Orthogonal frequency division multiplexing (OFDM) is very sensitive to frequency errors caused by frequency differences between transmitter and receiver local oscillators. In this paper, this sensitivity is analyzed in terms of the complex weighting coefficients which give the contribution of each transmitter subcarrier to each demodulated subcarrier. Previously described windowing and self-intercarrier interference (ICI) cancellation methods are analyzed in terms of these weighting coefficients. New ICI cancellation schemes with very much improved performance are described. A condition for orthogonality of windowing schemes is derived in terms of the discrete Fourier transform (DFT) of the windowing function.