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In this study, we present a visible light communication (VLC) system that analyzes the performance of an optical camera communication (OCC) system, utilizing a mobile phone camera as the receiver and a computer monitor as the transmitter. By creating color channels in the form of a 4 × 4 matrix within a frame, we determine the parameters that affect the successful transmission of data packets. Factors such as the brightness or darkness of the test room, the light color of the lamp in the illuminated environment, the effects of daylight when the monitor is positioned in front of a window, and issues related to dead pixels and light bleed originating from the monitor's production process have been considered to ensure accurate data transmission. In this context, we utilized the PyCharm, Pydroid, Python, Tkinter, and OpenCV platforms for programming the transmitter and receiver units. Through the application of image processing techniques, we mitigated the effects of daylight on communication performance, thereby proposing a superior system compared to standard VLC systems that incorporate photodiodes. Additionally, considering objectives such as the maximum number of channels and the maximum distance, we regulated the sizes of the channels, the distances between the channels, and the number of channels. The NumPy library, compatible with Python–Tkinter, was employed to determine the color levels and dimensions of the channels. We investigate the effects of RGB and HSV color spaces on the data transmission rate and communication distance. Furthermore, the impact of the distance between color channels on color detection performance is discussed in detail. [ABSTRACT FROM AUTHOR]

Large-scale indoor 3D reconstruction with multiple robots faces challenges in core enabling technologies. This work contributes to a framework addressing localization, coordination, and vision processing for multi-agent reconstruction. A system architecture fusing visible light positioning, multi-agent path finding via reinforcement learning, and 360° camera techniques for 3D reconstruction is proposed. Our visible light positioning algorithm leverages existing lighting for centimeter-level localization without additional infrastructure. Meanwhile, a decentralized reinforcement learning approach is developed to solve the multi-agent path finding problem, with communications among agents optimized. Our 3D reconstruction pipeline utilizes equirectangular projection from 360° cameras to facilitate depth-independent reconstruction from posed monocular images using neural networks. Experimental validation demonstrates centimeter-level indoor navigation and 3D scene reconstruction capabilities of our framework. The challenges and limitations stemming from the above enabling technologies are discussed at the end of each corresponding section. In summary, this research advances fundamental techniques for multi-robot indoor 3D modeling, contributing to automated, data-driven applications through coordinated robot navigation, perception, and modeling. [ABSTRACT FROM AUTHOR]

ns2 ions‐doped lead‐free perovskites have garnered significant attention for their potential in diverse optoelectronic applications, owing to their broad emission characteristics arising from self‐trapped excitons (STEs). Herein, high‐performance white light‐emitting diodes (WLEDs) for intelligent lighting are developed by Bi3+/Te4+co‐doped Cs2SnCl6. Effective energy transfer between the dual STE emissions results in tunable broadband emissions covering the full‐color region. Adjustable WLEDs containing cold‐ and warm‐white lighting are fabricated. The WLEDs have excellent luminescent performances coupled with adjustable correlated color temperatures of 6417 and 3829 K. This versatility allows them to meet lighting demand for different scenarios, which is essential for future WLEDs to achieve healthy lighting. In addition, the excellent white light emission characteristics can also be applied in the visible light communication (VLC) system, achieving a −3 dB bandwidth of 13.3 MHz and opening eye diagrams in the data rate range of 10–60 Mbps. This work represents a significant advancement toward building intelligent health lighting applications and achieving high‐quality light sources for VLC based on lead‐free perovskites. [ABSTRACT FROM AUTHOR]

This research presents a detailed methodology for indoor positioning using visible light communication (VLC) technology, focusing on overcoming the limitations of traditional satellite-based navigation systems. The system is based on an optical positioning framework that integrates trilateration techniques with a semi-spherical array of photodiodes, designed to enhance both positional accuracy and orientation estimation. The system effectively estimates the receiver's position and orientation with high precision by utilizing multiple white-light-emitting diodes (LEDs) as transmitters and leveraging angular diversity. The proposed method achieves an average position error of less than 3 cm and an angular accuracy within 10 degrees, demonstrating its robustness even in environments with obstructed line of sight. These results highlight the system's potential for significant indoor positioning accuracy and reliability improvements. [ABSTRACT FROM AUTHOR]

The intelligent transportation systems (ITS) using radio frequency (RF) face challenges like interference and limited bandwidth compared to visible light communication (VLC). Integrating vehicular VLC (V-VLC) utilizing the existing light-emitting diodes (LEDs) in automobiles could provide a complementary approach to mitigate RF constraints. Performance degradation by background noise from sunlight can undermine signal quality. So, improving performance and managing interference are the keys to better V-VLC operation. This work proposes a solar noise suppression method for a V-VLC system, leveraging Allan variance and an extended Kalman filter (EKF). Based on the obtained Allan variance, updates are made to the observation model, state vector, and observation noise covariance matrix to achieve superior performance. Minimum mean square error (MMSE) equalization is used. The proposed filter efficiently minimizes the notable autocorrelation triggered by the solar noise, resulting in a bit error rate (BER) reduction of approximately 88% compared to the system without the adaptive filter. This increased convergence highlights the possibility of higher communication performance and reliability. Hence, this work provides a novel adaptive EKF design and offers valuable perspectives on the importance of Allan variance in enhancing the V-VLC system. [ABSTRACT FROM AUTHOR]

