A 75-Mb/s RGB PAM-4 Visible Light Communication Transceiver System With Pre- and Post-Equalization

Simultaneous illumination and communication using solid-state lighting devices like white light-emitting diode (LED) light sources is gaining popularity. The white light LED comprises a single-colored yellow phosphor excited by the blue LED chip. Therefore, color-quality determining parameters like color-rendering index (CRI), correlated color temperature (CCT), and CIE 1931 chromaticity coordinates of generic white LED sources are poor. This article presents the development of multi-color phosphors excited by a blue LED to improve light quality and bandwidth. A multi-layer stacking of phosphor layers excited by a blue LED led to the quenching of photoluminescence (PL) and showed limited bandwidth. To solve this problem, a lens-free, electrically powered, broadband white light source is designed by mounting multi-color phosphor LEDs in a co-planar ring-topology. The CRI, CCT, and CIE 1931 chromaticity coordinates of the designed lamp (DL) were found to be 90, 5114 K, and (0.33, 0.33), respectively, which is a good quality lamp for indoor lighting. CRI of DL was found to be 16% better than that of white LED (WL). Assessment of visible light communications (VLC) feasibility using the DL includes time interval error (TIE) of data pattern or jitter analysis, eye diagram, signal-to-noise ratio (SNR), fast Fourier transform (FFT), and power spectral density (PSD). DL transmits binary data stream faster than WL due to a reduction in rise time and total jitter by 31% and 39%, respectively. The autocorrelation function displayed a narrow temporal pulse for DL. The DL is beneficial for providing high-quality illumination indoors while minimizing PL quenching. Additionally, it is suitable for indoor VLC applications.

Indoor visible light positioning becomes attractive due to the increasing demands of location-based services. In this paper, we presented a model of an indoor positioning system based on visible light communication technology firstly. The system uses white light emitting diodes (LED) as light sources, so it has the dual role of communication and lighting. Then, the transmitter and receiver of visible light communication in the system have been designed and realized. Next, a coding protocol was designed and implemented, which can be used to transmit ID of each light source. Finally, the error performance in experiments of the proposed system is analyzed and several suggestions on future research of indoor positioning based on visible light communication were given.

Light-emitting diodes (LEDs), which will be increasingly used in lighting technology, will also allow for distribution of broadband optical wireless signals. Visible-light communication (VLC) using white LEDs offers several advantages over the RF-based wireless systems, i.e., license-free spectrum, low power consumption, and higher privacy. Mostly, optical wireless can provide much higher data rates. In this paper, we demonstrate a VLC system based on a white LED for indoor broadband wireless access. After investigating the nonlinear effects of the LED and the power amplifier, a data rate of 1 Gb/s has been achieved at the standard illuminance level, by using an optimized discrete multitone modulation technique and adaptive bit- and power-loading algorithms. The bit-error ratio of the received data was $1.5\cdot 10^{-3}$ , which is within the limit of common forward error correction (FEC) coding. These results twice the highest capacity that had been previously obtained.

Visible light communications (VLC) use modern solid-state light-emitting diodes (LEDs) to broadcast information. Emerging white-light LEDs allow the combination of lighting and optical wireless communication in one optical source. In this paper, a new LED lighting design using one-chip-type white LEDs is proposed for efficient illumination and optical wireless communications under the existence of several obstacles. Lighting and communication performance are analyzed to show the effectiveness of the proposed LED lighting. Specifically, the signal-to-noise ratio considering intersymbol interference and the bit-error rate of variable pulse position modulation (VPPM) with dimming control are considered.

Advances in high brightness light emitting diode (LED) technology are enabling myriad applications in lighting including visible light communications (VLC) technology that has the potential to complement RF technology to provide wireless data access for indoor coverage. This chapter reviews various dimming techniques suitable for VLC, and presents an LED driver circuit architecture incorporating digitally controlled analog circuit blocks to deliver concurrent dimming control and data transmission for VLC-enabled lighting. To achieve this target, a bi-level pulse-width modulation (PWM) driving scheme is applied to enable data transmission during the “off” period of the LED drive current while concurrently providing dimming control. The proposed architecture is compatible with digital baseband modulation schemes and implements a mechanism for ease of integration with commercial off-the-shelf (COTS) LED drivers for VLC system realization. This chapter also discusses a dimming compatible analog baseband modulation scheme. The reverse polarity optical orthogonal frequency-division multiplexing (RPO-OFDM) is a recent approach to realize compatibility between any format of an analog OFDM signal suitable for optical transmission and the concept of a digital pulse-width modulation (PWM) technique for dimming control. We also describe an implementation of the RPO-OFDM approach as part of a wireless access testbed. Experiments reveal that bit-error and bit-rate performances are maintained over a wide range of dimming.

