Database Users

Assisted GPS - Don't use it!

My Touch Pro ran TomTom flawlessly until a couple of months ago when I got a problem with the GPS device (not the signal) being lost every few seconds. It would reappear again for about 5 secs then off again. Despite soft resets etc, I suspected it might be the SD card at first as I tried many restart combinations with the card in/out etc and as it seemed to help on one occasion I put it down to that. But it did happen on a regular basis.
I now have the X1 with its superb GPS implementation, I was very impressed for a few days... until you guessed it, this problem started happening again!
Luckily I remembered the only setting I had done prior to this occuring was to use the Advanced Config application, where I enabled the AGPS feature. So... I went back in and disabled it and the problem disappeared immediately. I used Advanced Config on the Touch too, so that must have been the problem for sure.
I notice that AGPS is disabled by default. Why HTC did this must mean there is a problem with this feature.
So be advised, not to use the AGPS unless anyone knows good reason to and has a fix for the problem I mentioned.

I ran into the same problem. Turned on agps in advance config, used tomtom 7 and keep getting drop signal. It would pick up the sat signal for a few second and lose it, what interesting though when I use google map it would track me fine, no lost of signal. I can see my "dot" on google map moving along. When I drive, haven't tried it with other nav software to see if this was an issue. I still wonder why they have agps turned off though as default.

i think even if its set to "disabled", its enabled. a-gps must be hard coded in the hardware itself!
ps: i have the same problems when its "enabled".

I think it's the AGPS file that might have corrupted. You can solve this by re-download AGPS file and everything will be fine.
It happened to me once or twice, but it's not a reocurring problem so I did not bother much.

which agps file?

Guess you talk about an A-GPS setting in Tom Tom?
I cannot follow your conversation. With Mobile Navigator, which has no switch to enable or disable A-GPS it works pretty fine.
Sat-fix within seconds - thanks to the provided A-GPS function of the X1, which I don't think can be disabled on teh X1, until you don't update the information frequently with the Quick-GPS application.
Maybe Tom Tom can't interpret the A-GPS information?
How long does a Sat-Fix in Tom Tom take, when you disable A-GPS (in Tom Tom)?
Eric

we are talking about a tool called "advanced config tool". there is an option of enabling and disabling a-gps. "disabled" works best for most users...
you can have a 3d fix in seconds also with no a-gps.

Eric X1 said:
I cannot follow your conversation. With Mobile Navigator, which has no switch to enable or disable A-GPS it works pretty fine.
Sat-fix within seconds - thanks to the provided A-GPS function of the X1, which I don't think can be disabled on teh X1, until you don't update the information frequently with the Quick-GPS application.
Maybe Tom Tom can't interpret the A-GPS information?
How long does a Sat-Fix in Tom Tom take, when you disable A-GPS (in Tom Tom)?
Eric
Click to expand...
Click to collapse
It's incredibly quick (even indoors) to fix a position without AGPS. I admit I haven't knowingly had any noticable problems outside of TomTom but this is something I use a lot. It copes admirably inside, in built-up or shaded areas. No real need for AGPS then! I did try updating my QuickGPS file by the way, to no avail. Disabling was the only fix!

The FIX IS TOO FAST!!!
But I don't have this problem.......

DocMAX said:
we are talking about a tool called "advanced config tool". there is an option of enabling and disabling a-gps. "disabled" works best for most users...
you can have a 3d fix in seconds also with no a-gps.
Click to expand...
Click to collapse
My X1i doesnt have an "adavanced configuration tool" application. Is this a 3rd party addon that you have installed, or is my device just configured differently?

