A cellular communications system includes a plurality of base stations and a plurality of user devices. In use, each user device is associated with a base station and is operable to communicate with the associated base station over a communication channel having a plurality of frequency resources. Each user device has a respective initial allocation of said frequency resources. Each user device is operable to apply a frequency shift to its initially allocated frequency resource in accordance with a frequency hopping sequence. The user devices that are associated with the same base station are operable, in use, to use the same frequency hopping sequence and are synchronized with each other so that, at any point in time, a common frequency shift is applied by the user devices associated with the same base station. User devices associated, in use, with different base stations use different frequency hopping sequences.