CTN Issue: November 2016

A note from the editor:

This month the good people of PureLiFi are giving us an update on the state of light based wireless communications and exactly where they are in developing a commercial product. How big will LiFi be in ultra dense networking? Read on, and don't forget to comment.

Alan Gatherer, Editor-in-Chief

LiFi Unlocking Unprecedented Wireless Pathways for Our Digital Future

Professor Harald Haas, pureLiFi Chief Scientific Officer and Dr. Nikola Serafimovski, pureLiFi Director of Business Strategy

We live in an increasingly connected world. The demand for mobile wireless communications is increasing at over 50% per year according to the Cisco Visual Networking Index. This demand is expected to continue to increase as the Internet of Things (IoT) becomes a reality, and the number of connected devices grows from 5 billion to over 20 billion by 2020. Unsurprisingly, in 2016, over 50% of all wireless data went through a WiFi access point. This enormous utilisation results in a need for a continued increase in capacity of wireless networks, depending directly on the availability of additional unlicensed spectrum.

Undeniably, there are multiple solutions that can provide an increase in the available spectrum and increased confinement of the RF signal. As an example, WiGig solutions, defined in IEEE 802.11ad and being revised in 802.11ay, that operate in the 60 GHz spectrum have access to around 14 GHz of bandwidth in the USA. However, WiGig and other mm-wave RF solutions all exhibit similar challenges.  First, ICT (information and communication technology) has gone through a radical transformation driven by efforts to reduce the carbon footprint. To achieve the required data densities, it is inevitable that WiFi/WiGig solutions implement beamforming. This poses a number of technical challenges: i) beamforming requires multiple antennas and phase shifters which increases hardware complexity and cost, and ii) while current beamforming works well in a downlink point-to-multipoint scenario, beamforming in the uplink, i.e., multipoint-to-point scenarios of a mobile communication system where place and orientation of the mobile terminal can vary greatly, is still a challenging problem. 

In this context, it is vital to remember that RF is only one part of the electromagnetic spectrum and that visible light spectrum and the infrared spectrum has, for the most part, been an underutilised share of this spectrum. The visible light spectrum alone stretches from approximately 430 THz to 770 THz, which means that there is potentially more than 1000x the bandwidth of the entire RF spectrum of approx. 300 GHz. Both the visible light spectrum and the infrared spectrum are unlicensed. 

There are wireless technologies that are harnessing this vast spectrum resource. Specifically, ‘LiFi’ (Light Fidelity), first demonstrated to the public and coined by pureLiFi CSO, Professor Harald Haas in at TED Global talk “Wireless from Every Light Bulb” in 2011, has attracted significant international interest. LiFi refers to the high-speed, bidirectional and networked wireless communications using light to provide a seamless wireless user experience much like traditional mobile communications [1]. It, therefore, advances visible light communication (VLC), which was first introduced by Prof. Nakagawa at Keio University [2], as LiFi is a complete mobile communication solution to augment 5G and beyond. LiFi offers secure and safe wireless communications in a globally unlicensed spectrum that repurposes the energy used for lighting to provide wireless data. This technology is, therefore, expected to be a key part of future 5G Systems.

There is another important aspect in modern wireless communications: ‘Security'.  The proliferation of mobile devices has resulted in an increase of the amount of secure information being exchanged over the wireless network. As a result, we're facing a sharp increase in cyber vulnerability. Indeed, in a rush to provide market-ready solutions for the IoT, companies have often neglected cyber security requirements for their products. This has dramatically increased the attack surface for many cyber-attacks and has resulted in one of the world's most powerful distributed denial of service (DDoS) incidents in modern history – attacking everything from wireless baby monitors to wireless CCTV cameras [3].

Light is very directional, well understood and easily confined using simple lenses. Therefore, beamforming can be achieved with low hardware complexity and in a cost effective manner. Moreover, because of the small wavelength in the region of hundreds of nanometers, the size of the electronic components that emit light and detect light, i.e., light emitting diodes (LEDs) and photodetectors (PDs) can be very small in the region of tens and hundreds of micro meters. This has two key advantages: First, LiFi systems are not subject to the same multipath fading typically modelled as Rayleigh fading in the case of non-line-of-sight, and Rician fading in the case of line-of-sight in RF systems. Multipath fading is the result of in-phase and out-of-phase signals combining at the antenna and cancelling each other out which then results in outage and rapid and random signal to noise degradations. LiFi systems are immune to this effect as the large size of the detector relative to the signal wavelength ensures that all signal paths integrate constructively – resulting in lower hardware complexity and potentially more robust systems. This effect can also be exploited for co-channel interference mitigation when there are multiple sources in confined space transmitting independent data [4]. Second, it is straightforward to build very compact transceivers that are composed of multiple LEDs and multiple PDs [5]. As a result, systems of very high diversity order can be generated without a massive size and cost increase.

Statements and opinions given in a work published by the IEEE or the IEEE Communications Society are the expressions of the author(s). Responsibility for the content of published articles rests upon the authors(s), not IEEE nor the IEEE Communications Society.