An Orthogonal Time Frequency Space Covert Modulation Scheme Based on Modified Weighted Fractional Fourier Transform

To enhance the covert communication capacity of the orthogonal time frequency space (OTFS) system, this manuscript proposes an OTFS covert modulation scheme founded on modified multi-parameter weighted fractional Fourier transform (MP-WFRFT). Within this methodology, utilizing time of day (TOD) and cryptography key synchronized at the transmitter and cooperative receiver generates non-stationary code hopping spread spectrum (CHSS) patterns and initial phases of constellation rotation. Theoretical analysis and simulation results substantiate that the proposed scheme enables the transmitting signal resembling Gaussian white noise (WGN), facilitating demodulation and decoding by the cooperative receiver even in low SNR circumstances. Meanwhile, the eavesdropper faces significant challenges in detecting the signal, either signal analysis or decoding, thus significantly augmenting the covertness of the communication waveform.