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Dynamic Adaption of DCF and PCF mode of IEEE 802.11 WLAN

Abhishek Goliya


IEEE 802.11 specifies the most famous family of WLANs. It features two basic mode of operation: Distributed Coordinating Function (DCF) and Point Coordinating Function (PCF). Both PCF and DCF mode of IEEE 802.11 do not perform equally well under all traffic scenarios. Their behavior varies depending upon current network size and traffic load. It is useful to use the DCF mode for low traffic and small network size, and the PCF mode for high traffic loads and to reduce contention in large size network. In this thesis, we have designed three protocols to dynamically adapt IEEE 802.11 MAC under varying load. One of them is designed to dynamically switch between either modes.Our Dynamic Switching Protocol (DSP) observes network traffic to decide switching point and switches dynamically to suit current traffic load and network size. PRRS is our second contribution that aims to reduce polling overheads.A major drawback of polling scheme in PCF, is their inefficiency when only a small number of nodes have data to send. Unsuccessful polling attempts causes unnecessary delays for station with data.We have presented network monitoring based scheme that replaces simple Round Robin scheduling in PCF with our Priority Round Robin Scheduling (PRRS). Result shows considerable increase in throughput especially when small fraction of node has data to transmit. In addition, we have presented the need to dynamically adapt various configuration parameters in both PCF and DCF. Statically configured values results in degraded performance under varying scenarios .We have showed the performance variation of PCF with PRRS by using different CFP repetition intervals. Our proposed CFP repetition interval adaption algorithm dynamically adjust the value of CFP repetition interval, depending upon last CFP usage.

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