Spectrum Management: Further Consideration of Options to Improve Receiver Performance Needed
Published: 2013-02-22T00:00:00

Fast Facts:

Highlights:
section_title: Why GAO Did This Study
paragraphs: The growth of commercial wirelessbroadband services and government missions, including public safety and defense, has increased demand for radio-frequency spectrum. FCC and NTIA attempt to meet this demand while protecting existing users from harmful interference that can arise as new services and users come on line. To manage harmful interference, FCC and NTIA have historically focused on transmitters—the equipment that emitssignals. But, receivers also play a role. Congress and others are considering if further action to improve receiver performance to reduce harmful interference could help enhance spectrum efficiency and meet the growing demand for spectrum.
The Middle Class Tax Relief and Job Creation Act of 2012 directed GAO to study spectrum efficiency and receiver performance; GAO studied four areas related to improving receiver performance, including (1) actions taken by manufacturers and commercial licensees, (2) actions taken by the federal government, (3) challenges, and (4) options identified by stakeholders. GAO reviewed federal regulations and reports prepared by FCC, NTIA, industry stakeholders, and other researchers, and interviewed spectrum users, industry associations, and other stakeholders.
section_title: What GAO Found
paragraphs: Manufacturers and commercial licensees have taken a variety of actions to improve receiver performance. For some services, industry associations-- comprised of manufacturers, commercial licensees, and others--have developed voluntary standards that are often used to design and procure receivers, such as those in cell phones and televisions, and to help improve receiver performance. Stakeholders also reported privately negotiating to resolve interference problems and sharing of information as having helped improve receiver performance.
The federal government has used standards and taken other actions to improve receiver performance. Some federal spectrum users, like the Coast Guard and Department of Transportation, have specified or mandated use of industry standards for receivers using certain agency spectrum-based services. The National Telecommunications and Information Administration (NTIA), which manages the federal government's use of spectrum, has also mandated receiver standards for many federal spectrum assignments, such as those for land mobile radios used by emergency responders and radar systems. The Federal Communications Commission (FCC), which manages commercial and other nonfederal spectrum use, believes it lacks general authority to impose receiver standards and rather relies on the marketplace to improve receiver performance. In specific cases, FCC has provided incentives for nonfederal spectrum users to improve receivers. Both NTIA and FCC have taken additional actions to improve receiver performance, like undertaking studies and hosting public workshops.
Although industry and government have taken actions, stakeholders identified three challenges to improving receiver performance:
Lack of coordination across industries when developing voluntary standards: Standards are often developed for a single industry and not coordinated with those using adjacent spectrum.
Lack of incentives for manufacturers or spectrum users to incur costs associated with using more robust receivers: The benefits of improved receiver performance, namely freed-up spectrum for new services and users, often accrue to others and not those incurring the costs to improve receivers.
Difficulty accommodating a changing spectrum environment: When spectrum is repurposed for a new use, upgrading or replacing receivers currently in use to mitigate interference can be difficult and take considerable time.
In addition to greater use of voluntary industry standards, stakeholders GAO interviewed identified several other options to improve receiver performance. For example, interference limits would explicitly set a level of interfering signals that a receiver must tolerate before a user could seek government action to resolve interference problems. Each option entails trade-offs, and many stakeholders noted that a one-size-fits-all solution is likely not desirable or possible. Further, some options, such as interference limits, have not been implemented, and others, such as mandatory standards, have only been implemented for a limited number of users, primarily federal users. Therefore, the practical effects of these options--that is, what would happen if these options were individually or collectively implemented--are not well known, particularly for nonfederal users.
section_title: What GAO Recommends
paragraphs: FCC should consider collecting information on the practical effects of options to improve receiver performance. FCC replied that it had initiated such a fact-gathering process; GAO believes FCC's process to date may not provide information on the practical effects of these options.

section_title: Letter
paragraphs: Radio frequency spectrum is a natural resource used to provide an array  of wireless communications services that are critical to the U.S. economy  and a variety of government functions, such as national defense, air traffic  control, weather forecasting, and public safety. As new spectrum- dependent technologies and services are brought to market in the private  sector and government users develop new mission needs, the demand  for spectrum continues to increase. A primary driver of the increased  demand for spectrum has been the significant growth in commercial  wireless-broadband services, including third and fourth generation  technologies that are increasingly used with smart phones and tablet  computers. Yet, much of the usable spectrum has already been allocated  and assigned. Accommodating commercial wireless broadband and  unanticipated future services and users, while protecting existing services  and users, has proven challenging for the nation’s spectrum management  agencies—the Federal Communications Commission (FCC) and the  National Telecommunications and Information Administration (NTIA). For  example, LightSquared LLC proposed a nationwide, wireless broadband  network that would employ both terrestrial and satellite-based technology.  However, NTIA and others identified problems with LightSquared’s  proposal, including potential interference with Global Positioning System  (GPS) receivers which are deployed in a variety of applications, including  navigation for commercial and military aircraft.
Concern about interference, such as the potential interference between  LightSquared’s planned network and GPS receivers, has been a factor in  managing spectrum. Historically, FCC and NTIA have used guard  bands—idle spectrum that serves as a buffer between systems—and  focused on transmitters—the equipment that emits signals, such as  television and radio broadcasting—to manage interference between users  in adjacent spectrum. However, guard bands occupy valuable spectrum  that could be allocated for current and future services and users and  transmitters represent only half of a transmission system. The other half  of a transmission system is the receiver, and receiver performance, such  as a receiver’s ability to filter out signals from undesired transmitters, can  also affect interference and spectrum efficiency. For example, if receivers,  such as receivers in cell phones, do not filter out signals from transmitters  in adjacent spectrum, the receivers can be vulnerable to interference,  which can inhibit use of adjacent spectrum or require a guard band.  Therefore, improved receiver performance can reduce the risk of  interference and allow for more intensive and efficient use of spectrum.  As a result, Congress and others are considering whether additional  federal or industry action to improve receiver performance could help aid  spectrum efficiency, among other efforts to make more efficient use of  spectrum. In July 2012, the President’s Council of Advisors on Science  and Technology (PCAST) made several spectrum management findings  and recommendations, including that NTIA, in collaboration with FCC,  establish spectrum management methodologies that consider both  transmitter and receiver characteristics, stating that receiver  characteristics increasingly constrain effective and efficient spectrum  use.
