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Visible light communication (VLC) technology enabling data transmission by modulating solid-state light-emitting diode (LED) devices has attracted much attention recently. However, the transmission rate of VLC remains low due to the low bandwidth performance of LEDs. We present a VLC transmitter consisting of an LED array to enable implementation o...
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... This concise control logic alleviates the linearity constraints of the illuminating LED chips. Comparing with the single carrier VLC systems [11,14,15], orthogonal frequency division multiplexing (OFDM) based VLC systems are immune to baseline wander and low frequency interference from ambient light. Besides, the inherent supporting for multiuser access of OFDM further reinforces its advantages to be a promising technology for VLC systems. ...
Commercial-off-the-shelf (COTS) devices enabled visible light communication (VLC) for Internet of things (IoT) applications has attracted extensive attentions from both academic and industrial communities, thanks to the pervasive deployments of light emitting diode (LED) lighting infrastructure. However, due to the limitation of frequency response and non-linearity of the commercial illuminating LED light consisting of multiple LED chips, the achievable data rate is far less than that provided by the experimental VLC system with a single LED with specialized devices, e.g., lens. To this end, we propose a power-of-2 arrangement scheme for LED chips to generate spatial summing modulation with low control complexity, and demonstrate its availability in an orthogonal frequency division multiplexing (OFDM) VLC system purely built upon COTS devices. It significantly differs from a conventional OFDM VLC system relying on digital-to-analog converter (DAC) and analog signal chain, which is complex and confined by LED’s non-linearity, thanks to we design a novel digital-to-light converter (DLC) which can output 256 light intensities linearly and be directly controlled by the discrete digital signals generated by the OFDM modulator. An experimental demonstration with employing the QAM-OFDM modulation scheme successfully confirms the effectiveness of the proposed spatial summing VLC system, which can achieve low BERs of below the forward error correct (FEC) threshold of $3.8\times 10^{-3}$ 3.8 × 10 − 3 for both QAM8 and QAM16 running transmission frequency of 300 kHz under a communication distance of 0.8 m. It demonstrates the promising potential for delivering a data rate at hundred kbps level with this novel spatial summing based OFDM VLC system, which is sufficient for many IoT applications.
... One straightforward approach is to choose a two-level modulation format that is inherently immune to system nonlinearities at the expense of reduced spectral efficiency [19]. On the other hand, with an LED array, multi-level modulation can be realized by optical superimposition to increase spectral efficiency, and at the same time to resist the modulation nonlinearities of an LED [20][21][22][23][24][25]. The effective solution in VLC bring us enormous enlightenment on future UWOC using LED arrays as light sources. ...
In this work, we propose an underwater wireless optical communication (UWOC) system using an arrayed transmitter/receiver and optical superimposition-based pulse amplitude modulation with 4 levels (PAM-4). At the transmitter side, we design a spatial summing scheme using a light emitting diode (LED) array, which is divided into two groups in a uniformly interleaved manner. With on-off keying (OOK) modulation for each group, optical superimposition-based PAM-4 can be realized. It has enhanced tolerance to the modulation nonlinearities of LEDs. We numerically investigate the feasibility of the proposed spatial summing scheme in various underwater channels via Monte Carlo simulation. With the increase of divergence angle of LEDs and link distance, the optical power distribution tends to be more uniform at the reception plane. It can significantly relax the requirement on the link alignment. Furthermore, we conduct a proof-of-concept experiment employing two blue LEDs. A multi-pixel photon counter (MPPC), containing an array of single-photon avalanche diodes (SPADs), is used as the detector. It has a much higher sensitivity and can further relax the requirement for pointing. Over a 2-m tap water channel, data rates of 6.144 Mb/s, 8.192 Mb/s, and 12.288 Mb/s were achieved by using the PAM-4 signal generated by optical superimposition, within a 2.5-MHz system bandwidth. With 0.570-mg/L Mg(OH)2, the measured optical power is just 12.890 µW after a 2-m underwater channel. The corresponding bit error rate (BER) of the 12.288-Mbs PAM-4 signal is 2.9 × 10⁻³, which is still below the forward error correction (FEC) limit of 3.8 × 10⁻³. It implies that the UWOC system based on the high-sensitivity MPPC with array structure has superior power efficiency and robustness.
... One straightforward approach is to choose a two-level modulation format that is inherently immune to system nonlinearities at the expense of reduced spectral efficiency [19]. On the other hand, with an LED array, multi-level modulation can be realized by optical superimposition to increase spectral efficiency, and at the same time to resist the modulation nonlinearities of an LED [20][21][22][23][24][25]. The effective solution in VLC bring us enormous enlightenment on future UWOC using LED arrays as light sources. ...
... Orthogonal frequency division multiplexing (OFDM) [8,9], carrierless amplitude and phase modulation (CAP) [10] and pulse amplitude modulation (PAM) [7,11] have been studied in the context of LED-based links and implemented in VLC system demonstrators. In [8], a 3 Gb/s single-LED OFDMbased wireless VLC link using a GaN micro-pixelated LED (μLED) was implemented. ...
