Research On Key Technologies Of Internet Connectivity For Wireless Mesh Networks

Wireless Mesh Network (WMN) is a new distributed multi-hop broadband wireless access network architecture, which is regarded as an important developing direction of wireless communications technology due to its features of high reliability, flexibility and scalability. With the development of WMN and popularization of intelligent terminals, global informatization has gradually become a reality. Meanwhile the demands for wireless users accessing Internet have been greatly stimulated as well. Therefore, the interconnection of WMN and Internet has arised great interest of industrial communities and academic institutions in the world. In connection with high-speed change of WMN topology, unidirectional links, limited banwidth and other issues, how to choose an effective interconnection mechanism to get best interconnection performance while making a minimal consumption of the scarce network resources is the focus and difficulty in this field.Supported of the project from National "863" Program of China and National Science Fundation of China, a series of key technologies of internet connectivity for wireless mesh networks are investigated in depth, including unidirectional links avoidance scheme, adaptive gateway discovery mechanism,802.11s multi-channel WLAN mesh access strategy and etc. The research results have been published in Journal of Beijing University of Posts and Telecommunications, and etc. The main innovative work in the dissertation can be summarized as follows:Firstly, an adaptive hybrid gateway discovery algorithm for connecting wireless mesh networks to Internet is proposed to overcome the limitation that the Internet connectivity performance is greatly degraded due to blindly rebroadcasting gateway discovery message when obvious unidirectional links are ignored. Based upon the modification for AODV, through rebroadcasting the gateway discovery messages and gateway advertisement messages, both of which are extended with local connectivity information, unidirectional links are successfully removed from global route computations. Furthermore, an adaptive Internet working scheme was adopted to provide the best coverage of gateway advertisement according to dynamically adjusting broadcast range and sending interval of gateway advertisement messages in terms of network conditions. Simulation results show that the proposed algorithm can effectively avoid unidirectional links with reasonable overhead and provide better connectivity performance than others.Secondly, on the analysis of carrier sense and random backoff scheme of 802.11s MAC layer, an available bandwidth measurement algorithm based on network allocation vector (NAV) is proposed. The algorithm obtains the NAV information of its neighbors through MAC "listening" mechanism, stores the information into buffers, and calculates the available bandwidth of the investigated node by the ratio of its channel accessible time to the measurement duration. The algorithm uses a passive measurement method without any additional communications load to wireless mesh network. Simulation results show that, compared with other measurement algorithms, the proposed scheme can more accurately estimate the available bandwidth of channel with significant cost improvement, which completely reflects the collision and contention between nodes.Thirdly, a cross-layer design and path quality based adaptive gateway discovery algorithm is designed for WMN accessing Internet. The proposed algorithm adopts an integrated metric taking into account the combination of residual bandwidth, packet delivery ratio and node load to meet the QoS requirement of multimedia traffic transmission. Furthermore, an adaptive algorithm was proposed to provide the best coverage of gateway advertisement according to dynamically adjusting broadcast range and sending interval of gateway advertisement messages in terms of gateway load and network topology. Simulation results show that the proposed algorithm can effectively improve Internet connectivity performance and balance network control load simultaneously.Finally, considering to overcome the existing problems that, directed towards the interconnection of 802.11s multi-channel WMN and Internet, the default path chosen metric of hybrid wireless network protocol is not well considered link difference and channel interference at multi-channel network environment, a 802.11s multi-channel mesh network internet accessing algorithm is proposed. On the basis of optimization for default 802.11s path selection strategy, we establish a new path selection metric, which is called Enhanced Weighted Cumulative Expected Transmission Time/Bandwidth Adjusted ETX (En-WCETT). The quality of the links state between source nodes and Internet gateways can be accurately measured according to using En-WCETT to instead the default metric of 802.11s. Simulation results show the proposed path selection metric can significantly improve the performance of Internet connectivity for WMN over existing metrics, in terms of the throughput and end-to-end delay of network interconnection.