Doppler Spread Estimation by Tracking the Delay-Subspace for OFDM   Systems in Doubly Selective Fading Channels
  A novel maximum Doppler spread estimation algorithm for OFDM systems with comb-type pilot pattern is presented in this paper. By tracking the drifting delay subspace of time-varying multipath channels, a Doppler dependent parameter can be accurately measured and further expanded and transformed into a non-linear high-order polynomial equation, from which the maximum Doppler spread is readily solved by resorting to the Newton's method. Its performance is demonstrated by simulations. 
Xiaochuan Zhao (1), Tao Peng (1), Ming Yang (1) and Wenbo Wang (1)   ((1) Beijing University of Posts and Telecommunications...