Modulation Techniques for Li Fi
Modulation techniques for light fidelity(Li Fi) are reviewed in this paper.Li Fi is the fully networked solution for multiple users that combines communication and illumination simultaneously.Light emitting diodes(LEDs) are used in Li Fi as visible light transmitters,therefore,only intensity modulated direct detected modulation techniques can be achieved.Single carrier modulation techniques are straightforward to be used in Li Fi,however,computationally complex equalization processes are required in frequency selective Li Fi channels.On the other hand,multicarrier modulation techniques offer a viable solution for Li Fi in terms of power,spectral and computational efficiency.In particular,orthogonal frequency division multiplexing(OFDM) based modulation techniques offer a practical solution for Li Fi,especially when direct current(DC) wander,and adaptive bit and power loading techniques are considered.Li Fi modulation techniques need to also satisfy illumination requirements.Flickering avoidance and dimming control are considered in the variant modulation techniques presented.This paper surveys the suitable modulation techniques for Li Fi including those which explore time,frequency and colour domains.