The Middle Class Tax Relief and Job Creation Act of 2012 required that  we conduct a study of efforts to ensure that transmission systems are  designed and operated so as to not compromise reasonable use of  adjacent spectrum, with a focus on receiver performance as it relates to  increasing the efficient use of spectrum. following questions: (1) What actions have selected manufacturers and  commercial licensees taken to improve receiver performance? (2) What  actions has the federal government taken to improve receiver  performance? (3) What are the challenges, if any, to improving receiver  performance? (4) What options have stakeholders and reports identified  to improve receiver performance?
Pub. L. No. 112-96, § 6408, 126 Stat 156, 232 (2012). efficiency; actions taken by commercial licensees, manufacturers, and the  federal government—both federal spectrum users and spectrum  management agencies—to improve receiver performance; and actions  that could be taken to improve receiver performance. Finally, we analyzed  the actions taken by commercial licensees, manufacturers, and the  federal government for a judgmental sample of cases of interference  wherein receiver performance played or could play a role. These cases  involved (1) interference between cellular and public safety services in the  800 MHz band, (2) potential interference between satellite radio and  wireless communication in the 2.3 GHz band, and (3) potential and  realized interference with radar systems. We selected these cases to  ensure variation in application or use (e.g., cellular telephone, navigation),  federal and nonfederal users, and existence of receiver standards, among  other characteristics. For more information on our scope and  methodology, see appendix I.
We conducted this performance audit from July 2012 to February 2013 in  accordance with generally accepted government auditing standards.  Those standards require that we plan and perform the audit to obtain  sufficient, appropriate evidence to provide a reasonable basis for our  findings and conclusions based on our audit objectives. We believe that  the evidence obtained provides a reasonable basis for our findings and  conclusions based on our audit objectives.
subsections: section_title: Background
paragraphs: In the United States, responsibility for spectrum management is shared  between two federal agencies: FCC, an independent agency, and NTIA,  an administration within the Department of Commerce. FCC manages  spectrum use for nonfederal users, including commercial, private, and  state and local government users. NTIA manages spectrum for federal  government users and acts for the President with respect to spectrum  management issues. FCC and NTIA, with direction from Congress and  the President, jointly determine the amount of spectrum allocated to  federal and nonfederal users, including the amount to be shared by  federal and nonfederal users. FCC and NTIA manage the radio  frequency spectrum in the United States through allocation and  assignment:
Allocation involves segmenting the radio spectrum into bands of  frequencies that are designated for use by particular types of radio  services or classes of users. (Fig. 1 illustrates examples of services  by frequency band.) In addition, spectrum managers specify service  rules, which include the technical and operating characteristics of  equipment.
Assignment, which occurs after spectrum has been allocated for  particular types of services or classes of users, involves providing  users, such as commercial entities or government agencies, with a  license or authorization to use a specific portion of spectrum. FCC  assigns licenses within frequency bands to commercial enterprises,  state and local governments, and other entities, while NTIA authorizes  spectrum use through frequency assignments to federal agencies.
There are several entities that advise FCC and NTIA in their spectrum  management activities.
FCC’s Technological Advisory Council (TAC) consists of  approximately 50 telecommunications experts that provide technical  advice to FCC and make recommendations on the issues and  questions presented to it by FCC. TAC is a federal advisory  committee organized under the Federal Advisory Committee Act.  TAC is currently focused on key issues affecting the deployment of  new broadband technologies and services, seeking to spur  opportunities for innovation, greater efficiencies, and job creation.  (CSMAC)—also organized under the Federal Advisory Committee  Act—provides advice and recommendations to NTIA on a broad  range of issues regarding spectrum management. CSMAC consists of  approximately 25 private sector spectrum policy experts that offer  insight and perspective on reforms, including long-range spectrum  planning. Members are selected based on their technical background  and expertise as well as to ensure diversity and balanced viewpoints.
NTIA’s IRAC—an interagency advisory committee—comprised of  representatives from 19 federal agencies that use spectrum, was  established in 1922 to coordinate federal use of spectrum and provide  policy advice on spectrum issues. It was originally organized by  federal agencies that were seeking a way to resolve issues related to  federal spectrum use in a cooperative manner. IRAC and its  subcommittees assist NTIA in assigning frequencies for federal  spectrum users and developing and executing policies, programs,  procedures, and technical criteria pertaining to the allocation,  management, and use of spectrum.
The purpose of a communications system using spectrum is to relay  information—audio, visual, and data—from a transmitter to a receiver  (see fig. 2). A variety of technical methods exist to encode information  such that it can be transmitted as electromagnetic radiation. Antennas are  components of both transmitters and receivers used to emit and admit,  respectively, electromagnetic radiation-carrying signals.
