[time-nuts] Time syncing question

[Didier Juges]

The first phone I had where I observed the time zone error, after the 
plane had landed in a new time zone and the phone had not been turned 
off during the flight (and no, the plane did not crash, not that time) 
was an Alltel phone. Alltel uses CDMA.

Again, this was just an observation.

I suspect the radio inside the phone knows time precisely (to within uS) 
so it can encode and decode the signals, but it only knows the time 
modulo some period of milliseconds or seconds. It does not need to know 
time of day, only relative time with respect to the sync signal from the 
cell tower. The processor driving the UI knows time of day, but does not 
necessarily share the precise clock with the radio.

I have also observed that systems with an acurate time base needed for 
some specific processing do not necessarily use the same time base for 
general uP operation, or even for time of day. It is sometimes simpler 
and cheaper and less troublesome to have a cheap XO near the processor 
just so that you do not need to carry the sensitive precise clock all 
over the equipment.

Didier KO4BB

>
> 	I assume most members of this august group know that all CDMA cellphones
> MUST know the correct time to within about 1 us or so in order to correctly
> spread and despread the forward and reverse channel signals.
>
>