Dissertations / Theses: 'Visible light wireless communications'

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Singh, Ravinder. "Physical layer techniques for indoor wireless visible light communications." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/13818/.

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The growing demand for bandwidth-hungry applications and increasing number of smart interconnected devices has increased the data traffic on radio access networks. Subsequently, the saturating spectral efficiencies in crowded radio frequency spectrum has impelled the researchers to exploit the optical spectrum for communications. In particular, many developments in the visible light communication (VLC) as a combined lighting and communications system have taken place. Despite abundant optical bandwidth, the data transmission rates and power efficiencies in VLC are partly limited by the electrical channel bandwidth and the type of signalling sets which can be used in this intensity modulated, direct detected system. In order to improve the power and spectral efficiencies, this thesis focuses on physical layer (PHY) techniques. The state-of-the-art single channel modulations (SCM) based on M-PAM, multi-channel modulations (MCM) based on OFDM, and IEEE standardised multi-colour modulations are investigated comprehensively through simulations and theoretical analysis, over representative VLC channels considering the optical properties of front-end devices. The bit error performances and spectral efficiencies of DC-biased and non DC-biased MCM systems are compared. A new vector coding based MCM is proposed to optimally utilise the channel state information at the transmitter as an alternative to optical OFDM. The throughputs, peak-to-average power ratios and DC-bias requirements of SCM and MCM systems are investigated which show that the lower DC-bias requirements reduce power consumed for the same throughput in SCM systems when compared to MCM systems. A new quad-chromatic colour shift keying (CSK) system is proposed which reduces power requirements and complexity, enhances throughput and realises a four-dimensional signalling to outperform the IEEE standardised tri-chromatic CSK system. For improved power efficiency and throughput of VLC PHY, use of rate-adaptive binary convolutional coding and Viterbi decoding is proposed along with frequency domain channel equalisation to mitigate temporal dispersion over representative VLC channels.

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Camacho, Pedro Alexandre Armas. "Front-end design for visible light communications systems." Master's thesis, Universidade de Aveiro, 2017. http://hdl.handle.net/10773/23477.

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Mestrado em Engenharia Eletrónica e Telecomunicações
Communications are vital in the world today. Everything is connected and this means that communication technologies are constantly being pushed to their limits. Any kind of development and improvement that can be done to increase networks capabilities, will ﬁnd use in some speciﬁc application, or even in more common technologies if such is justiﬁed. One such case is VLC, it can be used to improve other communication methods capabilities, or as standalone solution, providing advantage in certain scenarios where regular wirelesscommunicationsmethodswouldnotperformaswell,orwouldnotsuit theapplication. VLCalsooffersthegreatadvantageofutilisinganewmedium of transmission for telecomunication systems, which is the visible light spectrum, and is not yet overused and overregulated as other typical mediums. This work was done in partnership with the integrated circuit systems groupd ofInstitutodeTelecomunicaçõesAveiroandaimstostudyanddevelopoptical front end systems for VLC to be used in future projects by this group.
As Telecomunicações são fundamentais nos nossos dias em que tudo está interligado, levando as tecnologias de telecomunicações constantemente ao seu limite. Todo o tipo de melhoria que possa ser feito para melhorar o desempenho de uma rede, encontrará aplicação em alguma área, mais especíﬁca, ou caso se justiﬁque, até mesmo em tecnologias de telecomunicação mais comuns. Um exemplo é o VLC (Visible Light Communication), que pode ser utilizado para melhorar as capacidades de outros tipos de redes de telecomunicações, ou em alternativa a outros tipos de redes, oferecendo vantagens em certos cenários onde métodos tradicionais de telecomunicações sem ﬁos não teriam tão bom desempenho, ou não serviriam a aplicação desejada. O VLC também tem como grande vantagem a hipótese de utilização de um novo meio de transmissão para sistemas de telecomunicações, que é o espectro da luz vísivel, que não se encontra ainda sobrelotado e tem regulamentos mais relaxados que outros meios de comunicação tradicionais. Este trabalho foi feito em colaboração com o grupo de sistemas e circuitos integrados do Instituto de Telecomunicações Aveiro, e visa o estudo de desenvolvimento de ‘frontends’óticosparaVLC,parautilizaçãofuturaemprojetosporpartedeste grupo.

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Tsonev, Dobroslav Antonov. "High speed energy efficient incoherent optical wireless communications." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10571.

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The growing demand for wireless communication capacity and the overutilisation of the conventional radio frequency (RF) spectrum have inspired research into using alternative spectrum regions for communication. Using optical wireless communications (OWC), for example, offers significant advantages over RF communication in terms of higher bandwidth, lower implementation costs and energy savings. In OWC systems, the information signal has to be real and non-negative. Therefore, modifications to the conventional communication algorithms are required. Multicarrier modulation schemes like orthogonal frequency division multiplexing (OFDM) promise to deliver a more efficient use of the communication capacity through adaptive bit and energy loading techniques. Three OFDM-based schemes – direct-current-biased OFDM (DCO-OFDM), asymmetrically clipped optical OFDM(ACO-OFDM), and pulse-amplitude modulated discrete multitone (PAM-DMT) – have been introduced in the literature. The current work investigates the recently introduced scheme subcarrier-index modulation OFDM as a potential energy-efficient modulation technique with reduced peak-to-average power ratio (PAPR) suitable for applications in OWC. A theoretical model for the analysis of SIM-OFDMin a linear additive white Gaussian noise (AWGN) channel is provided. A closed-form solution for the PAPR in SIM-OFDM is also proposed. Following the work on SIM-OFDM, a novel inherently unipolar modulation scheme, unipolar orthogonal frequency division multiplexing (U-OFDM), is proposed as an alternative to the existing similar schemes: ACO-OFDMand PAM-DMT. Furthermore, an enhanced U-OFDMsignal generation algorithm is introduced which allows the spectral efficiency gap between the inherently unipolar modulation schemes – U-OFDM, ACO-OFDM, PAM-DMT – and the conventionally used DCO-OFDM to be closed. This results in an OFDM-based modulation approach which is electrically and optically more efficient than any other OFDM-based technique proposed so far for intensity modulation and direct detection (IM/DD) communication systems. Non-linear distortion in the optical front-end elements is one of the major limitations for high-speed communication in OWC. This work presents a generalised approach for analysing nonlinear distortion in OFDM-based modulation schemes. The presented technique leads to a closed-form analytical solution for an arbitrary memoryless distortion of the information signal and has been proven to work for the majority of the known unipolar OFDM-based modulation techniques - DCO-OFDM, ACO-OFDM, PAM-DMT and U-OFDM. The high-speed communication capabilities of novel Gallium Nitride based μm-sized light emitting diodes (μLEDs) are investigated, and a record-setting result of 3.5Gb/s using a single 50-μm device is demonstrated. The capabilities of using such devices at practical transmission distances are also investigated, and a 1 Gb/s link using a single device is demonstrated at a distance of up to 10m. Furthermore, a proof-of-concept experiment is realised where a 50-μm LED is successfully modulated using U-OFDM and enhanced U-OFDM to achieve notable energy savings in comparison to DCO-OFDM.

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Duque, Alexis. "Bidirectional visible light communications for the internet of things." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEI072/document.

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Dans cette thèse, nous concevons et étudions un système de communication bidirectionnel par lumière visible (VLC) entre une diode électroluminescente (DEL) de couleur, intégrée à un objet connecté, et un smartphone. Le dispositif est ainsi capable d'envoyer et de recevoir des informations à travers sa DEL, tandis que le smartphone utilise sa caméra pour recevoir des données et son flash pour envoyer des informations. Nous mettons en œuvre et évaluons expérimentalement ce système VLC DEL-à-camera conçu spécifiquement pour les DELs de couleur à faible puissance. En nous appuyant sur les résultats d'une vaste étude expérimentale, nous modélisons, pour la première fois dans la littérature, le canal de communication DEL-à-caméra. Nous proposons alors un modèle de processus de Bernoulli modulé par une chaîne de Markov, qui nous permet d'étudier facilement l'efficacité de différentes stratégies de retransmission des messages. Nous exploitons ce modèle afin de concevoir un simulateur pour l'évaluation des performances des communications DEL-à-caméra. Afin d'obtenir un système de communication bidirectionnel, nous étudions ensuite les communications de type flash-vers-DEL entre un smartphone non-modifié et une petite DEL de couleur. Les performances, bien que limitées, sont suffisantes pour établir une voie retour qui permet de mettre en œuvre des mécanismes de fiabilisation. Nous proposons alors un mécanisme de codage linéaire pseudo-aléatoire, spécialement adapté aux conditions et contraintes du système DEL-à-caméra en ligne de visée directe. Notre évaluation expérimentale souligne que ce type d'approche augmente le rendement jusqu'à deux fois par rapport aux stratégies de retransmission classiques. Enfin, la plupart des objets que nous adressons ont des contraintes énergétiques importantes. Par conséquent, nous comparons la consommation d'énergie de notre système avec celle d'un module Bluetooth Low Energy avec une activité similaire. Nos résultats montrent que notre système réduit la consommation d'énergie dans le cadre d'un profil d'utilisation classique
With the exponential growth of the Internet of Things, people now expect every household appliance to be smart and connected. At the same time, smartphones have become ubiquitous in our daily life. Their continuous performance improvement and their compatibility with a broad range of radio protocols as WiFi, Bluetooth Low Energy (BLE) or NFC make them the most convenient way to interact with these smart objects. However, providing wireless connectivity with BLE or NFC means adding an extra chipset and an antenna, increasing the object size and price. Previous works already have demonstrated the possibility of receiving information through visible light using an unmodified smartphone thanks to its camera. Also, LED-to-LED communication for smart devices like toys has been shown previously. However, past efforts in LED to camera communication for IoT device communication have been limited. In this work, we design LightIoT, a bidirectional visible-light communication (VLC) system between a low-cost, low-power colored LED that is part of an IoT device and an off-the-shelf smartphone. The IoT device is thus able to send and receive information through its LED, while the smartphone uses its camera to receive data and its flashlight to send information. We implement and experimentally evaluate a LED-to-camera VLC system, designed specifically for small LEDs. The proposed solution exploits the rolling shutter effect of unmodified smartphone cameras and an original decoding algorithm, achieving a throughput of nearly 2 kb/s. Based on the insight gained from an extensive experimental study, we model, for the first time in the literature, the LED-to-camera communication channel. We propose a Markov-modulated Bernoulli process model, which allows us to easily study the performance of different message retransmission strategies. We further exploit this model to implement a simulator for LED-to-Camera communications performance evaluation. In order to achieve bi-directional communications, we evaluate flashlight-to-LED communications using non-rooted smartphones and small LEDs. With these constraints, our implementation achieves a throughput of 30 bits/second. While limited, this is enough for a feed-back channel coming to support the required redundancy mechanisms. Some of these redundancy mechanisms are based on random linear coding, never tested previously in VLC. Therefore, we design and implement, for the first time in the literature, a pseudo random linear coding scheme especially fitted for line-of-sight LED-to-camera conditions. Experimental evaluation highlights that this type of approach increases the goodput up to twice compared to classical retransmission strategies. Finally, we compare the energy consumption of LightIoT with the one of a BLE module with similar activity. Our results show that using the LED for communication purposes reduces the energy consumption under a normal usage behavior

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Tran, Tuan-Anh. "Multiple-input multiple-output optical wireless communications." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:094fbe23-88c3-49c4-b64b-a1de40674123.

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Visible-light optical wireless communications (OWC) is a potential technology that can help resolve the crowdedness of the radio-frequency bands, whilst conveniently exploiting energy-saving light-emitting diodes (LEDs) as transmitters for both illumination and communications. Since there usually are many LEDs in a lighting unit, OWC has a multi- input multi-output (MIMO) geometry which, thanks to its channel diversity, can offer wireless local networks at data-rates many times higher than possible with single-channel systems. In such systems, MIMO-detection methods to separate the different optical channels play an important role in improving the system performance by helping reduce cross-talk between channels. To measure the performance of a particular geometry for MIMO communications, a simulation study, reported in this thesis, found that, amongst the signal- independent metrics, the condition number may be used as a rough predictor of the performance, whilst the channel Signal-to-Interference-and-Noise Ratio (SINR) is the most appropriate for geometry assessment. Combined with the fact that the overall performance of a MIMO system is mostly dominated by its worst channel, this indicates that the most effective way to improve the system performance is to maximise the worst channel’s SINR. One of the possible solutions to improving the SINRs is to use holograms to steer the transmitter images such that their distributions over the photo-detectors reduce overlaps. As LEDs emit partially-coherent light, the beam steering has to be carried out with partially- coherent illumination. By using two lenses to parallelise and collect partially-coherent light before and after the hologram, respectively, the source and image intensity distributions, and the autocorrelation of the hologram can be related in a succinct mathematical relationship. This leads to the development of three computational algorithms based on the autocorrelation function to obtain a quantised hologram with the desired beam-steering capability. These algorithms have their cost functions and performance comparison done at the hologram plane instead of the image plane, which therefore takes less time than traditional image-based methods. Specifically, one of these algorithms is able to save significant time over both the other autocorrelation-based algorithms and the direct binary-search, by 33% and by 50% respectively. A simulation-based study and a corresponding experiment, both reported in this thesis, found that the one of the proposed algorithms had poor power efficiency, whilst the other two were both highly effective in generating digital holograms with precise and power-efficient beam-steering performance. Of these two algorithms, one had superior time performance and was likely the best of the three proposed autocorrelation-based algorithms for generating beam-steering holograms. MIMO-OWC simulation also demonstrated the capability of using beam-steering holograms to design the channel and improve the system performance. Combining reported findings, a strategy can be devised to optimise the throughput of an imaging MIMO-OWC system for a given transmitted power.

