Doppler rate estimation for OFDM based communication systems in high mobility

This paper considers OFDM (orthogonal frequency division multiplexing) based broadband wireless communications in high mobility with rapid time-varying Doppler shifts, where the received signal is significantly degraded by Doppler distortion, such as in a scenario of low-earth-orbit satellite communications. Since existing Doppler rate estimation methods are mainly designed for single carrier systems, two new CP (Cyclic Prefix) based Doppler rate estimators are proposed for OFDM based systems with discrete pilots, i.e. SOD (second order difference) estimator and ML (maximum likelihood) estimator. Furthermore in a time-dispersive channel a modification is conducted to improve both estimators accuracy in a fading channel. In the simulation part proposed estimators are compared with existing single-carrier Doppler rate estimators to verify the effectiveness and efficiency of the proposed estimators in an OFDM system. Specifically simulation results verify the low complexity of SOD estimator, the high accuracy of ML estimator, the insensitivity to initial Doppler shifts of both estimators and the accuracy improvement of modified estimators in a fading channel.