A variety of factors influence the ability of a receiver to properly capture  the transmitted signal and decode the information for use, including the  terrain, distance, and atmospheric conditions between the transmitter and  the receiver. For instance, buildings, mountains, and foliage can prevent  a transmitted signal from being properly received for some types of  communications systems. In other instances, the receiver may be located  too far away from the transmitter. In addition, communications systems  must operate in environments where a variety of natural and man-made  electromagnetic radiation is present. Such undesired radiation could  impede a communications system’s transmissions from reaching its  intended recipients, and such an occurrence is called interference. It is  impossible to eliminate all interference from communications systems and  not all interference will prevent the proper functioning of a  communications system. However, in some cases, the interference is  considered harmful, meaning that it “endangers the functioning of a  radionavigation service or of other safety services or seriously degrades,  obstructs, or repeatedly interrupts a radiocommunication service.”
Harmful interference can occur when two communications systems use  the same or adjacent frequencies in the same geographic area (see fig.  3). In the first case, co-channel interference occurs when two  communications systems operate on the same frequency assignment in  the same geographic area. In the second case, adjacent band  interference occurs between two communication systems operating on  different, but adjacent, frequency assignments in the same geographic  area. Adjacent band interference, the focus of this report, causes (see fig. 4):
Transmitters emit undesired emissions into adjacent frequencies that  can cause interference to receivers operating on those assigned  frequencies. This is generally known as out-of-band emissions.
Public Law 112-96 required GAO to study interference between adjacent spectrum  uses, rather than co-channel interference between users of the same spectrum.
Receivers admit undesired emissions from transmitters in adjacent  frequencies, causing those receivers to experience interference. In  other words, the receiver cannot reject this undesired energy,  impairing its use.
Concerns about harmful interference are a factor in FCC and NTIA  spectrum management decisions. To prevent harmful interference, FCC  and NTIA have primarily focused on setting emission limits on  transmitters and establishing guard bands—spectrum that is left unused  between different radio services. For instance, FCC and NTIA often place  limits on the out-of-band emissions of transmitters to prevent adjacent  band interference. In cases where out-of-band emissions cannot be  sufficiently lowered, FCC or NTIA establishes guard bands to separate  the assigned frequencies of adjacent communications systems. When a  spectrum user experiences interference, it can make a claim of harmful  interference to the relevant agency—FCC or NTIA—which will investigate  and work to resolve the problem. According to FCC, applying the  definition of harmful interference often requires case-by-case  consideration, as the definition does not provide objective guidance on  what level of service degradation or interruption meets the “harmful”  threshold and because several factors, including the type and purpose of  the service, must be taken into account.
In addition to regulatory actions, well-designed transmitters and receivers  can also help prevent harmful interference. Electronic components called  filters are used by transmitters and receivers to help ensure that a  transmitter only emits electromagnetic signals in its assigned frequency  and a receiver only admits electromagnetic signals from its assigned  frequency. Ideally, filters would only allow desired signals to pass and  block all undesired signals and hence, adjacent band interference would  never occur. However, in practice, filters are not perfect, which leads to  the potential for harmful adjacent-band interference (see fig. 5).
The potential for improving receivers to prevent adjacent-band  interference has been receiving increased attention by FCC and NTIA.  One of the most recent and high-profile examples, as described earlier, is  the potential interference between LightSquared’s proposed wireless  broadband network and GPS receivers. There have been a limited  number of other cases where interference concerns involved receiver  performance to date, including potential interference between mobile  communications services and satellite radio, comprised of several  proceedings over more than 10 years, and between television receivers  and unlicensed devices seeking to use spectrum between channels.  However, an FCC official stated in a recent testimony that receiver  performance is becoming increasingly important as a limiting factor in  repurposing spectrum for new uses and in packing services closer  together. FCC, working with NTIA, continues its efforts to repurpose  spectrum for new uses and technologies—that is, change its rules to  reallocate a band of spectrum from an existing use to a new use—to  accommodate the growing demand for spectrum.
section_title: Selected Manufacturers and Commercial Licensees Have Taken a Variety of Actions to Improve Receiver Performance
paragraphs: To improve receiver performance, manufacturers and commercial  licensees have developed voluntary standards that are used to design  and procure receiver equipment for some services. Manufacturers and  commercials licensees have also used private negotiation, improvements  to technology, and information sharing between and among spectrum  users to improve receiver performance.
subsections: section_title: Voluntary Industry Standards
paragraphs: Some industry-led organizations have adopted voluntary standards for  receivers. Standards can help guide receiver design to help prevent  interference from adjacent spectrum users and can be either voluntary or  mandatory. If voluntary, the specific industry members voluntarily agree to  meet them, but are not legally required to do so. If mandatory, the  standards would have been imposed by governmental action and industry  members would be legally required to meet them. Features of receiver  standards often include selectivity, the ability of a receiver to separate the  wanted from unwanted signals in the adjacent frequency; sensitivity, the  detection limit of the receiver to admit the weakest desired signal level;  and dynamic range, the range of desired signal levels from the weakest to  the strongest that a receiver can admit and function properly. Several  industry representatives told us that voluntary standards for receivers  adopted by industry-led organizations are working well to limit  interference.
Some industry organizations have developed voluntary standards for  receivers, including those in the aviation, satellite, and broadcast  industries. The processes these organizations use to develop standards  are similar and generally include bringing together a diverse group of  stakeholders (both commercial and government) for open discussions of  specific issues and a transparent, consensus-based decision making  process.
The Telecommunications Industry Association (TIA) is a trade  association representing the global-information and communications- technology industry, including equipment manufacturers and  commercial licensees, and is an American National Standards  Institute (ANSI) accredited standards developing organization.  Within TIA, there are committees that set standards for specific  spectrum uses, such as the committee that sets standards for land  mobile radios used by, among others, public safety agencies.  According to TIA officials, developing a new standard includes the  coming together of relevant industry stakeholders who have  determined that the creation or amendment of standards is necessary,  participation by industry and government stakeholders, and a  documented, open process. Standards are typically created or  amended within 1 to 3 years.
