1. A method of estimating impairment covariance associated with a received composite information signal comprising at least a first data stream transmitted from first and second antennas according to a first antenna weighting vector, the method comprising: constructing an impairment model including one or more model terms scaled by corresponding scaling parameters, wherein the model terms capture propagation channel effects and are independent of the first antenna weighting vector, and wherein the scaling parameters capture effects of the first antenna weighting vector; and computing a parametric estimate of the impairment covariance using the impairment model.