Control of Multiple Remote Servers for Quality-Fair Delivery of Multimedia Contents

This paper proposes a control scheme for the quality-fair delivery of several encoded video streams to mobile users sharing a common wireless resource. Video quality fairness, as well as similar delivery delays are targeted among streams. The proposed controller is implemented within some aggregator located near the bottleneck of the network. The transmission rate among streams is adapted based on the quality of the already encoded and buffered packets in the aggregator. Encoding rate targets are evaluated by the aggregator and fed back to each remote video server (fully centralized solution), or directly evaluated by each server in a distributed way (partially distributed solution). Each encoding rate target is adjusted for each stream independently based on the corresponding buffer level or buffering delay in the aggregator. Communication delays between the servers and the aggregator are taken into account. The transmission and encoding rate control problems are studied with a control-theoretic perspective. The system is described with a multi-input multi-output model. Proportional Integral (PI) controllers are used to adjust the video quality and control the aggregator buffer levels. The system equilibrium and stability properties are studied. This provides guidelines for choosing the parameters of the PI controllers. Experimental results show the convergence of the proposed control system and demonstrate the improvement in video quality fairness compared to a classical transmission rate fair streaming solution and to a utility max-min fair approach

Statistical multiplexing of distributed video streams

National audienceWe consider a media aware network element (MANE) fed by several remote video servers. The role of the MANE is to bufferize the encoded video contents and to build a multiplex containing all video programs to be broadcasted or multicasted over a wireless link. We design a decentralized control technique able to satisfy some video quality fairness constraint among programs. Unlike most statistical multiplexing systems, our scheme is partly decentralized. The bandwidth allocation among programs is centralized and done within the MANE, but takes into account the quality fairness constraint. Each video server is controlled independently from the others, requiring no exchange between servers. The MANE feds back to each video server the level of its associated buffer to help the remote video servers to adapt their rate-distorsion trade-off so that the buffer reaches some reference level. Experimental results show that in the case of Gaussian sources, compressed and delivered to the MANE, an equilibrium is reached, and that the fairness constraint is satisfied

Predictive Encoder and Buffer Control for Statistical Multiplexing of Multimedia Contents

International audienceStatistical multiplexing of video contents aims at transmitting several variable bit rate (VBR) encoded video streams over a band-limited channel. Rate-distortion (RD) models for the encoded streams are often used to control the video encoders. Buffering at the output of encoders is one of the several techniques used to smooth out the fluctuating bit rate of compressed video due to variations in the activity of video contents. In this paper, a statistical multiplexer is proposed where a closed-loop control of both video encoders and buffers is performed jointly. First, a predictive joint video encoder controller accounting for minimum quality, fairness, and smoothness constraints is considered. Second, all buffers are controlled simultaneously to regulate the buffering delays. This delay is adjusted according to a reference delay constraint. The main idea is to update the encoding rate for each video unit according to the average level of the buffers, to maximize the quality of each program and effectively use the available channel rate. Simulation results show that the proposed scheme yields a smooth and fair video quality among programs thanks to the predictive control. A similar buffering delay for all programs and an efficient use of the available channel rate are ensured thanks to the buffer management and to the predictive closed-loop control

Online Learning for QoE-based Video Streaming to Mobile Receivers

International audienceThis paper proposes a cross-layer control mechanism to stream efficiently scalable videos to mobile receivers. Its goal is to maximize the quality of the received video while accounting for the variations of the characteristics of the transmitted content and of the channel. The control problem is cast in the framework of Markov Decision Processes. The optimal actions to apply to the system are learned using reinforcement learning. For that purpose, the quality of the decoded frames at receiver is inferred by an observation (i) of the quality of the various scalability layers and (ii) of the level of queues at the Application and Medium Access Control layers of the transmitter only. Delayed as well as absence of information on the channel state are considered. Experiments show that the performance of the proposed solution is only slightly degraded with delayed or missing channel state information. The performance degradation is larger when considering a basic bitstream extractor, which serves as reference

Control of Distributed Servers for Quality-Fair Delivery of Multiple Video Streams

