Visible-light communication (VLC) has several advantages over the commonly used radio frequency (RF) spectrum, including high bandwidth and low crosstalk. These features have become of more significance, especially as the proliferation of wireless devices increases and causes spectrum crowding. The white light in VLC systems is typically obtained from blue/violet light-emitting diodes (LEDs) and phosphors partially converting blue light into longer wavelength colors spanning the visible-light band. One phosphor that is frequently used is cerium-doped yttrium aluminum garnet (YAG). However, YAG suffers from a low color-rendering index (CRI) and high correlated color temperature (CCT). Lead halide perovskites provide an alternative to YAG and have been extensively utilized for optoelectronic devices owing to their tunable bandgap and high photoluminescence quantum yield (PLQY). However, their drawbacks, e.g., lead toxicity and instability, hinder their widespread application. Herein, in order to take advantage of a high-performance lead-free tin-based halide perovskite phosphor that has a high absolute PLQY of near unity and a wide spectral emission ranging from 500 to 700 nm, we fabricated ultraviolet (UV) micro light-emitting diodes (micro-LEDs) with a peak wavelength at 365 nm to match the peak of the photoluminescence excitation (PLE) spectra of the material to obtain strong yellow-spectrum emission. Together with a blue LED, white light was obtained with a CRI of 84.9 and 4115-K CCT. Despite the long PL lifetime of the perovskite material, which is in the order of μs, a net data rate of 1.5 Mb/s was achieved using orthogonal frequency-division multiplexing (OFDM) with adaptive bit and power loading to take advantage of the exceptionally high PLQY of the phosphor to improve the data throughput of the VLC system using higher modulation orders. Furthermore, through improvements to the nanostructure of lead-free tin-based halide perovskite phosphor and the use of excitation sources with a higher power, the data rate is expected to be even higher. The lead-free nature of this material, along with its wide spectrum and high conversion efficiency, makes it a promising alternative to conventional toxic perovskite-based phosphors. As the first demonstration of VLC links using lead-free perovskite, this study paves the way for safer, more sustainable VLC systems.

Approximately, two-thirds of earth's surface is covered by water. There is a growing interest from the military and commercial communities in having, an efficient, secure and high bandwidth underwater wireless communication (UWC) system for tactical underwater applications such as oceanography studies and offshore oil exploration. The existing acoustic and radio frequency (RF) technologies are severely limited in bandwidth because of the strong frequency dependent attenuation of sound in seawater and the high conductivity of seawater at radio frequencies, respectively. Recently, underwater wireless optical communication (UWOC) has been proposed as the best alternative or complementary solution to meet this challenge. Taking advantage of the low absorption window of seawater in blue-green (400-550 nm) regime of the electromagnetic spectrum, UWOC is expected to establish secure, efficient and high data rate communication links over short and moderate distances (< 100 m) for versatile applications such as underwater oil pipe inspection, remotely operated vehicle (ROV) and sensor networks. UWOC uses the latest gallium nitrite (GaN) visible light-emitting diode (LED) and laser diode (LD) transmitters. Although some research on LED lased UWOC is being conducted, both the military and academic 5 research communities are favoring the use of laser beams, which potentially could enhance the available bandwidth by up to three orders of magnitude. However, the underwater wireless channel is optically very challenging and difficult to predict. The propagation of laser beams in seawater is significantly affected by the harsh marine environments and suffers from severe attenuation which is a combined effect of absorption and scattering, optical turbulence, and multipath effects at high transmission rates. These limitations distort the intensity and phase structure of the optical beam leading to a decrease in signal-to-noise ratio (SNR) which ultimately degrades the performance of UWOC links by increasing the probability of error. In this dissertation, we seek to experimentally demonstrate the feasibility of short range (≤ 20 m) UWOC systems over various underwater channel water types using different modulation schemes as well as to model and describe the statistical properties of turbulence-induced fading in underwater wireless optical channels using laser beam intensity fluctuations measurements.

