JPH0361385B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a privacy device, particularly to a spectral rotation or inversion rotation type privacy device suitable for digital arithmetic processing.

(Prior art) Various confidential communication systems and devices have been proposed to maintain confidentiality in telephone line or wireless line communication, one of which is the division of the frequency spectrum of the audio signal to be transmitted into the required number of sections. There is an inverted rotation spectrum type in which these signals are rearranged or inverted in order and then transmitted.

Although this method has superior demodulated sound quality and is easier to implement as a circuit compared to other methods, it has the disadvantage that the strength of secret speech is reduced by simple reverse rotation.

For this reason, conventionally, for example, as shown in Japanese Patent Application No. 21148 of 1982 (Secret Communication Device) or Japanese Patent Application No. 59-44141 (Secret Communication Method and Apparatus), the inverted rotational frequency position of the spectrum is determined by a predetermined coded signal. Methods and devices have been proposed in which the privacy is improved by changing the rotation irregularly or by changing the inversion and inversion rotation equally irregularly.

According to this method, as long as the coded signal is not known, confidentiality will not be impaired, and furthermore, since a band filter, which is difficult to manufacture, is not required in the configuration of the device, it is also effective in reducing the cost of the device. effective.

In order to facilitate understanding of the present invention, the above-mentioned conventional confidential communication device will be briefly explained.

That is, as shown in b and a of the same figure, the audio spectrum subjected to the required band restriction is divided into two parts, and the local frequency of one half is set to m (m is the highest frequency of the audio spectrum), and the high-frequency components of the mixed output are extracted. The output obtained through the frequency conversion circuit 1 and the audio signal divided into two are added to obtain a spectrum signal in which two spectra in the same configuration are arranged adjacently, as shown in FIGS. This signal is further divided into two and routed through two routes connecting two multipliers with a low frequency filter in between, and the outputs are connected to an adder ADD and a subtracter SUB, and the addition/subtraction output is switched to a switch SW.
At the same time, two local signals having different frequencies are applied to one route through a 90° phase shifter and directly to the other route to the four multipliers. The local signal is added to the multiplier located before the low-pass filter, and the switch SW is configured to connect an individual code signal generator to irregularly change the local frequency and switching operation. shall be.

The spectral waveforms of each part in the confidential communication device configured in this way are as shown in Figure b.Detailed explanation of the operation will be omitted, but the resulting output waveforms are as shown in Figure C and D. The encoded signal consists of the inverted and rotated voice spectrum and the simply rotated voice spectrum, which exhibits complex changes in which the voice spectrum alternates irregularly. I can do it.

However, since the above-mentioned confidential communication device requires a total of 10 calculation elements, including 5 multipliers, 2 adders, and 3 waveformers, when this is digitally processed, there is a finite amount of noise that occurs in each calculation element. A problem arises in that the noise component increases as a result of the accumulation of rounding errors (also called truncation errors) caused by the registers. That is, in digital signal processing, the fewer these arithmetic processing elements as possible, the smaller the rounding error and the better the quality of the demodulated signal on the receiving side.

Furthermore, when performing digital signal processing, the processing time generally increases in proportion to the number of calculation elements, so the conventional secret communication device described above is disadvantageous in terms of real-time processing of signals.

(Object of the Invention) The present invention has been made in order to eliminate the drawbacks of the conventional secret communication device as described above. The purpose is to provide a shortened confidential communication device.

(Summary of the Invention) A first frequency conversion circuit that branches an audio signal whose highest frequency is limited to m into two, one of which outputs components with a local frequency of _m and _below m; ( _K < m) and outputs m or more.
and a mixing circuit with a local frequency of m are connected in series to one input terminal of the adder.
The local frequency of the other split audio signal is m
It is connected to the other input end of the adder via a second route in which a second mixing circuit that can switch between + _K and _K and a delay circuit that provides a predetermined delay are connected in series. Further, two switches, first and second, are provided between the stage before the delay circuit and a multiplier and a high frequency converter constituting the second frequency conversion circuit, and a second switch is provided before the delay circuit. Third and fourth switches are inserted between the input end of the first switch and the output end of the second switch, and between the input end of the second switch and the output end of the delay circuit, respectively. and the first of these four switches
and a second, a third, and a fourth set, and the local frequencies of the second frequency conversion circuit and the second mixing circuit are alternately switched while being synchronized with each other. Furthermore, _K out of the local oscillation frequencies
By temporally irregularly changing the frequency of the oscillator that generates _K Configure.

