Direct Sequence Spread Spectrum-Based Radio Steganography

Direct sequence spread spectrum (DSSS) is a spread-spectrum modulation technique primarily used to reduce overall signal interference. DSSS is one of the so-called secondary modulation techniques, which makes the transmitted signal wider in bandwidth than the information bandwidth. On the other hand, this technique allows the transmitted information signal to be hidden in the noise. Thus, DSSS signals are classified as low probability of intercept/low probability of detection (LPI/LPD). DSSS modulation is also used in information hiding for both radio and audio signals. In this case, the DSSS-based steganography algorithms used various information-hiding mechanisms, e.g., modulation parameter modification. In the novel solution proposed in this paper, we use DSSS with variable processing gain for keying additional information. In this case, the hidden message is transmitted in a switching order of spreading sequences taken from a mapping dictionary known only to the notified parties.