A traditional problem programmers have is thinking the lower "EE" levels are more complicated than they really are. Such as assuming a mid 2010s era level of complication for a two way communication stream in something designed in the 80s for unidirectional listening.
The way GPS works is pretty much like LORAN (well, maybe more like OMEGA) but with embedded metadata. So you've got 40 satellites who know exactly where they are and exactly what time it is and exactly what frequency is the center of their spread spectrum spread, and they're more than glad to tell you all about it. All 40 of them. Maybe you can see a dozen of them at a time?
Anyway you sync up to the SS signal and that gives you a local offset for your clock and your local oscillator and you know the exact orbital position pertaining to that delta-t (aka distance) and delta-f (aka doppler velocity). Now average together a zillion satellites and solve a least squares puzzle for the most likely location for you. Which also feeds out an internal error correction signal for your internal osc and real time clock.
All the .mil signal does is squirt out a slightly more accurate encrypted signal so you need the same key all the satellites use and the key changes rather often.
The way GPS works is pretty much like LORAN (well, maybe more like OMEGA) but with embedded metadata. So you've got 40 satellites who know exactly where they are and exactly what time it is and exactly what frequency is the center of their spread spectrum spread, and they're more than glad to tell you all about it. All 40 of them. Maybe you can see a dozen of them at a time?
Anyway you sync up to the SS signal and that gives you a local offset for your clock and your local oscillator and you know the exact orbital position pertaining to that delta-t (aka distance) and delta-f (aka doppler velocity). Now average together a zillion satellites and solve a least squares puzzle for the most likely location for you. Which also feeds out an internal error correction signal for your internal osc and real time clock.
All the .mil signal does is squirt out a slightly more accurate encrypted signal so you need the same key all the satellites use and the key changes rather often.