Patent ID: 6031882
Filing Date: 2000-02-29
Classification: G01S,H04B

Abstract:
A method for compensating for the presence of one or more multipath signals in an electromagnetic signal received at a receiver, the method comprising the steps of:receiving at a receiver a composite incoming signal that is the result of propagation, over one or more propagation paths, of a transmitted message signal having a selected transmitted signal frequency and having a selected code shape signal with a code shape signal chip duration;forming a correlation function, having a selected time shift variable, between the incoming signal and the code shape signal over a selected time interval that includes at least one code shape signal chip duration;determining first and second distinct time shift values that produce equal amplitudes of the correlation function, using a difference between the second and first time shift values that is at least about 40 percent of the length of the code shape signal chip duration, and computing a wide time shift average .DELTA..tau..sub.w,avg of the first and second time shift values;determining third and fourth distinct time values that produce equal amplitudes of the correlation function, using a positive difference between the fourth and third time shift values that is no larger than about 20 percent of the length of the code shape signal chip duration, and computing a narrow time shift average .DELTA..tau..sub.n,avg of the third and fourth time shift values;forming a wide time shift difference between the wide time shift average and a selected peak time shift value for the maximum amplitude of the correlation function, and a narrow time shift difference between the narrow time shift average and the selected time shift peak value, where the selected peak time shift value is to be determined;providing a collection of pairs first and second coordinates, where the first coordinate is a simulated value of a difference between the wide time shift difference and the narrow time shift difference, and the second coordinate is the narrow time shift difference;determining an optimal linear approximation of each simulated second coordinate in the collection by the corresponding simulated first coordinate in the collection;using the optimal linear approximation to estimate a peak time shift value; andinterpreting the peak time shift value as a time of arrival of a direct signal at the receiver.