New Approach to the Characterization and Detection of Nonstationary Environments and Channels

摘要

A new method to study nonstationary systems and channels that applies to both the time-variant and time-invariant case has been developed. It is shown that a significant simplification occurs when systems are formulated in phase space. The phase space can be time-frequency for the usual formulation of channels/systems, or position-wave number for dispersive channels and pulses. In the standard textbook approach of input-output relations and system functions, the relations are formulated in time or frequency. We have derived input-output relations for time-varying channels. The method has led to practical solutions to a number of problems, both deterministic and random. Among them are defining the concept of quasi-stationarity, formulating features that are dispersion invariant, obtaining simple characterizations of pulses that propagate in dispersive channels with attenuation.