Channel Estimation for MIMO-OCDM with Fresnel Domain Pilots

Orthogonal chirp division multiplexing (OCDM) is a novel modulation scheme with increased spectral efficiency compared with conventional chirp spectrum spread systems. Meanwhile, it is well known that multiple-input multiple-output (MIMO) techniques can enhance diversity to combat channel fading. Thus, MIMO-OCDM is promising for reliable high-rate wireless communications. In MIMO-OCDM systems, channel estimation is crucial and challenging. In this paper, we apply the Alamouti technique to develop a MIMO-OCDM system and enable its spatial diversity under frequency-selective channels. In order to facilitate the channel estimation, a pilot-aided transmission (PAT) scheme is proposed. The pilots are designed in the Fresnel domain to inherit the double-spreading property of OCDM and be robust to burst interference. The corresponding channel estimator is provided to achieve the lower bound of the mean square error (MSE) of channel estimation. Simulation results verify the superior performance of the proposed channel estimation method for the pilot-aided MIMO-OCDM system.