UCLA Extension

Advanced Digital Communications Systems

This course provides state-of-the-art wireless technology in an organized way while focusing on digital signaling, modulation-waveform selection, error-correction coding, multiple-access, spread-spectrum, and bandwidth efficiency.  Students will learn how to make reasonable engineering choices based on a system’s specifications, and whether the system is bandwidth-limited, power-limited, or both. Students will examine multipath channels and learn how to mitigate against their degrading effects. The course will explore OFDM including OFDM’s special variant, called single-carrier OFDM (SC-OFDM). Examples of multiple-input, multiple-output (MIMO) systems, multi-user MIMO (MU-MIMO), and space-time coding (STC) are shown.  The course will also cover the astounding developments in both turbo and low-density parity-check (LDPC) codes whose properties allow us to approach the performance limitations predicted by Shannon.

Program Overview

  • To recognize if a system is bandwidth-limited, power-limited, or both.
  • To practice the subtle computations involved in defining, designing or evaluating digital systems.
  • To learn advanced techniques for meeting difficult requirements.
  • To learn how to make trade-offs amongst power, bandwidth, and error performance.
  • To learn how to characterize fading and how to mitigate its degrading effects.
  • To learn about efficient signaling and signal-processing techniques, such as: turbo codes, LDPC codes, OFDM, and MIMO.

Prerequisites

Each attendee should have completed a basic course in digital communications, or should be familiar with the fundamentals of digital signaling and coding.

Skills to be gained: After course completion, students should be able to follow an orderly approach when defining, designing, or evaluating systems. They will recognize when a system is bandwidth-limited, power-limited, or both. They’ll learn how to use advanced techniques for difficult requirements. They’ll understand the subtleties involved in specifying or designing a system, and will be able to make modulation and error-correction-coding design choices. They will become aware of possible tradeoffs amongst power, bandwidth, and error performance, and most important, they’ll learn to ask the right questions for determining if a system will meet its requirements in a cost-effective way.

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 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.

Course Topics

1. 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 does one select appropriate signaling methods? The subtle computations required, and the step-by-step approach used for evaluating most any digital communication system. Software examples; in-class training exercises.

2. How I Learned To Love the Trellis
Finite state machines, partial response signaling; how the Viterbi algorithm can uniquely operate as an equalizer/detector or a decoder; likelihood functions; bit-by-bit detection versus sequence estimation; detecting and decoding signals with memory; hard versus soft decisions, add-compare-select (ACS) architecture; similarities between convolutional decoding and equalization; applying the Viterbi equalizer in GSM.

3. 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; numerical examples of turbo decoding.

4. Fading Channels: Characteristics and Mitigation
Large-scale and small-scale fading and their mechanisms. What are the most serious degradation effects? Signal dispersion, channel-induced intersymbol interference (ISI). What is the difference between frequency-selective fading and flat fading? Fast fading and slow fading? Channels can be characterized as time-varying filters. Coherence bandwidth; coherence time; Doppler spread. In a fading channel, why is signal dispersion independent of fading rapidity? Degradation effects: loss in SNR, irreducible bit-error-rate, ISI distortion, pulse mutilation, Doppler spreading. How to design systems that can withstand fading degradations. Tools for coping: spread spectrum, OFDM, MIMO.

5. 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 is its ability to cope with severe channel multipath conditions, such as frequency-selective fading, without having to use complex equalization filters. SC-OFDM is an important variant of OFDM which ameliorates the peak-to-average power ratio (PAPR) problem inherent in OFDM.

6. 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). We focus on the source of the really magical part of MIMO spatial multiplexing and space-time coding. We see how MIMO systems work when only the receiver has channel state information (CSI), and then, 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. We show how this is achieved by effectively exploiting the multipath fading. We examine the possible tradeoffs between capacity and robustness.

7. Low-Density Parity-Check (Ldpc) 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. Training exercises and software examples are used to learn the basic concepts, and to compare LDPC with turbo codes.

8. CDMA and Cellular Telephony
FM versus TDMA versus CDMA versus OFDM. Interference suppression in CDMA; cellular structure; forward channels (pilot, synch, paging, traffic); open- and closed-loop power control; reverse channels (access, traffic); spreading codes, orthogonalizing codes; using the Rake receiver to exploit the effects of multipath.

9. Next Generation Wireless Technology
We examine the use of OFDM and MIMO in current and future systems, LTE, LTE-Advanced, WiFi, WiMAX, and fifth-generation (5G) wireless systems. We particularly focus on 5G, and the disruptive but innovative plans for using Massive MIMO and mm-Wave radio access. We outline the unique benefits as well as the challenges.

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

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