Dissertations / Theses: 'Visible-light'

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Hussein, Ahmed Taha. "Visible light communication system." Thesis, University of Leeds, 2016. http://etheses.whiterose.ac.uk/15894/.

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Visible light communication (VLC) systems have become promising candidates to complement conventional radio frequency (RF) systems due to the increasingly saturated RF band and the potentially high data rates that can be achieved by VLC systems. Over the last decade, significant research effort has been directed towards the development of VLC systems due to their numerous advantages over RF systems, such as the availability of simple transmitters (light emitting diodes, LEDs) and receivers (silicon photo detectors), better security at the physical layer, improved energy efficiency due to the dual functionally (i.e., illumination and communication) and hundreds of THz of license-free bandwidth. However, there are several challenges facing VLC systems to achieve high data rates (multi gigabits per second). These challenges include the low modulation bandwidth of the LEDs, co-channel interference (CCI), inter symbol interference (ISI) due to multipath propagation and the light unit (i.e., VLC transmitter) should be ‘‘ON’’ all the time to ensure continuous communication. This thesis investigates a number of techniques to overcome these challenges to design a robust high-speed indoor VLC system with full mobility. A RGB laser diode (LD) is proposed for communication as well as illumination. The main goal of using LD is to enable the VLC system to achieve multi-gigabits data rates when employing a simple modulation technique (such as on-off keying (OOK)), thus adding simplicity to the VLC system. A delay adaptation technique (DAT) is proposed to reduce the delay spread and enable the system to operate at higher data rates (10 Gb/s in our case). The thesis proposes employing angle diversity receivers (ADR) and imaging diversity receivers to mitigate the impact of ISI, CCI, reduce the delay spread (increase the channel bandwidth) and increase the signal to noise ratio (SNR) when the VLC system operates at high data rates (5 Gb/s and 10 Gb/s) under the effects of mobility and multipath dispersion. Moreover, the work introduces and designs three new VLC systems, an ADR relay assisted LD-VLC (ADRR-LD), an imaging relay assisted LD-VLC (IMGR-LD) and a select-the-best imaging relay assisted LD-VLC (SBIMGR-LD), which are modelled and their performance is compared at 10 Gb/s in two VLC room sizes (5m × 5m × 3m and 4m × 8m × 3m). As well as modelling in two different room scenarios: an empty room and a realistic environment were considered. The work also introduces and designs a high-speed fully adaptive VLC system that employs beam steering and computer generated holograms (CGHs), which has the ability to achieve 20 Gb/s with full receiver mobility in a realistic indoor environment. Furthermore, a new high-speed fast adaptive VLC system based on a divide-and-conquer methodology is proposed and integrated with the system to reduce the time required to identify the optimum hologram. The new system has the ability to achieve 25 Gb/s in the worst case scenario. This thesis also proposes four new infrared (IR) systems to support VLC systems when the light is totally turned off. In addition, it introduces the concept of a collaborative VLC/IR optical wireless (OW) system and investigates the impact of partial dimming on the VLC system performance. An adaptive rate technique (ART) is proposed to mitigate the impact of light dimming. Finally, an IROW system (cluster distributed with beam steering) is introduced to collaborate with a VLC system to maintain the target data rate in the case of partial dimming.

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Soleiman, Andreas. "Battery-free Visible Light Sensing." Thesis, Uppsala universitet, Avdelningen för datorteknik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-381370.

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In this thesis, we show that it is possible to design a battery-free light sensing system that can sense and communicate hand gestures while operating fully on harvested power from indoor light. We present two main innovations that push our system to tens of microwatts of power to enable battery-free operation. First, we introduce a novel visible light sensing system that can track variations in light intensity by using a solar cell as a sensor. Solar cells are unlike photodiodes optimized for energy yield in the visible light region and hence do not require any power hungry active components such as an operational amplifier. Furthermore, solar cells can operate under more diverse light conditions as they are not susceptible to saturation under bright light. Second, we devise two ultra-low power communication mechanisms based on radio frequency backscatter to transmit sensor readings at various resolutions without the need of any energy-expensive computational blocks. We design two battery-free and self-powered hardware prototypes that are based on these two innovations. Our first design utilizes an on-board comparator based circuit to perform a 1-bit digitization of changes in light readings, consuming only sub-microwatt of power for digitization. For our second prototype, we design an analog backscatter mechanism that can map raw sensor readings directly to backscatter transmissions. We demonstrate the feasibility of our designs when sensing significant changes in light intensity caused by shadows from hand gestures, and reconstruct these at a receiving device. Our results demonstrate the ability to sense and communicate various hand gestures at a peak power of 20 microwatts when performing 1-bit digitization, and a mean power of 60 microwatts when performing analog backscatter. Both designs represent orders of magnitude improvement in terms of power consumption over state-of-the-art visible light sensing systems. Battery-free Visible Light Sensing MobiCom: G: Battery-free Visible Light Sensing

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Raval, Manan. "Nanophotonic visible light phased arrays." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/109686.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2016. Cataloged from PDF version of thesis. Includes bibliographical references (pages 81-85). Previously demonstrated integrated optical phased arrays have primarily been implemented in silicon-based platforms and have therefore been limited to operation at infrared wavelengths, where silicon provides low-loss transmission. Developing integrated optical phased arrays for visible wavelengths would enable the exploration of new applications for this technology, such as autostereoscopic displays and neuronal targeting for optogenetics. The work presented in this thesis involves the development of visible light integrated optical phased array components and systems with a focus on autostereoscopic image projection applications. Practical 3D microdisplay applications will require (1) large-aperture phased array systems for diffraction minimization, (2) integrated phase modulation for implementing dynamically reconfigurable phased array antenna elements, and (3) a phased array system architecture for accurately encoding the light field of virtual objects. Integrated photonic architectures for all three aforementioned goals are investigated in this thesis. With respect to the first goal, a 1x1 mm2 aperture visible light phased array with a near diffraction limited far-field spot size is demonstrated. With respect to the second goal, the design of an integrated phase modulator based on the electro-optic tuning of a nematic liquid crystal waveguide cladding layer is developed and a near-x phase shift is demonstrated in a fabricated device. Finally, an autostereoscopic image projection system comprised of multiple tiled phased arrays configured to project a virtual image with parallax in one dimension within an 8.58° field of view is demonstrated. by Manan Raval. S.M.

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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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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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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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Xia, Zhonghua. "Gold(I) Catalysis Under Visible Light." Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS606.

