Στα ασύρματα αδόμητα δίκτυα, οι κόμβοι μπορούν να συνεργαστούν για τη μετάδοση δεδομένων σε απομακρυσμένουσ κόμβους. Συνήθως, η συνεργασία αυτή επιτυγχάνεται χρησιμοποιώντας βοηθητικούς ενδιάμεσους κόμβους για τη μετάδοση δεδομένων από ένα κόμβο πηγή σε ένα κόμβο προορισμό, μέσω point-to-point ή point-to-multipoint συνδέσμους. Πρόσφατα, μεγάλο ενδιαφέρον έχει αποκτήσει η τεχνική της συνεργατικής μετάδοσης, όπου περισσότεροι του ενός κόμβοι συμμετέχουν για τη μετάδοση του ίδιου σήματος σε έναν απομακρυσμένο κόμβο. Ο παραλήπτης ανακατασκευάζει το αρχικό σήμα συνδυάζωντας τα διαφορετικά σήματα που έφτασαν σε αυτόν. Εδώ, αναπτύσσεται και εκτιμάται ένας πολυ-κριτηριακός αλγόριθμος συνεργατικής δρομολόγησης που λαμβάνει υπόψην την εναπομένουσα ενέργεια και την απαιτούμενη ισχύ μετάδοσης των κόμβων. Ο αλγόριθμος για ένα ζευγάρι κόμβων πηγής – προορισμού ανακαλύπτει όλα τα δυνατά υποψήφια μονοπάτια λαμβάνοντας υπόψη και συνδέσμους με την δυνατότητα συνεργασίας των κόμβων για την αποστολή των δεδομένων. Τελικά επιλέγεται το μονοπάτι που βελτιστοποιεί μια συνάρτηση κόστους. Τα κριτήρια είναι η εναπομένουσα ενέργεια και η συνολική ισχύς μετάδοσης στους κόμβους του μονοπατιού. Εκτελούμε πειράματα προσομοίωσης σε δίκτυα με κόμβους που έχουν σταθερή ισχύ μετάδοσης και με κόμβους που μπορούν να προσαρμόσουν την ισχύ μετάδοσής τους. Τα αποτελέσματα δείχνουν ότι ο αλγόριθμός μας πετυχαίνει σημαντική εξοικονόμηση ενέργειας και μεγαλύτερο αριθμό επιτυχημένων αποστολών πακέτων σε σχέση με την περίπτωση που δεν χρησιμοποιείται συνεργασία. / In wireless ad-hoc networks, nodes cooperate to make possible the communication between otherwise distant nodes. Usually, this cooperation is in the form of nodes acting as intermediate relays that forward data from a source to a destination node using point-to-point or point-to-multipoint links. A technique that has gained considerable recent attention is cooperative diversity, where nodes are organized for transmitting the same signal to a given, often otherwise unreachable, node. The receiver combines the multiple receptions to reconstruct the original signal. In this work, we present and evaluate a multi-criteria cooperative routing algorithm that uses as parameters the nodes’ residual energy and their transmission power. This algorithm selects for each source-destination pair a path, in the form of a sequence of groups of cooperative nodes, and the nodes’ transmission powers. We perform a number of simulation experiments, assuming nodes with variable or fixed transmission power, evaluating the benefits of the proposed multi-criteria cooperative routing algorithm. The results show that our algorithm achieves significant energy savings and larger number of successfully delivered packets than the case where cooperation is not applied.

