Responding to claims that LTE Unlicensed (LTE-U) will interfere with Wi-Fi under certain conditions, Qualcomm (NASDAQ:QCOM) ran additional tests to show that LTE-U not only plays nice with Wi-Fi, but it also protects Wi-Fi to a greater degree than Wi-Fi protects itself.
The additional tests are detailed in Qualcomm's filing with the FCC, which opened a public notice to gather industry comments on LTE-U and LAA after hearing concerns that they could have a detrimental impact on unlicensed or shared spectrum users. Reply comments were due June 26.
As one of the developers of the technology, Qualcomm has insisted all along that LTE-U and LAA will not harm Wi-Fi users. While not the only users of unlicensed spectrum, they represent a huge contingent. Qualcomm says all three versions of LTE Unlicensed (LTE-U, LAA and its own MuLTEfire) will successfully share spectrum with Wi-Fi.
MuLTEfire is one of Qualcomm's branded versions that uses unlicensed spectrum exclusively and may be particularly suitable for entities like cable companies, even though cable companies, through CableLabs and the National Cable & Telecommunications Association (NCTA), are lodging their suspicions about LTE in unlicensed spectrum.
Dean Brenner, senior vice president of government affairs at Qualcomm, told FierceWirelessTech that conducting technology tests is something the company does on an ongoing basis. He said LTE Unlicensed is one of the most tested groups of technology that Qualcomm has ever launched.
But to suggest that Qualcomm would want to put anything into the world that would harm Wi-Fi is wrong. "The last thing that Qualcomm would want to do is have an adverse impact on Wi-Fi," he said. "That's why we have tested it so extensively."
The Open Technology Institute at New America, Public Knowledge, Free Press and Common Cause filed comments with the FCC jointly under the collective "Public Interest Organizations" label. They said coexistence and fair-sharing standards are built into Wi-Fi's DNA, and they're concerned that the LTE-U version that U.S. carriers plan to deploy next year coexists poorly with Wi-Fi, degrading both throughput and latency.
In their filing, the public interest organizations said Qualcomm has "strong patent licensing incentives to promote licensed carrier-based unlicensed technologies in a manner that crowds out or disadvantages Wi-Fi deployments. A major patent-holding company like Qualcomm stands to make more licensing revenues, block more competitors and monopolize more strongly a field based on a standard promulgated by 3GPP than one based on a standard promulgated by IEEE," their filing states.
Brenner said the patents have nothing to do with LTE-U. "It's like why don't we talk about Greek debt?" he said, adding that the company continues to roll out various 802.11 products. Qualcomm does have differences with the IEEE's patent policy, but those differences have "zero, zero, zero" to do with its LTE Unlicensed initiatives, he said.
Qualcomm has met and will continue to meet with all the stakeholders around the LTE-U/LAA efforts, he said. Qualcomm also supports LTE with Wi-Fi Aggregation (LWA), which some suggest is a more palatable solution for Wi-Fi proponents. It's going to be part of Release 13--3GPP approved it as a work item, and the standardization work is expected to be done early next year, Kai Tang, director, technical marketing at Qualcomm, told FierceWirelessTech. LAA is also part of Release 13.
LWA is a perfect technology for carriers that have their own Wi-Fi access points deployed, Brenner said. If a carrier has deployed both Wi-Fi access points and LTE, LWA presents a "very good way" to aggregate the two and deliver a better user experience, he said, adding that a carrier that doesn't have its own access points wouldn't find LWA to be a good fit.
With LTE-U, LAA, MuLTEfire and LWA, "each of those technologies has different pluses and minuses and attributes" and each is best suited to parties in different situations," he said. "Our perspective is LWA is moving forward quite nicely globally," although it hasn't generated the controversy and attention that the others have.
Whether Qualcomm's tests and their results presented in the FCC's record will allay concerns is not clear. Qualcomm said its tests have been conducted in various scenarios, including outside and in what's considered real-world type scenarios versus just in a lab.
"We probably will do more tests. That's what Qualcomm does. That's why hopefully the technology, when it's ultimately deployed, will be so good," Brenner said.
He also said there are different ways to accomplish coexistence. In the LTE-U small cell, it senses the presence of Wi-Fi nodes adjacent to it before transmitting. It looks for a clear channel, and if there's a clear channel available, that's where it goes. If there is no clear channel, it senses the presence of the nodes and finds the least occupied channel. If it finds a channel with four Wi-Fi access points, for example, it sets a cycle where it goes on and off; it can be on the spectrum only one-fifth of the time. The other four-fifths of the time, the Wi-Fi nodes have the spectrum.
The LTE-U Forum specs, which are published at www.lteuforum.org, also define the maximum continuous "on" time of being 50 milliseconds. So if there were four Wi-Fi users and an LTE user on the spectrum, the longest the LTE user can be on continuously is 50 milliseconds, and then it needs to be in the "off" mode and not transmitting for 200 milliseconds to let all the Wi-Fi nodes have the spectrum. Because some Wi-Fi applications are sensitive to latency, like VoIP calls or gaming, even when LTE-U is on, it has off times to ensure--and this has been shown in testing--that the latency-sensitive Wi-Fi nodes are not adversely affected, he said.
Just like in LTE, "the small cell is constantly talking to the wireless network over the licensed band and sending signals, interference measurements back to the network and asking the network, should I go on the unlicensed band or do I not need it? It uses the unlicensed spectrum only to the extent it's necessary to do the transmission that it's doing and then it gets off. Remember, LTE-U is downlink only. There are no uplink transmissions, so the phone is just the receiver for LTE," and it's not transmitting.
"We've done a lot of testing on how Wi-Fi shares spectrum with other Wi-Fi users, and actually what we found is there's a wide variety of variations," including many poor Wi-Fi implementations that don't meet the Wi-Fi-to-Wi-Fi interoperability spec, he said.
In one scenario, Qualcomm tested two Wi-Fi access points (APs) and it turned out that there were times when one Wi-Fi AP would get the channel most of the time rather than sharing it 50-50. LTE-U is never on the spectrum more than 50 percent of the time; in fact, it's always on the channel for slightly less than 50 percent of the time, so "whatever definition one wants to construct of fairness, in terms of access to the spectrum, LTE-U is extremely fair, actually to a fault, because if we were trying to get every last ounce out of the spectrum, we would make sure that LTE-U was on the spectrum exactly 50 percent of the time, and actually that's not the case," he said.
For more:
- see this Open Technology Institute filing
- see this Qualcomm filing
- see this Network World article
Related articles:
Qualcomm responds to interference concerns: LTE-U won't interfere with cable Wi-Fi
Is there an alternative to LTE-U/LAA that won't tick everyone off?
Qualcomm's new MuLTEfire would create LTE networks in unlicensed spectrum
Qualcomm introduces MuLTEfire for unlicensed spectrum