Johns Hopkins University

Stephen J Stafford

Lloyd A Linstrom

Mark S Asher

Thomas L Kusterer

Martin G Sommerville

Methods and systems to detect navigation signals, including to identify up to multiple range-Doppler hypotheses from each of j range-Doppler correlation grids based on a relatively low first threshold, generate navigation solutions from combinatorial sets of k of the identified hypotheses, evaluate the navigation solutions to identify plausible solutions, iteratively and combinatorially augment the plausible solutions with additional hypotheses from grids that are not represented in the corresponding k-hypotheses based navigation solutions, replace plausible solutions with corresponding augmented plausible solutions when appropriate, and select one of a plurality of plausible solutions as a best plausible solution, j and k being positive integers. Where a grid energy peak exceeds a second threshold, a corresponding hypothesis may be identified as a sole hypothesis for the corresponding navigation signal. The relatively low first threshold permits detection of weaker signals. Subsequent evaluations effectively transform a per-navigation-signal false alarm rate to per-navigation-solution false alarm rate.

Methods and systems to diminish false-alarm rates in multi-hypothesis signal detection through combinatoric navigation

Methods and systems are provided for accessing GPS signals in faded environments. Means are provided for predicting the nonlinear phase induced by the receiver's own clock, when there is at least one GPS satellite link strong enough to calculate a phase profile. In an embodiment, GPS signals are accessed in faded environments by increasing the sensitivity of a GPS receiver by increasing the processing gain of received GPS signals through increased integration time. Matching a near-baseband signal requires removing a nonlinear part of the phase which may arise from several sources, including: the phase drift of the GPS satellite's atomic clock, the phase drift due to the motion of the GPS receiver, the phase drift due to the motion of the GPS satellite, and the phase drift due to the GPS receiver's clock.

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Derwood, MD, United States of America

Stephen J Stafford