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| Johnson... |
 Posted: Tue Nov 03, 2009 11:26 am |
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http://www.3g.co.uk/PR/April2006/2970.htm
"The benefit of fine time aiding is that the device now knows where to
look for a GPS signal. This enables a more aggressive search and is
equivalent to 6 dB more sensitivity than can be achieved with any amount
of GPS hardware correlator in the terminal. So powerful is this
assistance that it also enables software-only GPS solutions to operate
reliably in all environments. "
Could anybody please explain how the 6dB or more sensitivity is
achieved? Does it come from longer integration time? Or from long
coherent integration versus non-coherent sum?
Thanks.
Johnson |
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| claudegps... |
| Posted: Tue Nov 03, 2009 11:26 am |
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On 3 Nov, 17:26, Johnson <gpsab... at (no spam) yahoo.com> wrote:
[quote]http://www.3g.co.uk/PR/April2006/2970.htm
"The benefit of fine time aiding is that the device now knows where to
look for a GPS signal. This enables a more aggressive search and is
equivalent to 6 dB more sensitivity than can be achieved with any amount
of GPS hardware correlator in the terminal. So powerful is this
assistance that it also enables software-only GPS solutions to operate
reliably in all environments. "
Could anybody please explain how the 6dB or more sensitivity is
achieved? Does it come from longer integration time? Or from long
coherent integration versus non-coherent sum?
Thanks.
Johnson
[/quote]
Apart from technichal terms, the more sensitivity is achieved because
you know with a very good approximation where to search for the
signal.
This allow the receiver to use longer integration times that you could
not use on the full search range that is needed for acquisition
without any aiding.
It's similar to the situation you have in a hot start |
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| Johnson... |
| Posted: Tue Nov 03, 2009 5:09 pm |
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claudegps wrote:
[quote]On 3 Nov, 17:26, Johnson <gpsab... at (no spam) yahoo.com> wrote:
http://www.3g.co.uk/PR/April2006/2970.htm
"The benefit of fine time aiding is that the device now knows where to
look for a GPS signal. This enables a more aggressive search and is
equivalent to 6 dB more sensitivity than can be achieved with any amount
of GPS hardware correlator in the terminal. So powerful is this
assistance that it also enables software-only GPS solutions to operate
reliably in all environments. "
Could anybody please explain how the 6dB or more sensitivity is
achieved? Does it come from longer integration time? Or from long
coherent integration versus non-coherent sum?
Thanks.
Johnson
Apart from technichal terms, the more sensitivity is achieved because
you know with a very good approximation where to search for the
signal.
This allow the receiver to use longer integration times that you could
not use on the full search range that is needed for acquisition
without any aiding.
It's similar to the situation you have in a hot start
I think that I possibly figure out how the 6db comes from.[/quote]
1. Without precise time stamp, it is impossible to do coherent
integration over 20ms. Thus non-coherent sum is likely the option. There
is a 3db loss.
2. An example of non-coherent sum: Sum of 10ms coherent integration. Due
to the present of the navigation bit transition, the sum without prior
knowledge of navigation data bits is about 50% less than the sum if the
navigation data bit transition can be located (for the worst case).
Another 3db.
However, assume the chance of data bit transition is 50%, not 100%, 2
actually is not true. |
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| Terje Mathisen... |
| Posted: Wed Nov 04, 2009 1:50 am |
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Johnson wrote:
[quote]claudegps wrote:
On 3 Nov, 17:26, Johnson <gpsab... at (no spam) yahoo.com> wrote:
http://www.3g.co.uk/PR/April2006/2970.htm
"The benefit of fine time aiding is that the device now knows where to
look for a GPS signal. This enables a more aggressive search and is
equivalent to 6 dB more sensitivity than can be achieved with any amount
of GPS hardware correlator in the terminal. So powerful is this
assistance that it also enables software-only GPS solutions to operate
reliably in all environments. "
Could anybody please explain how the 6dB or more sensitivity is
achieved? Does it come from longer integration time? Or from long
coherent integration versus non-coherent sum?
Thanks.
Johnson
Apart from technichal terms, the more sensitivity is achieved because
you know with a very good approximation where to search for the
signal.
This allow the receiver to use longer integration times that you could
not use on the full search range that is needed for acquisition
without any aiding.
It's similar to the situation you have in a hot start
[/quote]
Right.
[quote]I think that I possibly figure out how the 6db comes from.
1. Without precise time stamp, it is impossible to do coherent
integration over 20ms. Thus non-coherent sum is likely the option. There
is a 3db loss.
2. An example of non-coherent sum: Sum of 10ms coherent integration. Due
to the present of the navigation bit transition, the sum without prior
knowledge of navigation data bits is about 50% less than the sum if the
navigation data bit transition can be located (for the worst case).
Another 3db.
However, assume the chance of data bit transition is 50%, not 100%, 2
actually is not true.
[/quote]
The article stated that they supplied "1-2 us clock information", which
together with a ~100m initial position would be enough to lock onto the
1.023 Mhz data rate almost instantaneously. (I do assume they also
supply updated sat ephemeris data!)
This seems very similar to simply re-acquiring the GPS signals after a
very short-term loss, like a tunnel transition.
Terje
--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching" |
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