167 research outputs found

    Quality of service and dependability of cellular vehicular communication networks

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    Improving the dependability of mobile network applications is a complicated task for many reasons: Especially in Germany, the development of cellular infrastructure has not always been fast enough to keep up with the growing demand, resulting in many blind spots that cause communication outages. However, even when the infrastructure is available, the mobility of the users still poses a major challenge when it comes to the dependability of applications: As the user moves, the capacity of the channel can experience major changes. This can mean that applications like adjustable bitrate video streaming cannot infer future performance by analyzing past download rates, as it will only have old information about the data rate at a different location. In this work, we explore the use of 4G LTE for dependable communication in mobile vehicular scenarios. For this, we first look at the performance of LTE, especially in mobile environments, and how it has developed over time. We compare measurements performed several years apart and look at performance differences in urban and rural areas. We find that even though the continued development of the 4G standard has enabled better performance in theory, this has not always been reflected in real-life performance due to the slow development of infrastructure, especially along highways. We also explore the possibility of performance prediction in LTE networks without the need to perform active measurements. For this, we look at the relationship between the measured signal quality and the achievable data rates and latencies. We find that while there is a strong correlation between some of the signal quality indicators and the achievable data rates, the relationship between them is stochastic, i.e., a higher signal quality makes better performance more probable but does not guarantee it. We then use our empirical measurement results as a basis for a model that uses signal quality measurements to predict a throughput distribution. The resulting estimate of the obtainable throughput can then be used in adjustable bitrate applications like video streaming to improve their dependability. Mobile networks also task TCP congestion control algorithms with a new challenge: Usually, senders use TCP congestion control to avoid causing congestion in the network by sending too many packets and so that the network bandwidth is divided fairly. This can be a challenging task since it is not known how many senders are in the network, and the network load can change at any time. In mobile vehicular networks, TCP congestion control is confronted with the additional problem of a constantly changing capacity: As users change their location, the quality of the channel also changes, and the capacity of the channel can experience drastic reductions even when the difference of location is very small. Additionally, in our measurements, we have observed that packet losses only rarely occur (and instead, packets are delayed and retransmitted), meaning that loss-based algorithms like Reno or CUBIC can be at a significant disadvantage. In this thesis, we compare several popular congestion control algorithms in both stationary and mobile scenarios. We find that many loss-based algorithms tend to cause bufferbloat and thus overly increase delays. At the same time, many delay-based algorithms tend to underestimate the network capacity and thus achieve data rates that are too low. The algorithm that performed the best in our measurements was TCP BBR, as it was able to utilize the full capacity of the channel without causing bufferbloat and also react to changes in capacity by adjusting its window. However, since TCP BBR can be unfair towards other algorithms in wired networks, its use could be problematic. Finally, we also propose how our model for data rate prediction can be used to improve the dependability of mobile video streaming. For this, we develop an algorithm for adaptive bitrate streaming that provides a guarantee that the video freeze probability does not exceed a certain pre-selected upper threshold. For the algorithm to work, it needs to know the distribution of obtainable throughput. We use a simulation to verify the function of this algorithm using a distribution obtained through the previously proposed data rate prediction algorithm. In our simulation, the algorithm limited the video freeze probability as intended. However, it did so at the cost of frequent switches of video bitrate, which can diminish the quality of user experience. In future work, we want to explore the possibility of different algorithms that offer a trade-off between the video freeze probability and the frequency of bitrate switches.Die Verbesserung der Zuverlässigkeit von mobilen Netzwerk-basierten Anwendungen ist aus vielen Gründen eine komplizierte Aufgabe: Vor allem in Deutschland war die Entwicklung der Mobilfunkinfrastruktur nicht immer schnell genug, um mit der wachsenden Nachfrage Schritt zu halten. Es gibt immer noch viele Funklöchern, die für Kommunikationsausfälle verantwortlich sind. Aber