[time-nuts] GPS Outage..

Bob Camp kb8tq at n1k.org
Sat Feb 27 13:29:40 EST 2016


Hi


All CDMA systems are directly locked to GPS time. None of them do the Gold Code
sync based on central office timing. Prior to CDMA, the AMPS system was frequency 
domain based not time. Those basestations did not use anything more than an OCXO
to keep them up and running on the wireless side of the system. 

Regardless of the ultimate backhaul sync source above the CO, the basestation will keep
talking based on whatever sync pulse it gets on the backhaul link. If the CO goes off and away
network wise, that is only a problem for traffic that leaves the local area. Indeed much of “that stuff”
(Stratum 1,2,3) is based on various timing sources. It also was designed in an era of “top down” 
timing. That is a very different approach than the “bottom up” timing of the over the air codes 
on CDMA or some (but not all) advanced TDMA systems. 

Bob

> On Feb 27, 2016, at 9:50 AM, Tom McDermott <tom.n5eg at gmail.com> wrote:
> 
> The reason many cell sites went to GPS for time and frequency
> synchronization is that in many cases
> it was either less expensive or only possible to backhaul the cell site
> traffic to the MTSO (Mobile Telephone
> Switching Office) via microwave radio rather than wireline copper or fiber
> carrier.
> 
> That microwave backhaul did not always provide sufficiently precise phase
> and frequency reference
> needed at the cell site.
> 
> -- Tom, N5EG
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