Efficient algorithm for processing GPS signals

Abstract

A disclosed algorithm enables fast and efficient location of a mobile unit by obtaining and processing a snapshot of signals from all satellites in view of a constellation such as the Global Positioning System. The method is capable of dealing with weak signals and requires minimal use of processing time and use of communications resources. Each satellite transmits a signal that consists of a series of frames of a pseudo-noise sequence whereupon is superimposed a satellite data message. The total signal received from the satellite network by the mobile unit is arranged as columns of a matrix and is processed coherently to provide estimated pseudo-ranges and estimated rates of change of pseudo-ranges for in-view satellites. The coherent processing includes performing an initial orthogonal transform on the rows of the matrix and, uses prior knowledge to select that portion of the matrix containing a particular satellite signal for further processing. A reference vector, containing the respective pseudo-noise sequence, is prepared for each satellite in view by cyclically transposing the elements thereof to match the phase of the same sequence in the received signal from the satellite and multiplying the elements of the vector by Doppler compensation factors. Then, for each satellite in view, the columns of the selected matrix portion are convolved with the prepared reference vector for that satellite. Prior knowledge is again used to refine the selection and the satellite data message is demodulated to enable precise location of the start of a pseudo-noise sequence frame and the Doppler shift of the received signal. The process is repeated for at east four satellites in view to determine location and velocity of the receiving station by methods well known in the art.

Dependencies are inferred from the claim text.