Les réseaux à radios cognitives sont des réseaux émergeants donnant une possibilité d'accès dynamique au spectre dans le but de l'utiliser de façon plus efficace. Le problème de routage dans ce type de réseaux est assez complexe vu l'aspect dynamique et flexible d'un environnement cognitif opportuniste. Notre travail consiste à suggérer une solution de routage efficace et performante en débit et délai de transmission de bout en bout. Dans ce mémoire, nous proposons un nouveau protocole de routage réactif en s'inspirant des protocoles de routage déjà existant dans les réseaux sans fil classiques car ils présentent une grande maturité. Les simulations effectuées démontrent que l'algorithme permet d'atteindre un débit de transmission élevé avec un petit délai de transmission de bout en bout, ainsi qu'un bon maintien de chemins face à l'activation de transmission d'utilisateurs primaires. ______________________________________________________________________________ MOTS-CLÉS DE L’AUTEUR : réseaux à radios cognitives, routage réactif, multi-interface, utilisateur primaire, utilisateur secondaire.

Vehicular Ad Hoc Networks (VANETs) are no longer a futuristic promise but rather an attainable technology. Vehicles are already equipped with a variety of computational devices that control or assist drivers in many tasks such as localization, safely breaking, parking and passengers entertainment. The majority of services envisioned for VANETs either require the provision of multimedia support or have it as an extremely beneficial additional feature. In particular, video streaming capabilities over VANETs are crucial to the development of interesting and valuable services. However,VANETs’ highly dynamic topology poses as a demanding challenge to the fulfillment of video streaming’s stringent requirements. The main goal on this thesis is the development of feasible solutions that support the streaming of video content over VANETs. Initially, the main issues of VANETs are explained through both a discussion of its characteristics and the results of some preliminary conclusions. Based on this understanding of VANETs’ peculiarities, three distinguishing solutions are designed REACT-DIS, REDEC and VIRTUS; the two first for video dissemination and the later for video unicast. These solutions offer a great advancement towards the provision of video streaming capabilities but packet loss is still an issue at high data rates. In order to improve the delivery ratios reached by the previous solutions, redundancy is used as an error correction mechanism. The use of redundancy is ideal for VANETs in handling packet loss as they do not require any interaction between source and receivers nodes. Sophisticated coding techniques were used for an efficient use of the increase on entropy of the information sent by the source node. It was also evaluated the selective use of redundancy solely on packets carrying the crucial information of I-frames. Although this selective approach obtained lower overall delivery ratios than when redundancy is used for all packets, the video quality obtained similar improvements under a much lower cost. The evaluation on the use of redundancy has considered the impact on the rate by which unique video content is received at end-users which is fundamental to understand the resolution of videos that can be displayed. This thesis provides several contributions as it advances the knowledge in the peculiarities of VANETs, solutions for video streaming over VANETs and the use of redundancy as an error correction mechanism for video streaming over VANETs.

Vehicular Ad Hoc Networks (VANET), a derivative of mobile networks, has the capability to increase the safety, e ciency and comfort of transportation systems, and provide users on-the-road Internet connectivity. Because of its impetus and signi cance in practical scenarios, it becomes a sought after topic in both industry and academia. In this thesis, we focus on the vehicle-to-infrastructure (V2I) drive-thru Internet services in a highway scenario. The road side unit (RSU) along a highway can provide network services for vehicles within the coverage. To enhance the network performance, we propose two strategies. First, to ensure a high network throughput, the RSU uses an admission control strategy to limit the competition among vehicles, and avoid the waste of channel time to the low-data-rate users. Second, based on the vehicle density, we also propose a contention window (CW) adjustment strategy which can reduce the collision probability when the network is congested, and reduce the idle time otherwise. Extensive simulations using network simulator (NS-2) are given, which demonstrate the e ectiveness of the proposed solutions. / Graduate

During the route discovery process, each node receiving the route request packet (RReq) will retransmit it exactly once. A distant neighbor may accidentally receive/loose the only RReq and use it to announce a new route, although that link is inferior/superior for route reply packets (RRep) or actual message routing. Overall, the constructed route may be far from the optimal. All existing route discovery schemes (including DSR/AODV) apply retransmission during route discovery exactly once (1R). Based on a realistic physical layer model, we propose two new route discovery schemes: n-retransmission (nR, retransmitting exactly n times) and n-retransmission c-reception (ncRR), retransmitting until we either reach a total of n own retransmissions or c copies from neighbors are heard. We compare our two new scheme with the traditional one, under otherwise identical conditions (same metric, same packet reception probability on each link) and the same choices about possibly retransmitting again upon discovering a better route (R+) or discarding it (R1), generating route reply packet for every received RRep (B*), or for first and better discovered routes only (B2), and retransmitting RRep exactly once (A1), up to a maximum of three times (A3), or optimally u times decided by link quality (Au). Experimental results show that the proposed ncRR scheme (for n=2 and c=3 or c=4) achieves the best tradeoff between quality of route, success rate and message overhead in the route discovery process, followed by the nR scheme, and both of them are superior to the existing traditional schemes.

Bluetooth is a low cost and low power wireless technology for connecting portable and / or fixed Bluetooth enabled devices to form short-range wireless ad hoc personal area networks (PANs). As the Bluetooth specification does not specify a protocol to form ad hoc Bluetooth networks, a method for forming an efficient Bluetooth network under a practical networking scenario is still an open research problem. This thesis introduces an approach to implement an indoor ad hoc Bluetooth wireless network, Bluetooth information exchange network (BIEN). This network formation is based on Bluetooth and Java technologies. A set of Bluetooth enabled devices configured with the BIEN software application are able to spontaneously establish a dynamic multi-hop wireless network using Bluetooth technology without the need of formal network infrastructure, centralized administration, fixed routers or access points. In this study, the performance evaluation focuses on the relation between network capacity and topology by testing end-to-end performance in terms of throughput and the latency of communication links with various parameters, including the hop number between nodes and the number of slaves in piconets. The evaluation results show that the throughput reduces with the increased length of a path, and with an increase in the number of slaves in a piconet in the network. The latency also increases with path length, and with the number of slaves in a piconet in the different experimental BIENs, whether if there is traffic or not in the networks. Experimental results have further confirmed the necessity to minimize the number of bridge nodes in the Bluetooth networks due to their traffic bottleneck effect. This work is an attempt at implementation of a distributed multi-hop scatter net with an integrated routing protocol in the practical environments, while most of the literature focuses on covering the modelling of it. It intends to demonstrate how Bluetooth technology with Java technology can be used to design, develop and deploy ad hoc wireless networks with the commercial Bluetooth devices, and examine how well Bluetooth technology supports ad hoc multi-hop wireless network technology.

Zugl.: Kiel, Univ., Diss., 2005 u.d.T.: Hewicker, K. F. Johannes: Persönliche Aussenhaftung der Vorstände börsennotierter Aktiengesellschaften für fehlerhafte und unterlassene Ad-hoc-Meldungen

Thesis (M. Phil.)--University of Hong Kong, 2008. / Also available in print.

Universiẗat, Diss.--Trier, 2007.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Includes bibliographic references (p.100-103).

Thesis (M.S.E.C.E.)--University of Massachusetts Amherst, 2008. / Includes bibliographical references (p. 74-77).