Optimization And Simulation Of Low Complexity Decoding Algorithm For SCMA Uplink

This paper mainly studies the sparse code multiple access technology and multi-user detection algorithm.SCMA combines multidimensional modulation with sparse spread spectrum for codebook design.The user information is mapped directly by the encoder into the corresponding codeword in the predefined codebook.The SCMA multiuser detection algorithm detects user information based on the sparseness principle of the codebook.The message passing algorithm is a multi-user detection algorithm based on the factor graph,and approaches the performance of the maximum a posteriori probability detection algorithm,but its complexity is still high,Therefore,this paper studies the multiuser detection algorithm of SCMA system,including the following four parts:First of all,this article mainly expounds the basic principle and key technology of SCMA,and analyzes the SCMA system model.This article illustrates the key technologies in SCMA: codebook design.In addition,this paper analyzes the overload factor of SCMA.the study shows that the overload factor is not only related to the number of subcarriers and non-zero dimensions,but also affect the performance of the system.Secondly,this paper studies the multi-user detection algorithm and proposes a MPA detection algorithm based on dynamic factor graph,which reduces the detection complexity and processing delay at the expense of less performance.Based on the research of serial message update mode,a mixed MPA algorithm is proposed.The algorithm improves the convergence of message delivery and utilizes the advantages of parallel computing to improve its BER performance and reduce the complexity of the algorithm.Then,SCMA multi-user detection algorithm can be combined with multi-antenna technology.Using multiple antennas at the SCMA receiver will increase the detection performance of the MPA at the expense of increased complexity.This paper proposes a MPA detection algorithm based on QR decomposition.Using QR decomposition to change the iterative process of MPA factor graph design,the detection performance close to the original MPA detection algorithm is realized.Finally,the paper mainly summarizes the research algorithms and puts forward the shortcomings of this study,and analyzes the next research direction.