Research On The Low-complexity Detection Of SCMA System

Considering future radio access in the 2020 s,the higher spectrum efficiency and massive device connectivity requirements pose new challenges for the 5th Generation of Mobile Communication System(5G),especially for 5G air interface technology.However,traditional multiple access technologies are restricted by the orthogonal resources and do not meet the massive connectivity needs in a 5G system.Compared with the orthogonal multiple access technology,the non-orthogonal multiple access technology could accommodate more users with the same time-frequency resources,and therefore it is more applicable to the massive network connection,and Sparse Code Multiple Access(SCMA)is one of most promising 5G multiple access scheme.Message passing algorithm(MPA)is used for decoding in SCMA system,however,as the number of modulation orders and interference users on the same resource block increases,the decoding complexity is too high to be achieved.Therefore,how to reduce the computational complexity has become an urgent issue.This thesis propose two low-complexity detection algorithms aiming to reduce the signal detection complexity for SCMA systems.The specific research topics are presented as follows:1.An MPA detection idea based upon setting appropriate stopping criteria is proposed to solve the problem of traditional MPA,which requires a fixed number of iterations.This idea makes the sparse factor graph is sparser by ending the decoding of users with good channel performance,which reduces the complexity of MPA.A dynamic grouping strategy is proposed to avoid decoding information missing,this grouping strategy make the convergence speed of MPA is faster than traditional serial grouped MPA due to no information missing during decoding.Finally,an improved MAX-LOG-MPA low-complexity detection scheme based upon above two improvements is proposed to reduce the high complexity of MPA.2.The decoding complexity is still relatively high as the number of modulation orders and interference users on the same resource block increases.Therefore,an improved MPA scheme based upon expectation propagation idea is proposed,this scheme makes the complexity of MPA detection tends to be linear with few performance loss by simplifying the calculation of the message from the user node to the resource node and the posterior probability in original Gauss approximation MPA algorithm,and makes MPA decoder easy to implement in hardware.3.A solution scheme of the SCMA system decoding is proposed finally This thesis combines the multiple-input multiple-output(MIMO)system and the SCMA system,and proposes a joint solution scheme for MIMO-SCMA decoding.The simulation results prove solution scheme is feasible and superior.