Research Of LT Code And Its Unequal Error Protection Schemes

With the development of communication technology and Internet,the rapid growth of the data scale and more and more diverse business needs place a greater demand on the communication system's service ability.The digital fountain code is a new type of forward error correction method developed in recent years,which has the characteristics of simple encoding and decoding,no rate limit and no feedback information.In addition,digital fountain code has obtained the general attention of academic circle.In this thesis,it starts the relevant research based on Luby Transform(LT)code and mainly focuses on the distribution function in LT encoding process and the application in unequal error protection.This thesis gives the basic principles of digital fountain code in outline,which mainly involves the binary erasure channel model in experiment,encoding theory and two kinds of decoding algorithms – BP algorithm and GE algorithm.Simulate the performance of LT code with different code lengths and two decoding algorithms.The degree distribution function plays a key role in the LT encoding process.The thesis mainly studies several kinds of commonly used distribution fuctions and focused analyses the improved robust soliton distribution(iRSD).Based on the structural thought of the switch degree distribution,a novel distribution is proposed,which combines the divantages of the binary exponential distribution and the iRSD.The simulation shows that when the switching point ?=0.1,the novel switch degree distribution requires the least coded packets to decode successfully,effectively improves the decoding performance of LT code,and has advantages of encoding and decoding complexity and simulation time.In order to solve the problem of high complexity of encoding and decoding in the existing Expanding Window Fountain(EWF)coding scheme,to ensure the performance of the less important bits(LIB)at the same time,this thesis obtains an effective optimization scheme based on EWF code by the And-Or tree analysis.Simulation results show that the decoding performance of more important bits(MIB)and LIB in this scheme is improved to a certain extent.By combining the advantages of Weighted Unequal Error Protection(WUEP)code and EWF code,the thesis designs a new coding scheme of W-EWF code with feedback,since the feedback information in fountain code has a great influence on the encoding and decoding processes and the release probability of the undecoded packets.Simulation results demonstrate that the scheme can not only enhance the protection of MIB,but also ensure the decoding performance of LIB.