A method of operation of a filter (12) of a receiver (10) of a mobile station or a base station of a radio access network and corresponding equipment, the method for use in suppressing co-channel interference and based on separating the in-phase (I) and quadrature phase (Q) components of the received signal and then performing whitening on a symbol-by-symbol basis, i.e. the whitening operation is done within one symbol. The invention provides a filter (12) including a module (12b) for performing IQ whitening (either according to the invention or otherwise), and also provides a switch (12a) that can be used to enable or disable IQ whitening, depending on the character of the received signal, and in particular based on the noise plus interference correlation matrix ({tilde over (R)}_ii)