> The ephemeris is the precise orbital data used to calculate position. Each satellite broadcasts only its own ephemeris, which takes up to about 50s. This is where AGPS can help - if you can get that data from some other channel then you don't have to wait.
Don't celltowers provide AGPS data to connected client devices (i.e. phones)? Those towers need the AGPS data for enhanced 911 cellular service.
Thats what the AGPS system is, the Almanac and Ephemeris data is provided over a data channel from a server rather than directly from the satellites.
The idea being that receiving the data over a dedicated data channel is much quicker than a low-power broadcast from a sat.
This is often confused for a similar mechanism for triangulation of a position using the relative powers of multiple cell towers. This provides a low-resolution position fix suitable for use as the initial seed of the kalman filter (which narrows down the position iteratively).
Don't celltowers provide AGPS data to connected client devices (i.e. phones)? Those towers need the AGPS data for enhanced 911 cellular service.