Description:FIELD OF INVENTION
The invention relates to optical wireless communication systems, specifically employing visible light spectrum for high-efficiency data transfer, enabling faster, secure, and energy-efficient communication between devices in smart environments.

BACKGROUND OF INVENTION
The invention relates to a light-based communication system that employs the visible light spectrum for high-efficiency data transfer. Traditional wireless communication systems, such as radio frequency (RF) and infrared, face challenges including limited bandwidth, interference, and security vulnerabilities. With the increasing demand for faster and more reliable data transmission, there is a growing need for alternative communication methods. Visible Light Communication (VLC) technology utilizes light-emitting diodes (LEDs) as transmitters and photodiodes or image sensors as receivers to transmit data through modulated light signals. This system offers high-speed data transfer, low power consumption, enhanced security, and immunity to electromagnetic interference, making it ideal for environments such as hospitals, aircraft cabins, and smart cities where RF communication is restricted or undesirable.
The patent application number 202027007537 discloses a dynamic calibration for audio data transfer. The invention enables adaptive calibration of audio signals for data transfer, dynamically adjusting frequency, amplitude, and noise parameters to ensure reliable, high-quality transmission across varying environments. The patent application number 202127058075 discloses a data transfer for integrated access and backhaul system using full-duplex. The invention enables simultaneous uplink and downlink data transfer in integrated access and backhaul systems using full-duplex communication, improving spectrum efficiency, latency, and network throughput.
The patent application number 202227011887 discloses a unidirectional field device data transfer. The invention enables secure, one-way data transfer from field devices to control systems, preventing reverse communication to protect sensitive data and ensure system integrity.
The patent application number 202241064590 discloses a system and method for data transfer and request handling among a plurality of resources. The invention enables efficient data transfer and request handling among multiple resources through coordinated communication, load balancing, and dynamic resource allocation to optimize performance and reliability.
The patent application number 202341062699 discloses a system and method for hardware-based data transfer. The invention provides a hardware-based system enabling fast, secure, and direct data transfer between devices using dedicated circuitry, reducing latency, power consumption, and software dependency.

SUMMARY
The invention relates to a light-based communication system that utilizes the visible light spectrum (VLC) for high-efficiency wireless data transfer. The system employs LED-based transmitters to modulate light intensity at high speeds, transmitting encoded digital information to photo-detector receivers capable of converting optical signals back into electrical data. It enables simultaneous illumination and communication, offering a secure, interference-free, and energy-efficient alternative to traditional radio frequency systems. The invention integrates adaptive modulation schemes, error correction, and synchronization techniques to ensure reliable data transmission even under varying ambient lighting conditions. Designed for indoor, vehicular, and IoT applications, the system enhances data rates, bandwidth utilization, and security while minimizing power consumption and electromagnetic interference.

DETAILED DESCRIPTION OF INVENTION
Electromagnetic (EM) waves are fundamental to modern wireless communication, encompassing applications such as cellular networks, Wi-Fi, and radio broadcasting. EM waves span a broad spectrum, including radio waves, infrared, visible light, ultraviolet, and X-rays. While radio frequency (RF) signals provide wide-area coverage and are relatively resilient to minor interference, they face limitations in bandwidth, interference susceptibility, crowded spectrum, transmission power constraints, and safety considerations. To overcome these challenges, Visible Light Communication (VLC) has emerged as an alternative, utilizing the 380–780 nm visible spectrum to achieve high-bandwidth, interference-free wireless communication. VLC technology simultaneously provides illumination and high-speed data transmission, making it particularly promising for indoor networking, vehicular communication, industrial IoT, and underwater applications. Li-Fi, a practical implementation of VLC, has garnered significant attention in the past decade, enabling lighting-based wireless connectivity.
Advantages of Optical Wireless Communication
Immunity to Electromagnetic Interference:
VLC is not affected by electromagnetic waves, making it suitable for environments where RF signals may cause interference, such as hospitals, airplanes, and sensitive industrial settings. Unlike copper shielding or device restrictions, VLC provides a naturally interference-free communication channel.
Energy Efficiency:
LEDs and laser diodes consume less power than RF transmission. By modulating light intensity rather than generating RF waves, battery-powered devices can transmit data more efficiently. This is critical for mobile devices, IoT sensors, and low-power embedded systems.
Directional Communication:
Beam steering and VLC positioning techniques allow directional data transmission between the light source and receiver, enhancing security and efficiency. Using modulated retroreflectors (MRRs) in mobile devices can mitigate alignment and power issues while enabling bidirectional communication.
Simultaneous Illumination and Data Transmission:
By modulating light at frequencies imperceptible to the human eye, VLC systems provide both illumination and data transfer without affecting user experience.

