Research On Key Techniques Of Non-orthognal Multiple Access SCMA System

The 5G wireless network increases 1000 times the channel capacity to 1000 times,supports the data transmission rate of the individual user up to 10Gb/s,and accompanies by extremely low delay and response time.The new wireless multiple access technology is the key technology to 5G,and sparse code multiple access technology(SCMA)is one of the wireless multiple access technologies.Sparse code multiple access can be considered as the generalization of low-density signature(LDS)multiple access technology.It is a non-orthogonal sparse spread spectrum technology based on milti-dimensional codebook.It is the sparse property that allows us to use the message passing algorithm(MPA)to reduce the computation complexity and obtain a detection performance that is close to the ML algorithm.Simulation shows that the MPA demodulation algorithm can achieve the best detection probability for the cycle-free factor graph SCMA.This paper systematically describes the SCMA codebook design method.Because the SCMA system is a complex system,there are a variety of design methods proposed.This article describes main principles for SCMA codebook design,meanwhile,performing AWGN channel and rayleigh single-path fading channel simulation.Mainly includes Taherzadeh codebook design method,this article is called T-SCMA,Haonan's constellation diagram design method is called star-QAM SCMA,Haonan's another SCMA codebook design method is called Top-down SCMA,Jinchen Bao's two The SCMA coding design method is called MI-SCMA and sphere-code SCMA.This paper proposes a SCMA codebook design method based on multi-dimensional rotated constellation.This method can obtain high detection probability under high SNR conditions.This paper studies the demodulation algorithms of the SCMA receiver,including the original MPA algorithm,the LOG-MPA algorithm and the MAX-LOG-MPA algorithms which were proposed to reduce the number of exponent operations;the LSD-MPA algorithm which were proposed to reduce the search area of MPA algorithm.This paper deduces theoretically the demodulation algorithm mentioned above,simulates the bit error rate in the AWGN channel and Rayleigh fading channel as well,finally simulates and analyzes the convergence characteristics.Based on the LOG-MPA algorithm,this paper proposes an Max-Re-LOGMPA to improve the numerical instability of LOG-MPA under high signal-to-noise ratio(SNR).Simulation proves the numerical stability of the LOG-MPA algorithm can be improved,and the method also improves the BER performance of the MAX-LOG-MPA.Finally,this paper proposes an application scenario for SCMA,namely,UAV(unmanned aerial vehicle)cooperative communication system.Based on the IEEE 802.11 a protocol,the system is designed to adapt to the communication system under UAV.At the same time,the system model is built based on the simulink platform.Ultimately,BER performance in the UAV communication system is simulated.