FAA Keeps Watch on UWB
At the (U.S.) Federal Aviation Administration, we have been closely involved with the ultra-wideband (UWB) issue since the National Telecommunications and Information Administration (NTIA) brought to our attention requests by three manufacturers of UWB technology for waivers of Part 15 of the Federal Communications Commission (FCC) rules.
We found your articles in the February 2001 issue (starting on page 20) to be accurate and are encouraged by the interest shown by the aviation community. We hope other interested parties will express their views to the FCC.
The FAA believes that UWB technology has the potential to be beneficial for many applications, although all of the applications are not proven. Our goal is to ensure that if UWB technology is implemented, it is done in a responsible way (perhaps licensed operation for some types of UWB systems) that is not detrimental to our existing aeronautical systems and does not impede our ability to modernize the National Airspace System (NAS). Aviation safety and regularity of flight are our highest priorities.
As mentioned in James Miller's article (page 28), UWB is not a new technology. "Time domain" operation is no more than the well-understood pulse-position-modulation that has been around for a number of years. What has changed, however, is that at a relatively low cost, the capacity to transmit information has increased by using very narrow pulses resulting in very large transmitted bandwidths.
The FAA, as delegated by NTIA, is responsible for managing the spectrum used by civil aviation in the United States. Our concern with regard to UWB systems comes from the fact that the large bandwidths (some 2 to 3 GHz) of these systems overlap several allocated frequency bands, including those used by the FAA for safety-of-life operations.
Reports on independent test programs by the Department of Transportation (DoT) and NTIA recently were released. They show that the Global Positioning System (GPS) is susceptible to interference from some UWB signals. NTIA and DoT concluded that the effects of the UWB signals on GPS varied depending on their signal characteristics.
NTIA also released reports that characterize UWB signals and assess the impact of UWB signals on selected federal systems (excluding the GPS). NTIA reported that UWB technology can have different effects on aeronautical systems. There is potential for interference from a single UWB device to aeronautical systems, such as distance measuring equipment, air traffic control radar beacon systems, air route surveillance radar, airport surveillance radar, weather radars, and the microwave landing system.
Aggregate models show that an accumulation of UWB devices only compound the problem, but we share the author's concern that aggregate effects are largely an unexplored issue. Also, it has not been shown that, absent any frequency discrimination capability, UWB receivers will not be degraded from existing systems and/or other UWB systems.
George K. Sakai
Program Director Spectrum
Policy and Management
Federal Aviation Administration
Runway Incursions: Another Idea
In reference to your article in the April 2001 issue on the new systems being developed to prevent runway incursions (page 16), I started doing extensive research on the subject after submitting a suggestion to my employer, the Airway Facilities Branch, Federal Aviation Administration, Eastern Region.
Compared to products listed in your article, mine is not high-tech. But I feel it will be a step in a positive direction for smaller airports.
If General Motors has the OnStar system to track vehicles when stolen or in distress, and GEOSat Solutions offers Sea Trac to track your boat or yacht 24 hours a day, where is the GPS transponder system for aviation? As a technician with 21 years of experience, I think such a system could be developed, using off-the-shelf technology at a relatively low cost.
A no-frills, 12-satellite GPS receiver with RS-232 data transfer can be purchased for under $200, and I estimate the transponder cost at about $2,000. The GPS receiver could be used as the positioning module in the transponder. The GPS position information then would be digitally combined with the aircraft or vehicle identification number. This data could be compressed and placed on a radio frequency (RF) carrier, transmitting to a tower receiver that would, in turn, send the data to a computer. The computer would decode and display the aircraft and/or ground-vehicle identification and position.
The computer screen would be formatted to present the airport's layout, and the computer program would be performing constant calculations, to predict an incursion and alert controllers. If the system were based on a VHF frequency modulated carrier, incursions could be predicted from as far away as three nautical miles.
I realize that general aviation owners may object to buying a mandatory GPS incursion transponder. And some will question what frequency spectrum would be used. I suggest assigning a frequency from the 140-to150-MHz spectrum nationwide. (I would choose this frequency range because FM modulation would provide the best coverage at the airport. The process of "de-fruiting"--separating two transponder transmissions transmitted simultaneously--also would have to be addressed.
Other questions exist (mainly costs). However, the system would increase the capability of saving lives.
And isn't that what it's all about?
Dennis M. Golman
Continuous Altitude Rule
I found the recent Editor's Note on "Bats and Air Traffic Control" (March 2001, page 4) very interesting. I'm an aerospace research engineer at NASA Ames Research Center, and I have another idea that you might find fascinating. I call it the "continuous altitude rule." The idea is that designated cruising altitudes should be a linear function of heading or course, as opposed to the discrete function that is used now (a flight level every 1,000 or 2,000 feet).
This rule spreads the cruising traffic vertically and provides a default vertical separation that is proportional to path crossing angle. I had a paper on the subject published in the Fall 2000 issue of Air Traffic Control Quarterly. In that paper, I showed that this rule can greatly reduce the chance of a collision. It also reduces the closing speeds of the remaining potential collisions, giving pilots and controllers much more time to react.
Of course, the continuous altitude rule has drawbacks. Please understand that it is still a research concept and has not been endorsed by NASA, the Federal Aviation Administration or any other organization. You can find the ATC Quarterly paper in PDF format at http://RussP.org/publist.htm.