JPH04189042A - Method and device for preventing intercept of cordless telephone set - Google Patents

Abstract

PURPOSE:To prevent intercept with simple constitution by subtracting a reproduced white noise from a received signal so as to obtain a voice signal. CONSTITUTION:A correlation detector 17 obtains a mutual relation between a delayed white noise and a reception signal 43 from an amplitude limiter 16 and applies a cross correlation output to a phase control circuit 14. The phase control circuit 14 sends a phase control signal to a delay circuit 13 and a pseudo random pulse generator 11 to control it that the cross correlation output represents a maximum value. A voice signal 44 from which a white noise is eliminated is obtained from an output of a subtractor 32.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cordless telephone eavesdropping prevention method and device. Specifically, an improved eavesdropping prevention method and device that eliminates the possibility of a third party intercepting the content of wireless signal communication between a base unit and a handset in a cordless telephone device and improves communication privacy. We aim to provide the following.

[Prior Art] A wireless signal between a base unit and a slave unit in a cordless telephone device is a simple signal that is obtained by amplitude modulating or FM modulating an audio signal, which has the advantage that the device can be realized at a low cost. There were also digital telephones that digitized and modulated voice signals, and were characterized by high confidentiality.

[Problem to be solved by the invention] However, although simple analog methods that perform amplitude modulation or FM modulation on audio signals are extremely inexpensive, they have the disadvantage that they can be easily intercepted by third parties and privacy cannot be maintained. There was a problem to be solved.

Digital telephones that digitize and modulate voice signals have the advantage of extremely high privacy compared to analog telephones, but they have the unresolved problem of being expensive.

[Means for Solving the Problems] The present invention has been made to solve such problems, and when a cordless telephone device including a base unit and a handset transmits and receives data, One of the base unit and slave unit adds white noise having a predetermined pattern to the audio signal to mask the audio signal to be transmitted, and sends it out as a transmission signal, and the other of the base unit and slave unit transmits this transmission signal. The white signal included in the received signal is
Why has a pattern that is substantially the same as the noise?
1. Regenerate the noise 5 and reproduce it from the received signal.
↑・-Noid 7 I'm going to reduce the noise and get the alpine signal that was sent, f, TL.

This is used as a means of realizing this, and on the main unit side, the type of stomach is assigned according to the assigned ID number;...7
A base unit pseudo-random pulse generator that controls the base unit white noise, which is noise, and a clock for generating the base unit white noise to the base unit pseudo-random pulse generator. -J Tsuk generator, base unit adder for adding the high mountain signal to be transmitted from the base unit and base unit Holy [-5 noise, and base unit white...
, a base unit delay circuit for applying the base unit phase control signal and delaying the noise, which is the round trip time of the wireless signal between the slave unit and the base unit, and f. 1 Noise 1 to 2 The voice signal transmitted from the slave unit to the transmitter due to noise is the received signal from the slave unit that is masked, and the base unit reception signal is the delayed base unit A base unit correlation detector to obtain a base unit cross-correlation value with white noise, and a base unit delay circuit that controls the phase of the base unit white 7 noise so that the base unit cross-correlation value is equal to that of the base unit. An MR phase control circuit that generates a base unit phase control signal to control the delay time, and a delayed base unit transmission reason from the base unit reception signal to reduce noise and reduce the audio signal by 1q. A subtractor for the base unit is provided, and a subtractor for the slave unit (this includes a pseudo random pulse generator for the slave unit that generates the same white noise for the slave unit as the white noise for the base unit according to the identification number of the slave unit; A handset clock means for extracting a clock for generating slave white noise in a random pulse generator from a handset received signal which is a signal received from a base unit; A slave unit adder for adding machine white noise and f machine white noise are delayed by applying a slave unit phase control circuit and delaying the f machine white noise by the delay time of unrelated Buddha 3 between the base unit and the base unit. The handset delay circuit to obtain the handset white noise, and the handset receiver (3 signals and the delay M
A handset correlation detector to obtain a correlation value with the handset phase noid noise, and a handset correlation detector to obtain a handset phase correlation value with the handset white noise.
..., a handset phase control circuit that synchronizes and controls the phase of noise with the handset clock and generates a handset phase control signal for controlling the delay time in a3 of the handset delay circuit; and handset reception signal. a clock detection means for extracting a clock from a slave unit to obtain a slave unit clock; and a slave unit reduction device for reducing delayed slave unit reply white noise from a slave unit reception signal to obtain a C voice A word. has been established.

