5
Findings and Recommendations

The allocation and use of radio frequencies constitute a complex issue at the center of many different fields of inquiry, from engineering to economics. The committee was tasked to “prepare a report exploring the scientific uses of the radio spectrum which will:

  • Portray the science that is currently being conducted using the radio spectrum;

  • Identify the spectrum requirements necessary to conduct research;

  • Identify the anticipated future spectrum requirements for at least the next 10 years; and

  • Advise spectrum policy-makers on the value to the nation of accommodating scientific uses of the spectrum, recognizing the need to balance multiple communities.”

The committee chose to focus its efforts on the passive uses of the spectrum, primarily in Earth remote sensing and radio astronomy. The committee recognizes that there are many other scientific uses of the spectrum, but it focused on the passive uses because these activities pose unique challenges to the nation’s spectrum allocation and management policies.

During the course of the study, the committee identified a number of key findings and formulated recommendations concerning passive uses of the radio spectrum for scientific purposes over the next two decades. The findings identify the operational and educational value of these uses to the broader society as well



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5 Findings and Recommendations The allocation and use of radio frequencies constitute a complex issue at the center of many different fields of inquiry, from engineering to economics. The committee was tasked to “prepare a report exploring the scientific uses of the radio spectrum which will: • Portray the science that is currently being conducted using the radio spectrum; • Identify the spectrum requirements necessary to conduct research; • Identify the anticipated future spectrum requirements for at least the next 10 years; and • Advise spectrum policy-makers on the value to the nation of accommodat- ing scientific uses of the spectrum, recognizing the need to balance multiple communities.” The committee chose to focus its efforts on the passive uses of the spectrum, primarily in Earth remote sensing and radio astronomy. The committee recognizes that there are many other scientific uses of the spectrum, but it focused on the passive uses because these activities pose unique challenges to the nation’s spectrum allocation and management policies. During the course of the study, the committee identified a number of key findings and formulated recommendations concerning passive uses of the radio spectrum for scientific purposes over the next two decades. The findings identify the operational and educational value of these uses to the broader society as well 

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sPectrum management science 21st century  for in the as describe the rapidly developing threats to the viability of some areas of this sci- ence as a result of increasing use of the spectrum by active systems. Active use of the spectrum has in and of itself generated unprecedented degrees of economic prosperity, enlightenment, and security. Although the pressure for active use of the spectrum cannot and should not be reduced, the committee nonetheless identified a number of measures that can be taken to help ensure the viability of the passive uses. The recommendations stemming from the committee’s study and the findings on which they are based are presented in this chapter.1 5.1 SOCIETAL VALUE OF THE PASSIVE SERVICES In addressing the first and fourth bulleted items in its statement of task, the committee focused on the purpose of the various passive applications within the Earth Exploration-Satellite Service (EESS) and the Radio Astronomy Service (RAS), and on how these purposes align with societal needs. A wide range of pas- sive applications exist in Earth remote sensing and radio astronomy that facilitate day-to-day environmental services, scientific inquiry into basic physics and envi- ronmental processes, and both formal and outreach education. The committee expects that the societal value of the passive services will grow in importance over the next two decades. Passive microwave remote sensing observations provide a valuable and impor- tant set of tools that contribute to the monitoring, understanding, and predicting of the many key components of Earth’s natural system and that are essential for the understanding of the interaction of these components so that weather and climate can be analyzed and predicted. Passive EESS measurements are increasingly used directly in numerical environmental models that help predict weather and analyze global climate change. These observations represent the only viable means by which certain key environmental parameters can be measured. They are a cornerstone of the ability of the United States to maintain its preeminence in Earth science and are critical to the economic vitality and health and safety of the nation’s people. Finding: Passive remote sensing observations are essential for monitoring Earth’s natural systems and are therefore critical to human safety, the day-to-day opera- tions of the government and the private sector, and the policy-making processes governing many sectors of the U.S. economy. While Earth scientists study the natural radiation from Earth and the atmo- sphere, radio astronomers use similar techniques to study the natural radiation 1 The committee’s findings, as originally presented in the context of the discussion in Chapters 1 through 4, are reiterated here.

