NASA RNSS Spectrum Protection Activities

Beryl Brodsky, James E. Hollansworth, James J. Miller, A.J. Oria

Abstract:	This paper reviews recent National Aeronautics and Space Administration (NASA) activities regarding Radionavigation Satellite Service (RNSS) spectrum protection from potentially harmful electromagnetic interference. These activities include: (1) studies on an instance of cell phone spurious emissions on-board aircraft in the Global Positioning System (GPS) radio frequency band; (2) research on man-made radiation in four frequency bands, including GPS; (3) tests of an ultrawideband (UWB) pulse radio source to explore and evaluate electromagnetic interference (EMI) effects on various aircraft radio systems’ performance; (4) tests on applicability of data collected on aircraft parked on the ground in relation to the conditions of a pressurized cabin during all the phases of flight operations; and (5) involvement in issues concerning the licensing of GPS reradiators in the U.S. The study of cell phone spurious emissions was a result of a report to the Federal Aviation Administration (FAA) of a particular E-911 enabled cell phone model that apparently caused interference to several GPS receivers on-board a small single engine aircraft despite being compliant with data filed at the time with the Federal Communications Commission (FCC) by the manufacturer. NASA and industry tests showed that, while there is an emission in the 1575 MHz GPS band due to a specific combination of amplifier output impedance and load impedance that induces instability in the power amplifier, these spurious emissions are similar to those measured on non-intentionally transmitting devices such as, for example, laptop computers. Studies were undertaken to identify the man-made radiation, or noise-floor, present in four bands used by rather different services, namely, L1 Band (1563.42 – 1587.42 MHz), the Unified S-Band (2025 – 2110 MHz), the 2.4 GHz Industrial, Scientific and Medical (ISM) Band (2400 – 2482.50 MHz), and the 23.6-24.0 GHz Passive Sensing Band. Results show that there were distinctive differences in the measurement data in the frequency bands, which should be expected based on the function/regulation associated with each. The GPS L1 Band had little to none terrestrial man-made sources, but the ISM 2.4 GHz Band had a large number of man-made sources regardless of the site and the time. The Unified S Band showed mixed results depending on the sites. The Passive Sensing Band does not contain appreciable manmade radiation. Studies were conducted using an UWB pulse radio source to explore and evaluate EMI effects on various aircraft radio systems’ performance. Interference incidents had been documented and reported on the Traffic Alert and Collision Avoidance System (TCAS) and Instrument Landing Systems (ILS). While the National Telecommunication and Information Administration (NTIA) completed some analytical studies exploring potential EMI to aeronautical radio systems from UWB, no one had performed testing on airplanes to screen for unforeseen effects or to verify analytical studies. As a result, NASA’s Office of Space Communications and Spectrum Management organizations became interested in supporting further UWB EMI tests on airplanes after becoming aware of the airplane EMI testing. Test results showed that aeronautical radio systems operating below 960 MHz are at-risk to UWB EMI from handheld consumer products meeting existing FCC rules. Aeronautical radio systems operating above 960 MHz were found unlikely to be affected by UWB Emissions at levels meeting the FCC 15.519 limit mask for handheld UWB systems, but interference margins for these aeronautical systems will be adversely affected if FCC UWB emission limits are increased Another issue of concern has been the applicability of technical data collected on aircraft parked on the ground is to the conditions of all the phases of flight operations. The NASA HQ Spectrum Policy Office and the Department of Transportation sponsored the data collection and analysis of path loss coupling data between on board test transmitters and key Communication and Navigation systems while on the ground and in-flight at various altitudes and pressures representative of the different phases of flight. The comparison of the Insertion Path Loss (IPL) coupling data on the ground and at altitude revealed effects due to aircraft proximity to the ground and variations in radio frequency (RF) leakage out of doors due to aircraft altitude/pressurization. Finally, GPS signal re-radiators have been available, illegally, in U.S. retail stores despite an FCC ‘Cease & Desist’ order since 2001. Re-radiators are used to broadcast GPS signals inside a close environment such as a hangar or a garage. There have been external efforts from the manufacturers to treat these under Part-15 requirements, i.e. as background noise, but NASA believed the equipment should be licensed and operated only by qualified end users under controlled conditions. As a result of a number of tests the FCC sent out enforcement letters to stop commercial sales of reradiators.
Published in:	Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008) September 16 - 19, 2008 Savannah International Convention Center Savannah, GA
Pages:	2440 - 2449
Cite this article:	Brodsky, Beryl, Hollansworth, James E., Miller, James J., Oria, A.J., "NASA RNSS Spectrum Protection Activities," Proceedings of the 21st International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2008), Savannah, GA, September 2008, pp. 2440-2449.
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