Energy-efficient resource and power allocation for uplink multi-user OFDM systems

In this paper, we consider the problem of energy-efficient resource and power allocation in the uplink of multiuser multi-channel Orthogonal Frequency Division Multiplexing (OFDM) based systems subject to constraints on user equipment (UE) transmit power. This problem is non-deterministic polynomial-time hard and an optimum solution for a system with U users and N resource units requires a complexity of at least O(NU^N). Using an iterative solution approach, we propose two sub-optimal, yet efficient, scheduling algorithms that maximize the energy efficiency (EE) considering both UE circuit power (P_c) and rate-dependent transmit power with an upper limit of P_max. Simulation results show that the proposed algorithms provide near-optimal solutions with much lower computational burden of O(UN) and O(UN²/2). Further performance studies indicate that the proposed algorithms can offer an EE of more than 2 times with a throughput reduction of less than 13% as compared to the spectral-efficient greedy algorithm. Our studies also reveal that the EE is quickly increased with P_max when ≪ P_c and then reach saturation as Pmax approaches P_c.