Management and routing algorithms for ad-hoc and sensor networks

Large scale wireless adhoc networks of computers, sensors, PDAs etc. (i.e. nodes) are revolutionizing connectivity and leading to a paradigm shift from centralized systems to highly distributed and dynamic environments. An example of adhoc networks are sensor networks, which are usually composed by small units able to sense and transmit to a sink elementary data which are successively processed by an external machine. Recent improvements in the memory and computational power of sensors, together with the reduction of energy consumptions, are rapidly changing the potential of such systems, moving the attention towards datacentric sensor networks. A plethora of routing and data management algorithms have been proposed for the network path discovery ranging from broadcasting/floodingbased approaches to those using global positioning systems (GPS). We studied WGrid, a novel decentralized infrastructure that organizes wireless devices in an adhoc manner, where each node has one or more virtual coordinates through which both message routing and data management occur without reliance on either flooding/broadcasting operations or GPS. The resulting adhoc network does not suffer from the deadend problem, which happens in geographicbased routing when a node is unable to locate a neighbor closer to the destination than itself. WGrid allow multidimensional data management capability since nodes' virtual coordinates can act as a distributed database without needing neither special implementation or reorganization. Any kind of data (both single and multidimensional) can be distributed, stored and managed. We will show how a location service can be easily implemented so that any search is reduced to a simple query, like for any other data type. WGrid has then been extended by adopting a replication methodology. We called the resulting algorithm WRGrid. Just like WGrid, WRGrid acts as a distributed database without needing neither special implementation nor reorganization and any kind of data can be distributed, stored and managed. We have evaluated the benefits of replication on data management, finding out, from experimental results, that it can halve the average number of hops in the network. The direct consequence of this fact are a significant improvement on energy consumption and a workload balancing among sensors (number of messages routed by each node). Finally, thanks to the replications, whose number can be arbitrarily chosen, the resulting sensor network can face sensors disconnections/connections, due to failures of sensors, without data loss. Another extension to {WGrid} is {W*Grid} which extends it by strongly improving network recovery performance from link and/or device failures that may happen due to crashes or battery exhaustion of devices or to temporary obstacles. W*Grid guarantees, by construction, at least two disjoint paths between each couple of nodes. This implies that the recovery in W*Grid occurs without broadcasting transmissions and guaranteeing robustness while drastically reducing the energy consumption. An extensive number of simulations shows the efficiency, robustness and traffic road of resulting networks under several scenarios of device density and of number of coordinates. Performance analysis have been compared to existent algorithms in order to validate the results.

Design of wireless sensor networks for fluid dynamic applications

In fluid dynamics research, pressure measurements are of great importance to define the flow field acting on aerodynamic surfaces. In fact the experimental approach is fundamental to avoid the complexity of the mathematical models for predicting the fluid phenomena. It’s important to note that, using in-situ sensor to monitor pressure on large domains with highly unsteady flows, several problems are encountered working with the classical techniques due to the transducer cost, the intrusiveness, the time response and the operating range. An interesting approach for satisfying the previously reported sensor requirements is to implement a sensor network capable of acquiring pressure data on aerodynamic surface using a wireless communication system able to collect the pressure data with the lowest environmental–invasion level possible. In this thesis a wireless sensor network for fluid fields pressure has been designed, built and tested. To develop the system, a capacitive pressure sensor, based on polymeric membrane, and read out circuitry, based on microcontroller, have been designed, built and tested. The wireless communication has been performed using the Zensys Z-WAVE platform, and network and data management have been implemented. Finally, the full embedded system with antenna has been created. As a proof of concept, the monitoring of pressure on the top of the mainsail in a sailboat has been chosen as working example.

