The prospect of replacing existing fixed networks with cheap, flexible and evenmobile low-power wireless network has been a strong research driver in recent years.However, many challenges still exist: reliability is hampered by unstable and burstycommunication links; the wireless medium is getting congested by an increasingnumber of wireless devices; and life-times are limited due to difficulties in developingefficient duty-cycling mechanisms. These challenges inhibit the industry to fullyembrace and exploit the capabilities and business opportunities that low-powerwireless devices offer. In this thesis, we propose, design, implement, and evaluateprotocols and systems to increase flexibility and improve efficiency of low-powerwireless communications. First, we present MobiSense, a system architecture for energy-efficient communicationsin micro-mobility sensing scenarios. MobiSense is a hybrid architecturecombining a fixed infrastructure network and mobile sensor nodes. Simulations andexperimental results show that the system provides high throughput and reliabilitywith low-latency handoffs. Secondly, we investigate if and how multi-channel communication can mitigate theimpact of link dynamics on low-power wireless protocols. Our study is motivated bya curiosity to reconcile two opposing views: that link dynamics is best compensatedby either (i) adaptive routing, or (ii) multi-channel communication. We perform acomprehensive measurement campaign and evaluate performance both in the singlelink and over a multi-hop network. We study packet reception ratios, maximumburst losses, temporal correlation of losses and loss correlations across channels.The evaluation shows that multi-channel communication significantly reduces linkburstiness and packet losses. In multi-hop networks, multi-channel communicationsand adaptive routing achieves similar end-to-end reliability in dense topologies,while multi-channel communication outperforms adaptive routing in sparse networkswhere re-routing options are limited. Third, we address the problem of distributed information exchange in proximitybasednetworks. First, we consider randomized information exchange and assess thepotential of multi-channel epidemic discovery. We propose an epidemic neightbordiscoverymechanism that reduces discovery times considerably compared to singlechannelprotocols in large and dense networks. Then, the idea is extended todeterministic information exchange. We propose, design and evaluate an epidemicinformation dissemination mechanism with strong performance both in theory andpractice. Finally, we apply some of the concepts from epidemic discovery to the designof an asynchronous, sender-initiated multi-channel medium access protocol. Theprotocol combines a novel mechanism for rapid schedule learning that avoids perpacketchannel negotiations with the use of burst data transfer to provide efficientsupport of ’multiple contending unicast and parallel data flows. / De senaste åren har forskning inom trådlös kommunikation drivits av önskemåletom att kunna ersätta nuvarande trådbundna kommunikationslänkar med trådlösa lågenergialternativ.Dock kvarstår många utmaningar, såsom instabila och sporadiskalänkar, överbelastning på grund av en ökning i antal trådlösa enheter, hur maneffektivt kan växla duty-cycling mekanismen för att förlänga nätverkens livstid,med flera. Dessa utmaningar begränsar industrin från att ta till sig och utnyttjade fördelar som trådlösa lågenergialternativ kan medföra. I den här avhandlingenföreslår, designar, implementerar och utvärderar vi protokoll och system som kanförbättra de nuvarande trådlösa lågenergialternativen. Först presenterar vi MobiSense, en systemarkitektur för energibesparande kommunikationi mikro-mobila sensorscenarier. MobiSense är en hybridarkitektur somkombinerar ett fast infrastrukturnätverk med rörliga sensornoder. Simulerings- ochexperimentella resultat visar att systemet uppnår en högre överföringskapacitet ochtillförlitlighet samtidigt som överlämnandet mellan basstationer har låg latens. I den andra delen behandlar vi hur effekterna från länkdynamiken hos protokollför lågenergikommunikation kan minskas, och försöker förena idéerna hos två motståendesynsätt: (i) flerkanalskommunikation och (ii) adaptiv routing. Vi analyserarenkanals- och flerkanalskommunikation över en-stegslänkar i termer av andelenmottagna paket kontra andelen förlorade, den maximala sporadiska förlusten avpaket, tidskorrelation för förluster och förlustkorrelation mellan olika kanaler. Resultatenindikerar att flerkanalskommunikation med kanalhoppning kraftigt minskardet sporadiska uppträdandet hos länkarna och korrelationen mellan paketförluster.För flerstegsnätverk uppvisar flerkanalskommunikation och adaptiv routingliknande tillförlitlighet i täta topologier, medan flerkanalskommunikation har bättreprestanda än adaptiv routing i glesa nätverk med sporadiska länkar. I den tredje delen studeras distribuerat informationsutbyte i närhetsbaseradenätverk. Först betraktas det slumpmässiga fallet och vi fastställer potentialen hosflerkanalig indirekt utforskning av nätverket. Vi analyserar ett trestegs protokoll,som möjliggör en snabbare utforskning av nätverket. Sedan föreslår vi en ny algoritmför att upptäcka grannarna i ett flerkanalsnätverk, som kraftigt minskarutforskningstiden i jämförelse med ett enkanalsprotokoll. Vi utökar även problemettill det deterministiska fallet och föreslår en mekanism för informationsspridningsom påskyndar utforskningstiderna för deterministiska protokoll. Utvidgningen hartvå huvudförbättringar som leder till kraftigt ökad prestanda samtidigt som degaranterar att utforskningsprocessen är deterministisk. Till sist applicerar vi koncepten rörande indirekt utforskning för att designa,implementera och evaluera ett asynkront sändare-initierat flerkanals MAC protokollför trådlös lågenergikommunikation. Protokollet kombinerar en ny mekanism försnabbt lärande av tidsschemat, vilket undviker kanalförhandling för varje paket,med sporadisk dataöverföring. Detta möjliggör ett effektivt tillhandahållande avflera konkurrerande och parallella dataflöden. / <p>QC 20151204</p>