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

FIG. 1 is a block diagram showing one embodiment of the present invention.

In the figure, 2 is an audio signal input terminal, into which an audio signal with a maximum frequency limited to m is input, and this is branched into two, one of which is connected to the local output of an oscillator 3 with an oscillation frequency of m. The output is input to the first multiplier 4 as a signal and the cutoff frequency is
The signal is input to the second multiplier 6 via the first low frequency filter 5, which is set to m. Furthermore, a second oscillator 7 that oscillates by switching between _K and _K +m as a local signal is connected to the other input of the multiplier 6, and the output of the multiplier 6 is connected to the cut-off frequency via the switch _SW1 .
This output is inputted to a high frequency generator 8 having a frequency of m, and this output is inputted to a third multiplier 10 whose one input is the output of a third oscillator 9 that generates a frequency m. The output of 10 is connected to one input terminal of adder 11.

On the other hand, the other of the two-branched audio signal is input to a fourth multiplier 12, and the other input of the multiplier 12 is connected to a fourth oscillator 13 that switches and outputs _K +m and _K. , the output of the multiplier 12 is connected to the other input terminal of the adder 11 via a second switch SW ₂ and a delay circuit 14. Further, between the input terminal of the second switch SW ₂ and the output terminal of the first switch SW ₁ , and between the output terminal of the delay circuit 14 and the input terminal of the first switch SW ₁ , respectively. 3rd and 4th switch
SW ₃ and SW ₄ are connected cross-wise to each other, and among these four switches, the first and second switches and the third and fourth switches are each set as a set, and one of these two sets of switches is ON. The controller 15 controls the other switch so that the other switch is turned off. Further, the second and fourth oscillators 7 and 13 are controlled in time by the controller 15 in synchronization with the switching of the switches SW ₁ to SW ₄ so that one becomes _K and the other becomes _K + m. By making regular changes, a desired confidential speech spectrum is obtained at the output end 16 of the low frequency filter connected to the output end of the adder 11.

In addition, to further improve confidentiality, the local frequency _K
It is also possible to change the components over time.

The secret speech device constructed in this manner has two different circuit configurations depending on the operation of the switch and changes in the local frequency, and the ultimately obtained secret speech spectra are different.

The operation of these two circuit combinations will be explained separately for each case.

Figure 1b shows the state shown in Figure 1a, that is, SW ₁ and SW ₂ of the switches are ON and the other switches
FIG. 4 is a spectrum diagram showing the operation of each part when SW ₃ and SW ₄ are OFF.

First, b and a in the same figure are the original audio signals whose maximum frequency is limited to m, and one of the two halves is the first signal, which is composed of a multiplier 4, an oscillator 3, and a low-frequency wave generator 5.
The frequency conversion circuit generates a signal whose spectrum is inverted as shown in b and b of the same figure. Similarly, this signal is converted from K to m by a second frequency conversion circuit composed of a multiplier 6, an oscillator 7 that generates the frequency _K , and a high frequency converter 8, as shown in _b and c of the same figure. is formed into a missing spectrum, and further comprises a multiplier 10 and an oscillator 9 m.
As shown in Figures b and d of the same figure, the spectrum of C is symmetrically shifted and its reduction is lost, with the frequency zero as the base axis, and the signal is converted into a parallel-shifted signal, which is input to one of the inputs of the adder 11. It becomes a signal.

On the other hand, the other half of the audio signal is m+ _K
The spectral position is shifted by m+ _K as shown in FIG. After being adjusted so that they are at the same position, it becomes the other input of the adder 11, and its output produces a spectrum in which d and d are added together, as shown by the dotted line in the same figure, of which m is Only the spectrum shown by the solid line in the figure is extracted by the low-frequency filter with the cutoff frequency.

As is clear from the figure, the audio spectrum obtained in this way is a spectrum that is rotated and inverted at _K , and _{the K} changes irregularly over time.

