This thesis paper proposes a Medium Access Control (MAC) protocol for wireless networks, termed as CD-MMAC that utilizes multiple channels and incorporates opportunistic cooperative diversity dynamically to improve its performance. The IEEE 802.11b standard protocol allows the use of multiple channels available at the physical layer but its MAC protocol is designed only for a single channel. The proposed protocol utilizes multiple channels by using single interface and incorporates opportunistic cooperative diversity by using cross-layer MAC. The new protocol leverages the multi-rate capability of IEEE 802.11b and allows wireless nodes far away from destination node to transmit at a higher rate by using intermediate nodes as a relays. The protocol improves network throughput and packet delivery ratio significantly and reduces packet delay. The performance improvement is further evaluated by simulation and analysis. / sabbir@linuxmail.org

Abstract Substantially growing data traffic over wireless networks poses increased challenges for mobile network operators in deploying sufficient network resources and managing user mobility. This dissertation considers these challenges to providing satisfactory Quality of Service (QoS) for end-users and studies solutions for better utilization of the heterogeneous network environment. First, the dissertation examines what solutions mobile devices and network management entities can use to dynamically collect valid cross-layer information from different network entities. Cross-layer information allows monitoring of the condition of the network in multiple layers on a user and application basis. The second research topic considers the techniques the network management entities can use to improve resource usage in wireless networks based on the collected cross-layer information. The IEEE 802.21 standard, specified to facilitate handovers between heterogeneous networks, is used as the basis for cross-layer information delivery. This dissertation also focuses on utilization of the standard beyond the inter-access technology handovers. In order to improve resource usage in wireless networks dynamically, event delivery enhancements are proposed for the standard so that it better applies to the requirements of different techniques. Such techniques are traffic priority adjustment, traffic adaptation, packet aggregation, and network protocol header compression. The results show that when a handover is not feasible, these techniques effectively allow sharing of the limited radio resources for the user data according to applications’ importance and type. Mobility management is studied in terms of network information service, one of the main services of IEEE 802.21. The thesis proposes enhancing the information service with a base station cell coverage area database. The database provides significant improvements for the selection of a handover target in a dense base station environment. With all the results taken together, the dissertation provides mobile network operators various means to improve the usage of wireless networks on the basis of applications’ varying QoS requirements. / Tiivistelmä Voimakkaasti kasvava langattomien tietoverkkojen dataliikenne aiheuttaa verkko-operaattoreille haasteita tarjota riittävät verkkoresurssit ja hallita käyttäjien liikkuvuutta. Väitöskirja huomioi nämä haasteet tarjota loppukäyttäjille tyydyttävä palvelunlaatu (QoS) ja tutkii ratkaisuja, joilla heterogeenistä verkkoympäristöä voidaan hyödyntää tehokkaammin. Aluksi väitöskirja tutkii, mitä ratkaisuja päätelaitteet ja verkkohallintatoimijat voivat käyttää keräämään protokollakerrosten välistä (cross-layer) tietoa eri verkkotoimijoilta. Protokollakerrosten välinen tieto mahdollistaa verkon tilan seuraamisen usealla eri kerroksella käyttäjä- ja sovelluskohtaisesti. Toinen tutkimusaihe tarkastelee protokollakerrosten välistä tietoa hyödyntäviä tekniikoita, joita verkonhallintatoimijat voivat käyttää tehostamaan resurssien käyttöä langattomissa verkoissa. IEEE 802.21-standardia, joka on määritetty helpottamaan verkonvaihtoja heterogeenisten verkkojen välillä, käytetään pohjana protokollakerrosten välisen tiedon jakelulle. Väitöskirjassa keskitytään standardin hyödyntämiseen myös muussa kuin verkkoteknologioiden välisen verkonvaihdon yhteydessä. Väitöskirja ehdottaa parannuksia standardin tapahtumatietovälitykseen, jotta se täyttäisi paremmin eri tekniikoiden asettamat vaatimukset dynaamisesti toteutettavista toimista langattomien verkkojen resurssikäytön tehostamiseksi. Nämä tekniikat ovat liikenteen prioriteetin muutokset, liikenteen adaptointi, pakettien yhdistäminen ja verkkoprotokollaotsikoiden pakkaus. Tulokset osoittavat, että kun tukiasema- tai verkonvaihto ei ole mahdollinen, nämä tekniikat mahdollistavat rajattujen verkkoresurssien jakamisen tehokkaasti sovellusten tärkeyden ja tyypin mukaan. Liikkuvuudenhallintaa tutkitaan verkkoinformaatiopalvelun, joka on myös yksi IEEE 802.21-standardin pääpalveluista, kautta. Väitöskirja ehdottaa, että informaatiopalvelua tehostetaan liittämällä siihen tietokanta tukiasemasolujen peittoalueista. Tietokanta tehostaa huomattavasti verkonvaihdon kohteen valintaa tiheissä tukiasemaympäristöissä. Kun väitöskirjan tulokset huomioidaan kokonaisuutena, väitöskirja tarjoaa verkko-operaattoreille useita tapoja tehostaa langattomien verkkojen käyttöä sovellusten vaihtelevien palvelunlaatuvaatimusten perusteella.

