Research On Sparse Code Division Multiple Access Systems In 5G

The fifth-generation mobile communication technology has promoted economic and social development.What's more,its low data transmission delay and high data transmission speed has brought unlimited possibilities for human future production and life.Traditional wireless communication is based on orthogonal multiple access.For example,in the Orthogonal Frequency Division Multiplexing(OFDM)system,different users occupy different resource blocks for communication.Although it has good anti-channel fading capabilities and anti-inter-carrier interference capabilities,low spectrum resource utilization is far from meeting the needs of massive user access.Therefore,Non-Orthogonal Multiple Access(NOMA)technology,which supports the superimposed transmission of several user data on the same resource block,was proposed by related scholars and was quickly determined as the core access technology of 5G.In this paper,we propose a simple codebook design method for the NOMA system,and optimize the time complexity performance of the message passing algorithm at the receiver.The main research contents and work done in this paper are as follows:(1)In the uplink of Sparse Code Division Multiple Access(SCMA)system,we propose a SCMA codebook design scheme based on alternating Gray coding in the QAM modulation constellation diagram.In the SCMA codebook design scheme based on alternating Gray coding,the number of concentric circles is determined according to the maximum modulation order M of the system,and the coding order is determined according to the number of times the user appears.In addition,for establishing the constellation diagram model of the codebook,we conduct a simulation study on the radius ratio of the inner and outer rings and the rotation angle parameters between the resource blocks.Simulation results show that under reasonable inner and outer ring radius ratios and resource block rotation angle parameters,the SCMA codebook design scheme based on alternating Gray coding proposed in this paper has better bit error rate performance than the several existing ones introduced in Chapter 3.(2)Aiming at the original message passing algorithm(MPA)at the receiving end of the SCMA system,a simplified message passing algorithm,namely the selective message passing algorithm,is proposed in this paper.The idea of the proposed algorithm is that when the receiving end iterates to the specified number of iterations,the resource node selectively updates the user node,so it can effectively reduce the time complexity of the original message passing algorithm.Experimental simulation shows that,as it optimizes the iterative steps of the original message passing algorithm,the selective message passing algorithm proposed in this paper can effectively reduce the time complexity of the sparse code division multiple access system.