OFDM channel estimation in the presence of asynchronous interference

A frequency-domain channel estimation algorithm for a single-user orthogonal frequency division multiplexing (OFDM) wireless system in the presence of synchronous interference has recently been proposed in [1]. However, the interference cyclic prefix does not usually align with the desired user's cyclic prefix (i.e., the interferer is asynchronous) and thus a different approach is required. For an asynchronous interferer in a rich multipath environment, the received frequency-domain measurement is correlated in space with full-rank covariance matrix on each subcarrier. Therefore, the synchronous algorithms may give poor detection performance since they assume reduced rank interference and use smaller number of parameters. We overcome these problems by employing an appropriate structured model with properly defined number of covariance parameters. We estimate the interference covariance parameters using a residual method of moments (RMM) estimator and the mean (i.e., the desired user's channel) parameters by maximum likelihood (ML) estimation. Since the RMM estimates are invariant to the mean, we obtain simple non-iterative estimates of the covariance parameters while having optimal statistical efficiency. Numerical results illustrate the applicability of the proposed algorithm.