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Li, Yichen. "Enhancing communication link performance in visible light communication." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25666.

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With data throughput increasing exponentially in wireless communication networks, the limited radio frequency (RF) spectrum is unable to meet the future data rate demand. As a promising complementary approach, optical wireless communication (OWC) has gained significant attention since its licence-free light spectrum provides a considerable amount of communication bandwidth. In conventional OWC systems, the information-carried signal has to be real-valued and non-negative due to the incoherent light output of the conventional optical transmitter, light emitting diode (LED). Therefore, an intensity modulation and direct detection (IM/DD) system is used for establishing the OWC link. Some modified orthogonal frequency division multiplexing (OFDM) schemes have been proposed to achieve suitable optical signals. In previous research, three OFDM-based schemes have been presented, including DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM), asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) and unipolar orthogonal frequency division multiplexing (U-OFDM). Basic concepts of SPAD receivers are studied and a novel application in OWC is proposed for a permanent downhole monitoring (PDM) system in the gas and oil industry. In this thesis, a complete model of the SPAD-based OWC system is presented, including some related SPAD metrics, the photon counting process in SPAD and a specific nonlinear distortion caused by passive quenching (PQ) and active quenching (AQ) recharged circuits. Moreover, a practical SPAD-based visible light communication (VLC) system and its theoretical analysis are presented in a long-distance gas pipe with a battery-powered LED and a basic on-off keying (OOK) modulation scheme. In this thesis, two novel optical orthogonal frequency division multiplexing (O-OFDM) technologies are proposed: non-DC-biased orthogonal frequency division multiplexing (NDCOFDM) and OFDM with single-photon avalanche diode (SPAD). The former is designed for optical multiple-input multiple-output (O-MIMO) systems based on the optical spatial modulation (OSM) technique. In NDC-OFDM, signs of modulated O-OFDM symbols and absolute values of the symbols are separately transmitted by different information carrying units. This scheme can eliminate clipping distortion in DCO-OFDM and achieve high power efficiency. Furthermore, as the indices of transmitters carry extra information bits, NDC-OFDM gives a significant improvement in spectral efficiency over ACO-OFDM and U-OFDM. In this thesis, SPAD-based OFDM systems with DCO-OFDM and ACO-OFDM are presented and analysed by considering the nonlinear distortion effect of PQ SPAD and AQ SPAD. A comprehensive digital signal processing of SPAD-based OFDM is shown and theoretical functions of the photon counting distribution in PQ SPAD and AQ SPAD are given. Moreover, based on Bussgang theorem, a conventional method for analysing memoryless distortion, close-formed bit-error rate (BER) expressions of SPAD-based OFDM are derived. Furthermore, SPAD-based OFDM is compared with conventional photo-diode (PD) based OFDM systems, and a gain of 40 dB in power efficiency is observed.

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Chowdhury, H. (Helal). "Data download on the move in visible light communications:design and analysis." Doctoral thesis, Oulun yliopisto, 2016. http://urn.fi/urn:isbn:9789526213620.

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Abstract In visible light communication (VLC), light emitting diodes (LEDs) are used as transmitters; the air is the transmission medium and the photodiodes are used for receivers. This is often referred to as light fidelity (Li-Fi). In this thesis, we provide the methodology to evaluate the performance of VLC hotspot networks in the context of data downloading on the move scenarios by using throughput-distance relationship models. In this context, first we study the different properties of optical transceiver elements, noise sources, characterization and modelling of artificial light interference, different link topologies and then we introduce the throughput-distance relationship model. Secondly, the analytically based throughput-distance relationship has been developed for evaluating the performance of VLC hotspot networks in indoor environment in both day and night conditions. Simulation results reveal that background noise has a significant impact on the performance of VLC hotspots. As expected, in both indoor and outdoor environments the VLC hotspot performs better at night than during day. The performance of VLC hotspot networks is also quantified in terms of received file size at different bit error rate requirements and velocities of the mobile user. Thirdly, we study the performance of hybrid (Radio-Optical) WLAN-VLC hotspot and compare its performance with stand-alone VLC-only or WLAN-only hotspot cases. In this case, we also consider the data download on the move scenarios in an indoor environment for a single-user as well as for multi-user cases. In this hybrid WLAN-VLC hotspot, both the WLAN and the VLC are characterized by their throughput and communication range. Simulations have been performed to evaluate the performance of such network for data downloading on the move scenario by taking into account performance metrics such as filesize, average connectivity and system throughput. Simulation results reveal that the considered hybrid WLAN-VLC performs always better than stand-alone VLC-only or WLAN-only hotspot both for a single and multi-user cases. Finally, this thesis analyses the feasibility and potential benefits of using hybrid radio-optical wireless systems. In this respect, cooperative communication using optical relays are also introduced in order to increase the coverage and energy efficiency of the battery operated device. Potential benefits are identified as service connectivity and energy efficiency of battery operated device in an indoor environment. Simulation results reveal that user connectivity and energy efficiency depend on user density, coverage range ratio between single-hop and multi-hop, relay probabilities and mobility of the user
Tiivistelmä Näkyvään valoon pohjautuvassa tiedonsiirrossa (VLC) valodiodeja (LED) käytetään lähettiminä, ilma on siirtokanava ja valoilmaisimia käytetään vastaanottimina. Tätä kutsutaan usein nimellä light fidelity (Li-Fi). Tässä työssä tarjoamme menetelmiä VLC ”hotspot” verkkojen suorituskyvyn arviointiin tiedonsiirtonopeus-etäisyysmalleilla skenaarioissa, jossa tietoa ladataan liikkeessä. Tässä kontekstissa tutkimme ensin optisen lähettimen komponenttien eri ominaisuuksia, kohinan lähteitä, keinovalon häiriömalleja ja tiedonsiirtolinkkien topologioita, jonka jälkeen esittelemme tiedonsiirtonopeuden ja etäisyyden välisen mallin. Toiseksi kehitetyn analyyttisen tiedonsiirto-etäisyys mallia käytetään arvioitaessa VLC hotspot verkkojen suorituskykyä sisäympäristössä sekä päivä että yö olosuhteissa. Simulointien tulokset osoittavat, että taustakohinalla on suuri vaikutus VLC verkkojen suorituskykyyn. Kuten odotettua, sisä- ja ulkotiloissa VLC hotspot toimii paremmin yöllä kuin päivällä. VLC hotspot verkkojen suorituskyky arvioidaan myös vastaanotetun tiedoston koon, eri bittivirhesuhteen vaatimuksilla ja liikkuvan käyttäjän nopeuden suhteen. Kolmanneksi tutkimme hybridi WLAN-VLC hotspot verkon suorituskykyä ja vertaamme sen suorituskykyä pelkän VLC- tai WLAN hotspot tapauksessa. Käsittelemme myös skenaarioita jossa tiedoston lataus tapahtuu liikkeessä sisätilassa yhden käyttäjän sekä monen käyttäjän tapauksissa. Tässä hybridi WLAN-VLC hotspot, sekä erilliset WLAN- ja VLC verkot ovat määritelty niiden tiedonsiirtonopeuden ja kantaman perusteella. Näiden verkkojen suorituskykyä arvioitaessa on tehty joukko tietokonesimulointeja verkossa tapahtuvasta tietojen lataamisesta liikkeessä ottamalla huomioon suorituskyvyn mittarit kuten tiedoston koko, keskimääräinen yhteyden kesto ja saavutettu läpäisy. Simuloinnin tulokset paljastavat, että hybridi WLAN-VLC toimii aina paremmin kuin pelkkä VLC tai WLAN hotspot sekä yhden että monen käyttäjän tapauksessa. Lopuksi työssä analysoidaan ehdotetun järjestelmän toteutettavuus ja mahdolliset edut käytettäessä hybridejä radio-optisia langattomia järjestelmiä. Tältä osin esitellään myös kooperatiiviseen viestintään perustuvat optiset releet parantamaan verkon kattavuutta ja energiatehokkuutta akkukäyttöisissä laitteissa. Mahdolliset hyödyt tunnistetaan palvelun konnektiivisuudessa ja energiatehokkuudessa akkukäyttöisissä laitteissa sisätiloissa. Simulointien tulokset osoittavat, että käyttäjien konnektiivisuus ja energiatehokkuus riippuvat käyttäjätiheydestä, kantaman ja etäisyyden välisestä suhteesta yhden hypyn ja monen hypyn välillä, releointi todennäköisyydestä ja käyttäjien mobiliteetista

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Azim, Ali Waqar. "Signal Processing Techniques for Optical Wireless Communication Systems." Thesis, Université Grenoble Alpes (ComUE), 2018. http://www.theses.fr/2018GREAT059/document.

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Le spectre radiofréquence (RF) diminue en raison d'une augmentation de la demande d'applications sans fil. Par conséquent, il existe une demande importante de régions de spectre alternatifs pour les communications afin d'incliner le spectre RF conventionnel. Dans ce contexte, les communications optiques sans fil (OWC) sont explorées comme un candidat potentiel pour compléter les communications RF. Le travail actuel se concentre sur les techniques d'atténuation des déficiences et les approches de modulation efficaces en énergie pour OWC. Dans un premier temps, on étudie le rapport de puissance crête à moyenne (PAPR) pour le multiplexage par répartition orthogonale de la fréquence optique (O-OFDM) et on présente deux techniques de réduction de PAPR orientées vers la décision. La complexité de ces méthodes est comparativement plus faible que celle des autres méthodes de réduction PAPR, tandis que leurs performances sont également analogues à celles des autres alternatives. Deuxièmement, une approche d'accès multiple par répartition en fréquence optique-porteuse unique (O-SCFDMA), appelée O-SCFDMA sans symétrie d'Hermitain (HSFO-SCFDMA) est proposée. Ce dernier évite la symétrie hermiatienne normalement attendue pour d'autres O-OFDM et Approches O-SCFDMA. Les résultats de la simulation affirment que HSFO-SCFDMA est plus efficace que toute autre approche O-SCFDMA pour OWC et manifeste le plus faible PAPR parmi les autres alternatives. Troisièmement, la performance du précodage est analysée pour l'O-OFDM (LACO-OFDM) asymétriquement en couches. Deux types de précodage sont utilisés, à savoir le précodage par transformée de Fourier et le précodage par transformée d'Hartley. Il est établi que le LACO-OFDM précodé a transformée Hartley présente le PAPR le plus faible et est moins vulnérable à la distorsion non linéaire introduite par les diodes électroluminescentes (LED), mais le rapport signale sur bruit (SNR) augmente ( électrique et optique à la fois) en raison de la structure en couches qui est plus élevée que le LACO-OFDM conventionnelle
The radio-frequency (RF) spectrum is dwindling due to an increase in the demand of wireless applications. Hence, there is substantial demand of alternative spectrum regions for communications to recline the conventional RF spectrum. In this context, optical wireless communications (OWC) is explored as a likely candidate to supplement the RF communications. The current work focuses on impairment mitigation techniques and energy-efficient modulation approaches for OWC. Firstly, the peak-to-average power ratio (PAPR) for optical-orthogonal frequency division multiplexing (O-OFDM) is studied and two decision-directed PAPR reduction techniques are presented. The complexity of these methods is comparatively lower than other PAPR reduction methods, whilst, their performance is likewise analogous with other alternatives. Secondly, an optical-single-carrier frequency division multiple access (O-SCFDMA) approach, referred to as Hermitain symmetry free O-SCFDMA (HSFO-SCFDMA) is proposed, that averts Hermiatian symmetry which is normally expected for other O-OFDM and O-SCFDMA approaches. The simulation results affirm that HSFO-SCFDMA is more efficient than any other O-SCFDMA approach for OWC and manifests the lowest PAPR among the other alternatives. Thirdly, the performance of precoding is analyzed for layered asymmetrically clipped O-OFDM (LACO-OFDM). Two types of precoding are employed, i.e., Fourier transform precoding and Hartley transform precoding. It is established that Hartley transform precoded LACO-OFDM exhibits the lowest PAPR and is less vulnerable to non-linear distortion introduced by the light emitting diodes (LEDs), howbeit, the signal-to-noise ratio (SNR) increase (both electrical and optical) owing to the layered structure is higher than conventional LACO-OFDM

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Hoang, Thai Bang. "Infrared and visible wireless optical technology for body sensor connectivity." Thesis, Limoges, 2019. http://www.theses.fr/2019LIMO0027/document.

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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

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Yu, Zhenhua. "Optical wireless communications with optical power and dynamic range constraints." Diss., Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51784.