The exponentially increasing demand for high-speed wireless communications will no longer be satisfied by the traditional radio frequency (RF) in the near future due to its limited spectrum and overutilization. To resolve this imminent issue, industrial and research communities have been looking into alternative technologies for communication. Among them, visible light communication (VLC) has attracted much attention because it utilizes the unlicensed, free and safe spectrum, whose bandwidth is thousand times larger than the entire RF spectrum. Moreover, VLC can be integrated into existing lighting systems to offer a dual-purpose, cost-effective and energy-efficient solution for next-generation small-cell networks (SCNs), giving birth to the concept of optical attocell networks. Most relevant works in the literature rely on system simulations to quantify the performance of attocell networks, which suffer from high computational complexity and provide limited insights about the network. Mathematical tools, on the other hand, are more tractable and scalable and are shown to closely approximate practical systems. The presented work utilizes stochastic geometry for downlink evaluation of optical attocell networks, where the co-channel interference (CCI) surpasses noise and becomes the limiting factor of the link throughput. By studying the moment generating function (MGF) of the aggregate interference, a theoretical framework for modeling the distribution of signal-to-interference-plus-noise ratio (SINR) is presented, which allows important performance metrics such as the coverage probability and link throughput to be derived. Depending on the source of interference, CCI can be classified into two categories: inter-cell interference (ICI) and intra-cell interference. In this work, both types of interference are characterized, based on which effective interference mitigation techniques such as the coordinated multipoint (CoMP), power-domain multiplexing and successive interference cancellation (SIC) are devised. The proposed mathematical framework is applicable to attocell networks with and without such interference mitigation techniques. Compared to RF networks, optical attocell networks are inherently more secure in the physical layer because visible light does not penetrate through opaque walls. This work analytically quantifies the physical-layer security of attocell networks from an information-theoretic point of view. Secrecy enhancement techniques such as AP cooperation and eavesdropper-free protected zones are also discussed. It is shown that compared to AP cooperation, implementing secrecy protected zones is more effective and it can contribute significantly to the network security.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2018-11-19T12:44:23Z No. of bitstreams: 1 luizeduardomendesmatheus.pdf: 1606990 bytes, checksum: 2736fa2230ff16ef4aaa41155178b616 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2018-11-23T13:06:46Z (GMT) No. of bitstreams: 1 luizeduardomendesmatheus.pdf: 1606990 bytes, checksum: 2736fa2230ff16ef4aaa41155178b616 (MD5) / Made available in DSpace on 2018-11-23T13:06:46Z (GMT). No. of bitstreams: 1 luizeduardomendesmatheus.pdf: 1606990 bytes, checksum: 2736fa2230ff16ef4aaa41155178b616 (MD5) Previous issue date: 2018-09-03 / Na última década, o interesse (acadêmico e comercial) em torno da Comunicação por Luz Visível (VLC) aumentou consideravelmente, devido a fatores como a crescente demanda por recursos sem fio na Internet e às vantagens oferecidas pela transmissão de dados através da luz visível. Entretanto, a utilização da luz como meio de comunicação, principalmente em ambientes internos, oferece diversos desafios, como interferência e bloqueios criados por obstáculos. Ao mesmo tempo, este tipo de ambiente oferece uma rica infraestrutura de fontes de luz, que podem ser utilizadas para auxiliar na comunicação através de mecanismos multi-hop. A maioria dos trabalhos presentes na literatura adotam técnicas simples para construção de mecanismos multi-hop em redes VLC, focando principalmente em aumento de distância. Neste trabalho, foi desenvolvido um protocolo de roteamento dinâmico, DYRP-VLC (DynamicRoutingProtocolforVisibleLightCommunication),quetemcomoobjetivo aumentar o desempenho de sistemas VLC em ambientes dinâmicos, enquanto reage à obstáculos construindo rotas alternativas