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Abstract

A method for improving the accuracy of signal signature determinations in wireless location finding systems advantageously uses transmitter velocity estimates to accurately and reliably determine in real time a present signal covariance matrix for a transmitter. In a preferred embodiment of the invention, a method for determining a likely location of a transmitter in a wireless transmitter location finding system comprises coherently measuring transmitter signals received at an antenna array, and calculating a current signal covariance matrix from the measured transmitter signals. The method further comprises calculating an average covariance matrix by forming a linear combination of the current signal covariance matrix with past average covariance matrices. The coefficients of the linear combination are selected such that the average covariance matrix is derived primarily from covariance matrices measured over a range of recent transmitter locations within a predetermined distance D from the present location. This distance D preferably corresponds to a spatial span of calibrated signatures. In a preferred embodiment, this condition is satisfied by selecting the coefficients in dependence upon the distance D and an estimated current velocity of the transmitter. The method also includes determining a likely current transmitter location by measuring a similarity between the average covariance matrix and a set of calibrated covariance matrices corresponding to calibrated transmitter locations.

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First Claim