A method in a network node in control of a cell in a cellular telecommunication network for reducing intra-cell interference between user equipments (UE) residing in said cell and performing random access (RA). The method comprises the steps of arranging groups of preamble sequences where the sequences within each group are orthogonal to each other, assigning one such group to the cell, from which group the UEs performing RA randomly selects a preamble, and assigning one or more additional group(s) of preamble sequences to said cell if the RACH or traffic load exceeds a certain threshold. The invention further relates to a radio network node in a cellular telecommunication system, capable of carrying out said method.