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findings r e c o m m e n d at i o n s  and of sources in space. Radio astronomy has made fundamental contributions to the understanding of the nature, origin, and evolution of the universe, galaxies, stars, and planets. Finding: Radio astronomy has great potential for further fundamental discoveries, including the origins and evolution of the universe, the nature of matter, and life in other solar systems, which will have an enormous impact on our understanding of fundamental physics and the place of humanity in the universe. Radio astronomers and remote sensing scientists often push the state of the art in system design, leading to new developments in advanced signal processing, low-noise receivers, and novel antenna designs, among other areas. Computer algorithms developed for the RAS and EESS have also found routine application in medical imaging. Finding: In addition to the intellectual benefits that they provide, radio astronomy and passive microwave remote sensing studies provide many technological benefits to American society. Radio astronomers have produced many opportunities for scientific and engi- neering education, ranging from the K-12 through graduate levels. Scientific results from radio astronomy and Earth remote sensing continue to capture the imagina- tion of the public, which is excited and awed by new discoveries about the universe and concerned about extreme weather events and possible climate change. Public interest is reflected in the large numbers of people who visit radio observatories every year and regularly follow weather and climate forecasts. The development of passive microwave sensors for both the EESS and RAS also provides an important training ground for the next generation of radio scientists and engineers. Finding: Radio astronomy and passive microwave Earth remote sensing provide a diverse and valuable set of educational opportunities. The federal government has historically recognized the importance of both of these fields to the nation. One measure of that recognition is the level of resources that the nation has invested in these endeavors. Fulfilling the scientific promise of radio astronomy and Earth remote sensing has required investment in a diverse group of observatories, sensors, and instrumental capabilities. Further progress in environmental modeling and forecasting, astronomy, and related areas of physics depends on continual improvements in the sensitivity of radio telescopes and pas- sive microwave sensors on surface-based, airborne, and spaceborne platforms.

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sPectrum management science 21st century 0 for in the 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. 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. Recommendation 1: Recognizing that the national investment in passive radio astronomy and Earth remote sensing is dependent on access to the radio spectrum, the committee recommends that the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA) ensure that access to spectrum for passive radio and microwave observations of Earth environmental variables and radio astronomical observations of the sky is protected in the development of future spectrum policy. 5.2 CHARACTERISTICS OF THE PASSIVE SPECTRUM SERVICES The committee noted the following broad characteristics of passive EESS and RAS activities and applications. RAS and passive EESS equipment receive natural radio emissions from space or Earth (respectively) and use no transmissions. Accordingly, they do not cause radio frequency interference (RFI) to any other service. The signals received from cosmic or natural terrestrial sources are typically far weaker than the internal noise levels of the receivers. The required sensitivity of RAS and EESS systems is determined by the natural, minute level of radio emis- sions. Spectral band needs are determined by basic physical processes, and many measurements require spectrum at specific frequencies set by the spectral lines from the quantum transitions of atoms and molecules. These characteristics of RAS and EESS systems are likely to remain true over the next two decades, as they are intrinsic to the conduct of these activities. However, unmet spectral allocation requirements exist. Finding: Effective passive microwave band allocations are necessary for the perfor- mance of environmental and radio astronomy observations. Finding: Owing to their receive-only nature, the passive Earth Exploration- Satellite Service and Radio Astronomy Service, operating from 10 MHz to 3 THz, are incapable of interfering with other services. Finding: Radio wave bands (10 MHz to 3 THz) are indispensable for collecting information associated with specific astronomical and environmental phenomena.