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Cette thèse s'intéresse à l'étude d'un double processus catalytique, la catalyse à l'or et la photocatalyse. Nous avons cherché à synthétiser des dérivés enzofuranique à partir d'o-alkynylphénols et de sels d'aryle diazonium ou d'iodoalcynes en présence d'un mélange catalytique d'un complexe d'or (I) et d'un photocatalyseur sous irradiation à la lumière visible. Dans un premier temps, nous présentons un nouveau procédé de catalyse duale photoredox/or par cyclisation arylative d'o-alkynylphénols avec des sels d'aryle diazonium. Cette réaction s'effectue dans des conditions douces à température ambiante en l'absence de base et/ou d'additifs et offre une approche efficace pour la formation de squelettes hétérocycliques. La réaction proposée fait intervenir un intermédiaire vinyl or(III) formé par addition du radical aryle sur le catalyseur d'or et par modulation de l'état d‟oxydation du complexe par le photocatalyseur. Après élimination réductrice le produit de couplage hétérocyclique est obtenu. Dans un deuxième temps, nous avons mis au point une nouvelle méthode pour la synthèse de dérivés alcynylbenzofuraniques élaborés à partir d'o-alkynylphénols et d'iodoalkynes en présence d'un mélange catalytique d'Au (I) et d'Ir (III) sous irradiation de LEDs bleues. Sous irradiation à la lumière visible, le triplet excité de l'intermédiaire vinyl-or(I) et de l'iodure d‟alcyne partenaire s'engage facilement dans une séquence d'isomérisation par addition trans-cis-oxydante, enfin l'élimination réductrice permets la formation des produits de couplage croisé Csp2-Csp. Les études mécanistiques et de modélisation ont mis en évidence un phénomène de transfert d'énergie plutôt qu'un processus redox. Ce double procédé catalytique or/photoredox fournit un nouveau mode d'activation dans la catalyse homogène à l'or This thesis has focused on the study of a dual catalytic process involving gold catalysis and photocatalysis. We aimed to synthesize benzofuran derivatives from o-alkynylphenols and aryl diazonium salts or iodoalkynes in the presence of a catalytic mixture of a gold(I) complex and a photocatalyst under visible light irradiation. Firstly, we present a novel dual photoredox/gold catalysis process by arylative cyclization of o-alkynylphenols with aryldiazonium salts. This reaction occurs smoothly at room temperature in the absence of base and/or additives and offers an efficient approach to heterocyclic scaffolds. The reaction is proposed to proceed through a photoredox-promoted generation of a vinylgold(III) intermediate, formed by addition of the aryl radical to the gold catalyst and modulation of the oxidation state by the photocatalyst, which undergo reductive elimination to provide the heterocyclic coupling adduct. Later, we developed a new method for the synthesis of valuable alkynyl benzofuran derivatives devised from o-alkynylphenols and iodoalkynes in the presence of a catalytic mixture of Au(I) and Ir(III) under blue LED irradiation. Under visible light irradiation, the triplet excited state of the vinylgold(I) intermediate and the alkynyl iodide partner readily engaged in a oxidative addition–trans/cis isomerization sequence, deliver Csp2-Csp cross coupling products after reductive elimination. An energy transfer event rather than a redox pathway was demonstrated by the mechanistic and modeling studies. This dual gold/photo catalytic process provides a novel mode of activation in gold homogenous catalysis

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Chen, Xi. "Noble metal photocatalysts under visible light and UV light irradiation." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/47008/1/Xi_Chen_Thesis.pdf.

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One of the greatest challenges for the study of photocatalysts is to devise new catalysts that possess high activity under visible light illumination. This would allow the use of an abundant and green energy source, sunlight, to drive chemical reactions. Gold nanoparticles strongly absorb both visible light and UV light. It is therefore possible to drive chemical reactions utilising a significant fraction of full sunlight spectrum. Here we prepared gold nanoparticles supported on various oxide powders, and reported a new finding that gold nanoparticles on oxide supports exhibit significant activity for the oxidation of formaldehyde and methanol in the air at ambient temperature, when illuminated with visible light. We suggested that visible light can greatly enhance local electromagnetic fields and heat gold nanoparticles due to surface plasmon resonance effect which provides activation energy for the oxidation of organic molecules. Moreover, the nature of the oxide support has an important influence on the activity of the gold nanoparticles. The finding reveals the possibility to drive chemical reactions with sunlight on gold nanoparticles at ambient temperature, highlighting a new direction for research on visible light photocatalysts. Gold nanoparticles supported on oxides also exhibit significant dye oxidation activity under visible light irradiation in aqueous solution at ambient temperature. Turnover frequencies of the supported gold nanoparticles for the dye degradation are much higher than titania based photocatalysts under both visible and UV light. These gold photocatalysts can also catalyse phenol degradation as well as selective oxidation of benzyl alcohol under UV light. The reaction mechanism for these photocatalytic oxidations was studied. Gold nanoparticles exhibit photocatalytic activity due to visible light heating gold electrons in 6sp band, while the UV absorption results in electron holes in gold 5d band to oxidise organic molecules. Silver nanoparticles also exhibit considerable visible light and UV light absorption due to surface plasmon resonance effect and the interband transition of 4d electrons to the 5sp band, respectively. Therefore, silver nanoparticles are potentially photocatalysts that utilise the solar spectrum effectively. Here we reported that silver nanoparticles at room temperature can be used to drive chemical reactions when illuminated with light throughout the solar spectrum. The significant activities for dye degradation by silver nanoparticles on oxide supports are even better than those by semiconductor photocatalysts. Moreover, silver photocatalysts also can degrade phenol and drive the oxidation of benzyl alcohol to benzaldehyde under UV light. We suggested that surface plasmon resonance effect and interband transition of silver nanoparticles can activate organic molecule oxidations under light illumination.

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Chen, Cheng. "Downlink system characterisation in LiFi Attocell networks." Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/25420.

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There is a trend to move the frequency band for wireless transmission to ever higher frequencies in the radio frequency (RF) spectrum to fulfil the exponentially increasing demand in wireless communication capacity. Research work has gone into improving the spectral efficiency of wireless communication system to use the scarce and expensive resources in the most efficient way. However, to make wireless communication future-proof, it is essential to explore ways to transmit wirelessly outside the traditional RF spectrum. The visible light (VL) spectrum bandwidth is 1000 times wider than the entire 300 GHz RF spectrum and is, therefore, a viable alternative. Visible light communication (VLC) enables existing lighting infrastructures to provide not only illumination but also wireless communication. In conjunction with the concept of cell densification, a networked VLC system, light fidelity attocell (LAC) network, has been proposed to offer wide coverage and high speed wireless data transmission. In this study, many issues related to the downlink system in LAC networks have been investigated. When analysing the downlink performance of LAC networks, a large number of random channel samples are required for the empirical calculation of some system metrics, such as the signal-to-interference-plus-noise ratio (SINR). However, using state-of-the-art approaches to calculate the non-line-of-sight (NLoS) channel component leads to significant computational complexity and prolonged computation time. An analytical method has been presented in this thesis to efficiently calculate the NLoS channel impulse response (CIR) in VLC systems. The results show that the proposed method offers significant reduction in computation time compared to the state-of-the-art approaches. A comprehensive performance evaluation of the downlink system of LAC networks is carried out in this thesis. Based on the research results in the literature in the field of optical wireless communication (OWC), a system level framework for the downlink system in LAC networks is developed. By using this framework, the downlink performance subject to a large number of parameters is evaluated. Additionally, the effect of varying network size, cell deployment and key system parameters are investigated. The calculation of downlink SINR statistics, cell data rate and outage probability are considered and analysed. The results show that the downlink performance of LAC networks is promising in terms of achievable data rate per unit area compared to other state-of-the-art RF small-cell networks. It is found that co-channel interference (CCI) is a major source of signal impairment in the downlink of LAC network. In order to mitigate the influence of CCI on signal distortion in LAC networks, widely used interference mitigation techniques for RF cellular systems are borrowed and extensively investigated. In this study, fractional frequency reuse (FFR) is adapted to the downlink of LAC networks. The SINR statistics and the spectral efficiency in LAC downlink system with FFR schemes are evaluated. Results show that the FFR technique can greatly improve the performance of cell edge users and as well the overall spectral efficiency. Further performance improvements can be achieved by incorporating angular diversity transmitters (ADTs) with FFR and coordinated multi-point joint transmission (JT) techniques.

