Covert communications enable a transmitter to send information reliably in the presence of an adversary, who looks to detect whether the transmission took place or not. We consider covert communications over quasi-static block fading channels, where users suffer from channel uncertainty. We investigate the adversary Willie’s optimal detection performance in two extreme cases, i.e., the case of perfect channel state information (CSI) and the case of channel distribution information (CDI) only. It is shown that in the large detection error regime, Willie’s detection performances of these two cases are essentially indistinguishable, which implies that the quality of CSI does not help Willie in improving his detection performance. This result enables us to study the covert transmission design without the need to factor in the exact amount of channel uncertainty at Willie. We then obtain the optimal and suboptimal closed-form solution to the covert transmission design. Our result reveals fundamental difference in the design between the case of quasi-static fading channel and the previously studied case of non-fading AWGN channel.

中文翻译：

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具有通道不确定性的准静态衰落下的隐蔽无线通信

隐蔽通信使发送方能够在出现对手的情况下可靠地发送信息，该对手希望检测是否发生了传输。我们考虑在准静态块衰落信道上进行隐蔽通信，其中用户遭受信道不确定性的困扰。我们在两种极端情况下调查对手威利的最佳检测性能，即，仅在完美信道状态信息（CSI）和仅信道分布信息（CDI）情况下。结果表明，在较大的检测误差范围内，这两种情况下威利的检测性能基本无法区分，这说明CSI的质量并不能帮助威利提高其检测性能。该结果使我们能够研究隐蔽传输设计，而无需考虑Willie上信道不确定性的确切数量。然后，我们为隐式传输设计获得了最优和次优的闭式解。我们的结果揭示了准静态衰落信道情况与先前研究的非衰落AWGN信道情况之间在设计上的根本差异。