Optimization of Rateless Coded Systems for Wireless Mulitmedia Multicast
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Rateless codes, also known as fountain codes, are a class of erasure error-control codes that are particularly well suited for broadcast/multicast systems. Raptor codes, as a particularly successful implementation of digital fountain codes, have been used as the application layer forward error correction (FEC) codes in the third generation partnership program (3GPP) Multimedia Broadcast and Multicast Services (MBMS) standard. However, the application of rateless codes to wireless multimedia broadcast/multicast communications has yet to overcome two major challenges: first, wireless multimedia communications usually has stringent delay requirements. In addition, multimedia multicast has to overcome heterogeneity. To meet these challenges, we propose a rateless code design that takes the layered nature of source traffic as well as the varying quality of transmission channels into account. A convex optimization framework for the application of unequal error protection (UEP) rateless codes to synchronous and asynchronous multimedia multicast to heterogeneous users is proposed. A second thread of the thesis addresses the noisy, bursty and time- varying nature of wireless communication channels that challenge the assumption of erasure channels often used for the wired internet. In order to meet this challenge, the optimal combination of application-layer rateless code and physical layer FEC code rates in time-varying fading channels is investigated. The performance of rateless codes in hybrid error-erasure channels with memory is then studied, and a cross-layer decoding method is proposed to improve decoding performance and complexity.