Sparse Code Multiple Access And The Applicaton In MIMO System

With the rapid development of the wireless communication technology,the traditional orthogonal multiple access technology has been unable to meet the needs of the multi-user access.Non-orthogonal multiple access technology,as an alternative multiple access scheme for the 5G standard,has attracted much attention,because multiple users' data can be overloaded on the same time-frequency resources.Sparse Code Multiple Access(SCMA)is one of the non-orthogonal multiple access technologies.In SCMA,at the transmitter,the binary data is directly encoded to multi-dimensional codewords selected from a predefined codebook set,and the codewords from different layers are multiplexed over the same resources.At the receiver,the users' data is detected jointly due to sparsity of the codewords.And then the corresponding binary data is demodulated by the channel decoding.Compared with orthogonal multiple access,SCMA can greatly improve the system spectral efficiency by using the same time-frequency resources.Firstly,the basic encoding principles and some key technologies of SCMA are introduced in this dissertation,including SCMA encoding and multiplexing,multi-dimensional codebook design and classical detection algorithms at receiver.And then the performance of two classical detection algorithms are compared by simulation.Generally,based on the above research the uplink system capacity are analyzed.And aiming at the problem of codebook and power allocation for improving the system capacity,a codebook allocation scheme based on channel state information is analyzed.But the interference between users is not considered in this scheme.So in this dissertation,a codebook allocation and power allocation scheme based on capacity maximization is presented,taking into account the interference between users.And then this scheme is compared with several classical schemes by simulation.The result show that the new scheme can further improve the system capacity.Finally,for the downlink multiuser MIMO system,the combination of SCMA and multiuser MIMO systems are studied in this dissertation.Based on the Non-Orthogonal Multiple Access(NOMA)clustering model,the SCMA clustering system model and system capacity are given.And in order to reduce the inter-cluster interference and improve the system capacity,two inter-cluster precoding methods and a user clustering scheme based on channel correlation are introduced.However,this clustering scheme is only applicable to users with high channel correlation,and only applies to two-user clusters.In addition,a clustering scheme applied to both the correlated channel and the non-correlated channel is proposed.This scheme not only reduces the complexity of clustering,but also applies to the clusters with more than two users.