Novatel Inc.

Novatel Communications Ltd.

Airsys Atm Limited

Albert J Van Dierendonck

Patrick C Fenton

Craig Alan Stull

Lee Etnyre

Stephen Vance Rowson

Glenn Raymond Courtney

GNSS receiver includes a subsystem that reduces the adverse effects of multipath signals on punctual and early-minus-late correlation measurements by making the correlation measurements using a &ldquo;blanked-PRN code.&rdquo; The blanked-PRN code is all zeros except for adjacent positive and negative short pulses that occur at every code bit transition in a locally-generated PRN code. Using the blanked-PRN code, the receiver makes non-zero correlation measurements only near the code bit transitions in the local PRN code. If the local PRN code and the PRN code in the received GNSS satellite signal are closely aligned, the non-zero correlation measurements are made at the times of the bit transitions in the received PRN code. The contributions to the correlation measurements of the multipath signals that do not have bit transitions during the adjacent positive and negative pulses in the blanked-PRN code cancel when the correlation measurements are accumulated&mdash;since these multipath signals are constant during the pulse times. The GNSS receiver includes blanked-PRN code logic that produces the blanked-PRN code from the locally-generated PRN code. The blanked-PRN code logic thus produces a code that is zero-valued except for the adjacent pulses. Alternatively, the blanked-PRN code logic produces the zero-valued portions of the code by selectively disabling the blanked-code correlators in between the code bit transitions in the local PRN code. The result is the same, namely, a system that produces non-zero correlation measurements near the code bit transitions in the local PRN code.

Global navigation satellite system receiver with blanked-PRN code correlation

A GPS receiver that acquires and tracks a split-C/A code separately aligns with the received signal the phases of a locally-generated 10.23 MHz square wave, which can be thought of as a 20.46 MHz square-wave code, and a locally-generated 1.023 MHz C/A code. The receiver first aligns the phase of the locally-generated square-wave code with the received signal, and tracks one of the multiple peaks of the split-C/A code autocorrelation function. It then shifts the phase of the locally-generated C/A code with respect to the phase of the locally-generated square-wave code, to align the local and the received C/A codes and position the correlators on the center peak of the split-C/A. The receiver then tracks the center peak directly, using a locally-generated split-C/A code.

Split C/A code receiver

A differential GPS landing system having at least three GPS receivers at known locations in spatial proximity to each other, wherein each GPS receiver independently receives GPS signals from the plurality of GPS satellites and at least three reference stations, wherein each reference station receives a signal from a different two of the at least three GPS receivers and calculates two separate differential corrections for each satellite, wherein each differential correction is independently calculated using the signals received from a different one of the two GPS receivers. The reference stations preferably average the two calculated differential corrections for each satellite to produce an averaged differential correction for each satellite. The system then validates the averaged differential correction for each satellite calculated by each reference station using two integrity monitors, wherein each integrity monitor receives the averaged differential corrections from a different two of the at least three reference stations, and each integrity monitor compares, with respect to each GPS satellite, the averaged differential corrections from the two of the at least three reference stations to produce a validated set of differential corrections, and broadcasts the averaged differential correction for each satellite calculated by one of the three reference stations. The preferred differential GPS landing system further includes a method that utilizes current differential correction error statistics, prior differential correction error statistics and a Bayesian interval estimation bounding process to provide an error bound on the broadcast differential corrections.

Differential GPS landing system

A receiver for pseudorandom noise (PRN) encoded signals consisting of a sampling circuit, multiple carrier and code synchronizing circuits, and multiple digital autocorrelators. The sampling circuit provides digital samples of a received composite signal to each of the several receiver channel circuits. The synchronizing circuits are preferably non-coherent, in the sense that they track any phase shifts in the received signal and adjust the frequency and phase of a locally generated carrier reference signal accordingly, even in the presence of Doppler or ionospheric distortion. The autocorrelators in each channel form a delay lock loop (DLL) which correlates the digital samples of the composite signal with locally generated PRN code values to produce a plurality of (early, late), or (punctual, early-minus-late) correlation signals. The time delay spacing between the (early, late), and (punctual, early-minus-late) correlation signals are dynamically adjusted, such that in an initial acquisition mode, the delay spacing is relatively wide, on the order of approximately one PRN code chip time; once PRN code lock is achieved, the code delay spacing is narrowed to a fraction of a PRN code chip time.

Pseudorandom noise ranging receiver which compensates for multipath

A receiver for pseudorandom noise (PRN) encoded signals consisting of a sampling circuit, multiple carrier and code synchronizing circuits, and multiple digital autocorrelators. The sampling circuit provides digital samples of a received composite signal to each of the several receiver channel circuits. The synchronizing circuits are preferably non-coherent, in the sense that they track any phase shifts in the received signal and adjust the frequency and phase of a locally generated carrier reference signal accordingly, even in the presence of Doppler or ionospheric distortion. The autocorrelators in each channel form a delay lock loop (DLL) which correlates the digital samples of the composite signal with locally generated PRN code values to produce a plurality of (early, late), or (punctual, early-minus-late) correlation signals. Thus, during an initial acquisition mode, the delay spacing is relatively wide, on the order of approximately one PRN code chip time. However, once PRN code synchronism has been achieved, the code delay spacing is narrowed, to a fraction of a PRN code chip time. There are several advantages to this arrangement, especially in environments wherein multipath distortion in the received composite signal is of the same order of magnitude as a PRN code chip time.

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Los Altos, CA, United States of America

Albert J Van Dierendonck