Research And Optimization Of Multi-user Detection Algorithm For SCMA System

The three major scenarios of 5G put forward higher service function requirements for mobile communication technology.Multiple access technology is closely related to system capacity and access capability.In addition,the effective use of channel coding technology can ensure reliable transmission of information.The sparse code multiple access technology can improve the spectral efficiency and provide coding gain for the system,but the high complexity of its multi-user detector at the receiving end does not meet the needs of 5G low-latency scenarios.Polar code has excellent performance and is practical,which can reach Shannon channel capacity.How to combine polar code with a multi-user detector to provide a higher data rate under the premise of ensuring system error performance is also worth studying.Therefore,the research directions and main research contents selected in this paper are as follows:1.The basic structure of SCMA system and the key technologies that affect the performance of SCMA system are studied.An optimized codebook design scheme is described in detail as the basis for research and optimization of multi-user receiver.2.A multi-user detection algorithm VFG-MPA which is based on dynamic variable factor graph is proposed to solve the problem of high complexity of multi-user detectors using MPA algorithm.First,the edge residual values which related to the message reliability is calculated after each iteration to obtain the node reliability that determines the priority of VNs in subsequent update.Then,based on the residual value of each user node,it is determined whether the node has reached the convergence of detection and decoding.Convergent nodes and related edges are deleted from the subsequent factor graphs and do not participate in the subsequent iterative detection process.This algorithm accelerates the convergence speed of the overall detector,and reduces the redundant iteration and the computational complexity of the detector.3.A joint iterative detection and decoding receiver scheme based on a serial structure for transmitting verified messages(VJDD)is proposed as an optimized application scheme of a polar code decoder at the receiving end of a sparse code multiple access system.VJDD improves the iterative convergence speed of the receiver by transmitting verified messages to each node in the factor graph in time.At the same time,the soft information update algorithm of the polar code decoder is simplified,and the VFG-MPA detector scheme is applied to the proposed VJDD receiver.The VJDD scheme makes maximum use of the internal information of the polar code decoder,which can reduce the computation complexity of the receiver on the premise of ensuring the superior performance of the receiver.