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Many modifications are proposed in the literature to improve the throughput performance of the distributed coordination function (DCF) under congested environments. These improvements are achieved by modifying the contention-window reset mechanism used in the DCF protocol. However, the main drawback with these modifications is the high backoff process overhead. We have recently proposed a new modification to DCF (N-DCF) to improve the throughput performance by reducing the average backoff overhead. In this paper, we propose a throughput model for N-DCF, which is applicable for arbitrary load conditions. We verify the throughput model by NS-2 simulations. Then, we compare the performance of N-DCF with other recently proposed DCF enhancements in the literature. Comparisons reveal that only N-DCF provides throughput improvement in the request-to-send/clear-to-send access mechanism. Finally, we propose two more schemes to further improve the performance of our original N-DCF scheme.