1 Effect 1 Both the base unit received signal and the slave unit received signal are
Since it is 7 times affected by noise, it is impossible to detect @Hoshinkyu without processing. Calculate the difference between the received signal and the same pattern of white noise generated by the base unit and slave unit based on the assigned ID number. It is now possible to obtain an eavesdropping prevention function with a simple configuration.

Therefore, even if a third party who does not know the 10 number and the noise pattern were to intercept it, it would be masked by the noise and could not be heard as an alpine signal.

1st Embodiment J An embodiment of each of a master unit and a slave unit used in the apparatus of the present invention is shown in FIGS. 1A and 1B and will be described.

Figure] Δ shows the circuit configuration of the base unit 10. As shown in FIG.

Reference numeral 11 denotes a pseudo-random pulse generator, which generates white noise for masking the transmitted audio signal 41. One pseudo-random pulse generator is composed of, for example, seven stages of feedback registers, and the nine longest connection taps are connected to an ID indicating an input ID (identification) number.
According to signal 49, 9X8×...x3x2x1″53
One type out of 60,000 types is selected to generate M-sequence white noise with a code length of 127×9 bits (here, 127=27-1). In generating this white noise, the clock from the clock generator 12 is used, and the phase control signal from the phase control circuit 14 causes the white noise to be generated.
Controls the phase of the noise.

The clock frequency of this clock generator 12 is, for example, 5k)-1z, and the clock frequency of the pseudorandom pulse generator 11 is, for example, 5k)-1z.
The length of one bit of the pseudorandom pulse, which is the white noise generated by
: This is the frequency (bandwidth for low-power cordless telephones).

, pseudorandom pulse generator] 1 is added to the audio signal 41 to be transmitted in the adder 31, and the transmitted signal 42 is sent as a wireless signal to the destination slave device via the wireless transceiver 19. Sent out. This wireless transceiver 19 is the same as a conventional device. In the past, even if a third party were to receive this radio signal, they would not be able to understand it because the audio signal would be masked by white noise.

Since the white noise included in the transmission signal 42 from the base unit 10 is generated based on the assigned ID, the same white noise as that generated at the base unit 1810 is generated on the slave unit side as well. A procedure for extracting only the voice signal @ 44 from the received signal 43 from the handset that is masked by the white noise will be explained.

The white noise pattern included in the received signal 43 is the same as the white noise generated by the pseudo-random pulse generator 11, but the distance between the base unit 10 and the destination slave unit and the transmission between them Both whites for loss
There is a phase difference and an amplitude difference between the noises. By subtracting the white noise from which the phase difference and the amplitude difference have been removed from the received signal 43 in the subtracter 32, an audio signal 44 free of white noise can be obtained.

The delay circuit 13 receives the clock from the clock generator 12,
In response to the phase control signal from the phase control circuit 14, the white noise from the pseudo-random pulse generator 11 is delayed by the delay time of the wireless signal between the parent 11110 and the slave unit, thereby generating delayed white noise. Output. This delay circuit 13 is constituted by, for example, a 64-stage shift register, and changes the phase in time units of approximately 1/64 bit length.

This delayed white noise passes through a low-pass filter 15, and the frequency components of the delayed white noise are filtered in the band (0.3 to 3 kHz) assigned to low-power cordless telephones.
) is applied to the amplitude controller 16.

A received signal 43 is also applied to the amplitude controller 16, and is delayed so that the signal level of white noise included in the received signal 43 and the level of delayed white noise from the low-pass filter 15 are substantially equal. Limit the amplitude of white noise.

