Channel Capacity and Power Allocation of MIMO Visible Light Communication System

In this paper,the channel capacity of the multiple-input multiple-output(MIMO)visible light communication(VLC)system is investigated under the peak,average optical and electrical power constraints.Finding the channel capacity of MIMO VLC is shown to be a mixed integer programming problem.To address this open problem,we propose an inexact gradient projection method to find the channel capacity-achieving discrete input distribution and the channel capacity of MIMO VLC.Also we derive both upper and lower bounds of the capacity of MIMO VLC with the closed-form expressions.Furthermore,by considering practical discrete constellation inputs,we develop the optimal power allocation scheme to maximize transmission rate of MIMO VLC system.Simulation results show that more discrete points are needed to achieve the channel capacity as SNR increases.Both the upper and lower bounds of channel capacity are tight at low SNR region.In addition,comparing the equal power allocation,the proposed power allocation scheme can significantly increase the rate for the low-order modulation inputs.

Optimizing Optical Attocells Positioning of Indoor Visible Light Communication System

Visible light communication(VLC),which is a prominent emerging solution that complements the radio frequency(RF)technology,exhibits the potential to meet the demands of fifth-generation(5G)and beyond technologies.The random movement of mobile terminals in the indoor environment is a challenge in the VLC system.The model of optical attocells has a critical role in the uniform distribution and the quality of communication links in terms of received power and signal-to-noise ratio(SNR).As such,the optical attocells positions were optimized in this study with a developed try and error(TE)algorithm.The optimized optical attocells were examined and compared with previous models.This novel approach had successfully increased minimum received power from−1.29 to−0.225 dBm,along with enhanced SNR performance by 2.06 dB.The bit error rate(BER)was reduced to 4.42×10−8 and 6.63×10−14 by utilizing OOK-NRZ and BPSK modulation techniques,respectively.The optimized attocells positions displayed better uniform distribution,as both received power and SNR performances improved by 0.45 and 0.026,respectively.As the results of the proposed model are optimal,it is suitable for standard office and room model applications.

Modelling and Performance Analysis of Visible Light Communication System in Industrial Implementations

Visible light communication(VLC)has a paramount role in industrial implementations,especially for better energy efficiency,high speed-data rates,and low susceptibility to interference.However,since studies on VLC for industrial implementations are in scarcity,areas concerning illumination optimisation and communication performances demand further investigation.As such,this paper presents a new modelling of light fixture distribution for a warehouse model to provide acceptable illumination and communication performances.The proposed model was evaluated based on various semi-angles at half power(SAAHP)and different height levels for several parameters,including received power,signal to noise ratio(SNR),and bit error rate(BER).The results revealed improvement in terms of received power and SNR with 30 Mbps data rate.Various modulations were studied to improve the link quality,whereby better average BER values of 5.55×10^(−15) and 1.06×10^(−10) had been achieved with 4 PAM and 8 PPM,respectively.The simulation outcomes are indeed viable for the practical warehouse model.

Robust Artificial Noise-Aided Beamforming for A Secure MISO-NOMA Visible Light Communication System

Visible light communication(VLC)and non-orthogonal multiple access(NOMA)have been deemed two promising techniques in the next wireless communication networks.In this paper,secure communications in the presence of potential eavesdropper are investigated for a multiple-input single-output VLC system with NOMA.The artificial noise jamming and beamforming technologies are applied to improve secure performance.A robust resource allocation scheme is proposed to minimize the total transmit power taking into account the constraints on the quality of service requirement of the desired users and the maximum tolerable data rate of the eavesdropper,and the practical imperfect channel state information of both the desired users and the eavesdropper.The formulated non-convex optimization problem is tackled based onS-Procedure and semi-definite programming relaxation.Simulation results illustrate that our proposed resource allocation scheme can effectively guarantee communication security and achieve transmit power saving.Moreover,the height and number of LED can significantly affect system performance and the optimum LED height can be obtained for different LED numbers.

Performance Analysis of ACO-OFDM Visible Light Communication System Based on SCMA

A SCMA ACO-OFDM downlink visible light communication(VLC)system is proposed.Six users share four spectrum resources,four of which are 4 primary color LED lights.ACO-OFDM technology is used to convert the user’s sparse codebook mapped signal into a positive real value signal that can be carried on the light wave,which can realize high-speed parallel communication.Simulation verifies the feasibility of the system.At the same time,the channel model of visible light communication is constructed,and the signal-to-noise ratio(SNR)and channel gain of the visible light channel are systematically analyzed.Finally,the theoretical bit error rate formula using MPA decoding algorithm under different codebook constellation mapping points is given.Through simulation,it is verified that the theoretical bit error rate formula is basically consistent with the simulation bit error rate formula.