This work aims to provide the hardware (HW) design of the optoelectronics interfaces for a visible-light communication (VLC) system that can be employed for several use cases. Potential applications include the transmission of ultra-high-definition (UHD) streaming video through existing reading lamps installed in passenger vans. In this use case, visible light is employed for the downlink, while infrared light is used for the uplink channel, acting as a remote controller. Two primary components -a Light Fidelity (LiFi) router and a USB dongle—were designed and implemented. The 'LiFi Router', handling the downlink channel, comprises components such as a visible Light-Emitting Diode (LED) and an infrared receiver. Operating at a supply voltage of 12 V and consuming current at 920 mA, it is compatible with standard voltage buses found in transport vehicles. The 'USB dongle', responsible for the uplink, incorporates an infrared LED and a receiver optimized for visible light. The USB dongle works at a supply voltage of 5 V and shows a current consumption of 1.12 A, making it well suited for direct connection to a universal serial bus (USB) port. The bandwidth achieved for the downlink is 11.66 MHz, while the uplink's bandwidth is 12.27 MHz. A system competent at streaming UHD video with the feature of being single-input multiple-output (SIMO) was successfully implemented via the custom hardware design of the optical transceivers and optoelectronics interfaces. To ensure the system's correct performance at a distance of 110 cm, the minimum signal-to-noise ratio (SNRmin) for both optical links was maintained at 10.74 dB. We conducted a proof-of-concept test of the VLC system in a passenger van and verified its optimal operation, effectively illustrating its performance in a real operating environment. Exemplifying potential implementations possible with the hardware system designed in this work, a bit rate of 15.2 Mbps was reached with On–Off Keying (OOK), and 11.25 Mbps was obtained with Quadrature Phase Shift Keying (QPSK) using Orthogonal Frequency-Division Multiplexing (OFDM) obtaining a bit-error rate (BER) of 3.3259 × 10−5 in a passenger van at a distance of 72.5 cm between the LiFi router and the USB dongle. As a final addition, a solar panel was installed on the passenger van's roof to power the user's laptop and the USB dongle via a power bank battery. It took 13.4 h to charge the battery, yielding a battery life of 22.3 h. This characteristic renders the user's side of the system entirely self-powered. [ABSTRACT FROM AUTHOR]

The intelligent reflecting surface (IRS) is an emerging technology that can conquer visible light communication's (VLC) dependency on the line-of-sight (LoS) channel by offering additional non-light-of-sight (NLoS) communication links. In this paper, a newly proposed electro-tunable intelligent reflecting metasurface is deployed in dimmable single-input single-output (SISO) VLC systems. We aim to improve the bit error rate (BER) performance by jointly optimizing the transmit constellation and the reflectance of the IRS units. To this end, the optimization problem can be solved in two steps. The minimum distance of the received constellation is firstly maximized by a convex problem, which guarantees the minimum BER. Then, the transmit constellation and the synchronously-tunable reflectance of the IRS units that correspond to the optimal received constellation are determined with an iterative alternate optimization algorithm. Finally, the simulation results show the BER performance improvement and the dimming relaxation benefit of the tunable IRS-aided SISO VLC systems. [ABSTRACT FROM AUTHOR]

RGB LED bulbs have entered the market as a promising alternative to traditional phosphor-coating LEDs to meet illumination standards. In this article, we introduce and propose solutions to address the challenges of RGB LED lighting for the Internet of Things applications, performing communication, harvesting energy, and sensing tasks. Through experiments, we demonstrate that we can use RGB LEDs for multiple tasks. We can achieve a bandwidth in the order of 50 kHz and distances of around 3.5 m using commercial RGB LED bulbs as transceivers, without using any dedicated photodetector. RGB LED links are composed of three main colors, and we show that red is the best color both for communicating to another receiving RGB LED bulb, as well as for harvesting with a solar cell; green and blue can instead be exploited for standard-compliant lighting and/or sensing purposes. We evaluate the system in two proofs of concept and provide insights for operating RGB LEDs for multiple tasks including vertical farming. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) is a short-range optical wireless communication technology that attempts to achieve communication alongside illumination using existing infrastructure in the band of 430–790 THz. One of the crucial research gaps in VLC is the absence of an experimental evaluation of performance metric parameters like zero frequency (DC) channel gain, received power, bit error rate (BER) and signal-to-noise ratio at divergent wavelengths and luminous intensities for different optical output power levels. The second research gap is the need for an empirical formulation to estimate the BER for a defined data rate and luminous intensity of the light emitting diode (LED). The objective of this experimental work is to bridge the above two research gaps under a realistic illumination setup. The first gap is addressed by analyzing the impact of divergent output optical power levels of LEDs having different values of luminous intensities and wavelength on QoS parameters. The quality of service (QoS) parameters like transmitted optical power, received optical power, DC gain, quality factor and BER are evaluated and analyzed at a data rate of 1.2 Mbps for a maximum distance of 1 m. The work also evaluates the band of forward LED currents in the range of 12–20 mA to achieve a minimum BER of 10−5–10−7 for a maximum distance of 1 m. The second research gap is worked on by proposing a novel mathematical empirical formulation using fifth-order polynomial curve fitting to estimate the bit error rate (BER) by considering factors of luminous intensity and data rate for a maximal distance of 1 m. The empirical formulation is done using Microsoft EXCEL2010® and MATLAB2023®. [ABSTRACT FROM AUTHOR]

There is a growing demand for indoor positioning systems (IPSs) in a wide range of applications. However, traditional solutions such as GPS face many technical challenges. In recent years, a promising alternative has been emerging, the visible light communication (VLC)-based IPS, which offers a combination of high accuracy, low cost, and energy efficiency. This article presents a comprehensive review of VLC-based IPSs, providing a tutorial-like overview of the system. It begins by comparing various positioning systems and providing background information on their inherent limitations. Experimental results have demonstrated that VLC-based systems can achieve localization accuracy to within 10 cm in controlled environments. The mechanisms of VLC-based IPSs are then discussed, including a comprehensive examination of their performance metrics and underlying assumptions. The complexity, operating range, and efficiency of VLC-based IPSs are examined by analyzing factors such as channel modeling, signal processing, and localization algorithms. To optimize VLC-based IPSs, various strategies are explored, including the design of efficient modulation schemes, the development of advanced encoding and decoding algorithms, the implementation of adaptive power control, and the application of state-of-the-art localization algorithms. In addition, system parameters are carefully examined. These include LED placement, receiver sensitivity, and transmit power. Their impact on energy efficiency and localization accuracy is highlighted. Altogether, this paper serves as a comprehensive guide to VLC IPSs, providing in-depth insights into their vast potential and the challenges that they present. [ABSTRACT FROM AUTHOR]

