Civilian, military spectrum sharing

US agencies trial the sharing of a 150 MHz-wide portion of the 3.5 GHz ‘Innovation Band’.

The US Federal Communications Commission (FCC), with help from the US National Institute of Standards and Technology (NIST) and other agencies, will soon make it possible for a 150 MHz-wide section of the RF spectrum to be shared.

“This will be the first time that commercial broadband users share spectrum dynamically with government users, and if it works, the FCC may allocate other currently protected RF bands for shared use,” said Michael Souryal, lead for the spectrum sharing support project within NIST’s Communications Technology Laboratory.

“More spectrum sharing could provide less-congested wireless channels for densely populated areas and more reliable connections for advanced communications needs such as 5G wireless and internet of things applications.”

Since 2015, FCC rules have been in place that pave the way for commercial wireless users to employ the commonly called 3.5 GHz, or ‘Innovation Band’, when not needed for its current primary use, offshore radar operations by the US Navy.

LTE vendors and service providers such as AT&T, Google, Nokia, Qualcomm, Sony and Verizon have been eager to access this band (between 3550 and 3700 MHz) because it will expand product markets and give end users better coverage and higher data rate speeds in a variety of environments where service is traditionally weak.

Under the rules of the FCC-regulated 3.5 GHz Citizens Broadband Radio Service (CBRS), the Navy maintains first right to the band and private use only occurs during its downtimes.

Providers and other organisations will be granted access using a three-tier priority allocation structure:

1. Incumbent users such as the US Navy.
2. LTE providers and other organisations that pay licence fees for the right to share.
3. General users.

NIST has played a major role in the development of standards, test procedures and certification tools that will allow service providers and other potential users to prove that they can operate in the 3.5 GHz band under FCC regulations and assure the Navy that the band can be successfully shared without RF interference.

Recently, the Wireless Innovation Forum Spectrum Sharing Committee (WINNF SSC) — the public-private standards body for the CBRS — approved 10 standards for operating the service, including the algorithm for protecting military incumbent users. A NIST-designed computer reference model of that algorithm will be an integral part of the certification process.

One example of the NIST model simulates 45,000 LTE small cells using the 3.5 GHz band in the north-eastern United States. In response to a simulated need for the band by an offshore Navy vessel, the model calculates which small cells must be shut down and which can continue transmitting.

NIST simulation showing wireless users of shared RF spectrum in the Boston to Cape Cod, Massachusetts, region. Coloured markers identify users that can continue operating (blue) or must be shut off (red) to accommodate the priority need for the wireless band by naval vessels within the offshore ‘designated protection area’ (grey). Credit: Michael Souryal/NIST (using Google Earth map of Massachusetts coast).

These simulations, along with others modelling wireless networks in other US coastal regions, will enable the FCC to test and evaluate how effectively a commercial LTE provider can share the band with the Navy.

“Dynamic spectrum sharing is poised to revolutionise the industry by unleashing wireless capabilities and performance that have not been possible in conventional licensed or unlicensed spectrum bands,” said Kurt Schaubach, chief technology officer for Federated Wireless.

“The efforts of our company, NIST and the other members of the WINNF SSC to establish standards, testing and certification for spectrum sharing are setting the stage for improving wireless service indoors, expanding broadband services to rural areas and providing private wireless capabilities for industrial users,” he added.

“It’s an outstanding example of public-private collaboration.”

Warship image courtesy US Navy.

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