Figure 1. Schematic of a VLC system.
VLC System Architecture
A VLC system consists of an optical transmitter (Tx) and an optical receiver (Rx). Data is first preprocessed and encoded into a binary stream, which drives the light source (LED or laser diode). Electrical signals are converted to optical signals via modulation. At the receiver, equalization techniques compensate for channel distortions, phase noise, and inter-symbol interference. Advanced coding and high-order modulation formats such as CAP, OFDM, and M-QAM enhance data rates and spectral efficiency. The overall performance depends on the light source characteristics, modulation bandwidth, and photodetector response.
LED-Based VLC Systems
Light-emitting diodes (LEDs) are widely used for VLC due to their efficiency, affordability, and availability. White light generation can be achieved using:
RGB-LEDs: Combining red, green, and blue chips or using color phosphors to produce white light.
Phosphor-converted LEDs (pc-LEDs): Blue LEDs excite yellow phosphors to generate white light.

Figure 2. White light generation: (a) UV-chip with phosphors; (b) Blue-chip with yellow phosphor conversion.
Challenges with LEDs:
Limited modulation bandwidth, typically a few MHz.
Influence of quantum-confined Stark effect (QCSE), crystal orientation, carrier lifetime, and recombination rates on signal response.
Phosphor conversion can reduce signal-to-noise ratio (SNR) and data rate.

Enhancements:
Discrete Multitone (DMT) modulation, carrier-less amplitude and phase (CAP), and M-QAM improve throughput.
Experiments show data rates of 1 Gbps with pc-LEDs (2012) and up to 3.2 Gbps with RGB LEDs using CAP-OFDM (2013).
Micro-LEDs (µ-LEDs):
Extremely small (<100 μm), high brightness, and low power consumption.
Faster response due to reduced carrier lifetime and lower RC time constants.
Can be assembled into arrays to increase output for monochromatic or polychromatic VLC systems.
Higher modulation bandwidth enables tens of Gbps, significantly reducing bit error rates.
LED Modulation Equation:
f_(-3"dB" )=√3/2π(1/τ_r +1/τ_nr +1/τ_RC )

Where τ_rand τ_nrare radiative and non-radiative carrier lifetimes, and τ_RCis the RC time constant.
Crystal Orientation:
Semipolar or non-polar GaN LEDs reduce QCSE, improving electron-hole overlap.
Faster recombination increases modulation bandwidth and luminous efficiency, essential for high-speed VLC.
Laser Diode (LD)-Based VLC Systems
Laser diodes surpass LEDs in bandwidth, coherence, and spectral control, supporting data rates exceeding 100 Gbps. Laser sources can generate white light using:
RGB mixing, or
Phosphor conversion of blue/green laser light.
Advantages of LDs:
Modulation speed controlled by photon lifetime (~ps), enabling ultra-fast transmission.
Narrow beam transmission suitable for long-range applications.
High optical output power and energy efficiency.
LD Types:
Edge-Emitting Laser Diodes (EELDs): High modulation bandwidth; blue EELDs with phosphor conversion produce eye-safe white light.
Superluminescent Diodes (SLDs): Combine LD coherence with LED broadband emission, achieving multi-Gbps data rates.
Vertical-Cavity Surface-Emitting Lasers (VCSELs): Compact devices with high beam quality and GHz-range modulation, ideal for short-range high-speed VLC.