Abstract This thesis proposes cross-layer approaches which enable to improve energy efficiency of wireless sensor networks and wireless body area networks (WSN & WBAN). The focus is on the physical (PHY) and medium access control (MAC) layers of communication protocol stack and exploiting their interdependencies. In the analysis of the PHY and MAC layers, their relevant characteristics are taken into account, and cross-layer models are developed to study the effect of these layers on energy efficiency. In addition, cross-layer analysis is applied at the network level by addressing hierarchical networks' energy efficiency. The objective is to improve energy efficiency by taking into account that substantial modifications to current standards and techniques are not required to take advantage of the proposed methods. The studied scenarios of WSN take advantage of the wake-up radio (WUR). A generic WUR-based MAC (GWR-MAC) protocol with objective to improve energy efficiency by avoiding idle listening is proposed. First, the proposed cross-layer model is developed at a general level and applied to study the forward error correction (FEC) code rate selection effect on the length of the transmission period and energy efficiency in a star topology network. Then an energy efficiency model for intelligent hierarchical architecture based on GWR-MAC is proposed and performance comparison with a duty-cycle radio (DCR) approach is performed. Interactions between different layers' devices are taken into account, and the WUR and DCR approaches are compared as a function of event frequency. The third cross-layer model focuses on the effect of the FEC code rate and data packet payload length on the energy efficiency of the IEEE Std 802.15.6-based WBANs using IR-UWB PHY. The results acquired by using analytical modelling and simulations with the Matlab software clearly illustrates the potential energy gains that can be achieved with the proposed cross-layer approaches. The developed WUR-based MAC protocol, analytical models and achieved results can be exploited by other researchers in the WSN and WBAN field. The contribution of this thesis is also to stimulate further research on these timely topics and foster development of short-range communication, which has a crucial role in future converging networks such as the Internet of Things. / Tiivistelmä Tässä väitöskirjassa ehdotetaan protokollakerrosten välistä tietoa hyödyntäviä (cross-layer) lähestymistapoja, jotka mahdollistavat energiatehokkuuden parantamisen langattomissa sensori- ja kehoverkoissa. Työ kohdistuu fyysisen- ja kanavanhallintakerroksen välisen vuorovaikutuksen tutkimiseen. Fyysisen- ja kanavanhallintakerrosten analyysissä huomioidaan niiden tärkeimmät ominaisuudet ja tutkitaan kerrosten yhteistä energiatehokkuutta. Lisäksi kerrosten välistä analyysiä sovelletaan verkkotasolle tutkimalla hierarkkisen verkon energiatehokkuutta. Tavoitteena on energiatehokkuuden parantamisen mahdollistaminen siten, että merkittäviä muutoksia nykyisiin standardeihin ja tekniikoihin ei tarvitse tehdä hyödyntääkseen ehdotettuja menetelmiä. Tutkitut sensoriverkkoskenaariot hyödyntävät heräteradiota. Väitöskirjassa ehdotetaan geneerinen heräteradiopohjainen kanavanhallintaprotokolla (GWR-MAC), jolla parannetaan energiatehokkuutta vähentämällä turhaa kanavan kuuntelua. Kerrosten välinen malli kehitetään ensin yleisellä tasolla ja sen avulla tutkitaan virheenkorjauskoodisuhteen valinnan vaikutusta lähetysperiodin pituuteen ja energiatehokkuuteen tähtitopologiaan pohjautuvissa sensoriverkoissa. Sitten väitöskirjassa ehdotetaan energiatehokkuusmalli älykkäälle GWR-MAC -protokollaan perustuvalle hierarkkiselle arkkitehtuurille ja sen suorituskykyä vertaillaan toimintajaksoperiaatteella toimivaan lähestymistapaan. Eri kerroksilla olevien laitteiden väliset vuorovaikutukset huomioidaan heräteradio- ja toimintajaksoperiaatteella toimivien verkkojen suorituskykyvertailussa tapahtumatiheyden funktiona. Kolmas malli kohdistuu virheenkorjauskoodisuhteen ja datapaketin hyötykuorman pituuden energiatehokkuusvaikutuksen tutkimiseen IEEE 802.15.6 -standardiin perustuvissa langattomissa kehoverkoissa. Analyyttinen mallinnus ja Matlab-ohjelmiston avulla tuotetut simulointitulokset osoittavat selvästi energiatehokkuushyödyt, jotka saavutetaan ehdotettuja menetelmiä käyttämällä. Kehitetty GWR-MAC -protokolla, analyyttiset mallit ja tulokset ovat hyödynnettävissä sensori- ja kehoverkkotutkijoiden toimesta. Tämän väitöskirjan tavoitteena on myös näiden ajankohtaisten aiheiden jatkotutkimuksen stimulointi sekä lyhyen kantaman viestinnän kehityksen vauhdittaminen, sillä niillä on erittäin merkittävä rooli tulevaisuuden yhteen liittyvissä verkoissa, kuten esineiden ja asioiden Internetissä.

