A novel subcarrier and bit allocation algorithm for multiuser OFDM system is presented in this paper. The algorithm aims to achieve a maximum transmit rate subject to the overall transmit power constraint and user rate proportionality constraint. The algorithm consists of two steps. In the subcarrier allocation step, the power is assumed to be uniformly allocated on each subcarrier and the subcarriers are allocated to users under the proportional rate constraint. Then, at each bit assignment iteration of the bit allocation step, the algorithm assigns one bit to the user with the least normalized transmit rate and the user greedily allocates the bit and corresponding power to the subcarrier which requires the least additional power to carry one more bit. The computational complexity of the proposed algorithm is analyzed, as well as the fairness performance. Simulation results show that the algorithm can achieve a better performance than the existing algorithms.
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