Spectrally efficient 16 quadrature amplitude modulation‐orthogonal frequency division multiplexing (QAM‐OFDM) system using specifications of commercially available high‐power phosphorous coated LED (PLED) is proposed in this study. To address the challenges of signal attenuation and limited bandwidth, systems integrated with a band pass filter (BPF) after the photodetector and optical preamplifier. The effect of BPF bandwidth and preamplifier gain on the performance of 16 QAM‐OFDM system have been investigated. Results demonstrated that 375 MHz bandwidth evaluated from 1.5 × symbol rate, offered an optimum performance achieving minimum bit‐error‐rate of 3.05 × 10−4. For preamplifier gain of 20 dB, we achieved a maximum distance of 3 m which is limited to 1.5 m for lower gain values. With BPF‐optimized bandwidth and a preamplifier gain of 20 dB, we have achieved a data rate of 5 Gbps for maximum distance up to 2 m while considering the super‐forward‐error‐correction limit of 1.863 × 10−2. With data rate of 6 and 7 Gbps, the distance lower down to 1.8 and 1.5 m, respectively. [ABSTRACT FROM AUTHOR]

This paper presents an indoor positioning strategy based on Visible Light Communication that relies on LED luminaires as transmitters, whose luminous flux is modulated at different frequencies, and a light sensor as a receiver. Then, a previously trained Artificial Neural Network (ANN) uses the illuminance signal gathered by the receiver as input to estimate the sensor's position. The main contribution of the technique is that the ANN is trained by using an illuminance estimator based on the lighting distribution of the luminaires, which is obtained through the IES file provided by the luminaire's manufacturer, without the need to collect data from the environment. In this work, the designed illuminance estimator is validated by comparing it to the well-known commercial software DIALux and Relux. The algorithm's setting and the performance evaluation of the ANN are explained. Then, the impact of the lighting uniformity and the environment's number of divisions on the accuracy of the results is analyzed. Error analyses are also made by adding uncertainty to the illuminance measurements obtained by the sensor. Finally, the work is compared to several papers in the field. [ABSTRACT FROM AUTHOR]

End-to-end systems have been introduced to address the issue of independent signal processing module design in traditional communication systems, which prevents achieving global system optimization. However, research on indoor end-to-end Visible Light Communication (VLC) systems remains limited, especially regarding the channel modeling of high-speed, high-capacity Direct Current-biased Optical Orthogonal Frequency Division Multiplexing (DCO-OFDM) systems. This paper proposes three channel modeling methods for end-to-end DCO-OFDM VLC systems. The accuracy of the proposed methods is demonstrated through R-Square model fitting performance and data distribution analysis. The effectiveness of the proposed channel modeling methods is further validated by comparing the bit error rate (BER) performance of traditional receivers and existing deep learning (DL)-based receivers. The results show that the proposed methods can effectively mitigate both linear and nonlinear distortions. By employing these channel modeling methods, communication systems can reduce the spectral occupancy of pilot signals, thereby significantly lowering the complexity of traditional channel estimation methods. Thus, these methods are suitable for use in end-to-end VLC communication systems. [ABSTRACT FROM AUTHOR]

Indoor Optical Wireless Communication (OWC) provides a promising solution for high-capacity, low-latency, and electromagnetic interference-resistant wireless communication. Over the past decade, there has been extensive research addressing key challenges in indoor OWC. This article provides an overview of the current development status, key technologies, and challenges faced in the field of indoor OWC. Furthermore, at the end of this overview, an experimental demonstration of an indoor non-line-of-sight (NLOS) OWC system utilizing a spatial light modulator (SLM) for beam steering is demonstrated, which is expected to inspire research on related technologies. [ABSTRACT FROM AUTHOR]

Inspired by natural swarm systems, robotic swarms aim to solve complicated problems through the emergent behaviour of coordinating robots (agents). Communication among the robots is of paramount importance for their effective coordination, cooperation, and overall performance. This research presents a colour light-based communication system for miniature mobile swarm robots, on which a pre-trained supervised machine learning model runs and is responsible for effective colour recognition, enhancing inter-robot local communication. The performance of various supervised machine learning techniques was examined, and XGBoost performed best overall, with a classification accuracy of 96.66%, an execution time of 0.403 ms, an average sensing distance of 87.38 cm, and an acceptable size of 402.1 kilobytes while running on a 32-bit embedded microcontroller. The current work also demonstrates various swarming behaviours, utilising the developed communication as proof of concept. [ABSTRACT FROM AUTHOR]

It is predicted that the radio frequency spectrum will be insufficient in the near future due to the increase in wireless data. Visible Light Communication (VLC) is an alternative solution, which promises high speeds. Similar to other wireless communication systems, VLC systems prefer Multicarrier Modulation (MCM), but the signals are converted to be real and unipolar before transmission for optical communication. In this paper, two optical MCM groups that utilize Discrete Fourier Transform (DFT) and Discrete Trigonometric Transform (DTT) are questioned with respect to Bit Error Rate (BER), spectral efficiency and complexity. DFT based techniques use complex mapped signals together with their Hermitian symmetries to obtain real output signals, while DTT based techniques already output real signals when the input signal is real mapped. It is seen that DFT based techniques have lower BERs because of used mapping. DTT based techniques improve spectral efficiency, but they are limited to real mappings with higher error rates. For both transformations, the real signals are made unipolar by adding a bias (DCO-MCM), by asymmetrically clipping (ACO-MCM) or by sending positive and negative values separately (UnO-MCM). It is shown that, adding a dc bias (DCO-MCM) increases BERs, where ACO-MCM and UnO-MCM have close performances with lower BERs. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) based on superluminescent diode (SLD) is a promising technology with great potential for future 6G optical wireless network. In this work, a 405 nm violet SLD device is fabricated with an 8° tilted facet at one end of the waveguide based on InGaN/GaN quantum wells. The device has an optical power of 14.67 mW under continuous‐wave operation. The full width at half maximum (FWHM) of the SLD at 400 mA is 12.52 nm, which is significantly larger than that in a violet laser diode (LD). Using the SLD as transmitter in VLC system, a high data transmission rate of 3.299 Gbps has been achieved using the discrete multiple tone (DMT) modulation. The corresponding bit error ratio (BER) is measured to be 1.67 × 10−3, which satisfies the forward error correction (FEC) threshold of 3.8 × 10−3. The results suggest that such device can be used as a promising light source for VLC and light fidelity (LiFi) applications. [ABSTRACT FROM AUTHOR]

