Indoor Wireless Networks Use White LEDs

WHITE LIGHT-EMITTING DIODES (LEDs) are considered the "green" alternative to conventional lighting methods. After all, they offer lower power consumption, lower voltage, longer lifetime, smaller size, and cooler operation than other lighting options. LEDs also can be used as a wireless communications transmitter. This capability stems from the fast response time and modulation of visible light for wireless communications. An optical wireless communications system that uses white LEDs for indoor wireless networks was recently investigated by Yonsei University's (Seoul, Korea) Yong-Hwan Son, Sung-Chan An, Hyun-Seung Kim, Yong-Yuk Won, and Sang-Kook Han.

The researchers faced a challenge in that the visible-light-communication (VLC) link had to be efficiently connected to the existing optical access network. Their solution was to use a VLC link based on an optical access network that relied on both LED and an electro-absorption transceiver (EAT). The EAT, in turn, is based on an electro-absorption modulator. When it is used as an optical network unit, the EAT can be connected with the FLC link based on the white LED and photodiode (PD) without requiring additional RF or optical devices.

The researchers demonstrated the proposed architecture in an experimental fashion. They then verified a total of 5 Mb/s downlink and uplink transmission through 23.2-km singlemode fiber and a wireless channel. The Q-factor performance was degraded under ambient-light conditions. See "Visible Light Wireless Transmission Based on Optical Access Network Using White Light-Emitting Diode and Electroabsorption Transceiver," Microwave And Optical Technology Letters, April 2010, p. 79

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