A non-linear channel code for covert communications

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.