 SIGNAL AND SYSTEM

What is a Signal?

A signal is deﬁned as any physical quantity that carries information and varies with time,space, or any other independent variable or variables.The world of science and engineering is ﬁlled with signals: speech, television, images from remote space probes, voltages generated by the heart and brain, radar and sonar echoes, seismic vibrations, signals from GPS satellites, signals from human genes, and countless other applications.

What is a System?

Asystemisdeﬁnedmathematicallyasatransformation thatmapsaninputsignalx(t) into an output signal y(t) as illustrated in Figure 1.1. This can be denoted asSWITCHING THEORY AND LOGIC DESIGN
yt =ℜ[x(t)] Signal And System SEMICONDUCTOR ROBOT DYNAMICS AND CONTROL
where ℜ is an operator. For example, a communication system itself is a combination of transmitter, channel, and receiver. A communication system takes speech signal as input and transforms it into an output signal, which is an estimate of the original input signal.GRAPH THEORY

Analog and Digital Signals

An analog signal is a continuous-time signal whose amplitude can take any value in a continuous range. A digital signal is a discrete-time signal that can only have a discrete set of values. The process of converting a discrete-time signal into a digital signal is referred to as quantization.

Deterministic and Random Signals

For any given time, the values of deterministic signal are completely speciﬁed as shown in Figure 1.12(a). Thus, a deterministic signal can be described mathematically as a function of time. Signal And System A random signal takes random statistically characterized random values as shown in Figure 1.12(b) at any given time. Noise is a common example of random signal.MATERIALS SCIENCE AND ENGINEERING