Subject: [NEXTEL-1] Perspectives: Protecting Safety-Of-Life Radio Frequencies]

From: [email-masked]
Date: Fri, 29 Aug 2003 04:37:49 -0400

[Avionics]                                                             July 2003
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Perspectives:Protecting Safety-Of-Life Radio Frequencies

By James J. Miller

Radio frequency spectrum is the lifeblood of wireless communications. Without it,
satellites would uselessly orbit the globe, and communications towers, cell phones
and radios would fall silent or echo the chaotic noise of electromagnetic static.
Many transportation sectors would simply grind to a halt. Spectrum is thus an
integral enabler of the worldâ€™s information and transportation systems. It
is the invisible infrastructure that brings the world together and needs to be
managed with great care.

The U.S. Department of Transportation (DoT) takes the value of this precious
resource seriously and is committed to work with partner government organizations
and industry constituents to protect the integrity of safety-of-life radio
applications. This ranges from interference-free communications between
controllers and pilots to use of GPS for positive train control and wireless E-911
position location. In all of these instances, lives depend on the uninterrupted
transmission and reception of radio waves that are protected under the auspices of
the International Telecommunication Union (ITU).

In recent years, however, tremendous pressure has been placed on "safety
regulator" organizations to share these government-restricted frequencies with
emerging commercial ventures. While the DoT firmly supports new, innovative
technologies, safety-of-life radio bands simply may not be the best place to
initiate radio experiments for new gadgets or wireless techniques. This is
especially true when there is little technical understanding of the scope of
safety and economic costs to incumbent band users when radio frequency
interference (RFI) develops.

This became obvious when a newer radio transmission technique, Ultra-Wideband
(UWB), was introduced on a grand scale. UWB uses short pulses of energy to
transmit data rather than using traditional modulated-carrier techniques. It could
be considered the resurrection of the "spark-gap" transmission approach that was
outlawed in the 1930s due to harmful RFI. The military has used this form of
communications in controlled environments since the 1960s; however, the widespread
commercialization of UWB on an unlicensed basis has caused concern among safety
regulators.

This is because initial assumptions were made based on testing a limited number of
UWB emitters. In reality, however, market success in the communications world
requires the technology to "take hold" and grow to become economically viable. In
the case of UWB, this introduces what is termed a "disruptive technology" as an
unlicensed overlay on critical frequencies. Without technical data that determines
the aggregate effects of such use, there is serious potential for harmful RFI to
public safety systems.

Faced with this scenario, DoT would argue that the first burden of proof lies with
the new technology to show that it is safe, rather than public safety
agenciesâ€™ being forced to prove applications are unsafe after they have
entered the marketplace. No matter how rushed new wireless ventures are for market
share, safety remains non-negotiable.

The easiest solution to protect all, then, may be to simply allocate spectrum for
experimental use and unlicensed overlays in bands where RFI poses the least
threat. Fortunately, the Federal Communications Commission (FCC) was responsive to
tests showing that UWB can interfere with GPS and other crucial systems, and
eventually approved an emissions mask that appears to provide some level of
protection. More data and real science are needed before these protection limits
are relaxed further.

The UWB debate is only the tip of the iceberg in terms of what is evolving in
spectrum management. The FCCâ€™s Spectrum Policy Task Force outlines several
interesting initiatives, including moves towards a more "market oriented"
approach, greater approval of unlicensed services, and even "interference
temperature" receivers. While these concepts are all innovative, it is important
that the necessary "command and control" of public safety bands is not compromised
or subjected to unnecessary risk to further commercial experimentation.

It is vital that current communications and navigation equipment continue to
function properly and not need to be modified to operate in the new, busier
spectral environment. One way to ensure this happens is to monitor and respond to
proposals posted in the U.S. Federal Register. The Register is a "guide post" to
new spectrum initiatives. It is the first chance for public review and comment on
notices of proposed rulemaking, notices of inquiry, and other relevant documents.

Good government encourages transparency and active debate, and the first step in
helping to shape a positive, collaborative environment is to provide feedback to
proposed policy actions. Not responding means acceptance of the status quo. DoT
wants to find solutions that balance the needs of national safety, security and
economy. It is when our constituents are well informed and vocal that this process
works the best.

James J. Miller is the program manager of the DoTâ€™s Office of Navigation
and Spectrum Policy. He can be reached at [email-masked].
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