Covert Communications with Simultaneous Multi-Modal Transmission

In this paper, we develop an approach to exploit multiple disparate wireless communication technologies simultaneously to enhance covertness of a communication link. Specifically, given two available communication modalities between a pair of friendly nodes (Alice and Bob), the goal is to evade detection by an adversary (Willie) who is equipped with a radiometer covering the frequency bands of both modalities. We propose a joint detection threshold optimization technique from Willie's point of view. We also develop a joint transmit power optimization strategy for Alice to maximize covertness while meeting the throughput requirement at Bob. Through numerical simulations we show that the proposed scheme matches the performance of exhaustive search method while reducing the computational time by 98% and also improves the covertness by 56% compared to a naïve benchmark scheme.