ABSTRACT
In this chapter, we introduce the concept of signals. Signals are classified according to their basic characteristics and properties. Furthermore, several elementary basic signals are introduced. A signal is defined as any natural quantity that varies according to one or more independent variables such as time or space. Time is usually the independent variable, but other variables like frequency can also be considered. Examples of signals are a sound, an image, an electrical current or voltage, a transmitted message, and many others. From a mathematical point of view, a signal is described by a function of one or more independent variables. According to the number of independent variables, a signal is characterized as a one-dimensional (1-D), a two-dimensional (2-D), or a multidimensional signal.