DocMAX said:
which agps file?
Click to expand...
Click to collapse
xtra.bin in \Windows directory I believe
one way to verify if the problem is due to the AGPS corrupted file, is if you encounter the problem, delete the xtra.bin and see if the problem goes away.

kiwiandy said:
My X1i doesnt have an "adavanced configuration tool" application. Is this a 3rd party addon that you have installed, or is my device just configured differently?
Click to expand...
Click to collapse
you have to download it http://forum.xda-developers.com/showthread.php?t=317070
it's our swiss army knife, but be careful

I think people may be getting confused between a-gps and what quickgps does.
My take on this is:
QuickGps downloads a file which contains a list of satellites to speed up getting a signal. Works very well on the x1
this is governed by HKLM/Software/HTC/QuickGPS
A-gps gets an approximate location from your cell tower and feeds 6 virtual satellites signals through the com port set up in the control panel.
It constantly does this, using memory-map software you can see that the signal drops and comes back every second or so. it seems to overwrite what is actually coming from the gps chip as I've seen 4 high quality satellite signals disappear to be replaced with 6 from the a-gps nowhere near where I was.
There's a setting in the registry section concerning A-gps which has "GPSmode" which is set to 2 I wonder what the other values are and do, I havent played with those yet.
You can change the refresh interval I set mine to be 5 when on foot
HKLM/Software/HTC/SUPL_AGPS

I agree with pretty much what you have said (the difference between Quick GPS [sometimes also known as Assisted/A-GPS] and the conventional, location-based AGPS)
However, I don't believe, unless somebody scientifically, or empirically prove, that the phone will receive virtual satellite feed/signal once it acquire the proximity based on the LBS signal. Because to do that, you need to have a data carrier, and it's either via GPRS/UMTS data connectivity (not possible since I would have noticed the data transmission), or radio frequency that satellites transmit on. It can't be GSM/W-CDMA since they operate on the different frequency as GPS, or if it indeed transmit the "virtual satellite signal" on the GSM/W-CDMA network, then I'm sure you will notice it as part of your monthly telco billing?
You may argue that the server is transmitting the virtual satellite signal on the GPS radio frequency, if so, that'll be new development in the AGPS technology since HP iPAQ 6515 first come out employ. However, there are few consideration point;
1. GPS radio frequency does not operate well across barriers, which means the 'virtual satellite transmitter' must be transmitting at a higher ground otherwise it won't work
2. The GPS receiver must be able to reconcile signal from virtual satellite signal and 'real' satellite signal, which means added layer of processing at the phone end, which in my opinions offer more complexity than effective solution.
That said, I just read that the Quick GPS service provider supports 50bit navigation raw data streaming, so I might be wrong afterall.
fards said:
I think people may be getting confused between a-gps and what quickgps does.
My take on this is:
QuickGps downloads a file which contains a list of satellites to speed up getting a signal. Works very well on the x1
this is governed by HKLM/Software/HTC/QuickGPS
A-gps gets an approximate location from your cell tower and feeds 6 virtual satellites signals through the com port set up in the control panel.
It constantly does this, using memory-map software you can see that the signal drops and comes back every second or so. it seems to overwrite what is actually coming from the gps chip as I've seen 4 high quality satellite signals disappear to be replaced with 6 from the a-gps nowhere near where I was.
There's a setting in the registry section concerning A-gps which has "GPSmode" which is set to 2 I wonder what the other values are and do, I havent played with those yet.
You can change the refresh interval I set mine to be 5 when on foot
HKLM/Software/HTC/SUPL_AGPS
Click to expand...
Click to collapse

