What is AGPS Assisted GPS

I have heard two versions of AGPS
1. It is the use of cell towers to assist satelites in getting a position fix, so not true 100% satelite gps. What about when one is beyond cell tower range?

2. It is the use of the providers main computers to transmit the ephemeris data and almanac data directly to your phone much sooner than the satelites can transmit this data thereby acquiring a faster first fix via satelite. The ephemeris contains the data for satelite position, speed, altitude etc. enabling your phone to acquire more satelites sooner and getting a more accurate fix.

So which is true? Or is there yet another explanation, or is it a combination of 1 & 2?

Is the ephemeris transmitted at regular intervals so that when one strays out of cell tower range they still have the most recent ephemeris for the sooner time to first fix?. Just how does this AGPS function anyway?

1 Answer from the Community

  • Best Answer:

    It is #1 when you are in range of cell towers and 100% satellite when not. I use the iPad on my boat with a navigation app far offshore.

    • Answered by William C from Longmont
    • Sep 25, 2013