Abstract: A radio channel control method for a narrow-zone mobile communication system in which a plurality of base stations share a plurality of channels and each selects any of the channels for setting up a call independently of the others, e.g. a portable telephone system or a cordless telephone system. Installed in each of all the base stations are transceiver, free to use all the channels, a device capable of indentifying channels on which radio waves have reached the own station based on reception sensitivity, a device for selecting a channel, a device for transmitting a pilot signal and others, and a device for setting up a call. The channel for a pilot signal is adequately changed to shorten a duration of cochannel interference. Connection of multiple base stations to a single mobile station is eliminated by causing each base station to add to the pilot signal identification data which is particular to the base station.

Abstract: In a radio communication system, a mobile station (11) includes a detecting circuit (16) for producing a detection signal during presence of an audio signal, a producing circuit (31) for delivering a predetermined coded data signal to an audio signal circuit (14) and for supplying a duration signal to a power unit (17) at the end of the detection signal. The power unit disables the transmitting circuit during absence of the detection signal and the duration signal. The transmitting circuit transmits a transmission radio signal modulated by the audio signal and the predetermined coded data signal. A fixed station (12) comprises a separating circuit (44) for separating a reproduction of the predetermined coded data signal from a reproduction of the audio signal. A discriminating circuit (45) discriminates the reproduction of the predetermined coded data signal. Consequently, the fixed station is able to discriminate between presence and absence of the audio signal.

Abstract: In order to either permit communication to continue or to permit a call to be placed while a mobile unit is located in a zone of weak signal strength such as a tunnel or underground parking, a booster is disposed in the zone and arranged to establish communication with the mobile unit over a booster channel. When the mobile unit detects the signal strength being below a level at which communication is possible, the unit switches to the booster channel and establishes temporary communication with the booster. This enables the booster to be conditioned to establish a communication link between the land site and the mobile unit over a voice channel. The mobile unit is responsive to the conditioning of the booster to switch to the voice channel. Hence the need for wholesale relaying of all channels is obviated by the selective relaying which is possible via the provision of the booster channel.