International audienceThis paper proposes a quality-fair video delivery system able to transmit several encoded video streams to mobile users sharing some wireless resource. Video quality fairness, as well as similar delivery delay is targeted among streams. The proposed control system is implemented within some aggregator located near the bottleneck of the network. This is done by allocating the transmission rate among streams based on the quality of the already encoded and buffered packets in the aggregator. Encoding rate targets are evaluated by the aggregator and fed back to each remote video server, or directly evaluated by each server in a distributed way. Each encoding rate target is adjusted for each stream independently based on the corresponding buffering delay in the aggregator. The transmission and encoding rate control problems are addressed with a control-theoretic perspective. The system is described with a multi-input multi-output model and several Proportional Integral (PI) controllers are used to adjust the video quality as well as the buffering delay. The study of the system equilibrium and stability provides guidelines for choosing the parameters of the PI controllers. Experimental results show that better quality fairness is obtained compared to classical transmission rate fair streaming solutions while keeping similar buffering delays

Bayesian multi-user detection based on a state-space model of the DS-CDMA system

In this paper, we propose a new multiuser detector based on a symbol rate state-space model of the CDMA system. This state-space model presents a non-Gaussian state noise characteristic. Therefore, the Kalman filtering approach looses its MMSE optimality. As a solution, we propose to apply the Weighted Sum of Gaussian (WSG) approximation. We demonstrate that the WSG is propagated during iterations through a NKF structure. At each iteration, we inject only one gaussian term having the mean and the covariance matrix of the last obtained MMSE estimate of the state vector. The proposed structure improves the performance compared to the linear structures such as: the MMSE, the Kalman filter and the feedback structure such as DFE.Dans cet article, nous proposons un détecteur multi-utilisateurs basé sur une représentation d'état au rythme symbole du système AMRC (Accès Multiple par Répartition de Codes). Le modèle d'état met en évidence un bruit de transition non Gaussien. Par conséquent, l'application du filtre de Kalman comme un détecteur multi-utilisateurs perd son optimalité au sens de l'erreur quadratique moyenne minimale (EQMM). Pour remédier à ce problème, nous proposons d'utiliser l'approximation par une somme pondérée de gaussiennes (SPG) de la densité de probabilité a posteriori des symboles à estimer sachant les observations. Nous montrons que la SPG se propage au cours des itérations à travers une structure de réseau de filtres de Kalman (RFK) fonctionnant en parallèle. À chaque itération, nous proposons de réinjecter une seule gaussienne ayant la moyenne et la matrice de covariance de l'estimée EQMM du vecteur d'état obtenue. La structure proposée présente des performances nettement meilleures que les structures linéaires (EQMM, décorrélateur, filtre de Kalman) et à retour de décision (DFE)

Class-Based MDP for improved multimedia transmission over LTE

International audienceThis paper proposes an improved cross-layer control mechanism to efficiently stream videos to mobile users over an LTE network. A proxy-based filtering algorithm among scalable layers is considered to decide the number of SVC layers to transmit for each frame according to the communication conditions and to the class to which the video belongs to. The problem is cast in the context of Markov Decision Processes which allow the design of foresighted policies maximizing some long-term accumulated reward. Optimal actions to apply to the system are obtained by reinforcement learning. The proposed solution is implemented in an LTE simulation platform. Experiments show the performance of the proposed class-based layer filtering algorithm for a single video transmission and its robustness to content changes

A Heavy Traffic Approach for Queue-Aware Power Control in Interfering Wireless Links

978-1-4673-0970-7International audienceIn this work, we address the problem of power allocation for interfering transmitter-receiver pairs so that the probability that each queue length exceeds a specified threshold is fixed at a desired value. One application is satisfying QoS requirements in a dense cellular network. We address this problem using heavy traffic approximation techniques which lead to an asymptotic model described by a (controlled) stochastic differential equation. The power control strategy consists in allocating most of the power according to the wireless channel state and a smaller fraction according to the queue lengths. Simulation results in a simple setting illustrate that the proposed control policy can yield desirable results in practical systems

Contrôle de puissance et détection multicode conjointe dans une liaison descendante à haut débit de l'UMTS

Dans ce papier, nous nous intéressons à l'optimisation conjointe des paramètres des récepteurs linéaires joints multicodes, proposés récemment dans [4], et du contrôle de puissance, afin d'améliorer la qualité du lien descendant haut-débit de l'UMTS. L'approche proposée nous permet de minimiser la puissance transmise par la station de base et d'obtenir la répartition optimale des puissances des codes au niveau de la station de base