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  1. Thread Author  Thread Author    #1  
    Mugler Infusion's Avatar
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    Default A-GPS, am I confused?

    I have done a little research and it has come to my attention that more research I do on A-GPS the more I seem confused, hopefully somebody can explain to me, since the Nexus 4 will only have A-GPS. Since the LG Optimus G has both GPS and A-GPS, just don't really know what the difference is, which is better?

    OK, my understanding is and I could be wrong or right, I am not sure, A-GPS is assisted GPS which means it is actually GPS but allows data to spot where your location is and use that location information to download maps from sources like Google to show the map information and cache in the system.

    OK what other people may not know but is also my understanding is that the phone with A-GPS is also a GPS system as well, meaning if you have maps pre-installed on the phone it will still use GPS satellite location detection to show your actual location on the pre-loaded maps but it takes much longer for the GPS system to actually locate you rather than if you were actually had data enabled.

    I suppose if your phone was actually GPS for some reason the chip would be different and would be able to spot more GPS satellites in the sky, I am not sure though.

    Glonass, I am really unsure about that, I assume from what I read is that it helps in locating more satellites but I could not really find a pertinent answer for Glonass.
  2. #2  

    Default Re: A-GPS, am I confused?

    A-GPS is a method to locate your GPS position faster, it uses the cellphone antennas near you (as well as wireless routers) so your cellphone knows where you are, meaning your phone will get a GPS fix faster.
    On some phones (as well as the Nexus 4) there's also a barometer inbuilt for your altitude, that helps getting a GPS fix faster.

    Without these assisting systems it could take up to 20 minutes or even more until your phone receives a correct GPS position (especially if you move far away from your last used GPS position).

    GLONASS is basically the russian version of GPS, but I'm not sure if that's even in use yet, I believe it's still in the testing stage, same with GALILEO which is the european GPS system.

    I hope this helped.
  3. #3  

    Default Re: A-GPS, am I confused?

    Well, I don't think there is a difference between GPS and aGPS chip, in terms of what it can do.
    but aGPS has additional configuration like standalone GPS(Normal GPS with no network), GPS + Cellular Network and some additional config which i don't know.
    and the way its implemented is up to OEM/carriers, In this case Google/LG

    They are all the same, They are GPS receiver and both see the same no of satellite in the sky(I believe)

    but the whole difference is how "Time to First Fix" is done. Cellular network towers have GPS receivers and those receivers are constantly pulling down satellite information and computing the data. Cell phones can request those data to pinpoint your location. so, basically all the work is done by the cellular which saves the time required to compute it in phone.

    so, if you have the capability to use as a standalone GPS then that config is added to the phone.
    so my conclusion is Nexus 4 might have GPS and maybe they don't for a fall back.
  4. Thread Author  Thread Author    #4  
    Mugler Infusion's Avatar
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    Default Re: A-GPS, am I confused?

    That is good, I know that some specs on like phonearena and gsmarena mentions both GPS and A-GPS but nowhere have I actually seen A-GPS actually mentions that it is a standalone GPS, but I suppose they actually have the maps preloaded for the GPS versions.

    That is good, but if I am in places that doesn't allow roaming I guess it best to have pre-loaded maps just in case the phone turns off and all the map caching is gone or you decide to make another route to your desired destination.
  5. #5  

    Default Re: A-GPS, am I confused?

    I teach a class on GPS for court use and had not heard of A-GPS so your post caught my eye.
    Wikipedia has a good primer on it.

    Assisted GPS - Wikipedia, the free encyclopedia

    GPS receivers struggle a bit when they are shut down and moved to another distant location. I suspect this is one objective that A-GPS is attempting to deal with.
  6. Thread Author  Thread Author    #6  
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    Default Re: A-GPS, am I confused?

    Great I will read up on this myself, did lots of research about 3 months ago and didn't come across this one, thanks.

    It does say this: Some aGPS devices do not have the option of falling back to standalone or autonomous GPS.

    I am hoping the N4 will use autonomous GPS and also Glonass.
  7. #7  

    Default Re: A-GPS, am I confused?

    Quote Originally Posted by Arctic Prodigy View Post
    Great I will read up on this myself, did lots of research about 3 months ago and didn't come across this one, thanks.

    It does say this: Some aGPS devices do not have the option of falling back to standalone or autonomous GPS.

    I am hoping the N4 will use autonomous GPS and also Glonass.
    I hope so.. but i believe it will have standalone GPS. the reason why i say is because there are some navigation app in playstore which works without data.
    so it must be using GPS in devices like GNexus
  8. #8  

    Default Re: A-GPS, am I confused?

    Quote Originally Posted by Lazer1 View Post
    GPS receivers struggle a bit when they are shut down and moved to another distant location. I suspect this is one objective that A-GPS is attempting to deal with.

    The GPS Satellites do submit their location data to your phone, the problem with that is that it takes a long time (I can't remember the exact time, but it was between 10-20 Minutes) until all of the data was submitted to your phone. Now with A-GPS your phone already knows approximately where you are, and thus the software knows where the satellites should be, and the whole process will at most just take a few seconds then to get a fix.

    Either way I'm 100% sure that the Nexus 4 will have A-GPS as well as standard GPS, that's just a standard nowadays.
  9. #9  

    Default Re: A-GPS, am I confused?

    Not only does the Nexus 4 have gps, a-gps and s-gps, it supports GLONASS too.
    http://www.qualcomm.com/media/blog/2...ion-your-phone

    It will probably be very good when it comes to GPS accuracy.

