IEEE 802.11e performance study of the retransmission mechanism in QoS capable Wireless LANs

• Main Authors: Chih-wei Wu, 吳志偉
• Other Authors: Chie Dou
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/36581488912868648503

碩士 === 國立雲林科技大學 === 電機工程系碩士班 === 94 === IEEE 802.11e MAC layer applies various methods to achieve the goal of the quality of service (QoS) assurance. It has two main access mechanisms which are HCCA (HCF Controlled Channel Access) and EDCA (Enhanced Distributed Channel Access). Real-time streaming data are generally transmitted by polling through the HCCA mechanism. The HCCA mechanism guarantees the real-time transmission of data by scheduling the polling sequence of QoS-stations (QSTAs) in advance and allocating the polling time for each QSTA properly. As regards, the non real-time data are generally transmitted by contention through the EDCA mechanism. The EDCA mechanism uses time backoff to avoid collision problems between stations, which is time consuming and not suitable for real-time data delivery. This thesis focuses on the performance study of the retransmission mechanism in the HCCA of IEEE 802.11e Wireless LANs. Constricted by the polling time for each QSTA, we give QSTAs limited retry opportunities to reduce the frame error rate (FER) and in the meanwhile keep the system throughput as possible. Furthermore, this thesis also studies the performance of the BlockAck mechanism. We observe that the BlockAck mechanism can further enhance the system throughput and reduce the polling time for each QSTA under the same FER performance. The simulaiton system consists of the HCCA access mechanism of IEEE 802.11e MAC layer written in MATLAB, and CommAccess Technologies’ IEEE 802.11a PHY layer Toolbox.