GPS sensitivity: hot start vs. A-GPS (PND vs. mobile)

[Leofly]

I’m trying to collect some data about A-GPS benefits in real life and my main question now is whether assisted GPS (supported by mobile phones) is really more advanced than a standalone PND with similar chipset but assuming I have made fix in good conditions for a short time before?
To my understanding, the assisted data is actually the same as the data my PND can collect after first fix under open sky, so that it should behave like A-GPS for a while. Am I correct here?

[mikealder]

[Leofly]

Mike, I believe you are talking about so-called long term ephemeris. They can speed up the first fix, but are useless for satellite search.
On the contrary, cellular assistance can help GPS both in satellite search and in the following navigation. But this is just a theory, because once the GPS device knows where it was last time (+/-10km does not matter, I think) and keeps integrated clock working, it has actually everything, the mobile operator can provide.
At the end I read about some difference between European and US services (such as fine time aiding in America and coarse time aiding in Europe) which should make sense, but unfortunately there is no fully deployed A-GPS service in my area, so I can't even try. And I don't have a mobile with GPS.
Did you try to compare the mobile phone with activated A-GPS function and a PND when it can make hot start?

[robertn]

Another case where AGPS makes a difference is if you recently used you GPS, but it was long distance away from where you are now. The typical case is when you jump on a plane and fly across the country.

[Leofly]

Basically, what I’m asking is whether mobile based A-GPS indeed outperforms internet based A-GPS?

[Leofly]

http://www.abiresearch.com/Blog/Telematics_Blog/581

Unfortunately, the relentless activity in the GPS-handset, GPS-chipset and navigation software space is not matched by a similar trend in the roll out of A-GPS network infrastructure by European carriers, most of which remain passive

any comments?

[philpugh]

[robertn]

I agree wioth what you say.
A-GPS solves a problem that no longer exists. When it was developed, in the early 2000's, GPS chipsets were significantly less sensitive, and prone to problems getting the first fix. The idea in those days was to go outside, into a big open feild or carpark, and get a fix before doing anything (Searhc the archives for examples of advice given.....). A-GPS would have been useful then. Now, the recievers pick up any wif of a signal, and therefore get the first fix more reliably.

(the authorities track your evey move now, they don't need A-GPS to that)

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