Explain the GSM frame structure. OR With neat diagram describe the GSM Frame Structure. OR Explain GSM frame structure with neat diagram.


With neat labeled diagram describe GSM frame architecture.

Subject: Mobile Computing

Difficulty: Medium

Marks: 4 Marks

1 Answer

Frame structure in GSM:

• The length of GSM frame in a frequency channel is 4.615 ms.

• The frame is divided into 8 bursts of length of 0.577ms

• The timeslots in the uplink are derived from downlink by a time delay of 3 time slots

• This arrangement prevents an MS from transmitting and receiving at the same time

• However, due to propagation delay (when MS is far away from BTS) the 3 TS delay cannot be maintained accurately.

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GSM Burst structure:

• Each burst contains 148 bits (0.546ms) followed by 0.031ms guard time (8.25bits)

• The burst begins with 3 head bits and 3 tail bits (logical Zeroes)

• Two groups are data bits are separated by an equalizer Training sequence of 26 bits

• Each data group consists of 57 bit information bits and 1 flag that indicate whether the information bits are for user speech/ data or signaling.

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