Thesis (M.S.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 84-86). Also available via World Wide Web.

Includes bibliographical references (p. 45-47).

Corrosion of embedded reinforcement is the leading form of deterioration affecting the integrity of reinforced and prestressed concrete bridge members around the world. If undetected, corrosion can limit the service life of the bridge and lead to expensive repairs. The research team at the University of Texas at Austin has developed a new class of passive wireless corrosion sensors. The noncontact (NC) sensor platform provides an economical and nondestructive means for detecting corrosion initiation within concrete. The sensor is powered through the inductive coupling to an external mobile reader that can be handheld or mounted on a vehicle. It is envisioned that the four-dollar sensor will be embedded in concrete during construction and interrogated sporadically over the service life of the structure. The sensor output can be used to detect corrosion initiation within concrete and is expected to enhance the quality information collected during qualitative routine bridge inspections. The NC sensor prototype consists of a resonant circuit that is inductively coupled to a sacrificial transducer. Corrosion of the sacrificial element alters the measured sensor response and is used to detect corrosion within concrete. Electrochemical evaluations were conducted to ensure that the sacrificial element exhibited identical response as the reinforcement steel. In addition, the results of extensive experimental parametric studies were used in conjunction with circuit and electromagnetic finite element models to optimize the NC sensor design. Long-term exposure tests were used to evaluate the reliability of the passive noncontact sensors. Sensors were embedded in reinforced concrete specimens and successfully detected the onset of corrosion in the adjacent reinforcement. Unlike the traditional corrosion evaluation methods, such as half-cell potentials, the sensors output was insensitive to environmental variations. / text

ITC/USA 2013 Conference Proceedings / The Forty-Ninth Annual International Telemetering Conference and Technical Exhibition / October 21-24, 2013 / Bally's Hotel & Convention Center, Las Vegas, NV / Relay selection for optimal communication as well as multiple source localization is studied. We consider the use of dual-role nodes that can work both as relays and also as anchors. The dual-role nodes and multiple sources are placed at fixed locations in a two-dimensional space. Each dual-role node estimates its distance to all the sources within its radius of action. Dual-role selection is then obtained considering all the measured distances and the total SNR of all sources-to-destination channels for optimal communication and multiple source localization. Bit error rate performance as well as mean squared error of the proposed optimal dual-role node selection scheme are presented.

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / The selection of relay nodes (RNs) for optimal communication and source location estimation is studied. The RNs are randomly placed at fixed and known locations over a geographical area. A mobile source senses and collects data at various locations over the area and transmits the data to a destination node with the help of the RNs. The destination node not only needs to collect the sensed data but also the location of the source where the data is collected. Hence, both high quality data collection and the correct location of the source are needed. Using the measured distances between the relays and the source, the destination estimates the location of the source. The selected RNs must be optimal for joint communication and source location estimation. We show in this paper how this joint optimization can be achieved. For practical decentralized selection, an opportunistic RN selection algorithm is used. Bit error rate performance as well as mean squared error in location estimation are presented and compared to the optimal relay selection results.

This dissertation shows that with simple programming abstractions, network-wide resource coordination is efficient and useful for programming embedded sensor networks. Existing systems have focused primarily on managing resources for individual nodes, but a sensor network is not merely a collection of nodes operating independently: it must coordinate behavior across multiple nodes to achieve high efficiency. We need tools that can enable system-wide coordination at a higher level of abstraction than what exists today. We present three core contributions. The first is a service called IDEA that enables networkwide energy management for sensor networks. It unites energy monitoring, load modeling, and distributed state sharing into a single service that facilitates distributed decision making. Using simulation and testbed results, we show that IDEA enables improvements in network lifetime of up to 35% over approaches that do not consider energy distribution. Our second contribution is Karma, a system for coordinating insect-sized robotic microaerial vehicle (MAV) swarms, an emerging class of mobile sensor networks. Karmas system architecture simplifies the functionality of an individual MAV to a sequence of sensing and actuation commands called behaviors. Each behavior has an associated progress function, a measure of how much of that behavior has been completed. Programming is done by composing behaviors which are coordinated using input from the progress functions. Through simulation and testbed experiments, we demonstrate Karma applications can run on limited resources, are robust to individual MAV failure, and adapt to changes in the environment. Our final contribution is Simbeeotic, a testbed for MAV coordination algorithms. MAV sensors must be codesigned with the software and coordination algorithms that depend on them. This requires a testbed capable of simulating sensors to evaluate them before actual hardware is available and the ability to test with real flight dynamics for accurate control evaluation. In addition, simulation should be able to scale to hundreds or thousands of MAVs at a reduced level of fidelity in order to test at scale. We demonstrate that Simbeeotic provides the appropriate level of fidelity to evaluate prototype systems while maintaining the ability to test at scale. / Engineering and Applied Sciences

