JPS62257236A - Privacy radio transmission system - Google Patents

Abstract

PURPOSE:To attain the privacy communication system with a very simple constitution by using the output noise of a noise generating circuit so as to modulate a main carrier. CONSTITUTION:The output of a noise generating circuit 5 is fed to the output of a submodulation circuit 2 to modulate the main carrier. A reception noise generating circuit 12 generates the noise of the same waveform synchronously with the transmission noise. A local oscillation circuit 11 whose oscillation frequency is modulated by the circuit 12 receives the oscillation signal modulated by the noise and the S/N is improved by the output of a MIX 10. The output level and the phase of the reception noise generating circuit 12 are adjusted to optimize the S/N of the output signal of the mixing circuit 10 by varying the oscillation frequency of the local oscillation circuit 11.

Description

[Detailed Description of the Invention] [Industrial Application Fields] The present invention is mainly applicable to voice transmission, remote control, and convenience stores.
This is a secret wireless transmission method used to transmit digital signals, which cannot be received by ordinary receivers.

[Prior Art] Wireless transmission system: As long as radio waves are used, it cannot be prevented from being received by others. Various methods have been developed and put into practical use as methods for wirelessly transmitting confidential information that you do not want to divulge to others.

For example, if you do not directly modulate the carrier with an information signal such as voice, but instead modulate the subcarrier with the information signal and modulate the main carrier with this signal, you should immediately obtain the information signal from the received and detected signal. I can't come. That is,
I hope we can create a secret message transmission device. However, in this transmission method, simply by frequency-analyzing the detected signal using a spectrum analyzer or the like, it is possible to simultaneously determine that the main carrier is multiplex modulated with subcarriers and the frequency of the subcarriers. Therefore, an eavesdropper can easily obtain information signals by selecting subcarriers with a filter and detecting them. Therefore, you cannot escape the disadvantage of being eavesdropped on by others.

[Object of the present invention] An important object of the present invention is to provide a wireless transmission system that uses a confidential communication system with an extremely simple configuration.

In addition, an important purpose of the pond of the present invention is that the transmission radio wave is equivalent to a normal weak radio wave with a poor S/N ratio, which is not a confidential communication type.
To provide a secret radio transmission system that can ensure secure communication without allowing listeners to distinguish between confidential radio waves and ordinary radio waves.

[Means for Achieving the Object] The confidential wireless transmission system of the present invention includes a transmitter that sends an information signal and a receiver that receives radio waves sent from the transmitter. The transmitter includes a subcarrier oscillation circuit that oscillates a subcarrier, a submodulation circuit that modulates the subcarrier output from the subcarrier oscillation circuit with an information signal, and a main carrier that modulates the main carrier with the output signal of the submodulation circuit. and a main carrier oscillation circuit that supplies a main carrier to the main modulation circuit. On the other hand, the receiver includes a main detection circuit that detects the radio waves main modulated by the transmitter,
It includes a subcarrier filter that selects the subcarrier of the transmitter from this output signal, and a sub-detection circuit that detects the output signal of the subcarrier filter again to extract the information signal of the transmitter. The transmitter has a noise generation circuit, and modulates the main carrier with the output noise of this noise generation circuit.

[Operations and Effects] Since the radio waves received from the transmitter are modulated by noise, it is not possible to obtain an information signal unless the noise is removed.

As shown in FIG. 4, the spectrum of the transmitted radio wave that is not modulated by noise has subcarriers distributed on both sides of the main carrier. Therefore, by frequency-analyzing the received radio waves with a spectrum analyzer, the frequency of the subcarrier used to obtain the information radio waves can be easily determined. However, in the noise-modulated transmission system of the present invention, the transmitted radio waves are distributed in a gentle mountain shape centered around the low and main carriers, as shown in FIG. Therefore, it is not possible to easily determine whether the main carrier is modulated by a subcarrier or the frequency of the subcarrier, and it is not possible to find a method for obtaining an information signal from a received signal.

Further advantageously, the transmitted radio waves modulated with noise are
The /N ratio is similar to or the same as a weak radio wave, and an eavesdropper cannot even tell from the received signal that it is a confidential communication system, making it possible to transmit top secret information with peace of mind.

In other words, the inventor of the present invention has realized a confidential communication system by effectively utilizing the noise that has been tried to be reduced in conventional wireless transmissions. Achieve prevention effects.

Furthermore, since the confidential communication method of the present invention is a simple method in which the transmitter simply generates noise and modulates the main carrier with this, the overall circuit configuration can be significantly simplified and other features can be realized.

After the transmitted radio waves containing noise are detected on the receiving side, the noise is removed by a subcarrier filter. Since the subcarrier filter can adjust the passband width narrowly, noise can be effectively removed from the subcarrier.

[Preferred embodiment] Hereinafter, examples of the present invention will be explained based on the drawings.