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Ramakrishnan, Ayyappan. "Visible light induced catalytic sulfoxidation of alkanes." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=981136915.

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Ma, Hao. "Coordinated transmission for visible light communication systems." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/63348.

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Visible light communication (VLC) is an emerging optical wireless communication technology that employs the light-emitting diode (LED) as the data transmitter. It has great potential to alleviate the strain on the radio-frequency (RF) spectrum in the indoor environment. The integration of VLC into indoor communication networks establishes optical attocells, responsible for the downlink traffic from the network to user terminals. These attocells could be easily deployed wherever LEDs are adopted for general illumination, including in electromagnetic interference sensitive areas like hospitals and airplanes. Although opaque bounds effectively contain light signals, VLC attocells would generally not operate free of interference. Illumination designers aim to have a uniform illumination at a certain height in the indoor environment, which mandates a rich overlap between the emissions of luminaires and results in unavoidable inter-attocell interference (IAI) from a communications perspective. This reality encourages us to propose the coordination of multiple VLC attocells (i.e., VLC-enabled LED luminaires) to turn the problem of overlap and thus interference into an advantage. In this thesis, we study how the coordination of VLC attocells can be employed to improve the user performance. Two coordinated VLC architectures, both of which utilize single-carrier transmission but differ at the coordination level, are investigated first. The analysis primarily focuses on the beamforming design subjected to the limited dynamic range of LED transmitters. The design of robust beamformers is also considered to combat the uncertainty of channel information at the transmitter. Finally, we propose a multi-carrier coordinated VLC architecture that uses power lines as the backbone network for the VLC front-end. Several subcarrier allocation schemes with varying degrees of tradeoff among hardware, computational complexity, and performance for meaningful variations of this hybrid system are proposed. The system designs developed throughout the thesis enable the collaboration among multiple LED transmitters in VLC systems, and our results indicate that these collaborative designs can significantly improve the performance of indoor VLC systems. Applied Science, Faculty of Electrical and Computer Engineering, Department of Graduate

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譚祐怡 and Yau-yee Tam. "Dual use of visible light-emitting diodes." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2000. http://hub.hku.hk/bib/B31223436.

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Talukdar, Sumanta. "Microstereolithography implemented via visible light digital holography." Thesis, University of Sussex, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.404209.

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The amalgamation of the technologies of Microfabrication and Rapid Prototyping and Manufacturing is a field that has witnessed a surge of research activity in recent years. This thesis demonstrates the development of a novel microfabrication system characterised by the use of Computer Generated Holograms (CGHs) as part of a StereoLithographic rapid prototyping system in cohesion with applied microfabrication techniques. CGHs are reconstructed using a laser diode operating at a visible wavelength (407nm) and subsequently implemented in the fabrication of a microstructure. The hologram encoding method utilized two-pixel macropixels implemented on a smectic, analogue ferroelectric liquid crystal (AFLC) spatial light modulator (SLM). This, in conjunction with the bipolar nature of the modulating device, allows for full complex optical modulation. A commercial photopolymer is chosen as the target material. The underlying chemical processes comprising its photochemical behaviour in its native state, as well as in the presence of sensitizers or visible light photoinitiators, are described and the suitability of each to the StereoLithographic processes evaluated. Experimental determination of the effect of such holograms on the target material is undertaken, which include nondegenerate four wave mixing to investigate optical characteristics and cure depth measurement techniques to evaluate photochemical response. The beneficial effects of using a visible light source with respect to the final physical properties of the component are determined. Final product microstructures displaying a variety of topologies are experimentally realised, accompanied by descriptions of their respective fabrication techniques and formulation requirements

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Velasquez, Estuardo Rene Garcia. "Sending Location-Based KeysUsing Visible Light Communication." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-310907.

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In this thesis we present a Security Application based on Visible Light Communication(VLC). As VLC continues to develop, the need to protect valuable informationtransmitted using this type of communication is also growing. We aim to protect thisvaluable information by proposing a security application in which the data is encryptedin a multiple-light system and only recoverable in specific locations of a movingpattern within specific time. We use the Shamir Secret Sharing algorithm as basis forthe encryption combined with additional algorithms to provide a more securetransmission. The application is formed by the Physical Layer which is in charge ofproviding the optimal configuration for transmission and the Application Layer inwhich we implement the encryption and decryption algorithms for the application.The Physical Layer is formed by a group of LED bulbs controlled by an FPGA usingPWM to represent the information. We propose a scheduling algorithm in which thelights are scheduled in a bit-by-bit manner. The reception part is formed by theOPT101 optical receiver connected to the ultra-low power TS881 comparator. Asecond FPGA is in charge of demodulating the signals from the comparator bymeasuring the period of each signal to detect the corresponding bit. To evaluate theSecurity Application and to find best configurations for the Physical Layer we performa series of experiments in which we modify the responsivity of the receiver underdifferent scenarios including variations of transmission angles, data rates, and heights.The results show that adjusting the sensitivity of the receiver plays a major role in theapplication as we shows different types of configurations to adjust the areas in whichthe information can be received.

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Lourenço, Nuno Rafael Mendonça. "Communication systems using visible light : emitter/receiver." Master's thesis, Universidade de Aveiro, 2009. http://hdl.handle.net/10773/2097.

