Abstract: A mobile station is capable of quickly returning to its home system when roaming. A detecting system detects, when the home system is not available, signal-level of the present control channel. A control system determines a change in the signal-level and controls scan time between scans of band of the home system in response to the change in signal-level.

Abstract: A data retransmission method for a confirmation information transmission is provided which improves reliability of information transmission by preventing the loss of data when a transmission of data from layer 3 fails in layer 2. When transmitting layer-3-data from layer 3 to layer 2, layer 2 initiates timer observation and simultaneously transmits confirmation data to layer 1. If this transmission fails, a reply from layer 1 cannot be received and a retransmission procedure also fails, layer 2 notifies layer 3 of transmission failure, and simultaneously discards the layer-3-data. Layer 3 retransmits to layer 2 the layer-3-data which it previously transmitted, and layer 2 again transmits confirmation data to layer 1. If this transmission succeeds, layer 2 terminates the timer observation and notifies layer 3 of the successful transmission.