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Along with the rapidly increasing demand for wireless data while more and more crowded radio frequency (RF) spectrum, optical wireless communications (OWC) become a promising candidate to complement conventional RF communications, especially for indoor short and medium range data transmissions. Orthogonal frequency division multiplexing (OFDM) is considered for OWC due to its ability to boost data rates. However, the average emitted optical power and dynamic range of driving signals of LEDs are two major constraints in OWC. OFDM waveforms exhibits high upper and lower peak-to-average power ratios (PAPRs), which make OFDM signals optical power inefficient and easy to violate the dynamic range of LEDs, resulting clipping and nonlinear distortions. In this dissertation, we analyze and design optical power and dynamic range constrained OWC systems, for which OFDM is our major subject. We first derive distributions of upper PAPR and lower PAPR of OWC-OFDM signals. Then we analyze the clipped OFDM signals in term of error vector magnitude (EVM), signal-to-distortion ratio (SDR), and achievable data rates under both optical power and dynamic range constraints. The next part of this dissertation is the OFDM system design for visible light communications (VLC) considering illumination requirement. We investigate the illumination-to-communication efficiency (ICE) in VLC-OFDM, and design the brightness control and flickering mitigation schemes for VLC-OFDM. In the end, to reduce the complexity of driving circuits of LEDs , we propose using delta-sigma modulators in VLC-OFDM systems to convert continuous magnitude OFDM symbols into two-level LED driver signals without loss of the communication theory advantages of OFDM.

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Antolini, Alessio. "Valutazione delle prestazioni di reti ad accesso multiplo basate su visible light communication." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/11060/.

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Nella società odierna, le telecomunicazioni costituiscono un’esigenza fondamentale della vita quotidiana. Difatti, il mercato della ICT (Information and Communications Technology) è in costante espansione, e viene accompagnato da un rapido sviluppo di nuove tecnologie. In particolare, si assiste a un sempre più rilevante ruolo svolto dalle comunicazioni ottiche, ovvero sfruttanti la luce: in questo contesto, il quale comprende diversi rami ingegneristici, si stanno progressivamente affermando nuove forme di comunicazione basate sulla luce visibile, la cosiddetta Visible Light Communication (VLC). Con questa Tesi ci si propone di implementare con Simulink e stateflow di Matlab il livello MAC (Medium Access Control), basato sullo standard IEEE 802.15.7 per le VLC e valutarne le prestazioni. Prescinde da questa Tesi la parte di implementazione su scheda stessa che è lasciata per sviluppi futuri. Nel capitolo uno si introducono le VLC e si discutono i principali scenari attuali dove possono diffondersi. Nel capitolo 2, si mostrano le principali linee guida afferenti agli standard che sono risultate necessarie per sviluppare lo strato MAC. Nei capitoli 3 e 4 si mostra come il layer sviluppato possa essere utilizzato in due principali situazioni: nel capitolo 3 è descritta la realizzazione di una comunicazione punto-punto, ovvero con un trasmettitore e un ricevitore; nel capitolo 4 è descritta l’implementazione di una rete di nodi, ambito in cui il livello MAC risulta indispensabile. Per ognuna delle situazioni si illustrano scelte e caratteristiche dei sistemi simulati e i risultati ottenuti, cercando di coprire diverse eventualità che intercorrono, più in generale, nella gestione e implementazione di sistemi di telecomunicazione wireless.

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Li, Ketong. "LED CommunicationFor Short Range Wireless." Thesis, KTH, Skolan för informations- och kommunikationsteknik (ICT), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-209172.

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With the huge development of semiconductor lighting technologies, the light emitting diodes (LEDs) are promising technology that eventually replacing traditional incandescent and fluorescent lamps for their high power efficiency, environmental friendliness and long predicted product lifetime. Besides lighting, the advent of high-brightness, fast-switching LED lamps has facilitated LED Communication as a new form of Optical Wireless Communication (OWC) in the visible light spectrum. This thesis study model characteristics of LED communication for indoor optical environment. Based on Matlab and SPICE, an electrical and optical LED communication model is proposed to describe light power's conversion and propagation. In details, our models include (1) models for V-I characteristics and fro small signal behavior, (2) electro-electrical conversion and emitting, (3) optical channel with path loss and noise, (4) receiving model. Moreover, a test and measurement platform for LED communication has been established to validate the proposed model. A case of study on light power distribution within 30cmX30cmX10cm in line-of-sight was implemented by measuring for comparing the theoretical simulation and experimental results. Depending on our model and the case of study, we carried out an inspection of the LED communication performance using On-Off Keying (OOK) signals and a 500 kbps transmission data rate under 10e-3 BER was achieved in our lab.

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Sekkiou, Imene. "Design of communication systems based on broadband sources for fiber and free space optical links." Doctoral thesis, Universitat Politècnica de València, 2021. http://hdl.handle.net/10251/172542.

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[ES] Las comunicaciones ópticas inalámbricas (OWC) constituyen una tecnología muy prometedora para el desarrollo de futuras comunicaciones inalámbricas. De hecho, ha despertado un interés creciente entre los investigadores y varias empresas de todo el mundo trabajan actualmente en el desarrollo de redes inalámbricas de muy alta velocidad. Las comunidades científica e industrial consideran la OWC como una tecnología complementaria en sus diversas formas: comunicaciones ópticas en el espacio libre (FSO), comunicaciones de luz visible (VLC) o fidelidad de la luz (Li-Fi). El espectro óptico ha sido considerado durante muchos años como una gran oportunidad para las comunicaciones inalámbricas, especialmente debido a la saturación del espectro de radiofrecuencia (RF). Esta disertación trata del uso de fuentes de banda ancha en sistemas de transmisión de luz visible (VLC), así como en sistemas de transmisión en el espectro infrarrojo por fibra óptica. En el trabajo de investigación realizado se pueden distinguir tres partes: En la primera parte, se considera el estudio y la simulación de componentes de Diodos Emisores de Luz (LED) con el software WIEN2k centrándose en las propiedades ópticas y eléctricas de los elementos II-VI. La segunda parte trata del diseño, la implementación y las pruebas de diferentes prototipos de comunicación VLC para la transmisión analógica y digital en modo simplex y semidúplex. Hemos demostrado un sistema OWC empleando una fuente de banda ancha (LED) para la transmisión no sólo de datos, sino también para la transmisión inalámbrica de energía. Además, se aborda el problema de la sincronización y la detección del nivel "1" o "0" de un bit en los sistemas de comunicación inalámbrica óptica implementados que surge como consecuencia de la atenuación de la luz a lo largo de la distancia y al problema de la pérdida de línea de visión (NLOS) entre el emisor y el receptor. Para hacer frente a este problema, se ha proporcionado un protocolo de comunicación que garantiza la transmisión fiable de datos digitales con un algoritmo de detección de nivel de bits adaptativo y se ha demostrado su eficacia mediante la transmisión de textos e imágenes. Además, esta tesis aporta una solución para la implementación de transmisores multiplexados en redes con división de longitud de onda (WDM) para formatos de modulación con multiplexación por división de frecuencia ortogonal (OFDM) basados en el uso de fuentes de banda ancha en el espectro infrarrojo para redes de fibra bidireccionales centralizadas. A pesar de las limitaciones impuestas por la dispersión cromática en el uso de este tipo de fuentes ópticas, la inclusión de ciertas estructuras antes de la detección permite la transmisión de señales OFDM en enlaces ópticos. En este trabajo se ha demostrado experimentalmente la reutilización de portadoras, la asignación dinámica de ancho de banda y la transmisión de señales OFDM multibanda mediante el uso de fuentes ópticas de banda ancha en redes WDM. Los principales resultados obtenidos en cada parte de esta tesis doctoral muestran los procedimientos de estudio, la eficacia de las soluciones propuestas y las limitaciones encontradas.
[CA] Les comunicacions òptiques sense fils (OWC) constitueixen una tecnologia molt prometedora per al desenvolupament de futures comunicacions sense fils. De fet, ha despertat un interés creixent entre els investigadors i diverses empreses de tot el món treballen actualment en el desenvolupament de xarxes sense fils de molt alta velocitat. Les comunitats científica i industrial consideren la OWC com una tecnologia complementària en les seues diverses formes: comunicacions òptiques en l'espai lliure (FSO), comunicacions de llum visible (VLC) o fidelitat de la llum (Li-Fi). L'espectre òptic ha sigut considerat durant molts anys com una gran oportunitat per a les comunicacions sense fils, especialment a causa de la saturació de l'espectre de radiofreqüència (RF). Aquesta dissertació tracta de l'ús de fonts de banda ampla en sistemes de transmissió de llum visible (VLC), així com en sistemes de transmissió en l'espectre infraroig per fibra òptica. En el treball de recerca realitzat es poden distingir tres parts: ¿ En la primera part, es considera l'estudi i la simulació de components de Díodes Emissors de Llum (LED) amb el software WIEN2k centrant-se en les propietats òptiques i elèctriques dels elements II-VI. ¿ La segona part tracta del disseny, la implementació i les proves de diferents prototips de comunicació VLC per a la transmissió analògica i digital de manera simplex i semidúplex. Hem demostrat un sistema OWC emprant una font de banda ampla (LED) per a la transmissió no sols de dades, sinó també per a la transmissió sense fil d'energia. A més, s'aborda el problema de la sincronització i la detecció del nivell "1" o "0" d'un bit en els sistemes de comunicació sense fil òptica implementats, que sorgeix a conseqüència de l'atenuació de la llum al llarg de la distància i al problema de la pèrdua de línia de visió (NLOS) entre l'emissor i el receptor. Per a fer front a aquest problema, s'ha proporcionat un protocol de comunicació que garanteix la transmissió fiable de dades digitals amb un algorisme de detecció de nivell de bits adaptatiu i s'ha demostrat la seua eficàcia mitjançant la transmissió de textos i imatges. ¿ A més, aquesta tesi aporta una solució per a la implementació de transmissors multiplexats en xarxes amb divisió de longitud d'ona (WDM) per a formats de modulació amb multiplexació per divisió de freqüència ortogonal (OFDM) basats en l'ús de fonts de banda ampla en l'espectre infraroig per a xarxes de fibra bidireccionals centralitzades. Malgrat les limitacions imposades per la dispersió cromàtica en l'ús d'aquest tipus de fonts òptiques, la inclusió d'unes certes estructures abans de la detecció permet la transmissió de senyals OFDM en enllaços òptics. En aquest treball s'ha demostrat experimentalment la reutilització de portadores, l'assignació dinàmica d'amplada de banda i la transmissió de senyals OFDM multibanda mitjançant l'ús de fonts òptiques de banda ampla en xarxes WDM. Els principals resultats obtinguts en cada part d'aquesta tesi doctoral mostren els procediments d'estudi, l'eficàcia de les solucions proposades i les limitacions trobades.
[EN] Optical wireless communication (OWC) is a very promising technology for future wireless communications developments. It has attracted increasing interest from researchers and several companies around the world are currently working on the development of very high-speed wireless networks. The scientific and industrial communities believe that OWC will be a complementary technology in its various forms: Free Space Optical communications (FSO), Visible Light Communications (VLC), Light Fidelity (Li-Fi). In fact, the optical spectrum has been considered for many years as a great opportunity for wireless communications especially due to the saturation of the radio frequency (RF) spectrum. This dissertation deals with the use of broadband sources in visible light transmission systems (VLC) as well as fiber optic systems. To carry out the research, three parts can be distinguished: In the first part, we consider the study and simulation of Light Emitting Diode (LED) components with the WIEN2k software by focusing on the optical and electrical properties of elements II-VI. The second part deals with the design, implementation and testing of different VLC communication prototypes for analog and digital transmission in simplex and half-duplex mode. We have demonstrated that an OWC system using a broadband source (i.e. an LED) can be used not only for data transmission, but also for wireless power transmission. Moreover, the synchronization problem and the detection of level "1" or "0" of a bit often arise in the optical wireless communication systems. This is a result of the attenuation nature of the light over the distance and the problem of Non Line-Of-Sight (NLOS) between the emitter and the receiver. To deal with this problem, a communication protocol ensuring reliable digital data transmission with an adaptive bit level detection algorithm has been provided and its effectiveness has been demonstrated by the transmission of texts and images. In addition, this thesis provides a solution for the implementation of wavelength division multiplexed - orthogonal frequency division multiplexed (WDM-OFDM) transmitters based on the use of broadband sources in the infrared spectrum for centralized bidirectional fiber networks. Despite the chromatic dispersion that avoids the use of this type of optical sources, the inclusion of certain structures before detection allows the transmission of OFDM signals in optical links. Carrier reuse, dynamic bandwidth allocation and multiband OFDM signals transmission will be experimentally demonstrated by using optical broadband sources in WDM networks. The main results obtained during this thesis work demonstrate the study procedures, for each part, the effectiveness of the proposed solutions as well as the constraints encountered.
Sekkiou, I. (2021). Design of communication systems based on broadband sources for fiber and free space optical links [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/172542
TESIS

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Xi, Xiaojun. "New Stochastic Geometry Approaches to the Modeling and Analysis of Low and High Frequency Wireless Communication Networks." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS556.

