The disclosure relates to wireless networks, and particularly a method and apparatus for assigning carrier frequencies to base station antenna sites. Base stations are represented as a matrix of interconnected nodes and links, the nodes representing carrier frequency sites and the links being dimensioned in accordance with disallowed frequency slots. A first algorithm is used to assign carrier frequencies to the carrier frequency sites in a non-interfering manner resulting in a partial frequency assignment plan (3309). A second algorithm assigns carrier frequencies to the remaining vacant carrier sites in a manner which seeks to minimise the amount of interference. The order in which the carrier sites are assigned carrier frequencies is determined by either a random ordering, an order generated by simulated annealing, or an ordering generated by a genetic algorithm. A quality measure is generated from the resultant frequency plan (3411) and is used to modify the order in which the frequencies are assigned to carrier site nodes in subsequent iterations.