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Mestrado em Engenharia Electrónica e Telecomunicações A presente dissertação aborda o design de um transdutor optoelectrónico para um sistema de comunicações sem fios que utiliza a luz visível como meio de transmissão. Estes sistemas tiram partido dos conhecimentos tecnológicos existentes sobre sistemas de comunicações sem fios utilizando o espectro dos infravermelhos, e da recente introdução em massa de díodos emissores de luz de elevado brilho em diversas aplicações de iluminação. O trabalho apresentado foi desenvolvido dentro do projecto VIDAS, tendo em conta os respectivos cenários de aplicação propostos. Este projecto visa aumentar a segurança rodoviária através da introdução de sistemas de comunicação com luz visível, para estabelecer ligações veículo-a-veículo e/ou veículo-a-semáforo. Através destas ligações, poderão ser antecipadamente fornecidos diversos avisos de segurança aos condutores. O estudo do transdutor proposto, começa com uma introdução ao conceito e evolução dos sistemas de comunicação com luz visível. Segue-se uma apresentação do canal de transmissão, na qual são definidos os modelos de emissor, receptor e propagação. São também discutidas as diversas fontes de ruído óptico e suas influências na aplicação pretendida. A restante análise é dividida em dois dispositivos principais, o emissor e o receptor ópticos. Sobre o emissor, são apresentados os principais blocos funcionais, seguidos de uma exposição das características de diversos díodos emissores de luz e da análise de diferentes topologias de receptor. Para a topologia mais viável de ser implementada, são apresentados diversos resultados de simulação do circuito electrónico. Do lado do receptor, de forma análoga, são apresentados os diferentes blocos funcionais e as características de diversos fotodíodos. No entanto a experiência do grupo de trabalho levou à escolha de uma topologia de receptor mais específica. Desta, fazem parte diversos módulos, cuja análise e resultados de simulação dos respectivos circuitos electrónicos são apresentados. De forma a avaliar a performance dos dispositivos propostos, foram efectuados diversos ensaios e respectivas medições. Estes resultados permitiram obter informações sobre o comportamento da componente óptica do sistema. Deste conjunto de informações, diferentes considerações sobre a performance de módulos individuais e do transdutor são apresentadas. Estas permitem concluir sobre a viabilidade do transdutor optoelectrónico num cenário de aplicação real. ABSTRACT: This dissertation addresses the design of an optoelectronic transceiver for a wireless communication system, using visible light as the transmission medium. These systems take advantage from the available technological expertise on wireless communication systems using the infrared spectrum, along with the recent massive introduction of high brightness light emitting diodes in several lighting applications. The present work was developed within the scope of project VIDAS, regarding the proposed application scenarios. This project aims at increasing road traffic safety by introducing visible light communication systems to establish vehicle-to-vehicle and vehicle-to-traffic light communications. Through these connections, early safety warnings can be provided to drivers. The study of the proposed transceiver begins with an introduction to the concept and evolution of visible light communication systems. This is followed by the presentation of the transmission channel, in which the emitter, receiver and transmission models are defined. Also, the sources and influences of the various optical noise sources are discussed. The remaining analysis is divided between the two major devices, the optical emitter and receiver. From the emitter, the main building blocks are presented, followed by an exposition of several light emitting diodes characteristics and the analysis of diverse receiver topologies. In the case of the most viable topology for implementation, several simulation results of the respective electronic circuit are presented. On the receiver, the main building blocks and the characteristics of several photodiodes are presented in a similar fashion. However, the workgroup experience led to the choice of a specific receiver topology. This is made up of several modules, whose analysis and simulation results for the electronic circuits are presented. In order to evaluate the performance of the proposed devices, several tests and measurements were made. These results also provided information on the system’s optical component behavior. From this assortment of information, different considerations on the performance of the individual modules, as well as the transceiver are presented. They allow for a conclusion on the viability of the optoelectronic transceiver in a real application scenari

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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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Tam, Yau-yee. "Dual use of visible light-emitting diodes /." Hong Kong : University of Hong Kong, 2000. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21949001.

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Popova, Marina. "Visible Light-Triggered Carbon Monoxide-Releasing Molecules." DigitalCommons@USU, 2019. https://digitalcommons.usu.edu/etd/7500.

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Carbon monoxide (CO) is now well established as one of the signaling molecules in higher organisms, including humans. Due to its physiological roles, CO is now accepted as a potential therapeutic agent. The use of CO gas has been studied in multiple clinical trials. Vasodilation, anti-inflammatory, anti-apoptotic, anti-proliferative and cytoprotective effects are just a few of the pharmacological actions attributed to CO gas in various models of diseases. Use of inhaled CO gas as a therapeutic has many limitations which necessitate the development of a new approach for CO delivery. In order to handle CO safely, compounds that release CO (CO-releasing molecules, CORMs) have been developed. CORMs that release CO only when triggered, and with the ability to target certain tissue sites, are of particular interest. Our lab is developing molecules that release CO only when illuminated with visible light (photoCORMs). These photoCORMs are based on a motif found in naturally-occurring flavonols, which are chemical compounds found in wide variety of foods including fruits, vegetables, tea and dark chocolate. The research presented in this dissertation outlines the results of studies on extended flavonols as CO release agents. The specific studies described herein focus on understanding visible light-induced CO-releasing flavonols in terms of their: a) structure/reactivity relationships, especially in biological environments; b) interactions with metal ions and proteins; c) reaction pathway of CO release; and d) their properties when combined with a CO-sensing motif.

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Tucker, Joseph Walter. "Synthetic applications of visible-light photoredox catalysis." Thesis, Boston University, 2013. https://hdl.handle.net/2144/12865.

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Thesis (Ph.D.)--Boston University PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. Reduction and oxidation reactions are some of the most common chemical transformations occurring both in nature and chemical laboratories. The vast majority of redox reaction systems utilized by synthetic chemists require stoichiometric quantities of redox reagents and generate a corresponding amount of chemical waste. Furthermore, the utilization of visible light irradiation to promote organic transformations has long been recognized as an attractive means to make synthetic chemistry more sustainable and environmentally benign. This work describes our efforts to merge the fields of visiblelight mediated photoredox reactions of metal complexes with synthetic organic chemistry to enable the synthesis of valuable reactive organic intermediates under mild reaction conditions using substoichiometric quantities of redox catalysts. The majority of the work presented utilizes the single electron reducing abilities of photoredox catalysts to mediate the reductive displacement of activated organohalides to generate carbon-centered free radical intermediates. A variety of transformations, including reductive hydrodehalogenation, heterocycle functionalization, radical cyclizations and intermolecular atom transfer radical addition, were developed. Mechanistic experiments and observations lead to a better understanding of the operative pathway for the reactions studied. In addition to the synthesis of reactive free radical intermediates, photoredox methodology was employed for the net carbon-hydrogen bond oxidation of electron rich benzylic ethers to form oxocarbenium ions. This led to the development a novel protocol for the oxidative cleavage of para-methoxybenzyl ethers to afford the corresponding deprotected alcohols. Observation of the crude reaction mixture showed the sole redox by-product of this transformation was chloroform. As a result, this method is an attractive alternative to the use of other oxidants, as the production of a stoichiometric quantity of persistent by-product is avoided. Finally, the overall efficiency of a number of transformations which are mediated by photoredox catalysis was enhanced by the use of a photochemical flow reactor designed in our laboratories as part of a collaboration with Prof. Timothy Jamison of MIT. The reactor designed was inexpensive and could easily be implemented in any laboratory without specialized equipment. Furthermore, the flow reactor allowed for efficient and convenient scale-up of photochemical transformations, a process that persistently proved difficult using traditional batch reactors.

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Lucas, Rodrigues Leona. "Advanced photochemical reactions induced by visible light." Thesis, Queensland University of Technology, 2022. https://eprints.qut.edu.au/235925/1/Leona%2BLucas%2BRodrigues%2BThesis%283%29.pdf.

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Nature utilizes the energy of light for chemical transformations such as photosynthesis or the visual systems in human eyes, where wavelengths from predominantly high energetic UV to harmless visible light are consumed by the respective chromophores. Therefore, the herein presented thesis focusses on developing photoreactive molecules responsive to visible light to ensure minimal harm in form of photo-bleaching or degradation to molecules, polymers or materials via three major reaction pathways: light induced ligation, bond-cleavage/rearrangement and isomerization reactions. Here, a particular focus lays on the development of novel and advanced reactions to establish versatile platforms.

