Showing papers on "Wireless mesh network published in 2007"

Embracing wireless interference: analog network coding

Abstract: Traditionally, interference is considered harmful. Wireless networks strive to avoid scheduling multiple transmissions at the same time in order to prevent interference. This paper adopts the opposite approach; it encourages strategically picked senders to interfere. Instead of forwarding packets, routers forward the interfering signals. The destination leverages network-level information to cancel the interference and recover the signal destined to it. The result is analog network coding because it mixes signals not bits.So, what if wireless routers forward signals instead of packets? Theoretically, such an approach doubles the capacity of the canonical 2-way relay network. Surprisingly, it is also practical. We implement our design using software radios and show that it achieves significantly higher throughput than both traditional wireless routing and prior work on wireless network coding.

Physical Layer Network Coding

Abstract: A main distinguishing feature of a wireless network compared with a wired network is its broadcast nature, in which the signal transmitted by a node may reach several other nodes, and a node may receive signals from several other nodes simultaneously. Rather than a blessing, this feature is treated more as an interference-inducing nuisance in most wireless networks today (e.g., IEEE 802.11). The goal of this paper is to show how the concept of network coding can be applied at the physical layer to turn the broadcast property into a capacityboosting advantage in wireless ad hoc networks. Specifically, we propose a physical-layer network coding (PNC) scheme to coordinate transmissions among nodes. In contrast to “straightforward” network coding which performs coding arithmetic on digital bit streams after they have been received, PNC makes use of the additive nature of simultaneously arriving electromagnetic (EM) waves for equivalent coding operation. PNC can yield higher capacity than straightforward network coding when applied to wireless networks. We believe this is a first paper that ventures into EM-wavebased network coding at the physical layer and demonstrates its potential for boosting network capacity. PNC opens up a whole new research area because of its implications and new design requirements for the physical, MAC, and network layers of ad hoc wireless stations. The resolution of the many outstanding but interesting issues in PNC may lead to a revolutionary new paradigm for wireless ad hoc networking.

Four-Bit Wireless Link Estimation.

Abstract: We consider the problem of estimating link quality in an ad-hoc wireless mesh. We argue that estimating links well requires combining information from the network, link, and physical layers. We propose narrow, protocol-independent interfaces for the layers, which in total provide four bits of information: 1 from the physical layer, 1 from the link layer, and 2 from the network layer. We present a link estimator design with these interfaces that reduces packet delivery costs by up to 44% over current approaches and maintains a 99% delivery ratio over large, multihop testbeds.

An Analysis of Wireless Network Coding for Unicast Sessions: The Case for Coding-Aware Routing

Abstract: A recent approach, COPE, for improving the throughput of unicast traffic in wireless multi-hop networks exploits the broadcast nature of the wireless medium through opportunistic network coding. In this paper, we analyze throughput improvements obtained by COPE-type network coding in wireless networks from a theoretical perspective. We make two key contributions. First, we obtain a theoretical formulation for computing the throughput of network coding on any wireless network topology and any pattern of concurrent unicast traffic sessions. Second, we advocate that routing be made aware of network coding opportunities rather than, as in COPE, being oblivious to it. More importantly, our work studies the tradeoff between routing flows "close to each other" for utilizing coding opportunities and "away from each other" for avoiding wireless interference. Our theoretical formulation provides a method for computing source-destination routes and utilizing the best coding opportunities from available ones so as to maximize the throughput. We handle scheduling of broadcast transmissions subject to wireless transmit/receive diversity and link interference in our optimization framework. Using our formulations, we compare the performance of traditional unicast routing and network coding with coding-oblivious and coding-aware routing on a variety of mesh network topologies, including some derived from contemporary mesh network testbeds. Our evaluations show that a route selection strategy that is aware of network coding opportunities leads to higher end-to-end throughput when compared to coding-oblivious routing strategies.

