Research On Digital Fountain Codes And Its Application On Wide Area Diversity Network

Digital fountain code is a new kind of forward error coding scheme. It has become a research hotspots in the communication field because of its excellent decoding performance, efficient decoding algorisms and the rateless property which can adapt the channel conditions. The research on digital fountain codes include many fields such as the optimization of encoding and decoding algorisms, new code construction and its application in many environment. Digital fountain code has enriched the channel coding technology in both theoretical research and practical application. It has high research value and bright prospect.Firstly the basic conception and principle of digital fountain code are introduced. Meantime the channel model of binary erase channel is also introduced. The encoding and decoding algorisms of two classical digital fountain LT codes and Raptor codes are presented. The technical advantages of fountain and its typical implement environments are introduced briefly.The decoding algorithm of digital fountain codes in binary erase channel is the BP algorithm. The degree distribution is the key point to the decoding performance when the BP algorism is used. So based on the ripple size, the principle of degree distribution design is introduced. The parameters in the RSD is analyzed to find the way to balance the decoding complexity and decoding overhead. Then in order to decrease the decoding overhead, a feedback scheme is proposed to the fountain codes. The simulation results show that the proposed algorithm can effectively decrease the overhead.Next, a special kind of fountain codes is researched, which is named UEP fountain codes. This thesis researched two UEP algorithms with fountain codes, the UEP algorithm of virtual increase of source block size and the UEP algorithm of degree distribution improvement. And-Or tree analysis is a useful density evolution technique to investigate the recovery probability of input symbols. This thesis expands the applications of the And-Or tree analysis so that it can be used to the situation in which the encoded symbols are segmented. Then the UEP LT codes are constructed with And-Or tree, some simulation results are given.Finally, a receive diversity scheme based on fountain codes which can be used in wide area diversity network is researched. The system models in the SISO system and SIMO system are proposed. The application of UEP fountain codes in this SIMO system is investigated.