Transmitter Selection for Secrecy in Frequency-Selective Fading With Multiple Eavesdroppers and Wireless Backhaul Links

This article investigates the secrecy performance of sub-optimal transmitter selection and optimal selection schemes in a system comprising multiple transmitters, multiple eavesdroppers, and a single destination in frequency-selective fading channels with single-carrier cyclic-prefixed modulation. Considering unreliable backhaul links between the access point and the transmitters, we analyze secrecy performance in two scenarios: when backhaul activity knowledge is available (KA) and when backhaul activity knowledge is unavailable (KU). Closed-form expressions for the secrecy outage probability (SOP) and the ergodic secrecy rate (ESR) are derived. Our analytical results show that in the backhaul KA scenario, the asymptotic limit of the SOP and the slope of the ESR are affected only by the number of transmitters and the backhaul reliability factor, and not by other system parameters. In contrast, only the backhaul reliability factor affects these two performances in the backhaul KU scenario. These performances are independent of the number of eavesdroppers in both backhaul KA and KU scenarios. Our findings demonstrate that acquiring knowledge of the activity of backhaul links yields better secrecy performance as compared to acquiring knowledge of the channel state information of the eavesdroppers. We also show that the secrecy diversity order of both selection schemes under perfectly reliable (wired) backhaul links is identical.