A-GPS vs GPS
Maelmoro
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
DevilsPGD
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.
Doug Jewell
> 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?
with the addition of positioning based on mobile phone
towers to give faster and more accurate positioning - a bit
like WAAS.
However based on my observations with my Samsung Blackjack
II, I believe it is very much like you describe. My
Blackjack will not get any satellite fix at all if it is
outside mobile reception. Even if you are driving, with a
nice full constellation of satellites, if you drive outside
a mobile reception area, you instantly completely lose GPS.
Furthermore, battery life is pitiful whenever the GPS is on,
and network data is quite high. This all points me to
believe that it is indeed doing as you describe and
transmitting the raw GPS data back to a server somewhere
which does the number crunching, and sends the position back
to the phone.
As for your comment about reducing energy consumption, I
think it is more about the manufacturers taking shortcuts to
cut manufacturing costs, than about energy consumption. Full
GPS receiver chips do not use a lot of power, but
transmitting a mobile data signal does. I have a bluetooth
GPS receiver with a battery much smaller than my mobile
phone, which can operate for 24 hours on battery. My Garmin
handheld unit can run for a similar period on a pair of
AA's. My Blackjack OTOH is lucky to run for an hour with the
GPS turned on. And the difference is not just the display.
Playing games the Blackjack lasts for hours, but running GPS
with the screen turned off on the blackjack only marginally
improves battery life.
There may be some mobile phones out there that do have real
GPS chipsets in them, but the above is my observation of how
the blackjack works. My sister has a Nokia (not sure of
specific model) and her experience has been the same, so I'd
guess it uses the same method.
>
> 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.
Firstly, real GPS isn't quite real time - it usually only
updates approx every few seconds. (some programs will
interpolate during the gap to give the impression of being
real time). My impression of the Blackjack is that it is
slightly laggy compared to conventional GPS, but the
difference isn't a lot - maybe an extra half second. In
practice for driving, or for walking it is not noticeably slow.
>
> In other terms: does an addition chipset (like GSM) improve the GPS quality
> on our navigators?
Well in theory it should. If the receiver was able to
triangulate from Mobile phone towers in addition to the
satellite it should give extra accuracy. Similarly, by
getting satellite positioning information from the network
rather than from the satellite, it should be able to get a
fix much quicker.
In practice though, that's not what I've found with my
Blackjack. Compared to my conventional GPS's I find the
Blackjack seldom gets to within 20m of an accurate fix,
often up to 50m out. This is ok for driving, but for
anything where you want a reasonably accurate fix (eg
geocaching) it is hopeless. On occasions it has been several
km out of whack, and for about two weeks it was constantly a
few thousand km out. I'm in southern Queensland, Australia,
and for 2 weeks it was telling me I was in the vicinity of
New Caledonia and travelling in random directions at about
700km/hr. Another time, I was trying to use it to navigate
through Brisbane one morning, and it had been going nicely,
but suddenly jumped me onto a road about 5km away from where
I really was. I found a shop where I could buy a TomTom
street navigator, which had no problems positioning me. I
had the 2 on just to compare, and it took several hours
before the phone suddenly jumped to the right location
again. My sister has reported similar issues with her Nokia
also.
Real GPS will occasionally have a positioning hiccup, but if
it does you can usually rectify it by turning it off and
back on again or forcing it to do a refresh of the
satellites (depending on model). With my mobile if it has a
positioning problem, turning it off and back on won't reset
the problem - further indication that all the processing is
taking place remotely. You just have to wait until it gets
itself together again, which can be anything from a couple
of hours to several days.
If I was to describe it in two words, they would be "FUCKING
USELESS".
>
> Massimo
>
>
--
What is the difference between a duck?
Andrew
<a...@and.maybe.ill.tell.you> wrote:
>However based on my observations with my Samsung Blackjack
>II, I believe it is very much like you describe. My
>Blackjack will not get any satellite fix at all if it is
>outside mobile reception. Even if you are driving, with a
>nice full constellation of satellites, if you drive outside
>a mobile reception area, you instantly completely lose GPS.
>Furthermore, battery life is pitiful whenever the GPS is on,
>and network data is quite high. This all points me to
>believe that it is indeed doing as you describe and
>transmitting the raw GPS data back to a server somewhere
>which does the number crunching, and sends the position back
>to the phone.
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.
--
Andrew, contact via http://interpleb.googlepages.com
Help make Usenet a better place: English is read downwards,
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Check groups.google.com before asking an obvious question.
John Tserkezis
> If I was to describe it in two words, they would be "FUCKING USELESS".
Also keep in mind that real GPS is free to use (once purchased) AGPS cost
money to use. Not in the form of royalties, but there is some data going back
and forth between the phone and the base towers to confirm numbers and thus
location.
