Research

11 pages, 1846 KiB

Open AccessArticle

K-Means-Based DNN Algorithm for a High Accuracy VLP System

by Jianli Jin, Shouwei Wang, Lu Yang, Huimin Lu, Jianping Wang, Danyang Chen, Lifang Feng, Hongyao Chen and Hongyu Zhang

Photonics 2024, 11(3), 209; https://doi.org/10.3390/photonics11030209 - 26 Feb 2024

Viewed by 654

Abstract

In this paper, a positioning algorithm based on the combination of K-means clustering and deep neural networks (DNNs) is first presented for multiple light emitting diodes (LEDs) integrated with visible light positioning (VLP) systems. We extracted the maximum value from the collected optical [...] Read more.

In this paper, a positioning algorithm based on the combination of K-means clustering and deep neural networks (DNNs) is first presented for multiple light emitting diodes (LEDs) integrated with visible light positioning (VLP) systems. We extracted the maximum value from the collected optical power of LEDs, utilizing the ratio of each optical power to this maximum optical power as the input training data. The experimental results demonstrate that the proposed algorithm outperformed the conventional DNN algorithm in terms of anti-jamming capability and positioning accuracy. In addition, the positioning accuracy of the proposed system reached a millimeter level, which is the highest experimental VLP accuracy, to the best of our knowledge. Full article

(This article belongs to the Special Issue Visible Light Communications)

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14 pages, 949 KiB

Open AccessArticle

On the Performance of Intelligent Reconfigurable Surfaces for 6G Indoor Visible Light Communications Systems

by Milton Román Cañizares, Pablo Palacios Játiva, Javier Guaña-Moya, William Villegas-Ch and Cesar Azurdia-Meza

Photonics 2023, 10(10), 1117; https://doi.org/10.3390/photonics10101117 - 04 Oct 2023

Viewed by 969

Abstract

Indoor visible light communication (VLC) systems have been extensively studied; however, they present some problems when the main propagation channel component, called Line-of-Sight (LoS), is partially or totally blocked. The effect of this blockage can cause degradation of the received optical signal and [...] Read more.

Indoor visible light communication (VLC) systems have been extensively studied; however, they present some problems when the main propagation channel component, called Line-of-Sight (LoS), is partially or totally blocked. The effect of this blockage can cause degradation of the received optical signal and decrease the performance of the VLC system. Therefore, in recent years, research has focused on proposing solutions to mitigate this issue. Under this context, in this paper, we propose the use and implementation of intelligent reconfigurable surfaces (IRS) in the VLC indoor system to improve the propagation channel component produced by reflections, called non-line-of-sight (Non-LoS). Furthermore, we have analyzed and established the mathematical expressions of the channel components, including the effect of the IRS on the VLC system. These expressions have been evaluated in a simulated indoor VLC scenario in terms of the channel impulse response (CIR) and the bit error rate (BER). The findings achieved allow us to demonstrate that the use of IRS in the VLC system improves the performance of the system in terms of the parameters evaluated. These results also allow us to highlight the possible use of improvements in the VLC system for inclusion as a 6G enabling technology. Full article

(This article belongs to the Special Issue Visible Light Communications)

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13 pages, 3490 KiB

Open AccessArticle

BiGRU-Based Adaptive Receiver for Indoor DCO-OFDM Visible Light Communication

by Yi Huang, Dahai Han, Min Zhang, Yanwen Zhu and Liqiang Wang

Photonics 2023, 10(9), 960; https://doi.org/10.3390/photonics10090960 - 22 Aug 2023

Viewed by 742

Abstract

Nonlinear devices and channel interference can significantly impact the received signal in visible light communication (VLC). While recent research has explored receiver recovery using deep learning, existing approaches often involve replacing traditional channel estimation and equalization modules with neural network models. However, these [...] Read more.

Nonlinear devices and channel interference can significantly impact the received signal in visible light communication (VLC). While recent research has explored receiver recovery using deep learning, existing approaches often involve replacing traditional channel estimation and equalization modules with neural network models. However, these models introduce additional data processing steps after fast Fourier transform (FFT), leading to increased complexity. To address these challenges, this study introduces a novel direct time-domain waveform equalization approach using a bidirectional gated recurrent unit (BiGRU) neural network for indoor VLC employing direct current (DC)-biased orthogonal frequency division multiplexing (DCO-OFDM). Unlike previous methods, our proposed scheme utilizes time-domain waveform data from photodiode outputs for direct balancing, harnessing the potent nonlinear processing capabilities of the BiGRU model. We first analyze the nonlinear processing capacity of the BiGRU model and subsequently compare the performance of different receiving methods on a constructed indoor visible-light communication platform. Experimental results demonstrate that the BiGRU-based approach exhibits low complexity and exceptional nonlinear channel learning capabilities. Notably, the proposed method outperforms other strategies in terms of bit error rate without the need for pilot signals. These findings validate the potential of the BiGRU-based DCO-OFDM receiving scheme as a promising solution for future VLC systems. Full article