Cooperative communication and distributed detection in wireless sensor networks

Recent progress in microelectronic and wireless communications have enabled the development of low cost, low power, multifunctional sensors, which has allowed the birth of new type of networks named wireless sensor networks (WSNs). The main features of such networks are: the nodes can be positioned randomly over a given field with a high density; each node operates both like sensor (for collection of environmental data) as well as transceiver (for transmission of information to the data retrieval); the nodes have limited energy resources. The use of wireless communications and the small size of nodes, make this type of networks suitable for a large number of applications. For example, sensor nodes can be used to monitor a high risk region, as near a volcano; in a hospital they could be used to monitor physical conditions of patients. For each of these possible application scenarios, it is necessary to guarantee a trade-off between energy consumptions and communication reliability. The thesis investigates the use of WSNs in two possible scenarios and for each of them suggests a solution that permits to solve relating problems considering the trade-off introduced. The first scenario considers a network with a high number of nodes deployed in a given geographical area without detailed planning that have to transmit data toward a coordinator node, named sink, that we assume to be located onboard an unmanned aerial vehicle (UAV). This is a practical example of reachback communication, characterized by the high density of nodes that have to transmit data reliably and efficiently towards a far receiver. It is considered that each node transmits a common shared message directly to the receiver onboard the UAV whenever it receives a broadcast message (triggered for example by the vehicle). We assume that the communication channels between the local nodes and the receiver are subject to fading and noise. The receiver onboard the UAV must be able to fuse the weak and noisy signals in a coherent way to receive the data reliably. It is proposed a cooperative diversity concept as an effective solution to the reachback problem. In particular, it is considered a spread spectrum (SS) transmission scheme in conjunction with a fusion center that can exploit cooperative diversity, without requiring stringent synchronization between nodes. The idea consists of simultaneous transmission of the common message among the nodes and a Rake reception at the fusion center. The proposed solution is mainly motivated by two goals: the necessity to have simple nodes (to this aim we move the computational complexity to the receiver onboard the UAV), and the importance to guarantee high levels of energy efficiency of the network, thus increasing the network lifetime. The proposed scheme is analyzed in order to better understand the effectiveness of the approach presented. The performance metrics considered are both the theoretical limit on the maximum amount of data that can be collected by the receiver, as well as the error probability with a given modulation scheme. Since we deal with a WSN, both of these performance are evaluated taking into consideration the energy efficiency of the network. The second scenario considers the use of a chain network for the detection of fires by using nodes that have a double function of sensors and routers. The first one is relative to the monitoring of a temperature parameter that allows to take a local binary decision of target (fire) absent/present. The second one considers that each node receives a decision made by the previous node of the chain, compares this with that deriving by the observation of the phenomenon, and transmits the final result to the next node. The chain ends at the sink node that transmits the received decision to the user. In this network the goals are to limit throughput in each sensor-to-sensor link and minimize probability of error at the last stage of the chain. This is a typical scenario of distributed detection. To obtain good performance it is necessary to define some fusion rules for each node to summarize local observations and decisions of the previous nodes, to get a final decision that it is transmitted to the next node. WSNs have been studied also under a practical point of view, describing both the main characteristics of IEEE802:15:4 standard and two commercial WSN platforms. By using a commercial WSN platform it is realized an agricultural application that has been tested in a six months on-field experimentation.

Packet erasure correcting codes for wireless sensor networks: implementation and field trial measurements

This thesis regards the Wireless Sensor Network (WSN), as one of the most important technologies for the twenty-first century and the implementation of different packet correcting erasure codes to cope with the ”bursty” nature of the transmission channel and the possibility of packet losses during the transmission. The limited battery capacity of each sensor node makes the minimization of the power consumption one of the primary concerns in WSN. Considering also the fact that in each sensor node the communication is considerably more expensive than computation, this motivates the core idea to invest computation within the network whenever possible to safe on communication costs. The goal of the research was to evaluate a parameter, for example the Packet Erasure Ratio (PER), that permit to verify the functionality and the behavior of the created network, validate the theoretical expectations and evaluate the convenience of introducing the recovery packet techniques using different types of packet erasure codes in different types of networks. Thus, considering all the constrains of energy consumption in WSN, the topic of this thesis is to try to minimize it by introducing encoding/decoding algorithms in the transmission chain in order to prevent the retransmission of the erased packets through the Packet Erasure Channel and save the energy used for each retransmitted packet. In this way it is possible extend the lifetime of entire network.

