In this paper, we present a routing and channel assignment protocol for multi-channel multi-hop wireless net-works. We view a multi-hop network as an extension to infrastructure networks, where a mobile host may connect to an access point using multi-hop wireless routes, via other mobile hosts or wireless routers. The access points are configured to operate on one of multiple available channels. Mobile hosts and wireless routers can select its operating channel dynamically through channel switching. In this environment, we propose a routing protocol that finds routes and assigns channels to balance load among channels while maintaining connectivity. The protocol works with nodes equipped with a single network interface, which distinguishes our work with other multi-channel routing protocols that require multiple interfaces per node. Supporting nodes with single network interface is beneficial because having multiple interfaces can be costly for small and cheap devices. The protocol discovers multiple routes to multiple access points, possibly operating on different channels. Based on traffic load information, each node selects the “best ” route to an access point, and synchronizes its channel with the access point. With this behavior, the channel load is balanced, removing hot spots and improving channel utilization. The channel assignment assures every node has at least one route to an access point, where all intermediate nodes are operating on the same channel. Our simulation results show that the proposed protocol successfully adapts to changing traffic conditions and improves performance over a single-channel protocol and a protocol with random channel assignment.

Abstract — Despite years of research and development, pioneering deployments of multihop wireless networks have not proven successful. The performance of routing and transport is often unstable due to contention-induced packet losses, especially when the network is large and the offered load is high. In this paper we propose RAIN, a reliable wireless network architecture for large-scale multihop wireless networks. A RAIN network enforces contention control by limiting the queue length at intermediate wireless routers to the minimum. To keep the queue short a RAIN network enforces congestion control through in-network implicit back-pressure. RAIN congestion control is built on wireless datalink layer mechanisms, e.g., mandatory per-frame acknowledgement and inter-frame backoff in popular CSMA/CA wireless transceivers, therefore very efficient and effective compared with those defined at the network or transport layer for the wired Internet. As a result of the built-in contention and congestion control, RAIN presents the end hosts a highly reliable network service model, even more reliable than that of the wired Internet. The end hosts only need to deal with packet losses due to router or routing failures. Therefore, the transport protocol can be significantly simplified. This is in stark contrast to the existing approach of adding more and more complexity to adapt TCP for multihop wireless networks. We propose the details of RAIN datalink layer protocol, and a simple transport protocol at the end hosts. Performance evaluation through intensive simulations shows that RAIN improves the throughput by up to 92 % and fairness by up to 48%, with packet losses due to contention and congestion significantly reduced. I.

This thesis presents a measurement-parameterized performance study of deploy-ment factors in wireless mesh networks using four performance metrics: client cov-erage area, backhaul tier connectivity, protocol-dependent throughput, and per-user fair rates. For each metric, I identify and study deployment factors which strongly influence mesh performance via an extensive set of Monte Carlo simulations capturing realistic physical layer behavior. My findings include: (i) A random topology is un-suitable for a large-scale mesh deployment due to doubled node density requirements, yet a moderate level of perturbations from ideal grid placement has minor impact. (ii) Multiple backhaul radios per mesh node is a cost-effective deployment strategy as it leads to mesh deployments costing 50 % less than with a single-radio architecture. This work adds to the understanding of mesh deployment factors and their general impact on performance, providing further insight into practical mesh deployments. Acknowledgments First and foremost, I would like to thank my advisor, Dr. Edward Knightly, for the guidance, support, and opportunities he has provided me. He has been a

Abstract — Multicast is a key technology that provides efficient data communication among a set of nodes for wireless multi-hop networks. In sensor networks and MANETs, multicast algorithms are designed to be energy efficient and to achieve optimal route discovery among mobile nodes, respectively. However, in wireless mesh networks, which are required to provide high quality service to end users as the “last-mile ” of the Internet, throughput maximization conflicting with scarce bandwidth has the paramount priority. We propose a Level Channel Assignment (LCA) algorithm and a Multi-Channel Multicast (MCM) algorithm to optimize throughput for multi-channel and multiinterface mesh networks. The algorithms first build a multicast structure by minimizing the number of relay nodes and hop count distances between the source and destinations, and use dedicated channel assignment strategies to improve the network capacity by reducing interference. We also illustrate that the use of partially overlapping channels can further improve the throughput. Simulations show that our algorithms greatly outperform the single-channel multicast algorithm. We observe that MCM achieves better throughput and shorter delay while LCA can be realized in distributed manner.

