Residual frequency offset compensation for IEEE 802.11a

We propose residual frequency offset estimation using outputs of an equalizer and a decoder. Since orthogonal frequency division multiplexing (OFDM) is sensitive to the carrier frequency offset, carrier frequency offset estimation should be performed to keep the orthogonality of received signals. Even though most systems compensate the frequency offset with initial training sequences, there still remains a frequency offset because of the estimation error. The proposed algorithm utilizes the phase differences of two consecutive symbols which are acquired at the equalizer and the decoder outputs. Compensating the residual frequency offset in every symbol, the residual frequency offset is reduced to a negligible level and the system performance is greatly increased. The mean of the residual frequency offset with the proposed algorithm is below 500 Hz, which does not degrade the performance of IEEE 802.11a receivers. And its variance is below 10^-8.