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The promise of high speed (over 1Gbps) wireless transmission rate at the physical layer can be significantly compromised with the current design in 802.11 DCF. There are three overheads in the 802.11 MAC that contribute to the performance degradation: DIFS, random backoff and ACK. Motivated by the current progress in OFDM and self-interference cancellation technologies, in this poster, we propose a novel MAC design called REPICK (REversed contention and PIggy-backed ACK) to collectively address these problems. The key idea in our proposal is to take advantage of OFDM subcarriers in the frequency domain to enhance the MAC efficiency. Specifically, in REPICK, we propose a novel reverse contention algorithm which enables receivers to contend for channel access with subcarriers in the frequency domain (reversed contention). We also design a mechanism which allows ACKs from receivers to be piggy-backed through subcarriers together with the contention information (piggy-backed ACK). We demonstrate REPICK's efficiency through both analysis and simulations.