How satellite positioning works

Timing, not signalling.

Trilateration

Each satellite broadcasts the time and its position. Your receiver measures the delay to work out distance from each, and four of them fix position and correct the receiver clock.

The receiver only listens; it never transmits.
Relativistic effects on satellite clocks must be corrected or the fix drifts kilometres a day.

Beyond GPS

GPS, Galileo, GLONASS and BeiDou are separate systems; modern receivers use several at once, which improves accuracy in awkward places.