Download Introduction to Communications for

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
Biot
Ampere
Faraday
Hertz
Coulomb
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Maxwell
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
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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.
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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.
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Table of Contents
Chapter 1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
1.8
1.9
1.10
1.11
An Overview of Computer Communication
Analog and Digital Signals
Two Kinds of Media: Electrical and Electro-magnetic
The Fourier Transform
Carrier and Analog Modulation
Digital Modulation
The Real Time and Non-real Time Transmission Problems
The Multiplexing Receiving Problem
The Multiplexing Transmission Problem
The Basic Electromagnetic Theory
The Transmission Lines
The Antennas
Chapter 2
Conversions Between Analog and Digital
Information
2.1
2.2
2.3
Pulse Code Modulation
Minimum Sampling Rate - Nyquist Rate
Reconstruction of the Analog Signal
Chapter 3
3.1
3.2
3.3
Vector Space
Signal Space
Summary
Chapter 4
4.1
4.2
4.3
4.4
4.5
Signal Space Representation
Fourier Representations for Signals
Fourier Series
Fourier Series in Complex Exponentials
The Fourier Transform
Properties of Fourier Transform
FT Representations for Periodic Signals
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4.6
4.7
4.8
The Discrete Fourier Transform
The Inverse Discrete Fourier Transform
The Physical Meaning of the Fourier Trans-form
Chapter 5
5.1
5.2
5.3
5.4
5.5
Amplitude Modulation
Double Sideband Suppressed-Carrier (DSB-SC)
Single Sideband Modulation (SSB)
Frequency Modulation (FM)
Frequency Division Multiplexing
Chapter 6
6.1
6.2
6.3
6.4
6.5
6.6
6.7
8.4
8.5
Multiple Access Communications
Frequency-Division Multiple Access (FDMA)
Time-Division Multiple Access (TDMA)
Code-Division Multiple Access (CDMA)
Carrier Sense Multiple Access (CSMA)
The Multiplexing Transmission Problem
Chapter 8
8.1
8.2
8.3
Digital Modulation Techniques
Baseband Pulse Transmission
Amplitude-Shift Keying (ASK)
Binary Phase-Shift Keying (BPSK)
Binary Frequency-Shift Keying (FSK)
Quadriphase-Shift Keying (QPSK)
Orthogonal Frequency Division Multiplexing (OFDM)
The Role of Inner Product in Digital Modulation
Chapter 7
7.1
7.2
7.3
7.4
7.5
Analog Modulation Techniques
Spread-Spectrum Communications
The Basic Concept of Spread Spectrum
Power Spectral Density
Baseband Transmission for Direct-Sequence Spread-Spectrum
(DSSS) Communications
BPSK Modulation for DSSS
Pseudo-Random Binary Sequence
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8.6
8.7
Frequency-Hopping Spread Spectrum
Application of Spread Spectrum Techniques to Multi-access
Systems
Chapter 9
9.1
9.2
9.3
9.4
9.5
9.6
Source Coding and Channel Coding
Average Codeword Length of Source Coding
Prefix Codes
Huffman Coding
Channel Coding
Error Correcting Capability and Hamming Distance
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
10.3
10.4
10.5
10.6
10.7
10.8
10.9
Integral of a Vector Field
The Divergence of a Vector Field
The Curl of a Vector Field
The Electrostatic Fields
Magnetostatic Field
A Review of Electrostatic and Magnetostatic Fields
Maxwell’s Equations
The Plane Waves Equations Derived from the Maxwell’s
Equations
Chapter 11 Transmission Lines
11.1
11.2
11.3
11.4
11.5
The Inductance
The Capacitance
The Phasor Expression
The Equivalent Circuit of Lossless Transmission Lines
The Determination of Voltage and Current in a Transmission
Line
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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
12.1
12.2
12.3
12.4
12.5
12.6
12.7
Antennas
The Spherical Coordinate System
The Vector Magnetic Potential
The Electric Dipole
The Infinitesimal (Hertzian) Dipole Antenna
The Magnetic Dipole Antenna of Infinitesimal Loop
Radiation Resistance
The Long Dipole Antennas
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