NOMA-based Power Control Optimization with Constraint of Outage Probability in Cloud Radio Access Network

Cloud radio access network (C-RAN) promises high spectral efficiency and energy efficiency due to its flexible architecture. However, the densely distributed C-RAN still meets some challenges: 1) the limited fronthaul capacity restricts further improvement of network capacity; 2) the nonideal channel state information (CSI) caused by the incomplete network feedback or transmission errors would lead to the degradation of transmission quality. With regard to the above bottlenecks, we study the power-domain non-orthogonal multiple access (PD-NOMA) scheme and apply a channel estimation method to characterize the impact caused by imperfect CSI. In this paper, the optimal power allocation of transmission beams and the beamforming scheme in the downlink are designed by solving the minimum energy consumption problem with outage probability constraint. In order to reduce the computational complexity, we decompose the original problem into two subproblems and propose a two-stage iterative optimization algorithm by applying minimum mean square error (MMSE) method and Langarian dual optimization method. Finally, simulation results verify the control effect of the proposed algorithm.