zenkinz said:
I agree with pretty much what you have said (the difference between Quick GPS [sometimes also known as Assisted/A-GPS] and the conventional, location-based AGPS)
However, I don't believe, unless somebody scientifically, or empirically prove, that the phone will receive virtual satellite feed/signal once it acquire the proximity based on the LBS signal. Because to do that, you need to have a data carrier, and it's either via GPRS/UMTS data connectivity (not possible since I would have noticed the data transmission)
Click to expand...
Click to collapse
when you enable a-gps in the registry it establishes a data connection, or at least it does on my phone.
In my house I get a variable signal, it can drop the data connection easily (and does)!
When I first tried A-gps enabled in the registry it tried to connect, couldnt and memory-map reported no signal. It then connected I got 6 satellites listed till the data connection dropped. This makes me think it's using a data connection.
I disabled all data connections using paul modacos "nodata" and didn't get any "satellites" picked up. My quickgps was upto date at the time and outside I would expect to get a decent "proper" satellite lock.
the SUPL-AGPS section of the registry also contains the following.
Server IP 10.1.101.63
Server Port 7275
Which suggests some form of data connection. Remember this has nothing to do with quickgps or the ephemeris data that gets.
Have a look at http://wmexperts.com/articles/gps_vs_agps_a_quick_tutorial.html
&
http://en.wikipedia.org/wiki/GPS_Phone
A typical A-GPS-enabled cell phone will use a data connection (internet, or other) to contact the assistance server.
Click to expand...
Click to collapse
-----------------------
edit Have just tried again to confirm what I wrote and not getting anything through a-gps at all! I wonder if there's something in this custom rom that's changed things.
But I am being told Ive got a HDop of 666.6m which is a bit spooky..
step outside and I got 9 satellites with 8m hdop back inside and I'm getting standard fix 5 sats 2m HDop flashing on and off every second (signal/no signal) but no data connection being used, so it looks like I'm wrong, so I'll take it all back!
Need to work out what's going on now..

I was having this same issue. At least its good that its not just my device. I tried deleting xtra.bin from both \windows and \temp and it did not help.
Just some clarification on QuickGPS and AGPS. For a regular stand alone GPS to connect, when it first finds a satellite it must download ephemeris data. The ephemeris data contains info about where all the GPS sats currently are in the sky. The ephemeris data is broadcasted by every satellite periodically. A regular GPS must wait for the beginning of the next transmission. If signal is lost mid transmission, the GPS reciever must wait for the next transmission and start all over again. Only once this data is downloaded can a lock begin to be calculated. What quickGPS does is download the ephemeris data from the internet so that next time you request a gps lock, this sometimes lengthy process can be skipped. quickGPS downloads a file called packed ephemeris and places it I believe in the windows directory.
AGPS on the other hand simply supplements info from the sattellites with info from the cell network. What towers you are currently near gives an approximate location (the mechanism that google my location uses) which then tells you which satellites to look for. When fards said it feeds virtual satellite info, he doesn't mean it actually broadcasts fake satellites via RF. It just feeds extra info to the GPS driver. Also, there are lots of calculations to do to maintain a lock. Once the receiver is getting sattelite signals it can send this information over the internet to the AGPS server which is a much more powerful computer that can do these calculations much faster. The server calculates the lock for you then sends you your position information back over the internet. This is why apgs enables a data connection.

blackstone is a real GPS ?

may be a dumb question.
Is blackstone has a GPS (not AGPS) ?
ie. without a sim phone card , it can still receive GPS signal for mapking ?

It's a real GPS, works great with, for example TomTom.

yes gps works without a sim card. agps is also available through registry settings but requires a Data connection.

lots of people seem to think that aGPS is a cheap substitute for normal gps
but thats not the case aGPS is normal gps plus the ability to get locations
from cellphone towers if one can't get a clear gps signal like if one enters
a long tunnel
http://en.wikipedia.org/wiki/GPS_Phone

aGPS is often mistaken as location-based service (LBS) or server-based GPS. mainly because the first generation of "Quick GPS" is also known as AGPS, which essentially is to download the satellite orbit path in advance instead of get it directly from the satellites at the point the receiver is trying to get a fix. The download process (receiving it from satellite) can be a lengthy process (30sec or longer depending on the reception level) thus the purpose of QGPS/AGPS.
I wrote a short article on the myth about AGPS, you can take a read if you are interested

Does anyone know what GPS chip is actually in the Touch HD? Is it a Sirf III? Is Static Navigation "ON" by default?

