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In the IEEE 802.16 recommendations family, the adjacent method for construction of the subchannel is adopted. In order to reduce the system complexity, the available subcarriers are grouped into equal groups of contiguous subcarriers, where each group is called a subchannel. The adaptive modulation and coding schema, AMC, is used in order to maximize the number of bit per symbol. In this case, subcarriers of subchannel present different SNR and the fundamental question is how to choose the best AMC for each subchannel. In this paper, an enhancement algorithm is proposed to response at this question in the context of Orthogonal Frequency Division Multiple Access, OFDMA, wireless systems in the downlink sense. The scheduler located at the base station computes subchannel gain based on the responses frequency dispersion, then the quality of the channel. This gain has a great importance in resource management. Numerical results show that the proposed algorithm outperforms an allocation scheme in terms of a lower BLOC Error Rate (BLER) and a higher system Capacity, compared to others methods.