. Extract the carrier signal for frequency shift. The switching of the switching circuit 40 is also performed in the same manner as the encoder. That is, the clock frequency _C of the clock generator 34 is divided by 1/1 by the frequency divider 42.
After the frequency is divided into N _K , it is supplied to the code generator 43 as a clock signal _K , and the code generator 43 sends a switching control signal K to the output side of the code generator 43 according to the code preset by the code key 44. is taken out, and the switching circuit 4 is controlled by this switching control signal.
Switch 0. For example, when K is 0, the switching circuit 40 is connected to the contact a side and takes out the output of the frequency divider 38, that is, the 2 ₁ signal, while when K is 1, the switching circuit 40 is connected to the contact b side. It functions to take out the output of the frequency divider 39, that is, the ₂₂ signal. Note that this switching control signal K is synchronized with the transmitting side. That is, the synchronous separation circuit 3
_{The P} synchronization carrier signal separated in step 2 is supplied to a comparator 45 and compared with a reference value, and then supplied to a synchronization signal generator 46.
A synchronizing signal S is generated from. This synchronizing signal S is supplied to frequency dividers 38, 39, and 42, and is also supplied to a code generator 43 as a reset signal. This code generator 43
The reset signal supplied to determines when the switching control signal K starts.

The frequency shift carrier signals ₁ and ₂ obtained in this way are sent to the USB from the bandpass converter 36.
It is supplied to the mixer 37 along with the waves. The output of the mixer 37 is then supplied to an output terminal 48 through a low frequency amplifier 47, and a descrambled audio signal is taken out at the output terminal 48.

Next, the operation of this decoder will be explained. Now, the input terminal 31 is supplied with an input signal as expressed by equation (11) above, and this signal is separated into a scrambled audio signal that becomes a synchronization carrier signal _P in the synchronization separation circuit 32. Ru. This separated scrambled audio signal is sent to the mixer 3.
The SSB carrier signal _O produced as described above is supplied from the frequency divider 35 to the other input terminal of the mixer 33. Therefore, the output side of the mixer 33 is the output obtained by multiplying the above equation (10) by cosω ₀ t, that is, A/2{(1-K)cos(Δω _S −Δω _K +a)t+Kcos
(Δω _S +Δω _K +a)t}・cosω ₀ t=A/4 [(1-
K) {cos
(ω ₀ +Δω _S −Δω _K +a)t +cos(ω ₀ −Δω _S +Δω _K −a)t}+K{cos(ω ₀ +
Δω _S +Δω _K +a)t+cos(ω ₀ −Δω _S −Δω _K −a)
t}]...
...(12) The output expressed as is retrieved. When this output is passed through the bandpass filter 36, only the USB component expressed by the following equation is extracted at its output side.

[USB]=A/4{(1-K)+cos(ω ₀ +Δω _S −Δω
_K + a) t + K・cos (ω ₀ + Δω _S + Δω _P + a) t}...
…
(13) The output signal of this band wave generator 36 is sent to the mixer 37.
while the mixer 37
₁ and ₂ frequency shift carrier signals selectively extracted as described above are supplied to the other input terminal of the . Assuming that the output from the frequency divider 41 supplied to the other input terminal of the mixer 37 is E _CS ', this E _CS ' is expressed as follows.

E _CS ′ _(t) = (1-K) cosω ₁ t + Kcosω ₂ t ... (14) Therefore, on the output side of the mixer 37, the product of the output of the bandpass filter 36 and the output from the frequency divider 41, that is, the following equation The signal is extracted as shown in .

[USB]・E _CS ′ _(t) = A/4 [(1-K) ² /2 {cos(
ω ₁ +ω ₀ +Δω _S −Δω _K +a)t+cos(ω ₀ +ω ₁ +Δ
ω _S −Δω _K +a)
t} +K ² /2{cos(ω ₂ +ω ₀ +Δω _S −Δω _K +a)t+cos
(ω ₀ −ω ₂ +Δω _S +Δω _K +a)t}]...(15) Then, when the output of this mixer 37 is passed through the wave reducer 47, the output terminal 48 has a signal expressed by the following equation. The scrambled signal or original audio signal is retrieved.