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Anutgan, Mustafa. "Nanocrystal Silicon Based Visible Light Emitting Pin Diodes." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612718/index.pdf.

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The production of low cost, large area display systems requires a light emitting material compatible with the standard silicon (Si) based complementary metal oxide semiconductor (CMOS) technology. The crystalline bulk Si is an indirect band semiconductor with very poor optical properties. On the other hand, hydrogenated amorphous Si (a-Si:H) based wide gap alloys exhibit strong visible photoluminescence (PL) at room temperature, owing to the release of the momentum conservation law. Still, the electroluminescence (EL) intensity from the diodes based on these alloys is weak due to the limitation of the current transport by the localized states. In the frame of this work, first, the luminescent properties of amorphous silicon nitride (a-SiNx:H) thin films grown in a plasma enhanced chemical vapor deposition (PECVD) system were analyzed with respect to the nitrogen content. Then, the doping effciency of p- and n-type hydrogenated nanocrystalline Si (nc-Si:H) films was optimized via adjusting the deposition conditions. Next, the junction quality of these doped layers was checked and further improved in a homojunction pin diode. Heterojunction pin light emitting diodes (LEDs) were fabricated with a-SiNx:H as the luminescent active layer. The EL effciency of the fresh diodes was very low, as expected. As a solution, the diodes were electro-formed under high electric field leading to nanocrystallization accompanied by a strong visible light emission from the whole diode area. The current-voltage (I-V) and EL properties of these transformed diodes were investigated in detail.

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Enlund, Åström Isabelle. "Mobility-based Key Sharing Using Visible Light Communication." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-333031.

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Visible Light Communication (VLC) has become an increasingly interesting topicamong researchers. The LEDs used in VLC have important characteristics which differfrom radio waves, and which enables a vast spectrum to be used with many security aspects. Light cannot pass through walls and can be directed. Directing different light sources to different locations, keys can be distributed to these locations. Using this, a mobility pattern can be defined by a user. This thesis considers the Shamir's Secret Sharing algorithm and how it can be used to create a mobility pattern where each distributed key need to be picked up in a specific order, following the pattern. A design solution has been created that considers some of the scenarios where and how this mobility pattern can be used.

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Mostafa, Ayman. "Physical-layer security for visible-light communication systems." Thesis, University of British Columbia, 2017. http://hdl.handle.net/2429/61328.

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Visible-light communication (VLC) is an enabling technology that exploits the lighting infrastructure to provide ubiquitous indoor broadband coverage via high-speed short-range wireless communication links. On the other hand, physical-layer security has the potential to supplement conventional encryption methods with an additional secrecy measure that is provably unbreakable regardless of the computational power of the eavesdropper. The lack of wave-guiding transmission media in VLC channels makes the communication link inherently susceptible to eavesdropping by unauthorized users existing in areas illuminated by the data transmitters. In this thesis, we study transmission techniques that enhance the secrecy of VLC links within the framework of physical-layer security. Due to linearity limitations of typical light-emitting diodes (LEDs), the VLC channel is more accurately modelled with amplitude constraints on the channel input, rather than the conventional average power constraint. Such amplitude constraints render the prevalent Gaussian input distribution infeasible for VLC channels, making it difficult to obtain closed-form secrecy capacity expressions. Thus, we begin with deriving lower bounds on the secrecy capacity of the Gaussian wiretap channel subject to amplitude constraints. We then consider the design of optimal beamformers for secrecy rate maximization in the multiple-input single-output (MISO) wiretap channel under amplitude constraints. We show that the design problem is nonconvex and difficult to solve, however it can be recast as a solvable quasiconvex line search problem. We also consider the design of robust beamformers for worst-case secrecy rate maximization when channel uncertainty is taken into account. Finally, we study the design of linear precoders for the two-user MISO broadcast channel with confidential messages. We consider not only amplitude constraints, but also total and per-antenna average power constraints. We formulate the design problem as a nonconvex weighted secrecy sum rate maximization problem, and provide an efficient search algorithm to obtain a solution for such a nonconvex problem. We extend our approach to handle uncertainty in channel information. The design techniques developed throughout the thesis provide valuable tools for tackling real-world problems in which channel uncertainty is almost always inevitable and amplitude constraints are often necessary to accurately model hardware limitations. Applied Science, Faculty of Electrical and Computer Engineering, Department of Graduate

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Windlin, Charles. "Visible Light Communication as a material for design." Thesis, KTH, Människa-datorinteraktion, MDI (stängd 20111231), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-189553.

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Visible light communication (VLC) is a novel complement to Radio Frequency Communication (RFC) and has many applications in wireless communication, indoor positioning and where RFC is not applicable. The problem is that the technology is black-boxed and therefore hard to apply in today’s design process. For designers to be able to use VLC in their creative process, this study uses the Inspirational Bits approach to expose the materiality of VLC by asking the question: How can we design artefacts that allow designers to engage in a conversation with Visible Light Communication as a material? Through Constructive Design Research, the technology was studied in iterations by building prototypes and reflecting on them. The prototypes are evaluated in two design workshops through observation and gathered feedback from 11 participants. As a result, seven artefacts were constructed to expose seven potential material properties of VLC. The observations and collected feedback show also that the artefacts help designers to gain tacit knowledge about VLC. The artefacts use the Arduino platform and standard electrical components. A by-product of this study is the "lumoino" toolkit for tinkering and prototyping with VLC. Eventually, strengths and weaknesses are discussed, and future work sections show the potential extensions of the artefacts and expansions of the toolkit. ”Kommunikation med synligt ljus” (VLC) som ett design material är ett komplement till ”radio frekvens kommunikation” och har många applikationer inom trådlös kommunikation, Inomhuspositionering, och situationer där RFC inte är applicerbart. Problematiken med teknologi är att den ofta inte är synlig, och därför är svår att inkludera i dagens design processer. För att designers ska kunna använda sig av VLC i deras kreativa process, utgår denna studie från ”Inspirational Bits” förhållningsätt till design, och ämnar utforska följande frågeställning: Hur kan vi designa artefakter som tillåter designers att engagera sig i en konversation med ”kommunikation med synligt ljus” (VLC) som ett design material? Genom ”konstruktiv designforskning”, studerades prototyper av teknologin följt av analys. Processen upprepades med ett flertal modeller. Prototyperna utvärderades i två design-workshops, genom observation av och respons från 11 deltagare. Som resultat, byggdes sju stycken artefakter för att belysa sju stycken potentiella materiella egenskaper av VLC. Observationerna och den samlade responsen visade också att artefakterna hjälpte designers att få taktil kunskap om VLC. Artefakterna baserades på ”the Arduino Platform” och elektriska standard komponenter. En biprodukt av denna studie är ”the lumoino toolkit for tinkering and prototyping with VLC”. Eventuella styrkor och svagheter diskuteras och stycket framtida arbete visar potentiella utvecklingar och expantioner av ”the lumoino toolkit”.