Monitoring and controlling smart grid assets in a timely and reliable manner is highly desired for emerging smart grid applications. Wireless Sensor Networks (WSNs) are anticipated to be widely utilized in a broad range of smart grid applications due to their numerous advantages along with their successful adoption in various critical areas including military and health care. Despite these advantages, the use of WSNs in such critical applications has brought forward a new challenge of ful lling the Quality of Service (QoS) requirements of these applications. Providing QoS support is a challenging issue due to highly resource constrained nature of sensor nodes, unreliable wireless links and harsh operation environments. In this thesis we critically investigate the problem of QoS provisioning in WSNs. We identify challenges, limitations and requirements for applying QoS provisioning for WSNs in smart grid applications. We nd that the topic of data prioritization techniques at the MAC layer to provide delay bounds in condition monitoring applications is not well developed. We develop six novel QoS schemes that provide data di erentiation and reduce the latency of high priority tra c in a smart grid context. These schemes are namely; Delay-Responsive Cross layer (DRX), Fair and Delay-aware Cross layer (FDRX), Delay-Responsive Cross layer with Linear backo (LDRX), Adaptive Realistic and Stable Model (ARSM), Adaptive Inter-cluster head Delay Control (AIDC) and QoS-aware GTS Allocation (QGA). Furthermore, we propose a new Markov-based model for IEEE 802.15.4 MAC namely, Realistic and Stable Markovbased (RSM). RSM considers actual network conditions and enhances the stability of the WSNs. We show through analytical and simulation results that all of the presented schemes reduce the end-to-end delay while maintaining good energy consumption and data delivery values.

Recent development has lead to the emergence of distributed Wireless Sensor and Actor Networks (WSAN), which are capable of observing the physical environment, processing the data, making decisions based on the observations and performing appropriate actions. WSANs represent an important extension of Wireless Sensor Networks (WSNs) and may comprise a large number of sensor nodes and a smaller number of actor nodes. The sensor nodes are low-cost, low energy, battery powered devices with restricted sensing, computational and wireless communication capabilities. Actor nodes are resource richer with superior processing capabilities, higher transmission powers and a longer battery life. A basic operational scenario of a typical WSAN application follows the following sequence of events. The physical environment is periodically sensed and evaluated by the sensor nodes. The sensed data is then routed towards an actor node. Upon receiving sensed data, an actor node performs an action upon the physical environment if necessary, i.e. if the occurrence of a disturbance or critical event has been detected. The specific characteristics of sensor and actor nodes combined with some stringent application constraints impose unique requirements for WSANs. The fundamental challenges for WSANs are to achieve low latency, high energy efficiency and high reliability. The latency and energy efficiency requirements are in a trade-off relationship. The communication and coordination inside WSANs is managed via a Communication Protocol Stack (CPS) situated on every node. The requirements of low latency and energy efficiency have to be addressed at every layer of the CPS to ensure overall feasibility of the WSAN. Therefore, careful design of protocol layers in the CPS is crucial in attempting to meet the unique requirements and handle the abovementioned trade-off relationship in WSANs. The traditional CPS, comprising the application, network, medium access control and physical layer, is a layered protocol stack with every layer, a predefined functional entity. However, it has been found that for similar types of networks with similar stringent network requirements, the strictly layered protocol stack approach performs at a sub-optimal level with regards to network efficiency. A modern cross-layer paradigm, which proposes the employment of interactions between layers in the CPS, has recently attracted a lot of attention. The cross-layer approach promotes network efficiency optimization and promises considerable performance gains. It is found that in literature, the adoption of this cross-layer paradigm has not yet been considered for WSANs. In this dissertation, a complete cross-layer enabled WSAN CPS is developed that features the adoption of the cross-layer paradigm towards promoting optimization of the network efficiency. The newly proposed cross-layer enabled CPS entails protocols that incorporate information from other layers into their local decisions. Every protocol layer provides information identified as beneficial to another layer(s) in the CPS via a newly proposed Simple Cross-Layer Framework (SCLF) for WSANs. The proposed complete cross-layer enabled WSAN CPS comprises a Cross-Layer enabled Network-Centric