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Dans cette thèse, nous avons développé de nouveaux cadres d'analyse pour analyser et optimiser les futurs réseaux cellulaires à l'aide de la géométrie stochastique et des processus ponctuels. Cette thèse fournit quatre contributions techniques principales.Nous analysons d’abord les réseaux émergents capables de communiquer en utilisant la lumière plutôt que les ondes radio. Dans ce contexte, nous proposons un cadre analytique innovant qui nous permet d’estimer la probabilité de couverture et le débit moyen des réseaux distribués dans l’espace, qui sont utilisés pour mieux comprendre l’optimisation du système.Deuxièmement, nous proposons une méthodologie innovante pour modéliser des réseaux cellulaires spatialement corrélés en utilisant des processus ponctuels non homogènes. L'approche proposée est testée par rapport au déploiement pratique de réseaux cellulaires et s'est révélée pratique et précise. Il est appliqué à l'analyse des réseaux de communication à lumière visible et l'impact de la corrélation spatiale est étudié.Troisièmement, nous abordons le problème ouvert de la modélisation de réseaux cellulaires MIMO massifs. Nous étudions les réseaux cellulaires montants et descendants et proposons de nouvelles limites supérieures et inférieures pour l'efficacité spectrale moyenne, ce qui nous permet d'identifier le nombre optimal d'utilisateurs à desservir dans chaque cellule du réseau et l'impact de plusieurs paramètres clés du système.Quatrièmement, nous présentons et analysons les performances d'un nouvel algorithme de planification prenant en compte les interférences pour une application sur la liaison montante des réseaux cellulaires. L’approche proposée consiste à assourdir certains utilisateurs afin de réduire le niveau d’interférence. La performance réalisable et l'équité utilisateur de l'approche proposée sont discutées et quantifiées analytiquement
In this thesis, we have developed new analytical frameworks for analyzing and optimizing future cellular networks with the aid of stochastic geometry and point processes. This thesis provides four main technical contributions.First, we analyze emerging networks that can communicate by using light instead of radio waves. In this context, we propose an innovative analytical framework that allows us to estimate the coverage probability and the average rate of spatially distributed networks, which are used to gain insight for system optimization.Second, we propose an innovative methodology for modeling spatially correlated cellular networks by using inhomogeneous point processes. The proposed approach is tested against practical deployment of cellular networks and found to be tractable and accurate. It is applied to the analysis of visible light communication networks, and the impact of spatial correlation is studied.Third, we tackle the open problem of modeling Massive MIMO cellular networks. We study uplink and downlink cellular networks and propose new upper and lower bounds for the average spectral efficiency, which allow us to identify the optimal number of user to serve in each cell of the network and the impact of several key system parameters.Fourth, we introduce and analyze the performance of a new interference-aware scheduling algorithm for application to the uplink of cellular networks. The proposed approach is based on muting some users in order to reduce the level of interference. The achievable performance and the user-fairness of the proposed approach are discussed and quantified analytically

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Gao, Shuo. "Performance Study for Indoor Visible Light Communication Systems." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/23986.

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The field of Optical Wireless Communications (OWC) has seen rapid development during the recent years. This growing popularity is due to several characteristics of considerable importance to consumer electronics products, such as large bandwidth that is also not having spectrum regulations imposed, low cost, and license free operation. As a branch of OWC, visible light communication (VLC) systems have their own unique advantages, with several new technologies, products and patents having been developed during since the end of last century. In this research, a VLC system for indoor application is proposed. In this work, we focus on reducing cost, and for that, we had to make appropriate selection of system’s components, e.g. modulation, coding, filtering. Our objective was to achieve acceptable bit error rate (BER) performance for indoor use, with a low cost system. Through our research we met this objective. Our designs were evaluated through computer simulations. The acquired results proved the suitability of the proposed schemes and the performance’s degree of dependency on several parameters such as distance, incidence angle and irradiance angle. A software tool was created allowing easy assessment of the communication system. It is using a user friendly GUI through which the user enters the system’s parameters and the system outputs the corresponding BER value.

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Maré, Renata Maria. "Proposta e avaliação de um sistema complementar de posicionamento baseado em comunicação por luz visível aplicado a sistemas inteligentes de transporte." Universidade de São Paulo, 2017. http://www.teses.usp.br/teses/disponiveis/3/3141/tde-26022018-144410/.

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O uso crescente de dispositivos móveis e o advento da Internet das Coisas têm demandado esforços para prover alternativas de comunicação sem fio. A utilização de sistemas óticos para a transmissão de dados apresenta-se como uma tecnologia promissora e complementar à comunicação por radiofrequência, especialmente devido aos desenvolvimentos consideráveis na tecnologia de iluminação por estado sólido e sua adoção em vários domínios. Os diodos de emissão de luz podem ser utilizados na promoção de comunicação por luz visível em ambientes internos e externos. Nos ambientes externos há inúmeras oportunidades a serem exploradas no que concerne aos Sistemas Inteligentes de Transporte, visto que os diodos de emissão de luz têm sido utilizados em luminárias públicas, semáforos e veículos. Esta pesquisa propôs o desenvolvimento e a avaliação de um sistema de comunicação por luz visível entre elementos da infraestrutura urbana e veículos, mais especificamente, luminárias públicas baseadas em diodos de emissão de luz e o modal de transporte público representado pelos ônibus que circulam em faixas exclusivas. A metodologia foi composta por simulação computacional e pela construção de um protótipo para auxiliar na validação das soluções propostas. O sistema complementar de comunicação sem fio por meio da luz proposto fornece pode fornecer subsídios à determinação do posicionamento preciso dos ônibus, suprindo as deficiências do sistema GPS em locais menos favoráveis à recepção de seus sinais em uma cidade. Essas informações auxiliam os usuários e os gestores do transporte público, atendendo alguns domínios de serviço em Sistemas Inteligentes de Transporte, de acordo com a norma ISO 14813. Os resultados obtidos nos testes com o protótipo, bem como, aqueles observados na simulação, comprovaram a viabilidade do sistema proposto, com o estabelecimento da comunicação entre luminária e ônibus, inclusive quando trafegando a 60 km/h.
The increasing use of mobile devices and the advent of the Internet of Things have called for efforts to provide alternatives for wireless communication. The use of optical systems for data transmission is a promising and complementary technology to radiofrequency communication, especially due to the considerable developments in solidstate lighting technology and its adoption in various domains. Light-emitting diodes can be used to promote visible light communication in indoor and outdoor environments. In outdoor environments there are numerous opportunities to be explored with regard to Intelligent Transport Systems, since light-emitting diodes have been used in public luminaires, traffic lights and vehicles. This research proposed the development and evaluation of a visible light communication system between elements of the urban infrastructure and vehicles, more specifically, public luminaires based on light-emitting diodes and the mode of public transport represented by buses that circulate in exclusive lanes. The methodology was composed by computational simulation and the construction of a prototype, to assist in the validation of the proposed solutions. The proposed complementary wireless communication system through light provides subsidies to determine the precise positioning of buses, supplying deficiencies of the GPS system in places less favorable to the reception of their signals in a city. This information helps the users and the managers of the public transport, attending some service domains in Intelligent Transport Systems, according to the ISO 14813 standard. The results obtained in the tests with the prototype, as well as those observed in the simulation, proved the feasibility of the proposed system, with the establishment of communication between luminaire and bus, even when traveling at 60 km/h.

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Guo, Shangyuan. "Device Pairing Using Visible Light Communications." Thesis, Mittuniversitetet, Avdelningen för informations- och kommunikationssystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-21601.

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Device authentication in ad hoc networks is becoming more and more important. Nowadays, there are many interesting applications which communicate via the short-rang wireless communication channel (such as Bluetooth or WiFi). In the communication, a great deal of sensitive information is required to be transmitted. Therefore, device authentication is significant. In order to build a secure authentication mechanism, protocols are proposed using human control visual channels. However, this method brings many challenges, the main one being the burden placed on humans. Therefore, in this thesis, these protocols are optimized using visible light communication techniques, which significantly reduce the work faced by humans.

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Boubezari, Rayana. "Smartphone to smartphone visible light communications." Thesis, Northumbria University, 2018. http://nrl.northumbria.ac.uk/36194/.

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Visible light communications (VLC) is an emerging technology of optical wireless communications, which has been in the research spotlight recently, thanks to the remarkable development of light emitting diodes. Furthermore, optical camera communications, a timely VLC topic, has earned a great share of researchers'interest in the last few years, given the wide availability of digital cameras. This thesis proposes to merge two separate technologies: image processing and VLC, to create a camera-based VLC system. Moreover, the work presented in this thesis describes a short-range mobile-to-mobile communication link, where the transmitter and the receiver are the smartphone’s screen and camera, respectively. In addition, the data is encoded into images and subsequently beamed out of the transmitter's screen, and the receiver's camera captures consecutive frames containing the transmitter's screen to extract the data. The proposed system offers inherent advantages in terms of portability and simplicity of implementation as it uses available screens and smartphone cameras. Additionally, the system is software-based and does not require any hardware modifications on the devices, thus making a high potential for millions of consumers. The system proposed in this thesis is designed for mobile users. Therefore, high performance in dynamic environments is required. Moreover, combining image processing and VLC for smartphone to smartphone VLC is an innovative topic and very few works reported similar communication links. As such, it is imperative to investigate the impact of computer vision challenges on the system's performance, such as the detection of the transmitter by the receiver's camera, in dynamic conditions. Consequently, this work focuses on the development of an effective algorithm to capture frames containing the transmitter as well as other objects in the background, detect the transmitter contained in the received frames, and then finally extract the originally transmitted information. The end-to-end system is fully implemented on a mobile platform and a range of experiments are carried out in order to evaluate the system's performance. It is proved that the system is able to achieve very high success rate that reaches 98% data recovery of transmitted images under test conditions, demonstrating a practical link with a possible 100 kbps data transmission capability.

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Ferreira, Ricardo Xavier da Graça. "Gallium nitride light-emitting diode enabled visible light communications." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=28805.

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This thesis focuses on the development, measurement and application of novel micrometre-sized light emitting diodes (micro-LEDs) based on Gallium Nitride (GaN) for visible light communications (VLC) in both free-space and guided wave configurations. The goal is to set benchmarks for LED-based wireless optical communications. An overview of the field integrating research, industry and standards is presented. A top-down approach is taken with application requirements driving development of new micro-LEDs with simultaneously increased optical power and modulation bandwidth. This was achieved by mitigating two limitations, namely current crowding and mutual device heating. Two novel techniques were developed to access pixel performance: spatially-resolved mapping of modulation bandwidth and spectral characteristics, and thermal imaging. On this basis, broad-area LEDs were used to understand the independent benefits, providing insight for the design of novel micro-LEDs. Circular segmented micro-LEDs emitting at 450nm achieved modulation bandwidths in excess of 800MHz, the highest reported for LEDs, while maintaining optical power above 2mW. In data transmission using systems with 1.8GHz bandwidth,the devices achieved 8Gbps in free-space and guided-wave operation at wavelengths of 400nm, 450nm and 520nm. Ring and half-ring micro-LEDs introduced here have shown modulation bandwidths that scale with the increase of active area and consequently optical power. Bandwidths in excess of of 600MHz were achieved at optical powers over 5mW. In data transmission using a system limited to 1GHz bandwidth, these devices achieved 7Gbps in free-space operation.

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Rae, Katherine Jeanne. "Micro-transfer printing for visible light communications applications." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=29591.

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The work presented in this thesis focuses on the transfer printing of InGaN-based blue emitting light emitting diodes (LEDs) onto various non-native substrates for visible light communications applications. The controlled mechanical integration of photonic structures onto non-native substrates using micro-transfer printing (μTP) techniquesis paving the way to high-performance, heterogeneous and multi-functional integrated photonic devices. 2μm-thick 100μm x 100μm LEDs are transfer printed onto these non-native, capability enhancing, substrates using a modified nano-lithography system. Blue-emitting μLEDs in this thin, transfer printable format, were integrated into an array of green-emitting μLEDs to create a dual-colour μLED on a single chip. This chip is then electrically andoptically characterised and demonstrated to examine its potential for data communications applications. The same blue-emitting μLEDs are also integrated with colloidal quantum dot (CQD) colour-converting structures. This yields integrated red, green and orange colour-converting structures all pumped by the blue-emitting transfer printed μLEDs. The μTP technique is finally used to fabricate an integrated optical transceiver device.

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Alsolami, Ibrahim. "Visible light communications with single-photon avalanche diodes." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:744eeb47-8bb6-4776-8b8f-f7b6374d89bd.

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This thesis explores the use of single-photon avalanche diodes (SPADs) for visible light communications (VLC). The high sensitivity of SPADs can potentially enhance the performance of VLC receivers. However, a SPAD-based system has challenges that need to be addressed before it can be considered as a viable option for VLC. The first challenge is the susceptibility of SPAD-based receivers to variations in ambient light. The high sensitivity of SPADs is advantageous for signal detection, but also makes SPADs vulnerable to variations in ambient light. In this thesis, the performance of a SPAD-based receiver is investigated under changing lighting conditions. Analytical expressions to quantify performance are derived, and an experiment is conducted to gain further understanding of system performance. It is shown that a SPAD-based receiver is highly sensitive to illumination changes when on-off keying (OOK) is employed, and that pulse-position modulation (PPM) is a preferred modulation scheme as it is more robust. The second challenge is broadcasting to SPAD-based receivers with different capabilities. A traditional broadcasting scheme is time-sharing, whereby a transmitter sends data to receivers in an alternating manner. Broadcasting to SPAD-based receivers is challenging as receivers may have diverse capabilities. In this thesis, a new multiresolution modulation scheme is proposed, which can potentially improve system performance over the traditional timesharing approach. The performance of the proposed scheme is analyzed, and a proof-of-concept experiment is performed to demonstrate its viability.

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Melo, Santos João Miguel. "Hybrid GaN-based optoelectronics for visible light communications." Thesis, University of Strathclyde, 2017. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27924.