Anaerobic oxidation of ethanol over spinel mixed oxides: the first step in the steam-iron process for H2 production

The future hydrogen demand is expected to increase, both in existing industries (including upgrading of fossil fuels or ammonia production) and in new technologies, like fuel cells. Nowadays, hydrogen is obtained predominantly by steam reforming of methane, but it is well known that hydrocarbon based routes result in environmental problems and besides the market is dependent on the availability of this finite resource which is suffering of rapid depletion. Therefore, alternative processes using renewable sources like wind, solar energy and biomass, are now being considered for the production of hydrogen. One of those alternative methods is the so-called “steam-iron process” which consists in the reduction of a metal-oxide by hydrogen-containing feedstock, like ethanol for instance, and then the reduced material is reoxidized with water to produce “clean” hydrogen (water splitting). This kind of thermochemical cycles have been studied before but currently some important facts like the development of more active catalysts, the flexibility of the feedstock (including renewable bio-alcohols) and the fact that the purification of hydrogen could be avoided, have significantly increased the interest for this research topic. With the aim of increasing the understanding of the reactions that govern the steam-iron route to produce hydrogen, it is necessary to go into the molecular level. Spectroscopic methods are an important tool to extract information that could help in the development of more efficient materials and processes. In this research, ethanol was chosen as a reducing fuel and the main goal was to study its interaction with different catalysts having similar structure (spinels), to make a correlation with the composition and the mechanism of the anaerobic oxidation of the ethanol which is the first step of the steam-iron cycle. To accomplish this, diffuse reflectance spectroscopy (DRIFTS) was used to study the surface composition of the catalysts during the adsorption of ethanol and its transformation during the temperature program. Furthermore, mass spectrometry was used to monitor the desorbed products. The set of studied materials include Cu, Co and Ni ferrites which were also characterized by means of X-ray diffraction, surface area measurements, Raman spectroscopy, and temperature programmed reduction.

Power consumption analysis for self-diagnosis of Wireless Sensor Nodes

Wireless sensor networks can transform our buildings in smart environments, improving comfort, energy efficiency and safety. Today however, wireless sensor networks are not considered reliable enough for being deployed on large scale. In this thesis, we study the main failure causes for wireless sensor networks, the existing solutions to improve reliability and investigate the possibility to implement self-diagnosis through power consumption measurements on the sensor nodes. Especially, we focus our interest on faults that generate in-range errors: those are wrong readings but belong to the range of the sensor and can therefore be missed by external observers. Using a wireless sensor network deployed in the R\&D building of NXP at the High Tech Campus of Eindhoven, we performed a power consumption characterization of the Wireless Autonomous Sensor (WAS), and studied through some experiments the effect that faults have in the power consumption of the sensor.

Deidrogenazione catalitica di cherosene per la produzione di H2 "on-board": studio della disattivazione dei catalizzatori

Questo lavoro di tesi è stato sviluppato nell’ambito del progetto europeo “GREEN AIR” (7FP – Transport), svolto in collaborazione con diversi enti europei, pubblici e privati. Si tratta di un programma finalizzato alla produzione di idrogeno “on – board” per deidrogenazione catalitica di cherosene avio, da alimentare ad un sistema di fuel cells per la produzione dell’energia elettrica necessaria al funzionamento della strumentazione e dei sistemi di comando degli aeroplani. In questo lavoro di tesi ci si è concentrati sullo studio dei meccanismi di reazione e disattivazione coinvolti nella reazione di deidrogenazione di carburanti. Sono stati studiati approfonditamente le caratteristiche peculiari della reazione di deidrogenazione di miscele complesse di idrocarburi, ponendo particolare attenzione ai meccanismi di disattivazione. Lo studio è stato affrontato, prima analizzando la disattivazione per formazione di depositi carboniosi, utilizzando catalizzatori classici per reazioni di deidrogenazione ed alimentando miscele di idrocarburi prive da zolfo, quindi la disattivazione data da quest'ultimo elemento proponendo una serie di catalizzatori a base di fosfuri. I primi studi si sono concentrati su sistemi Pt-Sn supportati su allumina, utilizzati industrialmente per la produzione di olefine leggere a partire da miscele semplici di alcani, il cui comportamento è noto, nella seconda parte sono stati presi in considerazione sistemi a base di CoP e Ni2P, originariamente progettati per la reazione di idrodesolforazione. In conclusione, è stato possibile individuare gli aspetti chiave relativi ai meccanismi di disattivazione dei sistemi catalitici tradizionalmente impiegati nella deidrogenazione. In particolare ha permesso di individuare interessanti possibilità per ridurre, attraverso la rigenerazione e la riduzione del fenomeno di disattivazione, l’impatto del costo del catalizzatore sul processo. Inoltre sono stati individuati sistemi alternativi per la produzione di idrogeno molto interessanti, mettendo in luce gli aspetti che necessitano di essere ancora approfonditi per ottimizzarne l’applicazione.

