ATM Modernization, Business & GA, Commercial, Military

Special Report: UWB: A Wakeup Call to GPS Users

By James J. Miller | February 1, 2001
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Some ultra-wideband (UWB) proponents say UWB is poised to change the world. USA Today, New York Times, and the Chicago Tribune have touted the benefits of this intriguing technology. USA Today went so far as to describe UWB as "an invention that might be as important as the transistor or the electric light bulb."

Truth is, UWB is not new at all. In the 1920s, Marconi used UWB in its spark-gap radio. Oddly enough, one of the last known commercial marine uses of this airwave manipulation technique was on the Titanic’s ill-fated maiden voyage, where other highly publicized assumptions (unsinkable?) were proven false.

UWB is not a mystique technology. Rather, it is a method of transmitting data via pulses of energy across wide swaths of spectrum (greater than 1.5 MHz in bandwidth), instead of using continuous waves in assigned regulated radio bands. And UWB is not the communications mode accepted worldwide by the International Telecommunications Union (ITU) to manage and protect global radio allocations, including safety-of-life aeronautical frequencies.

UWB applications present interesting opportunities (see accompanying story). For example, the military uses it for clandestine communications, radar and intrusion detection. But a look at the technology’s total impact reveals critical questions that must be answered before it is widely utilized–especially with UWB being fast-tracked through arguably inappropriate U.S. Federal Communication Commission (FCC) regulatory processes for unlicensed broadcasting in aeronautical safety-of-life and other vital radio frequency bands.

Why more scrutiny into UWB? Consider the 1927 Radio Act. It divided radio spectrum into 80 initial channels to allow multiple users within the same geographic area access to interference-free signals. Pulsed radio waves could not be controlled this way, so the regulatory structure for spectrum management was built on the frequency domain, not the time domain in which UWB operates. Amplitude and frequency modulation of continuous waves within specific bands thus defines the foundation for implementing and using radio equipment and services.

UWB devices pose a problem within this scenario, as no regulatory structure exists to assess their impact on present operating systems and services. As a result, with radio spectrum being a finite resource, UWB’s intrusion into the spectral "slices" (i.e., bands) simply "dices" stable radio waves with fluctuating pulses of energy.

Not Like Hair Dryers

Currently, one UWB company, aptly named Time Domain, isn’t letting little things like non-existing rules or minute operational experience between wave and pulsed systems slow them down. Rather, the Alabama-based firm is working hard to insert its pulsed systems into the busy spectral environment through a waiver granted by the FCC that allows operation of their devices under FCC Part 15 Rules.

Part 15 is intended to protect restricted bands from unintentional emissions interference from such devices as hair dryers and electric shavers. UWB, Time Domain argues, should be allowed to operate in protected bands because the intentional electromagnetic pulses emitted from their devices will radiate no more interfering noise than millions of Part 15 appliances already in use.

Admittedly, hair dryers are used everywhere, but not all the time. And they are not networked and do not have an antenna beaming information to, say, a Palm Pilot. Nevertheless, without rules covering time-based systems, Time Domain’s logic has gained for the company FCC approval to manufacture 2,500 UWB devices, with broader market options dependent on test results relative to the outstanding notice for proposed rule-making (NPRM-ET Docket 98-153). It cleverly uses the protective language of Part 15 to cloak aggressive business plans that will not wait for suitable regulations.

A bad precedent for managing aeronautical spectrum has been set, even though the World Radiocommunications Conference (WRC)-2000 emphasized last May that spectrum schemes must consider the following: All safety-of-life frequencies, such as the ICAO Global Navigation Satellite System (GNSS) band from 1559 to 1610 MHz, are protected under international rules set forth by the International Telecommunications Union (ITU). Therefore, intrusive, non-aeronautical services are precluded from operating in this specific frequency grouping, designated as an Aeronautical Radio Navigation Service/Radio Navigation Satellite Service (ARNS/RNSS).

The Conference reiterated the importance of protecting this global ARNS/RNSS allocation when a three-year challenge by Mobile Satellite Service (MSS) interests to "share" the bottom eight MHz portion of this band (1559 to 1567 MHz) was killed to protect aviation operators from harmful interference.

Time Domain’s new, UWB spectrum-sharing proposal seeks to circumvent the protections affirmed by this ITU action, claiming its pulsed systems merely "reuse" existing spectrum and do not require a band allocation. Again, very clever, because radio bands are being auctioned for billions of dollars, and if Time Domain gets its way, it will secure broadcasting rights without having to purchase any spectral rights.

Impact on Airlines

The airline industry is working hard to develop a seamless air traffic control (ATC) infrastructure, to increase capacity and reduce gridlock. The evolving satellite-based architecture hinges on advanced communications, navigation, surveillance/air traffic management (CNS/ATM) tools and will use GNSS position, velocity and time (PVT) information for many applications.

Transitioning to GNSS requires the preservation of a stable international platform on which technical standards can be defined, avionics equipment can be manufactured, users can equip, and new procedures can be devised. This model relies on rigorous validation and certification.

Airlines don’t oppose UWB implementation in this carefully regulated environment, but insist on a responsible integration of a new technology or service that seeks to operate in the ARNS/RNSS bands. Injecting unlicensed, mobile, wireless UWB devices and networks into this mix without safeguards minimizes the importance of aviation safety.

And the haste to commercialize UWB has been apparent. For example, even before the agency rules on UWB’s widespread use, FCC Commissioner Susan Ness agreed to be a featured speaker for the Dec. 13, 2000, European Commission Workshop on UWB.

