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Visible Light Communication Using Receivers of Camera Image Sensor and Solar Cell
(2016-02-01)
Liu, Yang
;
Chen, Hung-Yu
;
Liang, Kevin
;
Hsu, Chin-Wei
;
Chow, Chi-Wai
We propose an electronic label and sensor system using visible light communication (VLC). The downlink signal is transmitted by a white-light light-emitting diode (LED) lamp that can provide lighting, VLC, and energy harvesting for mobile devices. The downlink is received by a solar cell. The uplink can be captured by a surveillance camera image sensor. However, using the camera image sensor as a VLC receiver (Rx) is challenging since the data rate is limited by the frame rate and due to uneven light exposure. The rolling shutter effect of the image sensor can be used to increase the data rate. In this paper, we propose and demonstrate how to demodulate the obtained rolling shutter pattern using a second-order polynomial (SOP) extinction ratio (ER) enhancement scheme, together with iterative and modified quick adaptive thresholding schemes. The ER enhancement scheme can significantly reduce the large ER fluctuation. Experimental results show that by using the proposed SOP ER enhancement scheme, the bit error rate (BER) improvement can be up to two orders of magnitude. We also believe that the proposed electronic label and sensor system may be applicable to Internet-of-Things sensing networks for connecting a number of mobile devices.
Light Encryption Scheme Using Light-Emitting Diode and Camera Image Sensor
(2016-02-01)
Liu, Yang
;
Liang, Kevin
;
Chen, Hung-Yu
;
Wei, Liang-Yu
;
Hsu, Chin-Wei
Visible light communication (VLC) is regarded as relatively secure communication when compared with other wireless communications using radio frequency (RF). However, due to the visual nature, the VLC signals are still subject to eavesdropping when they are emitted by the light source. Here, we propose a light encryption scheme using devices having light-emitting diode (LED) and a camera image sensor, such as a mobile phone. The original visible signal sending from the lamp can be first received by the proposed light encrypter. The information can be encrypted and then emitted. The light encrypter acts as an encryption gateway for signals in optical domain. The rolling shutter effect of the complementary metal-oxide semiconductor (CMOS) camera in the mobile phone can be used. By demodulating the rolling shutter pattern, the data information can be obtained. We also propose and demonstrate using the Otsu thresholding scheme to define the data logic in the rolling shutter pattern. We show that the Otsu scheme is effective for estimating the bit error rate (BER). The optimum number of intervals (segmentations) and the process time of the Otsu method are also studied.
Network Architecture of Bidirectional Visible Light Communication and Passive Optical Network
(2016-06-01)
Chow, Chi-Wai
;
Yeh, Chien-Hung
;
Liu, Yang
;
Hsu, Chin-Wei
;
Sung, Jiun-Yu
Network architectures to combine the fiber network outside the building and the visible light communication (VLC) access network inside the building are important for effectively distributing the high-capacity data to different users. In this paper, we propose a bidirectional network combining the VLC access network and the time-wavelength-division-multiplexed passive optical network (TWDM-PON). Orthogonal frequency division multiplexed modulation is used since it offers high spectral efficiency for both the TWDM-PON and the VLC access network. Low-cost phosphor-based white-light light-emitting diodes are (LEDs) used; hence, the VLC access network can combine with the lighting systems.
Color-Shift Keying and Code-Division Multiple-Access Transmission for RGB-LED Visible Light Communications Using Mobile Phone Camera
(2014-12-01)
Chen, Shih-Hao
;
Chow, Chi-Wai
;
光電工程學系
;
光電工程研究所
;
Department of Photonics
Light-emitting diodes (LEDs) have been deployed for various applications in our daily lives. Similarly, image sensors or cameras integrated into mobile phones have become common. Hence, visible light communication (VLC) using LED and mobile phone cameras is attractive and provides low-cost wireless communication. In this paper, we propose and demonstrate a VLC system using color-shift-keying (CSK) modulation and code-division multiple-access (CDMA) technology simultaneously for the first time; a mobile phone camera is used as the receiver (Rx). CSK is used to enhance the VLC system capacity and to mitigate the single color light interference, whereas CDMA allows multiple users to access the network. The system design and operation mechanism of the proposed CSK-CDMA VLC system are discussed. A proof-of-concept demonstration is performed, and error-free transmission is achieved for multiple-access users. A 3-dB transmission gain is also obtained in each user when compared with the traditional on-off keying (OOK) modulation.
