Abstract: In an OFDM receiver, a synchronisation pulse for defining a Fast Fourier Transform window is generated by examining the output of a correlator to find a sub-interval within which there is maximum correlation between samples of the symbol separated by the length of the useful part of the symbol. The synchronisation pulse is generated during this sub-interval (102). Adjustments to the timing of the synchronisation pulse are made only if the current error is significant and persistent. A signal representing the amount of adjustment is used to determine phase rotations applied to the output of the FFT circuit.

Abstract: A filter, in which digital representations of a signal are stored as samples in a store (8) preferably in the order of their occurrence. Multipliers (9) multiply the samples by coefficients (C1 to C36) representing a function with which the samples are to be convolved. To compensate for the variable time delays in the signal, sets of coefficients representing the function with different time delays are stored. The set to be convolved with the signal is chosen in dependence upon the time delay of the signal. A signal indicative of the time delay is derived from an input to the shift register and fed-forward. The filter is preferably used in a digital demodulator of phase and/or amplitude modulated signals. The function is then an impulse function defining (at least in part) a desired frequency response of the filter, and the filter corrects the timing of symbols represented by the signal.