The international aircraft-aerospace industry has a problem. Aeronautical telemetry, the industry's only way to measure and analyze the performance and safety of aircraft, could be headed into a tailspin. At issue is the fierce competition for available radio spectrum, which is a finite resource.

Radio spectrum, also known as radio frequency, makes up the choicest eddies of electromagnetic energy that envelop the Earth. It supports the growing industries of cell phones, television, radio, and other wireless devices. These industries—as well as many government agencies—are now vying for control of the very same bands of radio spectrum. One of these industries is aviation. Every new aircraft must pass a series of flight tests before it's certified as airworthy, and these tests depend upon spectrum waves to send flight test data from airborne transmitters to ground stations. A MITRE team is working to help the government balance the need for spectrum among many players while protecting the critical testing of aircraft.

	What Is Spectrum?
	The electromagnetic spectrum is what makes all wireless devices work. Spectrum is a swirling admixture of differing radiant energies made of countless trillions of tiny energy bundles called photons. Created from thermonuclear reactions deep within the Sun's interior, this radiant energy careens headlong into the Earth in galactic-size waves, where it's filtered by the outer atmosphere. What energy remains streaks earthward to become the spectrum. Each range of the spectrum has different qualities. For example, radio waves are made of low-energy photons, whereas microwaves have a little more energy and infrared have still more. At the other end of the spectrum, with the most energetic photons of all, are gamma rays. Below: The diagram shows the entire spectrum of electromagnetic waves. The atmospheric opacity determines what radiation reaches the Earth's surface.

Why are flight tests so important? Imagine an Airbus A330 high over the Atlantic, too far out to turn back to New York's Kennedy Airport when one of its two massive engines suddenly stops working. On a single engine, the aircraft might attempt to make it to London's Heathrow Airport, three hours distant. Would the lone engine overheat under the strain of keeping the 230-ton widebody aloft? What's the optimum airspeed and altitude for that situation? What other on-board systems might be in jeopardy because of engine stoppage? These issues are examined and solved during flight tests—not when the A330 is full of passengers.

Adding to the need for increased testing is the fact that today's newer aircraft are designed almost entirely by computers. They are not tested until after they are completely built. Making sure that all 3 million individual parts on a skyliner are working—individually as well as collectively—falls to the science of aeronautical telemetry, and to flight testing, its principal method of gathering, recording and analyzing such information.

While the need for spectrum is growing quickly, the available amount is limited by Nature herself. Before the advent of the wireless industry in 1996, the amount of spectrum was sufficient to meet every need. Not any longer. The use of devices such as cell phones, PDAs, pagers, GPS locators, Wi-Fi devices, baby monitors, and garage door openers has severely encroached upon the spectrum supply. In 1996 there were 100 million mobile phone subscribers worldwide; by the end of 2005, that number will jump to more than 3 billion. The wireless industry is clamoring for the rights to more spectrum—or to the rights already allotted to others.

The dilemma facing Congress is to simultaneously nurture the growth of the wireless industry while at the same time fulfilling the needs of essential services, including satellite navigation, rescue operations, and defense.

Achieving Balance

Because spectrum affects many of MITRE's government sponsors, our staff has developed notable expertise in spectrum challenges and possible solutions (such as ways to share the same range of spectrum). Wireless communications are mission-critical to the Federal Communications Commission (FCC), Federal Aviation Administration, National Telecommunication and Information Administration, the Department of Defense (DOD), and the Interdepartmental Radio Advisory Committee, which represents 22 government departments and agencies. MITRE's role as an unbiased government partner working in the public interest helps us to guide government agencies as they seek a fair and balanced use of the national spectrum.

The MITRE Team: (left to right) Ed Cross, Darrell Ernst, Director of Spectrum Management Jim Chadwick, David Portigal, Brian Ramsay, and Yan-Shek Hoh.

