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Hurricane LTE-U: Don’t Let Wi-Fi Get Blown Away

November 4, 2015

A storm is brewing over use of the 5.8 GHz unlicensed band of the radio spectrum as telecommunications companies plan to expand their LTE networks outside their traditional, licensed ranges and into the same unlicensed bands used by Wi-Fi, cordless headsets, and plenty of other consumer technology.

You can call it Hurricane LTE-U, where U refers to the unlicensed spectrum. Right now it’s a whirlwind of letters and emails, with dozens of companies and organizations weighing in on both sides, such as Google, which issued a report that LTE-U would seriously interfere with Wi-Fi. Six U.S. senators separately sent a letter to the FCC demanding more oversight. The FCC in turn demanded clarification from LTE-U proponents, who came back with their own letter addressing the concerns point-by-point. Meanwhile, Qualcomm, which is developing the technology, plied journalists with breakfast and lunch in an effort to convince them LTE-U was totally benign.  Wi-Fi advocates remain unconvinced.

The only thing we know for sure is that there’s an enormous amount of controversy about how LTE-U technology will perform in the real world.

A quick primer on the terms here:

  • Licensed refers to the part of the radio spectrum that you can only transmit on with specific permission from the FCC. This generally requires paying licensing fees, sometimes on the scale of billions of dollars. 
  • Unlicensed refers to the part of spectrum anyone can transmit on as long as their device meets certain requirements about maximum transmission power. This is used by Wi-Fi devices and other personal electronics.
  • LTE, which stands for Long-Term Evolution, is a technological standard used in cell phone networks operating in the licensed portion of the spectrum. When your phone displays “4G” and/or “LTE” in the corner, that means you’ve connected to a network running on that standard. 
  • LTE-U is a separate proposal to use LTE technology in the unlicensed 5.8 GHz ISM band. The LTE-U standard has been proposed by the LTE-U Forum, which is a cooperative effort between Qualcomm, Samsung, and Ericsson, and headed by Verizon.

The LTE-U Forum has made assurances that the technology won’t interfere with existing unlicensed technology, such as Wi-Fi, and has even presented testing data from their labs supporting those assurances. Tests by others have shown the exact opposite, so a lot of organizations—such as the National Cable & Telecommunications Association, Public Knowledge, and of course EFF—remain skeptical. And worried.

Why do some people think LTE-U will disrupt Wi-Fi?

As with many things, the answer is technical. First, we need to understand a concept known as Listen Before Talk.

Listen Before Talk is exactly what it sounds like: before transmitting (or “talking”), a device must listen to the channel it wants to transmit on and make sure it wouldn’t be interrupting anyone else if it immediately started transmitting itself. It’s kind of like talking at a crowded dinner table. If everyone just shouted out what they wanted to say all at the same time, all you would hear is a cacophonous jumble. But by waiting and taking turns, everyone gets a chance to speak (and be heard) without being interrupted.

This seems like common sense, and it’s how Wi-Fi works.1 It’s also how LTE-U will work in Europe and Japan, since regulations there require Listen Before Talk for devices that want to use the unlicensed spectrum.2 But there’s no such requirement in the U.S., which is why the LTE-U Forum is trying to get away with leaving it out. Instead, LTE-U “shares” a channel by counting how many other devices are using that same channel, and then only transmitting part of the time based on that number. For example, if four other devices are on the same channel, an LTE-U device might transmit for 20 msec, then stay silent for 80 msec, then transmit for 20 msec, and so on—theoretically giving each device an equal share of time to transmit.

