Visible Light Communication Transmitter Research Articles

Experimental demonstration of an indoor visible light positioning system using RGB LEDs for multi‐cell networks

AbstractA visible light positioning (VLP) system for multi‐cell networks based on multi‐colour LED that combines frequency division multiplexing with the received signal strength and a trilateration method is proposed. First, it employs experimental measurements to model the designed visible light communication (VLC) system under the characteristics of the target scenario. Second, it introduces a low‐cost VLC transmitter that exploits the chromatic space to transmit the VLP information. Third, it characterizes the VLC transmitter and proposes a linearization for electro‐optical responses of RGB LED. An RGB digital colour sensor and simple method calibrate the chromatic emission. The experimental results show that the proposed VLP multi‐cell architecture achieves a positioning accuracy lower than .

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.

Bi-Directional Free-Space Visible Light Communication Supporting Multiple Moveable Clients Using Light Diffusing Optical Fiber.

In this work, we put forward and demonstrate a bi-direction free-space visible light communication (VLC) system supporting multiple moveable receivers (Rxs) using a light-diffusing optical fiber (LDOF). The downlink (DL) signal is launched from a head-end or central office (CO) far away to the LDOF at the client side via a free-space transmission. When the DL signal is launched to the LDOF, which acts as an optical antenna to re-transmit the DL signal to different moveable Rxs. The uplink (UL) signal is sent via the LDOF towards the CO. In a proof-of-concept demonstration, the LDOF is 100 cm long, and the free space VLC transmission between the CO and the LDOF is 100 cm. 210 Mbit/s DL and 850 Mbit/s UL transmissions meet the pre-forward-error-correction bit error rate (pre-FEC BER = 3.8 × 10-3) threshold.

Increasing Vehicular Visible Light Communications Range Based on LED Current Overdriving and Variable Pulse Position Modulation: Concept and Experimental Validation

Due to its unique advantages, the integration of Visible Light Communications (VLC) in vehicle safety applications has become a major research topic. Nevertheless, as this is an emergent technology, several challenges must be addressed. One of the most important of these challenges is oriented toward increasing vehicular VLC systems' communication range. In this context, this article proposes a novel approach that provides a significant communication distance enhancement. Different from most existing works on this topic, which are based on refining the VLC receiver, this new article is focused on improving the VLC system based on the benefits that can be achieved through the VLC transmitter. The concept is based on Light-Emitting Diode (LED) current overdriving and a modified Variable Pulse Position Modulation (VPPM). Therefore, LED current overdriving provides the VLC receiver higher instantaneous received optical power and improved Signal-to-Noise Ratio (SNR), whereas the use of the VPPM ensures that the VLC transmitter respects eye regulation norms and offers LED protection against overheating. The concept has been experimentally tested in laboratory conditions. The experimental results confirmed the viability of the concept, showing an increase of the communication range by up to 370%, while maintaining the same overall optical irradiance at the VLC transmitter level. Therefore, this new approach has the potential to enable vehicular VLC ranges that cover the requirements of communication-based vehicle safety applications. To the best of our knowledge, this concept has not been previously exploited in vehicular VLC applications.

Optimal Adaptive Waveform Design Utilizing an End-to-End Learning-Based Pre-Equalization Neural Network in an UVLC System

Visible light communication (VLC) has emerged as a promising communication method in the special field of 6G, such as intersatellite communication (ISC) and underwater wireless optical communication (UWOC). Green light-emitting diode (LED)-based underwater visible light communication (VLC) is considered a potential candidate for UWOC of mobile autonomous underwater vehicle (AUV) and remotely operated underwater vehicle, particularly in coastal and harbor environments. However, due to bandwidth limitations and variable underwater channels, implementing high-speed underwater VLC remains a challenge. In this paper, a neural network-based auto equalization model (NNAEM) using end-to-end learning is proposed to achieve a high-speed underwater VLC link with a bandwidth-limited green LED. The entire NNAEM includes a neural network-based channel model, a pre-equalization neural network, and a post-equalization neural network. Based on the data-driven channel model, our auto equalization (AE) method can dynamically pre-equalize the discrete multitone (DMT) modulated signal in different bandwidth-limited cases and various nonlinearity cases. An underwater VLC link with a data rate of 3.451 Gbps and a transmission distance of 1.2 m is experimentally demonstrated by employing the proposed NNAEM under the hard decision-forward error correction (HD-FEC) threshold of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> . The data rate improvement is up to 30.4% compared to other advanced digital signal processing (DSP) methods. The scenario adaptation and robustness of the NNAEM are also verified in the experiments, which demonstrate that the NNAEM can serve an important role in underwater high-speed VLC transmission.

