LED-based Visible Light Communication System Research Articles

A 3.84-Gbit/s FBMC-NOMA-based VLC transmission system using DAC-based pre-equalization and DHT precoding technique

The transmission data rate of visible light communication (VLC) systems is mainly limited by the modulation bandwidth of light-emitting diodes (LEDs). Pre-equalization (PE) techniques in combination with advanced modulation formats have been employed to enhance the data rate of LED-based VLC systems. In this paper, we experimentally demonstrated a high spectral-efficiency filter bank multi-carrier (FBMC) and non-orthogonal multiple access (NOMA)-based VLC transmission system using digital-to-analog converter-based PE (DAC-PE) and discrete Hartley transform (DHT) precoding technique. Two PE techniques, i.e., DAC-PE and digital pre-equalization (DPE), are comparatively investigated in both orthogonal frequency-division multiplexing (OFDM)-NOMA-based VLC systems and FBMC-NOMA-based VLC systems. The results exhibit that, with the help of DHT precoding, the DAC-PE scheme outperforms the DPE scheme at the optimal power ratios (PRs). Besides, the FBMC-NOMA scheme can provide better bit error rate (BER) performance and higher data rate than OFDM-NOMA. At the optimal PR of 6 dB, the FBMC-NOMA signal with a record net data rate of 3.84 Gbit/s after 2.3-m free-space link transmission can be achieved with the BER below 3.8 × 10−3.

Key Technologies for High-Speed Si-Substrate LED Based Visible Light Communication

Nowadays, the demand for high-speed information transmission is increasing rapidly. Visible light communication (VLC) based on light-emitting diodes (LEDs) is supposed as a potential candidate for future 6G communication networks. However, as an emerging field of optical communications, the data rate of VLC systems is restricted to the extremely limited modulation bandwidth and nonlinear characteristics of optoelectronic devices. In this paper, we outline the state of art and challenges of VLC, and introduce the key technologies for high-speed Silicon (Si) -substrate LED-based VLC systems. Based on an optimized integrated 4×4 8-wavelength LED array and advanced digital signal processing (DSP) methods, we demonstrate an ultrahigh-speed VLC system. Digital Zobel network (DZN) pre-equalization and transfer learning bidirectional gate recurrent unit (TL-Bi-GRU) based post-equalization are proposed to mitigate linear and nonlinear impairment. The yellow and green LEDs are especially enhanced in high-efficacy, and achieve the impressive data rates of 3.45Gbit/s, and 3.83Gbit/s respectively, which is a remarkable improvement. The achievable overall data rate of the device is 28.93 Gbit/s. As far as we know, it's the highest data rate achieved by a single-chip Si-substrate LED array.

Secure Visible Light Communication System via Cooperative Attack Detecting Techniques

With the recent development of fourth industrial technology, the need for a broadband short-range wireless communication system to realize an ultraconnected, ultra-low latency, and ultra-realistic intelligent information society has emerged. Among the next-generation communication network technologies that can fulfill the technical demands, visible light communication (VLC) is a promising technology that can use illuminated light as a communication light source, which is convenient and environmentally friendly and has high energy and frequency efficiency. However, although VLC has a high level of security owing to the straightness and transparency of visible light, if some of the VLC nodes in a dense mesh network environment are hacked by external attacks, there can be critical performance degradation by jamming attacks. Although several studies have suggested the possibility of VLC jamming attacks, only a few have studied how to effectively detect and respond to these attacks. This study proposes a method to collaboratively detect and respond to jamming attacks in smart LED-based VLC systems. According to the experimental results of this study, the proposed cooperative method showed 91% attack detection accuracy and 1.82 times better than the k-random method. The proposed method showed a minimum detection rate of 84% even in an obstacle-rich environment, proving outstanding attack detection performance 1.68 times better than the k-random method.

