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Workshop Participants Offer Ideas for New 3.5 GHz Band

On Wednesday the FCC held an all-day workshop on technology for small cells, database management, and spectrum sharing in the context of the FCC's NPRM making 3.55-3.65 GHz available for shared small cell use. The morning panel covered small cell technology, network design and the 3.5 GHz band with experts from Virginia Tech, Nokia Siemens Networks, Motorola Solutions, T-Mobile, Brighthouse Networks and the WhiteSpace Alliance. The afternoon panel was titled “The Spectrum Access System – Innovative Approaches to Dynamic Spectrum Sharing” and included technology experts from the University of Southern California, Vanu, Qualcomm and white space database administrators Spectrum Bridge and iconectiv (formerly Telcordia).

As expected with such a diverse group of experts, some had their own ideas as to how best to use the new 3.5 GHz spectrum and manage spectrum overall. The recorded Webcast of the event was not available Wednesday evening, some of the panelists’ slide presentations are available on the FCC 3.5 GHz Workshop Webpage. The Webcast recording will be available soon on that page.

The first presentation was from Jeffrey H. Reed from Virginia Tech. He was one of the experts disclosing LTE Vulnerable to Jamming last November. His presentation, Current and Future Research Goals for Spectrum Sharing with Small Cells focused on LTE self-organizing networks (SON), specifically self-configuration, self-optimization and self-healing.

Reed presented a list of “Needed Future Technologies.” These included “Customization of self configuration, optimization and healing to contend with the legacy signal environment,” “Strategies for mixing shared access with dedicated licensed spectrum,” “Propagation measurement & experimental work,” and not surprisingly, “Security, information assurance, and privacy vulnerabilities: military and civilian.” He mentioned that the SON will also require “Automated regulatory and enforcement methods.” His presentation concluded with “Ability to immediately use this new spectrum is in reach.”

Prakash Moorut, Senior Research Specialist at Nokia Siemens Networks' presentation was titled LTE and Authorized Shared Access – Unlocking 3.5 GHz Spectrum for Small Cells. After illustrating the opportunities available with this new spectrum, a slide was presented showing that TDD (Time Domain Duplex) LTE would drive economy of scale through harmonization with global standards, which use TDD in this band. Coverage maps showed the technology supports either dedicated or shared spectrum for the small cells. The paper stated that: “Cleared, exclusively licensed spectrum is strong preferred for predictable Quality of Service,” and added: “Only when not possible or available in reasonable time frame/cost, consider Authorized Shared Access.”

Other panelists preferred shared access, both licensed and unlicensed.

One of the best summaries of this approach was from Dr. Preston Marshall at the Viterbi School of Engineering at the University of California. His presentation, Opportunity in the Small Cell Operation in 3.5 GHz NPRM noted that the NPRM can provide a framework for sharing many spectrum bands (tailored for issues specific to 3.5 GHz) in addition to providing a path to a solution to the specific issues of 3.5 GHz. Marshall pointed out that “Receiver coexistence is often the constraint for maximizing density of spectrum usage--not deconfliction of frequencies.” If receiver characteristics are visible to the SAS (Spectrum Access System) it can avoid adjacent channel conflicts without requiring the “massive uncertainty margins” required for a closed loop interference system.

Qualcomm's presentation ASA, Small Cells, LTE showed an “Authorized Shared Access” model instead of exclusive use or unlicensed shared use. Qualcomm states, “Exclusive use on a shared and binary basis--Time, Location, and/or Frequency--with incumbent (defense, government, etc.) ensures quality of service.”

The system would leverage existing 3GPP standards, but Qualcomm didn't enter the debate over FDD (frequency domain duplex) which is most commonly used in the United States, and TDD, which doesn't require separate bands and a duplex gap.

The presentations from the database managers providing TV White Space (TVWS) access authorization showed how their proven systems could provide protection of incumbent users while dynamically optimizing the efficient use of the spectrum.

John P. Mayer, Chief Architect at iconectiv concluded his presentation with “The future of spectrum access... is here today. Peter Sanforth, CTO of Spectrum Bridge, in the presentation Implementation Experiences, noted that “There is much more to sharing than a database--the entire focus in TVWS was on protecting the incumbent.”

“Left out was the protection of the secondary user,” he stated.

Mayer added that the system can be changed if the rules change, and asked if anyone had noticed the change to the 2012 rules from the 2010 rules that SBI was certified with.

Vanu Bose from Vanu had a very interesting presentation showing how software radio could be used in the Spectrum Access System in his Vanu Software Radio. Sensing available from cellphone measurement reports and Wi-Fi scanning can be used to provide timely local information and combined with databases to provide capabilities that cannot be achieved otherwise. One example would be that better devices could get better access--devices can be granted smaller exclusion zones if their receivers can tolerate the interference. With the device characteristics determining where it can operate, Bose suggested that “self-certification” of such devices would probably be sufficient for the purpose.

While the presentations mostly focused on the 3.5 GHz, they also showed the potential for more sharing in other spectrum. The FCC 3.5 GHz Workshop Webpage has links to available presentations that I didn't cover here.