Figure 3: Surface-mount LD package. Laser excites phosphor to produce white light.

Figure 4: Schematic of SLD.

Figure 5: VCSEL structure for VLC applications.
Comparative Analysis of VLC Light Sources
Light Source Bandwidth Data Rate Advantages Limitations
RGB-LED Few MHz Up to 3 Gbps Simple white light generation Limited bandwidth; complex multi-color control
pc-LED Few MHz 1–2 Gbps Simplified structure SNR loss due to phosphor conversion
µ-LED Hundreds MHz 10s Gbps High brightness, low power Requires arrays for high output
LD GHz >100 Gbps High coherence, long range Higher cost; eye safety concerns

VLC technology leverages visible light to deliver high-speed, secure, and energy-efficient wireless communication, overcoming RF limitations. LEDs, µ-LEDs, and LDs each provide unique advantages depending on bandwidth, brightness, and modulation requirements. Continued advances in micro-LED arrays, laser sources, and advanced modulation schemes promise further improvements in data rate, efficiency, and application scope, including indoor networks, IoT, vehicular communication, and long-distance free-space links. The integration of directional beamforming, color conversion, and high-speed photodetectors is crucial for next-generation VLC systems.
VLC Receiver Technology
In a visible light communication (VLC) system, photodetectors are critical for converting optical signals into electrical signals. The key requirements for photodetectors include:
High Responsivity: The device should generate a maximum photocurrent for a given incident optical power.
Fast Response Speed: The detector must support high-speed broadband communication.
Low Noise: Minimizing noise ensures better signal quality and reduces errors.
Linearity: The detector should convert light to electrical signals with minimal distortion.
Compact Size and Long Lifespan: Practical systems require small, durable photodetectors.
Three critical parameters define photodetector performance: responsivity, bandwidth, and dark current.
Responsivity (R): Measures the output electrical signal per unit optical power, typically in amperes per watt (A/W):
R=I/P

where Iis the output current and Pis the incident optical power. Quantum efficiency (η) relates to the fraction of incident photons generating electron-hole pairs, reaching 100% when all photons contribute to current. Responsivity can also be expressed as:
R=ηqλ/hc
where qis the electron charge, λis the incident wavelength, his Planck’s constant, and cis the speed of light.
Bandwidth (BW): Determines how fast the detector can respond and is linked to its rise time t_r:
BW=0.35/t_r
Two main factors affect bandwidth:
Transit Time: Time for carriers generated by light to travel through the active region, dependent on carrier mobility (μ) and electric field (E):
v=μE
Saturation effects modify mobility as:
μ_sat=μ/√(1+(μE/v_sat )^2 )

The transit-time-limited bandwidth is:
f_transit=0.38 v_sat/h_PD

where h_PDis the photodetector thickness.
RC Time Constant: The electrical impedance of the circuit limits bandwidth:
f_RC=1/2πRC

The total bandwidth accounting for both effects is:
BW=〖(1/(f_RC^2 )+1/(f_transit^2 ))〗^(-1/2)

Dark Current: Even in the absence of light, photodetectors may produce a current. High dark current reduces the signal-to-noise ratio. It arises from bulk generation (due to lattice defects) and surface generation (due to surface defects), and is calculated as:
I_dark=J_bulk A+J_surf √4πA

where Ais the junction area. The associated shot noise is:
I_n=√(2qI_dark BW)