But that’s not how it always works in practice. Wi-Fi devices aren’t equipped to recognize the presence of an LTE-U device and don’t know that they should only transmit when the LTE-U device has scheduled itself to remain silent. Since the LTE-U device doesn’t listen for silence before it starts to transmit, any Wi-Fi device that starts transmitting just before the LTE-U device comes on will get interrupted and drowned out. Depending on how the Wi-Fi and LTE-U devices are configured, this can result in a serious loss of bandwidth for Wi-Fi devices.

he LTE-U Forum claims that despite this, LTE-U will coexist fairly with Wi-Fi. Other organizations don’t think the issue is so cut and dried. Why should anyone but a wireless policy wonk care? Because Hurricane LTE-U is heading toward your neighborhood and could seriously interfere with the existing wireless ecosystem. Even if you don’t understand the technical details, the fact remains that nobody knows how LTE-U and Wi-Fi will coexist once LTE-U is deployed on a large scale. So if you rely on Wi-Fi hotspots (either at businesses or at home), you have a very real stake in what happens next.

What can be done? 

One option would be for the government to get more involved. The FCC could start a long, difficult, and tedious rulemaking process that could lead to more complicated regulations and restrictions for everyone in the unlicensed band. Everyone involved agrees that’s a terrible idea.

Here’s a better solution: the LTE-U Forum could just act responsibly. The LTE-U Forum could develop its new specification jointly with other broad-based technology standards organizations, like the IEEE (the Institute of Electrical and Electronics Engineers), which developed the standards for Wi-Fi and Ethernet, or 3GPP (the Third Generation Partnership Project, a coalition of many different standards bodies), which developed the LTE specification. In fact, many of the same companies in the LTE-U Forum have worked within 3GPP to develop a standard very similar to LTE-U, known as License Assisted Access, or LAA, for use in Europe and Japan. It’s only in countries without a Listen Before Talk requirement, like the U.S., South Korea, and Indian, that the LTE-U Forum has decided to break ranks and develop their own standard.

But what if the LTE-U Forum persists in going it alone? In that case, we agree with Harold Feld of Public Knowledge that the FCC should pay close attention to the effect of LTE-U deployments—not in order to issue new regulations, but in order to enforce existing ones: specifically section 333 of the Communications Act, which states:

No person shall knowingly or maliciously interfere with or cause interference to any radio communications of any station licensed or otherwise authorized under this Act.

We agree with Feld’s suggestion that the FCC should clarify that deploying technology which someone knows will cause significant, widespread interfere across the existing unlicensed ecosystem counts as “knowing” interference. 

This way, if the LTE-U Forum really thinks that LTE-U won’t interfere with Wi-Fi, it can go forward with deployment. But if it turns out that LTE-U is as bad as some of its opponents say, the FCC could force carriers to back off and play nice—without dictating specific coexistence mechanisms or technological solutions.

A funny thing we noticed about the LTE-U Forum’s website: the banner graphic is actually a Creative Commons-licensed image that EFF created to promote open Wi-Fi.

Some would find that ironic. We see it as a good omen.  If the telecommunications industry is using artwork that represents neighborly sharing of Internet access, then maybe it will embrace the idea of being a good neighbor to other users of the unlicensed spectrum as well.

For more analysis, check out Public Knowledge Senior Vice President Harold Feld’s “insanely long” (his words) two-part essay on LTE-U politics (Part 1, Part 2). Although the two pieces clock in at 15,000 words, Feld makes it fun by drawing from Game of Thrones and Babylon 5 to describe the current state of play, and he even throws in a Dr. Seuss-inspired rhyme to explain Qualcomm’s role. You can also read a response to Feld's piece by Sherif Hanna here.

Correction: This post was updated on Nov. 5, 2015 to correct an error. The post originally stated that LTE-U was only going to be deployed in the U.S.; it is also being planned for deployment in other countries including India and South Korea. We apologize for the mistake. 

  • 1. Wi-Fi also makes use of a technique known as exponential backoff, which would also be necessary to ensure that LTE-U plays nicely with Wi-Fi.
  • 2. Technically, the standard being proposed for Europe and Japan is called License Assisted Access, but it’s essentially the same thing: LTE over the unlicensed spectrum.
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