Introduction to Communications for
Non-Electrical-Engineering Students
Mao-Ching Chiu, R. C. T. Lee, Eric S. Li, Jung-Shan Lin, Tai-Ping Sun
Fourier Ampere Faraday Maxwell
Biot Hertz Coulomb Dirac
The Preface
We decided to write this book for one simple reason: Most of the poor computer science students are just ignorant about communications and there is no good textbook on this subject suitable for them. If you ask a typical computer science student why we have to perform modulation, he usually cannot answer although he is familiar with AM broadcasting. Perhaps the most puzzling aspect of communications for computer scientists is that two bits can be mixed and sent together at the same time. To a computer science student, a bit is a bit. How can two bits mixed together? Besides, although there are courses in computer science departments with the fancy title like “wireless”, the students who have taken these courses still cannot say that they know how electromagnetic waves are caused and how they propagate because electromagnetic theory is usually not touched in these courses. We cannot blame them. The electromagnetic theory is a big problem even for electrical engineers and there are not many computer science professors who can teach this subject.
As the computer science students get into the chip design field, they suddenly find out that they have know transmission line, for instance because an extremely short line in a chip is actually a transmission line for high frequency signals. They also have to know inductance and capacitance. It is by no means easy for them to grasp the main ideas about how to measure inductance and capacitance under various circumstances. When they take a course in electronic circuit, the circuits are all lumped circuits. The frequency of the signal is not high enough for voltages and currents to behave like waves in a wire. But, in communications, we always talk about high frequencies. How can we ignore the transmission line concept?
Of course, our poor computer science students can take communications courses offered by electrical engineering departments. This is often impossible as there are so many such courses. A computer science student has limited time to take courses in other departments. It is impractical for him to go to the electrical engineering department and get humilaited.
This book was born because of such a need. We performed an analysis and selected a certain areas which we believe a computer science student should understand. Perhaps this is the first, and the only, communications book which presents QPSK, CDMA, OFDM together with Maxwell’s equations. It is not easy to do so. We have to be careful in making sure that the necessary basic background material is all there. For instance, when we introduce Maxwell’s equations, we still start with Coulomb’s law. Although this is a concise book because we have to put many ideas into one book, we work hard to make sure that this book is self-contained. That is, a diligent computer science student, hopefully, can read this book and understand most of the material inside it without a teacher.
To make this book readable, we employ two approaches: (1) Examples and figures are given as much as we can. (2) Physical meaning is emphasized.
Let us consider one example. Many students who learned Fourier transform actually do not understand it thoroughly. For instance, a positive frequency is easy to comprehend. But, if you ask students why there are negative frequencies in the Fourier transform, they usually cannot answer. In our book, we not only just give a formula for Fourier transform, we make a big effort to explain the physical meaning of it.
In Fourier transform, we all know that if a signal is multiplied with a cosine function with a certain frequency f, the entire spectrum of the signal is shifted towards this frequency f. This can be proved formally by using the convolution theory, for instance. But it can be easily explained in an informal way, as we did in this book.
We taught a course in communications for essentially computer science students in both National Chi Nan University and National Tsing Hua University using this book as the textbook. In both universities, many electrical engineering students took the course. These electrical engineering enjoyed the course enormously because this gave them somehow a global view of communications. Besides, they appreciated the physical meanings of different concepts introduced in this book. For instance, the electromagnetic theory is not presented in this book as a bunch of terrifying mathematical formulas with weird vector operators, such as ▽. Whenever we present a new theory, we tried our best to mention some phenomenon which the students are familiar with. Through this way, we hope that the scary electromagnetic theories are presented with a human face. In other words, to each electromagnetic theory, it is our hope that the reader can easily associate with it a phenomenon which he learned in high school.
We are of course happy that the computer science students can more or less communicate with their electrical engineering counterparts without inferior complex. It is hard for an electrical engineering student to use such terms such as OFDM, SSB, the plane wave equation to humiliate their computer science friends now.
A very positive contribution of this book is for the computer science students to have an awe to the great scientists, such as Fourier, Maxwell, Faraday, Hertz, Ampere and so on. Many computer science students often think they are some kind of genius as they can write clever programs. They think that they are wonder boys. After taking this course, there was not a single proud student left. They were all humbled. None of them can understand why Coulomb, a retired general of the French army, could design such excellent devices to come up with the so called Coulomb’s law. As for the displacement current concept, it is even more amazing for Maxwell to propose it. After all, Maxwell did not have any experimental evidence about the existence of such a current. He was simply brilliant enough to be able to have such a conjecture. After learning what Maxwell contributed to the world, the once arrogant computer science students have all become humble.
Actually, many students from mechanical engineering, civil engineering and chemistry took the course. To our surprise, many civil engineering students performed very well. We believe this is due to the fact that they are better in engineering mathematics. Originally, we only thought of computer science students. Now, we have the confidence that this book can be used to teach all science and engineering students the basic concepts of communications.