MITRE's spectrum guru James Chadwick has seen just about everything during his four decades of working with spectrum issues and giving technical counsel to the government. As Chadwick sees it, the biggest challenge today is the unabated growth of mobile telecommunications services. "They're demanding 'beachfront' spectrum regions," he claims, "while relegating the government to "swamp" spectrum." The biggest assault is on the prime radio bands in the 100 MHz to 3 gigahertz (GHz) range, where power requirements are lower and antenna sizes can be smaller.

To help the government determine how to balance use of the spectrum—and use it as efficiently as possible—MITRE has developed extensive tools, databases, and contacts, which are key enablers in keeping customers current and in building consensus. The information gathered through these channels will give the government compelling scientific justification for why agencies require a certain amount of spectrum to do their jobs. "MITRE is providing technical content for these justifications," says Chadwick.

MITRE engineer Darrell Ernst is working on the front lines with the U.S. aircraft-aerospace industry on behalf of both the FAA and the DOD. Ernst is attempting to retain and, if possible, gain more spectrum for flight testing. "Flight tests are expensive to conduct and risky for pilots to fly," he says. "To constrain those tests to weekends when spectrum is more abundant or to limit full testing because of a lack of sufficient spectrum is destructive to safety, as well as to aerospace economics. Getting a new airliner to the marketplace on time is essential for the aviation industry. Delays in flight testing can kill off that advantage."

MITRE's Carolyn Kahn has looked at the economic impact of test telemetry on the U.S. aerospace industry. She forecasts the telemetry market to triple to a $3.3 billion industry by 2006. Every aircraft—from huge widebodies to single-engine sport planes, from rockets to satellites, from military to commercial—must pass muster on a flight test range prior to certification. The U.S. aerospace industry creates 11 million U S. jobs, is a leader in exports, and generates some 15 percent of the nation's Gross Domestic Product. The telemetry business is also growing, which means that its need for spectrum is growing as well. Decreased spectrum, she reports, results in longer testing periods, which results in increased costs.

Emerging Trends

Based on emerging trends in aeronautical telemetry, the need for spectrum can only increase. The newest trend, pioneered by Air France, is to extend the testing process long after new aircraft are first checked out and in regular service. Air France, for example, tests throughout the entire life cycle of its A330 aircraft. While these planes are airborne, on-board computers monitor engine performance and send the data to ground units via satellite-based datalinks. Troubleshooting potential problems—maybe even preventing a disaster—can now take place during actual flights.

MITRE is at the forefront of assisting the government to get more out of the finite spectrum. For example, we established a method for evaluating U.S. spectrum use, developed techniques for identifying favorable frequency ranges, and compared those ranges to actual present-day spectrum allocations. While there are ways to use the spectrum more efficiently, many feel that complete spectrum reform is the only truly viable solution. To that end, the FCC established the Spectrum Policy Task Force, admitting that, "The government has an almost impossible task in trying to keep pace with the ever-increasing demand for spectrum and the continuing advances in wireless technology." The Task Force will reexamine 90 years of U.S. spectrum policy. As part of its work, it will look at the future needs of aeronautical telemetry.

Common ground must be found somewhere between the needs of commercial wireless interests and those of flight testing. Reallocation of its existing frequency bands and getting pushed ever higher into the electromagnetic spectrum won't work for aeronautical telemetry. "It's not feasible to operate above, say, 16 GHz," comments Ernst. "There are neither transmitters above that range nor any emerging transmitter technology that will get us there anytime soon. Atmospheric absorption of signals increases at these higher frequencies, and tracking and signal acquisition become more difficult. The most practical range for telemetry is between 6 and 15 GHz."

Equitable sharing by all parties of what Chadwick calls "beachfront" spectrum would be the ideal solution. Ernst and his MITRE colleagues are busy drafting technical justifications designed to ensure that flight testing is kept far from the "swamp."

—by Tom Green

Related Information

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• Center for Advanced Aviation System Development (CAASD)

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