Asymmetric hybrid full-duplex POF-based VLC transmission links

This paper presents an asymmetric full-duplex solution based on visible light communications (VLC) for indoor wired and wireless hybrid signal transmission. The signal is distributed by a polymer optical fiber (POF) link and passively radiated. The proposed system includes two VLC links: a low-speed downlink and a high-speed uplink using an image sensor (IS) and photodiode detection (PD) based receivers. PD-based system communication performance is evaluated by means of error vector magnitude (EVM) for different modulation orders quadrature phase shift keying (QPSK), 16- and 64-quadrature amplitude modulation (QAM), while the IS-based system is characterized in terms of the success of reception (SoR). High-speed data transmission up to 160 Mbps with a 16-QAM modulation scheme and low-speed data transmission up to 500 bps with 98.6% of SoR using a non-return zero on–off keying (NRZ-OOK) scheme over a 1.5 m optical wireless link are demonstrated. Finally, simulations of the wireless channel are performed to evaluate the misalignment tolerance of the system; and, to estimate the uplink performance at longer distances.

Machine Learning in Visible Light Communication System: A Survey

With the widespread adoption of high bandwidth utilisation, visible light communication (VLC) has emerged as a potential solution to meet the demands for high-speed data communication due to its simultaneous illumination and transmission. However, numerous nonlinear distortions in VLC cause substantial signal processing challenges and diminish the system’s efficacy. VLC communication based on machine learning (ML) approaches provides a greater ability to offset the negative impacts of transceiver nonlinearity. ML is applicable to a variety of VLC challenges, including channel estimation, jitter compensation, position tracking, modulation detection, phase estimation, and security. This study provides a detailed review of several machine learning (ML) algorithms to reduce the design complexity of indoor VLC transmission, as well as ML applications in different design aspects to improve system performance. Furthermore, various applications, challenges, and future research directions based on machine learning algorithms in VLC are addressed.

Full-duplex visible light communication system based on single blue mini-LED acting as transmitter and photodetector simultaneously

GaN-based light emitting diodes (LEDs) have potential as photodetectors (PDs) for visible light communication (VLC). In current studies on LED-based PDs, devices are operated in a reverse-biased or zero-biased state. In this work, the performance of an 80 × 120 μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> blue mini-LED as both a PD and light source was studied. An aluminum oxide passivation was deposited on the sidewalls of the active region using atomic-layer deposition. In addition to improving the external quantum efficiency of mini-LEDs and reducing leakage current, sidewall passivation can also increase the responsivity of mini-LED PD. At the injection current used for display, the mini-LED device still worked as a PD with a good response to illumination. At a bias of 3 V (corresponding to injection current of 11.5 mA), the mini-LED PD had a response of 0.243 A/W and a high on-off ratio of 1.33 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> . A cascaded bridged-T amplitude equalizer was used to extend the OE −3 dB bandwidth of mini-LED PD from 16 MHz to 116 MHz at 3V bias. Based on the system above, a VLC link over 1 m with a data rate of 528 Mbps is achieved using 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing. Moreover, the mini-LED PD could simultaneously act as an uplink detector and a downlink transmitter in the same full-duplex VLC system. With transmission distance of 1m/ 1m, a transmission rate of 350 Mbps in the uplink and downlink was achieved. With transmission distance increasing to 1.2 m/1.2 m and 1.5 m/1.5 m, full-duplex VLC systems are also capable of achieving transmission rates of 300 Mbps and 225 Mbps, respectively. The proposed method allows the same mini-LED to be used simultaneously as a display and VLC transmitter and receiver, which not only simplifies the structure of the full-duplex communication system and reduces system power consumption, but also facilitates the integration of multifunctional small LED devices.

Intelligent MRI Room Design Using Visible Light Communication with Range Augmentation

