Frequency-domain oversampling for OFDM systems: Exploiting inter-carrier interference and multipath diversity

By using frequency-domain oversampling, we propose a frequency-domain fractionally-spaced linear minimum mean-square error (FDFS-LMMSE) receiver for orthogonal frequency-division multiplexing (OFDM) systems. The proposed FDFS-LMMSE receiver is shown to significantly outperform the conventional LMMSE receiver (without oversampling) in multipath fading channels. This is because the FDFS-LMMSE receiver is able to exploit multipath/frequency diversity inherent to the channel to improve performance. Next, based on a Gaussian approximation to inter-carrier interference (ICI), we present a semi-analytical performance analysis for the FDFS-LMMSE receiver. The accuracy of the theoretical analysis is confirmed by simulations. Finally, we study the effect of the oversampling factor on the system performance, aiming at finding an optimal oversampling factor in terms of both performance and complexity. It is found that the optimal frequency oversampling factor, usually much smaller than 2, is determined by the number of subcarriers and the number of multipath components.