Realizing the full potential of a multi-radio mesh network involves two main challenges: how to assign channels to radios at each node to minimize interference and how to choose high throughput routing paths in the face of lossy links, variable channel conditions and external load. This paper presents ROMA, a practical, distributed channel assignment and routing protocol that achieves good multi-hop path performance between every node and one or more designated gateway nodes in a dual-radio network. ROMA assigns nonoverlapping channels to links along each gateway path to eliminate intra-path interference. ROMA reduces inter-path interference by assigning different channels to paths destined for different gateways whenever possible. Evaluations on a 24-node dual-radio testbed show that ROMA achieves high throughput in a variety of scenarios.

Capacity limitation is one of the fundamental issues in wireless mesh networks. This paper addresses capacity improvement issues in multi-radio multi-channel wireless mesh networks. Our objective is to find both dynamic and static channel assignments and corresponding link schedules that maximize the network capacity. We focus on determining the highest gain we can achieve from increasing the number of radios and channels under certain traffic demands. We consider two different types of traffic demands. One is expressed in the form of data size vector, and the other is in the form of data rate vector. For the first type of traffic demand, our objective is to minimize the number of time slots to transport all the data. For the second type of traffic demand, our objective is to satisfy the bandwidth requirement as much as possible. We perform a trade-off analysis between network performance and hardware cost based on the number of radios and channels in different topologies. This work provides valuable insights for wireless mesh network designers during network planning and deployment. I.

Abstract — This paper analyzes the impact of different MAC (Medium Access Control) and transmission rate adaptation schemes on wireless mesh networks. The considered protocols include three different MAC protocols specified in IEEE 802.11 standards, i.e., 802.11, 802.11e, and 802.11n, and three rate adaptation schemes, i.e., ARF (Automatic Rate Fallback), RBAR (Receiver-Based Auto Rate), and 802.11n rate adaptation. We also study the interactions of these MAC strategies with the state-of-the-art routing metric ETT (Expected Transmission Time). Through comparative simulation evaluations, we investigate the effectiveness of these protocols when they coexist on both single-hop and multi-hop wireless mesh network environments. As these MAC strategies are designed for single-hop WLANs, we observed their limitations on multi-hop wireless mesh networks. We analyze their performances and suggest solutions for improvements. Based on our simulation results, we also argue for the need of a new routing metric that takes advantage of the new emerging MAC features. I.

Many efforts have been devoted to maximizing the network throughput with limited channel resources in multi-radio multi-channel wireless mesh networks. It has been believed that the limited spectrum resource can be fully exploited by utilizing partially overlapping channels in addition to nonoverlapping channels in 802.11b/g networks. However, there are only few studies of channel assignment algorithms for partially overlapping channels. In this paper, an extension to the traditional conflict graph model, weighted conflict graph, is proposed to model the interference between wireless links more accurately. Based on this model, we first present a greedy algorithm for partially overlapping channel assignment, and then propose a novel genetic algorithm, which has the potential to obtain better solutions. Through evaluation, we demonstrate that the network performance can be dramatically improved by properly utilizing the partially overlapping channels. In addition, the genetic algorithm outperforms the greedy algorithm in mitigating the interference within the network and therefore leads to higher network throughput.

Abstract — Wireless Building Automation is a complex problem dealing with a lot of trade offs: on one hand sensors and actuators have to be as energy-efficient as possible, while on the other hand the overall network should be performant and resilient enough to extend or even replace a wired backbone. In addition, the network should be able to serve existing IEEE 802.11 devices such as PDAs, cameras and laptops. Furthermore, surveillance, fire detection and other critical building automation applications require end-to-end Quality of Service support to ensure the bandwidth and delay requirements also in the case of high network loads. A networking technology that simultaneously fulfills all those requirements does not exist. This paper introduces a system architecture that combines heterogeneous technologies into an appropriate networking solution. I.

Abstract- Multicast is a key technology that provides efficient data communication among a set of nodes for wireless multi-hop networks. In sensor networks and MANETs, multicast algorithms are designed to be energy efficient and to achieve optimal route discovery among mobile nodes, respectively. However, in wireless mesh networks, which are required to provide high quality service to end users as the "last-mile " of the Internet, throughput maximization conflicting with scarce bandwidth has the paramount priority. We propose a Level Channel Assignment (LCA) algorithm and a Multi-Channel Multicast (MCM) algorithm to optimize throughput for multi-channel and multiinterface mesh networks. The algorithms first build a multicast structure by minimizing the number of relay nodes and hop count distances between the source and destinations, and use dedicated channel assignment strategies to improve the network capacity by reducing interference. We also illustrate that the use of partially overlapping channels can further improve the throughput. Simulations show that our algorithms greatly outperform the single-channel multicast algorithm. We observe that MCM achieves better throughput and shorter delay while LCA can be realized in distributed manner.