to the Internet data packets for Li-Fi application. The modulation bandwidth of the LED will determine the communication data rate.
Figure-2: VLC Transmitter
The basic blocks of a VLC transmitter are shown in Figure-2. The driving circuit helps to control or modulate the LED light intensity based on the data input. Various modulation techniques are employed for this and the data rate will vary accordingly. On-Off Keying (OOK), Pulse-Position Modulation (PPM) and Frequency-Shift Keying are the popular modulation schemes used for VLC transmission. But the use of OFDM (Orthogonal Frequency Division Multiplexing) for intensity modulation is the most recent one and it provides high data rate also. OFDM is suitable for situations where multiple transmitters are used for reducing shadowing effect. For effective VLC transmission, highbrightness LED is required, which operates with high forward current. So data modulation on high-brightness LED while maintaining the illumination makes VLC transmitter design more complex.
Figure-3: VLC Receiver
In a VLC receiver (Figure-3), photodiode is generally used as the light sensor along with optical filter, amplifier and signal recovery circuit. Optical filter is to reject unwanted DC noise components in the recovered data signal due to sunlight and other illumination. VLC Consortium (VLCC) in Japan, Wireless World Research Forum (WWRF) in Europe, IEEE in USA, Telecommunication Technology Association (TTA) in South Korea etc. are engaged in promoting technology exchange, system development, demonstration and standardisation activities of VLC. IEEE introduced the standard 802.15.7 for VLC, which is expected to be improved in 2012. Li-Fi/VLC can find application in aircraft, hospitals or other sensitive areas where Wi-Fi or radio interference is banned. Range of communication is a limitation of Li-Fi. In indoor environment, line-of-sight 10ď ŽExecutive Knowledge Linesď ŽApril 2012