Performance of dimming control scheme in visible light communication system

MPPM based dimming control scheme in visible light communication systems

Visible light communication(VLC), which combines communication and illumination, is regarded as a potential wireless communication. For illumination requirements of VLC systems, dimming control is a significant function. Many schemes have been proposed for multi-input multi-output (MIMO) VLC systems or dimmable VLC systems, but few schemes combine the two. The dimming control scheme that has been proposed for MIMO-VLC systems in the reference still has a probability for improvement in spectral efficiency and error performance. This paper proposes a dimming control scheme that utilizes the constant weight space-time codes (CWSTC) to improve spectral efficiency and error performance for MIMO-VLC systems. Simultaneously, we also present the codeword structure and a low implementation complexity detection algorithm for the scheme. Finally, performance analysis and simulation results provide comparisons between the proposed scheme and other existing dimming control schemes.

In this paper, relaying technique and non-orthogonal multiple access (NOMA) are adopted to improve performance of visible light communication (VLC) system. Due to the adoption of relay terminal, the link reliability and communication coverage of VLC system are boosted. Besides, the utilization of NOMA can greatly increase spectral efficiency and support massive connectivity. So, a cooperative NOMA-based DCO-OFDM VLC system is proposed. All the optical transmission links use DCO-OFDM to accomplish information transmission. The relay terminal in the proposed system not only forwards the source signal but also sends its own signal simultaneously. The signals over the links between relay and two users are superposed based on NOMA. Under different cases, the total throughput is analyzed and the optimal power allocation factor is obtained. In addition, the OMA-based system is taken as the benchmark system. The simulation results further verify the theoretical results and the superiority that the proposed system has.

• 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.

Recently, multiple-input multiple-output (MIMO) has been proposed in visible light communications (VLC) systems to boost the data rate by utilizing spatial multiplexing. Unlike RF systems in VLC, lighting requirements, such as dimming control, should be taken into consideration for the design of a VLC transceiver. Moreover, VLC systems are inherently nonlinear and dynamic-range-limited. To drive an LED transmitter, the signal is bounded by a turn-on value and a saturation value. In this letter, we show how the dynamic-range constraint and dimming control impact the design of MIMO transceiver. Three different MIMO schemes are proposed and studied by theoretical analysis and simulation.

Smart city planners pay more attention towards visible light communication (VLC) system to achieve seamless high speed connectivity. A light emitting diode (LED) acts as a transmitter in VLC system. However, the nonlinear characteristics and dimming nature of LED limits the performance of the VLC system by degrading the quality of transmitted signal. In this paper, we propose an adaptive-learning-architecture (ALA) based predistortion technique to estimate and compensate for LED nonlinearities as well as increase the spectral efficiency of a VLC system. A DC-biased optical orthogonal frequency division multiplexing (DCO-OFDM) signal is considered. The performance with and without predistorter is analysed assuming optical line-of-sight (LOS) channel. It is shown that degradation due to LED nonlinearity can be compensated by using ALA-based predistortion, and the overall Predistorter-LED system is able to approach near-linear performance. Further, we investigate the impact of dimming on the performance of nonlinear LED in VLC system. Simulation results based on symbol error rate (SER), amplitude distortion (AM/AM) curves and constellation plots validate the performance of our proposed technique.

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.

Our recent progresses in visible light communication (VLC) systems are reviewed. The methods to improve performances of VLC system for single user and multi-user are described. The principle and performance under dimming control scheme are also studied.

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.

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).

While the traditional Visible Light Communication (VLC) system has attracted a lot of research attentions on boosting throughput, using Commercial Off-The-Shelf (COTS) devices, e.g. existing cameras on the smartphones, is a recent trend to implement readily deployable VLC systems. In particular, since LED-Camera VLC systems have shown a promising potential in large indoor communication due to the growing deployment of LED lighting infrastructure, a comprehensive VLC system with cooperative transmission and roaming support has become an impending need. To this end, we propose a novel VLC and visible light sensing (VLS) system to address that by leveraging LED sensing and effective encoding/decoding schemes. It is achieved first by utilizing LED sensing via converting parts of LED luminaire into light sensors to detect diffuse reflection change caused by presence of the user. After the users are detected and located, the system employs rateless codes and newly designed code assignment scheme to collaboratively transmit to detected users in their communication cells. We believe the proposed system has the potential to a roaming support VLC system in the whole building or indoor areas.

Dimming control is of vital importance for visible light communication (VLC) systems. Conventional dimmable transmission schemes based on compensation are spectrally inefficient. In this paper, we propose the use of two techniques, i.e., time-sharing and superposition, to construct spectral-efficient dimmable transmission schemes. For VLC systems with on–off keying (OOK) signaling, we present a general framework to construct dimmable transmission scheme by time-sharing among different dimming control codes. Arbitrary dimming target is achieved by adjusting the proportion of each dimming control code. We, then, give a practical construction of dimming control codes with semi-constant weight codes. We obtain optimal proportions of the semi-constant weight codes, which maximize the asymptotic spectral efficiency using linear programming. We also compute achievable rates of the proposed scheme under different dimming targets and different signal-intensity-to-noise-amplitude ratios. To achieve higher spectral efficiency ( $>$ 1.0 (b/s)/Hz), we present a dimmable multilevel transmission scheme based on superposition. In the proposed scheme, the first $\ell$ $-1$ levels adopt traditional OOK modulation, whereas the $\ell$ th level adopts the dimmable transmission scheme for OOK modulation. The transmitted signal is formed by superimposing modulated signals of the $\ell$ levels. Analysis shows that the proposed scheme achieves a higher spectral efficiency than the state-of-the-art schemes. Hence, it provides an attractive candidate for dimmable VLC systems with demanding spectral efficiency.

Power control technology is necessary in Visible Light Communication (VLC) systems because of the multipath distortion and shadowing. When a power control algorithm is applied to the system, feedback error is inevitable. In this paper, we analyze the closed-loop power control algorithm and the influence of the power control error (PCE) in VLC systems. To analyze the effect of the PCE in VLC systems, the proposed system is studied with different modulation schemes and coding rates in terms of BER.

This paper investigates the effect of light emitting diodes (LEDs) positioning and allocation in the channel analysis performance for an indoor intra-vehicle visible light communication (VLC) system. The MATLAB simulation results focus on the received power and the signal to noise ratio (SNR) within a sports utility vehicle. Furthermore, this work aims to validate by investigating two different scenarios, one utilizing two sources of power and the other using three sources of power with various locations, how LED’s spatial positioning affects the VLC system and the probability of error. Proving the demand for considering LEDs layout positioning while designing a VLC system.

Visible light communication (VLC) system based on orthogonal frequency division multiplexing (OFDM) is promising for its ability to link a huge number of devices with high reliability and low latency. However, OFDM-based VLC systems are very sensitive to the symbol timing offsets. Thus, synchronisation algorithm is very important for OFDM-based VLC system. In this study, the authors first propose zero correlation code pair (ZCC pair) and investigate the periodical impulse-shaped correlation property of ZCC pair. Then the authors propose a novel timing offset estimation algorithm based on ZCC pair. The preamble is processed via peak-to-average power ratio (PAPR) reduction algorithms to overcome the PAPR problem in VLC systems. This algorithm achieves high accuracy and has low synchronisation error probability. The effectiveness of the authors' proposed algorithm has been demonstrated using computer simulation under non-light-of-sight VLC and Gaussian channels. The results show that the authors' algorithm outperforms the Schmidl Cox's and Park's algorithms in terms of synchronisation error probability and mean square error of timing error.