In a cellular wireless communications network, measurements are received from a plurality of user equipments relating to the reference signal received powers from a plurality of other cells of the cellular wireless communications network For other cells of the cellular wireless communications network having a physical cell identity (such as a scrambling code) that is the same as a physical cell identity of that first cell, it is determined from the received measurements whether a mutual potential interference level with that cell exceeds a threshold If so, an alternative physical cell identity is proposed, that would cause a mutual potential interference level between the cell or the potentially interfering cell and another cell already using that alternative physical cell identity that is lower than the mutual potential interference level between the cell and the potentially interfering cell.