Radio waves and strong magnetic fields are used by Magnetic Resonance Imaging (MRI) scanners to detect tumours, wounds and visualize detailed images of the human body. Wi-Fi and other medical devices placed in the MRI procedure room produces RF noise in MRI Images. The RF noise is the result of electromagnetic emissions produced by Wi-Fi and other medical devices that interfere with the operation of the MRI scanner. Existing techniques for RF noise mitigation involve RF shielding techniques which induce eddy currents that affect the MRI image quality. RF shielding techniques are complex and lead to RF leakage. VLC (Visible light Communication) is an emerging and efficient technology to avoid RF interference near MRI scanners. Range augmentation with power conservation of the LED is a big challenge in existing VLC systems. The major objective of the proposed work is to develop an intelligent-MRI room design without RF interference using visible light communication and enhance the distance between VLC transmitter and VLC receiver. In this paper, it is proposed to implement VLC using On-Off keying modulation and enhance distance using large active area photodiodes with Automatic Gain Control Circuit (AGC) using software and hardware. The performance of the proposed intelligent MRI-VLC system is analyzed by calculating Bit Error Rate at an inclined distance of 50 cm away from line of sight of the LED. The Experimental results showed that the maximum distance achieved was 400 cm at Bit Error Rate (BER) of 1.5 × 10−5.

Bandwidth enhancement with DAC-enabled pre-equalization and real-valued precoding for a FBMC-VLC

Modulation bandwidth limitation is one of the major drawbacks in light-emitting diode (LED)-based visible light communication (VLC) systems. Various advanced physical-layer modulation formats with digital/analog pre-equalization or adaptive modulation techniques are usually employed to improve the transmission rate of VLC systems. In this Letter, we use a radio frequency (RF) digital-to-analog converter (DAC) to directly realize signal pre-equalization without additional digital or analog signal processing. In addition, low-complexity real-valued precoding techniques are applied to reduce the peak-to-average power ratio (PAPR) and equalize the subcarrier signal-to-noise ratio (SNR). The proposed hybrid scheme is experimentally investigated in a spectral-efficient filter bank multi-carrier (FBMC)-based VLC transmission system. The results exhibit that the PAPR can be reduced by more than 3 dB at the complementary cumulative distribution function of 1 × 10-4 with the real-valued precoding techniques. By using the proposed hybrid scheme, the modulation bandwidth can be increased to 515 MHz for 16QAM-FBMC with a bit error rate below 3.8 × 10-3 after 2.3-m free-space transmission. The net bit rate is improved by more than 45% compared with the conventional FBMC-VLC.

A Deep Learning-Assisted Visible Light Positioning Scheme for Vehicles With Image Sensor

Visible light communication (VLC) based on image sensor (IS) as the receiver is one of the supplementary technologies of radio frequency communication. By combining with image processing technology, VLC has various applications in smart home, underwater communication and intelligent transportation system (ITS). In the paper, it focuses on the vehicle positioning service provided by VLC in ITS. For the weak image spatial separability caused by long-distance VLC transmission between the vehicle and the infrastructure, it will lead to serious deterioration in communication and positioning performance. Thus, a deep learning-assisted IS-based visible light positioning (VLP) scheme is proposed and experimentally demonstrated. At the transmitter, a novel coding method is proposed to support both short-distance and long-distance communication based on VLC in ITS. Meanwhile, it can meet the dimming requirements of LED road infrastructure. In addition, in the proposed VLP scheme, it uses an artificial neural network (ANN) to predict the location of the vehicle. It is demonstrated that long-distance communication, high-accuracy positioning, and LED dimming can be realized simultaneously. The results show that, by using the proposed scheme, as the transmission distance is 2 m, the bit error rate (BER) of system is 1.25 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> . And the average positioning error is 19.8 mm at the maximum simulated distance of 30 m.

An off-line single-switch VLC transmitter for low data rate applications

This work details a single-stage flyback power factor correction (PFC) converter operating in discontinuous conduction mode (DCM) for visible light communication (VLC). The role of the converter is to regulate the average output current via the duty cycle value for lighting purposes and to modulate digital data by means of the first switching harmonic of the output current. Both features can be achieved simultaneously by modulating the PWM signal fed to the single switch of the flyback converter. In order to allow for the transmission of VLC data, the converter output low-pass filter has been replaced by a 3rd order band-stop (notch) filter and an additional feedforward loop was introduced. This strategy maintains the simplicity of the original topology while granting it the functionality of transmitting VLC data with a reduced component count. Experimental results taken from a 14-W prototype supplied from a 127-V 60-Hz grid were carried out in order to verify the modulation scheme and the feasibility of the VLC transmitter, which was able to transfer data with a bit rate of 15 kb/s over a distance of 2 m with a global efficiency of 93.3% while keeping a good input power factor.

