Visible Light Communication Link Research Articles

Characterization of a VLC system in real museum scenario using diffusive LED lighting of artworks

Visible light communication (VLC) is currently recognized as a relevant technology for a wealth of possible application scenarios. New classes of services can be designed in both outdoor and indoor environments, exploiting the directionality of the optical channel and the low attainable latencies. Such features allow VLC to offer both spatial localization of users and wireless communication by using widespread high-power LEDs as simultaneous illumination and information sources. In the indoor scenario, one of the most promising deployments is expected in museums, where digital data can be cast by the specific illumination system of each artwork and received by visitors placed nearby. This would enable a full set of services, aiming, e.g., at an immersive experience in the augmented reality approach or at real-time localization of visitors. In this work, we characterize for the first time the performance of a photodiode-based VLC system in a real museum environment, performing an extensive measurement campaign on several masterpieces (wall, canvas, and wood paintings) in the Basilica of Santa Maria Novella in Florence, Italy. In particular, we demonstrate the possibility of using indirect (diffused) illumination light to deliver specific information on each artwork to a visitor. We characterize the quality of such non-line-of-sight VLC links by performing packet error rate measurements as a function of angle and distance from the artwork, and we measure the effective field of view (FoV) of our receiving stage, as well as the influence of side displacements of the receiver on the transmission quality, demonstrating that diffusive VLC links can also be used for efficient localization of users in front of each artwork in museum applications. With observed baud rates up to 28 kbaud and FoV values up to 60° for realistic distances up to 6 m, we believe our work could pave the way for future studies involving VLC in a wealth of indoor applications, beyond the cultural heritage sector.

Beam steering in a narrow-beam phosphor down-converted white light visible light communication link using transmitter lens decentering.

Indoor visible light communication (VLC) systems with narrow beams can achieve practical few-meters-long wireless optical links. Such links can operate at low power levels and high data rate for supporting point-to-point or multipoint communication. The narrow-beam VLC links can, however, benefit from beam steering to support mobility of user equipment and cater to multiple users. Simple beam-steering techniques with minimal changes to the existing optical hardware are required to enable widespread adoption of beam steering in VLC links. We study the performance of a simple transmitter-lens-decenter-based beam-steering scheme in a VLC link, utilizing a phosphor down-converted blue laser transmitter. The beam-steering angle and hence the receiver coverage depend on the transmitter lens decenter and the choice of the transmitter and receiver lens's focal lengths. Optical ray tracing is used to quantify the collection efficiency achievable with beam steering, choose a suitable receiver lens, and understand the role of off-axis aberration in the system performance. In our experimental implementation, the transmitter lens decentering technique results in a maximum steering angle of 7.1°. This corresponds to a receiver coverage of 30 cm per cm of transmitter lens decenter for a fixed link length of 300 cm. The measured on-axis white light color coordinates of (0.286, 0.253) is found to shift toward warmer white colors with beam steering. The on-axis illuminance level of ∼19lux decreases slightly with beam steering and is found to be below the maximum permissible exposure limit for indoor illumination. We also quantify the data communication performance as a function of beam steering using on-off modulated data. Bit-error rates below the forward error correction limit are obtained for receiver coverage diameter of 75 cm and 60 cm for 1.25 Gbps and 1.5 Gbps data rates, respectively.

EVM Loss: A Loss Function for Training Neural Networks in Communication Systems.

Neural networks and their application in communication systems are receiving growing attention from both academia and industry. The authors note that there is a disconnect between the typical objective functions of these neural networks with regards to the context in which the neural network will eventually be deployed and evaluated. To this end, a new loss function is proposed and shown to increase the performance of neural networks when implemented in a communication system compared to previous methods. It is further shown that a ‘split complex’ approach used by many implementations can be improved via formalisation of the ‘concatenated complex’ approach described herein. Experimental results using the orthogonal frequency division multiplexing (OFDM) and spectrally efficient frequency division multiplexing (SEFDM) modulation formats with varying bandwidth compression factors over a wireless visible light communication (VLC) link validate the efficacy of the proposed method in a real system, achieving the lowest error vector magnitude (EVM), and thus bit error rate (BER), across all experiments, with a 5 dB to 10 dB improvement in the received symbols EVM overall compared to the baseline implementation, with bandwidth compressions down to 40% compared to OFDM, resulting in a spectral efficiency gain of 67%.