Coverage in a Wireless Sensor Network reflects how well a sensor network monitors an area. Many times it is impossible to provide full coverage. The key challenges are to prolong the lifetime and ensure connectivity to provide a stable network. In this thesis we first define p-percent coverage problem in which we require only p% of the whole area to be monitored. We propose two algorithms, Connected P-Percent Coverage Depth First Search (CpPCA-DFS) and Connected P-Percent Connected Dominating Set (CpPCA-CDS). Through simulations we then compare and analyze them for their efficiency and lifetime. Finally in conclusion we prove that CpPCA-CDS provides 5 to 20 percent better active node ratio at low density. At high node density it achieves better distribution of covered area however the lifetime is only 5 to10 percent shorter then CpPCA-DFS. Overall CpPCA-CDS provides up to 30 percent better distribution of covered area.

Τα Ασύρματα Δίκτυα Αισθητήρων (Wireless Sensor Networks, WSN) αποτελούν σήμερα ένα πολλά υποσχόμενο πεδίο έρευνας στον τομέα των ασύρματων επικοινωνιών. Ωστόσο, λόγω κάποιων από τις ιδιαιτερότητές τους, οι κόμβοι ενός WSN υπόκεινται σε λειτουργικούς και σχεδιαστικούς περιορισμούς, που δημιουργούν νέες προκλήσεις και αντικείμενα έρευνας με σκοπό τη βελτιστοποίηση της απόδοσης του δικτύου. Ένα τέτοιο αντικείμενο έρευνας αποτελεί και η συνδεσιμότητα του συνολικού δικτύου, μια έννοια καθοριστική για τη δυνατότητα επικοινωνίας μεταξύ των κόμβων και ανταλλαγής πληροφοριών επί της παρατηρούμενης διεργασίας. Η χρησιμότητα των WSN σε συνδυασμό με την απαίτηση για συνδεσιμότητα αποτέλεσαν το σημείο εκκίνησης για την παρούσα διπλωματική εργασία. Ποιο συγκεκριμένα, επιχειρήθηκε η μεγιστοποίηση της περιοχής επικοινωνιακής κάλυψης σε ένα WSN αλλά και του αριθμού των επικοινωνούντων κόμβων. Η ιδιαιτερότητα της έρευνας εντοπίζεται στη χρήση του Δείκτη Ισχύος Ληφθέντος Σήματος (RSSI) για την εξαγωγή συμπερασμάτων για τη συνδεσιμότητα του δικτύου. Υλοποιήθηκε συνεπώς ένα WSN, αποτελούμενο από ένα ζευγάρι κόμβων αποστολέας-παραλήπτης, των οποίων η επικοινωνία βασίζεται στο πρότυπο της IEEE 802.15.4. Στόχος της πειραματικής διαδικασίας αποτέλεσε η μέτρηση (στην μεριά του παραλήπτη) του RSSI και ο υπολογισμός του ποσοστού των επιτυχώς ληφθέντων πακέτων για την επικοινωνία μεταξύ αποστολέα-παραλήπτη, μεταβάλλοντας την προγραμματιζόμενη ισχύ εκπομπής του αποστολέα αλλά και τη θέση του παραλήπτη σε μια δεδομένη περιοχή ενδιαφέροντος. Από το στάδιο αυτό της πειραματικής διαδικασίας προέκυψε η περιοχή επικοινωνιακής κάλυψης ενός κόμβου για τα διάφορα προγραμματιζόμενα επίπεδα ισχύος εκπομπής. Τα αποτελέσματα αυτά συνέβαλαν στην ανάπτυξη αλγορίθμου βελτιστοποίησης της συνδεσιμότητας του δικτύου, με βάση τον οποίο αναζητήθηκε η μέγιστη επικοινωνιακή κάλυψη του δικτύου και ο μέγιστος αριθμός ζευγών επικοινωνούντων κόμβων. / Wireless Sensor Networks consist a new research domain in the field of wireless communications. However, they are under many constraints, whisch open new research in this field. One such field consitutes connectivity in Wireless Sensor Networks, which was the stimulus of this Diploma Thesis. The initial goal was the extraction of the maximization of the connunication range of the network and of the number of the nodes tha communicate. The parsticularity of the reserch is the m,easurement of the Received Signal Strength. We deployed tow nodes in the area of interest and measured this indicator. Then the results wereused in an algorithm for the optimization of the communication range and the number of communicating nodes in the network.

