GSM SCH(Synchronization Channel)

This page describes GSM Synchronization channel(SCH).

Once the Mobile is frequency synchronized with BTS, it need to be time synchronized which is done using GSM SCH transmitted by BTS in downlink. SCH stands for synchronization channel. It uses SB (synchronization burst).

SCH carry frame number and BSIC (Base Station Identity Code) which helps Mobile synchronize with GSM frame structure as well as helps in identification of the Base station in the GSM network. SCH is carried in 51 frame multi frame structure and it follows the FCCH in the GSM TDMA frame.

SCH carries 25 bits of information divided into 19 bits of reduced frame number and 6 bits of BSIC. 6 bits of BSIC consists of 3 bits of BCC (Base station Color code) and 3 bits of NCC (Network Color code).

SCH processing

•  25 bits of SCH information is added with 10 bits of CRC which gives 35 bits.
•  4 tail bits of all zeros are added to 35 bits which gives total 39 bits of uncoded data.
•  This 39 bits of data are fed to the rate 1/2 convolutional encoder to produce 78 bits of coded data.
•  This gets easily fits into information field of Synchronization burst(SB) and no interleaving is performed on this set of data.
•  This SB is modulated and transmitted over the air from BTS to GSM Mobile or UE(User Equipment).

GSM Channels

GSM RELATED LINKS

RF and Wireless Terminologies