Structure of Main BCCH in GSM
The TDMA/FDMA multiplexing is used in GSM, the information needed in the synchronization between MS and BTS is provided by FCCH+SCH.
The MS determines the frequency of the BCCH carrier by searching for the frequency correction Burst transmitted via FCCH; then it finds the SCH (synchronization channel) according to the relationship between SCH and FCCH and decodes the current frame number and BSIC for synchronization with BTS. Furthermore, it determines whether the cell is barred or not and decodes the system information on BCCH.
In the structure diagram of extended BCCH, except that the F and S timeslots are replaced by Idle timeslots, the rest of the structures are the same as that of the main BCCH.