| WLAN (Wireless Local-Area Network) is the production of computer network and wireless communication technology. Comparing with the traditional wired network, wireless network has the advantages of high effectivity and full flexibility. WLAN guarantees the QoS (Quality of Service) of the traffic flows by MAC (Medium Access Control) layer in the network system. Since the increase of the users' demands, the former IEEE 802.11 standard can not fulfill the requirement any more .Then the IEEE 802.11 E-task Group presents the IEEE 802.11e standard which can ensure the QoS of the network system. IEEE 802.11e EDCA (Enhanced Distributed Channel Access) standard introduces a new conception of prioritization. In the network system, different AC (Accessing categories) takes different system parameters for accessing channel. When a collision occurred in a period, the system will lose the low-priority packet and transmit the high-priority packet to assure the QoS of the system.First, this work expatiates on the theory of the WLAN 802.11e EDCA and analyses the advantages of ensuring the system QoS compared with 802.11 DCF.Second, this paper presents Markov chain model for the EDCA with Markov chain analysis method, which takes into account both the competition between the nodes and the internal scheduler when contentions occur in the node. System throughput, packet lost and packet delay analysis for different ACs in the collision period are also analyzed.At last, this paper presents the IEEE802.11e EDCA network system simulation on the NS2 simulation platform with the tools of Tcl, Gawk and Gunplot, while considering the effect on the system throughput, packet lost and packet delay by changing nodes number, data rate and the CW parameters in the simulation. This paper also presents the simulation and the analysis theory of complex 802.11e network which has the features of multi-transference and multi-path. Simulation results validate the validity of that simulation and the analysis theory. |
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