In the aviation industry, RTCA, Inc. develops minimum performance  standards for aviation-related receivers. According to RTCA officials, these standards typically include requirements for rejecting signals  from users in adjacent and other bands. Meetings are publicly  announced and open to anyone with an interest in the topic or  standard under consideration. The timelines for developing a standard  can vary greatly, but typically take 3 to 5 years.
In the broadcast industry, the Advanced Television Systems  Committee (ATSC) has established voluntary industry recommended  practices for television receivers, which include requirements for  rejecting signals from adjacent spectrum users. ATSC practices are  created by a multi-stakeholder group—representing the broadcast,  broadcast equipment, motion picture, consumer electronics,  computer, cable, satellite, and semiconductor industries—and usually  take at least 1 to 2 years to achieve consensus.
Once developed, voluntary industry standards may be used by  manufacturers and commercial licensees to design and procure  equipment. Representatives of the cellular industry told us that their  industry relies on a voluntary approach to receiver standards and receiver  performance, pointing out that voluntary industry standards are used on a  daily basis between handset manufacturers and wireless companies.  Officials at the National Public Safety Telecommunications Council said  that the TIA standards for land mobile radios are commonly referenced by  public safety agencies when procuring equipment, including receivers.  Representatives of two different land mobile radio manufacturers told us  that standards form a baseline for performance and that their receivers  typically exceed the relevant performance standards.
When procuring equipment, compliance and certification processes can  be used to assure users that equipment meets the voluntary industry  standards. In some cases, there is a general certification program that  covers a particular service. For example, the National Institute of  Standards and Technology—in partnership with other industry  representatives, the public safety community, and other government  agencies—has a testing process for public-safety land mobile radios. In  other cases, compliance testing might be carried out by those purchasing  the equipment. For example, TIA representatives told us that many of  TIA’s member companies are involved in testing equipment against  standards, although TIA is not itself involved in the certification process.
section_title: Negotiation, Improvements to Technology, and Information Sharing
paragraphs: Negotiation. In addition to developing and using voluntary industry  standards, some manufacturers and commercial licensees privately  negotiate interference concerns. Representatives of the cellular industry  told us that their industry deals with interference on a daily basis, as  interference problems are increasing and have become a regular part of  doing business. Several industry representatives highlighted the cellular  industry as a sector in which the wireless companies and manufacturers  work in concert to maximize efficiency; these efforts often occur within the  cellular spectrum bands and among like services. According to one  industry representative, voluntary negotiations helped resolve  interference to fixed microwave services that occurred in the past. The  interference occurred when a new service began operating next to a  microwave service in the 1.9 GHz band, where the microwave receivers  had been in operation for 30 years. To resolve the interference, the  parties discussed whether to add filters to the transmitters or the  receivers and decided to add filters to the receivers.
Improvements to Technology. Some manufacturers and commercial  licensees also apply technological advancements to receivers and their  components to improve the performance of receivers. For example,  RTCA representatives told us that advances in filtering technology have  been utilized in modern aviation equipment to reduce interference. One  manufacturer of land mobile radios told us the company is continually  making changes to equipment to improve performance and reduce  interference. During the discussions to resolve interference to public  safety operations using land mobile radios in the 800 MHz band, this  manufacturer examined technical advances in receiver design that could  help alleviate the interference.
Information Sharing. Some manufacturers and commercial licensees  share information to help improve receiver performance. The creation of  standards, discussed earlier, is one area where manufacturers and  commercial licensees, as well as other stakeholders, share information  for the purpose of improving receiver performance. One equipment  manufacturer told us that bringing together different stakeholders brings  forth the best ideas to solve problems. Another example of  communication helping to improve receiver performance was the sharing  of information by commercial licensees, manufacturers, and industry  associations to create guidance in response to interference between  cellular and public safety services in the 800 MHz band. In this instance,  after reports of interference were made in a number of locations,  representatives of the public safety community and the wireless company  involved came together to help resolve the interference. An equipment  manufacturer said that there was a lot of cooperation and coordination  among the stakeholders as they wanted to quickly eliminate the  interference adversely affecting the mission-critical communications of  public safety agencies using land mobile radios. As a result of this  coordination and information sharing, a Best Practices Guide was created  that contained information on how to prevent interference and mitigate  existing interference.
section_title: The Federal Government Has Used Standards, Procurement, and Other Actions to Improve Receiver Performance
paragraphs: To improve receiver performance, federal spectrum users have mandated  use of industry standards for receivers, specified system requirements to  procure equipment, and negotiated with other spectrum users to resolve  interference concerns. NTIA has mandated the use of standards for many  federal spectrum users while FCC has not done so for nonfederal  spectrum users, but both spectrum management agencies have taken  actions to resolve specific cases of interference and conducted research  to improve receiver performance.
subsections: section_title: Federal Spectrum User Actions
paragraphs: Some federal spectrum users have specified, and in some cases  mandated, standards for receiver performance that are often based on  industry-developed standards. Federal agencies use spectrum to  operate systems both for internal use and for external use by other  parties. For external systems, federal agencies can mandate standards  that parties must meet to use the system. For example, the Department of  Transportation uses ASTM International standards for emerging  communication applications among vehicles and roadside equipment to  enable safety, mobility, and environmental benefits. Similarly, the  Federal Aviation Administration (FAA) publishes Technical Standard  Orders (TSO) for communication and navigation systems that incorporate  by reference RTCA standards for aviation receivers. According to RTCA  officials, compliance with TSOs can be used as one basis for FAA  certification of communications, navigation, and surveillance equipment.  RTCA standards for receivers typically include requirements for rejecting  signals from adjacent and other bands to limit interference.
