Carrier frequency offsets mitigation for broadband OFDM in a multiuser environment

OFDM (orthogonal frequency division multiplexing) is an enabling technology for multimedia wireless communications due to its ability in mitigating the effects of multi-path propagation. However, OFDM is sensitive to the carrier frequency offset (CFO), which destroys the orthogonality among sub-carriers and induces inter-carrier interference (ICl). When OFDM is employed in a multiple access scenario, with clusters of sub-carriers allocated to different users (often referred to as OFDMA). CFOs induced both ICI and MUI (multi-user interference), which result in significant performance degradation. In this paper, the CFU estimation methodologies for OFDM/OFDMA are first reviewed. We then present a scheme to compensate for the CFOs in OFDMA systems. In the proposed scheme, circular convolutions are employed to reduce the interference after the DFI (discrete Fourier transform) processing. The interference is then removed from the original received signal to reduce the MUl. Simulation results show that the proposed scheme can significantly improve system performance.