AGPS or Assisted GPS

[+LukeTrocity]

I figured I would post some knowledge about cell phone triangulation known as AGPS or Assisted GPS. Most modern day smartphone's come with not only GPS installed but also AGPS. AGPS is exactly what it says, it assists your GPS to find your position faster. The first time you turned on your GPS R you probably noticed the "?" symbol somewhere on it while it locked onto your location. Your initial boot probably took quite a while because your GPS was trying to find satellites, and they were trying to find you with no point of reference. After that initial boot, as long as you turned on your GPS R somewhere near that area you should get a relatively quick lock. Now if you were to turn off your GPS R again and travel across country you would experience probably a similar boot to your initial loading because again your reference points are all off. This is exactly what AGPS is good for.

 

AGPS if turned on, uses cell tower triangulation to give a very rough approximation of where you are. I would say if your phone only had AGPS you would never find a geocache you were looking for....its simply not accurate enough. However this coupled with the GPS feature of your smartphone should give you quick accurate readings. The cell towers first give your rough position and your GPS chipset finishes the job. This provides some advantages in heavy cover as well. It will help give a better, more accurate lock than normal on a smartphone.

 

For these reasons I would suggest that users keeps AGPS on while using your phone to geocache. Again this should be used in conjunction with your GPS chipset and not standalone.

 

Here is an example of searching for caches with just AGPS on turned on:

 

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Here is with AGPS and GPS turned on and functioning.

 

 

Pretty huge difference in distance. So remember AGPS is GOOD, and should be used in conjunction with your GPS enabled smartphone!

 

(I use Android based smartphones. I have used the Droid Incredible, Droid Pro and Droid X. I can't attest to your iphone or blackberry sorry.)

[+StarBrand]

Units with Garmin's predictive sat startup feature also get a rapid lock on coordinates.Smartphones need access to a cell signal to use the assisted GPS feature. Many areas out my way can't get a signal in rural areas. Furthermore - no smartphone I have seen can stand up to the general outdoor roughness that a unit can be subjected to (rain, snow, dust, drops, etc).

[+LukeTrocity]

Units with Garmin's predictive sat startup feature also get a rapid lock on coordinates.Smartphones need access to a cell signal to use the assisted GPS feature. Many areas out my way can't get a signal in rural areas. Furthermore - no smartphone I have seen can stand up to the general outdoor roughness that a unit can be subjected to (rain, snow, dust, drops, etc).

How did this turn into gps vs smartphone? I'm simply informing people of agps for smartphones...

[+dfx]

The first time you turned on your GPS R you probably noticed the "?" symbol somewhere on it while it locked onto your location. Your initial boot probably took quite a while because your GPS was trying to find satellites, and they were trying to find you with no point of reference. After that initial boot, as long as you turned on your GPS R somewhere near that area you should get a relatively quick lock. Now if you were to turn off your GPS R again and travel across country you would experience probably a similar boot to your initial loading because again your reference points are all off.

I find this somewhat misleading, as the boot time isn't affected by the GPS fix. You're talking about TTF (time to fix) and not boot time, even though you probably mean the right thing.

 

You should probably also mention that AGPS means that the phone downloads vital information about the current GPS status (ephemeris/almanac) off the internet or the cell network and uses that to get a faster fix. I don't know if the GPS chip would be able to get any faster fix time without that information, or if knowing the approximate location is any help at all.

 

This provides some advantages in heavy cover as well. It will help give a better, more accurate lock than normal on a smartphone.

Got any references? I find that somewhat questionable.

[+LukeTrocity]

@dfx

 

http://gps.about.com/od/glossary/g/A-GPS.htm

[+dfx]

@dfx

 

http://gps.about.com...ary/g/A-GPS.htm

 

That says that the almanac is downloaded from the cell network to obtain a faster TTF. And it says that it uses the cell network to determine coarse location information when GPS isn't available. It doesn't say that it improves GPS accuracy over a stand-alone GPS mode (which I believe is not true), and it doesn't say that knowing coarse location information helps it to get a faster TTF (which I don't know if it's true or not).

[+LukeTrocity]

@dfx

 

http://gps.about.com...ary/g/A-GPS.htm

 

That says that the almanac is downloaded from the cell network to obtain a faster TTF. And it says that it uses the cell network to determine coarse location information when GPS isn't available. It doesn't say that it improves GPS accuracy over a stand-alone GPS mode (which I believe is not true), and it doesn't say that knowing coarse location information helps it to get a faster TTF (which I don't know if it's true or not).

GPS satellite signals may be impeded by tall buildings, and do not penetrate building interiors well. A-GPS uses proximity to cellular towers to calculate position when GPS signals are not available.

