Showing papers by "Aman Kansal published in 2007"

Power management in energy harvesting sensor networks

Abstract: Power management is an important concern in sensor networks, because a tethered energy infrastructure is usually not available and an obvious concern is to use the available battery energy efficiently. However, in some of the sensor networking applications, an additional facility is available to ameliorate the energy problem: harvesting energy from the environment. Certain considerations in using an energy harvesting source are fundamentally different from that in using a battery, because, rather than a limit on the maximum energy, it has a limit on the maximum rate at which the energy can be used. Further, the harvested energy availability typically varies with time in a nondeterministic manner. While a deterministic metric, such as residual battery, suffices to characterize the energy availability in the case of batteries, a more sophisticated characterization may be required for a harvesting source. Another issue that becomes important in networked systems with multiple harvesting nodes is that different nodes may have different harvesting opportunity. In a distributed application, the same end-user performance may be achieved using different workload allocations, and resultant energy consumptions at multiple nodes. In this case, it is important to align the workload allocation with the energy availability at the harvesting nodes. We consider the above issues in power management for energy-harvesting sensor networks. We develop abstractions to characterize the complex time varying nature of such sources with analytically tractable models and use them to address key design issues. We also develop distributed methods to efficiently use harvested energy and test these both in simulation and experimentally on an energy-harvesting sensor network, prototyped for this work.

SenseWeb: An Infrastructure for Shared Sensing

Abstract: Peer-produced systems can achieve what might be infeasible for stand-alone systems developed by a single entity The SenseWeb's goal is to enable these kinds of capabilities Using SenseWeb, applications can initiate and access sensor data streams from shared sensors across the entire Internet The SenseWeb infrastructure helps ensure optimal sensor selection for each application and efficient sharing of sensor streams among multiple applications

Mobiscopes for Human Spaces

Abstract: Mobiscopes extend the traditional sensor network model, introducing challenges in data management and integrity, privacy, and network system design. Researchers need an architecture and general methodology for designing future mobiscopes. A mobiscope is a federation of distributed mobile sensors into a taskable sensing system that achieves high-density sampling coverage over a wide area through mobility.

Mobiscopes for Human Spaces

Abstract: MOBILE AND UBIQUITOUS SYSTEMS www.computer.org/pervasive Mobiscopes for Human Spaces Tarek Abdelzaher, Yaw Anokwa, Peter Boda, Jeff Burke, Deborah Estrin, Leonidas Guibas, Aman Kansal, Samuel Madden, and Jim Reich Vol. 6, No. 2 April–June 2007 This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder. © 2005 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. For more information, please see www.ieee.org/portal/pages/about/documentation/copyright/polilink.html.

FlashDB: dynamic self-tuning database for NAND flash

Abstract: FlashDB is a self-tuning database optimized for sensor networks using NAND flash storage. In practical systems flash is used in different packages such as on-board flash chips, compact flash cards, secure digital cards and related formats. Our experiments reveal non-trivial differences in their access costs. Furthermore, databases may be subject to different types of workloads. We show that existing databases for flash are not optimized for all types of flash devices or for all workloads and their performance is thus subop- timal in many practical systems. FlashDB uses a novel self-tuning index that dynamically adapts its storage structure to workload and underlying storage device. We formalize the self-tuning nature of an index as a two-state task system and propose a 3-competitive online algorithm that achieves the theoretical optimum. We also provide a framework to determine the optimal size of an index node that minimizes energy and latency for a given device. Finally, we propose optimizations to further improve the performance of our index. We prototype and compare different indexing schemes on multiple flash devices and workloads, and show that our indexing scheme outperforms existing schemes under all workloads and flash devices we consider.

Image text replacement

Abstract: Image text enhancement techniques are described. In an implementation, graphically represented text included in an original image is converted into process capable text. The process capable text may be used to generate a text image which may replace the original text to enhance the image. In further implementations the process capable text may be translated from a first language to a second language for inclusion in the enhanced image.

Automated Location Estimation Using Image Analysis

Abstract: An implementation of automated location estimation using image analysis is described. In this implementation, an image of a place is obtained and matched with previously stored images. The matching may be achieved by employing methods based on key feature extraction algorithm, color histogram analysis, pattern matching or other image comparison techniques. Upon determining a match, the location information associated with the matched previously stored images provides the location. The location information may be in the form of location tags or location keywords and the location information may be used by the user or other applications for the purposes of location determination. The above technique also allows for the user to enter location information to improve accuracy. The location information may also be assigned to the previously stored images residing in local and remote databases for users and applications to automatically assign information or keywords to images.

