Theoretical Research On Multi-user MIMO Based On SCMA Codebook

Sparse code multiple access(SCMA)is a novel non-orthogonal multiplexing technique based on codebook.The non-orthogonal property of SCMA enables overloading of users in the system,increasing user capacity and spectrum efficiency.The sparsity of SCMA allows reception with low complexity.As a result,SCMA is a promising candidate for multiple access scheme.Multiple Input Multiple Output(MIMO)technology can make full use of space freedom to improve system performance.Combining SCMA and MIMO technologies can further improve the reliability and effectiveness of the system.This thesis mainly studies the implementation scheme and performance analysis of MIMO system based on SCMA codebook.Firstly,this thesis analyzes the SCMA downlink system model and signal structure,presents the design scheme of SCMA codebook based on constellation rotation and then carry out theoretical analysis of its capacity.Then this thesis deduces the diversity characteristics of SCMA signals and proposes message passing algorithm(MPA)based on maximum ratio combining.In addition,according to the proposed model,the theoretical upper and lower bound of bit error rate of SCMA codebook under Additive Gaussian White Noise(AWGN)channel and Rayleigh flat fading channel are derived.Then,this thesis proposes an Antenna Resource SCMA(AR-SCMA)system,which can significantly increase the capacity of the system under ideal conditions.In order to achieve low complexity detection,joint zero forcing(ZF)-MPA and minimum mean square error(MMSE)-MPA detection are introduced for AR-SCMA systems.Simulation results show that the bit error rate performance and the capacity performance of the proposed antenna resource SCMA scheme are improved,compared with the conventional systems.Furthermore,this thesis studies the model,detection algorithm and performance of multi-antenna systems based on time resource SCMA(TR-SCMA)in time-varying fading channels.Among them,the repetition coding and Alamouti coding schemes introduce new diversity gains for the system and improve the reliability;while the VBLAST scheme increases the freedom of the system and improves the effectiveness of the system.Interleaving the SCMA signal in time-varying channel can make full use of its diversity characteristics,thus further improving the anti-fading ability of the system.Finally,the Orthogonal Frequency Division Multiplexing(OFDM)-SCMA,i.e.OFDM-SCMA system,is proposed for frequency-selective fading channels and combined with MIMO techniques.This scheme can further enhance the effectiveness and reliability of the system.