High Speed WDM VLC System Based on Multi-Band CAP64 With Weighted Pre-Equalization and Modified CMMA Based Post-Equalization

• Core Innovation & Objective • Developed a novel, integrated system architecture combining a modified USRP X310 software-defined radio platform with a custom-designed high-power LED optical transceiver. • Achieved high-speed, low-latency, and highly reliable audio-video transmission over Visible Light Communication (VLC) for intelligent transportation and vehicle-to-vehicle (V2V) applications, particularly in electromagnetically sensitive environments. • Key Technical Breakthroughs • LED Bandwidth Extension: Designed an innovative active pre-equalization circuit (based on a 4th-order high-pass RC bypass and op-amps) that dramatically increased the 3dB modulation bandwidth of a commercial 15W LED from 3 MHz to 120 MHz. • High-Speed Modulation: Successfully implemented 64QAM-OFDM modulation/demodulation using GNU Radio on the USRP, enabling spectrally efficient data transmission. • Advanced Optical Design: Custom-designed optical lenses (transmitter and receiver) and a high-power Bias-T circuit for efficient AC/DC coupling, ensuring the LED operates in its linear region and maximizing optical power transfer. • Stable Link Performance: Incorporated an Automatic Gain Control (AGC) circuit at the receiver, stabilizing the output voltage between 1.2V - 2.0V and maintaining a modulation signal-to-noise ratio (SNR) > 23 dB over varying distances. • Outstanding System Performance • The experimentally demonstrated performance metrics are exceptional for a VLC system: • Peak Data Rate: 500 Mbps • Communication Distance: 0 - 110 meters • Bit Error Rate (BER): As low as 1.74 × 10⁻⁵ (far below the 1 × 10⁻⁴ target) • End-to-End Latency: < 0.1 s • Beam Angle: 11.5° (Transmitter) • Field of View (FOV): ≤ 18° (Receiver) • System Integration and Design • Hardware-Software Co-Design: Seamless integration of the USRP X310 (handling digital baseband processing) with the custom analog optical front-end. • Compact and Practical: The system is designed for external mounting on vehicles, offering a practical solution for real-world deployment. • Simulation-Guided Design: Used LightTools for optical design and Optisystem for communication link simulation to validate the design before implementation. • Significance and Application Value • Solves Critical Challenges: Provides a high-speed, secure, and EMI-free communication alternative to traditional RF in environments like military operations, petroleum facilities, and intelligent transportation systems. • 6G Potential: Serves as a practical reference for the development of VLC as a complementary technology in 6G networks. • Demonstrates Feasibility: Successfully proves the viability of using commercial LEDs and USRP platforms for building high-performance, medium-to-long-range optical communication systems. • This work represents a significant step forward in practical high-speed VLC system design, combining theoretical innovation with robust engineering to achieve state-of-the-art performance. Existing vehicular VLC systems suffer from limited bandwidth, short transmission distances, low data rates, and support only a narrow range of communication services. To address these issues, this paper proposes a vehicle-mounted high-speed LED visible light communication (VLC) system based on Universal Software Radio Peripheral (USRP). Leveraging 64QAM-OFDM digital modulation, an improved USRP X310 hardware platform, and a PC, we establish a novel architecture comprising digital baseband and optical transceiver modules. The baseband module eliminates traditional spectrum-shifting circuits and antennas, retaining only FPGA and ADC/DAC units. Audio/video files undergo 64QAM-OFDM modulation directly on the PC, with modulated signals output via DAC to a custom-designed wide-bandwidth LED transceiver. A broadband hardware equalization network based on a fourth-order RC bypass circuit was designed expands the 3dB bandwidth of high-power LEDs from 3 MHz to 120 MHz. Combined with automatic gain control (AGC), this achieves an optical transceiver with 12–15 W output power, >23 dB optical modulation signal-to-noise ratio (SNR), and stable receiver output voltage (1.2–2.0 V). The resulting compact system delivers low latency, high data rates, and high reliability. Under aligned optical path conditions, the system achieves >1 Mbit/s at 110 m (BER 0.49 × 10⁻⁵, delay 0.009-0.05s) and a peak rate of 500 Mbit/s at 10 m (BER 7.4 × 10⁻⁵), with an 11.5° transmit angle and a receiver field of view (FOV) of less than 18°. This work demonstrates the feasibility of high-power LED-based 64QAM-OFDM communication using USRP X310 for medium- to long-range vehicular links, providing a reference for intelligent transportation systems.