Preliminary Characterization of Coverage for Water-to-Air Visible Light Communication Through Wavy Water Surface

In this paper, we establish a water-to-air (W2A) visible light communication (VLC) link using green light emitting diode (LED), and investigate the coverage characteristics of the designed W2A-VLC link under calm and wavy water conditions. By transmitting a high-frequency sinusoid signal, we extract the variation of link gain. Based on the received signals of an experimental W2A-VLC system, we obtain the real link gains at different receiver points and analyze the channel temporal properties in good link conditions (called link “on” state). It is seen that the mean channel gain under wavy water surface condition can be larger than that under calm water surface condition, especially when the transmitter and receiver are not perfectly aligned, due to the random spatial modulation effect of wavy water surface. Moreover, the “on” state duration and interval can be well fitted by a shifted exponential distribution and a shifted lognormal distribution, respectively. Bit error rate (BER) results reveal the effect of expanded link gain variation under wavy water surface condition. This work provides significant guidance for future works on the communication protocol design and related performance analysis.

Time Difference of Arrival Based Indoor Positioning System Using Visible Light Communication

Visible Light Communication (VLC) is a novel optical wireless communication technology which uses Light Emitting Diodes (LEDs) and Photodiodes for coherent detection and very-high-data rate data communication system. The stringent Line of Sight (LoS) requirement in VLC makes it very suitable for Indoor Positioning System (IPS), to be used for autonomous and smart city infrastructure. The current work aims to implement a real time IPS system using VLC link in Network Simulator (NS-3). The VLC module is implemented by modelling real-time attributes of LEDs, optical channel, and the photodiodes. The localization is carried out using trilateration schemes which measures the Received Signal Strength Indication (RSSI) and the Time Difference of Arrival (TDoA) for position estimation of the target. The project is further extended to obtain a comparative analysis between VLC link and other existing technology, Wi-Fi, as far as positioning accuracy and other important performance metrics are concerned. The simulation results show significant improvement for the VLC link over the Wi-Fi link specially for the TDoA scheme accompanied by increasing number of beacon nodes.

Hybrid RF/VLC Systems: A Comprehensive Survey on Network Topologies, Performance Analyses, Applications, and Future Directions

Wireless communications refer to data transmissions in unguided propagation media through the use of wireless carriers such as radio frequency (RF) and visible light (VL) waves. The rising demand for high data rates, especially, in indoor scenarios, overloads conventional RF technologies. Therefore, technologies such as millimeter waves (mmWave) and cognitive radios have been adopted as possible solutions to overcome the spectrum scarcity and capacity limitations of the conventional RF systems. In parallel, visible light communication (VLC) has been proposed as an alternative solution, where a light source is used for both illumination and data transmission. In comparison to RF links, VLC links present a very high bandwidth that allows much higher data rates. VLC exhibits also immunity to interference from electromagnetic sources, has unlicensed channels, is a very low power consumption system, and has no health hazard. VLC is appealing for a wide range of applications including reliable communications with low latency such as vehicle safety communication. Despite the major advantages of VLC technology and a variety of its applications, its use has been hampered by its cons such as its dependence on a line of sight connectivity. Recently, hybrid RF/VLC systems were proposed to take advantage of the high capacity of VLC links and better connectivity of RF links. Thus, hybrid RF/VLC systems are envisioned as a key enabler to improve the user rates and mobility on one hand and to optimize the capacity, interference and power consumption of the overall network on the other hand. This paper seeks to provide a detailed survey of hybrid RF/VLC systems. This paper represents an overview of the current developments in the hybrid RF/VLC systems, their benefits and limitations for both newcomers and expert researchers.

A Manchester-OOK Visible Light Communication System for Patient Monitoring in Intensive Care Units

Visible Light Communication (VLC) is an interesting solution in Intensive Care (IC) medical environments to, among others, prevent the spread of emerging diseases. This work presents the design of a low-cost and stable VLC transceiver system in addition to practical characterizations and experimental performance evaluations for application in IC environments. The application focuses on the transmission of Manchester-based on-off keying signals, in a proof-of-concept apparatus that makes use of the Eye Opening Penalty (EOP) metric to illustrate a comprehensive picture of the potentials of the evaluated VLC system. Parameters such as Light-Emitting Diode (LED) bias current, modulation frequency, line-of-sight link distance, and signal pattern were analyzed here. Experimental results show an outstanding behavior considering an LED bias current of 400 mA, a signal frequency of 1 MHz and a VLC transmission link length of 2.5 m. To validate our system, vital parameters as heart rate, oxygen saturation, pulse rate, respiration rate, temperature and non-intrusive blood pressure signals were transmitted for VLC links of 1.5, 5 and 15 m, which were received by a multi-parameter monitor, with EOP values of 0.89, 0.96 and 2.67 dB, respectively.

