Performance Analysis of IEEE 802.11-based Networks

• Main Authors: Yan-Wun Lai, 賴彥文
• Other Authors: Kuang-Hui Chi
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/63520923973258285339

碩士 === 國立雲林科技大學 === 電機工程系碩士班 === 94 === The distributed coordination function (DCF) is essential for IEEE 802.11 medium access control (MAC) services. DCF employs a carrier sense multiple access with collision avoidance technique, defining two mechanisms for data frame transmissions with or without using RTS (Request to Send) and CTS (Clear to Send) frame exchanges beforehand. The former is referred to as the RTS/CTS access mechanism, while the latter is the basic access mechanism. In this thesis we use a Markov chain to model IEEE 802.11 networking behavior under the DCF. Under consideration is the IEEE 802.11b High Rate direct sequence spread spectrum physical layer. We take into account the retry limit and backoff time whereby wireless stations avoid collisions of transmitted packets. Additionally we consider two types of preambles (long and short) as per IEEE 802.11b. The long preamble mode supports transmission rates of 1, 2, 5.5, and 11 Mbps, whereas the short preamble supports transmission rates of 2, 5.5, and 11 Mbps. We study the throughput of IEEE 802.11 networks in terms of the probabilities of packet transmissions and collisions in multiple transmission rates. Our performance analysis is carried out quantitatively using the RTS/CTS and basic access mechanisms, meanwhile in the context of long and short preambles, respectively. Analytical results explicitly show the relationship between packet collisions and retransmissions by a varying number of stations following the exponential backoff procedure. It can be seen that the probability of successful transmissions decreases when the backoff stage increases and when the number of stations contending for channel access increases. In addition, the probability of colliding packets is reduced along with the increasing backoff stage but increases as the number of stations increases. Further, the network throughput increases along with the increasing backoff stage but decreases when the number of contending stations grows larger. Moreover, performance results indicate that transmissions in short preamble mode can generally achieve a higher throughput as opposed to transmissions in long preamble mode. Our analytical model applies to IEEE 802.11g settings as well.