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Development of light-emitting diode technology is driven mainly by the need for efficient solid-state lighting, but it is also creating opportunities for new applications such as visible light communications (VLC). Here, the solid-state visible light sources are used to transmit data with the added requirement of a short excited-state lifetime so that sources can be modulated at high speed. This research focuses on hybrid optical sources for visible light communications with an emphasis on novel formats of colour-converters for multi-wavelength photoluminescence as well as white-light generation. Such converters include red and green colloidal quantum dots, the organic semiconductor BBEHPV andII-VI / III-V epitaxial structures. Solution-processable and environmentally stable polymeric films based on red and green colloidal quantum dots are demonstrated. Modulation bandwidth up to 24 MHz, photoluminescence quantum yields up to 61% and peak emission tunability across the visible spectrum makes these materials interesting as colour-converters for VLC. Free-space data transmission was demonstrated in this case with data rates up to 400 Mbit/s and 500 Mbit/s using 2-PAM modulation scheme for green and red quantum dots, respectively. Hybrid sources consisting of 450nm InGaN LEDs with capillary-bonded micron-thick ZnCdSe/ZnCdMgSe multi-quantum-well colour-converting membranes with peak emission at 540 nm are reported. After processing, the membrane was capillary bonded onto the sapphire side of the μLED resulting in a maximum converted average power of 37 μW. The -3dB optical modulation bandwidth of the bare LED, hybrid device and II-VI were 79 MHz, 51 MHz and 145 MHz, respectively. Visible light communication using both InGaN LEDs and a InGaN laser diode, down-converted by a red-emitting AlInGaP multi-quantum-well nanomembrane are also reported. Similarly to the previous devices, the AlInGaP nanomembrane was bonded onto the μLED array. For the down-converted laser diode approach, the nanomembrane can be sandwiched between a sapphire lens and optionally onto a distributed feedback reflector. The down-converter structure is remotely excited by the laser diode. Data transmission up to 870 Mb/s using M-PAM andOFDM modulation schemes is demonstrated for the μLED integrated nanomembrane. ODFM transmission at 1.2Gb/s is achieved for the laser diode pumped sample.

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Calisti, Alex. "Simulation of visible light communications in vehicular networks." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amslaurea.unibo.it/7597/.

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The rapid development in the field of lighting and illumination allows low energy consumption and a rapid growth in the use, and development of solid-state sources. As the efficiency of these devices increases and their cost decreases there are predictions that they will become the dominant source for general illumination in the short term. The objective of this thesis is to study, through extensive simulations in realistic scenarios, the feasibility and exploitation of visible light communication (VLC) for vehicular ad hoc networks (VANETs) applications. A brief introduction will introduce the new scenario of smart cities in which visible light communication will become a fundamental enabling technology for the future communication systems. Specifically, this thesis focus on the acquisition of several, frequent, and small data packets from vehicles, exploited as sensors of the environment. The use of vehicles as sensors is a new paradigm to enable an efficient environment monitoring and an improved traffic management. In most cases, the sensed information must be collected at a remote control centre and one of the most challenging aspects is the uplink acquisition of data from vehicles. My thesis discusses the opportunity to take advantage of short range vehicle-to-vehicle (V2V) and vehicle-to-roadside (V2R) communications to offload the cellular networks. More specifically, it discusses the system design and assesses the obtainable cellular resource saving, by considering the impact of the percentage of vehicles equipped with short range communication devices, of the number of deployed road side units, and of the adopted routing protocol. When short range communications are concerned, WAVE/IEEE 802.11p is considered as standard for VANETs. Its use together with VLC will be considered in urban vehicular scenarios to let vehicles communicate without involving the cellular network. The study is conducted by simulation, considering both a simulation platform (SHINE, simulation platform for heterogeneous interworking networks) developed within the Wireless communication Laboratory (Wilab) of the University of Bologna and CNR, and network simulator (NS3). trying to realistically represent all the wireless network communication aspects. Specifically, simulation of vehicular system was performed and introduced in ns-3, creating a new module for the simulator. This module will help to study VLC applications in VANETs. Final observations would enhance and encourage potential research in the area and optimize performance of VLC systems applications in the future.

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Nagabhairava, Nitish. "Implementation of Visible Light communications For Indoor Applications." Thesis, Blekinge Tekniska Högskola, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-17292.

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In recent years there is growing research in optical wireless communication. This growing popularity isdue to several characteristics like such as large bandwidth that is also not having spectrum regulationsimposed, low cost and license-free operation. Since visible light communications (VLC) is a branch ofoptical wave communications (OWC), it is used for replacing RF communications. The other primaryreason for the use of visible light communications [1], because it uses 400 THz of unlicensed secure andradio free media for wireless communications which are 1000 times more than that of radiocommunications. For transmission of VLC, we use LED as light sources.Due to the high efficiency and less power consumption LED have replaced the oldfluorescence lamps, LED provide the dual functionality they can provide lighting and can providecommunications (transfer of data) just like Wi-Fi. In LED the on and off state is so fast that the humaneye can’t even perceive it. The on and off state can be taken as 1 and 0’s and through this we can transferthe data, this type of modulation is called OOK keying modulation it is used for single carrier modulationscheme. We can interpret the data that is received from the transceiver side with the help of thephotodiode at the receiver’s side. This communication technique can provide better security as there is nointerference, as light can't penetrate through walls leaving the data transfer to the room itself. ThroughVLC we can offer better security to data over RF communications.In this thesis, the implementation process has been performed in MATLABsimulations where we analyse different modulation techniques and parameters. We design a room withdimensions as 5m*5m*3m as length, width and height. We take multiple LED’s at the top and determinethe illumination parameters in the room due to the light emitted from the LED. The receiver is located ona desk and we calculate the number of data rates received at the receiver. The modulation techniques usedin this thesis are OOK keying modulation. We estimate the data rates in two methodologies directdetection (Line of sight) and also, we take reflections from the wall into consideration (Non-line of sight).The effect of data rates due to illumination and distance are also determined. In this thesis we transfer dataover the transmitter and receive the information at the receiver for obtained information the calculation of bit error rate (BER) is performed for both single LED and multiple LED array. The analysis is performed between the performance metrics of a single LED’s and multiple LED’s arrays to determine better-LEDarray.Key Words: OOK modulation scheme, MATLAB-Simulation, Light Emitting Diodes .

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Azhar, Ahmad Helmi. "Visible light commuinications using optical OFDM." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:9e4c363b-27ba-4e47-8660-39f4e0a077f8.

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This thesis presents an investigation into designs and developments of indoor visible light communication (VLC) systems using orthogonal frequency division multiplexing (OFDM) schemes. The novel contribution of this thesis is a development of a visible light communication system that incorporates OFDM and imaging-diversity multiple-input multiple-output (MIMO) techniques, which allows robust transmissions on multiple channels at high data rates. The characteristics of VLC systems are presented, one of which is VLC communications channel exhibits high Signal-to-Noise Ratio (SNR). The major constraint however, is the low modulation bandwidth of typical high power white LED sources. The performance of OFDM as a modulation scheme is investigated. OFDM offers the possibility for bit and power loading to increase bandwidth efficiency, as well as a straightforward equalisation in time and frequency domains to compensate the low pass frequency response of the LED. This allows transmission rates of up to ~310Mbps at a BER of 2x10-3 on a single-channel link using 16- QAM DCO-OFDM. Further increase in data rates for this transmission is constrained by the available signal power due to a dynamic range limitation at the receiver. An increase in signal power will results in the OFDM waveform to be clipped, which incurs a clipping noise. MIMO systems offer a linear capacity gain to a number of transmission channels in an ideal configuration. These systems mitigate the dynamic range limitation, as power is divided between multiple channels. The performance of a MIMO transmission system is investigated under the same dynamic range constraint. A 4-channel MIMO transmitter is built using four sets of transmitter components of the single-channel link. An imaging system is used to separate the received optical power onto multiple detectors, and MIMO processing relaxes the requirements for precise mechanical alignments. The experiment has shown that the imaging MIMO system further improves data rates and transmissions of up to ~1.1Gigabit/s at a BER of 2x10-3 are achieved. To the best of the author’s knowledge, this is the highest reported for an indoor VLC MIMO-OFDM transmission. Also presented is an analysis of MIMO system scalability to provide room-wide coverage. Finally, this thesis presents an extended analysis of several other optical OFDM approaches, and concludes with recommendations of future work to increase the data rates of indoor VLC systems.

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Ain-Ul-Aisha, FNU. "Fundamental Limits of Poisson Channels in Visible Light Communications." Digital WPI, 2017. https://digitalcommons.wpi.edu/etd-dissertations/475.

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Visible Light Communications (VLC) has recently emerged as a viable solution for solving the spectrum shortage problem. The idea is to use artificial light sources as medium to communicate with portable devices. In particular, the light sources can be switched on and off with a very high-frequency corresponding to 1s and 0s of digital communication. The high-frequency on-off switching can be detected by electronic devices but not the human eyes, and hence will not affect the light sources' illumination functions. In VLC, if a receiver is equipped with photodiodes that count the number of arriving photons, the channels can be modeled as Poisson channels. Unlike Gaussian channels that are suitable for radio spectrum and have been intensively investigated, Poisson channels are more challenging and are not that well understood. The goal of this thesis is to characterize the fundamental limits of various Poisson channels that models different scenarios in VLC. We first focus on single user Poisson fading channels with time-varying background lights. Our model is motivated by indoor optical wireless communication systems, in which the noise level is affected by the strength of the background light. We study both the single-input single-output (SISO) and the multiple-input and multiple-output (MIMO) channels. For each channel, we consider scenarios with and without delay constraints. For the case without a delay constraint, we characterize the optimal power allocation scheme that maximizes the ergodic capacity. For the case with a strict delay constraint, we characterize the optimal power allocation scheme that minimizes the outage probability. We then extend the study to the multi-user Poisson channels and analyze the sum-rate capacity of two-user Poisson multiple access channels (MAC). We first characterize the sum-rate capacity of the non-symmetric Poisson MAC when each transmitter has a single antenna. We show that, for certain channel parameters, it is optimal for a single-user to transmit to achieve the sum-rate capacity. This is in sharp contrast to the Gaussian MAC, in which both users must transmit, either simultaneously or at different times, in order to achieve the sum-rate capacity. We then characterize the sum-rate capacity of the Poisson MAC with multiple antennas at each transmitter. By converting a non-convex optimization problem with a large number of variables into a non-convex optimization problem with two variables, we show that the sum-rate capacity of the Poisson MAC with multiple transmit antennas is equivalent to a properly constructed Poisson MAC with a single antenna at each transmitter. We further analyze the sum-rate capacity of two-user Poisson MIMO multiple-access channels (MAC), when both the transmitters and the receiver are equipped with multiple antennas. We first characterize the sum-rate capacity of the Poisson MAC when each transmitter has a single antenna and the receiver has multiple antennas. We show that similar to Poisson MISO-MAC channels, for certain channel parameters, it is optimal for a single user to transmit to achieve the sum-rate capacity, and for certain channel parameters, it is optimal for both users to transmit. We then characterize the sum-rate capacity of the channel where both the transmitters and the receiver are equipped with multiple antennas. We show that the sum-rate capacity of the Poisson MAC with multiple transmit antennas is equivalent to a properly constructed Poisson MAC with a single antenna at each transmitter.

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Chun, Hyunchae. "Multi gigabit/s visible light communications : modelling and demonstrations." Thesis, University of Oxford, 2015. https://ora.ox.ac.uk/objects/uuid:646e24a9-244b-45de-a528-d4ea788f60da.

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Traffic in wireless communications is expected to increase exponentially due to demands such as multiple up/downloading, and streaming of ultra-high-definition or multi-dimensional content. This demand requires the development of multi-Giga bit/s communication systems. Insufficient radio spectrum is the main barrier to developing such high-speed wireless systems. Visible light communications (VLC) has the potential to overcome this barrier by providing THz of unlicensed spectrum. This thesis reports a new generalized modelling method and demonstrations for multi Gigabit/s VLC. For the optimum design of such system, a comprehensive investigation is presented, including the review of existing investigations. Novel design methods, such as optimisation for band-limited optical orthogonal-frequency-division-multiplexing schemes, generalisation of multi-input-multi-output (MIMO) VLC channels, and consideration of device characteristics in the modelling, are introduced for the first time. Then, various VLC techniques are compared considering practical constraints from various VLC channels and devices. Demonstrations of multi-Gb/s VLC systems are also presented: A 3-Gb/s wireless link with a single Gallium Nitride micro light-emitting-diode (μLED), a 1.68 Gb/s white-light communication link using a conjugated polymer and the μLED, and laser diode (LD) based remote phosphor approach leading to data-rates of up to 6.52 Gb/s for single channel and 10 Gb/s for 2-channel imaging system. These are the fastest demonstrations through a single LED source, and white-light generating LED and LD sources, respectively, at the time this thesis was written.

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Zhang, Shuailong. "High performance III-nitride light-emitting diodes for visible light communications and micro-displays." Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=24549.

