Modulation Techniques for Li-Fi
摘要
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.