Access Mechanism Selection And Dynamic Optimization For Intelligent Wireless Local Area Networks

In recent decades,IEEE 802.11 wireless local area networks(WLANs)have become more and more popular in people's learning,work and life due to their mobility,low cost and high speed.In order to meet the growing network demand of high-speed,low-latency,the optimization and improvement of the network performance of WLANs has always been a research hotspot.The 802.11 standard is a common standard for WLANs and designed to enable compatible interconnection of wireless devices within a wireless LAN.The performance improvement of the IEEE 802.11 Media Access Control(MAC)layer is becoming a key bottleneck restricting the evolution of IEEE 802.11 technology.Therefore,this thesis takes the access mechanism selection and dynamic performance optimization in the next generation of intelligent WLANs as the main research problems,and research from theory and simulation.Firstly,this thesis introduces the research background and significance of the subject,the research status at home and abroad and the key techniques of the IEEE 802.11 MAC layer.The major focus is put on the Distributed Coordination Function(DCF)access protocol based on Carrier Sense Multiple Access with Collision Avoidance(CSMA/CA)mechanism,and analyzes the workflow of basic access mechanism and Request To Send/Clear To Send(RTS/CTS)mechanism,and the specific process of binary exponential backoff algorithm in detail.Moreover,the accuracy of the 802.11 MAC module within NS-3 simulation platform is evaluated based on the unified analytical framework for IEEE 802.11 DCF network.In particular,by considering different network scenarios,different traffic conditions,varying system parameters,distinct access mechanisms,and different network topologies,a number of simulation experiments have been conducted to verify the credibility of IEEE 802.11 MAC module of NS-3.Secondly,the accuracy of the IEEE 802.11 MAC layer module of the NS-3 simulation platform is evaluated using the unified framework theory model of Dai's IEEE 802.11 DCF network.Different network scenarios,including different network states,changing system parameters,different access mechanisms,and different network topologies,are fully considered in the simulation verification of the NS-3MAC layer.The theoretical and simulation results show that the NS-3 platform can be used as a reliable simulation tool for the performance design and implementation of IEEE 802.11 WLANs.Thirdly,the RTS threshold in the current IEEE 802.11 WLANs is set to a fixed value,which makes it difficult to adaptively switch between the basic access mechanism and the RTS/CTS mechanism.To tackle this issue,this thesis derives the explicit expression of the optimal RTS threshold,and the accuracy of the optimal RTS threshold and the feasibility of the access mechanism selection are verified by the NS-3 platform.According to the relationship between the optimal RTS threshold and the network system parameters,the WLAN with adaptive access mechanism selection is designed and implemented on the NS-3 simulation platform,,which can be easily applied in practical systems.With the proposed network design,IEEE 802.11 WLANs can always work adaptively under the optimal access mechanism,and the network throughput can be significantly improved.Finally,to solve the problem that throughput performance significantly declines when the number of nodes grows with the current fixed backoff parameters,the current standard sets static backoff parameters,which leads to the decline of network throughput performance,this paper analyzes and compares Bianchi's classical two-dimensional Markov model with Dai's theoretical model.It is found that with the explicit expression of the optimal initial backoff window size obtained in Dai's theoretical model,the network throughput can be maximized.Based on the relationship between the optimal initial backoff window and the network system parameters,optimized IEEE 802.11 WLANs is adaptively designed and implemented in NS-3 platform.The proposed network design provides important theoretical guidance for the dynamic optimization of IEEE 802.11 WLANs.