The Optimal Precoded Faster-Than-Nyquist Signaling for Covert Communications

In this letter, we consider the covert communications under precoded faster-than-Nyquist (FTN) signaling. We first propose a general framework to analyze the detection performance of an illegal adversary for the precoded FTN signaling, and then derive a general principle for the optimal precoding scheme maximizing the covert throughput under the Kullback-Leibler (KL) divergence-based constraint. The covert throughput of the optimal precoding scheme is obtained based on the proposed framework, and it is theoretically proved to be higher than that of the non-precoded FTN as well as Nyquist ones. Numerical results also verify the superiority of the optimal precoded FTN signaling in terms of the covert throughput.