High-speed visible light communication systems based on Si-substrate LEDs with multiple superlattice interlayers

High-speed visible light communication (VLC), as a cutting-edge supplementary solution in 6G to traditional radio-frequency communication, is expected to address the tension between continuously increased demand of capacity and currently limited supply of radio-frequency spectrum resource. The main driver behind the high-speed VLC is the presence of light emitting diode (LED) which not only offers energy-efficient lighting, but also provides a cost-efficient alternative to the VLC transmitter with superior modulation potential. Particularly, the InGaN/GaN LED grown on Si substrate is a promising VLC transmitter to simultaneously realize effective communication and illumination by virtue of beyond 10-Gbps communication capacity and Watt-level output optical power. In previous parameter optimization of Si-substrate LED, the superlattice interlayer (SL), especially its period number, is reported to be the key factor to improve the lighting performance by enhancing the wall-plug efficiency, but few efforts were made to investigate the influence of SLs on VLC performance. Therefore, to optimize the VLC performance of Si-substrate LEDs, we for the first time investigated the impact of the SL period number on VLC system through experiments and theoretical derivation. The results show that more SL period number is related to higher signal-to-noise ratio (SNR) via improving the wall-plug efficiency. In addition, by using Levin-Campello bit and power loading technology, we achieved a record-breaking data rate of 3.37 Gbps over 1.2-m free-space VLC link under given optimal SL period number, which, to the best of our knowledge, is the highest data rate for a Si-substrate LED-based VLC system.

Si-substrate LEDs with multiple superlattice interlayers for beyond 24 Gbps visible light communication

High-speed visible light communication (VLC) using light-emitting diodes (LEDs) is a potential complementary technology for beyond-5G wireless communication networks. The speed of VLC systems significantly depends on the quality of LEDs, and thus various novel LEDs with enhanced VLC performance increasingly emerge. Among them, InGaN/GaN-based LEDs on a Si-substrate are a promising LED transmitter that has enabled VLC data rates beyond 10 Gbps. The optimization on the period number of superlattice interlayer (SL), which is a stress-relief epitaxial layer in a Si-substrate LED, has been demonstrated to be an effective method to improve Si-substrate LED’s luminescence properties. However, this method to improve LED’s VLC properties is barely investigated. Hence, we for the first time experimentally studied the impact of SL period number on VLC performance. Accordingly, we designed and fabricated an integrated 4 × 4 multichromatic Si-substrate wavelength-division-multiplexing LED array chip with optimal SL period number. This chip allows up to 24.25 Gbps/1.2 m VLC transmission using eight wavelengths, which is the highest VLC data rate for an InGaN/GaN LED-based VLC system to the best of our knowledge. Additionally, a record-breaking data rate of 2.02 Gbps over a 20-m VLC link is achieved using a blue Si-substrate LED with the optimal SL period number. These results validate the effectiveness of Si-substrate LEDs for both high-speed and long-distance VLC and pave the way for Si-substrate LED design specially for high-speed VLC applications.

Sparsity-Aware Nonlinear Equalization With Greedy Algorithms for LED-Based Visible Light Communication Systems

The nonlinearity of light emitting diode (LED) in visible light communication (VLC) systems is considered as one major limiting factor that deteriorates the systems’ performance. In this paper, the nonlinear equalization in VLC systems is deemed to be a sparse recovery problem. Three different greedy sparse recovery algorithms, namely matching pursuit (MP), orthogonal MP (OMP), and regularized OMP (ROMP) are employed in constructing the sparsity-aware nonlinear equalizer for LED-based VLC systems. By adopting these greedy algorithms, the number of kernels in the nonlinear equalizer can be significantly reduced with minor performance loss, which enables low-complexity and high-performance nonlinear equalization. The performance of the proposed sparsity-aware nonlinear equalizers is investigated experimentally in orthogonal frequency division multiplexing (OFDM) based VLC systems with commercially available red-green-blue LEDs. The results show that, with the help of greedy sparse recovery algorithms, the number of kernels in nonlinear equalization can be reduced by 32.5%∼62.5% for only 0.5-dB signal-to-noise ratio loss. The compatibility of the proposed sparsity-aware nonlinear equalizer in a ∼1 Gbit/s adaptive bit-power loading OFDM VLC system is also experimentally demonstrated. The ROMP-based nonlinear equalizer is found to be the best choice that offers the optimal balance between performance and complexity, which achieves almost the same performance as the conventional Volterra time domain nonlinear equalizer in OFDM VLC systems with approximately halved number of kernels.

