Performance Tradeoff between User Fairness and Energy Conservation in Downlink NOMA Systems

Non-orthogonal multiple access (NOMA) has been recognized as an efficient means to boost the spectral utilization and increase the number of connections for the next generation mobile communications systems. User fairness is a crucial performance metric in the design of downlink NOMA systems, but its optimum is reaped at the cost of excessive power consumption. In this paper, we study the performance tradeoff between user fairness and energy conservation by means of power allocation, and we formulate the problem as a bi-objective optimization. To obtain the complete Pareto optimal solutions, we transfer the above bi-objective optimization into a single-objective one using the weighted Tchebycheff method and solve the resulting non-convex optimization with the generalized Benders decomposition. In addition, we investigate several important properties of the proposed mechanism, including the convergence, computational complexity, and applicability to the case with imperfect successive interference cancellation. Based on the Monte Carlo simulations, we validate the necessity of conducting the tradeoff optimization and the efficiency of the proposed mechanism.