Minimum Secrecy Throughput Maximization in Wireless Powered Secure Communications

This paper investigates a wireless powered secure communication network (WPSCN), in which the legitimate users have no constant energy supply and need to be wireless powered for information transmitting. The harvest-then-transmit protocol is adopted in the WPSCN, i.e., the energy access point (EAP) first transfers energy to legitimate users through energy beamforming, and then, the legitimate users transmit their data to the information access point (IAP) by time-division multiple access. Since an eavesdropper intercepts users’ uplink information, the EAP creates artificial noise to cripple the interception capability of the eavesdropper. For providing a secrecy throughput balancing across different legitimate users, we aim to maximize the minimum secrecy throughput of all users via time allocation, energy beamforming, and artificial noise design. To this end, a low-complexity two-stage algorithm is proposed. In the first stage, without taking into account the eavesdropper's wiretapping, we design time allocation and energy beamforming by solving the problem of minimum throughput maximization, which is convex and can be easily solved. In the second stage, two easily implementable strategies are proposed for artificial noise design so as to strengthen the noise power at the eavesdropper and simultaneously reduce the noise power at the IAP. Simulation results show that the performance of the proposed approach is close to the upper bound and not sensitive to scenario settings, which confirms the effectiveness of the proposed method.