LED-based Visible Light Communication Research Articles

A 3.84-Gbit/s FBMC-NOMA-based VLC transmission system using DAC-based pre-equalization and DHT precoding technique

The transmission data rate of visible light communication (VLC) systems is mainly limited by the modulation bandwidth of light-emitting diodes (LEDs). Pre-equalization (PE) techniques in combination with advanced modulation formats have been employed to enhance the data rate of LED-based VLC systems. In this paper, we experimentally demonstrated a high spectral-efficiency filter bank multi-carrier (FBMC) and non-orthogonal multiple access (NOMA)-based VLC transmission system using digital-to-analog converter-based PE (DAC-PE) and discrete Hartley transform (DHT) precoding technique. Two PE techniques, i.e., DAC-PE and digital pre-equalization (DPE), are comparatively investigated in both orthogonal frequency-division multiplexing (OFDM)-NOMA-based VLC systems and FBMC-NOMA-based VLC systems. The results exhibit that, with the help of DHT precoding, the DAC-PE scheme outperforms the DPE scheme at the optimal power ratios (PRs). Besides, the FBMC-NOMA scheme can provide better bit error rate (BER) performance and higher data rate than OFDM-NOMA. At the optimal PR of 6 dB, the FBMC-NOMA signal with a record net data rate of 3.84 Gbit/s after 2.3-m free-space link transmission can be achieved with the BER below 3.8 × 10−3.

Double Bus Provider Asymmetrical Half Bridge Converter With a Resonant DCX-Derived Auxiliary Circuit to Supply a LED-Based VLC Postregulator

The wide and settled use of Light-Emitting Diodes (LEDs) in lighting has made Visible Light Communication (VLC) an interesting option. Given the way LEDs are driven in VLC, the Two-Input Buck converter fits perfectly as a post regulator for VLC-LED lamps. Its main drawback is that it needs two input voltages with specific requirements tied to the VLC feature. One needs to be regulated according to the LEDs knee voltage thermal drift, while the other needs to be constant. With the objectives of avoiding complex circuits with cross regulation and using two converters performing the bus provider, the present work proposes a converter with two outputs that meet those voltage requirements. This converter is the integration of an Asymmetrical Half Bridge converter and a resonant unregulated Half Bridge converter. This integration is achieved thanks to the primary side similarity of both converters and the integration of both transformers in one magnetic core, achieving a solution with fewer components. In addition, one output can be fully regulated by a standard control variable while the other remains naturally constant, and is independent from any control variable. This greatly simplifies the control stage, avoiding cross regulation while fully complying with the application requirements. This work presents the circuit concept and how it relates to the intended application. The principle of operation will be explained and used to define the wide operational region where the topology meets the requirements imposed by the application. To validate the proposed topology, a 45-W prototype is built and tested, archiving the output voltage requirements and an overall efficiency near 94%.

Experimental Investigation into the Influence of LED Bias Setup on VLC Frequency Domain Characteristics: Beyond Non-Negativity

Different from the radio frequency bipolar complex signalling, LED-based visible light communication (LED-VLC) meets the non-negativity requirement by adding a bias component (BC) to a bipolar real-valued signal. Although many people know that there is a relationship between BC and LED characteristics, unfortunately, most of them chose to ignore it, and thus there has been little exploration of its impact on VLC. In this paper, we have experimentally measured the frequency domain characteristics of several LEDs commonly used in home and business applications. The numerical calculations show that the logarithmic domain absolute frequency response is approximately linear, where the corresponding intercepts and slopes can be quadratically expressed with respect to BC with a very low fitting error. This experimental investigation reveals that the BC value will remarkably influence the VLC system performance beyond non-negativity, and the LED-VLC transceiver designs should jointly take the BC and LED communication characteristic into consideration.

Key Technologies for High-Speed Si-Substrate LED Based Visible Light Communication

Nowadays, the demand for high-speed information transmission is increasing rapidly. Visible light communication (VLC) based on light-emitting diodes (LEDs) is supposed as a potential candidate for future 6G communication networks. However, as an emerging field of optical communications, the data rate of VLC systems is restricted to the extremely limited modulation bandwidth and nonlinear characteristics of optoelectronic devices. In this paper, we outline the state of art and challenges of VLC, and introduce the key technologies for high-speed Silicon (Si) -substrate LED-based VLC systems. Based on an optimized integrated 4×4 8-wavelength LED array and advanced digital signal processing (DSP) methods, we demonstrate an ultrahigh-speed VLC system. Digital Zobel network (DZN) pre-equalization and transfer learning bidirectional gate recurrent unit (TL-Bi-GRU) based post-equalization are proposed to mitigate linear and nonlinear impairment. The yellow and green LEDs are especially enhanced in high-efficacy, and achieve the impressive data rates of 3.45Gbit/s, and 3.83Gbit/s respectively, which is a remarkable improvement. The achievable overall data rate of the device is 28.93 Gbit/s. As far as we know, it's the highest data rate achieved by a single-chip Si-substrate LED array.

