A-GPS vs GPS

I know A-GPS consists in a GPS usually installed into mobile phone combined
to mobile technology to let heavy math operations are done on the server
instead of the mobile device in order to reduce energy consumption. Is it
right?

What I don't know is if A-GPS position is in real-time like GPS one and if
A-GPS position is more accurate than GPS one.

In other terms: does an addition chipset (like GSM) improve the GPS quality
on our navigators?

Massimo

was claimed to have wrote:


It all depends on what the device means by "A-GPS"

Some devices without GPS chips have called themselves "A-GPS", meaning
that they provide a location based on mobile network or wifi
triangulation rather then GPS. Other devices use A-GPS to assist a true
GPS receiver. This is a "best of both worlds"

A-GPS triangulation is very fast, but at best you'll get a rough
approximation of where you, potentially within a few dozen meters in a
high density area, or at least within a few blocks in a low density
area. However, you'll get this information within a couple seconds
rather then the minutes it can take a GPS to get a lock from a cold
start. The downside is when wifi base stations move around in the real
world it usually takes time before the A-GPS world finds out about it,
so you'll occasionally get very inaccurate information.

Real GPS can take minutes from a cold start, many seconds from a hot
start, but can provide a much more accurate location.

Combined, A-GPS can bring enough information to the GPS receiver to
create an almost-hot-start scenario, downloading satellite locations and
providing the GPS with some clues, so by working together A-GPS and GPS
can get you a moderately accurate location almost instantly and a true
GPS lock in a fraction of the worst-case-scenario time it could have
taken.

They also complement each other well in "urban canyons" (downtown in any
large city), GPS has trouble getting a solid lock without something
resembling line of sight access to multiple satellites, whereas A-GPS
tends to get more reliable in high density urban areas. A-GPS isn't
good enough for turn by turn directions, but in a major urban center it
can usually tell you within a block of your real location while true GPS
may not have a usable signal at all.

On Sat, 17 Oct 2009 10:36:59 +1000, Doug Jewell


Not my experience at all with a HTC Touch 3G or my iPhone 3GS, I get
fast locks thanks to the cell tower triangulation when I can get a
phone signal, but works fine with or without a phone signal. There is
no hidden backend number crunching going on.
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Except that it *does* work like that.

Grab yourself an iPod Touch (no GPS, no cell radio) and try the Google
Maps app, it can identify your location based on the wifi access points
nearby.

The same thing happens when you move a wifi access point a significant
distance (like when I relocated cities a few months back) on an iPhone
3G, cell tower location (with wifi off) gets me within a few dozen
blocks from a concrete basement. Turn on wifi, try again, and the
identified location is my old house in my old city. Now move somewhere
that the GPS can get a lock and watch the iPhone get a GPS based
location.

http://www.skyhookwireless.com/howitworks/ gives a bit of glossed over
technical details.

Take a look at http://www.skyhookwireless.com/howitworks/coverage.php
under "Automated Self-Healing Network" for how Skyhook deals with access
points that move, and/or new access points.

DevilsPGD wrote:

It


Except that it *doesnt* work like that.

The SkyHook Wireless system is not related to AGPS, or regular GPS other
than it's just another locational system.
It doesn't "link" to, or talk to the WiFi systems it uses, other than just
observing it's signal. The *location* of the WiFi Access Point it's observing
is in an internal database, and it uses that.

So, with worse coverage than AGPS, it needs WiFi Access Points AND it needs
those points to have been pre-processed by the SkyHook people beforehand.

Wow. That's nice, if you happen to live with the 70% of Canada or USA where
points are logged, great. For the rest of the world, it's more money for a
product that's going to do basically jack shit.
Not to mention this system needing an infrastructure to work, adding to the
cost for something that's only going to be useful for me - never.


I'm not going to grab an iAnything. I have a low tolerance for shit that
doesn't work, so I pick my hardware and software separately. That way, it's
cheaper, I get exactly what I want, not what someone tells me is all the rage.

Especially since I occasionally spend time out in the middle of nowhere -
and don't see the point in duplicating hardware (and cost) where one does the
job nicely thanks.


Ah, that's where we do things differently.
I already know where my basement is. I don't need several hundred dollars
worth of electronic gadgetry to tell me.



Oh, that's nice. "Submit a Wi-Fi Access Point"? So they're getting users to
update points now. Someone should invent an Online Encyclopaedia that takes
users' updates. Just imagine the content, the update time, the incredible
accuracy. Yes, the accuracy should be astonishing.
--
Linux Registered User # 302622