abstract: A Fiber-Wireless (FiWi) network integrates a passive optical network (PON) with wireless mesh networks (WMNs) to provide high speed backhaul via the PON while offering the flexibility and mobility of a WMN. Generally, increasing the size of a WMN leads to higher wireless interference and longer packet delays. The partitioning of a large WMN into several smaller WMN clusters, whereby each cluster is served by an Optical Network Unit (ONU) of the PON, is examined. Existing WMN throughput-delay analysis techniques considering the mean load of the nodes at a given hop distance from a gateway (ONU) are unsuitable for the heterogeneous nodal traffic loads arising from clustering. A simple analytical queuing model that considers the individual node loads to accurately characterize the throughput-delay performance of a clustered FiWi network is introduced. The accuracy of the model is verified through extensive simulations. It is found that with sufficient PON bandwidth, clustering substantially improves the FiWi network throughput-delay performance by employing the model to examine the impact of the number of clusters on the network throughput-delay performance. Different traffic models and network designs are also studied to improve the FiWi network performance. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2015

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.

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.

It is well known that TCP performs poorly in wireless mesh networks. There has been intensive research in this area, but most work uses simulation as the only evaluation method; however, it is not clear whether the performance gains seen with simulation will translate into benefits on real networks. To explore this issue, we have implemented ATP (Ad-hoc Transport Protocol), a transport protocol designed specifically for wireless ad hoc networks. We have chosen ATP because it uses a radically different design from TCP and because reported results claim significant improvement over TCP. We show how ATP must be modified in order to be implemented in existing open-source wireless drivers, and we perform a comprehensive performance evaluation on mesh testbeds under different operating conditions. Our results show that the performance of ATP is highly sensitive to protocol parameters, especially the epoch timeout value. To improve its performance we design an adaptive version that utilizes a self-adjustable feedback mechanism instead of a fixed parameter. A comprehensive measurement study demonstrates the advantages of our adaptive ATP under various operating conditions. For networks with high bit-rate, low quality links, our adaptive version of ATP demonstrates an average of more than 50% gain in goodput over the default ATP for a single flow case. With respect to fairness, the adaptive ATP generally outperforms the default ATP by an order of magnitude in most results.

Internet rate control protocols, such as TCP, encounter severe performance problems in wireless mesh networks. Because wireless networks use shared communication channels, contention and interference can significantly degrade flow throughput and fairness. Existing research takes either an engineering-based or optimization-based approach to solve the performance problems. The engineering-based approach usually solves a specific observed problem, but does not necessarily optimize the overall performance. The optimization-based approach mathematically models the network to find the optimal resource allocation among competing flows. The model can lead to a distributed rate control algorithm with performance guarantees, but relatively little work has been done to verify that the algorithm leads to good performance in real networks. This dissertation develops a more accurate network optimization model, implements the derived distributed rate control algorithm in a mesh testbed, and discusses observations in the extensive experiments. We first synthesize models used for optimizing fair rate control for wireless mesh networks, and discuss their tradeoffs. We then propose a partial interference model which uses more accurate objective functions and constraints as compared to the binary interference model. Numerical results show that the partial interference model outperforms the binary interference model in all scenarios tested, and the results also suggest that partial interference should be modeled separately from contention. Our experimental results confirm the prevalence of partial interference in our mesh testbed, and show that the partial interference model results in significantly improved performance in a typical interference topology. We also observe a significant deviation between theory and practice, whereby, the assumption of a linear relationship between interfering links breaks in our experiments. We discuss several directions to further investigate this issue.

When used in a wireless mesh network, TCP has shortcomings in the areas of throughput and fairness among traffic flows. Several methods have been proposed to deal with TCP's weakness in a wireless mesh, but most have been evaluated with simulations rather than experimentally. We evaluate several major enhancements to TCP – pacing, conservative windows, and delayed ACKs – to determine whether they improve performance or fairness in a mesh network operating in the BYU Computer Science building. We also draw conclusions about the effectiveness of wireless network simulators based on the accuracy of reported simulation results.