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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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Theorell, Axel, and Anton Osika. "Distinguishing Visual Information from Visible Background Light Sources." Thesis, KTH, Tillämpad fysik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-129277.

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This thesis regards problems of the form: Two light sources are present. The two sources have dierent light spectra. One of the sources carries information and the other source can be regarded as background light. How can we maximize the contrast between the information and the background light using optical ltering techniques? A relevant question when working with this problem is the theoretical limit of how big dierence a lter can make. The dierence is calculated with regards to the optimal lter for a particular setup. An algorithm for nding the optimal lter for a given setup is implemented. An experiment showing that contrast increase through optical ltering is possible is conducted. In this report introductions to colorimetry and photometry are included as well as some basic facts on screens and optical lters.

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Peard, J. M. "The visible-light induced polymerisation of methyl methacrylate." Thesis, University of Liverpool, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372728.

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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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Hilmia, Abdalah. "Sending Location-Based Keys Using Visible Light Communication." Thesis, Uppsala universitet, Institutionen för informationsteknologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-276338.

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In this thesis we explore the possibilities of using Visible Light Communication (VLC) to build a system that is capable of securely sharing small amounts of data in the form of encryption keys in a boundary defined area. We design and implement the MAC and Physical layers of the system. On the transmission part, the system uses BFSK and Manchester encoding to modulate the signal. The reception is handled in windows of fixed size where the Goertzel algorithm is applied to detect the transmitted frequencies. The transmitters synchronize their transmissions using a simple static scheduling method. Based on this system we then build a secret sharing platform where we utilize Shamir's Secret Sharing protocol. We finally create different scenarios for this platform and test them. Those scenarios include variations of transmitter angles, different kinds of receivers with different sensitivity levels and different heights of the receiver. The results of this research show that the angle of the transmitters and the sensitivity of the receiver are in close relation to how the contours of the reception area would look like. The results also show that the height of the receiver and its sensitivity play a major role of how large this area is.

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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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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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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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Kumar, Navin. "Visible light communication systems for road safety applications." Doctoral thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/8176.

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Doutoramento em MAP-Tele Esta tese apresenta um estudo exploratório sobre sistemas de comunicação por luz visível e as suas aplicações em sistemas de transporte inteligentes como forma a melhorar a segurança nas estradas. Foram desenvolvidos neste trabalho, modelos conceptuais e analíticos adequados à caracterização deste tipo de sistemas. Foi desenvolvido um protótipo de baixo custo, capaz de suportar a disseminação de informação utilizando semáforos. A sua realização carece de um estudo detalhado, nomeadamente: i) foi necessário obter modelos capazes de descrever os padrões de radiação numa área de serviço pré-definida; ii) foi necessário caracterizar o meio de comunicações; iii) foi necessário estudar o comportamento de vários esquemas de modulação de forma a optar pelo mais robusto; finalmente, iv) obter a implementação do sistema baseado em FPGA e componentes discretos. O protótipo implementado foi testado em condições reais. Os resultados alcançados mostram os méritos desta solução, chegando mesmo a encorajar a utilização desta tecnologia em outros cenários de aplicação. This thesis presents a study carried out on the exploration of visible light communication (VLC) for road safety applications in intelligent transportation systems (ITS). We developed conceptual and analytical models for the usage of VLC technologies for human safety. A low cost VLC prototype traffic broadcast system was hardware designed and implemented. In order to realize this prototype a number of exhaustive steps have been designed and implemented. An optimized illumination distribution was achieved in a defined service area from LED-based traffic lights associated with a VLC emitter. A traffic light system set-up was modeled and designed for optimum performance. The optical wireless channel was characterized and examined. Depending on the characteristics of the channel and specific applications, a robust modulation technique based on direct sequence spread spectrum using sequence inverse keying (DSSS SIK) was analyzed, developed, and implemented. The complete prototype VLC transceiver system was then implemented with field programmable gate arrays (FPGA) and discrete components. Simulation and experimental validation of system was performed in different scenarios and environments. The obtained results have shown the merits of our approach. A number of findings was experienced which are illustrated at the end. These observations would enhance and encourage potential research in the area and optimize performance of VLC systems for a number of interesting applications in future. A summary of future research challenges is presented at the end.

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Rodrigues, Luís Filipe Abade. "Error correcting codes for visible light communication systems." Master's thesis, Universidade de Aveiro, 2015. http://hdl.handle.net/10773/15887.

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Mestrado em Engenharia Eletrónica e Telecomunicações Over the past few years, the number of wireless networks users has been increasing. Until now, Radio-Frequency (RF) used to be the dominant technology. However, the electromagnetic spectrum in these region is being saturated, demanding for alternative wireless technologies. Recently, with the growing market of LED lighting, the Visible Light Communications has been drawing attentions from the research community. First, it is an eficient device for illumination. Second, because of its easy modulation and high bandwidth. Finally, it can combine illumination and communication in the same device, in other words, it allows to implement highly eficient wireless communication systems. One of the most important aspects in a communication system is its reliability when working in noisy channels. In these scenarios, the received data can be afected by errors. In order to proper system working, it is usually employed a Channel Encoder in the system. Its function is to code the data to be transmitted in order to increase system performance. It commonly uses ECC, which appends redundant information to the original data. At the receiver side, the redundant information is used to recover the erroneous data. This dissertation presents the implementation steps of a Channel Encoder for VLC. It was consider several techniques such as Reed-Solomon and Convolutional codes, Block and Convolutional Interleaving, CRC and Puncturing. A detailed analysis of each technique characteristics was made in order to choose the most appropriate ones. Simulink models were created in order to simulate how diferent codes behave in diferent scenarios. Later, the models were implemented in a FPGA and simulations were performed. Hardware co-simulations were also implemented to faster simulation results. At the end, diferent techniques were combined to create a complete Channel Encoder capable of detect and correct random and burst errors, due to the usage of a RS(255,213) code with a Block Interleaver. Furthermore, after the decoding process, the proposed system can identify uncorrectable errors in the decoded data due to the CRC-32 algorithm. Ao longo dos últimos anos o número de utilizadores de redes sem fios tem aumentado. Até ao momento, a tecnologia RF (Radio Frequência) dominado este segmento. No entanto, a saturação nessa região do espectro eletromagnético exige tecnologias alternativas para redes sem fios. Recentemente, com o crescimento do mercado da iluminação LED (Díodo Emissor de Luz), as Comunicações por Luz Visível têm atraído as atenções dos investigadores. Em primeiro lugar, é uma fonte de luz eficiente para aplicações de iluminação. Em segundo lugar, o LED é um dispositivo que é facilmente modulado e com grande largura de banda. Por último, permite combinar iluminação e comunicação no mesmo dispositivo, ou seja, permite a implementação de sistemas de comunicação sem fios altamente eficientes. Um dos aspetos mais importantes num sistema de comunicação é a sua fiabilidade quando sujeitos a canais com ruído. Nestes cenários, a informação recebida pode vir afetada de erros. Para garantir o correto funcionamento do sistema, é muito comum o uso de um codificador de canal. A sua função é codificar a informação a ser enviada para melhorar a performance do sistema. O uso de Códigos de Correção de Erros é muito frequente permitindo anexar informação redundante aos dados originais. No recetor, a informação redundante é usada para recuperar possíveis erros na transmissão. Esta dissertação apresenta os passos da implementação de um Codificador de Canal para VLC. Foram consideradas várias técnicas tais como os códigos Reed-Solomon e os códigos Convolucionais, Interleaving (Bloco e Convolucional), CRC e Puncturing. Foi efetuada uma análise das características de cada técnica a fim de avaliar quais as mais apropriadas para o cenário em questão. Numa primeira fase, vários modelos foram implementados em Simulink a fim de simular o comportamento dos mesmos em diferentes cenários. Mais tarde os modelos foram implementados e simulados em blocos de hardware. Para obter resultados de uma forma mais rápida, foram elaborados modelos de co-simulação em hardware. No final, diferentes técnicas foram combinadas para criar um Codificador de Canal capaz de detetar e corrigir erros aleatórios e em rajada, graças ao uso de códigos Reed-Solomon em conjunto com técnicas de Interleaving. Adicionalmente, usando o algoritmo CRC, após o processo de descodficação, o sistema proposto é capaz de identificar possíveis erros que não puderam ser corrigidos.

