PHY security improvement of a threshold-based multiuser selection scheme using co-operative jamming

Abstract

This thesis investigates the secrecy performance of a transmit antenna selection with threshold-based selection diversity (TAS/tSD) using co-operative jamming and with the existence of passive eavesdroppers. Two practical scenarios are investigated in an effort to quantify the secrecy performance of the considered system, i.e. scenario I, the channel state information (CSI) of the eavesdroppers at the base station (BS) is unavailable whereas for scenario II, CSI is available at the BS. The legitimate transmission suffers from the presence of collaborating (Col) and non collaborating (Non-Col) passive eavesdroppers. While the source transmits it's message signal to its destination, a single multi-antenna jammer transmits jamming signals to create interference at the eavesdropper. For scenario I, closed-form expressions for the secrecy outage probability (SOP) for both Col and Non-Col passive eavesdroppers are derived. Additionally, at the high signal-to-noise ratio (SNR) values, closed-form expressions for asymptomatic secrecy outage probability (ASOP) are derived. For scenario II, the worst eavesdropping case is considered, ie. Col eavesdroppers and closed-form expressions for the ergodic secrecy rate are derived. Numerical results are obtained to justify the theoretical analysis. It is observed that increasing either the threshold SNR or the number of jammer antennas improves the secrecy performance of the system. This is because with the increase in the threshold SNR, the system has more opportunities to adopt to TAS/SC scheme at the expense of higher complexity and the increase in the number of jammer antennas, the eavesdroppers suffer from high values if interference.