gregwee said:
Is it a Sirf III?
Click to expand...
Click to collapse
No, it isn't. GPS is integrated in the MSM chip, I think its called something like Qualcomm MSM7201A gpsOne.

zenkinz said:
aGPS is often mistaken as location-based service (LBS) or server-based GPS. mainly because the first generation of "Quick GPS" is also known as AGPS, which essentially is to download the satellite orbit path in advance instead of get it directly from the satellites at the point the receiver is trying to get a fix. The download process (receiving it from satellite) can be a lengthy process (30sec or longer depending on the reception level) thus the purpose of QGPS/AGPS.
I wrote a short article on the myth about AGPS, you can take a read if you are interested
Click to expand...
Click to collapse
thanks very much ..

thanks all for explaining ...

[Q] aGPS question

Hi
Does aGPS require you to have a cellular data connection in order for it to work? Or will it work with any internet connection (eg. using my laptop's connection through wifi)? I'm asking because I don't have a data plan (yet), and my phone has locked only _once_ since I bought it a month or so ago. I've tried switching to MS based in LbsTestmode, changing the supl server to supl-google-com and supl-nokia-com (can't post links yet).
The one time it did lock was when I was testing the GPS without an internet connection, and I entered a WiFi covered area and it suddenly locked (5-10m accuracy). It wasn't WiFi-based positioning because it was my laptop's WiFi hotspot. And I was using the default settings at that time (www-spirent-lcs-com, Standalone mode). Since then I've tried different combinations of settings but it hasn't ever locked.
Another question: What's the difference between MS based and MS assisted modes?
My phone is an I9000 Galaxy S.

ssj4Gogeta1 said:
Hi
Does aGPS require you to have a cellular data connection in order for it to work? Or will it work with any internet connection (eg. using my laptop's connection through wifi)? I'm asking because I don't have a data plan (yet), and my phone has locked only _once_ since I bought it a month or so ago. I've tried switching to MS based in LbsTestmode, changing the supl server to supl-google-com and supl-nokia-com (can't post links yet).
The one time it did lock was when I was testing the GPS without an internet connection, and I entered a WiFi covered area and it suddenly locked (5-10m accuracy). It wasn't WiFi-based positioning because it was my laptop's WiFi hotspot. And I was using the default settings at that time (www-spirent-lcs-com, Standalone mode). Since then I've tried different combinations of settings but it hasn't ever locked.
Another question: What's the difference between MS based and MS assisted modes?
My phone is an I9000 Galaxy S.
Click to expand...
Click to collapse
Correct me if i am wrong, but as i know aGPS doesn´t need any Data Connection to make the triangulation between the GSM Antennas. So no need for Internet Connection to use aGPS.

TMReuffurth said:
Correct me if i am wrong, but as i know aGPS doesn´t need any Data Connection to make the triangulation between the GSM Antennas. So no need for Internet Connection to use aGPS.
Click to expand...
Click to collapse
AFAIK aGPS is different from cellular triangulation. It refers to downloading satellite information from a server for a quicker fix.

ssj4Gogeta1 said:
AFAIK aGPS is different from cellular triangulation. It refers to downloading satellite information from a server for a quicker fix.
Click to expand...
Click to collapse
I thought it would make a triangulation between the next availabe antennas in range and get over a dedicated channel (not data channel as mentioned above) localisation informations. Because my Nokia N80 had aGPS but not real GPS and in the manual they said something about this triangulation.
But of course i know the download of the actual satelite coordenates from my Touch HD in Windows Mobile with a dedicated App. Just thougth it is something diferent.

