# 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