Some alternatives in transform-domain suppression of narrow-band interference for signal detection and demodulation

Conventional detection and demodulation rules are not ideally suited for use with discrete Fourier transform (DFT) based narrow-band interference suppression, if the DFT incorporates time-weighting to localize the interference spectrally. Detection rules which are adapted to the time-weighting are introduced and shown to offer significant improvements in performance, but their implementation is complex. It is found that if a spectrally-contained orthogonal transform (SCOT) is employed in place of the windowed DFT however, the conventional detection rules have a level of performance comparable to that obtained with DFT based suppression and the adapted rules. In addition to yielding good interference localization, SCOTs benefit from the fact that they provide a Karhunen-Loeve like transform for each component of the observation. The primary focus of the paper is the application of interference suppression for the detection of the presence of covert signals; however, it is also demonstrated that SCOT based suppression is potentially better suited than DFT based suppression for data demodulation in commercial code-division multiple-access (CDMA) network overlays.