Li-Fi stands for Light-Fidelity. This technology is very new and was proposed by the German physicist Harald Haas in 2011. Light based communication system is the backbone of the future of the communication system. Li-Fi is a wireless technology that uses light emitting diodes (LEDs) for transmission of data. The development of the wireless communication leads to advance research in LiFi technology. The term Li-Fi states to visible light communication (VLC) technology that uses as medium to deliver high-speed communication in a fashion similar to Wi-Fi. Li-Fi comprises a wide range of frequencies and wavelengths, from the Infrared through visible and down to the Ultraviolet spectrum. The immense use of Li-Fi may solve some bottleneck of data transmission in Wi-Fi technology. With the innovation in technology and the number of users, the existing radio-wave spectrum fails to accommodate this need. To resolve the issues of scalability, availability and security, we have come up with the concept of transmitting data wirelessly through light using visible light communication (VLC) technology. This paper objective is to study and describe the LiFi technology. The improvement of the wireless communication leads to advance research in LiFi technology through Visible Light Communications (VLC) Technology.

Three different types of white light emitting diodes (LEDs) and three types of single color LEDs were tested as light sources for stroboscopic scanning white light interferometry (SSWLI) for dynamic (MEMS) characterization. Short, intense, light pulses and low duty cycle (< 10%) are required to freeze the motion of an oscillating sample. A custom designed LED driver was built utilizing a Metal-Core Printed Circuit Board. At the core of the circuit is a CMOS high speed high current gate driver (IXDD415SI). The LED pulser is compact (50×110 mm 2 ), has good thermal resistivity (0.45 °C/W), wide bandwidth (~DC-10 MHz), and can drive single LEDs at 5A peak current (0.7% duty cycle at 1 MHz). The shortest measured electrical pulses were 6.2 ± 0.1 ns FDHM. The minimum measured Full Duration at Half Maximum (FDHM) of the optical pulse was 8.4 ± 0.1 ns using nonphosphor white LED and 32.1 ± 0.1 ns using white phosphor-converted LED (0.7 % duty cycle at 1 MHz in both cases). The minimum optical pulse FDHM for a single color blue/green LED was 6.4 ± 0.1 ns. The maximum intensity of these pulses was 630 ± 40 μW and 540 ± 30 μW, respectively. All types of white LEDs could be used for stroboscopic SWLI measurements at frequencies up to 2 MHz. For higher frequencies, non-phosphor white LEDs must be used together with a cyan LED to avoid ringing in the SWLI interferogram.

Driven by the increase in Internet of Things (IoT) devices for smart home technologies, visible light communications (VLC) using multiple light emitting diodes (LEDs) have been attracting much attention in order to cope with depleted radio frequency spectrum. This paper presents a suboptimal LED selection algorithm for distributed multiple-input multiple-output (D-MIMO) VLC systems. When total ceiling LEDs are turned on to send information while illuminating an indoor environment, the problems of low energy efficiency and mutual interference between VLC channels arise. The proposed algorithm begins by selecting the LED associated with the largest VLC channel gain and adds the LED supporting the largest level of uncorrelation with the maximum VLC channel gain in each step. Simulation results showed that the proposed scheme achieves a capacity similar to an optimal selection algorithm with reduced computational complexity. With a larger distance between the light terminals and a shorter distance between the LEDs, better channel capacity performance of the proposed scheme can be achieved.

Red, green, and blue (RGB) light-emitting diodes (LEDs) are widely used in everyday illumination, particularly where color-changing lighting is required. On the other hand, digital cameras with color filter arrays over image sensors have been also extensively integrated in smart devices. Therefore, optical camera communications (OCC) using RGB LEDs and color cameras is a promising candidate for cost-effective parallel visible light communications (VLC). In this paper, a single RGB LED-based OCC system utilizing a combination of undersampled phase-shift on&#x2013;off keying (UPSOOK), wavelength-division multiplexing (WDM), and multiple-input&#x2013;multiple-output (MIMO) techniques is designed, which offers higher space efficiency (3 bits/Hz/LED), long-distance, and nonflickering VLC data transmission. A proof-of-concept test bed is developed to assess the bit-error-rate performance of the proposed OCC system. The experimental results show that the proposed system using a single commercially available RGB LED and a standard 50-frame/s camera is able to achieve a data rate of 150 bits/s over a range of up to 60 m.

