Peaceful Coexistence on the Radio Spectrum
The trials of a small team of engineers who set out to reanimate paralyzed limbs demonstrate the virtues of dynamic spectrum sharing
One day in 2003, Joseph Schulman faced a half-dozen or so military officers in a cheerless high-rise office outside the U.S. capital of Washington, D.C. He was 68 then, with piercing blue eyes and a full head of hair dyed chestnut. People who knew him called him a “visionary” and a “mad, brilliant scientist.” For nearly 20 years, he had been president of the Alfred Mann Foundation, a medical research center in Santa Clarita, Calif., known for developing cutting-edge electronic aids, including pacemakers and cochlear implants. Normally a self-assured guy, Schulman suddenly felt, he says, “a little frightened.”
He had come to what was then the Defense Spectrum Office to present his case for allowing a new medical technology to use some of the radio frequencies assigned to the U.S. military. He began by pulling from his pocket several small ceramic cylinders, which he passed around.
Those fuse-like tubes, Schulman explained, were intended to restore function to muscles whose nerves had been damaged. “Microstimulators,” he called them. A surgeon could implant one in the body simply by using probing tools and a syringe. Inside the microstimulator were a battery and electronics, which controlled a pair of electrodes that could send pulses of current into a paralyzed limb. The electrodes could also pick up signals from healthy nerves, such as in the stump of an amputated arm, where the devices could be used to guide a prosthetic hand.
To perform these tasks, the microstimulators would need to be controlled by a pocketable radio. It was important that this be done wirelessly. Placing wires inside the body would take time, raising the risk of surgical complications and providing conduits for bacterial infections.
The trouble was that operating a wireless network of tiny implants in the body’s wet, salty interior required a special portion of radio spectrum. And Schulman knew the military owned the rights to it. But he believed that if he just asked nicely, he could persuade the uniformed men across the table to share a slim slice of their electromagnetic pie with this potentially revolutionary invention, seeing as it might one day help wounded soldiers.
“I was naive,” Schulman says. In fact, the spectrum campaign he began in 2003 lasted eight years and cost the foundation more than US $3 million in travel expenses, legal fees, and independent testing. But the quest proved more than a simple fight for frequencies. In their drive to get microstimulators on the market, Schulman and his colleagues would find themselves swept up in a monumental restructuring of the divisions that make radio spectrum artificially scarce.
Since the invention of radio, people have had to figure out how to share the spectrum. Early wireless telegraphs, which appeared in the late 1800s, were colossal spectrum hogs. Operators attempted to avoid interference by listening to one another and taking turns sending signals. A common message was GTH OM QRT (“Go to hell, old man, and keep quiet, I’m busy”). By the early 1900s, hundreds of stations in the United States were trying to talk over one another. Then on 15 April 1912, the ocean liner RMS Titanic sank. An investigation revealed that jabbering shore operators had hampered communications with the rescue ship. The incident reinforced an already growing opinion among lawmakers that rules were needed to establish order on the airwaves.
The Radio Act of 1912 empowered the U.S. government to control radio usage by issuing licenses, parceling out spectrum as if it were land. Later acts further refined the rules, eventually establishing two distinct regulatory bodies: the National Telecommunications and Information Administration (NTIA), which manages the federal government’s spectrum use, and the Federal Communications Commission (FCC), which manages everyone else’s.
As wireless technology evolved, outmoded bands were cleared or subdivided to make way for new services. Often, regulators permitted more than one service to occupy a single band, and many federal users shared bands with nonfederal ones. To prevent interference, they were expected to coordinate their use, for example by divvying up frequencies, locations, or time slots. Interested parties collaborated, as most still do, through trade associations or with the help of consulting engineers.
This approach worked well—for a while. But as radios proliferated in the decades after World War II, bands filled and competition for spectrum grew. As the end of the 20th century approached, network operators, particularly mobile phone companies struggling to meet exploding demand for data, were lobbying fiercely to take over federal frequencies and offering hundreds of millions of dollars to buy still more spectrum from their competitors. Increasingly, there was talk of spectrum scarcity, shortage, and “drought.” Would there be enough of the precious stuff to go around?
