Efficient encoding techniques are described for encoding resource allocation data to be signalled to a number of user devices in a communication system. In one encoding technique, a resource allocation bit pattern is transmitted to all the users together with a resource ID for each user. Each user then identifies its allocated sub-carriers using the received allocation bit pattern and the received resource ID. In another encoding technique, a code tree is used to generate a value representing the sub-carrier allocation. The user device then uses the code tree to determine the sub-carrier allocation from the signalled value.