How Does Repetition Coding Enable Reliable and Covert Communications

This letter tackles whether and how repetition coding enables reliable and covert communications by considering binary phase shift keying. Communication reliability and covertness are analyzed in terms of the bit error rate $P_{e}$ and the minimum detection error probability $\xi ^{\ast }$ . Our examination shows that, when a warden Willie knows the codeword structure, both $P_{e}$ and $\xi ^{\ast }$ are determined by the total power nP and do not depend on the codeword length ${n}$ or the transmit power ${P}$ individually. However, this conclusion does not hold for the unknown codeword structure, where increasing ${n}$ can significantly improve the communication reliability under the same covertness constraint, and vice versa.