FREQUENCY DOMAIN TECHNIQUES FOR FAST GPS ACQUISITION AND INTERFERENCE DETECTION/REJECTION

In earlier work, methods for using fast Fourier transform (FFT) techniques to process digitized GPS and GLONASS signals were presented. This paper presents data collected among the largest buildings in Hartford, Connecticut. Consistent with our laboratory findings, field analysis suggests that the FFT method is able to extract the times of arrival (TOAs) of the satellite signals given only brief glimpses of the signals, resulting in a receiver that can track more satellites than conventional receivers when operating in urban canyons. In addition, a method based on dynamic programming is presented which makes use of local maxima in the cross-correlation functions to find the optimal trajectory, thereby further increasing fix availability. Finally, a method of implementing the optimum matched filter for colored noise and interference is described. It is shown that the filter improves performance even when noise and interference are limited to white noise and other satellites, and notching/filtering noise as wide as 1.44 MHz centered in the GPS band is illustrated.