Performance Analysis of IEEE 802.11 Modified Distributed Coordination Function for Wireless LANs Based on Data rate

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IEEE has standardized 802.11 protocol for Wireless Local Area Networks.The 802.11 MAC standard specifies two access mechanisms, the Distributed Coordination Function (DCF) and Point Coordination Function (PCF). DCF is considered as the basic MAC mechanism, based on the carrier sensing multiple access with collision avoidance (CSMA-CA) protocol, which is introduced to avoid the collision.The main problem with 802.11 MAC layer is the implementation defects of DCF.The Distributed Coordination Function (DCF) in the IEEE 802.11 standard preserves fairness for all clients at the frame level. That is, all clients would achieve the same throughput (in terms of numbers of frames transmitted or received) in the long run without considering their data rates. As a consequence, it will take much longer time for a low data rate client to transmit / receive a frame than clients with higher data rates.It results in the low throughput of fast clients and a poor performance of the whole system. This is regarded as a major problem in IEEE DCF interms of their performance . DCF allows a uniform packet delivery irrespective of the data rate. In the existing system the throughput is independent of the data rate. This can be observed from the throughput analysis. But in the modified version of DCF called MDCF gives a far better performance for nodes with high data rate. Thus in the proposed method high data rate node traffic is optimized. This is achieved by making changes to the MAC layer of IEEE 802.11. The frames and packets are dropped only after analyzing the data rate. Packets from nodes with high data rate are given preference over packets from nodes with low data rate.Performance Analysis is done based on various parameters and results show that proposed sysytem(MDCF)is better than normal DCF.