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Reliable Communications under Limited Knowledge of the Channel Open Access


Other title
ldpc codes
llr approximation
channel estimation errors
timing error
channel mismatch
irregular decoders
low-density parity-check codes
channel estimation
channel codes
insertion/deletion channels
piecewise linear approximation
concatenated coding
watermark codes
error-correcting codes
Type of item
Degree grantor
University of Alberta
Author or creator
Yazdani, Raman
Supervisor and department
Ardakani, Masoud (Electrical and Computer Engineering)
Examining committee member and department
Schuurmans, Dale (Computing Science)
Duman, Tolga (Electrical and Computer Engineering, Arizona State University)
Jing, Yindi (Electrical and Computer Engineering)
Tellambura, Chintha (Electrical and Computer Engineering)
Department of Electrical and Computer Engineering
Date accepted
Graduation date
Doctor of Philosophy
Degree level
For successful correction of errors in a digital communication system, information about the channel, such as timing, noise power, fading gain, etc., should normally be available at the receiver. To this end, most receivers use channel parameter estimation and timing recovery modules. However, these modules are costly in terms of overhead, occupied chip area, power dissipation, and are usually imperfect. Thus, the need for high-speed communication systems motivates finding other solutions. In this thesis, we seek efficient coding solutions for reliable communication under limited channel and timing information. We address the problem by considering three important scenarios: First, we consider Gaussian channels with unknown noise power at the receiver. By using low-density parity-check (LDPC) codes, we propose a robust decoding method which provides better performance compared to the existing methods. Second, we consider decoding on wireless fading channels where the fading gain and/or noise power are unknown at the receiver. Most modern error-correcting codes require soft metrics, usually log-likelihood ratios (LLRs), to be calculated at the receiver. This calculation is cumbersome on fading channels especially when the fading gain is unknown. Thus, we first propose an LLR accuracy measure, propose an efficient approximate LLR calculation technique, and then show that the performance under approximate LLRs is extremely close to that of exact LLRs. Third, we seek practical coding for channels with imperfect timing at the receiver. In vast majority of the coding schemes invented, perfect synchronization is assumed between the transmitter and receiver. In most communication systems, however, achieving perfect synchronization is not possible. This leads to random symbol insertions and deletions in the received signal and poses a great challenge for error correction since conventional error-correcting codes fail at these situations. In this thesis, we propose a practical coding strategy which allows recovering insertions, deletions, and substitution errors without sacrificing the transmission resources.
Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.
Citation for previous publication
R. Yazdani and M. Ardakani, “Robust LDPC decoding using irregular decoders,” IEEE Commun. Lett., vol. 12, no. 12, pp. 888–890, Dec. 2008.R. Yazdani and M. Ardakani, “Linear LLR approximation for iterative decoding on wireless channels,” IEEE Trans. Commun., vol. 57, no. 11, pp. 3278–3287, Nov. 2009.R. Yazdani and M. Ardakani, "Efficient LLR calculation for non-binary modulations over fading channels,” IEEE Trans. Commun., vol. 59, no. 5, May 2011.R. Yazdani and M. Ardakani, "Piecewise linear LLR approximation for non-binary modulations over Gaussian channels with unknown noise variance,” in Proc. 2010 IEEE Int. Conf. on Telecommun. (ICT), Doha, Qatar, Apr. 2010, pp. 1–7.R. Yazdani and M. Ardakani, “Reliable communication over non-binary insertion/deletion channels,” IEEE Trans. Commun., Jul. 2012, accepted for publication.

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