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The IEEE 802.11a can provide up to 54Mbps data rate and the IEEE 802.11n provide much higher data rates by the supporting PHY layer technique such as MIMO (Multiple Input Multiple Output). However, the medium access control of IEEE 802.11 WLANs were designed for low data rate such as 2Mbps. So, in high data rate WLANs, IEEE 802.11 WLANs are not efficient. Due to fixed overhead (control frames, preamble, and PLCP header are transmitted low data rate and IFS time is fixed irrespective of transmission rate), increasing of data transmission rate is not easy. To reduce fixed transmission overhead, frame aggregation has been proposed. However, in a noisy channel environment, frame aggregation leads to longer frame and it may be provoked transmission errors. In this paper, we propose the Dynamic Frame Aggregation (DFA) scheme. The DFA can aggregate frames according to channel condition properly. And the DFA works based on optimal pair of transmission rate and transmission frame length. So the DFA can avoid transmission errors and reduce transmission overhead simultaneously. The performance of the proposed scheme is evaluated by analytic modeling. The results show that the DFA provides better throughput than the frame aggregation scheme.