A distributed wireless MAC scheme for service differentiation in WLANs.

Mobile communications is evolving due to the recent technological achievements in wireless networking. Today, wireless networks exist in many forms, providing different types of services in a range of local, wide area and global coverage. The most widely used WLAN standard today is IEEE 802.11. However, it still has problems with providing the QoS required for multimedia services using distributed methods. In this thesis, a new distributed MAC scheme is proposed to support QoS in wireless LANs. In the scheme, stations use CSMA for channel access, with collisions between stations being resolved by sending a set of beacons in a predefined manner, and virtual collisions being resolved by schedulers at the stations. The proposed MAC scheme is analyzed mathematically, for two-priority case, and the results obtained are validated by simulation. The mathematical model estimates the average delay experienced by data packets of priority one and two under different conditions. A performance evaluation study of the proposed MAC scheme as well as the IEEE 802.11 DCF, and IEEE 802.11e EDCF MAC schemes is also done by means of stochastic simulation. It is found that the results obtained by simulation are in very good agreement with the analytical results, thereby validating them. Moreover, the simulation study evaluated different performance measures of these MAC schemes. The results showed that the IEEE 802.11 DCF scheme does not support QoS, but the proposed MAC scheme and the upcoming IEEE 802.11 EDCF both do. In general, the results show that the proposed MAC scheme performs equally or better than the current IEEE 802.11 DCF scheme in every case considered. It is also found that the proposed MAC scheme performs equally well as the upcoming IEEE 802.11e EDCF scheme, in every case considered in this thesis