Wi-Fi and LTE-U: What’s the real story on unlicensed spectrum?

Today The Wall Street Journal highlighted a debate over unlicensed wireless spectrum that’s been brewing for the last few months. On one side, mobile carriers like Verizon and T-Mobile are planning to roll out a new technology known as LTE-U that will make use of the existing unlicensed spectrum most commonly used for Wi-Fi. LTE-U is designed to deliver a similar capability as Wi-Fi, namely short-range connectivity to mobile devices. As billions of mobile devices and Web video continue to strain wireless networks and existing spectrum allocations (see “The Immersive Internet Needs More Wireless Spectrum”), mobile service providers (and everyone else) is looking for good sources of spectrum. For the meantime, they’ve found it in the 5 GHz ISM band. The 5 GHz band is a good place in which to deploy “small cells” (think miniature cell towers delivering transmissions over a much smaller area) which can greatly enhance the capacity, reach, and overall functionality of wireless services.

Google and the cable companies, such as Comcast, however, are opposed to the use of LTE-U because they say  LTE-U could interfere with Wi-Fi. The engineering department at the Federal Communications Commission (FCC) has been looking into the matter for the last few months to see whether the objections are valid, but the agency has not yet reported any firm conclusions.

Is this a technical issue? Or a business dispute?

Until I see some compelling technical evidence that LTE-U interferes with Wi-Fi, this looks like a business dispute. Meaning the FCC probably should not get involved. The 2.4 GHz and 5 GHz spectrum in which Wi-Fi (and Bluetooth and other technologies) operate is governed by just a few basic rules. Most crucially, devices must not exceed certain power thresholds, and they can’t actively interfere with one another. Wi-Fi was designed to share nicely, but as everyone knows, large numbers of devices in one area, or large numbers of Wi-Fi hotspots can cause interference and thus degrade performance. The developers of LTE-U have spent the last couple years designing it specifically to play by the rules of the unlicensed spectrum and to play nicely with Wi-Fi.

The early results are encouraging. In real world tests so far,

  • LTE-U delivers better performance than Wi-Fi,
  • doesn’t degrade nearby Wi-Fi performance, and
  • may in fact improve the performance of nearby Wi-Fi networks.

For more commentary and technical analysis, see Richard Bennett’s recent posts here and here. Bennett was an early co-inventor of Wi-Fi and thus knows what he’s talking about. Also, Qualcomm has a white paper here and some good technical reports here and here.

Another line of opposition to LTE-U says that the mobile service providers like Verizon and T-Mobile will use LTE-U to deliver services that compete with Wi-Fi and will thus disadvantage competitive service providers. But the mobile service providers already operate lots of Wi-Fi hotspots. They are some of the biggest operators of Wi-Fi hotspots anywhere. In other words, they already compete (if that’s the right word) with Google and cable firms in this unlicensed space. LTE-U is merely a different protocol that makes use of the same unlicensed spectrum, and must abide by the same rules, as Wi-Fi.  The mobile providers just think LTE-U can deliver better performance and better integrate with their wide area LTE-based cellular networks. Consider an analogy: the rental fleets of Hertz and Avis are both made up of Ford vehicles. Hertz then decides to start renting Fords and Chevys. The new Chevys don’t push Fords off the road. They are both cars that must obey the rules of the road and the laws of physics. The two types of vehicles can coexist and operate just as they did before. Hertz is not crowding out Avis because it is now using Chevys.

I’ll be looking for more real world tests that either confirm or contradict the initially encouraging evidence. Until then, we shouldn’t prejudge and block a potentially useful new technology.

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