Cross-layer Design For Wireless Mesh Networking

The traditional network is divided into seven layers, and each of them is designed for different function. According to the analysis of related works in wireless mesh network (WMN), the author believes this is unsuitable way to improve its performance. Hence by adopting corss-layer methodology, this thesis mainly focuses on implementing cooperation of various layters to improve the performance of WMN. The cooperation between physical layer and medium access control (MAC) layer, and that of MAC layer and routing layer will be discussed respectively. By adopting various ways and methodologies to cooperate, the performance of the whole network can be improved significantly.Firstly, how to improve the efficiency of routing protocol will be investigated. Most routing protocols only make use of the hops and some other information collected by routing layer itself. In this thesis, to achieve the target of load balance, we propose an integrated routing metric, which takes frame delivery ratio, available bandwidth and traffic load of the MAC layer into consideration. This metric reflects the variations of wireless environment promptly and accurately since MAC layer is closer to it. Meanwhile, the original routing scheme is modified to guarantee that sources can detect the optimal routes to destinations. In our new scheme, when an intermediate node receives route requests, it will decide whether to forward them with the help of checking the information taken with them other than only considering the sequence numbers. In this way, the source receives the path with shortest delay and the optimal route determined by the route decision at the same time. Eventually, routes except for the optimal route can be used when the optimal one is broken.Secondly, to provide different service (Diff-Serv) for various types of traffic in route layer, this thesis proposes a traffic aware routing protocol (TARP). TARP provides different schemes to select routes for various traffics since what they desire are distinct. Hence, various traffic of the same node can use different paths to delivery their packets. If one node has more than one types of traffic, multi-path technology will be used in this case. Compared with the traditional multi-path technology, TARP can avoid the out-of-order problem. The related simulations demonstrate that TARP can achieve the target of Diff-Serv and load balance at the same time.Thirdly, opportunistic routing protocol is a novel way to provide reliability for wireless networks. However, it relies on the global topology information. To release this limitation, this thesis proposes a scheme by combining opportunity routing and dynamic routing protocol together. The path obtained by DSR can bypass the collision area, so it reaches load balance. Hence, the long-term channel variation can be handled. Opportunistic transmissions can be conducted with the local information and the direction of the destination. Due to the nature of broadcast, the influence caused by the short-term channel variation is eliminated. Eventually, both the short-term and long-term channel variations in wireless networks can be taken into consideration.Then, this thesis intends to design an admission control scheme for flows to guarantee WMN works on an unsaturated state. Based on the information of network allocation vector and hidden terminal, we firstly estimate the available bandwidth accurately. Then, an admission control algorithm (ACA) is designed to guarantee the quality of service of realtime and non-realtime traffic. For realtime traffic, all nodes on a route make an admission control decision based on the estimated available bandwidth. For non-realtime traffic, a rate adaptation algorithm is proposed to adjust the sending rates of sources to prevent the network from entering the congestion state.Finally, we study the impacts of physical carrier sensing and channel rate on the performance of 802.11 wireless networks with chain topology. We show that by adopting different carrier sensing thresholds for the RTS and CTS transmissions, the blocking problem caused by exposed terminals can be greatly alleviated. In 802.11 wireless networks with this modification, the spatial reuse ratio under certain channel rates can be increased to 1/3, which is the highest value to our best knowledge. Furthermore, in multi-rate networks, we demonstrate that 1/3 is still the best value in terms of maximizing the achievable data rate under certain conditions. Then, this thesis proposes a new method to address the intra-flow contention by decreasing the carrier sensing threshold of the source node. This method requires less response time than that of the traditional method which adjusts the back-off window size.