| The traditional channel coding technology mainly has the problems of fixed code rate and the need to obtain a priori information of the channel.Therefore,adopting a coding method with adaptive code rate and high coding reliability is a feasible method to improve the transmission performance of information in the wireless channel.The digital fountain code with no code rate is an error correction code with good coding and decoding performance.The transmitter does not need to obtain channel information and does not set a fixed code rate during encoding.Instead,it continuously generates encoding packets and sends them.Until the decoding completion information fed back by the receiving end is received.Therefore,the digital fountain code can encode any code rate according to the change of the channel state under the condition of unknown channel prior information,and has good channel adaptability.In view of the shortcomings of existing channel coding,how to better apply digital fountain codes to wireless channels is worthy of in-depth study.The thesis optimizes the performance of digital fountain codes from three aspects: digital fountain code coding algorithm,digital fountain code cascade transmission scheme and feedback transmission scheme.The main research contents of the paper are as follows:1.In-depth study of the equivalent erasure channel system model to improve the coding and decoding algorithm of the digital fountain code under the erasure channel.Aiming at the problems such as short loop and incomplete coverage of source information caused by the uniform selection of digital fountain codes,this paper improves the degree distribution function and selection method,and proposes a non-uniform selection encoding algorithm.Aiming at the problem that the two decoding algorithms of digital fountain code cannot take into account the complexity and decoding efficiency,the joint decoding algorithm combining the advantages of the two is studied,and the performance of the improved joint coding and decoding algorithm is verified.2.Study the digital fountain code transmission scheme under the wireless channel.The thesis deeply studies the scheme of direct application of digital fountain codes to wireless channels,introduces an improved digital fountain code encoding algorithm on the basis of existing direct application schemes,and performs performance simulation on the improved direct application of digital fountain codes.Simulation results show that the performance of the improved direct application scheme is improved compared with the existing direct application scheme,but it is still worse than the channel coding scheme.In response to this problem,the paper deeply studies the digital fountain code cascade transmission scheme,introduces an improved digital fountain code joint coding and decoding algorithm on the basis of the existing cascade scheme,and improves the digital fountain code cascade scheme from the internal and external code long code rate Combination,channel coding and channel environment selection,complexity and other aspects are simulated and demonstrated.3.Introduce an appropriate amount of feedback based on the improved digital fountain code cascading scheme,and study the digital fountain code feedback transmission scheme.Aiming at the problems of high coding redundancy and insufficient reliability in the existing digital fountain code feedback mechanism,a feedback mechanism based on stop set screening is proposed.From the aspects of decoding overhead and feedback overhead,the performance simulation of the digital fountain code cascading scheme combined with the stop set filtering feedback mechanism is performed.Simulation results show that the introduction of this feedback mechanism can enable cascaded codes to reduce coding redundancy,increase transmission reliability,and achieve adaptive code rate transmission on wireless channels while paying a low feedback cost. |
