BOULDER, Colo. – Spectrum sharing were the buzzwords of the week as a bevy of federal agencies came together at the National Institute of Standards and Technology to discuss the topic with industry and academia. Google was one of the companies on-hand that shared how it is working on technology to enable the Federal Communications Commission’s vision of how the 3.5 GHz band can be shared.
Google demonstrated the third version of the Spectrum Access System it has built, which is software running on Google infrastructure that is capable of dynamically managing the relationships among three proposed tiers of users at 3.5 GHz: federal and nonfederal incumbents, Priority Access Licensees and General Authorized Access users, each of which would have to abide by various rules governing its interactions and interference with one another. It has been running several wireless transmission sites at 3.5 GHz to develop and test the technology.
The FCC has been working for several years to expand access to 3.5 GHz, where there are a number of incumbents operating – most notably, shipborne naval radar systems, as well as fixed-satellite service users and wireless Internet service providers. Following a workshop on 3.5 GHz spectrum in January, the commission issued proposed rules recently for what it is calling the Citizens Broadband Radio Service, and is known as the innovation band or small cell band, with up to 150 MHz of spectrum to become available. While spectrum access in most of the country would be relatively uncomplicated, port cities with a naval presence such as Norfolk, Va., and San Diego, Calif., represent some significant technical challenges for coordinated use.
According to the FCC’s proposed rulemaking, the incumbents would be protected from “harmful interference” – which as attendees at this week’s International Symposium on Advanced Radio Technologies conference made clear, has no single or simple definition – while a minimum of 50% of the band would be reserved for GAA use. After taking into account incumbents needs, the rest of the spectrum would be available as 10 MHz licenses where priority access would be granted: GAA users could make use of PAL bandwidth when it’s available, but would have to bow out and jump to another frequency once a PAL-level device showed up in the band. The FCC has proposed that a Spectrum Access System would be central to the coordination necessary for three different types of users to successfully share the spectrum and “[builds] upon the use of databases to manage television white spaces devices.” (Where, it should be mentioned, Google is also a player.)
Preston Marshall, principal wireless architect for Google Access, said that the company began its work on a SAS, in part, simply to prove that it could be built and function, and that telecom industry skepticism about whether a SAS would actually be viable could only be answered if one was built.
The idea is that Google would be one of a number of SAS providers for 3.5 GHz – creating a new ecosystem and taking Google beyond what it has done to date in mobile devices and the Android operating systems, into software for the management of wireless spectrum systems that leverages fast processing speeds and the cloud. Speculation as to what exactly Google’s goal is for its 3.5 GHz testing and lobbying for freeing up the spectrum has been going on for some time, with The Wall Street Journal framing it as a potential competition with wireless carriers via an unlicensed network as well as a way of “draining some of the cost out of the wireless industry.” Engineering consultant Steven Crowley noted late last year in his blog that the company had requested permission for 3.5 GHz testing at its Mountain View, Calif., headquarters as well as in suburban Washington, D.C. (along with a number of other bands, including millimeter wave, which were not discussed at ISART).
Marshall said that Google’s current SAS can handle 10 million devices under management, although it estimates that only about 1 million to 5 million devices would ultimately end up receiving protection through a SAS. Because, as Marshall put it, the SAS “is an ‘Internet of Things’ device – it talks to devices, not people.” Google also developed a planning tool for the SAS that it used for the demonstration. (See screenshots of the planning tool and other info in Marshall’s presentation, available here.)
So if the spectrum is available and a SAS can make sharing workable, what would be potential use cases for unlicensed access at 3.5 GHz? For one, both Marshall and Kurt Schaubach, CTO of Federated Wireless – another SAS provider – mentioned the potential for enterprises to make use of LTE in the band. Mobile data is now primarily used indoors and few buildings are covered by distributed antenna systems or small cells due to cost (DAS) or carrier-specificity (small cells), Schaubach noted, and enterprise Wi-Fi connections can be unstable. Unlicensed LTE at 3.5 GHz could offer businesses the opportunity to deploy and manage low-cost LTE systems themselves, which allow their own IT departments visibility into applications and wireless networks that is not available with carrier-owned infrastructure, he said.
In addition to the three tiers of users, the FCC is leaning toward dynamic frequency assignments made in real-time for the spectrum, which traditional wireless telecom players are not excited about. Both Google and WISPA argued to the FCC in support of dynamic frequency assignment through a SAS, the FCC said, while “commenters including AT&T, T-Mobile, CTIA, and Ericsson argued for designated, fixed channel assignments, claiming that dynamic frequency assignments would interfere with network planning and channel aggregation.”
The FCC’s proposed rules at this point take into consideration both sides while leaning toward dynamic assignments – the SAS would dynamically assign bandwidth within a geography to PALs and GAAs, with the exception that the SAS would “be permitted to assign specific frequencies to Priority Access Licensees upon their request, when available and on a dynamic basis. … Dynamically assigning spectrum based upon the demand within a geographic area at a given time would promote efficient use of the band across wider geographic areas without compromising flexibility.”
CTIA representatives who spoke at ISART made it clear that spectrum sharing is not the wireless industry’s preferred approach, although they indicated that they do support exploration of the concept. Meredith Attwell Baker, CTIA’s president and CEO, reminded the audience of the numbers the group shared earlier this week that licensed spectrum generates more than $400 billion per year in economic activity. She also said that the need for spectrum will outstrip any gains from efficiency and that a better long-term spectrum plan is needed. In his talk on key considerations for spectrum sharing in mobile networks, Tom Sawanobori, CTO for CTIA, had first on the list that the spectrum must “truly” be unsuitable for the traditional spectrum auction and clearing processes as a core requirement, along with clear spectrum rights. However, industry members have been at least discussing the concept with Google and others via the Wireless Innovation Forum.
Lawrence Strickling, assistant secretary of commerce, reminded ISART attendees that President Obama has set the goal of opening up 500 MHz of spectrum for commercial mobile technologies and that a presidential technical advisory committee “concluded that the traditional approach of clearing spectrum used by government agencies and then auctioning it off for exclusive private sector use was becoming too costly, too time-consuming and too disruptive to be sustainable. The future … lies in sharing spectrum across time, space and other dimensions.”
President Obama followed up that report with a memorandum directing NTIA to work with the FCC to promote increased spectrum sharing by federal agencies and enterprise, and the work at 3.5 GHz is part of the federal response. (Read Strickling’s full remarks here.)
However, “it won’t matter how much spectrum we make available for sharing if the frequencies are too congested or too chaotic to be usable,” Strickling said, referring to ISART’s other major theme of how test and measurement will factor into design, planning and enforcement for spectrum sharing. He also added that “there is more be done to bring widespread spectrum sharing to reality.”
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