Hybrid Modulation Scheme Combining PPM With Differential Chaos Shift Keying Modulation

In conventional M-ary differential chaos shift keying modulation (DCSK) systems, the distance between constellation points gets closer as M increases, resulting in poor performance. A hybrid modulation scheme based on pulse position modulation (PPM) and DCSK is proposed in this letter to improve bit-errorrate (BER) performance. In this scheme, one part of the bits is modulated by PPM while the other part is modulated by DCSK. Thus, information bearing signals are simultaneously modulated by the information bit and the selected pulse position of PPM which is determined by extra information bits. Analytical BER performance of the proposed scheme is derived and verified by simulations. Results show that the considered scheme outperforms conventional M-DCSK, code index modulation DCSK, and commutation code index DCSK in additive white Gaussian noise and multipath Rayleigh fading channels.