Covert communication prevents legitimate transmission from being detected by a warden while maintaining certain covert rate at the intended user. Prior works have considered the design of covert communication over conventional low-frequency bands, but few works so far have explored the higher-frequency millimeter-wave (mmWave) spectrum. The directional nature of mmWave communication makes it attractive for covert transmission. However, how to establish such directional link in a covert manner in the first place remains as a significant challenge. In this paper, we consider a covert mmWave communication system, where legitimate parties Alice and Bob adopt beam training approach for directional link establishment. Accounting for the training overhead, we develop a new design framework that jointly optimizes beam training duration, training power and data transmission power to maximize the effective throughput of Alice-Bob link while ensuring the covertness constraint at warden Willie is met. We further propose a dual-decomposition successive convex approximation algorithm to solve the problem efficiently. Numerical studies demonstrate interesting tradeoff among the key design parameters considered and also the necessity of joint design of beam training and data transmission for covert mmWave communication.

中文翻译：

---

隐秘毫米波通信的联合波束训练和数据传输设计

秘密通信可防止监护人检测到合法的传输，同时又可以保持目标用户一定的秘密率。先前的工作已经考虑了在常规低频频带上进行秘密通信的设计，但是到目前为止，很少有工作探索更高频率的毫米波（mmWave）频谱。mmWave通信的方向性使其对于隐蔽传输具有吸引力。然而，如何首先以秘密方式建立这种定向链路仍然是一个重大挑战。在本文中，我们考虑一个秘密的毫米波通信系统，其中合法方爱丽丝和鲍勃采用波束训练方法进行定向链路建立。考虑到训练的开销，我们开发了一个新的设计框架，可以共同优化射束训练的持续时间，训练能力和数据传输能力，以最大程度地提高Alice-Bob链路的有效吞吐量，同时确保满足守望者Willie的隐蔽性约束。我们还提出了一种双分解逐次凸逼近算法来有效地解决该问题。数值研究表明，在考虑的关键设计参数之间进行了有趣的折衷，同时也提出了针对隐蔽毫米波通信进行波束训练和数据传输联合设计的必要性。