Research On Non-orthogonal Multiple Access Technique In 5G System

The fifth generation mobile communication(5G)is envisaged to meet the increasing demand of data traffic explosion and support massive connection with reduced latency.To cope with these anticipated challenges,non-orthogonal multiple access(NOMA)technique has been considered as one of the key technologies due to its high efficiency of spectrum.NOMA can exploit power degrees of freedom by allowing multiuser to share the resource block with the different transmit power level and adopting successive interference cancellation(SIC)receiver to achieve multiuser detection.However,on the one hand,as the signal interference noise ratio(SINR)is the only characteristic to distinguish users' data,the NOMA receiver heavily depends on the users paired together and corresponding power allocation scheme.Furthermore,beamforming can suppress interference and improve data rate,but the performance of NOMA beamforming is susceptible to the channel state information(CSI)estimation error and not robust enough.To deal with the problem that NOMA receiver relies heavily on the grouped user and the power allocation scheme,this thesis investigate the user grouping and power allocation algorithm for multicarrier NOMA(MC-NOMA)system.Specifically,in the MC-NOMA system,a weighted sum throughput maximization problems under the transmit power constraint is formulated.In view of combinatorial nature of the subcarrier allocation,this thesis tackles a non-linear programming problem in two steps.First,a dynamic user clustering scheme is derived.Through maximizing the gap of channel gain between grouped users in overall perspective,the proposed scheme can enhance the system throughput.In addition,the WMMSE algorithm is adopted to solve the intractable power allocation problem.Local optimal solution can be obtained with several low-complexity literates,and simulation results verify the convergence and effectiveness of the proposed algorithm.To tackle the influence of CSI estimation error on NOMA system robustness with beamforming design,this thesis studies the robust beamforming design for single carrier NOMA(SC-NOMA)system in multiple-input-single-output(MISO)channels.In particular,two types of CSI error are considered: quadratic bounded CSI error and quadratic unbounded CSI error.In the ellipsoidal bounded CSI error model,a rate maximization problem without outage events under the transmit power constraint is formulated.To solve this problem,this thesis decomposes it into a set of power minimization problems.Resorting to convex optimization theory,the proposed algorithm can achieve a quite good performance against channel uncertainties.For the unbounded CSI error,the thesis aim to minimize the transmit power while maintaining the user's quality of serves(Qo S)in terms of the outage probability.The outage probability constraint makes the original problem hard to solve.This thesis handles this intractable problem and attains robust beamforming vectors that can satisfy the outage probability requirement.Simulation results validate the effectiveness and superiority of the proposed algorithm.