LED Nonlinearity Research Articles

Kernel MSER-DFE Based Post-Distorter for VLC Using Random Fourier Features

Visible light communication (VLC) has emerged as a promising technology that facilitates high speed green communication for the next generation communication systems. However, some of the performance-limiting impairments in VLC include intersymbol interference (ISI), LED's nonlinearity, and multiplicative fading distortion due to user mobility, which present a significant gap between the promised and the achieved throughput of VLC based systems. To mitigate the aforementioned channel impairments, this paper proposes a random Fourier feature (RFF) based kernel minimum symbol error rate (KMSER) decision feedback equalizer (DFE) based post-distorter for VLC, which supports post distortion under finite memory budget. Furthermore, the feedforward, and feedback filter weights are jointly optimized by using a stronger minimum symbol error rate criterion as opposed to the conventional minimum mean square error criterion. Simulations indicate that the proposed RFF-KMSER-DFE based post-distorter exhibits superior BER performance and lower computational complexity over the existing dictionary based post-distorters. Lastly, an analytical bound for BER is derived for the proposed algorithm, and corroborated through simulations.

LED nonlinearity compensation and bandwidth expansion techniques in visible light communication

Visible light communication (VLC) is a promising technology that complements existing wireless communication networks to provide high-speed, low-latency, and multi-device access. With the high-performance code modulation technology of traditional wireless communication, various physical layer communication technologies adapted to VLC systems have been designed and implemented. Different from traditional radio frequency (RF) communication, VLC uses LED as the signal source. The modulation of LED is easy to produce nonlinear distortion and the modulation bandwidth is limited. It has become the technical bottleneck of VLC high-speed communication. In view of the challenges of these two aspects, taking white LED as the starting point, this paper expounds that white LED can effectively balance the characteristics of illumination and communication, summarizes and classifies various techniques of nonlinear distortion compensation and extended modulation bandwidth. Finally, this paper proposes open research issues such as LED package materials and processes, new Micro-LED device research, light source layout design, and intercode interference cancellation technology are expected to improve the performance of visible light communication systems.

Realization of a Laboratory Tuneable Colour Light Source

A spectrally tuneable colour light source (TCLS) has been designed and constructed at Physikalisch-Technische Bundesanstalt (PTB), Germany. It consists of an integrating sphere with 24 LEDs which are driven by a computer-controlled power supply. It is intended for producing any visible spectral distribution and to mimic various light sources for use in laboratories as a calibration source. With the help of an integrated spectrometer, a closed loop operation was introduced to improve the performance of the TCLS and to spectrally stabilize its output spectrum. Before practical realization of the TCLS a series of simulations have been made to predict its performance and capability with a number of different target spectrums. During the practical implementation we have encountered difficulties, namely optimization of the output spectrum, dependency of LED spectra on the electric current through the LED and temperature of the LED, non-linearity of LED’s luminous flux with respect to electric current through the LED and some difficulties with small synthesis coefficient values, which were all successfully solved.

可见光通信光正交频分复用系统符号分解技术抑制LED非线性失真研究

可见光通信光正交频分复用系统符号分解技术抑制LED非线性失真研究

LED非线性对可见光通信系统性能的影响

LED非线性对可见光通信系统性能的影响

A CDMA-based high-speed multi-access VLC system with OOK modulation

An overall bit rate of 625 Mb/s real-time multi-access VLC system is presented in this paper. In order to decrease the effect of ambient light and deal with the non-linearity of LED, we propose a new algorithm to get orthogonal codes which is suitable for OOK modulation. By employing a single white LED and three photo diodes, three users are provided access to the VLC system individually at the same time. A data frame and CRC32 are adopted to realize a reliable and continuous data interaction between Ethernet and VLC system. All the numerical calculations are implemented by FPGAs so as to provide a practical high-speed transmission.

Compressed sensing-based channel estimation for ACO-OFDM visible light communications in 5G systems

In this paper, we propose a compressive sensing (CS)-based channel estimation technique for asymmetrically clipped optical-orthogonal frequency division multiplexing (ACO-OFDM) visible light communications (VLC) in 5G systems. We proposed a modified version of sparsity adaptive matching pursuit (SAMP) algorithm which is named as self-aware step size sparsity adaptive matching pursuit (SS-SAMP) algorithm. It utilizes the built-in features of SAMP and with additional ability to select step size according to the present situation, hence term self-aware, can provide better accuracy and low computational cost. It also does not require any prior knowledge of the sparsity of the signal which makes it self-sufficient. CS-based algorithms such as orthogonal matching pursuit (OMP), SAMP, and our proposed SS-SAMP were implemented on ACO-OFDM VLC. The paper is supported by simulation results which demonstrate performance of proposed scheme in terms of bit error rate (BER), mean square error (MSE), computational complexity, and key VLC parameter (LED nonlinearity, shot noise, thermal noise, channel response, and peak-to-average power ratio (PAPR). It is shown that the SS-SAMP is a good candidate for ACO-OFDM-based VLC that are mobile and have limited processing power, based on its performance and computational complexity.

Visible light wireless communications based on predistorted OFDM

OFDM scheme is considered to enhance the data rate of visible light communication using lighting LEDs. In implementing this system, the inherent nonlinearity of LEDs is one of the factors of performance degradation. In this study, this LED nonlinearity is compensated by predistortion and performance enhancement is shown. Characterization and predistortion procedures of LEDs are proposed and experimental results are provided.

LED非线性对基于正交频分复用可见光通信系统的影响

LED非线性对基于正交频分复用可见光通信系统的影响