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Ad hoc networking protocols enable the formation of self-organizing networks with automatic selfhealing operation in dynamic environments. There are a number of existing or planned ad hoc implementations and a body of research on protocols and performance. Ad Hoc technologies promise significant impact in future communications architectures. This paper presents a general overview of ad hoc networking and presents specific examples, including a recent implementation of a prototype ad hoc networked sensor system. The protocols used have unique characteristics derived by tailoring particular protocols to the specific application requirements. The potential relevance of ad hoc networking to possible telemetry applications is discussed.

Progress in micro-electromechanical systems (MEMS) and radio frequency (RF) technology has fostered the development of wireless sensor networks (WSNs). Different from traditional networks, WSNs are data-centric, self-configuring and self-healing. Although WSNs have been successfully applied in built environments (e.g. security and services in smart homes), their applications and benefits have not been fully explored in areas such as disaster recovery and rescuing. There are issues related to self-localisation as well as practical constraints to be taken into account. The current state-of-the art communication technologies used in disaster scenarios are challenged by various limitations (e.g. the uncertainty of RSS). Localisation in WSNs (location sensing) is a challenging problem, especially in disaster environments and there is a need for technological developments in order to cater to disaster conditions. This research seeks to design and develop novel localisation algorithms using WSNs to overcome the limitations in existing techniques. A novel probabilistic fuzzy logic based range-free localisation algorithm (PFRL) is devised to solve localisation problems for WSNs. Simulation results show that the proposed algorithm performs better than other range free localisation algorithms (namely DVhop localisation, Centroid localisation and Amorphous localisation) in terms of localisation accuracy by 15-30% with various numbers of anchors and degrees of radio propagation irregularity. In disaster scenarios, for example, if WSNs are applied to sense fire hazards in building, wireless sensor nodes will be equipped on different floors. To this end, PFRL has been extended to solve sensor localisation problems in 3D space. Computational results show that the 3D localisation algorithm provides better localisation accuracy when varying the system parameters with different communication/deployment models. PFRL is further developed by applying dynamic distance measurement updates among the moving sensors in a disaster environment. Simulation results indicate that the new method scales very well.

