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Spectrum Management for Science in the 21st Century Committee on Scientific Uses of the Radio Spectrum Marshall Cohen, Co-Chair Albin J. Gasiewski, Co-Chair on behalf of the full committee Committee Membership • Radio Astronomy – D. Backer UC Berkeley – S. Ellingson Virginia Tech – M. Cohen Caltech (co-chair) – D. Emerson NRAO – A. Evans UVA / NRAO – P. Kolodzy Kolodzy Consulting – J. Moran Harvard – A. Tanner JPL – L. Mundy U. Md. – J. Johnson Ohio State – T. Pearson Caltech • Remote Sensing • • Interference and Mitigation – A. Gasiewski U. Colorado, (co-chair) – D. Kunkee Aerospace Corp. – C. Ruf U. Michigan – F. Solheim Radiometrics Corp. – D. Staelin MIT Staff: Donald Shapero, BPA Director Brian Dewhurst, Program Officer David Lang, Program Officer • Policy – R. Balstad Columbia U. – M. Macauley Resources for the Future Origin of the Study • Both the Committee on Radio Frequencies (CORF) and the scientific community were in need of a detailed forward-looking technical study on: – Current and future scientific use of the spectrum – Trends in active use of the spectrum – Potential RFI mitigation technologies and strategies • Motivated by the FCC and others considering the use of “unused” passive frequencies and investigating methods to increase “efficient” use of spectrum • NSF, NASA, and DOC agreed to support the study Statement of Task “The committee will prepare a report exploring the scientific uses of the radio spectrum emphasizing the passive services which will: 1. Portray the science and applications that are currently being conducted by passive observations using the radio spectrum; 2. Identify the spectrum requirements necessary to conduct such research and facilitate such applications; 3. Identify the anticipated future spectrum requirements for at least the next 10 years; and 4. Advise spectrum policy-makers on the value to the nation of accommodating scientific uses of the spectrum by the passive services, recognizing the need to balance multiple communities. The committee will comment on spectrum use by the relevant scientific communities but will not make recommendations on the allocation of specific frequencies.” The Passive Services Radio Astronomy Service (RAS) Study all ranges of the heavens, from the Sun to the most distant galaxies and beyond. Study exotic objects, yielding new information about the nature of matter, the origins of the Universe, and man’s place in it. Earth Exploration Satellite Service (EESS) Measure terrestrial variables such as surface temperature, soil moisture, atmospheric profiles, and many more. Weather prediction, climate studies. Strong economic value. Protecting Passive Science Observations • Spectrum for passive purposes can be likened to parkland preserved for public use: it defies monetization, and as such requires proactive measures for its preservation and shared use. • Use of spectrum to make scientific observations is regulated and, in places, protected, but the proliferation of wireless technology challenges engineers’ abilities to mitigate unwanted radio interference. • Most regulations are not aligned with or cognizant of the special needs of passive scientific users. U.S. Investments in Passive Observatories Finding: Large investments have been made in satellite sensors and sensor networks, and in major radio observatories. New facilities costing billions of dollars are under construction or are being designed. Finding: Scientific advances have required increasing measurement precision by passive radio and microwave facilities in order to obtain more accurate and thus more useful data sets. This need for precision will continue to increase. Technological and Educational Benefits of Passive Observations Finding: Passive microwave Earth remote sensing provides a diverse and valuable set of educational opportunities. Finding: In addition to the intellectual benefits it provides, passive microwave remote sensing studies provide many technological benefits to American society. Extreme Sensitivity & Interference Potential Signals from natural radio emissions are weak, and the equipment used to measure them is necessarily becoming ever-more sophisticated and sensitive. The minimum detected or detectable signal in flux density vs. year of measurement. The sensitivity is proportional to receiver system temperature and inversely proportional to collecting area and the square root of both bandwidth and integration time. For measurements after year 1990 an integration time of 12 hours is assumed. The rapid improvement over time is due to system improvements. The improvement from 1933 to 1983 is about 10 orders of magnitude. 26 W 1 Jy 10 2 m Hz Trends in Radio Astronomy Large new telescope systems with continuous coverage over an extremely wide frequency band, often using instantaneous bandwidth > 1 GHz, with integration time > 1 day. [ex: red-shifted hydrogen from early universe] GBT (Robert C. Byrd Green Bank Telescope) eVLA (extended VLA) SKA (Square Kilometer Array, 2020?, strong US participation) SKA pathfinders in Australia, South Africa Large new high-altitude millimeter telescopes. [ex: astrochemistry in star-forming clouds] ALMA (Atacama Large Millimeter Array) CCAT (Cerro Chajnantor Atacama Telescope) The Importance of EESS • Microwave measurements from satellites are vital for weather forecasting (eg: Hurricane Katrina) Long-range climate studies (eg: ice cover) (Left) Image of the wind speed of Hurricane Katrina (in knots), observed by passive microwave radiometers on WindSat, a Naval Research Laboratory satellite, as the hurricane makes landfall near New Orleans on August 28, 2005. (Right) Output from a model that combines data from WindSat and other remote sensing instruments. The model provides information on the hurricane’s windspeed. The values over land are extrapolations. Spectrum Usage Radio Frequency Interference (RFI) and its Mitigation Interference Potential • Both the active and the passive services are increasing their use of the spectrum, and so the potential for interference, already strong, is increasing. • Satellites cannot “hide” from ground-based interference, in the way that RAS observatories can. 400 China Mobile Subscribers (millions) 350 300 The number of Chinese cellular subscribers grew by more than 250 million between 2002-2007. Source: China Mobile Ltd Annual Reports. 