Research at the Li-Fi Centre, University of Edinburgh

Wireless communication has already shaped our daily lives, and multi-media devices such as smart phones and tablet PCs affect the way that we work, entertain and socialise. In addition, in the next couple of years, it is expected that wireless communication will become part of our lives in other ways such as real-time health monitoring. Therefore engineers are required to develop the technology that will meet the future needs for wireless communication. Until recently, wireless communication has been mainly accomplished using radio waves but the available Radio Frequency (RF) spectrum is now not going to be enough, and this has been the main factor for the latest evolution of modern communication.

Since 2000s, multi-antenna RF communication, also termed Multiple-Input Multiple-Output (MIMO) communication has been developed as solution to this technical challenge. In MIMO systems, the transmitter and the receiver both deploy multiple antennas. Researchers have shown that MIMO communication provides more efficient communication, in terms of data rate [1]. However, is the new MIMO technology going to cover all our future needs? Probably not. To provide more communication channels, engineers have developed Visible Light Communication (VLC) [2]. Using VLC we can form Light-Fidelity (Li-Fi), first coined in 2011 in a TEDTalk by Professor Harald Haas. In Li-Fi, binary communication is transferred via different levels of light intensity at speeds of hundreds of millions of bits per second, not perceived from the human eye. Compared to RF communication, Li-Fi offers increased security; higher data rates by having more access points (access point densification); and more energy efficient communication by the simultaneous use of energy for lighting, as verified by recent research see [2, 3] below.

Schematic of Li-Fi MIMO from a researcher's notebook - can we remove the shadows using Li-Fi?
Schematic of Li-Fi MIMO from a researcher’s notebook – can we remove the shadows using Li-Fi?

The question then arises: can we introduce the concept of MIMO in Li-Fi, by using multiple light emitting diodes (LED lights), and photo-detectors (PD) and obtain additional combined benefits from both concepts? Researchers use the schematic shown in the figure in order to describe a Li-Fi MIMO system (for more details see [4] below) – and can this now become a reality? The techniques of RF MIMO communication are not directly transferable to VLC. The communication engineer has to consider very carefully the unique characteristics of the VLC channel and develop novel methods. Such an example is our recent work [4], where it is shown how the VLC channel affects the behavior of different MIMO communication techniques compared to the traditional RF communication. Therefore, as a communication engineer with a background in RF MIMO communication, I strongly believe that the research area of MIMO Li-Fi hides many surprises yet to be explored.

[1] P. Wolniansky, G. Foschini, G. Golden, and R. Valenzuela, V-BLAST: An Architecture for Realizing Very High Data Rates Over the Rich-Scattering Wireless Channel, in Proc. International Symp. Signals, Systems, Electronics (ISSSE98), Pisa, Italy, pp. 295-300, September 1998.

[2] D. Tsonev, S. Videv, and H. Haas, “Light Fidelity (Li-Fi): Towards All-Optical Networking,” in Proc. SPIE, Broadband Access Commun. Technol. VIII, vol. 9007, Dec. 18 2013.

[3] D. Tsonev, H. Chun, S. Rajbhandari, J. McKendry, S. Videv, E. Gu, M. Haji, S. Watson, A. Kelly, G. Faulkner, M. Dawson, H. Haas, and D. O’Brien, “A 3-Gb/s Single-LED OFDM-Based Wireless VLC Link Using a Gallium Nitride μLED,” IEEE Photon. Technol. Lett., vol. 26, no. 7, pp. 637–640, Apr. 2014.

[4] A. Stavridis, and H. Haas, “Performance Evaluation of Space Modulation Techniques in VLC Systems”, IEEE International Conference on Communications 2015 (ICC 2015) (1ST Visible Light Communications and Networking (VLCN) Workshop), 8-12 June 2015, London, UK.

Athanasios Stavridis

Li-Fi PhD Research Student