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findings r e c o m m e n d at i o n s  and Often the same bands are similarly indispensable for both passive Earth remote sensing and radio astronomy, and the passive nature of both services enables them to share the spectrum productively. The preceding findings have a number of important implications with respect to how radio astronomy and Earth remote sensing are currently conducted. Since the science requirements drive the need for additional bands and band - width beyond those allocated to the services, the RAS and EESS communities routinely use spectrum beyond these allocations on a non-interference basis, and with varying degrees of success. Such opportunistic sharing is essential for certain scientific measurements; it requires the careful design of experiments to avoid RFI. Whereas technological advances have rapidly increased the channel capacity of spectrum available to active users, the same cannot be said for the passive services: they cannot use their allocated spectrum more efficiently. For instance, the passive services cannot use coding and compression techniques to expand the capacity of this bandwidth. Passive microwave sensors rely on their entire allocated band- widths, and often much more, to achieve required measurement precisions. Finding: Currently, 2.07 percent of the spectrum below 3 GHz is allocated to the RAS and EESS on a primary basis, and 4.08 percent is allocated on a secondary basis (measured in hertz). Debilitating postlaunch RFI occurred in one major international passive envi- ronmental sensor mission at C-band (Advanced Microwave Scanning Radiometer- Earth [AMSR-E]), rendering soil moisture measurement impossible over several populated areas. Such RFI also occurred at C-band in a non-mission-critical manner in another U.S. passive microwave military sensor (WindSat). A spectral allocation at C-band is currently required for observations of soil moisture and sea surface temperature, and a wider allocation at X-band would be valuable for observing ocean wind direction. While, the spectral band from 10.6 to 10.8 GHz is still relatively free of RFI over the United States, growth in use of this band and C-band by active applications is anticipated. 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. A further characteristic of EESS measurements is that they are made on a con- tinuous and global basis. Passive microwave and millimeter-wave sensor beams pass approximately 20 times per day over a typical location in the United States.

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sPectrum management science 21st century  for in the Because there is no EESS allocation within C-band and this portion of the spec- trum is heavily utilized, measurements of brightness temperature at C-band over land are currently only considered observations of opportunity. RFI in this band not only biases measurements but causes observation failure. Global protection is needed due to the band’s wide application in observing sea surface temperature, soil moisture, and ocean surface wind direction—elements critical to the under- standing and predicting of Earth’s environment. Recommendation 2: The FCC and NTIA should move toward developing a pas- sive EESS reference band allocation within 6-8 GHz to facilitate unilateral RFI mitigation. To be effective, this band should be at least 20 MHz wide and should be established on a global basis. Such a reference band allocation would benefit radio astronomy as well. It would be advantageous for the RAS if this band included the methanol transition line, for example, which provides strong maser emission from star-forming regions in the Milky Way. Finding: Whereas most frequency regulations for active services are defined on local or regional bases, passive EESS observations are global by nature. As a result, a high level of international cooperation is required to maintain and enforce passive allocations. Recommendation 3: The United States should actively engage the international community on passive EESS and RAS frequency allocations in order to improve the availability of global measurements of environmental variables and radio astronomy observations. 5.3 THREATS TO THE EESS AND THE RAS FROM UNINTENTIONAL RADIO FREQUENCY INTERFERENCE The radio environment in the United States and around the globe is rapidly changing due to the proliferation of active devices. This trend is likely to continue in the foreseeable future. It threatens the ability to use the spectrum for passive scientific purposes through inadvertent radio frequency interference. The commit- tee assessed both the current state of the occurrence of RFI to the passive services (Chapters 2 and 3) and trends in spectrum usage (Chapter 4). The most salient change in the use of the radio spectrum over the past 20 years has been the explosive growth in commercial use of the spectrum. Active commer- cial use of the spectrum will continue to grow in the number of links (2 billion or more cellular telephone users plus many additional data networks), the modes

