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WiFi/3GPP relations thaw over LTE-LAA but not LTE-U

Beijing workshop successful in addressing some technical coexistence issues in 5 GHz, but US disputes over LTE-U intensify

In a workshop in China this weekend, there appeared to be some thawing of the cold war between the WiFi community and those promoting LTE implementations in the licence-exempt 5 GHz band. However, the attempts at harmonious coexistence were heavily focused on the upcoming LTE-LAA (Licensed Assisted Access) standard, which is likely to be commercialized from late 2016 – not on its already standardized stablemate, LTE-Unlicensed, which could potentially come to the US and Japanese markets far earlier.

Attendees from both sides said that the Beijing session had been constructive and made progress on technical mechanisms to prevent LTE-LAA interfering with WiFi. The workshop was hosted by Huawei under the auspices of the 3GPP and chaired by Dino Flore, chairman of the 3GPP RAN TSG (technical specification group) and also senior director of technical standards at Qualcomm, one of the most significant contributors to the would-be standard. Over 200 people took part in the session, which was the culmination of a week of technical meetings.

Among the prominent companies taking part were the usual suspects such as Ericsson, Cisco, Alcatel-Lucent and Samsung; plus those which have been deeply sceptical of letting LTE into 5 GHz, such as CableLabs and Cablevision. The presence of General Motors highlighted that wireless technology debates are of relevance to companies beyond the mobile operators and their vendors, with the onset of the internet of things. Other companies involved included Intel, Panasonic, Cisco and Ruckus Wireless.

Flore told FierceWirelessTech that the meeting achieved “a better mutual understanding of each other’s processes” and added: “We do expect the collaboration between our organizations to continue and even improve as the LAA standard gets further developed … so that in the end we can achieve the ultimate goal of fair sharing of unlicensed spectrum between LAA and WiFi.”

However, the WiFi community is feeling far less reassured when it comes to LTE-U, which is already part of the 3GPP standards. It runs LTE in unlicensed spectrum, without the ‘listen before talk’ (LBT) mechanisms which will be included in LAA. While some markets like Europe mandate LBT in the 5 GHz band, the US, Japan and others do not.

The latest row over LTE-U was rumbling on for most of August. Last week, Qualcomm, T-Mobile USA and others wrote to the FCC with a strongly worded objection to a new request, from the WiFi Alliance (WFA), that it effectively takes over coexistence testing between LTE running in the 5 GHz band, and WiFi.

The Alliance has expressed concerns that LTE would adversely affect WiFi, and other WiFi players, including the cable industry R&D body CableLabs, have been more outspoken, with some accusing the cellular companies of conducting inadequate tests or presenting over-optimistic results. In addition, the WFA claims: “LTE-U was developed in private, in contrast to LAA and in contrast to recognized standard development methods.”

The WFA recently wrote to the FCC demanding very stringent tests and rules to govern coexistence with LTE-U, which is currently going through 3GPP standards processes and is likely to be available in mainstream devices from late 2016. It proposed a Co-Existence Evaluation Program, which would be run under its auspices.

“To advance the constructive collaboration that is required in order to potentially permit use of LTE-U technologies in unlicensed spectrum, and particularly in the 5 GHz band, WiFi Alliance is taking several significant actions in which it hopes the LTE-U Forum and equipment manufacturers will readily join,” it said. “First, we are developing a comprehensive coexistence test plan aimed at assessing the level of fair sharing between LTE-U and Wi-Fi for equipment supporting a range of applications. Second, we will work with LTE-U vendors as soon as possible to test their products to determine if they pass the Wi-Fi Alliance co-existence tests across all allowable configurations.”

This has provoked strong responses from the cellular community, which clearly fears that some of its traditional power over wireless standards – and regulatory policy – will be usurped by the ‘other side’. That, in turn, would reflect an uncomfortable truth for US mobile operators – that, though they may find WiFi useful for offload and HetNet, it is a far more disruptive weapon in the hands of cablecos and other companies which have traditionally had to rely on MVNO deals with spectrum owners in order to provide wireless and multiplay services – but can now tap carrier-class WiFi, seamless authentication via the WFA’s Passpoint, WiFi Calling and other advances, to offer comparable services to those of the MNOs in many areas.