Visible Light Communication (VLC) has emerged as an attractive alternative to radio frequency (RF) communication, due to cost-effectiveness and being license free. It has also proved its applicability in automotive applications, as an alternative and/or a complement to the traditional RF-based communications. We investigate the suitability of VLC in Intelligent Transportation Systems (ITS) and discuss its advantages in terms of safety enhancement and improved efficiency of the ITS. In this thesis, a VLC-based Vehicle-to-Vehicle (V2V) system in practical environments, considering both Line-of-Sight (LOS) and Non-Line-of-Sight (NLOS) paths are presented. The thesis investigates robust communication between a Light Emitting Diodes (LEDs) based VLC emitter and Photodiodes (PDs) based VLC receiver. For consideration of a V2V communication system, we consider transmitter on vehicle headlights and receivers on taillight making 2 _ 2 Multiple-Input-Multiple-Output (MIMO) communication link. A closed-form expression of the Channel Impulse Response (CIR) is derived and the effect of various channel parameters is analyzed. Optical-Orthogonal Frequency Division Multiplexing (O-OFDM) with adaptive modulation schemes is proposed for system improvement. Its performance is evaluated in terms of Inter Symbol Interference (ISI) mitigation, and data rate improvement. Moreover, the effect of sunlight on the V2V-VLC Two denoising schemes are proposed and evaluated as a solution to combat the effect of the solar irradiance on the VLC signal. Firstly, we use a differential receiver for denoising purposes followed by k-Nearest Neighbour (kNN) based adaptive _ltering algorithm, which is a supervised Machine Learning (MLE) technique. The shadowing effect is also studied. Moreover, an application of VLC in Foglet based ITS is described. The simulation validation of the VLC-based V2V system is performed under various environmental conditions and scenarios. Obtained results emphasize the suitability of VLC technology for automobile applications,.

This article reviews the visible light communications (VLC), a technology in which the visible spectrum is modulated to transmit data. It presents the VLC communication system: the transmitter, the channel, and the receiver. The single and multichannel transceivers are presented. The channel for a system that uses a single light‐emitting diodes (LED) and the matrix representing the multicolor channel are discussed. Various modulation schemes, basic techniques used to implement a VLC system, and different causes of dimming are discussed. In addition, standardization of the VLC technology, applications, as well as challenges for VLC practical implementation and commercialization are reviewed.

Visible light communication (VLC) has emerged as a viable complement to traditional radio frequency (RF) based systems and as an enabler for high data rate communications for beyond-5G (B5G) indoor communication systems. In particular, the emergence of new B5G-based applications with quality of service (QoS) requirements and massive connectivity has recently led to research on the required service-levels and the development of improved physical (PHY) layer methods. As part of recent VLC standards development activities, the IEEE has formed the 802.11bb “Light Communications (LC) for Wireless Local Area Networking” standardization group. This paper investigates the network requirements of 5G indoor services such as virtual reality (VR) and high-definition (HD) video for residential environments using VLC. In this paper, we consider such typical VLC scenarios with additional impairments such as light-emitting diode (LED) nonlinearity and imperfect channel feedback, and propose hyperparameter-free mitigation techniques using Reproducing Kernel Hilbert Space (RKHS) methods. In this context, we also propose using a direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM)-based adaptive VLC transmission method that uses precomputed bit error rate (BER) expressions for these RKHS-based detection methods and performs adaptive BER-based modulation-order switching. Simulations of channel impulse responses (CIRs) show that the adaptive transmission method provides significantly improved error rate performance, which makes it promising for high data rate VLC-based 5G indoor services.

built environment the mixed blessing of Phosphor-based White leDs

With the expanding application of light-emitting diodes (LEDs), the color quality of white LEDs has attracted much attention in several color-sensitive application fields, such as museum lighting, healthcare lighting and displays. Reliability concerns for white LEDs are changing from the luminous efficiency to color quality. However, most of the current available research on the reliability of LEDs is still focused on luminous flux depreciation rather than color shift failure. The spectral power distribution (SPD), defined as the radiant power distribution emitted by a light source at a range of visible wavelength, contains the most fundamental luminescence mechanisms of a light source. SPD is used as the quantitative inference of an LED’s optical characteristics, including color coordinates that are widely used to represent the color shift process. Thus, to model the color shift failure of white LEDs during aging, this paper first extracts the features of an SPD, representing the characteristics of blue LED chips and phosphors, by multi-peak curve-fitting and modeling them with statistical functions. Then, because the shift processes of extracted features in aged LEDs are always nonlinear, a nonlinear state-space model is then developed to predict the color shift failure time within a self-adaptive particle filter framework. The results show that: (1) the failure mechanisms of LEDs can be identified by analyzing the extracted features of SPD with statistical curve-fitting and (2) the developed method can dynamically and accurately predict the color coordinates, correlated color temperatures (CCTs), and color rendering indexes (CRIs) of phosphor-converted (pc)-white LEDs, and also can estimate the residual color life.

Light colour and intensity alters reproductive/seasonal responses in Japanese quail