na rede. A avaliação do protocolo foi realizada em um ambiente real, utilizando a plataforma embarcada OpenVLC 1.0 e métricas adotadas para problemas de roteamento. Os resultados obtidos mostram que, usando o DYRP-VLC, a rede foi capaz de se adaptar a mudanças dinâmicas na comunicação, como sombras e obstáculos, com pouca sobrecarga. / In the last decade, the interest in Visible Light Communication (VLC) has increased considerably, from both academic and commercial perspectives, due to factors such as the growing demand for wireless resources and the advantages offered by the transmission of data through visible light. However, the use of light as a communication medium, especially in indoor environments, offers several challenges, which includes shadowing and interference caused by obstacles. At the same time, this type of environment offers a rich infrastructure of light sources, which can be used to aid communication through multi-hop mechanisms. Most of the works present in the literature adopt simple techniques to construct multi-hop mechanisms in VLC networks, focusing mainly on increasing distance. Inthisthesis,wedevelopedDYRP-VLC(DynamicRoutingProtocolforVisibleLight Communication), a reactive routing protocol which aims to increase the performance ofVLCsystemsindynamicenvironments,whilereactingtoobstaclesbyconstructing alternative routes in the network. The evaluation of the protocol was performed in a real environment, using OpenVLC 1.0 embedded platform and adopting metrics for routing problems. The results show that, by using DYRP-VLC, the network was able to adapt to dynamic changes in communication, such as shadows and obstacles, with low overhead.

This work is focused on free space optical communication in visible electromagnetic spectrum known as visible light communication (VLC). Basic parameters of standard IEEE 802.15.7, advantages and disadvantages are discussed in the theoretical part of this work. Furthermore, optical link and it´s parts are described. The largest part of the work is focused on design and simulation of optical receiver for visible spectrum. Selection of component, noise and SNR calculation is discussed as well. This work also includes calculation of power energy in different parts of optical connection, PCB design of optical receiver, transmitters and power supply and output board. Behavior and parameters of electronic circuits, components and optical connection are explored, measured and compared with theoretical values.

En réponse aux problèmes croissants liés aux transports routiers - accidents, pollutions,congestions - les véhicules à faibles émissions, équipés de systèmes de transports intelligents (ITS)sont progressivement développés. Si la finalité de cette démarche est le véhicule entièrementautonome, on peut néanmoins s'attendre à voir d'abord sur nos routes des véhicules automatisés surdes phases de conduite spécifiques. C'est le cas du convoi automatisé, qui permet à plusieursvéhicules de rouler en convois de manière automatique et donc d'augmenter la capacité des voies decirculation tout en réduisant la consommation de carburant. La fiabilité de cet ITS repose surplusieurs briques technologiques, et en particulier sur la mesure de distance et la transmission dedonnées véhicule-véhicule (V2V).De nombreux systèmes permettent de réaliser ces deux fonctions vitales comme, par exemple, lesradars ou lidars pour la mesure de distance et la technologie IEEE 802.11p pour la communicationvéhiculaire. Si ces différents dispositifs présentent de très bonnes performances, ils sont néanmoinsparticulièrement sensibles aux interférences, qui ne cessent de se multiplier à mesure que le nombrede véhicules équipés augmente et que le trafic est dense. Pour pallier les dégradations deperformances induites par de telles situations, des technologies complémentaires pourraient donc êtreutiles. Le récent développement des diodes électroluminescentes (LED) blanches, en particulier pourl'éclairage automobile, a permis l'émergence des communications optiques visibles sans fil (VLC).Les phares à LED sont alors utilisés pour transmettre des données entre véhicules et avec lesinfrastructures. Malgré la puissance limitée de ces éclairages, plusieurs études ont montré qu'unetransmission de qualité est possible sur quelques dizaines de mètres, faisant de la VLC uncomplément particulièrement intéressant