15.73 Gb/s Visible Light Communication With Off-the-Shelf LEDs

Visible light communication (VLC) can provide high-speed data transmission that could alleviate the pressure on the conventional radio frequency spectrum with the looming capacity crunch for digital communication systems. In this paper, we present experimental results of a VLC system with a data rate of 15.73 Gb/s after applying forward error correction coding over a 1.6 m link. Wavelength division multiplexing is utilized to efficiently modulate four wavelengths in the visible light spectrum. Four single color low-cost commercially available light emitting diodes (LEDs) are chosen as light sources. This confirms the feasibility and readiness of VLC for high-data rate communication. Orthogonal frequency division multiplexing (OFDM) with adaptive bit loading is used. The system with the available components is characterized and its parameters, such as LED driving points and OFDM signal peak-to-peak scaling factor, are optimized. To the best of our knowledge, this is the highest data rate ever reported for LED-based VLC systems.

An LED-based visible light communication system for multicast

<p>Visible Light Communication is a communication method that transmits data through light by pulsing an LED at high speed, performing broadcast communication for all devices existing in its coverage. Broadcast-based Visible Light Communication is limited to application to Internet of Things services, where various applications exist, although all receivers can communicate within the range of light sources. Therefore, this paper proposes an LED based Visible Light Communication system for multicast. The proposed system performs individual multicast by participating in communication only with receivers configured to use a specified ID value input at the transmitting side during data transmission. Experimental results show that the receiver can receive files individually according to a specified ID value.</p>

Impact of blue filtering on effective modulation bandwidth and wide-angle operation in white LED-based VLC systems

This work studies the impact of employing blue filters on the resulting effective modulation bandwidth of visible light communication (VLC) systems using phosphor-coated white light emitting diodes (LEDs) under wide-angle operation. Effective modulation bandwidths are assessed and compared for VLC systems with ideal and non-ideal transmission blue filters at the receiver. Angle tolerance capabilities of the employed filters have also been investigated in the study. Commercially available phosphor-coated white LED and photodetector (PD) models are utilized to obtain realistic results. We show that the choice of the blue filter structure, combined with the white LED and PD, affects the system’s effective modulation bandwidth. We also show that there exists a trade-off between obtaining a relatively large modulation bandwidth and preserving the wide-angle operation of the system. A figure of merit (FOM) is also introduced to represent such a trade-off. Moreover, a simple estimation of the expected effective modulation bandwidth of a VLC system using phosphor-coated white LED is developed as a result of the weighted average of the blue and yellow light responsivity of the filter. A numerical example is also included in which the optical signal to noise ratio (OSNR) is computed in VLC systems with and without the addition of a blue filter. The OSNR shows enhancement when a blue filter with a wide rejection region is inserted in the studied VLC system.

Using adaptive equalization and polarization-multiplexing technology for gigabit-per-second phosphor-LED wireless visible light communication

In the demonstration, we propose and investigate a phosphor white-light LED gigabit-per-second visible light communication (VLC) system by utilizing adaptive filtering and polarization-multiplexing technology. Due to the incoherent light of LED, two orthogonal linear polarizers can be utilized in the LED transmitter (Tx) side and client receiver (Rx) side, respectively, to produce 2 × 2 polarization-multiplexing multi-input multi-output (MIMO) VLC transmission. Moreover, the Volterra nonlinear equalization (VNLE) filtering is proposed to improve the nonlinearity concern of LED-based VLC system, when the high spectral-efficient orthogonal frequency division multiplexing (OFDM) modulation is employed. Hence, the total VLC data rate of ∼1.4 Gbps is reached and the VLC performance is also discussed in the proposed wireless VLC system.

