Power Allocation Optimization For Uplink MIMO-NOMA System

With the increase of service types and smart terminals,limited spectrum resources are becoming increasingly scarce.As people's expectations,future communication systems are to provide higher transmission rates,more user access numbers,and better spectrum efficiency.Non-orthogonal multiple access technology(NOMA)has emerged,which allows multiple users to access the system simultaneously while sharing frequency resources.It can better increase system capacity and spectral efficiency.Multiple-input multiple-output(MIMO)technology can make full use of space resources and greatly increase the channel capacity without additional spectrum resources and antenna transmit power.Therefore,the combination of NOMA and MIMO technology is very helpful to enhance the system performance.Although NOMA technology provides an effective solution to the current scarcity of spectrum resources,how to mitigate the error propagation and improve the BER performance still needs more in-depth research.In this paper,an uplink MIMO-NOMA system model is established,and related issues such as power allocation optimization of uplink MIMO-NOMA system are studied.The main achievements and innovations are summarized in two aspects.First of all,a joint pilot and load power allocation optimization scheme is designed to alleviate the error propagation in the uplink MIMO-NOMA system.Multi-user detection is performed with maximum ratio combining and successive interference cancellation(MRC-SIC)in the base station.Taking into account of the channel estimation error,the average signal-to-noise ratio(ASINR)of each user in the MRC-SIC decoding process is analyzed.The minimum weighted ASINR maximization problem is formulated.It is a non-convex optimization problem,which can be solved by geometric programming algorithm after some equivalent transformation.Simulation results prove that the scheme can effectively reduce the error propagation of MRC-SIC and improve the detection performance.Secondly,a joint transceiver design scheme based on decision feedback equalization is proposed to mitigate user interference within the group.The receiver uses serial interference cancellation(SIC)method based on the minimum mean square error(MMSE)criterion to detect user signals.The problem of minimizing the mean square error of the detection signals is formulated and converted into the problem of maximizing the mutual information of the system.The QRS decomposition method is used to get optimal precoding matrix.In this uplink MIMO-NOMA system,the effect of the joint design of user precoding and base station detector is verified by MATLAB simulations.The results show that the proposed method can effectively improve BER performance.