Channel Assignment Strategies for Multiradio Wireless Mesh Networks: Issues and Solutions

Abstract: Next-generation wireless mobile communications will be driven by converged networks that integrate disparate technologies and services. The wireless mesh network is envisaged to be one of the key components in the converged networks of the future, providing flexible high- bandwidth wireless backhaul over large geographical areas. While single radio mesh nodes operating on a single channel suffer from capacity constraints, equipping mesh routers with multiple radios using multiple nonoverlap- ping channels can significantly alleviate the capacity problem and increase the aggregate bandwidth available to the network. However, the assignment of channels to the radio interfaces poses significant challenges. The goal of channel assignment algorithms in multiradio mesh networks is to minimize interference while improving the aggregate network capacity and maintaining the connectivity of the network. In this article we examine the unique constraints of channel assignment in wireless mesh networks and identify the key factors governing assignment schemes, with particular reference to interference, traffic patterns, and multipath connectivity. After presenting a taxonomy of existing channel assignment algorithms for WMNs, we describe a new channel assignment scheme called MesTiC, which incorporates the mesh traffic pattern together with connectivity issues in order to minimize interference in multi- radio mesh networks.

Minimum Interference Channel Assignment in Multi-Radio Wireless Mesh Networks

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.

PPR: partial packet recovery for wireless networks

Abstract: Bit errors occur in wireless communication when interference or noise overcomes the coded and modulated transmission. Current wireless protocols may use forward error correction (FEC) to correct some small number of bit errors, but generally retransmit the whole packet if the FEC is insufficient. We observe that current wireless mesh network protocols retransmit a number of packets and that most of these retransmissions end up sending bits that have already been received multiple times, wasting network capacity. To overcome this inefficiency, we develop, implement, and evaluate a partial packet recovery (PPR) system.PPR incorporates two new ideas: (1) SoftPHY, an expanded physical layer (PHY) interface that provides PHY-independent hints to higher layers about the PHY's confidence in each bit it decodes, and (2) a postamble scheme to recover data even when a packet preamble is corrupted and not decodable at the receiver.Finally, we present PP-ARQ, an asynchronous link-layer ARQ protocol built on PPR that allows a receiver to compactly encode a request for retransmission of only those bits in a packet that are likely in error. Our experimental results from a 31-node Zigbee (802.15.4) testbed that includes Telos motes with 2.4 GHz Chipcon radios and GNU Radio nodes implementing the 802.15.4 standard show that PP-ARQ increases end-to-end capacity by a factor of 2x under moderate load.

Static-Priority Scheduling over Wireless Networks with Multiple Broadcast Domains

Abstract: We propose a wireless medium access control (MAC) protocol that provides static-priority scheduling of messages in a guaranteed collision-free manner. Our protocol supports multiple broadcast domains, resolves the wireless hidden node problem and allows for parallel transmissions across a mesh network. Arbitration of messages is achieved without the notion of a master coordinating node, global clock synchronization or out-ofband signalling. The protocol relies on bit-dominance similar to what is used in the CAN bus except that in order to operate on a wireless physical layer, nodes are not required to receive incoming bits while transmitting. The use of bit-dominance efficiently allows for a much larger number of priorities than would be possible using existing wireless solutions. A MAC protocol with these properties enables schedulability analysis of sporadic message streams in wireless multihop networks.

Distributed Channel Assignment in Multi-Radio 802.11 Mesh Networks

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.

