Subcarrier and power allocation in OFDMA systems

In this paper, we suggest subcarrier and power allocation algorithms to maximise rate-sum capacity in downlink and uplink orthogonal frequency division multiple access systems. The optimization problems for both links can be formulated with the same constraints other than the power constraints. For the downlink, it can be proved to be an optimal solution that each subcarrier is allocated to the user with the best channel condition whose power is determined by water-filling over subcarriers. A practical greedy subcarrier and iterative power allocation algorithm is proposed for the optimality. For the uplink, due to distributive power constraints in the optimization problem formulation, the optimal solution cannot be explicitly obtained. Thus, we propose efficient resource allocation schemes from the necessary conditions for optimal solutions: the subcarrier allocation based on water-filling. Simulations are intended to provide its superiority to various implementations in terms of the achieved capacity.