Der Carrier DcuB als zweiter Sensor des Zweikomponentensystems DcuSR in Escherichia coli

Escherichia coli kann C4-Dicarboxylate und andere Carbonsäuren als Substrate für den aeroben und anaeroben Stoffwechsel nutzen. Die Anwesenheit von C4-Dicarboxylaten im Außenmedium wird über das Zweikomponentensystem DcuSR, bestehend aus der membranständigen Sensorkinase DcuS und dem cytoplasmatischen Responseregulator DcuR, erkannt. Die Bindung von C4-Dicarboxylaten an die periplasmatische Domäne von DcuS führt zu einer Induktion der Zielgene. Hierzu zählen die Gene für den anaeroben Fumarat/Succinat-Antiporter DcuB (dcuB), die anaerobe Fumarase (fumB) und die Fumaratreduktase (frdABCD). Unter aeroben Bedingungen stimuliert DcuSR die Expression des dctA Gens, das für den aeroben C4-Dicarboxylat-Carrier DctA kodiert. Für den Carrier DcuB konnte eine regulatorische Funktion bei der Expression der DcuSR-regulierten Gene gezeigt werden. Die Inaktivierung des dcuB Gens führte bereits ohne Fumarat zu einer maximalen Expression einer dcuB´-´lacZ Reportergenfusion und anderer DcuSR-abhängiger Gene. Diese Stimulierung erfolgte nur in einem dcuS-positiven Hintergrund. DcuB unterscheidet sich damit von den alternativen Carriern DcuA und DcuC, die diesen Effekt nicht zeigten. Mithilfe ungerichteter Mutagenese wurden DcuB-Punktmutanten hergestellt (Thr394Ile und Asp398Asn), die eine Geninduktion verursachten, aber eine intakte Transportfunktion besaßen. Dies zeigt, dass der regulatorische Effekt von DcuB unabhängig von dessen Transportfunktion ist. Durch gerichtete Mutagenese wurde die Funktion einer Punktmutation (Thr394) näher charakterisiert. Es werden zwei Modelle zur Membrantopologie von DcuB und der Lage der Punktmutationen im Protein vorgestellt. Da DcuB seine regulatorische Funktion über eine Interaktion mit DcuS vermitteln könnte, wurden mögliche Wechselwirkungen zwischen DcuB und DcuS als auch DcuR mithilfe von Two-Hybrid-Systemen untersucht. Für biochemische Untersuchungen von DcuB wurde außerdem die Expression des Proteins in vivo und in vitro versucht. Unter aeroben Bedingungen beeinflusst der C4-Dicarboxylat-Carrier DctA die Expression der DcuSR-abhängigen Gene. Eine Mutation des dctA Gens bewirkte eine stärkere Expression einer dctA´-´lacZ Reportergenfusion im Vergleich zum Wildtyp. Diese Expression nahm in einem dcuS-negativen Hintergrund ab, die Succinat-abhängige Induktion blieb jedoch erhalten. Unter anaeroben Bedingungen kann das dctA Gen auch durch Inaktivierung von DcuB induziert werden. Es wird ein Modell vorgestellt, das die Beteiligung beider Carrier an der DcuSR-abhängigen Regulation erklärt.

Wireless Sensor Networks for Monitoring Applications

Wireless Sensor Networks (WSNs) are getting wide-spread attention since they became easily accessible with their low costs. One of the key elements of WSNs is distributed sensing. When the precise location of a signal of interest is unknown across the monitored region, distributing many sensors randomly/uniformly may yield with a better representation of the monitored random process than a traditional sensor deployment. In a typical WSN application the data sensed by nodes is usually sent to one (or more) central device, denoted as sink, which collects the information and can either act as a gateway towards other networks (e.g. Internet), where data can be stored, or be processed in order to command the actuators to perform special tasks. In such a scenario, a dense sensor deployment may create bottlenecks when many nodes competing to access the channel. Even though there are mitigation methods on the channel access, concurrent (parallel) transmissions may occur. In this study, always on the scope of monitoring applications, the involved development progress of two industrial projects with dense sensor deployments (eDIANA Project funded by European Commission and Centrale Adritica Project funded by Coop Italy) and the measurement results coming from several different test-beds evoked the necessity of a mathematical analysis on concurrent transmissions. To the best of our knowledge, in the literature there is no mathematical analysis of concurrent transmission in 2.4 GHz PHY of IEEE 802.15.4. In the thesis, experience stories of eDIANA and Centrale Adriatica Projects and a mathematical analysis of concurrent transmissions starting from O-QPSK chip demodulation to the packet reception rate with several different types of theoretical demodulators, are presented. There is a very good agreement between the measurements so far in the literature and the mathematical analysis.

