Freshness of information has become of high importance with the emergence of many real- time applications like monitoring systems and communication networks. The main idea behind all of these scenarios is the same, there exists at least a monitor of some process to which the monitor does not have direct access. Rather, the monitor indirectly receives updates over time from a source that can observe the process directly. The common main goal in these scenarios is to guarantee that the updates at the monitor side are as fresh as possible. However, due to the contention among the nodes in the network over limited channel resources, it takes some random time for the updates before they are received by the monitor. These applications have motivated a line of research studying the Age of Information (AoI) as a new performance metric that captures timeliness of information. The first part of this dissertation focuses on the AoI problem in general multi-source multi-hop status update networks with slotted transmissions. Fundamental lower bounds on the instantaneous peak and average AoI are derived under general interference constraints. Explicit algorithms are developed that generate scheduling policies for status update dissem- ination throughout the network for the class of minimum-length periodic schedules under global interference constraints. Next, we study AoI in multi-access channels, where a number of sources share the same server with exponentially distributed service times to communicate to a monitor. Two cases depending on the status update arrival rates at the sources are considered: (i) random arrivals based on the Poisson point process, and (ii) active arrivals where each source can generate an update at any point in time. For each case, closed-form expressions are derived for the average AoI as a function of the system parameters. Next, the effect of energy harvesting on the age is considered in a single-source single- monitor status update system that has a server with a finite battery capacity. Depending on the server’s ability to harvest energy while a packet is in service, and allowing or blocking the newly-arriving packets to preempt a packet in service, average AoI expressions are derived. The results show that preemption of the packets in service is sub-optimal when the energy arrival rate is lower than the status update arrival rate. Finally, the age of channel state information (CSI) is studied in fully-connected wire- less networks with time-slotted transmissions and time-varying channels. A framework is developed that accounts for the amount of data and overhead in each packet and the CSI disseminated in the packet. Lower bounds on the peak and average AoI are derived and a greedy protocol that schedules the status updates based on minimizing the instantaneous average AoI is developed. Achievable average AoI is derived for the class of randomized CSI dissemination schedules.

Cette thèse a pour objectif de développer des techniques permettant d'améliorer l'efficacité énergétique des réseaux de capteurs destinés à la surveillance d'une chaîne de froid. La première approche développée dans cette thèse concerne la phase de transport des produits alimentaires. Les protocoles proposés VBS, WaS et eVBS s'adressent à la problématique posée par l'absence de station de base permanente au sein du petit réseau déployé dans un camion où les nœuds sont en visibilité directe. Ces méthodes ont le triple avantage de présenter un faible overhead, d'accroître l'ergonomie de l'application et l'intérêt économique du réseau. Dans l'état de l'art, il n'existe pas de déploiement de très grands réseaux de capteurs sans fil destinés à la surveillance d'une chaîne de froid. Le cœur de cette thèse se positionne ainsi autour de la problématique du passage à l'échelle, en proposant plusieurs approches permettant d'améliorer l'efficacité énergétique du réseau. Ainsi des optimisations du routage et des techniques de formation de clusters multi-sauts sont proposées grâce à quelques idées originales d'utilisation de l'indicateur de la qualité de lien. Le protocole L2RP de routage par répartition de charge, le mécanisme SNCR de réduction des clusters singletons ainsi que le protocole LQI-DCP d'optimisation du positionnement des chefs de clusters sont des contributions de cette thèse exploitant le LQI afin d'accroître l'efficacité énergétique du réseau. De plus, nous avons montré que l'heuristique MaxMin de formation de clusters multi-sauts n'est pas compatible avec la topologie de déploiement en grille qui est la plus fréquente dans les architectures de réseaux de capteurs. / Wireless Sensor Networks (WSN) are used today in many applications that differ in their own objectives and specific constraints. However the common challenge in designing WSN applications comes from the specific constraints of micro-sensors because of their limited physical resources such as limited battery lifetime, weak computational capability and small memory capacity. This thesis aims to develop techniques to improve the energy efficiency of wireless sensor networks intended to a cold chain monitoring application. In such area, existing solutions consist of walled temperature recorders in warehouses and transport vehicles, which essentially control the room storage temperature which is not necessarily the product one. By integrating wireless micro-sensor devices with pallets and trays, one allows full real-time tracking of the cold chain originating from factories to the shelves of retailers. The first approach developed in this thesis concerns the phase of transporting food. The proposed VBS, WaS and eVBS protocols address the main issue resulting from the absence of a permanent base station in the small network deployed in a truck where nodes are generally in the same transmission range. These methods have the triple advantages of having a low overhead, increasing the ergonomics of the application and enhancing the economic interest of the network. In the state of art, there is no very large scale deployment of WSN for a cold chain monitoring system. Thus, the core of this thesis addresses the scalability issues by offering several ways to improve overall energy efficiency of the network. So, routing techniques improvement and efficient multi-hop clustering protocols are proposed through some original ideas using the Link Quality Indicator (LQI) provided by the MAC sublayer. The LQI is defined in the IEEE 802.15.4 standard in which its context of use is not specified. The link reliability based routing protocol (L2RP) which load balances the traffic between nodes, the single-node cluster reduction mechanism (SNCR) and the LQI-DCP multi-hop clusters formation protocol which improves clusterhead locations are some of contributions of this thesis which exploit the LQI to, significantly, increase the WSN efficiency. We also show that the MaxMin d-cluster formation heuristic does not support the grid deployment topology which is the more often used in WSN architectures.

