In this letter, we develop a new framework to jointly characterize covertness and timeliness of short-packet communications, in which a new metric named covert age of information (CAoI) is first proposed and then a closed-form expression for the average CAoI is derived. Our examination explicitly reveals the tradeoff between communication covertness and timeliness affected by the block-length, transmit power and prior transmission probability. Multiple transmission designs are tackled in order to minimize the average CAoI subject to covertness constraint, where the resultant differences relative to the designs with traditional metrics (e.g., effective covert rate, AoI) as objective functions are clarified. Our examination demonstrates that the optimal block-length is not the largest one, which is optimal in delay-constrained covert communication without considering the communication timeliness, and the optimal prior transmission probability may not be 1/2, which has been widely assumed in the literature of covert communications.

中文翻译：

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短包隐蔽通信的信息时代


在这封信中，我们开发了一个新的框架来共同表征短包通信的隐蔽性和及时性，其中首先提出了一个名为隐蔽信息年龄（CAoI）的新度量，然后导出了平均 CAoI 的封闭式表达式。我们的检查明确揭示了受块长度、传输功率和先验传输概率影响的通信隐蔽性和及时性之间的权衡。解决了多种传输设计的问题，以便最大限度地减少受隐蔽性约束的平均 CAoI，其中澄清了相对于以传统指标（例如，有效隐蔽率，AoI）作为目标函数的设计所产生的差异。我们的研究表明，最佳块长度不是最大的，这在不考虑通信及时性的延迟受限隐蔽通信中是最佳的，并且最佳先验传输概率可能不是 1/2，这是在秘密通信的文献。