Google, Broadcom, Wi-Fi Alliance push for more collaboration between LTE-U/LAA and Wi-Fi

Broadcom, Ericsson (NASDAQ: ERIC), Google (NASDAQ: GOOG) and Verizon (NYSE: VZ) are just some of the stakeholders that weighed in on the FCC's request for information on current trends related to LTE-Unlicensed (LTE-U) and Licensed Assisted Access (LAA).

Several players in the Wi-Fi community made clear: The LTE-U/LAA and Wi-Fi communities need closer collaboration if they're going to make this whole sharing of unlicensed spectrum thing work out. Those that want to deploy LTE-U and LAA, however, unsurprisingly argued that plenty of collaboration has occurred since Verizon and its technology partners formed the LTE-Unlicensed Forum in April of last year.

The FCC called on the industry to supply comments on LTE-U/LAA after a number of organizations voiced concerns that LTE-U/LAA could interfere with or otherwise have a detrimental effect on existing and future users of unlicensed spectrum. The Wi-Fi community is concerned that LTE-U could essentially bully Wi-Fi users out of their space, while the LTE-U/LAA camp argues that their presence will make Wi-Fi work better.

Similar to Qualcomm (NASDAQ:QCOM), Ericsson points out that it's interested in seeing both LTE/LAA and 802.11 technologies succeed, and when LTE-U shares spectrum with 802.11/Wi-Fi, the Wi-Fi performance improves.

Ericsson also said in its FCC filing that LAA is based on 3GPP LTE Release 13, which is expected to be finalized this year. LTE-U is compliant with 3GPP Release 12 and incorporates multiple co-existence mechanisms for fair, shared usage between LTE-U and 802.11/Wi-Fi operations, as well as LTE-U. LTE-U is not a "pre-standard," as that implies that LTE-U still must be standardized. "The LTE-U specifications are complete," Ericsson said.

Ericsson also said "there has been extensive coordination between 3GPP and IEEE 802.11 on appropriate sharing characteristics to ensure coexistence between LTE-U/LAA and 802.11/Wi-Fi." Communication is done via liaison statements as well as presentations in person by the 3GPP RAN chair and the study item rapporteur directly to IEEE.

However, according to a June 3 filing by Paul Nikolich, IEEE 802 LAN/MAN standards committee chairman, "there has been no coordination between IEEE 802 and any standards body associated with LTE-U, because LTE-U was not developed by a standards body." It is the understanding of the IEEE 802 that LTE-U is a proprietary solution that implements a duty cycle approach to medium sharing that does not use appropriate sharing mechanisms to ensure coexistence with IEEE 802.11 family of standards.

With respect to LAA, "it is the understanding of IEEE 802 that the only process 'for coming to agreement on appropriate sharing characteristics to ensure coexistence with the IEEE 802.11 family of standards' is to work within the 3GPP organization," he wrote, adding that there has been no coordination between 3GPP and IEEE 802 on LAA, although some presentations have been given.

"Although the exchange of written liaisons has proved useful, responses received are not always as complete as desired and often lead to more questions," the filing states. IEEE 802 believes that 3GPP should engage with stakeholders like IEEE 802 in a joint forum such as a workshop or a series of workshops to facilitate understanding of the potential spectrum sharing issues for IEEE 802.11 and LAA and come to agreement on appropriate ways to ensure fair co-existence.

The Wi-Fi Alliance is not at all convinced that LTE-U and LAA are going to play fair with Wi-Fi. According to the alliance, there is insufficient information about how both LTE-U and LAA will coexist with Wi-Fi and other users of unlicensed spectrum. While efforts are underway to foster collaboration between the affected parties, it urges the commission to continue monitoring developments to ensure there is sufficient dialogue and consideration on how unlicensed spectrum will be shared fairly so that LTE-U and LAA do not impede the development of Wi-Fi and other technologies.

The Wi-Fi Alliance also took issue with the FCC referring to LTE-U as a "pre-standard" version, but for a different reason than Ericsson. "Referring to something as a 'pre-standard' version typically implies that it is based on an unapproved draft of a standard," the Wi-Fi Alliance said. "However, this is not the case with LTE-U."

LTE-U is a proprietary system developed privately by a few companies, and it employs carrier sensing adaptive transmission (CSAT) technology that is not under consideration by 3GPP. "This lack of industry standard implementation of CSAT means that its impact on other users of shared spectrum will be variable and unpredictable." 

The Wi-Fi Alliance is working on coexistence evaluations and said Qualcomm recently offered to work with the alliance to enable it to better understand the Qualcomm LTE-U sharing scheme and to replicate some of the testing Qualcomm has done. The alliance said it welcomes the opportunity to work with other LTE-U stakeholders in a similar fashion. 