In the rapidly evolving landscape of smart cities, the integration of advanced technologies is crucial for ensuring safety, optimizing traffic flow, and enhancing the urban living experience. Vehicle-to-vehicle (V2V) communication and visible light communication (VLC) have emerged as promising solutions to address these challenges. This paper explores the integration of V2V communication and VLC at smart pedestrian crosswalks to enhance pedestrian safety and traffic management in smart cities. It explores the impact of neighbouring vehicles on V2V-VLC performance and proposes novel methodologies to assess traffic density effects. Results indicate a significant chance of encountering nearby cars during rush hours, emphasizing the importance of these integrated systems for safety and mobility in urban environments. The outcomes show that the chance of running into extra cars in nearby lanes is independent of the particular lane and increases to 80% through rush hours, but falls to a lower amount than 20% through off-peak and initial morning hours. [ABSTRACT FROM AUTHOR]

This paper presents an analytical study of signal clipping that leads to the noise/distortion in the waveform of DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM)-based visible light communication (VLC) systems. The pilot-assisted (PA) technique is used to reduce the high peak-to-average power ratio (PAPR) of the time-domain waveform of the DCO-OFDM system. The bit error rate (BER) performance of the PA DCO-OFDM system is investigated analytically at three different clipping levels as well as without any clipping. The analytical BER performance is verified through simulation and then compared to that of the conventional DCO-OFDM without PAPR reduction at the selected clipping levels. The PA DCO-OFDM system shows improved BER performance at all three clipping levels. [ABSTRACT FROM AUTHOR]

A significant deployment limitation for visible light communication and positioning (VLCP) systems in energy- and light-source-restricted scenarios is the reliance of photodetectors (PDs) on external power supplies, compromising sustainability and complicating receiver charging. Solar cells (SCs), capable of harvesting and converting environmental light into electrical energy, offer a promising alternative. Consequently, we first propose an indoor VLCP system that utilizes an SC array as the receiver, alongside a right-angled tetrahedron trilateration visible light positioning (RATT-VLP) algorithm based on a single light source and multiple receivers. The proposed system uses an SC array in place of PDs, utilizing binary phase shift keying (BPSK) signals for simultaneous communication and positioning. In experiments, we verified the system's error-free communication rate of 1.21 kbps and average positioning error of 3.40 cm in a 30 cm × 30 cm area, indicating that the system can simultaneously satisfy low-speed communication and accurate positioning applications. This provides a viable foundation for further research on SC-based VLCP systems, facilitating potential applications in environments like underwater wireless communication, positioning, and storage tank inspection. [ABSTRACT FROM AUTHOR]

Metal halide perovskites are promising light source materials for visible light communication (VLC) due to their excellent photoelectric properties and small resistance‐capacitance time constant. However, previous reports mainly used perovskites as the passive light sources, which not only makes it susceptible to posterior excitation light sources, but also complex in the integration process. Herein, the quasi‐2D PEA2Csn‐1PbnBr3n+1 perovskite light–emitting diodes (PeLEDs) as an active light source in VLC link is demonstrated. It is found that the charging/discharging process of PeLEDs is an important factor governing the ‐3 dB bandwidth (f‐3 dB) of the VLC. To improve this, 3‐sulfopropyl methacrylate potassium salt (SMPS) molecules are introduced into perovskite to simultaneously passivate deep and shallow energy level defects at grain boundaries. Additionally, the multiple quantum wells structures of PEA2Csn‐1PbnBr3n+1 are modified to be flat. At the optimal SMPS concentration, the maximum external quantum efficiency of PeLEDs reaches 21.5%. Meanwhile, the VLC achieves 3.2 MHz f‐3 dB with data transmission of 18.6 Mbps, which is the highest f‐3 dB in PeLEDs with the same active area. Hence, it provides a versatile method to improve the performance of VLC links based on active light sources and advances toward the goal of high‐speed, energy‐efficient and secure free communication. [ABSTRACT FROM AUTHOR]

Mobile visible light communication (VLC) is key for integrating lighting and communication applications in the 6G era, yet there exists a notable gap in experimental research on mobile VLC. In this study, we introduce a mobile VLC system and investigate the impact of mobility speed on communication performance. Leveraging a laser-based light transmitter with a wide coverage, we enable a light fidelity (LiFi) system with a mobile receiving end. The system is capable of supporting distances from 1 m to 4 m without a lens and could maintain a transmission rate of 500 Mbps. The transmission is stable at distances of 1 m and 2 m, but an increase in distance and speed introduces interference to the system, leading to a rise in the Bit Error Rate (BER). The mobile VLC experimental system provides a viable solution to the issue of mobile access in the integration of lighting and communication applications, establishing a solid practical foundation for future research. [ABSTRACT FROM AUTHOR]

Summary: LEDs are a prominent technique for a pervasive communication system using visible light communication (VLC), since LED includes long life expectancy, fast switching, and being visible light and is less expensive, which is safe for the human body, though still many technical problems presented to be addressed, especially in an indoor environment. Due to this, the major aim of this task is to afford a hybridized optimization algorithm that is highly suitable for enabling the signal to noise ratio (SNR) and received signal strength (RSS) maximization in VLC. Here, the coordinate of each point of the receiver photo detector in the VLC system is tuned by the new hybridized algorithm. The fusion of two optimization algorithms like Deer Hunting Optimization Algorithm (DHOA) and Dragonfly Algorithm (DA) termed as Fitness‐oriented Dragonfly‐based DHOA (FD‐DHOA) is used to attain the objective concerning the RSS or received power and SNR. The proposed model tries to attain maximum RSS and SNR at the receiver instead of calculating it at every angle. Moreover, the experimental analysis proves that the developed model validates the orientation that generates an optimum RSS and SNR value at the receiver. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) can serve as a supplement to the radio frequency to address its inherent constraints. VLC can be easily implemented in vehicles using their existing LED components. Sunlight interference can cause significant variation in the background noise powers, leading to signal-to-noise ratio (SNR) degradation in vehicular VLC (VVLC) communication. Hence, it is necessary to improve the performance besides interference. Allan variance is a temporal analysis approach that can extract the noise from the received data. In this article, an Allan variance-based adaptive noise canceller for a VVLC system is proposed and evaluated. Based on the Allan variance obtained, the step size and the number of taps of the adaptive filter are adjusted for superior performance. This proposed filter effectively mitigates the pronounced autocorrelation induced by the noise interference. It yields about an 85% bit error rate (BER) reduction compared to the conventional filter. This improved convergence underscores the potential for enhanced communication performance and reliability. The balanced distribution of the Manchester encoded signal outperforms NRZ encoding. Thus, this work contributes a novel adaptive noise canceller design for a VVLC system and also provides valuable insights to the significance of Allan variance in the VLC system performance. [ABSTRACT FROM AUTHOR]

