Research On Transmission Strategy Of Digital Fountain Codes In Wireless Communicaton

Digital fountain codes(DFC)are a kind of rateless codes,they can realize adaptive transmission in different channel environments without channel prior information,and show good adaptability to complex and variable wireless channels.However,there are some problems in traditional encoding and decoding methods of DFC,such as high encoding redundancy and high probability of decoding failure,and how to extend DFC from deletion channel to wireless channel also needs further studied.Under the background of wireless communication,the encoding\decoding algorithm and transmission scheme of digital fountain codes are deeply studied in this paper,different application schemes of digital fountain codes and its performance are also further discussed and simulated.including:1)The basic theory of DFC and degree distribution functions are studied at first.Then LT code is simulated with different RSD parameters,and the performance of BP and GE decoding algorithms is simulated and comparative analyzed.2)For the problems that the LT uniform selection coding algorithm is inefficient,and the BP and GE algorithms are difficult to balance the complexity of algorithm and the decoding efficiency,an improved joint encoding and decoding algorithm is proposed.In which,source symbol selection probability is adjusted during the encoding process,and the instant decoding is performed on the basis of BP and GE joint decoding.Simulation reasults show that the improved algorithm performs better under different conditions.3)In order to realize reliable transmission with low encoding redundancy under different channel conditions,based on the research of existing DFC transmission schemes combined with feedback,analysing the undecoded source symbols and designing from two aspects: feedback information extraction and retransmission encoding,the DFC transmission scheme based on key information feedback is put forward.And it could realize successfully decoding with lower cost..4)Two application methods of DFC in wireless communication are studied: directly as channel coding and cascaded with channel coding,and respectively simulated and analyzed.DFC is similar to fixed rate coding when directly used as channel coding,the performance is not ideal under wireless channel.When LT code is concatenated with LDPC code,wireless channel can be equivalent to deleted channel by the encoding and decoding process of LDPC code,so that LT code can continue to play the advantage of rateless.On the basis of the improved encoding and decoding algorithm and the transmission scheme based on key information feedback,taking the number of source symbols and the length of source symbols as variables,performance of the cascading transmission scheme is simulsted and analysed from the perspectives of frame error rate,encoding redundancy and retransmission times.