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AssigneeNEC Corporation
InventorMitsunori Morishima
Estimating the term…
In a radio frequency communication system in which a radio frequency communication signal is transmitted between a radio terminal (14) and a mobile station (24), it may be that an unauthorized third person uses a scanner-receiver (60) to intercept the communication signal. In order to prevent such an interception, the unit comprises a detecting circuit (30) for detecting an internal signal which is transmitted between a telephone exchange (12) and the radio terminal (14) and is concerned with an ordinary voice signal. The detection circuit produces a detection signal when the internal signal is absent. Responsive to the detection signal, a control circuit (32) controls the internal signal to prevent the interception, as by sending a dummy voice signal whenever the ordinary voice signal is absent. Alternatively, the control circuit may produce a control signal while the communication signal is received from the mobile station and consequently while the internal signal is sent form the radio terminal to the exchange. In this event, the control signal is used either in attenuating or switching off an echo signal which usually results from the internal signal reaching the exchange.
A unit for use in a fixed facility of a radio frequency communication system between a telephone exchange of said fixed facility and a radio terminal thereof in preventing an interception of a radio frequency communication signal which carries a voice signal transmitted between said radio terminal and a mobile station of said radio frequency communication system, said unit being operable in response to a first internal signal transmitted from said radio terminal towards said telephone exchange and a second internal signal transmitted from said telephone exchange towards said radio terminal, said first and said second internal signals being produced in said radio terminal and said telephone exchange in relation to said radio frequency communication signal, respectively, wherein the improvement comprises:
A unit for use in a fixed facility of a radio frequency communication system between a telephone exchange of said fixed facility and a radio ternimal thereof in preventing an interception of a radio frequency communication signal transmitted between said radio terminal and a mobile station of said radio frequency communication system, said radio frequency communication signal being divisible into reception and transmission radio signals which are directed from said mobile station towards said fixed facility and from said fixed facility towards said mobile station, respectively, said reception radio signal carrying an ordinary voice signal and a control signal which is representative of presence of said ordinary voice signal, said unit comprising:
A mobile station for use in a radio frequency telephone communication system to produce a radio signal concerned with an ordinary voice signal, wherein the improvement comprises:
Dependencies are inferred from the claim text.