Research On Scheduling Mechanism In WiMAX Mesh Network

Due to the high bandwidth, flexible mobility and QoS demands in wireless access system, the BWA (Broadband wireless Access) has gained an increased interest these years. The WiMAX (World interoperability for Microwave access) based on IEEE 802.16 standard is one of the most promising technologies in the future. As the last-mile solution, WiMAX can offer greater wireless coverage of 5 miles, with LOS (Line of Sight) transmission with bandwidth up to 70 Mbps. The optional mesh network connection defined in IEEE 802.16-2004 is the supplement of the single hop PMP (Point to Multipoint) mode. In the Mesh mode, several Mesh SS (Subscriber Station) can constitute a small multipoint to multipoint wireless connection, without specific uplink and downlink sub-frame.IEEE 802.16 mesh protocol specifies two scheduling mechanisms: centralized scheduling mechanism and distributed scheduling mechanism. In the centralized scheduling mechanism, BS node has information of the overall network and is responsible for the bandwidth allocation. In the distributed scheduling mechanism, nodes are self organized and negotiate bandwidth allocation by three-way handshake process. Both the centralized and distributed scheduling mechanism has a large extent influence on the overall performance of the network. While the IEEE 802.16 standard has not specified the details of the scheduling algorithm, defining a good bandwidth allocation algorithm to improve network performance becomes research issue in WiMAX Mesh network. It is also the focus of this thesis.In the first part of the thesis, it introduces the rise of WiMAX Mesh network and IEEE 802.16 standard. Then the thesis lists current research work in WiMAX Mesh network and points out some challenge in scheduling mechanism. Consiquently, data frame structure, network access process, centralized and distributed scheduling etc., are discussed in Chapter 2.Secondly, a scheduling model based on flow-fairness is established on centralized scheduling mechanism to analysis the interference condition of nodes and fairness of data flow. Then the thesis proposes a flow-fairness centralized scheduling algorithm (FFCS) to solve scheduling problem. FFCS contains a random initial algorithm and an exchange algorithm. Simulation results show that FFCS provides a better throughput and fairness performance in all size networks. Then, the thesis studies the three-way handshake process under coordinated distributed scheduling mechanism. The relationship of three-way handshake time, the number of neighbors, and three-way handshake parameters of nodes and its neighbors are derived from a mathematical analysis. Based on the relationship, the thesis proposes a scheme called QoSDx to dynamically adjust handshake parameters according to node's QoS demands. The QoSDx scheme effectively guarantees different demand of data service especially delay-sensitive service.Finally, the thesis analyzes the link scheduling model in WiMAX mesh network and proposes a Fair Rate-Balance link Scheduling scheme (FRBS). FRBS calculates the scheduling parameters under stability constraint to balance the arrival data and the outgoing data. At the grant step, FRBS assigns bandwidth using a max-min fair Round Robin algorithm for link fairness. Simulation results show that FRBS has much better performance in both light load and heavy load network.On the whole, the proposed scheduling scheme in WiMAX Mesh network which characterized by the efficiency and fairness can provide high throughput and low delay services and further improve the user experience. The study of this thesis provides a strong foundation for other related research in WiMAX Mesh network in the future.