A Relevant Energy-Efficient Metric in OFDM for Opportunistic Users

In this paper, we consider an Orthogonal-Frequency Division Multiplexing (OFDM) system composed of the opportunistic secondary users (SUs) and the primary users (PUs. We analyze an energy-efficient (EE) power allocation problem for opportunistic user under feasibility constraints. When the SU is allowed to transmit with an OFDM technique, these constraints guarantee: a minimum SU’s Quality of Service (QoS) level, a maximum average transmit power and the protection of the PUs by maximum average interference levels at the PUs receivers. In this paper, we study a relevant EE metric which is the weighted difference between overall achievable rate and power consumption. It is difficult to solve this EE power allocation problem via optimization tools since the opposing character of the constraints. Thus, we propose a novel method based on a flowchart algorithm. We have shown that our proposed power allocation solution outperforms the classical water-filling solution and the sub-optimal one. We have shown also, that Quadrature Amplitude Modulation (MQAM) modulation can guarantee a lowest Bit error Rate (BER) for the SU transmission performance.