Recent advances in Wireless Mesh Networks (WMNs) have overcome the drawbacks of traditional wired networks and wireless ad hoc networks. WMNs will play a leading role in the next generation of networks, and the question of how to provide smooth mobility for WMNs is the driving force behind the research. The inherent characteristics of WMNs, such as relatively static backbones and highly mobile clients, require new handoff management solutions to be designed and implemented. This thesis first presents our research work on handoff management schemes in traditional WMNs. In general, a handoff process includes two parts, the MAC layer handoff and the network layer handoff. For the MAC layer handoff, a self-configured handoff scheme with dynamic adaptation is presented. Before the mobile node starts the probe process, it configures parameters for each channel to optimize the scan process. Moreover, a fast authentication scheme to reduce authentication latency for WiFi-based mesh networks is introduced. A tunnel is introduced to forward data packets between the new access router and the original reliable access router to recover data communication before the complete authentication process is finished. To minimize the network layer handoff latency, a hybrid routing protocol for forwarding packets is proposed: this involves both the link layer routing and the network layer routing. Based on the hybrid routing protocol, both intra-domain and inter-domain handoff management have been designed to support smooth roaming in WMNs. In addition, we extend our work to Vehicular Mesh Networks (VMNs). Considering the characteristics of VMNs, a fast handoff scheme is introduced to reduce handoff latency by using a multi-hop clustering algorithm. Using this scheme, vehicle nodes are divided into different multi-hop clusters according to the relative mobility. Some vehicle nodes are selected as assistant nodes; and these assistant nodes will help the cluster head node to determine the next access router for minimizing handoff latency. Extensive simulation results demonstrate that the proposed scheme can reduce handoff latency significantly.

Magister Scientiae - MSc / This thesis presents an analysis of the impact of node mobility on the quality of service for voice over Internet Protocol in wireless mesh networks. Voice traffic was simulated on such a mesh network to analyze the following performance metrics: delay, jitter, packet loss and throughput. Wireless mesh networks present interesting characteristics such as multi-hop routing, node mobility, and variable coverage that can impact on quality of service. A reasonable deployment scenario for a small organizational network, for either urban or rural deployment, is considered with three wireless mesh network scenarios, each with 26 mesh nodes. In the first scenario, all mesh nodes are stationary. In the second scenario, 10 nodes are mobile and 16 nodes are stationary. Finally, in the third scenario, all mesh nodes are mobile. The mesh nodes are simulated to move at a walking speed of 1.3m per second. The results show that node mobility can increase packet loss, delay, and jitter. However, the results also show that wireless mesh networks can provide acceptable quality of service, providing that there is little or no background traffic generated by other applications. In particular, the results demonstrate that jitter across all scenarios remains within humanacceptable tolerances. It is therefore recommended that voice over Internet Protocol implementations on wireless mesh networks with background traffic be supported by quality of service standards; otherwise they can lead to service delivery failures. On the other hand, voice-only esh networks, even with mobile nodes, offer an attractive alternative voice over Internet Protocol platform. / South Africa

<p>Voice over IP (VoIP) traffic in a multi-hop wireless mesh network (WMN) suffers from a large overhead due to mac/IP/UDP/RTP headers and time collisions. A consequence of the large overhead is that only a small number of concurrent VoIP calls can be supported in a WMN[17]. Hop-to-hop packet aggregation can reduce network overhead and increase the capacity. Packet aggregation is a concept which combines several small packets, destined to a common next-hop destination, to one large packet. The goal of this thesis was to implement packet aggregation on a Linux distribution and to increase the number of concurrent VoIP calls. We use as testbed a two-hop WMN with a fixed data rate of 2Mbit/s. Traffic was generated between nodes using MGEN[20] to simulate VoIP behavior. The results from the tests show that the number of supported concurrent flows in the testbed is increased by 135% compared to unaggregated traffic.</p>

<p>Wireless mesh networks has rapid development over the last few years. However, due to properties such as distributed infrastructure and interference, which strongly affect the performance of wireless mesh networks, developing technology has to face the challenge of architecture and protocol design issues. Traditional layered protocols do not function efficiently in multi-hop wireless environments. To get deeper understanding on interaction of the layered protocols and optimize the performance of wireless mesh network, more recent researches are focusing on cross-layer measurement schemes and cross-layer protocol design. The goal of this project is to implement a distributed monitoring mechanism for IEEE802.11 based wireless mesh networks. This module is event-based and has modular structure that makes it flexible to be extended. This project results a novel Cross-Layer Monitoring Module, CLMM, which is a prototype that monitors each layer of the nodes locally and dynamically, calculates the average values of the metrics, compares these values with thresholds and handles the cross-layer messages of each node. The CLMM also has a routing module structure that can be extended to distribute the metrics to its neighbors.</p>

Thesis (M.Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2009.

This thesis proposes a potential solution for future ubiquitous broadband wireless access networks, called a cellular wireless mesh network (CMESH), and investigates a number of its performance issues. A CMESH is organized in multi-radio, multi-channel, multi-rate and multi-hop radio cells. It can operate on abundant high radio frequencies, such as 5-50 GHz, and thus may satisfy the bandwidth requirements of future ubiquitous wireless applications.<p> Each CMESH cell has a single Internet-connected gateway and serves up to hundreds of mesh nodes within its coverage area. This thesis studies performance issues in a CMESH, focusing on cell capacity, expressed in terms of the max-min throughput. In addition to introducing the concept of a CMESH, this thesis makes the following contributions.<p> The first contribution is a new method for analyzing theoretical cell capacity. This new method is based on a new concept called Channel Transport Capacity (CTC), and derives new analytic expressions for capacity bounds for carrier-sense-based CMESH cells.<p> The second contribution is a new algorithm called the Maximum Channel Collision Time (MCCT) algorithm and an expression for the nominal capacity of CMESH cells. This thesis proves that the nominal cell capacity is achievable and is the exact cell capacity for small cells within the abstract models.<p> Finally, based on the MCCT algorithm, this thesis proposes a series of greedy algorithms for channel assignment and routing in CMESH cells. Simulation results show that these greedy algorithms can significantly improve the capacity of CMESH cells, compared with algorithms proposed by other researchers.

