Transmission of Signals Using White LEDs for VLC Application
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Transmission of Signals Using White LEDs for VLC Application P. Louro1,2, V. Silva1,2, J. Costa1,2, M. A. Vieira1,2, M. Vieira1,2,3 1
Electronics Telecommunication and Computer Dept. ISEL, R. Conselheiro EmÃdio Navarro, 1949-014 Lisboa, Portugal Tel: +351 21 8317290, Fax: +351 21 8317114, [email protected] 2 CTS-UNINOVA, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal. 3 DEE-FCT-UNL, Quinta da Torre, Monte da Caparica, 2829-516, Caparica, Portugal
ABSTRCT In this paper a photodetector working as an active optical filter device is used to detect modulated visible optical signals for applications based on Visible Light Communication (VLC). The proposed application demonstrates the viability of indoor positioning using VLC technology established by the modulation of indoor ultra-bright RGB white LEDs. The signals of the internal red and blue chips of the white LEDs were modulated at specific frequencies and the generated photocurrent was measured by a pin-pin photodetector based on a-SiC:H/aSi:H. This device operates as a visible optical filter with controlled wavelength sensitivity through the use of adequate optical biasing light. Thus it is able to detect different wavelengths which allow the detection of the individual components of the tri-chromatic white LED. This possibility is the basis for the indoor location algorithm. We demonstrate the possibility of decoding four transmission optical channels supplied by two different wavelengths of white LEDs modulated under different bit sequences. The identification of the signals received by the photodetector allows the location identification of the photodetector position and supplies indoor navigation. INTRODUCTION VLC technology makes use of the visible part of the light spectrum to modulate specific wavelengths and encode and transmit information [1]. The most common optical sources are the widely used white LED lamps that besides being an excellent energy saver lighting mode can also be easily modulated, fulfilling the VLC requirements. An interesting application of VLC technology is for indoor positioning and navigation resources [2]. Its use can be extended from in-house navigation to guide users inside large buildings [3] to location detection of products inside large warehouses [4]. We propose a communication system operating in the visible range using four ultra-bright white RGB and photodetector device based on two stacked multilayered a-SiC:H/a-Si:H structures that act as optical filters in the visible range [5, 6]. The LEDs enable four transmission optical channels supplied by the modulation t different frequencies of the internal red and blue chips. The possibility of tuning the spectral device sensitivity is analyzed and discussed using several optical bias conditions that induce different modulations of the electrical field along both front and back heterostructures, amplifying or cutting specific wavelengths [7]. This enables the identification of the transmitted individual input channels allows the location identification of
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