In this paper, a downlink energy efficiency maximization problem is investigated in an intelligent reflective surface (IRS)-assisted visible light communication system. In order to extend wireless communication coverage of the onshore base station, an IRS mounted on a unmanned aerial vehicle (UAV) is introduced to assist an onshore lighthouse with simultaneously providing remote ship users wireless communication services and illumination. Aiming to maximizing the energy efficiency of the proposed system, a resource allocation problem is formulated as the ratio of the achievable system sum rate to the total power consumption under the constraints of the user's data requirement and transmit power budget. Due to the non-convexity of the proposed problem, the Dinkelbach method and mean-square error (MSE) method are adopted to turn the non-convex origin problem into two equivalent problems, namely transmit beamforming and reflected phase shifting. The Lagrangian method and semidefinite relaxation technique are used to obtain the closed-form solutions of these two subproblems. Accordingly, an alternative optimization-based resource allocation scheme is proposed to obtain the optimal system energy efficiency. The simulation results show that the proposed scheme performs better in terms of energy efficiency over benchmark schemes. [ABSTRACT FROM AUTHOR]

In this paper, a novel method is demonstrated to sustain vehicle-to-vehicle (V2V) communication on curvy roads via the arrangement of the lateral position of a self-angle-adjustable mirror–reflective road sign (SAAMRS) and light-direction-sensing wide-angle complementary photodiodes (CPDs). Visible light communication (VLC) between vehicles attracts attention as a complementary technology to radio-frequency-based (RF-based) communication technologies due to its wide, license-free spectrum and immunity to interferences. However, V2V VLC may be interrupted on curvy roads due to the limited field of view (FOV) of the receiver or the line of sight (LOS) being interrupted. To solve this problem, an experiment was developed using an SAAMRS along with wide-angle light-direction-sensing CPDs that used a precise peak detection (PPD) method to sustain communication between vehicles in dynamic environments by rerouting the incident light with the highest signal intensity level to the receiver vehicle on curvy roads. We also used real images of curvy roads simulated as polynomials to calculate the necessary rotation angles for the SAAMRS and regions where communication exist. Our experimental results overlapped almost completely with our simulations, with small errors of approximately 4.8% and 4.4% for the SAAMRS angle and communication region, respectively. [ABSTRACT FROM AUTHOR]

In indoor visible light communication (VLC), the received signals are subject to severe interference due to factors such as high-brightness backgrounds, long-distance transmissions, and indoor obstructions. This results in an increase in misclassification for modulation format recognition. We propose a novel model called VLCMnet. Within this model, a temporal convolutional network and a long short-term memory (TCN-LSTM) module are utilized for direct channel equalization, effectively enhancing the quality of the constellation diagrams for modulated signals. A multi-mixed attention network (MMAnet) module integrates single- and mixed-attention mechanisms within a convolutional neural network (CNN) framework specifically for constellation image classification. This allows the model to capture fine-grained spatial structure features and channel features within constellation diagrams, particularly those associated with high-order modulation signals. Experimental results obtained demonstrate that, compared to a CNN model without attention mechanisms, the proposed model increases the recognition accuracy by 19.2%. Under severe channel distortion conditions, our proposed model exhibits robustness and maintains a high level of accuracy. [ABSTRACT FROM AUTHOR]

In this work, polycrystalline n-CrSe2 nanosheets with thickness of 100 nm are grown on p-type Si wafers by the thermal deposition technique under vacuum pressure of 10−5 mbar. Structural and optical investigations showed the preferred growth of the trigonal phase of CrSe2 on Si substrates. Direct allowed transitions within an energy band gap of 2.60 eV were found to be dominant in the films. Silver contacts on the layers allowed construction of hybrid optoelectronic device structure formed from Ag/p-Si Schottky arm and p -Si/ n -CrSe2 pn junction. The device runs in such a way that forward biasing of the Schottky arm is accompanied by a reverse biasing of the pn junction. It is observed that the hybrid device structure can perform as a high-frequency capacitor. The capacitance–voltage characteristic curves show that these capacitors can respond to ac signals with frequencies of 100 MHz. They also exhibit bandstop filter characteristics allowing the passing of signals with return loss and voltage standing wave ratios exceeding 10 dB and 1.76, respectively, at 60 MHz. The device under study displayed rectifying and photo-sensing properties with an asymmetry ratio of 60 in the dark and 217 under excitation of visible light. Visible light excitation of these photosensors displayed voltage biasing dependence in their current responsivity, external quantum efficiency and specific detectivity, reaching values of 0.24 A/W, 65.2% and 4.83 × 109 Jones, respectively. The features of the hybrid devices which use CrSe2 nanosheets as active media make them good candidates for use in radio wave and visible light communication technologies. [ABSTRACT FROM AUTHOR]

LED-to-LED visible light communication (VLC) is a technology that LEDs are used as both transmitters and receivers. In this paper, we studied a micro-LED-to-micro-LED VLC since micro LEDs have faster modulation speed and are used in various applications recently. The frequency responses and SNRs were measured for all possible combinations of four LED colors (red, green, blue, and white) in the transmitter and the receiver. Through this, the theoretical maximum channel capacity was estimated for each combination case. Finally, we conducted an experiment with the optimal transmitter and receiver LED set and investigated its performance.

