A Countermeasure for Traffic Analysis Attacks: Covert Communications With Digital Modulation

In this letter, we provide a physical layer supported defense mechanism against traffic analysis attacks by exploring the covert communication capability of digital modulation schemes. We analyze and compare the performances of M-PSK, M-QAM, M-ASK and M-APSK modulations in terms of the probability of detection by a warden and the maximum achievable throughput at the receiver. We obtain a lower bound for the covert transmission probability at Willie, which can be utilized as a covertness limit to maximize the throughput. Numerical studies highlight the tightness of the presented lower bound and show the maximum achievable throughput limits without being detected by a traffic analysis attacker.