auch an Orten, an denen Infrastruktur ausreichend vorhanden ist, stellt die Mobilität der Nutzer eine große Herausforderung für die Zuverlässigkeit der Anwendungen dar: Wenn sich der Nutzer bewegt, kann sich die Kapazität des Kanals stark verändern. Dies kann dazu führen, dass Anwendungen wie Videostreaming mit einstellbarer Bitrate die in der Vergangenheit erreichten Downloadraten nicht zur Vorhersage der zukünftigen Leistung nutzen können, da diese nur alte Informationen über die Datenraten an einem anderen Standort enthalten. In dieser Arbeit untersuchen wir die Nutzung von 4G LTE für zuverlässige Kommunikation in mobilen Fahrzeugszenarien. Zu diesem Zweck untersuchen wir zunächst die Leistung von LTE, insbesondere in mobilen Umgebungen, und wie sie sich im Laufe der Zeit entwickelt hat. Wir vergleichen Messungen, die in einem zeitlichen Abstand von mehreren Jahren durchgeführt wurden, und untersuchen Leistungsunterschiede in städtischen und ländlichen Gebieten. Wir stellen fest, dass die kontinuierliche Weiterentwicklung des 4G-Standards zwar theoretisch eine bessere Leistung ermöglicht hat, dass sich dies aber aufgrund des langsamen Ausbaus der Infrastruktur, insbesondere entlang von Autobahnen, nicht immer in der Praxis bemerkbar gemacht hat. Wir untersuchen auch die Möglichkeit der Leistungsvorhersage in LTE-Netzen, ohne aktive Messungen durchführen zu müssen. Zu diesem Zweck untersuchen wir die Beziehung zwischen der gemessenen Signalqualität und den erreichbaren Datenraten und Latenzzeiten. Wir stellen fest, dass es zwar eine starke Korrelation zwischen einigen der Signalqualitätsindikatoren und den erreichbaren Datenraten gibt, die Beziehung zwischen ihnen aber stochastisch ist, d. h. eine höhere Signalqualität macht eine bessere Leistung zwar wahrscheinlicher, garantiert sie aber nicht. Wir verwenden dann unsere empirischen Messergebnisse als Grundlage für ein Modell, das die Signalqualitätsmessungen zur Vorhersage einer Durchsatzverteilung nutzt. Die sich daraus ergebende Schätzung des erzielbaren Durchsatzes kann dann in Anwendungen mit einstellbarer Bitrate wie Videostreaming verwendet werden, um deren Zuverlässigkeit zu verbessern. Mobile Netze stellen auch TCP Congestion Control Algorithmen vor eine neue Herausforderung: Normalerweise verwenden Sender TCP Congestion Control, um eine Überlastung des Netzes durch das Senden von zu vielen Paketen zu vermeiden, und um die Bandbreite des Netzes gerecht aufzuteilen. Dies kann eine schwierige Aufgabe sein, da es nicht bekannt ist, wie viele Sender sich im Netz befinden, und sich die Netzlast jederzeit ändern kann. In mobilen Fahrzeugnetzen ist TCP Congestion Control mit dem zusätzlichen Problem einer sich ständig ändernden Kapazität konfrontiert: Wenn die Benutzer ihren Standort wechseln, ändert sich auch die Qualität des Kanals, und die Kanalkapazität des Kanals kann drastisch sinken, selbst wenn der Unterschied zwischen den Standorten sehr gering ist. Darüber hinaus haben wir bei unseren Messungen festgestellt, dass Paketverluste nur selten auftreten (stattdessen werden Pakete verzögert und erneut übertragen), was bedeutet, dass verlustbasierte Algorithmen wie Reno oder CUBIC einen großen Nachteil haben können. In dieser Arbeit vergleichen wir mehrere gängige Congestion Control Algorithmen sowohl in stationären als auch in mobilen Szenarien. Wir stellen fest, dass viele verlustbasierte Algorithmen dazu neigen, einen Pufferüberlauf zu verursachen und somit die Latenzen übermäßig erhöhen, während viele latenzbasierte Algorithmen dazu neigen, die Kanalkapazität zu unterschätzen und somit zu niedrige Datenraten erzielen. Der Algorithmus, der bei unseren Messungen am besten abgeschnitten hat, war TCP BBR, da er in der Lage war, die volle Kapazität des Kanals auszunutzen, ohne den Pufferfüllstand übermäßig zu erhöhen. Ebenso hat TCP BBR schnell auf Kapazitätsänderungen reagiert, indem er seine Fenstergröße angepasst hat. Da TCP BBR jedoch in kabelgebundenen Netzen gegenüber anderen Algorithmen unfair sein kann, könnte seine Verwendung problematisch sein. Schließlich schlagen wir auch vor, wie unser Modell zur Vorhersage von Datenraten verwendet werden kann, um die Zuverlässigkeit des mobilen Videostreaming zu verbessern. Dazu entwickeln wir einen Algorithmus für Streaming mit adaptiver Bitrate, der garantiert, dass die Wahrscheinlichkeit des Anhaltens eines Videos eine bestimmte, vorher festgelegte Obergrenze nicht überschreitet. Damit der Algorithmus funktionieren kann, muss er die Verteilung des erreichbaren Durchsatzes kennen. Wir verwenden eine Simulation, um die Funktion dieses Algorithmus zu überprüfen. Hierzu verwenden wir eine Verteilung, die wir durch den zuvor vorgeschlagenen Algorithmus zur Vorhersage von Datenraten erhalten haben. In unserer Simulation begrenzte der Algorithmus die Wahrscheinlichkeit des Anhaltens von Videos wie beabsichtigt, allerdings um den Preis eines häufigen Wechsels der Videobitrate, was die Qualität der Benutzererfahrung beeinträchtigen kann. In zukünftigen Arbeiten wollen wir die Möglichkeit verschiedener Algorithmen untersuchen, die einen Kompromiss zwischen der Wahrscheinlichkeit des Anhaltens des Videos und der Häufigkeit der Bitratenwechsel bieten

