The Society of Broadcast Engineers told the FCC last week that a proposal to allow new wideband medical micropower networks (MMN) to use 24MHz of spectrum on a secondary basis between 413MHz and 457MHz should be rejected because incumbent users of the band, including broadcasters employing remote pickup stations, are likely to cause harmful interference to the medical devices.
Filing comments Aug. 11, the SBE was responding to a Notice of Proposed Rulemaking issued in March regarding the use of neuromuscular microstimulation devices using wireless technology in the 413MHz-419MHz, 426-432MHz, 438-444MHz and 451-457MHz bands. The commission issued the notice after receiving a petition for rulemaking submitted by the Alfred Mann Foundation seeking to market the devices.
While expressing concern that allowing the MMN devices to use the proposed bands would subject them to interference from a range of incumbents, the SBE comments focused mostly on Part 74, Subpart D, Remote Pickup (RPU) stations, particularly those operating in the 450MHz-451MHz and 455MHz-456MHz bands.
According to the comments, “RPU remote broadcasts can have long transmit duty cycles and effective radiated powers in the 40W-100W range. These lawful Part 74 transmissions are likely to interfere with, and therefore pose risks to, patients using MMN devices.”
The SBE reminded the commission that there currently is spectrum reserved for medical applications in the Part 95 Wireless Medical Telemetry Service. To allow the proposed devices (even on a secondary basis) into the desired spectrum would in effect downgrade incumbents to a de facto secondary service status to maintain the health of users of the MMN devices.
It is unlikely that MMN devices will have interference rejection capabilities sufficient to “withstand high power, cochannel transmissions from RPUs, military radars, land mobile systems, amateur radio and other licensed, mobile and itinerant transmitting facilities without danger to patients,” the filing said.
The SBE cautioned the commission not to walk down a path similar to one it traversed when it authorized body-worn Part 15 medical telemetry devices to use TV Channels 7, 9 and 11. Doing so required primary-service, full-power DTV channels to first check with community healthcare facilities before transitioning to those channels despite the fact that Part 15 rules require acceptance of interference from licensed users.
The SBE also rejected the assertion by the Alfred Mann Foundation that using redundant coding can protect MMN devices from cochannel interference. According to the SBE, “... there are limits to what redundant coding can do in the presence of a strong cochannel interfering signal.” “An MMN implanted device will have an ERP of -7dBm, while typical RPU base stations may have 46dBm to 50dBm ERP. Perhaps multiple layers of redundant coding would protect MMNs from
adjacent-channel RPU operations at 450MHz-451MHz, but practical applications have shown that no amount of redundant coding will protect a 451MHz-457MHz MMN from
cochannel RPU operations at 455MHz-456MHz,” the filing said.