Leica Geosystems Ag

Magnavox Electronic Systems Company

The Directv Group, Inc.

Thomas A Stansell, Jr

Richard Gerald Keegan

Charles Robert Cahn

Jerry Eugene Knight

Richard G Keegan

A technique for minimizing or eliminating the effect of multipath signals in a receiver processing pseudorandom (PRN) code signals, such as in a global positioning system (GPS) receiver. The presence of multipath signals adversely affects both code measurements and carrier phase measurements of received PRN signals. One aspect of the invention provides for improved code tracking in the presence of multipath signals, by sampling the received code with a multipath mitigation window (MMW) (FIG. 25D) that results in a code error function (FIG. 25F) that reduces or eliminates the multipath effects. The MMW, which may be any of a number of preferred waveforms (FIGS. 35B-35E), provides a code error function that varies in opposite directions from zero at a desired tracking point (402), but assumes a nearly zero value when the MMW is advanced from the tracking or synchronization point by more than a small fraction of a code chip. Because of this nearly zero code error value on the early side of the desired tracking point, delayed multipath signals will have a corresponding code error function that is nearly zero (FIG. 25F) at the desired tracking point of the directly received signals, and the multipath signals will, therefore, have little or no effect on the desired tracking point and on code synchronization. The effects of multipath signals on carrier phase measurements are minimized by sampling the received signals, together with their possible multipath components, before and immediately after code transitions (vectors A and B, respectively). The vector relationship of the directly received (D) and multipath (M) signals is such that performing a vector average of the two types of samples (A and B) produces the directly received signal (D) and its correct phase, with many, if not all, of the multipath components (M) eliminated.

Mitigation of multipath effects in global positioning system receivers

Method and apparatus for improving the speed and accuracy of processing signals from global positioning system (GPS) receivers by ensuring access to GPS carrier signals that have been modulated with an encrypted P-code sequence. In one disclosed embodiment of the invention, GPS L1 and L2 signals are correlated with a locally generated P-code signal, bandpass filtered to enhance signal-to-noise ratio performance, and then cross-correlated to obtain a signal with an L1-L2 frequency component that facilitates the resolution of carrier cycle ambiguity. In another embodiment, received GPS signals are immediately converted to digital form, then digitally correlated with in-phase and quadrature components of a locally generated P-code signal. Signals resulting from the correlation are then integrated over timing intervals corresponding to a previously determined encryption period to provide in-phase (I) and quadrature (Q) samples. In one variant of this embodiment, the I and Q samples derived from the L2 GPS signal are digitally squared to obtain an L2 carrier. In another variant, I and Q samples derived from both L1 and L2 signals are cross-correlated to obtain a digital carrier with an L 1-L2 component. Tracking errors for the L1 and L2 P-code signals are computed using a similar digital technique.

Global positioning system (GPS) receiver for recovery and tracking of

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Rancho Palos Verdes, CA, United States of America

Thomas A Stansell, Jr