à l'IEEE 802.11p, en particulier pour les convoisautomatisés. Par analogie, on peut alors se demander si les phares ne pourraient pas être aussi utiliséspour mesurer la distance V2V.Le but de cette thèse est donc de proposer et évaluer un système dédié aux situations de convoisautomatisés qui, à partir des phares avant et arrière des véhicules, transmet des données et mesuresimultanément la distance V2V. Dans un premier temps, une étude détaillée de l'état de l'art de laVLC pour la communication V2V est effectuée afin de déterminer l'architecture de base de notresystème. La fonction de mesure de distance est ensuite ajoutée, après une revue des différentestechniques usuelles. Une fois l'architecture générale du système établie, elle est dans un premiertemps validée par des simulations avec le logiciel Simulink. En particulier, les différents paramètressont étudiés afin de déterminer leur impact sur la résolution de mesure de distance et les performancesen transmission de données, puis afin de les optimiser. Si ces simulations fournissent des indicateursimportants pour la compréhension du système, elles ne peuvent cependant remplacer les tests d'unprototype réel. L'implémentation de ce prototype est alors détaillée ainsi que les tests réalisés dansdifférentes configurations. Ces différents tests démontrent l'intérêt des solutions proposées pour lamesure de distance et la communication V2V en convois automatisés. / In response to the growing issues induced by road traffic - accidents, pollution, congestion- low-carbon vehicles equipped with intelligent transportation systems (ITS) are being developed.Although the final goal is full autonomy, the vehicles of the near future will most probably be selfdrivingin certain phases only, as in platooning. Platooning allows several vehicles to moveautomatically in platoons and thus to increase road capacity while reducing fuel consumption. Thereliability of this ITS is based on several core technologies and in particular on vehicle-to-vehicle(V2V) distance measurement and data transmission.These two vital functions can be implemented with several kinds of systems as, for instance, radars orlidars for range-finding and IEEE 802.11p-based devices for vehicular communication. Althoughthese systems provide good performances, they are very sensitive to interferences, which may be agrowing issue as the number of vehicles equipped will increase, especially in dense traffic scenario.In order to mitigate the performance degradation occurring in such situations, complementarysolutions may be useful. The recent developments of white light-emitting diodes (LED), especiallyfor the automotive lighting, has allowed the emergence of visible light communication (VLC). WithVLC, the vehicle headlamps and taillights are used to transmit data to other vehicles orinfrastructures. Despite the limited optical power available, several studies have shown thatcommunication over tens of meters are possible with a low bit error rate (BER). VLC could thus bean interesting complement to IEEE 802.11p, especially in platooning applications. By analogy, onecould wonder if the automotive lighting can also be used for V2V range-finding.The goal of this thesis is thus to propose and evaluate a system dedicated to platooning configurationsthat can perform simultaneously the V2V distance measurement and data transmission functionsusing the headlamps and taillights of the vehicles. The first step of this study is thus a detailed stateof-the art on VLC for V2V communication that will lead to a first basic architecture of our system.Then, the range-finding function is added, after a careful review of the classical techniques. Once thegeneral architecture of the system is drawn, it is validated through simulations in the Simulinkenvironment. The different degrees of freedom in the system design are especially studied, in orderfirst to evaluate their impact on the measurement resolution and the communication performances,and then to be optimized. Although these simulations provide crucial keys to understand the system,they cannot replace real prototype testing. The implementation of the prototype is thus fullydescribed, along with the results of the different experiments carried out. It is finally demonstratedthat the proposed solution has a clear interest for V2V range-finding and communication inplatooning applications.

