Research On Sparse Code Multiple Access Low Complexity Detection Algorithms In Satellite-ground Link

Satellite communication systems have always faced series of problems such as mass access users,the spectrum resources available for satellite use and the limited processing capacity on the satellite.Therefore,efficient satellite-to-ground multiple access technology is needed to help satellites accommodate more users,and satellites can use spectrum more efficiently.Low-complexity multi-user detection algorithms can help satellite communications systems reduce overhead.Sparse code multiple access technology can accommodate more users than existing satellite-to-ground multiple access technology,and its low-complexity detection algorithm can also help satellites reduce system overhead.Therefore,this dissertation focuses on the application of sparse multiple access techniques to satellite links,and focuses on its low-complexity algorithms.First,this paper analyzes the research background of the subject and the significance of the research on access technology between the satellite and earth link,and discusses the development and future research direction of the satellite ground link access technology in the world integration.Then,the satellite-earth link access technology is analyzed,including access scenario,access priority,and business type common access protocol.Secondly,this paper discusses the model of sparse code multiple access technology,including the modulation model of the sparse code multiple access technology,the signal multiplexing of the sparse code multiple access access to the user,the representation of the index matrix and factor graph,the signal of the sparse code multiple access,the overview of the detection technology and the model of the uplink.Type.Because the codebook design of SCMA has a great influence on its system performance,this paper also summarizes the codebook design.Finally,the establishment of the satellite ground channel model is presented.The satellite earth channel model adopted in this paper is the single state model of the Lutz satellite to ground channel model.In order to give theoretical analysis,this paper gives the theoretical expression of the symbol error rate when SCMA adopts the maximum likelihood detection scheme.The Message Passing Algorithm(MPA)is a classic low complexity detection algorithm used in SCMA system.In this paper,the third chapter gives a detailed description of the Message Passing Algorithm.At the same time,three low complexity detection schemes based on the Message Passing Algorithm are studied in this paper,which are PartialMarginlized MPA(PM-MPA),the low complexity Message Passing Algorithm based on the sort(SB-MPA)and the beleif selection low complexity detection algorithm(BS-MPA),these three algorithms have different degrees of reduction in computational complexity compared with the traditional Message Passing Algorithm,but at the same time the BER degradation exits.Sphere Decoding(SD)has been widely used in multi antenna systems.Since 2017,some researchers have applied SD to SCMA system.In this paper,two kinds of spherical decoding schemes are studied,which are the spherical decoding scheme based on mapped matrix and the spherical decoding scheme based on codebook design,it can be seen that in the 6 user,the error rate of the spherical decoding scheme is agreed on the maximum likelihood algorithm and the computation is very low,but the complexity of the algorithm will rise sharply when the number of users becomes larger.