Performance Evaluation for Sum Capacity in OFDMA Systems with Proportional Fairness

The challenge of resource allocation which consists of both power and sub channel allocations on the downlink OFDMA system is studied in this paper. Shen et al proposed a power allocation method that is dependent of Lagrange multipliers but a complicated root finding method is involved [1]. To avoid complicated calculation in root finding, we develop new expressions for optimal power with three power initialization schemes for all users and sub-channels. The other merit of these new expressions is that all Lagrange multipliers can be obtained directly without using a sub gradient method and hence optimal power can be rapidly obtained. Computed results show that the proposed method consistently yields higher sum capacity as compared to [1] but there is a minor degradation of proportional fairness. This situation involves a trade-off between system capacity and proportional fairness.