Title page for ETD etd-05102000-13390004


Type of Document Master's Thesis
Author Khan, Anwer Ali
Author's Email Address nonukhan@vt.edu
URN etd-05102000-13390004
Title Iterative Decoding and Channel Estimation over Hidden Markov Fading Channels
Degree Master of Science
Department Electrical and Computer Engineering
Advisory Committee
Advisor Name Title
Ebel, William J. Committee Chair
Bostian, Charles W. Committee Member
Gray, Festus Gail Committee Member
Tranter, William H. Committee Member
Keywords
  • Trellis Decoding
  • Hidden Markov Models
  • Iterative Decoding
  • Channel Estimation
  • Turbo Codes
  • Baum-Welch Algorithm
  • Fading Chanels
Date of Defense 2000-05-03
Availability unrestricted
Abstract

Since the 1950s, hidden Markov models (HMMS) have seen widespread use in electrical engineering. Foremost has been their use in speech processing, pattern recognition, artificial intelligence, queuing theory, and communications theory. However, recent years have witnessed a renaissance in the application of HMMs to the analysis and simulation of digital communication systems. Typical applications have included signal estimation, frequency tracking, equalization, burst error characterization, and transmit power control. Of special significance to this thesis, however, has been the use of HMMs to model fading channels typical of wireless communications. This variegated use of HMMs is fueled by their ability to model time-varying systems with memory, their ability to yield closed form solutions to otherwise intractable analytic problems, and their ability to help facilitate simple hardware and/or software based implementations of simulation test-beds.

The aim of this thesis is to employ and exploit hidden Markov fading models within an iterative (turbo) decoding framework. Of particular importance is the problem of channel estimation, which is vital for realizing the large coding gains inherent in turbo coded schemes. This thesis shows that a Markov fading channel (MFC) can be conceptualized as a trellis, and that the transmission of a sequence over a MFC can be viewed as a trellis encoding process much like convolutional encoding. The thesis demonstrates that either maximum likelihood sequence estimation (MLSE) algorithms or maximum a posteriori (MAP) algorithms operating over the trellis defined by the MFC can be used for channel estimation. Furthermore, the thesis illustrates sequential and decision-directed techniques for using the aforementioned trellis based channel estimators en masse with an iterative decoder.

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