Robust overlapping covert communication against partialband interference via chaotic multi-tone spread spectrum

The article presents an overlapping covert communication scheme based on the dynamic adjustment of the spread spectrum factor within a predefined range under a chaotic multi-tone framework, aiming to mitigate partialband interference. In this approach, legitimate communication signals are exploited as masking signals, whereas covert signals are modeled as parasitic components. Covert transmission is theoretically achieved by establishing a signal-to-noise ratio (SNR) wall for non-cooperative receivers, where the robustness of this SNR wall is essential for ensuring communication reliability. Furthermore, the study addresses the challenge of distinguishing between host and parasitic signals in the presence of partial-band interference through frequency-band partitioning. To overcome this difficulty, the relationship between the power ratio of masking to covert signals and the probability of detection error for eavesdroppers is investigated. Based on this analysis and prior research, a communication scheme is proposed to enhance overall system performance. Theoretical evaluations are conducted to assess its resistance to partial-band interference and communication reliability. Experimental results further validate system performance by examining the bit-error rate (BER) under varying levels of masking-signal strength and by comparing the reliability and security of the proposed scheme with those of chaotic spread-spectrum modulation schemes employing BPSK signals under equivalent average spread-spectrum gain.