The fundamental information-theoretic limits of covert, or low probability of detection/intercept (LPD/LPI), communication have been extensively studied for over a decade, resulting in the square root law (SRL): only $L\sqrt{n}$ covert bits can be reliably transmitted over time-bandwidth product $n$, for constant $L>0$. Transmitting more either results in detection or decoding errors. The SRL imposes significant constraints on hardware realization of mathematically-guaranteed covert communication. Indeed, they preclude using standard link maintenance operations that are taken for granted in non-covert communication. Thus, experimental validation of covert communication is underexplored: to date, only two experimental studies of SRL-based covert communication are available, both focusing on optical channels. Here, we report a demonstration of provably-secure covert radio-frequency (RF) communication using software-defined radios (SDRs). This validates theoretical predictions, opens practical avenues for implementing covert communication systems, and raises further research questions.

翻译：隐蔽通信，即低检测/截获概率（LPD/LPI）通信的基本信息论极限已被广泛研究十余年，其核心结论是平方根定律（SRL）：在时间-带宽积 $n$ 下，仅能可靠传输 $L\sqrt{n}$ 比特的隐蔽信息，其中 $L>0$ 为常数。试图传输更多比特将导致被检测或解码错误。SRL 对实现具有数学保证的隐蔽通信的硬件提出了重大限制。事实上，它排除了在非隐蔽通信中视为理所当然的标准链路维护操作的使用。因此，隐蔽通信的实验验证研究尚不充分：迄今为止，仅有两项基于 SRL 的隐蔽通信实验研究，且均聚焦于光信道。本文报道了利用软件定义无线电（SDR）实现可证明安全的射频（RF）隐蔽通信的演示。这项工作验证了理论预测，为实施隐蔽通信系统开辟了实用途径，并提出了进一步的研究问题。