Photodetector Types: Avalanche photodiodes (APD), PIN photodiodes, metal-semiconductor-metal (MSM) PDs, superlattice APDs, waveguide PDs, and cavity-enhanced PDs are commonly used. Modern receivers, including large-area APDs, micro-PDs, and perovskite solar cells, achieve bandwidths up to hundreds of MHz with high responsivity and low noise.
Modulation Technology in VLC Systems
VLC modulation schemes must balance high data rates with human visual comfort, addressing two key aspects:
Dimming: Adjusting illuminance for different environments (30–100 lux for typical tasks) while ensuring visual comfort. The human eye adapts pupil size to varying light levels.
Flicker Reduction: Light intensity must change faster than the human eye can detect (≥200 Hz) to prevent physiological effects, as per IEEE 802.15.7.
After preprocessing and encoding, the binary data stream drives the LED or laser diode via intensity modulation. Each modulation scheme encodes data into symbols, with more symbols allowing more bits per symbol. Gray coding ensures that adjacent symbol errors affect only one bit.
Common VLC Modulation Schemes:
Multilevel Pulse Amplitude Modulation (M-PAM): Generalization of NRZ-OOK, with M intensity levels. The bit error rate (BER) for M-PAM is:
BER_(M-PAM)=(M-1)/(M〖log⁡〗_2 M) Q(√(SNR(M-1)))

Phase Shift Keying (PSK): Modulates data by altering the phase of the carrier. Binary PSK (BPSK) uses two phases; M-ary PSK (MPSK) increases bandwidth efficiency. BER for BPSK:
BER_BPSK=1/2 "erfc"(√SNR)

M-ary Quadrature Amplitude Modulation (M-QAM): Combines PSK and amplitude shift keying, increasing spectral efficiency. BER for M-QAM:
BER_(M-QAM)≈(√M-1)/(√M 〖log⁡〗_2 M) Q(√((3〖log⁡〗_2 M)/(M-1) SNR))
Orthogonal Frequency Division Multiplexing (OFDM): Uses multiple orthogonal subcarriers to efficiently utilize bandwidth. Data streams are mapped onto subcarriers via PSK or QAM. Hermitian symmetry ensures real-valued IFFT outputs.
Color Shift Keying (CSK): Uses RGB LED intensities to encode data. The chromaticity diagram maps the perceived color to x and y coordinates. BER for 4-CSK:
BEP_(4-CSK)=1/2^k Q(0.81572√(N_0 ))+1/2^k Q(0.8172√(N_0 ))

Power and Spectral Efficiency:
The required optical power for a given SNR is:
P=1/R √(σ_N^2 SNR)

Normalized power for common schemes:
■(P_(M-PAM)^(NRZ-OOK)&=√((M-1)/(〖log⁡〗_2 M))@P_BPSK^(NRZ-OOK)&=√(1/2)@P_QPSK^(NRZ-OOK)&=√(1/2) 〖"erfc" 〗^(-1) (BER)/〖"erfc" 〗^(-1) (2BER))

