A Non-Orthogonal Modulation Based High Spectral Efficiency and High Security Multi-Carrier Differential Chaos Shift Keying for Maritime Communications

The Space-Air-Ground-Sea Integrated Networks (SAGSIN) will place higher requirements on both spectral efficiency and security for future maritime communications. To simultaneously address these two challenges, in this paper, a non-orthogonal modulation based multi-carrier differential chaos shift keying system (namely MCNO-DCSK) is proposed and demonstrated. The most remarkable feature of MCNO-DCSK is that the strict orthogonality between subcarriers is no longer required. In this way, frequency intervals between subcarriers can be much smaller than ever, which leads to a high spectral efficiency. Meanwhile, the frequency interval can be set more flexibly to make the symbol more difficult to be deciphered. Therefore, a high level of security can also be guaranteed. In this design, multiple modulated non-orthogonal subcarriers are sequentially delayed and directly superimposed in time domain to construct the MCNO-DCSK symbol. At the receiver, information bits are demodulated through solving a system of linear equations. The spectral efficiency, computational complexity, and security are analyzed, and the bit-error-rate expressions are derived. Moreover, as subcarriers are non-orthogonal and time delayed, the MCNO-DCSK will suffer severe interference over the multi-path channel. Therefore, the effect of the multi-path interference on the system performance is discussed, and a method to mitigate this interference is designed. Finally, simulation results are provided to verify the theoretical analysis and demonstrate the superiority of MCNO-DCSK.