The satellites are not geo stationary.hence the requirement for a constellation of upwards of 24. They are much closer to earth than that. If your GPS unit , such as my Tom Tom has a satellite view, it indicates which satellites are above the horizon at any instant. You will readily see a variation over a period of hours. Without checking, an orbital period of 12hours comes to mindYes, that's exactly the process along with examination of incoming frequency of time carrier signal.
All satellites are geo stationary so as unit picks each one up it calculates distance from it and when enough have been found gives a circle of overlapping signals, in which it knows unit is in. A position in space. To give us that position it must approximate to our lines of lat/long and then give an elevation.
Not sure protocols are available for units to send raw (accurate) time data. It has to display its position in a language we understand....hence the problem.
My only thoughts are that I can't see how Galileo can be so much more accurate when limiting factors are not the units but the system inherent in our navigation system.But, I know nothing about Galileo...
The quality of the clocks installed on each satellite are the fundemental timing error. There Therewill have been advances in the precision of theses atomic clocks since the inception of the original US system. There are other tricks up the sleeve of the designers, including a mode based on phase detection of the carrier between the different radio channels. .. in essence a reworking of the old Loran C radio beacon system, but with much higher frequencies, and consequently higher spatial resolution.
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