Recently a number of communications schemes have been proposed for Vehicular Ad hoc Networks (VANETs). One of these, the Universal Geocast Scheme (UGS) proposed by Hossein Pishro-Nik and Mohammad Nekoui, provides for a diverse variety of VANET-specific characteristics such as time-varying topology, protocol variation based on road congestion, and support for non line-of-sight communication. In this research, the UGS protocol is extended to consider inter-vehicle multi-hop connections in intersections with surrounding obstructions along with single-hop communications in an open road scenario. Since UGS is a probabilistic, repetition-based scheme, it supports the capacity-delay tradeoffs crucial for periodic safety message exchange. The approach is shown to support both vehicle-to-vehicle and vehicle-to-infrastructure communication. This research accurately evaluates this scheme using network (NS-2) and mobility (SUMO) simulators, verifying two crucial elements of successful VANETs, received packet ratio and message delay. A contemporary wireless radio propagation model is used to augment accuracy. Results show a 6% improvement in received packet ratio in intersection simulations combined with a decrease in average packet delay versus a previous, well-known inter-vehicle communication protocol.

No description available.

<p dir="ltr">The advancement of terrestrial networks has improved communication services for users in densely-populated areas, outpacing improvements in rural regions. The projected surge in connected devices in upcoming networks entails that the lack of rural and remote connectivity is limiting emerging applications like digital agriculture and intelligent transportation. Thus, expanding rural and remote wireless connectivity requires addressing the limitations of existing terrestrial infrastructure. In this work, we explore two emerging solutions aimed at enhancing wireless connectivity in rural and remote regions. The first approach considers non-terrestrial networks as an alternative to existing terrestrial technology. Specifically, a vertically-integrated, multi-layered architecture involving unmanned aerial vehicles, high-altitude platforms, and satellites serves as complementary elements, offering diverse pathloss, delay, data rates, and network backbone proximity. We address issues such as multi-hop performance degradation, node mobility, placement, and power distribution to optimize network design. The second approach focuses on wireless-powered communication networks, particularly backscatter communications, to overcome challenges associated with the timely data collection of emerging rural applications such as precision agriculture. We utilize ambient orthogonal frequency division multiplexing (OFDM) signals from cellular base stations to facilitate low-power, low-cost, and real-time data collection while eliminating the need for dedicated radio-frequency emitters. Non-coherent detection and modulation schemes are employed to obviate the necessity for accurate channel state information at the power-limited sensors and reader devices. Moreover, we introduce techniques for simultaneous sensor multiplexing by leveraging OFDM signal structure. Our approaches demonstrate substantial improvements in communication performance, offering versatile, scalable, and cost-effective solutions for rural and remote areas.</p>

京都大学 / 新制・課程博士 / 博士(情報学) / 甲第24930号 / 情博第841号 / 新制||情||141(附属図書館) / 京都大学大学院情報学研究科知能情報学専攻 / (主査)特定教授 黒橋 禎夫, 教授 河原 達也, 教授 鹿島 久嗣 / 学位規則第4条第1項該当 / Doctor of Informatics / Kyoto University / DFAM

No description available.