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findings r e c o m m e n d at i o n s  and of usage (including data, voice, and active sensing applications), and geographic deployment (including near-rural and rural environs). These devices will be highly mobile, will use more of the spectrum, and will extend to geographic locations previously considered to be radio-quiet. Finding: Radio frequency interference threatens the scientific understanding of key variables in Earth’s natural system, now and in the future. Weak cosmic signals of fundamental importance to radio astronomy are easily masked by human-made radio emissions. Even signals far below the sensitivity of high-quality receivers used by the active services can interfere with routine astro- nomical observations. Finding: The emergence of practices for the dynamic use of the spectrum will result in more active devices with greater variability in active spectrum usage, and the EESS and RAS communities could be impacted with more unintentional radio interfering devices. The proliferation of wireless devices and high-speed digital radio technology around the globe diminishes the value of Earth observations from remote sensing platforms, leading to an irrevocable loss of environmental data. When affected by RFI, EESS observations have increased potential for introducing errors in environ- mental forecasts on both local and regional bases. Finding: Geographical separation of radio telescopes from transmitters (e.g., through the establishment of radio quiet zones and the remote siting of observa- tories) is currently effective in avoiding much radio frequency interference, but the proliferation of airborne and satellite transmissions and the widespread deploy- ment of mobile, low-power personal devices threaten even the most remote sites. Unlike Earth remote sensing applications, which require global coverage, radio astronomy has historically taken advantage of the benefits provided by geographi- cal separation; large observatories have been built in remote, largely radio-quiet areas. Finding: Important scientific inquiry and applications enabled by the Earth Exploration-Satellite Service (EESS) and the Radio Astronomy Service (RAS) are significantly impeded or precluded by radio frequency interference (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.

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sPectrum management science 21st century  for in the Despite these findings, the current knowledge of actual spectrum usage is inadequate to address RFI threats to the EESS and RAS. The federal government collects more information about many other economic variables than it does for the current usage of the radio spectrum. A monitoring capability would aid in both mitigation and instrument design and in the identification of dynamic sharing opportunities. This information would also aid in enhancing current passive radio science as well as aiding the expansion of current EESS and RAS capabilities. Finding: Greater efforts to collect and analyze radio emission data 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 are 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 the scientific communities. Recommendation 4: The Department of Commerce/National Telecommunica- tions and Information Administration (NTIA), in collaboration with the National Science Foundation (NSF), NASA, and the National Oceanic and Atmospheric Administration (NOAA), should spearhead the development of a national spec- trum assessment system that measures the radio frequency (RF) environment with appropriately high resolution in time, space, and frequency for purposes of spectrum development and management, based on the spectral and spatial density of emitters. The assessment of spectrum usage needs to occur at time, space, and fre- quency scales commensurate with actual usage. To this end, 1 microsecond (μs) would resolve many pulsed radar applications, and 1 kHz would be sufficient to separate and identify almost all individual signals in bands above and below 30 MHz for both voice and data. Spatial and angular resolution requirements are more difficult to identify. The necessary angular resolution would be frequency- dependent, such that the survey would achieve lower resolution at lower frequen- cies and higher resolution at higher frequencies. Since different communications systems use a very wide variety of spatial scales, finding a single spatial resolution necessary to conduct a useful survey is impossible; it comes down to what can be afforded. Crucially, however, all of these measurements should be of sufficient resolution to determine the adverse impact of most radio transmissions on the RAS and EESS. Spectrum monitoring with these guidelines would provide both statistical and operational information for the RAS and EESS, as well as providing

