Internet of Things (IoT) systems are of paramount importance to provide ubiquitous wireless connectivity for smart cities. However, such systems are facing security challenges due to the broadcast and openness nature of wireless channels. This article studies the performance of covert communication under a scenario consisted of a source–destination pair, a passive warden, and multiple relays. We first propose two relay selection schemes, one is random selection and another is superior-link selection. Based on these two schemes, we then examine the transmission strategy design for the source and thus define the necessary condition that the source can transmit covert messages. We further derive the detection error probability of warden and covert capacity based on two relay selection schemes and also explore the covert capacity maximization through efficient numerical searches. Finally, numerical results are provided to illustrate our theoretical findings and the performance of covert communication in such systems. Remarkably, the superior-link selection scheme has 108% improved to the random selection scheme for the maximum covert capacity performance under the same transmission power at the source.

中文翻译：

---

中继辅助物联网系统中的隐蔽通信

物联网（IoT）系统对于为智慧城市提供无处不在的无线连接至关重要。然而，由于无线信道的广播和开放性，这样的系统面临安全性挑战。本文研究了在由源－目的地对，无源守望者和多个中继组成的情况下秘密通信的性能。我们首先提出两种中继选择方案，一种是随机选择，另一种是上级链路选择。基于这两种方案，然后我们检查源的传输策略设计，从而定义源可以传输隐蔽消息的必要条件。我们基于两种中继选择方案进一步推导了守望者和隐蔽能力的检测错误概率，并通过有效的数值搜索来探索隐蔽能力的最大化。最后，提供了数值结果来说明我们的理论发现以及此类系统中隐蔽通信的性能。值得注意的是，对于在源端具有相同传输功率的情况下，最大隐蔽容量性能，上级链路选择方案比随机选择方案有了108％的改进。