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.

Wireless mobile internet market is still an unprecedented, uncaptured territory for cellular service providers. The shortage and high cost of downlink data bandwidth in a cellular network has remained a huge factor for the slow growth of data services in mobile devices. Although there has been a significant evolution in telephony infrastructures in form of 3G and 4G systems, the potential of high speed ad hoc network for sharing cellular spectrum have not been realized to its full potential. Like (e.g. Verizon) users can share voice minutes with friends, there is a potential for sharing the unutilized cellular bandwidth among friends to increase net data speed. In a scenario like a football stadium where people visit in groups, although a lone phone cannot stream a high quality replay video, unused cellular bandwidth of proximate friend’s devices can automatically be used in real time to view the replays. An available secondary ad hoc network such as Wi-Fi or Bluetooth in phone can be used for sharing this cellular bandwidth. Thus, we propose BuddyShare, a novel social-based automatic bandwidth sharing overlay platform on short range ad hoc devices to increase net data speed. The motivation stems from the fact that the location of mobile users tends to be clustered to form “people hotspots” such as conferences, stadiums, stations, buses and trains. For example, in a scenario like a football stadium where people visit in groups, although a lone phone cannot stream a high quality replay video, unused cellular bandwidth of proximate friends’ devices can automatically be used in real time to view the replays. Our work creates an overlay on horizontal ad hoc network to enable users to form a group among socially trusted members who can collaboratively share their data connections. Social trust is automatically derived from social relationships obtained by mining mobile-phone behavior pattern. This work aims to improve the overall utilization of the data connection, and increase the data rate of individual users without compromising their privacy and unauthenticated usage. The user privacy is preserved by using the bandwidth resources of only socially trusted member of the user, which also guarantees against unauthenticated exploitation of expensive bandwidth. Our proposed work promises to deliver win-win situation to users, content providers and service providers. The advantages of users are: 1) Increased data rate for the same cost.2) Secure and trusted overlay based communication for sharing resources. The advantages for the service providers are manifold: 1) Customer increase: More customers will avail the data plan due to social influence. 2) Customer retention: [18] Customers part of the social-cum-adhoc network are least likely to leave the network.3) Group subscription: Service provider can get bulk subscriptions as collaborative groups increase data rate. In this work, we address some key technical issues of developing a socially aware overlay collaborating medium. Some of the addressed functionalities associated with the overlay formations are group discovery, creation, management and actual data distribution. This proposal also accounts the computation of social trustworthiness by using standard social networking analytics. We also account the several key technical challenges associated with management of overlay on mobile nodes and trust computation using abstract social network. In order to verify the usefulness of BuddyShare, we collected realistic datasets from various sources (questionnaires, mobile device logs, social networking portal) and conducted analyses and simulations on it. The analyses concluded that sample users from the dataset shared sufficient social trustworthiness. The real events from the datasets were captured in the simulations. These simulations showed that, by using Bluetooth as a horizontal ad hoc medium, an user can scale his data speed three times on average for sufficient duration per day. This thesis achieves the following objectives: 1) It presents a comprehensive design for an overlaid social based internet sharing platform called BuddyShare. 2) It presents a social analysis to validate the concept of social trust among users. 3) It delivers a flexible simulation platform to realistically simulate mobile phones with dual interfaces. 4) It presents the results of simulations of real events captured from the device logs of sample users. These results conclude the usefulness of BuddyShare work.

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Recent accomplishments in link-level and radio technologies have significantly improved the performance of wireless links. Wireless mobile ad hoc networks, however, typically only take limited advantage of these enhancements. In this research, the medium access control protocol and ad hoc routing protocol are extended to take advantage of radios offering multi-user interference cancellation and direct-sequence spread-spectrum functionality, by encouraging multiple simultaneous connections and adaptively changing communication parameters on a per-packet basis. Through its environment characterization techniques, the adaptive direct sequence spread spectrum MAC protocol for non-broadcast multiple access networks (ADIM-NB) improves several aspects of the wireless mobile ad hoc network performance, including throughput, delay, stability, and power consumption, through its use of spread-spectrum multiple access and four different adaptive algorithms. The four adaptive algorithms change processing gain, forward error correction coding rate, transmit power, and number of simultaneous connections. In addition, the ad hoc routing protocol is extended with the clustering algorithm for mobile ad hoc network (CAMEN). With ADIM-NB in mind, CAMEN discourages the use of broadcast messages, supplements ADIM-NB's functionality at the network level, and improves the network scalability by aggregating nodes into clusters. Both protocols are intended to lead to more powerful and flexible communication capabilities for wireless nodes. Simulation models have been developed and simulated to verify the performance improvements of both protocols at the network-level as well as provide a means to perform trade-off analysis. Results indicate that the network capacity is increased between 50% in a moderately loaded network to 100% in a heavily loaded network over a non-adaptive MAC protocol. The delay also improve significantly in most scenarios of interest. / Ph. D.

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

The increasing popularity of wireless networks over the last years indicates that there will be a demand for communicating devices providing high capacity communication together with QoS requirements. There are two types of wireless networks, infrastructure and Ad Hoc networks. The variation of topology caused by the mobility of hosts in the Ad Hoc networks results in a long latency, large jitter and low throughput. In infrastructure wireless networks, a base station (BS) or an Access Point (AP) is in charge of the data transmission. Therefore, the wireless hop can be considered as another hop of the transmission path. With the rapid growth of wireless traffics, the future wireless network is expected to provide services for heterogeneous data traffics with different quality of service requirements. Most proposed schemes do not have mechanisms to adapt to environment changes. In real situation, bandwidths, error rates, and loss rates of wireless links vary frequently. The QoS issues are very important in modern networks. There are many proposed service models and mechanisms to support QoS in wireline networks. Most of these QoS mechanisms are not suitable for direct application to the wireless network because of the characteristics of wireless communication which includes: 1) high error rates and bursty errors, 2) location-dependent and time-varying wireless channel capacity, 3) scarce bandwidth, 4) user mobility, and 5) power constraints of the mobile hosts. All of these above characteristics make the development of QoS in wireless networks very difficult and challenging. We try to cope with the bandwidth variations caused by the high error rate and bursty errors in wireless links, and the location-dependent and time-varying natures of wireless channel capacity. Furthermore, we expect to utilize the scarce wireless bandwidth more efficiently. In our proposed scheme, the higher priority flow is capable of broadcasting a message to inform the lower priority flows to change their priorities to adapt to environment variations. We will base on the differentiated service model and propose a Wireless Differentiation (WD) scheme for UDP flows and a Wireless Differentiation with Prioritized ACK (WDPA) scheme for connections with TCP flows which provide QoS support for IEEE 802.11b and do not change the basic access mechanism of IEEE 802.11b.

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