Indoor Positioning System Infrastructure Based on Triangulation Method through Visible Light Communication

Autonomous mobile robots are widely used in industry to help human’s work, but the concept has a weakness, that is robot still does not know its position in a room so it can not detect whether the robot has been at destination point. The technology commonly used to determine the position of objects is the Global Positioning System (GPS). However, GPS does not detect objects that are indoors. Previous research used Wi-Fi as a reference for designing an indoor positioning system, but the system could not determine the position in detail because Wi-Fi could only detect object zones. Based on these problems, this research will propose the infrastructure prototype design of an indoor positioning system based on Visible Light Communication (VLC). The main focus of this research is designing a VLC transmitter and receiver system, estimating the distance between the receiver and transmitter based on the received signal strength, and estimating the receiver's position using the triangulation method based on a minimum of 3 distance estimates. The estimating distance system get average accuracy is 76.47%. The estimated accuracy of the x-coordinate position has the best accuracy is 77.05% and the y-coordinate estimate has the best accuracy is 86.54%.

On the Use of Class D Switching-Mode Power Amplifiers in Visible Light Communication Transmitters.

Visible Light Communication (VLC) is a wireless communication technology that uses visible light to transmit information. The most extended implementation of a VLC transmitter employs a DC-DC power converter that biases the High-Brightness LEDs (HB-LEDs), and a Linear Power Amplifier (LPA) that reproduces the communication signal. Unfortunately, the power efficiency of LPAs is very low, thus reducing the overall system efficiency and requiring huge cooling systems to extract the heat. In this work, the use of Class D Switching-Mode Power Amplifiers (SMPAs) is explored in order to overcome that limitation. It is important to note that this SMPA is widely used for different applications, such as audio and RF power amplifiers. Therefore, there are a lot of versions of a Class D SMPA depending on the topology used for the implementation and the modulation strategy used to control the switches. Hence, this work aims to identify, adapt and explain in detail the best approach for implementing a Class D SMPA for VLC. In order to validate the proposed idea, a power-efficient VLC transmitter intended for short-range and low-speed applications was built and evaluated.

Enabling 5G indoor services for residential environment using VLC technology

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.

Multiple Optical Beam Switching for Physical Layer Security of Visible Light Communications

Visible light communications (VLC) techniques are viewed as promising candidates for the upcoming B5G&6G mobile wireless networks. Due to the broadcast nature of VLC channel, physical layer security (PLS) techniques have been considered and explored to improve the confidentiality of VLC transmission. Nevertheless, almost all current designs focus on application scenarios including sufficient transmitters and fail to match the scenarios with limited, even just two transmitters. For addressing this challenge, in this article, multiple optical beam switching scheme is proposed. Unlike conventional Lambertian beam based technique paradigm, the given scheme tentatively utilize two asymmetry non-Lambertian beams to configure each VLC transmitter. Numerical results show that, for the typical center legitimate receiver, compared with about 0.92 bps/Hz average secrecy capacity (SC) of the conventional Lambertian beam configuration, up to 5.55 bps/Hz average SC gain is acquired through the proposed beam switching scheme. Moreover, this potential gain will be enhanced to about 5.86 bps/Hz when three candidate non-Lambertian beams are available for each transmitter.

Effects of Optical Beams on MIMO Visible Light Communication Channel Characteristics

Under 5G envision, for pushing visible light communication (VLC) channel model evolution to various non-Lambertian beams, this paper introduces the typical commercial non-Lambertian beams, such as Luxeon rebel and side emitter, into the conventional analytical VLC channel model. The numerical results illustrate that the non-Lambertian beams can significantly affect the VLC channel frequency response characteristics. Compared with the traditional Lambertian beam, Side Emitter optical beam could naturally bring up to about 56.8% VLC multi input multi output channel capacity deviation, which objectively opens a new discussion dimension for enhancing VLC transmission performance.

Transmitter Fingerprinting for VLC Systems via Deep Feature Separation Network

Visible light communication (VLC) is a promising technology with a high data rate that can supplement radio frequency communication. Although VLC systems have a natural advantage of high security due to the line-of-sight light propagation characteristic, they are still vulnerable when facing an open environment. Device fingerprinting is a technique that is widely viewed to detect transmitter impersonation attack in radio frequency (RF) based wireless systems. In this paper, we introduce the fingerprinting technique to discriminate illegal transmitting devices in VLC systems. We first investigate the hardware imperfections of the VLC transmitter, which can provide a unique device ID. Then we implement a feature separation network for transmitter fingerprinting (TF-FSN) and design a two-stage training strategy to obtain a stable classifier. Finally, we experimentally demonstrate the feasibility and performance of the proposed method. The results show that the accuracy of identification and verification is 92.65% and 98%, respectively. Moreover, our method is robust over different distances and a wide range of signal-to-noise ratios.

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.