Simultaneous Transmission and Reception for Improved Wireless Network Performance

Abstract: One of the limiting factors in ad hoc wireless mesh networks using traditional physical layer techniques is the inability to transmit and receive at the same frequency simultaneously. As a consequence, careful time-slot or frequency-reuse planning is required. This has adverse network data-rate and latency implications. The focus of this paper is a demonstration of signal processing techniques that enable simultaneous transmission and reception. These techniques employ informed-transmittermultiple-input multiple-output (MIMO) links. A combination of adaptive transmit and receive antenna array approaches is exploited. A number of important types of networking limitations can be resolved given simultaneous transmit and receive technology. The first example is the simultaneous link problem. By employing transmit and receive spatial adaptivity, two links can operate in close proximity using the same frequency at the same time. Another example is the full duplex relay node. Using the same frequency for both links, a given node can simultaneously receive packets from one node while forwarding them to another. For practical systems, two issues dominate performance: channel estimation error, often caused by stale estimates of the channel at the transmitter, and dynamic range limitations of the transmitter and receiver. These issues are investigated. Theoretical, simulated, and experimental results are presented.

Efficient Mesh Router Placement in Wireless Mesh Networks

Abstract: The placement of mesh routers (MRs) in building a wireless mesh network (WMN) is the first step to ensure the desired network performance. Given a network domain, the fundamental issue in placing MRs is to find the minimal configuration of MRs so as to satisfy the network coverage, connectivity, and Internet traffic demand. In this paper, the problem is addressed under a constraint network model in which the traffic demand is non-uniformly distributed and the candidate positions for MRs are pre-decided. After formulating the MR placement problem, we first provide the theoretical analysis to validate the traffic demand and determine the optimal position of Internet gateway (IGW). To reduce complexity of determining the locations of MRs while satisfying the traffic constraint, we propose an effective heuristic algorithm to obtain an close-to-optimal solution. Finally, our simulation results verify our analytical model and show the effectiveness of our proposed algorithm.

Home electrical device control within a wireless mesh network

Abstract: In embodiments of the present invention improved capabilities are described for associating a first node in a mesh network with an electrical device, wherein the electrical device comprises a home control device, enabling the mesh network to perform channel adjustment, transmitting data through the mesh network between the first node and a second node in the mesh network, wherein the transmission utilizes channel adjustment; and performing an action based at least in part on the transmitted data.

Communications network for distributed sensing and therapy in biomedical applications

Abstract: An implantable medical device system is provided with multiple medical devices implanted in a patient's body and a wireless mesh communication network providing multiple communication pathways between the multiple medical devices. A communication pathway between a first and a second implanted device of the multiple medical devices can comprise one or more of the other implanted multiple medical devices.

Node Placement Algorithm for Deployment of Two-Tier Wireless Mesh Networks

Abstract: In the deployment of wireless mesh networks (WMNs) the placement of Mesh Nodes (MNs) is an important design issue. The performance of WMNs is greatly affected by the location of the MNs. As it is difficult to place the MNs in a regular pattern in the real deployment, finding the optimal locations in the deployment environment is of much interest for the service providers. For a given possible locations for the MNs and the user density in the deployment environment, we aim to find the locations of the MNs to be used that maximizes the coverage and the connectivity of the network together. Due to high computational complexity of the exhaustive searching algorithm, an efficient local searching algorithm is proposed. Numerical results show that, the local search algorithm can give close to optimal performance with much lower time complexity than exhaustive searching.

mTreebone: A Hybrid Tree/Mesh Overlay for Application-Layer Live Video Multicast

Abstract: Application-layer overlay networks have recently emerged as a promising solution for live media multicast on the Internet. A tree is probably the most natural structure for a multicast overlay, but is vulnerable in the presence of dynamic end-hosts. Data-driven approaches form a mesh out of overlay nodes to exchange data, which greatly enhances the resilience. It however suffers from an efficiency-latency tradeoff, given that the data have to be pulled from mesh neighbors with periodical notifications. In this paper, we suggest a novel hybrid tree/mesh design that leverages both overlays. The key idea is to identify a set of stable nodes to construct a tree-based backbone, called treebone, with most of the data being pushed over this backbone. These stable nodes, together with others, are further organized through an auxiliary mesh overlay, which facilitates the treebone to accommodate node dynamics and fully exploit the available bandwidth between overlay nodes. This hybrid design, referred to as mTreebone, is braced by our real trace studies, which show strong evidence that the performance of an overlay closely depends on a small set of backbone nodes. It however poses a series of unique and critical design challenges, in particular, the identification of stable nodes and seamless data delivery using both push and pull methods. In this paper, we present optimized solutions to these problems, which reconcile the two overlays under a coherent framework with controlled overhead. We evaluate mTreebone through both simulations and PlanetLab experiments. The results demonstrate the superior efficiency and robustness of this hybrid solution.

