Abstract
Complementary Metal-Oxide-Semiconductor (CMOS) image sensors are widely used in mobile-phone and cameras. Hence, it is attractive if these image sensors can be used as the visible light communication (VLC) receivers (Rxs). However, using these CMOS image sensors are challenging. In this work, we propose and demonstrate a VLC link using mobile-phone camera with data rate higher than frame rate of the CMOS image sensor. We first discuss and analyze the features of using CMOS image sensor as VLC Rx, including the rolling shutter effect, overlapping of exposure time of each row of pixels, frame-to-frame processing time gap, and also the image sensor "blooming" effect. Then, we describe the procedure of synchronization and demodulation. This includes file format conversion, grayscale conversion, column matrix selection avoiding blooming, polynomial fitting for threshold location. Finally, the evaluation of bit-error-rate (BER) is performed satisfying the forward error correction (FEC) limit.
Highlights
Visible light communication (VLC), known as optical wireless communication (OWC) or Light-Fidelity (Li-Fi) has gained increasing attention recently [1,2,3,4,5,6]
As there is a shortage of radio frequency (RF) spectra in traditional wireless communications, VLC can be a supplementary form
Light emitting diode (LED) can be a promising transmitter (Tx) for VLC, since it can be modulated at a relatively high speed when compared with traditional light sources
Summary
Visible light communication (VLC), known as optical wireless communication (OWC) or Light-Fidelity (Li-Fi) has gained increasing attention recently [1,2,3,4,5,6]. Most mobilephones available in the market nowadays have embedded Complementary Metal-OxideSemiconductor (CMOS) cameras allowing users to take photos and videos It is attractive if these already existing mobile-phone or vehicle image sensors can be used as the VLC receivers (Rxs). Signal data loss will occur due to the relatively long processing time gap in frame-to-frame [11] proposed using the rolling shutter effect of the CMOS image sensor to increase the VLC data rate; our work provides detail discussion of the features of CMOS sensors, including the overlapping of exposure time of each row of pixels, frame-to-frame processing time gap, and the image sensor “blooming” effect. Bit-error-rate (BER) analysis is provided [12] demonstrated a special image sensor with specific pixels for imaging and specific pixels for high speed VLC; this sensor requires relatively complicated fabrication process, and may not be available as embedded device in mobilephone and vehicle camera in the near future. The data rate is 1.68 kbit/s in the proof-of-concept demonstration; we believe that this data rate may enough for sending secure identification (ID) or authorization information in wireless communication; or sending position information in indoor navigation system
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