Adaptive Nonparametric Acquisition of FH-SS Signals in Jamming

Abstract

A matched filter receiver for frequency-hopped spread spectrum code acquisition in jamming is analyzed. The receiver uses an adaptive, nonparametric distribution-free Median Test detector requiring no knowledge or "side-information" about the signal, jammer, and thermal noise parameters to implement an asymptotically constant false alarm rate test. The median of a reference sample set, empirically describing the code-absent probability distribution, determines the threshold used in the nonparametric detector. By updating the reference set every hop epoch, the threshold adapts to the channel condition. Adaptive threshold setting introduces memory so that tests are no longer independent, making exact closed-form analysis difficult. Performance approximations are developed and compared to simulation results illustrating acquisition performance.