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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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Ireland, Christopher. "Niobium oxide based material for visible light photocatalysis." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/8713/.

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The primary aim of the work presented in this thesis was to design and synthesise well-characterised material that would exploit visible light to promote photocatalysis, involving the degradation of organic compounds in water, or generation of hydrogen from the water splitting reaction. In doing so, both environmental concerns, such as the removal of pollutants in wastewater, and energy concerns, such as the generation of a clean and safe form of hydrogen for use as a renewable fuel could be addressed. The approach used was to employ existing methods to synthesise high surface area quasi-amorphous material that is active in UV light for photocatalysis, and then design and employ post synthetic modification to promote the material for visible light photocatalysis. Niobium (V) oxide was synthesised in a high surface area form, successfully scaling up the synthesis from 2 g to over 200 g quantities of as made material. This UV active photocatalyst was fully characterized by methods including X-ray diffraction and thermal gravimetric analysis. The material was used to degrade the model dye Methyl Orange and generate hydrogen from a methanol / water solution without further modification. By adding platinum group metals (PGMs) to the niobium (V) oxide, a greatly enhanced efficiency for hydrogen generation was realized. A survey of metals (platinum rhodium and palladium) and weight percentages of metal added (0.01 – 1%) was carried out, with the PGM added materials characterised for hydrogen generation using a methanol / water sacrificial reagent system, as well as PGM dispersion, TEM imaging, EDX and X-ray photoelectron spectroscopy for characterising the higher weight percentage material. Finally, chromium (III) oxide was added to the surface of the niobium (V) oxide in various weight percentages (1% - 5%). The optical properties of this composite material, in comparison with the starting materials were investigated, in particular the difference in diffuse reflectance of the starting materials and composite were highlighted to demonstrate charge transfer between the chromium (III) on the surface, and niobium (V), in the bulk of the material, with the oxidation states being confirmed by XPS. Furthermore, this material was found to degrade methyl orange under visible light. An action spectrum was carried out measuring the quantum efficiency of the reaction at different wavelengths, which proved it was the chromium – niobium charge transfer absorbance in isolation that was responsible for the methyl orange degradation.

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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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39

Clapp, Paula Jean 1968. "Visible-light induced reactions in lamellar phospholipid assemblies." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/282185.

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Cyanine photosensitizers are visible-light absorbing dyes commercially useful in photography and available in a variety of structures with tunable redox, absorptivity and excited state properties. The areas of research described in this dissertation all utilize cyanine dyes to photosensitize various processes to visible-light within the confines of lamellar phospholipid assemblies. In Chapter III, an efficient three component, liposome-bound photochemical molecular device for transfer of energy and electrons is described. A porphyrin (free base or metallated) serves as the energy donor, a cyanine functions as the energy acceptor/electron acceptor and Ph₃BnB- acts as an electron donor. In Chapter IV, the first example of visible-light sensitized bilayer polymerization is presented. Sensitizing the polymerization of two-dimensional lipid assemblies to visible-light is part of a current research effort to exploit the properties of polymerized supramolecular structures. Extending the polymerization sensitivity of such amphiphile aggregates to lower energy visible-light creates possibilities for applications where UV photolysis would not be useful. Applications of liposomes as drug delivery vehicles thus far have relied upon such release mechanisms as pH sensitivity or target specific interactions to empty the liposome contents to the cell. Chapter V describes a new system for the successful destabilization of liposomes at pH 4.5 via visible-light sensitive polymerization of lipids. Visible-light sensitized polymerization induces the release of liposome aqueous contents providing temporal and spatial control over the release event and lower energy irradiation with more tissue penetration than UV photolysis.

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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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CALAFIORE, GIUSEPPE. "Nanoimprinting of Photonic Devices for Visible Light Applications." Doctoral thesis, Politecnico di Torino, 2016. http://hdl.handle.net/11583/2640840.

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The science of photonics is increasingly enabling the discovery of unprecedented proprieties that stem from the interaction of light with nanostructured matter. On the other hand, nanotechnology provides a key support to the research in photonics. In particular nanoimprint lithography (NIL) proved important to accelerate the development and prototyping of novel photonic device concepts. In this thesis, NIL was analyzed as a suitable, flexible, low-cost lithography solution for photonics. The purpose of this work is to research and evaluate novel nanofabrication technologies, materials and device concepts to support and innovate the fields of photonics and nanotechnology. In doing so, different implementations of NIL were experimentally investigated on the imprint of novel photonic devices into purely organic and hybrid organic-inorganic sol-gel materials. Two main research themes on printable photonics are explored in parallel. The first concerns the development and testing of nanoimprint technologies to pursue the fabrication of progressively more challenging device concepts, from 2D to 3D. As a second research theme, the idea to couple top-down nano-patterning approaches (NIL) with bottom-up functionalities that emerge from engineering material proprieties at the chemistry level is put forward. To explore these research courses, two photonic devices were designed, fabricated and tested: an integrated holographic planar circuit for on-chip spectroscopy, and a photonic crystal slab printed out of a functional, high-refractive index material. The amount of integration, complexity and variety of the printed optical components presented here allow us to extend the validity of the work to an even broader range of photonic devices. This work advances the field of printable photonics and demonstrates its leverage to innovation, which encompasses several scientific fields.

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In, Su-Il. "Catalysts and light : synthesis and application of new, visible light activated photocatalytic materials." Thesis, University of Cambridge, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.612014.

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Shen, Yangyang. "Visible Light Photoredox Promoted Transformations of Inert Chemical Bonds." Doctoral thesis, Universitat Rovira i Virgili, 2018. http://hdl.handle.net/10803/665125.

