# Communication Systems/Communications Introduction

## Introduction

People are prone to take for granted the fact that modern technology
allows us to transmit data at nearly the speed of light to locations
that are very far away. 200 years ago, it would be deemed preposterous
to think that we could transmit webpages from China to Mexico in less
than a second. It would seem equally preposterous to think that people
with cellphones could be talking to each other, clear as day, from miles
away. Today, these things are so common, that we accept them without
even asking how these miracles are possible.

### What is Communications?

Communications is the field of study concerned with the transmission of
information through various means. It can also be defined as technology
employed in transmitting messages. It can also be defined as the
inter-transmitting the content of data (speech, signals, pulses etc.)
from one node to another.

## To Whom is This Book For?

This book is for people who have read the Signals and
Systems wikibook, or an equivalent
source of the information. Topics considered in this book will rely
heavily on knowledge of Fourier Domain representation and the Fourier
Transform. This book can be used to accompany a number of different
classes spanning the 3rd and fourth years in a study of electrical
engineering. Knowledge of integral and differential calculus is assumed.
The reader may benefit from knowledge of such topics as semiconductors,
electromagnetic wave propagation, etc., although these topics are not
necessary to read and understand the information in this book.

## What will this Book Cover

This book is going to take a look at nearly all facets of electrical
communications, from the shape of the electrical signals, to the issues
behind massive networks. It makes little sense to be discussing these
subjects outside the realm of current examples. We have the Internet, so
in discussing issues concerning digital networks, it makes good sense to
reference these issues to the Internet. Likewise, this book will attempt
to touch on, at least briefly, every major electrical communications
network that people deal with on a daily basis. From AM radio to the
Internet, from DSL to cable TV, this book will attempt to show how the
concepts discussed apply to the real world.

This book also acknowledges a simple point: It is easier to discuss the
signals *and* the networks simultaneously. For this kind of task to be
undertaken in a paper book would require hundreds, if not thousands of
printed pages, but through the miracle of Wikimedia, all this
information can be brought together in a single, convenient location.

This book would like to actively solicit help from anybody who has
experience with any of these concepts: Computer Engineers,
Communications Engineers, Computer Programmers, Network Administrators,
IT Professionals. Also, this book may cover all these topics, but the
reader doesn\'t need to have prior knowledge of all these disciplines to
advance. Information will be developed as completely as possible in the
text, and links to other information sources will be provided as needed.

## Where to Go From Here

Since this book is designed for a junior and senior year of study, there
aren\'t necessarily many topics that will logically follow this book.
After reading and understanding this material, the next logical step for
the interested engineer is either industry or graduate school. Once in
graduate school, there are a number of different areas to concentrate
study in. In industry, the number is even higher.

## Division of Material

Admittedly, this is a very large topic, one that can span not only
multiple printed books, but also multiple bookshelves. It could then be
asked \"Why don\'t we split this book into 2 or more smaller books?\"
This seems like a good idea on the surface, but you have to consider
exactly where the division would take place. Some would say that we
could easily divide the information between \"Analog and Digital\"
lines, or we could divide up into \"Signals and Systems\" books, or we
could even split up into \"Transmissions and Networks\" Books. But in
all these possible divisions, we are settling for having related
information in more than 1 place.

### Analog and Digital

It seems most logical that we divide this material along the lines of
analog information and digital information. After all, this is a
\"digital world\", and aspiring communications engineers should be able
to weed out the old information quickly and easily. However, what many
people don\'t realize is that digital methods are simply a subset of
analog methods with more stringent requirements. Digital transmissions
are done using techniques perfected in analog radio and TV broadcasts.
Digital computer modems are sending information over the old analog
phone networks. Digital transmissions are analyzed using analog
mathematical concepts such as modulation, SNR (signal to noise ratio),
Bandwidth, Frequency Domain, etc\... For these reasons, we can simplify
both discussions by keeping them in the same book.

### Signals and Systems

Perhaps we should divide the book in terms of the signals that are being
sent, and the systems that are physically doing the sending. This makes
some sense, except that it is impossible to design an appropriate signal
without understanding the restrictions of the underlying network that it
will be sent on. Also, once we develop a signal, we need to develop
transmitters and receivers to send them, and those are physical systems
as well.

### *Systems* Approach

It is a bit confusing to be writing a book about *Communication System*s
and also considering the **pedagogical** *Systems Approach*. Although
using the same word, they are not quite the same thing.

This approach is almost identical to the description above (Signals &
Systems) except that it is not limited to the consideration of signals
(common in many university texts), but can include other technological
drivers (codecs, lasers, and other components).

In this case we give a brief overview of different communication systems
(voice, data, cellular, satellite etc.) so that students will have a
context in which to place the more detailed (and often generic)
information. Then we can then zoom in on the mathematical and
technological details to see how these systems do their magic. This
lends itself quite well to technical subjects since the basic systems
(or mathematics) change relatively slowly, but the underlying technology
can often change rapidly and take unexpected terns.

I would like to suggest that the table of contents in this book be
rearranged to reflect this pedagogical approach: Systems examples first,
followed by the details.

### Why would anyone want to study (tele)communications?

Telecommunications is an alluring industry with a provocative history
filled with eccentric personalities: Bell, Heavyside, Kelvin, Brunel and
many others. It is fraught with adventure and danger: adventure spanning
space and time; danger ranging from the remote depths of the ocean floor
to deep space, from the boardrooms of AT&T to the Hong Kong stock
exchange.

Telecommunications has been heralded as a modern Messiah and cursed as a
pathetic sham. It has created and destroyed empires and institutions. It
has proclaimed the global village while sponsoring destructive
nationalism. It has come to ordinary people, but has remained largely in
the control of the 'media' and even \'big brother\'. Experts will soon
have us all traveling down a techno-information highway, destination ---
unknown.

Telecommunications has become the lifeblood of modern civilization.
Besides all that, there's big bucks in it

## About This Book

There are a few points about this book that are worth mentioning:

-   The programming parts of this book will not use any particular
    language, although we may consider particular languages in dedicated
    chapters.
