[fortysixdegrees]

Not so much. Modern GPS will get a first fix pretty quickly regardless, you don't need to seed it.

AGPS is used when satellite coverage is poor, like urban canyons in a city, also a situation where there are a lot of cell towers and triangulation is somewhat useful

[bri3d]

AGPS refers to a specific set of technologies, MSB where the almanac and time seed is provided over the cellular network, and MSA where the unit sends GPS data to the AGPS server and the server solves for location using whatever data it would like (which can include a multitude of corrections).

I think what you're referring to with cell tower triangulation (and also WiFi location, etc.) is generally referred to as "hybrid location service" and is usually done at a higher level (ie - in software) using AGPS as one input to a sensor fusion algorithm.

[marsokod]

The time to first fix is mainly impacted by whether the receiver knows which satellites to listen to. This requires two things: having the ephemeris for the constellation (either 10min of listening to GPS signal, or getting that through AGPS), and it's approximate own position/time (done through cell antenna locations, and NTP) to know which satellites should be visible.

Once this is available, the receiver can then focus on the signals that are expected and will then be able to provide a 3D fix as soon as it receives something from 4 satellites, which would be in a few seconds.