Hybrid Equalization and Interference Suppression for Orthogonal Chirp Division Multiplexing Systems

Orthogonal Chirp-Division Multiplexing (OCDM) has emerged as a promising modulation scheme for high-speed communication: it uses orthogonal linear chirps to spread data symbols across both time and frequency domains. OCDM offers better Bit Error Rate (BER) performance than Orthogonal Frequency Division Multiplexing (OFDM) over frequency-selective channels, since multiple low-complexity OCDM receivers designed to leverage channel diversity have already been proposed in the literature. However, the performance of OCDM state-of-the-art receivers becomes significantly poor under jamming or in interference contexts. In this paper, we propose a novel receiver design to mitigate the impact of interference on the OCDM system performance. The receiver first estimates and suppresses interference in the frequency domain before proceeding with channel estimation and equalization. Residual Inter-Symbol Interference (ISI) and interference may persist in the Fresnel domain. Therefore we propose to use an adaptive linear filter in the Fresnel domain to enhance the system performance. Furthermore, in heavily jammed environments, we propose to reduce the system spectral efficiency and by utilizing underloaded OCDM and optimizing filter coefficients across all known symbols, including the added zero symbols. Simulations demonstrate that our proposed receiver design significantly improves OCDM system robustness against interference.