Is there an alternative to LTE-U/LAA that won't tick everyone off?


Given how much the industry has discussed LTE in unlicensed spectrum during the past several months or so, some stakeholders might have gotten the impression that all the questions have been asked and answered, thank you very much. But that's not the case.

From all indications--not the least of which is the FCC's public notice seeking industry input--the debate is alive and well. Understandably, the Wi-Fi community is concerned that there is insufficient information about how LTE-Unlicensed (LTE-U) and Licensed Assisted Access (LAA) protocols will manage coexistence with Wi-Fi and other devices that use unlicensed spectrum. Wi-Fi, while not the only user of unlicensed spectrum, accounts for a pretty big percentage of it, and the Wi-Fi community is worried that LTE won't be as "polite" as Wi-Fi, which employs to a listen-before-talk (LBT) etiquette.

Carriers like T-Mobile US (NYSE:TMUS) insist that work to date suggests both LTE-U and LAA can provide valuable supplemental capacity to carrier networks without threatening existing unlicensed technologies such as Wi-Fi. To hear Verizon (NYSE: VZ) tell it, LTE-U has a spectrum-sensing capability to identify open frequencies--channels not occupied by other unlicensed users. Its "adaptive duty cycle" also allows it to take turns with other users. 

By way of background, LTE-U is the version of LTE unlicensed that was proposed in 2013 by Qualcomm (NASDAQ:QCOM) and Ericsson (NASDAQ: ERIC), according to a Senza Fili Consulting report that was filed in the FCC's LTE-U/LAA proceeding. LTE-U relies on 3GPP Release 10-12 functionality, with specifications defined by the LTE-U Forum, which was established by Verizon in collaboration with Alcatel-Lucent (NYSE: ALU), Ericsson, LG, Qualcomm Technologies and Samsung. While it's the first version of LTE unlicensed to be available in commercial deployments, it does not employ a listen-before-talk mechanism. For that reason, LTE-U can only be used in markets where regulation doesn't require LBT, including the U.S., Korea, China and India.

LAA is the version of LTE unlicensed that 3GPP is standardizing in Release 13 and it supports LBT, in addition to carrier aggregation. "In the long term, we expect operators and vendors worldwide to support LAA-LTE because it provides a globally harmonized solution that leads to better scalability and choice among equipment and device vendors," Senza Fili said in its report.

But there's another option that doesn't get discussed nearly as much. Ruckus Wireless has posited that LTE + Wi-Fi Link Aggregation (LWA) could be much more palatable to the broader industry due to its use of 802.11 at the Physical (PHY) and Medium Access Control (MAC) layers. LWA is said to achieve similar results to LTE-U and LAA-LTE.

Senza Fili notes that LWA is being standardized as well by 3GPP and it gives mobile operators a way to use unlicensed bands that is well integrated within their network. With LWA, mobile operators use Wi-Fi for access, with Wi-Fi transmission integrated in the cellular RAN. The RAN manages the traffic and all signaling goes through LTE in a licensed channel.

The main advantage of LWA is it requires little intervention in existing networks and devices. In LWA, Wi-Fi is used only for the downlink, with LTE carrying all the uplink traffic and optionally, downlink traffic as well.

At the Small Cells World event in London earlier this month, the workshop titled "Small Cells and License Exempt Spectrum: Carrier Wi-Fi, Wi-Fi Calling and LAA" proved to be its most successful workshop event to date, according to the Small Cell Forum. It created "productive debate" over the merits of LAA, LTE-U and LWA. Significant discussions are expected over the next few Small Cell Forum plenary sessions, starting with the meeting in September in Rome, according to the forum.

All of this is to say it ain't over yet. Surely, representatives from all sides of the issue--those with a stake in licensed spectrum and those solely focused on unlicensed, as well as those who dabble in both--are passionate about their stances and are not going to easily budge. The FCC should be commended for opening the LTE-U/LAA proceeding, giving vendors and operators a chance to lay out their concerns in public, as well as see what their peers are saying. Interested stakeholders from all sides are capable of having healthy disagreements and discourse. Or put another way: Sometimes the right thing to do is listen before talk.--Monica

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