Research On IEEE 802.11 MAC Layer Channel Access Technology

With the advent of the Internet age,wireless LAN is one of the two most important wireless networks.Characterized with the significant advantages such as high system throughput efficiency,low cost of deployment and utilize and networking and high flexibility,it plays a fundamental role in daily life.With the popularization of various types of mobile device terminals and the promotion of various wireless products,the customary requirements for data service transmission rate and network experience are more and more harsh.However,the occurrence of the wireless local area network standard IEEE 802.11 ac relieves extent this situation to some certain.Therefore,it is necessary to study the series of IEEE 802.11 standards.Further optimization and improvement of the protocol are also need.As the kernel part of the channel access mechanism,Distributed Coordination Function(DCF),is always been put highlight in this field.For the reasons above,this thesis has carried on the thorough research to the DCF access mechanism in the following two respects.On one hand,according to the current IEEE 802.11 DCF mechanism analysis and research model,most research is concentrate on the performance of homogeneous traffic sources(i.e.,with the same arrival rate),only a few literatures focus on heterogeneous mixed service networks(i.e.,saturated or nonsaturated).In the current research,the analysis and summarizations of the network nonsaturated and backoff freezing etc.are not accurate.This thesis proposes a new and improved bi-dimensional Markov chain model to analyze the performance of the DCF mechanism under heterogeneous traffic sources with the M/G/1 queuing model.Through the solution on the steady state,this model allows the calculation of the three important parameters: per-station and network throughput,mean delay and transmission packet loss.Through the theoretical analysis and simulation results,it is proved that the model not only can analyze the performance of the DCF mechanism,but also give better analysis of the performance of the DCF mechanism better than others under heterogeneous traffic sources with consideration of the actual application scenarios.On the other hand,an improved RTS(Request To Send)/CTS(Clear To Send)access mode based on the RTS/CTS access mode is proposed to cover the shortcomings of the two access transmission modes in the DCF channel access mechanism and the existence of the hidden terminal problem.This model is used to supplement the content of the DCF access mechanism and improve the performance of the series of IEEE 802.11 standard.Through simulation results,it is proved that the proposed improved RTS/CTS mode has considerable advantages over the two transmission modes in the DCF mechanism in many aspects and can further improve the performance of the protocol.