Tom Bruhns wrote:

W7WKR was doing some experimenting in that area a few years ago (w/FCC
permission), and likely would share some info. I don't have his email
address handy, but perhaps you can find it with a search.

Since very accurate time is available, it should be possible to get
close in the sequence. A typical way to lock onto pseudorandom things
is through correlation. But how do you optimize things when there's
fading and very weak signals to begin with?

Well, the nice thing about spread spectrum is that it effectively
integrates all that under-the-noise signal and produces something with
a lot more amplitude. And yes, the autocorrelation properties of the
PN sequences are very important in synchronization: the output of the
correlator is something close to 1/n for out-of-sync and 1 for in-
sync.

The difficulty is knowing roughly where in a long sequence to start
the search, and that's why the military GPS receivers use the C/A
(Coarse Acquisition) signals to get the Precise Positioning Service
parts of the receivers in the ball park. Once they've done that, it's
the same old game: slew the clock and look for a jump in the output of
the correlator.

--
Mike Andrews

Tired old sysadmin, math jock very much interested in SS