Currently, M-QAM OFDM, NRZ-OOK, and M-PAM are widely used. M-PAM offers higher spectral efficiency but requires a higher SNR to achieve the same BER.
Optical Wireless Communication Standards
Visible Light Communication (VLC) is a highly promising communication technology, driven by the rapid development and declining cost of LED lighting. However, several challenges must be addressed for its practical deployment:
Integration of VLC with existing communication standards.
Mitigation of ambient light interference.
Handling mobility issues, including handover between transmitters.
Specification of forward error correction (FEC) to enhance system performance.
Management of interference among multiple VLC devices as network density increases.
To address these, the IEEE developed standard 802.15.7, which defines the physical (PHY) and medium access control (MAC) layers. Key objectives of this standard include:
Access to hundreds of terahertz of frequency bands.
Resistance to electromagnetic interference.
Support for additional services complementing current visible light systems.
Specification of FEC schemes, modulation formats, and transmission rates.
Definition of channel access mechanisms, including contention access period (CAP) and contention-free period (CFP).
Physical layer parameters such as optical mapping, TX-RX and RX-TX turnaround times, flicker mitigation, and dimming support.
VLC devices are categorized into three types: vehicles, mobile equipment, and infrastructure.
VLC Applications
VLC has diverse applications ranging from high-speed indoor networks to interplanetary and quantum communications. Key applications include:
1. Li-Fi:
Li-Fi is a bidirectional, visible light wireless communication system similar to Wi-Fi. It offers a viable alternative in environments sensitive to electromagnetic interference, such as airplanes and hospitals.
2. Vehicle-to-Vehicle Communication:
VLC enables low-latency vehicle safety systems, including collision warnings, emergency braking signals, lane-change alerts, and traffic violation notifications.
3. Underwater Communication:
Due to the poor propagation of RF and near-infrared signals underwater, VLC-based underwater optical communication (UWOC) is ideal. Blue and green wavelengths penetrate clear water more efficiently, whereas red light may perform better in turbid environments.
4. Information Display Signboards:
LEDs can broadcast information at airports, bus stations, museums, and hospitals, providing real-time instructions or guidance.
5. Visible Light ID and Positioning Systems:
VLC can be used for indoor positioning and identification systems, functioning similarly to GPS but indoors.
6. Wireless Local Area Networks (WLANs):
VLC can achieve ultra-high-speed, full-duplex LANs with star topologies, enabling speeds exceeding 10 Gb/s.
Challenges in VLC
Despite its advantages over RF, VLC faces several challenges:
Commercialization: Coordination between lighting and mobile device manufacturers is required for future VLC-enabled devices.
Standardization: Existing standards need updates to incorporate technological advances.
Noise and Interference: Background light can degrade signal quality; Manchester coding helps mitigate this.
Light Quality and Stability: Dual-function VLC devices need stable white light converters for prolonged use.
Line-of-Sight Limitations: Laser diode (LD)-based systems may face misalignment and link outages.
Eye Safety: Prolonged exposure to high-intensity light could harm vision or disrupt circadian rhythms.
Bandwidth Limitation: Conventional LEDs have limited bandwidth; micro-LEDs and LDs offer higher transmission rates.
Additional solutions being explored include:
Bandwidth Enhancement: High-speed μ-LEDs and high-contrast grating μ-LEDs have demonstrated data rates above 5 Gbit/s.
Broadband Si-Based Detectors: Black silicon photodetectors offer high responsivity across 400–1600 nm while reducing dark current.
MIMO and Spatial Multiplexing: Novel QAM-based MIMO schemes mitigate channel correlation and enhance data throughput.
Compact Antennas: Fresnel lenses and optical phased antennas allow directional transmission with rapid wide-angle switching.
Quantum Communication Integration
Quantum communication allows secure transmission of quantum states between a transmitter (Alice) and receiver (Bob). Key aspects include:
Quantum Key Distribution (QKD): The BB84 protocol ensures secure key exchange, leveraging the principles of quantum mechanics to detect eavesdroppers.
Photon Sources: Weak coherent state (WCS) lasers or LEDs can generate low-photon pulses for secure QKD.
Detection Schemes: Discrete variable (DV-QKD) uses single-photon detectors, while continuous variable (CV-QKD) employs homodyne/heterodyne detection.
Security Guarantees: Unclonability and non-orthogonality of quantum states prevent undetected eavesdropping.
Cost-Effective QKD: LED-based decoy-state QKD reduces system costs while maintaining security.
Applications of the Invention
The invention enables high-efficiency visible light communication across a variety of practical applications:
Indoor High-Speed Networking (Li-Fi):
The system can transform LED lighting infrastructure into a high-speed bidirectional data network.