The emerging visible light communication (VLC) technology, which has the advantages of short-distance communication and indoor lighting, has become a research hotspot of indoor wireless communication technology. Polar codes, as the only forward error correction (FEC) coding technology that has been theoretically proven to achieve Shannon's capabilities, are adopted to reduce the bit error rate (BER) in VLC systems. However, the individual polar codes are still unable to correct burst errors in VLC channels. This paper proposes concatenated polar codes with interleaving technology for VLC systems. The results show that it can effectively correct random errors and burst errors in VLC systems. Compared to the non-systematic polar codes, the systematic polar codes are more suitable as the inner code of the concatenated polar codes. The concatenated polar codes exhibit a lower error floor in VLC systems under burst errors than the individual polar codes. Compared with BCH-polar schemes, Convolutional-polar schemes have better robustness.

Inter-symbol interference (ISI) in visible light communication (VLC) systems has been considered as a major problem that seriously deteriorates system performance. A series of equalization algorithms have been widely investigated and utilized to eliminate ISI and improve the system performance. In this paper, we propose a novel algorithm called scalar modified cascaded multi-modulus algorithm (S-MCMMA) used in VLC system with PAM modulation. Furthermore, we experimentally demonstrate a red LED based PAM VLC system employing hardware pre-equalization technology and S-MCMMA equalization. A data rate of 525-Mbit/s for 8-PAM is successfully achieved in 1-m indoor free space transmission with the bit error rate (BER) below the 7 % forward error correction (FEC) limit of 3.8 × 10−3. Compared to the LMS equalization, the performance of S-MCMMA behaves quite similar (with a slight of advantage of S-MCMMA). However, the scheme is blind post-equalization without any training sequence aided thus higher bandwidth efficiency is achieved.

We propose a configuration of a wavelength division multiplexing (WDM)-visible light communication (VLC) system using orthogonal frequency division multiplexing (OFDM) modulation and an adaptive Nyquist windowing of the OFDM signal in the receiver. Based on this configuration, we demonstrate a 750-Mb/s WDM-VLC transmission based on RGB light-emitting diode (LED) with a distance of 70 cm. The measured bit error rate (BER) for all channels are under the pre-forward error correction limit of 3.8 \times 10-3. The BER performances of all the channels of the proposed WDM-VLC system show considerable improvement compared with those of the system without Nyquist windowing.

In this paper, we propose and investigate an adaptively 84.44 to 190 Mb/s phosphor-LED visible light communication (VLC) system at a practical transmission distance. Here, we utilize the orthogonal-frequency-division-multiplexing quadrature-amplitude-modulation (OFDM-QAM) modulation with power/bit-loading algorithm in proposed VLC system. In the experiment, the optimal analogy pre-equalization design is also performed at LED-Tx side and no blue filter is used at the Rx side for extending the modulation bandwidth from 1 MHz to 30 MHz. In addition, the corresponding free space transmission lengths are between 75 cm and 2 m under various data rates of proposed VLC. And the measured bit error rates (BERs) of &lt; 3.8×10^-3 [forward error correction (FEC) limit] at different transmission lengths and measured data rates can be also obtained. Finally, we believe that our proposed scheme could be another alternative VLC implementation in practical distance, supporting &lt; 100 Mb/s, using commercially available LED and PD (without optical blue filtering) and compact size.

SummaryWith the development of new generation lighting sources, visible light communication (VLC) system has become a complementary solution to traditional radio frequency wireless system. However, the error performance of VLC system is degraded because of multipath effects and interference from other lighting sources that, in turn, reduce the communication range. This work targets the issue of performance degradation of VLC systems in terms of communication range and demonstrates a VLC system design that utilizes forward error correction (FEC) codes as the main tool to fix this issue. Furthermore, the work also covers practical implementation of the proposed VLC system using UART modules programmed in MATLAB. The hardware results demonstrate that the communication range of the proposed VLC system is enhanced up to 0.5 m. Over and above, it is also shown through simulations that the coding gain of the proposed design is more when compared with existing VLC system(s).

