Browsing by Author "Liu, Y. F."

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AC-based phosphor LED visible light communication by utilizing novel signal modulation
(2013-10-01)
Liu, Y. F.
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Yeh, C. H.
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Chow, C. W.
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Liu, Y. L.
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光電工程學系
We propose and demonstrate a new AC-light emitting diode based visible light communication system, in which the message signal is up-converted to 400 kHz frequency band and combine with the 60 Hz AC-power from the outlet. A special design bias-tee circuit is first implemented to combine the message signal and the AC-power for minimizing the signal distortion. Thus, the spectra of both signals are well separated. A special design clock recovery is used to synchronize the AC-power with the message signal; hence the message signal can be correctly applied to the rectified AC-power cycle.
Adaptive Control of OFDM Data Rate for LED Visible Light Communications in Different Free Space Transmission Distances and Offsets
(2012)
Liu, Y. F.
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Yeh, C. H.
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Chow, C. W.
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Liu, Y.
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光電工程學系
Using orthogonal-frequency-division-multiplexing (OFDM) for light-emitting-diode (LED) visible-light-communication (VLC) is a promising approach. Here we demonstrate an LED communication link with adaptive control of the OFDM data rate for different communication environments.
Adaptive scheme for maintaining the performance of the in-home white-LED visible light wireless communications using OFDM
(2013-04-01)
Chow, C. W.
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Yeh, C. H.
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Liu, Y. F.
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Huang, P. Y.
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Liu, Y.
Spectral-efficient orthogonal frequency division multiplexing (OFDM) is a promising modulation format for the light-emitting-diode (LED) optical wireless (OW) visible light communication (VLC). VLC is a directional and line-of-sight communication; hence the offset of the optical receiver (Rx) and the LED light source will result in a large drop of received optical power. In order to keep the same luminance of. the LED light source, we propose and demonstrate an adaptive control of the OFDM modulation-order to maintain the VLC transmission performance. Experimental results confirm the feasibility of the proposed scheme. (C) 2012 Elsevier B.V. All rights reserved.
Alternating-Signal-Biased System Design and Demonstration for Visible Light Communication
(2013-08-01)
Liu, Y. F.
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Yeh, C. H.
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Chow, C. W.
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光電工程學系
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Department of Photonics
In the literature, previous system designs are mainly focused on the use of direct-current light-emitting diodes (DC-LEDs) with fixed voltage bias. As alternating-current (AC)-LEDs are more energy efficient and becoming more and more popular, a driving system supporting AC-LEDs providing lighting and visible light communication (VLC) functions is highly desirable. This paper investigates the alternating-signal-biased system design for VLC, which combines the AC bias voltage signal and electrical data signal to modulate both DC-and AC-LEDs. In the experiment, a 40-LED array is modulated by our proposed system that makes use of current from AC power source while maintaining nondistorted message signal transmission. On-off-keying and quadrature-phase-shift-keying formats are used, and data rates of 60 and 120 kb/s are demonstrated, respectively. The threshold voltage effect and the system extension to support AC-LED are discussed. The alternating-signal-biased system design supporting both DC-and AC-LEDs is also discussed.
Background Optical Noises Circumvention in LED Optical Wireless Systems Using OFDM
(2013-04-01)
Chow, C. W.
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Yeh, C. H.
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Liu, Y. F.
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Huang, P. Y.
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光電工程學系
Background optical noises generated by the conventional fluorescent light sources or AC-power light-emitting diode (LED) can significantly affect the performance of the LED optical wireless communication and produce challenges to implementation. We demonstrate using orthogonal frequency division multiplexing (OFDM) to effectively circumvent the optical background noises. Besides, by using simple equalization at the receiver side, the transmission capacity can be extended from 1 Mb/s to 12 Mb/s. The theory and analysis of the equalization are presented. Experiments at different data rates and different OFDM subcarriers are preformed, and results show that, by adjusting the number of OFDM subcarriers, the influence of the background optical noises can be significantly circumvented.
Carrier Distributed PON Using SSB-CS Signal for Rayleigh Backscattering Suppression
(2010)
Chow, C. W.
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Yeh, C. H.
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Liu, Y. F.
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Wang, C. H.
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Wu, C. L.
We demonstrate using single-sideband-carrier-suppressed (SSB-CS) signal to suppress the Rayleigh-Backscattering (RB) in a carrier-distributed PON. The SSB signal is generated by a dual-parallel Mach-Zehnder modulator (DP-MZM). The split-ratio and reach are also investigated and analyzed.
Demonstration of bi-directional LED visible light communication using TDD traffic with mitigation of reflection interference
(2012-10-08)
Liu, Y. F.
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Yeh, C. H.
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Chow, C. W.
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Liu, Y.
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Liu, Y. L.
In this work, we experimentally demonstrate a bi-directional transmission link using light emitting diode (LED) visible light communication (VLC) for both downlink and uplink paths. Time-division-duplex (TDD) is proposed and demonstrated to significantly eliminate the reflection interference in VLC. A free space bi-directional transmission of 2 m using simple on-off keying (OOK) modulation with bit error rate (BER) of < 10(-5) in both directions are achieved. Moreover, the influence of reflection interference is analyzed, showing the proposed scheme can significantly eliminate the reflection interference. (C) 2012 Optical Society of America
Equalization and Pre-distorted Schemes for Increasing Data Rate in In-door Visible Light Communication System
(2011)
Liu, Y. F.
