GSM Broadcast Control Channel (BCCH) Explained

This page describes the GSM Broadcast Control Channel (BCCH). This channel is very critical as it is transmitted/broadcasted to all mobiles within a cell.

It’s a downlink-only signalling channel that carries information to mobiles, organized into different System Information (SI) messages. The BCCH is transmitted within a 51-frame multiframe structure, specifically in the frame following the Synchronization Channel (SCH) on Timeslot 0 (TS0).

It requires at least four consecutive TDMA frames to transmit the complete BCCH information. If necessary, the next four frames are also utilized. The Base Station continuously broadcasts these critical system information (SI) messages.

Once the mobile phone achieves front-end synchronization, it reads this information. This information is crucial for the mobile to determine whether it can “camp on” (i.e., register with) the GSM cell and subsequently access the GSM network.

Some SI messages are mandatory, while others are optional. Some SI messages are even transmitted using the Slow Associated Control Channel (SACCH).

For detailed information on the content of SI-1, SI-2, SI-2bis, SI-2ter, SI-3, SI-4, SI-7, SI-9, SI-13, SI-16, and SI-17 messages, follow the link mentioned below.

BCCH Processing Image

GSM BCCH Broadcast Control Channel: This figure describes the BCCH channel information processing through the physical layer.