Cooperative Relaying in Wireless Networks under Spatially and Temporally Correlated Interference

We analyze the performance of an interference-limited, decode-and-forward, cooperative relaying system that comprises a source, a destination, and $N$ relays, placed arbitrarily on the plane and suffering from interference by a set of interferers placed according to a spatial Poisson process. In each transmission attempt, first the transmitter sends a packet; subsequently, a single one of the relays that received the packet correctly, if such a relay exists, retransmits it. We consider both selection combining and maximal ratio combining at the destination, Rayleigh fading, and interferer mobility. We derive expressions for the probability that a single transmission attempt is successful, as well as for the distribution of the transmission attempts until a packet is transmitted successfully. Results provide design guidelines applicable to a wide range of systems. Overall, the temporal and spatial characteristics of the interference play a significant role in shaping the system performance. Maximal ratio combining is only helpful when relays are close to the destination; in harsh environments, having many relays is especially helpful, and relay placement is critical; the performance improves when interferer mobility increases; and a tradeoff exists between energy efficiency and throughput

Packet Travel Times in Wireless Relay Chains under Spatially and Temporally Dependent Interference

We investigate the statistics of the number of time slots $T$ that it takes a packet to travel through a chain of wireless relays. Derivations are performed assuming an interference model for which interference possesses spatiotemporal dependency properties. When using this model, results are harder to arrive at analytically, but they are more realistic than the ones obtained in many related works that are based on independent interference models. First, we present a method for calculating the distribution of $T$. As the required computations are extensive, we also obtain simple expressions for the expected value $\mathrm{E} [T]$ and variance $\mathrm{var} [T]$. Finally, we calculate the asymptotic limit of the average speed of the packet. Our numerical results show that spatiotemporal dependence has a significant impact on the statistics of the travel time $T$. In particular, we show that, with respect to the independent interference case, $\mathrm{E} [T]$ and $\mathrm{var} [T]$ increase, whereas the packet speed decreases

The knapsack problem : applications in cryptography

Günther BrandnerKlagenfurt, Alpen-Adria-Univ., Dipl.-Arb., 2009KB2009 26(VLID)241086

Experimental evaluation of firefly synchronization and cooperative relaying in wireless networks

Die Forschung und Entwicklung in der Informationstechnik beschäftigt sich, unter anderem, mit der Modellierung von Konzepten und dem Entwurf von Kommunikationsprotokollen für drahtlose Übertragungstechniken und Netzwerke. Traditionell wird die Einsetzbarkeit und die Leistungsfähigkeit dieser Konzepte und Protokolle mit mathematischen Analysen oder mit Computersimulationen evaluiert. Die Entwicklung von programmierbaren Hochfrequenz-Sendern und -Empfängern - so genannte Software Radios - ermöglicht deren experimentelle Erprobung unter realistischen Rahmenbedingen. In dieser Doktorarbeit verwenden wir Software Radios um zwei dieser Konzepte unter realistischen Bedingungen zu erproben. Bei dem ersten Konzept handelt es sich um die sogenannte Glühwürmchen-Synchronisation. Dabei handelt es sich um eine von der Natur inspirierte Methode um Geräte in einem drahtlosen Netzwerk zu synchronisieren. Es gibt eine Unzahl an Arbeiten, die die Leistungsfähigkeit dieser Methode mit Hilfe von mathematischen Analysen oder Simulationen evaluieren. Die Anzahl an Arbeiten, die diese Methode unter realistischen Bedingungen testen, ist jedoch limitiert. Um diese Lücke zu verkleinern, testen wir diese Methode experimentell und evaluieren ihre Leistungsfähigkeit. Die Experimente zeigen, dass einige Faktoren die Leistungsfähigkeit negativ beinflussen. Allen voran wirken sich (leicht) unterschiedliche Taktraten zwischen den Geräten, bedingt durch Toleranzen in der Herstellung, negativ auf die Synchronisationsgenauigkeit aus. Diese Erkenntis inspirierte uns zur Entwicklung eines verteilen Algorithmus, welcher die Taktraten zwischen den Geräten anpasst und so die Synchronisationsgenaugkeit um ein Vielfaches verbessert. Bei dem zweiten Konzept handelt es sich um das des kooperativem Relayings. Die Idee dabei ist, dass die drahtlose Übertragung von Daten zwischen zwei Geräten, dem Sender und dem Empfänger, durch einen drittes Gerät, dem Relay, untersützt wird. Eine Vielzahl von mathematischen und simulativen Analysen zeigt die Vorteile dieses Konzepts. Forschungsarbeiten über deren experimentelle Evaluering, unter realistischen Rahmenbedingungen, sind jedoch, wie zuvor für die Glühwürmchen-Synchronisation, nicht vorhanden. Aus diesem Grund testen wir kooperatives Relaying in Fahrzeug-zu-Fahrzeug Kommunikation. Wir führen dazu mehrere Messungen durch und evaluieren dessen Leistungsfähigkeit in Hinblick auf die Datenübertragungsrate. Im Besonderen gehen wir auf die Frage ein wie groß die Vorteile dieser Methode verglichen mit herkömmlichen Übertragungstechniken sind.The research community in the field of wireless communications is concerned with the modelling of concepts and the design of communication protocols. Traditionally, the applicability and the performance of these concepts and protocols are evaluated with theoretical considerations or with computer simulations. In recent years, however, the emergence of software radios facilitates their experimental evaluation in the intended application domain. In this thesis, we apply such radios to evaluate the performance of two concepts in wireless networks. The first concept is that of firefly synchronization, a bio-inspired method for synchronizing radios in a network in a completely distributed manner. We perform experiments and evaluate the performance of firefly synchronization with respect to synchronization convergence, precision and speed. The experiments show that several factors influence the performance of firefly synchronization, among which is, for example, the influence of non-homogeneous clock speeds of radios. The experiments clearly show that these non-homogeneous clock speeds limit the achievable synchronization precision. Inspired by this observation, we propose a distributed algorithm applicable to all firefly synchronization algorithms that exchange packets rather than pulses, to mitigate the detrimental effects of non-homogeneous clock speeds. Furthermore, the experiments also verify that the concept of stochastic interaction between the radios is important for achieving convergence of synchronization. A novel insight, however, is that the degree of stochastic interaction also impacts synchronization precision. The second concept is that of cooperative relaying, where a radio, called relay, helps out in transmitting data from a sender to a receiver. Many publications address the benefits of cooperative relaying from an analytical or simulative point of view. Real-world experiments and performance evaluations of cooperative relaying are, however, largely missing. To narrow this gap, we experimentally evaluate the performance of cooperative relaying in vehicular communications. Several measurement campaigns are conducted and the performance of cooperative relaying is evaluated and compared to that of time diversity, where the same data is sent twice with some time interval between the transmissions. The experiments show, that for vehicular environments with high temporal correlation of packet delivery, the duration of this time interval plays an important role in whether or not cooperative relaying outperforms time diversity in terms of packet delivery ratio.Dr. techn. Günther BrandnerAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersZusammenfassung in deutscher SpracheAlpen Adria Universität Klagenfurt, Dissertation, 2015OeBB(VLID)240976

