GPS vs. a-GPS question

[garybeck]

Hello,
I could use a little help understanding GPS and a-GPS and how devices are labeled on this site. Its my understanding that a-GPS requires a data connection to work. I want to operate my GPS in areas where there is no data connection available. I also may have a no-data account. So it is essential that my device will have full GPS operation without a data connection.

I have noticed that devices are labeled in a variety of ways on this site, in regards to gps. Some say "yes, with a-gps support." Some say "yes, a-gps".

I interpret "yes, with a-GPS support" to mean that it has a true GPS that can operate independently of a data account, but if there is a data connection available, it will use the a-GPS along with the GPS. (for example T-mobile G2)

I interpret "yes, a-GPS" to mean that it doesn't have a truly independent GPS that can operate without a data connection. (for example HTC Droid INcredible). Is it really possible to have a-GPS without the "regular" basic GPS?

I interpret a simple "yes" to mean it has the basic GPS, with no a-GPS, and will operate just fine without a data connection. (for example T-mobile G1)

Am I correct?

 

[chrlswltrs]

If it has GPS it will work fine. a-GPS just helps finding a location lock faster and inside buildings, etc when GPS is not as reliable. If a phone has a-GPS it still can use GPS only

 

[EarlyMon]

a-GPS means assisted GPS. The initial lock and position data will be taken from cell data towers.

Without that, unlike a traditional GPS unit, an a-GPS unit may take several minutes to lock on.

Quality of GPS tracking varies by make and model and is often influenced by obstructions to a clear sky.

If no such obstructions exist, an a-GPS unit will track via satellite data only. If obstructions occur, an a-GPS unit will augment location data by triangulating from cell phone towers.

If in doubt on a particular phone's rating, best check the manufacturer web or phonearena.com for specs.

AFAIK, most, if not all, Android phones use a-GPS.

Also - visit our individual phone forums once you've zeroed in on a model or two - ask existing users how that phone's GPS works, users are the only ones you can really trust on this.

 

[takeshi]

Its my understanding that a-GPS requires a data connection to work.

That's incorrect. Data requirements come from your GPS app, not your GPS receiver. aGPS receivers do pull assistance data for a faster fix but that's not the same as what you're asking. Most aGPS receivers can fall back on standalone mode if assistance data is not available.

I want to operate my GPS in areas where there is no data connection available.

Again, you need to focus on GPS apps that do not require data. For example, Google Maps Nav requires data since it doesn't store maps or other info locally (except for cached data). However, nav apps such as CoPilot and Navigon do store map data locally.

If obstructions occur, an a-GPS unit will augment location data by triangulating from cell phone towers.

aGPS is not tower triangulation. That's a common misunderstanding. The assistance servers are contacted only to download ephemeris data for a faster initial lock. That's it. If the device isn't using GPS satellites to determine location then the device isn't using GPS of any type.

 

[garybeck]

That's incorrect. Data requirements come from your GPS app, not your GPS receiver. aGPS receivers do pull assistance data for a faster fix but that's not the same as what you're asking. Most aGPS receivers can fall back on standalone mode if assistance data is not available.


Again, you need to focus on GPS apps that do not require data. For example, Google Maps Nav requires data since it doesn't store maps or other info locally (except for cached data). However, nav apps such as CoPilot and Navigon do store map data locally.


aGPS is not tower triangulation. That's a common misunderstanding. The assistance servers are contacted only to download ephemeris data for a faster initial lock. That's it. If the device isn't using GPS satellites to determine location then the device isn't using GPS of any type.

thanks, yes I do realize I need an app that has all the map data stored locally. on my last (Windows) phone I installed Garmin Mobile and it worked great without a phone connection.

it sounds like you are saying that any phone that has anything besides "no" listed in the GPS field will work for me, and the slight variations in the contents of this field are incidental. (even "yes, aGPS" still has a traditional GPS that will work fine without a phone connection, provided I have the standalone software)

 

[takeshi]

You might want to see if you can verify if an aGPS device you're considering can fall back on standalone mode to verify but I've rarely seen this on the spec sheets that I've looked at.

it sounds like you are saying that any phone that has anything besides "no" listed in the GPS field will work for me, and the slight variations in the contents of this field are incidental. (even "yes, aGPS" still has a traditional GPS that will work fine without a phone connection, provided I have the standalone software)

Pretty much -- at least what I can think of off the top of my head. sGPS has nothing to do with data reliance either. It just indicates that the GPS and CDMA radios share an antenna and are designed for simultaneous use with the shared antenna.