RF Energy Harvesting by D2D Nodes Within a Stochastic Field of Base Stations via Mobility Diversity

Abstract

Device-to-device (D2D) where users communicate directly with each other with limited base station involvement can significantly improve spectral efficiency, energy efficiency, and throughput in future cellular networks. Moreover, RF (radio frequency) energy harvesting (EH) promises to prolong the battery life and improve energy efficiency of D2D communication. Mobility diversity refers to the gains accrued via user mobility. Is it possible to exploit the mobility of D2D terminals via user movements to enhance their ability to harvest RF energy? To this end, we analyze the performance of a mobile D2D device powered by EH from the transmissions of underlying cellular base stations (BSs), whose locations are modeled as a homogeneous Poisson point process. We model the movements of D2D nodes via a modified random waypoint model. Log-distance path loss is considered, and it is assumed that EH takes place solely within harvesting zones surrounding each BS and that each D2D user requires a fixed number of charging time slots before being able to transmit. We derive the probability of a D2D device being within an EH region surrounding BSs after multiple transitions, and the probability of being within the the fully charged state using a Markov-chain approach taking into account temporal effects. It is shown that the number of transitions required to be within a harvesting region increases significantly when the harvesting threshold power increases.