Proprietà morfologiche e strutturali di catalizzatori a base di Pt e Pd per la produzione di H2

In questo lavoro di tesi è stato affrontato uno studio mirato alla comprensione ed alla correlazione delle proprietà chimico-fisiche e morfologiche di catalizzatori a base di Pd/Pt supportati su allumina impiegati nella produzione di idrogeno mediante deidrogenazione di miscele complesse di idrocarburi contenenti elevati tenori di zolfo. La produzione di idrogeno mediante deidrogenazione parziale di fuel direttamente su aeromobili necessita di catalizzatori altamente performanti dei quali siano note tutte le caratteristiche in modo da prevedere, in un ampio margine di sicurezza, le possibili cause di malfunzionamento. L’applicabilità di materiali a base di Pd/Pt in questa reazione risiede nella loro capacità di resistere all’avvelenamento da zolfo, rivendicata in letteratura per reazioni di idrogenazione e della quale si sono trovate evidenze sperimentali in alcune prove preliminari svolte nello stesso ambito di ricerca. Le prove catalitiche hanno evidenziato che la deposizione su allumina dei due metalli in ragione di un rapporto molare Pd:Pt=2 con un carico di metalli complessivo del 2% in peso mostra i migliori risultati in termini di resistenza all’avvelenamento da zolfo e da deposizione di composti carboniosi.

Oligomerisation, localisation and interaction of the sensor histidine kinases DcuS and CitA in Escherichia coli

The two-component system DcuSR of Escherichia coli regulates gene expression of anaerobic fumarate respiration and aerobic C4-dicarboxylate uptake. C4-dicarboxylates and citrate are perceived by the periplasmic domain of the membrane-integral sensor histidine kinase DcuS. The signal is transduced across the membrane by phosphorylation of DcuS and of the response regulator DcuR, resulting in activation of DcuR and transcription of the target genes.rnIn this work, the oligomerisation of full-length DcuS was studied in vivo and in vitro. DcuS was genetically fused to derivatives of the green fluorescent protein (GFP), enabling fluorescence resonance energy transfer (FRET) measurements to detect protein-protein interactions in vivo. FRET measurements were also performed with purified His6-DcuS after labelling with fluorescent dyes and reconstitution into liposomes to study oligomerisation of DcuS in vitro. In vitro and in vivo fluorescence resonance energy transfer showed the presence of oligomeric DcuS in the membrane, which was independent of the presence of effector. Chemical crosslinking experiments allowed clear-cut evaluation of the oligomeric state of DcuS. The results showed that detergent-solubilised His6-DcuS was mainly monomeric and demonstrated the presence of tetrameric DcuS in proteoliposomes and in bacterial membranes.rnThe sensor histidine kinase CitA is part of the two-component system CitAB of E. coli, which is structurally related to DcuSR. CitAB regulates gene expression of citrate fermentation in response to external citrate. The sensor kinases DcuS and CitA were fused with an enhanced variant of the yellow fluorescent protein (YFP) and expressed in E. coli under the control of an arabinose-inducible promoter. The subcellular localisation of DcuS-YFP and CitA-YFP within the cell membrane was studied by means of confocal laser fluorescence microscopy. Both fusion proteins were found to accumulate at the cell poles. The polar accumulation was slightly increased in the presence of the stimulus fumarate or citrate, respectively, but independent of the expression level of the fusion proteins. Cell fractionation demonstrated that polar accumulation was not related to inclusion bodies formation. The degree of polar localisation of DcuS-YFP was similar to that of the well-characterised methyl-accepting chemotaxis proteins (MCPs), but independent of their presence. To enable further investigations on the function of the polar localisation of DcuS under physiological conditions, the sensor kinase was genetically fused to the flavin-based fluorescent protein Bs2 which shows fluorescence under aerobic and anaerobic conditions. The resulting dcuS-bs2 gene fusion was inserted into the chromosome of various E. coli strains.rnFurthermore, a protein-protein interaction between the related sensor histidine kinases DcuS and CitA, regulating common metabolic pathways, was detected via expression studies under anaerobic conditions in the presence of citrate and by in vivo FRET measurements.