UCLA Extension

Digital Communication: Part II–Optimizing System Performance

This course benefits engineers, programmers, IC designers, and engineering managers involved in the design, planning, implementation, or testing of advanced communication systems. Both young engineers and seasoned managers find this structured course beneficial.

Complete Details

Instruction begins with system specifications and participants learn to make reasonable design choices based on what is needed for meeting these specifications. The requirements drive us toward candidate systems. Instruction reviews the computational subtleties that enter into designing and evaluating digital systems, and emphasizes fading channels and how to mitigate the degrading effects of multipath. Specific examples illustrate how various mobile systems have been designed to withstand fading, such as OFDM in 802.11. Course participants also examine the astounding developments in both turbo codes and low-density parity-check (LDPC) codes, whose error-correcting properties allow us to approach the ultimate limitations predicted by Shannon.

In multiple input-multiple output (MIMO) systems and space-time coding (STC), time is complemented with the spatial dimension, which comes from using several spatially-distributed antennas. Explore both MIMO and STC as well as how a MIMO channel can provide improved robustness, capacity, or both without expending additional power or bandwidth.

This course is ideal for those wanting more advanced instruction in digital communication or as a follow-on to the basic course, Digital Communication: Part I—Fundamental Architecture.

Upon completing this course, participants should be able to:

  • Follow an orderly approach when defining, designing, or evaluating systems
  • Recognize when a system is bandwidth-limited, power-limited, or both, and learn to use advanced techniques to meet difficult requirements
  • Understand the subtleties involved in specifying or designing a system and be able to make design choices regarding modulation methods and error-correction coding
  • Learn how to verify that a particular code meets system requirements
  • Become aware of the trade-offs among power, bandwidth, and error performance that are possible, and—most importantly—learn to ask the right questions to determine if a communication system will meet its requirements in a cost-effective manner

Prerequisite

Successful completion of a basic course in digital communications, such as Digital Communication: Part I—Fundamental Architecture; familiarity with the fundamentals of digital signaling and channel coding; or consent of instructor.

Course Materials

Participants receive lecture notes on the first day of the course. These notes are for participants only and are not for sale or unauthorized distribution.

Coordinator and Lecturer

Bernard Sklar, PhD, President, Communications Engineering Services, Tarzana, California. Dr. Sklar was previously at The Aerospace Corporation and has acquired over 50 years of experience in the electronics industry in a wide variety of technical design and management positions. He has worked at Republic Aviation Corporation, Hughes Aircraft Company, and Litton Systems, and has taught communications at both the University of Southern California and UCLA. He is currently associated with the University of Cape Town, South Africa as an external examiner. He also has taught at other universities and has presented numerous short courses throughout the United States, Europe, and the Far East. Dr. Sklar has published and presented scores of technical papers, is the recipient of the 1984 Prize Paper Award from the IEEE Communications Society for his tutorial series on digital communications, and is the author of Digital Communications: Fundamentals and Applications, Second Edition (Prentice-Hall, 2001). He is a past chairman of the Los Angeles Council IEEE Education Committee.

Program

Defining, Designing, and Evaluating Systems
A systematic approach for meeting bandwidth- and error-performance requirements; criteria for choosing modulation and coding schemes for various channel types; given only the system requirements, how one selects appropriate signaling methods; subtle computations required and the step-by-step approach used for evaluating almost any digital communication system; and in-class training exercises.

Turbo Codes and the Map Algorithm
Concatenated codes and the fundamentals of turbo codes; extrinsic information; iterative decoding and near-Shannon-limit performance; the MAP algorithm, how it differs from the Viterbi algorithm and how it is implemented to yield bit-by-bit a-posteriori probabilities; and numerical examples of turbo decoding.

Fading Channels: Characteristics and Mitigation
Large- and small-scale fading, and their mechanisms; the most serious degradation effects of fading; signal dispersion, channel-induced intersymbol interference (ISI); the difference between frequency-selective fading and flat fading, and fast fading and slow fading; characterizing the channel as a time-varying filter; channel coherence bandwidth; time-variant structure of the channel due to motion; channel coherence time; Doppler spread; in a mutipath mobile channel, why signal dispersion is independent of fading rapidity; degradation effects: loss in SNR, irreducible bit-error-rate, ISI distortion, pulse mutilation, and Doppler spreading; how to design a system that can withstand fading; tools for coping, such as spread spectrum and orthogonal FDM (OFDM); different effects call for different mitigation types; and training exercises.

OFDM and SC-OFDM
Orthogonal frequency division multiplexing (OFDM) is a scheme that utilizes many closely-spaced orthogonal sub-carriers; data is partitioned into groups; each group is assigned a sub-carrier which is then modulated in a conventional way; the primary advantage of OFDM over a conventional single-carrier scheme is its ability to cope with severe channel multipath conditions, such as frequency-selective fading, without complex equalization filters; and SC-OFDM is a variant of OFDM which ameliorates the peak-to-average power ratio (PAPR) problem inherent in OFDM.

Low-Density Parity-Check Codes
Fundamentals of LDPC codes; Tanner graphs; bit nodes, check nodes, and the message-passing algorithm; iterative decoding and how these codes asymptotically approach the Shannon limit; comparison of LDPC and turbo; and use of training exercises to learn the basic concepts.

MIMO (Multiple Input-Multiple Output) Systems
The uniqueness of MIMO stems from space-time signal processing, whereby time is complemented with the spatial dimension obtained by using several spatially distributed antennas (at the transmitter and receiver). This session emphasizes the source of the real MIMO magic: spatial multiplexing and space-time coding. Instruction focuses on how MIMO systems operate when only the receiver has channel state information (CSI) and how further improvements can be realized when the transmitter has CSI as well. MIMO systems can be employed to improve BER or increase capacity (or both) without expending additional power or bandwidth. This is achieved by exploiting multipath.

For more information contact the Short Course Program Office:
shortcourses@uclaextension.edu | (310) 825-3344 | fax (310) 206-2815

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