Military Considers Sharing Radar Frequencies with Wireless Networks
While commercial wireless networks are congested, frequencies set aside for military purposes are lightly used. Now wireless researchers and the U.S. Navy will get a chance to see whether some of those airwaves can be shared, which could lead to innovative new services.
In a test on Monday, the Navy will fire up an AN/SPY 1 radar—a powerful system that normally scans for incoming missiles and bombers—on an island off Virginia’s eastern shore. At the same time, visiting academic and corporate researchers will tune portable wireless transmitters to the same frequency to see what happens.
“We will be running an LTE signal and understanding the impact of radar on that LTE signal,” says Jeff Reed, director of the wireless research center at Virginia Tech, one of the researchers involved in the test. “Hopefully no missile will be fired as part of this test.”
The spectrum skirmish—on Wallops Island, a NASA launch site that is also home to the Naval Sea Systems Command—is the first step in the next phase of spectrum sharing to open up airwaves. It could pave the way for 4G LTE networks that institutions like hospitals or public safety agencies could set up without relying on the major carriers.
“It’s a big deal,” says Vanu Bose, CEO of Vanu, a Cambridge, Massachusetts, company that makes custom wireless communications systems. “The majority of federal spectrum use is for radars of one kind or another, but many of these systems are used sparingly.”
This test is one of many ways that the government could implement White House recommendations on spectrum sharing to free up bandwidth now locked down by government, broadcasters, and others (see “Spectrum of Issues”).
The concept is similar to the approach of using so-called “white spaces”—in which TV spectrum can be borrowed for use at certain times and in certain places to provide Internet broadband or cellular service (see “TV Airwaves Fill the Broadband Gaps”). But sharing military spectrum could have much bigger effects. Whereas TV spectrum can be borrowed mainly in rural areas, frequencies are reserved even in big cities for radar used by the Navy and other branches of the military. They cover 60 percent of the American population, where the most wireless congestion is now experienced.
Policymakers and researchers hope the radar bands (3550 to 3650 megahertz) could provide another way to provide long-range Wi-Fi with only small modifications to existing transmitters, known as small cells, that support existing LTE and Wi-Fi (see “Tiny Transmitters Could Help Avert Data Throttling”).
Not everyone will get to use the Pentagon’s spectrum. Hospitals and other institutions with public safety functions —including utilities and law-enforcement agencies—would get first crack. “A hospital might need a high-bandwidth wireless network within its walls—right now they would have to rely on a wireless carrier. This would present a new way for them to do it,” saving money and increasing privacy while not clogging commercial networks, Reed says.
Sharing military spectrum will be a little trickier than sharing TV white spaces. Both approaches rely on databases that keep track of when and where spectrum can be shared. But unlike TV stations, Navy ships and radar systems can move around—and the government doesn’t necessarily want everyone knowing where they are.
But Peter Stanforth, chief technology officer of Spectrum Bridge—a company in Florida that facilitates the use of TV white spaces and is participating in the Wallops tests—says there can be ways to obscure this information. And in any event, he says, it’s possible today to use sensors to detect if any transmissions are occurring in the 3550 to 3650 megahertz band. Any such transmissions must be military. “If it is shared, I can’t be sure who is using it,” he says.
After wireless transmissions are made in the vicinity of high-power Navy radars during next week’s tests, researchers will have a better idea of the precise conditions under which the spectrum sharing is feasible. The next step will be for the U.S. Federal Communications Commission to formally define a rule, which could take at least a year.
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