250 200 150 100 50 0 2002 2003 2004 2005 2006 2007 Impact of Radio Frequency Interference (RFI) Finding: Important scientific inquiry and applications enabled by EESS and RAS are significantly impeded or precluded by RFI. Such RFI has reduced the societal and scientific return of EESS and RAS observatories, and necessitates costly interference mitigation, which is often insufficient to prevent RFI damage. The effect of RFI on an astronomical image made at the VLA. At left is an image of a faint “OH/IR star” made in a narrow band at 1612.22 MHz, within the band 1610.6 – 1613.8 MHz that is allocated to the RAS on a primary basis. At right is the same field of observation made when an Iridium satellite was 22 degrees from the star. This image is made useless by the RFI. Unpublished images courtesy of G.B. Taylor, NRAO. (LEFT) Electronically-Scanned Thinned Array Radiometer (ESTAR) image at 1413 MHz from the Southern Great Plains experiment (SGP97). The vertical lines west of Oklahoma City are distortions due to RFI. (RIGHT) Example of RFI in the vicinity of Oklahoma City during SGP97. The signal represents total power and was recorded west of the arrow in part (a). SOURCE: D. Le Vine, “ESTAR experience with RFI at L-band and implications for future passive microwave remote sensing from space,” in Proc. Int. Geosci. and Remote Sens. Symp. (IGARSS), Toronto, ON, Canada, 2002, pp. 847 – 849. Current RFI Problems Finding: The rules for out-of-band and spurious emissions in the primary allocated EESS bands (e.g., 1400-1427 MHz) do not provide adequate interference protection for EESS purposes. Finding: There is currently inadequate protected spectrum in C-band and X-band for operational passive microwave observations of sea surface temperature, soil moisture, and ocean surface wind speed and direction. Finding: The rules for out-of-band and spurious emissions in the primary allocated RAS bands (e.g., 1400-1427 MHz) do not provide adequate interference protection for RAS purposes. Finding: Geographical separation of radio telescopes from transmitters (e.g., radio quiet zones and remote observatories) is currently effective in avoiding much RFI, but proliferation of airborne and satellite transmissions and the widespread deployment of mobile, low power personal devices threaten even the most remote sites. Unilateral RFI Mitigation Recommendation: Investment in mitigation technology development should be increased to be commensurate with the costs of data denial experienced using systems without mitigation. To this end, NSF and NASA should support research and development for unilateral RFI mitigation technology in both EESS and RAS systems. NASA, NOAA, and DoD should require that appropriate RFI analyses and tests, and practical RFI mitigation techniques, be applied to all future satellite systems carrying passive microwave sensors. Finding: While unilateral RFI mitigation techniques are a potentially valuable means to facilitate spectrum sharing, they are not a substitute for primary allocated passive spectrum and enforcement of regulations. There is no one-sided technological solution to RFI Cooperative RFI Mitigation & Spectrum Sharing Finding: The emergence of practices for the dynamic use of the spectrum will result in more devices with greater variability in active spectrum usage, and the EESS and RAS communities could be impacted with more unintentional radio interfering devices. Finding: Nascent technologies exist for cooperative spectrum usage but the standards and protocols do not. Finding: New cooperative spectrum management techniques that could be beneficial for enhanced interference management and increased spectral utilization have been investigated by regulators but have not been implemented. New methods for cooperative spectral sharing should be explored Cooperative RFI Mitigation & Spectrum Sharing Recommendation: The NSF, NASA, and NTIA should jointly support research and development for cooperative RFI mitigation techniques and the associated forums and outreach necessary to enable standards development for higher spectral utilization and interference avoidance. Recommendation: As cooperative spectrum sharing techniques come into use the NSF and NASA spectrum managers should work with the regulatory agencies to enable observations that require an extremely wide spectral range. Such observations would provide a useful metric for the effectiveness of spectrum sharing techniques for the passive services. U.S. Spectrum Usage Finding: Greater efforts for radio emission data collection and analysis are needed to support the enforcement of existing allocations and to support the discussion and planning of spectrum use. Finding: Better utilization of the spectrum and reduced RFI for scientific as well as commercial applications is possible with better knowledge of actual spectrum usage. Progress toward these goals would be made by gathering more information through improved and continuous spectral monitoring. This would be beneficial to both the commercial and scientific communities. Recommendation: The Department of Commerce/NTIA, in collaboration with NSF, NASA, and NOAA, should spearhead the development of a national spectrum assessment system that measures the RF environment with appropriately high resolution in time, space, and frequency for spectrum development and management purposes, based on the spectral and spatial density of emitters. Outreach, Community, and Collaboration Recommendation: The EESS and RAS communities should be provided additional support through NSF, NASA, and NOAA to increase their participation in spectrum management forums within the ITU, FCC, NTIA, and other organizations. The goal is to foster outreach, understand interference and regulation issues, and initiate mutual cooperation in interference mitigation. Recommendation: OSTP should create a new permanent representative technology advisory body to identify technical and regulatory opportunities for improving spectrum sharing among all active and passive users, both government and non-government. Conclusions (1/2) • The radio spectrum is a finite resource, and has been managed as such for the past 75 years by the federal government. • The passive services provide both a critical return to society through operations in support of environmental prediction, and scientific intellectual value. • Management of the spectrum for passive purposes can be compared to management of other U.S. commons such as public parklands, which defy monetization. Conclusions (2/2) • Technological innovations continue to increase the scientific utility of the radio spectrum. • Unilateral RFI mitigation is not a universally feasible solution to RFI, but cooperative mitigation has significant untapped potential. • The next generation of spectrum management policies must enable better sharing of the spectrum as well as contribute to fully understanding the actual use of the RF spectrum. • The new initiatives necessary for spectrum management and sharing will neither be easy nor will they make successful management and sharing a certainty. The End