How A-GPS works. Myths explained, gps simplified.

Discussions about AccuTracking software and web tracking.
Post Reply
madrabbitt
Senior Member
Posts: 188
Joined: Fri Feb 04, 2005 1:56 am

How A-GPS works. Myths explained, gps simplified.

Post by madrabbitt » Tue Jun 14, 2005 1:15 pm

All nextel phones that are GPS enabled are A-GPS.
This means Assisted GPS, not advanced gps as some people are saying.

Basically explained, the network tells the phone roughly where it is, based upon triangulation, and then the phone confirms it with the gps sat's it can view.

This allows faster and more accurate fixes, which is important in a 911 situation.

To see a good example of this, go outside to a clear area. Turn accutracking on and get a manual fix. See how quickly it refreshes and does it.

Then turn "Airplane mode" on in the phone and try a manual fix again... its going to take a LONG while to get the fix.


This is why accutracking and similar programs work when in the car, or inside, or in a holster with the gps chipset facing inward.

Skibum
Senior Member
Posts: 451
Joined: Thu Feb 12, 2004 5:52 pm
Location: Canton, Ct
Contact:

Post by Skibum » Thu Jun 23, 2005 6:31 am

My phone works inside because it can see 4 or more satellites!

What you are suggesting is a phone can get a fix anywhere there is a connection to NEXTEL. This is NOT true. If you watch, Accutracking will not send any location data until there are at least 4 satellites in view.

AGPS is just that... GPS which receives assistance from tower triangulation. No GPS, No location.
I can't be tracked anymore... :(

madrabbitt
Senior Member
Posts: 188
Joined: Fri Feb 04, 2005 1:56 am

Post by madrabbitt » Thu Jun 23, 2005 12:32 pm

I dont know where you're going with this. YOu said I was wrong, but then you said exactly what I said.

I didnt say the phone can get a fix anywhere theres a connection. I said the network tells the phone roughly where it is, then the phone confirms it.

That was the simplest explination for how the system works, which would help the largest amout of people understand how it works.

If you wanted a completely technical explination on the entire process, i'd be glad to copy a few pages out of a technical manual.

Also, I didnt know that accutracking requires 4 sat's in view. In fact, i think there have been times that mine has sent with 2 or 3 sat's.
Can anyone on the accuracking staff confirm that?

In a 911 call, the phone will transmit its location in accordance to the fcc's e-911 standards, even if it can only get a rough fix from one sat.

ATSupport
AccuTracking Staff
Posts: 1842
Joined: Tue Jan 27, 2004 4:36 pm
Contact:

Post by ATSupport » Thu Jun 23, 2005 2:41 pm

That 4 satellites thing involves a little math/Algebra if you would not mind looking into:

To pinpoint an arbitrary point in three dimension space, you need 3 variables. In Cartesian coordinates: x, y, z; In GPS words: Lat, Lon, Alt. To solve 3 unknowns, you need 3 determinate equations. So at least 3 satellite needed for this (satellites positions are known variables). In the case of GPS signals, the 4th satellites is required because the signal (based on which you calculate the distance to the satellite) from the 3 satellites are likely not received at the exact same time and you need the 4th one as the base for synchronizing time.

In conclusion, GPS systems require at least 4 satellites to uniquely solve the Lat/Lon/Alt. In case any 2 satellites give the indeterminate equations, you need an extra one to uniquely solve the equations.
Last edited by ATSupport on Fri Jun 24, 2005 12:03 am, edited 1 time in total.
AccuTracking Support
support(at)accutracking.com

Skibum
Senior Member
Posts: 451
Joined: Thu Feb 12, 2004 5:52 pm
Location: Canton, Ct
Contact:

Post by Skibum » Thu Jun 23, 2005 6:12 pm

Sorry Rabbit... I was mainly commenting on your phrase "This is why accutracking and similar programs work when in the car, or inside, or in a holster with the gps chipset facing inward."

IMHO the fact that the phone uses AGPS has no relation to GPS working in a car or holster. No Sats, No location.

Also... you cannot get a "Rough Fix" from 1 satellite. Not possible.
Also... Locations are no more accurate with AGPS.


I didn't mean to get your cottontail all in a bunch! I was just trying to correct what I see as misinformation. :)
I can't be tracked anymore... :(

madrabbitt
Senior Member
Posts: 188
Joined: Fri Feb 04, 2005 1:56 am

Post by madrabbitt » Thu Jun 23, 2005 7:04 pm

no, locations arent more accurate with the radio assisting the fix, its just a quick fix.

