As I understand, GPS is supposed to work because :
You have 4 (or more, but let's say 4) satellites whose clocks are extremely highly synchronized (through atomic onboard clocks)
You have a receiver that receives 4 pings / messages from these satellites, each containing a timestamp of date of emission wrt to the "GPS time"
Supposing the receiver time / clock only has a bias wrt to GPS time (ie, a fixed, constant error), you can from these 4 signals and the map of satellites position, deduce your 3 cartesian coordinates + the time bias error of your receiver clock wrt to GPS time.
That's all fine in theory, but in practice :
The timing accuracy we are looking for is in nanoseconds (as there is c involved and the goal is to achieve metric-like accuracy on pseudo-ranges)
So is it technologically "easy" to ensure that the actual "sending" of the signal by the GPS satellites is at the actual timestamp of the atomic clocks ? I mean, it's going through an electronic system, then a real-world, physical, analog antenna. I'm not talking about adding a known delay (which is not a problem as it can be accounted for as long as it is known), but what about unknown delay / jitter ? For example, is it "easy" to ensure that the analog antenna's emission date is within requirements / specs ?
Same question with the antenna / circuitry of the receiver ?
Additionally, on the receiving end, there is also problem of jitter / repeatability of the "time bias" wrt to the GPS clock. Since we're actually looking for nanoseconds, this seems not obvious. I get / guess the receiver has a well-known stable quartz (or similar) low frequency clock and a jittering VCO for nanoseconds granularities ? And the jitter of this VCO is low enough to allow ignoring it when solving the GPS equation system supposing a fixed biais ?
Of course, feel free to move the question elsewhere if Electrical Engineering is not the adequate community (in the end the question is I think more about pure circuitry than aeronautics, so I chose to ask it here, but I may be wrong).