1

Background

In this chapter, background material that will be referred to in the subsequent chapters is reviewed. In Section 1.1, the statistical characterization of persistent (finite-power) nonstationary stochastic processes is presented. Second-order statistics in both time, frequency, and time-frequency domains are considered. In Section 1.2, definitions of almost-periodic functions and their generalizations (Besicovitch 1932) and related results are reviewed. Almost-cyclostationary (ACS) processes (Gardner 1985, 1987d) are treated in Section 1.3. Finally, in Section 1.4, some results on cumulants are reviewed.