Congestion Control Mechanism Over IEEE 802.11s Based Mesh WLAN

Wireless Mesh Network (WMN) is a new type of broadband wireless access network that combines the advantages of WLAN and Ad hoc Network. In the investigation of WMN, there are many key technologies to be solved, which play a key role for the design and practical application of WMN. Local congestion exists in both wired and wireless networks but the performance degradation it causes in wireless networks is even worse than in wired network because of the very nature of wireless medium being a shared resource. Furthermore, those congestion control mechanisms in the higher layers of the network stack can not totally well solve the prolem. So it's necessary to research the congestion control mechanism at the data link layer. Simulating and performance analysis of congestion control strategies based on the second layer for WMN are the main parts of this thesis.In chapter one, the basis of WMN, investigation situation of congestion control mechanism, necessity of congestion control, the structure and contribution of this thesis are outlined. Then, some theories, key technologies, congestion control frames for IEEE 802.11s which are the basis of the congestion control mechanism are introduced in chapter two. A hop-by-hop congestion control strategy in the second protocol layer for 802.11s based mesh network is proposed in the third part of the thesis, considering the exorbitant transmitting rate of upstream node will lead to local congestion. Simulation results indicate that the local congestion is alleviated and network performance is enhanced significantly. Considering the case of network resource which is not utilized sufficiently and the local congestion which is caused by neighbor node, an improved congestion control mechanism based on the third chapter is proposed in chapter 4. Simulation results indicate that the improved mechanism is sensitive and stable. It can mitigate the pressure of the congestion control in the higher layer and improve the network performance effectively. Compatibility of the proposed congestion control mechanism is analyzed at the end of the fourth capter.Finally, the thesis is concluded and the future work is prospected.