Dickson, LUC, RSA and Williams : a study on four polynomial-type public-key cryptosystems

In this work we focus on four public-key cryptosystems, namely the Dickson, LUC, RSA and Williams cryptosystem. All of these cryptosystems are of polynomial-type, i.e. polynomials build the foundation of en- and decryption. After discussing the cryptosystems and their mathematical backgrounds in detail, we give insights on relevant cryptanalyses. We also focus on the implementability of the cryptosystems, where we address relevant algorithms and give insights on how to implement them efficiently. In particular we present and apply, besides standard and simple to implement algorithms, heuristic approaches to improve the computational performance. For the Dickson and LUC system, for example, we apply an algorithm by P.L. Montgomery to evaluate Lucas sequences and also Dickson polynomials more efficiently. For the Williams system we discuss and apply an evaluation strategy, which improves the performance of en- and decryption to almost the level of the LUC system. Further, we also observe the impact of applying commonly used techniques (e.g. Montgomery's reduction, Chinese remainder theorem) on the performance of the cryptosystems. Finally, we conclude this work by a thorough study on the computational performance of the cryptosystems.Diese Dissertation behandelt die vier public-key Kryptosysteme Dickson, LUC, RSA und Williams. Alle dieser Kryptosysteme sind polynom-basiert, d.h. die Ver- und Entschlüsselungsfunktionen basieren auf Polynomen. Nach einer eingehenden Diskussion der theoretischen Grundlagen der Kryptosysteme wird deren Sicherheit betrachtet und relevante Kryptoanalysen aufgezeigt. Ferner wird detailliert auf die Implementierbarkeit der Systeme eingegangen und es werden relevante Algorithmen besprochen. Im Besonderen präsentieren und wenden wir, neben Standardalgorithmen, heuristische Algorithmen an, die die Performanz der Systeme verbessern. Zum Beispiel verwenden wir für das Dickson und LUC System einen Algorithmus von P.L. Montgomery, mit dem die Auswertung von Lucas Folgen und Dickson Polynomen effizienter durchgeführt werden kann. Für das Williams System diskutieren wir eine Auswertungsstrategie, welche die Performanz der Ver- und Entschlüsselung auf das Niveau des LUC Systems verbessert. Des Weiteren untersuchen wir auch die Anwendung von häufig verwendeten Techniken wie z.B. Montgomery Reduction und Chinesischem Restsatz. Eine detaillierte Studie der Performanz der Kryptosysteme schließt diese Dissertation ab.Günther BrandnerAbweichender Titel laut Übersetzung der Verfasserin/des VerfassersKlagenfurt, Alpen-Adria-Univ., Diss., 2011KB2011 26OeBB(VLID)240914

Search for substellar companions using AO - first results obtained with NAOS-CONICA

We present first results of our NAOS-CONICA search for close substellar companions around young nearby stars. This program was started only a few months ago. We have obtained 1st epoch images of several targets which are unpublished young stars (age<100 Myrs), hence ideal targets to look for planetary companions. For one target star we could even take a 2nd epoch image. By comparing both images we could look for co-moving companions of the target star. Those data show clearly that the detection of planetary companions m <13 Mjup inward a saturn-like orbit (r<10 AU) is feasible with NAOS-CONICA and in addition that the astrometric confirmation of those companions is doable with only a few weeks of epoch difference

ICNMM2006-96190 SELECTIVE ADSORPTION OF SOLVENTS IN A MULTISCALE DEVICE

ABSTRACT We have incorporated microspheres, 50 µm to 80 µm in diameter, of periodic mesoporous organosilica (inner surfaces up to 1000 m 2 /g and pore sizes in the nanometre range) with two types of organic functionalities (benzene and ethane bridges, respectively) inside microstructured channels (each 200 µm wide and 100 µm deep) and, exemplarily, monitored by Raman microscopy that the temperature characteristics of the adsorption-desorption equilibria of benzene and ethanol vary significantly with the type of organic functionality of the microspheres and the pore morphology. The integration of this class of nanostructured material into devices by means of microchannels is a promising novel approach to, among others, substance separation in analytics, micro process engineering, and micro chemistry