Let There Be Light

pureLiFi Kitefin system
Military interest in optical wireless communications is growing. In April, the US Army procured the Kitefin Li-Fi system shown here to support operations in Africa and Europe following a 2019 pilot study.

How can optical wireless communications help militaries satisfy their insatiable appetite for data as the radio spectrum becomes more congested and contested?

Much of Armada’s military communications coverage focuses on conventional radio and Satellite Communications (SATCOM) technology. However, other communications techniques are coming to the fore. Optical Wireless Communications, OWC for short, is one such example. Visible, infrared and ultraviolet light can all be used to move voice and data traffic. Light typically occupies a segment of the electromagnetic spectrum stretching from three terahertz up to three petahertz.

OWC is beyond the spectrum’s radio segment and has garnered military interest in recent years. In April 2023, the US Army announced a purchase of pureLiFi’s Kitefin Li-Fi (Light Fidelity) system. Kitefin Li-Fi was procured to support the US Army in Europe and Africa. The acquisition followed a 2019 US Army pilot study of the technology. In 2021, two researchers from Maharshi Dayanand University in Haryana, northern India, published an instructive paper entitled Emerging Military Applications of Free Space Optical Communication Technology: A Detailed Review. Papers have also been published by the US Army looking at OWC to support tactical communications.

Benefits

One of OWC’s key attractions is that, as it does not use the radio spectrum, it is not subject to the congestion and contention that characterises military use. Military radar, SATCOM and conventional communications must share, and occasionally yield, some of the spectrum to civilian users. This has the corresponding effect of reducing available radio spectrum for the military.

In addition, the radio spectrum is a contested place. Adversaries seek to deny its use by their opponents, even in peacetime. Witness recent examples of Global Navigation Satellite System (GNSS) disruption in the Black Sea. This disruption has been blamed on GNSS jamming by Russian naval vessels active there. The jamming is believed to be performed to protect Russian vessels from targeting by GNSS-guided weapons.

One key benefit of OWC is that it can potentially carry mind-bending quantities of data. Li-Fi technology, according to reports, can achieve data rates of one gigabit-per-second/gbps. Eavesdropping on optical wireless communications is challenging. Anyone wanting to intercept the communications will have to be so close to the beams of light that they could risk disrupting the link. An interruption would deprive them of the traffic they wish to exploit and alert legitimate users that something might be amiss if the link suddenly goes down.

OWC is clearly an emerging technology with much to offer military communications with some forces, notably the US Army, already taking the plunge. It was noteworthy that this year’s United Kingdom Defence Science and Technology Laboratory’s Operating in the Future Electromagnetic Environment (OFEME) symposium had a presentation on optical wireless communications.

Professor Harald Haas, chair of mobile communications at the University of Edinburgh, Scotland and co-founder and chief scientific officer of pureLiFi took delegates through some recent OWC developments. As noted above, capacity is a key benefit heralded by optical wireless communications. One terabit-per-second of data is needed to send a moving holographic human face across a link in real time. At a rate of ten bits-per-second such a task could require bandwidths of up to 100 gigahertz. This could simply overwhelm what is possible using current radio systems and available spectrum. Laboratory experiments cited by Prof. Hass have shown data rates of up to 105 gigabits-per-second using lasers.

Experiments

Prof. Haas and his colleagues have been involved in experiments on behalf of the North Atlantic Treaty Organisation’s (NATO’s) Science and Technology Organisation. Work has included examining ship-to-ship optical communications over distances of between 200 metres (656 feet) and 1.1 nautical miles (two kilometres). Data rates of between six gigabits-per-second and 600 megabits-per-second respectively were achieved during these experiments. The effect of the roll and movement of the ships on the communications was mitigated by tracking systems which ensured the two lasers remained precisely aligned. This helped avoid gaps in transmission.

OWC is not a panacea but neither is any single form of electromagnetic communications. For example, terahertz communications, which Armada has discussed in the past hold, promise regarding wideband links. Optical wireless communications, like terahertz, avoids a crowded radio spectrum promising impressive data rates. Militaries in the future will use an ensemble of links from conventional radio through to terahertz and optical capabilities to ensure connectivity. Thanks to optical wireless communications, the future is looking bright.

by Dr. Thomas Withington