Experimental demonstration of 62.5 Mbps VLC link for healthcare infrastructures by incorporating limiting amplifier as an amplification scheme

The ongoing pandemic situation of COVID-19 has alarmed global public healthcare and epidemic response mechanisms to a significant extent. In this context, communication services can play an important role in hospitals to drive emergency response mechanisms accurately. Visible light communication (VLC) can become an excellent solution to provide communication services in hospitals as it uses low-cost LEDs to transmit information in the form of light signals which can not interfere with medical equipment and does not impact patient health. However, low bandwidth of LEDs is one of the major challenges, which limits the transmission capacity and distance in VLC system. In this work, we propose a post-amplification scheme based on low-pass filter and limiting amplifier to overcome the inherent bandwidth limitation of commercial LEDs. A 62.5Mbps non-return to zero on-off keying (NRZ-OOK) modulation-based VLC link with error-free transmission can be achieved over a transmission distance of 6 ​m.

Flexible photoluminescent waveguide amplifiers to improve visible light communication platforms

Commercial light-emitting diodes are a low-cost and energy-efficient solution for the implementation of optical wireless communication, known as visible light communication (VLC). This technology has a huge growing interest, being recently a research spotlight in the scientific community, especially due to the increasing popularity and rapid development of self-sustainable smart houses and the Internet of Things. As the VLC link is free space, big challenges arise in its implementation. To improve the VLC performance, this work proposes an enhanced system solution integrating an optical amplifier. In this context, organic–inorganic hybrids incorporating a blue-emitting conjugated polymer with high quantum yield (>50%) were synthesised and processed as planar waveguides. The waveguides were tested in a testbed scenario, showing a signal amplitude improvement of 2.5 dB, establishing the proposed approach as a promising cost-effective solution for optical amplification in VLCs.

Indoor Fine Particulate Matter Monitoring in a Large Area Using Bidirectional Multihop VLC

These particulate matter (PM) causes lethal diseases to humans, and both short term and long term exposure are known to have hazardous effects. PM10 and PM2.5 have diameters less 10 and $2.5~\mu \text{m}$ , respectively, which makes them more dangerous to the human body. Thus, information regarding PM concentrations in indoor environments of dust-sensitive places is essential for proper precaution. In this study, we measured PM values in a large area and transferred this information using visible light communication (VLC) to the monitoring node. VLC is considered as an efficient technique due to its unique advantages and is currently unregulated. We applied bidirectional VLC to transfer information to ensure two-way communication. We also applied a multihop strategy to make the system function as a query answering system at extended distances. At one end, we generated a request to relay the request to the proper node and received the response in the form of PM data. In our experiment, we implemented four nodes and conducted multihop communication utilizing only a VLC link. We achieved a distance of 13.5 m with a zero-error rate between the two nodes using nonreturn to zero on-off keying (NRZ-OOK) modulation. In case of multihop, we achieved a distance greater than 40 m using four nodes to send dust information with a minimal error rate. This can be applied to large indoor areas where radio frequency is restricted.

User Pairing, Link Selection, and Power Allocation for Cooperative NOMA Hybrid VLC/RF Systems

Despite the promising high-data rate features of visible light communications (VLC), they still suffer from unbalanced services due to blockages and channel fluctuation among users. This paper introduces and evaluates a new transmission scheme which adopts cooperative non-orthogonal multiple access (Co-NOMA) in hybrid VLC/radio-frequency (RF) systems, so as to improve both system sum-rate and fairness. Consider a network consisting of one VLC access point (AP) and multiple strong and weak users, where each weak user is paired with a strong user. Each weak user can be served either directly by the VLC AP, or via the strong user which converts light information received through the VLC link, and forwards the information to the weak user via the RF link. The paper then maximizes a network-wide weighted sum-rate, so as to jointly determine the strong-weak user-pairs, the serving link of each weak user (i.e., either direct VLC or hybrid VLC/RF), and the power of each user message, subject to user connectivity and transmit power constraints. The paper tackles such a mixed-integer non-convex optimization problem using an iterative approach. Simulations show that the proposed scheme significantly improves the VLC network performance (i.e., sum-rate and fairness) as compared to the conventional NOMA scheme.