The correlation detector 17 obtains the cross-correlation between the delayed white noise from the amplitude controller 16 and the received signal 43, and applies the cross-correlation output to the phase control circuit 14. The phase control circuit 14 sends a phase control signal to the delay circuit 13 and the pseudo-random pulse generator 11 to control the cross-correlation output so that it reaches its maximum value.

In this way, the delayed white noise applied from the amplitude-side m-unit 16 to the subtracter 32 becomes substantially equal to the white noise included in the received signal 43 not only in pattern but also in phase and amplitude. , the output of the subtractor 32 is the audio signal @4 from which white noise has been removed.
You can get 4.

FIG. 1B shows the circuit configuration of the handset 110.

111 is a pseudo-random pulse generator that generates white noise to mask the audio signal 141 to be transmitted. The pseudo-random pulse generator 111 is configured with, for example, seven stages of feedback registers, and connects nine types of longest connection taps to 9x8x...X3X2X according to an ID signal 149 indicating an input ID (identification) number.
1 - = 360,000 types are selected to generate M-sequence white noise with a code length of 127 x 9 bits (here, 127 = 27 - 1). In generating this white noise, A zero cross detector 121 outputs a pulse every time the voltage of the received signal 143 received by the wireless transmitter/receiver 19 crosses the O level, and
The received signal 14 receives the pulse output from the pulse detector 121.
The phase of the white noise is controlled by the phase control signal from the phase control circuit 114 using the clock from the PLi 122 using a 7-lock loop for extracting the clock from 1-3. There is.

The clock frequency from this F)LL 112 is, for example, 6 kHz, and is synchronized with the clock generated by the clock generator 12 of the base unit 10.

Why 1 generated by pseudo-random pulse generator 111
~・Noise is the audio signal 141 to be transmitted and adder 1
31 and the transmitted signal 142 is sent out via the radio transceiver 119.

However, even if a third party receives this radio signal, it cannot be understood because the audio signal is masked by white noise.

White included in the transmission signal 142 from the handset 110
Since the noise is generated based on the assigned ID, it is possible to generate the same white noise as that generated 10 km from the base unit.

The white noise pattern included in the received signal 143 is the same as the why 1~ noise generated by the pseudo-random pulse generator 111, but
There is a phase difference and an amplitude difference between both white noises due to the distance between them and the transmission loss therebetween. By subtracting Why1~ noise from which the phase difference and amplitude difference have been removed from the received signal 143 in the subtracter 132, an audio signal 144 free of white noise can be obtained.

The delay circuit 1'73 receives the clock from pH22 and the phase control signal from the phase control circuit 114, and converts the white noise from the pseudo-random pulse generator 111 into mmq.
The noise is output to the delay voice 1 by delaying the round trip time of the radio 13 between the voice and the handset 110. This delay circuit 113 is constituted by, for example, a 64-stage shift register, and changes the phase in time units of about 1.64 bit length.

This delayed white noise is filtered by a low-pass filter 115.
The frequency components of the delayed white noise pass through the ``band'' (0.3~
3kl-4z) and applied to the amplitude controller 116.

A received signal 143 is also applied to the amplitude controller 116, and is delayed so that the signal level of white noise included in the received signal 143 and the delayed white noise from the low-pass filter 115 are substantially equal. Limit the amplitude of white noise.

The correlation detector 117 calculates the cross-correlation between the delayed white noise from the amplitude controller 116 and the received signal 143 by (q,
The cross-correlation output is applied to the phase control circuit 114. The phase control circuit 114 transfers the phase control signal to the delay circuit 1.
13 and a pseudo-random pulse generator 111 to control the cross-correlation output to show the maximum value.

Thus, the delayed white noise applied from amplitude controller 116 to subtracter 132 is substantially equal to the white noise included in received signal 143 not only in pattern but also in phase and amplitude. The output of the subtracter 132 provides an audio signal 144 from which white noise has been removed.