The potential problems from UWB broadcasting over aeronautical frequencies was first raised by the FAA Office of Spectrum Policy and Management, which feared that UWB pulses could disrupt GPS (GNSS) signals if they were not properly filtered or "notched out" of the 1559 to1610 MHz band. This threat could penalize airlines and other GNSS users, as an unreliable signal would force air traffic service (ATS) providers to limit GNSS’s use in their airspace. Liability and related issues could undermine aviation industry efforts to fully modernize the ATC system, thus reducing avionics investment returns and complicating current and future certification processes.

Air carriers already feel the financial burdens of spectrum shortages and frequency interference, as they are forced to upgrade to new "hardened" FM Immunity radios with 8.33-KHz channel spacing. Corruption of ARNS/RNSS bands from UWB can only compound these costs and further impact industry growth.

Is There a Resolution?

Acting on FAA concerns, the U.S. Department of Transportation (DoT) initiated an ongoing technical study at Stanford University in the fall of 1999. It found that UWB does interfere with GPS. Since then, other organizations’ testing has shown the interfering qualities of unfiltered UWB. For example, a videotaped demonstration by UWB company Multi-Spectral Solutions Inc. (MSSI) shows UWB knocking television reception off the air. (The video has since been shown to FCC Chairman William Kennard). MSSI wants to protect the fledgling UWB industry by advocating protection of ARNS/RNSS bands.

Time Domain, not liking these findings, has financed its own studies, at University of Texas and Johns Hopkins University. The technical debates on allowing UWB to operate in safety-of-life bands have now been drawn into the political quagmire of these dueling studies. Additionally, the National Telecommunications Information Administration (NTIA)–which oversees government spectrum, where GPS operates–is evaluating operational scenarios that may be impacted by UWB. The intoxicating mixture of test results from Stanford, UT, JHU and NTIA are also being reviewed by the FAA advisory organization RTCA, in Special Committee 159, Working Group 6, to be included in an upcoming report to the DoT.

What these study efforts don’t address, however, is the aggregate effect that innumerable UWB devices will have on the "noise floor" that nav and com receivers operate against. This is crucial, as a comprehensive assessment of the national noise floor in the United States has not been conducted for several decades. The National Academy of Sciences proposed examining this issue in 1999, but never received funding to begin. The Academy estimates the study would take 18 to 24 months, far too long a wait when new services want to enter the spectrum world yesterday.

Not analyzing UWB’s effects to the noise floor is an unfortunate missing link, especially since Time Domain clearly is looking beyond the limited use (2,500 units) of UWB. At the recent COMDEX computer industry trade show, it boasted of providing wireless, synchronized networks at data rates up to 1 gigabit per second (Gbit/sec) by 2004.

In addition, current testing largely considers average-power output rather than the peak-power spikes that UWB produces. So, Time Domain is investigating not whether UWB interferes with GPS, but rather how much interference can GPS tolerate before the signal is no good.

The FCC has set a tentative deadline of Feb. 28 to accept the myriad test reports and analyses. Depending on the results, another round of public comments or a provisional rulemaking may be granted. Regardless of the outcome, the airline industry should not blindly bet their collective future on FCC rulings or WRC allocations without being heard. Silence makes you a victim service, accepting leftovers.

A New Role for Aviation

Spectrum "protection" is not a traditional airline concern. Air transport must rely on the FAA, DoT and NTIA to protect the government radio frequencies necessary for our operational survival. The FCC has a different mission and is charged with overseeing private spectrum in a manner that maximizes access to the most users.

The 1996 Communications Act strengthens this policy agenda, directing the FCC to hasten the adoption of new technologies and services. Meanwhile, the NTIA is squeezed in the middle of these conflicting interests.

For the aviation industry, technical points alone will not win the UWB argument. They must be accompanied by political and economic interests. Time Domain has successfully secured the support of important members of Congress and potential investors.

All is not lost, however. The aviation industry has awoken to the economic threats posed by the hazard of a compromised GPS signal. In the U.S., the Air Transport Association (ATA) Flight Systems Integration Committee has coordinated industry responses with other trade groups such as Aircraft Owners and Pilots Association and the National Business Aviation Association. And the ATA governmental affairs organization put together a UWB Steering Group to inform, educate and publicize airline concerns to key Congressmen. Additionally, ARINC, through the Aeronautical Frequency Committee (AFC), responded jointly with the ATA to the FCC NPRM. On the international front, the International Air Transport Association is addressing the UWB issue in its Spectrum Protection Steering Group, and the International Civil Aviation Organization has submitted a paper to the ITU requesting that UWB applications be examined prior to WRC-2003.

No doubt, spectrum is becoming scarce. And new methods of transmitting data such as UWB may provide benefits. First, however, long-term solutions must be tried–perhaps an experiment that uses conventional band segmentation to limit UWB operations from 3 GHz to 9 GHz on a licensed basis until more is known on blending the characteristics of wave and pulsed systems. To open up the safety-of-life bands at this stage takes air carriers and their passengers for a dive into murky waters before anyone knows what lies beneath.

James Miller is senior staff specialist within the Flight Operations Technology department of United Airlines. He is the airline’s primary representative on the ARINC Aeronautical Frequency Committee and IATA Spectrum Protection Steering Group, and serves on the ATA Flight Systems Integration Committee, ATA UWB Steering Group, and other related forums. He was an observer at WRC-97 in Geneva and a delegate at WRC-2000 in Istanbul.

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