Performance Of Visible Light Communication Research Articles

Symmetry of constellation diagram-based intelligent SNR estimation for visible light communications.

Visible light communication (VLC) technology with rich spectrum resources is thought of as an essential component in the future ubiquitous communication networks. Accurately monitoring its transmission impairments is important for improving the stability of high-speed communication networks. Existing research on intelligently monitoring the signal-to-noise ratio (SNR) performance of VLC focuses primarily on the application of neural networks but neglects the physical nature of communication systems. In this work, we propose an intelligent SNR estimation scheme for VLC systems, which is based on the symmetry of constellation diagrams with classical deep learning frameworks. In order to increase the accuracy of the SNR estimation scheme, we introduce two data augmentation methods (DA): point normalization and quadrant normalization. The results of extensive simulations demonstrate that the proposed point normalization method is capable of improving accuracy by about 5, 10, 14, and 26%, respectively, for 16-, 64-, 256-, and 1024-quadrature amplitude modulation compared with the same network frameworks without DA. The effect of accuracy improvement can be further superimposed with traditional DA methods. Additionally, the extensive number of constellation points (e.g., 32, 64, 128, 256, 512, 1024, and 2048) on the accuracy of SNR estimation is also investigated.

Effect of the correlated color temperature of a phosphor-converted LED on indoor visible light communication

Correlated color temperature (CCT) is an important parameter of the phosphor-converted LED (PC-LED); international standards specify its range in different scenarios. However, little has been done to investigate the effect of CCT on the performance of visible light communication (VLC). In this paper, we propose an analytical model for the transmission performance of an LED VLC system based on the dual components of blue and yellow light from the luminescence mechanism of the PC-LED. On this basis, the effects of CCT on the PC-LED’s input current and output optical power between the dual components are analyzed. The simulation results show that the increase of CCT expands the modulation bandwidth of the PC-LED, and the trend of the BER with CCT is also related to the transmission data rate. In addition, the maximum data rate of the PC-LED with CCT from 2700 K to 6500 K under a certain transmission distance is also simulated in this paper.

Enhanced Performance of Visible Light Communication Using Three-Dimensional Spatial Multi-User Holographic Multiplexing

Enhanced Performance of Visible Light Communication Using Three-Dimensional Spatial Multi-User Holographic Multiplexing

Effect of ion migration on lead halide perovskite on visible light communication system

Benefiting from the high modulation bandwidth (BW), low energy consumption and excellent optical performance, lead halide perovskite has attracted wide attention in visible light communication (VLC). However, the ion migration which results in mobile point defects in perovskite structures is recognized as a crucial key factor inducing the performance degradation. Here, the influence of ion migration in perovskite devices on the performance of VLC was systematically studied. The ion migration process is realized by mixing CsPbBr3 and CsPbI3 quantum dots, during which, the performance of the VLC system is reduced, but it can return to its initial state after stabilization. The on-off keying (OOK) modulation scheme of the perovskite light-emitting diode (LED) device was carried out, achieving a data rate of 90 Mbps.

Intelligent Reflecting Surface for MIMO VLC: Joint Design of Surface Configuration and Transceiver Signal Processing

With the capability of reconfiguring the wireless electromagnetic environment, intelligent reflecting surface (IRS) becomes a new paradigm for designing future wireless communication systems. In this paper, we consider optical IRS for improving the performance of visible light communication (VLC) under a multiple-input and multiple-output (MIMO) setting, where the mean square error (MSE) of the IRS-aided MIMO VLC is minimized by jointly designing the IRS and transceiver signal processing. To this end, the MIMO channel gains of the IRS-aided VLC are first derived under the point source assumption, based on which the MSE minimization problem is formulated subject to the emission power constraints and the IRS configuration constraints. Next, we propose an alternating optimization algorithm, which decomposes the original problem into three subproblems, to iteratively optimize the IRS configuration, the precoding and detection matrices for minimizing the MSE. Moreover, theoretical analysis on the performance of the proposed algorithm in high and low signal-to-noise ratio (SNR) regimes is investigated, revealing that the joint optimization process can be simplified in such special cases, and the algorithm’s convergence property and computational complexity are also discussed. Finally, numerical results show that IRS-aided schemes significantly reduce the MSE as compared to their counterparts without IRS, and the proposed algorithm outperforms other baseline schemes.