Table of Contents
Chapter 1 An Overview of Computer Communication
1.1 Analog and Digital Signals
1.2 Two Kinds of Media: Electrical and Electro-magnetic
1.3 The Fourier Transform
1.4 Carrier and Analog Modulation
1.5 Digital Modulation
1.6 The Real Time and Non-real Time Transmission Problems
1.7 The Multiplexing Receiving Problem
1.8 The Multiplexing Transmission Problem
1.9 The Basic Electromagnetic Theory
1.10 The Transmission Lines
1.11 The Antennas
Chapter 2 Conversions Between Analog and Digital Information
2.1 Pulse Code Modulation
2.2 Minimum Sampling Rate - Nyquist Rate
2.3 Reconstruction of the Analog Signal
Chapter 3 Signal Space Representation
3.1 Vector Space
3.2 Signal Space
3.3 Summary
Chapter 4 Fourier Representations for Signals
4.1 Fourier Series
4.2 Fourier Series in Complex Exponentials
4.3 The Fourier Transform
4.4 Properties of Fourier Transform
4.5 FT Representations for Periodic Signals
4.6 The Discrete Fourier Transform
4.7 The Inverse Discrete Fourier Transform
4.8 The Physical Meaning of the Fourier Trans-form
Chapter 5 Analog Modulation Techniques
5.1 Amplitude Modulation
5.2 Double Sideband Suppressed-Carrier (DSB-SC)
5.3 Single Sideband Modulation (SSB)
5.4 Frequency Modulation (FM)
5.5 Frequency Division Multiplexing
Chapter 6 Digital Modulation Techniques
6.1 Baseband Pulse Transmission
6.2 Amplitude-Shift Keying (ASK)
6.3 Binary Phase-Shift Keying (BPSK)
6.4 Binary Frequency-Shift Keying (FSK)
6.5 Quadriphase-Shift Keying (QPSK)
6.6 Orthogonal Frequency Division Multiplexing (OFDM)
6.7 The Role of Inner Product in Digital Modulation
Chapter 7 Multiple Access Communications
7.1 Frequency-Division Multiple Access (FDMA)
7.2 Time-Division Multiple Access (TDMA)
7.3 Code-Division Multiple Access (CDMA)
7.4 Carrier Sense Multiple Access (CSMA)
7.5 The Multiplexing Transmission Problem
Chapter 8 Spread-Spectrum Communications
8.1 The Basic Concept of Spread Spectrum
8.2 Power Spectral Density
8.3 Baseband Transmission for Direct-Sequence Spread-Spectrum (DSSS) Communications
8.4 BPSK Modulation for DSSS
8.5 Pseudo-Random Binary Sequence
8.6 Frequency-Hopping Spread Spectrum
8.7 Application of Spread Spectrum Techniques to Multi-access Systems
Chapter 9 Source Coding and Channel Coding
9.1 Average Codeword Length of Source Coding
9.2 Prefix Codes
9.3 Huffman Coding
9.4 Channel Coding
9.5 Error Correcting Capability and Hamming Distance
9.6 Hamming Codes
Chapter 10 Electric Field, Magnetic Field, Maxwell’s Equations and Plane Waves
10.1 The Dot and Cross Products of Vectors
10.2 The ▽ Operator, the Gradient of a Scalar Field and the Line
Integral of a Vector Field
10.3 The Divergence of a Vector Field
10.4 The Curl of a Vector Field
10.5 The Electrostatic Fields
10.6 Magnetostatic Field
10.7 A Review of Electrostatic and Magnetostatic Fields
10.8 Maxwell’s Equations
10.9 The Plane Waves Equations Derived from the Maxwell’s Equations
Chapter 11 Transmission Lines
11.1 The Inductance
11.2 The Capacitance
11.3 The Phasor Expression
11.4 The Equivalent Circuit of Lossless Transmission Lines
11.5 The Determination of Voltage and Current in a Transmission Line
11.6 The General Rules of Determining Voltage and Current in a Transmission Line
11.7 The Steady State Sinusoidal Case Analysis
11.8 The Physical Properties of the Voltage and Current Waves with the Sinusoidal Input Source
11.9 The Voltage Reflection Coefficient at the Load
11.10 Voltage and Current as a Function of Location along the Transmission Line
11.11 The Input Impedance
Chapter 12 Antennas
12.1 The Spherical Coordinate System
12.2 The Vector Magnetic Potential
12.3 The Electric Dipole
12.4 The Infinitesimal (Hertzian) Dipole Antenna
12.5 The Magnetic Dipole Antenna of Infinitesimal Loop
12.6 Radiation Resistance
12.7 The Long Dipole Antennas
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