JPS61208933A - Device for preventing interception - Google Patents

Abstract

PURPOSE:To prevent simultaneous interception for two-way taking in monitoring an outgoing channel by using a talking busy signal sent from a mobile set side at the transmission of a mobile set so as to increase the return loss of the exchange side. CONSTITUTION:A transmission sound signal from a microphone 5 is inputted to a vogad amplifier 6 in a mobile set 1, and the output of the amplifier 6 is sent to an incoming channel via a synthesizing amplifier 9 and a transmitter/ receiver 10. When the output of the amplifier 6 is detected by a detector 7, a talking busy signal in a specific frequency (e.g., 3.5kHz) is inputted to the amplifier 9 from a talking busy signal generator 8 and the signal is sent while being superimposed on the sound signal. A radio base station 3 demodulates the reception signal of the incoming channel onto the sound signal and amplifies (11) the result and a taking signal blocking circuit 12 eliminates the talking busy signal in the specific frequency and applies the result to a hybrid transformer 16. The talking busy signal passes through a BPF 13 and detected by a detector 14. The detection signal of the detector 14 controls an automatic attenuator 15 inserted in the outgoing transmission circuit from the transformer 16 to increase the attenuation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an eavesdropping protection device that prevents calls between a mobile radio and a radio base station from being intercepted simultaneously in both directions using a commercially available scanner receiver or the like. .

SUMMARY OF THE INVENTION The present invention provides that when a mobile device transmits a call, a busy signal indicating that the call is in progress is superimposed on a voice call signal and sent to an uplink channel, and a radio base station side transmits a busy signal indicating that the call is in progress. This eavesdropping protection device increases the return loss of an automatic attenuator inserted in the transmission circuit when it detects this, thereby preventing the upstream audio signal from going around to the downstream channel and being sent out.

When the downlink channel is monitored, it is possible to prevent both the sending and receiving voices from being eavesdropped at the same time, and also to eliminate interruptions in communication.

Prior Art In the conventional mobile radio communication system, as shown in FIG. An echo suppressor circuit 18 is inserted in the transmitter to prevent the audio signal sent from the mobile 4!11 to the upstream channel from being transmitted through the hybrid transformer 16 to the downstream channel. The echo suppressor circuit 18 normally has a high loss when there is a downstream audio signal (from the switching device 4 to the mobile device 1).

Low loss. However, because it is necessary to prevent malfunctions when uplink channel fading occurs or due to external noise, low-level downlink audio signals may be interrupted. If an attempt is made to prevent this interruption, sufficient return loss cannot be taken, and the upstream audio from the mobile device is routed in the downstream direction and sent out to the downstream channel. For this reason, for example, if a commercially available scanner receiver automatically scans wireless channels and stops at a channel where radio waves are being transmitted, there is a drawback that calls in both directions may be intercepted at the same time.

Problems to be Solved by the Invention The present invention attempts to prevent calls in both directions from being wiretapped at the same time by monitoring one channel. The content is far less clear than if two calls were simultaneously wiretapped.

Means for Solving the Problems The eavesdropping protection device of the present invention is a mobile radio communication system in which a mobile device communicates with a radio base station, and in which the mobile device transmits a signal of a specific frequency to indicate that the mobile device is transmitting a call. A signal sending circuit is provided that superimposes a busy signal on a transmitting signal and transmits it to an uplink channel, and the wireless base station side includes a detection circuit that detects a busy signal of the specific frequency received on the uplink channel, and a detection circuit that detects the busy signal of the specific frequency received on the uplink channel. and an automatic attenuator inserted into the transmitter circuit to increase return loss by the output of the detection circuit.

The system is characterized in that the transmitting and receiving signals are prevented from being tapped simultaneously by monitoring the downlink channel.

Embodiments of the Invention Next, the present invention will be described in detail with reference to the drawings.

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

That is, the mobile device 1 inputs the transmitted voice signal output from the microphone 5 to the Bogard amplifier 6, and the output of the Pogard amplifier 6 is sent to the uplink channel via the synthesis amplifier 9 and the transceiver 10. Further, when the output of the Pogard amplifier 6 is detected by the detector 7, a busy signal of a specific frequency (for example, 3 or 4 KHz) is input from the busy signal generator 8 to the synthesis amplifier 9, and the busy signal is combined with the voice signal. It is superimposed on the signal and sent to the uplink channel.

The radio base station device 3 demodulates the uplink channel reception signal into an audio signal, inputs it to the Pogard amplifier 11, and uses the busy signal blocking circuit 12 to block the specific frequency! Supply to 8.

On the other hand, the busy signal of the specific frequency passes through the busy signal passing filter 13 and is detected by the detector 14 . An automatic attenuator 15 is inserted in the downstream transmission circuit of the hybrid transformer te, and the automatic attenuator 15 maximizes the return loss based on the output of the detector 14. Therefore, the signal from the upstream voice signal that has passed through the hybrid transformer IEI to the downstream circuit is blocked by the automatic attenuator 15 and is not input to the radio base station device 3. Furthermore, the automatic attenuator 15 detects that there is no busy signal. At this time, the attenuation amount is set to O, and the downlink audio signal from the switching device 4 to the mobile station 1 is input to the radio base station device 3, and the radio base station device 3 sends it out to the downlink channel. Therefore, the transmission signal from the switching device 4 to the mobile device 1 is never interrupted.

This embodiment has the advantage that even if the downlink channel is eavesdropped on by the scanner receiver 17, it is possible to prevent calls in both directions from being eavesdropped at the same time.

If a relay or the like is used instead of the automatic attenuator 15, it is easy to make the return loss infinite during a mobile phone call.

Effects of the Invention As described above, in the present invention, when a mobile device transmits a call, the return loss on the switching equipment side is increased by the busy signal sent from the mobile device, so that the downlink channel This has the effect of preventing calls in both directions from being intercepted at the same time. It is possible to easily protect against eavesdropping with a simple circuit, and unlike conventional echo cancellers, calls will not be interrupted.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing an example of a conventional mobile radio system using an echo canceller. In the figure, 1: mobile device, 2: spatial radio waves, 3: wireless base station equipment, 4: switching equipment, 5: microphone, 6: Bogard amplifier, 7: detector, 8: busy signal generator, 9: synthesis Amplifier, 10: Transmitter/receiver, 11: Pogard amplifier, 12: Busy signal blocking circuit, 13: Busy signal passing filter,
14: Detector, 15: Automatic attenuator, 16: Hybrid transformer, 17: Scanner receiver, 18: Echo suppressor circuit.

Claims (1)

[Scope of Claims] In a mobile radio communication system in which communication is performed between a mobile device and a radio base station, the mobile device side superimposes a busy signal of a specific frequency on the transmitted signal to indicate that the mobile device is transmitting. The radio base station includes a detection circuit for detecting a busy signal of the specific frequency received on the uplink channel and a busy signal blocking circuit for blocking the specific frequency. , an automatic attenuator inserted into the transmission circuit to increase the return loss by the output of the detection circuit, so as to prevent the transmission and reception signals from being eavesdropped at the same time by the downstream channel monitor. eavesdropping protection device.