[Effect of the invention 1] As is clear from the above explanation, even if a third party tries to intercept using the handset according to the present invention, the ID of the handset in communication is unknown, so white noise The pattern is unknown. For example, if a 7-stage feedback register is used, there are 81 types of patterns.
Its interception is extremely difficult. Moreover, since it is impossible to intercept the information using a conventional handset, it is possible to maintain a high degree of privacy. Furthermore, the present invention can be implemented by simply adding a few circuits to a conventional wireless transceiver.

Therefore, the effects of the present invention are extremely large.

[Brief explanation of the drawing]

FIG. 1A is a circuit configuration diagram of an embodiment of the master device in the device of the present invention, and FIG. 1B is a circuit diagram of an embodiment of the slave device in the device of the present invention. 10... Base unit 11.111... Pseudo random pulse generator 12.
... Clock generator 13.113 ... Delay circuit 14.114 ... Phase control circuit 15.115 ... Low-pass filter 16.116 ...
...Amplitude controller 17.117...Correlation detector 19.119...Radio transceiver 31.131...Adder 32.132...Subtractor 41.44. ．． 141, 144...Audio signal 42.1
42...Transmission signal 43.143...Reception signal 49.149-...ID signal 110...Slave device 121...Zero cross detector 122...PLL0

Claims (1)

[Claims] 1. When a cordless telephone device including a base unit (10) and a handset (110) transmits and receives, an audio signal to be transmitted by one of the base unit and the handset is masked. white noise having a predetermined pattern is added to the audio signal and sent as a transmission signal, and the other of the base unit and the slave unit receives the transmission signal and combines the white noise with the white noise. A method for preventing eavesdropping on a cordless telephone, comprising reproducing white noise having substantially the same pattern and subtracting the reproduced white noise from the received signal to obtain the audio signal. 2. In a cordless telephone including a base unit (10) and a handset (110) each having a wireless transmitter/receiver, the base unit has its phase controlled by a base unit phase control signal, and has an assigned ID number (49). ); base unit pseudo-random pulse generation means (11) for generating base unit white noise which is white noise having different types of patterns according to the base unit pseudo-random pulse generation means; - Base unit clock generation means (12) that provides a clock for generating noise, adds the audio signal to be transmitted and the base unit white noise, and sends the result via the wireless transmitter/receiver (19) of the base unit. a base unit addition means (31) for transmitting to the slave unit; and controlled by the base unit phase control signal, the base unit white noise is delayed by the round trip time of the communication signal with the slave unit. a base unit delaying means for obtaining delayed base unit white noise; base unit correlation detection means (17) for obtaining a base unit correlation value with white noise; and the base unit for controlling the delay time in the base unit delaying unit and generating the base unit pseudo random pulse generation means. base unit phase control means (14) for outputting the base unit phase control signal for controlling the phase of white noise; and subtracting the delayed base unit white noise from the base unit reception signal to obtain an audio signal. base unit subtraction means (32) for the subunit, wherein the slave unit has a phase controlled by a slave unit phase control signal and is substantially identical to the base unit white noise according to an identification number (149) of the slave unit itself. handset pseudo-random pulse generation means (111) that generates handset white noise, which is white noise having a pattern of white noise; Handset clock generation means (12) extracts a clock from the handset reception signal output from the transmitter/receiver (119) and supplies it to the handset pseudo-random pulse generation means as a clock for generating the handset white noise.
1, 122), a handset adding means (131) for adding the audio signal to be transmitted and the handset white noise and transmitting the result to the base unit via the wireless transceiver of the handset; a handset delay unit controlled by the handset phase control signal to delay the handset white noise by a delay time of a communication signal with the base unit to obtain delayed handset white noise; Handset correlation detection means (117) for obtaining a handset correlation value between the handset reception signal and the delayed handset white noise.
and a slave unit that outputs the slave unit phase control signal for controlling the delay time in the slave unit delay means and controlling the phase of the slave unit white noise generated by the slave unit pseudo-random pulse generating means. phase control means (114); and handset subtraction means (132) for subtracting the delayed handset white noise from the handset reception signal to obtain an audio signal.
An anti-wiretapping device for cordless telephones, including: