Doppler spread estimation for wireless OFDM systems

We present a method for estimating the Doppler spread in mobile orthogonal frequency division multiplexing (OFDM) systems. The estimation is based on finding the autocorrelation function of time domain channel estimates over several OFDM symbols. In OFDM systems, channel estimation is popularly performed in the frequency domain. Channel frequency response estimates are affected by noise and intercarrier interference (ICI). As a result, Doppler estimates based on frequency domain channel estimates are affected significantly. We show that the use of channel estimates in the time domain can greatly improve the performance of Doppler estimates. The channel impulse response (CIR) can be obtained by taking the IDFT of the channel frequency response (CFR). Consequently, the proposed method reduces processing time and memory usage. Computer simulations support our claim for a broad range of Doppler spread and signal-to-noise ratio (SNR) values in Rayleigh fading channels