The Research And Applications Based On Digital Fountain Codes

Digital fountain codes (DFC) are a new class of erasure codes. They can yield limitless encoding symbols and have flexible rate-control. In implementation, DFC adopts a simplex mechanism of asynchronous transfer, which possesses high-efficiency and low-delay, and adapts the time-variant of channel easily. In addition, because of its low complexity of coding, DFC is easy to realize.Due to the aforementioned advantages, DFC can be applied in wide scenarios, and it enters into practical field gradually. So far, many patents are proposed, and DFC is accepted by some international standards, such as 3GPP, DVB, IETF, etc. Therefore, DFC is very promising in the future.In this paper, the history of DFC is referred, and we introduce some typical schemes in detail, including LT codes and Raptor codes. By some inductions, the related problems and the current researches are concluded.For the problem of duplicate associates in practical LT encoding, we conduct some detailed analyses and discussions theoretically. The reason why invalid encoding symbols are produced is revealed, and the probability that invalid encoding symbols appear is inferred. Moreover, we propose some improved algorithms which can eliminate duplicate associates effectively by the restriction of random associations.For distributed applications, the scheme of Raptor codes based is realized and discussed. By combining the characteristics of the scenario and coding, we conduct some analyses. And the importance of degree-one symbols (DOS) and the specificity of parity in distributed scenario are illustrated. Furthermore, we propose an assumption of DOS, and design an optimized encoding algorithm.