The Analysis and Performance Study on the Surplus Bandwidth Allowance in IEEE 802.11e WLANs

• Main Authors: Yu-ming Li, 李郁明
• Other Authors: Chie Dou
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/67720331975531515741

碩士 === 國立雲林科技大學 === 電機工程系碩士班 === 95 === The goal of IEEE 802.11e MAC layer is to provide QoS-enabled WLANs and it adopts various methods to achieve the goal. Among which HCCA (HCF Controlled Channel Access) and EDCA (Enhanced Distributed Channel Access) are two main access mechanisms. 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. To reduce FER is an important task in QoS-enabled WLANs. Two frequently used methods are retransmissions in MAC layer and link adaptation in PHY layer. We investigate how to specify the SBA (Surplus Bandwidth Allowance) parameter in the TSPEC (Traffic Specification) of real-time traffic stream under HCCA mechanism. The SBA parameter can be specified by assigning additional number of retries for the application to reduce FER. We study on the relationship between the FER and the SBA for CBR (Constant Bit Rate) traffic stream. The calculated FER performance can be used to specify the required SBA for the traffic stream so that the QoS requirement of the application is satisfied. This thesis also investigates the performance improvement and fairness problem of how to distribute the allocated additional retries among the given transmitted frames if these frames are transmitted across multiple service intervals (SIs). This may cause unequal error performance of transmitted frames within different SIs and the result can be applied to video streaming over wireless with UEP (unequal error protection) data partitions. The analytical result obtained for CBR traffic can also be used to emulate the FER performance of VBR (variable bit rate) traffic over QoS-enabled WLANs. A discrete-time Markov chain model is proposed to generate the number of transmitted frames, not including the retries, within each SI for the VBR traffic. Stochastic simulation has justified the effectiveness of this approach.