Analog Angle Blog

Li-Fi: Great in principle, maybe not so much in practice

We’re all familiar with Wi-Fi, the ubiquitous RF-based connectivity standard which has stitched together so many untethered, wireless devices since its introduction and commercialization in the late 1990s and early 2000s.The success of Wi-Fi and its incorporation into just about every smart device, going well beyond PCs, is well known.

But there’s another standard which is also wireless: Li-Fi, short for Light Fidelity and obviously a play on Wi-Fi. The term was first introduced by Prof. Harald Haas during a 2011 TEDGlobal talk, where he envisioned a merging of LED-based illumination and Internet access nodes.

Li-Fi has its own Li-Fi Consortium, news website, and logo, shown in Figure 1. Most Li-Fi efforts support IEEE Standard 802.15.7, but that standard does not yet cover the recent developments, such as optical orthogonal frequency-division multiplexing (O-OFDM) methods, which have been optimized for higher data rates, multiple access and energy efficiency.

Figure 1 The Li-Fi logo looks very much like that of Wi-Fi. Source: LiFi.co

I thought about Li-Fi again when I read that the U.S. Army recently signed another multimillion-dollar contract with Li-Fi vendor and champion pureLiFi for thousands of their Kitefin connectivity units. There are other Li-Fi vendors as well, such as Oledcomm.

Like Wi-Fi, Li-Fi is wireless, but not in the conventional meaning of being RF-based. While both are governed by Maxwell’s equations for electromagnetic energy, in reality, they are in very different technology worlds. When people say “wireless” they almost always are referring to an RF link. Perhaps “tetherless” would be a better description of both Wi-Fi and Li-Fi, but I don’t think that’s going to happen.

Using light for communication is not a new development, of course, as it has been done by using fires, incandescent light bulbs and shutters, ubiquitous IR-based remote controls, and commercially available line-of-sight laser-based free-space optical (FSO) links operating over about 10 kilometers (Figure 2). The latter has even been tried as experimental links for the orbiting of deeper-space vehicles.

Figure 2 Free-space laser-based optical links are widely used for point-to-point links over several kilometers. That bypasses the need to lay optical fiber or establish a wideband, high-speed licensed RF link. Source: Laseroptronics Inc.

What’s the analog angle of interest in Li-Fi? Whenever the project involves electro-optic components, whether as integrated devices or an assembly of discrete components, it’s part of that analog world of optical sources and drivers, optical receivers and preamplifiers, and power-related circuity. There are often follow-on benefits as higher volumes drive lower cost and technology innovations at the physical-interface level and these advances are also often leveraged in other unrelated applications as well.

Though market acceptance has been slow, proponents of Li-Fi are obviously enthusiastic and herald it as the next big thing in connectivity. They point to its inherent characteristics as major benefits and, in some situations, they certainly are. Among these are its potential Gbps-class data rate and wide bandwidth supporting many users as well as its security aspects. It is highly immune to detection and eavesdropping (snooping), jamming, and intrusion. The 10-kilometer range is both a benefit and a limitation, depending on the user’s situation and perspective.

The primary anticipated settings promoted for Li-Fi installations are office and educational institutions with the network access node established via overhead, ceiling-mounted LED illumination units that provide both illumination and optical transceiver functions (Figure 3). Outdoor use is also viable with suitable hardware and optical wavelengths, and due to the modulated nature of the data signal, blinding by the sun is not a problem in most cases.

Figure 3 The Li-Fi approach is conceptually simple and relies, in practice, on ceiling-mounted luminaires (lighting fixtures) which also support high-rate modulation for conveying data. Source: LiFi.co

Advocates say that for appropriate “use-cases” Li-Fi is a better solution than Wi-Fi. Still, no standard laptop PCs come equipped with built-in Li-Fi connectivity. So, USB to Li-Fi dongle is needed for the laptop PC.

Perhaps this is another case of the “chicken and egg” dilemma which Wi-Fi overcame via a major “let’s make it so” initiative from Intel and other key industry players. There’s no incentive to incorporate it into laptops unless there are widespread access nodes; there’s no point in building nodes until enough laptops already come with it.

Is Li-Fi destined to remain a niche solution, somewhat like powerline networking? After all, you can buy standard plug-in nodes for both techniques, each has clear benefits and limitations, and each solves a specific class of connectivity problem. As Li-Fi becomes widely available, do you foresee any of its technologies, products, and manufacturing know-how benefiting unrelated applications?

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