Security enhanced underwater visible light communication system based on chaotic phase scrambling and conjugate frequency hopping

We propose an encryption technique for underwater visible light communication[UVLC]based on chaotic phase scrambling[PS]and conjugate frequency hopping[CFH].The technique is experimentally tested using an 8-level pulse amplitude modulation[PAM-8]and a 1.2 m underwater link.The security key of the phase scrambling code is generated according to a logistic map,and the frequency hopping is achieved by adding the same zero frequency points to the signal spectrum.The maximum transmission rate of 2.1 Gbit/s is measured with bit-error-rate[BER]below 7%the hard-decision forward error correction[HD-FEC]threshold of 3.8×10^(-3).

Adaptive multiple-input multiple-output mode switching for indoor visible light communication system with orthogonal frequency division multiplexing modulation

We propose and experimentally demonstrate an adaptive multiple-input multiple-output(MIMO) mode switching scheme for an indoor visible light communication system combined with orthogonal frequency division multiplexing modulation.Only requiring 1 bit feedback from the receiver,the MIMO mode at the transmitter switches between spatial multiplexing and transmit diversity adapting to the channel correlation.In such a way,we can take advantage of both spatial multiplexing and transmit diversity,where the spatial multiplexing benefits for its multiplexing gain in the low channel correlation environment,and the transmit diversity is robust to high channel correlation.Experimental results validate the performance improvement over the pure spatial multiplexing or transmit diversity system.With the increasing of the channel correlation,the measured bit error rates of the proposed system are below the 7% pre-forward error correction(pre-FEC) limit of 3.8 × 10^(-3)when the transmitted data rate is 50 Mb/s,and below the 20% pre-FEC threshold of 5.0 × 10^(-2) when the transmitted data rate is raised up to 100 Mb/s.

Carrier-less amplitude and phase modulated visible light communication system based on a constellation-shaping scheme

In this Letter,we propose a novel constellation-shaping carrier-less amplitude and phase(CAP) modulation scheme to alleviate the systematic nonlinearity in visible light communication(VLC) systems.A simple geometric transformation shaping method is employed to convert the normal square lattice constellation into multiple circular constellations.The feasibility and performance are investigated and experimentally demonstrated by a 1.25 Gb/s CAP-modulated VLC system.The results indicate that the circular constellation has better resistance to systematic nonlinearity compared with a rectangular constellation.The dynamic range of input signal peak-to-peak values promotes 20% at a low bias voltage nonlinear area and 50% at a high bias voltage nonlinear area.To the best of our knowledge,this is the first time constellation-shaping CAP has ever been reported in indoor high data rate VLC systems.

HY-PC:Enabling Consistent Positioning and Communication Using Visible Light

Visible light(VL)plays an important role in achieving high-precision positioning and low bit error radio(BER)data communication.However,most VL-based systems can not achieve positioning and communication,simultaneously.There are two problems:1)the hybrid systems are difficult to extract distinguishable positioning beacon features without affecting communication performance,2)in the hybrid systems,the lost data bits in the inter-frame gap(IFG)are hard to recover,which affects positioning and communication performance.Therefore,in this article,we propose a novel VL-based hybrid positioning and communication system,named HY-PC system,to solve the above problems.First,we propose the robust T-W mapping for recognizing specific Light Emitting Diodes(LEDs),which can provide stable LED recognition accuracy without adding extra beacon data and does not decrease the communication rate.Furthermore,we also propose the novel linear block coding and bit interleaving mechanism,which can recover the lost data bits in the IFG and improve data communication performance.Finally,we use commercial off-the-shelf devices to implement our HY-PC system,extensive experimental results show that our HY-PC system can achieve consistent high-precision positioning and low-BER data communication,simultaneously.

Characteristic of Line-of-Sight in Infrastructure-to-Vehicle Visible Light Communication Using MIMO Technique

Visible Light Communication(VLC)technology is aggressive research for the next generation of communication.Currently,Radio Frequency(RF)communication has crowed spectrum.An Intelligent Transportation System(ITS)has been improved in the communication network for Vehicle-to-Vehicle(V2 V),Vehicle-to-Infrastructure(V2I),and Infrastructure-to-Vehicle(I2V)by using the visible light spectrum instead of the RF spectrum.This article studies the characterization of Line-of-Sight(LOS)optical performance in an Outdoor Wireless Visible Light Communication(OWVLC)system employing a Multiple-Input Multiple-Output(MIMO)technique for I2V communications in ITS regulations.We design the new configuration of the OWVLC-I2V system,which is an alternative approach to communication for I2V system at nighttime.The results show the Channel Impulse Response(CIR)of the LOS links in visible light communication for I2V system in ITS by investigating the receiver on the vehicle moving along the coverage communication area.Furthermore,the OWVLC-I2V system using the MIMO technique depicts the performance of throughput and Bit Error Rate(BER)vs.vehicle speed while the vehicle passes a street light.

