Performance Study of Wireless Powered Sensor Networks In wireless powered sensor networks (WPSNs), wireless sensor nodes can harvest energy from ambient environment or receive energy from energy transmitters for operation. However, the energy chargingharvesting rate at wireless sensor nodes is usually unstable because of the timevarying characteristics of wireless channels. When wireless sensor nodes have data to be sent but no energy is available, the throughput and delay performance may be degraded. To find some key issues of WPSNs, this work investigates the performance of WPSNs under different parameter settings by simulations. The impact of wireless charging rate and battery capacity which is rarely considered in the literature on the delay of data packets and energy shortage probability at a wireless sensor node is studied. Simulation results show that a larger battery capacity or wireless charging rate achieves much better performance of WPSNs.

Optimal Charger Placement for Wireless Power Transfer Abstract   As a promising technology to achieve perpetual operation of batterypowered wireless sensor devices, wireless power transfer has attracted much attention recently. In wireless power transfer, the charger enables the energy to be wirelessly transmitted to the rechargeable sensor devices that are hungry for energy. Previous works mainly focus on maximizing the charging utility or minimizing the charging delay. This paper concerns two more practical issues of placing wireless chargers, the first one aims at minimizing the deployment cost of chargers while satisfying the overall requirement for charging levels, and the second one aims at maximizing the total charging levels subject to a deployment cost budget constraint. We investigate the above two optimal charger placement problems under two typical scenarios in which omni chargers and directional chargers are used, respectively. To resolve these two problems under the two charging models, we first prove their NPhardness and then propose four approximation algorithms with proven performance guarantees. Finally, we conduct extensive simulation experiments to validate our designs, and the experimental results demonstrate that the proposed algorithms significantly outperform the baselines.