Sensor Networks have been proposed for a multitude of location-dependent applications. For such systems, the cost and limitations of the hardware on sensing nodes prevent the use of range-based localization schemes that depend on absolute point- to-point distance estimates. Because coarse accuracy is sufficient for most sensor network applications, solutions in range-free localization are being pursued as a cost-effective alternative to more expensive range-based approaches. In this paper, we present APIT, a novel localization algorithm that is range-free. We show that our APIT scheme performs best when an irregular radio pattern and random node placement are considered, and low communication overhead is desired. We compare our work via extensive simulation, with three state-of-the-art range-free localization schemes to identify the preferable system configurations of each. In addition, we study the effect of location error on routing and tracking performance. We show that routing performance and tracking accuracy are not significantly affected by localization error when the error is less than 0.4 times the communication radio radius.

/pdf/range-free-localization-schemes-for-large-scale-sensor-4mnvfgp8nx.pdf

Range-Free Localization Schemes for Large Scale Sensor Networks 1

Wireless Sensor Networks have been proposed for a multitude of location-dependent applications. For such systems, the cost and limitations of the hardware on sensing nodes prevent the use of range-based localization schemes that depend on absolute point-to-point distance estimates. Because coarse accuracy is sufficient for most sensor network applications, solutions in range-free localization are being pursued as a cost-effective alternative to more expensive range-based approaches. In this paper, we present APIT, a novel localization algorithm that is range-free. We show that our APIT scheme performs best when an irregular radio pattern and random node placement are considered, and low communication overhead is desired. We compare our work via extensive simulation, with three state-of-the-art range-free localization schemes to identify the preferable system configurations of each. In addition, we study the effect of location error on routing and tracking performance. We show that routing performance and tracking accuracy are not significantly affected by localization error when the error is less than 0.4 times the communication radio radius.

/pdf/range-free-localization-schemes-for-large-scale-sensor-5absoou7dq.pdf

Range-free localization schemes for large scale sensor networks

We demonstrate that it is possible to achieve accurate localization and tracking of a target in a randomly placed wireless sensor network composed of inexpensive components of limited accuracy. The crucial enabler for this is a reasonably accurate local coordinate system aligned with the global coordinates. We present an algorithm for creating such a coordinate system without the use of global control, globally accessible beacon signals, or accurate estimates of inter-sensor distances. The coordinate system is robust and automatically adapts to the failure or addition of sensors. Extensive theoretical analysis and simulation results are presented. Two key theoretical results are: there is a critical minimum average neighborhood size of 15 for good accuracy and there is a fundamental limit on the resolution of any coordinate system determined strictly from local communication. Our simulation results show that we can achieve position accuracy to within 20% of the radio range even when there is variation of up to 10% in the signal strength of the radios. The algorithm improves with finer quantizations of inter-sensor distance estimates: with 6 levels of quantization position errors better than 10% are achieved. Finally we show how the algorithm gracefully generalizes to target tracking tasks.

/pdf/organizing-a-global-coordinate-system-from-local-information-2c479pqenf.pdf

Organizing a global coordinate system from local information on an ad hoc sensor network

Recent advances in miniaturization and low-cost, low-power design have led to active research in large-scale networks of small, wireless, low-power sensors and actuators. Time synchronization is a critical piece of infrastructure in any distributed system, but wireless sensor networks make particularly extensive use of synchronized time. Almost any form of sensor data fusion or coordinated actuation requires synchronized physical time for reasoning about events in the physical world. However, while the clock accuracy and precision requirements are often stricter in sensor networks than in traditional distributed systems, energy and channel constraints limit the resources available to meet these goals. 
New approaches to time synchronization can better support the broad range of application requirements seen in sensor networks, while meeting the unique resource constraints found in such systems. We first describe the design principles we have found useful in this problem space: tiered and multi-modal architectures are a better fit than a single solution forced to solve all problems; tunable methods allow synchronization to be more finely tailored to problem at hand; peer-to-peer synchronization eliminates the problems associated with maintaining a global timescale. We propose a new service model for time synchronization that provides a much more natural expression of these techniques: explicit timestamp conversions . 
We describe the implementation and characterization of several synchronization methods that exemplify our design principles. Reference-Broadcast Synchronization achieves high precision at low energy cost by leveraging the broadcast property inherent to wireless communication. A novel multi-hop algorithm allows RBS timescales to be federated across broadcast domains. Post-Facto Synchronization can make systems significantly more efficient by relaxing the traditional constraint that clocks must be kept in continuous synchrony. 
Finally, we describe our experience in applying our new methods to the implementation of a number of research and commercial sensor network applications.

/pdf/time-synchronization-in-wireless-sensor-networks-428uscgove.pdf

Time synchronization in wireless sensor networks

Monitoring applications define an important class of applications used in wireless sensor networks In these applications the network perceives the environment and searches for event occurrences (phenomena) by sensing different physical properties, such as temperature, humidity, pressure, ambient light, movement, and presence (for target tracking) In such cases the location information of both phenomena and nodes is usually required for tracking and correlation purposes In this work we summarize most of the concepts related to localization systems for WSNs as well as how to localize the nodes in these networks (which allows the localization of phenomena) By dividing the localization systems into three distinct components -distance/angle estimation, position computation, and localization algorithm - besides providing a didactic viewpoint, we show that these components can be seen as subareas of the localization problem that need to be analyzed and studied separately

http://sarstudent.persiangig.com/Book/search2/11_localization%20system%20for%20wsn.pdf

Localization systems for wireless sensor networks

Embedded networked sensors promise to revolutionize the way we interact with our physical environment and require scalable, ad hoc deployable and energy-efficient node localization/positioning.This paper describes the motivation, design, implementation, and experimental evaluation (on sharply resource-constrained devices) of a self-configuring localization system using radio beacons. We identify beacon density as an important parameter in determining localization quality, which saturates at a transition density. We develop algorithms to improve localization quality by (i) automating placement of new beacons at low densities (HEAP) and (ii) rotating functionality among redundant beacons while increasing system lifetime at high densities (STROBE).

/pdf/self-configuring-localization-systems-design-and-4cw9jviilq.pdf

Tommy Tran

Papers

Self-configuring localization systems: Design and Experimental Evaluation

Self-configuring Localization Systems: Design and Experimental Evaluation