Joint Design of Power Control and SIC Decoding Order for Max-Min Fairness optimization in Uplink NOMA Systems

Non-orthogonal multiple access (NOMA) is an effective technique to improve spectral efficiency and connectivity level of multi-user systems by means of successive interference cancellation (SIC) decoding. However, the optimization of NOMA scheme for uplink systems has not been well addressed in the literature. This work tackles the joint design of the users' transmit power levels and the SIC decoding order at the BS for a multi-user uplink system. Since it is difficult to find the optimal solution, an iterative algorithm is proposed that alternately optimizes transmit powers and SIC decoding order until convergence is reached. The optimization of transmit powers is addressed by adopting the majorization minimization (MM) approach. The SIC decoding order is designed by evaluating per-user mean squared error (MSE) at each SIC decoding step. Numerical results are presented to identify the configurations in which the proposed design achieves relevant gains.