1. A method of processing a received signal, comprising: determining a first set of combining weights based on a first impairment covariance estimate derived assuming a low signal quality environment; determining a second set of combining weights based on a second impairment covariance estimate derived assuming a high signal quality environment; determining a metric corresponding to the difference between symbol estimates derived from the second set of combining weights and hard symbol decisions; and demodulating the received signal based on the second set of combining weights if the metric satisfies a threshold indicating high signal quality and otherwise based on the first set of combining weights.