Energy Harvesting for Physical-Layer Security in OFDMA Networks

In this paper, we study the simultaneous wireless information and power transfer in downlink multiuser orthogonal frequency-division multiple access systems, where each user applies power splitting to coordinate the energy harvesting and secrecy information decoding processes. Assuming equal power allocation across subcarriers, we formulate an optimization problem to maximize the aggregate harvested power of all users while satisfying secrecy rate requirements of individual users by joint subcarrier allocation and power splitting ratio selection. Due to the NP-hardness of the problem, we propose two suboptimal algorithms to solve the problem. The first one is an iterative algorithm that optimizes subcarrier allocation and power splitting ratios by an alternating way in dual domain. The second algorithm is based on a two-step approach that allocates subcarriers and selects power splitting ratios sequentially. The numerical results show that the proposed methods outperform the conventional methods and provide good trade offs between performance and complexity.