| WirelessAdHocnetworkisamulti-hopandtemporallyself-rulesystemcomposedby a group of mobile nodes such as router with many terminals and mobilecommunicationequipments. It canbeusedinmanyenvironments, forexample,military,law executing, and disaster rescuing fields. Ad-hoc has increasingly become a veryactiveresearchfiledinrecent years.In these MAC protocols, theyhave different kind of advantage. But the main pointaffecttheperformanceishideorexposureterminal,andtheequitableness.Baseoftheseproblems we have comfortable solution. In this paper we research on IEEE 802.11which adopted as a standard of MAC level in Ad Hoc network. At the basis of anyaccess to the channel in IEEE 802.11 is the so-called distributed coordination function(DCF) which adopted BEB algorithm. DCF has an advantage in increasing the networkthroughput, but it can bring unfair among different nodes. MILD and MIMLD improvethe network in different parts, and improve the fair channel access. But the throughputof the network should be improved. So in this paper, we bring forward a new backoffalgorithm (EMIMLD), insert an new concept which named Average ContentionWindow (E[CW]).This algorithm aims to achieve fair channel access withoutknowledge of the network topology, self adapting to changes in the traffic load as wellas topological changes in the network. Through adjust time interval and window size,decreasetheissueencountedinIEEE802.11.To validate the algorithm, we analyze the implementation of MAC layer in Opnetsimulation system and paymore attention to the implementation of BEB algorithm. Wechange BEB algorithm with improved algorithm, simulate the two algorithmsrespectively and implement the simulation work. Based on the simulation results, weanalyze and compare two performance parameters of network, fairness index andthroughput. The analysis presents that his algorithm improves the throughput anddecrease the delayin Ad Hoc network. And maybe this algorithm has more implementsinfuture. |
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