In addition to using existing industry-developed standards, federal  spectrum users work with standards-setting bodies and other  organizations to create standards in response to particular cases of or  concerns about interference. For example, the Coast Guard worked with  a standards-setting body—the Radio Technical Commission for Maritime  Services (RTCM)—to create new standards for receivers when its marine  radio system—used for applications such as distress calls and port  navigation—experienced interference from neighboring services that were  operating in compliance with federal rules for transmitters.one Coast Guard official, the standards were created in a few months and  equipment manufacturers began producing receivers that met the new  standards in 1 to 2 years. Similarly, the National Aeronautics and Space  Administration (NASA) is currently working with other space-faring  nations to create standards to help maintain the spectrum performance of  highly sensitive satellite downlink receivers used to obtain data from  interplanetary spacecraft missions (e.g., Mars exploration rovers). One  NASA official said that adjacent band interference is a concern given the  sensitive natures of these receivers and that both transmitter and receiver  standards can help to address a majority of interference problems.
When procuring equipment, federal spectrum users also specify system  and component requirements, including those for receiver performance.  The Department of Defense (DOD) uses acquisition guidance that  emphasizes the need to address the potential for adjacent-channel and  adjacent-band interference when designing and procuring equipment. As  part of this guidance, DOD has established receiver performance  requirements that apply to all procurements by military departments. NOAA also specifies system performance, including receiver  performance, when procuring equipment. According to NOAA officials,  the agency defines a system’s expected availability—that is, the time that  a system or equipment is capable of being used—when procuring  equipment, which is then used to determine specifications for system  components and subcomponents including receivers.
The requirements are included in DOD MIL-HDBK-237D, Electromagnetic  Environmental Effects and Spectrum Certification Guidance for the Acquisition Process  and DOD MIL STD 461F, Requirements for the Control of Electromagnetic Interference  Characteristics of Subsystems and Equipment, among other documents. between adjacent spectrum users. According to NTIA officials and IRAC  members, interference cases are handled on a case-by-case basis, which  can result in making changes to individual systems such as adding filters  to transmitters or receivers. For example, a National Science Foundation  official said the agency is currently working to resolve interference to  receivers that collect and process satellite signals from a nearby TV  transmitter that was operating in compliance with FCC rules. IRAC  members said that negotiation among federal spectrum users is aided by  access to NTIA’s database on federal spectrum use and by each agency  having a designated spectrum manager. NTIA officials told us that most  cases of harmful interference involving federal spectrum users are  resolved between the cognizant parties rather than through NTIA.
section_title: Spectrum Management Agency Actions
paragraphs: NTIA has mandated the use of standards for receiver performance for  many federal users. NTIA sets mandatory standards for federal spectrum  users in its Manual of Regulations and Procedures for Federal Radio  Frequency Management. According to NTIA officials, these mandatory  standards for receivers apply to about 60 percent of federal spectrum  assignments, including land mobile radio, fixed, radar, and aeronautical  mobile telemetry systems, and additional mandatory standards set by  federal spectrum users like FAA cover another 10 percent of federal  spectrum assignments. NTIA and federal spectrum users adopt industry- developed standards when they are available for a given service. For  federal spectrum uses that have very specific applications or lack a  commercial equivalent, NTIA can establish its own standards, as it did for  radar systems, or choose to not establish standards. NTIA’s mandatory  standards, whether set from industry standards or established by NTIA,  are used to certify federal equipment, and when procuring equipment,  federal spectrum users must set specifications that comply with the NTIA  mandatory standards. NTIA has reported that these mandated standards  have done much to prevent interference to federal spectrum users and  that mandated standards establish a baseline of performance but do not  prevent users from moving to more efficient or better receivers.
FCC has not set mandatory receiver standards for nonfederal spectrum  users. FCC has specific statutory authority to establish minimum  performance standards for home electronic equipment, like televisions, but FCC officials said that the Commission lacks direct authority to  impose regulations governing receiver performance in other cases  outside home electronics. Therefore, FCC has generally relied on the  marketplace to incentivize nonfederal licensees and manufacturers to  produce receivers that can reject unwanted signals and limit interference.  As noted in the previous section, manufacturers and commercial  licensees have taken actions such as adopting industry standards to  improve receiver performance. While FCC has generally relied on the  marketplace to improve receiver performance, it has provided incentives  to spectrum users to do so in specific cases. For example, FCC defined  the minimum levels of performance that a receiver must meet to make a  claim of harmful interference in the 800 MHz band. Specifically, FCC set  minimum levels for receiver performance for non-cellular systems,  primarily public safety radios, as part of the reconfiguration of the 800  MHz band to mitigate interference between non-cellular and cellular  systems. Therefore, spectrum users that choose to use receivers that  do not meet the minimum levels are not entitled to full protection from  interference. The public safety community and manufacturers  recommended that FCC set objective criteria to qualify for interference  protection. In this case, FCC reported that taking further action to improve  receiver performance, like requiring public safety radios to fully comply  with industry standards to claim harmful interference, would impose costs  that outweighed the resulting interference protection.
