Orthogonal Chirp Division Multiplexing With Index Modulation

Orthogonal chirp division multiplexing (OCDM) is a new multi-carrier scheme based on chirp spread spectrum (CSS) recently introduced and shown to be more robust to interference. In this paper, we propose a novel OCDM system based on index modulation (IM). In this scheme, information is conveyed not only by M -ary signal constellation in classic OCDM, but also by subchirp indices activated in accordance with the input bitstream. We design a receiver structure based on single-tap frequency domain equalization (FDE) and maximum likelihood (ML) detection. To address the exponential complexity growth caused by ML detection, we also propose a novel reduced-complexity maximum likelihood (RC-ML) detector. The new detector offers a comparable BER performance to the ML one with a substantially reduced complexity. A theoretical peak-to-average power ratio (PAPR) performance analysis of the new scheme is given to illustrate the advantages of combining OCDM with IM. We provide an extensive performance analysis of the new scheme in terms of bit error rate (BER), diversity gain, and minimum Euclidean distance (MED). Simulation results are presented to demonstrate that the PAPR and BER performances of the proposed scheme are significantly better than those of the OCDM scheme due to the information bits carried by the OCDM subchirp indices. Moreover, our numerical results verify the robustness of the system in the presence of carrier frequency offsets (CFO).