Exploring the Effects of LED-Based Visible Light Communication on Reading and Color Perception in Indoor Environments: An Experimental Study.

Visible light communications (VLC) is a technology that enables the transmission of digital information with a light source. VLC is nowadays seen as a promising technology for indoor applications, helping WiFi to handle the spectrum crunch. Possible indoor applications range from Internet connection at home/office to multimedia content delivery in a museum. Despite the vast interest of researchers in both theoretical analysis and experimentation on VLC technology, no studies have been carried out on the human perceptions of objects illuminated by VLC-based lamps. It is important to define if a VLC lamp decreases the reading capability or modifies the color perception in order to make VLC a technology appropriate for everyday life use. This paper describes the results of psychophysical tests on humans to define if VLC lamps modify the perception of colors or the reading speed. The results of the reading speed test showed a 0.97 correlation coefficient between tests with and without VLC modulated light, leading us to conclude that there is no difference in the reading speed capability with and without VLC-modulated light. The results of the color perception test showed a Fisher exact test p-value of 0.2351, showing that the perception of color is not influenced by the presence of the VLC modulated light.

High-speed long-distance visible light communication based on multicolor series connection micro-LEDs and wavelength division multiplexing

Multicolor series connection micro-LED arrays with emission wavelengths of violet, blue, green, and yellow were fabricated, and their optoelectronic properties and communication performances were investigated. The designed series connection micro-LED array exhibited the light output power of multiple milliwatts, whereas mostly keeping a slightly reduced modulation bandwidth, thus, enabling a higher signal-to-noise ratio compared to a single pixel and showing superior performance in the field of long-distance visible light communication (VLC). The achievable data rates of 400-, 451-, 509-, and 556-nm micro-LED arrays using bit/power loading orthogonal frequency division multiplexing were 5.71, 4.86, 4.39, and 0.82 Gbps, respectively. The aggregate data rate of 15.78 Gbps was achieved for the proof-of-concept wavelength division multiplexing system under a transmission distance of 13 m, which was the best data rate-distance product performance for the LED-based VLC to the best of our knowledge. In addition, the long-distance VLC based on yellow micro-LED was also demonstrated for the first time in this paper.

Deep learning based end-to-end visible light communication with an in-band channel modeling strategy.

Aside from ambient light noise, shot noise, and linear/nonlinear effects, strong low-frequency noise (LFN) severely affects the signal quality in LED-based visible light communication (VLC) systems, which hinders the implementation of data-driven end-to-end (E2E) deep learning approaches in real LED-VLC systems. We present a deep learning-based autoencoder to deal with this challenge. A novel modeling strategy is proposed to bypass the influence of the LFN and other low signal-to-noise ratio data when training the channel model of our E2E framework. The deep learning-based autoencoder then embeds the differentiable channel model and learns to combat the majority of channel impairments. In the E2E LED-VLC experiment, 1.875 Gbps transmission is achieved under the 7% HD-FEC threshold, 0.325 Gbps faster than the baseline. The E2E framework is robust to signal bias and amplitude variations, implying dimming support in the indoor environment.

ARM-Based Indoor RGB-LED Visible Light Communication System

As a new green solid-state light source, semiconductor light-emitting diodes (LEDs) have the advantages of low power consumption, small size, long life, short response time, and good modulation performance. At the same time, the frequency band to which LED light sources belong does not require regulatory registration, thus alleviating the current problem of spectrum scarcity for wireless communications. However, white LED-based visible light communication (VLC) systems suffer from limited bandwidth and low energy efficiency. Therefore, an ARM-based indoor RGB-LED VLC system is proposed. Firstly, the three RGB colours are mixed into white light, thus obtaining a larger modulation bandwidth than normal white LEDs while illuminating normally. Secondly, the S3C6410 processor is used to modulate and demodulate the RGB-LEDs with biased light OFDM, thus obtaining a high spectrum utilisation while ensuring system transmission stability. Then, according to the characteristics of the light source of the VLC system, the leading and window functions used in the optical network transceiver module are designed to improve the communication energy efficiency of the system. Finally, functional tests were carried out on an ARM development board. The experimental results show that with a single RGB-LED light source, the maximum transmission distance is 5 cm, the maximum average delay is 68 ms, the maximum throughput is 25 Mbps, and the BER is controlled below 3.2 × 10−3, which meets the basic communication requirements.

