"Atheist Chaplain" <abused@[EMAIL PROTECTED]
> wrote in message
news:RF7Sj.6489$ko5.3857@[EMAIL PROTECTED]
> "Doug Jewell" <ask@[EMAIL PROTECTED]
> wrote in message
> news:48185535$0$9716$5a62ac22@[EMAIL PROTECTED]
>> Atheist Chaplain wrote:
>>
>>> how can aGPS help you to lock on to a satellite signal any quicker ??
>> It's inherent to the way GPS works. They constantly transmit a signal
>> that includes the time according to the satellite's atomic clock, and
>> also the satellite's postion. The receiver uses the time taken for the
>> signals to reach it to determine the distance from the satellite. Using
a
>> bit of math, as long is it knows the distance to 4 or more satellites,
>> and the position of those satellites, it can triangulate. But there's a
>> catch - the satellite transmits this data at a fairly low bitrate, and
so
>> it takes 30 seconds for the whole data packet to be transmitted. In a
>> best-case scenario, it will take 30 seconds to get the position
>> information from the satellite, but if the signal is interrupted,
>> corrupted etc during this 30 seconds, the GPSr doesn't know where the
>> satellite is, so it can't compute the position accurately (or at all).
>> This can cause delays in getting a fix of sometimes several minutes.
>> Additionally, the satellite position data can be up to 2 hours old, and
>> it takes approx 12 minutes for the entire catalog of satellite data to
be
>> downloaded. Until this is received, the accuracy of the fix can be
poor.
>> To speed this process up though, and to get a more accurate fix, some
>> GPSr's allow you to download predicted satellite positions. Because the
>> GPSr already knows the satellite position, it only needs the timecode
>> from the satellite, not the whole packet. This allows a faster, and
more
>> accurate fix.
>>> that's just another rort by the Telco's to extort money from the
>>> gullible, I though aGPS was to download things like voice direction
and
>>> POI's (things that were intentionally stripped out of the Telco
supplied
>>> GPS software so they could then charge you for it at exorbitant data
>>> transfer fee rates)
>>>
>
> while that may be true I have yet to see a time when my Navman GPS
doesn't
> see at least 5 satellites and currently my Tom tom phone system is
> tracking 9 sats. Admittedly I'm not in the concrete jungle of ****ney
but
> even when I am,
And your navman and tom tom have slightly better GPS antenna, and don't
have
a 3G transmitter sitting right next to them causing interference.
> the only time I have lost signal was when I was in one of the tunnels.
to
> be fair I have never been driving so fast in ****ney that the GPS
couldn't
> keep up with my position so I fail to see any benefit from aGPS.
I've turned mine off, but definitely saw quicker lock times for the short
period I had it active.
--
Kwyj.
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