[+julianh]

Some smart-phones go beyond just cell-phone tower triangulation to get the A (Assisted) in AGPS. My HTC Wildfire (Android) also uses Wi-Fi, so if you have Wi-Fi turned on, and there is a Wi-Fi network within range which has been mapped by Google's StreetView cars, it can use the very limited reception range of Wi-Fi to get an approximate location within 50 metres or so, even with no GPS reception at all. This is significantly better accuracy than can be achieved using cell phone tower triangulation. This system works really well in urban areas with good StreetView coverage, not much value in rural areas with no Wi-Fi connectivity. You don't have to be connected to the Wi-Fi network, just have it within range.

 

For example, sitting in my office building, with zero GPS Sat's visible, Google Maps will still find my location to the correct corner of my building! I suspect many current generation smartphones have similar capability.

[+LukeTrocity]

Some smart-phones go beyond just cell-phone tower triangulation to get the A (Assisted) in AGPS. My HTC Wildfire (Android) also uses Wi-Fi, so if you have Wi-Fi turned on, and there is a Wi-Fi network within range which has been mapped by Google's StreetView cars, it can use the very limited reception range of Wi-Fi to get an approximate location within 50 metres or so, even with no GPS reception at all. This is significantly better accuracy than can be achieved using cell phone tower triangulation. This system works really well in urban areas with good StreetView coverage, not much value in rural areas with no Wi-Fi connectivity. You don't have to be connected to the Wi-Fi network, just have it within range.

 

For example, sitting in my office building, with zero GPS Sat's visible, Google Maps will still find my location to the correct corner of my building! I suspect many current generation smartphones have similar capability.

 

Good point, I have tried that as well and noticed its quite accurate.

[+dfx]

GPS satellite signals may be impeded by tall buildings, and do not penetrate building interiors well. A-GPS uses proximity to cellular towers to calculate position when GPS signals are not available.

 

Yeah, so no GPS reception -> uses cell network for approximate location. That doesn't mean that it helps when GPS reception is poor, it means it helps when GPS reception is none.

[+LukeTrocity]

GPS satellite signals may be impeded by tall buildings, and do not penetrate building interiors well. A-GPS uses proximity to cellular towers to calculate position when GPS signals are not available.

 

Yeah, so no GPS reception -> uses cell network for approximate location. That doesn't mean that it helps when GPS reception is poor, it means it helps when GPS reception is none.

 

Assisted GPS (also known as AGPS or A-GPS) is often found on mobile devices such as phones. It improves accuracy and availability of location information in two ways. First, it uses the mobile phone network to retrieve satellite location information. This enables the GPS receiver to obtain a faster “time to first fix” (TTFF). This means that the information does not need to be downloaded from the satellite and the receiver can get valid position data more quickly. Second, if the GPS signal is WEAK or unavailable, AGPS will use position information for mobile phone base stations to triangulate a position.

 

http://blog.prosig.com/2010/04/12/everything-you-ever-wanted-to-know-about-gps-but-were-afraid-to-ask/

[+StarBrand]

Units with Garmin's predictive sat startup feature also get a rapid lock on coordinates.Smartphones need access to a cell signal to use the assisted GPS feature. Many areas out my way can't get a signal in rural areas. Furthermore - no smartphone I have seen can stand up to the general outdoor roughness that a unit can be subjected to (rain, snow, dust, drops, etc).

How did this turn into gps vs smartphone? I'm simply informing people of agps for smartphones...

...and I was pointing out that you do not need a smartphone to gain virtually the same advantage while also not worrying about destroying your phone.

[+Cacheoholic]

GPS satellite signals may be impeded by tall buildings, and do not penetrate building interiors well. A-GPS uses proximity to cellular towers to calculate position when GPS signals are not available.

 

Yeah, so no GPS reception -> uses cell network for approximate location. That doesn't mean that it helps when GPS reception is poor, it means it helps when GPS reception is none.

 

Assisted GPS (also known as AGPS or A-GPS) is often found on mobile devices such as phones. It improves accuracy and availability of location information in two ways. First, it uses the mobile phone network to retrieve satellite location information. This enables the GPS receiver to obtain a faster “time to first fix” (TTFF). This means that the information does not need to be downloaded from the satellite and the receiver can get valid position data more quickly. Second, if the GPS signal is WEAK or unavailable, AGPS will use position information for mobile phone base stations to triangulate a position.

 

http://blog.prosig.com/2010/04/12/everything-you-ever-wanted-to-know-about-gps-but-were-afraid-to-ask/

 

Ok…so 0.5 – 0.25 mile accuracy AGPS beats no GPS lock. I guess that makes AGPS + GPS more accurate than GPS?

