No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
NIDES: Ein Verfahren zur Multihop-Distanzschätzung mittels Nachbarschaftsanalyse
Abstract
Die Bestimmung räumlicher Entfernungen zwischen einzelnen Knoten ist ein wichtiger Aspekt in drahtlosen Sensornetzwerken.
In diesem Beitrag präsentieren wir ein neuartiges Verfahren zur Abstandsschätzung, welches auf dem Vergleich von Nachbarschaftslisten
basiert. Es nutzt die Tatsache aus, dass zwei dicht zusammen liegende Knoten mehr gemeinsame Nachbarn haben als solche, die
weiter voneinander entfernt liegen. Das Verfahren bietet zwei besondere Vorteile gegenüber anderen Ansätzen. Zum einen kommt
es gänzlich ohne zusätzliche Hardware aus und zum anderen basiert es nicht auf der Messung physikalischer Größen, wie etwa
der Funksignalstärke, welche durch Umwelteinflüsse oft stark verfälscht werden. Wir erläutern die grundlegende Funktionsweise
dieses Schätzverfahrens zwischen direkt benachbarten Knoten und präsentieren anschließend ausführliche Untersuchungen zur
Anwendung dieser Technik über mehrere Hops hinweg. Anhand von Simulationsergebnissen demonstrieren wir, dass diese Art der
Abstandsschätzung auch im Multihopfall zuverlässige Ergebnisse liefert.
Das Forschungsgebiet des Pervasive Computing hat in den letzten Jahren zunehmend an Bedeutung gewonnen. Hauptziel ist die Integration von Computertechnologie in Alltagsgegenstände und die Nutzung dieser hierdurch elektronisch angereicherten Benutzerumgebung, ihrer Geräte und Dienste für die Ausführung von Anwendungen. Dafür müssen diese Anwendungen in die Lage versetzt werden, sich dynamisch an wechselnde Umgebungen anzupassen, beispielsweise durch Verlagerung ihrer Funktionalität zwischen Geräten. Bedingt durch dynamische Umgebungen, Nutzermobilität sowie drahtlose Kommunikationstechnologien ist die Entwicklung von Anwendungen für Pervasive Computing Umgebungen hochkomplex. Daher wurden in diesem Projekt grundlegende Konzepte und Algorithmen entwickelt, um eine automatisierte Nutzerunterstützung in diesen Umgebungen zu ermöglichen. Hierbei lag der Schwerpunkt auf der Entwicklung von Algorithmen zur Selbstkonfiguration von Anwendungen mittels automatisierter Komposition und Adaption. Neben dynamischen, homogenen Ad Hoc Umgebungen sollten außerdem heterogene Umgebungen, in denen zusätzlich ressourcenstarke Infrastrukturgeräte vorhanden sind, berücksichtigt werden, um eine effiziente Ausführung von Konfigurationen und Adaptionen auch in solchen Umgebungen zu ermöglichen.
This paper describes the concept of sensor networks which has been made viable by the convergence of micro-electro-mechanical systems technology, wireless communications and digital electronics. First, the sensing tasks and the potential sensor networks applications are explored, and a review of factors influencing the design of sensor networks is provided. Then, the communication architecture for sensor networks is outlined, and the algorithms and protocols developed for each layer in the literature are explored. Open research issues for the realization of sensor networks are also discussed.
In this paper, we investigate the impact of radio irregularity on the communication performance in wireless sensor networks. Radio irregularity is a common phenomenon which arises from multiple factors, such as variance in RF sending power and different path losses depending on the direction of propagation. From our experiments, we discover that the variance in received signal strength is largely random; however, it exhibits a continuous change with incremental changes in direction. With empirical data obtained from the MICA2 platform, we establish a radio model for simulation, called the Radio Irregularity Model (RIM). This model is the first to bridge the discrepancy between spherical radio models used by simulators and the physical reality of radio signals. With this model, we are able to analyze the impact of radio irregularity on some of the well-known MAC and routing protocols. Our Results show that radio irregularity has a significant impact on routing protocols, but a relatively small impact on MAC protocols. Finally, we propose six solutions to deal with radio irregularity. We evaluate two of them in detail. The results obtained from both the simulation and a running testbed demonstrate that our solutions greatly improve communication performance in the presence of radio irregularity.
