SummaryIn this paper, a simple self-adaptive contention window adjustment algorithm for 802.11 WLAN is proposed and analyzed. Numerical results show that the new algorithm outperforms the standard 802.11 window adjustment algorithm. Compared with the standard and previously proposed enhancement algorithms, a salient feature of our algorithm is that it performs well in both heavy and light contention cases regardless of the packet sizes and physical versions. Moreover, the adaptive window adjustment algorithm is simpler than previously proposed schemes in that no live measurement of the WLAN traffic activity is needed.
Reliable data delivery and congestion control are two fundamental transport layer functions. Due to the specific characteristics of Wireless Sensor Networks (WSNs), traditional transport layer protocols (e.g. Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)) that are widely used in the Internet may not be suitable for WSNs. In this paper, the characteristics of WSNs are reviewed and the requirements and challenges of reliable data transport over WSNs are presented. The issues with applying traditional transport protocols over WSNs are discussed. We then survey recent research progress in developing suitable transport protocols for WSNs. The proposed reliable data transport and congestion control protocols for WSNs are reviewed and summarised. Finally, we describe some future research directions of transport protocol in WSNs.
-In a realistic WLAN environment, frame losses may be caused by collisions or channel noise. The existence of noise-induced losses reduces the effectiveness of the standard WLAN backoff algorithm for contention resolution, which assumes that all losses are caused by collisions and always doubles the contention window to reduce contention upon a frame loss. In this paper, we propose new backoff algorithms that take advantage of a new capability to differentiate the losses, and thereby sharpen the accuracy of the contention resolution process. Analytical models are developed to analyze the performance of these algorithms under heterogeneous link conditions in a WLAN. Both analysis and simulation results show that significant improvement of throughput and fairness can be obtained for WLANs in which contention resolution is enhanced by the loss differentiation ability.
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