Energy-Efficient Transmission Schemes for Cooperative Wireless Powered Cellular Networks

Wireless powered cellular networks (WPCNs) are promising solution for the future wireless communication systems. This paper proposes a system model of WPCNs, in which the cellular users (CUs) and the device-to-device (D2D) users harvest energy from the hybrid access point (HAP). Some D2D users can help the cell-edge CU to relay its uplink/downlink transmission in exchange for the D2D communication opportunity. For achieving green WPCNs, we formulate two energy efficiency (EE) maximization problems for both uplink and downlink transmissions, respectively. The energy beamformer of the HAP and the time resource allocation are jointly optimized subject to the transmission rate requirements and the available energy constraints of CUs and D2D users. Based on the fractional programming theory and semi-definite relaxation (SDR) method, we transform the originally non-convex EE maximization problems into the equivalent convex problems. This allow us to develop the resource allocation algorithm toward global optimization. The optimal solution in semi-closed form is derived based on Lagrangian method. Extensive simulation results are provided to demonstrate the convergence of the proposed iterative algorithm and the EE gain of the proposed system over the other two baselines.