Covert Communication in a Multirelay-Assisted Wireless Network With an Active Warden

Wireless connectivity in smart cities relies on widely deployed Internet of Things (IoT) systems. However, the broadcast and open nature of wireless channels in such systems also raise serious security concerns. Covert communication technology presents a promising solution for tackling these challenges. In the multi-relay assisted wireless systems where the warden acts as a jammer, this paper investigates the performance of covert communication. First, the transmission model is introduced and the warden behavior is defined, which will perform detection and jamming throughout the covert communication process. Due to the warden's jamming, the transmitter must increase its transmit power in order to ensure successful decoding, which increases the risk of detection. To explore this tradeoff in depth, this paper proposes a new theoretical framework to analyze the performance metrics of covert communication. These performance metrics are analyzed and derived under two relay selection schemes, i.e., random selection scheme and superior-link selection scheme. The maximum covert rate is optimized by power control under the condition that the covertness and outage requirements are satisfied. Finally, the results of simulations and numerical experiments confirm the theoretical analysis and visualize the performance of covert communication in systems with active warden.