The use of 802.11-based wireless mesh networks (WMNs) as an alternative network backbone technology is growing rapidly. The primary advantages of this approach are ease of deployment and lower cost. However, such networks typically exhibit poor fairness properties, often starving nodes if they are too many hops distant from the gateway. Researchers have shown a growing interest in this problem in recent years. Many solutions proposed amount to some level of source rate control, either by policing directly at the source, or via TCP congestion control reacting to a gateway-enforced rate limit. However, there has been limited study on the effectiveness of source rate control. In this thesis we first demonstrate that source rate control can only partially solve the fairness issue in 802.11-based WMNs, with some routers experiencing an undesirable degree of unfairness, which we call structural unfairness. We then identify the four necessary factors that cause structural unfairness. If we can eliminate or reduce any one of these conditions, we can eliminate or ameliorate the unfairness problem. We first investigate two techniques to improve 802.11 MAC scheduling: fixing the contention window and packet spacing at every router node, both means achievable with commodity 802.11 hardware. We show that the combination of these mechanisms provides a significant gain in fairness. We also perform case studies using another three techniques, channel re-assignment, routing changes, and careful router placement, to remove or reduce other necessary conditions. We demonstrate that these techniques, whenever applicable, can eliminate the unfairness problem entirely at times, or at least improve the situation.

The use of 802.11-based wireless mesh networks (WMNs) as an alternative network backbone technology is growing rapidly. The primary advantages of this approach are ease of deployment and lower cost. However, such networks typically exhibit poor fairness properties, often starving nodes if they are too many hops distant from the gateway. Researchers have shown a growing interest in this problem in recent years. Many solutions proposed amount to some level of source rate control, either by policing directly at the source, or via TCP congestion control reacting to a gateway-enforced rate limit. However, there has been limited study on the effectiveness of source rate control. In this thesis we first demonstrate that source rate control can only partially solve the fairness issue in 802.11-based WMNs, with some routers experiencing an undesirable degree of unfairness, which we call structural unfairness. We then identify the four necessary factors that cause structural unfairness. If we can eliminate or reduce any one of these conditions, we can eliminate or ameliorate the unfairness problem. We first investigate two techniques to improve 802.11 MAC scheduling: fixing the contention window and packet spacing at every router node, both means achievable with commodity 802.11 hardware. We show that the combination of these mechanisms provides a significant gain in fairness. We also perform case studies using another three techniques, channel re-assignment, routing changes, and careful router placement, to remove or reduce other necessary conditions. We demonstrate that these techniques, whenever applicable, can eliminate the unfairness problem entirely at times, or at least improve the situation.

This thesis proposes a potential solution for future ubiquitous broadband wireless access networks, called a cellular wireless mesh network (CMESH), and investigates a number of its performance issues. A CMESH is organized in multi-radio, multi-channel, multi-rate and multi-hop radio cells. It can operate on abundant high radio frequencies, such as 5-50 GHz, and thus may satisfy the bandwidth requirements of future ubiquitous wireless applications.<p> Each CMESH cell has a single Internet-connected gateway and serves up to hundreds of mesh nodes within its coverage area. This thesis studies performance issues in a CMESH, focusing on cell capacity, expressed in terms of the max-min throughput. In addition to introducing the concept of a CMESH, this thesis makes the following contributions.<p> The first contribution is a new method for analyzing theoretical cell capacity. This new method is based on a new concept called Channel Transport Capacity (CTC), and derives new analytic expressions for capacity bounds for carrier-sense-based CMESH cells.<p> The second contribution is a new algorithm called the Maximum Channel Collision Time (MCCT) algorithm and an expression for the nominal capacity of CMESH cells. This thesis proves that the nominal cell capacity is achievable and is the exact cell capacity for small cells within the abstract models.<p> Finally, based on the MCCT algorithm, this thesis proposes a series of greedy algorithms for channel assignment and routing in CMESH cells. Simulation results show that these greedy algorithms can significantly improve the capacity of CMESH cells, compared with algorithms proposed by other researchers.

With the wireless mesh network in the embedded systems related applications booming in recent years, the demand of enhancing the overall end to end network traffic and ensuring a stable connection is growing. We proposed a Dynamic Multi-channel Multi-path Routing Protocol (DMMR Protocol) to decompose contending traffics over different channel, different time and different paths to enhance the end to end network traffic. Choosing channel dynamically according to the channel usage around node in the process of finding paths can avoid inter-flow and intra-flow channel competition. We tend to choose paths with less intersection nodes to reduce the probability of multiple paths are broken at same time when a single node cannot work. We can enhance end to end network traffic further by using multiple interfaces at one node. We use NS2 to test DMMR Protocol, and analyzing the overall end to end traffic when multiple connections are setting up in the network. If the network can accept a new connection, the increment of end to end traffic is same as the traffic of the new connection. In connection robust test, a single path broken will not affect other flows in same connection and the end to end traffic in the connection will recovery immediately when the broken path is repaired.