Combined kernel with parameter optimization for least squares support vector machine postdistorter in visible light communications

The nonlinearity and memory effects induced by light-emitting diode distort the transmitted signal, which significantly limits the performance of visible light communication (VLC) system. With the characteristics of low computational complexity, fast convergence speed, and strong generalization ability, least squares support vector machine (LSSVM) is investigated in this paper and employed to alleviate the nonlinear effect. Since the performance of LSSVM is largely determined by the type of the adopted kernel functions, we utilize Gaussian and Laplace functions and propose a new combined kernel, which can increase the reproducing kernel Hilbert space and thus enhance the global expressive power compared with conventionally used Gaussian kernel. To further improve the performance, a hybrid parameter optimization algorithm is exploited to optimize the proposed kernel, based on genetic algorithm and particle swarm optimization. The property of the proposed postdistortion method is verified by numerical simulations, and better performance is obtained in VLC systems compared with the Gaussian-kernel LSSVM and conventional memory polynomial method.

Recent Advances in Micro-LEDs Having Yellow–Green to Red Emission Wavelengths for Visible Light Communications

Visible light communication (VLC), which will primarily support high-speed internet connectivity in the contemporary world, has progressively come to be recognized as a significant alternative and reinforcement in the wireless communication area. VLC has become more popular recently because of its many advantages over conventional radio frequencies, including a higher transmission rate, high bandwidth, low power consumption, fewer health risks, and reduced interference. Due to its high-bandwidth characteristics and potential to be used for both illumination and communications, micro-light-emitting diodes (micro-LEDs) have drawn a lot of attention for their use in VLC applications. In this review, a detailed overview of micro-LEDs that have long emission wavelengths for VLC is presented, along with their related challenges and future prospects. The VLC performance of micro-LEDs is influenced by a number of factors, including the quantum-confined Stark effect (QCSE), size-dependent effect, and droop effect, which are discussed in the following sections. When these elements are combined, it has a major impact on the performance of micro-LEDs in terms of their modulation bandwidth, wavelength shift, full-width at half maximum (FWHM), light output power, and efficiency. The possible challenges faced in the use of micro-LEDs were analyzed through a simulation conducted using Crosslight Apsys software and the results were compared with the previous reported results. We also provide a brief overview of the phenomena, underlying theories, and potential possible solutions to these issues. Furthermore, we provide a brief discussion regarding micro-LEDs that have emission wavelengths ranging from yellow-green to red colors. We highlight the notable bandwidth enhancement for this paradigm and anticipate some exciting new research directions. Overall, this review paper provides a brief overview of the performance of VLC-based systems based on micro-LEDs and some of their possible applications.

Three-Dimensional Division of Visible Light Communication Irradiation Area

In this article, we divide the irradiated area of visible light communication (VLC) into three parts, according to the influence of diffuse reflection, the irradiance half angle at the source and the communication distance on VLC. We present a volume ratio method to quantitatively analyze each divided part. In this work, based on the Lambertian reflection model of the VLC system in line-of-sight channels, five factors affecting the VLC performance are compared and discussed. A VLC system of a single white-light-emitting diode in a 10 m line-of-sight channel indoors is designed by using the intensity modulation and direct detection technique, and a three-dimensional model of the irradiated area is established.By comparing the distribution of the bit error rate (BER) of the optical signal at different lampshade heights, the volume ratio method is used to calculate the volume percentage of the three irradiated areas. The experimental results show that area II with a volume ratio greater than 50% is the best signal receiving area when compared with areas I and III, having a volume ratio in the range 20∼30%.

Volterra-Aided Neural Network Equalization for Channel Impairment Compensation in Visible Light Communication System

This paper addresses the channel impairment to enhance the system performance of visible light communication (VLC). Inspired by the model-solving procedure in the conventional equalizer, the channel impairment compensation is formulated as a spatial memory pattern prediction problem, then we propose efficient deep-learning (DL)-based nonlinear post-equalization, combining the Volterra-aided convolutional neural network (CNN) and long-short term memory (LSTM) neural network, to mitigate the system nonlinearity and then recover the original transmitted signal from the distorted one at the receiver end. The Volterra structure is employed to construct a spatial pattern that can be easily interpreted by the proposed scheme. Then, we take advantage of the CNN to extract the implicit feature of channel impairments and utilize the LSTM to predict the memory sequence. Results demonstrate that the proposed scheme can provide a fairly fast convergence during the training stage and can effectively mitigate the overall nonlinearity of the system at testing. Furthermore, it can recover the original signal accurately and exhibits an excellent bit error rate performance as compared with the conventional equalizer, demonstrating the prospect and validity of this methodology for channel impairment compensation.