We present a novel radio interference based sensor localization method for wireless sensor networks. The technique relies on a pair of nodes emitting radio waves simultaneously at slightly different frequencies. The carrier frequency of the composite signal is between the two frequencies, but has a very low frequency envelope. Neighboring nodes can measure the energy of the envelope signal as the signal strength. The relative phase offset of this signal measured at two receivers is a function of the distances between the four nodes involved and the carrier frequency. By making multiple measurements in an at least 8-node network, it is possible to reconstruct the relative location of the nodes in 3D. Our prototype implementation on the MICA2 platform yields an average localization error as small as 3 cm and a range of up to 160 meters. In addition to this high precision and long range, the other main advantage of the Radio Interferometric Positioning System (RIPS) is the fact that it does not require any sensors other than the radio used for wireless communication.
sent out by a central facility that addresses a particular receiver unit (beeper) and produces an audible signal. In addition, it may display a number to which the called-party should phone back (some systems allow a vocal message to be conveyed about the call-back number). It is then up to the recipient to use the conventional telephone system to call-back confirming the signal and determine the required action. Although useful in practice there are still circumstances where it is not ideal. For instance, if the called party does not reply the controller has no idea if they: 1) are in an area where the signal does not penetrate 2) have been completely out of the area for some time 3) have been too busy to reply or 4) have misheard or misread the call-back number. Moreover, in the case where there are a number of people who could respond to a crisis situation, it is not known which one is the nearest to the crisis and therefore the most suitable to contact. A `tagging system' does not
The wireless sensor networks community, has now an increased understanding of the need for realistic link layer models. Recent experimental studies have shown that real deployments have a "transitional region" with highly unreliable links, and that therefore the idealized perfect-reception-within-range models used in common network simulation tools can be very misleading. In this paper, we use mathematical techniques from communication theory to model and analyze the low power wireless links. The primary contribution of this work is the identification of the causes of the transitional region, and a quantification of their influence. Specifically, we derive expressions for the packet reception rate as a function of distance, and for the width of the transitional region. These expressions incorporate important channel and radio parameters such as the path loss exponent and shadowing variance of the channel; and the modulation and encoding of the radio. A key finding is that for radios using narrow-band modulation, the transitional region is not an artifact of the radio non-ideality, as it would exist even with perfect-threshold receivers because of multi-path fading. However, we hypothesize that radios with mechanisms to combat multi-path effects, such as spread-spectrum and diversity techniques, can reduce the transitional region.
Many ad hoc network protocols and applications assume the
knowledge of geographic location of nodes. The absolute location of each
networked node is an assumed fact by most sensor networks which can then
present the sensed information on a geographical map. Finding location
without the aid of GPS in each node of an ad hoc network is important in
cases where GPS is either not accessible, or not practical to use due to
power, form factor or line of sight conditions. Location would also
enable routing in sufficiently isotropic large networks, without the use
of large routing tables. We are proposing APS - a distributed, hop by
hop positioning algorithm, that works as an extension of both distance
vector routing and GPS positioning in order to provide approximate
location for all nodes in a network where only a limited fraction of
nodes have self location capability
Instrumenting the physical world through large networks of
wireless sensor nodes, particularly for applications like environmental
monitoring of water and soil, requires that these nodes be very small,
lightweight, untethered, and unobtrusive. The problem of localization,
that is, determining where a given node is physically located in a
network, is a challenging one, and yet extremely crucial for many of
these applications. Practical considerations such as the small size,
form factor, cost and power constraints of nodes preclude the reliance
on GPS of all nodes in these networks. We review localization techniques
and evaluate the effectiveness of a very simple connectivity metric
method for localization in outdoor environments that makes use of the
inherent RF communications capabilities of these devices. A fixed number
of reference points in the network with overlapping regions of coverage
transmit periodic beacon signals. Nodes use a simple connectivity
metric, which is more robust to environmental vagaries, to infer
proximity to a given subset of these reference points. Nodes localize
themselves to the centroid of their proximate reference points. The
accuracy of localization is then dependent on the separation distance
between two-adjacent reference points and the transmission range of
these reference points. Initial experimental results show that the
accuracy for 90 percent of our data points is within one-third of the
separation distance. However, future work is needed to extend the
technique to more cluttered environments
In this paper, we propose some improvements to the flooding protocols that aim to efficiently broadcast a given information through the whole ad-hoc network. These improvements are based on probabilistic approach and decrease the number of emitted packets and hence, the medium occupation. Indeed, it is more interesting to privilege the retransmission by nodes that are located at the radio border of the sender. We observe that the distance between two nodes with full duplex communication can be approximated by comparing their neighbor lists. This leads to broadcasting schemes that do not require position or signal strength information of nodes. Moreover, proposed broadcast protocols require only knowledge of one hop neighborhood and thus need only short hello message. Such protocols are more able to support high mobility networks than protocols that need knowledge of two or more hops neighborhood and then need longer hello messages. We compare our new schemes with variable density and experiments show that the probabilistic approach is efficient.