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III-nitride micro-pixellated light-emitting diodes (micro-LEDs) are a novel format of light source capable of generating micro-scale, spatially and temporally-controllable light patterns. These devices consist of arrays of LED pixels with diameters in the range of 1 µm to 100 µm and emit light across the ultraviolet-blue-green-red part of the spectrum. In addition, compared with conventional broad-area LED devices, micro-LEDs show improved device performance in many aspects, such as high output power densities and the capability to withstand high injection current densities. For these reasons, micro-LEDs allow the study of interesting LED properties in regimes not accessible to conventional broad-area LEDs and also a wide range of novel LED applications. The research work presented in this thesis focuses on the novel applications of micro-LEDs in visible light communications (VLC) and micro-displays. Due to a reduced current crowding effect and superior thermal management capabilities, micro-LEDs can be driven at very high current densities, resulting in high modulation bandwidths of the devices. For this reason, optical data transmission was demonstrated from individual micro-LED pixels at bit rates of up to 1 Gbit/s using a high-speed probe under a binary amplitude modulation scheme. To make a more practical VLC system, micro-LED devices were integrated with specifically-designed complementary metaloxide-semiconductor (CMOS) electronics, which allow individual micro-LED pixels to be conveniently controlled via a simple computer interface. Such CMOS-controlled micro-LED devices have been demonstrated for data transmission at bit rates of up to 512 Mbit/s by modulating a single CMOS/micro-LED pixel and 1.5 Gbit/s by modulating four CMOS/micro-LED pixels simultaneously. Apart from the application in VLC, CMOS-controlled micro-LED devices can also be used to implement micro-display systems. A colour-tunable micro-display system capable of delivering high-resolution microscale dynamic images and tuning its colour from red to green has been demonstrated based on new LED epitaxial LED structures, micro-LED fabrication, and the CMOS technology. Other work reported in this thesis includes using micro-LEDs for data transmission in plastic optical fibre and investigating the modulation characteristics of colour-converters such as colloidal quantum dots and light-emitting polymer. A detailed study on size-dependent capacitance in III-nitride micro-LEDs, especially the negative capacitance (NC) effect, has also been reported in this thesis. This capacitance research sheds light on the mechanisms underlying the NC effect and is potentially useful for improving the LED performance for VLC and other applications.

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Zeng, Lubin. "Indoor Optical Wireless Communications Using White Light LEDs." Thesis, University of Oxford, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.515048.

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Farias, Gonçalo Nuno Brás. "Low data rate visible light communication system." Master's thesis, Universidade de Aveiro, 2014. http://hdl.handle.net/10773/14542.

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Mestrado em Engenharia Eletrónica e Telecomunicações
Recent advances in light emission diodes (LED) technology led them to an important place on lighting systems. This conquer allied to its switching speed permitted the development of new visible light communication systems (VLC), these are included in unguided optical communications. In the past, unguided optical communications were restricted to infrared spectrum due to LEDs ine ciency, but nowadays this is changing. Visible light communication systems can o er viable or complementary alternatives to the existing communication systems, due to its easy integration in certain environments. One possible integration environment are the mobile communications, and that fact is in the origin of this work. Old mobile phones had interfaces that allowed optical communication, for example IrDA but with the advances of technology these become obsolete and were eliminated. Due to that, modern smartphones do not o er any kind of interface for optical communications. However most of them have one camera that uses a ash device based on high intensity LEDs. Controlling with some precision one smartphone ash allows the implementation of one low data rate VLC systems which can be used for smart tagging, remote control of electronic devices or to control access to buildings. The main goal of this project is study the viability of the use of one smartphone as emitter in a VLC system.
Os recentes avanços na tecnologia dos diodos emissores de luz (LED) levaram a que estes conquistassem um lugar muito importante nos sistemas de iluminação. Esta conquista aliada à sua velocidade de comuta ção levou ao desenvolvimento de sistemas de comunicação por luz visível (VLC), estes incluem-se nos sistemas de comunicação ópticos não guiados. No passado as comunicações ópticas não guiadas restringiam-se ao espectro infravermelho, devido a ine ciência dos LEDs, mas hoje em dia isso está a mudar. Os sistemas de comunicação por luz visível podem oferecer alternativas viáveis ou complementares aos actuais sistemas de comunicação, devido à sua facilidade de integração em certos meios. Um dos meios em que este tipo de comunicação se pode integrar, e que deu origem a este trabalho, são as comunicações móveis. Os telemóveis antigos possuíam interfaces que permitiam comunicações ópticas como por exemplo IrDA, mas com os avanços tecnológicos estes tornaram-se obsoletos e foram eliminados. Devido a isso os smartphones modernos não oferecem qualquer tipo de interface óptica de comunicação. Privilegiam no entanto o uso de câmaras que têm associado um dispositivos de ash baseados em LEDs de alta intensidade. Conseguindo controlar com alguma precisão o ash de um smartphone consegue-se implementar um sistema VLC de baixo débito que pode ser usado em sistemas de smart tagging, controlo de remoto de dispositivos electrónicos ou mesmo controlo de acesso a edifícios. O principal objectivo deste trabalho é o estudo da viabilidade do uso de um smartphone como emissor num sistema VLC de baixo débito.

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OKADA, Hiraku, Toshiaki FUJII, Tomohiro YENDO, Masaaki KATAYAMA, Takaya YAMAZATO, and Toru NAGURA. "Tracking an LED Array Transmitter for Visible Light Communications in the Driving Situation." IEEE, 2010. http://hdl.handle.net/2237/14462.

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Diaz, Ariel Gomez. "Ultrafast indoor optical wireless communications." Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:2bd2257f-ae58-40f0-a10f-04e7b5336519.

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Traffic from wireless and mobile devices is predicted to increase 10-fold between 2014 and 2019, surpassing wired data traffic by 2016. Given the expected radio frequency (RF) capacity crunch, this growing wireless demand will have to be met using a variety of new technologies exploiting other parts of the electromagnetic spectrum. Promising research areas include the Millimetre Band as well as Optical Wireless Communications (OWC). Millimetre Band demonstrations have accomplished ultrafast multi-Gigabit links, making use of state-of-the-art fibre transmission systems. However, complex opto-electronic (OE) interfaces are required to convert the optical carrier into Millimetre wireless signals. To avoid these interfaces, an all-optical transparent network is proposed here, spanning over both the fibre and OWC domains, in order to deliver ultrahigh data rates to mobile end-users in indoor environments. This is supported by the recent deployment of fibre-to-the-home (FTTH) networks creating the potential for Terabit aggregate connections at the user's doorstep. Therefore, infrared fibre-wireless-fibre (FWF) links are studied to support data rates over 100 Gb/s in nomadic applications. The link coverage is achieved via narrow beam beamsteering over a wide field-of-view (FOV) using suitable localization and tracking techniques. The proposed model is inherently bidirectional and transparent, i.e. independent of the data rate and modulation format. In this thesis, the potential for ultrafast wide coverage OWCs using SMF-based transceivers and coherent transmission is demonstrated. A record data rate of 418 Gb/s and 209 Gb/s with a wide FOV of θ_FOV=±30° and θ_FOV=±20°, respectively, is shown at a free space range of 3 m. To the best of our knowledge, this is the fastest demonstration of an indoor wireless link that offers practical room-scale coverage. The automated alignment of this FWF link is also demonstrated with the design and implementation a mm-accurate localization and tracking system. Finally, architectures for point-to-multipoint communications are explored in order to adapt the system to multiple users.

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Haigh, Paul. "Using equalizers to increase data rates in organic photonic devices for visible light communications systems." Thesis, Northumbria University, 2014. http://nrl.northumbria.ac.uk/21415/.

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This thesis proposes to marry two separate technologies together. The first technology is that of visible light communications (VLC), and the second is small molecule and polymer organic photonic devices. These two technologies both offer outstanding potential in their respective fields of information communications and optoelectronics, with both being proposed as two of the most important technologies about to emerge in the next decades by their respective research communities. As such, it is imperative to investigate and analyse the performance of organic photonic devices in the context of VLC broadcasting networks. There have been no experimental results in the literature reporting on organic-VLC systems until the work proposed in this thesis and therefore the focus is on improving transmission speeds.

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Matus, Icaza Vicente. "Development of a visible light communications versatile research platform with potential application on vehicular networks." Tesis, Universidad de Chile, 2018. http://repositorio.uchile.cl/handle/2250/152113.

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Ingeniero Civil Eléctrico
Las redes vehiculares ad-hoc (VANets) son un nuevo paradigma en comunicación móvil que se plantea que podría permitir el despliegue de sistemas de transporte inteligente (ITS), más seguros, eficientes y amigables con el medioambiente. Se cuenta con el estándar DSRC de comunicaciones vehiculares pero no está comprobado que sea capaz de ofrecer la robustez y seguridad que necesitan los ITS. Las comunicaciones por luz visible (VLCs), son tecnologías de comunicación inalámbricas basadas en la modulación de intensidad de luz. Se realizan con dispositivos opto-electrónicos como diodos LED y foto-diodos. Se plantea que éstas podrían complementar a las radio-frecuencias (RF), como las del protocolo DSRC, por ejemplo, y permitir a las VANets entregar un mejor servicio, sobre todo en ambientes congestionados. En el presente trabajo, se realizó el desarrollo de una plataforma con herramientas para prototipado de enlaces VLC con aplicación en VANets bajo la hipótesis que las tecnologías existentes de illuminación en automóviles y señales de tránsito son una infraestructura que permite implementar VLCs en ambientes vehiculares. Primero se consultó el estado del arte de VANets y de VLCs, enfocado en entender el origen del interés por la implementación de redes vehiculares, así como sus desafíos y cómo las VLCs pueden mejorar el desempeño de dichos sistemas. Se estudiaron tecnologías aplicables a los sistemas de información y comunicaciones de las redes vehiculares con enfoque en las VLC. Un grupo fueron las plataformas de hardware programable como radios definidas por software (SDRs) y las placas Arduino. Otro tema fue la red de control interna de los vehículos y cómo existen interfaces para acceder a ella y obtener mediciones de los sensores e incluso dar instrucciones a los actuadores del auto. También, se revisaron los transductores de una red VLC: los diodos LED y fotodiodos, incluyendo la electrónica necesaria para su funcionamiento. Finalmente, se implementó un sistema de comunicaciones por VLC, basado en SDRs y optoelectrónica, y también un sistema adquisición de datos para la red de control del vehículo, basado en Arduino y un circuito integrado ELM327. Ambos sistemas se diseñaron modulares y se construyeron robustos. Se logró con ellos la transmisión de datos por luz y la lectura de datos del area de control del vehículo. Actualmente, el sistema desarrollado está en manos de un grupo de investigación que se dedica a estudiar las tecnologías de comunicación vehicular. También se está trabajando en una publicación con la evaluación de los sistemas implementados.
Este trabajo ha sido parcialmente financiado por ERANet-LAC Proyecto "RETRACT" Código ELAC2015/T10-0761, FONDECYT iniciación N° 11160517, FONDECYT Posdoctorado N° 3170021

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Stefan, Irina Adriana [Verfasser], Harald [Akademischer Betreuer] Haas, Mathias [Akademischer Betreuer] Bode, and Murat [Akademischer Betreuer] Uysal. "Enabling Networked Visible Light Communications / Irina Adriana Stefan. Betreuer: Harald Haas. Gutachter: Harald Haas ; Mathias Bode ; Murat Uysal." Bremen : IRC-Library, Information Resource Center der Jacobs University Bremen, 2014. http://d-nb.info/108729522X/34.

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Seguel, González Fabián Esteban. "Robust localization system using Visible Light Communication technology for underground mines." Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0012.

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En raison des progrès des appareils électroniques et des technologies de communication, de nouvelles règles de sécurité doivent être appliquées afin d'exploiter les mines souterraines de façon sécuritaire et optimale. En 2006, le gouvernement américain a mis à jour ses politiques de sécurité et a adopté la PUBLIC LAW109-236. Cette nouvelle réglementation établit que l'emplacement actuel, ou immédiatement avant l'accident, de tout le personnel souterrain doit être livré à une station de surveillance extérieure. Malgré les récents progrès des systèmes de suivi et de positionnement pour les environnements intérieurs, les mines souterraines constituent un cadre unique, qui impose des contraintes différentes aux technologies actuelles. Au cours des dernières années, les communications par lumière visible (VLC) ont attiré l'attention des chercheurs, grâce principalement aux progrès récents dans la fabrication des diodes électroluminescentes. Le développement rapide des systèmes VLC a encouragé les chercheurs à proposer des solutions de positionnement basées sur cette technologie. Le positionnement par lumière visible (VLP) présente plusieurs avantages par rapport aux méthodes de positionnement traditionnelles. La plupart des méthodes VLP ont été évaluées dans des scénarios où un réseau VLC dense et bien déployé existe. Les mines souterraines, d'autre part, sont un environnement dynamique et intrinsèquement dangereux et la plupart des hypothèses formulées pour les environnements intérieurs traditionnels ne sont pas satisfaites. La faisabilité de l'utilisation d'un système VLP dans de telles conditions et capable de répondre aux exigences de positionnement reste une question ouverte. Afin de répondre à cette question, nous étudions les contraintes, limites et exigences des technologies actuelles lorsqu'elles sont appliquées en milieu minier souterrain afin de déterminer la meilleure architecture garantissant le service de positionnement tout en répondant aux exigences de localisation. Nous avons développé une plate-forme réelle à faible coût et à grande échelle pour évaluer les performances des méthodes de positionnement en lumière visible. Finalement, une nouvelle méthode de positionnement robuste est présentée. Contrairement à la plupart des méthodes existantes dans la littérature, notre proposition n'est pas directement dérivée des méthodes basées sur les RF. La robustesse de notre méthode à plusieurs perturbations a été testée
Advances in electronics and communications technology have created new safety regulations that must be applied in order to operate underground mines safely and optimally. In 2006, the U.S. government updated its safety policies and adopted PUBLIC LAW109-236. As a result, monitoring of personnel inside underground tunnels is now mandatory for mining operations. This new regulation establishes that the current location, or immediately prior to the accident, of all underground personnel must be delivered to an external monitoring station. Despite recent advances in tracking and positioning systems for indoor environments, underground mines provide a unique environment that places different constraints on current technologies. In recent years, Visible Light Communications (VLC) has attracted the attention of researchers, mainly due to recent advances in the manufacture of Light Emitting Diodes. The rapid development of VLC systems has encouraged researchers to propose positioning solutions based on this technology. Visible light positioning (VLP) has several advantages over traditional positioning methods. Most VLP methods have been evaluated in scenarios where a dense and well-deployed VLC network exists. Underground mines, on the other hand, are a dynamic and inherently hazardous environment and most of the assumptions made for traditional indoor environments are not met. The feasibility of using a VLP system under such conditions and capable of meeting positioning requirements remains an open question. In order to answer this question, we study the constraints, limitations and requirements of current positioning technologies when applied in an underground mining environment in order to determine the best architecture to guarantee the positioning service while meeting the location requirements. Our proposal uses the positioning limitations, capabilities and requirements to design a low-cost, large-scale positioning architecture. Using this design, we have developed a real-world platform to evaluate the performance of visible light positioning methods. Finally, a new robust positioning method is presented. Unlike most existing methods in the literature, our proposal is not directly derived from RF-based methods. The robustness of our method to multiple perturbations (errors in the measurement of height, tilt angles, and multipath propagation due to light reflections from walls) has been tested

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Fisher, Edward Michael Dennis. "Parallel reconfigurable single photon avalanche diode array for optical communications." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/11690.

