| Summary: | 碩士 === 國立中興大學 === 電機工程學系 === 93 === With the emerging use of real-time multimedia applications over wireless networks, support of Quality of Service (QoS) becomes a key problem. The IEEE 802.11e Medium Access Control (MAC) protocol is an emerging standard to support QoS.
Some recent works prove that 802.11e Hybrid Coordination Function (HCF) can improve the QoS support significantly. A simple HCF scheduler has been proposed in 802.11e which takes the QoS requirements of flows into account and allocates time to stations on the basis of the mean sending rate. As we show in this paper, this HCF scheduling algorithm is only efficient for flows with strict Constant Bit Rate (CBR) characteristics but not for non- Constant Bit Rate traffic flows. There are many real time applications, such as videoconferencing, may have bit rate variations and have Variable Bit Rate (VBR) characteristics. In this thesis, we propose a new HCF scheduling algorithm, FHCF, that aims to be fair for both CBR and VBR flows and also can reduce the latency of VBR traffic packets. The FHCF scheme uses queue length estimation to tune its time allocation to stations. We present a set of simulations and provide performance comparisons with other schemes.
Finally, we used Network Simulator Version 2 (NS2) to simulate the performance of FHCF scheme’s QAP scheduler and QSTA scheduler with two network topologies. Finally, we compare the performances between FHCF、standard HCF and EDCF schemes. Our performance study indicates that FHCF provides good fairness while supporting bandwidth and delay requirements for a large range of network loads.
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