I never understood the "G" bit in the AGPS acronym, because there's nothing
"Global" about it. Basically, if you don't have GOOD all-round coverage of
towers, you're not going to get any useful location lock.
To the original poster:
AGPS does *NOT* use WiFi. And never will. For something like this to work
you need to have some known givens. One of those is location of base stations.
With WiFi, by their very nature, cannot, and do not "know" where they are,
have no provision to be told where they are, and thus cannot forward any
useful information to the 'receiver' on where it might be located.
As far as AGPS having problems with WiFi stations moving around, and needing
some time before the real word finds out about them, that is not the case. It
doesn't work like that. And never will.
--
Linux Registered User # 302622
<http://counter.li.org>
DevilsPGD
Tserkezis <j...@techniciansyndrome.org.invalid> was claimed to have wrote:
> AGPS does *NOT* use WiFi. And never will. For something like this to work
>you need to have some known givens. One of those is location of base stations.
> With WiFi, by their very nature, cannot, and do not "know" where they are,
>have no provision to be told where they are, and thus cannot forward any
>useful information to the 'receiver' on where it might be located.
>
> As far as AGPS having problems with WiFi stations moving around, and needing
>some time before the real word finds out about them, that is not the case. It
>doesn't work like that. And never will.
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.
John Tserkezis
>> As far as AGPS having problems with WiFi stations moving around, and needing
>> some time before the real word finds out about them, that is not the case. It
>> doesn't work like that. And never will.
> Except that it *does* work like that.
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.
> 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.
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.
> 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.
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.
> 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.
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.
claudegps
wrote:
> Doug Jewell wrote:
> > If I was to describe it in two words, they would be "FUCKING USELESS".
>
> Also keep in mind that real GPS is free to use (once purchased) AGPS cost
> money to use. Not in the form of royalties, but there is some data going back
> and forth between the phone and the base towers to confirm numbers and thus
> location.
>
> I never understood the "G" bit in the AGPS acronym, because there's nothing
> "Global" about it. Basically, if you don't have GOOD all-round coverage of
> towers, you're not going to get any useful location lock.
GPS is global.
Assistance is not. But GPS remains global.
> AGPS does *NOT* use WiFi. And never will.
You can have assistance using WiFi.
There are many ways to "assist" you GPS and WiFi is one of them. You
can download ephemeris for example.
There are mamy diffente types of "A-" for A-GPS :)
claudegps
> Maelmoro wrote:
> > 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?
>
> As far as I was aware A-GPS was supposed to be normal GPS
> with the addition of positioning based on mobile phone
> towers to give faster and more accurate positioning - a bit
> like WAAS.
WAAS is not designed to give faster positioning. :)
DevilsPGD
Tserkezis <j...@techniciansyndrome.org.invalid> was claimed to have wrote:
>DevilsPGD wrote:
>
>>> As far as AGPS having problems with WiFi stations moving around, and needing
>>> some time before the real word finds out about them, that is not the case. It
>>> doesn't work like that. And never will.
>
>> Except that it *does* work like that.
>
> 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.
Skyhook does need internet access, yes.
> 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.
Again,
> 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.
So because *you* have no use for a technology, it shouldn't exist? Since
my grandmother has no use for GPS, I would request you cease using it
immediately, and we petition the gov't to discontinue the GPS satellite
network immediately.
Either that, or we'll all use what works best for us.
>> 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.
>
> 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.
Good for you. Grab whatever hardware or software you want, the point is
that you can find a surprisingly accurate location without anything
beyond an 802.11b radio and internet access.
> 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.
GPS can't always get a useful lock in an urban canyon, whereas Skyhook
tends to work better in high density areas.
Given the choice of one or the other, I'd take GPS over Skyhook every
time, but together gives you a best-of-both-worlds combination,
especially if you already have always-on internet.
>> 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.
>
> 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.
You might know where *your* basement is, but if you're in a hotel in an
unfamiliar city you might not know where you are to find yourself on a
map. GPS will likely take several minutes to get a fix in a new city
from inside a hotel, whereas Skyhook gets you an answer nearly
instantly.
Sure, sometimes that answer will be "Not a clue" in which case you fall
back to GPS, and you do need internet access for it to work, but it adds
significant value when an approximate location available instantly is of
more use then a location in 30 seconds to 30 minutes.
> Oh, that's nice. "Submit a Wi-Fi Access Point"? So they're getting users to
>update points now.
Skyhook also sends cars around to refresh the database, and updates
dynamically when the opportunity is available. Submitting a wifi access
point is as simple as firing up an iPhone with wifi and GPS enabled,
opening Google Maps and waiting until you have a solid GPS lock.