Wireless Local Area Network Mac Protocol Of Ieee802.11 E Performance Optimization

Wireless Local Area Network (WLAN) is a network which relys on the wirelessmedium to make different terminal to communicate with each other, and it is theproduct of computer network and mobile communication technology. People have paidmuch attention to WLAN from it coming out, especially after IEEE802.11standard hasbeen issued for enforcement, WLAN is extensively applied owing to its efficiency,agility, and low price.With the success of WLAN, it is hoped to supply multimediaapplications such as voice and video by people. The multimedia applications havehigher reqirements for quality of service, but channel efficiency of WLAN is poor,which is difficult to test and control collisions, so WLAN cannot satisfy these needs. Toachieve the goal, IEEE Std.802.11eTMis published in2005, which can provide guidanceto implement QoS Guarantees.Based on Distributed Coordination Function (DCF) and Point CoordinationFunction (PCF), Hybrid Coordination Function (HCF) is proposed by IEEE802.11e.HCF consist of a contention-based channel access method, called the EnhancedDistributed Channel Access (EDCA) mechanism for prioritized QoS services, and acontrolled channel access method, referred to as the HCF Channel Access (HCCA)mechanism for parameterized QoS services. In EDCA mechanism, business is dividedinto four Access Categorys (ACs), which has different QoS level. The chance to get thechannel is different for different ACs, which implement priority differentiated service.In HCCA mechanism, Access Point (AP) negotiates with stations, allocate TransmissionOpportunity (TXOP) to allowed stations. HCCA make specific buissness in each stationto get service without competition.Based on the standard EDCA and HCCA mechanism, some improved algorithmsare proposed in the thesis. In EDCA mechanism, Competition Window (CW) for eachstation is a static set value, so it wastes some network resource for collision. In thisthesis, we propose a dynamic adjustment algorithm according to the network status. Thealgorithm according to the stations’ collision in the network situation to infer currentnetwork load conditions, and reset current CW with the value, which causeses the stations’ collision probability reduce, improves the network throughput.In order toanalyze the validity of this algorithm, we compare CB-EDCA with Half-CW algorithm,which halve the CW, the result show that Half-CW algorithm is a specific case ofCB-EDCA algorithm.The traditional HCCA mechanism with fixed service interval (SI) and TXOP,which make accepted user less, and dealing with variable bit rate (VBR) businesspoorly. The improved algorithm is put forward in this thesis, HCCA according to user’sdifferent SI need to set common SI, and according to the loss rate of VBR business toadjust TXOP value dynamicly.This algoritm ensure customer QoS based on theincreased number of users can be hold, so network performance has been improved.