Compensating for multipath errors, ionospheric time delay and noise

Abstract

Method and apparatus for reducing the contributions of ionospheric propagation time delay error, multipath signal error and receiver noise error from signals received in a Satellite Positioning System (SATPS) from one or more SATPS satellites by formation and appropriate filtering of differences of signals DD that are differences of SATPS signals received by the SATPS receiver/processor. A difference signal DD of code-phase-derived, ionosphere-free signals and carrier-phase-derived, ionosphere-free signals is formed, and this difference signal is passed through a first statistical processing filter with an associated time constant .tau.1 in the approximate range 50-500 sec, to produce smoothed or filtered first difference signal with the estimated receiver noise error reduced or removed. The difference signal DD is passed through second and third statistical processing filters having associated time constants .tau.2=5-20 sec and .tau.3=50-500 sec, and the difference of the output signals of the second and third statistical processing filters is formed and subtracted from the filtered first difference signal to form a new difference signal that is primarily due to multipath error. This new difference signal is subtracted from thge pseudorange measaurement values to produce a signal with reduced multipath error.