Overlay Communications Using Empirical Mode Decomposition

A signal overlay technique employing the empirical mode decomposition procedure is presented here. A weak narrowband signal is added to the primary signal that shares the same frequency band. Careful signal design reduces interference caused to primary users while ensuring successful recovery of the added signal. At the receiver a stationary filtering approach is ineffective in separating the signals because a fixed filter designed to isolate one of the signals will also capture significant portion of the other signal energy due to overlapping spectrums. However, the empirical mode decomposition technique, that isolates signal components based on their instantaneous frequencies, is ideally suited to separate these time-varying signals with overlapping frequency components. The choice of overlay signal transmission frequencies relative to that of the primary signal is made in such a way that leads to greater resemblance of one of the extracted components to the original overlay signal. An application to commercial frequency modulation overlay is presented with associated analysis and empirical performance results.