SAN FRANCISCO – Qualcomm wants to convince unbelievers that LTE-Unlicensed (LTE-U) will be a good neighbor to Wi-Fi for next generation communications. Following debate about the realities of sharing spectrum, the chip giant discussed coexistence tests conducted at its San Diego lab.
LTE-U aims to extend LTE Advanced to unlicensed 5 GHz spectrum, boosting cellular data speeds over short distances without requiring users to login to a Wi-Fi network. The technology has met with criticism from companies who rely on Wi-Fi and worry about LTE-U inference.
As a test, Qualcomm configured nine access points for media streaming and did not try to counterbalance interference. Engineers measured the throughput of each access point when using Wi-Fi only, then measured again with eight APs configured for Wi-Fi and one using LTE-U over 5 GHz.
Qualcomm found –- and third party firm Signal Research confirmed –- that Wi-Fi access points from different OEMs had variable throughput speeds regardless of the presence of absence of a cellular connection, and LTE-U shared spectrum when it was turned on. The average throughput for the top two access points was 5.8 Mbits/second using all Wi-Fi communications. Using a mix of Wi-Fi with LTE-U, LTE-U use decreased downlink delay by 0.06 milliseconds and increased the uplink delay by 10 milliseconds though LTE-U over 5 GHz has yet to include uplink in its spec.
“LTE-U is inherently a good neighbor to Wi-Fi,” said Mingxi Fan Qualcomm’s vice president of engineering and corporate R&D.
When deployed the technology will rely heavily on small cells and an improved air interface to listen for unused spectrum to offload data to LTE-U, Fan said. In addition, Qualcomm has designed LTE-U chips with “variable on” modes or tiny gaps in use that allow the channels to complete throughput without interference and with low latency, he added.
“[LTE-U is] a great new technology that has tremendous performance advantages for consumers and it coexists very, very well with Wi-Fu,” said Dean Brenner, Qualcomm’s senior vice president of government affairs. “We envision a very long future for Wi-Fi; this is not replacing Wi-Fi.”
The Wi-Fi Alliance recently submitted a request to the FCC requesting additional information about LTE-U and its cousin Licensed Assisted Access (LAA) — a form of unlicensed cellular that will be deployed in Europe and Japan with LTE release 13. The Allaince and others fear unlicensed cellular will degrade performance of services delivered over Wi-Fi. To the contrary, Qualcomm claims that Wi-Fi throughput would improve with more LTE-U access points in use than Wi-Fi but did not provide details.
“I think there is fear, uncertainty, and competitive aspects. Basically there’s a lot of trepidation,” Brenner said. “So we’re doing everything we can to show that this is how it works, how we’ve designed LTE-U for coexistence.”
A Verizon official said the company expects to have small cell technology commercially available in late 2016. Qualcomm will host field trials of this technology alongside its LTE-U capable Snapdragon 820 chip in October 2015.
In the meantime, Qualcomm’s Brenner said the company has weekly conference calls with the Wi-Fi Alliance and will present at an Alliance-sponsored coexistence workshop in November.
— Jessica Lipsky, Associate Editor, EE Times