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findings r e c o m m e n d at i o n s  and many ancillary benefits to other scientific, commercial, and government applica - tions and services. 5.4 TECHNOLOGY FOR MITIGATION OF RADIO FREQUENCY INTERFERENCE Given the increasing threat to the passive uses of the spectrum posed by human-made transmissions, the RAS and EESS communities have studied the potential for the mitigation of unintentional RFI on both unilateral and cooperative bases. Bilateral mitigation technologies could potentially lead to effective spectral sharing between the active and passive services and could be particularly valuable for facilitating passive observations in non-allocated bands. The following find- ings and recommendations pertain to the current and projected future status of unilateral and cooperative RFI mitigation strategies suitable for maintaining the ability to use the spectrum for passive scientific purposes. Finding: While unilateral radio frequency interference mitigation techniques are a potentially valuable means of facilitating spectrum sharing, they are not a substitute for primary allocated passive spectrum and the enforcement of regulations. Techniques for the excision or subtraction of RFI continue to be developed, but they are only partially successful. For example, unilateral RFI mitigation tech- niques for passive EESS systems have been and continue to be explored. Only limited reports of success are available, however, especially with regard to levels of RFI comparable to the system sensitivity. Radio astronomy currently makes use of bands allocated to other services but sometimes is faced with the need for RFI mitigation. No set of universally effective techniques has been identified. Unilateral RFI mitigation could be facilitated by improved a priori information (e.g., time- space-frequency-angle structure) on spectrum usage, as recommended in Recom- mendation 4 in the preceding section. Recommendation 5: The National Telecommunications and Information Adminis- tration (NTIA) and the appropriate National Science Foundation (NSF) and NASA units should promote the development of inexpensive out-of-band interference mitigation technology and testing capabilities (e.g., filters, modulation techniques, etc.) that could be added to and required for type-approved consumer devices for the protection of EESS and RAS bands. As these technologies become affordable, the technical regulatory rules should reflect these new capabilities. Supporting the development of mitigation technology for application to the appropriate future radiating devices could preempt much interference to the pas-

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sPectrum management science 21st century  for in the sive services. As the technology matures and cost falls, the efficacy and availability of the technology should be reflected in regulations moderating spectrum use. Recommendation 6: Investment in the development of mitigation technology should be increased so that it is commensurate with the costs of data denial that result from the use of systems without mitigation. To this end, NSF and NASA should support research and development for unilateral2 RFI mitigation technol- ogy in both EESS and RAS systems. NASA, NOAA, and the Department of Defense should require that appropriate RFI analyses and tests and practical RFI mitigation techniques be applied to all future satellite systems carrying passive microwave sensors. A secondary benefit of such research would be to quantify the qualitative and limited documentation of unilateral RFI mitigation capabilities and their ultimate utility, as well as to help quantify spectrum usage. The committee believes that an effort of several million dollars per year over 5 years could yield substantial results in this area. Finding: Nascent technologies exist for cooperative spectrum usage, but the stan- dards and protocols do not. Cooperative spectrum usage is potentially more useful than is unilateral RFI mitigation, but the requisite ability to assign spectrum usage dynamically is cur- rently undeveloped. Anticipating that the commercial, military, and scientific uses of the spectrum will continue to grow, there will be a commensurately growing need to cooperate on the usage of spectrum. Spectrum is underutilized over time, space, frequency, and angle, and cooperative spectrum usage offers a means of taking advantage of this underutilization. One example of cooperative spectrum usage is time-domain multiplexing of spectrum over broad bandwidths. In such a scheme, the EESS or RAS would have exclusive use of spectrum for certain intervals, while tolerating transmissions from active services during the remaining time. This technique would be one way in which the anticipated evolution of spectrum utilization and management could result in a mutually successful scenario for both passive and active services, albeit with some increase in the complexity of equipment. The anticipated technical requirement is similar to proven existing technology that facilitates the time-division-multiplexed use of spectrum in cellular telephone systems such as the Global System for Mobile communications (GSM). However, since RAS experiments usually require a fixed integration time to achieve statistical accuracy, a time-domain multiplexing sys- 2As discussed in Chapter 4.

