1. A method of estimating impairment covariance associated with a first 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 a first impairment model comprising at least first and second model terms corresponding to the first and second antennas respectively, wherein the model terms capture propagation channel effects and are independent of the first antenna weighting vector, and wherein the first impairment model omits cross-antenna interference terms; and computing a first parametric estimate of the impairment covariance, using the first impairment model, by calculating the first and second model terms as a function of propagation channel estimates corresponding to the first and second antennas, respectively, measuring impairment covariance or data covariance associated with the received composite information signal, and estimating values for two or more unknown parameters of the first impairment model using the measured impairment covariance or data covariance and the computed first, second, and third model terms.