Investigation into Using Compensation for the Nonlinear Effects of the Output of LEDs in Visible Light Communication Systems

This paper investigate the effects of the nonlinear output power to the input current transfer function of a light emitting diode (LED) used as the transmitter in visible light communication systems, and proposes a compensation technique to mitigate the non-linearity. Using an off the shelf red, amber, blue, green (RAGB) LED the nonlinear transfer function is measured and then compensated for. The results show that, for the green LED, which has the highest degree of nonlinearity, an improvement in the received error vector magnitude (EVM)of almost 7 dB can be achieved. We also show that, the improvement in EVM over the uncompensated scheme decreases with increased LED linearity

Experimental Demonstration of High-Speed 4 × 4 Imaging Multi-CAP MIMO Visible Light Communications

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 Bsig. From all the values tested, we show that a data rate of ~249 Mb/s can be maximally achieved for m = 20, Bsig = 20 MHz, and L = 1 m, at a bit error rate of 3.2 × 10-3 using LEDs with ~4 MHz bandwidth

Real-Time 262-Mb/s Visible Light Communication With Digital Predistortion Waveform Shaping

A digital predistortion waveform shaping scheme combined with a blue filter is proposed to optimize both the rise and fall times of a light-emitting diode (LED) and the optical receiver current of the signal of the real-time visible light communication (VLC) system. The proposed scheme is implemented on a field-programmable gate array (FPGA) and a digital-to-analog converter based test bed, which is flexible and reconfigurable by programming the FPGA to match different LED characteristics and varied data rates. A 262-Mb/s non-return-to-zero on-off keying modulation based real-time VLC link with a bit error rate of less than 1.0×10−6 is achieved over a transmission distance of 5.0 m, which uses a single white phosphorous LED with a limited power of 0.1 W

Experimental Demonstration of High-Speed 4 × 4 Imaging Multi-CAP MIMO Visible Light Communications

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 Bsig. From all the values tested, we show that a data rate of ~249 Mb/s can be maximally achieved for m = 20, Bsig = 20 MHz, and L = 1 m, at a bit error rate of 3.2 × 10-3 using LEDs with ~4 MHz bandwidth

Multi-band Carrier-less Amplitude and Phase Modulation for VLC: An Overview

The rapid development of solid-state lighting technologies has been the stimulus for visible light communications (VLC) to be the focus of enormous interest over the last decade. The key feature of simultaneous data transmission and illumination using white light-emitting diodes (LEDs) makes VLC a potential candidate for future power efficient communication networks that aim to meet the ever-increasing demands for high-speed internet services. Researchers, motivated by the success of VLC technology, have developed a number of techniques and methods to support communication systems with both high transmission speeds and spectral efficiency. Here, we provide an overview of the multi-band carrier-less amplitude and phase (m-CAP) modulation technique enabling highly spectrally efficient VLC links in bandlimited environments

Multi-band carrier-less amplitude and phase modulation for highly bandlimited visible light communications - Invited paper

In this paper we present new numerical results for the signal-to-noise ratio and bit error rate (BER) performances of multi-band carrier-less amplitude and phase (m-CAP) modulation in the context of a highly bandlimited visible light communications (VLC) link. Light-emitting diodes are used as the transmitter and are modelled in this work as an ideal first order analogue low-pass filter. The link bandwidth is given as unity, while the filter cut-off frequency is set to 0.1. The number of bands, or subcarriers, is selected as m = 1, 2, 5 and 10. Here, we show that under such a high bandwidth constraint, using m = 10 subcarriers can result in 40% and 17% improvement in bit rate compared to m = 1 and 2, and m = 5 subcarriers, respectively for the same BER target

Visible Light Communications for Indoor Applications

The field of visible light communications (VLC) has undergone a rapid development in recent years. The increased utilization of light emitting diodes (LEDs) has opened new possibilities for especially indoor services such as broadband internet connection and po- sitioning. Thus, a research within VLC is the main focus of the thesis and is divided into two main parts. At rst, the multiband carrier-less amplitude and phase (m-CAP) mod- ulation, introducing a newly adopted format for spectrally e cient VLC links, is under investigation using both theoretical and experimental approaches. The recommendations for m-CAP transmitter site design are proposed. Next, the channel modeling of indoor VLC is investigated with emphasis on the dynamically changing environments caused by moving people and non-line of sight (NLOS) propagation and new statistical models are derived.Katedra elektromagnetického pol