I've gotten a location fix with one or two sats with the radio on, however it was off by several thousand feet.

I dont think i've gotten a fix in the same area with the radio off (not switched off, but no signal)

Theres a canyon and a cave that we go camping around once a month or so. In the canyon i rarely get more then 2 sats in view, accutracking does not send (that makes sense now) however, if i have service, the unit will eventually give me a location.

The location, when punched manually into a computer mapping program, however shows about a quarter mile east of where we actually are (shows us that we're on the outside ridge of the mountain, not inside the canyon)

bmack-4

No Signal on i860

Post by bmack-4 » Mon Jun 27, 2005 9:51 am

Heck, I can't even get a signal on my brand new i860 inside the building where I work. My i88s does much better. The building is a one story infrastructure that I should be getting great signal in. However, NO satellites. Bmack

zardiw
Junior Member
Posts: 39
Joined: Thu Jun 15, 2006 8:10 pm

Post by zardiw » Sun Jun 18, 2006 12:57 pm

BTW, any way to access the tower triangulation data?.....Not the tower position, but the rough position using tower triangulation....z

ATSupport
AccuTracking Staff
Posts: 1842
Joined: Tue Jan 27, 2004 4:36 pm
Contact:

Post by ATSupport » Sun Jun 18, 2006 9:08 pm

The traditional tower trangulation can only be performed by the phone company.
AccuTracking Support
support(at)accutracking.com

Pegtech

AGPS

Post by Pegtech » Sun Jun 10, 2007 10:55 am

AGPS does have a direct impact on whether or not your phone will get a fix indoors. With Assisted GPS, because the GPS receiver knows approximately where it is located when it starts looking for the GPS satellites, it knows exactly which Sats should be in view and thus which Sats to look for. Normally when looking for Sats without AGPS, the GPS receiver must scan all Satellite radio channels which means that it is looking at each radio signal for only a small fraction of the time. When it knows which satellites to look for, it can spend a longer period, or dwell time, on each radio channel which basically increases its sensitivity. So, AGPS basically increases the sensitivity of the GPS receiver by telling it which Sats to look for, similar to a HOT GPS start compared to a cold start.

madrabbitt
Senior Member
Posts: 188
Joined: Fri Feb 04, 2005 1:56 am

Re: How A-GPS works. Myths explained, gps simplified.

Post by madrabbitt » Sun Sep 28, 2008 8:58 pm

And, this came up when discussing if an external antenna will help GPS location or not, so I figured it be a good addition here:

The external antenna port is strictly for reception on the radio (voice, walkie, data) and not for the gps at all.
However, you have to understand how the assisted GPS works.

When the radio communicates with a tower, it knows how strong or weak the signal from the primary tower is, as well as any other tower in range (Cell sites overlap, but your phone communicates only with the strongest one) Since the towers are in fixed locations, the radio basically knows where it is, generally. In turn, the gps system uses that to pinpoint where it generally is, before it calculates range from the sat's that it can see. This allows the GPS to calculate its location much faster, and with fewer signals from the sat's, which in turn gives you a faster location, a more accurate location, and better battery life since the gps doesnt have to be in active recieve as long.

So, adding an external antenna helps assisted GPS, because it not only allows the phone to communicate better with the primary tower, it also could potentially communicate faster with additional towers, letting it triangulate its general location more accurately before the GPS system even goes into active recieve.
Dude! Wheres my car?

Oh, wait. Here it is.

Guest

Re:

Post by Guest » Sun Jun 20, 2010 3:04 pm

ATSupport wrote:The traditional tower trangulation can only be performed by the phone company.

sdfsdss
New member
Posts: 1
Joined: Tue Aug 14, 2012 3:26 am

Re: How A-GPS works. Myths explained, gps simplified.

Post by sdfsdss » Tue Aug 14, 2012 3:44 am

My phone works inside because it can see 4 or more satellites!

What you are suggesting is a phone can get a fix anywhere there is a connection to NEXTEL. This is NOT true. If you watch, Accutracking will not send any location data until there are at least 4 satellites in view.

AGPS is just that... GPS which receives assistance from tower triangulation. No GPS, No location.

_________________

Post Reply