Visible Light Communication for Vehicular Applications: A Novel Architecture with Proof-of-Concept Prototype

When there is an increasing interest in visible light communication(VLC), outdoor vehicle VLC has emerged as a promising candidate technology for future intelligent transportation systems. However, in VLC based vehicular applications, several challenges impede successful commercial application of VLC based products. This article first provides a thorough overview of the existing challenges. To overcome these challenges, we propose a novel architecture with tracking and environment sensing ability for practical vehicular applications. Moreover, a proof-ofconcept prototype is implemented to validate the feasibility of the proposed system. Experimental and simulation results show that the proposed VLC system can provide reliable communications with a bit-error rate less than 10-4for vehicles under strong interference lights. Finally, based on the evaluations, we propose some key design issues for future studies in this research area.

Stable yellow light emission from lead-free copper halides single crystals for visible light communication

Yellow light-emitting diodes(LEDs) as soft light have attracted abundant attention in lithography room, museum and art gallery. However, the development of efficient yellow LEDs lags behind green and blue LEDs, and the available perovskites yellow LEDs suffer from the instability. Herein, a pressure-assisted cooling method is proposed to grow lead-free CsCu2I3single crystals, which possess uniform surface morphology and enhanced photoluminescence quantum yield(PLQY) stability, with only 10% PLQY losses after being stored in air after 5000 h.Then, the single crystals used for yellow LEDs without encapsulation exhibit a decent Correlated Color Temperature(CCT) of 4290 K, a Commission Internationale de l’Eclairage(CIE) coordinate of(0.38, 0.41), and an excellent 570-h operating stability under heating temperature of 100°C. Finally, the yellow LEDs facilitate the application in wireless visible light communication(VLC), which show a-3 dB bandwidth of 21.5 MHz and a high achievable data rate of 219.2 Mbps by using orthogonal frequency division multiplexing(OFDM) modulation with adaptive bit loading. The present work not only promotes the development of lead-free single crystals, but also inspires the potential of CsCu2I3in the field of yellow illumination and wireless VLC.

Intelligent MRI Room Design Using Visible Light Communication with Range Augmentation

Radio waves and strong magneticfields are used by Magnetic Reso-nance 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 leak-age.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).

High Capacity Data Rate System:Review of Visible Light Communications Technology

Wireless communications have become an integral part of global convergence as global connectedness has gradually become dependent on its efficient deployment.The need for"more-broadband"techniques in relation to the ever increasing growth rate of the data hungry society now necessitates novel techniques for the high-speed data transmission.While advancements have been made in this regard,the projection of having an eventual Internet of everything (IoE) deployment will result in an unimaginable transmission data rate requirement as huge data traffic will be conveyed per time within the communications network,which will require a capacity upgrade of the existing infrastructure.Visible light communications (VLCs),as an integral part of optical wireless communications (OWCs),have been reviewed in this article,having the capacity to extend the achievable data rate requirement of the wireless communications network.The technologies,techniques,and best practices have been presented alongside technology integration for the seamless high capacity wireless broadband deployment.

Design and Analysis of Traffic Information Transmission System Based on Visible Light Communication

Visible Light Communication( VLC) based on LED is a new wireless communication technology with high response rate and good modulation characteristics in the wavelengths of 380- 780 nm. Compared with conventional methods,the waveband of VLC is harmless to human and safe to communication because of no magnetism radiation. An audio information transmission system using LED traffic lights is presented based on VLC technology. The system is consisted of transmitting terminal,receiving terminal and communication channel. Some experiments were made under real communication environment. The experimental results showed that the traffic information transmission system works steadily with good communication quality and achieves the purpose of transmitting audio information through LED traffic lights,with a data transfer rate up to 250 kbps over a distance of 5 meters.

