Two-Layer Carrier Index Modulation Scheme Based on Differential Chaos Shift Keying

In this paper, a novel carrier index differential chaos shift keying (DCSK) modulation system is proposed for increased energy and spectral efficiencies. The new system splits all data bits into two groups, which are carried by the chaotic signals and their Hilbert transforms, respectively. For each group, one active subcarrier is selected from all candidate subcarriers according to the index bits, and the signal transmitted via the active subcarrier carries one modulated bit through DCSK modulation. By correlating with the exact or the Hilbert filtered chaotic reference signals, the two data groups can be demodulated separately. In each group, the index bits are determined by the maximum energy comparator, while the threshold verdict helps to estimate the modulated bit. Analytical bit error rate expressions over additive white Gaussian noise and multipath Rayleigh fading channels are derived. Simulations and comparisons are also performed to verify the advantages of this new proposed design.