Actuation Control with Data Prioritization (CL-NCAC-DP) application layer (APPL) protocol, a Cross-Layer enabled Cluster-based Hierarchical Energy/Latency-Aware Geographic Routing (CL-CHELAGR) network layer (NETL) protocol and a Cross-Layer enabled Carrier Sense Multiple Access with Minimum Preamble Sampling and Duty Cycle Doubling (CL-CSMA-MPS-DCD) medium access control layer (MACL) protocol. Each of these protocols builds on an existing simple layered protocol that was chosen as a basis for development of the cross-layer enabled protocols. It was found that existing protocols focus primarily on energy efficiency to ensure maximum network lifetime. However, most WSAN applications require latency minimization to be considered with the same importance. The cross-layer paradigm provides means of facilitating the optimization of both latency and energy efficiency. Specifically, a solution to the latency versus energy trade-off is given in this dissertation. The data generated by sensor nodes is prioritised by the APPL and depending on the delay-sensitivity, handled in a specialised manor by every layer of the CPS. Delay-sensitive data packets are handled in order to achieve minimum latency. On the other hand, delay-insensitive non critical data packets are handled in such a way as to achieve the highest energy efficiency. In effect, either latency minimization or energy efficiency receives an elevated precedence according to the type of data that is to be handled. Specifically, the cross-layer enabled APPL protocol provides information pertaining to the delay-sensitivity of sensed data packets to the other layers. Consequently, when a data packet is detected as highly delay-sensitive, the cross-layer enabled NETL protocol changes its approach from energy efficient routing along the maximum residual energy path to routing along the fastest path towards the cluster-head actor node for latency minimizing of the specific packet. This is done by considering information (contained in the SCLF neighbourhood table) from the MACL that entails wakeup schedules and channel utilization at neighbour nodes. Among the added criteria, the next-hop node is primarily chosen based on the shortest time to wakeup. The cross-layer enabled MACL in turn employs a priority queue and a temporary duty cycle doubling feature to enable rapid relaying of delay-sensitive data. Duty cycle doubling is employed whenever a sensor node’s APPL state indicates that it is part of a critical event reporting route. When the APPL protocol state (found in the SCLF information pool) indicates that the node is not part of the critical event reporting route anymore, the MACL reverts back to promoting energy efficiency by disengaging duty cycle doubling and re-employing a combination of a very low duty cycle and preamble sampling. The APPL protocol conversely considers the current queue size of the MACL and temporarily halts the creation of data packets (only if the sensed value is non critical) to prevent a queue overflow and ease congestion at the MACL By simulation it was shown that the cross-layer enabled WSAN CPS consistently outperforms the layered CPS for various network conditions. The average end-to-end latency of delay-sensitive critical data packets is decreased substantially. Furthermore, the average end-to-end latency of delay-insensitive data packets is also decreased. Finally, the energy efficiency performance is decreased by a tolerable insignificant minor margin as expected. The trivial increase in energy consumption is overshadowed by the high margin of increase in latency performance for delay-sensitive critical data packets. The newly proposed cross-layer CPS achieves an immense latency performance increase for WSANs, while maintaining excellent energy efficiency. It has hence been shown that the adoption of the cross-layer paradigm by the WSAN CPS proves hugely beneficial with regards to the network efficiency performance. This increases the feasibility of WSANs and promotes its application in more areas. / Dissertation (MEng)--University of Pretoria, 2009. / Electrical, Electronic and Computer Engineering / unrestricted

This thesis dissertation addresses the problem of energy constraints in ad hoc wireless networks. In this sort of networks nodes are generally powered by means of batteries, which involves significant limitations regarding the time of operation of devices. The nodes whose battery level describes important energy depletion represent potential elements for loss of connectivity, which results in an increase of packet loss rate. Therefore, the management of energy expenditure is one of the main research challenges to face in ad hoc networks, especially when developing applications in real scenarios. However, energy management is not a trivial task due to the inherent features of this kind of networks, such as the distributed operation as well as the access medium mechanism. In that sense, traditional solutions of energy optimization based on the definition of power-saving intervals (sleep mode) are not suitable considering the operational characteristics