Adaptive equalization system for visible light wireless communication utilizing multiple white LED lighting equipment

• Published in: IEEE transactions on wireless communications 2009-06, Vol.8 (6), p.2892-2900
• Main Authors: Komine, T., Jun Hwan Lee, Haruyama, S., Nakagawa, M.
• Format: Article
• Language: English
• Subjects: adaptive equal izers; Adaptive equalizers; Adaptive systems; Applied sciences; Business and industry local networks; communication systems; Detection, estimation, filtering, equalization, prediction; Diodes; Energy consumption; Equalization; Exact sciences and technology; Fluorescence; Illumination; Information, signal and communications theory; Intersymbol interference; LED lamps; Light emitting diodes; Lighting; Lighting equipment; Networks and services in france and abroad; Optical communication; Optical communication equipment; Optical telecommunications; Signal and communications theory; Signal, noise; Systems, networks and services of telecommunications; Telecommunications; Telecommunications and information theory; Teleprocessing networks. Isdn; Transmission and modulation (techniques and equipments); Voltage; Wireless communication; Wireless communication systems; Wireless communications; wireless LAN; Wireless optical communications
• ISSN: 1536-1276; 1558-2248
• DOI: 10.1109/TWC.2009.060258

White LEDs were invented the 1990's. Since then they have been extensively researched and applied in various ways. Compared with conventional lighting devices, the white LED has lower power consumption, lower voltage requirements, longer lifetime, smaller size, faster response, and cooler operation. The white LED will eventually replace incandescent or fluorescent lights in offices and homes. We have proposed an indoor visible light wireless communication system that utilizes multiple white LED lighting equipment. In this system, the equipment is used not only for illuminating rooms but also for an optical wireless communication system. The system has significantly higher power levels than infrared wireless communication systems, since it also functions as the main lighting equipment. One problem is we tend to install many lighting sources on a ceiling in order to illuminate the room as evenly as possible. While the number of sources permits site diversity transmission over LOS links, the optical path difference between the multiple sources triggers intersymbol interference (ISI), which significantly degrades system performance. This paper overcomes the ISI problem by proposing an adaptive equalization system. We elucidate the most effective training sequence interval for channel estimation in a mobile environment. And we show that the adaptive equalization system with the effectual interval alleviates the influence of shadowing.