Advanced Trends in Wireless Communications

Abstract

The visible light communication (VLC) refers to the communication technology which utilizes the visible light source as a signal transmitter, the air as a transmission medium, and the appropriate photodiode as a signal receiving component. The visible light communication technology has a short history compared with other communication technology, for example, public old telephone service, Ethernet, high-speed optical communication, wireless cellular communication, IrDA, etc. It is due to that the development and commercialization of light emitting diodes (LEDs) which emits the light in visible wavelength range have been successful for illumination in recent decade. It is said that the illumination LEDs will replace the conventional illumination lightings such as incandescent bulbs and fluorescent lamps since they have the characteristics of long lifetime, mercury free, color mixing, fast switching, etc. By utilizing the advantage of fast switching characteristic of the LEDs compared with the conventional lightings, i.e., modulating the LED light with the data signal, the LED illumination can be used as a communication source. Since the illumination exists everywhere, it is expected that the LED illumination device will act as a lighting device and a communication transmitter simultaneously everywhere in a near future. There have been researches on application of visible LEDs. The audio system using visible light LEDs was reported in Hong Kong by G. Pang et al. (Pang, 1999) and the visible light communication with the power line communication was reported in Japan by Komine et al. It can be considered that the active research has been started since 2005. Still the VLC system is not close to commercialization, but in the basic research. From the above technical backgrounds, the technical issues will be described in system viewpoint with the recent developments and research results. The VLC link configuration is explained in Section 2. The VLC transmitter (Section 3) and the VLC receiver (Section 4) are described. Section 5 is about VLC considerations including LED characteristics and data format considering the illumination perspectives, including the international efforts on standardization for helping commercialization. The chapter will be concluded with Section 6. 2. System description 2.1 Channel configuration The optical wireless communication (OWC) is a general term for explaining wireless communication with optical technology. Usually, OWC includes infrared (IR) communication for short range (Knutson, 2004) and free-space optics (FSO) communication (FSO website) for longer range. Physical limitations on wireless communication channels impose huge challenges to reliable communication. Bandwidth limitations, propagation loss, noise and interference make the wireless channel a narrow pipe that does not readily accommodate rapid flow of data. Thus, researches aim to design systems that are suitable to operate in such channels, in order to have high performance quality of service. Also, the mobility of the commu...