Also, the connection state of the switches is reversed, that is, the first and second switches SW ₁ and SW ₂ are OFF, and the third,
The circuit configuration when the fourth switch is turned on is as shown in Figure 3a. In this case, the outputs of the local oscillators 7 and 13 become _K + m and _K , respectively, which is the opposite of the case in Figure 1. Therefore, the spectrum of each part at that time becomes as shown in figure b.

That is, FIG. 3a is a redrawn version of FIG. 1a for ease of understanding, and in this case, the delay circuit 14 is no longer involved in the operation.
In addition, both the first route and the second route have a configuration including one frequency conversion circuit and one mixing circuit.

The operation of the confidential communication device having such a configuration is as shown in FIG. A spectrum rotated in different _K can be obtained.

As explained above, according to this embodiment, the configuration of the privacy device is such that the inversion and rotation of the spectrum, as well as the rotation and inversion rotation position of the spectrum, can obtain an extremely highly confidential audio spectrum signal in which the rotation and inversion rotation positions of the spectrum change irregularly over time. Compared to the conventional system shown in FIG. 2, the number of calculation elements is one multiplier and one adder, two fewer in total, so that the rounding errors and calculation time can be reduced as described above.

In carrying out the present invention, it is not necessarily limited to the embodiments described above; for example, it is possible to use one oscillator with the same local frequency,
The local oscillation signals of _K and m may be provided by combining the oscillator outputs of _K and m.

Furthermore, although only the transmitting device is illustrated in the above-described embodiment, a receiving device can be realized with a substantially similar configuration.

In this case, it goes without saying that it is necessary to synchronize with the local frequency changed on the transmitting side.

(Effects of the Invention) Since the present invention is configured as described above, it has an extremely large effect in reducing rounding errors and shortening calculation time by reducing the number of calculation elements compared to the conventional confidential communication device. play.

[Brief explanation of drawings]

1A and 1B are a block diagram showing an embodiment of the present invention and a spectrum diagram explaining its operation; FIGS. 2A and 2B are spectral diagrams showing a conventional confidential communication device for obtaining the same confidential spectrum; Figure 3a
and b are a block diagram illustrating one state in the embodiment of the present invention shown in FIG. 1, and a spectrum diagram illustrating the operation at that time. 1... Frequency conversion circuit, 2... Audio signal input terminal, 3, 7, 9 and 13... Oscillator, 4, 6, 1
0 and 12... multiplier, 5, 8 and 16... wave unit, 11... adder, 15... controller. SW ₁ ~
SW ₄ ...Switch.

Claims (1)

[Claims] 1. A first method that divides the input signal into two and extracts frequency components of m or less from one of the two halves, with the local frequency being m.
frequency conversion circuit, and the local frequencies are _K and _K +
( _K < m) and
A second frequency conversion circuit that extracts m or more and a mixing circuit that has a local frequency of m are connected in series and are supplied to one input terminal of the adder, and the other of the two divided audio signals is supplied to one input terminal of the adder. The other input terminal of the adder is connected to the other input terminal of the adder via a second route in which a second mixing circuit whose local frequency can be switched to both m+ _K and _K and a delay circuit which provides a predetermined delay are connected in series. and first and second switches are respectively injected between the delay circuit and the output terminal of the second mixing circuit and between the multiplier and the high frequency converter constituting the second frequency conversion circuit. and third and fourth switches between the input end of the first switch and the output end of the second switch, and between the input end of the second switch and the output end of the delay circuit, respectively. are inserted, and these four switches are set as a first and second switch and a third and fourth switch, and each set is opened and closed mutually, and the second switch is synchronized with the opening and closing timing of these switches.
By switching one of the local frequencies of the frequency converter circuit and the second mixing circuit so that m+ _K and the other are _K , a low frequency signal having a cutoff frequency of m is connected to the output terminal of the adder. 1. A secret communication device characterized in that a desired secret communication signal is outputted through a wave transmitter. 2. Opening and closing of the two sets of switches and switching of the local frequencies of the second frequency conversion circuit and the second mixing circuit are controlled by a predetermined coded signal that changes irregularly over time. A secret communication device according to claim 1, characterized in that: 3. The confidential communication device according to claim 1 or 2, characterized in that the _K component of the local frequency is also changed irregularly over time.