Secure Visible Light Communication System via Cooperative Attack Detecting Techniques

With the recent development of fourth industrial technology, the need for a broadband short-range wireless communication system to realize an ultraconnected, ultra-low latency, and ultra-realistic intelligent information society has emerged. Among the next-generation communication network technologies that can fulfill the technical demands, visible light communication (VLC) is a promising technology that can use illuminated light as a communication light source, which is convenient and environmentally friendly and has high energy and frequency efficiency. However, although VLC has a high level of security owing to the straightness and transparency of visible light, if some of the VLC nodes in a dense mesh network environment are hacked by external attacks, there can be critical performance degradation by jamming attacks. Although several studies have suggested the possibility of VLC jamming attacks, only a few have studied how to effectively detect and respond to these attacks. This study proposes a method to collaboratively detect and respond to jamming attacks in smart LED-based VLC systems. According to the experimental results of this study, the proposed cooperative method showed 91% attack detection accuracy and 1.82 times better than the k-random method. The proposed method showed a minimum detection rate of 84% even in an obstacle-rich environment, proving outstanding attack detection performance 1.68 times better than the k-random method.

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.

Architecting an MBSE Black-Box System Model for the Physical Layer of a Visible Light Intersatellite Communication System

Fast and reliable high-speed intersatellite communication (ISC) between small satellites is dependent on the physical layer (PL) design of the onboard communication system. However, as with nonlegacy systems, the lack of architecture and design information pertaining to the development of the PL of an LED-based visible light communication (VLC) system for ISC poses significant challenges to architecting the communication system. Addressing these challenges requires a holistic approach to the specification of the system design. To this end, we explore the use of model-based systems engineering (MBSE) principles in mitigating the design complexity of the PL architecture for the VLC system. Design concerns and gaps are addressed by developing an executable black-box system model that specifies the conceptual architecture of the system, and a parametric model that analyzes multiple system configurations based on generated values for the signal-to-noise ratio and bit error rate parameters. We utilize the structural, behavioral, and parametric semantics of SysML to define, specify, visualize, and analyze the various system design configurations. The resulting PL black-box system specification is verified through model execution.

LED-based chromatic and white-light vortices of fractional topological charges

Based on an LED light source, we present an experimental scheme to produce chromatic and white-light optical vortices carrying fractional topological charges. In theory, we develop a general formula to simulate the propagation dynamics of such fractional chromatic and white-light vortices based on the eigenmode decomposition of orbital angular momentum within the Gaussian–Schell model. In the experiment, for the generation of the chromatic and white-light optical vortices, we use a phase-only spatial light modulator to prepare the desired holographic gratings and a prism to compensate for the dispersion for three primary colors (red, green, and blue). The experimental observations, e.g., the seal-healing effect of dislocation lines, are in good agreement with the simulation results. The present work extends the studies of fractional optical vortices not only from highly coherent to partially coherent region but also from monochromatic to chromatic (white-light) source, which may find potential applications in LED-based visible light communication and optical displaying.

Carrierless amplitude and phase modulation in wireless visible light communication systems.

Visible light communications (VLCs) have attracted considerable interest in recent years owing to the potential to simultaneously achieve data transmission and illumination using low-cost light-emitting diodes (LEDs). However, the high-speed capability of such links is typically limited by the low bandwidth of LEDs. As a result, spectrally efficient advanced modulation formats have been considered for use in VLC links in order to mitigate this issue and enable higher data rates. Carrierless amplitude and phase (CAP) modulation is one such spectrally efficient scheme that has attracted significant interest in recent years owing to its good potential and practical implementation. In this paper, we introduce the basic features of CAP modulation and review its use in the context of indoor VLC systems. We describe some of its attributes and inherent limitations, present related advances aiming to improve its performance and potential and report on recent experimental demonstrations of LED-based VLC links employing CAP modulation. This article is part of the theme issue 'Optical wireless communication'.

1.7 to 2.3 Gbps OOK LED VLC Transmission Based on 4 × 4 Color-Polarization-Multiplexing at Extremely Low Illumination

To achieve the high traffic rate of a GaN LED-based visible light communication (VLC), a 4 × 4 color-polarization-multiplexing system is demonstrated by using two blue and two green LEDs. In the measurement, an available bandwidth of blue and green LEDs can be greater than 465 MHz for VLC modulation traffic by using the suitable analogy front end circuit. Hence, the proposed VLC system can deliver 1.7 to 2.3 Gbit/s on – off keying traffic rates in the free space transmission length of 1–4 m under the extremely low illumination of 6.9–136.1 lux for the indoor application. Moreover, the measured BER of each LED is less than the forward error correction target of 3.8 × 10−3 to maintain the better signal performance.

