VLC for vehicular communications: A multiple input multiple output (MIMO) approach

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.

• 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 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.

Driven by the increase in Internet of Things (IoT) devices for smart home technologies, visible light communications (VLC) using multiple light emitting diodes (LEDs) have been attracting much attention in order to cope with depleted radio frequency spectrum. This paper presents a suboptimal LED selection algorithm for distributed multiple-input multiple-output (D-MIMO) VLC systems. When total ceiling LEDs are turned on to send information while illuminating an indoor environment, the problems of low energy efficiency and mutual interference between VLC channels arise. The proposed algorithm begins by selecting the LED associated with the largest VLC channel gain and adds the LED supporting the largest level of uncorrelation with the maximum VLC channel gain in each step. Simulation results showed that the proposed scheme achieves a capacity similar to an optimal selection algorithm with reduced computational complexity. With a larger distance between the light terminals and a shorter distance between the LEDs, better channel capacity performance of the proposed scheme can be achieved.

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.

Visible Light Communication (VLC) has emerged as a powerful technique for wireless communication systems. Providing high data rate and increasing capacity are the major problems in VLC. Recent evidence suggests that Multiple Input Multiple Output (MIMO) technique can offers improved data rates and increased link range. This paper describes the design and implementation of visible light communication system in indoor environment exploring the benefits of MIMO. The specific objective of this research was to implement a 4×4 Multiple Input (LEDs) Multiple Output (photodetectors)-VLC communication system, where a 16 white power LEDs in four arrays are setting up at transmitter and four RX modules are setting up at receiver side without the need for additional power or bandwidth as well as analyze a mathematical model for a VLC- 4×4 MIMO with different modes such as the suitable angles to cover the entire room. The research designs practically an electronic circuit for the transmitter and receiver with inexpensive components. The power distribution of different propagation modes is calculated for Single Input Single Output (SISO) and MIMO channels in typical room dimensions. The results in this paper indicate that the power is distributed uniformly for entire room when implemented VLC-MIMO as compared to VLC-SISO. Furthermore, a 4×4 MIMO implementing VLC is compared in term of BER vs. SINR with SISO communication system for both Line of Sight (LOS) and Non Line of Sight (NLOS) propagation modes. Comparing the two results of LOS and NLOS, it can be seen that a 4×4 MIMO implementing VLC for LOS perform better than the same system with NLOS due to decreasing in the received power resulted from the multipath effect.

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.

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.

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%.

The enhanced proliferation of connected entities needs a deployment of innovative technologies for the next generation wireless networks. One of the critical concerns, however, is the spectrum scarcity, due to the unprecedented broadcast penetration rate nowadays. Based on this, visible light communication (VLC) has recently emerged as a viable solution to secure high-speed communications. VLC, a high data rate communication technology, has proven its stature as a promising complementary to its radio frequency (RF) counterpart. VLC is a cost-effective, energy-efficient, and secure technology that exploits the current infrastructure, specifically within indoor and underwater environments. Yet, despite their appealing capabilities, VLC systems face several limitations which constraint their potentials such as LED’s limited bandwidth, dimming, flickering, line-of-sight (LOS) requirement, impact of harsh weather conditions, noise, interference, shadowing, transceiver alignment, signal decoding complexity, and mobility issue. Consequently, non-orthogonal multiple access (NOMA) has been considered an effective technique to circumvent these shortcomings. The NOMA scheme has emerged as a revolutionary paradigm to address the shortcomings of VLC systems. The potentials of NOMA are to increase the number of users, system’s capacity, massive connectivity, and enhance the spectrum and energy efficiency in future communication scenarios. Motivated by this, the presented study offers an overview of NOMA-based VLC systems. This article provides a broad scope of existing research activities of NOMA-based VLC systems. This article aims to provide firsthand knowledge of the prominence of NOMA and VLC and surveys several NOMA-enabled VLC systems. We briefly highlight the potential and capabilities of NOMA-based VLC systems. In addition, we outline the integration of such systems with several emerging technologies such as intelligent reflecting surfaces (IRS), orthogonal frequency division multiplexing (OFDM), multiple-input and multiple-output (MIMO) and unmanned aerial vehicles (UAVs). Furthermore, we focus on NOMA-based hybrid RF/VLC networks and discuss the role of machine learning (ML) tools and physical layer security (PLS) in this domain. In addition, this study also highlights diverse and significant technical hindrances prevailing in NOMA-based VLC systems. We highlight future research directions, along with provided insights that are envisioned to be helpful towards the effective practical deployment of such systems. In a nutshell, this review highlights the existing and ongoing research activities for NOMA-based VLC systems, which will provide sufficient guidelines for research communities working in this domain and it will pave the way for successful deployment of these systems.

