Linear systems: be discrete-then continuous

A description is given of the key fundamental concepts needed for an introductory treatment of signals and systems. The position is taken that the discussion of discrete-time systems should precede the discussion of continuous-time systems. The advantages of this approach include reduced initial complexity, an early opportunity to introduce signal processing applications and computer methods, and a better route to the understanding of models, analysis, and design of signals and systems. Several key concepts for discrete and continuous linear systems are compared to demonstrate the benefits of the `discrete-first´ approach