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GSM frequency offset tracking

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esourour

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crystal frequency offset gsm

This is a question for specialists. I am designing a GSM algorithm for estiamting and tracking the frequency offset. According to the GSM specifications, the crystal offset must be < 0.1 PPM. This is normally achieved by locking to the Frequency Correction Channel, prior to a call.

A collegue in the field told me that the GSM chip must, in addition track a possible frequence offset during a call (or file download on GPRS mode) due possibe teperature variation or vibrations. According to him, this is done with the training sequence inside the GSM slot.

Any one knows if this is truly needed? If, yes, any reference for a method or algorithm?

Thanks
 

eda4you

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gsm frequency tracking

hi esourour!

The gsm chip (receive path) synchronize the frequency to the received signal. there is a channel called synchronisation channel which also synchronize the f which has to be locked. As I can remember the offset is a possibility for providers to adjust the frequ. for it needs.
 

gied

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frequency offset estimation for gsm and edge

Hi Esourour!

FCCH appears only once in a while - GSM specs will tell you how often. Please, consider if that is often enough to do estimation.

If FCCH occurs not often enough then you should do what your collegue offered - go for midamble in every burst. While FCCH is purely sinusoidal, midambles are not due to GMSK modulation. Midambles are known in advance as they help to identify BTS. BCC, NCC and TCC parameters control which midamble is used per carrier. Please note that midambles are used to identify EDGE coding scheme, besides providing means for channel estimation.

In case your algorithm is going to run over the air, I am curious, how are planning to cope with doppler shifts and multipath propagation.
 

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