Les réseaux sans fil multi-saut (WMN : Wireless multi-hop Networks) sont passés du stade de simple curiosité pour revêtir aujourd'hui un intérêt certain aussi bien du point de vue de la communauté de recherche que des opérateurs de réseaux et services. En analysant les services et applications fournis au sein des réseaux WMNs, nous pouvons constater que certaines applications telles que la visioconférence, la VoIP, etc sont sensibles au délai et nécessitent une certaine qualité de service (QoS). D'autres applications telles que le transfert de fichier, le streaming vidéo, etc. sont gourmands en terme d'utilisation de bande passante. Par conséquent, les architectures de communication des réseaux WMNs doivent intégrer des mécanismes de routage efficaces et adaptés pour répondre aux besoins des services et applications envisagés. Dans cette thèse, Nous nous intéressons à la problématique du routage dans les réseaux WMNs. Notre objectif est de proposer une nouvelle approche de routage qui prend en compte différents métriques de coûts. Tout d'abord, nous avons montré que le routage sous contraintes multiples est un problème NP complet et que trois étapes sont nécessaires à la conception d'une nouvelle solution de routage: (i) modélisation de l'interférence, (ii) l'estimation de la de la bande passante restante, (iii) l'estimation du délai à un saut. Suivant cette vision, nous avons proposé deux variantes du protocole de routage OLSR (SP-OLSR, S2P-OLSR) se basant sur la métrique SINR. Les résultats des simulations ont montré l'intérêt de la proposition dans un contexte de communication vocale (VoIP). Ensuite, nous avons proposé un algorithme d'estimation d'interférence à 2 sauts (2-HEAR) afin d'estimer la bande passante disponible. Puis, et sur la base de cet algorithme, nous avons proposé une nouvelle métrique de routage pour les WMNs: Estimated Balanced Capacity (EBC) en vue de parvenir à l'équilibrage de charge entre des différents flux. La dernière question abordée dans cette thèse est celle de l'estimation du délai à un saut. La solution proposée donne une borne du délai en se basant sur un modèle de file d'attente de type G/G/1. Enfin, nous avons englobé toutes les précédentes contributions pour mettre en place une nouvelle approche de routage hybride sous contraintes multiples. Ce protocole comporte une partie proactive utilisant la nouvelle métrique de routage (EBC) et une partie réactive qui permet de prendre en compte le délai relative à une connexion donné. / There is a growing interest in wireless multi-hop networks (WMNs) since there are promising in opening new business opportunity for network operators and service providers. This research field aims at providing wireless communication means to carry different types of applications (FTP, Web browsing, video streaming, in addition to VoIP). Such applications have different constraints and their specific requirements in terms of Quality of Service (QoS) or performance metrics (delay jitter, end-to-end delay). We examine, in this thesis, the problem of routing in WMNs. Our main goal is to propose a new multi-metrics routing capable to fit these particular needs. In this thesis, we make several contributions toward WMN multi-constrained routing. First, we show that the multi-constrained path finding problem is NP-Complete and inherently a cross-layer issue, and that three steps are necessary to design the multi-metric routing protocol: (i) modeling of the inferring signal, (ii) estimation of the remaining bandwidth, (iii) estimation of the one-hop delay. Second, moving in such direction, we propose two enhanced versions of the OLSR routing protocol. The suggested protocols consider the SINR as a routing metric to build a reliable topology graph. Performance evaluation shows that utilizing such routing metric helps to improve significantly the VoIP application quality in the context of ad hoc network while maintaining a reasonable overhead cost. Third, we have proposed a 2-Hop interference Estimation Algorithm (2-HEAR) in order to estimate the available bandwidth. Then, and based on such algorithm, we have proposed a novel routing metric for WMNs: Estimated Balanced Capacity (EBC) in order to achieve load-balancing among the different flows. The next issue tackled in this thesis is the one-hop delay estimation, the one-hop delay is estimated by means of an analytical model based on G/G/1 queue. Finally, we have encompassed all the previous contributions to address our main goal, i.e. the design of a multi-constrained routing protocol for WMNs. A hybrid routing protocol is then proposed. This protocol is a junction of two parts : a proactive part that makes use of the previously estimated constraint, and a reactive part, which is triggered ”on demand” when news applications are expressed.

