JPH0153948B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a confidential communication device, for example, in a communication device such as a cordless telephone device,
Concerning what made secret communication possible.

Conventionally, confidential communication methods in various communication devices are as follows:
A complex modulation method is used depending on the degree of confidentiality.
The modulation frequency is also high, and the frequency band tends to be wide.

For example, in conventional phase modulation methods, the modulation frequency is set at 10 to 30kHz, requiring a fairly wide exclusive band.

It is inappropriate to use such a confidential communication method in a simple communication device such as a cordless telephone device from the standpoint of effectively using the frequency allocation range.

By the way, in a cordless telephone device, a base unit is installed adjacent to a telephone set, and one or more handset units are installed in response to the base unit, and the handset allows the telephone to receive and send calls from the telephone. This is done at a remote location. That is, in such a cordless telephone device, it is sufficient to communicate confidentially with another person's adjacent telephone.

For this reason, the phase of the audio signal is alternately inverted at predetermined time intervals in synchronization with a synchronizing pulse with a repetition frequency below the low frequency of the audio signal frequency, or with a zero cross point that is the intersection of the audio signal and the reference level. A phase inversion method that enables confidential communication has been proposed.

Therefore, an object of the present invention is to provide a confidential communication device that uses encryption processing using such phase inversion to improve the reliability of confidential communication.

That is, the confidential communication device of the present invention includes a transmitter that selectively inverts the phase of an audio signal in synchronization with a synchronization signal and transmits an audio signal having a phase inversion section together with the synchronization signal; In the confidential communication device, the transmitting unit includes a reception unit that inverts the phase of the phase inversion section of the audio signal in synchronization with the signal and reproduces the audio signal of normal phase. a comparator that compares the signal with a reference level set within the amplitude range;
A first pulse generation circuit generates a first pulse in response to the output of the comparator, and a second pulse generation circuit generates a second pulse in response to the first pulse generated by the first pulse generation circuit. a pulse generating circuit; a logic circuit that forms the synchronizing signal of two levels, high and low, with different high level time and low level time from the first and second pulses; and the high level time or the low level of the synchronizing signal. a first phase inverter for selectively inverting the phase of the audio signal over time, the receiving unit inverting the phase of the phase inversion section of the audio signal in synchronization with the received synchronization signal; and second phase inverting means for reproducing the audio signal of normal phase.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 1 shows an embodiment of the transmitting section in the confidential communication device of the present invention, and FIG. 2 shows an embodiment of the receiving section in the confidential communication device of the present invention.

In FIG. 1, audio input from a microphone 2 is amplified by an amplifier 4 and then applied to a synchronization signal generation circuit 6 and also to a phase inverter 8 as a first phase inverter. The synchronization signal generation circuit 6 synchronizes with a zero cross point, which is the intersection of the audio signal and a reference level set within the range of the audio signal amplitude, and also makes the high level time and the low level time different by a fixed ratio. Generates a synchronization signal.

The synchronization signal generation circuit 6 includes a low-pass filter 10,
Comparator 12, differentiation circuit 14, waveform shaping circuit 16,
A T flip-flop circuit 18 as a first pulse generation circuit, a T flip-flop circuit 20 as a second pulse generation circuit, and a logic circuit.
An AND circuit 22 is installed. The low-pass filter 10 removes high-frequency components from the audio signal components,
The comparator 12 compares the audio signal from which the high-frequency components have been removed with a reference level, and the comparison output is differentiated by the differentiator 14. The differential waveform is shaped by a waveform shaping circuit 16, and in response to this output, a first pulse synchronized with the zero-crossing point of the audio signal is formed from a T flip-flop circuit 18. This pulse is applied as a trigger input to the T flip-flop circuit 20 to obtain a second pulse of twice its period. These first and second pulses are applied to an AND circuit 22 that forms a synchronizing signal in which the high level time and the low level time are different, and the high level time and the low level time are different depending on the logical product of the two. A two-level synchronization signal is obtained.

This synchronization signal is applied to the phase inverter 8 and also to the FS modulator 24.
Then, the phase of the audio signal is selectively inverted during the high level time in synchronization with the synchronization signal. Further, in response to the synchronization signal, the FS modulator 24 obtains an FS signal (f±Δf) having a frequency deviation Δf with respect to the reference frequency f.

The signal combiner 26 combines the phase inverted output and the FS signal to obtain a combined signal. This composite signal is applied to the FM modulator 28, and the FM modulator 28
In this case, a transmission signal is generated by subjecting a carrier wave made of a high frequency signal to frequency modulation using a composite signal.
This transmission signal is transmitted from the antenna 30 toward the receiving section.

Next, in FIG. 2, the transmission signal from the transmitter is received by the antenna 32 of the receiver, demodulated by the FM demodulator 34, and then sent to the synchronization signal detection circuit 36 and notch filter 38 for detecting the synchronization signal. It is being

The synchronization signal detection circuit 36 detects a synchronization signal from the demodulated output of the FM demodulator 34, and is composed of a tone synchronization circuit 40 and an FS modulator 42. That is, the tone synchronization circuit 40 detects the FS signal, and this FS signal is applied to the FS demodulator 42. In the FS demodulator 42, a synchronization signal is detected from the frequency deviation of this FS signal, and this synchronization signal is used as a second synchronization signal.
is added to a phase inverter 44 as phase inverting means.

