Optimal placement and number of energy transmitters in wireless sensor networks for RF energy transfer

Energy efficiency is one of the most critical design issues in wireless sensor networks (WSNs). Recently, RF energy transfer emerges as a promising solution to enhance energy efficiency. In RF energy transfer, energy is supplied to wireless networks through dedicated energy transmitters. WSNs can be equipped with the RF energy charging capabilities such that the WSNs are referred as wireless rechargeable sensor networks. This paper aims to 1) optimally place the energy transmitters and 2) determine optimal number of energy transmitters in WSNs with RF energy transfer. For optimal placement of energy transmitters, a trade-off between maximum energy charged in the network and fair distribution of energy is studied. We present a mechanism by defining a utility function to maximize both total energy charged and fairness. For optimal number of energy transmitters, an optimization problem is formulated and solved while satisfying the constraint on minimum energy charged by each sensor node. Simulation results illustrate the performance of WSNs with RF energy transfer in terms of average energy charged, fairness, and optimal number of energy transmitters.