Non-orthogonal Multiple Access Technologies For 5G Mobile Communication Systems

With the rapid development of mobile communication and intelligent terminals,the demand for data rate will show explosive growth in the near future.Some new multiple access schemes have been actively investigated since traditional multiple access technologies will be unable to meet requirements of networks in next generation cellular systems.Power domain non-orthogonal multiple access(NOMA)is one of the new multiple access schemes where users are multiplexed in the power domain.Power domain NOMA has its own advantages especially for its easy principle to realize.In addition,NOMA combined with multiple input multiple output(MIMO)can greatly improve system spectral efficiency.In this thesis,the power domain NOMA technology is studied.Firstly,the system model of power domain NOMA is introduced and the comparison of capacity between power domain NOMA and orthogonal multiple access(OMA)is discussed.Then the basic principles and key features of pattern division multiple access(PDMA),multi-user shared Access(MUSA)and sparse code multiple access(SCMA)are presented,as well as their receivers.In order to remove the multiple access interference,successive interference cancellation(SIC)receiver is utilized by NOMA,MUSA and PDMA.Due to the sparsity of SCMA codewords,message passing algorithm(MPA)based receiver can be used to recover signals.Secondly,user pairing schemes and power allocation algorithms for power domain NOMA in downlink are studied.The system model of downlink power domain NOMA is firstly introduced and the principle of SIC detection is depicted in details.Then the impact of user pairing on the performance of system capacity is proved and two sort-based user pairing schemes are proposed to improve detection performance and system capacity.After user pairing,a power allocation method is proposed to maximize the system capacity and another power allocation scheme based on fairness is proposed.Simulation results show that the proposed two sort based user pairing schemes greatly outperform the user pairing scheme in existing work both in error probability and spectral efficiency.Besides,the power allocation scheme which aims to achieve maximal system capacity,can improve the system spectral efficiency but reduce the detection performance.The power allocation scheme based on fairness can ensure the fairness between users at the cost of spectral efficiency.Finally,a multiple user grouping scheme and a power scheduling algorithm for uplink NOMA are pro-posed.A new multiple user grouping scheme is given when the number of users in each cluster is more than two.The principle of the multiple user grouping scheme is to increase the gap of channel gains of users in the same cluster.After multiple user grouping,a power scheduling algorithm based on Karush-Kuhn-Tucker(KKT)criterion is proposed,which aims to derive the closed-form solution of optimal power allocation.The concavity of the objective function is proved and the closed-form solution of optimal power allocation is achieved using KKT criterion.