    Naval Postgraduate School Academic Catalog - February 2023

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    Naval Postgraduate School Academic Catalog - September 2022

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    Naval Postgraduate School Academic Catalog - 09 July 2021

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    Mobile and Wireless Communications

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    Mobile and Wireless Communications have been one of the major revolutions of the late twentieth century. We are witnessing a very fast growth in these technologies where mobile and wireless communications have become so ubiquitous in our society and indispensable for our daily lives. The relentless demand for higher data rates with better quality of services to comply with state-of-the art applications has revolutionized the wireless communication field and led to the emergence of new technologies such as Bluetooth, WiFi, Wimax, Ultra wideband, OFDMA. Moreover, the market tendency confirms that this revolution is not ready to stop in the foreseen future. Mobile and wireless communications applications cover diverse areas including entertainment, industrialist, biomedical, medicine, safety and security, and others, which definitely are improving our daily life. Wireless communication network is a multidisciplinary field addressing different aspects raging from theoretical analysis, system architecture design, and hardware and software implementations. While different new applications are requiring higher data rates and better quality of service and prolonging the mobile battery life, new development and advanced research studies and systems and circuits designs are necessary to keep pace with the market requirements. This book covers the most advanced research and development topics in mobile and wireless communication networks. It is divided into two parts with a total of thirty-four stand-alone chapters covering various areas of wireless communications of special topics including: physical layer and network layer, access methods and scheduling, techniques and technologies, antenna and amplifier design, integrated circuit design, applications and systems. These chapters present advanced novel and cutting-edge results and development related to wireless communication offering the readers the opportunity to enrich their knowledge in specific topics as well as to explore the whole field of rapidly emerging mobile and wireless networks. We hope that this book will be useful for students, researchers and practitioners in their research studies

    Recent Advances in Wireless Communications and Networks

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    This book focuses on the current hottest issues from the lowest layers to the upper layers of wireless communication networks and provides "real-time" research progress on these issues. The authors have made every effort to systematically organize the information on these topics to make it easily accessible to readers of any level. This book also maintains the balance between current research results and their theoretical support. In this book, a variety of novel techniques in wireless communications and networks are investigated. The authors attempt to present these topics in detail. Insightful and reader-friendly descriptions are presented to nourish readers of any level, from practicing and knowledgeable communication engineers to beginning or professional researchers. All interested readers can easily find noteworthy materials in much greater detail than in previous publications and in the references cited in these chapters

    Naval Postgraduate School Academic Catalog - September 2021

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    Intelligent Circuits and Systems

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    ICICS-2020 is the third conference initiated by the School of Electronics and Electrical Engineering at Lovely Professional University that explored recent innovations of researchers working for the development of smart and green technologies in the fields of Energy, Electronics, Communications, Computers, and Control. ICICS provides innovators to identify new opportunities for the social and economic benefits of society.  This conference bridges the gap between academics and R&D institutions, social visionaries, and experts from all strata of society to present their ongoing research activities and foster research relations between them. It provides opportunities for the exchange of new ideas, applications, and experiences in the field of smart technologies and finding global partners for future collaboration. The ICICS-2020 was conducted in two broad categories, Intelligent Circuits & Intelligent Systems and Emerging Technologies in Electrical Engineering

    Cost-Effective and Energy-Efficient Techniques for Underwater Acoustic Communication Modems

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    Finally, the modem developed has been tested experimentally in laboratory (aquatic environment) showing that can communicates at different data rates (100..1200 bps) compared to state-of-the-art research modems. The software used include LabVIEW, MATLAB, Simulink, and Multisim (to test the electronic circuit built) has been employed.Underwater wireless sensor networks (UWSNs) are widely used in many applications related to ecosystem monitoring, and many more fields. Due to the absorption of electromagnetic waves in water and line-of-sight communication of optical waves, acoustic waves are the most suitable medium of communication in underwater environments. Underwater acoustic modem (UAM) is responsible for the transmission and reception of acoustic signals in an aquatic channel. Commercial modems may communicate at longer distances with reliability, but they are expensive and less power efficient. Research modems are designed by using a digital-signal-processor (DSP is expensive) and field-programmable-gate-array (FPGA is high power consuming device). In addition to, the use of a microcontroller is also a common practice (which is less expensive) but provides limited computational power. Hence, there is a need for a cost-effective and energy-efficient UAM to be used in budget limited applications. In this thesis different objectives are proposed. First, to identify the limitations of state-of-the-art commercial and research UAMs through a comprehensive survey. The second contribution has been the design of a low-cost acoustic modem for short-range underwater communications by using a single board computer (Raspberry-Pi), and a microcontroller (Atmega328P). The modulator, demodulator and amplifiers are designed with discrete components to reduce the overall cost. The third contribution is to design a web based underwater acoustic communication testbed along with a simulation platform (with underwater channel and sound propagation models), for testing modems. The fourth contribution is to integrate in a single module two important modules present in UAMs: the PSK modulator and the power amplifier
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