Achieving service differentiation in IEEE 802.11e enhanced distributed channel access systems

The IEEE 802.11e standard allows for contention-based quality of service (QoS) provisioning using enhanced distributed channel access (EDCA). By tuning the contention parameters for EDCA, the system can adapt to changes in the network scenario. The benefits of this adaptation include the ability to maximise the system capacity while also achieving the service differentiation necessary to provide QoS. The use of fixed sized contention windows is one simple and effective way to improve EDCA performance and this can be modelled as p-persistent carrier-sense multiple access (CSMA). In this study a straightforward throughput and delay analysis is provided for p-persistent CSMA that can be easily applied to an EDCA system within the rules of the current 802.11 standard. Several versions of the analysis are provided to show how further parameters of EDCA can also be included and their effects on system performance are shown. These further parameters include transmission opportunities, internal collision resolution, AIFS differentiation and retry limits. Any number and combination of these further parameters can be included at the same time making this new form of analysis extremely flexible as well as accurate to model a wide variety of EDCA system scenarios.