520.465 Digital
Communications I
Spring 2008
A. Brinton Cooper III
(abcooper@jhu.edu)
The study of digital communications builds upon the foundation
laid in Basic Communications 520.401. A digital communications
system conveys information by means of discrete symbols selected from a
(usually) finite alphabet. The channel is "noisy," and
the study of the effects of noise on communications signals is paramount.
Following an introduction to random signal theory, signal representations, and
the essentials of signal detection, we develop the optimal receiver for
the additive white Gaussian noise channel and study the performance of
that receiver. We investigate Important modulation systems for the
Gaussian channel and compare their power and spectral efficiencies.
As the speed of information transmission is increased, we discover that many
channels become dispersive: the pulse duration increases and the
spectral components of the signal experience unequal time delays. Methods
for mitigating the dispersion are studied. The obvious and logical sequel
to this course is Digital Communications II The study of Error Control Coding is relevant to Digital
Communications but not dependent upon it.
1. Introduction to Random Signal
Theory
A brief
review of probability is followed by an introduction to the theory of discrete
and continuous random processes, including a brief examination of their
spectral properties. Characterizations of baseband and bandpass
narrowband signals, orthonormal expansions of deterministic and random signals,
and the elements of detection theory conclude the introductory material.
2.
Digital Communication on the Gaussian Channel
An introduction to modulation and demodulation for the Gaussian channel
includes the concepts of coherent and noncoherent receivers. Performance
measures including bandwidth efficiency and probability of error are presented.
3. Digital Modulation Systems
Important
digital modulation systems are introduced. Properties of signal
modulation constellations are studied in order to determine their performance
and efficiency on noisy channels. Partially coherent receivers and other
design issues may be included. Both baseband and carrier modulated
representations are considered.
4.
Intersymbol Interference
High data rates often interact with narrow bandwidths
to introduce memory into the channel response, so that adjacent received
symbols are not independent of one another. This intersymbol interference
channel is modeled, and error probability bounds are derived. Optimum and
robust receivers are studied.
Text (required):
J.G. Proakis, Digital Communications,
4-th Edition, Prentice-Hall
Grading:
2 (closed book) mid-term exams @ 25% each.
1 (closed book) final
exam @ 40%.
Homework assignments and lab experiments
@ 10%.
Schedule:
Monday, Wednesday, Friday
11:00-11:50
Prerequisites:
Basic Communications (520.401) and Probability
(550.310 or 420)
NOTE: You should be able to "ace" this
probability self-test. If one or more of the
questions is difficult for you, see me before you commit to taking the course.
Some notes (PDF files):
Optimal Receivers for the Gaussian Channel
Coherent Receiver Performance, Memoryless Modulations, Gaussian Channel (NOTE: Rev. 1: 03/20/08)
Modulations with Memory (Posted 04/25/08)
Spectra of Signals (Posted 04/27/08)
Problem sets: Here!
Software-Defined Radio Lab Experiments
Discussions:
The Class Assistant will be named
here. Please take questions about homework to the
My office is 210
Barton Hall. I am available whenever my door is open; try MWF around
2:30. Also, I encourage you to contact me by e-mail to
arrange other meeting times.
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Note:
For an excellent overview of the impact of digital communications, I
recommend The World Is Flat: A Brief History of the Twenty-first Century
by Thomas L. Friedman, |