GSM Burst types

This page of GSM tutorial on covers GSM burst types which includes gsm burst power spectrum,normal burst,frequency correction burst,Synchronization burst, dummy burst and access burst with fields each burst carries.

GSM Burst RF Power Spectrum

RF power spectrum of GSM burst is as shown in the figure-1 below.

gsm burst power spectrum

Normal burst(NB)

Following figure-2 depicts GSM normal burst.

gsm normal burst

The fields in each slot are described below.

• Trail bits (TB): These are 3 bits at beginning and end of each time slot. Used for synchronization.

• Coded data: This encrypted data coded data are placed in two 57-bit fields in each time slot.

• Stealing bit: It is used to indicate decoder at receiver whether the incoming burst is carrying signaling data or it is carrying user data.

• Training sequence: It is used for multipath equalization, this is used to extract the desired signal from unwanted reflections. This training sequence also used to determine channel the burst has travelled, this helps in correcting rest of the frame and hence helps in decode the transmitted information properly.

• Guard bits: These are about 8.25 bits, used to avoid overlap of different bursts.

Frequency Correction Burst(FB)

Following figure-3 depicts GSM frequency correction burst.

gsm frequency correction burst

It is composed of following fields.
TB (8 bits)
Fixed bit sequence (142 bits)
TB (3 bits)
Guard Time (8.25 bits)

Synchronization Burst(SB)

Following figure-4 depicts GSM synchronization Burst.

gsm synchronization burst

TB (3 bits)
Coded Data (39 bits)
Synchronization sequence (264 bits)
Coded Data (39 bits)
TB (3 bits)
Guard Time (8.25 bits)

Dummy Burst

Following figure-5 depicts GSM dummy Burst.

gsm dummy burst

TB (3 bits)
Mixed (142 bits)
TB (3 bits)
Guard period (8.25 bits)

Access Burst(AB)

Following figure-6 depicts GSM Access Burst.

gsm access burst

Extended TB (8 bits)
Synch sequence bits(41)
Encrypted bits (36)
TB (3 bits)
Extended Guard period (68.25 bits)

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