Dae-Kwang Jung

High data rate multiple input multiple output (MIMO) optical wireless communications using white led lighting

Solid-state lighting is a rapidly growing area of research and applications, due to the reliability and predicted high efficiency of these devices. The white LED sources that are typically used for general illumination can also be used for data transmission, and Visible Light Communications (VLC) is a rapidly growing area of research. One of the key challenges is the limited modulation bandwidth of sources, typically several MHz. However, as a room or coverage space would typically be illuminated by an array of LEDs there is the potential for parallel data transmission, and using optical MIMO techniques is potentially attractive for achieving high data rates. In this paper we investigate non-imaging and imaging MIMO approaches: a non-imaging optical MIMO system does not perform properly at all receiver positions due to symmetry, but an imaging based system can operate under all foreseeable circumstances. Simulations show such systems can operate at several hundred Mbit/s, and up to Gbit/s in many circumstances.

100-Mb/s NRZ Visible Light Communications Using a Postequalized White LED

This letter describes a high-speed visible light communications link that uses a white-light light-emitting diode (LED). Such devices have bandwidths of few megahertz, severely limiting the data rates of any communication system. Here, we demonstrate that by detecting only the blue component of the LED, and using a simple first-order analogue equalizer, a data rate of 100 Mb/s can be achieved using on-off keying nonreturn-to-zero modulation.

High-Speed Visible Light Communications Using Multiple-Resonant Equalization

White light-emitting diodes (LEDs) are becoming widespread in commercial lighting applications, and there are predictions that they will be in common use in domestic applications in the future. There is also growing interest in using these devices for both illumination and communications. One of the major challenges in visible light communications is the low modulation bandwidth (BW) available from devices, which is typically several megahertz. In this letter, we describe a link that uses 16 LEDs which are modulated using a resonant driving technique, creating an overall BW of 25 MHz. This is used to implement a 40-Mb/s nonreturn-to-zero on-off keying link which operates at low error rates, and also provides illumination at levels sufficient for a standard office environment.

OSNR monitoring technique using polarization-nulling method

We report on the simple technique for monitoring the optical signal-to-noise ratios (OSNRs) of wavelength-division-multiplexed (WDM) signals. This technique, based on the polarization-nulling method, was implemented simply by using a rotating quarter-wave plate and rotating linear polarizer. However, the performance of this technique could be affected by nonlinear birefringence and polarization-mode dispersion (PMD). The result shows that this technique is suitable for monitoring the OSNRs of highspeed (>10-Gb/s) WDM signals transported over the fiber link with low PMD.

Indoor visible light communications: challenges and prospects

The rapid improvement in the efficiency of solid-state lighting has led to predictions that it will be the dominant source used for most indoor lighting applications in the future. At present an attractive candidate for generating white-light are blue LEDs that excite a yellow phosphor, with a resultant colour emission. Such solid state sources can be used for both illumination and communications simultaneously, offering the possibility of creating wireless broadcasting within a room or office space. In this paper we outline a typical basic configuration, and the performance available using simple modulation schemes. Unmodified LEDs typically have modulation bandwidths of several MHz, but typical lighting levels provide a communications channel with a Signal to Noise Ratios in excess of 40dB. Techniques such as equalisation can be used to improve available data rate significantly, and in this paper we outline several approaches that have the potential to offer data rates of 100Mb/s and above.

Improvement of Date Rate by using Equalization in an Indoor Visible Light Communication System

In this paper, an optical wireless communication system that uses white LEDs is described. Equalization is employed at the receiver to improve the data rate. Simulation shows a highly reliable communication channel with an SNR of up to 81 dB. Moreover, the data rate can be improved from 16 Mb/s to 32 Mb/s NRZ-OOK at a BER of 10-6.

80 Mbit/s Visible Light Communications using pre-equalized white LED

This paper reports an 80 Mbit/s OOK-NRZ visible light communications experimental link using a single pre-equalized 45-MHz bandwidth white LED.

Equalisation for high-speed Visible Light Communications using white-LEDs

The performance of visible light communications (VLC) system that uses white LEDs is limited by the bandwidth of the LED emitters. In this paper we report LED equalisation techniques that can improve the data transmission rate in VLC systems significantly. Equalisation is employed in the VLC transmitter and receiver and both experiment and simulation results show a significant improvement in the OOK-NRZ data rate when compared with the unequalised devices. This increases from 15 Mbit/s to 75 Mbit/s, whilst maintaining a low bit error rate (BER).

Reduction of polarization-induced performance degradation in WDM PON utilizing MQW-SLD-based broadband source

We report on the reduction of polarization-induced performance degradation in WDM PON utilizing MQW-SLD-based ASE source for injection locking to FPLD. The results show that, to suppress the polarization-induced Q penalty sufficiently less than 0.5 dB, the MQW-SLD output should be depolarized within the locking range of the wavelength-locked FPLD.

VLC transceiver design for short-range wireless data interfaces

We define the requirement of the visible-light communication (VLC) transceiver for bidirectional high-speed and short-range communications and examine its practicability. VLC transceivers were implemented with edge-emitting laser diode and silicon photo diode, designed primarily to operate in a full duplex mode at 120 Mbit/s. The design of an optical antenna was also included in this paper, which is to alleviate the performance degradation due to tilting. Their bit error rate performance was examined experimentally with respect to the transmission distance, the coverage range and the tilt degree.