Spectrum sharing is no simple matter

The government is eager to make more federal spectrum available on the commercial market to fuel the explosion of data-hungry mobile broadband apps and services. But moving government spectrum to market can be a slog.

A recent auction of 65 MHz of prime spectrum fetched about $45 billion for federal coffers, but getting the military to agree to vacate most of the highly desirable paired frequency sets (which have uplink and downlink bands) took the better part of a decade and required a lot of political arm twisting.

The concept of sharing spectrum is almost as old as radio. The 1912 Radio Act, passed in the wake of the Titanic’s sinking, required private telegraph operators at busy seaports to stay off the air for the first 15 minutes of each hour to give naval and other military stations exclusive use of the airwaves.

One hundred years later, the Federal Communications Commission created rules for Medical Body Area Networks, which give health care facilities access to a 30 MHz swath of spectrum and reserve 10 MHz for the operation of wireless medical information devices in the home. To reduce the chances for interference, the MBAN spectrum operates on the ground at very low power and shares frequencies with airborne mobile telemetry systems, which operate in the air at very high power.

In 2015, the FCC approved rules for sharing spectrum in the 3.5 GHz band. The plan allows for incumbent federal users, mostly ship-borne radar systems, to maintain their first rights while creating two other tiers for licensed and unlicensed users.

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That approach could be characterized as “cooperative sharing,” said Peter Tenhula, deputy associate administrator for spectrum management at the National Telecommunications and Information Administration, which manages federal spectrum holdings.

“The devices are working with each other or are controlled by a centralized database and sharing information,” he added.

A working database is essential for dynamically allocating frequencies and maintaining protocols for user priority. Currently, narrow bands of unlicensed spectrum between licensed TV channels — known as “white spaces” — are allocated by use of an FCC database. Dynamic spectrum access for the 3.5 GHz band would allocate as much as 150 MHz of spectrum in real time based on demand and priority.

As the government tries to get more spectrum to commercial users, sharing has some intriguing possibilities for agencies. For federal users, “the goal is to make sure that there’s no need to displace equipment that is still within its useful life,” Tenhula told FCW.

Additionally, as large swaths of sharable spectrum open up, there is the potential for agencies to gain access to new frequencies as new regulatory thinking allows for a blurring of the lines between federal and non-federal users.