Building a sensor network of mobile phones

Abstract: Mobile phones have two sensors: a camera and a microphone. The widespread and ubiquitous nature of mobile phones around the world makes it attractive to build a large-scale sensor network using the phones as its sensor nodes. There are several interesting challenges in realizing such a system, such as providing efficient methods for the sensor nodes to make their data available to the network, allowing the sensor network applications to access the data from potentially disconnected and highly mobile devices, ensuring that privacy constraints are met, and allowing application developers to program the sensor network as required to build new applications. We demonstrate an initial system prototype that addresses some of these concerns.

Automated capture of information generated at meetings

Abstract: Meeting information is collected in an automatic or automated manner utilizing user devices among other devices likely to be present at meetings. Devices can detect the occurrence of a meeting and initiate data capture. Subsequently, aggregated data can be processed to facilitate access and/or dissemination of the data. For instance, data can be contextualized and/or indexed. Further, data can be generated in or converted to forms more suitable for information distribution (e.g., summary, points of interest . . . ).

Virtual reality enhancement using real world data

Abstract: Techniques for enhancing virtual reality using transformed real world data are disclosed. In some aspects, a composite reality engine receives a transmission of the real world data that is captured by embedded sensors situated in the real world. The real world data is transformed and integrated with virtual reality data to create a composite reality environment generated by a composite reality engine. In other aspects, the composite reality environment enables activation of embedded actuators to modify the real world from the virtual reality environment. In still further aspects, techniques for sharing sensors and actuators in the real world are disclosed.

Reconfiguration methods for mobile sensor networks

Abstract: Motion may be used in sensor networks to change the network configuration for improving the sensing performance. We consider the problem of controlling motion in a distributed manner for a mobile sensor network for a specific form of motion capability. Mobility itself may have a high resource overhead, hence we exploit motility, a constrained form of mobility, which has very low overheads but provides significant reconfiguration potential. We present an architecture that allows each node in the network to learn the medium and phenomenon characteristics. We describe a quantitative metric for sensing performance that is concretely tied to real sensor and medium characteristics, rather than assuming an abstract range based model. The problem of determining the desirable network configuration is expressed as an optimization of this metric. We present a distributed optimization algorithm which computes a desirable network configuration, and adapts it to environmental changes. The relationship of the proposed algorithm to simulated annealing and incremental subgradient descent based methods is discussed. A key property of our algorithm is that convergence to a desirable configuration can be proved even though no global coordination is involved. A network protocol to implement this algorithm is discussed, followed by simulations and experiments on a laboratory test bed.

Location and Mobility in a Sensor Network of Mobile Phones

Abstract: Mobile phones have two sensors: a camera and a microphone. Our goal in this position paper it to explore the use of these sensors for building an audio-visual sensor network that exploits the deployed base of millions of mobile phones worldwide. Among the several salient features of such a sensor network, we focus on mobility. Mobility is advantageous since it yields significant advantage in spatial coverage. However, due to the uncontrolled nature of device motion, it is difficult to sample a required region with a given device. We propose a data centric abstraction to deal with this difficulty. Rather than treating the physical devices as our sensor nodes, we introduce a layer of static virtual sensor nodes corresponding to the sampled data locations. The virtual nodes corresponding to the required region to be sensed can be queried directly to obtain data samples for that region. We discuss how the locations of the virtual sensor nodes can be enhanced, and sometimes derived, using the visual data content itself. Experiments with real data are presented to expose some of the practical considerations for our design approach.

Efficient access of flash databases

Abstract: Techniques for efficient access to flash databases are described. In one implementation, a method includes performing an operation on a flash database, supplementing at least one portion of a node translation table corresponding to at least one node involved in the operation, and semantically compressing at least one portion of the node translation table. The semantic compression includes discarding at least one log entry that is rendered obsolete by at least one subsequent log entry, and incrementing a version number of the log entries corresponding to the at least one portion of the node translation table. In further embodiments, discarding at least one log entry includes discarding at least one log entry that is at least one of opposed by or overruled by at least one subsequent log entry.

