标题: IEEE 802.11n性能异常现象之改进
Improvement of IEEE 802.11n Performance Anomaly
作者: 王启宇
Wang, Chii-Yeu
杨启瑞
Yuang, Maria C.
网路工程研究所
关键字: IEEE 802.11;基础架构模式;无线网路;竞争视窗;吞吐量;IEEE 802.11;Minimal Contention Window Size;Transmission Rate;Throughput;Delay
公开日期: 2013
摘要: 在IEEE 802.11的规范中,支援多种不同的传输频宽。在基础架构模式(Infrastructure mode)下,当所有装置处于同一个基本服务集(Basic Service Set, BSS),因为距离无线网路基地台(Access Point)较远等原因,装置的传输频道发生干扰较严重的情形时,会自动选择频宽较低的调变类型,降低传输速度,提高封包传送成功率。在目前已知的研究中已提出,当多个装置以高速的频宽传输时,只要存在一个装置以低速频宽传输,就会降低其他装置的传输效率,导致其他高速率传输装置的吞吐量(Throughput),会降低至与低速率传输装置吞吐量相同的数量级。而在IEEE 802.11的研究中,通常称此现象为“性能异常”(Performance Anomaly)。
IEEE 802.11n自2009年发表以来,相关支援的Wi-Fi认证产品已非常普及。而本篇论文主要探讨,在IEEE 802.11n的规格参数设定下,在饱和(Saturation)与非饱和状态下,以调整最小竞争视窗大小(minimum contention window size,简称CW_min),改善异常现象之效果。
在研究的过程中,我们先证明以自行撰写之模拟程式,可以模拟出性能异常现象。再逻辑性的去实验解决此问题之方法,以分别调整频宽、流量、最小竞争窗框大小、共同竞争装置数等参数之后,讨论对于高传输速率之装置有何影响。实验结果指出,当装置数够多的时候,将高传输速率装置的CW_min设定为最小值,低传输速率装置的CW_min设定为最大值,可以让高传输装置的效能,在吞吐量、延迟时间等方面的数据结果达到最明显的改进。
There are many different specifications of transmission rate which are set by IEEE 802.11 standards. Under the infrastructure mode, mobile stations which are far away from the AP, will suffer much more signal interference. In this circumance, those stations will change their transmission rate to a lower value. It has been known that, the existence of the low rate stations will affect the other high rate stations severely. In the related research work of IEEE 802.11, we often refer it as performance anomaly.
Since the IEEE 802.11n standard had been released in 2009, it has been widely applied among many products around the world. The purpose of our work is to solve the performance anomaly problem by tuning the minimum contetion window size(CW_min), under the 802.11n specifications.
First, we prove that the self-developed simulation program can simulate the abnormal phenomenon mentioned above. Second, we make experiments with different parameters such as transmission rate, traffic arrival rate, CW_min and number of contending stations. And observe the variations of throughput, mean delay and delay jitter.
Throughout our experiments, we show that when the number of contending stations are large enough, maximizing the CW_min of the low rate stations and minimizing the CW_min of the high rate stations highly improved the performance of the high rate stations.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT070056501
http://hdl.handle.net/11536/74429
显示于类别:Thesis