Research On Medium Access Control Protocol For Wireless Network

MAC(Medium Access Control) is an important factor that impacts a netwok's performance. The MAC standard of IEEE802.11 has been widely used in wireless netwok.Our research focuses on IEEE802.11DCF(Distributed Coordination Function) and IEEE802.11e. The main contents and innovations this thesis brings forth are as follows:1.According to the survey and analysis of topology, typical application ,current research and development trend of WLAN,Manet(Mobile Ad hoc Network) and WMN(Wireless Mesh Network) respectively, the value and significance of research on IEEE802.11DCF and IEEE802.11e are illustrated.2. IEEE 802.11 architecture and the series standards of IEEE 802.11 are briefly introduced. This section emphasizes on the mechanism of basic access mode,RTS/CTS(Request To Send/Clear To Send) mode and BEB(Binary Exponential Backoff) in IEEE802.11DCF.3. With respect to IEEE802.11DCF,the minimum contention window, probability distribution and the growth and decline factor of contention window are important factors that impact a network's performance. Then related works to improve IEEE802.11DCF are showed in this section.We also point out the algorithms such as Slow Contention Window Decrease fail in gaining optimal performance when the network's congestion level varies. In light of the limitations of these algorithms, our thesis proposes SCWGF(Self-adaptive algorithm of adjusting Contention Window's Growth Factor).4. With the aid of two-dimensional Markov chain, there exists the optimal value of contention window's growth factor when the number of competing nodes is fixed. Then we bring forth our criteria, collision occupancy ratio reflecting the network's congestion level. Next, the pseudo-code of SCWGF is induced. The simulation results illustrate that SCWGF outperforms DCF and EIED in terms of the normalized saturated throughput.5.QoS consists of two service models, namely, Integrated Service and Differentia -tion Service. And IEEE802.11e provides a Differentiation Service The research of existing works concentrates on admission control, improving EDCA's entire performance and equality problem. Absorbing these analysis method ,we put forward an algorithm to meet the QoS demand of quantitative bandwidth. To realize such a QoS, it estimates AIFS(Arbitration Inter-frame Space) based on the value of bandwidth on demand and uses the difference between the real bandwidth and the requested one to tune the estimation equation.