Research And Implementation Of SCMA Decoder

Mobile communication gradually become an indispensable tool for social development with the rapid development of 30 years.In the face of traffic demand of the emerging mobile communication,the fifth generation mobile communication system arises at the historic moment.In the vision of a new era of internet of thing,at the same time the fifth generation mobile communication system is still faced with new challenges and development.Multiple accessing technology is one of the core technologies of the physical layer in wireless communication.The traditional orthogonal multiple access technology can not meet the requirements of large capacity and mass access in 5G.The sparse multiple access code(SCMA)is designed to meet the 5G demand.SCMA uses sparse codebook to achieve overloading,which effectively improves the spectrum utilization.And we can design a good multi-dimensional constellation and SCMA codebook to improve system performance.We use the message passing algorithm(MPA)to decode,and bettering the MPA decoding algorithm can also reduce the complexity of the multi-user detection algorithm.In this paper,firstly the architecture and principle of SCMA are studied,and the system model and coding principle of SCMA are introduced.We focus on three SCMA codebook design methods,including the codebook design based on QAM,the codebook design based on star-QAM and the codebook design based on constellation rotation and interleaving,then we have performance simulation and comparison for different generated codebooks under the same condition.Next we study the SCMA decoding algorithm.Because the traditional message detection algorithm involves a large number of nonlinear exponential operations,we propose a low-complexity Max-Log-MPA decoding algorithm.The Max-Log-MPA decoding algorithm only have about 0.5d B performance loss based on 1 / 2Turbo rate.A new joint iterative multiuser decoding algorithm is proposed based on the MPA and turbo algorithm,and the performance simulation is completed.Finally,based on the theory of this paper,the system verification and hardware implementation of SCMA decoding is completed on the FPGA based on Max-Log-MPA detection.The results of hardware test are consistent with the results of software performance simulation.And under the 240 MHz clock frequency,the throughput of the decoding module can reach 720 Mbps.