For its part, Google assigned a couple of its wireless systems engineers, Nihar Jindal and Donald Breslin, to investigate, and the results show that in many circumstances, "LTE-U co-exists poorly with Wi-Fi in the 5 GHz band," the company said in its FCC filing.

As Google explains it, LTE-U is being developed by an industry consortium, the LTE-U Forum. The primarily 5 GHz band technology is designed for countries without a listen-before-talk (LBT) requirement, such as the United States. Unlike LTE-U, LAA is expected to perform LBT, as required by certain regulatory regimes, including those in Europe. The European Telecommunications Standards Institute (ETSI) established specific requirements for LBT.

Google's filing goes on to point out flaws in LTE-U and LAA. Many of the coexistence challenges presented by LTE-U apply equally to LAA, it says. Jindal and Breslin's evaluation of LTE-U found problems with its lack of duty-cycled approach to sharing with co-channel Wi-Fi devices, as well as with LTE-U's lack of an effective coexistence mechanism when Wi-Fi is received at a power level below -62 dBm. Fair co-existence with Wi-Fi might be possible with LAA if it implements LBT effectively, "but only with close collaboration with all stakeholders, especially the IEEE 802.11 and the Wi-Fi Alliance, can this outcome occur," they said.

Broadcom laid out concerns about LTE-U's coexistence with Wi-Fi and believes that it's unlikely to be a good neighbor because the coexistence algorithms are proprietary, there are variations in equipment, and ultimately, coexistence is controlled at time of operation, among other reasons.

Broadcom does not believe that LTE-U as envisioned by the LTE-U Forum meets the normal criteria of a standard. Participation in the group is restricted, detailed specifications are not provided and sharing algorithms are proprietary, the company said.

"Closer collaboration between 3GPP, IEEE, and Wi-Fi Alliance would ensure that critical technical characteristics are carefully considered in the 3GPP Study Items on LAA," Broadcom said. "In particular, the standards-setting process should evaluate coexistence with Wi-Fi as it is currently deployed in the market: it should recognize that Wi-Fi devices can operate using 20 to 160 MHz channels, incorporate multiple-input multiple-output (MIMO) technology, and use explicit transmit beamforming (TxBF)."

Verizon plans to deploy LTE-U on a small cell basis to supplement its existing licensed network in specific areas, a fact that it says further mitigates any concern that it might displace or disrupt other unlicensed operations. William Stone, executive director of radio access network planning for Verizon, submitted a declaration to the FCC saying LTE-U has a spectrum-sensing capability that senses the RF environment to identify open frequencies--channels not occupied by other unlicensed users. If one is open, LTE-U will transmit only on that channel, thus avoiding the need to transmit on any channel being used by anyone else. If there are no open channels, LTE-U will select the least interfering channel. "LTE-U will also continue to scan for open frequencies and select these channels as they become available," he said.

He also said that LTE-U's adaptive duty cycle feature allows it to take turns with other users. If another user is operating on a particular unlicensed frequency, LTE-U can still operate on the same spectrum without degrading the other user's performance. LTE-U does that that via CSAT.

Verizon and technology partners Alcatel-Lucent, Ericsson, LG Electronics, Qualcomm Technologies and Samsung formed the LTE-U Forum in April 2014. Since then, they have conducted extensive review of LTE-U/Wi-Fi coexistence through computer simulations, lab testing and over-the-air testing, according to Stone.

"All simulations show that when LTE is simply deployed in unlicensed spectrum without the above coexistence mechanism, LTE causes significant performance degradation on coexisting Wi-Fi access points," he stated. "But when these coexistence mechanisms are implemented, LTE-U behaves as a comparable neighbor to Wi-Fi compared to Wi-Fi as a neighbor, while LTE-U significantly outperforms Wi-Fi." 

T-Mobile US (NYSE:TMUS) has been one of the more aggressive U.S. operators to promote Wi-Fi calling and, in its filing, it reiterated its plans to deploy LTE-U in 2016. The carrier pointed out that there is meaningful overlap in membership of 3GPP, IEEE 802.11, as well as the Wi-Fi Alliance, to ensure collaboration.

For more:
- see this FierceCable story
- see the FCC's proceeding

Related articles:
FCC seeking comment on LTE-U, LAA tech
Wi-Fi, LTE worlds bump into each other in WIS panel debate
AT&T in no hurry to test and deploy LTE-Unlicensed
T-Mobile sets LAA deployment for 2016

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