Yeon-Ho Chung

Novel colour-clustered multiuser visible light communication

Visible light has a large spectral bandwidth spanning its wavelength between about 380 and 740nm. These wavelengths create a band of colours. In this study, we propose a novel multiuser MU access scheme exploiting colour bands, which we define as colour clusters. In the proposed colour-clustered MU visible light communication system, the users are allocated into separate colour clusters, and the intensity modulated user data are transmitted through the allocated coloured beams from the red, green and blue light emitting diodes. In order to increase user capacity, a secondary user separation is performed by assigning user specific intensity levels via on-off-keying modulation. At the receiver, the primary user separation is performed by a colour sensor that is capable of distinguishing the colours between red, green and blue colour bands. A secondary user separation criterion has also been proposed. The proposed MU-visible light communication VLC system is complete in that it encompasses transmission and detection methods for multiple user access while ensuring a colour-controlled flicker-free illumination. The simulations demonstrate that the proposed MU-VLC system provides an efficient MU VLC platform with significant performances over various transmission scenarios. Copyright

Color Clustered Multiple-input Multiple-output Visible Light Communication

A novel color clustered optical RGB multiple-input multiple-output (MIMO) system is presented. As visible light can be divided into three primary regions of red, green and blue, data can be modulated and transmitted separately using these three color clusters. Each color cluster comprised of 30 RGB LEDs is modulated using on-off-keying (OOK), and selection combining is performed at the receiver, producing a diversity effect within that color cluster. The simulations demonstrate that the proposed RGB MIMO VLC system provides high performance via a relatively simple design of MIMO. Moreover, the proposed system ensures sufficient illumination from LEDs and offers extended distance if more LEDs are applied.

Smart LED allocation scheme for efficient multiuser visible light communication networks

In a multiuser bidirectional visible light communication (VLC), a large number of LEDs or an LED array needs to be allocated in an efficient manner to ensure sustainable data rate and link quality. Moreover, in order to support an increasing or decreasing number of users in the network, the LED allocation is required to be performed dynamically. In this paper, a novel smart LED allocation scheme for efficient multiuser VLC networks is presented. The proposed scheme allocates RGB LEDs to multiple users in a dynamic and efficient fashion, while satisfying illumination requirements in an indoor environment. The smart LED array comprised of RGB LEDs is divided into sectors according to the location of the users. The allocated sectors then provide optical power concentration toward the users for efficient and reliable data transmission. An algorithm for the dynamic allocation of the LEDs is also presented. To verify its effective resource allocation feature of the proposed scheme, simulations were performed. It is found that the proposed smart LED allocation scheme provides the effect of optical beamforming toward individual users, thereby increasing the collective power concentration of the optical signals on the desirable users and resulting in significantly increased data rate, while ensuring sufficient illumination in a multiuser VLC environment.

Experimental Demonstration of VLC-Based Vehicle-to-Vehicle Communications Under Fog Conditions

Vehicle-to-vehicle (V2V) communication using visible light communication (VLC) technology under fog conditions is presented. Fog is known as one of the most detrimental atmospheric conditions that causes outdoor optical wireless communications to be unreliable. The effect of the fog conditions is experimentally analyzed in the VLC-based V2V system. Recognizing the least attenuation coefficient and a taillight color of a vehicle, a red light-emitting diode (LED) was employed in the experiment. In addition, a Fresnel lens and multiple photodiodes are utilized to efficiently counteract the impairment caused by fog. The experimental results demonstrate that the proposed VLC-based V2V system offers a reliable V2V data transmission over the fog-impaired optical channel with a relatively high signal-to-noise ratio (SNR), even under a heavy-fog condition.

Visible light communication based motion detection

In this paper, a unique and novel visible light communication based motion detection is presented. The proposed motion detection is performed based on white light LEDs and an array of photodetectors from existing visible light communication (VLC) links, thus providing VLC with three functionalities of illumination, communication and motion detection. The motion is detected by observing the pattern created by intentional obstruction of the VLC link. Experimental and simulation results demonstrate the validity of the proposed VLC based motion detection technique. The VLC based motion detection can benefit smart devices control in VLC based smart home environments.