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There is a pressing need to develop alternative communications links due to a number of physical phenomena, limiting the bandwidth and energy efficiency of wire-based systems or economic factors such as cost, material-supply reliability and environmental costs. Networks have moved to optical connections to reduce costs, energy use and to supply high data rates. A primary concern is that current optical-detection devices require high optical power to achieve fast data rates with high signal quality. The energy required therefore, quickly becomes a problem. In this thesis, advances in single-photon avalanche diodes (SPADs) are utilised to reduce the amount of light needed and to reduce the overall energy budget. Current high performance receivers often use exotic materials, many of which have severe environmental impact and have cost, supply and political restrictions. These present a problem when it comes to integration; hence silicon technology is used, allowing small, mass-producible, low power receivers. A reconfigurable SPAD-based integrating receiver in standard 130nm imaging CMOS is presented for links with a readout bandwidth of 100MHz. A maximum count rate of 58G photon/s is observed, with a dynamic range of ≈ 79dB, a sensitivity of ≈ −31.7dBm at 100MHz and a BER of ≈ 1x10−9. We investigate the properties of the receiver for optical communications in the visible spectrum, using its added functionality and reconfigurability to experimentally explore non-ideal influences. The all-digital 32x32 SPAD array, achieves a minimum dead time of 5.9ns, and a median dark count rate (DCR) of 2.5kHz per SPAD. High noise devices can be weighted or removed to optimise the SNR. The power requirements, transient response and received data are explored and limiting factors similar to those of photodiode receivers are observed. The thesis concludes that data can be captured well with such a device but more electrical energy is needed at the receiver due to its fundamental operation. Overall, optical power can be reduced, allowing significant savings in either transmitter power or the transmission length, along with the advantages of an integrated digital chip.

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Arrowsmith, Timothy William. "A NETWORK PROCESSING NODE FOR LIGHT UNMANNED AIRCRAFT." UKnowledge, 2007. http://uknowledge.uky.edu/gradschool_theses/422.

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Over the last decade, research into unmanned and autonomous vehicles has greatly increased. With applications ranging from science and exploration to humanitarian and military efforts, the rising need for autonomous vehicles demands constant innovation and growth. The Intelligent Dependable Embedded Architectures (IDEA) lab at the University of Kentucky is continually launching research oriented programs [1]. A few key projects focus on the development of Unmanned Aerial Vehicles (UAV). Through this research, at the University of Kentucky, the need to develop a reliable, lightweight, node based hardware for use in light UAVs and other unmanned and autonomous vehicles became apparent. This paper addresses the design and implementation of a network processing node for light UAVs. This system utilizes a Controller Area Network (CAN) noise tolerant communications bus, a low power ZigBee Wireless Network for expanded inner plane communications and Silicon Laboratories C8051F041 microcontrollers to provide the necessary inputs/output and data processing. The final result will be a flight ready light UAV featuring distributed processing nodes to handle the servo communications and controls.

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39

Abualhoul, Mohammad. "Communications par lumière visible et radio pour la conduite coopérative autonome : application à la conduite en convois." Thesis, Paris Sciences et Lettres (ComUE), 2016. http://www.theses.fr/2016PSLEM084/document.

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L'objectif de cette thèse CIFRE est de contribuer à la communication véhiculaire autonome et au développement de la mobilité urbaine. Les travaux sont basés sur les limitations et défis de la communication par radio pour les applications de sécurité et envisagent de déployer le système d'éclairage des véhicules en tant que solution de communication de soutien pour le platooning d'IVC-activées par VC Véhicules autonomes. L'objectif principale de cette recherche doctorale consiste à intégrer le système VLC dans l'architecture existante de C-ITS en développant un prototype VLC, ainsi que des algorithmes de transfert suffisants permettant VLC, RF et des solutions basées sur la perception afin d'assurer les exigences de sécurité maximales et l'échange continu d'informations entre les véhicules. La faisabilité et l'efficacité de la mise en oeuvre du système et des algorithmes de transfert ont fait l'objet de recherches approfondies sur six chapitres, destinés à faciliter une progression logique des matériaux et permettre un accès relativement facile. En plus de l'amélioration de la capacité routière en utilisant les systèmes de conduite autonome à la base de convoi. Les simulations réalisées ainsi que les résultats expérimentaux ont montré que l'intégration de VLC avec les solutions existantes RF a un avantage certain dans la qualité du canal de communication et les exigences de sécurité d'un système de platooning quand un algorithme approprié est utilisé
This thesis effort contributes to the autonomous vehicular communication and urban mobility improvements. The work addresses the main radio-based V2V communication limitations and challenges for ITS hard-safety applications and intends to deploy the vehicular lighting system as a supportive communication solution for platooning of IVC-enabled autonomous vehicles. The ultimate objectives of this Ph.D research are to integrate the VLC system within the existing C-ITS architecture by developing a VLC prototype, together with sufficient, hand-over algorithms enabling VLC, RF, and perception-based solutions in order to ensure the maximum safety requirements and the continuous information exchange between vehicles. The feasibility and efficiency of the VLC-RF system implementation and hand-over algorithms were subjects to deep investigations over six self-contained chapters meant to facilitate a logical progression of materials and to enable a relatively easy access. In addition to the improvement in road capacity by utilizing the convoy-based autonomous driving systems. The carried out simulations followed-up by experimental results proved that the integration of VLC with the existed RF solutions lead to a definite benefit in the communication channel quality and safety requirements of a platooning system when a proper hand-over algorithm is utilized

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40

Long, Shihe. "Modélisation du canal intra-bâtiment et transmission haut-débit pour les communications optiques dans le spectre visible." Thesis, Ecole centrale de Marseille, 2016. http://www.theses.fr/2016ECDM0005.

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Les communications optiques dans le spectre visible (VLC pour Visible-Light Communications) ont attiré une attention particulière depuis quelques années en tant qu'une solution prometteuse pour les réseaux sans fil à très haut-débit dans les milieux intra-bâtiment. Ainsi, cette technique exploite l'infrastructure d’éclairage basée sur les diodes électroluminescentes (LED) pour la transmission de l'information. Pour cette raison, elle offre de nombreux avantages, comparée aux techniques « classiques » basées sur les transmissions radiofréquences (RF), tels que l'existence d'une grande largeur de bande non réglementée, une sécurité de transmission intrinsèque et une immunité aux interférences électromagnétiques.Les principales contraintes liées à l'établissement d'une transmission VLC à très haut-débit dans ce contexte sont la propagation en trajets multiples et les caractéristiques non-idéales des LEDs commerciales, dites « blanches ». L'objectif de cette thèse est d'étudier l'impact réel de ces contraintes sur la transmission des données et de proposer des solutions efficaces de traitement du signal pour atténuer leurs effets. Nous commençons par étudier la réponse impulsionnelle du canal VLC grâce à l'élaboration d'un outil de simulation efficace. Nous évaluons ensuite la sélectivité en fréquence du canal de propagation en considérant différents critères, tels que la réponse fréquentielle, l'étalement temporelle du canal et le rapport signal à interférences. Dans un deuxième temps, compte tenu de la possibilité de la sélectivité en fréquence du canal et aussi la limitation de la bande passante des LEDs, nous étudions la pertinence de l'emploi de différentes techniques de transmission de signaux, notamment celle de l'OFDM optique (pour Orthogonal Frequency-Division Multiplexing) afin de garantir des débits de transmission compétitifs avec la RF. Etant donné le facteur de crête ou PAPR (pour Peak-to-Average Power Ratio) élevé des signaux modulés en OFDM et la dynamique limitée des LEDs, nous proposons ensuite un nouveau schéma de transmission basé sur la modulation CAP (pour Carrier-less Amplitude and Phase) en plus de l'égalisation dans le domaine fréquentiel (FDE pour Frequency-Domain Equalization) au niveau du récepteur. Nous analysons les performances des liaisons VLC utilisant cette technique et les comparons à l'OFDM optique, en prenant particulièrement en compte la non-linéarité des LEDs. Enfin, nous démontrons l'intérêt de l'utilisation du schéma de transmission CAP-FDE à travers des résultats expérimentaux
Visible Light Communications (VLC) have attracted particular attention in the research community since a few years as a promising solution for high-speed indoor wireless networks. By exploiting the existing solid-state light-emitting diode (LED) lighting infrastructure, VLC offer numerous advantages such as a large unlicensed bandwidth, transmission security, and immunity to electro-magnetic interference compared to their radiofrequency counterparts. Within the context of indoor VLC, the multipath propagation channel and the non-ideal characteristics of the commercial white LEDs cause the main limitations for achieving high data-rate transmission. The objective of this thesis is to investigate the true impact of these limitations on the data transmission and to propose efficient signal processing solutions to mitigate their adverse effects. We start by the study of the indoor VLC channel impulse response by developing an efficient simulation tool. We then consider evaluating the channel frequency selectivity through different metrics. Next, given the potentially frequency-selective channel and the limited modulation bandwidth of the LEDs, we investigate the suitability of employing different signal transmission techniques including optical orthogonal frequency-division multiplexing (O-OFDM) in order to achieve high data-rate transmission. Given the high peak-to-average power ratio (PAPR) of O-OFDM signals and the limited dynamic range of the LEDs, we then propose a novel transmission scheme, which consists of using carrier-less amplitude and phase (CAP) modulation together with frequency domain equalization (FDE) at the receiver. We analyze the performance of the VLC link using this technique and compare it with the O-OFDM schemes, especially by taking the non-linear characteristics of the LED into account. Lastly, we demonstrate the merits of using the CAP-FDE transmission scheme via some experimental results

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Kaňa, Leoš. "Návrh vnitřního optického spoje." Master's thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2011. http://www.nusl.cz/ntk/nusl-219165.

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In last years phenomena of wireless communication technologies became a primary interest of big development laboratories whole world. Domain of point to point links which are realized by laser technology with narrow beam divergence and very sensitive photo-detectors is ordinarily used these days. This trend of using light waves as carrier medium turned interests of scientist to the sphere of wide area networks which is domain of wi-fi radio technologies. One of new trends in this sphere is also in-door free space optics. With expansion which leads to using LED's in everyday applications and with technological progress of last years, also grows tendency of most effective utilization of LED systems. The result of this effort is thought which considerate LED as source of artificial lighting and source of carrier medium for modulated signal. This kind of device must fulfill hygienic standards for illumination and also must be able to work with high frequency by which is signal modulated. These systems can provide links with sufficient capacity in order of hundred megabits.

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Caputo, Stefano. "Advanced solutions of Visible Light Communication for Infomobility Applications." Doctoral thesis, 2020. http://hdl.handle.net/2158/1184579.

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The replacement of conventional light sources with Light Emitting Diodes (LEDs) has recently increased scientific and industrial activity in Visible Light Communications (VLC). In the VLC, the same optical radiation in the visible light spectrum used to standard illumination is also used for data communication through a fast modulation of the light source. VLC systems have a great potential for different applications, in particular for infomobility, due to their efficiency and low latency. The VLC for infomobility can be used for applications in offices, in museums and in Intelligent Transportation Systems (ITS). The main aim of this PhD dissertation is a characterization of communication channel between a traffic light and a vehicle for ITS applications. This is a typical example of communication Infrastructure to Vehicular (I2V). After creating a low-cost prototype IEEE802.15.7 complaint, the communication channel has been analyzed through some tests. Each test was necessary in order to characterize every singular components of the system. The propagation channel has been deeply investigated to characterize the irregular optical path of transmission of the regulatory traffic light and to study the optical lens used for receiving a signal. Finally, the performance of this system was evaluated in terms of Packet Error Rate (PER). The created system has been used also in 5G experiments in Prato, and the latency of a joint 5G-VLC communication has been measured. In addition, two other aspects of VLC are present in this PhD dissertation: a comparative study between lighting design standards for illumination system and the lighting design for optimization signal of VLC system and a study of human perceptions of objects illuminated by a lamp with VLC system integrated.

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Chen, Zhen-Yu, and 陳鎮愉. "Space-Multiplexing Technologies for Visible Light Wireless Communication System." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/62990464877482963118.

