The present invention relates to frequency hopping in wireless communication systems utilizing single-carriers with varying bandwidth. Frequency hopping is made possible by dividing the available bandwidth, associated to the available frequency spectrum, in a leveled structure, a bandwidth tree. By the use of a frequency hopping tree, which has the same structure as the bandwidth tree and wherein each leaf represent a hopping sequence, a frequency hopping scheme is determined. Orthogonality in-between the frequency hopping schemes for different users is ensured by letting a users hopping sequence value at a level n, be dependent on the hopping sequence value associated to the same branch structure on the adjacent level closer to the root of the tree, n−1, and an input sequence associated with the level n.