The recent advances in MEMS, embedded systems and wireless communication technologies are making the realization and deployment of networked wireless microsensors a tangible task. Vital to the success of wireless microsensor networks is the ability of microsensors to ``collectively perform sensing and computation''. In this paper, we study one of the fundamental challenges in sensor networks, node localization. The collaborative multilateration presented here, enables ad-hoc deployed sensor nodes to accurately estimate their locations by using known beacon locations that are several hops away and distance measurements to neighboring nodes. To prevent error accumulation in the network, node locations are computed by setting up and solving a global non-linear optimization problem. The solution is presented in two computation models, centralized and a fully distributed approximation of the centralized model. Our simulation results show that using the fully distributed model, resource constrained sensor nodes can collectively solve a large non-linear optimization problem that none of the nodes can solve individually. This approach results in significant savings in computation and communication, that allows fine-grained localization to run on a low cost sensor node we have developed.
The recent advances in MEMS, embedded systems and wireless communication technologies are making the realization and deployment of networked wireless microsensors a tangible task. Vital to the success of wireless microsensor networks is the ability of microsensors to ``collectively perform sensing and computation''. In this paper, we study one of the fundamental challenges in sensor networks, node localization. The collaborative multilateration presented here, enables ad-hoc deployed sensor nodes to accurately estimate their locations by using known beacon locations that are several hops away and distance measurements to neighboring nodes. To prevent error accumulation in the network, node locations are computed by setting up and solving a global non-linear optimization problem. The solution is presented in two computation models, centralized and a fully distributed approximation of the centralized model. Our simulation results show that using the fully distributed model, resource constrained sensor nodes can collectively solve a large non-linear optimization problem that none of the nodes can solve individually. This approach results in significant savings in computation and communication, that allows fine-grained localization to run on a low cost sensor node we have developed.
Review of the 4th edition "... The growing society of GPS users and designers could be very grateful for the efforts of both the authors and the publisher resulting in the fourth, revised edition of this splendid reference book within six years ... The continous updating and revising make this book an excellent standard reference on GPS for theoreticians and practicians in the future. Acta Geodaetica, Geophysica et Montanistica Hungarica
Distance estimation is important for localization and a multitude of other tasks in wireless sensor networks. We propose a
new scheme for distance estimation based on the comparison of neighborhood lists. It is inspired by the observation that distant
nodes have fewer neighbors in common than close ones. Other than many distance estimation schemes, it relies neither on special
hardware nor on unreliable measurements of physical wireless communication properties like RSSI. Additionally the approach
benefits from message exchange by other protocols and requires a single additional message exchange for distance estimation.
We will show that the approach is universally applicable and works with arbitrary radio hardware. We discuss related work
and present the new approach in detail including its mathematical foundations. We demonstrate the performance of our approach
by presenting various simulation results.
Information about distances to other nodes in wireless sensor networks has proven advantageous not only for location discovery but is also helpful for context aware applications in general. In this paper we present a novel approach to distance estimation that does neither depend on special hardware nor on unreliable measurements of physical wireless communication properties. Instead, it is inspired by the observation that distant nodes have fewer neighbors in common than close ones and calculates distances from intersection cardinalities of sets of adjacent nodes. We discuss related work and present the new approach in detail including its mathematical foundations. A simulative performance analysis comprising different scenarios shows that our scheme yields competitive results.
This paper studies the problem of determining the node locations in ad-hoc sensor networks. We compare three distributed localization algorithms (Ad-hoc positioning, Robust positioning, and N-hop multilateration) on a single simulation platform. The algorithms share a common, three-phase structure: (1) determine node–anchor distances, (2) compute node positions, and (3) optionally refine the positions through an iterative procedure. We present a detailed analysis comparing the various alternatives for each phase, as well as a head-to-head comparison of the complete algorithms. The main conclusion is that no single algorithm performs best; which algorithm is to be preferred depends on the conditions (range errors, connectivity, anchor fraction, etc.). In each case, however, there is significant room for improving accuracy and/or increasing coverage.
We describe a hybrid building navigation system consisting of stationary information booths and a mobile communication infrastructure feeding small portable devices. The graphical presentations for both the booths and the mobile devices are generated from a common source and for the common task of way finding, but they use different techniques to convey possibly different subsets of the relevant information. The form of the presentations is depending on technical limitations of the output media, accuracy of location information, and cognitive restrictions of the user. We analyze what information needs to be conveyed, how limited resources influence the presentation of this information, and argue, that by generating all different presentations in a common framework, a consistent appearance across devices can be achieved and that the different device classes can complement each other in facilitating the navigation task.
