Ensuring trustworthiness through mobile nodes is a serious issue. Indeed, securing the routing protocols in Mobile Ad Hoc Network (MANET) is of paramount importance. A key exchange cryptography technique is one such protocol. Trust relationship between mobile nodes is essential. Without it, security will be further threatened. The absence of infrastructure and a dynamic topology changing reduce the performance of security and trust in mobile networks. Current proposed security solutions cannot cope with eavesdroppers and misbehaving mobile nodes. Practically, designing a key exchange cryptography system is very challenging. Some key exchanges have been proposed which cause decrease in power, memory and bandwidth and increase in computational processing for each mobile node in the network consequently leading to a high overhead. Some of the trust models have been investigated to calculate the level of trust based on recommendations or reputations. These might be the cause of internal malicious attacks. Our contribution is to provide trustworthy communications among the mobile nodes in the network in order to discourage untrustworthy mobile nodes from participating in the network to gain services. As a result, we have presented an Elliptic Curve Diffie-Hellman key exchange and trust framework mechanism for securing the communication between mobile nodes. Since our proposed model uses a small key and less calculation, it leads to a reduction in memory and bandwidth without compromising on security level. Another advantage of the trust framework model is to detect and eliminate any kind of distrust route that contain any malicious node or suspects its behavior.

The proliferation of wireless ad-hoc networks especially wireless LAN (IEEE 802.11b Standard) in the commercial market in recent years has reached a critical mass. The adoption and strong support of wireless IEEE 802.11 standard, coupled with the consequent decline in costs, has made wireless LAN deployment as one of the fastest growth area in communication access technology. With the ever increasing use of wireless LAN technology the various networks are reaching their full capacity in terms of network throughput, number of users and interference level in the wireless channel. In this thesis work I propose to the use smart antenna technology and a power management scheme in the wireless ad-hoc networks to increase the network capacity in terms of throughput, number of simultaneous communication and to lower the average transmit power and consequently co-channel interference. Power management scheme can be used to maximize the power efficiency of the transmitter by choosing an optimum transmit power level. Smart antenna or adaptive antenna array technology has reached a level of sophistication that it is feasible to use it on small mobile terminals like handheld PDA, LAPTOP and other mobile devices with limited battery power. The simulation results of various ad-hoc network scenario shows that there are significant gains to be had if these technologies can be integrated in the existing wireless LAN physical layer and/or in the standard them self. Smart antennas along with slight modification in channel access scheme reduce co-channel interference dramatically and increases the number of simultaneous transmissions hence improves network throughput. Power management algorithm is shown to improve average transmission of a node. We present a mathematical framework to characterize the outage probability of cellular mobile radio system with selective co-channel interference receiver in overloaded array environments. The mathematical framework outlines a general numerical procedure for computing the probability of outage of a cellular mobile radio system that is equipped with a smart antenna to suppress a few strongest co-channel interferers (CCI) out of a total of NI active interferers by null steering. / Master of Science

Ad hoc networks are emerging as a cost-effective, yet, powerful tool for communication. These systems, where networks can emerge and converge on-the-fly, are guided by the forward-looking goals of providing ubiquitous connectivity and constant access to information. Due to power and bandwidth constraints, the vulnerability of the wireless medium, and the multi-hop nature of ad hoc networks, these networks are becoming increasingly complex dynamic systems. Besides, modern radios are empowered to be reconfigurable, which harbors the temptation to exploit the system. To understand the implications of these issues, some of which pose significant challenges to efficient network design, we study topology control using game theory. We develop a game-theoretic framework of topology control that broadly captures the radio parameters, one or more of which can be tuned under the purview of topology control. In this dissertation, we consider two parameters, viz. transmit power and channel, and study the impact of controlling these on the emergent topologies. We first examine the impact of node selfishness on the network connectivity and energy efficiency under two levels of selfishness: (a) nodes cooperate and forward packets for one another, but selfishly minimize transmit power levels and; (b) nodes selectively forward packets and selfishly control transmit powers. In the former case, we characterize all the Nash Equilibria of the game and evaluate the energy efficiency of the induced