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Old 07-24-2008, 01:56 PM   #1 (permalink)
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Default FAQ: Difference between GPS vs A-GPS vs Antenna Triangulate (all 3 different things)

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I wrote an article for a different discussion forum, but I am reposting here, because there is so much confusion about assisted GPS. Many people think "A-GPS" means Antenna GPS or Antenna Triangulation, which is incorrect. Here is the repost:


Quote:
Quote:
Assisted GPS > "true" GPS.
edit: The [BlackBerry] Bold has aGPS, as does the iPhone.
This is correct, but let's be clear there's some confusion:
Some people confuse "aGPS" as "Antenna GPS" versus "Assisted GPS".
Also you should call "true" GPS as "native-only GPS" because Assisted GPS is also true GPS. Some people call antenna triangulation as "Antenna GPS". This is incorrect. Sometimes people mix up "Antenna GPS" and "Assisted GPS" (The AGPS acronym) or make them the same thing. That is not true. One is true GPS and the other is not.

Let me clear up confusion with Plain English<tm>.
I'm writing this from scratch, here goes...

Quality Scale
OKAY: Antenna Triangulation or WiFi Location (Incorrectly called Antenna GPS)
GOOD: Native GPS
BETTER: Assisted GPS (except the Verizon type where you pay extra)
BEST: Assisted GPS with fallback to Native GPS and Antenna Triangulation

Lock Speed And Accuracy Scale
ANTENNA LOCATION - fast lock, less accurate, works indoors
WiFi LOCATION - fast lock, less accurate, works indoors
NATIVE GPS - slow lock, more accurate, outdoors only
ASSISTED GPS - medium-fast lock, more accurate, outdoors only

Difference between Native GPS and Assisted GPS
NATIVE GPS Can lock without phone reception, takes one minute to lock because it needs to search for satellites harder, slow lock, works badly indoors.
ASSISTED GPS Downloads information over the network on how to find the GPS satellites more easily, locks much faster if you have a 3G signal, works slightly better indoors in 1-level and 2-level buildings that aren't metal.

What is Satellite Ephemeris?
Native GPS downloads ephemeris directly from the GPS satellite to help it find the location of GPS satellites.
Assisted GPS downloads ephemeris over EDGE or 3G from the network, to help it find the location of GPS satellites.
Ephemeris is mathematical data to help the cellphone calculate its position. As a grossly over-simplified Math 101 or Excel Macro 101 example, you need to calculate
"Location = ExecuteFormula(A, B)"
where A is the location of the satellites and B is the doppler effect it is detecting in the satellite signal. (You've heard of doppler radar on weather forecasts.) It's possible to download A over the Internet instead of getting A directly from the satellites. All kinds of GPS always needs to get B from the satellite signal, however A doesn't need to be obtained from the satellite signal.
Native GPS can do A and B directly from satellite signal
Assisted GPS can only do B from the satellite signal, and download A over cellphone network.

What is Doppler Effect?
Doppler is the frequency/pitch change in signal from object moving towards or away from you. A train or car going towards you always sounds higher-pitched than when it is moving away from you. The phone listens to the varying pitch in the radio signal being transmitted by the moving GPS satellites, and uses that information to help calculate position.

...

Sometimes GPS can lock indoors in single-level and two-level buildings. For this, Assisted GPS works better than Native GPS because the location signal is easier to receive than the ephemeris signal (which can be downloaded off the Internet instead). Assisted GPS needs to download approximately 100 kilobytes of data for one day's worth of GPS lock capability outside cellphone reception areas. Your cellphone will need to download several day's advance of satellite ephemeris in order to gain GPS lock capability for extended time periods outside cellphone reception areas, if the GPS chip inside your cellphone has the inability to download ephemeris

The best cellphone software can do all the above simultaneously, for maximum speed and maximum accuracy. Locks onto antennas and WiFi, followed by GPS once satellite lock is achieved. My BlackBerry can only do two of the above, but I notice its behaviour: When I first launch Google Maps, it gives me a 1000-meter approximation immediately. A few seconds to a minute later, it improves to 3-meter accuracy as it achieves GPS lock outdoors.

Anything called "GPS" should be able to receive the satellite signal directly. Antenna Triangulation does not, while Assisted GPS does.. Native GPS is best if you're outside of reception, my BlackBerry Curve can lock onto a GPS signal even without a Rogers signal. Some Assisted GPS requires both the GPS signal and cellphone reception available simultaneously, so sometimes "GOOD" and "BETTER" needs to be swapped around for some people. Also, once Assisted GPS has locked on, you can safely go outside of reception, it's just the first lock that may not work on cellphones outside reception that only has Assisted GPS if it has the inability to download satellite ephemeris [wikipedia] over the GPS airwaves. More technical information found on Wikipedia and gpspassion.com

Devices with multiple location capabilities [i.e. support both assisted GPS and non-assisted GPS], can locate through multiple sources for maximum speed and accuracy. Less inaccuracy, less waiting for lock [and cellphone network reception becomes optional].