<p> Wireless mesh networks are now being used to deploy radio coverage in a large variety of outdoor applications. One of the major obstacles that these networks face is that of providing the nodes with electrical power and wired network connections. Solar powered mesh nodes are increasingly used to eliminate the need for these types of connections, making the nodes truly tether-less. In these types of networks however, the cost of the energy collection and storage components can be a significant fraction of the total node cost, which motivates a careful selection of these resources.</p> <p> This thesis focusses on key issues relating to the deployment and operation of solar powered wireless mesh networks. First, the problem of provisioning the mesh nodes with a suitable solar panel and battery configuration is considered. This is done by assuming a bandwidth usage profile and using historical solar insolation data for the desired deployment location. A resource provisioning algorithm is proposed based on the use of temporal shortest-path routing and taking into account the node energy-flow for the target deployment time period. A methodology is introduced which uses a genetic algorithm (GA) to incorporate energy-aware routing into the resource assignment procedure. Results show that the proposed resource provisioning algorithm can achieve large cost savings when compared to conventional provisioning methods.</p> <p> During post-deployment network operation, the actual bandwidth profile and solar insolation may be different than that for which the nodes were originally provisioned. To prevent node outage, the network must reduce its workload by flow controlling its input traffic. The problem of admitting network bandwidth flows in a fair manner is also studied. A bound is first formulated which achieves the best max/min fair flow control subject to eliminating node outage. The bound motivates a proposed causal flow control algorithm whose operation uses prediction based on access to on-line historical weather data. The results show that the proposed algorithm performs well when compared to the analytic bound that is derived for this problem.</p> <p> Finally, as user traffic evolves, the network resources need to be updated. This problem is considered using a minimum cost upgrade objective. A mixed integer linear programming (MILP) formulation is derived to obtain a lower bound on the network update cost. A genetic algorithm is used to determine practical cost-effective network resource upgrading. The results show that the proposed methodology can obtain significant cost savings.</p> / Thesis / Doctor of Philosophy (PhD)

The rapid advances in networking technology have enabled large-scale deployments of online video streaming services in today's Internet. In particular, wireless Internet access technology has been one of the most transforming and empowering technologies in recent years. We have witnessed a dramatic increase in the number of mobile users who access online video services through wireless access networks, such as wireless mesh networks and 3G cellular networks. Unlike in wired environment, using a dedicated stream for each video service request is very expensive for wireless networks. This simple strategy also has limited scalability when popular content is demanded by a large number of users. It is desirable to have a robust wireless access environment that can sustain a sudden spurt of interest for certain videos due to, say a current event. Moreover, due to the mobility of the video users, smooth streaming performance during the handoff is a key requirement to the robustness of the wireless access networks for mobile video users. In this dissertation, the author focuses on the robustness of the wireless mesh access (WMA) environment for mobile video users. Novel video sharing techniques are proposed to reduce the burden of video streaming in different WMA environments. The author proposes a cross-layer framework for scalable Video-on-Demand (VOD) service in multi-hop WiMax mesh networks. The author also studies the optimization problems for video multicast in a general wireless mesh networks. The WMA environment is modeled as a connected graph with a video source in one of the nodes and the video requests randomly generated from other nodes in the graph. The optimal video multicast problem in such environment is formulated as two sub-problems. The proposed solutions of the sub-problems are justified using simulation and numerical study. In the case of online video streaming, online video server does not cooperate with the access networks. In this case, the centralized data sharing technique fails since they assume the cooperation between the video server and the network. To tackle this problem, a novel distributed video sharing technique called Dynamic Stream Merging (DSM) is proposed. DSM improves the robustness of the WMA environment without the cooperation from the online video server. It optimizes the per link sharing performance with small time complexity and message complexity. The performance of DSM has been studied using simulations in Network Simulator 2 (NS2) as well as real experiments in a wireless mesh testbed. The Mobile YouTube website (http://m.youtube.com) is used as the online video website in the experiment. Last but not the least; a cross-layer scheme is proposed to avoid the degradation on the video quality during the handoff in the WMA environment. Novel video quality related triggers and the routing metrics at the mesh routers are utilized in the handoff decision making process. A redirection scheme is also proposed to eliminate packet loss caused by the handoff.

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