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Abstract

Method and apparatus for providing GPS pseudorange correction information over a selected geographic region S with a diameter of up to 300 km with an associated inaccuracy no greater than 5 cm. N spaced apart GPS reference stations (N>4), whose location coordinates (u.sub.n,v.sub.n,w.sub.n) are fixed and are known with high accuracy, are provided within or adjacent to the region R. Each reference station n(n=1, 2, . . . , N) receives GPS signals from at least four common-view GPS satellites, numbered m=1, 2, . . . , M (M.gtoreq.4), computes its own GPS-determined location coordinates, compares these coordinates with its known location coordinates, determines the pseudorange corrections PRC(t;t0;m;n) for its GPS-determined location, and transmits these correction signals to a central station located within or adjacent to the region S. The central station retransmits the pseudorange correction signals throughout the region S. A mobile GPS station within or adjacent to the region S has stored within it the coordinates (u',v',w') of the GPS-determined last location of that mobile station and the spatial coordinates (u.sub.n(k),v.sub.n(k),w.sub.n(k)) (k=1, 2 , . . . , K; K>3) of K GPS reference stations within S that are closest to the last-determined location of that mobile station. The mobile station then computes the differential GPS corrections for the GPS-determined present location of that mobile station. Alternatively, the reference stations can transmit to the central station unprocessed GPS signals for determination of the pseudorange correction signals at the central station. This approach can be modified if the region R is two-dimensional, where only two coordinates u and v are needed, or if the region R is one-dimensional, where only one coordinate u is needed. Suitable algorithms for selection of the coefficients a.sub.k' are discussed.

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First Claim