[[USB]・E _CS ′ _(t) ] _LPF = A/8 {(1-K) ²・cos
(ω ₀ −ω ₁ +Δω _S −Δω _K +a)t+K ²・cos(ω ₀ −ω
₂ +Δω _S −
Δω _K +a)t} ...(16) Here, ω ₀ −ω ₁ =−(Δω _S −Δω _K ), ω ₀ −ω ₂ =
−(Δω _S +Δω _K ), the above equation (16) is expressed by the following equation.

[[USB]・E _CS ′ _(t) ] _LPF = A/8 {(1-K) ²・cos
at+K ² cosat}=A/4cosat...(17) Here, the band expands by (Δ _S + Δ _K ), but this spread is about 10%, which is sufficient for privacy, and a relatively narrow band privacy system can be realized. .

As described above, according to the present invention, an audio signal to be transmitted is frequency-shifted and polarized based on a preset frequency change rule, and a synchronization signal is generated and added for transmission. The signal is received, the polarized audio signal and the synchronization signal are separated, and the original signal is obtained by multiplying this polarized audio signal with a carrier signal having the same frequency changing rule as that used during transmission. Since the audio signal is demodulated and the timing of changing the frequency of this carrier signal is set based on the synchronization signal, the audio confidential signal can be easily demodulated. In this case, according to the transmission device of the present invention, the frequency change rule for changing the frequency of the carrier signal is changeably coded, and this change rule can be selected by key operation. The changed rules can be easily set and changed on both the transmitting side and the receiving side, and the changing rules can be easily set according to the call status, and further voice privacy can be achieved.

In addition, in the above embodiment, the case where scrambling is performed with binary ( ₁ , ₂ ) FSK waves was explained.
The frequency division ratio of the frequency divider may be changed, that is, the frequency divider may be made into a variable frequency divider, and the frequency division ratio may be changed using a multi-value FSK wave.

Further, in the above-described embodiment, a case has been described in which the synchronization signal is added to the audio signal, but for example, when combining with the video signal and performing scrambling, the periodic signal of the video signal may be used.

Furthermore, in the above embodiment, the LSB is calculated by multiplying the audio signal and the _O SSB carrier signal on the encoder side.
On the decoder side, the signal is obtained by multiplying the audio scramble signal and the SSB carrier signal, which is almost the same as _O above.
I explained about the case where the USB wave is obtained, but conversely, the encoder side obtains the USB wave, and the decoder side obtains the USB wave.
The LSB wave may also be obtained.

[Brief explanation of drawings]

FIG. 1 is a system diagram showing an embodiment of an encoder used in the present invention, and FIG. 2 is a system diagram showing an embodiment of a decoder used in the invention. 2 is a phase shift network, 3, 4, 10, 33, 37 is a balanced mixer, 5, 34 is a clock generator, 6, 7, 11, 12, 14, 16, 20, 3
5, 38, 39, 41, 42 are frequency dividers, 8, 19
is an adder, 9 and 36 are band wave generators, 13 and 40 are switching circuits, 15 and 43 are code generators, and 17 and 4 are
4 is a code key, 18, 47 is a wave reducer, 2
2 and 46 are synchronization signal generators, 32 is a synchronization separation circuit, and 45 is a comparator.

Claims (1)

[Claims] 1. A lower sideband (LSB) wave or an upper sideband (USB) wave is formed by the product of an audio signal and a carrier signal of a predetermined frequency, and the frequency is changed based on a predetermined frequency change rule. forms a carrier signal whose frequency is changed as appropriate, and the product of the lower sideband (LSB) wave or upper sideband (USB) wave and the carrier signal whose frequency is changed as appropriate based on the predetermined frequency change rule. Thus, a voice confidential message signal is formed, a synchronization signal is added to the voice confidential message signal and transmitted, and the transmitted voice confidential message signal is received, the synchronization signal and the voice confidential signal are separated, and the voice confidential message signal is transmitted. Demodulating the original audio signal by multiplying the confidential signal and a carrier signal whose frequency is appropriately changed according to the frequency change rule, and changing the frequency of the carrier signal for the product with the received confidential signal. A transmission device for a voice confidential signal whose timing is set based on the received synchronization signal, wherein a plurality of types of frequency change rules are prepared in advance in the setting means on the transmitting side and the receiving side where the frequency change rules are set. A transmission device for audio confidential signals, in which a desired change rule is selected from among the plurality of types of frequency change rules by operating a predetermined key.