of an ad hoc network, due to the substantial deterioration of network connectivity. In addition, the exponential growth of applications focused on the transmission of multimedia contents (especially video) available on mobile devices involves specific quality of service levels. Consequently, the design of solutions for the optimization of energy resources should be carried out without degrading the Quality of Experience perceived by the users. The contributions of this thesis are focused, in the first place, on the analysis of those factors which generate an increase of the energy consumption in the wireless medium and are related to the principle of operation of the radio interface. In particular, the intense operation in reception mode on the interference areas, as a result of the overhearing effect, as well as the high number of transmission retries due to channel access contention, are defined as the main aspects that increase energy demand in the network. On the other hand, with the aim of optimizing energy resources in the nodes without causing damage on the Quality of Service, this thesis proposes meaningful improvements to the routing protocol by means of a cross-layer scheme. Specifically, the designed mechanism carries out an evaluation of both the energy capacity available in the nodes and the distribution of devices along the wireless medium. To that end, this proposal introduces a new metric in the routing computation process, called strategic value, which reports the importance of a node in the network in terms of connectivity (i.e. number of neighbor nodes). This scheme aims to reduce the energy expenditure caused by the overhearing effect along the areas with higher node density as well as to extend the lifetime for those nodes with higher number of neighbors which are strategic to preserve network connectivity. Additionally, considering the current pragmatic approach in ad hoc networks focused on the design of specific applications, the evaluation hereby presented has been performed by means of a simulation environment and also through the implementation of a testbed. Specifically, the operation of the proposed scheme has been analyzed on a set of ad hoc nodes which has been implemented through development platforms. Also, a software tool has been developed in order to control and configure the experiments. Results prove that the proposal allows to extend the lifetime of the network as well as to increase packet reception rate as a consequence of the prevention in the route breakages due to energy depletion. Finally, it is worth mentioning that the knowledge acquired by the design, configuration and analysis of experiments by means of hardware devices, has motivated the development of proposals and application studies of ad hoc networks in real environments, which represent an additional contribution of this thesis dissertation. / El presente trabajo de tesis doctoral aborda la problemática de las limitaciones de energía en redes inalámbricas ad hoc. En este tipo de redes, los nodos generalmente emplean baterías como fuente de alimentación, lo que limita de forma dramática la autonomía de funcionamiento. Los nodos con mayor agotamiento de energía constituyen potenciales elementos para la pérdida de conectividad parcial o total de la red ocasionando el incremento de la pérdida de paquetes. Por tanto, la gestión eficiente del gasto es uno de los principales desafíos a enfrentar en el ámbito de investigación de redes ad hoc, en especial para el desarrollo de aplicaciones en escenarios reales de operación. Sin embargo, dicha gestión no es una tarea trivial debido a las características inherentes de este tipo de redes, como por ejemplo la operación distribuida, así como el acceso compartido al medio inalámbrico. En tal sentido, los mecanismos usuales de optimización del gasto de energía basados en el establecimiento de períodos de bajo consumo (modo sleep), no se ajustan a las características operativas de una red ad hoc, debido al impacto notable que ocasionan sobre la conectividad en la red. Además, el crecimiento significativo de las aplicaciones y servicios de distribución de contenidos multimedia, especialmente tráfico de vídeo, demandan niveles específicos de calidad de servicio. Por consiguiente, el diseño de soluciones de optimización de los recursos de energía disponible en los nodos no debe implicar la degradación de la calidad de experiencia percibida por los usuarios finales. Las contribuciones del trabajo de tesis se centran, en primer lugar, en el análisis de los factores que incrementan el gasto de energía en el medio inalámbrico y que están relacionados con el principio de operación de la interfaz de radio. En particular, el incremento dramático del funcionamiento en modo recepción ocasionado sobre las zonas de interferencia por el efecto overhearing así como el mayor número de intentos de transmisión debido a la contienda por el acceso al canal, se definen como las principales causas que incrementan la demanda de energía en la red. Por otra parte, con el objetivo de optimizar los recursos de energía disponibles