In recent years, routing research concerning wired networks has focused on minimizing the maximum utilization of the links which is equivalent to reducing the number of bottlenecks while supporting the same traffic demands. This can be achieved using multipath routing with load balancing instead of single path routing using of routing optimizers. However, in the domain of ad hoc networks multipath routing has not been investigated in depth. We would like to develop an analogy between wired and wireless networks, but before that we need to identify the major differences between these two in the case of multipath routing. First, in order to increase the network throughput, the multiple paths have to be independent so they don't share the same bottlenecks. Then, due to radio propagation properties the link capacity is not constant. So using the maximum utilization metric for wireless networks is not suitable. Based on the research done in wired networks, which has shown that using multiple paths with load balancing policies between sourcedestination pairs can minimize the maximum utilization of the links, we investigate if this is applicable to ad hoc networks. This paper proposes a multipath routing algorithm with a load balancing policy. The results obtained from an indoor 802.11g network highlight two major points. The maximum throughput is not achieved with multipath routing, but with single path routing. However, the results on the delivery ratio are encouraging, indeed we observe a real improvement thanks to our multipath routing algorithm. / På senare år har routning forskningen angående trådnätverken focusen på att minska den maximala användingen av länkar vilket motsvarar än reducering av flaskhalsar medan man stöder samma trafikkrav. Det här kan åstadkommas genom att av multiväg routning med lasta balansering I stället för använder enkelvägrouting med routing optimizers. Emellertid har inom ad hoc nätverken multiväg routning har inte blivit undersökts på djupet. Vi skulle vilja utveckla en analogy emellan trådnätverk och trådlösnätverken.men främföre det behöver identifiera de store differenserna mellan dessa två vid multiväg routning. För det första måste de flerfaldiga vägarna vara oberoende för att öka nätverkens throughput så de inte delar samma flaskhalsar. Sedan är länkkapaciteten inte constant på grund av radiospridningsegenskaperna. Så den maximal användningsmetric för trådlös nätverken passar inte. Den här arbetetet föreslår en multiväg routning algoritm med lasta balanseringen. Resultaten få från en indoor 802.11g nätverk framhåller ger två store meningen. Den maximala throughput är inte åstadkoms med multiväg routing, men med enkelväg routning. Emellertid är resultaten på den leveransförhållande uppmuntrande; vi observera en verklig förbättring tack vare vår multiväg routning algoritmen.

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A wireless Mobile Ad Hoc Network (MANET) comprises of a number of mobile nodes that uses multi-hop routing to provide network connectivity. MANETs require self-organizing capabilities as there are no centralized points (base stations, access points etc), and each mobile node functions as router and/or hosts. The wireless topology in MANET can change rapidly with mobility of nodes in unpredictable ways or remain static for long periods of time. MANETs have applications in neighborhood area networks (NANs), impromptu communication among groups of people, disaster management and dynamic military systems. As progress in MANET continues, there is an increase in demand with regard to supporting content-rich video streaming in such networks. This is due to the fact that real-time video is far more substantive than simple data communication. This work involves implementing a Genetic Algorithm (GA) based multipath routing methodologies in a proactive routing protocol (Optimized Link State Routing Protocol) to send/forward/receive multimedia streams on experimental testbed. We study the problem of multipath video routing in wireless ad hoc networks by following an application-centric cross-layer approach. A full implementation of GA-based routing and real-time video conferencing application (server and client) written in C++ is presented. The robustness of our routing scheme was tested through experiments using five computer nodes. The performance of the routing protocol for video, as well as issues such as applicability and scalability in practice are addressed. / Master of Science

Video communication is an important application in wireless ad hoc network environment. Although current off-the-shelf video communication software would work for ad hoc network operating under stable conditions (e.g., extremely low link and node failures), video communications for ad hoc network operating under extreme conditions remain a challenging problem. This is because traditional video codec, either single steam or layered video, requires at least one relatively stable path between source and destination nodes. Recent advances in multiple description (MD) video coding have opened up new possibilities to offer video communications over ad hoc networks. In this thesis, we perform a systematic study on MD video for ad hoc networks. The theoretical foundation of this research is based on an application-centric approach to formulate a cross-layer multipath routing problem that minimizes the application layer video distortion. The solution procedure to this complex optimization problem is based on the so-called Genetic Algorithm (GA). The theoretical results have been documented in [7] and will be reviewed in Chapter 2. Although the theoretical foundation for MD video over dynamic ad hoc networks has been laid, there remains a lot of skepticisms in the research community on whether such cross-layer optimal routing can be implemented in practice. To fill this gap, this thesis is devoted to the experimental research (or proof-of-concept) for the work in [7]. Our approach is to design and implement an emulation testbed where we can actually implement the ideas and algorithms proposed in [7] in a controlled laboratory setting. The highlights of our experimental research include: 1. A testbed that emulates three properties of a wireless ad hoc network: topology, link success probability, and link bandwidth; 2. A source routing implementation that can easily support comparative study between the proposed GA-based routing with other routing schemes under different network conditions; 3. A modified H.263+ video codec that employs Unequal Error Protection (UEP) approach to generate MD video; 4. Implementation of three experiments that • compared the GA-based routing with existing technologies (NetMeeting video conferencing plus AODV routing); • compared our GA-based routing with network-centric routing schemes (two-disjoint paths routing); • proved that our approach has great potential in supporting video communications in wireless ad hoc networks. 5. Experimental results that show the proposed cross-layer optimization significantly outperforms the current off-the-shelf technologies, and that the proposed cross-layer optimization provides much better performance than network-centric routing schemes in supporting routing of MD video. In summary, the experimental research in this thesis has demonstrated that a cross-layer multipath routing algorithm can be practically implemented in a dynamic ad hoc network to support video communications. / Master of Science

