Vol. 3, Issue 2 (2018)
A study of modulation methods for light fidelity (Li-Fi)
Author(s): Nitesh Arya, Dr. Yash Pal Singh
Abstract: 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. The term Li-Fi denotes “light fidelity” and it is a form of bidirectional, networked, mobile, and high-speed wireless communications closely equivalent to Wireless Fidelity (WiFi). Unlike WiFi, the technology uses visible light spectrum instead of the increasingly congested radio frequency (RF) spectrum. Similarly to WiFi, this technology allows connection of different web-enabled devices such as computers, smart TVs, smart phones, etc. to internet; provides the inter-connection of WiFi enabled things such as refrigerators, watches, cameras, etc. in Internet of Things (IoT); and makes off-loading from cellular networks possible, addressing this way capacity needs for mobile broadband connections. In addition, Li-Fi has a huge amount of visible light spectrum that is unregulated and does not require licenses. It has to be ensured, however, that Li-Fi systems do not present any health hazards and that they are properly installed so as not to create any electromagnetic interference.