en los nodos sin ocasionar un perjuicio sobre la calidad de servicio, en el presente trabajo de tesis se proponen mejoras al protocolo de encaminamiento mediante un esquema cross-layer. En concreto, el mecanismo diseñado realiza una evaluación de la capacidad de energía disponible en los nodos, así como de la distribución de los dispositivos en el medio inalámbrico. Con tal fin, la propuesta introduce en el cómputo de enrutamiento una métrica nueva denominada valor estratégico, la cual reporta la importancia de un nodo en la red en términos de conectividad (número de dispositivos vecinos). El esquema apunta a reducir el gasto de energía ocasionado por el efecto overhearing en las zonas con mayor densidad de dispositivos, así como extender la autonomía de operación sobre aquellos nodos con mayor número de vecinos, que resultan estratégicos para conservar la conectividad en la red. Además, de forma consecuente con el actual enfoque pragmático en redes ad hoc orientado al diseño de soluciones para escenarios específicos de aplicación, la evaluación de la propuesta se ha realizado tanto en un entorno de simulación, así como mediante la implementación de un testbed. Específicamente, se ha analizado la operación del mecanismo de enrutamiento propuesto sobre un conjunto de nodos ad hoc implementados mediante plataformas de desarrollo. Adicionalmente, se ha desarrollado una herramienta para el control y configuración de los experimentos. Los resultados demuestran que la propuesta permite extender el tiempo de operación de la red, así como incrementar la tasa de paquetes en recepción como consecuencia de la prevención en la ruptura de los enlaces por agotamiento / El present treball de tesi doctoral aborda la problemàtica de les limitacions d'energia en xarxes sense fil ad hoc. En este tipus de xarxes, els nodes generalment empren bateries com a font d'alimentació, la qual cosa limita de forma dramàtica l'autonomia de funcionament. Els nodes amb major esgotament d'energia constituïxen potencials elements per a la pèrdua de connectivitat parcial o total de la xarxa, ocasionant l'increment de la pèrdua de paquets. Per tant, la gestió eficient de la despesa és un dels principals desafiaments a enfrontar en l'àmbit d'investigació de xarxes ad hoc, en especial per al desenvolupament d'aplicacions en escenaris reals d'operació. No obstant això, aquesta gestió no és una tasca trivial a causa de les característiques inherents d'este tipus de xarxes, com per exemple l'operació distribuïda així com l'accés compartit al mitjà sense fil. En este sentit, els mecanismes usuals d'optimització de la despesa d'energia basats en l'establiment de períodes de baix consum (mode sleep), no s'ajusten a les característiques operatives d'una xarxa ad hoc, a causa de l'impacte notable que ocasionen sobre la connectivitat a la xarxa. A més, el creixement significatiu de les aplicacions i serveis de distribució de continguts multimèdia, especialment tràfic de vídeo, demanden nivells específics de qualitat de servei. Per tant, el disseny de solucions d'optimització dels recursos d'energia disponible en els nodes no ha d'implicar la degradació de la qualitat d'experiència percebuda pels usuaris finals. Les contribucions del treball de tesi se centren, en primer lloc, en l'anàlisi dels factors que incrementen la despesa d'energia en el mitjà sense fil i que estan relacionats amb el principi d'operació de la interfície de ràdio. En particular, l'increment dramàtic del funcionament en mode recepció, ocasionat sobre les zones d'interferència per l'efecte overhearing, així com el major nombre d'intents de transmissió a causa de la contesa per l'accés al canal, es definixen com les principals causes que incrementen la demanda d'energia a la xarxa. D'altra banda, amb l'objectiu d'optimitzar els recursos d'energia disponibles en els nodes sense ocasionar un perjudici sobre la qualitat de servici, en el present treball de tesi es proposen millores al protocol d'encaminament mitjançant un esquema cross-layer. En concret, el mecanisme dissenyat realitza una avaluació de la capacitat d'energia disponible en els nodes així com de la distribució dels dispositius en el mitjà sense fil. Amb tal fi, la proposta introduïx en el còmput d'encaminament una nova mètrica denominada valor estratègic, la qual reporta la importància d'un node en la xarxa en termes de connectivitat (nombre de dispositius veïns). L'esquema reduix la despesa ocasionada per l'efecte overhearing a les zones amb major densitat de dispositius i estén l'autonomia d'operació sobre aquells nodes amb major nombre de veïns, que resulten estratègics per conservar la connectivitat a la xarxa. A més, de forma conseqüent amb l'actual enfocament pragmàtic en xarxes ad hoc orientat al disseny de solucions per a escenaris específics d'aplicació, l'avaluació de la proposta s'ha realitzat tant en un entorn de simulació així com per mitjà de la implementació d'un testbed. Específicament, s'ha analitzat l'operació del mecanisme d'encaminament proposat sobre un conjunt de nodes ad hoc implementats mitjançant plataformes de desenvolupament. Addicionalment, s'ha desenvolupat una eina per al control i configuració dels experiments. Els resultats demostren que la proposta permet estendre el temps d'operació de la xarxa així com incrementar la taxa de paquets en recepció com a conseqüència de la prevenció en la ruptura dels enllaços per esgotament d'energia. / González Martínez, SR. (2017). Diseño de un Esquema Cross-Layer para el Balance entre Eficiencia Energética y Calidad de Servicio en la Transmisión de Tráfico Multimedia en Redes Ad-Hoc [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/84284 / TESIS