High-Dimensional Radial Basis Function Extension Interpolation Nonlinear Post-Distorter in Visible Light Communication Systems

The nonlinearity induced by light-emitting diode (LED) affects the normal transmission and reception, which significantly limits the performance of visible light communication (VLC) system. To address the problem induced by the nonlinearity of LED, a post-distorter for orthogonal frequency division multiplexing (OFDM) based VLC is proposed in this paper. Radial basis function (RBF) interpolation, known as an excellent function approximation method, is investigated to implement the nonlinearity mitigations. To further remove the memory effect of LED, which could not be ignored, we propose to extend RBF to a high-dimensional interpolation so that it can eliminate both nonlinearity and memory effect simultaneously. The performance of the proposed RBF extension interpolation is verified by numerical simulations, and a better performance in suppressing nonlinearity is obtained in VLC-OFDM systems as compared with the frequency domain nonlinear compensation method. A signal-to-noise ratio gain of 2dB in terms of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{{E}_b} \mathord{/ {\vphantom {{{E}_b} {{N}_0}}} } {{N}_0}}$</tex-math></inline-formula> can be obtained when bit error rate is about 6*10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−7</sup> at 6dB power back-off (PBO), while 6dB gain can be achieved when BER is 2*10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> at 4dB PBO.

Joint Resource Management for Intelligent Reflecting Surface–Aided Visible Light Communications

Though visible light communication (VLC) is a significant supplement to current communication technologies, disadvantages such as the sensitivity to obstacles limit its development and commercialization. As a revolutionizing technology, intelligent reflecting surface (IRS) offers an ability to reconfigure the wireless environment dynamically and passively, which is considered beneficial to improve the performance of VLC. This paper devotes to investigating the effect of VLC IRS and putting forward a joint resource management method for an instantaneous IRS-aided VLC system. To this end, the line-of-sight (LoS) and non-LoS channel gains are first discussed under the point source assumption, after which the system model is established and the optimization problem is formulated. Then, the frozen variable algorithm and minorization-maximization algorithm are proposed to iteratively maximize the overall spectral efficiency (SE), and detailed discussions on the weak/severe interference cases and computational complexity analysis are carried out. Moreover, numerical results are provided to show the improvement of SE and the effects of the proposed algorithms, which offers beneficial insights on joint resource management of IRS-aided VLC.

Position-Dependent MIMO Demultiplexing Strategy for High-Speed Visible Light Communication in Internet of Vehicles

The context of the Internet of Vehicles (IoV) and the growing vehicular deployment of sensors and smart devices have demanded alternative wireless communication technologies. Despite the prevalent works on radio-frequency (RF)-based vehicular communication technologies, visible-light communication (VLC) is envisaged to be a promising candidate due to its unlicensed spectrum and high transmission rates. However, the long-distance and high-speed transmission performance of vehicular VLC needs more investigation considering the massive data transmission needs for automotive applications. In this article, a vehicular multiple-input–multiple-output (MIMO) VLC system based on two commercial headlights and a self-designed PIN array is experimentally demonstrated as a proof of concept for the IoV. Considering the relative movement of vehicles, different communication areas are divided based on the position-dependent receiver receiving states. The boundary condition of each area is derived. For the first time, the selection of the strategy that best suits the MIMO demultiplexing scheme is discussed by analyzing the rank and type of the channel matrix. A modified pilot-aided phase recovery method based on polynomial curve fitting (PCF) is proposed to compensate for the phase noise caused by the sampling frequency offset (SFO). The proposed method maintains good robustness even when the VLC system suffers from the strong nonlinearity and bandwidth limitation of the headlights. Based on the proposed MIMO VLC system, we achieve a record-breaking data rate of 3.08 Gb/s at a 2-m indoor transmission link. We further extend the transmission distance to 100 m, and successfully achieve overall data rates of 336 and 362 Mb/s during the daytime and nighttime, respectively. To the best of our knowledge, these are the highest transmission data rates ever reported for a 100-m vehicular VLC system. Our experimental demonstration clearly verifies the feasibility of VLC in the application of IoV.

