> Multipath on GPS normally requires a couple of things: > .... > 3) The signal path length has to be close enough that the normal firmware > does not reject > the solution. >
Expanding on this a bit, because it's relevant to the "aircraft causing multipath" question, the pseudo random noise ranging method allows discrimination in the time domain against sources of multipath further away than 300 m at worst, and much better in practice. At the L1C 1 MHz chip rate, the correlation function for the received PRN is zero more than 1 us == 300 m away. In practice, you're digitizing much faster than 1 MHz and you can use a more closely spaced set of correlators, perhaps improving by a factor of 10. This doesn't work though when a reflection is the only signal you are seeing, as in Bob's point (1). (The effect of multipath when there is a line of sight signal also visible is to distort the correlation function, which is triangular in the ideal case. This introduces errors into the interpolation used to improve the resolution of the PRN ranging.) Cheers Michael _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.