Ad Hoc Mobile Wireless Networks Routing Protocols - A Review

Abstract: Mobile ad hoc networks(MANET) represent complex distributed systems that comprise wireless mobile nodes that can freely and dynamically self organize into arbitrary and temporary ad-hoc network topologies, allowing people and devices to seamlessly internet work in areas with no preexisting communication infrastructure e.g., disaster recovery environments. An ad-hoc network is not a new one, having been around in various forms for over 20 years. Traditionally, tactical networks have been the only communication networking application that followed the ad-hoc paradigm. Recently the introduction of new technologies such as Bluetooth, IEEE 802.11 and hyperlan are helping enable eventual commercial MANET deployments outside the military domain. These recent revolutions have been generating a renewed and growing interest in the research and development of MANET. To facilitate communication within the network a routing protocol is used to discover routes between nodes. The goal of the routing protocol is to have an efficient route establishment between a pair of nodes, so that messages can be delivered in a timely manner. Bandwidth and power constraints are the important factors to be considered in current wireless network because multi-hop ad-hoc wireless relies on each node in the network to act as a router and packet forwarder. This dependency places bandwidth, power computation demands on mobile host to be taken into account while choosing the protocol. Routing protocols used in wired network cannot be used for mobile ad-hoc networks because of node mobility. The ad-hoc routing protocols are divided into two classes: table driven and demand based. This paper reviews and discusses routing protocol belonging to each category.

Wireless Mesh Networks: Current Challenges and Future Directions of Web-In-The-Sky

Abstract: Within the short span of a decade, Wi-Fi hotspots have revolutionized Internet service provisioning. With the increasing popularity and rising demand for more public Wi-Fi hotspots, network service providers are facing a daunting task. Wi-Fi hotspots typically require extensive wired infrastructure to access the backhaul network, which is often expensive and time consuming to provide in such situations. wireless mesh networks (WMNs) offer an easy and economical alternative for providing broadband wireless Internet connectivity and could be called the web-in-the-sky. In place of an underlying wired backbone, a WMN forms a wireless backhaul network, thus obviating the need for extensive cabling. They are based on multihop communication paradigms that dynamically form a connected network. However, multihop wireless communication is severely plagued by many limitations such as low throughput and limited capacity. In this article we point out key challenges that are impeding the rapid progress of this upcoming technology. We systematically examine each layer of the network and discuss the feasibility of some state-of-the-art technologies/protocols for adequately addressing these challenges. We also provide broader and deeper insight to many other issues that are of paramount importance for the successful deployment and wider acceptance of WMNs.

Wireless Network Coding: Opportunities & Challenges

Abstract: Wireless networks suffer from a variety of unique problems such as low throughput, dead spots, and inadequate support for mobility. However, their characteristics such as the broadcast nature of the medium, spatial diversity, and significant data redundancy, provide opportunities for new design principles to address these problems. There has been recent interest in employing network coding in wireless networks. This paper explores the case for network coding as a unifying design paradigm for wireless networks, by describing how it addresses issues of throughput, reliability, mobility, and management. We also discuss the practical challenges facing the integration of such a design into the network stack.

