US base stations do need time ... and yes they do have
have GPS receivers (which BTW are not cheap) at the towers.
However I assumed that we were talking about the UK
when I answered.
When the IETF TICTOC WG files its reports on the Paris Interim
that happened earlier this week I will point you to a
chart that shows current and NG services and what the timing
As for GSM referenced below, there is definitely no external
time reference used - just 50ppb or better frequency reference.
Andy Talbot wrote:
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.