Secrecy Analysis of Energy-Harvesting Backscatter Communication Networks with Multiple Eavesdroppers and Different Tag Selection Schemes

Addressing the vulnerability of multiple eavesdroppers, the challenge of energy harvesting by tags, and the secure transmission requirements in backscatter communication (BackCom) networks, this article investigates the secrecy performance of a passive BackCom network comprising a source, a destination, and multiple tags in the presence of multiple eavesdroppers. We propose four tag selection schemes namely optimal tag selection (OTS), suboptimal tag selection (STS), minimal eavesdropping tag selection (MTS), and random tag selection (RTS) to exploit diversity in delivering information securely from the source to the destination. The OTS scheme relies on complete channel state information (CSI), whereas STS and MTS utilize partial CSI, reducing their complexity compared to the OTS. The RTS scheme employs arbitrary random tag selection without relying on any CSI, serving as a baseline for performance comparison. The secrecy outage probability (SOP) and the ergodic secrecy rate (ESR) are employed as metrics to evaluate the secrecy performance of the system. We present generalized and unified approaches to derive closed-form expressions for SOP and ESR. Additionally, asymptotic closed-form expressions for SOP and ESR are derived for all tag selection schemes, providing valuable insights into the system's performance with respect to different parameters. Numerical simulation results reveal that, in general, the OTS scheme achieves superior secrecy performance compared to the other selection schemes. However, for a relatively small number of tags, the STS scheme performs comparably to the OTS, making it a cost-effective alternative. It is noteworthy that, for the same level of complexity, the MTS exhibits poor performance when compared to STS and OTS. This makes STS a suitable choice over OTS and MTS, offering an effective balance between the complexity and performance. We further demonstrate the effect of the number of tags, the number of eavesdroppers, and path loss parameters on SOP and ESR performances for the BackCom network under consideration.