On the Implementation of Carrierless Amplitude and Phase Modulation in Visible Light Communication

Carrierless amplitude and phase modulation (CAP) is one of the spectrally efficient schemes that have been proposed to tackle the limited modulation bandwidth challenge in visible light communication (VLC). The VLC technology leverages existing lighting fixtures to provide wireless data communication, which makes it attractive for many applications. However, the commercially available white light emitting diodes (LEDs) that are predominantly employed in VLC offer low modulation bandwidths that limit the achievable data rate. Thus, CAP modulation is employed to improve achievable data rate, primarily due to its implementation simplicity and high spectral efficiency. The CAP scheme also has a special feature in that it can be implemented as a single band or a multiband scheme which provides design flexibility. This paper presents an in-depth study of the implementation of CAP in LED-based VLC systems, highlighting the unique features that make it specially suited for VLC applications. Furthermore, a comprehensive investigation is carried out regarding the design parameters of the CAP modulation transceiver, its benefits, and techniques to mitigate the challenges of CAP-based VLC systems.

Enabling Technologies for High-Speed Visible Light Communication Employing CAP Modulation

High-speed light emitting diode (LED) based visible light communication (VLC) system is restricted by the limited LED bandwidth, low detector sensitivity, and linear and nonlinear distortions. Thus, single- and two-cascaded constant-resistance symmetrical bridged-T amplitude hardware pre-equalizers, carrierless amplitude and phase (CAP) modulation, and a three-stage hybrid postequalizer are investigated to increase transmission data rate for a high-speed LED-based VLC system. The schemes utilized by the hybrid postequalizer are modified cascaded multimodulus algorithm, Volterra series based nonlinear compensation algorithm and decision-directed least mean square algorithm. With these technologies, we successfully implement high-speed CAP32, CAP64, and CAP128 VLC experimental system over 1-m free space transmission with bit error rate under the hard decision-forward error correction threshold of 3.8 × 10–3. System performance improvement employing these key technologies is also validated through experimental demonstration. With the superposition of each stage of the hybrid postequalizer, system performance will be improved. And utilizing two-cascaded hardware pre-equalizer will provide more accurate channel compensation than a single pre-equalizer.

A high-speed phosphorescent LED-based visible light communication system utilizing SQGNRC precoding technique

Peak-over-average power ratio (PAPR) control utilizing precoding technique based on square root-generalized raised cosine function is proposed and verified experimentally through a visible light communication system employing phosphor-based white light-emitting diodes for the first time. The simulation results show that the improved precoding matrix can further reduce PAPR by nearly 1 dB compared with existing precoding matrix based on square root raised cosine function and significantly achieve 3.5 dB improvement in contrast to original signals without precoding. The experimental result also proves that the bit error rate performance can be effectively improved by 1.62 dB at the same bandwidth and 0.76 dB at the same raw data rate in terms of quality factor when proposed precoding technique is applied, which clearly demonstrates its benefit and feasibility.

DFT-spread combined with clipping method to reduce the PAPR in VLC-OFDM system

Orthogonal frequency division multiplexing (OFDM) is an attractive technique to realize high data rate in light emitting diodes (LEDs)-based visible light communication (VLC). However, high peak-to-average power ratio (PAPR) of OFDM makes VLC-OFDM very sensitive to the nonlinearity of LEDs. In this paper, the discrete Fourier transform-spread (DFT-spread) combined with clipping method is proposed to reduce the PAPR of OFDM signal in VLC system. Combining simulation with experiment, a performance comparison is made among conventional OFDM, DFT-spread-OFDM, and clipped DFT-spread-OFDM with different clipping ratios (CRs) in a single LED-based VLC system. The experimental results show that the proposed clipped DFT-spread-OFDM method can effectively improve the system performance compared with the other two methods. At the optimum signal peak-to-peak (PTP) value, by using the clipped DFT-spread-OFDM scheme with CR at 8 dB, the bit error rate (BER) of the system can be reduced from 0.003 7 to 0.000 287.1

