Re: Wireless patient devices at risk from proposed Internet use

[David Farber <dave () farber net>]

________________________________________
From: Matthew Kaufman [matthew () eeph com]
Sent: Wednesday, May 14, 2008 11:16 AM
To: David Farber
Cc: ip
Subject: Re: [IP] Wireless patient devices at risk from proposed Internet use

Dave, for IP...


David Reed says:
> > There is a germ of truth (perhaps a prion-sized germ or maybe just an
> > amino acid) in the idea that transmitters in "white spaces" in the TV
> > band *might* disrupt patient monitoring equipment if designed by a
> > lunatic who believes in sending massive pulses of energy in a whitespace
> > in the TV band (perhaps amplified by a large parabolic dish antenna the
> > size of a trashcan lid or larger, aimed at the patient monitor system.
> > But that risk is completely shared with zillions of other potential
> > radiators of energy in the entire electromagnetic spectrum.
> >
> > Engineers in safety related industries (airplanes, healthcare) are
> > required to shield their equipment against this risk.  There is an order
> > of magnitude GREATER, but identical risk in placing a hospital near a TV
> > broadcast antenna.   Yet this is extraordinarily common in cities
> > throughout the US.

There's actually a big difference here. The reason that in-hospital
wireless medical telemetry device makers and professional wireless
microphone makers (and users, like the Grand Ole Opry) are concerned
specifically about new uses of "white spaces" is that these "white
spaces" are already in use *by them*.

Professional wireless microphones and in-hospital patient monitoring
telemetry devices are two classes of equipment that are already
authorized to be tuned to frequencies that are within both the VHF and
UHF TV bands, as long as the channels chosen are those that are not in
use for TV broadcasting in the area. (VHF wireless microphones on
174-216 MHz, and UHF wireless microphones on 512-790 MHz... the latter
will be required to reduce the top end when 700 MHz goes from UHF TV to
land mobile in a few years). And both types of equipment are designed as
short-range low-power relatively narrowband devices, and with the
assumption that because they're between two TV channels and on
frequencies selected by the installer to not be subject to other types
of interference (e.g., intermodulation products), there isn't much need
to resist interference through engineering.

When large wireless microphones are set up at big events like political
conventions, the broadcasters and the stage folks all get together and
(using frequency coordination software, in many cases) pick channels
that are not in use as TV channels, not in use by each other, not
subject to intermodulation products or harmonics from things like the
security 2-way radios in use at the event, and not subject to
intermodulation products from each other. It works pretty well. Adding a
large number of new "white space" users that are picking channels on
their own and moving around the city as mobile devices to that mix would
clearly make this process not work as well, and require a new class of
wireless microphones that use techniques like spread spectrum and error
correcting codes to deal with the new reality. No surprise that there's
a concern being raised by the existing users.

> > As an engineer, I'm persuaded by actual analyses, not claims of
> > authority by companies "waving bloody shirts" about "people might die".
> > Let's scrutinize the analysis for a specific, well-documented piece of
> > healthcare equipment.   It's easy to test the vulnerability of such a
> > device.

As their attorney said, "there are no insurmountable technical hurdles
here." This isn't about people "waving bloody shirts", it is about
people who are the incumbent users of the "white spaces" asking to have
their uses considered before a bunch of additional radiators are added
to those frequencies. This happens *every* time someone tries to use
spectrum that someone else is already using for some new purpose, and it
always seems to get sorted out. There is a legitimate technical concern
that adding lots of new sources of RF in what was an "empty" part of the
band will disrupt devices that were designed with the assumption that
they'd be the only thing on that frequency.

Matthew Kaufman
matthew () eeph com

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