Analysis of Visible Light Communication using Integrated Avalanche Photodiode

The problem with Radio Frequency (RF) communication is that it has intrusion and high remission. Moreover, RF communication requires distinct configurations for transference and reception. To overcome these problems, Visible Light Communication (VLC) is recommended, as it has a high tolerance for bandwidth and interference. The usage of LEDs instead of fluorescent lamps uplifts the use of VLC. Visible light communication is a fast-evolving LED-based illumination and data transfer method. The performance of visible light communication over Mach-Zehnder Modulation has been investigated in this paper using the Opti-system simulation tool. The opti-system simulation programme predicts the quality factor and Bit Error Rate (BER) values of various link distances. The proposed system can handle 5 Gbps data rate over a 50-meter link distance with a Quality Factor of 15.71 and no external noise. The projected VLC system performance is further tested using a simulation tool in the case of external noise effects.

Estimation with Angular Parameters on Channel of Visible Light Communication

Performance of visible light communication (VLC) depends highly on channel conditions, which are sensitive to changes in user position. This paper presents estimation schemes of VLC parameters using a Kalman filter (KF), based on angular parameters of user position. The angular dynamic model is established so that the estimation process is directly in accordance with the Lambertian model of VLC channel. The use of angular model also gave way to use two parameters to describe a three-dimensional position. Estimations based on angular position are formulated, that is the KF estimation of position parameters, and the extended Kalman filter (EKF) where channel gain is estimated and also serves as a state parameter. The performance is observed in simulation and compared to reference models of Cartesian based estimation. The proposed angular model EKF with the channel gain as the state parameter showed comparably higher error than the Cartesian model EKF of 3:2 in comparison but required remarkably less processing time of 1:5 to the referred model.

Predistortion Approaches Using Coefficient Approximation and Bidirectional LSTM for Nonlinearity Compensation in Visible Light Communication

A Light-Emitting Diode (LED) has a nonlinear characteristic, and it contains fundamental limitations for the performance of Visible Light Communication (VLC) systems in indoor environments when using intensity modulation with Orthogonal Frequency Division Multiplexing (OFDM). In this paper, we investigate this nonlinear characteristic with analysis and proposal. At first, we identified the LED nonlinear characteristics in terms of bit-error performances. After analysis, we propose initial predistortion schemes to mitigate the nonlinearity matters. In the predistortion schemes, the nonlinear distortion compensation model contains predistortion features with the LED inverse characteristics. Considering a Direct-Current-biased Optical OFDM (DCO-OFDM) system, we compared the Bit-Error Rate (BER) performances with and without compensation via simulations. The performance on the LED with the compensation showed LED nonlinearity could significantly improve the bit-error performance. In addition, with consideration that the predistortion model is insufficient to represent LED distortion, we investigated possible opportunities of distortion correction using Bidirectional Long Short-Term Memory (BLSTM), one of the leading deep learning approaches. Its result showed promising improvement of the distortion compensation as well.

Research on multi-color visible light communication system using RZ-4PAM signals with 67% duty cycle

In order to improve the transmission performance of visible light communication (VLC) system and user’s demand for large-capacity and high-speed, one multi-color VLC scheme is proposed. This scheme uses red-green-blue light-emitting diode (RGB-LED) as the sender to transmit 4-ary pulse amplitude modulation (4PAM) signals with 67% return-to-zero (RZ). At the receiver, one optical bandpass filter is used for channel separation. By system simulation, we have measured the time-domain waveforms before and after transmission, eye diagrams of the three colors signals, and the bit error rate (BER) performance has been analyzed. The results show that at receiver power of -11dBm, the BER at back-to-back case is slightly lower than that of the signals transmitted in the 8m channel. Since 4PAM signals have higher spectral efficiency compared with the traditional binary signals, this scheme has potential application value in indoor broadband access system.

