Em 02/01/2013 14:35, alan.b.pearce@stfc.ac.uk escreveu:
>> As long as the GPS locks onto the time within 5 minutes, I think the cli=
ent will
>> be happy.  They are also fixed position.  Would this help?
>>
>> Maybe using the GPS to correct an on-board RTC would be a better option?
> The biggest thing that determines the time it takes a GPS to determine it=
s position is the number of channels it has. I have an old module with only=
 8 channels and it takes several minutes (well, it seems like it, anyway) t=
o get a fix. I have a more recent one that has 24 channels (I think, well, =
at least 16) and is a lot faster in getting a fix from a cold start. I susp=
ect you will find this is the case with most modern modules, so I don't see=
 it as a problem.


The "channels" you are referring to are indeed correlators, to speed up
the synching with the satellites DSSS sequences.
Usually a GPS will see at most 12 satellites (perhaps a little more when
some are just "rising" or  almost "setting" above the horizon).

The larger number of correlators is useful only at start-up when the GPS
doesn't know at which position in the DSSS sequences the satellites are.
This way it can try several starting points at the same time. Once the
DSSS sequence is acquired, it needs just one correlator for each satellite.

Isaac


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