On BER analysis of nonlinear VLC systems under ambient light and imperfect/outdated CSI

Visible light communication (VLC) has emerged as a promising supplement to the existing radio frequency (RF) technology, which facilitates high speed communication for next generation communication systems. Although promising, the performance in a practical VLC system is severely impaired by ambient light interference. Furthermore, nonlinearity of light emitting diodes (LEDs) and imperfect/oudated channel state information (CSI) are other factors that degrade the achievable bit error rate (BER) performance. In this work, an analytical framework for analyzing the expression for BER of a wide class of modulation techniques is derived for an impaired VLC system considering: (a) ambient light interference, (b) LED nonlinearity, and (c) imperfect and outdated CSI. The derived analytical expressions for BER are validated through extensive computer simulations performed over typical VLC channels. Lastly, the utility of the derived analytical framework is demonstrated in the context of high data-rate VLC systems, wherein the performance of DC biased optical orthogonal frequency division multiplexing (DCO-OFDM) is quantified for VLC links impaired by the aforementioned degradations.

Secure Cooperative Hybrid VLC-RF Systems

In this paper, a cooperative hybrid visible light communication (VLC)-radio frequency (RF) system with spatially random terminals is considered. Especially, a source node (<inline-formula> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula>) with a group of light-emitting diode (LED) lamps transmits information bits to a destination (<inline-formula> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula>), which is located out of <inline-formula> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula>&#x2019;s coverage area, via a relay node (<inline-formula> <tex-math notation="LaTeX">$R$ </tex-math></inline-formula>). <inline-formula> <tex-math notation="LaTeX">$R$ </tex-math></inline-formula> is equipped with a photodetector and an antenna to set up a VLC link between <inline-formula> <tex-math notation="LaTeX">$S$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$R$ </tex-math></inline-formula>, and a radio frequency (RF) link between <inline-formula> <tex-math notation="LaTeX">$R$ </tex-math></inline-formula> and <inline-formula> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula>, respectively. Meanwhile, an eavesdropper (<inline-formula> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula>) equipped with a photodetector and an antenna tries to overhear the information delivery over VLC and RF links. Also, diversity receiving scheme is considered at <inline-formula> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula>, while the same modulation scheme is considered over both VLC and RF links. Furthermore, decode-and-forward scheme is adopted at <inline-formula> <tex-math notation="LaTeX">$R$ </tex-math></inline-formula> to process and forward the received VLC signals. By employing stochastic geometry, we first characterize the probability density function and cumulative distribution function of the received signal-to-noise-ratio over both VLC and RF links, while considering the randomness of the locations of both <inline-formula> <tex-math notation="LaTeX">$R$ </tex-math></inline-formula>, <inline-formula> <tex-math notation="LaTeX">$E$ </tex-math></inline-formula>, and <inline-formula> <tex-math notation="LaTeX">$D$ </tex-math></inline-formula>. Then, the secrecy performance of the target system is studied by deriving the approximated expressions for the secrecy outage probability under various cases. Finally, the proposed analytical models are verified via Monte-Carlo simulations.

Enhanced tolerance against optical background noise in VLC link by using line coded signal with receiver filter

The performance of visible light communication (VLC) link is significantly affected by optical background noises generated by fluorescent light or AC driven light emitting diode (LED) and eventually degrades the data rate due to the in-band interference between signal and noise. Here, bandwidth efficient 8b10b dc-balanced line coding and post-detection electrical filter based VLC link is demonstrated to improve the system tolerance against the optical background noises. The 8b10b coded signal with low frequency components near DC ensure that the crosstalk noise is effectively minimized by spectral separation of signal and noise contributions. Moreover, the use of post detection filter for 8b10b coded signal gives an additional attenuation of noise frequency to further improve the system tolerance against optical background noise. The proposed VLC link is investigated thoroughly in several noise power levels as well as different noise frequencies, where the results indicate improved system tolerance against noise power by about 6.5 dB in compare to conventional data signal. The demonstration also shows that the proposed scheme maintains a low BER for the noise frequency up to 500 kHz for 10 Mb/s data modulation having a good eye opening.

Self-powered signal processing system for visible light communication based on solar panels

We propose a self-powered signal processing system that can transfer a single byte of data without needing any external power supply. The proposed system uses a local extreme point reconstruction algorithm for reconstructing the waveform. In addition, we use Manchester coding in the proposed method for reducing the byte error rate. The experimental results show that the self-powered processor needs 3 mW generated from the solar panel to maintain 1 MSa / s and 8-bit sample depth when the visible light communication link distance is fixed as 30 cm. The maximum bit rate is 500 kbit / s and the corresponding byte error rate is 6 × 10 − 2.

