Covert communications for UAV-assisted network: A comprehensive survey

Unmanned Aerial Vehicles (UAVs) have advantages such as high mobility, easy deployment, and low cost. Therefore, UAV-assisted networks have become one of the most promising architectures for next-generation wireless communications. However, due to the broadcast nature of the wireless channels, UAV-assisted networks are exposed to several types of security threats that need to be addressed with appropriate security technologies. Compared to traditional wireless security technologies such as encryption and Physical Layer Security (PLS), covert communication technology aims to conceal the presence of wireless transmissions to achieve a higher level of secure communication. In this survey, we first compare traditional wireless security technologies with covert communication technology. Then, we summarize the unique advantages of covert communication and briefly introduce its basic models. Besides, we introduce several typical covert scenarios in UAV-assisted networks. In addition, based on the common security threats in UAV-assisted networks, we present the existing generic solutions and investigate how the intrinsic mechanisms of covert communication can be exploited to mitigate these threats. Moreover, we outline the critical enabling techniques. Furthermore, two typical cases of UAV-assisted covert communication are presented, and some findings are also given along with simulation results. Finally, we point out several potential challenges and open issues.