Questions regarding maintaining synchronization of a mobile station

Sylvain Munaut 246tnt at
Fri Sep 21 14:18:53 UTC 2018


> 1. How often mobile station (MS) checks if the synchronization is kept?

They listen to the CCCH for their paging slots. The TOA and clock
error of that burst will be used to adjust the timing and frequency.

Between two CCCH, they just count samples ... their clock sync is good
enough to only drift a few samples over several seconds.

> 2. What is usually used to check if synchronization is kept, especially
> when a MS is on a traffic channel?

When it's on a TCH, it just derives the timing and clock from the
burst. The TOA allows you to know how well you're aligned to the TDMA.
And the average symbol rotation over the burst allows you to do fine
frequency tracking.

> 3. How MS regains synchronization? Does it always do full FCCH+SCH scan?

Well it's not a 'scan', they assume they stayed on the same ARFCN so
it will just listen for 12 frames to find FCCH and then SCH.



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