Honey I shrunk the cell

November 13, 2019

Professor Jean-Paul Linnartz explores whether, after 125 years of innovation in radio technology, a transition to LiFi is the easiest way to overcome today’s communication challenges

The demand for communication is growing as thousands of radio researchers try to solve the current spectrum crunch that limits radio systems. But is a transition to optical communication the solution?

Signify’s Trulifi technology is a new series of Light-Fidelity (LiFi) products that communicate via light instead of via radio waves. It’s cool to see LEDs that not only illuminate but which also carry information. In fact, it’s not just cool: it’s becoming necessary.

Faster than Moore

The amount of data that we exchange wirelessly continues to grow much faster than Moore’s law. According to Gordon Moore, co-founder of Intel, the number of transistors in a dense integrated circuit doubles each year.

And not only do such chips now process richer data, today’s users spend more time at their devices and run more apps. As the number of connected people and devices mushroom, it’s hardly surprising that radio links are straining under increasing pressure to carry all this data traffic.

Many teenagers would rather spend a day without food than a day without WiFi"

The transition from radio-based communication, such as WiFi, to LiFi, is the logical consequence of a long-lasting trend of data intensification in wireless communication.

The step towards light-wave systems, with their well-defined coverage, fulfills the growing need and demands for higher bit rates and interference-free, rock-solid connections.

The growth of wireless communication is often described as a trend that started in the last decade or two, but a deeper investigation reveals that the trend-lines are exponential, ever since Marconi sent his Morse code across the Atlantic.

While the use of radio waves was initially a privilege for broadcasters, and for the military to communicate with airplanes and ships, today it’s an everyday necessity. Many teenagers would rather spend a day without food than a day without WiFi!

The pace of technological change has been relentless. Early cell phones could only exchange text (SMS) messages of 160 characters, but today four and a half million YouTube videos are consumed every minute, many of them on mobile devices.

Trendwatchers identify Ultra High Definition TV and 3D-video as drivers spurring on the insatiable demand for communication and bandwidth. While virtual reality games, with instant interaction, will become widespread, higher resolution picture quality may lose its role as the only driver for higher video bit rates, as we have already attained impressive quality.

But in gaming, low latency is demanded to bypass even the slightest delays of a few milliseconds. Ever higher bit rates are needed to carry uncompressed, latency-free video.

The Internet of Things (IoT), is further accelerating this growth. The IoT will not only connect billions of humans, but also two or three orders of magnitude more devices. It’s been predicted that it will connect hundreds or even thousands of smart devices in every household. Tens of billions of devices will generate massive Internet traffic.

At Signify, we’re starting to see this unfold already and are planning accordingly. Today, a mere 53 million of the 26 billion light points in the world are connected. Yet in 2020 every new light bulb Signify creates will be connected or connectable.

In 2020 every new light bulb Signify creates will be connected or connectable"

Similarly, a billion cars in the world are waiting to become connected. Connectivity will assist safe autonomous driving while simultaneously entertaining the passengers. Consequently, the total wireless traffic-per-square-meter will also grow rapidly.

Radio community adapts to increasing demands

Radio communication has accommodated this growth in several ways. One is the use of higher and higher frequencies where more bandwidth is available. Another is denser reuse of available frequency in different locations to maximize efficiency.

Remarkably, Marconi sent his message 5,000 km across the Atlantic Ocean. Luckily, he also had a clear channel; he was the only one using the airwaves. Radio no longer needs to cover large distances. Today our systems communicate wirelessly over shorter and shorter distances and a global fiber backbone effectively carries long-haul communication traffic between continents.

The days when medium- and shortwave radio was needed for its huge coverage are long gone. Its heyday was the 1960s when powerful transmitters reached out with 1.3 Megawatts to listeners over a 500 km radius. Then, stations such as Radio Luxembourg were household names. Using the same frequency twice in neighboring countries wasn’t a goal.

Philips sold radio sets across Europe with the same international names of radio stations on the dial in multiple countries. But AM radio severely limited the variety of programs people could listen to.

FM radio densified the reuse of frequencies, allowing different nations to use the same channel. It was a first example of optimizing for density, not for coverage, with each FM transmitter rarely covering more than 100 km, to allow reuse in nearby regions.

The arrival of mobile phones changes the game

With the arrival of mobile telephony, a breakthrough was made possible by a shift in mindset. Radio links became smaller, covering 3 km or less. More importantly, attention was paid to reusing the channel as close as possible.

Antennas were kept low, to ensure a rapid fall-off of the signal strength at larger distances. This concept of well-defined ‘cells’ – essential to accommodate many subscribers within a limited chunk of the spectrum – even brought us a popular name for the mobile: cellphone. It refers to the honeycomb grid of cells reusing a few frequencies in a regular pattern.

When operators saw the growing number of subscribers, they sidestepped the need for more bandwidth by shrinking the cell size. This was achieved by positioning more base stations. Often, they barely covered a few hundred meters and reused the same channel with a separation of less than a kilometer.