We characterize the fundamental limits of localization using signal strength in indoor environments. Signal strength approaches are attractive because they are widely applicable to wireless sensor networks and do not require additional localization hardware. We show that although a broad spectrum of algorithms can trade accuracy for precision, none has a significant advantage in localization performance. We found that using commodity 802.11 technology over a range of algorithms, approaches and environments, one can expect a median localization error of 10 ft and 97th percentile of 30 ft. We present strong evidence that these limitations are fundamental and that they are unlikely to transcend without a fundamentally more complex environmental models or additional localization infrastructure.
In sensor networks the device localization is an interesting topic due to its relationship with routing and energy consumption. We propose a scheme to perform localization, based on the estimation of the power received by only two beacons placed in known positions. By starting from the received powers, eventually averaged on a given window to counteract interference and fading, the actual distance between the sensor and the beacons is derived and the position obtained by means of triangulation. The paper shows the effectiveness of this approach in different environments, by including the possible disturbance due to fading channels and sensor mobility.
We describe an ad-hoc localization system for sensor networks and explain why traditional calibration methods are inadequate for this system. Building upon previous work, we frame calibration as a parameter estimation problem; we parameterize each device and choose the values of those parameters that optimize the overall system performance. This method reduces our average error from 74.6% without calibration to 10.1%. We propose ways to expand this technique to a method of autocalibration for localization as well as to other sensor network applications.
The recent advances in radio and embedded system technologies have enabled the proliferation of wireless microsensor net works. Such wirelessly connected sensors are released in many diverse environments to perform various monitoring tasks. In many such tasks, location awareness is inherently one of the most essential system parameters. It is not only needed to report the origins of events, but also to assist group querying of sensors, routing, and to answer questions on the network coverage. In this paper we present a novel approach to the localization of sensors in an adhoc network. We describe a system called AHLoS (Ad-Hoc Localization System) that enables sensor nodes to discover their locations using a set distributed iterative algorithms. The operation of AHLoS is demonstrated with an accuracy of a few centimeters using our prototype testbed while scalability and performance are studied through simulation.
A new class of networked systems is emerging that involve very large numbers of small, low-power, wireless devices. We present findings from a large scale empirical study involving over 150 such nodes operated at various transmission power settings. The instrumentation in our experiments permits us to separate effects at the various layers of the protocol stack. At the link layer, we present statistics on packet reception, effective communication range and link asymmetry; at the MAC layer, we measure contention, collision and latency; and at the application layer, we analyze the structure of trees constructed using flooding. The study reveals that even a simple protocol, flooding, can exhibit surprising complexity at scale. The data and analysis lay a foundation for a much wider set of algorithmic studies in this space.
We describe a hybrid building navigation system consisting of stationary information booths and a mobile communication infrastructure feeding small portable devices. The graphical presentations for both the booths and the mobile devices are generated from a common source and for the common task of way finding, but they use different techniques to convey possibly different subsets of the relevant information. The form of the presentations is depending on technical limitations of the output media, accuracy of location information, and cognitive restrictions of the user. We analyze what information needs to be conveyed, how limited resources influence the presentation of this information, and argue, that by generating all different presentations in a common framework, a consistent appearance across devices can be achieved and that the different device classes can complement each other in facilitating the navigation task. Keywords: hybrid user interfaces, navigation, resource adaptivity,...
This paper presents the design, implementation, and evaluation of Cricket, a location-support system for in-building, mobile, locationdependent applications. It allows applications running on mobile and static nodes to learn their physical location by using listeners that hear and analyze information from beacons spread throughout the building. Cricket is the result of several design goals, including user privacy, decentralized administration, network heterogeneity, and low cost. Rather than explicitly tracking user location, Cricket helps devices learn where they are and lets them decide whom to advertise this information to; it does not rely on any centralized management or control and there is no explicit coordination between beacons; it provides information to devices regardless of their type of network connectivity; and each Cricket device is made from off-the-shelf components and costs less than U.S. $10. We describe the randomized algorithm used by beacons to transmit information, the use of concurrent radio and ultrasonic signals to infer distance, the listener inference algorithms to overcome multipath and interference, and practical beacon configuration and positioning techniques that improve accuracy. Our experience with Cricket shows that several location-dependent applications such as in-building active maps and device control can be developed with little effort or manual configuration. 1