Energy-Efficient Joint Power and Bandwidth Allocation for NOMA Systems

In this letter, we consider a downlink non-orthogonal multiple access (NOMA) system where a base station (BS) simultaneously communicates with multiple users. These users are grouped on multiple unequal-bandwidth sub-channels. The power and bandwidth allocation are jointly optimized in order to maximize the system energy efficiency (EE) under transmit power constraint at the BS and minimum rate constraints for individual users. The optimization problem is nonconvex because of the fractional objective function and the nonconvex constraints. To deal with the original problem, it is first converted into an equivalent DC (difference of two convex functions) program by introducing slack variables, and then an iterative algorithm based on the constrained concave-convex procedure is proposed to solve it. Our numerical results demonstrate that the proposed algorithm has better EE performance compared to the NOMA scheme with equal-bandwidth allocation and conventional orthogonal multiple access scheme.