Novel multi-patient biomedical data transmission using CPoLSK modulation technique

This paper presents a novel multi-patient biomedical data transmission scheme using coded polarization shift keying (CPoLSK) modulation in a visible light communication (VLC) link. Considering the importance of accurate and reliable multiple patient data transmission in an interference-prone indoor hospital environment, the proposed CPoLSK having inherent properties of the code shift keying (CSK) presents a salient feature of interference mitigation. In the CSK, the codes are generated from the circular phase shift of a single maximal length pseudorandom (PRN) code that is capable of mitigating the interference effect. Each circular shifted code is mapped to each patient biomedical data and then transmitted using the polarization shift keying (PoLSK) modulation. In the proposed study, two orthogonal states of polarization at the same frequency for the two information bits (0 and 1) are used. The system design and operation mechanism of the proposed CPoLSK scheme are discussed. Analytical expressions are also derived and validated using simulations. The proposed scheme exhibits interference mitigation capability and high reliability, compared with existing multiple patient data transmission schemes.

Fast Detection and Tracking of a Moving Transmitter via Visible Light Communication Link

We propose a passive detection and tracking methodology for CamCom receivers in intelligent transport systems. The implemented architecture maximizes the data rate and can maintain a BER of 1.9 × 10−4 while passively detecting and tracking the moving transmitter undergoing worst-case road vibration of 30.6 mm/s. The proposed methodology is also independent of the size and shape of the transmitter and thus finds promising application in intelligent transport.

Indoor Mixed Dual-Hop VLC/RF Systems Through Reconfigurable Intelligent Surfaces

In this letter, a reconfigurable intelligent surface (RIS)-assisted dual-hop visible light communication (VLC)/radio frequency (RF) system in indoor scenarios is proposed, in which the first link is a VLC link while an RIS is deployed in the second RF link. More specifically, a relay first converts the received optical signal into the RF signal blue using either decode-and-forward or amplify-and-forward protocols and then forwards it to the RIS. The RIS alters the electromagnetic response of the impinging waves to provide connectivity between the RF destination and optical source. Based on this model, closed-form expressions for the outage probability and bit error rate (BER) are derived. Also, an asymptotic analysis for the outage probability is presented. Finally, simulation results are provided to verify our analytical results.

Vertical Underwater Visible Light Communication Links: Channel Modeling and Performance Analysis

Underwater visible light communication (UVLC) has been introduced to support emerging high data rate applications such as real-time image and video transmission. Initial works on UVLC build upon the assumption of fixed turbulence strength through the transmission range which can be justified only for horizontal links. In vertical underwater links, the gradient of temperature and salinity changes with depth. This effectively results in ocean stratification where water with different values of salinity and temperature form non-mixing layers. In this paper, we first model the vertical underwater link as a cascaded fading channel where fading coefficients associated with different layers are modeled as independent and non-identical distributed. Based on the cascaded lognormal and Gamma-Gamma distributions respectively for weak and moderate/strong turbulence conditions, we first derive closed-form expressions for the bit error rate (BER) performance of UVLC systems. Then, we analyze the asymptotic BER performance and determine the diversity orders. In addition, we derive closed-form expressions for the average ergodic capacity of underwater cascaded fading channels under consideration. We present simulation results to confirm the analytical findings.

Deep Learning for Optimal Deployment of UAVs With Visible Light Communications

In this paper, the problem of dynamical deployment of unmanned aerial vehicles (UAVs) equipped with visible light communication (VLC) capabilities for optimizing the energy efficiency of UAV-enabled networks is studied. In the studied model, the UAVs can simultaneously provide communications and illumination to service ground users. Since ambient illumination increases the interference over VLC links while reducing the illumination threshold of the UAVs, it is necessary to consider the illumination distribution of the target area for UAV deployment optimization. This problem is formulated as an optimization problem which jointly optimizes UAV deployment, user association, and power efficiency while meeting the illumination and communication requirements of users. To solve this problem, an algorithm that combines the machine learning framework of gated recurrent units (GRUs) with convolutional neural networks (CNNs) is proposed. Using GRUs and CNNs, the UAVs can model the long-term historical illumination distribution and predict the future illumination distribution. Given the prediction of illumination distribution, the original nonconvex optimization problem can be divided into two sub-problems and is then solved using a low-complexity, iterative algorithm. Then, the proposed algorithm enables UAVs to determine the their deployment and user association to minimize the total transmit power. Simulation results using real data from the Earth observations group (EOG) at NOAA/NCEI show that the proposed approach can achieve up to 68.9% reduction in total transmit power compared to a conventional optimal UAV deployment that does not consider the illumination distribution and user association.