Research On Medium Access Control Strategy For Heterogeneous Wireless Mesh Network

Our life has been changed by the developing technology of wireless communication. Now, we can enjoy very convenient network services. The coverage range of conventional Wireless Local Area Network (WLAN) is very small, so it is expensive to build multiple WLANs to cover a large area. In order to overcome the disadvantages above, a new kind of wireless network, Wireless Mesh Network is deployed recently, and has been widely used in medical care system, oil and coal industry, public safety and so on. Now, several kinds of wireless communication technologies appear along with the development of technology and the reducing of cost of hardware, such as IEEE 802.16 (WiMAX), IEEE 802.15.3(UWB),3G and so on. Gradually, the conventional Wireless Mesh Network (WMN) based on IEEE 802.11 has turned into a new form:Heterogeneous Wireless Mesh Network, which is more compatible, robust and with high performance. In such a network, an area would be covered by several kinds of different wireless networks. When terminals have been equipped with multiple radios, each of which adopts different wireless technology, clients can choose the best radio to access the network to enjoy network service.In the heterogeneous wireless mesh network, radios of one terminal can access network simultaneously when they do not interfere with each other. How to make the coexistent radios cooperate with each other, to promote the performance of device and network, is a popular research area. Another research field is how to improve the transmission performance, fairness, network efficiency of each subnet, to finally promote the capability of the whole heterogeneous wireless mesh network. Furthermore, the traditional routing metric is not suitable for heterogeneous WMN, so it is a challenge to propose a unified routing metric for each subnet to accelerate merging of heterogeneous WMN.Aiming at promoting the performace of the whole heterogeneous WMN, we focus on the following three issues:network and radio cooperation, performance optimization of subnets, unified routing metric. We propose a tight cooperation scheme for WiFi and WiMAX radios, by modifying the MAC layer protocols of WiFi and WiMAX. We investigate scheduling algorithm for WiMAX and UWB Mesh subnet, as well as fairness transmission algorithm for mobile WiFi Mesh subnet, to improve network performance separately. By analyzing network parameters which should be taken into account by routing metric, we propose and implement a framework of routing metric for heterogeneous WMN. In a word, we design a novel solution for heterogeneous WMN from single hop transmission to multihop routing.First of all, in order to realize the cooperation of radio and network, we investigate the availability of coexistence of WiFi and WiMAX radios, and analyze the reason of low efficiency of WiFi DCF scheme, then based on the bandwidth requesting scheme of WiMAX Mesh, we propose a tight cooperation scheme of WiMAX and WiFi radios. WFW (WiMAX for WiFi) module is planted between the entitites of WiMAX MAC and WiFi MAC layer. By modified DSCH message, WiMAX radio helps WiFi accomplishing bandwidth request-grant-confirm procedure, to avoid the overhead of interaction between WiFi control messages (RTS/CTS and ACK). By this scheme, the efficiency and throughput of WiFi Mesh can reach the maximum value of theory,100% and 1Mbps, and without affecting the performance of WiMAX Mesh.Secondly, by investigate service differentiation and the manner of allocation and scheduling of data slots in WiMAX Mesh network, we design a QoS based throughput-efficiency optimization distributed data subframe scheduling algorithm. According to the characteristics of VBR flow and the manner of data slot allocation in UWB Mesh network, we propose a dynamic allocating and adjusting scheme, which also considers QoS guarantee. By theoretically analyzing the unfairness phenomenon when flows contending for wireless media in mobile WiFi Mesh network, we propose a dynamic packet size adjusting scheme to promote the fairness in mobile Mesh network, and also maintain a high level throughput of each data flow. The performance of the whole heterogeneous WMN is finally improved through the promotion of each subnet's transmission performance, fairness and network efficiency.Finally, in order to facilitate the merging of each subnet, the routing metric of heterogeneous WMN needs to consider two parameters:node quality and link quality. Furthermore, it is also required that the routing metric can depict the heterogeneity of nodes in each subnets. According to the above requirement, we propose a framework of routing metric for heterogeneous WMN, and realize a prototype:BLETX. It's proved that BLETX is suitable for each subnet, and with good performance.