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碩士
國立中山大學
光電工程學系研究所
101
In the information explosion era, people are desired to receive messages anywhere and anytime. The traditional wireless communication transmits messages via radiofrequency (RF) electromagnetic wave, but it cannot be used for some special cases. For instance, due to the health concerns raised about exposure to RF fields, it cannot be used in hospitals. In addition, considering low information security, it cannot be used in highly confidential situations, such as military applications. Alternative to RF wireless technologies, visible light communication (VLC) based on white light emitting diodes (LEDs) has attracted global attention, because of its advantages of worldwide availability, high security, and immunity to RF interference. In the thesis, we use commercially available LEDs as our emission source. Because the LEDs adopted in VLC are designed for illumination, so the modulation bandwidth is generally limited to about tens MHz. Accordingly, we used the carrier-less amplitude and phase (CAP) modulation, which has high bandwidth efficiency, to transmit signals over the limited bandwidth, and the pre-compensation is also employed in our high-speed VLC experiments to improve signal performance. On the other hand, how to increase the transmitted distance is also one of our major topics. At the receiver, we use the high photoelectric conversion efficiency avalanche photo-detectors (APDs) to increase our transmission distance and to improve signal quality. We insert unique word (UW) into CAP signals, in order to apply both frequency domain equalization (FDE) and decision feedback equalization (DFE) to overcome the uneven frequency response of the VLC channel. Moreover, 2×1 multiple-input-single-output (MISO) VLC system is also experimentally demonstrated, and Alamouti space-time block coding (STBC) is employed to CAP or orthogonal frequency division multiplexing (OFDM) signals to deal with the problem of multipath interference.

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44

Rahaim, Michael. "Heterogeneous integration of optical wireless communications within next generation networks." Thesis, 2015. https://hdl.handle.net/2144/13681.

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Unprecedented traffic growth is expected in future wireless networks and new technologies will be needed to satisfy demand. Optical wireless (OW) communication offers vast unused spectrum and high area spectral efficiency. In this work, optical cells are envisioned as supplementary access points within heterogeneous RF/OW networks. These networks opportunistically offload traffic to optical cells while utilizing the RF cell for highly mobile devices and devices that lack a reliable OW connection. Visible light communication (VLC) is considered as a potential OW technology due to the increasing adoption of solid state lighting for indoor illumination. Results of this work focus on a full system view of RF/OW HetNets with three primary areas of analysis. First, the need for network densication beyond current RF small cell implementations is evaluated. A media independent model is developed and results are presented that provide motivation for the adoption of hyper dense small cells as complementary components within multi-tier networks. Next, the relationships between RF and OW constraints and link characterization parameters are evaluated in order to define methods for fair comparison when user-centric channel selection criteria are used. RF and OW noise and interference characterization techniques are compared and common OW characterization models are demonstrated to show errors in excess of 100x when dominant interferers are present. Finally, dynamic characteristics of hyper dense OW networks are investigated in order to optimize traffic distribution from a network-centric perspective. A Kalman Filter model is presented to predict device motion for improved channel selection and a novel OW range expansion technique is presented that dynamically alters coverage regions of OW cells by 50%. In addition to analytical results, the dissertation describes two tools that have been created for evaluation of RF/OW HetNets. A communication and lighting simulation toolkit has been developed for modeling and evaluation of environments with VLC-enabled luminaires. The toolkit enhances an iterative site based impulse response simulator model to utilize GPU acceleration and achieves 10x speedup over the previous model. A software defined testbed for OW has also been proposed and applied. The testbed implements a VLC link and a heterogeneous RF/VLC connection that demonstrates the RF/OW HetNet concept as proof of concept.

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Sinha, Sujata. "OTFS Modulation in MIMO Visible Light Communication Systems." Thesis, 2022. https://etd.iisc.ac.in/handle/2005/5739.

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Visible light communication (VLC) technology is emerging as an attractive technology for wireless communication in indoor and vehicular environments. In VLS systems, light emitting diodes (LED) and photo diodes (PD) are used for wireless signal transmission and reception, respectively, using the visible light spectrum. VLC systems are gaining popularity because of their ability to provide lighting and short-range communication simultaneously. Recently, a new modulation scheme called orthogonal time frequency space (OTFS) modulation has been introduced in the radio frequency (RF) communications domain, where it has been shown that OTFS achieves significantly better performance compared to the widely used orthogonal frequency division multiplexing (OFDM). OTFS is a two-dimensional (2D) modulation scheme, where MN information symbols are multiplexed in the delay-Doppler (DD) domain using M Doppler bins and N delay bins. This is in contrast to OFDM where information symbols are multiplexed in the time-frequency (TF) domain. Because of the demonstrated superiority of OTFS in the RF communication domain, research in OTFS for VLC systems has gained importance recently. In this context, it is of interest to 1) adapt OTFS waveform to VLC settings, and 2) investigate the performance OTFS in indoor VLC environments. In this thesis, we propose efficient multi-LED OTFS modulation schemes suited for visible light communication and analyze their bit error performance in indoor communication environments. First, we propose two dual-LED transmission schemes, namely, non-DC-biased OTFS (NDC-OFTS) scheme and dual-LED complex modulation OTFS (DCM-OTFS) scheme. The NDC-OTFS scheme uses 2D Hermitian symmetry operation to convert complex signals to positive, real-valued signals suitable for transmission in the optical domain, and the DCM-OTFS scheme achieves this by exploiting the polar representation of complex signals. We obtain analytical upper bounds on the bit error performance of the proposed schemes, which are found to be tight at high signal-to-noise ratios (SNRs). Our analytical and simulation results show that the proposed OTFS schemes achieve better performance compared to their OFDM counterparts reported in the VLC literature. Further, using the ratio of the minimum distance of different normalized received signal sets as a metric, we quantify the spatial distribution of the SNR gain of the OTFS schemes compared to their OFDM counterparts. Next, we propose two quad-LED architectures, namely, quad-LED complex modulation OTFS (QCM-OTFS) scheme and spatial modulation DCM-OTFS (SM-DCM-OTFS) scheme. The QCM-OTFS scheme sends the magnitudes of real and imaginary parts of complex signals through intensity modulation and their sign information through spatial indexing of LEDs. The proposed SM-DCM-OTFS scheme sends the magnitude and phase of complex signals (polar representation) through a pair of LEDs and frame indexing across two pairs of LEDs. We also propose two multi-LED OTFS schemes, namely, quadrature spatial modulation OTFS (QSM-OTFS) scheme and dual mode index modulation OTFS (DMIM-OTFS) scheme. The proposed schemes use the dual-LED complex modulation block as the basic building block and offer enhanced rates compared to conventional index modulation schemes. The proposed schemes have the advantage of not requiring the Hermitian symmetry and DC bias operations to obtain real, positive-valued signals suited for intensity modulation of LEDs. Our results show that the proposed OTFS based schemes perform better than their OFDM counterparts. Finally, to mitigate the effect of channel correlation and achieve improved system performance, we investigate the use of the pairwise coding technique and singular value decomposition precoding in multiple-input multiple-output (MIMO) VLC systems. Our simulation results show that the pairwise coding is effective in alleviating the effect of spatial correlation.

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Chen, Cheng-Wei, and 陳勁威. "High Spectrum Efficiency Modulation Technologies for Visible Light Wireless Communication System." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/a3ydnk.

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碩士
國立交通大學
光電系統研究所
101
In the information explosion era, people taking over the information from the internet are growing day by day. It’s also increasing demand for wireless communication. Development next generation wireless communication system will be the important issue for many researches and companies, and Visible Light Communication (VLC) is one of them. For wireless communication system, VLC also call Li-Fi (light fidelity). Its research just starts from recent years, and it also presents many technical challenges owing to the commercial LEDs which using for illumination have the terrible frequency channel response, in only 100MHz to 200MHz bandwidth, it lose nearly 10 to 20dB. In this thesis, we use CAP and OFDM to maximize the data rate in our VLC system. We provide pre-compensation for CAP, and bit-loading for OFDM. Both methods can improve the channel response and increase the data rate. The result is over 3 Gbps in RGB LED – Si PIN by both methods.

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Seminara, Marco. "Development and characterization of systems for optical wireless and visible light communication." Doctoral thesis, 2022. http://hdl.handle.net/2158/1275219.

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This doctoral Thesis deals with several aspects of communication through visible and infrared light by exploiting and building on the expertise of our research group at LENS in the study and manipulation of light. Over the course of three years, the project has focused on the investigation and implementation of an optical wireless communication system in several application scenarios. A pivotal aspect is the use of appropriately modulated LED light sources, allowing for the realization of long-range (10–100 m) optical channels for the delivery of information over even shorter times than those achieved in radiofrequency transmissions. One of the key applications herein demonstrated is within the field of intelligent transportation systems: this contribution provides methods to increase vehicular safety, such as the real-time relaying of traffic information for quick response in critical road situations and platooning. Some original indoor applications are also proposed, including the first full optical characterization of a communication link exploiting the existing illumination system of a real museum to deliver dedicated information and services. Furthermore, efficient long-range transmission through free space is achieved using a mid-infrared laser source, whose behavior is modeled according to different possible extents of atmospheric absorption and scattering. Finally, we present a preliminary characterization of a new reception system consisting of an optical antenna coupled with a photodiode to overcome the étendue principle and achieve fast data transmission up to 100 m even under direct sunlight irradiation. In summary, this work shows the capabilities and potential of optical wireless communication, which is now almost mature for implementation in synergy with radiofrequency-based technologies to accomplish fast, reliable, and secure pervasive communication networks.

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Oubei, Hassan M. "Underwater Wireless Optical Communications Systems: from System-Level Demonstrations to Channel Modeling." Diss., 2018. http://hdl.handle.net/10754/628028.

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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.

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Chau, Jimmy C. "Multiple-input multiple-output visible light communication receivers for high data-rate mobile applications." Thesis, 2016. https://hdl.handle.net/2144/19427.

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Visible light communication (VLC) is an emerging form of optical wireless communication that transmits data by modulating light in the visible spectrum. To meet the growing demand for wireless communication capacity from mobile devices, we investigate multiple-input multiple-output (MIMO) VLC to achieve multiplexing capacity gains and to allow multiple users to simultaneously transmit without disrupting each other. Previous approaches to receive VLC signals have either been unable to simultaneously receive multiple independent signals from multiple transmitters, unable to adapt to moving transmitters and receivers, or unable to sample the received signals fast enough for high-speed VLC. In this dissertation, we develop and evaluate two novel approaches to receive high-speed MIMO VLC signals from mobile transmitters that can be practically scaled to support additional transmitters. The first approach, Token-Based Pixel Selection (TBPS) exploits the redundancy and sparsity of high-resolution transmitter images in imaging VLC receivers to greatly increase the rate at which complementary metal-oxide semiconductor (CMOS) active pixel sensor (APS) image sensors can sample VLC signals though improved signal routing to enable such high-resolution image sensors to capture high-speed VLC signals. We further model the CMOS APS pixel as a linear shift-invariant system, investigate how it scales to support additional transmitters and higher resolutions, and investigate how noise can affect its performance. The second approach, a spatial light modulator (SLM)-based VLC receiver, uses an SLM to dynamically control the resulting wireless channel matrix to enable relatively few photodetectors to reliably receive from multiple transmitters despite their movements. As part of our analysis, we develop a MIMO VLC channel capacity model that accounts for the non-negativity and peak-power constraints of VLC systems to evaluate the performance of the SLM VLC receiver and to facilitate the optimization of the channel matrix through the SLM.

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YE, CHENG-EN, and 葉承恩. "The Investigation of a Concentration Photovoltaic Module Based Laser Wireless Power Transmission and Visible Light Communication System." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/p42c5c.

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Abstract:

碩士
國立金門大學
電子工程學系碩士班
107
The aim of this research is to develop a wireless power transmission (WPT) and visual light communication (VLC) hybrid system based on a laser diodes (LD) array and a concentration photovoltaic (CPV) module. The Light Fidelity (Li-Fi), which is one of the novel VLC technology, could simultaneously transmit power and data by a photovoltaic (PV) module receiver. In this study, we further propose using an LD array and a CPV module as the transmitter and receiver to improve the developed Li-Fi system’s power efficiency and data rate. The hardware circuit and components, such as the LD driver, amplifier, filter, and modulator/demodulator, are specifically designed for the proposed novel Li-Fi system. In addition, the transmitted signals are modulated by frequency shift keying (FSK) and implemented by a programmable system on chip (PSoC). Furthermore, to mitigate the Gaussian laser beam spreading and wandering effect, which might result in partial shading condition (PSC) in the PV module, we developed a novel maximum power point tracking (MPPT) algorithm and a new reconfiguration circuit for the receiver. The proposed MPPT algorithm, namely modified firefly algorithm (MFA), integrates the firefly algorithm with neighborhood attraction (NaFA) and the simplified firefly algorithm (SFA) to avoid trapping at local maximum power points (LMPPs) and improve the convergence speed. In addition, the modified circuit reconfiguration (MCR) method was proposed in this study to dynamically switch the CPV array’s circuit connection according to different laser beam spreading patterns. The total-cross-tied (TCT) topology is adopted in the MCR to simplify its switching control algorithm and reduce the number of switches. Experimental results verify that the proposed MFA offers rapid response with high accuracy and efficiency for the MPPT of the laser receiver. Moreover, after applying the MCR, the P-V curves of the CPV module could be simplified and the system output power could be effectively increased. The main advantage of the experimental prototype system is that it can simultaneously transmit power and data with high conversion efficiency and data rate. In addition, the proposed prototype is capable of being extended to a larger scale laser beam with a larger CPV array receiver.

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