In this paper, feed-forward pre-equalization in conjunction with a PAM modulation scheme are proposed for use in wireless visible light communication (VLC) systems in order to enable the transmission of data rates >1 Gb/s. Simulation results demonstrate that simple few-tap feed-forward pre-equalization is able to remove the intersymbol interference caused by the limited link bandwidth of a line of sight VLC link, providing up to 5 dB better receiver sensitivity compared with postequalization. The pre-equalization scheme is implemented for a free-space VLC link using a PAM modulation scheme, which provides an enhanced spectral efficiency compared to NRZ modulation. Micropixelated LEDs (μLEDs) are used as the transmitter in this study, as they exhibit higher modulation bandwidth than conventional large-diameter LEDs. An avalanche photodiode is used at the receiver to provide an enhanced link power budget. Error-free (BER <;10
<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup>
) 2 Gb/s free-space VLC transmission over 0.6 m is demonstrated experimentally using a simple 3-tap feed-forward pre-equalizer and a PAM-4 modulation scheme. The results show that feed-forward pre-equalization with only a few taps can improve the μLED-based link performance greatly, providing a simple and cost-effective solution for high-speed VLC links.
La bombilla incandescente que ha sido largamente manejada para la iluminación en nuestro entorno desde que se inventó hace más de un siglo está siendo reemplazada paulatinamente debido a su extremada baja eficiencia energética. En las más modernas
bombillas incandescentes, no más del 10% de la energía eléctrica se convierte en luz emitida útil. Por otra parte, las bombillas fluorescentes compactas introducidas en la década de 1990 han ganado popularidad en la última década ya que proporcionan una
mejor eficiencia energética (más lúmenes por watt). Sin embargo, los más recientes avances en la iluminación están basados en tecnología LED, esta tecnología ha permitido una eficiencia energética y una prolongación de la luminaria muy satisfactoria. La
eficacia luminosa media (cuánta electricidad se utiliza para proporcionar la iluminación deseada) de los mejores LEDs en su clase es de hasta 113 lúmenes/watt en 2015, y se proyecta que sea de alrededor de 200 lúmenes/watt para el año 2020. De esta manera
se proyecta un aumento muy significativo en comparación con las bombillas incandescentes y fluorescentes actuales, que proporcionan una eficacia luminosa media de 15 y 60 lúmenes/watt
Visible Light Communication (VLC) systems relying on commercial-off-the-shelf (COTS) devices have gathered momentum recently, due to the pervasive adoption of LED lighting and mobile devices. However, the achievable throughput by such practical systems is still several orders below those claimed by controlled experiments with specialized devices. In this paper, we engineer CoLight aiming to boost the data rate of the VLC system purely built upon COTS devices. CoLight adopts COTS LEDs as its transmitter, but it innovates in its simple yet delicate driver circuit wiring an array of LED chips in a combinatorial manner. Consequently, modulated signals can directly drive the on-off procedures of individual chip groups, so that the spatially synthesized light emissions exhibit a varying luminance following exactly the modulation symbols. To obtain a readily usable receiver, CoLight interfaces a COTS PD with a smartphone through the audio jack, and it also has an alternative MCU-driven circuit to emulate a future integration into the phone. The evaluations on CoLight are both promising and informative: they demonstrate a throughput up to 80kbps at a distance of 2m, while suggesting various potentials to further enhance the performance.
Nowadays, the number of connected devices requiring access to mobile data is considerably increasing. The arrival of even more connected multimedia objects and the growing demand for more information per device highlighted the limits of the fourth generation of broadband cellular networks (4G). This pushed for the development of new methods, one of which is 5G. The goal is to be able to support the growth of wearable, sensors, or related internet-of-object (IoT) systems. The vision behind 5G is to enable a fully mobile and connected society with a consistent experience. In consequence, there is a fundamental need to achieve a seamless and consistent user experience across time and space.Small cells are the basis of advanced communications standards such as 4G and now, 5G. They exist as a result of using higher frequency bands for RF access in order to support new standards and the increasing demands in bandwidth. 5G use millimeter waves and requires a deployment across indoor and dense urban environment which may prove to be a challenge. This is where 5G will need to include hybrid networking solutions and be able to coexist with other wireless access technologies. Visible light communication (VLC) fits into that mold since visible light corresponds to the band between 400 and 800 THz. The available spectrum is multiple thousand times the size of the RF spectrum and it does not interfere with it. The technique combines illumination with communication at possibly tens of gigabits per second. It has the potential to offer a synergistic pairing with 5G in a hybrid network, offering high speed, no interferences, and more security at the cost of limited coverage and low technological maturity.The goal of this thesis is thus to propose and evaluate an experimental implementation of an indoor multi-user VLC system in order to answer the objectives of Li-Fi setup in the context of a small cell. The first step of this study is a detailed state-of-the-art on VLC in indoor wireless communication and multi-user access. It allows the design of our work to be better explained and to compare our approach with existing works. The second step is an analysis of the principles and hypothesis supporting the indoor multi-user VLC system in the study both on the modulation technique and the multi-user access schemes. The conclusions drawn from theoretical and numerical analysis are used as a basis for the rest of the work. The third step is the experimental setup investigations on the single-user broadcast performances optimization and then on the multi-user performances of the system using various schemes. The total throughput using an off-the-shelf white LED reaches 163 Mb/s with a bit-error rate decreased by a factor of 3.55 thanks to the performance optimization process. This technique has the advantage of increasing the flexibility for a multi-access scenario while not augmenting the complexity as it only optimizes the modulation filter parameters. The multi-user access is obtained for a cell size of 4.56 m² at a distance of 2.15 meter away from the transmitter. The user capacity can reach up to 40 users, or 40.62 Mb/s in a 4-user scenario. It is thus demonstrated that the proposed system could function as a cell at a realistic range, with high data rate and the ability to provide for a large amount of users while limiting the cost of implementation.
