Serially Concatenated Systematic Coding for Wireless Steganography with OFDM Signaling

We propose a practical covert communication technique for IoT networks based on serially concatenated systematic coded (SCSC) wireless steganography, where the secret information is transmitted by orthogonal frequency division multiplexing (OFDM) signal. Instead of sending the Gaussian artificial noise (AN) so as to prevent the detection by the warden, the secret OFDM signal is hidden into the cover DFT-spread OFDM (DFT-s-OFDM) signal as a public signal since it is suitable for low-cost IoT devices due to its low peak-to-average power ratio (PAPR) property. In our proposed system, the public signal is generated from the parity bits of the secret information by utilizing systematic encoding. As a result, the legitimate receiver improves the error rate performance by concatenating the likelihood corresponding to both secret and public signals. On the other hand, since the parity bits are broadcast as the public signal, there is a risk of the secret information being decoded by the unintended receiver, warden. Therefore, we derive the conditions for systematic codes so as to achieve secure covert communications. Through computer simulation, we demonstrate that the coded bit error rate (BER) performance of our proposed scheme significantly outperforms that of the conventional system, and this enhancement can be achieved without the expense of the secrecy evaluated in terms of the probability of event detection error at the warden.