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findings r e c o m m e n d at i o n s  and tem would increase the actual time per experiment and further strain the heavy demands on all of the world’s large radio telescopes. Recommendation 7: 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 the development of standards for greater spectral utilization and interference avoidance. The committee believes that an effort of several million dollars per year over 3 years would be sufficient to demonstrate core technologies and to develop an implementation roadmap for these technologies. One end goal of these efforts would be to enable dynamic spectrum-sharing technology that would facilitate the observation of astrophysical phenomena which require measurements over large fractional bandwidths, such as observation of the redshifted 21 cm emission from the universe’s Dark Ages and the epoch of reionization, pulsars, single pulses hypothesized to be associated with prompt emission from gamma-ray bursts and other extreme astrophysical phenomena. Such measurements are extremely difficult to make at this time and would provide effective benchmarks for the success of cooperative spectrum-sharing techniques. A moderate portion of this investment should justifiably be spent on informing the public and the relevant scientific and technical communities about EESS and RAS requirements, mitiga - tion needs, and capabilities, and on the development of standards. Recommendation 8: As cooperative spectrum-sharing techniques come into use, NSF and NASA spectrum managers should work with the regulatory agencies to enable observations that require an extremely wide spectral range. Such observa- tions would provide a useful metric for the effectiveness of spectrum-sharing techniques for the passive services. 5.5 PROTECTION OF THE EESS AND THE RAS The committee discussed at length actions that should be undertaken by U.S. agencies to ensure the continued benefits to the public of the passive services. Some of these actions can be undertaken solely within the United States and others would require international collaboration. The committee considered the costs and complexity versus expected benefits to the passive services care - fully. In some cases, the committee identified existing ambiguities in rulemaking that could lead to an eventual loss of utility of the primary passive bands, thus warranting a clarification of existing regulations. In other cases, more complex regulatory measures must be undertaken to ensure the viability of the passive services.

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sPectrum management science 21st century  for in the One example of such an ambiguity involves the differences between the Inter- national Telecommunication Union (ITU) and the Federal Communications Com- mission (FCC) regulations in out-of-band and spurious emissions. In some cases, emissions that create harmful levels of interference are currently permitted in EESS and RAS primary bands, although the ITU regulations state that “all emissions are prohibited.” The FCC regulations do not allow any primary emission, but out-of- band and/or spurious emissions from other bands are permissible. Thus, a device can meet the specific emission requirements and emit into the protected EESS and RAS primary bands. In order to protect primary EESS and RAS bands adequately, it should be required that out-of-band and spurious emissions be significantly attenuated when they fall within EESS or RAS primary bands. This may require the reconsideration of many of the emission limits of bands that are spectrally close to the EESS and RAS primary bands, for modification of the permitted OOB and spurious emission levels. Finding: The rules for out-of-band and spurious emissions in the primary allo- cated Earth Exploration-Satellite Service (EESS) and Radio Astronomy Service (RAS) bands (e.g., 1400-1427 MHz) do not provide adequate interference protec- tion for EESS and RAS purposes. The rules that pertain to the above finding are given in Appendix D. Recommendation 9: The NTIA and FCC, with the support of the NASA and NSF spectrum managers, should study rulemaking changes that require aggregate emis- sion protection and out-of-band and spurious noise protection in primary EESS and RAS bands. More complex methods of understanding and managing spectrum usage may also be required to enable more efficient spectrum usage. Finding: Current regulatory structure and support infrastructure (such as data- bases, etc.) are transmitter-centric. Methodologies to incorporate passive systems need to be developed. Finding: New cooperative spectrum management techniques that could be benefi- cial for enhanced interference management and increased spectral utilization have been investigated by regulators but have not been implemented. The current regulatory structure inhibits the distribution of critical informa- tion on how active systems can impact passive systems, and it also limits promotion