Wireless sensor networks are the collection of wireless nodes that are deployed to monitor certain phenomena of interest. Once the node takes measurements it transmits to a base station over a wireless channel. The base station collects data from all the nodes and do further analysis. To save energy, it is often useful to build clusters, and the head of each cluster communicates with the base station. Initially, we do the simulation analysis of the Zigbee networks where few nodes are more powerful than the other nodes. The results show that in the mobile heterogeneous sensor networks, due to phenomenon orphaning and high cost of route discovery and maintenance, the performance of the network degrades with respect to the homogeneous network. The core of this thesis is to empirically analyze the sensor network. Due to its resource constraints, low power wireless sensor networks face several technical challenges. Many protocols work well on simulators but do not act as we expect in the actual deployments. For example, sensors physically placed at the top of the heap experience Free Space propagation model, while the sensors which are at the bottom of the heap have sharp fading channel characteristics. In this thesis, we show that impact of asymmetric links in the wireless sensor network topology and that link quality between sensors varies consistently. We propose two ways to improve the performance of Link Quality Indicator (LQI) based algorithms in the real asymmetric link sensor networks. In the first way, network has no choice but to have some sensors which can transmit over the larger distance and become cluster heads. The number of cluster heads can be given by Matérn Hard-Core process. In the second solution, we propose HybridLQI which improves the performance of LQI based algorithm without adding any overhead on the network. Later, we apply theoretical clustering approaches in sensor network to real world. We deploy Matérn Hard Core Process and Max-Min cluster Formation heuristic on real Tmote nodes in sparse as well as highly dense networks. Empirical results show clustering process based on Matérn Hard Core Process outperforms Max-Min Cluster formation in terms of the memory requirement, ease of implementation and number of messages needed for clustering. Finally, using Absorbing Markov chain and measurements we study the performance of load balancing techniques in real sensor networks.

Vystyti mikrosensorinio tinklo duomenų perdavimą racionalaus maršrutizavimo sistemoje. Minimizuoti perdavimų skaičių, sudarant bevielį mikrosensorinį tinklą. Taip pat, trumpinti skaičiavimo procesus, kai mazgai turi atlikti racionalų maršrutizavimą. Bevielio mikrosensorinio tinklo trumpiausio kelio radimas turi būti paprastai realizuojamas ir skaičiuojamas. / In this paper it is described a method of creation of the shortest path algorithm for wireless sensor networks. Algorithm computes optimal shortest path and works on any wireless sensor networks topology. One of the limitations of wireless sensor nodes is their inherent limited energy resource. The limited available energy of sensor nodes is mainly problem making communication and computational processing. An energy efficient routing protocol can limit the number of nodes transmissions and the computational complexity of finding the shortest routing path. In the experimental part, the correct functionality of the algorithm is evaluated and the results are analized.