Each GSM user transmits data burst during a time slot that is assigned to it. The transmission of bursts occurs in a particular format called the GSM frame.
There are five types of data bursts for controlling the traffic bursts.
- Normal bursts
- FCCH full form burst
- RACH full form burst
- SCH full form burst
- Dummy burst
Normal burst :
The normal burst is used for TCH and the DCCH transmissions on the forward and reverses link. It consists of 148 bits that are transmitted at a rate of 270.83 Kbps. Only 114 bits are information bits that are transmitted as two sequences of 57 bits.
FCCH burst :
It consists of 3 start bits 3 stop bits with 142 bits between the start bits and stops bits. The stop bits are followed by a guard period of 8.25 bits.
RACH burst :
It consists of 8 start bits and 3 stop bits. It 41 bits for synchronization of transmitter and receiver, 36 bits of encrypted data an extended guard period of 68.25 bits.
It consists of 3 starts and 3 stop bits. It contains two parts of 58 mixed bits that are separated by 26 training bits and a guard period of 8.25 bits.
It consists of 8 start bits and 3 stop bits. It 41 bits for synchronization of transmitter and receiver, 36 bits of encrypted data an extended guard period of 68.25 bits.
SCH burst :
It consists of 3 start bits, 39 bits of encrypted data, 64 training bits, 3 stop bits and a guard period of 8.25 bits.
Dummy burst :
It consists of 3 starts and 3 stop bits. It contains two parts of 58 mixed bits that are separated by 26 training bits and a guard period of 8.25 bits.
The frame structure of GSM :
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GSM frame structure |