The whole over-air interface for the mobile phone system has to be
locked - the frame structure in GSM is critical to microseconds, and
has to be synchronised between all base stations.  I believe 3G is
even more time-critical, with the PN codes carefully adjusted for
multiple users, with fine tuning for base-mobile delay.  So they must
have accurate timing somewhere, but is it derived locally or is there
a central distribution.

-- 
Andy G4JNT
www.scrbg.org/g4jnt

2008/6/19 Chris Trayner <[email protected]>:
>> I had been told - clearly from a not too informed
> source - that GPS timing units were used at each base station.
>
>> Does the same apply to 3G (or GSM for that matter) mobile networks as well?
>
> I'd guess not. Why would they bother? They've got links (whether microwave or 
> landline) back to somewhere more central. The more central places could have 
> a time source, whether GPS or other. The time signals could be distributed in 
> some priviledged data frame which doesn't wait in any queue.
>
> Mobile systems are complicated, of course, and there might be an unobvious 
> reason to use GPS ...
>
> Regards,
> Chris G4OKW
>