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Analysis of Non-Hermitian symmetry (NHS) IFFT/FFT size efficient OFDM for multiple-client non-orthogonal multiple access (NOMA) visible light communication (VLC) system
(2020-10-01)
Adnan, Assaidah
;
Liu, Yang
;
Chow, Chi-Wai
;
Yeh, Chien-Hung
;
交大名義發表
Orthogonal-frequency-division-multiplexing (OFDM) format is widely deployed in visible-light-communication (VLC) systems due to its high spectral efficiency. To produce real-valued OFDM signal for VLC, Hermitian-symmetry (HS) is needed during the inverse-fast-Fourier-transform (IFFT) encoding process. However the HS requirement doubles the IFFT/FFT size and increase the encoding complexity. Non-Hermitian symmetry (NHS)-OFDM schemes are proposed, but they have different limitations. In this work, we propose and investigate a non-orthogonal multiple access (NOMA) VLC network serving 2, 3 or 4 clients simultaneously using NHS-OFDM IFFT/FFT size efficient (SE) OFDM format. Numerical analysis of signal amplitude effect to the bit-error-ratio (BER) performance for different users are performed, showing that the BER < 7% forward-error-correction (FEC) limit can be achieved as long as the required signal amplitude ratio of each user is fulfilled. We also compare the proposed system with a typical example of HS-OFDM modulation, i.e. direct-current optical (DCO)-OFDM NOMA-VLC system.
Angle-of-Arrival (AOA) Visible Light Positioning (VLP) System Using Solar Cells With Third-Order Regression and Ridge Regression Algorithms
(2020-06-01)
Hong, Chong-You
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Wu, Yu-Chun
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Liu, Yang
;
Chow, Chi-Wai
;
Yeh, Chien-Hung
We put forward and demonstrate a angle-of-arrival (AOA) based visible-light-positioning (VLP) system using quadrant-solar-cell (QSC) and third-order ridge regression machine learning (RRML) to improve the positioning accuracy.
Demonstration of Non-Hermitian Symmetry (NHS) IFFT/FFT Size Efficient OFDM Non-Orthogonal Multiple Access (NOMA) for Visible Light Communication
(2020-06-01)
Assaidah, Assaidah
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Liu, Yang
;
Chow, Chi-Wai
;
Yeh, Ching-Hua
;
交大名義發表
We propose and experimentally demonstrate a non-orthogonal multiple access (NOMA) visible light communication (VLC) system using non-Hermitian symmetry (NHS) inverse-fast-Fourier-transform (IFFT)/FFT size efficient (SE) orthogonal frequency division multiplexing (OFDM). Fix power allocation and successive interference cancellation (SIC) algorithms are realized. The power ratio between different users, transmission distance, network cell coverage are investigated. The proposed scheme is also compared with the HS based direct-current optical (DCO)-OFDM NOMA-VLC system.
Beacon Jointed Packet Reconstruction Scheme for Mobile-Phone Based Visible Light Communications Using Rolling Shutter
(2017-12-01)
Wang, Wei-Chung
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Chow, Chi-Wai
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Chen, Chia-Wei
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Hsieh, Hsiang-Chain
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Chen, Yen-Ting
Mobile-phone based visible light communication (VLC) is an attractive method for optical wireless communication. However, the data rate is typically limited by the complementary metal-oxide-semiconductor image sensor frame rate and the processing time gap in the rolling shutter mode operation. Here, we propose and demonstrate a packet-reconstruction scheme, known as beacon jointed rolling shutter pattern scheme. The mobile-phone based VLC data rate can be increased to a record 10.32 kb/s. The implementation algorithm is discussed; and the bit-error-rate experimental evaluations at different transmission distances and horizontal offsets are performed.
Adaptive Thresholding Scheme for Demodulation of Rolling-Shutter Images Obtained in CMOS Image Sensor Based Visible Light Communications
(2018-12-01)
Chow, Chi-Wai
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Liu, Yen-Chun
;
Shiu, Ruei-Jie
;
Yeh, Chien-Hung
;
光電工程學系
Light-emitting-diode transmitter and complementary-metal-oxide-semiconductor (CMOS) image sensor receiver based visible light communication is a promising scheme for an optical wireless communication. During the demodulation of the rolling shutter pattern obtained from the CMOS image sensor Rx, due to the high signal fluctuation introduced by the uneven light exposure, special thresholding schemes are needed to correctly identify the data logic. In this work, we propose and demonstrate a modified adaptive scheme (MQA) for the demodulation of the rolling shutter pattern. Experimental bit-errorratio (BER) measurements using different thresholding schemes at different illuminance are analyzed. The results show that the proposed MQA scheme can provide much lower BER, with similar process latencies when compared with other schemes.