AbstractVisible light communication (VLC) networks are emerging as a viable option to meet the ever-growing wireless data demand, primarily for indoor environments in recent years. However, developing a high data rate VLC system using off-the-shelf light emitting diodes (LEDs) is difficult due to the narrow modulation bandwidth of the white light emitting diodes. The existing studies have integrated Multiple-Input Multiple-Output (MIMO) and Non-Orthogonal Multiple Access (NOMA) schemes into the downlink VLC system so as improve its performance. Despite its apparent advantages, the NOMA scheme suffers from multi-user interference problem. For an efficient NOMA scheme, which uses successive interference cancellation (SIC) technique to decode the superimposed received signal of multipleusers, adaptive and fair power allocation methods are required. The existing power allocation schemes are inefficient when the number of users increases. In this work, a low complexity and efficient power allocation strategy is proposed for MIMO-NOMA based VLC systems. The proposed parametric power allocation strategy is based on the order of channel gain among end-users and overcomes the limitations of the existing schemes. The performance of the proposed power allocation scheme in an indoor 4[Formula: see text]4 MIMO-NOMA-based multi-user VLC was analyzed through simulation. A zero-forcing detection mechanism is used in the analysis. Simulation results using MATLAB depict the effectiveness of the proposed power allocation strategy. It achieves higher performance than the existing power allocation schemes, gain ratio power allocation (GRPA) and normalized gain difference power allocation (NGDPA) when the number of users are greater than two. Specifically, the proposed power allocation scheme improves the achievable sum rate of the NGDPA and GRPA schemes by 18.36% and 65.98%, respectively, in 4[Formula: see text] 4 MIMO-based visible light communication networks with eight uniformly distributed users.

Energy sustainability and interconnectivity are the two main pillars on which cutting‐edge architecture is based and require the realization of energy and intelligent devices that can be fully integrated into buildings, capable of meeting stringent regulatory requirements and operating in real‐world conditions. Luminescent solar concentrators, particularly those based on near‐infrared emitting reabsorption‐free quantum dots, are considered good candidates for the realization of semi‐transparent photovoltaic glazing, but despite important advances in optical property engineering strategies, studies of finished devices suitable for real‐world operation are still lacking. In this paper, the first example of a fully assembled quantum dot luminescent solar concentrator‐based photovoltaic glazing is demonstrated that meets all international standards for photovoltaic and building elements. It is also shown that these devices are capable of functioning as efficient Visible Light Communication (VLC) receivers even under full sunlight, thus combining energy and wireless connectivity functions in a realistic solution for smart, sustainable buildings. [ABSTRACT FROM AUTHOR]

As a contender in the competitive landscape of next-generation wireless communication technologies, visible light communication (VLC) stands out due to its potential for enhancing transmission rates and spectrum resource utilization. VLC offers various advantages, including license-free operation, high confidentiality, and cost-effectiveness. However, practical implementation faces challenges stemming from the limited modulation bandwidth of light-emitting diodes (LEDs), constraining system capacity and VLC communication rates. To address this limitation, non-orthogonal multiple access (NOMA) emerges as a novel multiple access strategy, particularly suitable for enhancing the capacity and communication rates of downlink VLC systems through power multiplexing. This paper delves into the energy-efficient design of joint LED association and power allocation (LA–PA) for downlink NOMA-based VLC systems. Through an analysis of channel capacity, we transform the non-convex energy-efficient optimization model, accounting for signal non-negativity, per-LED optical power constraints, and user rate constraints, into a convex form. Subsequently, we propose an iterative power allocation algorithm to attain solutions for the optimization problem with pre-established LED associations. Furthermore, we derive a feasibility condition for an LED association, considering signal non-negativity, per-LED optical power constraints, power constraints for successive interference cancellation (SIC), and channel gain between transceiver signals. This condition identifies feasible LEDs capable of maximizing energy efficiency (EE) when combined with the aforementioned power allocation algorithm. Finally, we illustrate the superiority of the joint LA–PA scheme in terms of the EE, transmission reliability, and transmission capacity performance gain over NOMA in the context of VLC. [ABSTRACT FROM AUTHOR]

In this paper, we explore the use of visible light positioning (VLP) technology in vehicles in intelligent transportation systems (ITS), highlighting its potential for maintaining effective line of sight (LOS) and providing high-accuracy positioning between vehicles. The proposed system (V2V-VLP) is based on a position-sensitive detector (PSD) and exploiting car taillights to determine the position and inter-vehicular distance by angle of arrival (AoA) measurements. The integration of the PSD sensor in vehicles promises exceptional positioning accuracy, opening new prospects for navigation and driving safety. The results revealed that the proposed system enables precise measurement of position and distance between vehicles, including lateral distance. We evaluated the impact of different focal lengths on the system performance, achieving cm-level accuracy for distances up to 35 m, with an optimum focal length of 25 mm, and under low signal-to-noise conditions, which meets the standards required for safe and reliable V2V applications. Several experimental tests were carried out to validate the results of the simulations. [ABSTRACT FROM AUTHOR]

Four-level pulse amplitude modulation (PAM4) can transmit more information in the same symbol interval, effectively improving the information transmission rate and frequency band utilization of visible light communication (VLC). This paper proposes a method for encoding and decoding the PAM4 signal based on FPGA. The PAM4 signal is studied and analyzed under different channel noise models. The research results show that the bit error rate (BER) performance of the PAM4 signal is the best under the additive noise model. The influence of the multiplicative noise on the BER of the PAM4 signal is much greater than that of the additive noise. The BER performance of the PAM4 signal depends on the variance of the noise data. The greater the variance, the worse the BER performance. At the same time, an indoor VLC system based on PAM4 is designed. The simulation results verify that the system scheme is feasible and provides a way to further realize high-speed signal transmission. [ABSTRACT FROM AUTHOR]

Photon counting has been proven to possess excellent signal detection capabilities at low power levels and has extensive potential applications in sixth-generation (6G) communications. However, the inherent dependency between the signal and noise complicates system analysis, and optimizing achievable rates in photon-counting visible light communication (VLC) systems remains unresolved. This paper introduces a new method aimed at minimizing multi-user interference (MUI) through a zero-forcing (ZF) scheme and maximizing the weighted sum rate of the proposed downlink multi-user photon-counting multiple-input multiple-output (MU-PhC-MIMO) VLC system by solving an optimization problem. The key point lies in our utilization of the ZF approach to derive a reasonable asymptotic approximation expression for the weighted sum rate. Subsequently, we use variable substitution and methods like successive convex approximation (SCA) to iteratively convexify the non-convex optimization problem and maximize the weighted sum rate under the ZF form. Compared to other algorithms, this approach can save 2.5 dB of transmission power to achieve the same system-weighted sum rate and significantly outperforms the repetition coding scheme at sufficient transmission power. [ABSTRACT FROM AUTHOR]

