Energy-Efficient Simultaneous Information and Power Transfer in OFDM-Based CRNs

In this paper, we consider the simultaneous information and power transfer (SIPT) in cognitive radio networks (CRNs) where the secondary receiver (SR) can harvest energy from both the primary transmitter (PT) and the secondary transmitter (ST). The SIPT-enabled SR turns the harmful interference from the PT into energy and uses it to prolong battery life. We assume that the ST and SR adopt orthogonal frequency division multiplexing (OFDM) modulation and our goal is to find the optimal power allocation and power splitting ratio that maximize the energy efficiency of the secondary system. To settle this non-convex problem, we utilize the fractional programming to transform the objective function into the counterpart subtractive form and then take advantage of an approximation to turn the problem convex. After that, the equivalent convex problem is solved by an efficient iterative algorithm. Numerical results illustrate that the proposed method performs well and achieves a good tradeoff between energy efficiency and capacity of the secondary system, especially in high signal interference-plus-noise-ratio (SINR) regions.