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The margin adaptive problem for the downlink of Orthogonal Frequency Division Multiple Access is tackled in this work. A subcarrier allocation algorithm is presented, which formulates the issue of subcarrier allocation as a combinatorial auction, where the base station auctions the OFDM subcarriers and the users compete for their allocation. A major feature of the proposed algorithm is its distributed nature, since each user decides independently which subcarriers to bid for, informs the base station for his preferences, and the base station is the entity that makes the decision on the allocation, based on power criteria. The presentation of the algorithm is followed by a series of simulations. The simulations indicate that the performance of the proposed algorithm approaches the performance of the optimal, Hungarian algorithm: the offered bit rate is at least 98.77% of the optimal while the transmit power lies within the range 0.20dB-1.62dB higher than the optimal one. Additionally, based on execution time measurements, it is shown that the necessary execution time is much lower than that of the optimal algorithm, indicating thus a much lower computational complexity.