TMReuffurth said:
I thought it would make a triangulation between the next availabe antennas in range and get over a dedicated channel (not data channel as mentioned above) localisation informations. Because my Nokia N80 had aGPS but not real GPS and in the manual they said something about this triangulation.
But of course i know the download of the actual satelite coordenates from my Touch HD in Windows Mobile with a dedicated App. Just thougth it is something diferent.
Click to expand...
Click to collapse
aGPS is a technology that downloads satellite data from agps servers at realtime (that is the time you are using the GPS): WIKI article
I guess that the app you are refering to, the one you used on the HTC, is Quick GPS. This program doesn't download satellite postition data in realtime but once in a while. (I believe the data are vallid for 48h) With Quick GPS one can still enjoy the features of aGPS while one hasn't a data connection with a aGPS server.
The Galaxy S GPS (BCM4751) seems to have both, aGPS and a sort of Quick GPS. Only the last is called LTO by broadcom. (see: http://www.broadcom.com/press/release.php?id=s443754 about BCM4571 specs and see here about LTO.

aGPS uses cell tower triangulation, and information from a server, in addition to satellite radio signals, to quickly assist in determining the coordinates of a phone's location. Since cell tower sites are precisely surveyed, they are a reliable source for locational data. A data connection is required. All modern cell phones, at least here in the United States, are required to have aGPS service for use in locating a phone by emergency responders. This is a part of the E911 and is required by FCC mandate. Data is used in tracking down the phone, but it happens behind the scenes and is paid for by fees charged to cellular users on their bills for E911 compliance.
On phones that allow the user to make use of the aGPS chip, there will generally be a setting that allows you to set for E911 use only, or for what is commonly referred to as "location based services." On my Android phones, there are actually two settings, both found in Location & Security Settings. One allows for location based upon use of wireless networks, and the other allowing a fix via GPS satellites. Even with any location based services turned off, emergency responders can still find the phone. The difference being that you cannot use it.
While it is technically possible for you to use your phone's aGPS without a data connection, your chances of getting a signal are sketchy, and your chances of getting a really accurate signal are, under most circumstances, slim to none. Much of the computational work in determining your location is done by the assistance server, and guess how that information moves to and from your phone? Yep, you guessed it, data!
GPS signals sent from satellites are simply radio signals, and your local pop music radio station probably sends its signals with more force. As they are radio signals, they have to contend with everything a radio signal has to deal with, and a large percentage of that is man-made. Signals confusingly bounce off of buildings, are weakened by passing through walls and foliage, or can even be absorbed in some cases by different materials.
Some aGPS chips cannot function as stand alone GPS, and will not work at all without a data connection.
Try this, turn off your cellular radio. Make sure that your WiFi is also off. Now, fire up Google Maps and ask it to start navigation. How did it work?

appelflap said:
I guess that the app you are refering to, the one you used on the HTC, is Quick GPS. This program doesn't download satellite postition data in realtime but once in a while. (I believe the data are vallid for 48h) With Quick GPS one can still enjoy the features of aGPS while one hasn't a data connection with a aGPS server.
.
Click to expand...
Click to collapse
Yeah, that i was talking about. Didn´t know this all I love this forum, you always learn more and more.

rasmith3530 said:
Try this, turn off your cellular radio. Make sure that your WiFi is also off. Now, fire up Google Maps and ask it to start navigation. How did it work?
Click to expand...
Click to collapse
Well, using Google Maps would not be a valid test, of course, since you need data connection to download the local map anyway. If you want to test whether data connection is requires by aGPS, you need to use an offline GPS application.

Thank you for your guys replies.
@rasmith3530: So can that data be downloaded over wifi? (My common sense says yes, just trying to confirm.) If it can, then aGPS isn't working for me at all. I see at max 2-3 satellites in LbsTestMode, without a lock on any of them.

No one said aGPS is working on SGS. They are broken and no fixes yet.

foxbat121 said:
No one said aGPS is working on SGS. They are broken and no fixes yet.
Click to expand...
Click to collapse
I think you're right. The fact that there are no ephemeris and almanac data recorded for satellites let me think that it may be the case that with a certain informed guess aGPS and the advertised LTO function doesn't work on none of the firmwares.