47 U.S.C. § 302a(a)(2).
FCC and NTIA have also taken specific actions in response to cases of  interference involving receiver performance. FCC and NTIA officials said  that interference cases, both potential and realized, are generally handled  on a case-by-case basis, so actions are taken that address the particulars  of each case. In rulemakings for new services, FCC often invites  comment about any receiver characteristics that should be taken into  account, particularly for receivers currently in use in adjacent bands. In  some cases, FCC has required that a new spectrum user protect the  incumbent services in the adjacent band from harmful interference  regardless of the performance of the receivers in use, a policy known as  “first-in-time rights.” The Advanced Wireless Services (AWS)-1 spectrum,  for example, was reallocated for flexible fixed or mobile service, such as  voice and data content, which raised concerns about potential  interference with incumbent licensees in the adjacent band used for  broadcast auxiliary services. The new AWS-1 licensee purchased and  arranged for the installation of new filters for the incumbent’s receivers to  avoid causing harmful interference as required by FCC rules for AWS-1  spectrum. NTIA’s Institute for Telecommunication Sciences (ITS)  investigates cases of potential or realized interference and identifies  strategies to mitigate interference. ITS officials told us that ITS tends to  work on interference cases that are particularly complicated or difficult to  remedy rather than on more general interference or receiver concerns.  For example, ITS investigated interference to fixed-satellite service  (space-to-earth) stations in the 4 GHz band from radar systems operating  in the adjacent band. The ITS report identified the source of the  interference, in this case primarily because of poor filtering, and listed  various solutions to remedy the interference. Moreover, NTIA is currently  leading an interagency working group to examine receiver performance  standards for GPS devices for federal users and the feasibility of  accommodating terrestrial broadband systems in the bands adjacent to  GPS. However, based on a 2011 Silicon Flatirons Center workshop of  experts from government, industry, and academia, one theme drawn from  reviewing case studies of adjacent band interference was that information  can be lost when interference problems are resolved on a case-by-case  basis, as other operators with similar problems might not have access to  the resolution of other cases.
In addition to mandatory standards and case-by-case actions, NTIA and  FCC have completed reports, requested research, held workshops, and  taken other actions on receiver performance.
Reports. NTIA’s reports on the topic include a 2003 report  summarizing existing receiver standards, both voluntary and  mandatory, established by federal agencies, industry associations,  and international groups, and a 2005 report compiling existing  interference protection criteria for various radio services used by the  federal government.
Requested research by federal advisory committees. In 2010, NTIA’s  CSMAC studied interference and dynamic spectrum access that  resulted in recommendations on guard bands, equipment standards,  and enforcement aimed primarily at NTIA and federal spectrum  users. In 2012, FCC’s TAC studied receivers and spectrum and  presented recommendations to FCC.
Public notices and workshops. FCC has taken steps to seek  stakeholder input and encourage dialogue on receiver performance  though public notices and workshops on receivers and spectrum  efficiency. In 2003, FCC issued a Notice of Inquiry seeking public  input on whether and how it should incorporate receiver performance  specifications into its spectrum policy. Stakeholders submitted  comments that varied in their support for greater action, whether  taken by FCC or the market, though a majority of comments favored a  market driven approach, like voluntary industry standards for  receivers. In 2007, FCC closed the proceeding stating that action did  not appear to be needed at that time; FCC officials said that the  comments from the rulemaking presented no clear solution,  particularly as no single solution fit all interference problems. More  recently, FCC held a 2-day workshop in March 2012 dedicated to  spectrum efficiency and receivers. Participants, including licensees,  federal agencies, equipment manufacturers, and component  providers, examined the characteristics of receivers and how their  performance can affect the efficient use of spectrum and opportunities  for the creation of new services. Most participants in the workshop’s  concluding panel, which was comprised of a mix of stakeholders,  noted that the status quo, as it relates to receiver performance, was  not sustainable and that further action is needed.
section_title: Several Challenges Impede Further Improvements to Receiver Performance
paragraphs: Although manufacturers, commercial licensees, and the federal  government have taken steps to improve receiver performance, many of  those with whom we spoke commented on what they perceive to be the  challenges to further improvements. These challenges include the lack of  coordination across industries when developing receiver standards, the  lack of incentives to improve receivers, and the difficulty accommodating  a changing spectrum environment.
subsections: section_title: Lack of Coordination among Those Developing Standards
paragraphs: Standards are often developed for a single industry operating within a  defined area of spectrum, such as the cellular industry. While members of  a particular industry coordinate with each other, they may have little or no  communication with services operating in adjacent spectrum bands.  Although standards-setting bodies have published receiver standards for  many services, FCC officials and several other stakeholders we  interviewed told us that standards are often not developed in coordination  with stakeholders representing adjacent services. For example, some  aviation equipment operates in the frequencies above the FM radio band.  The aviation community sets its own standards, while the FM radio  community develops its own standards. Each group has its own  representatives who communicate within their own industry but not with  those in the other industry. This lack of coordination and lack of  information sharing means that the impact of standards set by one group  upon other groups is not always assessed, and immunity to adjacent- band interference is not necessarily addressed.
There is also no publicly available compendium of current receiver  performance standards or specifications to facilitate coordination or  understanding across spectrum uses. FCC officials explained that while  receiver performance standards have been developed for some services,  there is no catalog of these standards, making it difficult to locate this  information. FCC officials also told us that information about actual  receiver performance is not readily available. Typically, this information  only surfaces in the context of a rulemaking. For example, FCC made  requests to equipment manufacturers for information about their receivers  and was told by several that the information was proprietary, as  companies did not want competitors to acquire information about signal  strength or the energy level of devices, among other information.
In addition, since standards are largely voluntary for commercial users,  the extent that industry standards are used remains unknown. In fact, just  because voluntary standards exist does not mean that licensees and  manufacturers will use them. For example, with regard to the  recommended practices for the manufacture of television sets, it is not  known whether all manufacturers adhere to the recommended practices  since the practices are voluntary and television licensees that broadcast  television signals do not manufacture television sets or specify their  operating characteristics—a situation known as decoupled receivers.
section_title: Lack of Incentives to Improve Receivers
paragraphs: A lack of incentives for spectrum users and equipment manufacturers to  improve receiver performance was another challenge that many industry  associations and other stakeholders we interviewed cited. As one industry  researcher explained, there are no incentives for manufacturers to build  more robust receivers, primarily because the manufacturers will not  receive the benefits. Rather, those who want to make more spectrum  available or share spectrum will benefit. One industry representative  stated that the real question is one of motivation. Improved receiver  performance to limit adjacent band interference often requires the  addition of filters and can increase the size, weight, power consumption,  and cost of the receiver. Additionally, there is no business case that can  explain why a business would accept these downsides so that others can  benefit when implementing a new system in an adjacent band. Another  industry representative echoed that position and told us that,  independently, the private sector has no motivation to spend its time and  resources to protect spectrum for other users, allow enhancements to  other services, or accommodate new entrants. Instead, as one  stakeholder commented, companies have an incentive to make the  cheapest receiver possible—that is, a receiver with poor filtering  capabilities that is more sensitive to emissions from other bands—and no  incentive to work with licensees in neighboring spectrum bands.
