Spectrum And Energy Efficiency Maximization In Non-orthogonal Multiple Access System

Faced with requirements of 5G on more massive connection,higher capacity,lower latency and higher spectral efficiency,the Non-orthogonal multiple access(NOMA)is one of the most potential technologies to meet the needs.In order to improve the performance of NOMA system,this thesis mainly studied the improvement of throughput,beamforming and energy efficiency.For the problem of inter-cluster and intra-cluster interference in the single-cell NOMA system of FDD,this thesis solved it from three aspects including user clustering,precoding and power allocation.Firstly,an improved k-means clustering algorithm is proposed to mitigate the inter-cluster interference.So all users are divided into different clusters based on the spatial correlation.As result,the second-order statistics between different clusters become approximately orthogonal;Then the inter-cluster interference is eliminated by using block diagonalization precoding to preprocess the transmit information;Moreover,power allocation is optimized to mitigate intra-cluster interference by improving the performance of successive interference cancellation(SIC).And the optimal power allocation coefficient of every user is found by solving the optimization problem of achievable throughput.Numerical simulation shows that the proposed method can improve the system throughput.In the multi-cell massive MIMO-NOMA system,For the problem of serious interference and poor quality of service to cell-edge users.A multi-cell cooperative two stage beamforming scheme is proposed to mitigate inter-cell interference and inter-cluster interference in the same cell.And two optimization sub-problems are obtained by decomposing the original optimization problem with the proposed beamforming scheme,one is related to cell-layer beamforming matrix and another one is about cluster-layer beamforming matrix.The problems can solve by asymptotic analysis in random matrix theory and the convex optimization theory.Therefore,the beamforming matrix and power allocation were found at last.Numerical simulation shows that the final beamforming matrix effectively suppresses inter-cell interference and inter-cluster interference.Meanwhile,the optimization of inter-cluster power allocation effectively improves the energy efficiency of the system.