Trimble Navigation Limited

George J Geier

Kelly Gene Johnson

Patricia W McLain

Ardalan Heshmati

An embodiment of the present invention is a combined GPS and dead-reckoning (DR) navigation sensor for a vehicle in which a pair of modifications are made to an otherwise conventional Kalman filter. Process noise is adapted to cope with scale factor errors associated with odometer and turning rate sensors, and correlated measurement error processing is added. When only two Doppler measurements (PRRs), or three with an awkward three-satellite geometry, are available, DR error growth can nevertheless be controlled. The measurement error correlations in the conventional Kalman filter covariance propagation and update equations are explicitly accounted for. Errors induced by selective availability periods are minimized by these two modifications.

Position and velocity estimation system for adaptive weighting of GPS

An embodiment of the present invention is a shipboard GPS positioning system having data links to outlying tailbuoys equipped with respective GPS receivers. On ship, an Intel 386-based microcomputer system collects data from various ship's equipment including the ship's GPS receiver and data from the several tailbuoy units. A computer-implemented process located in the microcomputer system controls the following processes. Periodically each GPS receiver produces updated pseudo ranges (PRs) and these are time-tagged. The time-tagged PRs for the ship are aligned according to their time tags with their counterpart PRs from the tailbuoys. The raw PRs are then passed through a Kalman mathematical filter to produce filtered pseudo-ranges (PRs). A position solution is then attempted for each GPS receiver using the PRs. The filters provide statistical data that is used to rate the quality of each PR in a weighted least squares solution process. Special measures are included to provide quality control/quality assurance, including the use of error ellipses on the display to present a graphic indication of expected solution accuracy, and the use of real time fault detection, isolation, and correction algorithms when redundant satellite information is available.

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Santa Clara, CA, United States of America

George J Geier