topologies. We develop a better-response-based dynamic that guarantees convergence to the minimal maximum power topology. We extend our analysis to dynamic networks where nodes have limited knowledge about network connectivity, and examine the tradeoff between network performance and the cost of obtaining knowledge. Due to the high cost of maintaining knowledge in networks that are dynamic, mobility actually helps in information-constrained networks. In the latter case, nodes selfishly adapt their transmit powers to minimize their energy consumption, taking into account partial packet forwarding in the network. This work quantifies the energy efficiency gains obtained by cooperation and corroborates the need for incentivizing nodes to forward packets in decentralized, energy-limited networks. We then examine the impact of selfish behavior on spectral efficiency and interference minimization in multi-channel systems. We develop a distributed channel assignment algorithm to minimize the spectral footprint of a network while establishing an interference-free connected network. In spite of selfish channel selections, the network spectrum utilization is shown to be within 12% of the minimum on average. We then extend the analysis to dynamic networks where nodes have incomplete network state knowledge, and quantify the price of ignorance. Under the limitations on the number of available channels and radio interfaces, we analyze the channel assignment game with respect to interference minimization and network connectivity goals. By quantifying the interference in multi-channel networks, we illuminate the interference reduction that can be achieved by utilizing orthogonal channels and by distributing interference over multiple channels. In spite of the non-cooperative behavior of nodes, we observe that the selfish channel selection algorithm achieves load balancing. Distributing the network control to autonomous agents leaves open the possibility that nodes can act selfishly and the overall system is compromised. We advance the need for considering selfish behavior from the outset, during protocol design. To overcome the effects of selfishness, we show that the performance of a non-cooperative network can be enhanced by appropriately incentivizing selfish nodes. / Ph. D.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The recent emergence of ubiquitous wireless connectivity and the increasing computational capacity of modern vehicles have triggered immense interest in the possibilities of vehicular connectivity. A plethora of potential applications for vehicular networks have been proposed in the areas of safety, traffic infrastructure management, information, and entertainment. The broad range of applications requires creative utilisation of the available wireless medium, using a combination of existing and novel wireless technologies. In this research the evaluation of one such configuration is performed. Dedicated short range communication for safety applications is assumed, and the use of Wi- Fi and WiMAX for non-safety applications is evaluated. Little is known about the media streaming performance of these wireless technologies in realistic vehicular ad-hoc network (VANET) scenarios. Due to the extreme mobility and unpredictable environmental aspects in a real road environment, an empirical evaluation is performed and presented. Evaluation of a multi-vehicle to infrastructure (V2V2I) VANET, using Wi-Fi for the vehicle-to-vehicle communication and WiMAX for the vehicle to infrastructure (V2I) communication is experimented. It is observed that Wi-Fi is unaffected by the vehicle speed; whenever nodes are within communication range, data gets transferred normally. A detailed characterisation of the network architecture is presented and the results show that a multitude of applications can be supported with this proposed network architecture. / AFRIKAANSE OPSOMMING: Die toenemende beskikbaarheid en digtheid van koordlose netwerke en die verhoogde verwerkingsvermoëns van moderne voertuie het die afgelope paar jaar aansienlike belangstelling gewek in die moontlikhede wat voertuig-kommunikasie bied. ʼn Magdom moontlike toepassings is voorgestel in ʼn wye verskeidenheid van velde insluitende veiligheid, verkeersinfrastruktuur, informasie en vermaak. Hierdie voorstelle vereis die kreatiewe benutting van die beskikbare en nuwe koordlose tegnologieë. Hierdie tesis evalueer een voorbeeld van so ‘n opstelling. ʼn Toegewyde kortafstand kommunikasie modus vir veiligheidstoepassings word aangeneem, terwyl Wi-Fi en WiMAX vir ander toepassings evalueer word. Daar is min navorsing oor die kapasiteit en seinsterkte van hierdie beskikbare netwerke onder realistiese voertuig netwerk (VANET) scenario‘s. Weens die hoë mobiliteit van voertuie en ook die onvoorspelbaarheid van hierdie omgewing word ʼn empiriese evaluasie beskou as die mees gepaste metode. Die navorsing ondersoek ʼn multi-voertuig-totinfrastruktuur- netwerk wat Wi-Fi gebruik vir voertuig-tot-voertuig (V2V) kommunikasie en WiMAX vir voertuig-tot-infrastruktuur (V2I) kommunikasie. Die navorsing bevind dat Wi-Fi nie beïnvloed word deur die spoed van die voertuig nie: wanneer die nodes binne die bereik is van die netwerk word data normaal oorgedra. ‗n Gedetailleerde karakterisering van dié netwerk word gedoen en die resultate dui aan dat ‗n groot hoeveelheid toepassings ondersteun kan word deur dié opstelling.

