Paul Anthony Haigh

Visible Light Communications: 170 Mb/s Using an Artificial Neural Network Equalizer in a Low Bandwidth White Light Configuration

In this paper, we experimentally demonstrate for the first time an on off keying modulated visible light communications system achieving 170 Mb/s using an artificial neural network (ANN) based equalizer. Adaptive decision feedback (DF) and linear equalizers are also implemented and the system performances are measured using both real time (TI TMS320C6713 digital signal processing board) and offline (MATLAB) implementation of the equalizers. The performance of each equalizer is analyzed in this paper using a low bandwidth (4.5 MHz) light emitting diode (LED) as the transmitter and a large bandwidth (150 MHz) PIN photodetector as the receiver. The achievable data rates using the white spectrum are 170, 90, 40 and 20 Mb/s for ANN, DF, linear and unequalized topologies, respectively. Using a blue filter to isolate the fast blue component of the LED (at the cost of the power contribution of the yellowish wavelengths) is a popular method of improving the data rate. We further demonstrate that it is possible to sustain higher data rates from the white light with ANN equalization than the blue component due to the high signal-to-noise ratio that is obtained from retaining the yellowish wavelengths. Using the blue component we could achieve data rates of 150, 130, 90 and 70 Mb/s for the same equalizers, respectively.

Visible light communications using organic light emitting diodes

Organic VLC is an emerging subset of visible light communications that uses organic photonic components as the link transmitter, receiver or both. Recent developments in organic LEDs have enabled high efficiency and brightness devices that can be used for data transmission as in conventional VLC systems. VLC utilizes the visible wavelength range of the electromagnetic spectrum (370-780 nm). Here we demonstrate an organic VLC link using an OLED with 93 kHz bandwidth as the source and a silicon photodetector with 5 MHz bandwidth and a 10 dB gain as the receiver. A wide range of modulation schemes are examined; and, as is commonplace in communications systems, equalization techniques are implemented to maximize data rates into the megabits per second region, and 2.7 Mb/s was achieved.

Channel Characteristics of Visible Light Communications Within Dynamic Indoor Environment

Visible light communications (VLC) is a new emerging technology, which provides both data transmission and illumination by utilizing the visible range (370-780 nm) of the electromagnetic spectrum. In order to maximize the available data rate and enhance the users mobility within an indoor environment, it is essential to characterize the communication channel. In this paper, we present both analytical and experimental results for a VLC system affected by movement of people for different indoor conditions (i.e., furnished office room, empty hall, and corridor). VLC systems utilize multiple light-emitting diodes mounted in the ceiling and the configuration is based on the nondirected line of sight. We consider random movement of people within the room, focusing on the impacts of shadowing and blocking on mobility and link system performance by investigating changes in the channel characteristics using the cumulative distribution function of the received power distribution and the delay profile. We demonstrate the behaviour of communication channels for different scenarios from corridor, the most robust against people movement induced fading, to the office rooms and halls, the most vulnerable to the received power fluctuation.

Exploiting Equalization Techniques for Improving Data Rates in Organic Optoelectronic Devices for Visible Light Communications

This paper presents the use of equalization techniques in visible light communication (VLC) systems in order to increase the data rate. Here we investigate two VLC links a silicon (Si) light emitting diode (LED) and an organic photodetector (OPD), and an organic LED (OLED) plus an Si photodetector (PD), together with three equalization schemes of an RC high pass equalizer, a fractionally spaced zero-forcing equalizer (ZF) and an artificial neural network (ANN). In addition we utilize a pre-distortion scheme to enhance the performance of the digital equalizers. For both systems the bit rate achieved are 750 kb/s from a raw bandwidth (BW) of 30 kHz and 550 kb/s from a raw BW of 93 kHz.