Interference is a defining feature of a wireless network. How to optimally deal with it is one of the most critical and least understood aspects of decentralized multiuser communication. This dissertation focuses on distributed transmission strategies that a transmitter can follow to achieve reliability while reducing the impact of interference. The problem is investigated from three directions : distributed opportunistic scheduling, multicast outage and transmission capacity, and ergodic transmission capacity, which study distributed transmission in different scenarios from a transmission-capacity perspective. Transmission capacity is spatial throughput metric in a large-scale wireless network with outage constraints. To understand the fundamental limits of distributed transmission, these three directions are investigated from the underlying tradeoffs in different transmission scenarios. All analytic results regarding the three directions are rigorously derived and proved under the framework of transmission capacity. For the first direction, three distributed opportunistic scheduling schemes -- distributed channel-aware, interferer-aware and interferer-channel-aware scheduling are proposed. The main idea of the three schemes is to avoid transmitting in a deep fading and/or sever interfering context. Theoretical analysis and simulations show that the three schemes are able to achieve high transmission capacity and reliability. The second direction focuses on the study of the transmission capacity problem in a distributed multicast transmission scenario. Multicast transmission, wherein the same packet must be delivered to multiple receivers, has several distinctive traits as opposed to more commonly studied unicast transmission. The general expression for the scaling law of multicast transmission capacity is found and it can provide some insight on how to do distributed single-hop and multi-hop retransmissions. In the third direction, the transmission capacity problem is investigated for Markovain fading channels with temporal and spatial ergodicity. The scaling law of the ergodic transmission capacity is derived and it can indicate a long-term distributed transmission and interference management policy for enhancing transmission capacity. / text

Performance and security are two critical functions of wireless ad-hoc networks (WANETs). Network security ensures the integrity, availability, and performance of WANETs. It helps to prevent critical service interruptions and increases economic productivity by keeping networks functioning properly. Since there is no centralized network management in WANETs, these networks are susceptible to packet drop attacks. In selective drop attack, the neighboring nodes are not loyal in forwarding the messages to the next node. It is critical to identify the illegitimate node, which overloads the host node and isolating them from the network is also a complicated task. In this paper, we present a resistive to selective drop attack (RSDA) scheme to provide effective security against selective drop attack. A lightweight RSDA protocol is proposed for detecting malicious nodes in the network under a particular drop attack. The RSDA protocol can be integrated with the many existing routing protocols for WANETs such as AODV and DSR. It accomplishes reliability in routing by disabling the link with the highest weight and authenticate the nodes using the elliptic curve digital signature algorithm. In the proposed methodology, the packet drop rate, jitter, and routing overhead at a different pause time are reduced to 9%, 0.11%, and 45%, respectively. The packet drop rate at varying mobility speed in the presence of one gray hole and two gray hole nodes are obtained as 13% and 14% in RSDA scheme.

