Asymptotic performance evaluation of space-frequency MMSE filters for OFDM

This paper proposes and analyzes two different linear space-frequency architectures for the reception of OFDM-modulated signals: the classical sample matrix inversion (SMI) algorithm and a new architecture that maximizes the output signal-to-interference-plus noise ratio (MSINR). The performance of these two linear receivers is compared in terms of asymptotic output SINR, taking into account the finite sample size effect through the asymptotic covariance of the filter weights. The analysis is asymptotic in the sense that the performance is analyzed, assuming that both the number of carriers and the prefix length of the OFDM signal increase without bound at the same rate, whereas their quotient remains constant. Assuming that the carrier frequencies become asymptotically close to one another, we are able to derive explicit equations that shed some light on the influence of the frequency selectivity of channel and interference on the relative performance of the two approaches. The results are useful in the sense that they provide first-order approximations to the (asymptotically) optimum number of adjacent carriers to be processed by a single beamformer in a finite sample size situation.