JPH07118689B2 - Confidential communication device - Google Patents

Description

DETAILED DESCRIPTION [Outline] In an angle modulation communication device, angle modulation and n-phase modulation are applied to a transmission signal, and secondary modulation is performed by n-phase modulation to prevent eavesdropping and narrow-angle modulation. This makes it difficult to capture a radio signal due to weak power consumption due to the above, and gives a secret communication characteristic.

[Industrial application field]

The present invention relates to a wireless communication device that can be used, for example, in a simple home cordless telephone.

It is desired that such a wireless communication device consumes less power, generates a weak electric field, and is configured as a simple device.

Further, since it is a wireless communication device, it is desirable to have a configuration that makes it difficult to eavesdrop on communication contents.

[Conventional technology]

Conventionally, in order to generate a weak radio wave, a narrow band frequency modulation communication device as shown in FIG. 5 has been used.

In the figure, a voice signal is input from a transmitter 1 to a transmitter and is transmitted to a narrow band frequency modulator 3 via a transmission voice processing circuit 2 including a differentiating circuit 201, a low frequency amplifying circuit 202 and an instantaneous amplitude limiting circuit 203. And frequency modulation is performed. The modulated audio signal is emitted from the antenna 4 as a radio frequency.

Further, the radio wave received from the antenna 5 is discriminated by the frequency discriminator 8 after passing through the narrow band filter 6 and the amplitude limiting amplifier 7 after frequency conversion, and the demodulated signal is a reception voice provided with the integrating circuit 91 and the low frequency amplifier 92. Handset via processing circuit 9
Given to 10.

Basically, the communication partner is identified by the radio channel frequency. For example, if a wireless channel, that is, a wireless frequency of 150.025MHz is allocated to the company A and 150.050MHz is allocated to the company B, the wireless channels are different from each other. Depending on the company's wireless device, it becomes impossible to hear the communication contents.

In addition, it is possible to limit a receivable distance by using a weak radio wave as a radio frequency.

However, if a general FM receiver is used, the volume is low, but reception is possible, and the confidentiality is not satisfactory.

As shown in FIG. 6, there is a system in which a radio channel frequency and tone squelch are combined to have a confidential communication characteristic, and only a specific communication partner can be identified even in a system using the same radio frequency. Due to limitations in using radio frequencies, frequencies below the voice band, for example 67-
A 250 Hz tone oscillator 11 is provided in the transmitter, and a 67 to 250 Hz tone demodulator 13 is provided in the receiver.

When the tone demodulator 13 of the receiver can demodulate the tone signal, the output of the tone demodulator 13 closes the switch 14. The reception signal from which the tone signal has been removed by the output tone remover 12 of the frequency discriminator 8 passes through the switch 14 and is supplied to the reception voice processing circuit 9 where it is converted into voice and received by the handset 10.

When the tone signal is not demodulated, the switch 14 remains open and the voice signal cannot be received.

[Problems to be solved by the invention]

In the conventional narrow band frequency modulation method, a method of identifying a specific communication partner by combining a radio channel frequency and tone squelch prevents interception by anyone other than a specific partner by the tone squelch effect in the same system using the same radio frequency. However, there is a problem in that it is possible to easily eavesdrop with a simple FM radio without tone squelch, that is, without the receiving side switch 14.

[Means for solving problems]

According to the present invention, the above-mentioned problem is caused by the angle modulator 30 for generating a narrow band angle modulated wave using the audio signal supplied from the transmission audio processing circuit 2 as shown in the principle diagram of the present invention in FIG.
And a transmitter having an n-phase modulator 16 for generating a broadband angle / n-phase modulation wave by using the pulse train transmitted by the pulse oscillator 15 and the narrow-band angle modulation wave and transmitting it as a transmission signal. In the confidential communication device described above, the received signal is multiplied by n to obtain an angle-modulated wave in a narrow band, and an output of the n multiplier added via a narrow band filter is demodulated to produce a voice signal. This is solved by the confidential communication device of the present invention, which is provided with the angle demodulator 80 for taking out and the receiver having the receiving voice processing circuit 9 for processing the taken out voice signal.

[Action]

In the device of the present invention, the transmitter performs angle modulation on the audio signal by the angle modulator 30, and further performs secondary modulation on the n-phase modulator 16 to which the pulse train is supplied from the pulse oscillator 15.

In the receiver, the received wave from the antenna 5 is band-limited by the wide band filter 17, and its output is input to the n multiplier 18.
By multiplying, the n-phase phase modulation of the secondary modulation is demodulated to restore the angle modulated wave. Here, since the modulation state of the angle modulation extracted from the n-multiplier is n-fold, the narrow band filter 6 and the angle demodulator 80, which will be described later, have a bandwidth corresponding to this.

Further, after the band is limited by the narrow band filter 6, the angle demodulator
The signal is demodulated at 80, and the output of the reception voice processing circuit 9 is restored to a voice signal by the receiver. The n-phase phase-modulated wave has confidentiality, and demodulation is realized by a simple n-multiplier, which simplifies the configuration of the device.

