Showing papers in "Center for Embedded Network Sensing in 2002"

DIMENSIONS: Why do we need a new Data Handling architecture for Sensor Networks?

Abstract: An important class of networked systems is emerging that involve very large numbers of small, low-power, wireless devices. These systems offer the ability to sense the environment densely, offering unprecedented opportunities for many scientific disciplines to observe the physical world. In this paper, we argue that a data handling architecture for these devices should incorporate their extreme resource constraints - energy, storage and processing - and spatio-temporal interpretation of the physical world in the design, cost model, and metrics of evaluation. We describe DIMENSIONS, a system that provides a unified view of data handling in sensor networks, incorporating long-term storage, multi-resolution data access and spatio-temporal pattern mining.

Root respiration in North American forests: effects of nitrogen concentration and temperature across biomes

Abstract: Root respiration rates have been shown to be correlated with temperature and root N concentration in studies of individual forest types or species, but it is not known how universal these relationships are across forest species adapted to widely different climatic and edaphic conditions. In order to test for broad, cross-species relationships, we measured fine root respiration, as O2 consumption, over a range of temperatures on excised root samples from ten forested study sites across North America in 1997. Significant differences existed among study sites in root respiration rates, with patterns among sites in respiration rate at a given temperature corresponding to differences among sites in fine root N concentrations. Root respiration rates were highly correlated with root N concentrations at all measurement temperatures (r2>0.81, P<0.001, for 6, 18 and 24°C). Lower root respiration rates in gymnosperms than in angiosperms were largely explained by lower fine root N concentrations in gymnosperms, and root N concentrations and respiration rates (at a given temperature) tended to be lower at warm sites (New Mexico, Florida, and Georgia) than at cool sites with short growing seasons (Michigan and Alaska). Root respiration rates increased exponentially with temperature at all sites. The Q10 for root respiration ranged from 2.4 to 3.1, but there were no significant differences among the forest types. The average Q10s for gymnosperms (Q10=2.7) and angiosperms (Q10=2.6) were almost identical, as were the average Q10s for roots of ectomycorrhizal species (Q10=2.7) and arbuscular mycorrhizal species (Q10=2.6). In 1998, fine root respiration at the study sites was measured in the field as CO2 production at ambient soil temperature. Respiration rates under field conditions were dependent on both ambient soil temperature and root N concentration. Relationships between respiration (adjusted for temperature) and root N concentration for the field measurements were similar to those observed in the 1997 laboratory experiments. For root respiration in tree species, it appears that basic relationships with temperature and nitrogen exist across species and biomes.

Highly Resilient, Energy Efficient Multipath Routing in Wireless Sensor Networks

Abstract: Previously proposed sensor network data dissemination schemes require periodic low-rate flooding of data in order to allow recovery from failure. We consider constructing two kinds of multipaths to enable energy efficient recovery from failure of the shortest path between source and sink. Disjoint multipath has been studied in the literature. We propose a novel braided multipath scheme, which results in several partially disjoint multipath schemes. We find that braided multipaths are a viable alternative for energy-efficient recovery from isolated and patterned failures.

Fine-Grained Network Time Synchronization using Reference Broadcasts

Abstract: 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 critical in sensor networks for diverse purposes including sensor data fusion, coordinated actuation, and power-efficient duty cycling. Though the clock accuracy and precision requirements are often stricter than in traditional distributed systems, strict energy constraints limit the resources available to meet these goals.We present Reference-Broadcast Synchronization, a scheme in which nodes send reference beacons to their neighbors using physical-layer broadcasts. A reference broadcast does not contain an explicit timestamp; instead, receivers use its arrival time as a point of reference for comparing their clocks. In this paper, we use measurements from two wireless implementations to show that removing the sender's nondeterminism from the critical path in this way produces high-precision clock agreement (1.85 ± 1.28μsec, using off-the-shelf 802.11 wireless Ethernet), while using minimal energy. We also describe a novel algorithm that uses this same broadcast property to federate clocks across broadcast domains with a slow decay in precision (3.68 ± 2.57μsec after 4 hops). RBS can be used without external references, forming a precise relative timescale, or can maintain microsecond-level synchronization to an external timescale such as UTC. We show a significant improvement over the Network Time Protocol (NTP) under similar conditions.