Meanwhile, radios were getting smarter. Under software control, radios could now switch between multiple frequencies, waveforms, transmission protocols, or applications.
One of the most ambitious early attempts to make use of this new agility began in the late 1990s at the U.S. military’s “mad-science” arm, the Defense Advanced Research Project Agency (DARPA). The project’s main goal was to create a network of portable radios that could overcome the disorderly spectrum environment of a battlefield. To accommodate data and video as well as voice, many of the radio channels would need to be very wide—about 10 megahertz, almost twice the bandwidth of a television channel. But when the project’s manager, Mark McHenry, pitched the idea to the military’s spectrum managers, he got the cold shoulder: “They told me, ‘There’s no way you can get that much spectrum.’ ”
But McHenry didn’t leave things there. He wondered how much of the supposedly crowded spectrum was really being used at any one time and place. So he commissioned a small study that measured all the radio activity in a large U.S. city during one week. Others may have had their suspicions about spectrum lying fallow, but McHenry was the first to gather hard data. And the results he got were surprising.
“The spectrum was absolutely empty,” he recalls. “It was 90 percent holes!” Radio spectrum was available, and there was plenty of it. The holes, or “white spaces,” were just waiting to be filled. But how?
That was the challenge. Unlike fixed band assignments, white spaces are dynamic; they vary by geographical location, and they can appear and disappear over time, often unexpectedly. To take advantage of them, a radio would need to know how other radios are using the airwaves and what the rules are. This could be done, for instance, through access to an Internet database of select white spaces, such as those left by television stations that don’t air in certain cities. Better yet, the intelligence for sensing and analyzing spectrum could be built into the radio itself—a holy grail known as cognitive radio.
DARPA accepted the challenge. In 1999, the agency created the neXt Generation Communications program to study what it called dynamic spectrum access. From there the concept spread, albeit slowly. The first civilian foray into this new territory came in 2003, when the FCC allowed unlicensed radios, including Wi-Fi routers and wireless broadband equipment, to share spectrum with government radars, such as those that airport weather forecasters use to detect brewing storms. To avoid compromising these critical radars, an Internet radio must “listen” to the airwaves before selecting a frequency and shift to a new channel when the one it’s currently using becomes occupied.
Around this time, Schulman and the other engineers at the Alfred Mann Foundation were realizing they needed to find white spaces of their own. The microstimulator’s power and stimulation schemes had been mostly worked out, and the team now faced the challenge of designing the communication system.
The technical demands were significant. Schulman determined that if a microstimulator were to simulate real nerve impulses, it had to receive about 20 intelligible messages per second from a master controller carried outside the body. But some transmissions were bound to get lost or garbled. So the engineers figured that each implant ought to receive and transmit a message about 90 times per second.
Altogether, the system had to be able to handle as many as several dozen—and perhaps one day even hundreds—of devices inside a person’s body. By permitting only one microstimulator to link up with the master controller at any given instant, the engineers could build them so that they all shared a single radio channel. But to conserve its tiny internal battery for other tasks, such as stimulation, each implant could use its radio only 0.1 percent of the time. The engineers calculated that the battery could then last for about three days before needing a recharge. (This would be done wirelessly, using a magnetic coil.)
Limiting the radio’s “on” time, however, presented a problem. It meant the system had to communicate sizable chunks of data in very short bursts. The dispatches required some 5 MHz of bandwidth, about the same as one television channel. Where could the engineers find that much spectrum?
Initially, Schulman ignored the question. “He thought the political problems were much smaller than the technical problems,” remembers Howard Stover, who headed the communications team. Stover sports the hallmarks of a fine engineer—suspenders, glasses, a beard, an affable chuckle. “Joe’s attitude was, ‘Just make it work. We’ll figure out all that other stuff later.’ ”
Stover thought that was the wrong attitude. He saw no sense in putting time and effort into engineering a product no one could legally use. So he thought about how to tackle the spectrum problem.
Four years earlier, in 1999, the FCC had designated a thin tract of frequencies near 400 MHz for what it called the Medical Implant Communications Service, intended for the radios in hearing aids, pain pumps, and heart defibrillators. In some ways, this band seemed ideal for microstimulators. Its prime attraction was its position on the spectrum: The frequencies were high enough to work with short antennas yet low enough to easily penetrate human tissue.
