CableLabs engineer: LTE-U must integrate 'listen before talk' features

CableLabs has taken the group of wireless companies developing LTE-Unlicensed (LTE-U) technology to task, accusing them of executing a go-it-alone standards process that doesn't do enough to ensure LTE-U won't interfere with cable Wi-Fi.

In a blog post, Jennifer Andreoli-Fang, principal architect at CableLabs, said the cable industry research consortium has been rebuffed in its attempts to join the LTE-U Forum, the group formed by Verizon (NYSE: VZ) to develop the technology along with Alcatel-Lucent (NYSE: ALU), Ericsson, LG Electronics, Qualcomm (NASDAQ:QCOM) and Samsung.

"But unfortunately, when it comes to development of LTE-U -- a different form of unlicensed LTE being developed outside of international standards for the U.S. market -- we haven't been in the 'club' -- and a small club it is," Andreoli-Feng said.

She noted that another technology for LTE transmissions in unlicensed spectrum -- Licensed Assisted Access (LAA) — has been developed in the confines of the 3rd Generation Partnership Project (3GPP), a group CableLabs has participated in. 

Within that framework, LTE LAA has adopted what Andreoli-Fang describes as a "most fundamental coexistence procedure" called "listen-before-talk" (LBT), which ensures LTE LAA and Wi-Fi devices operating on shared spectrum don't talk over each other. 

The LTE-U Forum outlined its own coexistence procedures in a presentation to the IEEE in July, but the deck didn't match specifications published earlier by the group, the CableLabs engineer said.

"One might expect that the coexistence spec would contain requirements consistent with the various features that the LTE-U Forum has talked about on numerous occasions, such as their July presentation to the IEEE, or their recent letter to the FCC," Andreoli-Fang said. "But unfortunately, it contains none of this detail."

"LTE-U Forum coexistence requirements simply entail an ability to duty cycle when it senses other operators are present," she added. "There is no requirement to share fairly in time, to avoid interrupting Wi-Fi transmissions mid-stream, or to adapt to different levels of Wi-Fi usage and traffic. And note that, in the 'off' state, LTE-U may still send discovery signals that can also interfere with Wi-Fi."

The most basic problem with LTE-U, she said, "is that LTE-U does not 'listen before talk,' a most basic politeness protocol."

Her note comes as cable companies, under the representation of the NCTA, lobby the FCC to intervene in the development of LTE-U. Qualcomm, meanwhile, has responded in its own ex parte filings that interference with cable Wi-Fi is not an issue. 

LTE-U, LAA and other, similar technologies promise to allow wireless operators to transmit LTE signals through unlicensed spectrum. The technology would allow wireless carriers to provide faster speeds to smartphone users and other cellular customers by expanding LTE transmissions beyond licensed spectrum and into unlicensed spectrum, like the unlicensed spectrum used by cable Wi-Fi.

The issue is key for cable operators that are in the process of rolling out millions of public Wi-Fi hotspots. Such hotspots give cable operators the ability to offer Internet access to users who are traveling outside their homes.

For more:
- read this CableLabs blog post

Related articles:
NCTA warns FCC that LTE-U could interfere with cable Wi-Fi
Qualcomm responds to interference concerns: LTE-U won't interfere with cable Wi-Fi
CableLabs wants to help forge unlicensed LTE, ensure it 'plays well' with Wi-Fi