Research On QoS Support Of IEEE 802.11e WLAN

With the increased popularity of wireless broadband networks and the growing demand for multimedia applications, there is a need to support diverse multimedia services over the wireless medium.To achieve the goal, IEEE Std. 802.11eTM, is published on Nov.2005 after years of research, and provide guidance to implement QoS Guarantees.The IEEE802.11e introduces a hybrid coordination function (HCF), which comprises two access mechanisms contention-based EDCA and contention-free HCCA. Scheduling in IEEE802.11e WLANs is considered the core function of the HCCA access, and the IEEE802.11e standard has introduced a reference scheduling algorithm. From the evaluation report of referenced scheduling algorithm provided in IEEE802.11e, we know that it does not perform well on traffic which is not strictly CBR. Moreover, having a fixed service interval where all flows have to be polled may not be adequate as some traffic sources generate data bursts periodically, while others generate data bursts sporadically. Therefore, it need to design a more flexible scheme to overcome these drawbacks in the reference scheduling algorithm coupled with the emergence of real-time and multimedia application.In this thesis, Prediction Selectivity Scheduling (PSS) scheme is proposed for these drawbacks of referenced scheduling algorithm. The PSS scheme aims at providing Quality of Service (QoS) assurance for different traffic types such as delay bound and throughput while maintaining fairness among flows and accommodating fluctuations of real-time applications. The PSS scheme calculates the TXOP for admitted traffic streams based on mean sending data rate prediction and the online observed PHY rate. The PSS scheme can dynamically adjust the prediction of TXOP allocated to the QSTA with different characteristics of applications and the fluctuations of channel quality. Moreover, the PSS scheme incorporates a selectivity function (SF) that differentiates between traffic streams and assigns polling priorities accordingly.PSS scheme appropriately calculates variable service interval lengths depending on actual traffic conditions. Simulation results indicate that the PSS scheme achieves better system performance in terms of mean delay and throughput and low packet drop ratio and fairness between different classes against reference scheduling algorithm , succeeds in providing QoS assurance for both constant bit rate (CBR) and variable bit rate (VBR) traffic.