Mobile connectivity these days is no more a privilege but a basic necessity. This has led to exponentially-increasing data rate demands over the network, causing tremendous pressure to the access network service planners. Orthogonal frequency division multiple access (OFDMA) is being considered for resource allocation in higher generation communication networks, where spectrum efficiency improvement while fulfilling the users' data rate demands is a key aspect of interest. Normally resource allocation is considered from the viewpoint of users, with the users selecting their best available subcarriers. In this chapter, the resource allocation problem is approached from the subcarrier's perspective. Besides the conventional user-based scheme, a recent subcarrier-based shared resource allocation scheme is presented that selects the best user(s) for each subcarrier and assigns the subcarrier either to a single user or more than one user on time-shared basis according to their current SNRs. Unlike the user-based schemes, in the proposed scheme each user can contend for any subcarrier.
