The resource allocation algorithm to minimize the overall required transmit power while satisfying the QoS requirements of real-time services in OFDMA systems is discussed in this paper. We develop the concept of marginal utility for each subcarrier, which corresponds to the maximal power reduction when the very subcarrier is allocated to a user. We also propose a low computational complexity algorithm to calculate the marginal utility. Based on this, a novel subcarrier and bit allocation algorithm is presented. In order to achieve the minimization of overall required power, the subcarrier with the largest marginal utility is assigned to its corresponding user at each subcarrier allocation iteration. Part of the bits required by the user are then redistributed to the newly assigned subcarrier by the proposed marginal utility calculation algorithm. Simulation results show that the proposed algorithm can achieve a better performance than Zhang's algorithm [6] at approximately the same computatotional complexity.
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