Enhancement of Signal Performance in LED Visible Light Communications Using Mobile Phone Camera
(2015-10-01)
Chow, Chi-Wai
;
Chen, Chung-Yen
;
Chen, Shih-Hao
;
光電工程學系
;
光電工程研究所
Visible light communication (VLC) is attractive as a supplementary method for future fifth-generation (5G) wireless communication owing to the shortage of radio-frequency bandwidth in conventional wireless communications. The VLC systems reported in the literature are mainly based on PIN receivers (Rxs). It is highly desirable if these VLC signals can be detected by using built-in complementary metal-oxide-semiconductor (CMOS) cameras as Rxs to provide flexible and low-cost wireless communications. However, using the CMOS camera is challenging. In this paper, we propose and demonstrate a VLC link using a CMOS mobile phone camera as Rx. By using the rolling shutter effect of the CMOS sensor, the VLC data rate can be significantly enhanced. We first use a second-order polynomial fitting to mitigate the "blooming effect" (saturation of pixels) of the CMOS sensor. In order to extend the VLC transmission distance and mitigate the influence of the background noise, we also propose and demonstrate using histogram equalization and Sobel filter to enhance VLC signal performance. Finally, a third-order polynomial fitting is used to define the threshold. The experimental results show that significant improvement of bit error rate (BER) for about an order of magnitude under different illuminances can be achieved.
Design of Visible Light Communication System for Maintaining Uniform Data Rate
(2014-01-01)
Sung, Jiun-Yu
;
Lin, Wan-Feng
;
Wu, Yu-Fu
;
Chow, Chi-Wai
;
Yeh, Chien-Hung
Light-emitting diode (LED) is gradually replacing the fluorescent lamp for lighting. Higher modulation bandwidth of LEDs makes the additional application of visible light communication (VLC) possible. Every location of a VLC system should be provided by equal data rate for smooth communication. However, locations away from the LED lamp have less power. These low-power locations have lower signal-to-noise ratio (SNR); and hence lower data rate can be achieved. For achieving high capacity VLC, strategies should be adequately provided to mitigate this problem. Moreover, for some real-time continuous applications, such as video and voice, latency reduction plan should also be considered. In this paper, an orthogonal frequency-division multiplexing access (OFDMA) based system was proposed to solve the above problem. Because we do not use time-division multiplexing access (TDMA) based system, the latency issue can be reduced. The OFDMA based system is also beneficial for large scale operation because the user bandwidth is not reduced by TDM mechanism. Signal-to-noise-plus-interference ratio (SNIR) distribution of the VLC system is designed to ensure uniform and optimal system capacity. Discrete multi-tone (DMT) is used for this VLC system. The DMT subcarriers are bit-loaded depending on the LED frequency response. More subcarriers are allocated for communication at low SNIR locations. Hence, nearly equal data rate can be provided everywhere. Demonstration of 17 Mb/s/LED data rate was provided.
Improvement of brightness uniformity by AC driving scheme for AMOLED display
(2004-11-01)
Lin, YC
;
Shieh, HPD
;
光電工程學系
;
Department of Photonics
We propose an ac voltage driving scheme which can improve the brightness uniformity of active-matrix organic light-emitting diode (AMOLED) displays. Through the use of a charge feed-through mechanism and an ac driving voltage, the voltage drop caused by the parasitic resistance can be compensated. A 2.2 in AMOLED panel with a resolution of 176 x RGB x 220 has been fabricated by low temperature polycrystalline silicon technology to evaluate the performance of the ac driving scheme. Experimental results show that a brightness uniformity of higher than 91.6%, achieved by the ac driving scheme, in contrast to that of 74% achieved by a dc driving scheme.
Light-output enhancement in a nitride-based light-emitting diode with 22 degrees undercut sidewalls
(2005-01-01)
Kao, CC
;
Kuo, HC
;
Huang, HW
;
Chu, JT
;
Peng, YC
We successfully fabricated nitride-based light-emitting diodes (LEDs) with similar to 22degrees undercut sidewalls. The similar to 22degrees etching undercut sidewalls were achieved by controllable inductively coupled plasma reactive ion etching. With a 20-mA current injection, the output powers of the LED with similar to 22degrees undercut sidewalls and standard LED were 5.1 and 3 mW, respectively-a factor of 1.7 times enhancement. It was found that such undercut sidewalls could enhance the probability of escaping the photons outside from the LED in the near horizontal and in-plane directions. This simple and controllable method is beneficial to fabricate brighter LEDs.
Background Optical Noises Circumvention in LED Optical Wireless Systems Using OFDM
(2013-04-01)
Chow, C. W.
;
Yeh, C. H.
;
Liu, Y. F.
;
Huang, P. Y.
;
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.
Mitigation of Optical Background Noise in Light-Emitting Diode (LED) Optical Wireless Communication Systems
(2013-02-01)
Chow, C. W.
;
Yeh, C. H.
;
Liu, Y. F.
;
Huang, P. Y.
;
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.

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