Signals and Systems - Electrical Engineering

CHAPTER 6 Application to Control and Communications...........................................

Who are you going to believe? Me or

your own eyes.

Julius “Groucho” Marx (1890–1977)

comedian and actor

6.1 Introduction

Control and communications are areas in electrical engineering where the Laplace and the Fourier
analyses apply. In this chapter, we illustrate how these transform methods and the concepts of trans-
fer function, frequency response, and spectrum connect with the classical theories of control and
communications.

In classical control, the objective is to change the dynamics of a given system to be able to achieve
a desired response by frequency-domain methods. This is typically done by means of a feedback
connection of a controller to a plant. The plant is a system such as a motor, a chemical plant, or an
automobile we would like to control so that it responds in a certain way. The controller is a system we
design to make the plant follow a prescribed input or reference signal. By feeding back the response of
the system to the input, it can be determined how the plant responds to the controller. The commonly
used negative feedback generates an error signal that permits us to judge the performance of the
controller. The concepts of transfer function, stability of systems, and different types of responses
obtained through the Laplace transform are very useful in the analysis and design of classical control
systems.

A communication system consists of three components: a transmitter, a channel, and a receiver. The
objective of communications is to transmit a message over a channel to a receiver. The message is a
signal, for instance, a voice or a music signal, typically containing low frequencies. Transmission of
the message can be done over the airwaves or through a line connecting the transmitter to the receiver,
or a combination of the two—constituting channels with different characteristics. Telephone commu-
nication can be done with or without wires, and radio and television are wireless. The concepts of

Signals and Systems Using MATLAB®. DOI: 10.1016/B978-0-12-374716-7.00009-0
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