(This article belongs to the Special Issue Visible Light Communications)

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15 pages, 4572 KiB

Open AccessArticle

An Optimal Adaptive Constellation Design Utilizing an Autoencoder-Based Geometric Shaping Model Framework

by Yuan Wei, Li Yao, Haoyu Zhang, Chao Shen, Nan Chi and Jianyang Shi

Photonics 2023, 10(7), 809; https://doi.org/10.3390/photonics10070809 - 12 Jul 2023

Cited by 2 | Viewed by 1035

Abstract

Since visible-light communication (VLC) has become an increasingly promising candidate for 6G, the field of underwater visible-light communication (UVLC) has also garnered significant attention. However, the impairments introduced by practical systems and the time-varying underwater channels always limit the performance of underwater visible-light [...] Read more.

Since visible-light communication (VLC) has become an increasingly promising candidate for 6G, the field of underwater visible-light communication (UVLC) has also garnered significant attention. However, the impairments introduced by practical systems and the time-varying underwater channels always limit the performance of underwater visible-light communication. In this paper, we propose and experimentally demonstrate an autoencoder-based geometric shaping model (AEGSM) framework to jointly optimize quadrature amplitude modulation (QAM) signals at the symbol-wise and bit-wise levels for underwater visible-light communication. Unlike traditional geometric shaping (GS) methods, which only give theoretically optimal shaping solutions, our framework can always obtain the globally optimal shaping scheme for a specific channel condition or different application scenarios. In our AEGSM framework, an autoencoder is used to find the optimal shaping scheme at the symbol-wise level and a revised pairwise optimization (RPO) algorithm is applied to achieve bit-wise optimization. In a real UVLC system, 2.05 Gbps transmission is achieved under the hard decision–forward error correction (HD-FEC) threshold of 3.8 × 10⁻³ by employing the autoencoder-based 8QAM (AE-8QAM) optimized by the AEGSM, which is 103 Mbps faster than the Norm-8QAM. The AE-8QAM also shows its resistance to nonlinearity and enables the UVLC system to operate within a larger dynamic range of driving voltages. The results substantiate the potential and practicality of the proposed AEGSM framework in the realm of underwater visible-light communication. Full article

(This article belongs to the Special Issue Visible Light Communications)

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11 pages, 3190 KiB

Open AccessEditor’s ChoiceArticle

Bandwidth Expansion of Zero-Power-Consumption Visible Light Communication System

by Yiwu Xu, Xiongbin Chen and Yufeng Wang

Photonics 2023, 10(4), 376; https://doi.org/10.3390/photonics10040376 - 28 Mar 2023

Viewed by 1447

Abstract

The data rate of the zero-power-consumption visible light communication system is limited due to the solar cell bandwidth limit. A new method has been proposed to improve the data rate of communication systems. The predistortion circuit based on the nonlinear compensation principle of [...] Read more.

The data rate of the zero-power-consumption visible light communication system is limited due to the solar cell bandwidth limit. A new method has been proposed to improve the data rate of communication systems. The predistortion circuit based on the nonlinear compensation principle of the communication system is added between the transmitter and the receiver to equalize the amplitude–frequency response of the solar cell. Based on the measurement of the original amplitude–frequency response of the system, the zero-pole of the predistortion circuit is calculated, and an accurate equalization circuit is designed by using separate components to expand the 3 dB bandwidth of the system. The test results show that the 3 dB bandwidth of the visible light self-powered communication system is increased from 85 kHz to 750 kHz, and the system bandwidth is expanded by nearly 10 times. Full article

(This article belongs to the Special Issue Visible Light Communications)

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16 pages, 8377 KiB

Open AccessArticle

Sixty-Nine-Element Voice Coil Deformable Mirror for Visible Light Communication

by Lv Jiang, Lifa Hu, Qili Hu, Xingyu Xu, Jingjing Wu, Lin Yu and Yang Huang

Photonics 2023, 10(3), 322; https://doi.org/10.3390/photonics10030322 - 17 Mar 2023

Cited by 1 | Viewed by 1256

Abstract

To overcome the atmospheric turbulence aberration, and improve the quality of light beam in visible light communication (VLC), a compact 69-element deformable mirror (DM) using micro voice coil actuators was designed based on systematic theoretical analysis. The structural parameters of the micro voice [...] Read more.