A Performance Study of Deployment Factors in Wireless Mesh Networks

Abstract: We present a measurement-parameterized performance study of deployment factors in wireless mesh networks using three performance metrics: client coverage area, backhaul tier connectivity, and fair mesh capacity. For each metric, we identify and study topology factors and architectural features which strongly influence mesh performance via an extensive set of Monte Carlo simulations capturing realistic physical layer behavior. Our findings include: (i) A random topology is unsuitable for a large-scale mesh deployment due to doubled node density requirements, yet a moderate level of perturbations from ideal grid placement has a minor impact on performance. (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, (iii) Dividing access and backhaul connections onto two separate radios does not use the second radio efficiently as it only improves fair mesh capacity 40% to 80% for most users. This is in contrast to using the second radio to move half the user population to a new network operated on the second radio. This work adds to the understanding of mesh deployment factors and their general impact on performance, providing further insight into practical mesh deployments.

Wireless data networking

Abstract: A meshing network comprising one full function controller (WDC) and a plurality of nodes (WDN, WSN), that is RF quiet capable with very low power consumption and the ability to quickly heal itself and create new network paths. The network uses an addressing scheme that allows for each node to not have a network map but still be able to route messages. A piping scheme allows a mesh to become a high throughput network. A sensor rail protocol definition allows sensor devices to connect to nodes and route messages through the network.

DARWIN: distributed and adaptive reputation mechanism for wireless ad-hoc networks

Abstract: Mobile ad-hoc networks are deployed under the assumption that participating nodes are willing to forward other nodes' packets. In reputation-based mechanisms cooperation is induced by means of a threat of partial or total disconnection from the network if a node is non-cooperative; however packet collisions and interference may make cooperative nodes appear selfish sometimes. In this paper we use a simple network model to first study the performance of some proposed reputation strategies and then present a new mechanism that we call DARWIN (Distributed and Adaptive Reputation mechanism for WIreless ad-hoc Networks). The idea is to avoid a retaliation situation after a node has been falsely perceived as selfish so cooperation can be restored quickly. We prove that our strategy is robust to imperfect measurements, is collusion-resistant and can achieve full cooperation among nodes.

A multi-channel assignment method for multi-radio multi-hop wireless mesh networks

Abstract: Techniques are described for automatically determining quasi-static per-link channel assignments for each radio in multiple-hop mesh networks having nodes with two or more radios and where only a small number of channels is available for use in the network. The method optimally assigns the channels to the radios of all of the nodes in the network so as to achieve the lowest interference among links and the highest possible bandwidth.

A unified peer-to-peer and cache system for content services in wireless mesh networks

Abstract: A method and apparatus for receiving content over a wireless network are described, including determining a first server from which to receive a content clip to be streamed, requesting the content clip to be streamed from the selected first server, receiving the streamed content clip from the selected first server, determining a peer device from which to receive a content clip to be downloaded, requesting the content clip to be downloaded and receiving the downloaded content clip. The first server is a mesh content server.

Wireless occupancy and day-light sensing

Abstract: A system to control energy consumption in a room uses a wireless mesh network that allows for continuous connections and reconfiguration around blocked paths by hopping from node to node until a connection can be established, the mesh network including one or more wireless area network transceivers adapted to communicate data with the wireless mesh network, the transceiver detecting motion by analyzing reflected wireless signal strength.

Capacity of a wireless ad hoc network with infrastructure

Abstract: In this paper we study the capacity of wireless ad hoc networks with infrastructure support of an overlay of wired base stations. Such a network architecture is often referred to as hybrid wireless network or multihop cellular network. Previous studies on this topic are all focused on the two-dimensional disk model proposed by Gupta and Kumarin their original work on the capacity of wireless ad hoc networks. We further consider a one-dimensional network model and a two-dimensional strip model to investigate the impact of network dimensionality and geometry on the capacity of such networks. Our results show that different network dimensions lead to significantly different capacity scaling laws. Specifically, for a one-dimensional network of n nodes and b base stations, even with a small number of base stations, the gain in capacity is substantial, increasing linearly with the number of base stations as long as b log b ≤ n. However, a two-dimensional square (or disk) network requires a large number of base stations b = Ω(√n) before we see such a capacity increase. For a 2-dimensional strip network, if the width of the strip is at least on the order of the logarithmic of its length, the capacity follows the same scaling law as in the 2-dimensional square case. Otherwise the capacity exhibits the same scaling behavior as in the 1-dimensional network. We find that the different capacity scaling behaviors are attributed to the percolation properties of the respective network models.

