1. 1 Introduction a Note: A continuous-time signal is defined at every instant of time. On the other hand, a discrete-time signal takes certain numerical values at specified discrete instants of time and between these specified instants of time the signal is not defined1.1 Introduction  Note: A continuous-time signal is defined at every instant of time. On the other hand, a discrete-time signal takes certain numerical values at specified discrete instants of time, and between these specified instants of time, the signal is not defined