This trend towards smaller ‘cells’ continued. With WiFi, radio coverage shrunk to just 10 meters. Today, variants of WiFi use multiple antennas to target signals to their destination and instead of using megawatts, they use milliwatts.

Evolution of wireless communication. The coverage area shrinks every decade to allow a huge increase in the density of users.

Densification in the 2020s

The pressure to reduce cell size has dominated many developments in radio communication research. With the reduction of the communication range, the footprint at which signals interfere with other signals also sharply reduces. Increasingly sophisticated signal processing is further used to steer dedicated, narrow beams to the intended recipient and to avoid interference. But in 5G, these algorithms become power hungry and steering radio waves requires many antennas, each with their own digitally processed signal.

When sketching the trend of reducing range and better targeting the signal to the end-user, LiFi emerges as the natural next step. Covering just a single room using light waves presents a natural way of increasing density. The entire spectrum can be used again in every room as walls form natural boundaries for cells. In contrast, just check how many WiFi access points are visible in a typical student dorm, for example. All competing for the same limited spectrum.

Unless increased demand suddenly halts after 125 years of exponential growth, we need breakthroughs."

Faster times denser

Unless increased demand suddenly halts after 125 years of exponential growth, we need breakthroughs. Radio systems are now under extreme pressure. This is down to the two key performance indicators for wireless communication systems

1) the maximum bit rate they can support
2)the density of users they can serve. LiFi is perfectly positioned to satisfy these demands.

Bit rate (Bits/s): the optical spectrum (near-IR, IR) has virtually no bandwidth limitation. It can utilize 1,000x the bandwidth of the entire radio spectrum. Laser beams, through open air, can carry at least as much data as optical fiber, while radio communication lags many orders of magnitude behind optical fiber throughputs.
Density (Bits/s/Hz/m2): In practice, WiFi is limited by interference among signals from multiple users. 5G takes extreme measures to cope with this problem. But Massive MIMO and beam steering of radio signals tend to be power hungry. However, with LiFi, confining coverage and achieving very high densities comes naturally. Light doesn’t go through opaque walls. And in the future, we expect optical beams will be steered to the target, permitting ultra-dense reuse.

In this respect, optical communication offers exactly what 5G communication tries to achieve via radio emissions: ultra-dense reuse, high bandwidth, low latency and the ability to connect IoT devices. While this is a stretch for radio communications, these requirements fit very well with LiFi.

The light spectrum offers a wealth of frequency space, which is unlicensed and free to use. The visible spectrum (400 to 700nm) offers no less than 320 THz of bandwidth, and the near-infrared spectrum, used for fiber-optic communication (1500 to 1600nm), offers 12.5 THz of bandwidth.

Spatial confinement of light to narrow beams, combined with huge bandwidths, will enable the creation of a dense grid of independent (‘atto’) cells. This effectively multiplies this huge bandwidth.

Combined with large spatial reuse, it offers the potential to deliver unrivalled wireless communication capacity. LiFi will do this relatively simply and is highly energy efficient as well.

Marconi crossed the oceans, what’ can LiFi do?

What makes LiFi stand out is the ability to not just deliver great quality light but also gigabits per second per user. And more importantly, to repeat this bandwidth for many users, even in close vicinity to each other.

For me, LiFi isn’t an isolated technological curiosity. It comes as a logical next step in wireless communication. It’s the next phase to shrink cell sizes to the scale of a single room or smaller, as the TruLifi system by Signify does today. Meanwhile, at Research we’re looking ahead, to make the beam narrower and to shrink the cells to a square foot, or smaller.

It’s the next phase to shrink cell sizes to the scale of a single room or smaller"

One thing is certain. The demand for communication will continue apace. Already 80% of wireless traffic is video, a format very much on the rise. Expectations are that the predicted 50 billion connected devices forming the IoT will further accelerate demand, and make new wireless technologies, such as LiFi, an absolute necessity. We stand ready.

About the author:

Jean-Paul Linnartz

Professor Jean-Paul Linnartz is a Research Fellow, leading Signify’s Research on LiFi and Optical Wireless Communication. Previously, as a Senior Director with Philips, he headed research departments on information security, radio communication and on IC design. Jean-Paul is professor at Eindhoven University of Technology and is Fellow of the IEEE.

For further information, please contact:

Signify Global Integrated Communications
Neil Pattie
Tel: + 31 6 15 08 48 17
Email: neil.pattie@signify.com

About Signify

Signify (Euronext: LIGHT) is the world leader in lighting for professionals, consumers and the Internet of Things. Our Philips products, Interact systems and data-enabled services, deliver business value and transform life in homes, buildings and public spaces. In 2023, we had sales of EUR 6.7 billion, approximately 32,000 employees and a presence in over 70 countries. We unlock the extraordinary potential of light for brighter lives and a better world. We have been in the Dow Jones Sustainability World Index since our IPO for seven consecutive years and have achieved the EcoVadis Platinum rating for four consecutive years, placing Signify in the top one percent of companies assessed. News from Signify can be found in the Newsroom, on X, LinkedIn and Instagram. Information for investors is located on the Investor Relations page.

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