Cellular and Wi-Fi clash in air war
The battle pits Wi-Fi vendors such as Broadcom and cable-TV carriers against Qualcomm, cellular carriers and their equipment suppliers. It foreshadows bigger battles ahead as engineers hammer out standards for 5G cellular, expected to span licensed and unlicensed frequency bands from below 900 MHz to above 60 GHz.
The stakes are high. Last year, the Wi-Fi Alliance submitted a request to the Federal Communications Commission (FCC), suggesting it withhold certification of any LTE-U equipment until the Alliance had coexistence tests in place. Ericsson, T-Mobile, Verizon, Qualcomm and others sent a rebuttal letter warning of “far-reaching, negative consequences” should the FCC delay LTE-U network deployments.
The WFA currently plans to issue on September 21 a version 1.0 of its LTE-U test plan, a suite it has been working on for more than a year. The group is ironing out final details in meetings this week with plans to issue a beta version of the test August 11 and conduct a plugfest starting August 22. A final workshop on the issue is tentatively slated for September 7.
“If they stick with the plan they have now that is so biased and lacking technical merit they are risking their credibility,” said Dean Brenner, senior vice president of government affairs at Qualcomm who has attended the meetings.
In presentations released online by the WFA, his opponents are equally vociferous. “LTE-U technology (CSAT) can ever effectively coexist with Wi-Fi in real deployments,” wrote Thomas Derham of Broadcom in a presentation last week made public on the WFA site.
Derham argues in part that LTE-U acts as a master of 5 GHz channel access, treating Wi-Fi contenders as slaves, unlike Wi-Fi links that negotiate for spectrum as peers. The draft WFA tests are not stringent enough, he wrote, suggesting they should include tests for more scenarios at signal sensitivity as low as -89 dBm.
Qualcomm’s Brenner says the -82 dBm test in the current draft suite is already too rigorous. Wi-Fi itself – along with Bluetooth and Zigbee – only back off at levels of -62 dBm, he notes. A related spec called License Assisted Access (LAA), already ratified by the 3GPP which sets cellular standards, compromised on a -72 dBm level and a listen-before talk approach to co-existence.
All sides agree that LTE-U should be as fair in sharing spectrum as existing Wi-Fi access points. However the two camps are divided over how to measure that sharing in today’s Wi-Fi products, with Qualcomm claiming the WFA test sets an unrealistically high bar.
Qualcomm claims the WFA plans to create future tests for LAA that could put new restrictions on the already finished 3GPP standard. In addition, the draft test already “tries to dictate [LTE-U] device features that have nothing to do with spectrum sharing,” said Brenner.
At last week’s meeting, a representative of CableLabs pressed the WFA to finalize the LTE-U tests based on its draft first released in April. At this point, only WFA technical staff should make any further changes in the tests based on results from the plugfest, wrote Jennifer Andreoli-Fang, a distinguished technologist at CableLabs, the R&D arm of major U.S. cable-TV carriers.
Andreoli-Fang noted that LTE-U backers want to remove several elements of the draft test. They include ones covering multi-channel LTE-U, the presence of more than one LTE-U base station and checks to ensure users can choose a Wi-Fi connection in the presence of LTE-U, she wrote in a presentation. In addition she defended use of the -82 dBm test level as “anchored to real-world network data and the minimum level of fairness of Wi-Fi in the 802 standard.”
Several WFA staff presentations last week made it clear the standards body is pressing forward with the current draft amid the ongoing debate. Contentious issues like the choice of the -82 dBm test level are now fixed, said Kevin Robinson, vice president of marketing for the WFA.
“There’s no doubt everyone has had to compromise in an effort to move the work along and deliver a successful coexistence test plan,” said Robinson. “Stakeholders have strong, passionate views on where the test plan lands,” he said.
The WFA expects its co-existence test plan will serve as basis for equipment vendors to determine whether their gear is fair in sharing 5 GHz spectrum, he said. The FCC is encouraging the industry to address concerns around coexistence and do it in Wi-Fi Alliance, he added.
The WFA debate over LTE-U at 5 GHz is just the start of what likely will be a long, difficult war over unlicensed spectrum between Wi-Fi and cellular camps. The technical debates are informed, in part, by conflicts over business models that represent billions of dollars in revenues
To date Wi-Fi has generally supported free services over unlicensed spectrum which make money by selling hardware or related services such as selling online ads. By contrast, cellular carriers generally make money on paid-for spectrum by charging users for managed services.
Smartphones put pressure on the profitability of cellular carriers as they scrambled to build out their networks to handle a rising tide of mobile data. The financial pinch forced carriers into consolidations and a search for more spectrum. Meanwhile over-the top Web services siphoned off a growing percentage of mobile data revenues.
In the tech culture clash that ensured, Wi-Fi backers resent cellular carriers encroaching on their free spectrum. For their part, cellular carriers resent Web services making enormous profits by taking a free ride on their networks.
Qualcomm currently serves both camps with cellular and Wi-Fi chips. However, it sees a break out opportunity to define in the 5G timeframe a new kind of network that can handle both free and paid-for services across both licensed and unlicensed bands.
The company’s MuLTEfire technology is a first step in that direction. It goes beyond LTE-U and LAA by supporting all the required cellular services – uplinks, downlinks and control channels – on licensed or unlicensed bands. Qualcomm already established a trade group promoting MuLTEfire with backers including Cisco, Ericsson, Intel, Nokia and Softbank.
Today the MuLTEfire technology is too expensive for consumer access points. So Qualcomm is working in its labs on a new air interface that would support licensed and unlicensed bands at lower cost and higher efficiency. It could essentially replace both 4G and Wi-Fi and probably form the basis of the company’s proposal for a 5G standard.
Today’s LTE-U and MuLTEfire technologies already deliver at least twice the throughput and coverage area of the current 802.11ac version of Wi-Fi, said Mingxi Fan, a vice president of engineering in Qualcomm’s R&D group. Because they are based on LTE, they also support mobile terminals, unlike Wi-Fi, he added.
“Our goal is to make sure in spectrum sharing the end user gets the highest quality technology with the most efficient sharing – most likely with a greenfield design,” said Fan.
If the company is successful, competitors fear they will owe Qualcomm significant royalties for both next-generation cellular and Wi-Fi products. They recall the relatively steep royalties Qualcomm charged when it dominated the market for 2G with its CDMA technology.
In an effort to calm such concerns Qualcomm’s Brenner said, “Wi-Fi has a long bright future.”
Market watcher Will Strauss of Forward Concepts (Mesa, Ariz.) notes that LTE-U is “one of the cobblestones on the road to 5G, incorporating and binding together channels for Wi-Fi and traditional LTE,” to deliver better throughput, range and mobility for users.
Strauss notes that 5G is expected to use small base stations in urban settings to deliver new levels of bandwidth, probably in unlicensed bands including 60 GHz. “All the children will have to learn to play fair,” he said.
Rick Merritt, Silicon Valley Bureau Chief, EE Times
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