The Wi-Fi industry is very worried about cellular operators’ plans to deploy an unlicensed version of LTE, the global 4G mobile phone standard, in spectrum already used by Wi-Fi networks.
In response, the Wi-Fi Alliance wants the Federal Communications Commission (FCC) to delay approval of unlicensed LTE (LTE-U) products that play by the same rules that enabled Wi-Fi to become what the Alliance describes as an “enormous economic engine.”
Specifically, the Wi-Fi Alliance has asked the FCC to withhold equipment authorizations for LTE-U products until the Alliance has developed and performed its own coexistence tests.
It seems unlikely that anyone is out to destroy Wi-Fi. We need to put this all in perspective.
There are more than 6 billion mobile phone subscribers worldwide, and they are upgrading to smartphones that generate dozens of times more wireless traffic than the basic mobile phones they are replacing.
The mobile phone industry believes, with good reason, that in order to continue growing, it is going to need 1,000 times as much capacity as it has today by the late 2020s. Although it’s going to require more than just additional spectrum to achieve a thousand-fold capacity increase, finding additional spectrum is a big part of the equation.
The capacity increase is needed not just to serve more users, but to deliver more data to each user. A technique called "carrier aggregation" that is part of the LTE standard enables mobile phone operators to create virtual broadband channels by stitching together non-contiguous channels scattered around the radio spectrum. By developing an unlicensed version of LTE, the cellular industry has theoretically added hundreds of megahertz of spectrum in the 5-GHz band to its pool of available spectrum.
The cellular industry insists that LTE-U is not a threat to Wi-Fi. LTE-U will use a single 20-MHz channel out of the approximately 500 MHz available in the 5-GHz band. According to the LTE-U Forum, LTE-U shares spectrum with Wi-Fi at least as well as different Wi-Fi access points share spectrum with each other. And many of the companies promoting LTE-U are heavily invested in Wi-Fi.
Still, the Wi-Fi community’s anxiety is understandable. Millions of homes and small businesses have come to depend on Wi-Fi. One way that the cellular industry has responded to soaring demand has been to offload data traffic to Wi-Fi networks. However, cellular operators have never been completely comfortable handing off subscribers to networks that they don’t control. LTE-U is designed to use a combination of licensed spectrum (the “anchor” spectrum, which handles all of the signaling and control) and 20 MHz of unlicensed spectrum (used to provide additional downlink capacity).
One fear is that mobile phone operators want to use LTE-U to head off competition from Internet companies (such as Republic Wireless) that use a mix of Wi-Fi and cellular access (with a preference for less expensive Wi-Fi). In a worst-case scenario, we could be witnessing an attempt by the cellular industry to muscle its way into and eventually dominate the 5-GHz band in public venues. A perhaps more realistic fear is that LTE-U isn’t the good neighbor that proponents claim and that it may disrupt nearby Wi-Fi hotspots.
The two sides have been busy conducting and documenting various performance tests. LTE-U proponents present test results that show LTE coexists well with Wi-Fi -- that adding an LTE-U node to a location is no worse than adding another Wi-Fi node. The Wi-Fi industry presents test results that show LTE-U nodes do not coexist well with Wi-Fi and cause neighboring Wi-Fi nodes to experience severe performance degradation. However, since commercial LTE-U equipment isn’t yet available, it was necessary to emulate LTE-U. My bet is that each side configured the equipment to produce the results it wanted.
To get a handle on all of this, we need to remember what unlicensed operation is all about. Many years ago, frequencies were allocated in different parts of the radio spectrum for industrial, scientific and medical (ISM) bands. The original purpose was to accommodate devices that generate radio signals for purposes other than communicating, such as microwave ovens. Later, it was decided that these bands could also be used for communicating, with some caveats. The communications devices must either transmit at very low power levels or use spread spectrum, a technology that is less likely to cause interference. FCC licenses would not be required to operate the devices, but they would not be protected from receiving interference. The rules governing these devices have been purposely kept simple, so they say nothing about how devices in the same vicinity must share the spectrum.
Wi-Fi has been phenomenally successful, in part, because the standards developed by the industry specify methods for neighboring networks to share the radio spectrum, such as by scanning for clear frequencies and using a “listen-before-talk” protocol. But Wi-Fi devices have always had to contend with non-Wi-Fi devices operating in the same spectrum that may not make any effort to share the spectrum.
Surely the solution is not to change the rules — rules that have been very successful until now — in the middle of the game. Others should have the same right to pursue business opportunities made possible by the unlicensed rules.
To start, everyone needs to calm down. We will know much more once the first LTE-U nodes are deployed. Not just how well LTE-U coexists with Wi-Fi, but how sincerely LTE-U equipment makers and operators are committed to working with the Wi-Fi community to avoid or at least minimize interference problems. It’s doubtful that cellular operators will recklessly deploy LTE-U and risk alienating their own subscribers.
I see two ways to head off serious problems. First, the LTE-U and Wi-Fi camps should work together on a voluntary basis to ensure optimal spectrum sharing. Neither side should seek special privileges from the FCC. And neither side should attempt to pull rank on the other.
Second, it’s understandable that some in the Wi-Fi industry feel they are at a disadvantage in that the cellular industry is vying for unlicensed spectrum to be used in addition to its substantial licensed spectrum. The Wi-Fi Alliance needs to develop a more effective spectrum strategy — a strategy that aggressively pursues the best options for additional unlicensed and perhaps even licensed spectrum for carrier Wi-Fi.
The ultimate solution is not more government regulation; it is smarter unlicensed devices that find and use clear channels so effectively that over time they are granted access to more and more spectrum.
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