Method and arrangement for providing a wireless mesh network

Abstract: A method and an arrangement for providing a wire-free mesh network are provided. An approval procedure is carried out in situations in which a subscriber who is registering on the mesh network transmits an MAC address which already exists in the mesh network, such that two different subscribers within the mesh network never have identical MAC addresses.

Security Issues in Wireless Mesh Networks

Abstract: Wireless mesh network (WMN) is a new wireless networking paradigm. Unlike traditional wireless networks, WMNs do not rely on any fixed infrastructure. Instead, hosts rely on each other to keep the network connected. Wireless Internet service providers are choosing WMNs to offer Internet connectivity, as it allows a fast, easy and inexpensive network deployment. One main challenge in design of these networks is their vulnerability to security attacks. In this paper, we investigate the principal security issues for WMNs. We study the threats a WMN faces and the security goals to be achieved. We identify the new challenges and opportunities posed by this new networking environment and explore approaches to secure its communication.

System and method for securing mesh access points in a wireless mesh network, including rapid roaming

Abstract: An authentication method in a mesh AP including using standard IEEE 802. 11i mechanisms between the mesh AP and an authenticator for authenticating the mesh AP to become a child mesh AP with a secure layer-2 link to a first parent mesh AP that has a secure tunnel to a Controller, including, after a layer-2 link between the child mesh AP and the first parent mesh AP is secured, undergoing a join exchange to form a secure tunnel between the child mesh AP and the Controller Further, a fast roaming method for re-establishing a secure layer-2 link with a new parent mesh AP including, while the mesh AP is a child mesh AP to the first parent mesh AP and has a secure layer-2 link to the first parent mesh AP, caching key information and wireless mesh network identity information.

Distributed channel allocation method and wireless mesh network therewith

Abstract: A distributed channel allocation method and a wireless mesh network with the same are provided herein. By the distributed channel allocation, interference situations are avoided in a wireless network communication, and the allocated bandwidth can then be fully utilized. Besides, unnecessary depletion of an allocated bandwidth due to the interference can be avoided. By this method, a time division technique is applied for dividing a transmission time of each wireless NIC, and different non-overlapping channels can be assigned to different timeslots. Different from other researches that require a symmetrical number of the NICs between a receiving node and a transmitting node, in this method, a unique wireless NIC may communicate with the wireless NICs. The method provides the feature that the number of the NICs on a certain node can be adjusted to meet a communication requirement, by which the efficiency of a network flow is also significantly improved.

Wireless Mesh Networks: A Survey

Abstract: In this paper, a survey on architectures, applications and design issues of wireless mesh networks (WMNs) is conducted. Wireless mesh network is a type of distributed, self-organizing, self-configuring and self-healing network. When access points in wireless local area networks (WLANs) start to communicate and get networked in an ad hoc fashion to relay packets for their neighbors, a wireless mesh network comes into being. Therefore, WLANs and ad hoc networks play significant roles during the development of wireless mesh networks. There are three types of architectures for wireless mesh networks, which are backbone WMN, client WMN and hybrid WMN, respectively. Among them, backbone WMN is the most common type and hybrid WMN is the most applicable type. For a better understanding of characteristics of wireless mesh networks, in this paper, several common features and main differences between wireless mesh networks and ad hoc networks are discussed. Moreover, some open issues existing in wireless mesh networks are investigated to provide some directions for further research. Keywords - Wireless mesh networks, Backbone WMN, Cross-layer design Wally Read Best Student Paper name: Yuting Liu IEEE membership number: 80529895