Actuellement les communications véhiculaires sont devenues une réalité guidée par diverses applications. Notamment, la diffusion de vidéo de qualité élevée avec des contraintes de faible latence requises par les applications temps réel. Grâce au niveau de compression jamais atteint auparavant, l’encodeur H.265/HEVC est très prometteur pour la diffusion de vidéos en temps réel dans les réseaux ad hoc véhiculaire (VANET). Néanmoins, la qualité de la vidéo reçue est pénalisée par les mauvaises caractéristiques du canal de transmission (disponibilité, non stationnarité, rapport signal à bruit, etc.). Afin d’améliorer et d’assurer une qualité vidéo minimale à la réception nous proposons dans ce travail une optimisation conjointe source-canal-protocole de la transmission en tenant compte à la fois des paramètres de transmission et d’encodage vidéo. Dans un premier temps, nous montrons l’intérêt et le gain apporté par les solutions dites inter-couches « cross-layer ». Par la suite, nous développons deux approches l’une exploitant un « cross-layer » entre la couche application et la couche MAC et une seconde exploitant les protocoles de transports dans l’adaptation du flux vidéo. En ce qui concerne la première approche nous proposons une solution utilisant une gestion hiérarchique des trames au niveau des files d’attentes de la couche MAC, basée sur l’importance des images du flux vidéo. Dans une seconde solution, nous retenons le codage par descriptions multiples comme solution de protection à la source. Les résultats de simulations obtenus pour plusieurs types de scénarios véhiculaires réalistes montrent que les différents schémas de transmission véhiculaire proposés offrent des améliorations significatives en termes de qualité vidéo à la réception et de retard de bout en bout par rapport aux schémas classiques. / At present, vehicular communications have become a reality guided by various applications. In particular, high-quality video delivery with low latency constraints is required for real-time applications. The new state-of-the-art high-effciency video coding (HEVC) standard is very promising for real-time video streaming in vehicular ad hoc networks (VANET). Nevertheless, these networks have variable channel quality and a limited bandwidth that penalizes the overall performances of end-to-end video transmission. In order to meet these constraints, we proposed in this work to consider both transmission and video encoding parameters through a joint source-channel-protocol coding approach to provide an improvement in video transmission. First, we have shown the interest and the gain brought by the "cross-layer" solutions. Then, we developed two approaches. The first one exploits a "crosslayer" solution between the application layer and the Medium Access Control (MAC) layer while the second exploits the transport layer protocols in the adaptation of the video stream. Regarding the first approach, we have proposed solutions to allocate the frames to the most appropriate Access Category (AC) queue on the MAC layer based on the image importance in the video stream. In another solution, we chose multiple descriptions source coding as an error resilient solution. Thus, the simluation results obtained for different realistic vehicular scenarios demonstrate that the proposed transmission schemes offer significant video quality improvements and end-to-end delay reduction compared to conventional transmission schemes.

Device-to-Device communications have the great potential to bring significant performance boost to the conventional heterogeneous network by reusing cellular resources. In cellular networks, Device-to-Device communication is defined as two user equipments in a close range communicating directly with each other without going through the base station, thus offloading cellular traffic from cellular networks. In addition to improve network spectral efficiency, D2D communication can also improve energy efficiency and user experience. However, the co-existence of D2D communication on the same spectrum with cellular users can cause severe interference to the primary cellular users. Thus the performance of cellular users must be assured when supporting underlay D2D users. In this work, we have investigated cross-layer optimization, resource allocation and interference management schemes to improve user experience, system spectral efficiency and energy efficiency for D2D communication underlaying heterogeneous networks. By exploiting frequency reuse and multi-user diversity, this research work aims to design wireless system level algorithms to utilize the spectrum and energy resources efficiently in the next generation wireless heterogeneous network.

Fourth Generation (4G) cellular technology Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) offers high data rate capabilities to mobile users; and, operators are trying to deliver a true mobile broadband experience over LTE networks. Mobile TV and Video on Demand (VoD) are expected to be the main revenue generators in the near future [36] and efficient video streaming over wireless is the key to enabling this. 3GPP recommends the use of H.264 baseline profiles for all video based services in Third Generation (3G) Universal Mobile Telecommunication System (UMTS) networks. However, LTE networks need to support mobile devices with different display resolution requirements like small resolution mobile phones and high resolution laptops. Scalable Video Coding (SVC) is required to achieve this goal. Feasibility study of SVC for LTE is one of the main agenda of 3GPP Release10. SVC enhances H.264 with a set of new profiles and encoding tools that may be used to produce scalable bit streams. Efficient adaptation methods for SVC video transmission over LTE networks are proposed in this thesis. Advantages of SVC over H.264 are analyzed using real time use cases of mobile video streaming. Further, we study the cross layer adaptation and scheduling schemes for delivering SVC video streams most efficiently to the users in LTE networks in unicast and multicast transmissions. We propose SVC based video streaming scheme for unicast and multicast transmissions in the downlink direction, with dynamic adaptations and a scheduling scheme based on channel quality information from users. Simulation results indicate improved video quality for more number of users in the coverage area and efficient spectrum usage with the proposed methods.