Other people seem to have locking/accuracy problems, they can at least see those satellites. Mine normally shows 0 or 1, so I thought maybe I'm doing something wrong.

ssj4Gogeta1 said:
Other people seem to have locking/accuracy problems, they can at least see those satellites. Mine normally shows 0 or 1, so I thought maybe I'm doing something wrong.
Click to expand...
Click to collapse
In JM1-JG5, I had that issue (couldn't lock onto anything). Switching to JM5 fixed that..

Slow gps signal search

hi guys,
when i try to use gps (with syngic), it takes a lot of time to search satellites. when i had WM, there was an app that downloaded satellite's data every week. there is a way to have a faster signal search in android?
thanks

loscassapalle said:
hi guys,
when i try to use gps (with syngic), it takes a lot of time to search satellites. when i had WM, there was an app that downloaded satellite's data every week. there is a way to have a faster signal search in android?
thanks
Click to expand...
Click to collapse
Mine does it already, when I enable GPS, the mobile connections kicks in and I get a fix in no time

as far as i know the aGPS ( assisted GPS ) can use the network towers to make a quick location fix within a radius of 1.5 Km, but you need to have this function active.
knowing roughly where you are helps the gps to select the needed data from the satellites.
last week i got a gps fix in less then 20 sec.

k.mooijman said:
as far as i know the aGPS ( assisted GPS ) can use the network towers to make a quick location fix within a radius of 1.5 Km, but you need to have this function active.
knowing roughly where you are helps the gps to select the needed data from the satellites.
last week i got a gps fix in less then 20 sec.
Click to expand...
Click to collapse
but AGPS needs data connection

[Quiestion] Does GPS know my location? And how

Im considering buying a new headunit for my Mitsubishi Lancer and just wondered how the gps apps know my location without LTE or WiFi. Thanks

kristiansja said:
Im considering buying a new headunit for my Mitsubishi Lancer and just wondered how the gps apps know my location without LTE or WiFi. Thanks
Click to expand...
Click to collapse
Ok... let's asume you're not trolling here, altho this kind of question is sorts of "I don't have gas in my kitchen, will the electric stove work and how"... and I'm kinda bored, so I'll do the explaining.
GPS or Global Positioning System works via more than 30 satellites in the orbit of the earth and devices with GPS have a chip, that can recieve the electromagnetic radio signal sent by the satellite, once the chip aquires signal from at least 3 of the satellites it's able to pinpoint your location via a method where it finds the point where all 3 of the satellite signals collide (your location)... Imagine drawing 3 circles and all 3 of them touch each other.. the point where they touch is the point you're at, and the more satellites you're connected to, the better is accuracy of the location.
WIFI and mobile network (edgem 3g or LTE) aren't really able to give you accurate location, altho, if they are available, both could be used to give you aproximate location (same technique as GPS - 3 radio towers and you can tell where aproximatelly in between them you are), to help the GPS find your location faster. There should be at least 8 visiable (reachable by GPS) satellites in any given time anywhere on the earth.
EDIT: as I could asume from your post, you don't know what WIFI and LTE are, so I'll do quick explaining to you
WIFI is just a standard, being used, to wirelessly transmit data fast, but in short range (ex. you router at home, transmiting data from your modem, or even your phone as a hotspot, transmiting data it's recieves and sends to the radio tower of the mobile operator)
So we get to LTE, which is also a standard being used for the 4th generation of mobile data transmiting, which works via radio transmiters by mobile operator.. those are placed on the ground and you can pretty much spot them everywhere (big towers with antennas)...
So conclusion: a GPS device does NOT need LTE or WIFI to operate, but it can use them for quicker GPS operation, if the GPS device supports aGPS standard ( more info: https://en.wikipedia.org/wiki/Assisted_GPS )
If you want more info on GPS: https://en.wikipedia.org/wiki/Global_Positioning_System

ok thanks