Covert Communications With Randomly Distributed Wardens in the Finite Blocklength Regime

This paper investigates covert communications with finite blocklength in the presence of multiple randomly distributed wardens, which are modeled as a Poisson point process (PPP). Specifically, the protection area, which is guarded by the transmitter against the wardens, is introduced in order to enhance the covert communication performance. First, the closed-form expressions of covert communication constraint are derived under both the non-colluding and colluding detection strategies over the channels suffering both path-loss and small scaling fading. Then, considering the constraint of maximum available blocklength, the transmit power and the blocklength are jointly optimized to maximize the average effective covert throughput (AECT). Differing from the existing literature with only one warden, it is demonstrated that the increasing of maximum available blocklength causes the improvement of maximum AECT only when the density of warden is small. In addition, our examinations show that the expansion of the protection area indeed improves the maximum AECT, and the improvement under the non-colluding detection strategy is more significant than that under the colluding detection strategy.