ivanivanovich wrote:Are you sure that's what A-GPS means? 'Cause Wikipedia and about.com don't agree.
Info from the cell towers Assists the GPS in resolving position faster or, when GPS signals aren't available, they step in to supply the position.
If a cell signal isn't available, the GPS receiver still functions normally - you get a GPS-based position when you have enough signals, and you don't when you don't.
Ivanovich, you are correct. In A-GPS, the "A" means two things:
- a cellular or Wi-Fi data signal is able to download the current GPS satellite hysterisis dataset. This is data as to what satellite is over what part of the earth for the next few days, and what frequencies that satellite broadcasts. If you don't get this data from the Internet, your GPS is able to download it from the satellite signal itself - but that can take a great deal of time, an un-interrupted view of the sky, and requires trial and error of what frequencies to listen on, given it doesn't know what satellites are overhead just yet.
- the nearest cell tower or wifi access point can be used to give an approximate location of the device, which helps it understand what satellites are overhead (by using hysterisis data), which allows it to immediately listen on the appropriate frequencies.
So, A-GPS can potentially get a time-to-first-fix of just a few seconds, while unassisted GPS could take up to a few minutes from a cold start. The Tab 10.1 can use either method.