Cette thèse est axée sur le domaine de la communication optique sans fil en intérieur pour la surveillance de la santé basée sur des capteurs corporels. L’état de l'art des communications optique sans fil dans les domaines infrarouge, visible et UV ainsi que l'analyse des systèmes liés à la santé utilisant cette technologie ont été fournis. Cela a permis de définir les objectifs et l'orientation de cette thèse. Nous avons étudié l'utilisation de la technologie infrarouge pour la transmission de données entre un capteur porté par un patient et des récepteurs situés aux coins d'un panneau d'éclairage central au plafond de l'environnement. Un lien en visible a été utilisé pour la transmission de données du luminaire vers le patient portant un smartphone équipé d'un décodeur. Les principaux défis étaient la robustesse des liens infrarouge et visible en ce qui concerne la mobilité du patient et l'impact du corps de l'utilisateur en raison de l'emplacement du capteur. Les simulations de canaux réalisées grâce à la technique de Ray-Tracing associée à la méthode de Monte-Carlo ont permis de déterminer le gain de canal qui est le paramètre principal représentant la performance. En raison de la mobilité du patient, l'analyse a été réalisée de manière statistique et en tenant compte de différents emplacements du capteur sur le corps, de la cheville à l'épaule. Les paramètres physiques et géométriques optimaux relatifs aux émetteurs et aux récepteurs afin de garantir les meilleures performances ont été déduites. Il a été démontré qu’il est essentiel de modéliser la présence du corps pour les deux liaisons montante et descendante. Les performances globales du système ont mis en évidence le potentiel des transmissions sans fil entièrement optiques pour la surveillance médicale basée sur des capteurs corporels. Cela a été en partie confirmé par des expérimentations menées à partir de prototypes de capteur communicant en infrarouge et de produits commerciaux pour la liaison en visible. / This thesis is focused on the field of indoor optical wireless communication for health monitoring based on body sensors. The state of the art of optical wireless in the infrared, visible and UV domains as well as the analysis of health related systems using this technology have been provided. This helped to define the objectives and orientations of this thesis. We have studied the use of infrared technology for data transmission between a sensor worn by a patient and receivers located at the corners of a central lighting panel at the ceiling of the environment. A link in visible was used for the transmission of data from the luminaire to the patient carrying a smartphone equipped with a decoder. The main challenges were the robustness of the infrared and visible links with regard to patient mobility and the impact of the user's body due to the location of the sensor. The channel simulations performed using the Ray-Tracing technique associated with the Monte-Carlo method allowed determining the channel gain, which is the main parameter representing the performance. Due to the patient mobility, the analysis was performed statistically and taking into account different locations of the sensor on the body, from the ankle to the shoulder. The optimal physical and geometrical parameters for transmitters and receivers to ensure the best performance have been deduced. It has been shown that it is essential to model the presence of the body for both uplink and downlink. The overall performance of the system has highlighted the potential of fully optical wireless transmissions for medical surveillance based on body sensors. This has been partly confirmed by experiments carried out from infrared communicating sensor prototypes and commercial products for the visible link.

Technology for wireless information access has enabled innovation of 'smart' portable consumer devices. These have been widely adopted and have become an integral part of our daily lives. They need ubiquitous connectivity to the internet to provide value added services, maximize their functionality and create a smarter world to live in. Cisco's visual networking index currently predicts wireless data consumption to increase by 61% per year. This will put additional stress on the already stressed wireless access network infrastructure creating a phenomenon called 'spectrum crunch'. At the same time, the solid state devices industry has made remarkable advances in energy efficient light-emitting-diodes (LED). The lighting industry is rapidly adopting LEDs to provide illumination in indoor spaces. Lighting fixtures are positioned to support human activities and thus are well located to act as wireless access points. The visible spectrum (380 nm - 780 nm) is yet unregulated and untapped for wireless access. This provides unique opportunity to upgrade existing lighting infrastructure and create a dense grid of small cells by using this additional 'optical' wireless bandwidth. Under the above model, lighting fixtures will service dual missions of illumination and access points for optical wireless communication (OWC). This dissertation investigates multiple-input multiple-output (MIMO) optical wireless broadcast system under unique constraints imposed by the optical channel and illumination requirements. Sample indexed spatial orthogonal frequency division multiplexing (SIS-OFDM) and metameric modulation (MM) are proposed to achieve higher spectral efficiency by exploiting dimensions of space and color respectively in addition to time and frequency. SIS-OFDM can provide significant additional spectral efficiency of up to (Nsc/2 - 1) x k bits/sym where Nsc is total number of subcarriers and k is number of bits per underlying spatial modulation symbol. MM always generates the true requested illumination color and has the potential to provide better color rendering by incorporating multiple LEDs. A normalization framework is then developed to analyze performance of optical MIMO imaging systems. Performance improvements of up to 45 dB for optical systems have been achieved by decorrelating spatially separate links by incorporating an imaging receiver. The dissertation also studies the impact of visual perception on performance of color shift keying as specified in IEEE 802.15.7 standard. It shows that non-linearity for a practical system can have a performance penalty of up to 15 dB when compared to the simplified linear system abstraction as proposed in the standard. Luminous-signal-to-noise ratio, a novel metric is introduced to compare performance of optical modulation techniques operating at same illumination intensity. The dissertation then introduces singular value decomposition based OWC system architecture to incorporate illumination constraints independent of communication constraints in a MIMO system. It then studies design paradigm for a multi-colored wavelength division multiplexed indoor OWC system.