Network coding is a technique used to increase the capacity of a network by combining messages sent over the network. The combined messages could be separated by using sufficient original messages which were used to combine the messages. Network coding can be implemented in different layers of the 051 stack, but to date a complete comparison between different implementations of network coding has not been done. The goal of this dissertation is to implement a wireless node model with network coding in the MAC layer and evaluate the performance characteristics of reference networks that implement the new node model. This will serve as the first step of a greater goal, namely finding the most favourable position in the 051 stack to implement network coding. The characteristics of the different implementations of network coding are presented in this dissertation. Simulations were done in OPNET® to find further attributes concerning the implementation of network coding in the MAC layer. The simulation process used is presented and explained, and the results from the simulations are analysed. Network coding in the simulations was implemented opportunistically. The results show that the more often different nodes send frames to the coding node, the better network coding performs. The work contributes to finding the best layer for implementing network coding for its increased throughput. A benchmark network was created so that network coding could be implemented in all the layers of the 051 stack, and then be compared to each other. An implementation of network coding in the MAC layer was simulated and analyzed. We conclude that, because there are so many different purposes for which networks are used, a single instance of network coding is unlikely to be similarly beneficial to all purposes. There still remains work to find the most favourable position for network coding in the 051 stack for all the different types of network coding. / Thesis (M. Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2011

Les réseaux de capteurs sans fils et mobiles constituent un champ de recherche dans lequel un grand nombre de capteurs de faible coût sont déployés dans un environnement pour observer un ou plusieurs phénomènes. Ces capteurs sont autonomes, communicant et disposent d'une réserve d'énergie limitée. Les problèmes issus de ce type de système sont nombreux : gestion de l'énergie, couverture, fusion de donnée, ...L'approche proposée dans cette thèse repose sur l'hypothèse que les réseaux de capteurs doivent exhiber des propriétés d'auto-organisation et d'autonomie. Chaque capteur est en soit autonome et peut interagir avec d'autres capteurs ce qui forme une organisation complexe. Ces capteurs ont un but à accomplir et le système possède les caractéristiques suivantes : i. le but du réseau ne peut généralement pas être résolu par un capteur uniqueii. Les capteurs doivent collaborer pour accomplir le but ou contribuer à une partie de ce but.iii. Chaque capteur réagit à son environnement en fonction de ses perceptions qui sont forcément locales et limitées.Après une introduction qui décrit le domaine et pose la problématique un état de l'art du domaine est présenté au chapitre 2. Deux contributions sont abordées dans cette thèse. D'une part, l'analyse des propriétés dynamiques de topologie des réseaux de capteurs sans fil et d'autre part la performance des liens de ce type de réseaux. Pour la topologie deux approches sont proposées : au chapitre 3 une première approche basée sur le modèle de mobilité et au chapitre 4 une approche basée sur des techniques de mesures. Pour la performance des liens, deux approches sont également proposées. La première, décrite dans le chapitre 5, est basée sur un modèle d'analyse linéaire. La deuxième, décrite au chapitre 6, repose sur une technique d'optimisation multi-objectif. / The measurability of Mobile ad hoc network (MANET) is the precondition of itsmanagement, performance optimization and network resources re-allocations. However, MANET is an infrastructure-free, multi-hop, andself-organized temporary network, comprised of a group of mobile nodes with wirelesscommunication devices. Not only does its topology structure vary with time going by, butalso the communication protocol used in its network layer or data link layer is diverse andnon-standard.In order to solve the problem of interior links performance (such as packet loss rate anddelay) measurement in MANET, this thesis has adopted an external measurement basedon network tomography (NT). To the best of our knowledge, NT technique is adaptable for Ad Hoc networkmeasurement.This thesis has deeply studied MANET measurement technique based on NT. The maincontributions are:(1) An analysis technique on MANET topology dynamic characteristic based onmobility model was proposed. At first, an Ad Hoc network mobility model formalizationis described. Then a MANET topology snapshots capturing method was proposed to findand verify that MANET topology varies in steady and non-steady state in turnperiodically. At the same time, it was proved that it was practicable in theory to introduceNT technique into Ad Hoc network measurement. The fitness hypothesis verification wasadopted to obtain the rule of Ad Hoc network topology dynamic characteristic parameters,and the Markov stochastic process was adopted to analyze MANET topology dynamiccharacteristic. The simulation results show that the method above not only is valid andgenerable to be used for all mobility models in NS-2 Tool, but also could obtain thetopology state keeping experimental formula and topology state varying probabilityformula.IV(2) An analysis technique for MANET topology dynamic characteristic based onmeasurement sample was proposed. When the scenario file of mobile models could notbe obtained beforehand, End-to-End measurement was used in MANET to obtain thepath delay time. Then topology steady period of MANET is inferred by judging whetherpath delay dithering is close to zero. At the same time, the MANET topology wasidentified by using hierarchical clustering method based on measurement sample of pathperformance during topology steady period in order to support the link performanceinference. The simulation result verified that the method above could not only detect themeasurement window time of MANET effectively, but also identify the MANETtopology architecture during measurement window time correctly.