Sources:
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Last edited by Mark Rejhon : 07-24-2008 at 01:58 PM.
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Old 07-24-2008, 03:19 PM   #2 (permalink)
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Hmm that's interesting. From the article it seems that 8830 definitely doesn't have native GPS. I can't get it to work without network connection, so it's assisted gps.
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Old 07-24-2008, 03:24 PM   #3 (permalink)
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Well that was a nice read, thanks Mark!
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Old 07-24-2008, 09:44 PM   #4 (permalink)
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An addendum to the Assisted GPS.

Appendix A

How Antenna Triangulation optionally helps Assisted GPS

It is also possible for Assisted GPS to take advantage of the GPS location of the antenna towers (or other forms of antenna triangulation) and use this information to only download the subset of ephmeris necessary, and for a short period. This means faster and smaller ephmeris downloads. Basically, the devices does not need to download ephmeris of satellites that are on the opposite side of Earth at the moment in time -- satellites below the horizon are useless for GPS lock at the time.

In this way, ephmeris downloaded more on-demand like this, can be much less than 100 kilobytes per day's of ephmeris, but it does mean that the assisted GPS is more dependant on being in reception location. It also means the ephmeris data becomes useless more quickly after losing GPS lock and cellphone reception. Thus, in exchange for a MUCH SMALLER ephmeris data download, some Assisted GPS devices are unable to function at all outside of the reception zone.

In other words, Antenna Triangulation, or even knowing the location of just a single celltower, can be used as a technique to reduce the size of the satellite ephmeris download -- because it only needs to download the positions of the satellites currently in view in the sky above, and not below the horizon. So thus, Assisted GPS, can optionally take advantage of Antenna Triangulation, to speed up the download of ephmeris necessary to do proper calculations on the doppler of the signal from the actual satellites.

[Note: This technique is frequently used on Verizon]
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Last edited by Mark Rejhon : 07-24-2008 at 09:57 PM.
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Old 07-31-2008, 08:09 PM   #5 (permalink)
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On the BlackBerry Bold, there is a setting labelled "GPS Extended Ephemeris" within the Options, and points to a configurable ephemeris server.

The word "Extended" suggests to me, that BlackBerry Bold is capable of both native GPS and assisted GPS. Basically faster accurate locks whenever there's 3G reception at the same time as GPS reception.
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Old 07-31-2008, 09:27 PM   #6 (permalink)
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Great information Mark. Thanks for sharing.
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Old 08-12-2008, 03:06 PM   #7 (permalink)
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i am looking a gps or trianglation tracking for my bb. I am a bounty hunter and what i want to be able to do is type in a random phone number and it tell me where that phone is. or with trianglation approx where it is. i heard this is legal to have and is available but i cant find anything on it or downloads for it either.
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Old 08-12-2008, 03:10 PM   #8 (permalink)
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Quote:
Originally Posted by theworld1 View Post
i want to be able to do is type in a random phone number and it tell me where that phone is. or with trianglation approx where it is.
Not. I don't think that is available.
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Old 08-12-2008, 03:48 PM   #9 (permalink)
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Quote:
Originally Posted by theworld1 View Post
i am looking a gps or trianglation tracking for my bb. I am a bounty hunter and what i want to be able to do is type in a random phone number and it tell me where that phone is. or with trianglation approx where it is. i heard this is legal to have and is available but i cant find anything on it or downloads for it either.
As per your other, now closed thread; i am a bounty hunter and a guy that i know also has the same profession. he cliams he uses him bb and types in a cell phone number of who he is looking for...

Why can't you just ask the "guy you know" what he's using?
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Old 08-24-2008, 02:27 AM   #10 (permalink)
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I have the BlackBerry Bold now.

I can confirm that it can do GPS both assisted AND un-assisted (natively). Very nice -- makes fixes quicker and easier, especially in marginal situations. The Bold does initial GPS fixes more quickly and easily than the Curve does.

There's an option to turn off the assist part during roaming, which is useful because assisted GPS requires data transfers...
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Old 09-23-2008, 12:33 PM   #11 (permalink)
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Great info and it explains a lot, however one question... on my 8800 and 8110 there is an option for "Location Aiding".... where does that fall within your explanations above?
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Old 10-21-2008, 11:53 AM   #12 (permalink)
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That would probably be AGPS, because it has an option to be disabled while roaming. I found it on my Curve too.
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