The expectations in performing high-performance cyber-physical applications in resource-constrained devices are continuously increasing. The available hardware is still a main limitation in this context, both in terms of computation capability and energy limits. On the other hand, one must ensure the robust and accurate execution of the applications deployed, since their failure may entail risks for humans and the surrounding environment. The limits and risks are enhanced when multiple applications are executed on the same device. The focus of this thesis is to provide a trade-off between the required performance and power consumption. The focus is on two fundamental applications in the mobile autonomous vehicles scenario: localization and object detection. The multi-objective optimization is performed in a cross-layer manner, exploring both applications and platform configurable parameters with Design Space Exploration (DSE). The focus is on localization and detection accuracy, detection latency and power consumption. Predictive models are designed to estimate the metrics of interest and ensure robust execution, excluding potential faulty configurations from the design space. The research is approached empirically, performing tests on the Nvidia Jetson AGX and NX platforms. Results show that optimal configurations for a single application are in general sub-optimal or faulty for the concurrent execution case, while the opposite is sometimes applicable. / Resursbegränsade enheter förväntas utföra mer och mer krävande cyberfysiska program. Hårdvaran är en av de huvudsakliga begränsningarna både vad gäller beräkningshastighet och energigränser. Samtidigt måste programmen som körs vara robusta och noggranna, eftersom ett fel kan påverka människor och deras omgivning. När flera program körs på samma enhet blir både begränsningar och risker större. Den här avhandlingen fokuserar på att göra en avvägning mellan krav på prestanda och energiförbrukning för två tillämpningar inom området autonoma fordon: lokalisering och objektigenkänning. Med hjälp av Design Space Exploration (DSE) utforskas parametrar både i applikationerna och på plattformen genom att utföra tvärlageroptimering med flera mål. Lokaliserings- och detekteringsnoggrannhet, fördröjning i igenkänning och energiförbrukning är egenskaper i fokus. Prediktiva modeller designas för att estimera måtten som är av intresse och garantera robust körning genom att utesluta potentiellt felaktiga konfigurationer. Empirisk forskning görs med tester på Nvidia Jetson AGXoch NX-plattformarna. Resultaten visar att de optimala konfigurationerna för ett enda program i allmänhet är suboptimala eller felaktiga vid körning av flera program samtidigt, medan motsatsen ibland är tillämplig.

The Internet of Things (IoT) is the next generation of networked society where billions of, everyday-life, devices are directly connected to the Internet and able to communicate with each other. In particular, the Constrained Application Protocol (CoAP) has become the de-facto IoT standard for communication at the application layer, as a lightweight web transfer protocol affordable also for resource-constrained platforms. However, as IoT devices are directly connected to the Internet, they are especially vulnerable to a number of security attacks including Denial of Service (DoS), which can seriously worsen their performance and responsiveness, and even make them totally unavailable to serve legitimate requests. In this Master's Thesis project, we have developed a cross-layer and context-aware approach that adaptively counteracts DoS attacks against CoAP server devices, by dynamically adjusting their operative state according to the attack intensity. This considerably limits the impact of DoS attacks and preserves service availability of victim devices to the best possible extent. The proposed approach leverages a trusted Proxy that adaptively shields victim devices, while effectively forwarding and caching messages if needed. We have made a proof-of-concept implementation of our solution for the Californium framework and the CoAP protocol, and experimentally evaluated its effectiveness in counteracting DoS and preserving availability of devices under attack. This Master's Thesis project has been conducted in collaboration with RISE SICS, a research institute for applied information and communication technology in Sweden. / Sakernas Internet (IoT) är nästa generations nätverkssamhälle där miljarder av, vardagliga, enheter är direkt anslutna till Internet och har