US 5,828,336 A · Robust real-time wide-area differential GPS navigation

Abstract

The present invention provides a method and a device for providing superior differential GPS positioning data. The system includes a group of GPS receiving ground stations covering a wide area of the Earth's surface. Unlike other differential GPS systems wherein the known position of each ground station is used to geometrically compute an ephemeris for each GPS satellite, the present system utilizes real-time computation of satellite orbits based on GPS data received from fixed ground stations through a Kalman-type filter/smoother whose output adjusts a real-time orbital model. The orbital model produces and outputs orbital corrections allowing satellite ephemerides to be known with considerable greater accuracy than from the GPS system broadcasts. The modeled orbits are propagated ahead in time and differenced with actual pseudorange data to compute clock offsets at rapid intervals to compensate for SA clock dither. The orbital and clock calculations are based on dual frequency GPS data which allow computation of estimated signal delay at each ionospheric point. These delay data are used in real-time to construct and update an ionospheric shell map of total electron content which is output as part of the orbital correction data, thereby allowing single frequency users to estimate ionospheric delay with an accuracy approaching that of dual frequency users.

A method for providing real-time, wide area differential GPS signals to allow users with a GPS receiver to obtain improved GPS positioning, the method of comprising the steps of:

collecting real-time dual frequency GPS signals from a network of stationary receiving stations;
compressing and accumulating the GPS signals so that data received over a predetermined slow time period forms one data point from each receiving station, the data points from the entire network forming a data set;
periodically producing and outputting a slow correction once each slow time period by processing the data sets with a dynamical orbit predictor to produce calculated GPS satellite orbits in a real-time mode so that the processing steps occur in a time period less than the slow time period, the producing and outputting comprising the steps of:
conditioning the data set with updated estimates GPS parameters from processing data sets of previous slow time periods;
using the conditioned data sets to compute model orbital trajectories;
introducing the model orbital trajectories into a dynamical orbit model and computing the dynamical orbit model to incorporate the model orbital trajectories;
using a Kalman filter/smoother to combine the computed dynamical orbit model with previously computed models to produce updated estimates of GPS parameters;
using the updated estimates of GPS parameters to propagate orbits forward in time to a next slow correction;
using the propagated orbits to calculate satellite ephemeris and clock corrections for the next slow correction;
and
outputting the next slow correction including satellite and ephemeris clock corrections to the users;
producing and outputting ionospheric maps indicating a magnitude of signal delay in ionospheric regions, producing ionospheric maps comprising the steps of:
weighting each data set according to the elevation angle of each GPS satellite relative to a receiving station receiving the data set;
processing the weighted data sets, predicted satellite and receiver frequency biases, and a previously computed ionospheric delay map using a Kalman filter/smoother and thereby computing a total electron content at a plurality of ionospheric points;
using the computed total electron content to update a Sun-fixed spherical ionospheric delay map;
and
outputting grid points of the updated ionospheric delay map to reflect changes in the ionospheric delay map;
and
periodically calculating and outputting a fast clock correction over a fast time period, calculating the fast clock correction comprising the steps of:
propagating GPS parameters from the most recent slow correction forward in time to an arrival of the next actual pseudorange data from the ground stations;
calculating predicted pseudoranges using the propagated GPS parameters;
differencing the predicted pseudoranges with the next actual pseudorange data;
accumulating at least one set of differences;
averaging accumulated differences for each satellite;
and
outputting the averaged differences to the users as the fast clock corrections for each satellite.

23 more elements

Facts

Application

08/628,566Filed 29 Mar 1996

Granted

27 Oct 1998

Term ends

Not estimatedThe source records don’t support an estimate.

Classification6 codes

G01S 19/32
Receivers: multimode operation in a single same satellite system, e.g. GPS L1/L2
G01S 19/071
Providing data for correcting measured positioning data, e.g. DGPS [differential GPS] or ionosphere corrections: dGPS corrections
G01S 19/072
Providing data for correcting measured positioning data, e.g. DGPS [differential GPS] or ionosphere corrections: ionosphere corrections
G01S 19/074
Involving a network of fixed stations: providing integrity data, e.g. WAAS

Robust real-time wide-area differential GPS navigation

Life of this patent

Robust real-time wide-area differential GPS navigation

Life of this patent

Abstract

Claims16