In a majority of research on covert communications, knowledge about channel state information (CSI) of main channel and/or warden channel is assumed to be known or partially known. However, a covert user may not afford to perform channel estimation in practice, and acquiring the warden’s CSI is even impossible. In this paper, we investigate covert communications over non-coherent Rayleigh fading channels, in both i.i.d. fast fading and slow fading cases. We observe that the purpose of covert communication in many scenarios is to hide the existence of the sender, not the receiver. Therefore, we allow the receiver to work in full-duplex mode such that it can emit artificial noise (AN) while receiving signals simultaneously. We analyse the achievable covert rates with fixed and varying AN power and show that in both fast and slow fading cases, it is possible to achieve a positive covert rate. For the slow fading case, we further extend the proposed strategy to a multi-user scenario, in which multiple other users share the same spectral resource and cause interference at the warden. Extensive simulations are performed to verify the correctness of our analysis, which provide new insights on the AN design problem in non-coherent channels.

中文翻译：

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非相干瑞利衰落下与全双工接收器的秘密通信

在秘密通信的大多数研究中，关于主信道和/或守望者信道的信道状态信息（CSI）的知识被假定为已知的或部分已知的。然而，秘密用户在实践中可能负担不起执行信道估计，并且获取监护人的CSI甚至是不可能的。在本文中，我们研究了在快速衰落和慢速衰落情况下，非相干瑞利衰落信道上的秘密通信。我们观察到，在许多情况下，秘密通信的目的是隐藏发送者而不是接收者的存在。因此，我们允许接收器以全双工模式工作，以便它可以在同时接收信号的同时发出人为噪声（AN）。我们分析了固定和变化的AN功率下可实现的隐蔽率，并表明在快速衰落和慢速衰落情况下，可以实现正的隐蔽率。对于慢衰落情况，我们将所提出的策略进一步扩展到多用户场景，其中多个其他用户共享相同的频谱资源并在看守上造成干扰。进行了广泛的仿真以验证我们分析的正确性，这为非相干通道中的AN设计问题提供了新的见解。