A method and a receiving node for determining a channel window length (l{circumflex over ( )}) for a transformed domain channel estimator, the channel window length (l{circumflex over ( )}) to be applied for a particular reference signal (RS) carrying symbol. At least two subsets (A1, A2, . . . ) of received RS carrying symbols are obtained out of a set of RS carrying symbols ({S1, S2, . . . }), where the particular RS carrying symbol is included in at least one of the at least two subsets (A1, A2, . . . ). A corresponding hypothesis channel window length (l*) is determined for the at least one of the subsets (A1, A2, . . . ) based on a set of channel responses. The channel window length (l{circumflex over ( )}) for the particular RS carrying symbol is then determined based on the corresponding hypothesis channel window length (l*).