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 here 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 KarhunenLoeve 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 demon...

Combined spatial and time-frequency signatures of signal arrivals at a multi-sensor array are used for nonstationary interference suppression in direct-sequence spread-spectrum (DS/SS) communications. With random PN spreading code and deterministic nonstationary interferers, the use of antenna arrays offers increased DS/SS signal dimensionality relative to the interferers. Interference mitigation through spatio-temporal subspace projection technique leads to reduced DS/SS signal distortion and improved performance over the case of a single antenna receiver. The angular separation between the interference and desired signals is shown to play a fundamental role in trading off the contribution of the spatial and time-frequency signatures to the interference mitigation process. The expressions of the receiver SINR implementing subspace projections are derived and numerical results are provided.

Interference suppression in spread spectrum communication systems is often essential for achieving maximum system performance. Existing interference suppression methods do not perform well for most types of nonstationary interference. We first consider interference suppression schemes based on adaptive orthogonal time-frequency decompositions, such as wavelet packet and arbitrary dyadic time-frequency tilings. These methods often reduce interference substantially, but their performance can vary dramatically with minor changes in interference characteristics such as the center frequency. To circumvent these drawbacks, we propose a multiple overdetermined tiling (MODT) with an accompanying blind interference excision scheme which appears very promising for mitigating time-frequency-concentrated interference. Simulations with narrowband, impulsive, and simultaneous impulsive and narrowband interference compare the performance of the various methods and illustrate the promise of approaches based on multiple overdetermined tilings.