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Title |
Hybrid adaptation of the maximum contention window (CWmax) and minimum contention window (CWmin) for Enhanced Service Differentiation in IEEE 802.11 Wireless Ad-hoc Networks |
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Author |
Hassan Takabi, Ali H. Moghadam, Ahmad Khonsari |
| Citation |
Vol. 6 No. 12 pp. 281-290 |
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Abstract |
The IEEE 802.11e draft standard that proposed by IEEE Task Group E, defines new MAC protocols for QoS in wireless networks, mainly HCF that combines functions from DCF and PCF with enhanced QoS-specific mechanisms and frame types. HCF has two modes of operation EDCA and HCCA. EDCA is a contention-based mechanism and HCCA is a polling-based mechanism for channel access. EDCA, in fact, is an extension to DCF and is a contention-based channel access method that provides prioritized access to the medium. In this paper, we propose to extend EDCA using a hybrid adaptation algorithm of the maximum contention window(CWmax) and minimum contention window(CWmin) for Enhanced Service Differentiation in IEEE 802.11 Wireless Ad-hoc Networks, that enables each station to adjust size of CWmax and CWmin used in its back-off algorithm at run time. The purpose of suggested scheme is to reduce delay and jitter and increase the efficiency of the transmission channel. Priorities between access categories are prepared by updating the size of the CWmax and CWmin according to application requirements and network conditions. The performances of the IEEE 802.11e EDCA, enhanced with our hybrid adaptation algorithm, are inquired by simulations. Our results show that the hybrid adaptation algorithm outperforms the 802.11e EDCA standard in terms of channel throughput, packet delay and utilization, specially at high traffic load conditions. Indeed our proposed scheme increases the total throughput for high priority access category by up to 27% and reduces the delay for high priority traffic more than 49%. Furthermore, channel utilization ratio also increases at least 23%. Moreover, throughput for medium and low priority access categories remains stable. |
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Keywords |
IEEE 802.11e, QoS, EDCA, back-off algorithm, wireless ad-hoc networks, hybrid adaptation algorithm, CWmax, CWmin |
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