Sum Rate Maximization for Intelligent Reflecting Surface-Aided Visible Light Communications

With the promotion of the solid-state lighting industry, visible light communication (VLC) has attracted increasing interests these years. However, the blockage problems in VLC due to the nanoscale wavelength of the visible light are severe. In this letter, a VLC system deployed with the intelligent reflecting surface (IRS) is modeled under the point source assumption, where both line-of-sight and specular non-line-of-sight paths are considered. By introducing a discrete matrix, the resource allocation process is simplified into a binary programming problem, and then we propose a low-complexity algorithm to maximize the achievable sum rate. Moreover, numerical results demonstrate that IRS can improve the rate performance and ease blockage problems of VLC.

Optical beam cooperation‐based secrecy capacity enhancement for visible light communications

To a large extent, the physical layer security (PLS) performance of a visible light communication (VLC) system is affected by light source radiation characteristics. Previous works are limited to well-known Lambertian beam configurations, which fail to support flexible coordinated coverage. Unlike existing works, this article proposes one secrecy capacity (SC) enhancement scheme based on asymmetric non-Lambertian optical beam cooperation. Without loss of generality, this article presents a numerical analysis of coordinated and non-coordinated PLS performance in a typical indoor application scenario. Compared with a non-coordinated benchmark, the numerical results illustrate that the proposed cooperation-based scheme could induce about 0.88 bps/Hz average SC gain without a transmission power increase. Therefore, non-Lambertian beam cooperation could be viewed as one promising secure VLC performance enhancement technology.

High-speed visible light communication systems based on Si-substrate LEDs with multiple superlattice interlayers

High-speed visible light communication (VLC), as a cutting-edge supplementary solution in 6G to traditional radio-frequency communication, is expected to address the tension between continuously increased demand of capacity and currently limited supply of radio-frequency spectrum resource. The main driver behind the high-speed VLC is the presence of light emitting diode (LED) which not only offers energy-efficient lighting, but also provides a cost-efficient alternative to the VLC transmitter with superior modulation potential. Particularly, the InGaN/GaN LED grown on Si substrate is a promising VLC transmitter to simultaneously realize effective communication and illumination by virtue of beyond 10-Gbps communication capacity and Watt-level output optical power. In previous parameter optimization of Si-substrate LED, the superlattice interlayer (SL), especially its period number, is reported to be the key factor to improve the lighting performance by enhancing the wall-plug efficiency, but few efforts were made to investigate the influence of SLs on VLC performance. Therefore, to optimize the VLC performance of Si-substrate LEDs, we for the first time investigated the impact of the SL period number on VLC system through experiments and theoretical derivation. The results show that more SL period number is related to higher signal-to-noise ratio (SNR) via improving the wall-plug efficiency. In addition, by using Levin-Campello bit and power loading technology, we achieved a record-breaking data rate of 3.37 Gbps over 1.2-m free-space VLC link under given optimal SL period number, which, to the best of our knowledge, is the highest data rate for a Si-substrate LED-based VLC system.

Si-substrate LEDs with multiple superlattice interlayers for beyond 24 Gbps visible light communication

High-speed visible light communication (VLC) using light-emitting diodes (LEDs) is a potential complementary technology for beyond-5G wireless communication networks. The speed of VLC systems significantly depends on the quality of LEDs, and thus various novel LEDs with enhanced VLC performance increasingly emerge. Among them, InGaN/GaN-based LEDs on a Si-substrate are a promising LED transmitter that has enabled VLC data rates beyond 10 Gbps. The optimization on the period number of superlattice interlayer (SL), which is a stress-relief epitaxial layer in a Si-substrate LED, has been demonstrated to be an effective method to improve Si-substrate LED’s luminescence properties. However, this method to improve LED’s VLC properties is barely investigated. Hence, we for the first time experimentally studied the impact of SL period number on VLC performance. Accordingly, we designed and fabricated an integrated 4 × 4 multichromatic Si-substrate wavelength-division-multiplexing LED array chip with optimal SL period number. This chip allows up to 24.25 Gbps/1.2 m VLC transmission using eight wavelengths, which is the highest VLC data rate for an InGaN/GaN LED-based VLC system to the best of our knowledge. Additionally, a record-breaking data rate of 2.02 Gbps over a 20-m VLC link is achieved using a blue Si-substrate LED with the optimal SL period number. These results validate the effectiveness of Si-substrate LEDs for both high-speed and long-distance VLC and pave the way for Si-substrate LED design specially for high-speed VLC applications.