Similar to commercial users, federal users also lack incentives to improve  receiver performance. The PCAST report stated that federal users  currently have no incentive to improve the efficiency with which they use  their own spectrum allocation, nor does the federal system as a whole  have incentives to improve its overall efficiency. Further, we have  previously reported that federal users often use proven, older  technologies that were designed to meet a specific mission and may be  less efficient than more modern systems. NTIA’s CSMAC also recently  recommended that the federal government, including NTIA, consider  incentives, rules, and policies to, among other things, improve the  capability of receiving devices to reject adjacent channel interference.
Lastly, the use of private negotiation, which has been used regularly to  resolve interference within the cellular industry, can be difficult in cases  where there are dissimilar services or many parties. When disputes  involve similar services in the same band, operators have similar  incentives that facilitate private dispute resolution. This may not be the  case when licensees with different services or in adjacent bands are  involved. Also, when the number of users is relatively small, negotiation  between parties may be able to resolve the problem. However, when  there are many users involved, the transaction costs may be prohibitively  high. For example, for services where receivers are decoupled from  licensees, as in the case of television, the large number of receivers and  potential lack of coordination among individual parties makes private  negotiation a less feasible option.
section_title: Difficulty Accommodating a Changing Spectrum Environment
paragraphs: Stakeholders we interviewed cited accommodating changes to the  spectrum environment as a challenge to improving receiver performance.  As FCC attempts to accommodate new services and users, the  Commission often alters how licensees can use spectrum bands. This  repurposing of spectrum, either from a prior use or from no use, often  gives rise to concerns over interference, concerns that involve receiver  performance because incumbent services have manufactured receivers  to operate without interference problems in the current environment.  However, if that environment changes, receivers currently in use may  experience increased interference. This was the case in the 2.3 GHz  band, where interference concerns arose between two different  services—Wireless Communications Service (WCS) and Satellite Digital  Audio Radio Service (SDARS)—allocated to adjacent spectrum. Although  the WCS allocation allowed for mobile service, the rules limiting out-of- band emissions for transmitters made mobile service impractical. After  years of attempting unsuccessfully to deploy a mobile service, the WCS  licensees petitioned for rule changes. In considering the WCS licensees  petition, the performance of the SDARS receivers was one of the critical  areas of contention. SDARS receivers were not capable of filtering out  stronger signals in adjacent spectrum. These receiver concerns required  technical rules that effectively created guard bands on each sides of the  SDARS spectrum to prevent interference.
Innovation on the part of current spectrum users is another factor that can  change the spectrum environment. Current spectrum users may decide to  make changes to the configuration of their system based on business  needs. Such changes can result in interference to adjacent spectrum  holders. For example, both Nextel, a cellular provider, and public safety  agencies had licenses to operate in the 800 MHz band. Nextel decided to  convert its mobile radio architecture from one that used high antenna  sites atop buildings or towers to one that used a short‐range cellular  architecture with low antenna sites to provide more capacity in crowded  urban areas. Even though Nextel’s transmitted power was below  customary levels, the low antenna sites caused interference for other  users, including public-safety land mobile-radio users, when they were  close to Nextel transmitter sites. In 2004, FCC, in response to input from  stakeholders including Nextel and the public safety community, proposed  reconfiguring the 800 MHz band to separate the two systems.
Current practices and policies related to receiver performance may  constrain repurposing of spectrum going forward. Representatives from  three industry associations told us that it is difficult to build receivers to  accommodate an unknown future. As one industry association member  told us, the problem is not a lack of information on the current  environment but a lack of predictability about the future environment. To  make meaningful decisions about current receiver performance, the  future use of spectrum would need to be better defined. FCC’s TAC  stated that part of the problem of increased receiver interference was the  result of receivers having been built without adequate knowledge of future  environmental performance constraints. Moreover, several stakeholders  we interviewed also said that it would be difficult and could take  considerable time to upgrade or replace receivers and equipment  currently in use once deployed. In November 2012, an FCC official also  testified that receiver performance is increasingly becoming a limiting  factor in the repurposing of spectrum for new uses and in packing  services closer together, and the official said that a continuing challenge  for FCC will be to maximize the amount of usable spectrum for cost  effective deployment of new communication services while sufficiently  protecting incumbent receivers. FCC officials also said that interference  problems between adjacent bands are growing and are more common in  rulemakings; as noted in a recent proceeding on wireless innovation and  investment, FCC stated that these rulemakings can be protracted, create  uncertainty, and discourage investment.
section_title: Stakeholders and Reports Identified Standards, Interference Limits, and Other Options to Improve Receiver Performance
paragraphs: Given the challenges that exist to improving receiver performance,  stakeholders we interviewed identified options that could be taken or led  by FCC and NTIA, with the aim of increasing spectrum efficiency. Below  we list several recurring options based on our interviews with industry  associations, manufacturers and commercial licensees, federal agencies,  and representatives from academia and research organizations, as well  as our review of reports from federal advisory committees and workshops  on this topic (see table 1). This list of options is not exhaustive, but  provides information on options that could be implemented alone or in  combination. Moreover, the options could be applied to varying degrees;  that is, applied to specific spectrum uses or boundaries between two  different uses or on a wider scale. In fact, many stakeholders we  interviewed indicated that each case of adjacent-band interference is  unique, so a one-size-fits-all solution is likely not desirable or possible.
