Wednesday, June 25, 2008

Medicine in the White Spaces

The drooling is well underway for whatever bones of the old VHF and UHF analog television service aren't already picked clean. The telcos, AT&T and Verizon, have already gobbled up the juiciest morsels of the 700 Hz spectrum that weren't already allocated for digital TV broadcasting. No one is going near the frequencies reserved for public safety service. Instead, everybody now wants in the cracks and crevices known as "white spaces" between the powerful signals of commercial television transmitters. That includes all that wireless medical equipment they hook you up to in the hospital.

Medical telemetry, also known as biotelemetry, refers to medical equipment that uses wireless data links. One popular use is wireless cardiac monitors that keep track of patients' heartbeat activity without tethering them to a bedside monitoring unit. It can also include a wide variety of hospital equipment including imaging, scanning, ultrasound and more. Just about anything that isn't voice and video and is designed for medical application fits the definition.

As it turns out, medical telemetry has already staked out its claim in the UHF TV band. Channel 37, covering the frequencies between 608 and 614 MHz, has been used since 2000 for this purpose.

But how can that be? DTV is just getting going in a big way and all the old analog transmitters are still running full bore. I thought white space transmissions were something that would spring up when the analog channels go dark next February?

Turns out that the FCC established the Wireless Medical Telemetry Service (WMTS) on three bands in June of 2000. Two of those are in the microwave region of the spectrum that were originally assigned for government use but no longer needed for that purpose. The other is 608 to 614 MHz, also known as TV channel 37.

But what happened to the TV stations on channel 37? There weren't any. Channels 37 was reserved for radio astronomy work. Since radio telescopes are few and far between, the channel can be shared between radio astronomers and hospitals with only rare situations of interference. So, in a way, medical telemetry is already in the white spaces.

Medical telemetry is one of the existing applications threatened by proposals to turn the TV white spaces into wireless Internet broadband, cellular backhaul, or other services yet to be conceived. Since only channel 37 is assigned to WMTS, one way to avoid trouble is to have white space transmitters include a spectrum mask to prevent transmissions on channel 37, plus one channel to each side for additional protection. The proposed white space transmitters would have to avoid channels being used for TV transmissions in a particular location anyway, so this is just a slight further constraint.

Medical electronics is a rapidly advancing technology that gobbles up bandwidth of all types, including wireless and wireline and fiber optic connections. Medical imaging alone needs all it can get to enable transmission of large image files in seconds, not hours. Compared with the requirements of CAT scan and MRI equipment, patient monitoring is currently a fairly narrowband operation. But with future advances, even this activity may need all the white space or other bandwidth it can get.

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