3550-3650 MHz

An innovative spectrum sharing model in the 3.5 GHz Citizens Broadband Radio Service (CBRS) band is coming closer to reality, NTIA senior spectrum advisor Derek Khlopin reported at the CBRS Alliance annual meeting in Charlotte, N.C. this week.

Since this band was initially targeted as a candidate to make available for commercial use nearly a decade ago, NTIA has engaged closely with the Department of Defense and the Federal Communications Commission (FCC) to bring the idea to fruition. The 3.5 GHz band affords an excellent mix of capacity and coverage capabilities, defining characteristics of mid-band spectrum,  making the band appealing for future 5G deployment.

NTIA’s engineers and scientists in the Office of Spectrum Management and the Institute for Telecommunication Sciences (ITS) in Boulder, Colorado, have worked closely through each stage of development with their counterparts in government and the private sector. From shrinking exclusion zones into smaller protection zones to designing the concept of dynamic protection areas (DPAs) to assisting the FCC in certifying the components of the spectrum sharing mechanism, it has been a long, complex process, but the light at the end of the tunnel is getting brighter by the day.

How can we get more use out of the radio spectrum? One way is by sharing radio bands between users who have never shared before. Consider radio frequencies near 3.5 GHz. Until recently, that part of the spectrum was used almost entirely by U.S. government radars, many of them on Navy aircraft carriers, enabling the same kind of air traffic control for the carriers as radars on land do at airports.

Now, we are preparing for new arrivals in the 3.5 GHz spectrum: communication systems such as cell phones. Operating on land, the new systems will be sharing frequencies with the Navy radars at sea.

More than decade ago, NTIA helped to blaze the trail for this kind of spectrum sharing when it did studies on exactly what it takes to share frequencies between regular radios and radars. Now NTIA has applied that knowledge to the new 3.5 GHz spectrum sharing. Industry and government, including NTIA, have developed a strategy to share 3.5 GHz without any interference from the new shore-based radios to the Navy’s aircraft carrier traffic control radars.

Here’s how it will work: When industry builds out a new 3.5 GHz network on shore, it will also build a network of shoreline radar detectors designed to see the Navy radar’s signal. When one of the Navy’s radars sails within about 120 miles of a detector, the station will see the radar’s signal, note its frequency, and alert the local on-shore communication network to immediately vacate that frequency.

Engineers at NTIA’s Institute for Telecommunication Sciences (ITS) have completed performance certification lab testing of Environmental Sensing Capability (ESC) equipment – the sensors that will help enable dynamic sharing in the 3.5 GHz band between U.S. Navy radars and Citizens Broadband Radio Service (CBRS) devices.

Completing the testing marks another significant step toward making sharing in the 3.5 GHz band a reality. The innovative approach to spectrum management that also includes the Spectrum Access System (SAS) has the potential to make significant spectrum resources available to meet our national broadband needs while preserving access to this critical spectrum for naval operations.

The 3.5 GHz band offers a unique mix of capacity and coverage capabilities, making it a potential ‘sweet spot’ for innovative services including 5G. The SAS-ESC combination successfully unlocking dynamic sharing could provide new tools in NTIA’s efforts to advance the nation’s 21st century spectrum imperatives while protecting vital federal missions.