A Satellite Overlapping Covert Communication Scheme Based on LDPC-DCSK Transmission Technology

Abstract

Traditional satellite covert communications mostly use periodic short code direct sequence spread spectrum (DSSS) technology. The risk of DSSS being deciphered is increasing with the development of signal detection technology. As a technology that can replace traditional spread spectrum, chaos shift keying (CSK) not only has the characteristics of low power spectrum density, but also has good correlation and long-term unpredictability compared with traditional DSSS, so it is more suitable for covert communication. However, CSK has the problem of decision threshold drift, which is difficult to apply in practice. This article uses differential chaos shift keying (DCSK) technology, which not only has the advantage of high concealment of chaotic signals, but also overcomes the problem of CSK threshold drift. Then non-binary low-density parity-check (LDPC) code is introduced to DCSK (LDPC-DCSK) for high reliability. In order to improve the concealment of LDPC-DCSK signal further, a satellite overlapping communication scheme that the LDPC-DCSK covert signal is superimposed on civil satellite service signal is proposed by this paper. This scheme realizes the overlap of the covert signals and the satellite service signals at the transmitter, and it uses a separation algorithm based on auxiliary information at the receiver. In the end, the scheme realizes the separation of the covert signals and the satellite service signals from the mixed signals, and the reliability and spectrum characteristics are evaluated. The simulation results show that under the circumstance which the chaotic signals and the noise power are roughly similar, the scheme not only achieves that the bit error rate of the satellite service signals is almost unaffected after superimposing the covert signals, but also realizes the accurate separation and restoration of the covert signals.