Covert Satellite Communication Over Overt Channel: A Randomized Gaussian Signalling Approach

In this article, we design a covert satellite communication scheme over an overt channel by randomizing the variance feature of the transmitted Gaussian signaling to realize a positive covert rate. The transmitter Alice sends an overt signal superimposed by a covert signal which is received by public user Carol, a covert user Bob, and a warden Willie. The received power in Willie is randomized because of the random variance. We derive the detection error probability of Willie and the covert rate of Bob in shadowed-Rician fading channel when channel state information (CSI) is perfectly known or only channel distribution information (CDI) is known. We give the closed-form optimal random range of the variance and the optimal covert rate when CSI is a known subject to the reliability and covertness constraints. When only CDI is known, we prove that there exists a unique value of the random variance to maximize the expected covert rate of Bob. Our numerical results confirm the correctness of the theoretical results and show that the optimal random distribution of the variance can be effectively adaptive to the system parameters and the covert rate when CSI is known is very close to that when only CDI is known.