1. A method of determining a composite impairment correlation term associated with a received signal from a set of modeled impairment correlation terms at a wireless communication apparatus, comprising: selecting a subset of the modeled impairment correlation terms using circuitry included in the wireless communication apparatus by selecting the modeled impairment correlation terms having N largest model fitting parameters, wherein N is a predetermined positive integer; and determining the composite impairment correlation term based on the subset of modeled impairment correlation terms using an impairment correlation estimator included in the wireless communication apparatus.