Proportional Fair Secrecy Beamforming for MISO Heterogeneous Cellular Networks With Wireless Information and Power Transfer

Simultaneous wireless information and power transfer (SWIPT) is a promising technique to address the energy scarcity problem in heterogeneous cellular networks (HCNs). Since information security is a critical issue in the SWIPT HCNs, we consider the secrecy beamforming design for a multiple-input single-output HCN with one macrocell base station (BS) and multiple femtocell BSs. In the considered system, all BSs send confidential messages to information receivers and energy signals to energy receivers (ERs). The ERs have the potential to wiretap the confidential messages. Consequently, by taking fairness into account, we propose a sum logarithmic secrecy rates maximization beamforming design problem under the energy harvesting constraints for ERs. The formulated design problem is nontrivial to solve due to the nonconvexity in the objective and the constraints. To tackle the design problem, a semidefinite relaxation and successive convex approximation-based centralized beamforming design algorithm is proposed. Our analysis reveals that using single-stream beamforming to transmit confidential messages does not cause any loss of optimality. Moreover, an alternating direction method of multipliers-based distributed beamforming design is also proposed. Simulation results demonstrate the effectiveness of the proposed algorithms.