Sum-Throughput Maximization in Dual-Hop Wireless Powered DF-Based Relay Networks

In this paper, we consider a dual-hop wireless powered communication network (WPCN) consisting of a hybrid access point (H-AP), multiple users, and multiple energy-constrained relays. While relay-assisted WPCNs have been investigated to mitigate the doubly near-problem in conventional WPCNs, they still suffer from this problem depending on the relay location. To address the issue, we modify the conventional harvest-then-transmit protocol to combine wireless power transfer (WPT) in the downlink and simultaneous wireless information and power transfer (SWIPT) with power splitting (PS) in the uplink. Specifically, we formulate an achievable sum-throughput maximization problem, and provide analytical solutions to optimal time allocation and power splitting coefficients. As a special case when the transmission time of the first hop is identical to that of the second hop in the uplink, we provide a more compact iterative algorithm with closed-form solutions. Simulation results show that the proposed algorithms achieve higher performance gain than the conventional scheme of optimizing either time allocation or power splitting coefficients, and reveal that the doubly near-far problem can be alleviated even when relay(s) is located far from the H-AP.