In this thesis, we investigate the optimization of Raptor codes for various channels of interest in practical wireless systems. First, we present an analytical asymptotic analy- sis of jointly decoded Raptor codes over a BIAWGN channel. Based on the analysis, we derive an optimization method for the design of efficient output degree distributions. We show that even though Raptor codes are not universal on other channels than the BEC, Raptor code optimized for a given channel capacity also perform well on a wide range of channel capacities when joint decoding is considered. Then, we propose a rate splitting strategy that is efficient for the design of finite length Raptor codes. We next investigate the extension of the analysis to the uncorrelated Rayleigh-fading chan- nel with perfect channel state information (CSI) at the receiver, and optimize Raptor codes for quasi-static fading channels when CSI is available at the receiver but not at the transmitter. Finally, we show that in presence of imperfect CSI at the receiver, it is possible to improve the performance with no additional complexity, by using an appropriate metric for the computation of the LLR at the output of the channel. In the second part of this thesis, we investigate the construction of efficient finite length LDPC codes. In particular, we present some improvements for the Progressive Edge- Growth algorithm that allow to construct minimal graphs. The proposed algorithm is used to construct protographs with large girth that perform well under iterative decoding. Moreover, we propose an efficient structured search procedure for the design of quasi-cyclic LDPC codes.
| Identifer | oai:union.ndltd.org:CCSD/oai:tel.archives-ouvertes.fr:tel-00764650 |
| Date | 01 November 2008 |
| Creators | Venkiah, Auguste |
| Publisher | Université de Cergy Pontoise |
| Source Sets | CCSD theses-EN-ligne, France |
| Language | English |
| Detected Language | English |
| Type | PhD thesis |
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