On the other hand, the demodulated output from which the FS signal component has been removed by the notch filter 38 is applied to the phase inverter 44, which inverts the phase of the phase inversion section of the demodulated output and converts it into a normal phase, and after being amplified by the amplifier 46, added to speaker 48.

Based on the above configuration, its operation will be explained in detail with reference to FIG.

FIG. 3A shows a signal waveform obtained by amplifying the output signal of the microphone 2 with the amplifier 4, and the high-frequency vibration component of this signal waveform is removed by the low-pass filter 10, as shown in FIG. 3B. is added to comparator 12. A reference level V _REF is set in the comparator 12, and the intersection of this reference level V _REF and the audio signal shown in FIG. 3B is detected, the output is inverted, and the pulse shown in FIG. 3C is generated. When this pulse is differentiated by the differentiating circuit 14, the pulse shown in FIG. 3D is obtained, and when this pulse is waveform-shaped by the waveform shaping circuit 16 and the negative component is inverted, the pulse shown in FIG. 3E is obtained. . Using this pulse as a trigger input, T
When added to the flip-flop circuit 18, FIG.
A first pulse shown in FIG. 3G is generated, and when this pulse is applied to the T flip-flop circuit 20, a second pulse shown in FIG. 3G is generated. That is, the second pulse has a period twice that of the first pulse. By adding these first and second pulses to the AND circuit 22 and performing a logical product, a synchronization signal shown in FIG. 3H is obtained. This synchronization signal has a ratio of three times the low level time to the high level time from the first and second pulses.

When this synchronization signal is applied to the phase inverter 8, its output becomes as shown in FIG. 3I, the high level time of the synchronization signal is inverted, and the inversion timing becomes the zero cross point.

Further, the FS modulator 24 adds the synchronization signal to generate the FS signal shown in FIG. 3K having a frequency deviation corresponding to the synchronization signal. The microphone and the audio signal with phase inversion are combined, and the combined signal is modulated by the FM modulator 28 and then transmitted from the antenna 30 as a transmission signal.

When this transmission signal is received by the antenna 32,
It is demodulated by the FM demodulator 34. This signal is applied to the tone synchronization circuit 40 of the synchronization signal detection circuit 36, which detects the FS signal, and the FS demodulator 42 demodulates the synchronization signal shown in FIG. 3H from this signal. , are added to the phase inverter 44.

On the other hand, the demodulated output applied to the notch filter 38 has its FS signal component removed, and is shown in FIG.
As shown in , only the audio signal component without the FS signal component is extracted. Then, the phase of the phase inversion section is inverted by the synchronization signal in the phase inverter 44,
As shown in FIG. 3A, the signal is converted into a normal phase audio signal. This audio signal is amplified by an amplifier 46 and then reproduced by a speaker 48.

With this configuration, since the phase inversion timing of the audio signal is set at the zero-crossing point of the audio signal, the frequency component at the time of phase switching can be minimized, transmission distortion can be suppressed, and the high level of the synchronization signal can be minimized. The ratio of level time to low level time is 1
Since the signals are made to differ in the ratio of 3, the ratio of phase inversion of the audio signal is different, and the degree of secrecy can be increased.

In addition, in the example, the high level time and low level time are set to 1/3, but n/m (m, n is m≠
The degree of privacy can be further increased by setting the ratio to n (assuming that both are integers) or by periodically changing the ratio.

As explained above, according to the present invention, the high level time and the low level time differ depending on the combination of the first and second pulses, which have different high level times and low level times with respect to the zero crossing point of the audio signal. A two-level synchronization signal, high and low, is formed, and this synchronization signal is used to invert the phase of the audio signal at the high-level time or low-level time and perform encryption processing, so transmission distortion at the time of phase switching can be suppressed. In addition, the distribution ratio of the phase inversion section and the normal phase section of the audio signal can be made different, and the reliability of confidential communication can be improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the transmitting section of the confidential communication device of the present invention, FIG. 2 is a block diagram showing an embodiment of the receiving section of the confidential communication device of the present invention, and FIG. 3 is similar to FIG. FIG. 3 is a diagram showing operational waveforms of the transmitting section of the private communication device shown in FIG. 2 and the receiving section of the private communication device shown in FIG. 2; 6... Synchronization signal generation circuit, 8... Phase inverter (first phase inverter), 12... Comparator, 18...
...T flip-flop circuit (first pulse generation circuit), 20...T flip-flop circuit (second pulse generation circuit), 22...AND circuit (logic circuit), 44...phase inverter (second phase inverter) means).

Claims (1)

[Claims] 1. A transmitting unit that selectively inverts the phase of an audio signal in synchronization with a synchronization signal and transmits an audio signal having a phase inversion section together with the synchronization signal, and a transmission unit that is synchronized with the received synchronization signal. and a reception unit that inverts the phase of the phase inversion section of the audio signal to reproduce the audio signal of normal phase, the transmission unit comprising: a comparator that compares the output with a reference level set within the range; a first pulse generating circuit that generates a first pulse according to the output of this comparator; a second pulse generating circuit that generates a second pulse in response to the first pulse; and forming the synchronization signal of two levels, high and low, with different high and low level times from the first and second pulses. The receiver includes: a logic circuit; and a first phase inverter that selectively inverts the phase of the audio signal at the high level time or the low level time of the synchronization signal; a second phase inversion means for inverting the phase of the phase inversion section of the audio signal in synchronization with the phase reversal period of the audio signal to reproduce the audio signal having a normal phase.