FHSS-Aided FDA Covert Communication With Instantaneous and Robust Optimization

In this paper, we utilize frequency hopping spread spectrum (FHSS) to help enhance covert performance in frequency diverse array (FDA) covert system. Compared to conventional FDA covert communication, FHSS signals can hide in different channels by rapidly switching the transmission frequency to avoid being detected. Therefore, FHSS-aided FDA covert system can effectively counter the warden with strong detection ability and enhance covert performance. We focus on maximizing the covert capacity during the entire transmission by jointly optimizing the beamfoming vector and antenna frequency vector at the transmitter. Based on the system equipment constraints, two different optimization schemes, i.e., instantaneous optimization scheme (IOS) and robust optimization scheme (ROS), are proposed to solve the problem. Moreover, to evaluate the covert performance provided by FHSS-aided FDA covert communication, we introduce three benchmark schemes, i.e., phased array (PA) and logarithmic distribution FDA (Log-FDA) and non-FHSS. Simulation results demonstrate that FHSS combined with IOS can significantly improve covert performance compared to other benchmark schemes. In contrast, FHSS combined with ROS can effectively enhance covert performance when transmitting signals over a wide bandwidth.