How to provide information security while fulfilling ultra reliability and low-latency requirements is one of the major concerns for enabling the next generation of ultra-reliable and low-latency communications service (xURLLC), specially in machine-type communications. In this work, we investigate the reliability-security tradeoff via defining the leakage-failure probability, which is a metric that jointly characterizes both reliability and security performances for short-packet transmissions. We discover that the system performance can be enhanced by counter-intuitively allocating fewer resources for the transmission with finite blocklength (FBL) codes. In order to solve the corresponding optimization problem for the joint resource allocation, we propose an optimization framework, that leverages lower-bounded approximations for the decoding error probability in the FBL regime. We characterize the convexity of the reformulated problem and establish an efficient iterative searching method, the convergence of which is guaranteed. To show the extendability of the framework, we further discuss the blocklength allocation schemes with practical requirements of reliable-secure performance, as well as the transmissions with the statistical channel state information (CSI). Numerical results verify the accuracy of the proposed approach and demonstrate the reliability-security tradeoff under various setups.

翻译：如何在满足超可靠和低时延需求的同时保障信息安全，是推动下一代超可靠低时延通信服务（xURLLC）面临的核心挑战之一，尤其在机器类通信场景中。本文通过定义"泄漏失效概率"这一联合刻画短分组传输可靠性与安全性能的指标，研究了可靠性-安全性的权衡关系。我们发现，反直觉地分配更少资源用于有限块长（FBL）编码传输，反而能够提升系统性能。为求解相应的联合资源分配优化问题，我们提出了一种利用FBL机制中译码错误概率下界近似值的优化框架。我们刻画了重构问题的凸性特征，并建立了一种收敛性可得到保证的高效迭代搜索方法。为展示该框架的可扩展性，进一步探讨了满足可靠-安全性能实际需求的块长分配方案，以及基于统计信道状态信息（CSI）的传输策略。数值结果验证了所提方法的准确性，并揭示了不同配置下可靠性-安全性的权衡关系。