Re: Another Cellular Vict

[Phil Karn <karn@qualcomm.com>]

>Well, I'm not sure how well that would work...  The "dither" on the
>RTT can't go negative (for obvious reasons :-) ).

Sure it can. We're not talking RTT in the Internet sense.  In a spread
spectrum system, deterministic pseudo-random sequences are used for
the spreading codes; the receiver always knows the future of the sequence.

We generate ours with conventional linear feedback shift
registers. The mobile phone tracks the code phase of the cell site and
slaves its own coded transmissions to that. All you'd have to do is to
add a random time-varying phase to the tracking loop. That would cause
the measured delay to be either greater than or less than the real
value.

There would be limits to how far you could vary the delay, but the
tolerance at the cell has to be on the order of the cell radius for
the system to work anyway.

Phil