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Chang, Y. C.
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Chow, C. W.
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Yeh, C. H.
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光電工程學系
We propose and demonstrate using signal pre-distortion and equalization schemes for increasing the data rate of the white-light LED communication system. Bit-error-rate of <10(-10) at 10-Mb/s operation was achieve using 1-MHz bandwidth white-light LED. (C) 2011 Optical Society of America
Improved modulation speed of LED visible light communication system integrated to main electricity network
(2011-07-21)
Chow, C. W.
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Yeh, C. H.
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Liu, Y. F.
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Liu, Y.
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光電工程學系
In addition to the illumination purpose, using a light-emitting diode (LED) for indoor optical wireless communication has attracted much attention recently. Proposed and demonstrated is the use of a simple on-off keying (OOK) predistortion scheme together with a simple first-order resistance-capacitance equalisation circuit to increase the modulation speed of a white-light high-brightness LED (HB-LED). Optical filtering and complicated modulation formats are not required. Since only OOK modulation is used, the signal modulation and detection are very simple. Also are compared the different combinations of the system designs. By using first-order equalisation together with a predistortion, a bit-error rate of <10(-10) at 10 Mbit/s can be easily achieved when using the 1 MHz bandwidth phosphor-based white HB-LED.
Investigation of 4-ASK modulation with digital filtering to increase 20 times of direct modulation speed of white-light LED visible light communication system
(2012-07-16)
Yeh, C. H.
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Liu, Y. F.
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Chow, C. W.
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Liu, Y.
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Huang, P. Y.
In this demonstration, we propose and experimentally investigate the quaternary-amplitude-shift-keying (4-ASK) modulation with digital filtering to enhance the direct modulation speed of white-light light-emitting-diode (LED) in visible light communication (VLC) system. Here, an ordinary LED commercially available for lighting application with a direct modulation speed of 1 MHz is used. Data rate of 20 Mbit/s can be achieved in a 1 m free space transmission without using optical blue filter. In the previous studies, the transmission rate of LED VLC could only be increased by 2 to 10 times of the direct modulation speed of the white-light LED if using electrical equalization only. Moreover, the adaptive-controlled FIR filter makes the system closer to the matched filtering condition for reducing the inter-symbol-interference (ISI) for the LED VLC. A recorded 20 times enhancement of the direct modulation speed of white-light LED VLC system is demonstrated by using digital filter only and without using optical blue filter. (C) 2012 Optical Society of America
LED-based Visible Light Communication Integratable to Main Power Line Network with Optical Background Noises Mitigation
(2014-01-01)
Chow, C. W.
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Yeh, C. H.
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Hsu, C. W.
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Huang, P. Y.
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Liu, Y. F.
Optical background noises from conventional fluorescent light sources can significantly affect the performance of the light emitting diode (LED)-based visible light communication (VLC). We demonstrate a LED-based VLC system that is integratable to the main power line network. By using orthogonal-frequency-division-multiplexing (OFDM) format, the optical background noises can be mitigated. Experimental results show that by adjusting the number of OFDM subcarriers, the influence of optical background noises can be significantly mitigated.
Mitigation of Optical Background Noise in Light-Emitting Diode (LED) Optical Wireless Communication Systems
(2013-02-01)
Chow, C. W.
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Yeh, C. H.
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Liu, Y. F.
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Huang, P. Y.
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光電工程學系
One challenge faced by the in-home light-emitting diode (LED) optical wireless communication is the optical noises. Here, we first experimentally characterize the effect of optical background noise to the performance of the LED optical wireless communication channel. We demonstrate using Manchester coding for the LED to mitigate the optical noise. No adaptive monitoring, feedback, or optical filtering is required. The theoretical and numerical analysis of Manchester decoding process to mitigate the optical background noise is provided. Our experimental result shows that Manchester coding can significantly eliminate optical noise generated by the AC-LED operated at < 500 kHz and fluorescent light.
Simple digital FIR equalizer design for improving the phosphor LED modulation bandwidth in visible light communication
(2013-08-01)
Yeh, C. H.
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Chow, C. W.
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Liu, Y. F.
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Huang, P. Y.
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光電工程學系
We propose and demonstrate a simple digital post-equalization technique to improve the bandwidth-limitation of light-emitting-diode (LED) visible-light-communication (VLC) channel. The design of finite-impulse-response equalizer according to the channel response is presented to improve the bandwidth limitation of LED VLC channel. Here, no optical blue filter is used. The simulation and experimental results show 10 times enhancement of the direct modulation speed of white-light LED VLC system. When compares with the previous demonstration using high-pass equalization circuit constructed by lumped capacitor and resistor, the proposed scheme shows an improvement in signal quality and transmission distance, and a 10 Mbit/s error-free free-space transmission over 1 m can be achieved under the bit error rate of .