Visible light communication system at 3.59 Gbit/s based on c-plane green micro-LED

Visible light communication(VLC)based on the micro light emitting diode(micro-LED)has attracted increasing attention owing to its high bandwidth,low power consumption,and high security.Compared with semi-polar or non-polar micro-LEDs,the commercial polar micro-LED has the advantages of low cost and more mature epitaxy technique.In this study,green micro-LEDs with different indium tin oxide(ITO)sizes are fabricated based on the commercial c-plane LED epitaxial wafer.The transmission performance of 80,100,and 150μm devices has been studied in detail.A partial pre-equalization scheme is utilized to increase data rates.Finally,the VLC system with a 100μm green micro-LED as the transmitter could achieve a maximum data rate of 3.59 Gbit/s.Such a result will be beneficial to promote the further development of low-cost,high-speed VLC devices in the future.

New spatial quadrature modulation scheme for indoor visible light communication systems

In this paper,a new spatial quadrature modulation(NSQM)scheme is proposed to improve the error performance of indoor visible light communication(VLC)systems.NSQM is different from generalized spatial quadrature modulation(SQM)in two aspects.First,the transmitted optical signal is directly detected at the receiver,which does not need to estimate the indices of the transmitted antenna.Second,an optimization approach is used with NSQM to minimize the upper error bound of the transmitted signals.In addition,several NSQM schemes are described in detail.Numerical results show that the proposed NSQM scheme achieves superior error performance compared with the SQM scheme.

Separate Least Mean Square Based Equalizer with Joint Optimization for Multi-CAP Visible Light Communication

Visible light communication(VLC) is expected to be a potential candidate of the key technologies in the sixth generation(6G) wireless communication system to support Internet of Things(IoT) applications. In this work, a separate least mean square(S-LMS) equalizer is proposed to compensate lowpass frequency response in VLC system. Joint optimization is employed to realize the proposed S-LMS equalizer with pre-part and post-part by introducing Lagrangian. For verification, the performance of VLC system based on multi-band carrier-less amplitude and phase(m-CAP) modulation with S-LMS equalizer is investigated and compared with that without equalizer,with LMS equalizer and with recursive least squares(RLS)-Volterra equalizer. Results indicate the proposed equalizer shows significant improved bit error ratio(BER) performance under the same conditions. Compared to the RLS-Volterra equalizer, SLMS equalizer achieves better performance under low data rate or high signal noise ratio(SNR) conditions with obviously lower computational complexity.

High-speed visible light communication based on micro-LED:A technology with wide applications in next generation communication

The evolution of next-generation cellular networks is aimed at creating faster,more reliable solutions.Both the next-generation 6G network and the metaverse require high transmission speeds.Visible light communication(VLC)is deemed an important ancillary technology to wireless communication.It has shown potential for a wide range of applications in next-generation communication.Micro light-emitting diodes(μLEDs)are ideal light sources for high-speed VLC,owing to their high modulation bandwidths.In this review,an overview ofμLEDs for VLC is presented.Methods to improve the modulation bandwidth are discussed in terms of epitaxy optimization,crystal orientation,and active region structure.Moreover,electroluminescent white LEDs,photoluminescent white LEDs based on phosphor or quantum-dot color conversion,andμLED-based detectors for VLC are introduced.Finally,the latest high-speed VLC applications and the application prospects of VLC in 6G are introduced,including underwater VLC and artificial intelligence-based VLC systems.

Design of Protograph LDPC-Coded MIMO-VLC Systems with Generalized Spatial Modulation

This paper investigates the bit-interleaved coded generalized spatial modulation(BICGSM) with iterative decoding(BICGSM-ID) for multiple-input multiple-output(MIMO) visible light communications(VLC). In the BICGSM-ID scheme, the information bits conveyed by the signal-domain(SiD) symbols and the spatial-domain(SpD) light emitting diode(LED)-index patterns are coded by a protograph low-density parity-check(P-LDPC) code. Specifically, we propose a signal-domain symbol expanding and re-allocating(SSER) method for constructing a type of novel generalized spatial modulation(GSM) constellations, referred to as SSERGSM constellations, so as to boost the performance of the BICGSM-ID MIMO-VLC systems.Moreover, by applying a modified PEXIT(MPEXIT) algorithm, we further design a family of rate-compatible P-LDPC codes, referred to as enhanced accumulate-repeat-accumulate(EARA) codes,which possess both excellent decoding thresholds and linear-minimum-distance-growth property. Both analysis and simulation results illustrate that the proposed SSERGSM constellations and P-LDPC codes can remarkably improve the convergence and decoding performance of MIMO-VLC systems. Therefore, the proposed P-LDPC-coded SSERGSM-mapped BICGSMID configuration is envisioned as a promising transmission solution to satisfy the high-throughput requirement of MIMO-VLC applications.