Fractionally Spaced Frequency-Domain MMSE Receiver for OFDM Systems

Based on frequency-domain oversampling and the Bayesian Gauss–Markov theorem, we propose a fractionally spaced frequency-domain minimum mean-square error (FSFD-MMSE) receiver for orthogonal frequency-division multiplexing systems. It is shown that frequency diversity inherent in a frequency-selective fading channel can be extracted and exploited by the proposed FSFD-MMSE receiver. This diversity advantage outweighs the effect of intercarrier interference generated by frequency-domain oversampling, due largely to the MMSE receiver's interference suppression capability. Numerical results show that the FSFD-MMSE receiver outperforms the conventional MMSE receiver under both ideal and practical situations (i.e., with frequency offset, channel estimation errors, and even doubly selective channel fading). In addition, the FSFD-MMSE receiver only needs a fast Fourier transform size that is no larger than
$N + Q - 1\ (N = \hbox{number of data subcarriers, and} \break Q = \hbox{number of resolvable multipath components})$
.