David H. wrote:
Thanks for the info, Caveat. Looks like I may have had run across one of your links
in all my searching

There are many question I have regarding SS, but one that's bothering me in
particular. Regarding the PN spreading sequence, these sequences obviously have to be
aligned perfectly in both transmitter and receiver. Naturally they could be kept in
sync if both circuits were initialized at the same time.

However, 3 things: 1) The circuits will not be initialized at the same time in 99% of
most cases, as in the use of, say, a portable field radio. 2) If they were
synchronized at the same time, well, no clock or oscillator is perfect. It would
eventually drift. 3) As I understand it, there is no initial "handshake" signal at
the beginning of transmission with the receiver to initialize/syncronize the PN
sequences on both ends.

So in short, how do the PN sequences became and remain synchronized through time?
Thanks.

Two ways that come to mind immediately:

1) The transmitter sending its state periodically, so that the
receiver can jam that into its spreading or hop control
registers and be instantly synchronized. No good for *secure*
comms, but great for insecure comms.

2) The transmitter using spreading or hop control based in some
way on (GPS) time, say by automatically loading new control
state periodically. The receiver would load the same control
state for that time period, and then could slew the clock
forward in time until it detected synchronization. This is a
variation on (1) which *is* good for secure comms.

Drift can be corrected by circuitry in the receiver, from the received
signal. If the link is via satellite, drift (and Doppler shift) *must*
be corrected in the receiver to maintain sync.

--
Mike Andrews

Tired old sysadmin