Cell tower needs to know timing advance [1] (how long it takes for the signal to travel between the tower and the handset) to make sure signals from different h

Cell tower needs to know timing advance [1] (how long it takes for the signal to travel between the tower and the handset) to make sure signals from different handsets do not overlap. Once you know which tower the phone is connected to, coordinates of that tower, antenna pattern, and distance (from timing advance and speed of light), you can calculate approximate cell phone location. You get more data if the phone moves or propagation changes and phone changes towers. In urban environment with many towers location obtained this way can be very precise. Not as good as GPS, but good enough to within a block. This is a simplification. Real systems also use signal strength, take into account multipath propagation, and apply some filtering from physical constraints (how fast a cell phone can move). [1] https://en.wikipedia.org/wiki/Timing_advance https://en.wikipedia.org/wiki/Timing_advance