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findings r e c o m m e n d at i o n s  and of the communications needed between active and passive users to enhance channel capabilities and limit inadvertent RFI. Beneficial cooperative spectrum management techniques include the use of interference metrics (e.g., interference temperature), the extension of enforcement technology (e.g., the development of commercial devices used for enforcement mea- surements and additional mobile measurement systems), and the inclusion of pas- sive systems in regulators’ databases (e.g., the FCC’s Universal Licensing System). Recommendation 10: FCC and NTIA regulators should actively define interference metrics, expand enforcement technology, and include descriptions of passive EESS and RAS systems in regulators’ databases. However, many of the current gaps in the regulatory system stem from a lack of communication between—or even within—the various user communities. For example, there is currently no forum in the United States for identifying EESS frequency allocation needs and vetting the merits of alternative allocations within the context of all competing services (both public and private). To engender the requisite communication, the committee makes the following recommendations. Recommendation 11: The EESS and RAS communities should be provided addi- tional support through NSF, NASA, and NOAA to increase their participation in spectrum management forums within the International Telecommunication Union (ITU), FCC, NTIA, and other organizations. The goal of such participation is to foster outreach, advance the understanding of interference and regulation issues, and initiate mutual cooperation in interference mitigation. For example, NASA and the National Oceanic and Atmospheric Administra- tion (NOAA) could jointly sponsor a workshop to explore alternative means of addressing RFI, seeking participation from the FCC, NTIA, industry, vendors, and the university community. This workshop could focus on the development of satel- lite and aircraft payloads and ground-based systems that characterize spectrum use. Such an endeavor would help determine the need for modified and/or tightened regulations and would increase the general level of understanding about interfer- ence. The planning of this workshop could be facilitated by professional societies already engaged in similar activities. Recommendation 12: The Office of Science and Technology Policy 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 nongovernment.

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sPectrum management science 21st century 0 for in the The advisory body recommended here should include representatives from all user and regulatory sectors. In a common forum, these representatives could bring to bear the technical and regulatory creativity, breadth, and depth necessary to identify and ensure that new opportunities for improving spectrum sharing and utilization are brought in a timely way to the attention of the many existing, relevant, government and private bodies that now separately address more limited and immediate spectrum issues. In addition to expanding communication, it is important to adjust the regula- tory process in such a manner as to discourage new instances of unintentional RFI from arising in the future. Recommendation 13: The FCC and NTIA should require active service users to use their allocated portions of the spectrum more effectively. Spectral efficiency requirements should be built into FCC and NTIA licensing policies for future spectral assignments. Although out-of-band emissions restrictions apply to individual devices and these restrictions generally preclude RFI by an individual device, there is currently no way to ensure that when such devices are sold, the aggregate emissions from a large number of them will not cause harmful RFI. Limitations on aggregate emis- sions may be difficult to enforce, but the likelihood of RFI can be minimized prior to the sale of devices by considering assessments of realistic market penetration and usage concentration when emissions standards are being developed. Recommendation 14: NASA, NOAA, NSF, and other agencies with interests in the EESS and RAS should oppose all type-approval licenses for equipment without source mitigation that impacts EESS and RAS bands. Recommendation 15: A combination of radio impact statements and/or statements of compliance with interference mitigation standards and emission standards should be mandated to accompany all proposals to federal agencies for the research and development of active service technology. Recommendation 16: The FCC and NTIA should follow up on specific recom- mendations of the U.S. Spectrum Policy Task Force (November 2002) to encourage spectral efficiency, maintain EESS and RAS spectral allocations, and be prepared to enforce spectrum protection. In its final report, the FCC’s Spectrum Policy Task Force made specific rec- ommendations including the following: (1) ensure that the FCC has sufficient resources to independently monitor and enforce spectrum management rules,

