Re: Does moving a GPS receiver delay acquisition?

On 23 mai, 20:41, Keith <nos...@xxxxxxxxxx> wrote:
On Fri, 23 May 2008 06:51:12 -0700 (PDT), jonasolof

<jonas.lonnr...@xxxxxxxxx> wrote:
I've spent considerable time experimenting with the satellite
messengar SPoT (www.findmespot.com). It contains a Nemerix GPs chip
specially designed for low power consumption. I have noticed that  if
I walk as the unit is started, acquisitin time seems to be
considerably longer than if the unit is held still, this regardless of
if there is an open sky above.

Is there any reason intrinsic to GPS why moving should delay getting a
fix? It could be that signals are anyhow interrupted while downloading
almanac and ephemeris data, i.e. the sky is not so clear of obstacles
as it seems to the eye. This could be trees, wires etc.

Yes, that would be the main reason, an Ephemeris download (in the case
of a warm start) that gets interrupted and you have to wait en extra
30 seconds.



I have noticed the same effect with the Garmin iQue 3600 which does
not have a modern SIRF III style chip with many correlators.

Jonas Lonnroth,
Brussels- Masquer le texte des messages précédents -

- Afficher le texte des messages précédents -

OK, we all agree and understand that if download of ephemeris is
interrupted, the receiver has to wait 30-40 seconds for the next
cycle. Could there be more reasons? Multipath should not be a reason.
Moving actually helps the receiver discard multipath signals since
they would shift all the time. Could movement have any effect on
correlators and the way the signal is decoded? If the receiver moves,
the next signal won't occcur exactly as expected. Maybe, I'm
guessing.
.

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