Design of Efficient and Reliable MAC protocol for Wireless Technologies

In this paper, the performance of IEEE 802.11 MAC protocol is analysed in terms of efficiency and reliability in wireless networks. In the IEEE 802.11, an exponential backoff has been adopted, which means whenever a collision occurs, the contention window (CW) of the station is doubled until it reaches the maximum value. The purpose of increasing CW is to reduce the collision probability by distributing the traffic into a larger time space. In this paper, fixed contention window scheme is used and then correlate the CW size and network size. The interaction of TCP with the MAC protocol is also analysed. For static multi hop network that uses IEEE 802.11 protocol for access, TCP performance is mainly determined by hidden terminal effects ( and not by drop probabilities at buffers) which limits the number of packets that can be transmitted simultaneously in the network. TCP throughput is improved by decreasing the ACKs flows, using delayed ACK, with d=2. Simulation results shows when choosing large maximum window, the delayed ACK considerably outperform standard TCP.