Exploiting Opportunistic Scheduling in Uplink Wiretap Networks

Opportunistic scheduling schemes are investigated for uplink wiretap channels with multiple asymmetrically located legitimate users (LUs) and eavesdroppers. To exploit multiuser diversity, the cumulative distribution function-based scheduling method is leveraged to schedule the transmissions of the LUs. Under this scheduling framework, the closed-form expressions of the secrecy outage probability and ergodic secrecy rate are derived, illustrating the interplay among the system parameters, such as the channel statistics and the number of LUs and eavesdroppers. Through the secrecy outage analysis of the proposed scheduling schemes, we observe that the secrecy throughput is not always maximized with a larger channel access ratio (CAR), and consequently, we design a CAR adjustment scheme to maximize the secrecy throughput while satisfying the required secrecy level. We also prove that under our proposed scheduling schemes, the secrecy diversity order of each LU is equal to the reciprocal of the LU's CAR, implying that full diversity order is achieved, and the ergodic secrecy rate of each LU normalized by its CAR achieves the optimal double-logarithmic growth when the number of LUs increases to infinity.