Wireless short-packet communications pose challenges to the security and reliability of the transmission. Besides, the proactive warder compounds these challenges, who detects and interferes with the potential transmission. An extra jamming channel is introduced by the proactive warder compared with the passive one, resulting in the inapplicability of analytical methods and results in exsiting works. Thus, effective system design schemes are required for short-packet communications against the proactive warder. To address this issue, we consider the analysis and design of covert and reliable transmissions for above systems. Specifically, to investigate the reliable and covert performance of the system, detection error probability at the warder and decoding error probability at the receiver are derived, which is affected by both the transmit power and the jamming power. Furthermore, to maximize the effective throughput, an optimization framework is proposed under reliability and covertness constraints. Numerical results verify the accuracy of analytical results and the feasibility of the optimization framework. It is shown that the tradeoff between transmission reliability and covertness is changed by the proactive warder compared with the passive one. Besides, it is shown that longer blocklength is always beneficial to improve the throughput for systems with optimized transmission rates. But when transmission rates are fixed, the blocklength should be carefully designed since the maximum one is not optimal in this case.

翻译：无线短包通信对传输的安全性和可靠性提出了挑战。此外，主动监控者（其会检测并干扰潜在传输）进一步加剧了这些挑战。与被动监控者相比，主动监控者引入了一个额外的干扰信道，导致现有工作中的分析方法和结果不再适用。因此，需要针对主动监控者场景下的短包通信设计有效的系统方案。为解决此问题，我们考虑在上述系统中进行隐蔽可靠传输的分析与设计。具体而言，为了研究系统的可靠性与隐蔽性能，推导了监控者的检测错误概率和接收端的解码错误概率，这些概率同时受发射功率和干扰功率影响。此外，为最大化有效吞吐量，在可靠性和隐蔽性约束下提出了一个优化框架。数值结果验证了分析结果的准确性以及优化框架的可行性。研究表明：与被动监控者相比，主动监控者改变了传输可靠性与隐蔽性之间的权衡关系。此外，当系统采用优化传输速率时，更长的块长度始终有利于提升吞吐量；但当传输速率固定时，需谨慎设计块长度，因为此时最大块长度并非最优选择。