Channel changing system

Claim 1

A channel changing system, which includes center station means for connecting a public telephone network (6) to a plurality of radio base stations (3) which communicates with movable stations (7) through radio channels, wherein said center station comprises: a private branch exchanger (1) electrically. connected to the public telephone network (6) and to a control means (2) which is connected to lines (4) extending from said plurality of radio base stations (3), wherein said control means (2) is operable to detect that the movable station (7) has transferred from the radio zone of a first one of said radio base stations (3) to the radio zone of an adjacent one of said radio base stations (3), by monitoring the signal 'receiving condition between the movable station (7) and said plurality of base stations (3), wherein said private branch exchanger (1) is connected to the control means via exchanger lines (5) which correspond to the plurality of radio base stations (3) respectively, and wherein said control means is operable to control the private branch exchanger (1) to transfer the extension from the exchanger line (5) corresponding to said first radio base station (3) to the exchanger line (5) corresponding to said adjacent radio base station (3).