A method and apparatus is provided for performing initial ranging at a receiver for establishing a time reference for a predefined received signature signal (30) for establishing a time reference overcoming round trip time between a receiver and a transmitter. There is performed (316, 3161) matched filtering in at least two matched sub-filters (M1, M2, M3, M4), each sub-filter having a matched filter sub-sequence (43—1, 2; 3, 4; 5,6; 7,8) corresponding to a fragment (39) of the basic sequence (33) of the predefined signature signal (30), wherein the fragments do not overlap one another with respect to the basic sequence, the matched filtering by each respective sub-filter providing peaks in dependence of the respective sub-sequence (43) correlating with a respective fragment of the received signature signal.