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01-Applied Mathematics & Information Sciences
An International Journal


Special Issues > Apr. 2012


A Dynamic and Adaptive Transmission Scheme for Both Solving Uplink/Downlink Unfairness and Performance Anomaly Problems in a Multi-Rate WLAN

PP: 531S-537S
Chih-Heng Ke, Chih-Cheng Wei, Kawuu W. Lin,
Uplink/downlink fairness and performance efficiency are both considerable issues in an IEEE 802.11 multi-rate Wireless Local Area Network (WLAN). The IEEE 802.11 Distributed Coordination Function (DCF) provides equal medium access probability to all transmitters that cause the access point (AP) to obtain less bandwidth than that of the wireless mobile stations to download traffic when the number of mobile stations is larger than one. Furthermore, the WLAN with infrastructure mode also has the performance anomaly problem that the system throughput was seriously degraded by the transmissions of lower date rate transmitters in a multi-rate environment. In the past studies, many mechanisms have been proposed to solve the uplink/downlink unfairness problem, such as the transmission opportunity mechanism (TXOP), the multiple backoff timer mechanism (MBT) and the asymmetric access point mechanism (AAP). In order to improve the performance efficiency, contention window differentiation mechanism (CWD), packet size differentiation mechanism (PSD) and interframe gap differentiation mechanism (IFG) have been proposed recently. The proposed mechanisms, however, did not take both uplink/downlink unfairness and performance anomaly problems into consideration at the same time. In fact, the two problems occur simultaneously in practical WLAN environments. In this paper, we propose a dynamic and adaptive transmission scheme (DAT) to deal with the both problems. Each wireless mobile station will consider its data rate to decide the number of packets to transmit when it gets the privilege to access medium. Moreover, the AP has more right to download more packets for the purpose of balancing total uplink traffic. The system throughput of the proposed DAT is discussed and validated by the simulations and analytical results. The simulations also show that the proposed DAT outperforms the previous mechanisms.

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