Effective Secrecy Throughput Maximization for WPT Enabled IoT in the FBL Regime

The inherent broadcast nature of wireless communication makes data transmissions vulnerable to eavesdropping, creating a critical need to balance communication reliability with security. This balance is especially important for applications where secure and dependable data transfer is essential. In this work, we consider a wireless power transfer (WPT) activated Internet of Things (IoT) including a passive legitimate sensor Alice, power transmitter and packet receiver Bob, as well as an eavesdropper Eve. To effectively balance the trade-off between communication reliability between legitimate users and security against eavesdropping, we characterize the effective secrecy throughput (EST) based on the concept of leakage-failure probability (LFP), and formulate a EST maximization problem by jointly optimizing the blocklengths of the energy harvesting (EH) phase and the wireless information transfer (WIT) phase. Nevertheless, the formulated problem is nonconvex and highly coupled in its variables. To address this issue, we first reformulate the original problem via successive convex approximation (SCA) and subsequently decompose it into two subproblems. An effective suboptimal solution is finally obtained via the alternating optimization (AO) algorithm. Numerical results demonstrate the efficiency and optimality of our design, as well as the performance advantage in achieving high effective secrecy throughput.