On Thu, 22 Nov 2001, Eugene Leitl wrote:

Given that a GPS receiver gets ephemeris data, almanach data and pseudorandom code from each currently visible sat it has probably to do with the latter. Consider S/A (which may or may not be switched off now, I haven't checked): if you've got a secret part of the key you can refine your position despite deliberate degradation (selective availability) than the party without the key.

Forgot the URL: http://www.csr.utexas.edu/texas_pwv/midterm/gabor/gps.html The PRN is a tapped feedback shift register.