The transmitter shown in FIG. 1 includes a subcarrier oscillation circuit 1 that oscillates subcarriers, a submodulation circuit 2 that modulates the subcarrier output from the subcarrier oscillation circuit 1 with an information signal, and a It includes a main modulation circuit 3 that modulates the main carrier with an output signal, a main carrier oscillation circuit 4 that supplies the main carrier to the main modulation circuit 3, and a noise generation circuit 5 that manually generates noise from the main modulation circuit 3. .

As shown in FIG. 2, the receiver includes a high-frequency amplification section 6 that selects and amplifies the radio wave that has been main modulated by the transmitter, a main detection circuit 7 that detects the output of the high-frequency amplification section 6, and a main detection circuit 7 that detects the output of the high-frequency amplification section 6. It includes a subcarrier filter 8 that selects a transmitter subcarrier from an output signal, and a subdetection circuit 9 that redetects the output signal of this subcarrier filter 8 and extracts a transmitter information signal from the subcarrier. There is.

In the subcarrier oscillation circuit 1, the oscillating subcarrier is
It is preferable to set a frequency that is sufficiently high compared to the highest frequency of the information signal to be transmitted, for example, 5 times or more, preferably 10 times or more, as high as the control signal, for example, about 30 KHz to 300 KHz.

The sub modulation circuit 2 modulates the subcarriers using the control signal.
The sub-detection circuit 9 of the receiver which extracts the control signal from the AM-modulated subcarrier is an AM detection circuit.

The wireless transmission device of the present invention can transmit audio signals, computer on/off signals, or other analog or digital signals as erotic signals.

The main modulation circuit 3 performs F\1 modulation on the main carrier oscillated by the main carrier oscillation circuit 4 with the subcarrier AM-modulated using the control signal. The frequency of the main carrier is preferably determined to be about 1OMHz to 500MHz.

The noise generation circuit 5 generates pink noise containing a frequency higher than the subcarrier frequency. This noise generation circuit 5
is a circuit that amplifies thermal disturbance noise, a circuit that generates noise by discharging it in a vacuum, or a microcomputer that generates random numbers at a constant cycle.
You can use a circuit that converts the output to A/D to obtain noise. The noise generated by random number generation can be made on the receiver side to be the same amount of noise as the noise on the transmitter side. In this case, it is necessary to generate noise of the same phase and waveform that is synchronized between the transmitting side and the receiving side. Therefore, the noise generating circuit 5 on the transmitting side generates a synchronizing signal at regular intervals and transmits it, and the receiving side receives only this synchronizing signal.

As for the noise waveform between the synchronization signals, if the microcomputers on both the transmitting side and the receiving side generate random numbers in the same sequence, the same waveform of noise can be obtained on both sides. Noise obtained from random numbers generated according to the same rule is not exactly pink noise. However, this waveform cannot be distinguished from pink noise even by listening to it.

Therefore, in this specification, noise generated by this method is also defined as noise.

The output of the noise generation circuit 5 is added to the output of the sub-modulation circuit 2 to modulate the noise main carrier.

When the main modulation circuit 3 is a FIVI modulation circuit, the output of the noise generation circuit does not necessarily have to be added to the output of the sub-modulation circuit 2, but is added to the main carrier oscillation circuit 4 as shown by the chain line in FIG. It is also possible to change and modulate the frequency of the main carrier oscillation circuit 40 with noise.

The high frequency amplification section 6 of the receiver includes a mixing circuit 10 that converts the frequency of the received signal to an intermediate frequency, a local oscillation circuit 11, and a circuit that changes the oscillation frequency of the local oscillation circuit 11 with noise.
It is provided with a reception noise generation circuit 12 that modulates and modulates the reception noise.

The local oscillation circuit 11 uses the main carrier frequency τ of the transmitter.
In other words, a frequency signal obtained by adding an intermediate frequency to the receiving frequency is oscillated.

Reception noise generation circuit 12B, as mentioned before, the transmission 1
When the same amount of noise is applied to the speech noise, it generates noise with the same waveform.

The reception noise generation circuit 12 modulates the oscillation frequency.
The filter local oscillation circuit 11 receives the noise-modulated oscillation (signal) and improves the S/N ratio with the output of the MIX 10. What is the output level and phase of the reception noise generation circuit 12? , or by varying the oscillation frequency of the local oscillation circuit 11. Therefore, adjust the S/N ratio of the output signal of the mixing circuit to be the best.

For example, suppose that the transmitter side raises the main carrier frequency with the positive phase of the noise of the noise generation circuit 5, and the receiver side; If it is set,
Adjust so that the oscillation frequency of the local oscillation circuit 11 is increased by the positive phase of the noise of the reception noise generation circuit 12.

That is, the receiver side receives the noise modulated field and adjusts the mixer circuit so that the output is an intermediate frequency signal from which the noise has been removed.

