Multiple accessing satellite communication system having standby central station

In a satellite communication system wherein a common channel is used for communication between a central station (10) and a plurality of remote stations (12) through a satellite transponder (11), in order to avoid system down due to fault of transmission of a broadcasting signal with a timing signal by the central station (10), the central station (10) comprises two portions (13, 14) positioned at different locations and a controller (15). When the first portion (13) detects fault of transmission of the broadcasting signal during the first portion (13) operates to communicate with the remote stations (12) under transmission of the broadcasting signal, the controller (15) is notified the fault and starts the second portion (14) in place of the first portion (13) so that the communication is maintained in the system without false. Those portions (13, 14) are assigned with ID numbers and can detect the fault by detecting operation of ID number. Each of remote stations (12) has timing offset data sets corresponding to the first and second portions (13, 14), selects one of the data sets by detection of the ID number in the broadcasting signal received, and determines a slot timing for transmitting a packet signal.