Well, GPS is more like radio, you only listen to the broadcast, you don't talk back.

But this is more like cellular access points. You have a private channel.

And they transmit with about 50 watts.

Look up the connection between Einstein's general relativity and GPS accuracy for more fun. Especially early on in its deployment.

That's actually a myth, since the GPS satellites all experience a similar relativistic time skew.

http://www.alternativephysics.org/book/GPSmythology.htm

"The presence of Special and General Relativity effects has no bearing on the accuracy of GPS operation. In summary, it wouldn’t matter whether clocks aboard GPS satellites ran faster or slower than Earth’s clocks or even changed their speed each day. Just so long as the satellites’ clocks remained synchronised with each other and the time-difference relative Earth’s clocks didn’t become too large, GPS receivers would continue to calculate their correct position."

That page constructs its own argument and then deconstructs it. It doesn't actually disprove the OP's statement.

The reason that GR and SR have "no bearing" is because they've already been designed into the system...

From "Understanding the NAVSTAR" 2nd Edition, by Tom Logsdon ( one of the designers of the system ) the time-dilation is compensated through:

1. Off-setting the clock ticking-rate during manufacture of each satellite.

2. Applying a unique onboard corrective factor according to the eccentricity ( egg-shapedness ) of each satellite's current orbit. The latter is correction is constantly recalculated for each satellite.

Without these corrections against relativistic effects the accuracy would suffer by 14 nm after 24 hours ( without tick-offsetting ) and 100 feet or so per day due to orbital eccentricity.

That's the one. There's pages one can get from Google with some of the data and illustrations if they can't get the book. It tripped me out when I found out they had to design relativity into it.

I knew I shouldn't have questioned you so flippantly... Lesson learned.

Feel free to question as Im a human acting on incomplete information like the rest. ;) Just don't assume or read in too much as that can get you. Happened to me plenty here, too, haha.