Wireless Power Transfer in Two-Way AF Relaying Networks

Abstract

In this paper, we study a wireless-powered communication network (WPCN) scenario, in which a multiple antenna amplify-and-forward (AF) two-way relay coordinates power transfer and information exchange to multiple pairs of users. A harvest-then- transmit protocol is assumed where the relay first transmits energy signals to the users in a power transfer phase. Multi-pair of users, which have rechargeable batteries, then use the harvested energy to exchange their independent signals through the relay in two phases, up-link (UL) and down-link (DL). In the UL phase, the users transmit their information signals to the relay and in the DL phase the relay amplifies and forwards the signals to the intended destinations. Furthermore, in order to cancel out the interference, zero-forcing reception and transmission (ZFR/ZFT) is implemented at the relay. In order to characterize the system performance, we consider ergodic spectral and energy efficiencies for two cases, based on the availability of the channel state information (CSI) at the relay during the power transfer, 1) unknown CSI 2) partially known CSI. In light of this, we derive new analytical expressions for the ergodic spectral and energy efficiencies for the two cases and Monte Carlo simulations are provided throughout our investigations to validate the mathematical analysis. The impacts of some system parameters such as EH time, EH efficiency, number of relay antennas and user-pairs, on the system performance are investigated.