A set of specific sequences comprising a set of root sequences and cyclic shifts thereof is searched, wherein it is started from a root sequence index indicating a root sequence of ordered root sequences, available cyclic shifts of the root sequence are included, and it is continued with a next root sequence if necessary for filling the set, wherein the ordered root sequences are obtained by ordering sequences of a predetermined length and number in accordance with cubic metric of each of the sequences and a size of a high mobility cell each of the sequences supports.