Research On Key Technology For Wireless Mesh Networks Based On Multi-Rate And Cognition

Wireless Mesh Network (WMN) has become a hot research field of wireless broadband communications, as the wireless extension of the core Internet network. In the future, the content carried by the Internet will be the multimedia, video conferencing, and so on, requiring high bandwidth and real-time, so there is a higher requirement for the Quality of Service (QoS) guarantee. It will be a new idea to reconsider some QoS problems faced by traditional wireless networks, through exploiting the features such as supporting Multi-Radio Multi-Channel in WMN. At the same time, the latest physical layer technologies applying in the traditional WMN such as collaboration and cognition, which also brings many of the issues to be addressed. With the development of multi-radio technology, the system capacity has been greatly improved; meanwhile the multi-channel allocation will be a critical and challenging issue, but also the key of QoS guarantee.This thesis focuses on some key technologies in WMN, including the QoS routing based on the multi-rate, the cross-layer channel allocation based on the multi-rate, the cross-layer channel allocation based on the cognitive technique and the Mesh access point selection based on the cooperation, in which carries out in-depth study. Along the main line of joint design ideas, there form a number of innovative achievements in the related technologies. The main research work and innovation include the following aspects:For the issue such as the inaccuracy of link quality and rate estimates in routing metric, as well as the routing protocol can not support QoS in multi-rate WMN, a multi-rate aware routing metric is proposed and a routing protocol with multi-index constraints of QoS is designed. Through the in-depth analysis of the relationship among the routing metric, the quality of wireless links and the rate adaptive algorithm, combined with QoS routing technology and multi-rate mechanism in WMN, the routing metric and rate adaptive algorithm are design jointly. Under the premise of the accurate link quality and rate, this method can get accurate routing metric, to guarantee bandwidth, delay and other QoS indexes at the same time. Through using the control overhead in the routing protocol and data transmission process cleverly, the packet collision probability and link rate is estimated, which reduces a large number of additional controls overhead. The simulation results show that, this method can effectively guarantee the QoS requirements of the business such as end-to-end delay and bandwidth, meanwhile reduce the overhead of protocol control.For the multi-rate sharing problem along with the multi-rate mechanism, a cross-layer channel allocation method is proposed, through using different orthogonal channels to distinguish between high and low rate link, by exploiting the feature of multi-radio multi-channel in the WMN. A throughput cost function is proposed, by quantifying the impact on the WMN system of multi-rate sharing problem. Through considering the network traffic and multi-rate, while ensuring the bandwidth requirement of the new business, a rate and channel allocation joint algorithm is designed, to achieve minimal system throughput loss cost. A new method is proposed, in which the rate and channel allocation are blend into routing process, so the route request and route reply packets are used to carry the rate and channel information, and the introduced control overhead are reduced as possible, to solve the large number of overhead problem brought by the rate and channel allocation process. The simulation results show that, compared with the CA-AODV algorithm which does not consider the impact of multi-rate, and the RL-CA algorithm considering the impact of multi-rate in the existing research literature, the system throughput has been greatly improved, while reducing the large number of control overhead, and effectively reducing the impact of performance anomaly.For the Common Control Channel (CCC) bottleneck of cooperative spectrum sensing and idle spectrum allocation issue in Cognitive Wireless Mesh Network, a joint design method among collaborative spectrum sensing, spectrum access and routing is put forward, by using the cross-layer design idea. Based on the in-depth analysis of the relationship among the three parts, it is proposed firstly that part of the collaborative spectrum sensing and channel allocation process are integrated into the route discovery and maintenance process, and the collaborative sensing node cluster is formed to the center of the routing node along the routing path. According to the on-demand principle, spectrum collaborative sensing and channel allocation are only worked for the active routing node, in order to reduce the control overhead and the number of active cognitive users. The idle spectrum available probability is proposed as one of the basis for channel allocation, and the channel allocation on activity routing node is realized, combining with channel usage of the cognitive user neighbor, to maximize the throughput of the cognitive network. The simulation results show that, the method improves the system throughput of the cognitive WMN, and reduces a large number of protocol controls overhead, meanwhile improves the efficiency of the CCC in the cognitive network.For the issue of the best access point selection for the new user accessing the network or roaming and switching process in the multi-rate WMN, a solution for improving the access link rate of the client accessing Mesh Access Point (MAP) is proposed, by exploiting the relay communication technology in cooperative transmission. Through jointly designing the MAP selection and cooperative relay selection, a joint selection criterion of the MAP and the relay is proposed, with considering the multi-hop routing in wireless mesh backbone network, meanwhile a multi-objective optimization model of joint selection relay and MAP is designed. Further more, a sub-optimal heuristic algorithm is proposed considering the different energy-saving requirements and QoS requirements for nodes, in order to simplify the complexity of the algorithm. The method solve the problem that, a certain MAP signal is detected relatively weak by the client in the access network, but these MAP may just be with the light load or a good multi-hop link performance, so as to expand the selection range of the MAP. The simulation results show that, compared with the classic RSSI-based methods and the CLASS algorithm in the literature, the method can improve the access speed of the access link to ensure the delay requirements of the business, and improve the system throughput while reducing protocol overhead, under the crowded access circumstances or low access rate.