On Low-Complexity MMSE Channel Estimation for OCDM Systems

In this letter, we first present a time-domain model for pilot-assisted MMSE channel estimation in the orthogonal chirp division multiplexing (OCDM) systems. Then by proposing a pilot selection criterion, the complexity of MMSE channel estimation is reduced by the simplification of matrix inversion. Meanwhile, we prove that the criterion can lead to the optimal mean square error (MSE) performance. Furthermore, based on the criterion, by adopting the Zadoff-Chu sequences as pilots and presenting a split-and-decomposition algorithm, we propose a low-complexity channel estimator for OCDM. The complexity of the proposed estimator is O( N log L/2), while the estimator in existing literature for OCDM is O(N logN), where L is the channel length and N is the number of subcarriers. Numerical results are provided to verify the performance of the proposed algorithm over frequency-selective Rayleigh fading channels. It turns out that the proposed estimator can significantly reduce the computational complexity without any MSE performance loss.