Covert Communications in Low-VHF/Microwave Heterogeneous Networks

In this paper, we explore covert communication in a heterogeneous network where a transmitter sends a confidential message to a receiver by utilizing two different radio frequency (RF) bands, low-very high frequency (low-VHF) and microwave frequency modalities. Since two RF modalities exhibit different characteristics in terms of channels and available bandwidths, it is important to efficiently leverage the modalities based on the wireless environment. Therefore, we develop a new algorithm that optimizes the transmit powers and bandwidths for the modalities and selects one modality with the goal of maximizing the detection error probability at a warden while guaranteeing a quality-of-service requirement of the receiver. We first derive a closed-form joint optimal power and bandwidth solution for a given modality, and then provide a modality selection method. From numerical simulations, it is validated that the proposed scheme achieves the optimal performance and the covertness can be enhanced by judiciously choosing one of the two modalities based on the channel condition.