Optimization on power splitting ratio design for K-tier HCNs with opportunistic energy harvesting

Future small cells are expected to be energy-efficient and utilize green technologies. To this end, a promising solution is to employ automatic energy harvesting techniques, such as power splitting (PS) which harvests energy from ambient radio frequency (RF) signals in modern communication systems. In this paper, optimization on PS ratio design is investigated to maximize the average harvested energy in the context of general largescale K-tier heterogeneous cellular networks (HCNs). Specifically, coverage probabilities and average energy harvesting expressions are derived with the stochastic geometry treatment to elucidate the performance of future green networks. Then optimal fixed PS ratios for each tier are obtained under coverage performance constraints. Moreover, with receivers´ position information effortlessly provided in future networks, a dynamic location-based PS ratio design (DLPS) is proposed to further enhance the energy harvesting performance. Simulation results are given to demonstrate that the average harvested energy is effectively increased by more than 30% when coverage probability requirement is greater than 0.7 by our proposed DLPS compared with the optimal fixed PS ratio while maintaining the coverage performance. Furthermore, rather than drawing the conclusions about the merits of our PS strategy, this work is to provide a tractable analytical framework for addressing the energy harvesting issues in such HCNs.