The use of wireless technology in the process industry is becoming increasingly important to obtain fast deployment at low cost. However, poor channel quality often leads to retransmissions, which are governed by Automatic Repeat Request (ARQ) schemes. While ARQ is a simple and useful tool to alleviate packet errors, it has considerable disadvantages: retransmissions lead to an increase in energy expenditure and latency. The use of Forward Error Correction (FEC) however offers several advantages. We consider a Hybrid-ARQ-Adaptive-FEC scheme (HAF) based on BCH codes and Channel State Information. This scheme is evaluated on AWGN and fading channels. It is shown that HAF offers significantly improved performance both in terms of energy efficiency and latency, as compared to ARQ.

Context: Video streaming over best-effort networks is complicated by a number of factors including unknown and time-varying bandwidth, transmission delay, and high packet losses. Excessive packet loss can causes significant degradation in quality of video perceived by users of real-time video applications. Recent studies suggest that error control schemes using Forward Error Correction (FEC) is a good candidate for decreasing the negative impact of packet loss on video quality. With FEC scheme, redundant information is transmitted along with the original information so that the lost original video data can be recovered at least in part from the redundant information. Although sending additional redundancy increases the probability of recovering lost packets, it also increases the bandwidth requirements which in turn increase loss rate of the video stream due to congestion. For this reason FEC is characterized as effective when the redundancy is sufficient to recover the lost data, ineffective when the redundancy is little to recover the lost data and inefficient when the redundancy is high for the lost data. To provide best performance for the streaming application and the network, it is important to determine, in real time, the proper amount of redundant information according to the loss behavior of the network. However it not clears how to choose optimal redundancy given the constraints mentioned above at any given point in time. Objective: This thesis investigated the limitations of existing static FEC schemes and suggested alternative approaches that can achieve effectiveness through sending the appropriate amount of FEC redundancy in real-time. Three dynamic redundancy adaptation control systems On-Off, Proportional, Proportional-Integral have been design and implemented based on existing conventional FEC mechanisms. Moreover the performance evaluation of each mechanism is performed on simulated environment. Method: A performance evaluation methodology using network simulation and key evaluation criteria to test the mechanisms under different network conditions and the scenarios for each different network are considered. The proposed mechanisms were implemented in a simulation environment by using NS2. After the implementation and validation of the techniques, several simulation experiments have been conducted to study the performance of each redundancy adjustment schemes. Results: The result of the simulation experiments and performance analysis showed that both Proportional and Proportional-Integral (PI) redundancy controller based on Adaptive Forward Error Correction (AFEC) mechanisms significantly reduce the number of discarded video blocks as compared with the On-Off based scheme. On the other hand On-Off based AFEC mechanisms added small number of excess redundancy. The amount of excess redundancy added by the Proportional and PI controllers significantly increases as the packet drop rate of the transmission channel increases. Conclusion: Based on the findings of this study, using the PI adaptation based AFEC mechanisms is potentially viable option for enhancing the performance of video streaming applications over the network. / +46762356096 +251929003705/+46739691250

L’un des défis majeurs dans la convergence des réseaux et des services vers la technologie IP est le maintien de la qualité de service (QoS) des flux audio/vidéo transmis sur des réseaux sans fil pour des utilisateurs mobiles et hétérogènes. Dans cet environnement, les services multimédia doivent faire face à plusieurs inconvénients engendrés par le manque de fiabilité d’un canal sans fil et son partage par plusieurs utilisateurs. Ces inconvénients sont accentués par l’hétérogénéité des terminaux de réception (capacité de décodage, espace de stockage, résolution d’affichage, etc.) qui doivent recevoir, décoder et afficher les flux multimédia. Afin d’assurer un accès universel aux services n’ importe où, n’importe quand et en utilisant n’importe quel terminal d’accès, les applications multimédia de nouvelle génération doivent interagir avec leur environnement pour, d’une part, informer les réseaux sous-jacents de leur besoins en QoS, et d’autre part, adapter dynamiquement leurs services en fonction des terminaux de réception et des variations intempestives des conditions de transmission. Dans ce contexte, nous proposons un nouveau système pour la transmission des flux audio/vidéo sur les réseaux 802.11 basé sur l’approche Cross-layer. Ce nouveau système, appelé XLAVS (Cross Layer Adaptive Video Streaming), communique activement avec l’ensemble des couches réseaux ainsi que le récepteur final pour déterminer l’adaptation optimale qui permet d’optimiser la QoS des flux audio/vidéo. Nos contributions se focalisent principalement sur les adaptations Cross-layer mises en œuvre par le XLAVS. Ces contributions sont organisées en deux grandes catégories : les adaptations ascendantes exécutées au niveau applicatif et les adaptations descendantes exécutées au niveau MAC 802.11. Dans la première catégorie, notre apport s’articule au tour de : (1) l’adaptation dynamique du débit vidéo en fonction du débit physique disponible dans le réseau 802.11 et (2) l’adaptation conjointe du taux de redondance FEC et du débit vidéo contrôlée par la puissance du signal et les taux de perte. Dans la deuxième catégorie, nous proposons deux mécanismes Cross-layer au niveau MAC 802.11 : (1) une fragmentation 802.11 adaptative pour trouver un compromis entre les pertes de paquets et l’overhead introduit par les couches 802.11 et (2) un groupage des images vidéo au niveau MAC pour permettre au flux vidéo d’avoir un accès au canal 802.11 proportionnel à son débit. / One of the big challenges in the convergence of networks and services to the IP technology is to maintain the Quality of service (QoS) for audio/video streams transmitted over wireless networks to heterogeneous mobiles users. In this environment, the multimedia services should face many shortcomings caused mainly by the wireless channel unreliability and its sharing among many users. These shortcomings are increased by the terminals heterogeneity (i.e. decoding capability, memory storage, display resolution, etc.) which should receive, decode and display the multimedia streams. In order to allow universal access to multimedia services anywhere, anytime and using any kind of terminal, the new generation of multimedia applications have to interact with their environment, on the one hand, to inform the underling network about their need in term of QoS, and on the other hand, to dynamically adapt their services according to the receiver terminal and the changing in network conditions. In this context, we have proposed a new Cross-layer based streaming system to transmit audio/video streams over 802.11 networks. This new system, called XLAVS (Cross layer Adaptive video streaming), actively communicates with all network layers and the end receiver to determine the optimal adaptation that optimize the QoS of audio/video streams. Our contributions focus mainly on the Cross-layer adaptations implemented on the XLAVS. These contributions are classified into two major categories: the bottom-up adaptations performed at the application level and the top-down adaptations performed at the 802.11 MAC level. In the first category, our proposals have revolved around: (1) a dynamic adaptation of video throughput according to the physical rate available in the 802.11 network and (2) a join FEC and video throughput adaptation steered by the signal strength and the loss ratio. In the second category, we have proposed two Cross-layer mechanisms at the 802.11 MAC level: (1) an adaptive 802.11 MAC fragmentation to find an optimal trade-off between the packet loss and the overhead introduced by the MAC layer and (2) a video frame grouping at MAC level that allows video stream to get access to the 802.11 channel proportionally to its throughput.