[+LukeTrocity]

Units with Garmin's predictive sat startup feature also get a rapid lock on coordinates.Smartphones need access to a cell signal to use the assisted GPS feature. Many areas out my way can't get a signal in rural areas. Furthermore - no smartphone I have seen can stand up to the general outdoor roughness that a unit can be subjected to (rain, snow, dust, drops, etc).

How did this turn into gps vs smartphone? I'm simply informing people of agps for smartphones...

...and I was pointing out that you do not need a smartphone to gain virtually the same advantage while also not worrying about destroying your phone.

 

My phone seems ok so far....and still way off topic.

[+dfx]

Assisted GPS (also known as AGPS or A-GPS) is often found on mobile devices such as phones. It improves accuracy and availability of location information in two ways. First, it uses the mobile phone network to retrieve satellite location information. This enables the GPS receiver to obtain a faster "time to first fix" (TTFF). This means that the information does not need to be downloaded from the satellite and the receiver can get valid position data more quickly. Second, if the GPS signal is WEAK or unavailable, AGPS will use position information for mobile phone base stations to triangulate a position.

 

http://blog.prosig.c...-afraid-to-ask/

 

And it's still saying the same thing. If GPS signals can't deliver position information with good enough accuracy, it falls back to using the cell network to get coarse position information. It's still either or. Either GPS fix or cell-based position information. It does not make a bad GPS fix better by using the cell network. Only if the GPS fix is so bad that its accuracy is actually worse than the location determined from the cell network, then the GPS fix will be disregarded and the other position used instead. This usually only happens when there's no GPS fix at all (which doesn't necessarily mean that there's no GPS signals, just that they're not strong enough to lock onto).

 

At least that's what the sources cited by you are saying so far.

Edited February 27, 2011 by dfx

[+StarBrand]

Units with Garmin's predictive sat startup feature also get a rapid lock on coordinates.Smartphones need access to a cell signal to use the assisted GPS feature. Many areas out my way can't get a signal in rural areas. Furthermore - no smartphone I have seen can stand up to the general outdoor roughness that a unit can be subjected to (rain, snow, dust, drops, etc).

How did this turn into gps vs smartphone? I'm simply informing people of agps for smartphones...

...and I was pointing out that you do not need a smartphone to gain virtually the same advantage while also not worrying about destroying your phone.

 

My phone seems ok so far....and still way off topic.

 

Not really off topic. Your obviously trying to tout the cellphone feature as being somehow superior to a standalone GPS unit or signal. I am simply pointing out similar alternatives.

[+LukeTrocity]

Units with Garmin's predictive sat startup feature also get a rapid lock on coordinates.Smartphones need access to a cell signal to use the assisted GPS feature. Many areas out my way can't get a signal in rural areas. Furthermore - no smartphone I have seen can stand up to the general outdoor roughness that a unit can be subjected to (rain, snow, dust, drops, etc).

How did this turn into gps vs smartphone? I'm simply informing people of agps for smartphones...

...and I was pointing out that you do not need a smartphone to gain virtually the same advantage while also not worrying about destroying your phone.

 

My phone seems ok so far....and still way off topic.

 

Not really off topic. Your obviously trying to tout the cellphone feature as being somehow superior to a standalone GPS unit or signal. I am simply pointing out similar alternatives.

 

No I'm obviously not. I am not even talking about GPS receivers except in an example. The example was only to help relate users to prior experiences.

[John E Cache]

I think I read the main reason for AGPS is that AGPS is required by law so emergency operators know approximately where your 911 call is coming from.

[+dfx]

I think I read the main reason for AGPS is that AGPS is required by law so emergency operators know approximately where your 911 call is coming from.

 

I don't think that has anything to do with AGPS. The cell operators can use that information or send it along independent of the phone used. And even if the phone knows its own location, I don't think that it would send it anywhere just when placing a call (unless some of them handle 911 specially).

[Andronicus]

My WM6.5 phone (HTC Touch 'Vogue') using A-GPS was quite good (fast lock, and high accuracy when static navigation isn't messing you up). The issue was that when no cell phone network was available to assist, the GPS was crap.

 

I should point out that not all A-GPSes are made equal. The one in the Vogue (QualComm GPSOne) obviously is a poor GPSr that relies heavily on the assistants. I have heard that other phones have better GPSrs that do not rely on the assistance except for faster lock time.

 

So I bought a bluetooth GPS. That one rocks!, and uses a form of A-GPS. You have to syncronize it via internet weekly. I don't bother using that though because it is quite good on its own.

 

As for StarBrand's issues, click the link in my signature. It has lots of tips for overcoming all those 'shortcomings'.

Edited March 2, 2011 by Andronicus