ABSTRACT
T RADITIONALLY, SIGNAL PROCESSING AS A DISCIPLINE has relied heavily on a theoreticalfoundation of linear time-invariant system theory in the development of algorithms for a broadrange of applications. In recent years, a considerable broadening of this theoretical base has begun to take place. In particular, there has been substantial growth in interest in the use of a variety of nonlinear systems with special properties for diverse applications. Promising new techniques for the synthesis and analysis of such systems continue to emerge. At the same time, there has also been rapid growth in interest in systems that are not constrained to be time-invariant. These may be systems that exhibit temporal fluctuations in their characteristics, or, equally importantly, systems characterized by other invariance properties, such as invariance to scale changes. In the latter case, this gives rise to systems with fractal characteristics.
