Inter-Cluster Interference Minimization Based Nonlinear Precoder for MIMO-NOMA Systems

In order to improve the bit error rate (BER) performance of a MIMO-NOMA system with successive interference cancellation (SIC) detector at user terminals, a nonlinear precoding scheme to directly minimize the inter-cluster interference is proposed in this paper. It jointly optimizes the weighted coefficients in the equivalent channel information of each user cluster and the precoded results under a total transmission power constraint. Furthermore, a solution procedure based on the alternating direction method of multipliers (ADMM) algorithm is designed for the above optimization problem. In addition, a user clustering scheme is given to coordinate with the proposed precoder to get the better performance. Simulation results demonstrate that the system whole BER performance of the proposed scheme is improved obviously compared with other precoders, such as the traditional zero force (ZF) precoder and so on. Especially, the average BER of the users with stronger channel in each cluster is reduced by nearly three orders of magnitude at signal to noise ratio (SNR) of 25dB.