Page 31 - Fundamentals of Communications Systems

Preface xxix

9. Orthogonality to Reduce Complexity. Almost all modern digital com-
munication systems use the concept of orthogonality but sometimes in dis-
parate forms. The traditional way of introducing these topics is for each
type of orthogonality to be a special advanced topic. For example, mobile
telephone service is often used to introduce the idea of code division mul-
tiplexing. Unfortunately, what is lost in this discussion is that the orthog-
onality is designed into modems primarily to reduce the complexity of the
demodulator. Modern communication engineers should be able to see the big
picture and consequently this book teaches a general idea (orthogonality)
and introduces code division multiplexing, frequency division multiplexing,
and Nyquist theory as the important examples of this general idea. Modern
engineers need modern training to understand the trade-offs these systems
offer.
10. Spectral Shaping in Communications. No modern communication sys-
tem can afford to ignore the spectral impacts of modulation as that is one
of the three dimensions that define the operating point of a modern com-
munication system. Since spectral efficiency has such importance in mod-
ern communications, techniques to achieve the practical spectral charac-
teristics are introduced in a separate chapter. The nontrivial idea of pulse
shaping in communications is one of the first steps a communication engi-
neer must take to really understand the practical aspects of communication
engineering. As an interesting contrast of practice versus academia, aca-
demics tend to dismiss this spectral shaping as relatively unimportant and
straightforward while most engineering teams in practice agonize over the
practical aspects of spectral shaping and meeting the prescribed spectral
mask.
11. Adding Memory to Improve Performance. While this is a first course
in communications, there is a final chapter that shows how far modern com-
munications has progressed and how close the profession of communication
engineering is to the bounds Shannon identified in certain situations. This
chapter highlights these ideas by showing the fundamental signal design
techniques from a communication theory perspective, i.e., signal design to
address the Euclidean distance spectrum and average energy spectrum.
This is a powerful final perspective on modern communication engineering
for an engineer/student to take away from the book.