IEEE 802.11 Medium Access Contorl (MAC) is proposed to support aysncbronous and time bounded delivery of radio packets. Distributed Coordination Function (DCF), which uscs Carricr Sense Multiple Access with Collision Avodance (CSMA/CA) and binary slotted exponedn-fial backolf, is the basis of the 802. 11 MAC. This paper proposes a throughput enhacernent for DCF by adjusting the Contention Window (CW)setting scherne, Moreover, an analystial model based on Markov chain is introduced to compute the enhanced throughput. The accuracy of the modcl and the enhancement of the proposed scheme are verificd by elaborate simulations.