There are many introductory textbooks on signals and systems, each organizing and presenting the material in a particular way. See, for example, Oppenheim, Willsky, and Nawab 1997; Haykin & Van Veen, 2002; and Kamen & Heck, 1999. For applications of signal models to specific engineering fields, see, for example, Gold & Morgan, 1999 for speech and signal processing; Haykin, 2000 for modulated signals in telecommunications; and Bruce, 2000 for biomedical signals. For further details on system properties, see Chen, 1999.