Visible light communications: real time 10 Mb/s link with a low bandwidth polymer light-emitting diode

This paper presents new experimental results on a polymer light-emitting diode based visible light communications system. For the first time we demonstrate a 10 Mb/s link based on the on-off keying data format with real time equalization on a field programmable gate array. The 10 Mb/s transmission speed is available at a bit error rate less than 4.6 × 10(-3), which is the limit for forward error correction. At a BER of 10(-6) a transmission speed of 7 Mb/s is readily achievable.

Multi-band carrier-less amplitude and phase modulation for bandlimited visible light communications systems

Visible light communications is a technology with enormous potential for a wide range of applications within next generation transmission and broadcasting technologies. VLC offers simultaneous illumination and data communications by intensity modulating the optical power emitted by LEDs operating in the visible range of the electromagnetic spectrum (~370-780 nm). The major challenge in VLC systems to date has been in improving transmission speeds, considering the low bandwidths available with commercial LED devices. Thus, to improve the spectral usage, the research community has increasingly turned to advanced modulation formats such as orthogonal frequency-division multiplexing. In this article we introduce a new modulation scheme into the VLC domain; multiband carrier-less amplitude and phase modulation (m-CAP) and describe in detail its performance within the context of bandlimited systems.

A European view on the next generation optical wireless communication standard

Optical wireless technology uses light for mobile communications. The idea is to simultaneously combine the illumination provided by modern high-power light-emitting diodes (LEDs) with high-speed wireless communications. There have been numerous practical demonstrations of this concept, and the technology is now well matured to be deployed in practice. Independent market analysts forecast a high-volume market for mobile communication devices connected to the ubiquitous lighting infrastructure. This paper aims to make optical and wireless industries aware of the requirement for standardization in this area. The authors present the view of the European COST 1101 research network OPTICWISE towards a next-generation optical wireless standard aiming at data rates from 1 Mbit/s to 10 Gbit/s. Besides key technical insights, relevant use cases and main features are described that were recently adopted by the IEEE 802.15.7r1 working group. Moreover, a channel model is introduced to enable assessment of technical proposals.

Experimental Error Performance of Modulation Schemes Under a Controlled Laboratory Turbulence FSO Channel

This paper experimentally investigates the performance of different modulation schemes under the atmospheric turbulence conditions for free space optical communication links. The experiments were carried out in a dedicated and controlled indoor atmospheric chamber. The turbulence environment was created by introducing hot air, while the temperature profile was monitored throughout the chamber to maintain a constant environment. By evaluating the error performance of different modulation schemes under identical conditions, it was observed that pulse position modulation offers the best performance, followed by subcarrier intensity modulation under weak turbulence environments.

1.4-Mb/s White Organic LED Transmission System Using Discrete Multitone Modulation

In this letter, we experimentally demonstrate the discrete multitone (DMT) modulation scheme for organic light emitting diode-based visible light communications (OLED-VLC). DMT is based upon quadrature modulation of orthogonally spaced frequencies, meaning the scheme is extremely spectrally efficient. With this technique, we set a new world record data rate of 1.4 Mb/s, which is far in excess of the previous record of 550 kb/s. We achieve this using a 32-level quadrature amplitude modulation (32-QAM) in conjunction with 1024 subcarriers. We show that it is possible to recover signals up to 1.4 Mb/s with an OLED of bandwidth less than 100 kHz, which is an increase of over 14 times.

A Multi-CAP Visible-Light Communications System With 4.85-b/s/Hz Spectral Efficiency

In this paper, we experimentally demonstrate a multiband carrierless amplitude and phase modulation format for the first time in VLC. We split a conventional carrierless amplitude and phase modulated signal into m subcarriers in order to protect from the attenuation experienced at high frequencies in low-pass VLC systems. We investigate the relationship between throughput/spectral efficiency and m, where m = {10, 8, 6, 4, 2, 1} subcarriers over a fixed total signal bandwidth of 6.5 MHz. We show that transmission speeds (spectral efficiencies) of 31.53 (4.85), 30.88 (4.75), 25.40 (3.90), 23.65 (3.60), 15.78 (2.40), and 9.04 (1.40) Mb/s (b/s/Hz) can be achieved for the listed values of m, respectively.