Améliorations des transmissions VLC (Visible Light Communication) sous contrainte d'éclairage : études théoriques et expérimentations

Abstract : Indoor visible light communication (VLC) networks based on light-emitting diodes (LEDs) currently enjoy growing interest thanks in part to their robustness against interference, wide license-free available bandwidth, low cost, good energy efficiency and compatibility with existing lighting infrastructure. In this thesis, we investigate spectral-efficient modulation techniques for the physical layer of VLC to increase throughput while considering the quality of illumination as well as implementation costs. Numerical and experimental studies are performed employing pulse amplitude modulation (PAM) and carrierless amplitude and phase (CAP) modulation under illumination constraints and for high modulation orders. Furthermore, the impact of LED nonlinearity is investigated and a postdistortion technique is evaluated to compensate these nonlinear effects. Within this framework, transmission rates in the order of a few hundred Mb/s are achieved using a test bench made of low-cost components. In addition, an imaging multiple input multiple-output (MIMO) system is developed and the impact on performance of imaging lens misalignment is theoretically and numerically assessed. Finally, a polynomial matrix decomposition technique based on the classical LU factorization method is studied and applied for the first time to MIMO VLC systems in large space indoor environments.Les réseaux de communication en lumière visible (VLC) s’appuyant sur l’utilisation de diodes électroluminescentes (LED) bénéficient actuellement d’un intérêt grandissant, en partie grâce à leur robustesse face aux interférences électromagnétiques, leur large bande disponible non-régulée, leur faible coût, leur bonne efficacité énergétique, ainsi que leur compatibilité avec les infrastructures d’éclairage déjà existantes. Dans cette thèse, nous étudions des techniques de modulation à haute efficacité spectrale pour la couche physique des VLC pour augmenter les débits tout en considérant la qualité de l’éclairage ainsi que les coûts d’implémentation. Des études numériques et expérimentales sont réalisées sur la modulation d’impulsion d’amplitude (PAM) et sur la modulation d’amplitude et de phase sans porteuse (CAP) sous des contraintes d’éclairage et pour des grands ordres de modulation. De plus, l’impact des non-linéarités de la LED est étudié et une technique de post-distorsion est évaluée pour corriger ces effets non-linéaires. Dans ce cadre, des débits de plusieurs centaines de Mb/s sont atteints en utilisant un banc de test réalisé à partir de composants à bas coûts. Par ailleurs, un système multi-entrées multi-sorties (MIMO) imageant est également développé et l’impact du désaxage de l’imageur sur les performances est étudié. Finalement, une technique de décomposition polynomiale basée sur la méthode de factorisation classique LU est étudiée et appliquée aux systèmes MIMO VLC dans des grands espaces intérieurs

Experimental Comparison of PAM and CAP Modulation for Visible Light Communication Under Illumination Constraints

International audienceIn this paper, we study different modulation techniques for visible light communication (VLC), taking illumination constraints into account. Two modulation schemes are compared, namely pulse amplitude modulation (PAM) and carrierless amplitude and phase (CAP) modulation, through both simulations and experimental measurements. The data link under study is based on low-cost components comprising a white light-emitting diode (LED) and a silicon PIN photodiode. Moreover, the proposed VLC system complies with illumination standards and limits the brightness level to that of a typical office room. The impact of the roll-off factor parameter, which is directly related to the total occupied bandwidth, and the maximum achievable throughput for PAM and CAP are studied. Moreover, adaptive postdistortion based on a Volterra series expansion is implemented to mitigate the effects of LED nonlinearity in practice. We also demonstrate that 8-PAM can outperform 64-CAP and discrete multitone (DMT) when the LED nonlinearity is adequately compensated

MIMO Techniques in a Visible Light Communication (VLC) Link with Imager

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Drug transporters are implicated in the diffusion of tacrolimus into the T lymphocyte in kidney and liver transplant recipients: Genetic, mRNA, protein expression, and functionality

International audienceBecause of a narrow therapeutic index and a wide inter- and intra-patient variability, therapeutic drug monitoring of the immunosuppressant drug tacrolimus (TAC) based on whole-blood concentrations (C(blood)) is mandatory in solid organ transplant recipients. Using peripheral blood mononuclear cells concentrations (C(PBMC)) could improve patient outcomes. The poor correlation between C(blood) and C(PBMC) makes hypothesize that drug transporters are implicated in the intracellular accumulation of TAC. The aim of this work was therefore to clinically study: i) the role of genetic variants and ii) the effect of mRNA and protein expression of 4 drug transporters on the TAC C(PBMC/blood) ratio. In addition, functional in vitro experiments were performed to mechanistically validate the clinical observations. Genetic variants of ABCB1/P-gp and SLC28A3/CNT3 did not influence TAC C(PBMC) in liver transplant recipients (LTR). ABCC2/MRP2 at the mRNA level; ABCB1/P-gp, SLC28A3/CNT3 and SLC29A1/ENT1 at the protein level; correlated with the C(PBMC/blood) in kidney and LTR. In vitro results suing transporter-expressing cells confirmed that TAC is substrate of P-gp but not MRP2, whereas experiments remained inconclusive for CNT3 and ENT1. In conclusion, the genetic-transcription-protein-functional approach presented in this work provides new insights in the understanding of TAC transport at the T lymphocyte plasma membrane