Optimized Scalable Image and Video Transmission for MIMO Wireless Channels

In this chapter, we focus on proposing new strategies to efficiently transfer a compressed image/video content through wireless links using a multiple antenna technology. The proposed solutions can be considered as application layer physical layer (APP-PHY) cross layer design methods as they involve optimizing both application and physical layers. After a wide state-of-the-art study, we present two main solutions. The first focuses on using a new precoding algorithm that takes into account the image/video content structure when assigning transmission powers. We showed that its results are better than the existing conventional precoders. Second, a link adaptation process is integrated to efficiently assign coding parameters as a function of the channel state. Simulations over a realistic channel environment show that the link adaptation activates a dynamic process that results in a good image/video reconstruction quality even if the channel is varying. Finally, we incorporated soft decoding algorithms at the receiver side, and we showed that they could induce further improvements. In fact, almost 5 dB peak signal-to-noise ratio (PSNR) improvements are demonstrated in the case of transmission over a Rayleigh channel

Hybrid propagation channel modelling for city area land mobile satellite communications

13 pagesInternational audienceIn this study, a hybrid model is proposed to simulate the realistic channel behavior for urban city land mobile satellite (LMS) communications. It associates the advantages of existing models in that different receiving states are predicted using a deterministic approach, whereas the channel behavior is simulated using adapted statistical laws. Using a geosynchronous satellite transmitter working at 1.5 GHz and a land mobile receiver, the hybrid model is validated for LMS channel. It leads to a high-performance simulation, combining accuracy (global simulation error less than 1 dBW) and small computation time (gain of about 10,000 times compared to a full deterministic reference model)

Transmission robuste de vidéo basée ondelette à travers un canal MIMO

National audienceCet article présente l'évolution d'un codeur pour images fixes basé ondelette vers le codage vidéo. Ce codeur associe une transformation en ondelette classique, une quantification vectorielle par sous-bande et une modulation de type MAQ-M. L'exploitation conjointe des éléments de la chaîne de transmission assure une qualité de services dans des conditions de transmission difficiles. Les redondances temporelles sont exploitées, dans le cadre du codage vidéo, par un algorithme spécifique d'estimation et de compensation de mouvement adapté à nos contraintes de codage. Nous proposons ainsi une méthode de codage permettant d'atteindre une bonne robustesse des vecteurs mouvement. Ce codeur nommé V-WTSOM présente une hiérarchisation importante des informations. Nous exploitons cette hiérarchisation en transmission à travers un canal MIMO incluant une possibilité de précodage diagonal. La décomposition en sous-canaux SISO parallèles et indépendants permet d'envisager des stratégies d'allocation basées sur le contenu et améliorant globalement la qualité de service

Une méthode Semi-déterministe pour Modéliser les Évanouissements Rapides de Signaux Satellites en Environnements Urbains et Suburbains

International audienceLes communications satellites en milieux urbains se font principalement par des liaisons radios pour lesquelles les ondes électromagnétiques interagissent avec l'environnement, induisant ainsi un phénomène de multitrajets et donc des évanouissements rapides. Afin de modéliser les fluctuations rapides des signaux satellites reçus en tenant compte des spécificités du site de réception, cet article propose une nouvelle approche. Elle permet de définir le paramètre principal de la loi de Nakagami-m en fonction de la caractéristique majeure des multitrajets à savoir les interactions électromagnétiques (réflexions, diffractions). Le logiciel Ergospace basé sur un tracé de rayons sert de support à cette étude

Sensitivity of the MIMO Channel Characterization to the Modeling of the Environment

International audienceAn important factor in electromagnetic wave propagation simulation, performed by a 3D ray-tracing method is the modeling of the environment. Results being sensitive to descriptive accuracy, this paper presents a study on the effect of indoor environment modeling precision on multiple input multiple output (MIMO) channel characterization. In order to give some diversity to the results, the investigation takes into account two unfurnished indoor environments. The first environment investigated is the entrance hall of a building at the University of Poitiers, while the second is a more confined environment and is represented by the first floor of the authors' laboratory. For these two indoor environments, four levels of description are proposed in order to establish the geometrical and electrical modeling impact on MIMO channel characterization. Results are obtained by analyzing the capacity, variation in correlation, multipath richness and eigenvalues in relation to the polarization, the presence of line-of-sight (LOS) or non-LOS (NLOS) configurations. The effects of the spacing between antennas and the number of transmitter and receiver antennas are also investigated

A hybrid radio propagation channel model for realistic confined environments

International audienceRadio communications often take place in confined environments like city areas. The propagation channel presents shadowing and multipath phenomena due to interactions between radio wave and environment. In this work, a general hybrid channel model concept is proposed to associate the advantages of existing deterministic and statistical models. One of the model applications is introduced using a geosynchronous satellite as transmitter and a land mobile as receiver

Efficient 2D ray-tracing method for narrow and wide-band channel characterization in micro-cellular configurations

International audienceChannel characterization is an essential step to the development of outdoor or indoor wireless networks. Indeed, for multimedia applications, new radio mobile systems must accurately take into account channel behavior. In this paper, we propose an efficient 2D ray-tracing method to characterize the narrow and wide-band radio channels for a very large number of receivers in micro-cellular configurations. It is based on a quick pre-calculation of an exact 2D visibility graph. The proposed method follows an ITU recommendation, which advocates, for wide-band characterization, only considering the paths included in a 18 dB dynamic range of power impulse response. Contrary to the classical approach, which consists in thresholding the complete impulse response in a post-treatment, our method only computes the significant paths. The interest of the proposed method resides in its significant computation time reduction factor, in comparison with the classical approach and this without any significant loss in accuracy. Received power and wide-band parameter maps are computed for about 40,000 receivers, in a dense urban environment, and are provided with an approximate reduction factor of 4 and 80% of null estimation error in comparison to a classical approach

Une optimisation en temps de calcul pour la prédiction de zones de couverture radioélectriques

International audienceThis article presents a method which optimises the computation time for the prediction of a radio coverage, whatever the propagation model used. The principle consists in reducing the number of ap- plication points of the propagation model in relation to a classical technique. The proposed method is based on a multi resolution analysis of measured signals carried out around 2 GHz, and on an electroma- gnetic analysis of the propagation environment. The performances of the method are evaluated in term of reduction in computation time and of accuracy, in comparaison with the classical technique

An acceleration technique for the radioelectric coverage prediction in small and microcell configurations

The purpose of this work is to optimise the necessary computation time for the coverage zone prediction. Several approaches exist to reduce the calculation time; they consist in simplifying the complexity of the used propagation model. Here, our method is different but complementary of the previous approaches. Indeed, it is independent of the propagation model and tries to reduce the number of application points of the considered model for the coverage prediction. Thus, the performances of our optimised method in term of accuracy and computation time is presented in this articl

Utilisation des techniques MIMO pour des transmissions robustes et haut-débit en tunnels.

National audienceCe papier illustre le gain de performance potentiel apporté par l'utilisation des techniques MIMO dans le cadre des communications radio en tunnel ferroviaire. Différents schémas de transmission sont testés et évalués dans le cas de canaux faiblement puis fortement corrélés