Since its inception, cognitive radio (CR) has quickly been accepted as the enabling radio technology for next-generation wireless communications. A CR promises unprecedented flexibility in radio functionalities via programmability at the lowest layer, which was once done in hardware. Due to its spectrum sensing, learning, and adaptation capabilities, CR is able to address the heart of the problem associated with spectrum scarcity (via dynamic spectrum access (DSA)) and interoperability (via channel switching). It is envisioned that CR will be employed as a general radio platform upon which numerous wireless applications can be implemented. For both theoretical and practical purposes, it is important for network researchers to model a cognitive radio ad hoc network (CRN) and optimize its performance. Such efforts are important not only for theoretical understanding, but also in that such results can be used as benchmarks for the design of distributed algorithms and protocols. However, due to some unique characteristics associated with CRNs, existing analytical techniques may not be applied directly. As a result, new theoretical results, along with new mathematical techniques, need to be developed. In this thesis, we focus on modeling and optimization of CRNs. In particular, we will study multicast communications in CRN and MIMO-empowered CRN, which we describe as follows. An important service that must be supported by CRNs is multicast. Although there are a lot of research on multicast in ad hoc networks, those results cannot be applied to a CRN, because of the complexity associated with a CR node (e.g., multiple available frequency bands, difference in available bands from neighboring nodes). In addition, a single-layer approach (e.g., multicast routing) is overly simplistic when resource optimization (i.e., minimizing network resource) is the main objective. For this purpose, a cross-layer approach is usually necessary, which should include joint consideration of multiple lower layers, in addition to network layer. However, such a joint formulation is usually highly complex and difficult. In this thesis, we aim to develop some novel algorithms that provide near-optimal solutions. Our goal is to minimize the required network-wide resource to support a set of multicast sessions, with a certain bit rate for each multicast session. The unique characteristics associated with CR and distinguish this problem from existing multicast research for ad hoc networks. In this work, we formulate this problem via a cross-layer approach with joint consideration of scheduling and routing. Although the problem formulation is in the form of mixed integer linear program (MILP), we are successful in developing a polynomial time algorithm that offers highly competitive solution. The main ideas of the algorithm include identification of key integer variables, fixing these variables via a series of relaxed linear program (LP), and tying up such integer fixing with a bottom-up tree construction. By comparing with a lower bound, we find that the proposed algorithm can provide a solution that is very close to the optimum. In parallel to the development of CR for DSA, multiple-input multiple-output (MIMO) has widely been accepted and now implemented in commercial wireless products to increase capacity. The goal of MIMO and how it operates are largely independent and orthogonal to CR. Instead of exploiting idle channels for wireless communications, MIMO attempts to increase capacity within the same channel via space-time processing. Assuming that CR and MIMO will ultimately marry each other and offer the ultimate flexibility in DSA and spectrum efficiency, we would like to inquire the potential capacity gain in this marriage. In particular, we are interested in how such marriage will affect the capacity of a user communication session in a multi-hop CRN. We explore MIMO-empowered CR network, which we call CRN^MIMO, to achieve ultimate flexibility in DSA and spectrum efficiency. Given that CR and MIMO handle interference at different levels (across channels vs. within a channel), we are interested in how joint optimization of both will maximize user capacity in a multi-hop network. To answer this question, we develop a tractable mathematical model for CRN^MIMO, which captures the essence of channel assignment (for CR) and degree-of-freedom (DoF) allocation (for MIMO). Based on this mathematical model, we use numerical results to show how channel assignment in CRN and DoF allocation in MIMO can be jointly optimized to maximize capacity. More important, for a CRN^MIMO with A_MIMO antennas at each node, we show that joint optimization of CR and MIMO offers more than A_MIMO-fold capacity increase than a CRN with only a single antenna at each node. / Master of Science

