This paper presents an explicit channel code design for covert communications in the Binary Symmetric Channel. The proposed architecture is composed of the serial concatenation of a linear code and a graph-based non-linear code baptized as moderate-density non-linear code. This non-linear code encompasses pulse position modulation as a particular case. In order to guarantee covertness, a scrambling sequence that is not known to the warden is employed.
Lamarca, M.; Matas, D. A non-linear channel code for covert communications. A: IEEE Wireless Communications and Networking Conference. "2019 IEEE Wireless Communications and Networking Conference (WCNC 2019) Marrakech, Morocco 15-18 April 2019". Institute of Electrical and Electronics Engineers (IEEE), 2019, p. 1-7.