Ideal for offices, homes, and public spaces where RF interference is a concern.
Supports ultra-fast internet access, low-latency streaming, and secure communication.
Vehicle-to-Vehicle Communication and Safety Signaling:
Vehicles equipped with LED or laser-based transmitters can communicate with each other in real time.
Supports collision warnings, lane change alerts, emergency braking signals, and traffic signal notifications.
High-speed visible light reduces latency compared to conventional RF-based vehicular communication.
Underwater Optical Communication:
Exploits the low attenuation of blue and green light underwater for high-speed data transfer.
Enables underwater sensor networks, autonomous vehicle control, and data collection in marine environments.
Provides an alternative to RF communication, which is heavily attenuated in water.
Information Display Boards and Visible Light ID Systems:
LED signboards at airports, bus stations, and public spaces can transmit data visually and digitally.
Supports indoor positioning, identification, and real-time data display.
Can integrate with smartphones or specialized receivers for navigation and notifications.
Wireless Local Area Networks (WLANs) Using Visible Light:
Enables high-speed, short-range networking in a full-duplex configuration.
Can serve multiple users simultaneously with minimal interference.
Provides a secure, energy-efficient alternative to traditional Wi-Fi networks.
Advantages and Benefits of the Invention
The proposed system offers several advantages over conventional RF and existing VLC systems:
High Data Rates: Utilizes the wide visible light spectrum to achieve fast data transmission.
Reduced Electromagnetic Interference: Ideal for environments where RF interference is problematic, such as hospitals or airplanes.
Enhanced Security: Line-of-sight transmission reduces interception risk, and integration with quantum key distribution can further secure communication.
Versatility: Can be deployed in indoor, vehicular, and underwater scenarios, providing flexible and robust communication.
Energy Efficiency: Leverages existing LED lighting infrastructure, reducing the need for additional power sources.
Possible Modifications and Embodiments
The system can be adapted and enhanced through several approaches:
Multiple Light Sources for Spatial Multiplexing (MIMO VLC): Improves coverage, throughput, and reliability in multi-device networks.
Integration with Micro-LED Arrays or Laser Diodes: Achieves higher bandwidth and data rates for next-generation communication.
Adaptive Modulation Schemes: Adjusts signal parameters dynamically based on channel conditions to maintain optimal performance.
Hybrid Systems Combining VLC with RF/Wi-Fi: Ensures seamless connectivity and extends coverage in scenarios where visible light may be blocked.
Recent advances in VLC including micro-LEDs, laser diodes, high-speed modulation schemes, and enhanced photodetectors position it as a strong alternative to RF communication. While line-of-sight and lighting constraints remain challenges, VLC offers significant advantages in bandwidth, energy efficiency, and electromagnetic compatibility.
VLC supports a wide range of applications, from indoor high-speed networking and vehicle-to-vehicle communication to underwater and quantum communications. As VLC matures, it is poised to drive future innovations in beyond-5G optical wireless networks and the Internet of Underwater and Underground Things (IoU²T), enabling new opportunities in connectivity, energy efficiency, and environmental monitoring.
DETAILED DESCRIPTION OF DIAGRAM
Figure 1. Schematic of a VLC system.
Figure 2. White light generation: (a) UV-chip with phosphors; (b) Blue-chip with yellow phosphor conversion.
Figure 3: Surface-mount LD package. Laser excites phosphor to produce white light.
Figure 4: Schematic of SLD.
Figure 5: VCSEL structure for VLC applications. , Claims:1. Light-Based Communication System Utilizing the Visible Light Spectrum for High-Efficiency Data Transfer claims that light-based communication system that transmits data using visible light emitted from LEDs, micro-LEDs, or laser diodes as a carrier for high-speed data transfer.
2. The system integrates a forward error correction (FEC) scheme to improve data integrity and minimize transmission errors during communication.
3. The system supports bidirectional communication, enabling both data transmission and reception using visible light channels.
4. The communication system is compatible with existing wireless and optical standards, allowing seamless integration with other networks.
5. The system employs mobility management features, including handover between transmitters, to maintain continuous communication with moving devices.
6. The system incorporates mechanisms to mitigate interference from ambient light sources and neighbouring visible light communication devices.
7. The system includes high-bandwidth detectors and receivers capable of detecting modulated visible light signals, supporting multi-gigabit per second data rates.
8. The system is applicable to a variety of scenarios, including indoor networking, vehicle-to-vehicle communication, underwater communication, information display, and positioning systems.