This paper presents a secrecy performance study of a wiretap communication system with finite blocklength (FBL) transmissions over Rayleigh fading channels, based on the definition of an average information leakage (AIL) metric. We evaluate the exact and closed-form approximate AIL performance, assuming that only statistical channel state information (CSI) of the eavesdropping link is available. Then, we reveal an inherent statistical relationship between the AIL metric in the FBL regime and the commonly-used secrecy outage probability in conventional infinite blocklength communications. Aiming to improve the secure communication performance of the considered system, we formulate a blocklength optimization problem and solve it via a low-complexity approach. Next, we present numerical results to verify our analytical findings and provide various important insights into the impacts of system parameters on the AIL. Specifically, our results indicate that i) compromising a small amount of AIL can lead to significant reliability improvements, and ii) the AIL experiences a secrecy floor in the high signal-to-noise ratio regime.

翻译：本文基于平均信息泄漏（AIL）度量指标，研究了在瑞利衰落信道上具有有限块长度（FBL）传输的窃听通信系统的保密性能。我们评估了仅掌握窃听链路统计信道状态信息（CSI）条件下的精确和闭式近似AIL性能。随后，揭示了FBL体制下AIL度量与经典无限块长度通信中常用保密中断概率之间的内在统计关系。为提升所考虑系统的安全通信性能，我们构建了块长度优化问题，并通过低复杂度方法求解。最后，通过数值结果验证了理论分析，并深入探讨了系统参数对AIL的影响规律。特别地，研究结果表明：i) 牺牲少量AIL可显著提升系统可靠性；ii) 在高信噪比条件下AIL会遭遇保密性能地板效应。