But this band had one big flaw. Although it was 3 MHz wide—almost enough bandwidth for microstimulators—the FCC limited radios to transmitting on only 300 kilohertz at a time while using no more than 25 microwatts of power, about 1/40 of the power a master controller needs to talk to microstimulators. The rules were meant to prevent interference with other low-power systems, such as weather probes, that share the same frequencies. But the rules made the band useless for microstimulators.
Not far away on the spectrum, however, was a band about 30 MHz wide that amateur radio operators share with the U.S. military as secondary users, meaning the hobbyists can use the airwaves so long as their equipment doesn’t interfere with defense systems. The bandwidth and power constraints here were much more lax. And Stover thought he knew how to persuade the amateurs to let microstimulators use some of the frequencies. Being an old “ham” himself, he was aware that amateurs were in constant fear of having to vacate the band. He could make the case that they would gain some staying power by sharing these airwaves with microstimulators. Surely no one would kick out a medical technology.
Stover prevailed upon Schulman to pitch the idea to representatives from the American Radio Relay League in Washington, D.C., the largest association of radio amateurs in the United States. The amateurs listened, but they expressed concerns about interference, and besides, they didn’t have much say in the matter. It wasn’t their spectrum to share. They suggested that Schulman approach the Defense Spectrum Office. When he met with the military officers there in 2003, they in turn referred him to the FCC and the NTIA, which must coordinate their decisions when a private party wants to use federal government spectrum.
After that, Schulman flew to Washington, D.C., almost every other week. The first few times he went alone, and in this respect he was like dozens of other innovators who come knocking on the doors of the two regulatory agencies every year looking for spectrum. “They have this great idea, but they have no idea about how spectrum management or the FCC works and how to take an idea and bring it to fruition,” says Julius Knapp, chief of the FCC’s Office of Engineering and Technology. Knapp’s first advice to Schulman was to get a lawyer.
At first it seemed Schulman was getting nowhere. “To be perfectly blunt, the two parties started 180 degrees apart,” remembers Edward Davison, who chairs the Interdepartmental Radio Advisory Committee (IRAC), which advises the NTIA on spectrum matters. “The Alfred Mann people thought things were going to be easy and the [Department of Defense] thought things were going to be impossible.”
The military’s main concern was interference. Microstimulators would have to operate in the same spectrum as high-power defense systems. “We’re talking about megawatt radars,” says Fred Moorefield, who was IRAC’s Air Force representative and the main liaison between the Alfred Mann Foundation and the military. No one worried, he says, about one-milliwatt microstimulators wiping out the military’s air-defense system. Rather, the scenario Moorefield and others feared most was that the radars would disable the microstimulators, with the disastrous outcome of both injuring patients and inciting empathetic lawmakers to kick the military out of the band. At the time, the military was facing a watered-down version of this very issue: Since their rollout began in 2004, new defense radios had reportedly impaired tens of thousands of garage-door openers, which used some of the military’s spectrum on a secondary basis.
But the radios in microstimulators were a lot more sophisticated. Using custom codes and protocols, they could already handle a fair amount of interference. Moreover, Stover’s team cleverly equipped the master controller with complex algorithms to essentially “notch out” radar and other fleeting narrowband signals from the faint wideband messages emerging from the body—like a cloud re-forming after a bullet passes through.
The military experts weren’t satisfied. These protections were nice, they said, but a big radar at close range could still overwhelm the system. What then?
Had this scenario played out a decade earlier, prospects for microstimulators might have ended then and there. But by the mid-2000s, spectrum regulators at the NTIA were warming to the idea that radios could be smart and flexible. So they suggested to Schulman and Stover that they design their system to work on more than one channel. Make it more dynamic, they said. They thought three was a good number. Maybe add a fourth channel outside the military’s spectrum, just in case the microstimulators happened to be inside a soldier.