Global Change and Mycorrhizal Fungi

Abstract: Mycorrhizae, due to their key position at the plant-soil interface, are important to consider in the study of ecosystem impacts of global changes. Human-induced changes in the earth’s environment are clearly multi-factorial. Examples of important factors are: elevated concentrations of atmospheric gases (for example carbon dioxide or ozone), increased input of nutrients into ecosystems by atmospheric deposition (for example nitrogen), climate change (including altered precipitation and temperature regimes), invasive species, and increased UV-radiation. All of these components of future or present global changes can have positive or negative impacts on mycorrhizal associations. However, a more fundamental distinction has to be made between these factors, paying tribute to the fact that in the mycorrhizal symbiosis we are dealing with two classes of organisms with partially independent biology. There are those factors that directly affect only the host plant (e.g., carbon fixation), and that only have indirect effects on mycorrhizal fungi (mycobionts) via altered carbon allocation from the host. Examples include atmospheric changes, against which soil serves largely as a buffer. Other factors can (in addition) directly affect the mycobionts, for example warming or altered precipitation. This distinction is crucial for a mechanistic understanding of the impact of global change factors, and for experimental approaches. Global change factors rarely occur in isolation. The complexity of regional combinations of global change factors further highlights the need for mechanistic studies, since direct experimental exploration of a large number of scenarios would be virtually impossible. Finally, processes and patterns at larger temporal and spatial scales have to be considered in an assessment of global change impacts on mycorrhiza. Most experiments only allow access to short-term responses, while longer-term responses are really relevant. Possible approaches include the use of natural experiments, for example, CO2 springs. Large-scale processes such as shifts in the global distribution of plant communities (or their regional extinction) due to climate change would affect mycorrhiza, for example, alter the current distribution of mycorrhizal types on the globe. With potential impacts on host biodiversity, mycobiont species diversity may also be impacted at regional scales. In addition, changes in the mycorrhizal fungal community that are independent of changes in the plant community may be one of the least-understood, but potentially most important, mycorrhizal responses to global change.

The Bits and Flops of the N-hop Multilateration Primitive for Node Localization Problems

Abstract: 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.

System-Architectures for Sensor Networks Issues, Alternatives, and Directions

Abstract: Our goal is to identify the key architectural and design issues related to Sensor Networks (SNs), evaluate the proposed solutions, and to outline the most challenging research directions. The evaluation has three scopes ndividual components on SN nodes (processor, communication, storage, sensors, actuators, and power supply), node level and networked system level. The special emphasis is placed on architecture and system software, and on new challenges related to the usage of new types of components in networked systems. The evaluation is guided by anticipated technology trends and both current and future applications. The main conclusion of the analysis is that the architectural and synthesis emphasis will be shifted from computation and to some extent communication components to sensors and actuators.

A Wireless Time-Synchronized COTS Sensor Platform, Part II: Applications to Beamforming

Abstract: In recent years, sensor network system has been proposed for various applications. In the past, most reported systems involve custom-made hardware. In this paper, we consider the use of Compaq iPAQ 3760s with their build-in StrongARM processors, ROM and RAM memories, and microphones and codecs for acoustic acquisition and processing, plus external wireless Ethernet cards for radio communication to form a distributed sensor network to perform acoustical beamforming. Time synchronization among the microphones is achieved by the Reference-Broadcast Synchronization method of Elson-Estrin. Two beamforming algorithms, based on the time difference of arrivals (TDOAs) among the microphones and least-squares estimation of the TDOAs method, and the maximum-likelihood (ML) parameter estimation method, are used to perform source detection, enhancement, localization, delay-steered beamforming, and direction-of-arrival estimation. Theoretical CramerRao bound analysis of the system performance and experimental beamforming results using the iPAQs and the wireless network are reported.

Energy-Efficient Data Multicast in Multi-Hop Wireless Networks

Abstract: Multi-hop wireless networks (MHWNs) are an emerging paradigm for bandwidth and energy-efficient wireless systems where each terminal communicates only with a few closely positioned neighbour nodes using low power communication schemes. High-rate (multimedia) data networks, sensor networks, and voice communications are seen as three main application domains of MHWNs. While MHWNs open many new research and economic opportunities, they simultaneously pose a number of new challenging technical problems. Among them, the fundamental role is reserved for energy- efficient data delivery. We address the problem of Data Multicast in Multi-Hop Wireless Networks that effectively captures requirements of all three of the scenarios. The problem focuses on how to minimize energy consumption while delivering data to all consumers that requested it. Since in the current and pending technologies communication dominates energy consumption, we aim to minimize the number of nodes that transmit data for the request data delivery problem instance. First, we formulate the problem and establish its computation complexity. Next, we develop an efficient heuristic which utilizes information about the geographical position of the nodes in the network to find the most energy-efficient communication path. Finally, we establish the effectiveness of the proposed approach by conducting comprehensive testing of our heuristic on typical ad-hoc networks and instances.

Fine root length, diameter, specific root length and nitrogen concentrations of nine tree species across four North American Biomes

Abstract: Author(s): Pregitzer, K.S; J.L. DeForest, A.J. Burton, M.F. Allen, R.W. Ruess,; R.L. Hendrick

Short paper: a wireless time-synchronized cots sensor platform part i: system architecture

Abstract: In this paper, we describe an implementation of a ad-hoc, distributed sensor platform that provides synchronized time to its users. By abstracting the time synchronization layer away, we allow developers to focus on the core challenges of their applications (e.g., signal processing,

An Electrochemical Detection Scheme for Identifications of Single-Nucleotide Polymorphism Using Hairpin-forming Probes

Abstract: Single nucleotide polymorphisms are implicated as having a significant role in regulating growth, development and, thereby, human health and disease. We have developed a method for identifying single nucleotide genetic alterations by combining hairpin-forming DNA probes and electrochemical detection of sandwich DNA hybridization. Incorporation of hairpin-forming competitor probes and the catalyzed reporter deposition amplification system further improves assay specificity by 7-fold and sensitivity by 100-fold. We have demonstrated that the system successfully identified the factor V Leiden mutations from human blood specimens.