Research On Access Control Of MAC Layer In Wireless Network

With the rapid development of wireless network and wide applications of multimedia business, people’s lives and social patterns have been changed completely, at the same time, people have increasingly demand for high Quality of Service (QoS) of wireless network, so it makes research of wireless network more challenging and useful. The MAC layer is the basis of achieving the stability and the efficient of the channel in the wireless network, and it have a decisive impact on the overall network performance, so it has a practical significance and application prospects for the research on the MAC layer in wireless network. This paper focuses on the wireless network MAC layer access, and it expands from the performance characteristics, congestion control, model analysis and the cross-layer design etc. aspects for further research between the MAC layer in the Wireless Local Area Networks (WLAN) and the Cognitive Radio Network (CRN).The main contribution of this paper is as follows:1. Performance simulation and model analysis for DCF and EDCA protocolStudy on the bottleneck bandwidth of current wireless base station, premise without changing the existing IEEE802.11DCF protocol, this paper proposes TCP/AQM fluid model based on MAC parameters of wireless network, and uses the2-D Laplace-z transform for the stability analysis of the time-delay system, which obtains the sufficient condition of system stability, and through the stability conditions we can get the best range of users. The simulation results show that the given theorem of this paper can calculat the best range of users, which ensures the stability and fairness of TCP, and improves the network performance.Against the problem that existing EDCA mechanism failurs causing by the parameter settings, this paper further researches the important parameters and performance model of the IEEE802.11e EDCA mechanism, the model analysis and simulation of the existing EDCA mechanism mainly from CFB mode, energy and mixed flow performance, and we verifies the effect of different priority user flows by network parameters, reasonable network parameter values can protect the QoS of different priority business.2. Improved design for the DCF protocol with hybrid flows Study on the problem that forwarding delay and the system cache overhead are larger when hybrid flows access channel with IEEE802.11DCF protocol, this paper proposes the improved scheme and theoretical model of the IEEE802.11DCF protocol with TCP/UDP hybrid flows. The improved DCF protocol can adjust the MAC frame size to an integer multiple of the packet length based on TCP/UDP packet length, that can avoid the increasing delay of TCP/UDP hybrid flow triggered retransmission. The simulation results show that the the improved DCF protocol can improve the access throughput of the wireless base station and reduce the forwarded delay of TCP/UDP hybrid flows.3. Research on the MAC layer access protocol for the cognitive radio networkFor the low performance problem of Cognitive Radio User (CRU) that leaded by bandwidth changed frequently, this paper proposes the cognitive backoff algorithm that CRUs can adjust the backoff window according to the channel busy rate. We gives the mathematical analysis model of CRN MAC layer based on the channel busy radio firstly, then we can compute the optimal value of backoff window through the maximum throughput value, each coginitive radio user can adjust the backoff window according by the channel busy state lastly. The method can decrease the wait and collision problem bring by BEB,which can improve the performance of CRU. Simulation results of NS2show that the method can protect improve the performance of CRU greatly.For the poor performance problem of CRU caused by channel switching or channel interruption. This paper proposes that uses freezing and buffer mechanism based on DCF protocol when the channel is switched and interrupted, that is freezing the backoff timer of node and caching the current state of information. Once the CRU regains the access opportunity, the CRU node will read the cache information and continue operation, which can reduce the delay and collision of reaccess channel and improve the throughput of the system. The NS2simulation results prove the effectiveness of the method.4. The cross-layer design Based on the MAC layer in CRNFor existing wired network can’t support cognitive function, and the end-to-end QoS of primary users can not be guaranteed, this paper proposes the network architecture and MAC access control protocol (CRMAC) combining with the characteristics of CRN firstly; then matching the priority and related parameters between CRMAC and DiffServ, the proposed cognitive edge router uses distinguished packet loss mechanism between the primary user and CRU. This system structure of cross-layer design provides end-to-end grading service for CRN, it protects primary users and its realtime business, and it improves the overall network performance simultaneously. NS2simulation results show that the method can really guarantee the end-to-end QoS of CRN.