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findings r e c o m m e n d at i o n s  and (2) improve the out-of-band interference performance of transmitters and receiv- ers, (3) adopt a standard method for measuring the noise floor, (4) create a public/private partnership for a long-term noise-monitoring network and for the archiving of data for use by the FCC and the public, (5) promote transmitter enhancements for interference control, (6) study the tightening of out-of-band emission limits, (7) accompany a clearer definition of interference with effective enforcement, (8) develop technical bulletins that explain interference rules for all radio services, and (9) develop the opportunistic or dynamic use of existing bands through either cognitive radio techniques to find white space in existing bands or use protocols to relinquish bands to primary users.3 5.6 THE PATH FORWARD The radio spectrum is a finite resource that has been managed as such for the past 70 years by the federal government. This management enabled the growth of strong commercial and scientific communities. The pursuit of better techniques to leverage the unique characteristics of the radio spectrum has led to discoveries and innovations of enormous scientific and societal value. Over the past 20 years, rapid technological improvements have increased the capabilities of both the scientific uses and commercial uses of the radio spectrum exponentially. The current regu- latory regime is struggling to enable the capabilities and desires of either of these communities, let alone both. A new path is needed to maintain the vital engines both for the scientific discoveries that lead to societal benefit and for the commerce that is straining to meet the demands of a mobile society. Technological innovations continue to increase the utility of the radio spec- trum. The onset of new technologies designed to exploit the diversity of the radio spectrum in space, frequency, polarization, and time will increase the efficiency of its use. However, the current means of managing spectrum use must be changed, as the current policies threaten to thwart scientific discovery, diminish the utility of important environmental observations, and limit economic growth. Therefore, new spectrum management policies need to be explored to foster these critical national capabilities. The next generation of spectrum management policies must enable better shar- ing of the spectrum as well as contribute to a full understanding of the actual use of the RF spectrum. This can be done by exploiting currently available technolo- gies and hastening the development of nascent technologies. New policies should encourage the following: 3 Federal Communications Commission, Report of the Spectrum Policy Task Force, Washington, D.C., November 2002.

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sPectrum management science 21st century  for in the • The deelopment of the means for direct interaction between the actie and passie spectrum users in order to protect current and future scientific uses of the spectrum. The nation needs to provide the policies to strike a balance between pursuing advanced technology to decrease the cost of communica- tions on the one hand and, on the other, to make the spectrum more usable and less noisy for all users; • A regulatory enironment that enables sharing the spectrum in both space and time. This is a “win-win” scenario that will enable additional scientific uses without impacting commercial development; and • Inestment in technology to enable spectrum sharing between actie and pas- sie users, oer the entire radio spectrum. This investment should become commensurate with the investment made in remote sensing technology. In one sense, the management of the spectrum for passive purposes can be lik- ened to the management of U.S. public parklands. While monetization of the spec- trum by the free market may be one value metric, the true societal value of EESS and RAS spectrum should more properly be assessed in a manner consistent with how public parklands have been valued. As history continues to show, parklands reserved for public enjoyment, with limited to no development being permitted, have a high intrinsic community value. Humankind has ultimately found a com- pelling need for such land, and this need has resulted in the preservation of parcels even within the most crowded urban areas where these parcels would otherwise sell on the open market at a premium price. There is a balance between development and preservation that recognizes the intrinsic value of parklands. More often than not, the very presence of such public land increases the value of adjacent private land beyond the value that it would otherwise have. In a similar manner, the EESS and RAS studies performed using passive spectrum often lead to improved communications technologies and scientific insights that engender efficiencies and hence enhance profits and improve services within the private and public sectors. The new initiatives necessary for spectrum management and sharing will not be easy to design and implement, nor will they make successful management and sharing a certainty. It will likely take a national effort to understand clearly the needs of both communities, the scientific and the commercial, and to motivate each to make the choices necessary to enable greater access for each to the radio spectrum. That said, it should be clear that the next generation of scientific users of the radio spectrum needs to be afforded the capacity to develop the technology that will open new horizons.

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findings r e c o m m e n d at i o n s  and 5.7 CONCLUSION The passive services both provide a critical return to society through operations in support of environmental prediction and offer scientific intellectual value. The impact of the latter is difficult to quantify, but it has been seen to make unique contributions to our nation’s progress. It would thus be in the strongest interests of the nation to see that access to spectrum for scientific purposes is maintained during the coming decades. The committee’s recommendations provide a pathway for putting in place the regulatory mechanisms and associated supporting research activities necessary to accomplish this important task. The committee believes that such a pathway will also lead to greater efficiency in the active use of the spectrum, which should benefit all direct and indirect consumers of wireless telecommunica- tions and data services.

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