Discrete-Fresnel Domain Channel Estimation in OCDM-Based Radar Systems

Orthogonal chirp-division multiplexing (OCDM) has been recently proposed as an alternative scheme to orthogonal frequency-division multiplexing (OFDM) for data communication. Among the reasons for that are its superior robustness, e.g., to frequency selectivity of channels and intersymbol interference. Furthermore, channel estimation in the discrete-Fresnel domain has been investigated for both communication and sensing, without, however, considering the effects of frequency shifts. This article investigates the discrete-Fresnel domain channel estimation in OCDM-based radar systems as an alternative to the correlation-based processing from the conventional OCDM (C-OCDM) radar-communication (RadCom) system, which yields high, transmit-data-dependent sidelobe level. In this context, a mathematical formulation for the investigated channel estimation approach is presented. In addition, extensions to multiuser/multiple-input–multiple-output (MIMO) and to a sector-modulated OCDM (SM-OCDM) RadCom operation are introduced. Finally, the performance of the proposed schemes is analyzed based on simulation and measurement results for an emulated automotive scenario. In summary, both OCDM-based radar and SM-OCDM RadCom systems yield improved peak-to-average power ratio and comparable or improved radar performance in terms of sidelobe level and Doppler shift robustness to their C-OCDM and OFDM counterparts for practical range and velocity values. In addition, equal communication performance robustness to C-OCDM, which outperforms OFDM, is experienced in the SM-OCDM case.