Dynamic tuning of the IEEE 802.11 distributed coordination function to derive a theoretical throughput limit
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RESEARCH
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Dynamic tuning of the IEEE 802.11 distributed coordination function to derive a theoretical throughput limit Yi-Hung Huang1* and Chao-Yu Kuo2
Abstract IEEE 802.11 is the most popular and widely used standard for wireless local area network communication. It has attracted countless numbers of studies devoted to improving the performance of the standard in many ways. In this article, we performed theoretical analyses for providing a solution to the maximum throughput problem for the IEEE 802.11 distributed coordination function, and an algorithm using a binary cubic equation for obtaining a much closer approximation of the optimal solution than previous algorithms. Moreover, by studying and analyzing the characteristics of the proposed algorithm, we found that the effects of backoff counter consecutive freeze process could be neglected or even disregarded. Using the NS2 network simulator, we not only showed that the proposed theoretical analysis complied with the simulated results, but also verified that the proposed approach outperformed others in achieving a much closer approximation to the optimal solution. Keywords: IEEE 802.11, distributed coordination function, performance analysis
1. Introduction Advances in wireless communication technology have increased the demand for wireless networks. The IEEE 802.11 standard [1] defines the specifications for medium access control (MAC) and the physical layers in a wireless local area network (WLAN). The IEEE 802.11 standard provides two mechanisms for the MAC protocol: the point coordination function (PCF) and the distributed coordination function (DCF). The PCF utilizes a basic access mechanism that supports contention-free services. Therefore, the PCF requires a base station that coordinates channel access among nodes. On the other hand, the DCF utilizes an access mechanism that supports contention-based services. The DCF access mechanism dictates that all the nodes should randomly access channels using the carrier sense multiple access/collision avoidance (CSMA/CA) mechanism. This mechanism employs the acknowledgment (ACK) feature to detect transmission failures. In other words, if an ACK response is not received, it is assumed that packet transmission has * Correspondence: [email protected] 1 Department of Mathematics Education, National Taichung University of Education, Taichung 40306, Taiwan Full list of author information is available at the end of the article
failed. The nodes wait for an interframe space (IFS), and then invoke the binary exponential Backoff algorithm, which uses a uniform random distribution called a contention window (CW) to generate a random Backoff value within the range of [0, CW - 1]. In this study, the initial value of CW is set to CWmin (the minimum CW). Subsequently, the CW value is doubled when packet transmission fails. For a node to obtain a Backoff value, it must first determine whether the channel is in use. If the channel is not busy, then the Backoff value decreases by 1 in every time slot and the
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