a writes:

Which of the two independent operating US GP Systems has your
approval, and how do you compare them with the upcoming one?

There is only one American GPS system. You may be confusing systems with
operational signals or frequencies. There are two frequencies in use, L1 and
L2, and two operational navigation signals, C/A and P(Y).

I think it was the DOD one, with precisions measured in centimeters,
that was compromised, not the one authorized during the Regan era ...

You mean the precision (P, now Y) code, as opposed to the coarse acquisition
code? These are parts of the same system. At one time, the idea was to start
with the coarse code, then improve positioning with the precision code, but
the military didn't want to extend use of the precision code to civilian
users, and also wanted to avoid spoofing, so it encrypted the precision code,
making P into Y.

The third frequency will be another dual-use frequency. Its main advantage
will be that it will provide a second frequency to civilians, which will make
it easier for receivers to measure sources of signal delay in the atmosphere.

The signals have only an indirect precision; much depends on the receivers.
For example, modern receivers obtain much better precision with the C/A code
than the original receivers, by employing various tricks. The P(Y) code has
potentially better precision because of its higher chip rate, and receivers
using both frequencies (only possible for P(Y), because the C/A code is only
broadcast on one frequency) can also correct for atmospheric effects better.

Yes, I'm a bit rusty, as it has been years since I was last into this. But
I've learned and forgotten more than most people will ever know about GPS. GPS
became less interesting to me when manufacturers started putting databases
into the receivers, eliminating the need for a lot of navigation skill, and
then every dork in town started considering himself an expert on the system.

The other two systems are Russia's shaky GLONASS and the vaporware Galileo
designed by Eurocrats, neither of which is as impressive as GPS.