An Improvement Protocol Of WLAN MAC Based On Fuzzy Logic Control

With the development of wireless technique and Internet, the application of WLAN grows step by step, especially multimedia operations such as video, voice and image. The different services need different network performances .Such as the video and voice service are very sensitive to delay and delay jilter, but are tolerant of the data lose. In contradiction to that, requirements of data service on delay and jitter are not very high, but the data service is very sensitive to the loss of the data itself and error.Compared with lineate network,WLAN has many inherent shortcomings such as a volatile link,low broadcast velocity. And in the Media Access Control layer,all notes in the same communication area need share the channel. So the probability of collision is very big, this will bring on heavy delay. Therefore the delay of MAC layer is an important parameter affecting the whole network performance. IEEE802.11 media access control mechanism on the support is extremely limited. Improving service quality and supporting multi-service are the critical and urgent issues that will directly impact on WLAN further development.In this dissertation, the QoS of WLAN and the protocol of IEEE802.11 and IEEE802.11e are intensively researched.IEEE802.11 DCF use CSMA/CA mechanism to coordinate access to the media, does not distinguish between type of service. So it cann't meet the voice , video and other business requirements. Although IEEE802.11e distinction between business priorities, but it can not adapt with service type and network changes in the environment.Based on the DCF protocol of IEEE802.11, considering the current network environment and the complex diversity of business types, the dissertation quotes principle of fuzzy logic control. There are two advantages. One is that it can simplify the changes to the protocol. The other is more important that the new MAC can adjust the MAC layer parameters adaptively to make the network and business get best performance. In the improving agreement, compare the channel's current performance with the business requirements. The results are as the input variable of the fuzzy logic controller. The fuzzy logic criteria is designed by different service ,and the corresponding MAC access parameters are made to obtain QoS guarantee. The minimum backoff window(CWmin) and the number of retransmission of the MAC (Nretry)are important parameters influencing the network performance. So in the paper, the minimum backoff window(CWmin) and the number of retransmission (Nretry)of the MAC are as access parameters to differentiate service.