Decoding CMOS Rolling-Shutter Pattern in Translational or Rotational Motions for VLC
(2019-04-01)
Chow, Chi-Wai
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Li, Zhi-Qing
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Chuang, Yu-Cheng
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Liao, Xin-Lan
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Lin, Kun-Hsien
We propose and demonstrate a CMOS rolling-shutter pattern decoding scheme based on two newly introduced schemes, named row grayscale redistribution and differential grayscale packet selection to improve the performance in decoding the CMOS rolling-shutter pattern in translational or rotational motions. Results show that even the CMOS image sensor is in translational or rotational motions, no significant signal degradation is observed at wireless transmission distance up to 150 cm. The maximum visible light communication data rate at different wireless transmission distances is also analyzed.
Secure Mobile-Phone Based Visible Light Communications With Different Noise-Ratio Light-Panel
(2018-04-01)
Chow, Chi-Wai
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Shiu, Ruei-Jie
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Liu, Yen-Chun
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Yeh, Chien-Hung
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Liao, Xin-Lan
We propose and demonstrate a visible light communication (VLC) system using a light-panel and a mobile-phone camera. We also propose the rolling-shutter-effect (RSE) pattern synchronization and demodulation algorithms. By using our developed mobile-phone application program, the RSE pattern can be demodulated even at very low illuminance. As the light-panel will have different advertisements on it, we also define a noise-ratio (NR) as the figure-of-merit; hence, different VLC data rates can be adjusted according to different advertisement NR values. Experimental bit error rate measurements at different free-space transmission distances and different NRs are performed.
Performance enhancement technique of visible light communications using passive photovoltaic cell
(2017-06-01)
Wu, Jhao-Ting
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Chow, Chi-Wai
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Liu, Yang
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Hsu, Chin-Wei
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Yeh, Chien-Hung
The light emitting diode (LED) based visible light communication (VLC) system can provide lighting and communication simultaneously. It has attracted much attenuation recently. As the photovoltaic cell (also known as solar cell) is physically flexible, low cost, and easily available, it could be a good choice for the VLC receiver (Rx). Furthermore, besides acting as the VLC Rx, the solar cell can convert VLC signal into electricity for charging up the Rx devices. Hence, it could be a promising candidate for the future internet-of-thing (IoT) networks. However, using solar cell as VLC Rx is challenging, since the response of the solar cell is highly limited and it will limit the VLC data rate. In this work, we propose and demonstrate for the first time using pre-distortion Manchester coding (MC) signal to enhance the signal performance of solar cell Rx based VLC. The proposed scheme can significantly mitigate the slow response, as well as the direct-current (DC) wandering effect of the solar cell; hence 50 times increase in data rate can be experimentally achieved.
Using pre-distorted PAM-4 signal and parallel resistance circuit to enhance the passive solar cell based visible light communication
(2018-01-15)
Wang, Hao-Yu
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Wu, Jhao-Ting
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Chow, Chi-Wai
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Liu, Yang
;
Yeh, Chien-Hung
Using solar cell (or photovoltaic cell) for visible light communication (VLC) is attractive. Apart from acting as a VLC receiver (Rx), the solar cell can provide energy harvesting. This can be used in self-powered smart devices, particularly in the emerging "Internet of Things (IoT)'' networks. Here, we propose and demonstrate for the first time using pre-distortion pulse-amplitude-modulation (PAM)-4 signal and parallel resistance circuit to enhance the transmission performance of solar cell Rx based VLC. Pre-distortion is a simple non-adaptive equalization technique that can significantly mitigate the slow charging and discharging of the solar cell. The equivalent circuit model of the solar cell and the operation of using parallel resistance to increase the bandwidth of the solar cell are discussed. By using the proposed schemes, the experimental results show that the data rate of the solar cell Rx based VLC can increase from 20 kbit/s to 1.25 Mbit/s (about 60 times) with the bit error-rate (BER) satisfying the 7% forward error correction (FEC) limit. (C) 2017 Elsevier B.V. All rights reserved.
Demonstration of Using Digital FIR Filter and Matched Filter to Increase Data Rate in Visible Light Communication
(2013)
Liu, Yu-Feng
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Yeh, Chien-Hung
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Chow, Chi-Wai
;
Huang, Po-Yen
;
Liu, Yang
Using digital-filters in time domain are demonstrated to enhance the modulation-speed of 1 MHz bandwidth white LED communication. Digital FIR filter and matched filtering are used to reduce the inter-symbol-interference (ISI). Hence, 20-Mbps is achieved by using 4-ASK modulation.

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