Verizon and T-Mobile were among the petitioners who argued to the FCC that the WFA would be setting a dangerous precedent if one technology community is given the right to impose limitations on another. “Allowing an organization that certifies interoperability for one particular technology to become the gatekeeper for another technology to use unlicensed spectrum would jeopardize the Commission’s entire framework that has made unlicensed spectrum so successful as an open platform for permissionless innovation,” the filing said.

Recently, TMO, accused the cablecos of using “parameters set at extremes that do not represent realistic deployments or do not reflect actual LTE-U specifications” in their own tests of LTE/WiFi coexistence, and some fear the WFA program could take a similarly hardline view.

The operators were joined by Qualcomm, Ericsson and Alcatel-Lucent, all of which have been deeply involved in developing various 5 GHz LTE technologies, in claiming the WFA had ignored invitations to engage in collaborative testing programs and had instead gone straight to the FCC. “The LTE-U Forum gave a second all-day technical briefing to the WiFi Alliance and 28 other associations and companies,” the letter said. “Both workshops included extensive technical presentations, robust question-and-answer sessions, and live LTE-U/WiFi coexistence demonstrations in Qualcomm’s test lab. In fact, immediately after these workshops Qualcomm invited the WiFi Alliance to do their own LTE-U/WiFi testing in Qualcomm’s lab. These offers were not accepted.

The disputes reflect global divisions, and similar arguments will be made over any licence-exempt LTE introduction, but in the US (and some other markets like Japan) operators have the opportunity to introduce LTE-U at an early stage. Other regions, including Europe, mandate LBT mechanisms to avoid interference in licence-exempt spectrum, so operators will have to wait for an implementation that supports this method. That will come with LTE-LAA (Licensed Assisted Access), a version that uses the 5 GHz spectrum for supplemental downlink, boosting the capacity of a host network in licensed frequencies; and LTE-LWA, which allows LTE to run standalone in unlicensed spectrum.

The WFA stood by its proposals, and particularly focused on the LTE-U version, saying in a statement: “The current LTE-U specification does not require products to include adequate fair sharing etiquette protocols … Furthermore, there is already a growing amount of research, such as that published by Google and CableLabs indicating that WiFi networks will be negatively impacted by the current version of LTE-U technology.”

As the WiFi and cable industries call for the race to licence-exempt LTE to be slowed down to allow for full testing, Qualcomm has adopted the slogan ‘Why Wait?’ as it seeks to maintain the momentum behind a technology which plays to all its core interests in 3GPP platforms. At a recent media workshop to “set the record straight” about LTE in 5 GHz, Qualcomm CTO Matt Grob implied the WiFi and cable sectors were engaging in delay tactics to protect their own interests, but that, in fact, the efficiencies of LTE-U would improve overall user experience and security when working alongside WiFi, and that the combined networks would set the stage for multi-RAT 5G.

Qualcomm claimed that, even in LTE-U, it implemented some LBT – “we really have to go above and beyond the regulatory requirements”, Grob said. LTE-U has an ‘adaptive duty cycle’ that allows it to take turns with other users and also uses Carrier Sensing Adaptive Transmission (CSAT) to sense the traffic on a particular channel, in order to schedule its own transmissions.

The FCC has itself come under fire for overstepping its remit by getting involved in a standardization process, for LTE-U and LTE-LAA. In May, the regulator opened a comment period on the two technologies in response to concerns about interference, which arose during its consultation on 5 GHz and 3.5 GHz spectrum. Earlier this month, the head of the FCC’s Office of Engineering and Technology, Julius Knapp, asked the cellular industry for more information, in particular about how CSAT works and why it would be allowed to transmit even on an occupied channel. In addition, aspects of the anchor channel were unclear, he said.