Analysis and enhancements of MAC protocol considering QoS in IEEE 802.11 wireless LANs

Abstract

IEEE 802.11 wireless LANs equipments have been widely deployed and the do-. mands are increasing rapidly. Basically, medium access control(MAC) protocol of the IEEE 802.11 standard is consisted of two different schemes, which are centralized medium control scheme called as point coordination function(PCF) and distributed medium control scheme called as distributed coordination function(DCF). The DCF scheme is based on a carrier sense multiple access with collision avoidance(CSMA/CA). The quality of service(QoS), which is not considered in original DCF scheme, will be important issue since multimedia traffics need different requirements. Hence, the new IEEE 802.1le standard is developed to support QoS. Enhanced distributed channel access(EDCA) scheme is an enhancement of the DCF scheme providing different access parameters according to access categories(ACs). EDCA scheme has four ACs and each AC has its own minimum and maximum of contention window and arbitrary interframe space(AIFS), which discriminate each AC``s access probability. In this dissertation, we have studied and analyzed MAC protocol focusing on DCF scheme and EDCA scheme considering voice and data services. First, we analyze throughput and delay performance in DCF scheme and compare the numerical results with simulation evaluations using IEEE 802.11a and IEEE 802.1lb physical layer parameters. In addition, the performance differentiation between EDCA stations and DCF stations when they are coexisting, is analyzed and it is shown that the numerical results from analysis are very close to simulation results. Second, we consider voice service through wireless LANs. The voice service via voice over IP(VoIP) has become important because it provides low cost and high capacity solution particularly at office environment. The maximum voice capacity in case of no data stations is analyzed and evaluated in consideration of duplex VoIP traffic generations. And the impact of legacy DCF data stations on voice c...