Unsynchronized Visible Light Communications using Rolling Shutter Camera: Implementation and Evaluation
Date Issued
2015
Date
2015
Author(s)
Lee, Hui-Yu
Abstract
The thesis presents a visible light communication (VLC) system that utilizes a single light-emitting diode (LED) light source as the transmitter and a CMOS rolling shutter camera as the receiver. VLC is a new data transmission technology. Unlike traditional RF wireless communication, VLC uses the optical signal to carry digital information by controlling the LED''s light intensity in free space. VLC has the properties of high directivity, high security and high bandwidth. In recent years, with the development of the LED technology, due to its advantages of low power consumption, high efficiency, and long life, LED has gradually replaced the traditional fluorescent lighting. The quick response time and the low cost also make LED a very attractive transmitter solution for communications. In our proposed system, we use CMOS rolling shutter camera as the receiver. Today, almost every modern mobile device is equipped with at least one built-in CMOS camera, and CMOS camera can receive signals from the LEDs without any modification, and thus, any additional cost. Our idea is to use the acquired images to extract the message transmitted from the LED. This technology can be used in many applications, such as advanced driver assistance system (ADAS), indoor positioning, and visual-associated application. Due to the wide range of frames rates of the cameras, it is common to receive redundant symbols or have symbol loss; Frames with more than one data symbols, i.e., mixed frames, may also happen because of the phase offset between the transmitter and the receiver. Both of the issues are due to the unsynchronized nature of our proposed system. In this thesis, we propose a number of schemes to address the issues caused by unsynchronized transmitter and receiver. To evaluate the feasibility of these schemes, we use software-defined radio (SDR) to implement the transmitter and use the built-in camera of several recent smartphones and an industrial camera as the receiver. We also develop a real-time decoding application on the smartphone. Our result shows that we can improve the packet reception rate (PRR) from 0.6 to 0.99 when the transmitting and receiving frame rates are close. We also can improve the PRR from 0.0 to 0.8~1.0 even when the transmitting and receiving frame rates have a large difference. The overall throughput can reach 18 bytes per second. We expect this technology can be widely used for a wide range of applications in the future.
Subjects
Visible Light Communications
Camera Communication
Rolling Shutter
Type
thesis
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