BCCH > Broadcast Control Channel FCCH > Frequency Correction Channel
BCCH
Network uses this channel to constantly broadcast messages to all device into that cell coverage.
System Information messages are transmitted in this channel. Those messages carry network/cell identity as well re-selection criteria, neighbor cells information and several other info.
It's a downlink only channel.
More Info:
http://www.rfwireless-world.com/Terminology/GSM-BCCH-Broadcast-Control-Channel.html
FCCH
In this channel, network sends specific data which is used by the mobile station for synchronization purposes. Based on this change, mobile can syncronize its frequency to that used by Base Station.
That specific data is a "all zeros" burst which produces continuous sine wave which has some dependency with RF centre frequency of that cell. Due to this dependency, it helps the Mobile to get synchronized with the cell.
It's a downlink only channel.
It is sent during BCCH Timeslot allows the mobile to synchronize its own frequency to that of the transmitting cell.
SCH
Synchronization Channel (SCH) is also used for synchronization purposes. However, it is more related to TDMA frame structure than the frequency. This channel carries the Synchronization Channel Information.
It is also send during BCCH TimeSlot.
Registration Procedure
All of those channels are Broadcast Channels
When device is trying to acquire service from a network, the first step is find the FCCH All-Zero burst. After that, it can assume the position of SCH and find it as well.
After finding FCCH and SCH, it can now find the BCCH and receive all Broadcasted information.