Στις ημέρες μας, η εμφάνιση των ασύρματων δικτύων σε πολλές πτυχές της καθημερινότητας, είναι συνεχώς αυξανομενη. Το γεγονός αυτό, έχει ως συνέπεια να υπάρχει μεγάλη ερευνητική δραστηριότητα γύρω από τα ασύρματα δίκτυα, η οποία αφορά όχι μόνο το σχεδιασμό τους και την ανάπτυξη διάφορων πρωτοκόλλων, αλλά και άλλες εφαρμογές, όπως είναι για παράδειγμα η εκτίμηση παραμέτρων. Στα πλαίσια της εργασίας αυτής, μελετάται η ανάπτυξη των αλγορίθμων φλυαρίας, οι οποίοι αφορούν μία κατανεμημένη προσέγγιση του προβλήματος της εκτίμησης παραμέτρων σε ένα δίκτυο. Πιο συγκεκριμένα, σε αντίθεση με τις κλασσικές μεθόδους στις οποίες αναλαμβάνει ένας κεντρικός κόμβος με μεγάλη υπολογιστική ισχύ να λύσει το πρόβλημα της εκτίμησης της παραμέτρου ενδιαφέροντος, με τους αλγόριθμους φλυαρίας αναιρείται η έννοια του κεντρικού κόμβου και η εκτίμηση στηρίζεται στη συνεχή ανταλλαγή πληροφοριών μεταξύ των κόμβων του δικτύου. Με τις προσομοιώσεις που έγιναν στα πλαίσια αυτής της εργασίας, αποδεικνύεται ότι οι εν λόγω αλγόριθμοι εξασφαλίζουν επιτυχημένη προσέγγιση του προβλήματος που καλούνται να επιλύσουν παρότι οι αλγόριθμοι φλυαρίας στηρίζονται σε υποβέλτιστες τεχνικές εκτίμησης παραμέτρων οι οποίες βασίζονται σε αναδρομικούς προσαρμοστικούς αλγορίθμους. Τέλος, αντιμετωπίζεται το πρόβλημα της εκτίμησης της θέσης ενός στόχου που κινείται στην περιοχή ενός δικτύου με βάση τη διαδικασία της φλυαρίας. / In recent years, the emergence of wireless networks in many aspects of daily life, is increasingly growing. This fact has as consequence a strong research activity around various types of wireless networks, not only in the design and development of various protocols, but also in other applications such as parameter estimation. In this thesis, we study the development of gossip algorithms that are related to a distributed approach to the problem of parameter estimation in a network. More specifically, in contrast with classical methods that assume a central node with high computational power to solve the problem of estimation of the parameter of interest, the use of gossip algorithms negates this concept and the estimation process is based on continuing exchange of information between network nodes. Additionally, despite the fact that gossip algorithms belong to suboptimal parameter estimation techniques, that are based on recursive adaptive algorithms, the simulation results presented show that these algorithms ensure successful approach to the problem they have to solve. Finally, the process of gossiping deals with the problem of estimating the position of a moving target in the region of a wireless network.

Wireless devices have become an integral part of our everyday lives. Cell-phones, PDA's, Wi-Fi enabled laptops, smart homes and appliances, and automated highway systems are some of the examples of wireless devices and networks in common use. More and more applications and functionalities are constantly being added to these devices, and to support these new applications high data rate communication is required between the wireless devices. Achieving high data rates with wireless communication is impeded by severe fluctuations in the received signal strength (called fading) due to mobility, the exponential attenuation of signal power with distance (called path loss), and interference due to simultaneous transmissions by different users at the same time or over same frequency band. Two of the promising techniques to mitigate the effects of fading, path loss, and interference are: using multiple antennas at the transmitter and receiver, and employing extra nodes (called relays) in between the transmitter and its receiver to relay the transmitter's message to its receiver. This dissertation identifies the optimal transmit and receive strategy with multiple antennas that maximizes the transmission capacity of an ad-hoc wireless network. The transmission capacity is defined as the maximum number of transmitter-receiver pairs that can simultaneously communicate under a per transmission quality of service constraint. This dissertation also presents novel relay transmission strategies for multiple antenna equipped relay based communication that achieve near optimal performance, with Shannon capacity and diversity-multiplexing tradeoff (DMT) as the performance metrics. The Shannon capacity is defined as the maximum rate of reliable communication, while the DMT characterizes the maximum diversity gain for a given value of multiplexing gain in a multiple antenna system. DMT is used as the benchmark, since transmission strategies that meet the DMT are guaranteed to leverage both the advantages of multiple antenna systems. / text