möjlighet att kommunicera med varandra. Särskilt har CoAP, ett lättviktsprotokoll för webbtrafik som även fungerar för plattformar med begränsade resurser, blivit Sakernas Internets standard för kommunikation på applikationslagret. Men eftersom IoT-enheter är direkt anslutna till Internet så är de också speciellt utsatta för ett antal säkerhetsattacker, inklusive DoS, som kan försämra deras prestanda och mottaglighet avsevärt och i värsta fall göra dem helt otillgängliga för legitima förfrågningar. I detta examensarbete har vi utvecklat en lageröverskridande och kontextmedveten metod som adaptivt motverkar DoS attacker mot CoAP serverenheter genom att dynamiskt anpassa enhetens operativa tillstånd i enlighet med attackintensiteten. Detta begränsar DoS-attackers påverkan på enheterna avsevärt samtidigt som det bibehåller tillgänglighet för tjänster på utsatta enheter till största möjliga utsträckning. Den föreslagna metoden utnyttjar en betrodd proxy som adaptivt skyddar utsatta enheter, samtidigt som den effektivt vidarebefordrar och sparar meddelanden om så behövs. I detta arbete har vi skapat en proof of concept-implementation av vår lösning för Californium-ramverket och CoAP protokollet. Arbetet har utvärderats experimentellt för att undersöka lösningens effektivitet när det gäller att motarbeta DoS-attacker samt hur den bibehåller enheters tillgänglighet under attacker. Detta uppsatsprojekt har utförts i samarbete med RISE SICS som är ett forskningsinstitut för tillämpad informations- och kommunikationsteknik i Sverige.

In the last decades, there has been a growing interest towards new use cases in the Internet of Things (IoT) domain, such as extended reality glasses, unmanned aerial vehicles (UAVs), and autonomous driving. The technological advancement observed in such scenarios has also been enabled by the increasing capabilities of small form factor devices. Although such devices allow to achieve remarkable computing performance with relatively low energy consumption, these are often used in contexts in which the trade-offs between power consumption and application performance play a key role (e.g., battery powered systems). Furthermore, if such trade-offs are not carefully set, the performance degradation can lead to system failure. The work proposed in this thesis aims at investigating this type of problems, and to propose a runtime model and controller pair based on the joint optimization of the platform and application parameters to reduce the likelihood of system failure. The proposed architecture is evaluated in a UAV emulated environment, in which the used platform embeds hardware features comparable to the ones of a drone, while the localization and mapping application executed on such device makes use of real-world visual-inertial datasets. The proposed runtime model-controller solution relies on the monitoring of the platform CPU peaks for identifying application failure. It has also been empirically demonstrated that the model-controller can substantially decrease the number of failures and, in specific scenarios, improve localization accuracy and power consumption even compared to the optimal static parameter configurations. Moreover, the solution has been proven to be simple and generalizable in scenarios characterized by different levels of concurrency, and in the datasets tested. / Under de senaste decennierna har det funnits ett växande intresse för nya användningsfall som Extended Reality-glasögon, obemannade flygfarkoster (UAV) och autonom körning. De tekniska framstegen som observerats i sådana scenarier har också möjliggjorts av den ökande kapaciteten hos små formfaktorenheter. Även om sådana enheter gör det möjligt att uppnå anmärkningsvärd datorprestanda med relativt låg energiförbrukning, används dessa ofta i sammanhang där kompromisserna mellan strömförbrukning och applikationsprestanda spelar en nyckelroll (t.ex. batteridrivna system). Dessutom, om sådana avvägningar inte är noggrant inställda, kan prestandaförsämringen leda till systemfel. Arbetet som föreslås i denna avhandling syftar till att undersöka denna typ av problem, och att föreslå en körtid modellstyrenhet baserad på gemensam optimering av plattformen och applikationsparametrar för att minska systemfel. Den föreslagna arkitekturen utvärderas i en UAV-emulerad miljö, där den använda plattformen har hårdvarufunktioner som är motsvarar en drönare, medan lokaliserings- och kartläggningsapplikationen som körs på en sådan enhet använder verkliga visuella tröghetsdatauppsättningar. Den föreslagna runtime-modellstyrningslösningen förlitar sig på övervakning av plattformens CPU-toppar för att identifiera programfel. Det har också visat sig empiriskt att modellstyrenheten avsevärt kan minska antalet fel och, i specifika scenarier, förbättra lokaliseringsnoggrannheten och strömförbrukningen även jämfört med de optimala statiska parameterkonfigurationerna. Dessutom har lösningen visat sig vara enkel och generaliserbar i scenarier som kännetecknas av olika nivåer av samtidighet och i de testade datamängderna.

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