Fourth Generation (4G) cellular technology Third Generation Partnership Project (3GPP) Long Term Evolution (LTE) offers high data rate capabilities to mobile users; and, operators are trying to deliver a true mobile broadband experience over LTE networks. Mobile TV and Video on Demand (VoD) are expected to be the main revenue generators in the near future [36] and efficient video streaming over wireless is the key to enabling this. 3GPP recommends the use of H.264 baseline profiles for all video based services in Third Generation (3G) Universal Mobile Telecommunication System (UMTS) networks. However, LTE networks need to support mobile devices with different display resolution requirements like small resolution mobile phones and high resolution laptops. Scalable Video Coding (SVC) is required to achieve this goal. Feasibility study of SVC for LTE is one of the main agenda of 3GPP Release10. SVC enhances H.264 with a set of new profiles and encoding tools that may be used to produce scalable bit streams. Efficient adaptation methods for SVC video transmission over LTE networks are proposed in this thesis. Advantages of SVC over H.264 are analyzed using real time use cases of mobile video streaming. Further, we study the cross layer adaptation and scheduling schemes for delivering SVC video streams most efficiently to the users in LTE networks in unicast and multicast transmissions. We propose SVC based video streaming scheme for unicast and multicast transmissions in the downlink direction, with dynamic adaptations and a scheduling scheme based on channel quality information from users. Simulation results indicate improved video quality for more number of users in the coverage area and efficient spectrum usage with the proposed methods.

This research investigates cross-layer design in multi-hop wireless networks with random access. Due to the complexity of the problem, we study cross-layer design with a simple slotted ALOHA medium access control (MAC) protocol without considering any network dynamics. Firstly, we study the optimal joint configuration of routing and MAC parameters in slotted ALOHA based wireless networks under a signal to interference plus noise ratio based physical interference model. We formulate a joint routing and MAC (JRM) optimization problem under a saturation assumption to determine the optimal max-min throughput of the flows and the optimal configuration of routing and MAC parameters. The JRM optimization problem is a complex non-convex problem. We solve it by an iterated optimal search (IOS) technique and validate our model via simulation. Via numerical and simulation results, we show that JRM design provides a significant throughput gain over a default configuration in a slotted ALOHA based wireless network. Next, we study the optimal joint configuration of routing, MAC, and network coding in wireless mesh networks using an XOR-like network coding without opportunistic listening. We reformulate the JRM optimization problem to include the simple network coding and obtain a more complex non-convex problem. Similar to the JRM problem, we solve it by the IOS technique and validate our model via simulation. Numerical and simulation results for different networks illustrate that (i) the jointly optimized configuration provides a remarkable throughput gain with respect to a default configuration in a slotted ALOHA system with network coding and (ii) the throughput gain obtained by the simple network coding is significant, especially at low transmission power, i.e., the gain obtained by jointly optimizing routing, MAC, and network coding is significant even when compared to an optimized network without network coding. We then show that, in a mesh network, a significant fraction of the throughput gain for network coding can be obtained by limiting network coding to nodes directly adjacent to the gateway. Next, we propose simple heuristics to configure slotted ALOHA based wireless networks without and with network coding. These heuristics are extensively evaluated via simulation and found to be very efficient. We also formulate problems to jointly configure not only the routing and MAC parameters but also the transmission rate parameters in multi-rate slotted ALOHA systems without and with network coding. We compare the performance of multi-rate and single rate systems via numerical results. We model the energy consumption in terms of slotted ALOHA system parameters. We found out that the energy consumption for various cross-layer systems, i.e., single rate and multi-rate slotted ALOHA systems without and with network coding, are very close.

In order to meet the increasing demand for higher data rates, next generation wireless networks must incorporate additional functionalities to enhance network throughput. Multihop networks are considered as a promising alternative due to their ability to exploit spatial reuse and to extend coverage. Recently, industry has shown increased interest in multihop networks as they do not require additional infrastructure and have relatively low deployment costs. Many advances in physical and network layer techniques have been proposed in the recent past and they have been studied mostly in single-hop networks. Very few studies, if any, have tried to quantify the gains that these techniques could provide in multihop networks. We investigate the impact of simple network coding, advanced physical layer and cooperative techniques on the maximum achievable throughput of wireless multihop networks of practical size. We consider the following advanced physical layer techniques: successive interference cancellation, superposition coding, dirty-paper coding, and some of their combinations. We achieve this by formulating several cross-layer frameworks when these techniques are jointly optimized with routing and scheduling. We also formulate power allocation subproblems for the cases of continuous power control and superposition coding. We also provide numerous engineering insights by solving these problems to optimality.