Micro-LED arrays exhibit high brightness, a long lifespan, low power consumption, and a fast response speed. In this paper, we have proposed a series-biased micro-LED array by using a nitride layer with multi-quantum wells epitaxial on sapphire substrate. The III-nitride multiple quantum wells serving as the micro-LED active material enable both luminescence and detection functionalities. The micro-LED array combines lighting, detection, and communication capabilities. We have conducted a thorough analysis of the micro-LED array's optoelectronic features in both lighting and detection modes. We also explore visible light communication performance across different arrangements of single micro-LED devices within the series-biased array. Our research achieves 720p video transmission via visible light communication using the micro-LED array, supporting a communication rate of up to 10 Mbps. Our contributions encompass the successful integration of lighting and detection functions and a comprehensive assessment of optoelectronic and communication performance. This study highlights the multifunctional micro-LED array's potential as a transceiver terminal in visible light communication systems, expanding its applications from smart lighting to visible light communication and photonic integrated chips. These innovations enhance our understanding of micro-LED technology and its versatile applications. [ABSTRACT FROM AUTHOR]

Intelligent Transportation Systems (ITSs) are being proposed, examined, and applied to enhance road safety and traffic efficiency. However, the automotive industry has stringent criteria for safety applications that demand connections that are dependable and have low latency, and high data rates. In this paper, it is widely agreed that both Visible Light Communication (VLC) and Free Space Optics (FSO) represent promising solutions, because of their complementary advantages compared to Radio Frequency (RF). VLC technology is chosen in ITS overall other optical wireless systems primarily due to its low cost and lack of licensing or new infrastructure requirements. Hence, a comparative study is applied between standalone VLC system, and a hybrid FSO/VLC system in term of Bit Error Rate (BER), coverage distance, and Signal to Noise Ratio (SNR). The VLC/FSO system provides a reliable communication link over a long distance (900 m) compared to VLC standalone system with 10−6 BER and acceptable SNR of ∼ 25 dB. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) is one of the fastest wireless communication systems compatible with 5G and beyond. Therefore, it was necessary to employ rapid modulation systems compatible with intensity modulation / direct detection (IM / DD), such as Flip-FBMC modulation technology. The distribution of illumination units across the entirety of the room poses the greatest difficulty for the VLC distribution system. Previous models suffered from dark spots or blind spots in the center of the room, which is the user's mobility area, as well as high power consumption, which is one of the most influential factors influencing the system. This is the first instance in which the illumination units are distributed in new locations by five lights installed in the ceiling in order to eradicate dark spots by using a laser diode (LD) instead of an LED due to its high-intensity illumination. The optimal semi-angle and field of view were calculated to be 43o and 45o, respectively, in order to obtain the best results in terms of the received optical power and the preferred performance of the SNR distribution in comparison to the previous models, as well as to improve the power consumption of the illumination units. using the optimal values of the semi-angle at 43° and FOV at 45°, the current findings indicate that Model 3 also attained the highest optical power received and the best SNR distribution performance compared to the previous models. In this way, a complete illuminate distribution is obtained for the room. [ABSTRACT FROM AUTHOR]

The role of inter-satellite communication (ISC) is of great significance in the contemporary era of satellite technology. In this context, visible light communication (VLC) has emerged as a highly promising alternative to conventional radio frequency (RF) communication. This is especially true for small satellites like CubeSats, where constraints related to size, weight, and power (SWaP) are of utmost importance. However, VLC systems’ limited bandwidth makes it challenging to achieve large data rates and capacity. This can be evaded with the utilization of non-orthogonal multiple access (NOMA) as a fundamental technology to augment ISC based on VLC. Such schemes have already been evaluated and published in the public domain literature. There is, nevertheless, lack of information on the efficacy of utilizing cooperative NOMA (Co-NOMA) scheme in conjunction with VLC for a constellation of satellites, with limited power resources. This research study investigates the utilization of NOMA as the access technique for inter-satellite connections when communication is done through VLC under power restrictions, with a particular emphasis on reducing the bit error rate (BER) while enhancing the average sum rate (ASR) for distant satellites through Co-NOMA. The efficacy of the proposed methodology is verified through simulation results.

Assessing the motion of moving objects from video footage captured using multiple recording devices requires precise timing and location data, which remains equally important in mobile recording systems. Although capturing high-precision clocks and analyzing these images are effective methods for obtaining accurate time information, a definitive method for precisely determining the capture time from images of rapidly time-varying clocks at various exposure durations is currently lacking. This paper introduces a design method for a dynamic optical marker called the Optical Clock Beacon (OCB), which indicates the current time by integrating multiple point light sources. Our goal is to enable accurate determination of the capture time from images. We present a method for estimating this time using image analysis and validate its accuracy. The simplest OCB configuration translates the binary representation of the current time into a Gray code, with each bit’s state indicated by light sources of positive and negative logic. This approach allows the determination of an image capture time with precision matching of the exposure duration. Furthermore, we outline a design strategy that improves the time accuracy by making the light source configuration of each digit redundant, thus providing substantial design flexibility for the OCB. We also detail the prototype hardware and the image analysis system of the developed OCB, demonstrating through evaluation experiments that the anticipated time accuracy is achievable.

The delay jitter in the visible light communication (VLC) network is analyzed in this work. First, the delay jitter under single-user and multi-user scenarios is investigated and a closed-form expression is obtained, whose accuracy is verified by simulation. Second, through analyzing the delay jitter under two typical indoor light emitting diode (LED) layouts, we find that the mean user delay jitter under cellular layout is a little lower than that of square layout. Then, we study the delay jitter for mobile users, and the relationship among user movement speed, arrival rate and delay jitter in different scenarios. The delay jitter performance is evaluated assuming perfect coordinated multiple points (CoMP) transmission strategy in VLC network. Simulation results show that in the context of VLC, static users can experience an average delay jitter of up to $10^{-6}$ s, while mobile users can experience an average delay jitter of up to $10^{-5}$ s. Therefore, VLC network can provide users with good delay jitter performance and customized services to meet the higher service quality requirements of future users.