The explosive demand for multimedia and fast transmission of continuous media on wireless networks means the simultaneous existence of traffic requiring different qualities of service (QoS). In this thesis, several efficient algorithms have been developed which offer several QoS to the end-user. We first look at a request TDMA/CDMA protocol for supporting wireless multimedia traffic, where CDMA is laid over TDMA. Then we look at a hybrid push-pull algorithm for wireless networks, and present a generalized performance analysis of the proposed protocol. Some of the QoS factors considered include customer retrial rates due to user impatience and system timeouts and different levels of priority and weights for mobile hosts. We have also looked at how customer impatience and system timeouts affect the QoS provided by several queuing and scheduling schemes such as FIFO, priority, weighted fair queuing, and the application of the stretch-optimal algorithm to scheduling.

Les travaux de recherche menés dans le cadre de cette thèse concernent l'amélioration du débit et de la qualité de service dans les réseaux sans fil basés sur les standards de la famille 802.11. Des simulations exhaustives ont été menées pour l'analyse et l'évaluation des performances des protocoles de routages réactifs AODV, DSR et DYMO ainsi que des protocoles de routage proactifs DSDV, FSR et OLSR. Plusieurs paramètres ont été considérés comme la mobilité des noeuds la charge du réseau et la mise à l'échelle. Nous pouvons observer que la métrique de qualité de lien est un paramètre important dans toute stratégie de routage. L'objectif du présent travail est de proposer une analyse comparative des différents protocoles de routage, basée sur les métriques de qualité de lien et de proposer une nouvelle métrique permettant d'améliorer le routage en termes de routage et de délai bout-en-bout. Dans la disparité des métriques proposées dans la littéraire, la métrique ETX (Expected Transmission Count) a été largement utilisée. Aussi, nous focaliserons, principalement, sur les métriques basées sur ETX. Notre constatation est que les besoins en termes de qualité de service dans les réseaux sans fil multi-saut, sont affecté entre autre par le protocole de routage adopté et la métrique de lien utilisée. Cependant, ceci est aussi strictement lié à la qualité des canaux de communication au niveau physique et l'état des files d'attente au niveau MAC. Aussi, une nouvelle métrique de qualité de lien est proposée, basée sur ETX et appelée IBETX (Interference and Bandwidth Adjusted ETX). Cette nouvelle métrique prend en considération les effets de l'interférence et de l'impact de l'état de la couche MAC sur les performances des liens de communication. Des simulations ont été conduites sous NS-2 afin de montrer l'intérêt de la métrique utilisée. Ainsi IBETX améliore le débit efficace de 19% par rapport à ETX et de 10% par rapport à ETP (Expected Throughput). Par ailleurs, la métrique proposée réduit le délai bout en bout de 16% par rapport à ELP ( Expected Link Performance) et de 24% par à ETX / This dissertation endeavors to contribute enhancements in goodputsof the IEEE 802.11-based Wireless Multi-hop Networks (WMhNs).By performing exhaustive simulations, for the deep analysis and detailed assessment of both reactive (AODV, DSR, DYMO) and proactive (DSDV, FSR, OLSR) protocols for varying mobilities, speeds, network loads and scalabilities, it is observed that a routing link metric is a significant component of a routing protocol. In addition to finding all available paths, the fastest end-to-end route is selected by a link metric for the routing protocol. This study aims the quality routing. In the class of quality link metrics, Expected Transmission Count (ETX) is extensively used. Thus, the most recently proposed ETX-based metrics have been analyzed. Though, newly developed metrics over perform ETX but still they can be improved. By profound analysis and particularized comparison of routing protocols depending upon their classes (reactive and proactive) and ETX-based metrics, we come to realize that users always demand proficient networks. In fact, WMhNs are facing several troubles which they expect to be resolved by the routing protocol operating them. Consequently, the protocol depends upon the link metric for providing quality paths. So, we identify and analyze the requirements to design a new routing link metric for WMhNs. Because, considering these requirements, when a link metric is proposed, then : firstly, both the design and implementation of the link metric with a routing protocol become easy. Secondly, the underlying network issues can easily be tackled. Thirdly, an appreciable performance of the network is guaranteed. Keeping in view the issues of WMhNs, increasing demands of users and capabilities of routing protocols, we propose and implement a new quality link metric, Interference and Bandwidth Adjusted ETX (IBETX). As, MAC layer affects the link performance and consequently the route quality, the metric therefore, tackles the issue by achieving twofold MAC-awareness. Firstly, interference is calculated using cross-layered approach by sending probes to MAC layer. Secondly, the nominal bit rate information is provided to all nodes in the same contention domain by considering the bandwidth sharing mechanism of 802.11. Like ETX, our metric also calculates link delivery ratios that directly affect throughput and selects those routes that bypass dense regions in the network. Simulation results by NS-2 show that IBETX gives 19% higher through put than ETX and 10% higher than Expected Throughput (ETP). Our metric also succeeds to reduce average end-to-end delay up to 16% less than Expected Link Performance (ELP) and 24% less than ETX