The intermediate frequency signal from which the noise component has been removed is sent to the main detection circuit 7, which is the next stage of FM detection circuit, advances the subcarriers from the output signal of the FNl main detection circuit, and further subcarriers to the subdetection circuit. At step P19, (rvt detection is performed to extract the information signal.

The subcarrier filter 8 may be one using LC or a mechanical filter such as a ceramic filter. LC or mechanical filters do not stand up immediately even if there is a human input signal, and are so-called flyhos.・−
This effectively eliminates the noise, although it introduces a delay due to channel effects.

Is it better to use negative polarity detection for the sub-detection circuit 9? This is because there is less possibility of noise remaining on the negative polarity side, where the peak of the wave is only up to =, than on the positive polarity side, where the peak of the wave exists up to infinity. This reduces erroneously reproduced signals due to noise.

The subcarrier filter 8 is a bandpass filter, and the center frequency of the passband is adjusted to the subcarrier frequency or its vicinity.

The output of the reception noise generation circuit 11 is as shown in FIG.
It is also possible to manually input the differential amplifier 13 connected to the output side of the main detection circuit 7. In this case, the output signal of the main detection circuit 7 contains noise, or the noise is subtracted by the differential amplifier 13, and the signal from which the noise has been removed is input to the subcarrier filter. However, in this case as well, the output level and phase of the receiver noise generating circuit 12 should be adjusted so that the S/N ratio of the output signal of the differential amplifier 13 is maximized. That is, the output waveform of the reception noise generation circuit 12 is
It should be in phase and have the same waveform as the noise of the noise generating circuit on the transmitting side, and its level should be adjusted to be equal to the noise level of the intermediate frequency signal.

As shown in FIG. 2, the transmission method that removes noise from the received signal using the reception noise generation circuit 12 on the reception side, even if the transmitted radio wave is deeply modulated with extremely loud noise,
On the receiving side, a good signal with S/>J can be obtained.

However, the present invention does not necessarily require a reception noise generation circuit on the reception side. Even if the signal received on the receiving side contains noise, the subcarrier filter can make the band considerably narrower, so the noise is removed by this subcarrier filter, and the signal is detected by the sub-detection circuit to obtain the information signal. is possible.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a transmitter showing an embodiment of the present invention, Fig. 2 is a block diagram of a receiver showing an embodiment of the invention, and Fig. 3 is a block diagram of a receiver showing an embodiment of the invention. FIG. 4 is a graph showing the spectrum of the transmitted radio waves in the conventional transmission method, and FIG. 5 is a graph showing the spectrum of the transmitted radio waves in the transmission method of the present invention. 1. Subcarrier oscillation circuit, 2. Submodulation circuit, 3. Main modulation circuit, 4. Main carrier oscillation circuit, 5. Noise generation circuit, 6. High frequency amplification section, 7. Main detection circuit. , 8...Subcarrier filter, 9...Sub-detection circuit, 10...Mixing circuit, 11...Local oscillation circuit, 12...Reception noise generation circuit, Ward 13...Differential amplifier.
.

Claims (4)

[Claims] (1) Consisting of a transmitter that sends an information signal and a receiver that receives radio waves sent from this transmitter, the transmitter includes a subcarrier oscillation circuit that oscillates subcarriers, and an output of this subcarrier oscillation circuit. a sub-modulation circuit that modulates a subcarrier with an information signal, a main modulation circuit that modulates a main carrier with an output signal of the sub-modulation circuit, and a main carrier oscillation circuit that supplies the main carrier to the main modulation circuit. On the other hand, the receiver includes a main detection circuit that detects the radio wave that is main modulated by the transmitter, a subcarrier filter that selects the subcarrier of the transmitter from this output signal, and a redetection of the output signal of this subcarrier filter. In a wireless transmission system including a sub-detection circuit for extracting an information signal of the transmitter, the transmitter has a noise generation circuit, and the main carrier is modulated by the output noise of the noise generation circuit. Confidential wireless transmission method. (2) The main modulation circuit of the transmitter is an FM modulation circuit, the main modulation circuit of the receiver is an FM detection circuit, and the receiver generates noise in synchronization with the noise generated by the noise generation circuit of the transmitter. 2. The confidential radio transmission system according to claim 1, further comprising a circuit, wherein the output of the reception noise generating means modulates the oscillation frequency of a local oscillation circuit of a receiver. (3) The receiver has a reception noise generation circuit that generates noise in synchronization with the noise generated by the noise generation circuit of the transmitter, and the output of this reception noise generation circuit is compared with the output of the main detection circuit,
2. The confidential wireless transmission system according to claim 1, wherein a difference component between both signals is input to a subcarrier filter. (4) The confidential wireless transmission system according to claim 1, wherein the subcarrier is determined to be 30 KHz to 300 KHz.