To overcome the atmospheric turbulence aberration, and improve the quality of light beam in visible light communication (VLC), a compact 69-element deformable mirror (DM) using micro voice coil actuators was designed based on systematic theoretical analysis. The structural parameters of the micro voice coil actuator were optimized by electromagnetic theory and the finite element method. The DM was optimized from the aspects of thermal deformation, response time, coupling coefficient, and other parameters. Finally, wavefront fitting and residual calculation were completed according to the influence function. The optimized voice coil deformable mirror (VCDM) has a large phase stroke, good thermal stability, a short response time of less than 0.7 ms, and a large first resonance of 2045 Hz. The fitting residuals of the VCDM for the first 10 Zernike modes with a PV value of 8 μm are all below 10 nm (RMS). Compared with a similar DM, the obtained results from our compact VCDM indicate that it has a higher wavefront fitting precision. VCDM corrected complex random aberrations in the VLC scenario and improved the coupling efficiency of the signal beam, proving that the compact VCDM with high performance and low cost has a good application prospect in VLC systems. Full article

(This article belongs to the Special Issue Visible Light Communications)

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17 pages, 6093 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Enhanced Performance of a Cascaded Receiver Consisting of a DNN-Based Waveform-to-Symbol Converter and Modified NN-Based DD-LMS in CAP Underwater VLC System

by Xianhao Lin, Fangchen Hu and Nan Chi

Photonics 2023, 10(1), 79; https://doi.org/10.3390/photonics10010079 - 10 Jan 2023

Cited by 4 | Viewed by 2607

Abstract

Underwater visible light communication (UVLC) based on LEDs has become a competitive candidate, which is able to provide high data rates, low latency and low cost for next-generation wireless communication technologies. However, it is still challenging to achieve high-speed communication because of bottleneck [...] Read more.

Underwater visible light communication (UVLC) based on LEDs has become a competitive candidate, which is able to provide high data rates, low latency and low cost for next-generation wireless communication technologies. However, it is still challenging to achieve high-speed communication because of bottleneck problems such as bandwidth limitation and linear and nonlinear distortions. Traditional Deep-learning Neural Network (DNN)-based waveform-to-symbol converter is verified to be an effective method to alleviate them, but impractical due to high complexity. To achieve a better tradeoff between communication performance and computation complexity, a cascaded receiver consisting of a DNN-based waveform-to-symbol converter and modified Neural Network (NN)-based decision-directed least mean square (DD-LMS) is then innovatively proposed. With fewer taps and nodes than the traditional converter, the front-stage converter could mitigate the majority of Inter-Symbol Interference (ISI) and signal nonlinear distortions. Then modified NN-based DD-LMS is cascaded to improve communication performance by reducing phase offset, making received constellation points more concentrated and closer to standard constellation points. Compared with the traditional converter, the cascaded receiver could achieve 89.6% of signal Vpp dynamic range with 12.4% of complexity in the 64APSK UVLC system. Moreover, the ratio of signal Vpp dynamic range and total trainable parameters is 1.24 × 10⁻¹ mV, while that of the traditional converter is 1.95 × 10⁻² mV. The cascaded receiver used in 64APSK UVLC systems is experimentally verified to achieve enhanced performance, thus as a promising scheme for future high-speed underwater VLC. Full article

(This article belongs to the Special Issue Visible Light Communications)

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14 pages, 646 KiB

Open AccessArticle

Volterra-Aided Neural Network Equalization for Channel Impairment Compensation in Visible Light Communication System

by Daming Tian, Pu Miao, Hui Peng, Weibang Yin and Xiaorui Li

Photonics 2022, 9(11), 845; https://doi.org/10.3390/photonics9110845 - 10 Nov 2022

Cited by 5 | Viewed by 1452

Abstract

This paper addresses the channel impairment to enhance the system performance of visible light communication (VLC). Inspired by the model-solving procedure in the conventional equalizer, the channel impairment compensation is formulated as a spatial memory pattern prediction problem, then we propose efficient deep-learning [...] Read more.

This paper addresses the channel impairment to enhance the system performance of visible light communication (VLC). Inspired by the model-solving procedure in the conventional equalizer, the channel impairment compensation is formulated as a spatial memory pattern prediction problem, then we propose efficient deep-learning (DL)-based nonlinear post-equalization, combining the Volterra-aided convolutional neural network (CNN) and long-short term memory (LSTM) neural network, to mitigate the system nonlinearity and then recover the original transmitted signal from the distorted one at the receiver end. The Volterra structure is employed to construct a spatial pattern that can be easily interpreted by the proposed scheme. Then, we take advantage of the CNN to extract the implicit feature of channel impairments and utilize the LSTM to predict the memory sequence. Results demonstrate that the proposed scheme can provide a fairly fast convergence during the training stage and can effectively mitigate the overall nonlinearity of the system at testing. Furthermore, it can recover the original signal accurately and exhibits an excellent bit error rate performance as compared with the conventional equalizer, demonstrating the prospect and validity of this methodology for channel impairment compensation. Full article

(This article belongs to the Special Issue Visible Light Communications)

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