(3) A MANET link performance inference algorithm based on linear analysis modelwas proposed. The relation of inequality between link and path performance, such as lossrate of MANET, was deduced according to a linear model. The phenomena thatcommunication characteristic of packets, such as delay and loss rate, is more similarwhen the sub-paths has longer shared links was proved in the document. When the rankof the routing matrix is equal to that of its augmentation matrix, the linear model wasused to describe the Ad Hoc network link performance inference method. The simulationresults show that the algorithm not only is effective, but also has short computing time.(4) A Link performance inference algorithm based on multi-objectives optimizationwas proposed. When the rank of the routing matrix is not equal to that of its augmentationmatrix, the link performance inference was changed into multi-objectives optimizationand genetic algorithm is used to infer link performance. The probability distribution oflink performance in certain time t was obtained by performing more measurements andstatistically analyzing the hypo-solutions. Through the simulation, it can be safelyconcluded that the internal link performance, such as, link loss ratio and link delay, can beinferred correctly when the rank of the routing matrix is not equal to that of itsaugmentation matrix.

The objective of this research is to investigate improved methods for distributing certificate revocation lists (CRLs) in vehicular ad hoc networks (VANETs). VANETs are a subset of mobile ad hoc networks composed of network-equipped vehicles and infrastructure points, which will allow vehicles to communicate with other vehicles and with roadside infrastructure points. While sharing some of the same limitations of mobile ad hoc networks, such as lack of infrastructure and limited communications range, VANETs have several dissimilarities that make them a much different research area. The main differences include the size of the network, the speed of the vehicles, and the network security concerns. Confidentiality, authenticity, integrity, and availability are some of the standard goals of network security. While confidentiality and authenticity at times seem in opposition to each other, VANET researchers have developed many methods for enhancing confidentiality while at the same time providing authenticity. The method agreed upon for confidentiality and authenticity by most researchers and the IEEE 1609 working group is a public key infrastructure (PKI) system. An important part of any PKI system is the revocation of certificates. The revocation process, as well as the distribution of revocation information, is an open research problem for VANETs. This research develops new methods of CRL distribution and compares them to existing methods proposed by other researchers. The new methods show improved performance in various vehicle traffic densities.

Network coding is a technique used to increase the capacity of a network by combining messages sent over the network. The combined messages could be separated by using sufficient original messages which were used to combine the messages. Network coding can be implemented in different layers of the 051 stack, but to date a complete comparison between different implementations of network coding has not been done. The goal of this dissertation is to implement a wireless node model with network coding in the MAC layer and evaluate the performance characteristics of reference networks that implement the new node model. This will serve as the first step of a greater goal, namely finding the most favourable position in the 051 stack to implement network coding. The characteristics of the different implementations of network coding are presented in this dissertation. Simulations were done in OPNET® to find further attributes concerning the implementation of network coding in the MAC layer. The simulation process used is presented and explained, and the results from the simulations are analysed. Network coding in the simulations was implemented opportunistically. The results show that the more often different nodes send frames to the coding node, the better network coding performs. The work contributes to finding the best layer for implementing network coding for its increased throughput. A benchmark network was created so that network coding could be implemented in all the layers of the 051 stack, and then be compared to each other. An implementation of network coding in the MAC layer was simulated and analyzed. We conclude that, because there are so many different purposes for which networks are used, a single instance of network coding is unlikely to be similarly beneficial to all purposes. There still remains work to find the most favourable position for network coding in the 051 stack for all the different types of network coding. / Thesis (M. Ing. (Computer and Electronical Engineering))--North-West University, Potchefstroom Campus, 2011