<p>A cognitive radio network is a multi-user system, in which different radio units compete for limited resources in an opportunistic manner, interacting with each other for access to the available resources. The fact that both users and spectrum holes (i.e., under-utilized spectrum sub-bands) can come and go in a stochastic manner, makes a cognitive radio network a highly non- stationary, dynamic and challenging wireless environment. Finding robust decentralized resource-allocation algorithms, which are capable of achieving reasonably good solutions fast enough in order to guarantee an acceptable level of performance, is crucial in such an environment. In this thesis, a novel dynamic spectrum management (DSM) scheme for cognitive radio networks, termed the self-organizing dynamic spectrum management (SO-DSM), is described and its practical validity is demonstrated using computer simulations. In this scheme, CRs try to exploit the primary networks’ unused bands and establish link with neighbouring CRs using those bands. Inspired by human brain, the CRs extract and memorize primary network’s and other CRs’ activity patterns and create temporal channel assignments on sub-bands with no recent primary user activities using self-organizing maps (SOM) technique. The proposed scheme is decentralized and employs a simple learning rule with low complexity and minimal memory requirements. A software testbed was developed to simulate and study the proposed scheme. This testbed is capable of simulating CR network alongside of a cellular legacy network. In addition to SO-DSM, two other DSM schemes, namely centralized DSM and no-learning decentralized DSM, can be used for CR networks in this software testbed. The software testbed was deployed on parallel high capacity computing clusters from Sharcnet to perform large scale simulations of CR network. The simulation results show, comparing to centralized DSM and minority game DSM (MG-DSM), the SO-DSM decreases the probability of collision with primary users and also probability of CR link interruption significantly with a moderate decrease in CR network spectrum utilization.</p> / Doctor of Philosophy (PhD)

Despite recent advances in wireless local area network (WLAN) technologies, today's WLANs still cannot offer the same data rates as their wired counterparts. The throughput problem is further aggravated in multi-hop wireless environments due to collisions and interference caused by multi-hop routing. Because all current IEEE 802.11 physical (PHY) standards divide the available frequency into several orthogonal channels, which can be used simultaneously within a neighborhood, increasing capacity by exploiting multiple channels becomes particularly appealing. To improve the capacity of wireless ad hoc networks by exploiting multiple available channels, I propose three principles that facilitate the design of efficient distributed channel assignment protocols. Distributed channel assignment problems have been proven to be <i>NP</i>-complete and, thus, computationally intractable. Though being a subject of many years of research, distributed channel assignment remains a challenging problem. There exist only a few heuristic solutions, none of which is efficient, especially for the mobile ad hoc environment. However, protocols that implement the proposed design principles are shown to require fewer channels and exhibit significantly lower communication, computation, and storage complexity, compared with existing approaches. As examples, I present two such protocols that build on standard reactive and proactive routing protocols. In addition, I prove the correctness of the algorithms and derive an upper bound on the number of channels required to both resolve collisions and mitigate interference. A new multi-channel medium access control (MC-MAC) protocol is also proposed for multi-hop wireless ad hoc networks. MC-MAC is compatible with the IEEE 802.11 medium access control (MAC) standard and imposes the minimum system requirements among all existing multi-channel MAC protocols. In addition, simulation results show that even with only a single half-duplex transceiver, MC-MAC, by exploiting multiple channels, can offer up to a factor of four improvement in throughput over the IEEE 802.11 MAC protocol. The reduction in delay is even more significant. Therefore, the MC-MAC protocol and the accompanying distributed channel assignment protocols constitute an effective solution to the aforementioned performance problem in a multi-hop wireless network. Finally, I generalize the cross-layer design principle to more general networking functions and present a network architecture to motivate and facilitate cross-layer designs in wireless networks. A literature survey is provided to validate the proposed cross-layer design architecture. Current cross-layer design research can be categorized into two classes: joint-layer design using optimization techniques, and adaptive techniques based on system-profile and/or QoS requirements. Joint-layer design based on optimization techniques can achieve optimal performance, but at the expense of complexity. Adaptive schemes may achieve relatively good performance with less complexity. Nevertheless, without careful design and a holistic view of the network architecture, adaptive schemes may actually cause more damage than benefit. / Ph. D.