The current dominate layered networking architecture, in which each layer is designed and operated independently, results in inefficient and inflexible resource use in wireless networks due to the nature of the wireless medium, such as time-varying channel fading, mutual interference, and topology variations. In this thesis, we focus on resource allocation and scheduling in wireless orthogonal frequency division multiplexing (OFDM) networks based on joint physical and medium access control (MAC) layer optimization. To achieve orders of magnitude gains in system performance, we use two major mechanisms in resource management: exploiting the time variance and frequency selectivity of wireless channels through adaptive modulation, coding, as well as packet scheduling and regulating resource allocation through network economics. With the help of utility functions that capture the satisfaction level of users for a given resource assignment, we establish a utility optimization framework for resource allocation in OFDM networks, in which the network utility at the level of applications is maximized subject to the current channel conditions and the modulation and coding techniques employed in the network. Although the nonlinear and combinatorial nature of the cross-layer optimization challenges algorithm development, we propose novel efficient dynamic subcarrier assignment (DSA) and adaptive power allocation (APA) algorithms that are proven to achieve the optimal or near-optimal performance with very low complexity. Based on a holistic design principle, we design max-delay-utility (MDU) scheduling, which senses both channel and queue information. The MDU scheduling can simultaneously improve the spectral efficiency and provide right incentives to ensure that all applications can receive their different required quality of service (QoS). To facilitate the cross-layer design, we also deeply investigate the mechanisms of channel-aware scheduling, such as efficiency, fairness, and stability. First, using extreme value theory, we analyze the impact of multiuser diversity on throughput and packet delay. Second, we reveal a generic relationship between a specific convex utility function and a type of fairness. Third, with rigorous proofs, we provide a method to design cross-layer scheduling algorithms that allow the queueing stability region at the network layer to approach the ergodic capacity region at the physical layer.

With the proliferation of mobile devices and the advance of audio/video coding technologies, there is an increasing demand to provide quality-of-service (QoS) guarantees for multimedia applications. A WLAN (wireless local are network) typically consists of an access point (AP) and a finite set of mobile stations. Since the AP is generally more powerful and less physical constraint than mobile stations, it is of great interest to consider the use of sectorized multi-beam antennas at the AP to boost the network throughput by exploiting the benefit of spatial reuse. IEEE 802.11 is current the de facto standard for WLANs. However, if we directly apply 802.11 to the WLAN with multi-beam AP without any modification, we will encounter many challenging problems. Although existing solutions modify the 802.11 DCF (distributed coordination function) to solve these problems, yet DCF does not provide any QoS support. On the basis of 802.11e HCCA (hybrid channel control access), in this thesis, we propose a novel MAC protocol, named MPCF (multi-beam AP-assisted point coordination function), which is not only backward compatible with DCF, but also supports QoS functionalities, including non-reversal prioritization, time-bounded reservation, admission control, and cross-layer rate adaptation for multimedia streaming. Simulation results show that, in terms of throughput, frame delay dropped rate, and energy throughput, MPCF significantly outperforms existing protocols even in imperfect beam-forming and mobility environments.

Wireless communication systems continue to face the challenge of time varying quality of the underlying communication channel. When a slow fading channel goes into a deep fade, the corresponding communication system might face successive decoding failures at the destination, and for delay-sensitive communication systems, this amounts to delays that are not desired. In such situations, it becomes a priority to get out of the deep fades. Many techniques and approaches are already available in the literature to counteract fading effects. This work is motivated by recent advances in fast reconfigurable antennas, which provide new means to change the statistical profile of fading channels, and hence reduce the probability of prolonged fades. Fast reconfigurable antennas are poised to improve overall performance, especially for delay-sensitive traffic in slow-fading environments. This potential enhanced performance motivates this study of the queueing behavior of point-to-point communication systems with reconfigurable antennas. We focus on finite-state channels with memory, and we analyze the queueing behavior of the wireless communication system over erasure channels, for a traditional system versus a reconfigurable antenna implementation. We provide numerical results for situations where using reconfigurable antennas yield substantial performance gains in terms of throughput, delay and buffer overflow.