Multidimensional Approach to 3.5 GHz Spectrum Sharing Seen as ‘Good Path’
The Department of Defense believes coordination of spectrum sharing in the 3.5 GHz band presents an opportunity to improve spectrum sharing efforts “across the board,” said Fred Moorefield, director-spectrum, policy and programs for DOD’s Office of the Chief Information Officer, at an FCBA event Thursday night. Sharing on the 3.5 GHz band will be one of the first indications of how spectrum sharing “is going to work on this type of scale,” Moorefield said. DOD is “really trying to help” the FCC and NTIA coordinate sharing on the band, which DOD has said it will need to use for radar services for the foreseeable future, he said. DOD will reflect its willingness to cooperate when it releases its spectrum strategy Dec. 11, Moorefield said. The spectrum strategy will focus on “adaptability, flexibility, resiliency, maneuverability, technology and more spectrum sharing both ways,” he said.
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Industry is working to create technological strategies to mitigate interference issues on the 3.5 GHz band, both from DOD radar and to C-band satellite operations. Technical fixes are an important part of a multidimensional approach that also includes creative licensing techniques, Moorefield said. A multidimensional approach is “a good path” for sharing on the band, but DOD is still trying to understand the technologies and strategies involved, he said. The Spectrum Access System (SAS) the FCC has proposed using to manage sharing on the band, for instance, could present cybersecurity issues given the information that would be stored on SAS databases, Moorefield said. “We need to be talking to cyber folks to figure out how to protect that information,” he said. Industry should develop interference mitigation technologies for the 3.5 GHz band that can operate in an environment “where you have high-powered radar,” Moorefield said. “The potential for devices being damaged is significant."
Incumbents in the C band are particularly concerned about regulatory limits on the use of small cells on the 3.5 GHz band, said Winston Caldwell, Fox TV Network vice president of spectrum engineering. Interference to TV distribution on the C band has the potential to cause “total system failure,” so incumbents on the C band are closely following possible limits on small-cell power, antenna gain, antenna height and out-of-band emissions, he said. Preston Marshall, Google Access Service principal wireless architect, defended the use of small cells in the 3.5 GHz band, noting that C-band incumbents are concerned about “worst case” scenarios for interference that would only be possible in northern portions of New England. The SAS approach would be able to address even “worst case” interference through adaptive and situational protection strategies, he said.
The FCC is continuing to collect input from stakeholders on its revised three-tiered “Citizens Broadband Service” licensing framework for the 3.5 GHz band, said FCC Wireless Bureau Legal Adviser Brian Regan. The revised framework left intact the tiers for band incumbents and general access, but expanded eligibility for access to the “Priority Access” tier to include traditional wireless providers. Comments on the revised framework are due Dec. 5 (CD Nov 5 p15). The one-year “Priority Access” licenses that the FCC would provide on the band are “innovative” because they do not “fit perfectly within the commission’s existing licensing and access regime,” Regan said. The licenses would provide rights “on a more targeted geographic basis” defined by the 74,000 U.S. census tracts, he said. Michael Calabrese, director of New America Foundation’s Wireless Future Project, said he believed the FCC should look at licensing the band for areas even smaller than a census tract. “If you can manage a database for 74,000 license areas,” one can manage a database for far more, he said.