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Digital fountain codes a novel deletion coding , which can generate unlimited output symbols , and flexible rate control . In implementation, it uses a one-way asynchronous transfer mechanism is an efficient , low - latency performance characteristics , and time variability of the channel has a high degree of adaptability . In addition , due to its lower encoding and decoding complexity , it is very easy to implement . Due to its many advantages , digital fountain codes have a very wide range of application scenarios , it also gradually into the practical field . So far, many technology patents available ; same time , some international organizations will also be incorporated into the relevant standards , including 3GPP, DVB, IETF , and its prospects are very impressive . In this paper , we introduce a course of development of the digital fountain codes , and detailed instructions for several typical implementations of LT codes , Raptor codes . Collation and induction , we summarize the current issues and the status quo of the field . For the LT encoding the repeat association problem , we theoretically do a detailed analysis and discussion , revealing generate invalid encoding symbols and deduce the probability of occurrence of an invalid symbol . Further , we design several possible improvement program , to prevent duplication associated random association limit . Scene for distributed applications , Raptor codes with the discussion , combined with the characteristics of the scene with the encoding and decoding analysis to clarify the degree a symbol of the importance of , and the particularity of Parity in distributed scenarios . Further , we propose a degree a symbol of improved vision and design specific encoding optimization algorithm .
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