De nos jours, le nombre d'appareils connectés nécessitant un accès aux données mobiles est en augmentation constante. L'arrivée d'encore plus d'ojects multimédias connectés et la demande croissante d'informations par appareil ont mis en évidence les limites de la quatrième génération de réseaux cellulaires (4G). Cela a poussé au développement de nouvelles méthodes, dont la 5G. L'objectif est d'être en mesure de prendre en charge la croissance des systèmes portables, des capteurs ou des sysèmes associés à l'internet des objets (IoT). La vision derrière la 5G est de permettre une société entièrement mobile et connectée avec une expérience consistente.Les petites cellules sont la base des normes de communication avancées telles que 4G et maintenant 5G. Ils résultent de l’utilisation de bandes de fréquences plus élevées pour l’accès radiofréquences (RF) afin de supporter de nouvelles normes et exigences croissantes en bande passante. La 5G utilise des ondes millimétriques et nécessite un déploiement dans un environnement urbain intérieur et urbain dense, ce qui peut s'avérer être un défi. C’est là que la 5G devra inclure des solutions de réseau hybrides et pouvoir coexister avec d’autres technologies d’accès sans fil. La communication par lumière visible (VLC) s’inscrit dans ce moule puisque la lumière visible correspond à la bande comprise entre 400 et 800 THz. Le spectre disponible est des milliers de fois plus large que le spectre RF et il n’interfère pas avec celui-ci. Le principe se base sur la combinaison de l'éclairage avec un lien de communication pouvant atteindre des dizaines de gigabits par seconde. Le potentiel est d’offrir un complément à la 5G dans un réseau hybride, offrant une vitesse élevée, aucune interférence et une sécurité accrue au prix d’une couverture limitée et d’une faible maturité technologique.L’objectif de cette thèse est donc de proposer et d’évaluer une implémentation expérimentale d’un système VLC en intérieur et multi-utilisateurs afin de répondre aux objectifs de la configuration light-fidelity (Li-Fi) dans le contexte d’une petite cellule. La première étape de cette étude est un état de l'art détaillé sur le principe de VLC dans la communication sans fil en intérieur et de l’accès multi-utilisateur. Cela permet de mieux expliquer le concept de notre désign et de comparer notre approche aux travaux existants. La deuxième étape consiste en une analyse des principes et des hypothèses pour le système VLC multi-utilisateurs en intérieur portant à la fois sur la technique de modulation et sur les schémas d’accès multi-utilisateurs. Les conclusions tirées des analyses théoriques et numériques servent de base pour la suite du travail. La troisième étape consiste en plusieurs analyses expérimentales sur l'optimisation des performances de diffusion pour un utilisateur unique, puis sur les performances multi-utilisateurs du système à l'aide de divers schémas d'accès. Le débit total avec une LED blanche commerciale atteint 163 Mb/s avec un taux d'erreur réduit d'un facteur de 3,55 grâce au processus d'optimisation des performances. Cette technique a l'avantage d'augmenter la flexibilité pour un scénario avec plusieurs utilisateurs sans augmenter la complexité car seuls les paramètres des filtres de modulation sont altérés. La taille de la cellule obtenue est de 4.56 m² à une distance de 2,15 mètres du transmetteur. Le capacité peut atteindre jusqu'à 40 utilisateurs, ou 40.62 Mb/s dans un scénario à 4 utilisateurs. Il est donc démontré que le système proposé pourrait fonctionner comme une cellule à une distance réaliste, avec un débit de données élevé et la capacité de répondre aux besoins d’un grand nombre d’utilisateurs tout en limitant les coûts de mise en œuvre. / Nowadays, the number of connected devices requiring access to mobile data is considerably increasing. The arrival of even more connected multimedia objects and the growing demand for more information per device highlighted the limits of the fourth generation of broadband cellular networks (4G). This pushed for the development of new methods, one of which is 5G. The goal is to be able to support the growth of wearable, sensors, or related internet-of-object (IoT) systems. The vision behind 5G is to enable a fully mobile and connected society with a consistent experience. In consequence, there is a fundamental need to achieve a seamless and consistent user experience across time and space.Small cells are the basis of advanced communications standards such as 4G and now, 5G. They exist as a result of using higher frequency bands for RF access in order to support new standards and the increasing demands in bandwidth. 