Rapid crash recovery for flash storage

Abstract: Recovery is expedited for crashes involving flash memory. Rather than requiring an entire flash memory to be read to reconstruct lost information, only a subset of the memory need be read thereby reducing system down time, among other things. In particular, state information such as a logical to physical mapping is captured via a checkpoint operation periodically. Moreover, a deterministic usage pattern is employed to facilitate recovery of actions performed after a checkpoint.

Programming techniques for distributed multi-party networks

Abstract: Architecture for programming in a distributed computing environment where different components of a system are owned or controlled by different entities and heterogeneous in terms of resource availability and a willingness to share. Multiple devices can be programmed when a task requires human intervention. Method are described for using a tolerance level provided by the application developer to control the execution of the application instructions at multiple devices with varying resources, and for using an involvement level provided by the sensor or computing device owner for the purpose of automatically adapting the execution of application code at multiple devices to suit the individual owner's willingness to share resources, and the capabilities of resources available with that owner. Code distribution allows an application developed by one entity to be distributed to multiple devices owned by multiple entities, where each of the entities has varying connectivity, resource availability, and sharing willingness.

Swarm sensing and actuating

Abstract: Sensing information from a multitude of remote sources can provide a user with a vast amount of information as well as a better granularity of the information. A user can also actuate or move remote sources to obtain the desired information or more information and/or to expend energy in a remote location with one or more of the remote sources. Thus, a swarm or large group of devices, sensors, actuators, equipment, and so on can be utilized to provide a user with a desired action.

Shared sensing system interfaces

Abstract: Various interfaces such as application programming interfaces (APIs) are employed to allow developers to construct applications that use multiple shared sensors. In one instance, a coordinator can be utilized to facilitate coordination of sensor data contributors and applications desirous of utilizing such data. Standardized interfaces can be employed to aid interaction between all entities including contributors, applications and a coordinator, amongst others.

Self-tuning index for flash-based databases

Abstract: Techniques for self-tuning indices for databases, including flash-based databases, are described. Using a data tree structure wherein the nodes of the data tree may operate in two modes (e.g. disk mode or log mode), a self-tuning index determines whether it is more economical to perform a requested operation on a node in its current mode or in an alternate mode. The operation is then performed on the node using the more economical mode.

Pixel extraction and replacement

Abstract: A method for pixel extraction and replacement is disclosed. In one implementation, the method includes generating a set of pixel values and pixel value frequencies for a pixel presented in a series of digital images of a scene. A digital image of the scene which includes a pixel value for the pixel is received and a comparison is made between the pixel value and the set of pixel values. A determination is performed to decide upon substitution of the pixel value with a different pixel value based on the comparison. Other techniques are also disclosed.

SenseWeb: Shared Macro-scopes for Scientific Exploration

Abstract: Many advances in science come from observing the previously unobserved. However, developing, deploying, and maintaining the instrumentation required to observe the phenomenon under investigation is a significant overhead for scientists. In most cases, scientists are restricted to collecting data using limited individual resources. As a first step to overcome this limitation, central archives for sharing data have emerged, so that data collected in individual experiments can be re-used by others. We take the next step in this direction: we build an infrastructure, SenseWeb, to enable sharing the sensing instrumentation itself among multiple teams. The key idea is as follows. A scientist deploys sensors to observe a phenomenon, say soil moisture, at their site. The sensors are shared over SenseWeb. Other scientists interested in soil moisture can conduct experiments using these sensors through SenseWeb. Further, other ecologists may deploy similar sensors at their sites and share them. The scientist can now use SenseWeb to access not only her own sensors but also these other similar ones. What emerges is a “macro-scope” of shared sensors measuring the phenomenon at a scale that no single scientist could instrument alone. New experiments are enabled, providing new insights by probing a phenomenon from multiple sites. Barrier to discovery is reduced as many experiments can begin without deployment overhead. SenseWeb addresses challenges in supporting highly heterogeneous sensors, each with their own capability, precision, or sharing willingness. It is built for scalability, allowing multiple concurrent experiments to access common resources. Its map based web interface provides data visualization. Our prototype is currently used by nearly a dozen research teams to share sensors observing different phenomenon ranging from coral ecosystems to urban activity.