Portable telephone set transmitting area identification signal indicative of a radio zone occupied thereby

Claim 1

A portable telephone set for use in a mobile communication system comprising a plurality of base stations disposed in respective radio zones, the base stations being assigned with area identifiers for identifying the respective radio zones, the base stations transmitting area identification signals indicative of the area identifiers on a control channel, said portable telephone set being located in a first one of said radio zones for a first one of the base stations so that said portable telephone set enables to communicate with said first one of the base stations via the control channel and a plurality of voice channels, said portable telephone set comprising: receiving means for receiving a first area identification signal transmitted from said first one of the base stations via the control channel; area identification holding means, connected to said receiving means, for holding the first area identification signal as a current area identification signal; determining means, responsive to an incoming call signal from said first one of the base stations, for determining whether or not a user of said portable telephone set answers to the incoming call signal within a predetermined time interval elapsed since the incoming call signal is received; ensuring means, connected to said determining means, for ensuring one of the voice channels as an ensured voice channel by carrying out an automatic answering for the incoming call signal when said user does not answer to the incoming call signal within the predetermined time interval; and transmitting means, connected to said ensuring means and said area identification holding means, for transmitting the current area identification signal on the ensured voice channel.