White-light phosphor-based light-emitting diode (LED) can be used to provide lighting and visible light communication (VLC) simultaneously. However, the long relaxation time of phosphor can reduce the modulation bandwidth and limit the VLC data rate. Recent VLC works focus on improving the LED modulation bandwidths. Here, we propose and demonstrate the use of adaptive Volterra filtering (AVF) to increase the data rate of a white-light LED VLC system. The detailed algorithm and implementation of the AVF for the VLC system have been discussed. Using our proposed electrical frontend circuit and the proposed AVF, a significant data rate enhancement to 700.68 Mbit/s is achieved after 1-m free-space transmission using a single white-light phosphor-based LED.

For channel estimation in the relay-assisted multiple-input multiple-output and orthogonal frequency division multiplexing indoor visible light communication (VLC) system affected by light source, there is a problem that the received signal cannot be separated by simple filtering. To solve this problem, a channel estimation by PARATUCK2-PARAFAC-based noise compensation which introduces tensors to construct the suitable model of VLC is proposed. First, the transmitting pilots for channel estimation and noise estimation are constructed separately with the Hermitian symmetry structure. Then the tensor-based transmission model of the indoor VLC system is established, and the signals for channel and noise estimations are received. Finally, an asymptotic estimation for separating signals from different sources and noise is proposed by PARATUCK2-PARAFAC. Simulation results show that the proposed algorithm provides a more effective scheme for channel estimation comparing with the state-of-the-art algorithms.

In the design of reconfigurable intelligent surfaces (RISs)-aided visible light communication (VLC) systems, most studies have focused on the deployment of mirror arrays and metasurfaces on walls to influence signal propagation and enhance communication performance. This paper provides a new research direction in the design and performance optimization of RIS-aided VLC systems whereby voltage-controlled tunable liquid crystals (LCs) are deployed as part of the VLC receiver. The purpose of the LC RIS is to provide incident light steering and intensity amplification in order to improve the received signal strength and the corresponding achievable data rate. More specifically, an LC RIS-based VLC receiver design is proposed and its operating principles and the channel model for a VLC system with such a receiver are provided. Since the refractive index of the LC RIS plays a critical role in the wave-guiding and light amplification capabilities of this novel receiver, a rate maximization problem is considered to achieve the optimal refractive index and the required voltage to obtain the best light amplification and data rate performances. This communication design problem is a non-convex optimization problem for which a metaheuristic approach is developed based on the sine-cosine algorithm. Simulation results are used to confirm the considerable data rate improvement by the proposed LC RIS-based VLC receiver and optimization algorithm when compared to a VLC receiver without the LC RIS and a baseline scheme, respectively.

Enhanced mobile broadband (eMBB) is a major scenario in the prospective fifth generation (5G) wireless communications. Achieving high user experienced data rate (UEDR) is one of vital goals of eMBB, which needs to consume massive bandwidth. Considering the limited radio frequency (RF) spectrum resource has got heavily congested, we explore the multi-packet reception (MPR) aided visible light communications (VLCs) system to support eMBB services in this paper. MPR can efficiently alleviate collisions for VLC system and enhance UEDR. However, the implementation of MPR in random access system is challenging because of dynamic and unpredictable transmissions of eMBB terminals. For fully utilizing MPR capability and promoting UEDR maximally, we design a two-period frame structure including the access request period (ARP) and the data transmission period (DTP). UEDR emphasizes not only the data rate measured in physical layer but also the network operation behaviour experienced by users which connects closely with quality of service (QoS). In this paper, effective capacity (EC) is employed to depict UEDRs for eMBB terminals for the first time, which provides an efficient link model to evaluate data rates with consideration of statistical delay QoS. Then, the aggregate UEDR is derived and defined as a system metric, which reflects the transmission features of both two periods. We formulate the hybrid access algorithm for eMBB terminals with heterogeneous QoS requirements as an aggregate UEDR maximization problem and find the optimum access probability (for ARP) and optimal resource allocation strategy (for DTP) via the particle swarm optimization-initialization intervention (PSO-II) algorithm.

Visible light communication (VLC) building on the existing illumination infrastructure utilizes light emitting diode (LED) luminaries as wireless transmitters. To achieve data rates on the order of gigabits per second in VLC systems, multiple-input multiple-output (MIMO) transmission has been identified as a key technology. In this paper, we consider a centralized network architecture where the ceiling LED luminaries act as transmitter elements of a distributed massive MIMO VLC system. To obtain the full benefits of massive MIMO, channel state information must be available at the transmitter side. Downlink (DL) channel estimation in a massive MIMO system requires huge pilot overhead in DL as well as feedback overhead in uplink. This makes the implementation of massive MIMO system infeasible if not properly designed. In our study, we address the design of massive MIMO VLC systems with a limited number of DL pilot signals. We explore different DL pilot patterns (PPs) in frequency, time, and spatial domains where interpolation is performed to obtain the global channel matrix taking advantage of the indoor environment geometry and layout of luminaries. We then present data rate results for different DL PPs under the consideration of varying number of active user equipments through Monte-Carlo simulations.