A method of signalling resource allocation data in a communication system which uses a plurality of sub-carriers arranged in a sequence of chunks. An allocation of the sub-carriers for each of a plurality of user devices is received. The received allocations are processed to determine, for each user device, data identifying a start chunk and an end chunk within the sequence of chunks, which depend upon the sub-carriers allocated to the user device. Different resource allocation data is generated for each of the user devices using a predetermined mapping which relates the data identifying the corresponding start chunk and end chunk determined by the processing step to resource allocation data comprising a unique value. The respective resource allocation data is signaled to each of the plurality of user devices.