Chin-Wei Hsu

Visible Light Communication Using Receivers of Camera Image Sensor and Solar Cell

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.

Visible Light Positioning and Lighting Based on Identity Positioning and RF Carrier Allocation Technique Using a Solar Cell Receiver

We propose and experimentally demonstrate an indoor positioning system which combines identity positioning and the radio frequency carrier allocation technique in order to reduce the signal interference from nearby light-emitting diodes (LEDs) and improve the accuracy of positioning. In addition, the solar cell is used as an optical receiver for the visible light positioning system. Due to the benefits of solar cells such as low-cost, high light sensitivity, and ease in integration with wearable devices, the proposed system could be an energy-efficient and environmentally friendly choice for indoor positioning in the future.

Light Encryption Scheme Using Light-Emitting Diode and Camera Image Sensor

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.

Comparison of thresholding schemes for visible light communication using mobile-phone image sensor

Based on the rolling shutter effect of the complementary metal-oxide-semiconductor (CMOS) image sensor, bright and dark fringes can be observed in each received frame. By demodulating the bright and dark fringes, the visible light communication (VLC) data logic can be retrieved. However, demodulating the bright and dark fringes is challenging as there is a high data fluctuation and large extinction ratio (ER) variation in each frame due. Hence proper thresholding scheme is needed. In this work, we propose and compare experimentally three thresholding schemes; including third-order polynomial curve fitting, iterative scheme and quick adaptive scheme. The evaluation of these three thresholding schemes is performed.

High Speed Imaging 3 × 3 MIMO Phosphor White-Light LED Based Visible Light Communication System

The phosphor light-emitting diode (LED) has been widely used not only for indoor illumination but for the optical transmitter (Tx) as well in visible light communication (VLC). However, the transmission data rate is significantly limited by the modulation bandwidth of LED because of the low-speed response of phosphor. In order to enhance the data rate of the VLC system, we demonstrate a 3 × 3 imaging multiple-input multiple-output (MIMO) VLC system. Besides, the pre-equalizer circuit is used to extend the bandwidth of the LED Tx. Orthogonal frequency division multiplexing (OFDM) with bit-loading algorithm is used. By using the proposed scheme, the original 1 MHz bandwidth commercially available phosphor white light LED can achieve 1 Gbps data rate over 1-m free-space transmission distance.

Narrow line-width single-longitudinal-mode fiber laser using silicon-on-insulator based micro-ring-resonator

In this work, we propose and demonstrate a stable single-longitudinal-mode (SLM) fiber laser with narrow line-width by using an integrated silicon-on-insulator micro-ring resonator (SOI MRR) and two subsidiary fiber rings for the first time, to the best of our knowledge. The laser is tunable over the wavelength range from 1546 to 1570 nm, with only step tuning of 2 nm steps. A maximum 49 dB side mode suppression ratio (SMSR) can be achieved. The compact SOI MRR provides a large free-spectral-range (FSR), while the subsidiary rings provide Vernier effect producing a single lasing mode. The FSR of the SOI MRR can be very large and controllable (since it is easy to fabricate small SOI MRR when compared with making small fiber-rings) using the complementary-metal–oxide–semiconductor (CMOS) compactable SOI fabrication processes. In our proposed laser, the measured single sideband (SSB) spectrum shows that the densely spaced longitudinal modes can be significantly suppressed to achieve SLM. The laser linewidth is only 3.5 kHz measured by using the self-heterodyne method. 30 min stability evaluation in terms of lasing wavelength and optical power is performed; showing the optical wavelength and power are both very stable, with fluctuations of only 0.02 nm and 0.8 dB, respectively.

Adaptive filtering for white-light LED visible light communication

Abstract. White-light phosphor-based light-emitting diode (LED) can be used to provide lighting and visible light communication (VLC) simultaneously. However, the long relaxation time of phosphor can reduce the modulation bandwidth and limit the VLC data rate. Recent VLC works focus on improving the LED modulation bandwidths. Here, we propose and demonstrate the use of adaptive Volterra filtering (AVF) to increase the data rate of a white-light LED VLC system. The detailed algorithm and implementation of the AVF for the VLC system have been discussed. Using our proposed electrical frontend circuit and the proposed AVF, a significant data rate enhancement to 700.68  Mbit/s is achieved after 1-m free-space transmission using a single white-light phosphor-based LED.

Network Architecture of Bidirectional Visible Light Communication and Passive Optical Network

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.

Visible light communications for the implementation of internet-of-things

It is predicted that the number of internet-of-things (IoT) devices will be >28 billion in 2020. Due to the shortage of the conventional radio-frequency spectrum, using visible light communication (VLC) for IoT can be promising. IoT networks may only require very low-data rate communication for transmitting sensing or identity information. The implementation of a VLC link on existing computer communication standards and interfaces is important. Among the standards, universal asynchronous receiver/transmitter (UART) is very popular. We propose and demonstrate a VLC-over-UART system. Bit error rate analysis is performed. Different components and modules used in the proposed VLC-over-UART system are discussed. Then, we also demonstrate a real-time simultaneous temperature, humidity, and illuminance monitoring using the proposed VLC link.