Combining weights are calculated in multiple stages based on an overall system impairment covariance matrix and a grouping of signal processing delays. Computing the combining weights in multiple stages avoids having to invert the entire system impairment covariance matrix. Instead, smaller matrix inversions are performed. In one embodiment, a received signal is processed by calculating an impairment covariance matrix for a set of processing delays used to derive a plurality of signal values from the received signal. A set of intermediate combining weights is calculated for each of at least two different subsets of the processing delays based on the impairment covariance matrix. The signal values derived across the subsets of processing delays are combined using the sets of intermediate combining weights and the impairment covariance matrix.