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L'última dècada ha estat testimoni del desenvolupament dramàtic de la catàlisi de fotògrafs de llum visible, s'han descobert algunes de les transformacions no reconegudes anteriorment i es van iniciar en condicions excepcionalment suaus. Les aplicacions habilitades per la tècnica de photoredox s'han trobat en síntesi orgànica, farmàcia i ciències dels materials. Tanmateix, la funcionalització dels enllaços químics inerts més enllà de la capacitat confinada dels fotocatalizadores convencionals segueix sent menys explorada. Tenint en compte l'interès investigador del grup Martín i el potencial d'una nova estratègia dissenyada per activar enllaços químics inerts, juntament amb la tècnica d'acompanyament de photoredox, hem donat a conèixer amb èxit el següent repte principal en fotoquímica: Per ampliar la ciclització radical de la transferència d'àtoms promoguda per llum visible als iodurs de alquils pràcticament inexplorats. Desenvolupar una fixació de CO2 fotoquímic de conformació d'enllaços cap a la síntesi d'àcid fenilacético valuós amb gran complexitat molecular. Desbloquejar un nou concepte per a la funcionalització d'enllaços C-H natives sp3 amb la sinergia de diarilcetona i catalitzador de níquel. La última década ha sido testigo del dramático desarrollo de la catálisis por fotorrespiración con luz visible, varias transformaciones no reconocidas previamente se descubrieron y procedieron en condiciones excepcionalmente suaves. Las aplicaciones habilitadas por la técnica de fotoredox se han encontrado en síntesis orgánica, productos farmacéuticos y ciencia de materiales. Sin embargo, la funcionalización de enlaces químicos inertes más allá de la capacidad confinada de los fotocatalizadores convencionales sigue siendo menos explorada. Teniendo en cuenta el interés de la investigación del grupo de Martín y el potencial de la nueva estrategia diseñada para activar enlaces químicos inertes, junto con la técnica de acomodación del fotoredox, revelamos con éxito el siguiente reto principal en la fotoquímica: Para expandir la luz visible promovió la transferencia de átomos y la ciclación radical a yoduros de alquilo inactivados virtualmente no explorados. Desarrollar una fijación fotoquímica de CO2 de formación múltiple de enlaces hacia la síntesis de ácido fenilacético valioso con alta complejidad molecular. Para desbloquear un nuevo concepto para la funcionalización de los enlaces nativos de sp3 C-H con la sinergia de la diarilcetona y el catalizador de níquel. Last decade has witnessed the dramatic development of visible light photoredox catalysis, a number of previously unrecognized transformations have been nicely discovered and proceeded under exceptionally mild conditions. Applications enabled by photoredox technique have been found in organic synthesis, pharmaceuticals and material science. However, functionalization of inert chemical bonds beyond the confined ability of conventional photocatalysts still remains less explored. Considering the research interest of Martín’s group and the potential of new designed strategy to activate inert chemical bonds, together with the accommodating technique of photoredox, we successfully disclosed the following main challenge in photochemistry: To expand the visible light promoted atom transfer radical cyclization to virtually unexplored unactivated alkyl iodides. To develop a multiple bond-forming photochemical CO2 fixation towards the synthesis of valuable phenylacetic acid with high molecular complexity. To unlock new concept for functionalizing native sp3 C-H bonds with the synergy of diaryl ketone and nickel catalyst.

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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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Ghasimi, Saman [Verfasser]. "Conjugated porous polymers for visible-light photocatalysis / Saman Ghasimi." Mainz : Universitätsbibliothek Mainz, 2017. http://d-nb.info/1123047847/34.

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Li, Xuan. "Design and optimisation of user-centric visible-light networks." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/419060/.

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In order to counteract the explosive escalation of wireless tele-traffic, the communication spectrum has been gradually expanded from the conventional radio frequency (RF) band to the optical domain. By integrating the RF band relying on diverse radio techniques and optical bands, the next-generation heterogeneous networks (HetNets) are expected to be a potential solution for supporting the ever-increasing wireless tele-traffic. Owing to its abundant unlicensed spectral resources, visible light communications (VLC) combined with advanced illumination constitute a competent candidate for complementing the existing RF networks. Although the advantages of VLC are multi-fold, some challenges arise when incorporating VLC into the classic RF HetNet environments, which may require new system architectures. This motivates our research on the system design of user-centric (UC) VLC. Our investigations are focused on system-level design of VLC and it is constituted by three major aspects, namely 1) by the cooperative load balancing (LB) in hybrid VLC and wireless local area network (WLAN) as discussed in Chapter 2; 2) by the UC cluster formation and multiuser scheduling (MUS) of Chapter 3; 3) as well as by the energy-efficient scalable video streaming design example of Chapter 4. Explicitly, we first study VLC as a complementary extension of the existing WLAN. In Chapter 2 we study various conventional cell formations invoked for networks in order to tackle the significant inter-cell interference (ICI) problem, including the traditional unity/nonunity frequency reuse (FR) techniques as well as the advanced combined transmission (CT) and vectored transmission (VT) schemes. Then a distributed LB algorithm is proposed for a hybrid VLC and WLAN network, which is then evaluated from various perspectives. In order to further mitigate the ICI in VLC networks, we focus our attention on novel UC-VLC cluster formation techniques in Chapter 3 and Chapter 4. The concept of UC cluster formation is a counterpart of the conventional network-centric (NC) cell formation, which is dynamically constructed according to the users’ location. Relying on graph theory, the joint cluster formation and MUS problem is solved in Chapter 3. Furthermore, another important optimisation aspect in most wireless networks is the achievable energy efficiency (EE). Hence, we design an energy-efficient scalable video streaming scheme for our UC-VLC network, which achieves superior performance compared to the NC cells in terms of its throughput attained, EE as well as the quality of service (QoS).

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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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48

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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Iyer, Akila. "Visible Light Photocatalysis of N-N Bond Based Compounds." Diss., North Dakota State University, 2016. http://hdl.handle.net/10365/25862.

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The well-established principles of organic photochemistry, offer chemists the fundamental understanding and tools for studying light induced chemical transformations. Employing visible light for photocatalysis, one can design and develop benign routes for the synthesis of new organic materials. In our present investigation, we have developed novel N-N bond based compounds for visible light mediated phototransformations. We have presented synthesis for targeting achiral/chiral N-N bond based compounds and their study for various light driven applications. To name a few applications, these compounds have shown to react smoothly under visible light, metal-free conditions for classical photoreactions, chloromethylation, asymmetric photocyclization and photopolymerization. A diverse range of compounds has shown to react smoothly to afford products in high yields. The scope of this methodology has been evaluated for both intermolecular and intramolecular reactions. Our work benefits from the ability of these compounds to undergo desired phototransformation in both solution and in crystalline media. We have provided photochemical and photophysical details that corroborates our experimental findings and highlights the role of excited state reactivity of the novel N-N bond based compounds. This thesis will be an effort to make chemists familiarize with potential of these compounds in light induced reactions. National Science Foundation NSF (CHE-1465075, 1213880) NDEPSCoR (EPS-IIA-1355466) North Dakota State University. Department of Chemistry and Biochemistry

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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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Dissertations / Theses on the topic 'Visible-light'

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