One afternoon, Stover sat down with a chart listing all the frequency assignments in the candidate spectrum plot and carefully selected four 5-MHz-wide bands, taking pains to avoid other low-power users, which the microstimulators could potentially disturb. These included satellite rescue beacons, radio telescopes, RFID tags, and amateur receivers used to capture very weak signals bounced off the moon. Stover chose two bands that would be shared with military radars and a third with fixed, mobile, and space research systems. The fourth band contained mostly civilian walkie-talkies and “remote pickup” equipment that television crews use to beam field reports back to a broadcast station. That last band wouldn’t be much use in cities, but it could be vital on military bases.
Together, the four bands could make the system reliable. Spectrum measurements showed it was a pretty sure bet that at least one—and more often two or three—would be available at any given time. That way, if the master controller encountered more interference than it could handle on one band, it could simply move the system to another. On the very rare occasion that all four channels became too crowded to use, the microstimulators would execute a preprogrammed series of actions to power down in a controlled fashion. “A graceful shutdown,” Stover calls it.
After Schulman retired as president of the Alfred Mann Foundation in 2007, his successor, David Hankin, took up the baton. As a leader, Hankin was antipodal to Schulman in almost every respect. Trained as a lawyer and a businessman, he was a savvy negotiator. He thought that the problems posed by politics were at least as important as the problems of engineering, if not more so. If Schulman was the visionary, Hankin was the executor. He lobbied politicians, had the foundation’s lawyer draft a formal proposal for the FCC, and kept in constant contact with staff there and at the NTIA.
Hankin also pushed Stover and the engineering team to ready the microstimulator’s communication system for prime time. Then he hired people outside the foundation to test it—people whom the military agreed would do a reliable, unbiased job. The independent evaluations cost the foundation several hundred thousand dollars and took more than a year, but they proved to be a turning point. Hankin filed the test reports with the FCC and sent copies to Moorefield. He and the other military experts were impressed. “So we said, ‘Yup, we like it. We think it does what you say,’ ” Moorefield recalls. “Let’s do it.”
At last, in November 2011, the FCC authorized microstimulators to operate as a secondary service within the four designated spectrum bands, provided that the radios dodge harmful interference by hopping from one band to another on the fly. In a statement he read after announcing the new law, FCC chairman Julius Genachowski praised the foundation’s efforts, calling the outcome a “model for making more efficient use of radio spectrum.”
Over the past decade, the FCC has approved the use of dynamic sharing in other contexts as well, starting with wireless broadband services back in 2003. In 2008, Wi-Fi and other unlicensed radios were allowed access using Internet databases to the white spaces between television stations. In 2012, wearable health sensors such as glucose monitors were welcomed into spectrum that the aerospace industry uses for flight testing. And later that year, the FCC proposed opening 100 MHz of government spectrum to miniature base stations, known as small cells.
Even mobile-phone companies, which continue to push hard for clearing federal frequencies for their exclusive use, are warming to sharing. This January AT&T, T‑Mobile, and Verizon announced an agreement to explore the possibility.
Moorefield says he now advises anyone who comes asking for bits and pieces of the military’s spectrum to follow this model. “The mantra today is sharing,” he says. “I think the old way of thinking—where you had segregated spectrum, move-me-out-so-that-someone-else-can-move-in spectrum—I think those days are over.”
On a crisp, sunny afternoon last November, Hankin, Stover, and two engineers gathered around a conference table at the Alfred Mann Foundation. They were trying to remember whether they had believed their crusade for spectrum would ever succeed.
“I thought it was going to be difficult.”
“I thought it would be impossible.”
“Why? Because who the hell are we?”
“We’re a small, tiny research foundation in California,” Hankin said. “The military guys, they don’t know us from anybody. And we’re knocking on their door asking to use valuable spectrum that they have some of their most precious installations in. And they’re asking ‘Why? What are you going to do for us that’s so meaningful?’ ”
Hankin went on to describe a time during the spectrum debates when he brought a few military experts to visit an Army hospital in Maryland where the foundation had previously tested an early version of the microstimulator. The test patient, having damaged his spine, had trouble moving his legs, and his doctor had injected four stimulators into his thighs, which helped him regain some motion. The experts spent 2 hours talking with the doctor and visiting other patients, many of them young soldiers who had lost limbs in Iraq or Afghanistan.
“This,” Hankin concluded, “was their answer.”
This article originally appeared in print as "Peaceful Coexistence."