Secrecy outage in a two-hop decode and forward relay network with accumulated harvested energy

Abstract

In this paper, physical layer security is investigated under the accumulation of harvested energy in a particular frame of communication by a selected relay in an eavesdropper attacking network. The energy is accumulated at the multiple decode and forward (DF) relays by the energy harvester over several frames. The communication occurs between the source and the destination in two-phases using half-duplex mode. The first phase is a broadcasting phase in which the source broadcasts the information signal to the relays where a selected relay decodes the message and the second phase is relaying phase in which the selected relay encodes the message and forwards the signal to the destination. In the relaying phase, the selected relay also transmits a jamming signal along with the information signal to jam the eavesdropper. The forwarded signal of the selected relay is also received by the passive eavesdropper who tries to eavesdrop the message. Each relay is helped by two omnidirectional antennas, while the source, destination and the EAV use a single omnidirectional antenna. The relay selection is based on the maximizing secrecy capacity. The selected relay uses the received signal from one antenna to harvest the energy, while it uses the received signal from another antenna to decode the message. The harvested energy by a relay over a single frame may not be sufficient for successful forwarding of information which requires accumulation of harvesting energy over multiple frames. We have analyzed the physical layer secrecy in terms of several metrics such as secrecy outage probability (SOP), ergodic secrecy capacity, probability of strictly positive secrecy capacity and the secrecy throughput under a scenario where accumulated harvested energy is used in a particular frame. The impact of source transmit power, number of relays, number of frames used for harvesting energy and target secrecy rate is investigated on secrecy outage probability, ergodic secrecy rate, probability of strictly positive secrecy capacity and secrecy throughput. The MATLAB based simulation results verify the analytical results. We observe that the performance in terms of the SOP improved by 98.29% for three relays with respect to a single relay at 20dBm source’s transmit power.