Research On Sparse Code Multiple Access Technology

The rapid development of the mobile Internet and the Internet of Things puts forward higher requirements for the multiple access technology of the next generation mobile communication.In order to meet the requirements of the massive connection of mobile communication in the future,a new non-orthogonal multiple access method must be proposed.As a new non-orthogonal multiple access method,sparse code multiple access(SCMA)has the advantage of satisfying the massive connection compared with the traditional orthogonal multiple access method.Compared with other non-orthogonal multiple access methods,SCMA can obtain better coding gain.Therefore,this paper mainly studies the related technologies of SCMA.The design of SCMA codebook and the design of receiver decoding algorithm are two key technologies of SCMA system.Therefore,this paper firstly analyzes the design principles of the current traditional SCMA codebook in detail.Because the quality of the codebook will directly affect the complexity of decoding and the bit error rate(BER)of system,this paper proposes an improved codebook design method based on star QAM from the perspective of improving the mother constellation diagram and making the energy of codebook different between users.In order to meet different requirements for different users in the same scene in future mobile communication,this paper also researches the design principle of irregular SCMA codebook,and then proposes a new irregular codebook design principle based on trellis coded modulation(TCM)subset segmentation theory in order to maximize the minimum Euclidean distance between the constellation points.Simulations show that the proposed codebook has better system performance.Subsequently,this paper researches the traditional multi-user detection algorithm-Message Passing Algorithm(MPA)for SCMA.Although the performance of MPA is close to the maximum likelihood decoding,its complexity is still very high.Therefore,in order to reduce the number of iterations of the algorithm and reduce the number of constellation points searched,this paper proposes a less complex SCMA detection algorithm based on partial marginalized serial strategy.The simulation shows that the complexity of the SCMA decoding algorithm is significantly reduced under the condition that the performance of the system is not reduced.Finally,the paper researches the downlink MIMO-SCMA link system.At present,there are few researches on the MIMO-SCMA system,and the complexity of the current downlink MIMO-SCMA link system detection algorithm increases exponentially with the increase of the number of antennas and the number of users,so this paper makes full use of the characteristic of MIMO channel and the sparsity of SCMA codeword,and then uses the idea of assigning different codewords to different antennas under the same user,and then proposes a downlink MIMO-SCMA detection algorithm based on joint factor graph.The simulation shows that the performance of the algorithm is almost the same as that of the maximum likelihood algorithm,but its complexity is significantly reduced.