A nine-tile algorithm for LPI signal detection using QMF filter bank trees

This paper describes a novel spread spectrum intercept receiver which uses orthogonal wavelet techniques and a quadrature mirror filter (QMF) bank tree to decompose a waveform into components representing the energy in rectangular "tiles" in the time-frequency plane. Specifically, a nine-tile algorithm is presented and discussed. By simultaneously examining multiple layers of the tree, the dimensions of concentrations of energy can be estimated with a higher resolution than is normally associated with linear transform techniques. This allows detection and feature extraction even when the interceptor's knowledge of the target signal is limited. For example, no prior knowledge of channelization or time segmentation is assumed. In addition, the receiver can intercept and distinguish between multiple signals.