Hadamard-Coded Modulation for Visible Light Communications

Visible light communication (VLC) systems using the indoor lighting system to also provide downlink communications require high-average optical powers to satisfy the illumination needs. This can cause high-amplitude signals common in higher-order modulation schemes to be clipped by the peak power constraint of the light emitting diode (LED) and lead to high-signal distortion. In this paper, we introduce Hadamard coded modulation (HCM) to achieve low error probabilities in LED-based VLC systems needing high-average optical powers. This technique uses a fast Walsh–Hadamard transform (FWHT) to modulate the data as an alternative modulation technique to orthogonal frequency division multiplexing (OFDM). HCM achieves a better performance for high-illumination levels because of its small peak to average power ratio (PAPR). The power efficiency of HCM can be improved by reducing the DC part of the transmitted signals. The resulting so-called DC-reduced HCM (DCR-HCM) is well suited to environments requiring dimmer lighting.

8-Gb/s RGBY LED-Based WDM VLC System Employing High-Order CAP Modulation and Hybrid Post Equalizer

In this paper, for the first time, we propose the use of a hybrid post equalizer in a high-order carrierless-amplitude-and-phase-modulation-based visible light communication (VLC) system. The hybrid equalizer consists of a linear equalizer, a Volterra-series-based nonlinear equalizer, and a decision-directed least mean squares equalizer to simultaneously mitigate the linear and nonlinear distortions of the VLC system. A commercially available red-blue-green-yellow light-emitting diode (RBGY LED) is utilized for four-wavelength multiplexing. By the hybrid equalizer, an aggregate data rate of 8 Gb/s is experimentally achieved over a 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 . To the best of our knowledge, this is the highest data rate ever reported in high-speed VLC systems.

Power and Rate Optimization for Visible Light Communication System With Lighting Constraints

Visible-light communication (VLC) will be deployed in various indoor environments, including those requiring different lighting colors, which imposes the needs for transmission optimization under certain lighting constraints. This work establishes a framework for the transmission power and rate optimization, for light emitting diode (LED)-based VLC systems under lighting constraints. We describe the system model of LED-based color-division VLC system, which incorporates the transmission power spectral density, the receiving optical filters, the human eye perception, and the lighting constraints. Then, we formulate the corresponding power and rate optimization problems, for both point-to-point communication system and broadcast communication system. More specifically, for a point-to-point communication system, it maximizes the transmission rate subject to the transmission power constraint and the lighting constraint; and for a broadcast system, it minimizes the total transmission power subject to some quality of service (QoS) constraint across all receivers. Various convex optimization problems have been formulated and solved analytically or using standard convex optimization solutions. It is obsesrved that the optimal symbol modulation power allocation scheme significantly outperforms the equal power allocation scheme.

Performance Comparison of OFDM Signal and CAP Signal Over High Capacity RGB-LED-Based WDM Visible Light Communication

We experimentally demonstrate a visible light communication (VLC) system based on a single commercially available RGB-type LED. High spectrally efficient carrierless amplitude and phase (CAP) modulation and orthogonal frequency-division multiplexing (OFDM) are adopted in the intensity-modulation and direct-detection VLC system of limited bandwidth. In order to achieve higher capacity of the uneven-frequency-response LED-based VLC system, OFDM signals are combined with the bit- and power-loading techniques, and CAP signals of various modulation are pre-emphasized to modulate one of the RGB chips. To reach the BER of less than 10-3, CAP and OFDM signals demonstrate the maximum data rates of 1.32 and 1.08 Gb/s, respectively, employing the blue chip. In addition to spectrally efficient formats, the wavelength-division-multiplexing (WDM) scheme is applied to further increase the capacity. After individually optimizing RGB chips, the maximum aggregate data rates of CAP and OFDM are 3.22 and 2.93 Gb/s, respectively, in our RGB-LED-based WDM VLC system. Hence, compared with OFDM, the CAP scheme shows competitive performance and provides an alternative spectrally efficient modulation for next generation optical wireless networks.