Doppler Spread Estimation by Subspace Tracking for OFDM Systems

In this paper, a novel maximum Doppler spread estimation algorithm is presented for OFDM systems with the comb-type pilot pattern. The least squared estimated channel frequency responses (CFR´s) on pilot tones are used to generate the auto-correlation matrices with/without a known lag, from which the time correlation function can be measured. The maximum Doppler spread is acquired by inverting the time correlation function. Since the noise term will bias the estimator, the estimated CFR´s are projected onto the delay subspace of the channel to reduce the bias term as well as the computation complexity. Furthermore, the subspace tracking algorithm is adopted to automatically update the delay subspace. Simulation results demonstrate the proposed algorithm can quickly converge to the true values for a wide range of SNR´s and Doppler spreads in Rayleigh fading channels.