The exponential rise in wireless communication demands and allied applications have revitalized academia-industries to develop an efficient and potential solution. Furthermore, the high-pace increasing scarcity of radio spectrum has also alarmed researchers to achieve better Quality of Service (QoS) centric solution. To meet such demands Visible Light Communication (VLC) systems have gained global attention; however, up surging high rate, range and reliability (3R) needs demand better performance. Towards these goals, Multiple Input Multiple Output (MIMO) based VLC systems is an efficient approach; though its efficacy under Multiple Users (MU) conditions remains least explored. Enabling MIMO-MU based VLC can achieve 3R objectives effectively; however, factors like multipath attenuation, interferences and varied impairment-affects makes classical approached confined. The MIMO-MU VLC systems require robust error, noise or interference resilient transmission even under adverse conditions such as non-linear LED, multipath attenuation and interference. Towards these objectives, in this paper a highly robust MIMO-MU VLC system is developed that incorporates an augmented MIMO channel design and combined pre-coding and post equalization schemes. To alleviate major interference probability in MIMO-MU environment, proposed model incorporates time (delay)-multiplexing based data transmission followed by signal adaptive precoding and Volterra Kernel based Hybrid-equalizer. This approach enables interference and noise removal as well as LED non-linearity handling under MIMO-MU VLC communication. The use of a Volterra Kernel based Decision Feedback Equalization with both linear as well as non-linear equalization enables proposed VLC system to exhibit low Bit Error Rate with low modulation index and taps, that optimizes trade-off between performance as well as complexity.

Since indoor visible light communication (VLC) systems can offer several potential advantages over their radio frequency and infrared counterparts, there has been a growing interest in VLC systems. Influenced by the complicated optical propagation environment, multipath effect existed which may result in intersymbol interference (ISI). Therefore, the bit error ratio (BER) performance is degraded excessively due to the effects of ISI. In this paper, we evaluate the performance of a nonlinear MAP (maximum a-posteriori probability) equalizer in indoor VLC environment. Moreover, Forward error correction (FEC) coding and interleaving is used. It will be shown that MAP equalization is well behaved in VLC systems. Besides, the systems with encoder and interleaver provide notable performance gain at the expense of higher computational complexity.

In this paper, we propose to apply the chaotic sequences to identify the users in high data rate visible light communication (VLC) system, and present a novel Logistics Iterative-chaotic-map-with-infinite-collapses Over Sampled Chaotic Map (L-I-OSCM) to generate the chaotic sequences. Specifically, we present a novel L-I-OSCM mapping scheme to improve the randomness of the chaotic sequences, with which the generated chaotic sequences have the property of having more complex and disordered phase space, being more sensitive to the initial value and having better randomness. Numerical analysis is performed to analyze and verify the better performance of L-I-OSCM scheme, and the property of chaotic sequences generated from different mapping patterns is compared. Since the chaotic sequences are noise-like and sensitive to the initial value, the access security is enhanced in L-I-OSCM chaos-based code division multiple access (C-CDMA) VLC system. Simulations are then provided to verify the effectiveness of the L-I-OSCM mapping C-CDMA VLC system, and the results demonstrate that both the bit error rate (BER) and the security performances are improved.

Facing the current shortage of radio frequency spectrum resources, visible light communications (VLC) technology has been proposed to be a candidate technology in the sixth generation (6G), especially in the application of Intelligent Transportation Systems (ITS). And the propagation characteristics of VLC channel are critical for VLC system design and optimization. Furthermore, the impact of weather conditions on VLC channel cannot be ignored considering the vehicular VLC in ITS. In this paper, we experimentally investigate the impact of different weather types including fog and relative humidity (RH) on VLC in a laboratory atmospheric chamber. To simulate adverse weather conditions, we change the levels of fog density and water vapor introduced into the chamber, respectively. Then we measure the power attenuation and the bit error rate (BER) performance of VLC system under fog and RH conditions. We find that the VLC system will exhibit worse BER performance in the fog impaired channel than RH conditions. Besides, the results show that the bit errors will not happen until the attenuation reaches the threshold, i.e. attenuated by about 60% for both fog and RH conditions in our experiments. After that, the BER will deteriorate badly even up to 20%.