In der vorliegenden Arbeit werden praktische Protokolle für spontane drahtlose Multi-Hop Maschennetze vorgestellt, diese betrachten das drahtlose System ganzheitlich und berücksichtigen damit die Besonderheiten des drahtlosen Mediums, wie Fading, Interferenz sowie starke Signaldämpfung aufgrund von Entfernung bzw. Hindernissen. Interferenz ist eine Hauptursache für Paketverlust, Durchsatz und Latenz können durch die gleichzeitige Verwendung mehrerer interferenzfreier Kanäle verbessert werden. In Sensor- bzw. Community-Netzen kommt preiswerte und energiesparende Hardware zum Einsatz, die Verwendung zusätzlicher Antennen bzw. Radios ist deshalb nicht möglich. Andererseits werden aber zukünftige drahtlose Netze eine 100-mal höhere Knotendichte, verglichen mit heutigen Netzen, zeigen. Durch die Ausnutzung der im System inhärent vorliegenden Ressource Nutzer (Multi-User Diversität) werden durch Kooperation virtuelle Multi-Antennen und Multi-Radiosysteme aufgebaut. Aufgrund des großen Abstands zwischen den Knoten erreicht man erstens eine hohe räumliche Diversität und zweitens lassen sich damit auch negative Effekte, wie Interferenz zwischen benachbarten Kanälen, minimieren. Es werden Algorithmen sowohl für die Mediumzugriff- als auch die Routing-Schicht vorgestellt. Da keine spezielle physikalische Schicht notwendig ist, kann IEEE 802.11 verwendet werden. Schließlich kann auch auf die bereits heute verfügbare IEEE 802.11 Hardware, die nur eine Kanalumschaltzeit im Millisekundenbereich erlaubt, zurückgegriffen werden. Die zwei vorgestellten Protokolle eignen sich für Umgebungen mit hoher bzw. geringer Interferenz durch fremde WiFi-Netze. Bezüglich Durchsatz werden moderne Protokolle, wie DSR auf Basis von IEEE 802.11 und ETX-Metrik, um ein Vielfaches übertroffen, außerdem ist die Latenz klein und das TCP/IP-Protokoll kann unverändert verwendet werden. / In this work practical protocols are introduced for spontaneous wireless multi-hop mesh networks which contemplate the wireless system integrally and therefore take into account particular features of the wireless medium, like fading, interference as well as strong signal attenuation due to distance or obstacles. Interference is one of the main causes for packet loss. Throughput and latency can be improved by the simultaneous use of several non-interfering channels. In sensor or community networks inexpensive and energy-saving hardware is used. Additional antennas or radios are impossible therefore; on the other hand future wireless networks will show a 100 times higher node density in comparison with today''s networks, however. By the usage of the resource user (multi-user diversity), that is inherently present in the system virtual multi-antennas and multi-radio systems can be built up by cooperation. Firstly, a high spatial diversity can be achieved due to the large distance between the nodes and secondly, negative effects like interference can be minimized between neighboring channels. Algorithms are introduced both for medium access and routing layer. Since a special physical layer is not required IEEE 802.11 can be used. These days already available 802.11 hardware, which allows a channel switching time in milliseconds, is finally usable. The two protocols introduced here are suitable for environments with a high or low interference caused by foreign WiFi networks. Regarding their performance modern protocols like DSR based on 802.11 and ETX metric are surpassed by far. Moreover, the latency is small and the TCP/IP protocol can be used in its unchanged form.

