Bandwidth Allocation And Channel Assignment In WiMax Mesh Networks

World Interoperability for Microwave Access(WiMax) is one of the leading technologies in the context of Broadband Wireless Access(BWA).The PHY and MAC layer specifications of WiMax networks are defined by the IEEE 802.16-2004 standard.According to this standard,WiMax systems can work in Point-to-Multipoint(PMP) mode or mesh mode.However,this standard does not specify the MAC layer bandwidth allocation and channel assignment algorithms for the mesh mode,which is decisive to the system performance in terms of throughput and quality of service.We investigate these issues in this thesis.As specified in the IEEE 802.16-2004 standard,time slot allocation for end-to-end traffic flow in WiMax mesh networks is controlled by a centralized scheduling algorithm.To support high-quality multimedia services on the network,the scheduling algorithm should be able to minimize the total transmission time for all traffic flows.Chapter 3 studies the multi-channel scheduling problem in order to explore the potential of simultaneous transmissions and thus minimize the total transmission time in WiMax mesh networks.For a given network topology with fixed routing tree,we first analyze how many channels are sufficient for the avoidance of interference.Then we present an efficient scheduling algorithm along with the channel assignment strategy for time slot allocation.The simulation results show that our scheme can improve the system performance substantially as compared with the single channel system.Also,we observe that double channel settings may provide a performance similar to the multiple channels.Chapter 4 studies the routing,time slot allocation and channel assignment problem in multi-channel multi-transceiver WiMax mesh networks,where multiple transceivers are supported on each station and can switch between different channels.We develop an interference-aware route construction algorithm,which construct a routing tree during the network entry process,in order to minimize the interference.We also propose a time slot allocation algorithm for multi-transceiver networks.In this algorithm,each transceiver is allowed to switch between at most 2 channels, according to the result of chapter 3.The simulation part shows the impact of channels and transceivers on total transmission time.In WiMax mesh networks,transient traffic between neighbor stations can be controlled by an uncoordinated distributed scheduling algorithm.According to this algorithm a three-way handshake must be initiated before data transmission.If the handshake fails,the transmitter must wait for a certain period before its next transmission,In Chapter 5 we analyze the performance of this algorithm. Due to the complexity of the problem,we only present a model for infinite networks with grid topology so all nodes can be considered identical.The behavior of each station in stable stage can be described as a Markov regeneration process.We analyze the impact of neighbor nodes on the transmission fail probability of a certain node,then calculate the throughput of each node.In the simulation part a custom simulator is used to show the effectiveness of our analytical model.Chapter 6 studies the problem of resource management on hybrid wireless mesh networks,where WiMax is used as the backbone.We propose resource publishing/discovery algorithms for two kinds of resources,resources that can only be provided by WiMax stations and resources that can be on both WiMax and client stations.In our solution we use the base station to coordinate the transmissions of resource publishing/discovery messages.We also propose a time slot allocation schema to support the application layer resource management.Although the PHY and MAC layer specifications of WiMax mesh networks has been well defined,there is still work to do in order to increase the system throughput and improve the quality of service.In final chapter,we summarize our main contribution and conclude this thesis by pointing out our future work.