Un réseau mobile ad hoc (Mobile Ad hoc Network, MANET) est un réseau sans fil, formé dynamiquement par un ensemble d'utilisateurs équipés de terminaux mobiles, sans l'utilisation d'une infrastructure préexistante, ou d'une administration centralisée. Les équipements utilisés dans les MANETs sont limités par la capacité de la batterie, la puissance de calcul et la bande passante. Les utilisateurs des MANETs sont libres de se déplacer, ce qui induit à des topologies dynamiques dans le temps. Toutes ces contraintes ajoutent plus de challenges aux protocoles et services de communications afin de fonctionner dans les MANETs. L'évolution des réseaux de 4ème génération (4G) est appelée à intégrer les MANETs avec les autres types de réseaux afin d'étendre leurs portées. Nous nous sommes intéressés dans la première partie de cette thèse à quelques challenges connus dans les MANETs en proposant des solutions novatrices utilisant des propriétés intéressantes des topologies de graphes. Dans un premier temps, nous avons effectué une étude sur la prédiction de la mobilité afin de maintenir une topologie d'ensemble dominant connecté dans les MANETs. Nous avons proposé dans un autre travail comment construire des topologies de graphes ayant des propriétés globales en se basant seulement sur des informations locales des nœuds mobiles. Ces topologies servent comme overlay aux MANETs. Nous avons proposé des algorithmes distribués pour construire des alliances offensives et défensives globales minimales. Nous avons aussi défini des heuristiques pour ces algorithmes afin de réduire les tailles des alliances obtenues. La première partie de cette thèse est achevée par la proposition d'un framework pour la conception et l'analyse des protocoles de contrôle de topologie dans les MANETs. Nous avons identifié les points communs des algorithmes de contrôle de topologie conçus pour les réseaux mobiles ad hoc et nous avons enrichi le simulateur NS-2 avec un ensemble d'extensions pour supporter le contrôle de topologie / We are interested in this thesis to graph-based approaches to deal with some challenges in networking, namely, graph topologies of mobile ad hoc networks (MANETs) and process model matchmaking in large scale web service. We propose in the first part: (1) a generic mechanism using mobility information of nodes to maintain a graph topology of the network. We show particularly, how to use the prediction of future emplacements of nodes to maintain a connected dominating set of a given MANET. (2) distributed algorithms to construct minimal global offensive alliance and global defensive alliance sets in MANETs. We also introduce several heuristics to get a better approximation of the cardinality of the alliance sets which is a desirable property for practical considerations. (3) a framework to facilitate the design and evaluation of topology control protocols in MANETs. We propose in the framework, a common schema for topology control based on NS-2 simulator and inspired from the commonalities between the components of the topology control algorithms in MANETs. In the second part, we focus on process model matchmaking. We propose two graph-based solutions for process model inexact matching to deal with high computational time of existing work in the literature. In the first solution, we decompose the process models into their possible execution sequences. After, we propose generic graph techniques using string comparator metrics for process model matchmaking based on this decomposition. In order to get better optimization of the execution time and to deal with process model matching in large scale web services, the second solution combines a spectral graph matching with structural and semantic proposed approaches. This solution uses an eigen-decomposition projection technique that makes the runtime faster

Nowadays most communication networks like GSM, WLan or WiMAX are based on pre-existing infrastructure. These infrastructures are complicated, costly and difficult to deploy in very short time. Whereas Wireless Ad Hoc Networks are infrastructure-free self organizing networks which consist of co-operating nodes. These networks are highly desirable for various emerging applications for military and to extend the range and capacity of infrastructure based wireless networks. One critical issue that we face in Ad Hoc Network is the problem of scheduling. Scheduling algorithms in an Ad Hoc Network allows the nodes to share the wireless channel efficiently. But on the other hand, the scheduling algorithm needs to be easily implementable in a distributed fashion with little, if any, coordination between nodes in the network. Spread spectrum technologies allow interference averaging and therefore are employed in Ad Hoc networks. There are two major types of spread spectrum physical layer, which are frequency hopping (FH) spread spectrum and direct sequence (DS) spread spectrum. FH-CDMA divides the bandwidth into M sub channels, the receiver only sees the interference from the transmitter side which is on the same sub channel whereas in DS-CDMA we increase the spreading code M to decrease the signal to interference plus noise ratio (SINR) requirement. The purpose of research is to study a hybrid spread spectrum based on physical layer, in which the direct sequence signal is also frequency hoped. The DS will reduce the region of dominating interferes, while frequency hopping will be used within this region intelligently and allow the dominating interferes to transmit on different frequencies. First the system bounds on the transmission capacity of the proposed scheme is evaluated, and than a comparative analysis of different multiple access schemes is done with our proposed model with respect to their transmission capacity to evaluate its performance.