17. A wireless communication apparatus, comprising: an impairment correlation estimator configured to determine a composite impairment correlation term associated with a received signal from a set of modeled impairment correlation terms; and circuitry configured to select a subset of the modeled impairment correlation terms by selecting the modeled impairment correlation terms having N largest model fitting parameters, wherein N is a predetermined positive integer and to direct the impairment correlation estimator to determine the composite impairment correlation term based on the subset of modeled impairment correlation terms.
17. A wireless communication apparatus, comprising: an impairment correlation estimator configured to determine a composite impairment correlation term associated with a received signal from a set of modeled impairment correlation terms; and circuitry configured to select a subset of the modeled impairment correlation terms by selecting the modeled impairment correlation terms having N largest model fitting parameters, wherein N is a predetermined positive integer and to direct the impairment correlation estimator to determine the composite impairment correlation term based on the subset of modeled impairment correlation terms. 37. The wireless communication apparatus of claim 17 , wherein the impairment correlation estimator is further configured to form the set of modeled impairment correlation terms by combining similar modeled impairment covariance terms into respective combined impairment covariance terms.