Low-complexity User Scheduling and Power Allocation for Downlink Multicarrier NOMA with Imperfect CSI

Due to its superior spectral efficiency, non-orthogonal multiple access (NOMA) is a promising candidate for future radio access. Most existing studies on NOMA are based on the assumption of perfect channel state information (CSI), which is difficult to achieve in practice. Instead, considering NOMA with imperfect CSI, we model the channel estimation error as a complex Gaussian random variable with a changeable variance affected by the signal-to-noise ratio (SNR) of the received signal. In this paper, we first derive an empirical formula between the variance and the SNR of the received signal via fitting. Then we formulate a sum-rate maximization problem based on the formula. Finally, we propose a low-complexity user scheduling scheme and an adaptive power allocation scheme tomaximize the sum-rate. Simulation results are presented to indicate that the proposed schemes provide better performance than the conventional orthogonal multiple access (OMA) scheme.