Power transfer in multi-pair two-way AF relaying networks with zero-forcing

Abstract

In this paper, we consider a wireless-powered communication networks (WPCNs), in which a multi-antenna two-way amplify-and-forward (AF) relay transfers power to multipair of single antenna users. A harvest-then-transmit protocol is adopted here, where the relay first broadcasts energy signals to all users during a power transfer phase. Multiple pairs of users, then use the harvested energy to exchange information signals through the relay over two phases, up-link (UL) and down-link (DL) phases. In the former phase, all the users simultaneously transmit their information signals to the relay, then in the latter phase the relay amplifies and forwards the received signals to their intended users. In addition, in order to mitigate the interference, zero-forcing reception and transmission is applied at the relay. In light of this, analytical expressions for the ergodic spectral and energy efficiencies are derived and Monte Carlo simulations are provided throughout to validate our analysis. The impacts of some important system parameters such as energy harvesting (EH) time, number of user-pairs and relay antennas, on the system performance are investigated. The results show that, good selection of the EH time is the key to achieve optimal system performance and increasing the number of relay antennas can reduce this factor.