Performance Analysis On MAC Protocol For Ad Hoc Network And Improvement Of Backoff Algorithm

Mobile Ad Hoc Network is a complex distributed system composed of wireless nodes which have enough intelligence to consecutively intercept,seek for other nodes,determine best transmission path of the data packet dynamically make and transmit it hop by hop.Ad Hoe network,which is not bound by the cable networks,does not need the fixed infrastructure and has the charateristics of efficiency,flexibility.So it has broad application prospects in the military and disaster rescue which is a very active research area in recent years.First,it's presented a review of Ad Hoc MAC layer protocols which has detail analysis of the problems in designing MAC protocol and the corresponding solutions.It's discussed the rationale,Markov performance model of IEEE 802.11 DCF and is proposed the unfairness of BEB back-off algorithm among the nodes derived from theoretical model.Second,it's analyzed the principle of the back-off mechanism,characteristics of MILD,SD,FCR and the problems needed to be improved.It's presented a new algorithm of SMFCR fusioned of algorithms above.It reduced problems between throughput and faimess in IEEE802.11 BEB algorithm by adjusting the window size.It's explored the MAC mechanism of differentiated service which adopted SMFCR back-off principle in 802.11e based on EDCF.The mechanism can satisfy the demand of realtime multimedia transmission in Ad Hoc.Finally,it's presented the modification and realization of BEB algorithm by NS2 to verify the algorithm proposed above.The simulation showed that the improved algorithm has better performance and has good potential in applications.