Types of Signals, Their Properties, Operation & Application What Is Signal? A signal is defined as any physical or virtual quantity that varies with time or space or any other independent variable or variables. Graphically, the independent variable is represented by horizontal axis or x-axis.

Graphically, the independent variable is represented by horizontal axis or x-axis. And the dependent variable is represented by vertical axis or y-axis. Mathematically, a signal is a function of one or more than one independent variables.

According to the strengths of signals, practical signals can be classified into two categories: energy signals and power signals. Energy signals: Those signals' energyare equal to a finite positive value, but their average powers are 0; 0<E=∫−∞∞s2(t)dt<∞{\displaystyle 0<E=\int _{-\infty }^{\infty }s^{2}(t)dt<\infty }

Generally, every message signal is a random signal because we are uncertain of the information to be conveyed to the other side. Time-shifting means movement of the signal across the time axis (horizontal axis).