The orthogonal frequency division multiplexing(OFDM) systems can be extended to the multi-user case by the OFDM-FDMA multiple access scheme. The multi-user OFDM systems require accurate carrier frequency synchronization for all users in order to avoid inter-carrier interference (ICI). But on the uplink of OFDM-FDMA scheme, frequency offset is necessarily induced and degrades the receiver performance because the signals come from different sources. To alleviate the performance degradation by frequency offset, we propose a new carrier frequency offset compensation algorithm for OFDM-FDMA systems. In OFDM-FDMA systems, frequency offset for each user signal can be estimated by conventional frequency offset estimation techniques for OFDM. The proposed algorithm compensates for ICI by frequency offset using frequency domain filters whose tap coefficients are obtained from estimated frequency offset. The proposed algorithm is simplified by shortening the number of frequency domain filter tap. The computational complexity is computed for both the proposed algorithm and its simplified scheme and it is shown by computer simulations that both algorithms improve signal to interference ratio(SIR) and BER performance under the WATM environment.