The work in hand considers energy efficiency of data transmission in wireless networks with low data rate (=sensor networks). Often the network nodes are battery operated thus calling for node lifetimes of months or even years. Thus, energy efficiency becomes an important optimisation criteria when designing hardware as well as for the physical transmission, protocol design etc. In order to meet the tight energy constraints, it is necessary to optimise the system as a whole, not just single parameters. This work first shows a derived analysis model for calculating the energy consumption during data transmission. This model is based on a complex state diagram which is evaluated using Mason rules. Using this model the impact of individual parameters on the energy consumption can be computed. Herein the interference of other nodes is included as well. The individual parameters investigated include detection method, modulation scheme, error correction and channel access. The main conclusion is, that higher transmit power can yield decreased energy consumption if the time, which nodes spend in the energy intense active mode, is reduced. Ultra-Wideband-transmission (UWB) using short pulses (Impulse Radio-IR) is currently developing. The potential of this technology is a very simple power-efficient transmitter. Moreover, due to the short pulses, transmission time is short. These two facts promise an energy efficient operation in transmit mode. Nevertheless, performance of simple receivers is still quite low, especially in multi-path environments. Moreover there is the need of powerful synchronisation algorithms. Sensor networks usually possess multi-hop functionality. However, only in severe (block) fading channels multi-hop is more energy efficient than direct transmission. Supposed the transmit power is the same for all nodes, then the transmit power has to be dimensioned for the weakest link. Then, under certain conditions, cooperative relaying schemes can not capitalize the spatial diversity gain. - (This manuscript is also available - in the form of a book - from Dresden: Vogt (Verlag), ISBN:3-938860-02-2) / Die vorliegende Arbeit beschäftigt sich mit der Energieeffizienz der Datenübertragung in Funknetzwerken mit geringer Datenrate (=Sensornetzwerke). Die Netzknoten solcher Netzwerke sind zumeist batteriebetrieben und sollen Betriebsdauern von Monaten bis Jahren erreichen. Daher ist Energieeffizienz ein wichtiges Designmerkmal sowohl beim Hardwareentwurf als auch bei der physikalischen Übertragung, im Protokolldesign usw. Um den energetischen Beschränkungen gerecht zu werden, sollen nicht Einzelparameter optimiert werden, sondern das System insgesamt. In dieser Arbeit wird zunächst ein Analysemodell zur Berechnung des Energieverbrauchs bei der Datenübertragung entwickelt, welches diesen Forderungen gerecht wird. Dieses basiert auf einem komplexen Zustandsdiagramm, welches mit der Mason'schen Regel ausgewertet wird. Dieses Modell nutzend, kann der Einfluss von Einzelparametern auf den Energieverbrauch unter Berücksichtigung der Interferenzen anderer Netzknoten berechnet werden. Als Einzelparameter werden exemplarisch Detektionsverfahren, Modulation, Fehlerschutzkodierung und Kanalzugriff untersucht. Die Grunderkenntnis dieser Betrachtungenen ist, dass höhere Sendeleistungen zu geringerem Energieverbrauch führen, wenn dadurch die Zeit des Netzknotens im energieintensiven Aktiv-Mode verkürzt wird. Ultra-Wideband-Verfahren (UWB) mittels kurzen Pulsen (IR-UWB) befinden sich noch in einer frühen Entwickungsstufe. Das Potential liegt in einem sehr einfachen Senderaufbau, der sehr leistungseffiziente Sender ermöglicht. Aufgrund der kurzen Pulse ist zudem die Übertragungszeit sehr gering. Diese beiden Gegebenheiten lassen auf einen geringen Energieverbrauch hoffen. Allerdings ist die Leistungsfähigkeit von einfachen Empfängern insbesondere in Mehrwegekanälen sehr gering. Desweiteren gibt es noch intensiven Forschungsbedarf für leistungsfähige Synchronisationsalgorithmen. Sensornetzwerke verfügen im Allgemeinen über Multi-Hop-Funktionalität. Energetisch betrachtet, ist deren Einsatz aber nur in starken Blockschwundkanälen sinnvoll. Wird die Sendeleistung aller Netzknoten als konstant angenommen, muss die Sendeleistung auf die schwächste Verbindung dimensioniert werden. Bei kooperativen Vermittlungsverfahren kann dadurch unter bestimmten Bedingungen der räumliche Diversitätsgewinn nicht genutzt werden. - (Die Dissertation ist veröffentlicht im Verlag Vogt, Dresden, ISBN:3-938860-02-2)