In this thesis, our objective is to improve the energy efficiency and load balance for wireless networks. We first study the relationships between the base station (BS) on/off operation and traffic distribution. A cooperative power saving method called clustering BS-off (CBSO) scheme is proposed. Instead of adopting a unified and consistent BS-off scheme in the whole network, the proposed centralized and distributed CBSO schemes can adaptively group BSs in several clusters based on the traffic fluctuations with space and time. Second, to further improve the network load balance and energy efficiency in distributed manner, we propose a power efficient self-organized virtual small networking (VSN) protocol. A heuristic firefly algorithm is applied to arrange the BSs' operation in small groups based on the traffic level. By jointly considering the load balance, the effectiveness of the proposed algorithm is demonstrated based on the average and min-max traffic levels of BSs' groups. Finally, the importance of detailed BS operation between active and sleep modes is considered. The operating procedure of femtocell base station, i.e., HeNB, is modeled as an MAP/PH/1/k queueing system. Such queueing analysis particularly focuses on the HeNB vacation process with user priorities. The HeNB's power on/off scheme is modeled as alternative service and vacation periods. The hybrid access is regarded as high and low priority users in the queuing system. We further propose the adaptive service rate and vacation length (ASV) method, so that the HeNB can work in a more energy-efficient way while satisfying QoS requirements such as blocking probability and users waiting time. Simulation results show the effectiveness of the proposed strategies and the overall network energy efficiency can be improved significantly. / October 2016

Wireless Networks is a very growing market. However, the security measures are not strong enough; the WEP security protocol is flawed. The 802.11 Task Group I is working on new security measures in order to strengthen the access control of users, the privacy and the integrity of data. We will describe the WEP flaws and the new security measures of 802.11 Task Group I. Finally, we will propose a new architecture to improve user identification for the wireless network of our department.

The convenience of IEEE 802.11-based wireless access networks has led to widespread deployment. However, these applications are predicated on the assumption of availability and confidentiality. Error-prone wireless networks afford an attacker considerable flexibility to exploit the vulnerabilities of 802.11-based mechanism. Two of most famous misbehaviors are selfish and malicious attacks. In this thesis we investigate two attacks: Spurious CTS attack (SCTS) and Jamming ACK attack (JACK). In the SCTS, malicious nodes may send periodic Spurious CTS packets to force other nodes to update their NAV values and prevent them from using the channel. In the JACK, an attacker ruins legitimate ACK packets for the intention of disrupting the traffic flow and draining the battery energy of victim nodes quickly. Correspondingly, we propose solutions: termed Carrier Sensing based Discarding (CSD), and Extended Network Allocation Vector (ENAV) scheme. We further demonstrate the performance of our proposed schemes through analysis and NS2 simulations.