Energy-Efficient Power Allocation for Hybrid Multiple Access Systems

In this paper, energy-efficient power allocation (PA) is studied for a hybrid system with non-orthogonal multiple access (NOMA) integrated into orthogonal multiple access (OMA). The considered energy efficiency (EE) maximization problem belongs to non-convex fractional functions. To tackle it, the corresponding spectral efficiency maximization problem for a given transmit power is first considered. By changing the variables from power coefficients to user rates, the non-convex problem is transformed into a convex one, for which a closed-form solution is obtained. On this basis, the optimal transmit power is determined to maximize the EE of the system by exploiting the property of pseudo-concave functions. Numerical results are presented to validate the effectiveness of the proposed energy-efficient PA strategy, as well as the superiority of the hybrid MA over OMA in terms of EE.