5G use millimeter waves and requires a deployment across indoor and dense urban environment which may prove to be a challenge. This is where 5G will need to include hybrid networking solutions and be able to coexist with other wireless access technologies. Visible light communication (VLC) fits into that mold since visible light corresponds to the band between 400 and 800 THz. The available spectrum is multiple thousand times the size of the RF spectrum and it does not interfere with it. The technique combines illumination with communication at possibly tens of gigabits per second. It has the potential to offer a synergistic pairing with 5G in a hybrid network, offering high speed, no interferences, and more security at the cost of limited coverage and low technological maturity.The goal of this thesis is thus to propose and evaluate an experimental implementation of an indoor multi-user VLC system in order to answer the objectives of Li-Fi setup in the context of a small cell. The first step of this study is a detailed state-of-the-art on VLC in indoor wireless communication and multi-user access. It allows the design of our work to be better explained and to compare our approach with existing works. The second step is an analysis of the principles and hypothesis supporting the indoor multi-user VLC system in the study both on the modulation technique and the multi-user access schemes. The conclusions drawn from theoretical and numerical analysis are used as a basis for the rest of the work. The third step is the experimental setup investigations on the single-user broadcast performances optimization and then on the multi-user performances of the system using various schemes. The total throughput using an off-the-shelf white LED reaches 163 Mb/s with a bit-error rate decreased by a factor of 3.55 thanks to the performance optimization process. This technique has the advantage of increasing the flexibility for a multi-access scenario while not augmenting the complexity as it only optimizes the modulation filter parameters. The multi-user access is obtained for a cell size of 4.56 m² at a distance of 2.15 meter away from the transmitter. The user capacity can reach up to 40 users, or 40.62 Mb/s in a 4-user scenario. It is thus demonstrated that the proposed system could function as a cell at a realistic range, with high data rate and the ability to provide for a large amount of users while limiting the cost of implementation.

People around the globe are immensely trying to connect using light as carrier due to its low power consumption and high data transfer rates. Sound and microwaves are examples of other carriers that can be used, although they aren't nearly as efficient as light. A method of communicating is using light beneath the surface of the water. As the depth of the water increases, the temperature, pressure, and salinity of the water are changed. The refractive index of water is determined by the combination of all of these variable parameters. The goal of this thesis is to establish a relationship between changes in water temperature, salinity, and pressure resulting in changes of the refractive Index of the sea water. This thesis will demonstrate an empirical model of travelling the ultraviolet wave under sea water. We are acknowledging all of the properties that are change as the depth of the water is increasing. MATLAB was used to create a simulation of this scenario. Based on previous model of light traveling which covers the wavelengths between 400-700 nm, we have extended the model to ultraviolet range of light (200-400 nm).We design an experimental set up according to sea water parameters and then the experimental results are compared to the simulation results. The comparison shows the validity of our extension model.