LAS VEGAS--Research firm Signals Research Group (SRG) presented its third-party assessment of LTE-U and Wi-Fi co-existence at the CTIA Super Mobility 2015 conference Wednesday, showing that the impact of LTE-U on real-time applications running over Wi-Fi was relatively modest and largely comparable to the impact of introducing a new Wi-Fi access point into the channel.
Of note: The study was supported by Verizon Wireless (NYSE: VZ) and Qualcomm (NASDAQ:QCOM), two of the most vocal proponents of using LTE in unlicensed bands, while the cable industry, which has a vested interest in Wi-Fi, and the Wi-Fi Alliance, among others, are concerned that LTE-U will use unlicensed specturm in a way that doesn't reflect fair sharing.
SRG is a well-known research firm that has been conducting third-party tests for various entities for years, and its results should weigh into the record. SRG conducted third-party performance analysis of Wi-Fi and LTE-U coexistence, with SRG founder Mike Thelander presenting the findings during a Super Mobility conference session.
Voice tests consisted of six bidirectional VoIP calls, using Voice over Wi-Fi, Skype Voice and simulated VoIP, with background Wi-Fi and LTE-U traffic. The tests leveraged Spirent Communications Nomad User Experience Analytics Platform to measure the voice quality of the Skype and VoWi-Fi calls using POLQA algorithms. Tests focused primarily on the three best Wi-Fi AP models under a range of conditions.
Mingxi Fan, vice president of engineering at Qualcomm Technologies, previously told FierceWirelessTech that it's important to bear in mind that there is no baseline Wi-Fi-to-Wi-Fi coexistence mechanisms, much less any enforcement of a Wi-Fi baseline. "As a result, our testing has shown that, today, Wi-Fi products have wide variation in product behaviors including unfair sharing with each other," he said.
That coincides with what Thelander found in his tests. "When we did our testing, we had one model of access point and we nicknamed it the FU 2000," he told FierceWirelessTech on the sidelines of CTIA Super Mobility. "It just did whatever it wanted, and that was in the presence of LTE. That was in the presence of Wi-Fi. It didn't matter."
He noted that while that was probably the extreme, there was another access point they tested and it behaved very friendly with another device, but when three devices were introduced to the picture, it wanted three times the bandwidth. It didn't behave well, he said, adding there are lots of permutations. Problems occur when one AP acts aggressive; another one acts "conservative" in how they grab the channel and the conservative one "just gets killed," he said.
"It's impossible to simulate this stuff because you may think you know how Wi-Fi is supposed to perform, but how it does perform is much different. So the only way to do this testing is to test it against other commercial products and then if you want to see the impact of LTE-U, if you put in LTE-U as an additional source of interference, you need to compare that to -- what if I add an additional Wi-Fi access point -- to do a fair comparison. Because anytime you add another access point or LTE-U, there's always going to be an impact. The question is it more or less and the answer is 'it kind of depends'" on several factors.
The test findings came the same day FCC Chairman Tom Wheeler told CTIA Super Mobility attendees that the FCC wants to get maximum efficiency out of both licensed and unlicensed spectrum, "and if they can work together to achieve that, that's good." But if some things end up negatively affecting the ability for Wi-Fi unlicensed to deliver, "that's bad."
The way it's traditionally been handled is through a broad-based standards process that can wrestle through all the interference and coexistence issues that have to exist because that is "far preferable to us coming in and saying, 'OK, you can't do it? We'll do it,'" he said during Wednesday's keynote. "I'm looking to the standards process to help answer some of the key questions about LTE-U" and to have a wide base of involvement that helps address for the licensed and unlicensed communities just how it works.
When does he expect to see key answers? "I think this is up to them, more than up to us," Wheeler said. The FCC last month sent a letter to industry asking for answers to outstanding questions, and there is an incentive on both sides to "move with dispatch" to find a solution, "but it needs to be a broad-based solution."
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