Spectrum clash builds around bionic implants
Medical networks around patients' bodies would need to share frequency bands with other uses
By Stephen Lawson | Published: 14:51, 25 November 2011
The battle over scarce radio spectrum that has embroiled the mobile broadband world even extends to a little-known type of wireless network that promises to reconnect the human nervous system with paralysed limbs.
At its monthly meeting next week, the US Federal Communications Commission will consider whether four sets of frequencies between 413MHz and 457MHz can be used by networks of sensors implanted in patients who suffer from various forms of paralysis. One intended purpose of these MMNS (medical micropower network systems) is to transmit movement commands from a sensor on a patient's spinal cord, through a wearable MCU (master control unit), to implants that electrically stimulate nerves. The same wireless technology might be used in devices to restore sight or hearing.
However, broadcast engineers are fighting the proposed rule that would allow this, saying TV and radio stations already use one of the bands to broadcast live from news events and this might interfere with the body networks. The main proponent of MMNS, the nonprofit Alfred Mann Foundation (AMF), says tests have proved that these systems can cope with interference as long as all four blocks of spectrum are available.
At the November 30 meeting, FCC staff will present its proposed rules for MMNS in the spectrum and turn them over to the commissioners for a vote and possible modifications. If approved, the rules would go into effect as soon as they are published in the Federal Register.
Frequencies are a battleground
As mobile devices drive up demand for wireless data networks, carriers, broadcasters and technology giants are fighting over limited radio spectrum. Access to frequencies is at the center of complex disputes over would-be hybrid network operator LightSquared, AT&T's proposed acquisition of T-Mobile USA, and unlicenced "white spaces" between TV stations. Though recent advances have led to networks that use spectrum more efficiently, faster connections do require more spectrum. The FCC's National Broadband Plan calls for allocating 500MHz of additional frequencies to mobile broadband over the next decade.
Whereas most of the spectrum debates have cited demand for mobile video and social networking applications, in the rancor over MMNS, there arguably is much more at stake. The microstimulator implants being developed by AMF could be used to treat neuromuscular disorders including spinal-cord and brain injuries, multiple sclerosis and cerebral palsy. The use of wireless networks between implants and MCUs could eliminate the need to implant trouble-prone networks of wires underneath a patient's skin, said AMF CEO David Hankin.
FES (functional electric stimulation) has been used for many years to cause unresponsive muscles to contract, Hankin said. It's one application of the merging of electronics and the human body, called bionics. The new microstimulators are about the size of a small fuse, so they can be implanted right next to a nerve, under local anesthesia, he said. Because of its greater precision, the new technology can gather more accurate input about how the patient wants to move and communicate that to specific nerves. The focused electrical charges hurt less than earlier ones, so patients who have sensation in their disabled limbs feel a tingling sensation at most, he said.
The MCU, which picks up and processes inputs from the spine or another source and passes it on to the microstimulators, can be carried in a backpack now, Hankin said. Eventually, the MCU may be as small as a cellphone, or even be built into the patient's own cellphone. Though the same type of technology can be used in physical therapists' offices, miniaturization and wireless links make it more practical for use as people go about their lives, he said.
Away from wired networks
Today, some patients have networks of microstimulators linked by wires implanted underneath their skin. This requires two or three days of operations and can lead to infections that travel down the wires, leading to another long operation to replace the wires, Hankin said. Wireless networks allow doctors to bypass that technique, he said.
MMNS requires very low frequencies in order to communicate with implants through the patient's skin, Hankin said. AMF looked to the 413-457MHz band, despite the fact that others were already using it, because it had the ideal characteristics for the job and AMF couldn't afford the billions that exclusive spectrum licenses cost at auction, he said.
The three lowest sections of the band are used by the federal government for defence radar and other purposes. The Department of Defense will allow MMNS in those bands, and the NTIA (National Telecommunications and Information Administration) is coordinating with the FCC on its own review of them, according to Hankin.
But AMF wanted one more band, 451-457MHz, to make sure that MMNS would have spectrum to use in situations where the other three bands were occupied. It's intended for use mainly in rural areas, according to Hankin. This band is home to many wireless devices, including land mobile radio (also called walkie-talkies) and broadcasting trucks that send live feeds back to their stations.
Broadcast engineers and others say MMNS need to stay out of this band. The Society of Broadcast Engineers (SBE), a smaller group called Engineers for the Integrity of Broadcast Auxiliary Services Spectrum (EIBASS), and walkie-talkie pioneer Motorola have all filed statements with the FCC opposing AMF's proposal. They said the foundation hadn't established that MCUs or implants could overcome interference from those nearby devices.
A different kind of interference
Broadcasting trucks using RPU (Remote Pickup) systems can transmit at thousands of times the power of MMNS, from antennas relatively close to the ground, said Dane Ericksen, co-chairman of EIBASS. AMF isn't asking the FCC for any legal protection from interference, saying it will coexist with other uses, but Ericksen thinks the MMNS proposal may be a Trojan horse.
"Neither SBE nor EIBASS have opposed this on the grounds that it will cause interference to RPU operations," Ericksen said. "Our concern is that RPU operations will wipe out MMNS, at which point the FCC will say, 'Oh my goodness, this is a medical application, and we're going to put restrictions on where RPUs can operate'."
If the FCC were to restrict use of the frequencies around health-care facilities, that might include retirement homes and many other locations, he believes.
"That would be a real burden, to force all RPU licensees to identify every health-care facility in their market and make sure they don't do any remotes within a half-kilometre, maybe, of that," Ericksen said.
AMF said tests by the DOD and defence contractor Aerospace Corp. proved that there are adequate mechanisms in MMNS to avoid interference. The medical devices can shift to another channel where there is less interference, and if there are no free channels, the system can carry out a "graceful shutdown." That would include an audible or vibration alert for the wearer, Hankin said.
Opponents say those tests didn't include a simulation of a radio transmitting continuously at high power for a long period of time, as a remote broadcast would. Hankin said he believed that was included.
In any case, the nightmare scenario of someone falling to the ground because interference caused his MMNS to shut down is not on the horizon, Hankin said. Because of the complexities of human gait, patients won't rely on MMNS to walk for many years, he said.