Secure Transmission for Energy-Harvesting Sensor Networks With a Buffer-Aided Sink Node

This article investigates secure transmission in an energy harvesting (EH) sensor network in the presence of noncolluding passive eavesdroppers, where the EH sensors communicate with a controller via a buffer-aided relay (sink node). Each sensor has a battery to accumulate the energy harvested from the radio-frequency (RF) signals transmitted by the relay, and purely relies on the harvested energy to perform transmission. Besides, equipping a data buffer at the relay for security improvement, each time slot can be allocated dynamically to the first hop or the second hop, but it also introduce a packet delay. To enhance the security, an adaptive link selection with user scheduling and cooperative jamming (ALS-USaCJ) scheme is proposed. For evaluating the secrecy performance, the coupled evolution of the batteries and data buffer should be dealt with. Specifically, discretizing the energy status of the batteries, the couple evolution is modeled as a Markov chain so that its steady-state distribution can be obtained. On this basis, the analytical expressions of the communication outage probability (COP), secrecy outage probability (SOP), secrecy throughput (ST), and average packet delay (APD) are derived. Finally, theoretical analysis and simulation results demonstrate that equipping a data buffer at the relay can significantly improve the secrecy performance, and the larger the buffer size, the better the performance, but the greater the APD. Moreover, the link selection factor in the proposed scheme, which is related to specific network configuration, can be properly set to achieve the optimal secrecy performance.