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LTE-U plays 'good neighbour' to Wi-Fi

Posted: 29 Sep 2015     Print Version  Bookmark and Share

Keywords:Qualcomm  Wi-Fi  LTE-U  Wi-Fi Alliance  cellular 

Qualcomm is pulling out all the stops in convincing unbelievers that LTE-Unlicensed (LTE-U) will be a good neighbour to Wi-Fi for next generation communications as it revealed the details of coexistence tests conducted at its San Diego lab.

LTE-U aims to extend LTE Advanced to unlicensed 5GHz 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 5GHz.

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 or 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 5.8Mb/s using all Wi-Fi communications. Using a mix of Wi-Fi with LTE-U, LTE-U use decreased downlink delay by 0.06ms and increased the uplink delay by 10ms though LTE-U over 5GHz has yet to include uplink in its spec.

"LTE-U is inherently a good neighbour to Wi-Fi," said Mingxi Fan, Qualcomm's VP 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-Fi," said Dean Brenner, Qualcomm's SVP 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 alliance 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
  EE Times

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