Signals and Systems

Gang Li, Liping Chang, Sheng Li, Tsinghua University Press

• Publisher: De Gruyter
• Year: 2015
• ISBN:
  9783110416848
• Edition: 1
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería eléctrica y telecomunicaciones

Signals and systems enjoy wide application in industry and daily life, and understanding basic concepts of the subject area is of importance to undergraduates majoring in engineering. With rigorous mathematical deduction, this introductory text book is helpful for students who study communications engineering, electrical and electronic engineering, and control engineering. Additionally, supplementary materials are provided for self-learners.

1 Introduction

This chapter is devoted to providing students a set of general concepts of signals and systems. We will begin our development with the intuitive questions that may be raised by most of the students at the beginning of the first class of this course: what is a signal and what is a system? Mathematical descriptions and representations of signals and systems are the most important concepts throughout this course and also play a role of corn-stone for other more advanced subjects. We will build on the foundation for developing these concepts and discuss some properties of systems as well as the relationship between signals and systems in this chapter.

1.1 Overview of signals and systems

Signals and systems are two of the words which are heard most frequently in our daily life. These concepts arise in virtually all areas, and particularly, play a very important role in engineering. In fact, it can be argued that much of the recent development of high technology, which has brought our life to a new dimension, is a result of advancements in the theory and techniques of signals and systems.

1.1.1 What is a signal?

Examples of signals we encounter frequently include speech/music signals, and, picture/image signals, which, in the signal processing community, are usually referred to as audio and video signals, respectively. A signal is actually a variable used to carry information. For example, a speech signal from the speaker of a research seminar represents air pressure that varies with time and stimulates the audience’s ears, and the information is reflected by the way how the air pressure (i.e. the signal) changes with time. A signal can be represented in different forms. Figure 1.1 shows the waveform of a recorded speech signal displayed on a computer screen. The physical meaning (i.e. information) carried by this signal is “di qiu” in Mandarin Chinese (it means “earth” in English) spoken by a Chinese male.

An image signal is the light intensity, also called gray level, that varies with two spatial coordinates (see Fig. 1.2), while a video signal consists of a set of pictures that occur in sequence and hence are the light intensity that changes with the two spa...