Sparsity-Aware Nonlinear Equalization With Greedy Algorithms for LED-Based Visible Light Communication Systems

The nonlinearity of light emitting diode (LED) in visible light communication (VLC) systems is considered as one major limiting factor that deteriorates the systems’ performance. In this paper, the nonlinear equalization in VLC systems is deemed to be a sparse recovery problem. Three different greedy sparse recovery algorithms, namely matching pursuit (MP), orthogonal MP (OMP), and regularized OMP (ROMP) are employed in constructing the sparsity-aware nonlinear equalizer for LED-based VLC systems. By adopting these greedy algorithms, the number of kernels in the nonlinear equalizer can be significantly reduced with minor performance loss, which enables low-complexity and high-performance nonlinear equalization. The performance of the proposed sparsity-aware nonlinear equalizers is investigated experimentally in orthogonal frequency division multiplexing (OFDM) based VLC systems with commercially available red-green-blue LEDs. The results show that, with the help of greedy sparse recovery algorithms, the number of kernels in nonlinear equalization can be reduced by 32.5%∼62.5% for only 0.5-dB signal-to-noise ratio loss. The compatibility of the proposed sparsity-aware nonlinear equalizer in a ∼1 Gbit/s adaptive bit-power loading OFDM VLC system is also experimentally demonstrated. The ROMP-based nonlinear equalizer is found to be the best choice that offers the optimal balance between performance and complexity, which achieves almost the same performance as the conventional Volterra time domain nonlinear equalizer in OFDM VLC systems with approximately halved number of kernels.

3.075 Gb/s underwater visible light communication utilizing hardware pre-equalizer with multiple feature points

We propose a flexible method for multiple feature frequencies-based bridge T hardware pre-equalizer that can better match the channel of an LED-based visible light communication (VLC) system and dramatically increase the system capacity. Based on this method, three kinds of equalizers are fabricated with the same maximum attenuation but different envelopes of frequency response. The performance of the three equalizers is experimentally compared in an underwater VLC system. The results show that the different shapes of the pre-equalizer can significantly impact the system SNR as well as the system capacity. By utilizing one of the optimally designed equalizers, an overall data rate of 3.075 Gb/s underwater VLC system can be achieved based on 64 QAM discrete multitone modulation over 1.2-m water channel. The measured bit error rate is under the hard decision-forward error correction threshold of 3.8 × 10 − 3.

Electrical and Thermal Effects of Light-Emitting Diodes on Signal-to-Noise Ratio in Visible Light Communication

Light-emitting diode (LED)-based visible light communication (VLC) has recently been promoted by the lighting industry for providing services and information for consumers in shopping malls. Communication system designs require well-defined signal-to-noise ratio (SNR). Being semiconductor devices, both LEDs and photodetectors are highly temperature-sensitive. This paper explores the electrical and thermal sensitivities of LED and photodetector together for VLC applications, and highlights the discoveries that the SNR of LED-based VLC could vary substantially over the full operating power range of the LED lighting systems. A new analysis of the SNR based on the photoelectrothermal theory has been developed. It can be used as the theoretical and design tool to predict such SNR variations. The validity of the new analysis has been confirmed with practical measurements that are consistent with theoretical predictions. The analytic approach can in principle be used as a design tool for LED-based VLC.

15.73 Gb/s Visible Light Communication With Off-the-Shelf LEDs

Visible light communication (VLC) can provide high-speed data transmission that could alleviate the pressure on the conventional radio frequency spectrum with the looming capacity crunch for digital communication systems. In this paper, we present experimental results of a VLC system with a data rate of 15.73 Gb/s after applying forward error correction coding over a 1.6 m link. Wavelength division multiplexing is utilized to efficiently modulate four wavelengths in the visible light spectrum. Four single color low-cost commercially available light emitting diodes (LEDs) are chosen as light sources. This confirms the feasibility and readiness of VLC for high-data rate communication. Orthogonal frequency division multiplexing (OFDM) with adaptive bit loading is used. The system with the available components is characterized and its parameters, such as LED driving points and OFDM signal peak-to-peak scaling factor, are optimized. To the best of our knowledge, this is the highest data rate ever reported for LED-based VLC systems.

An LED-based visible light communication system for multicast

<p>Visible Light Communication is a communication method that transmits data through light by pulsing an LED at high speed, performing broadcast communication for all devices existing in its coverage. Broadcast-based Visible Light Communication is limited to application to Internet of Things services, where various applications exist, although all receivers can communicate within the range of light sources. Therefore, this paper proposes an LED based Visible Light Communication system for multicast. The proposed system performs individual multicast by participating in communication only with receivers configured to use a specified ID value input at the transmitting side during data transmission. Experimental results show that the receiver can receive files individually according to a specified ID value.</p>