Protecting Safety-Of-Life Radio Frequencies

By James J. Miller | July 1, 2003
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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 world’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 agencies’ 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 FCC’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 DoT’s Office of Navigation and Spectrum Policy. He can be reached at jj.miller@ost.dot.gov.

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