Patent Number: 6,252,863

Title: Multipath compensation for pseudorange signals

Abstract: Method and apparatus for synchronizing to a reference signal the timing of a received composite, code phase SATPS signal, such as a GPS or GLONASS signal, that consists of a preferred, interference-free signal distorted by at least one interfering signal, to determine an undistorted timing point, such as the preferred signal time of arrival. A first autocorrelation function AC.sub.I (.tau.) is generated between the preferred, interference-free signal and a reference signal that replicates the preferred signal, as a function of the time shift .tau. between the two signals. A second autocorrelation signal AC.sub.M (.tau.) is measured between the reference signal and the incoming signal. Three amplitudes AC.sub.M (.tau..sub.M,e), AC.sub.M (.tau..sub.M,p) and AC.sub.M (.tau..sub.M,l) of the second autocorrelation function and the corresponding code phase time shift values .tau..sub.M,e, .tau..sub.M,p and .tau..sub.M,l are selected that satisfy at least one of the relations 0<.tau..sub.M,p -.tau..sub.M,e =f1.DELTA..tau..sub.chip and 0<.tau..sub.M,1-.tau..sub.M,p =f2.DELTA..tau..sub.chip, (0<f1, f2.ltoreq.0.5). A shift PRC(t;j;rcv) in a pseudorange value associated with the incoming signal, measured at the user receiver, from at least one SATPS signal source, number j, is determined by a ratio of a first linear combination of the amplitudes AC.sub.M (.tau..sub.M,e), AC.sub.M (.tau..sub.M,p) and AC.sub.M (.tau..sub.M,1), multiplied by a selected parameter K' and divided by a second linear combination of these amplitudes, plus a second selected parameter K". The parameters K' and K" are determined by examination of the first correlation function AC.sub.I (.tau.) and are independent of the values AC.sub.M (.tau..sub.M,e), AC.sub.M (.tau..sub.M,p), AC.sub.M (.tau..sub.M,1), .tau..sub.M,e, .tau..sub.M,p and .tau..sub.M,1, but may depend upon the selected fractions f1 and f2, upon the SATPS satellite number j, upon the characteristics of the receiver, and upon one or more of the coefficients in the linear combinations.

Inventors: Raby; Peter (London, GB), Riley; Stuart (San Francisco, CA)

Assignee: Trimble Navigation Limited

International Classification: G01S 1/00 (20060101); H04B 1/707 (20060101); H04B 007/212 (); H03D 001/04 ()

Expiration Date: 06/26/2018