Abstract—In this paper, we consider multi-hop wireless mesh networks, where each router node is equipped with multiple radio interfaces and multiple channels are available for communication. We address the problem of assigning channels to communication links in the network with the objective of minimizing overall network interference. Since the number of radios on any node can be less than the number of available channels, the channel assignment must obey the constraint that the number of different channels assigned to the links incident on any node is atmost the number of radio interfaces on that node. The above optimization problem is known to be NP-hard. We design centralized and distributed algorithms for the above channel assignment problem. To evaluate the quality of the solutions obtained by our algorithms, we develop a semidefinite program formulation of our optimization problem to obtain a lower bound on overall network interference. Empirical evaluations on randomly generated network graphs show that our algorithms perform close to the above established lower bound, with the difference diminishing rapidly with increase in number of radios. Also, detailed ns-2 simulation studies demonstrate the performance potential of our channel assignment algorithms in 802.11-based multi-radio mesh networks. I.

Abstract — To increase the utilization of the available frequency channel space in 802.11-based wireless mesh networks, recent work has explored solutions based on multi-radio stations. This paper reports on our design and experimental study of a distributed, self-stabilizing mechanism that assigns channels to multi-radio nodes in wireless mesh networks. We take a modular approach by decoupling the channel selection decision from the data forwarding mechanism, which makes our solution readily applicable to real-world operation when used with emerging multi-radio routing solutions. We demonstrate the efficacy of our protocol on a real-world, 14-node testbed comprised of nodes, each equipped with an 802.11a card and an 802.11g card. We show via extensive measurements on our testbed that our channel assignment algorithm improves the network capacity by 50 % in comparison to a homogeneous channel assignment and by 20% in comparison to a random assignment. I.

Wireless mesh networks (WMNs) have been proposed as a solution for ubiquitous last-mile broadband access. A critical limiting factor for many WMN protocols in realizing their throughput potential is the interference between nodes in the WMN. Understanding and characterizing such interference is important for a variety of purposes such as channel assignment, route selection, and fair scheduling. Instead of using ad hoc heuristics, a recent study proposed characterizing interference in a WMN by measuring two-way interference, i.e., interference between each pair of communicating links. In this paper, we study the extent of multi-way interference, i.e., the interference caused by multiple transmitters to a communicating link. We find through simulations and through measurements of a 32-node wireless testbed that even if these transmitters individually do not interfere significantly with a given communicating link, simultaneous transmissions of them have the potential to significantly affect the throughput of the communicating link. This implies that pairwise interference measurements may be optimistic when used to drive protocols in wireless mesh networks. Encouragingly, we find that this phenomenon, although significant when it occurs, is not widespread. In particular, multi-way interference caused significant additional throughput degradation compared to pairwise interference to a small fraction of the links in the testbed over our measurement period. In addition, we find that there is a strong correlation between the impact of multi-way interference and the quality of the link under consideration. We conclude with recommendations on how protocols should take multi-way interference into account.

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.

Motivated by the observation that channel assignment for multiradio multi-channel mesh networks should support both unicast and local broadcast 1, should be interference-aware, and should result in low overall switching delay, high throughput, and low overhead, we propose two flexible localized channel assignment algorithms based on s-disjunct superimposed codes. These algorithms support the local broadcast and unicast effectively, and achieve interference-free channel assignment under certain conditions. In addition, under the primary interference constraints 2, the channel assignment algorithm for unicast can achieve 100 % throughput with a simple scheduling algorithm such as the maximal weight independent set scheduling, and can completely avoid hidden/exposed terminal problems under certain conditions. Our algorithms make no assumptions on the underlying network and therefore are applicable to a wide range of MR-MC mesh network settings. We conduct extensive theoretical performance analysis to verify our design.

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.

Abstract. Fixed broadband wireless access is a promising technology allowing Internet service providers to expend their customer base in sparsely populated rural areas. Because the size of the target service area is humongous, relay infrastructure is essential. Installing and maintaining this relay infrastructure is the main cost associated with such networks. Thus, we develop an optimization framework which computes the minimum number of relay stations and their corresponding channel configurations such that a pre-specified subscribers ’ traffic demand can be satisfied. Since the problem is a mixed-integer program, we propose an efficient optimization algorithm to compute the optimal solution in a reasonable amount of time. Our numerical results show that by using a few relay stations in a rural community, broadband Internet access can be established in a cost effective manner.

A multi-channel wireless mesh network (MC-WMN) consists of a number of stationary wireless routers, where each router is equipped with multiple network interface cards (NICs). Each NIC operates on a distinct frequency channel. Two neighboring routers establish a logical link if each one has an NIC operating on a common channel. Given the physical topology of the routers and other constraints, four important issues should be addressed in MC-WMNs: logical topology formation, interface assignment, channel allocation, and routing. Logical topology determines the set of logical links. Interface assignment decides how the logical links should be assigned to the NICs in each wireless router. Channel allocation selects the operating channel for each logical link. Finally, routing determines through which logical links the packets should be forwarded. In this paper, we mathematically formulate the logical topology design, interface assignment, channel allocation, and routing as a joint linear optimization problem. Our proposed MC-WMN architecture is called TiMesh. Extensive ns-2 simulation experiments are conducted to evaluate the performance of TiMesh and compare it with two other MC-WMN architectures Hyacinth [1] and CLICA [2]. Simulation results show that TiMesh achieves higher aggregated network throughput and lower end-to-end delay than Hyacinth and CLICA for both TCP and UDP traffic. It also provides better fairness among different flows.

Fixed Broadband Wireless Access (FBWA) technology is designed to serve as a wireless DSL replacement to provide broadband Internet access in underserved areas where no other access technology exists. Due to the enormousness of the target service area, relay equipment play an important role in such networks, and the installation and maintenance cost of the network is directly proportional to the cost of the relay equipment. To minimize the network operational cost, an optimization framework which computes the minimum number of relay stations and their corresponding placements and channel assignments in the network is desired. Because the problem is NP-hard, we propose an efficient optimization algorithm based on a modified version of Bender’s decomposition to iteratively compute converging bounds to the problem solution. Our numerical results show that by using a few relay stations in a rural community, broadband Internet access can be established in a cost effective manner. Key words: Fixed broadband wireless access, relay stations, placement and channel assignment, Bender’s decomposition, mathematical programming/optimization.