Scheduling in IEEE 802.11e networks with quality of service assurance

Abstract

Wireless Local Area Networks (WLANs) have gained popularity at an unprecedented rate, at home, at work and in public hot spot locations. In this thesis, a Selectivity Function Scheduler (SFS) is proposed for IEEE 802.11e WLANs. The SFS 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 SFS defines several functionalities that accurately analyze and compute the number of data frames at each traffic stream’s transmission queue, and allocate adaptive transmission opportunities (TXOPs) to traffic streams based on online observed physical rate instead of minimum physical rate. Moreover, the SFS incorporates a selectivity function (SF) that differentiates between traffic streams and assigns polling priorities accordingly. SFS appropriately calculates variable service interval lengths depending on actual traffic conditions. The SFS scheme is evaluated under different mixes of traffic and for various characteristics of the IEEE 802.11e and compared with the performance of the standard scheduler. Simulation results indicate that the SFS scheme achieves better system performance in terms of high throughput and low packet drop ratio, succeeds in providing QoS assurance for both constant bit rate (CBR) and variable bit rate (VBR) traffic. The SFS scheme also shows higher fairness among users of a same class, as well as between different classes.