A wireless communication system is comprised of multiple radio access networks—RANs—which at least partly share the same frequency spectrum. Each RAN is provided with a gateway—GW—(GW1, GW2, GW3) for managing the network. Spectrum sharing in the system is achieved through a hierarchy of processes including long-term—LT—spectrum assignment, short-term—ST—spectrum assignment, and dynamic channel allocation, the latter process assigning sub-channels to base stations (BS1, . . . BS5; BS6, . . . BS10; BS11, . . . BS16) in each RAN. However, so-called “red” sub-channels (subject to interference) are liable to arise.