This paper analyzes the performance of a dual-hop hybrid radio frequency - visible light communications (VLCs) system. VLC exploits high frequencies for signal propagation for short-range and is highly susceptible to blockages. Hence, in this work, the sensitivity of the VLC toward the blockages is explored. This study examines outdoor-indoor communication for an urban scenario featuring an office environment. The VLC system is designed by considering multiple VLC access points serving the end users in the presence of human blockages. Selection combining is employed to select the access point which offers the maximum instantaneous signal-to-noise ratio at the user. To capture the outdoor scenario, path loss modeling is conducted to account for signal attenuation from outdoor to indoor spaces. The outdoor scenario is modeled using Nakagami-m fading channels while VLC is employed for the indoor scenario. System performance is assessed in closed-form expression for outage probability and the symbol error rate for binary phase shift keying and quadrature amplitude modulation. A deep learning-based approach detects the symbols by tracking dynamic changes in the channel. Simulation results corroborate the correctness of derived analytical expressions and reveal that blockages significantly impact both single and multiple LED based communication channels.

In the framework of future Internet of Things (IoT) systems, the number of connected devices is increasing, along with the requirement of environmentally friendly devices, which should have low power/cost/size features. Visible light communications (VLC) has been proposed as a complementary technology for a vast number of scenarios, in particular for IoT, where it can favour device density growth by enabling spectrum reuse within few meters. This paper presents a VLC-based communication system, using analog demodulation for multi-band carrierless amplitude and phase (m-CAP) modulated systems in IoT multi-user scenarios. The goal is to implement and validate an IoT system architecture where multiple simple and low cost/power receivers can receive and decode narrow-band information sent by a single and complex broadband transmitter, located at lighting fixtures. An experimental testbed is developed for the proposed system to evaluate its performance in terms of eye patterns, constellations, error vector magnitude, and bit error rate (BER) for two line-of-sight scenarios. The results show that the system is tolerant up to 2.5 m, achieving a BER lower than the forward error correction (FEC) limit. Moreover, it allows the device to be tilted up to 45° and still achieve a BER below the FEC limit, for distances below 1.7 m.

In this paper, we consider an indoor Visible Light Communication (VLC) system with a placement technique with and without an overlap formed, using four and five Light Emitting Diodes (LED), placements on a room roof. To support the better received signal power, this paper evaluated the performance of LED overlap using the 3-Watt transmit power. We did a computer simulation using the dimension closed communication room $5 \times 5\times 3 m^{3}$ . In this paper, we found that the VLC system with an overlap was better than the one without an overlap. The result showed that the received power could reach the minimum Bit Error Rate (BER) threshold $\leq 10^{-3}$ around −18 dBm for VLC system without an overlap and −20 dBm for VLC system with an overlap. From the simulation, it obtained that communication link coverage with an overlap was about 25 m2.

We investigate the performance of visible light communication (VLC) system with a pulse width modulation (PWM) dimming control scheme. Under this scheme, the communication quality in terms of number of transmitted bits and bit error rate (BER) of less than 10(-3) should be guaranteed. However, for on-off-keying (OOK) signal, the required data rate becomes 10 times as high as the original data rate when the duty cycle of dimming control signal is 0.1. To make the dimming control scheme easy to be implemented in VLC system, we propose the variable M-QAM OFDM VLC system, where M is adjusted according to the brightness of LED light in terms of duty cycle. The results show that with different duty cycles the required data rates are not higher than the original value and less LED lamp power is required to guarantee the communication quality, which makes the dimming control system that satisfies both communication and illumination requirements easy to be implemented and power-saving.

In visible light communication (VLC) systems, optical diversity improves system performance by utilizing multiple light sources at the transmitter. At the same time, orthogonal data transmission is used to distinguish overlapping optical signals at the photodetector. Based on these concepts, this paper suggests an innovative method to alleviate optical channel blockage by leveraging optical diversity and the orthogonality property; this is achieved by combining a modified version of frequency switching transmit diversity (FSTD) on the transmitter side with select best combining (SBC) on the receiver side in multiple input single output (MISO)-VLC systems. On this basis, the effectiveness of the suggested method is evaluated in free space optical across varying distances and different signal to noise ratio (SNR). The results indicate that the proposed approach outperforms conventional orthogonal techniques in MISO-VLC systems. Specifically, the proposed methodology achieved a bit error rate (BER) of 6.7 × 10−4 at a distance of 40 m with an SNR of 5 dB, whereas the FSTD technique recorded a BER of 1.5 × 10−3 under identical conditions. This superiority is attributed to integrating the SBC technique into the proposed approach, which allows for avoiding paths that lead to destructive interference with the optical signal.