Google, Nokia and Federated Wireless execs see momentum behind 3.5 GHz ecosystem, uses

WASHINGTON--Executives from Google (NASDAQ: GOOG), Nokia Networks (NYSE:NOK) and startup Federated Wireless said that they see momentum behind the creation of an ecosystem for devices and network equipment for the 3.5 GHz band. The FCC aims to use the band to create a so-called Citizens Broadband Radio Service (CBRS) with a three-tiered spectrum sharing system, and the executives said interested stakeholders are starting to work on how to overcome technical hurdles to the service.

Speaking on a panel here at the Spectrum 2025 conference, Preston Marshall, principal wireless architect at Google, said he thinks the FCC will finalize a rulemaking on the band in the next few months. Google has been one of the main cheerleaders for the 3.5 GHz band, especially for use by non-traditional wireless players.

The FCC has proposed to create a CBRS in the 3.5 GHz band, using a complicated three-tiered access and spectrum-sharing model that would be comprised of federal and non-federal users. The CBRS is being considered by some for use in small cells. The first tier is set aside for radar systems for the U.S Navy, which currently uses the band. However, Marshall said that there would not be any real worry about interference with Navy ships on land in the U.S.

The second tier is for so-called priority access licensees (PALs), which are likely to be wireless carriers. PAL users can get 10 MHz licenses for one year and must protect government users, but get no protection from government users.

The third tier is for general authorized access (GAA) users, which might be carriers, enterprises or unlicensed users like Wi-Fi users today. Marshall noted that GAA users are still registered users, and they have the same rights and privileges as PAL users in the second tier. Further, equipment that covers one part of the band has to work in all parts of the band for all users, so carrier equipment has to work for GAA users.

The FCC is defining the CBRS 3.5 GHz band as 3550-3650 MHz, with possibly 50 MHz more being added to take it to an upper limit of 3700 MHz. Half of the spectrum will be set aside for GAA users, Marshall said.

Currently, there are several challenges to commercializing the band, though Marshall said that wireless carriers and network infrastructure vendors are starting to overcome them. One is whether there will be a chipset and radio ecosystem for the 3.5 GHz band. Marshall said that the band is already being used for Band 42 and 43 LTE systems in parts of Asia, though that is not developed in the U.S.

3GPP has defined Bands 42 (3400-3600 MHz) and 43 (3600-3800 MHz) for TD-LTE use, and Marshall said the current assumption is that the U.S. system would be TD-LTE.

Seppo Yrjölä, principal innovator at Nokia, said that LTE technologies can definitely be used in the 3.5 GHz band. "There are so many features [of LTE] already developed and implemented that enables this sharing or enables efficient use of spectrum, as well as how to mitigate interference and how to coordinate interference," he said. "A lot of these building blocks exist already."

Yrjölä  said "there will be chipsets, handsets, radios for 3.5. We and our peers are working on the technology."

At the same time, Marshall acknowledged that carriers have never operated with such a system and that carriers need to be reassured that their operation in the band won't face interference. Google supports the FCC's plan to have a centralized spectrum manager, or Spectrum Access System (SAS), assign channels dynamically. In theory, devices will go on the band and interface with the SAS to request and obtain spectrum, and will be told whether there is sufficient spectrum and whether the user will cause interference. The SAS will engage in dynamic aggregation to assign the channels in real time.

Marshall said that Verizon Wireless (NYSE: VZ) has lead a carrier group to voice concerns of operators, but that none of the issues the group has raised "are showstoppers" that will be difficult to overcome. "We're going to have to learn how to work it out together, but again, we think that process is beginning," Marshall said.

Yet others see problems with the SAS. AT&T (NYSE: T), for example, had said the "novel" SAS may prove a good approach for managing the 3.5 GHz band, but said it strongly opposes the FCC's proposal to have the SAS make dynamic--as opposed to static--spectrum assignments for PALs. "In the case of PALs, real-time or near real-time interference management is not practical between PAL users due to stringent interference reporting requirements that will be difficult to be met by the proposed SAS architecture and also due to the disparity of technologies that can be used by PAL users," AT&T said in a July 2014 FCC filing.

Federated Wireless is a startup that launched last fall and is developing a product that it said will allow entities to dynamically manage spectrum on the fly. The goal is to help carriers, government entities and others navigate the tricky world of spectrum sharing in the 3.5 GHz spectrum band.

Federated Wireless CTO Kurt Schaubach said that the FCC designed the CBRS system to stimulate investment from non-traditional wireless players via the unique licensing scheme. The band is designed to let users access spectrum on a more or less as-needed or coordinated basis, he said, something that he thinks "will bring a lot of new entrants to the market."

Schaubach said that one use case for GAA users in the band could be for inbuilding solutions. "There hasn't been a good ecosystem to stimulate building owners or enterprises themselves to get involved," he noted, because they have not had access to licensed spectrum and have had to rely on Wi-Fi spectrum. "It's very clear as we look into the future that Wi-Fi is not going to scale in the way enterprises need it to."

Marshall noted that under the SAS system, users get the right to receive and be not interfered with, but don't have the right to exclude others. "If it's not in use and if it doesn't interfere with you, others get to use" the spectrum, he said.

Marshall added that the spectrum can be used on a city-by-city basis, the same way Google is rolling out Google Fiber. "You don't need to roll it out nationwide and spend billions of dollars," he said. Carriers might also use spectrum set aside for GAA users. "The beauty is in the flexibility," he said.

Ultimately, Marshall said the focus should be on making sure that the 3.5 GHz band can be commercialized. "We don't want to see something where we get a regulatory win but American consumers don't get any bandwidth out of it," he said.

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