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