MIMO Transceiver Design in Dynamic-Range-Limited VLC Systems

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.

In general, visible light communication (VLC) systems, which utilise white light-emitting diodes (LEDs), only offer a bandwidth limited to the lower MHz region. Therefore, providing VLC-based high data rate communications systems using VLC becomes a challenging task. To address this challenge, we propose a solution based on multiplexing in both the frequency and space domains. We experimentally demonstrate a 4 × 4 imaging multiple-input multiple-output (MIMO) VLC system (i.e., space multiplexing) utilising multiband carrierless amplitude and phase (m-CAP) modulation (i.e., frequency multiplexing). Independently, both MIMO and m-CAP have separately shown the remarkable ability to improve the transmission speeds in VLC systems, and hence, here we combine them to further improve the net data rate. We investigate the link performance by varying the number of subcarriers m, link distance L, and signal bandwidth B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sig</sub> . From all the values tested, we show that a data rate of ~249 Mb/s can be maximally achieved for m = 20, B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sig</sub> = 20 MHz, and L = 1 m, at a bit error rate of 3.2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> using LEDs with ~4 MHz bandwidth.

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.

Multiple-input multiple-output (MIMO) technique is now used in most new broadband communication system, and orthogonal frequency division multiplexing (OFDM) is also utilized within current 4^th generation (4G) of mobile telecommunication technology. With MIMO and OFDM combined, visible light communication (VLC) system’s diversity gain is increase, yet system capacity for dispersive channels is also enhanced. Moreover, with the emerging massive MIMO-OFDM VLC system, there are significant advantages than smaller systems’ such as channel hardening, further increasing of energy efficiency (EE) and spectral efficiency (SE) based on law of large number. This paper addresses one of the major technological challenges, system architecture design, which was solved by semispherical beehive structure (SBS) receiver and so that diversity gain can be identified and applied in Massive MIMO VLC system. Simulation results shows that the proposed design clearly presents a spatial diversity over conventional VLC systems.

• 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.

This study discusses delay modeling for Visible Light Communication (VLC) systems using a camera as the receiver. VLC is a communication technology that transmits information by modulating the intensity of light, which is then captured by a photo-detector or image sensor. While the delay characteristics of VLC have not been extensively studied, particularly in systems where a camera is used as the receiver, existing models have not adequately captured the unique properties of such systems. In this paper, we propose a delay modeling approach for camera-based VLC using queuing theory. Specifically, we model the system as a D/G/1 queue and compare the results from theoretical analysis, simulation, and real-world measurements. The results validate the accuracy of the proposed model. Moreover, the model shows promise for analytically evaluating scenarios that have not been previously addressed, such as multinode communication and retransmission-induced delays in VLC systems.

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.

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.

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.

A new precoding scheme for spectral efficient optical OFDM systems

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.

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.

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.

Modern hospitals are beginning to adopt E-HEALTH as efficient complements to the traditional healthcare services. To support the E-HEALTH services, a locatable, radiation-free and high-capacity communication system is urgently needed in hospitals. Power line communication (PLC) system can use the ubiquitous power line network to power the light-emitting diode (LED) lights while serving as the backbone network for the indoor visible light communication (VLC) systems naturally. In this paper, an integrated broadband power line and visible light communication systems with OFDM modulation is proposed for the indoor hospital applications. This gives a brand-new solution to replace the conventional wireless communication systems in hospitals.