PAPR reduced OFDM visible light communication using exponential nonlinear companding

In visible light communication (VLC), LEDs are used to transmit data using intensity modulation. LEDs have a limited operating voltage range and the voltage-current characteristic shows a nonlinear behavior. When an orthogonal frequency division multiplexing (OFDM) signal is used to drive these transmitter LEDs (VLC-OFDM), LED chip overheating and nonlinear distortions occur, due to high peak-to-average power ratio (PAPR) of the OFDM signal. Unlike radio frequency baseband communication systems, the VLC-OFDM signal is a real-valued signal. This would lend itself to the PAPR reduction in VLC-OFDM. In this paper, we propose to use exponential nonlinear companding transformation techniques in VLC-OFDM to reduce the PAPR. Simulation results demonstrate that with the exponential companding function employed in VLC-OFDM, the PAPR of the VLC-OFDM is significantly reduced, compared with previously considered methods.

Reduced training sequence using RLS adaptive algorithm with decision feedback equalizer in indoor Visible Light Wireless Communication channel

In this paper we present reduced training sequence in a Decision Feedback Equalizer (DFE) with Recursive Least Square (RLS) adaptive algorithm to mitigate the effect of inter-symbol interference (ISI) in an indoor Visible Light Communication (VLC) channel. We have analyzed the performance of the RLS algorithm with the DFE for the improvement of bit error rate (BER) in an indoor channel model. The wireless optical channel model consists of four sources of Light Emitting Diode (LED) transmitters that are used to illuminate the room as well as transmit data. The illumination pattern of the lights in the environment has also been considered. From this analysis, we have proven that with the proposed RLS equalizer, the training sequence can be reduced to allow more data bits to be transmitted for the identical Bit Error Rate (BER) performance.

Mobile Phone Camera-Based Indoor Visible Light Communications With Rotation Compensation

Downlink visible light communication (VLC) using a mobile phone camera is presented. The proposed scheme consists of an 8 × 8 light-emitting diode (LED) array for data transmission and eight white LEDs for an adequate level of illumination. The white LEDs are also used to acquire camera focus and light metering. Moreover, an efficient rotation compensation feature is provided in the form of a special header frame called keyframe to allow multiple users to receive the data simultaneously at 90°, 180°, and 270° orientations. Unlike conventional LED allocation methods for the rotation compensation, this keyframe-based method improves the data rate significantly. The experimental results demonstrate that the data rate achieves up to 1280 bps, whereas the theoretical simulations exhibit a potential data rate of up to 5120 bps using the identical LED array. The proposed scheme can be considered to be an efficient short-range camera-based VLC in an indoor environment with advanced features such as illumination, relatively high data rate, and robust camera rotation compensation for multiuser access.

3-Gbit/s Indoor Visible Light Communications Using Optical Diversity Schemes

A 3-Gb/s high-speed indoor visible light communication system using optical diversity schemes is presented. A double optical diversity (DOD) scheme in time and frequency is employed with selection combining (SC) on the basis of red, green, and blue (RGB) light-emitting diodes (LEDs). In the proposed scheme, the original data and the delayed versions of this data are transmitted simultaneously by multiplying with orthogonal frequency in order to create diversity effect over the transmission. In addition, RGB LEDs are used for parallel transmission of data, thus resulting in an increase in the data speed. At the receiver, color filters are used to filter out for the desired signal, and SC is performed to obtain the most probable bits. Simulation results demonstrate that the proposed scheme is robust and efficient to overcome the effect of multiple reflections with a link margin of approximately 10 dB, as compared with a conventional on-off keying (OOK) modulation scheme at a bit error rate (BER) of 10-6. Moreover, the scheme achieves a data rate of 3 Gb/s with a BER of 10-6 at a signal-to-noise ratio (SNR) value of 3.6 dB over most locations in an indoor visible light communication (VLC) environment.

Experimental Biomedical EEG Signal Transmission Using VLC

The proliferation of radio frequency (RF) communication technology in biomedical signal transmission is frequently flustered by electromagnetic interference. Even though the flexibility and mobility of RF-based communication have much attraction, the radiation brings damage to hospital equipments and even harm to humans. In this letter, we propose a novel scheme for transmission of electroencephalography (EEG) biomedical signal using a visible light communication (VLC) link. The data transmission is performed in line of sight (LOS) condition using ON-OFF keying nonreturn-to-zero modulation by utilizing all three components, red, green, and blue, of RGB LED. Experiments are carried out for transmitting EEG signals using the VLC link. The transmitter consists of RGB LEDs, and at the receiver side, three photodiodes with red, green, and blue color filters are installed. The experimental results show excellent reliability and accuracy of the proposed scheme.