first of all continuously receives the frequency in question (asynchronous reception), waiting for a signal from the base station.
The signal from the base station contains preamble bits repeated in a fixed pattern; the mobile station regenerates the transmission clock of the base station by receiving these and performs an operation to pull in the reception clock by synchronizing its own reception clock with this.
In addition, the signal from the base station contains synchronization bits; the mobile station receives these bits with the reception clock synchronized to the base station. The mobile station then performs synchronization establishment operation in which it seizes the TDMA timing of the base station from the position of the synchronization bits received and the frame structure, which are laid down beforehand; subsequently, it shiftsto synchronous reception of only this time slot transmitted by the base station.
Also, on synchronization reception, it performs a synchronization maintenance operation to maintain the TDMA timing produced by demodulation of the reception clock and synchronization bit reception.
However, in the above asynchronous reception, if the mobile station spuriously recognises noise as a signal from the base station, the base station may shift to synchronized reception with the wrong TDMA timing. As a result, it will only detect failure of synchronization on failure of reception a fixed number of times as the synchronization signal which it ought not to be receiving is repeated; it will then return to asynchronous reception.
Consequently, some considerable time may elapse before synchronization with the base station is established and communication becomes possible. In particular,