As shown in FIG. 4, the n-phase phase-modulated wave is for phase-modulating a carrier wave with a signal pulse a), and the modulation result is shown in b). The illustrated example is for a two-phase phase modulated wave. The phase-modulated carrier wave is output as a high-speed modulated wave having the frequency component of the signal pulse. By this action, for example, the bandwidth
The narrow-band frequency-modulated wave of 16 kHz becomes a high-speed pulse train of several hundred K to several M bits (the repetition frequency is ½ thereof), and has a bandwidth about 10 times the frequency of the original pulse train.

Here, a general radio receiver can receive only a very small partial band of emitted radio waves, for example, about 200 kHz. Therefore, demodulation becomes impossible due to insufficient information amount and insufficient received energy.

In this way, by using the phase modulation for the secondary modulation, it is possible to obtain a wireless device which prevents eavesdropping and makes it difficult to capture by weak radio waves.

〔Example〕

 Description will be given in accordance with the illustrated embodiment of the present invention.

FIG. 2 is a block circuit diagram of the confidential communication device of one embodiment of the present invention.

In the figure, the same functional blocks as those in the other drawings are indicated by the same reference numerals.

According to the present invention, n-phase modulation is used to improve the confidentiality characteristics. The n-phase modulator 16 is supplied with pulses from the pulse oscillator 15. A pulse pattern generation circuit using a multistage shift register can be used for the pulse oscillator 15.

The receiver uses an n-multiplier 18 to demodulate the secondary modulation provided by the transmitter.

The multiplier includes a non-linear multiplier and a linear multiplier. If the former is used, if there is an interfering wave whose amplitude is larger than that of the desired reception wave in the reception wave supplied to the n-multiplier 18 via the wide band filter 17, the desired wave is suppressed and reception interference occurs. Therefore, this has to be avoided because it has a drawback that the receiver is vulnerable to proximity interference. Therefore, in the present invention, the latter linear multiplier is selected and used for demodulation.

The linear multiplier does not have the above-mentioned drawbacks, and after demodulation, the narrow band filter 6 removes the interfering wave and gives it to the limiting amplifier 7, and limits the amplitude and supplies it to the frequency discriminator 8.

FIG. 2 is provided with a circuit for inserting a burst tone at the beginning of a talk in order to provide a distinguishing (secret talk) characteristic by n-phase modulation, but to provide mutual distinguishability in the same system.

At the start of transmission, the transmitter closes the transmission switch 19 and sends a burst signal from the talk signal generating circuit 20. As shown in FIG. 3, at the beginning of transmission signal transmission shown in column i),
ii) Send the burst signal shown in the column. The burst signal is composed of a first bit-number n bits taking values of combinations of frequency of the analog type frequency F1～f _n as shown in iii) column shown or iv) column, "1", "0" It can be given as a digital signal.

In the receiver, the signal obtained at the output of the frequency discriminator 8
When the predetermined speech signal is included, the speech signal demodulation circuit 22 demodulates it and outputs it to the switch 23. The reception signal passes through the switch 23 and is supplied to the reception voice processing circuit 9.

Although the above embodiment shows the case of frequency modulation, phase modulation can be used in the present invention, and a combination of both is called angle modulation.

〔The invention's effect〕

As described above, the present invention provides a wireless communication apparatus having excellent systematic confidentiality characteristics with a simple demodulator configuration by performing n-phase phase modulation as the secondary modulation, and its operational effects are extremely high. large.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention, FIG. 2 is a block circuit diagram of a confidential communication device of an embodiment of the present invention, FIG. 3 is a layout diagram of a talk burst signal of a transmission signal, and FIG. 4 is a two-phase phase modulation. Waveform diagram, FIG. 5 is a block circuit diagram of a conventional wireless communication device, and FIG. 6 is a block circuit diagram of a conventional tone squelch system. In the figure, 1 is a transmitter, 2 is a transmission voice processing circuit, 3 is a narrow band frequency modulator, 4 and 5 are antennas, 6 is a narrow band filter, 7 is a limiting amplifier, 8 is a frequency discriminator, and 9 is reception. Voice processing circuit,
10 is a handset, 11 is a tone transmitter, 12 is a tone remover, 13
Is a tone demodulator, 14, 23 are switches, 15 is a pulse oscillator, 16 is an n-phase modulator, 17 is a wide band filter, 18 is n
Multiplier, 19 is a transmission switch, 20 is a speech signal generation circuit, 22
Is a speech signal demodulation circuit, 30 is an angle modulator, and 80 is an angle demodulator.

Claims (1)

[Claims] 1. An angle modulator (30) for generating a narrow band angle modulated wave using a sound signal supplied from a transmission sound processing circuit (2), a pulse train transmitted by a pulse oscillator (15), and the narrow band. In a confidential communication device equipped with a transmitter having an n-phase modulator (16) which generates a wide-angle / n-phase modulation wave using a band-angle modulation wave, and outputs it as a transmission signal, N to obtain a narrow band angle modulated wave
Applied via a multiplier (18) and a narrow band filter,
An angle demodulator (80) for demodulating the output of the n-multiplier to extract an audio signal, and a receiver having a reception audio processing circuit (9) for processing the extracted audio signal. apparatus.