    Sent from my Nexus 7 using Tapatalk 2
  10. #10  
    mzanette's Avatar
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    Default Re: A-GPS, am I confused?

    Quote Originally Posted by Inkyape View Post
    Not only does the Nexus 4 have gps, a-gps and s-gps, it supports GLONASS too.
    GPS and GLONASS:

    It will probably be very good when it comes to GPS accuracy.

    Sent from my Nexus 7 using Tapatalk 2
    Does this mean you can use the GPS on your phone without a cell data connection?
  11. #11  

    Default Re: A-GPS, am I confused?

    Quote Originally Posted by mzanette View Post
    Does this mean you can use the GPS on your phone without a cell data connection?
    You can with any GPS, but of course you'll need maps and a navi program pre-loaded on your handset if you don't have an active data connection.
  12. #12  

    Default Re: A-GPS, am I confused?

    Quote Originally Posted by mzanette View Post
    Does this mean you can use the GPS on your phone without a cell data connection?
    Yes, like all GPS, but a good idea is to precache offline maps so you know where you are :-)

    Sent from my Nexus 7 using Tapatalk 2
  13. #13  
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    Default Re: A-GPS, am I confused?

    There's a lot of confusion about maps on this thread. Maps have nothing to do with GPS versus A-GPS.

    tl;dr version: A-GPS uses the nearest cell tower to approximate your location, which means it knows which satellites are nearby so it can start listening for those specific ones immediately. This process requires the use of a small amount of data, first to identify the cell tower and again to figure out where that tower is. Once the satellite lock is achieved and your GPS knows where you are, A-GPS and Standalone GPS are the EXACT SAME THING. The "Assisted" portion is only to narrow down the list of satellites to find to get that oh-so-precious initial lock. Once the lock is achieved, your phone already knows where it is and what satellites to listen for.



    The problem with unassisted GPS is that the satellite grid has a lot of satellites that are spread out over a large area, and your GPS can only "hear" one at a time (most are over the horizon at any given time). Your GPS does not know which ones to listen to, and your GPS has to find one by looking randomly (kinda like trying to find 8 specific TV shows on a 30-channel CableTV plan where 20 of the channels will be static. So it listens for a few satellites at random and as soon as it finds one it can narrow the search pattern for other satellites that are "reasonably close" to the one it found. Once it finds three or so, it can narrow your position to the point where it can search for satellites that are very likely to be in range. This can take up to a few minutes.

    Older standalone GPS units had a "directed search" feature where you could identify your approximate location (at the state level in the US, usually) and that would reduce the search because it would only have to listen for satellites it's likely to find. This can cut the search down to about 30 seconds or so. Some allowed you to specify your location a lot more precisely and could lock more accurately.

    Some older GPS units also had more discrete channels, so it could be searching for all 30 satellites simultaneously instead one. This would give you a near-instantaneous lock, but would also require a LOT of expensive hardware.

    A-GPS, or Assisted GPS, sends a signal to the cell tower you are connected to asking "what's your tower ID?" Then, using a database of tower IDs and their exact locations, the GPS instantly knows where you are within a few miles. Using this data, it can then search for satellites it's pretty damned sure are going to be in range already, and a successful GPS lock can occur in seconds.

    A-GPS requires very small amounts of data, because you have to get data from the local tower and then usually send a signal to a server that has a database of towers and their locations (not generally stored locally on the phone - you send the tower ID you found, the server sends back the location of that tower, your phone can then use that location to narrow the search). This is true whether you run an application that requires other data (such as maps) or not. Some apps like Google Maps will use the intermediate geolocation data to approximate your location until a true GPS fix is available (when the "big circle" starts narrowing down to the "little circle").

    Maps also require data, but it really has nothing to do with A-GPS, that just means you are running a mapping application. Mapping applications with offline data are available, but if you want to use A-GPS you will be using (very small amounts of) data just for the A-GPS functionality.

    Most phones that offer A-GPS allow you to turn off the "assist" portion, which is handy if you don't have a data plan or prefer not to use it. Plan on a long wait for a GPS lock, though.
    Thanked by 2:
  14. #14  

    Default Re: A-GPS, am I confused?

    You don't really need data plan for A-GPS, you forgeting about Skyhook Wireless which use Wifi databases:

    Skyhook: > Home

    in otherwords A-GPS will use any unprecice source of location to help, it does not need any data plan, you can have Wifi and as i know local Skyhook Wireless data is cached, my 1gen iPod touch could find my changeing location without connecting to network (Skyhook uses MAC addeses and signal strights) with quite good range and 100m precision (without GPS ofcorse)... but once you got GPS lock that does not matter.

    In past A-GPS made some manufactures to produce weak cheaper GPS chip that can't lock without assistance and require internet connection, but now days most phones on sale got good GPS chips that can work standalone, what why people are confused.

    And you right In Android as most mobile phone oprating system, app is not the one that handles localisation, Android it self is one providing ready location to apps and whatever app you use you should have exact same result as the use same API. And it's not only for GPS, it can use other sources too, as mentioned Skyhook that is precise enouth for things like Foursquere or Google Places or location based services in social apps, but it only works in limited covarage:

    Skyhook: Location Technology > Coverage Area
  15. #15  
    mzanette's Avatar
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    Default Re: A-GPS, am I confused?

    Quote Originally Posted by gone down south View Post
    You can with any GPS, but of course you'll need maps and a navi program pre-loaded on your handset if you don't have an active data connection.
    Yeah sorry that's what I meant thanks. When I travel down to the U.S. I plan to offline a bunch of maps to use GPS.

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