Spectrally Efficient Chirp Division Multiplexing

Orthogonal chirp division multiplexing (OCDM) has emerged as a promising multi-carrier scheme for future wireless communications. To further enhance its spectral efficiency (SE), we propose spectrally efficient chirp division multiplexing (SECDM), which introduces chirp-domain compression by reducing the sub-carrier spacing of OCDM. To address the extremely high complexity of maximum likelihood (ML) detector, we develop a preprocessing-aided fixed sphere decoder (FSD) for SECDM that delivers near-ML performance with low complexity. Compared to the representative non-orthogonal waveform, spectrally efficient frequency division multiplexing (SEFDM), the proposed SECDM exhibits stronger resilience to inter-carrier interference (ICI) caused by compression-induced non-orthogonality, owing to its chirp-based nature. Simulation results validate the superiority of SECDM over SEFDM in terms of both bit error rate (BER) and SE.