The low-pass characteristics of front-end elements including light-emitting diodes (LEDs) and photodiodes (PDs) limit the transmission data rate of visible light communication (VLC) and Light Fidelity (LiFi) systems. Using multiplexing transmission techniques, such as spatial multiplexing (SMX) and wavelength division multiplexing (WDM), is a solution to overcome bandwidth limitation. However, spatial correlation in optical wireless channels and optical filter bandpass shifts typically limit the achievable multiplexing gain in SMX and WDM systems, respectively. In this paper, we consider a multiple-input multiple output (MIMO) joint multiplexing VLC system that exploits available degrees-of-freedom (DoFs) across space, wavelength and frequency dimensions simultaneously. Instead of providing a new precoder/post-detector design, we investigate the considered joint multiplexing system from a system configuration perspective by tuning system parameters in both spatial and wavelength domains, such as LED positions and optical filter passband. We propose a novel spatial clustering with wavelength division (SCWD) strategy which enhances the MIMO channel condition. We propose to use a state-of-the-art black-box optimization tool: Bayesian adaptive direct search (BADS) to determine the desired system parameters, which can significantly improve the achievable rate. The extensive numerical results demonstrate the superiority of the proposed method over conventional SMX and WDM VLC systems.

The application of liquid crystal (LC)-based reconfigurable intelligent surface (RIS)-assisted transmitters in visible light communication (VLC) systems can guide and amplify the light emitted by light emitting diodes (LEDs). In this paper, we investigate the VLC system employing the RIS-assisted transmitter, where user fairness is maximized by optimizing the refractive index of the RIS module. To address the non-convex problem, we adopt the particle swarm optimization (PSO) algorithm. Simulation results illustrate that equipping the RIS-assisted transmitter in the system and using the proposed algorithm can significantly improve user fairness.

Advancements in unmanned aerial vehicle (UAV) technology, along with indoor hybrid LiFi-WiFi networks (HLWN), promise the development of cost-effective, energy-efficient, adaptable, reliable, rapid, and on-demand HLWN-capable indoor flying networks (IFNs). To achieve this, a unified physical layer (UniPHY) capable of simultaneous control communication, data transfer, and sensing is crucial. However, traditional block-based decoders, designed independently for LiFi and WiFi, perform poorly in complex and hybrid LiFi-WiFi-enabled UniPHY systems. In this study, we propose an end-to-end learning framework based on convolutional neural networks (CNNs) for UniPHY, which can be trained to serve hybrid LiFi-WiFi transmissions to improve error performance and simplify UAV hardware. In this work, the performance of the proposed framework is assessed and compared with that of the conventional independent block-based communication system. Furthermore, a comprehensive summary of optimal hyper-parameters for efficient training of our learning framework has been provided. It is shown that, with optimal hyper-parameters, the proposed CNN-based framework outperforms the conventional block-based approach by providing a signal-to-noise ratio gain of approximately 7 dB for the LiFi channel and 23 dB for the WiFi channel. In addition, we evaluate the complexity and training convergence for loss and accuracy.

This research delves into the application of Digital Twins (DTs) in the realm of smart agriculture, with a particular focus on greenhouse and underground environments. By integrating computer simulations with empirical testing, we validate our hypotheses. A novel approach has been introduced that uses Visible Light Communication (VLC) for data exchange within greenhouses, along with a distinct system tailored for subterranean applications. This investigation explores how various factors influence communication effectiveness. Comprehensive testing of these systems has been conducted to evaluate their performance under a range of conditions and with varying orientations of light sources. Specifically, for our greenhouse configuration, we discovered that adjusting the system in a specific manner can substantially enhance signal quality, by nearly 10 dB at a distance of four meters, in underground scenarios. Furthermore, we have conducted evaluations using the most current WiFi and mobile networks, as well as Free Space Optics (FSO) networks, to ensure that our digital twin model is robust and capable of accurately transmitting data to a control room.

Due to its ability to reconfigure the optical channel, intelligent reflecting surface (IRS) has revealed its great potential for enhancing the performance of visible light communication (VLC) systems. In this paper, we apply a mirror array-based IRS in typical multiple-input multiple-output based VLC (MIMO-VLC) systems and optimize the IRS configuration to minimize the system bit error rate (BER). By utilizing the tight analytical BER upper bound, a BER minimization problem is formulated subject to the IRS configuration constraints. To solve this problem, an optimization algorithm is proposed which decomposes the original problem into three sub-problems, and the complexity of the algorithm is analyzed. The superiority of the obtained optimal IRS configuration scheme over the baseline scheme in terms of BER performance has been successfully verified through simulations in an indoor IRS-aided $4\times 4$ MIMO-VLC system applying different MIMO techniques.

The use of visible light communication (VLC) to support wireless coverage has been receiving increasing interest, due to factors that include its operation in a large unregulated spectrum and immunity against electromagnetic interference. On the other hand, the sensitivity of VLC network performance to the line-of-sight (LOS) link quality affects the system reliability. The emergence of reconfigurable intelligent surfaces (RISs) in optical domain opens the door for minimizing the impacts of the LOS link degradation on VLC networks, given the possibilities they provide for enhancing the non-LOS channel gain. In this paper, we propose optimizing the RIS-assisted VLC systems by controlling the RIS elements to maximize the network sum-rate while maintaining fairness in the user achievable throughput. Two types of RIS elements are considered, where the addressed non-convex optimization problems are handled using the genetic algorithm and the particle swarm optimization techniques, presenting improvement in network performance in terms of sum rate, fairness, and link outage ratio. In addition, we investigate the RIS-assisted VLC system performance in cases of handling mobile users, highlighting the trade-off between the variation in the optimization rate and the network performance.

Recently, visible light communications (VLCs) have attracted attention as a complement to wireless communications by radio frequency. In addition, the demand for Internet of Things (IoT) communications has increased in the last decade, and VLC-based IoT systems are being considered. Because IoT devices operate at various data rates, multirate transmission is required. Herein, we propose a scheme that supports multirate data transmission for synchronous optical code division multiple access systems. This scheme employs a generalized modified prime sequence code and multiple extended bi-orthogonal codes. The proposed scheme realizes multirate transmission with an arbitrary number of data rate levels by superimposing spreading codes of different codelengths. In addition, the proposed scheme eliminates not only interference between users with the same data rate, but also interference between users with different data rates. Furthermore, we investigated the bit error rate performance and energy efficiency of the proposed scheme, considering the effects of background light, dark current, and PIN photodiode noise including shot noise, and thermal noise.