Doppler spread estimation for ofdm systems

A method of estimating a channel response of a received signal comprising two or more carriers different in a communications system Division Multiplexing Orthogonal Frequency (OFDM), the method comprising: for each of the carriers, determining a quantity rotating (312, 351, 357) which is at least partly a function of a frequency separation between two adjacent carriers, an extension channel delay, and a position of the carrier relative to other carriers within the received signal. process the received signal and thereby generating a processed signal, whereby the processing includes processing with a Fast Fourier Transform; prior to re Alizar frequency interpolation as part of a channel estimation process, rotating the carrier components (312, 351, 357) of the signal processed by the corresponding amounts of rotation signal; and estimating the channel response (315, 317, 319, 353, 355.359) performing the channel estimation process at least in part on the rotated processed signal. characterized by determining the amounts of rotation and rotating components carrier processed by the corresponding amounts of rotation signal comprises: for each of the carriers, generating an initial amount of rotation which is at least in part a function of the frequency separation between two adjacent carriers, an extension channel delay, and a position of the carrier relative to other carriers within the received signal. rotating carrier components (1305) of the corresponding processed by the amounts of rotation signal; and iteratively adjust the amounts of initial rotation (1311) based on a comparison of rotated signals on different pilot frequencies with another (1307) and then again rotate the processed signal previously rotated by the set amount of rotation until it is satisfied a condition of iteration termination.