Each of the options listed below entail advantages and disadvantages, as  identified by stakeholders and reports, and thus implementing any of  these options would involve trade-offs. Through our interviews, a  commonly mentioned disadvantage of improving receiver performance  was that receivers would cost more, as more components are used in  their manufacture. In addition, many stakeholders also said that actions to  upgrade or replace existing, legacy receivers could be costly or take a  long time, particularly in the case of equipment designed to last for many  years. Stakeholders frequently stated that an advantage of improving  receiver performance was increased spectrum efficiency. It is difficult to  quantify or estimate the overall costs and benefits of improving receiver  performance or the amount of spectrum to be gained through improving  receiver performance, especially given the numerous and varied uses of  spectrum. FCC, NTIA, and others have studied many of these options,  and at a conceptual level, the advantages and disadvantages are well  known. However, some of these options have not been implemented,  while others have only been implemented in limited cases. Therefore, the  practical effects of each option, that is, what would happen if the option is  implemented, are not well known. Many of the stakeholders we  interviewed indicated that receiver performance is an important aspect of  spectrum efficiency, so that it warrants further consideration as spectrum  management agencies and spectrum users look for ways to make more  efficient use of spectrum. For example, a group of experts convened by  the Silicon Flatirons Center agreed that the advance of wireless  technologies and maturing infrastructures had reached an inflection point  where past methods of governance were no longer adequate and  generally supported that spectrum management agencies more explicitly  consider receivers when drafting rules.
Many stakeholders we interviewed and reports we reviewed stated that  greater use of industry standards could take different forms. Use of  standards, voluntary and mandatory, has been long discussed and is  widely understood since standards are currently used by nonfederal and  federal spectrum users to varying degrees. For instance, NTIA has  mandated use of industry standards for receivers for many federal  spectrum uses, as noted earlier. Stakeholders offered three main ways  that industry-developed standards could be used: voluntary, a safe harbor  allowing spectrum users that meet standards to receive protection from  harmful interference, and mandatory, all described in greater detail in  table 1.
Stakeholders we interviewed varied in their support for these options, but  many opposed mandatory standards. Many stakeholders told us they  prefer the industry-led, voluntary standard-creating process, in contrast to  government-created and mandated standards, as they believe industry- developed voluntary standards can be responsive and flexible to  changing conditions. While mandatory standards were often opposed as  an overall option to improve receiver performance, some stakeholders  told us mandatory standards could be used in limited cases, such as  when market forces do not sufficiently incentivize the production of robust  receivers or when receivers are not tied to the licensee (i.e., decoupled  receivers). For the safe harbor option, whereby compliance with extant  industry standards would serve as a prerequisite for receiving protection  from interference, several industry associations and individual  stakeholders we spoke with supported this option. In 2003, NTIA  recommended that FCC adopt industry standards on a voluntary or  recommended basis, with FCC only granting protection for services with  receivers that meet standards, and in doing so, NTIA suggested that FCC  give priority to bands being reallocated to avoid problems encountered  with legacy systems. In addition, federal programs have encouraged  compliance with industry standards among nonfederal spectrum users  through grants or other funding. For example, the Department of  Homeland Security’s Emergency Communications Grant program  requires that funds used by public safety agencies to purchase land  mobile radio systems comply with industry standards set by TIA. As part  of the transition from analog to digital television, NTIA offered coupons to  subsidize consumer purchases of converter boxes, but the coupons could  only be used to purchase converter boxes that met minimum performance  standards.
Regardless of the form of standards used, there are some overarching  advantages and disadvantages. Advantages of greater use of industry- developed standards are that this option makes use of existing standards  and that the open, consensus-based process used to develop most  industry standards helps ensure they reflect the knowledge and input of a  range of industry and government perspectives. Disadvantages are that  standards may not keep pace with industry change and can be  prescriptive, limiting flexibility of manufacturers and licensees. Also,  industry standards do not exist for all services. Further, as discussed  earlier, industry standards tend to focus within a band or service rather  than looking across boundaries; however, a few stakeholders we  interviewed said FCC or NTIA could encourage standards-settings bodies  to address particular problems, such as interference, or encourage more  cross-industry bodies to help enhance industry standards. Some  additional advantages and disadvantages apply to different forms of  greater use of industry-developed standards, as listed in table 1.
subsections: section_title: Interference Limits
paragraphs: Another option identified by stakeholders we interviewed and cited by  reports was interference limits. The interference limits approach would  explicitly set the level of energy—that is, the strength of the unwanted  signal from adjacent bands—that a receiver would have to tolerate before  making a claim of harmful interference. This is in contrast to the current  situation where expectations of receiver performance have almost always  been implicit—that is, receivers have been expected to operate within the  same parameters as their associated transmitters—which can lead to  conflicts when parties have a different understanding of these  expectations. Interference limits differ from the safe-harbor standards  option discussed above, since under the interference limits approach, the  prerequisite for claiming harmful interference is demonstrating that the  level of energy the receiver is exposed to exceeds a predetermined level,  rather than demonstrating a receiver complies with industry standards,  typically stated as specific performance characteristics.
Recently, reports from both a working group within FCC’s TAC and  PCAST recommended that FCC test interference limits. The TAC working  group recommended that FCC identify one or more pieces of spectrum,  specifically adjacent spectrum allocations, that are good candidates for  interference limits and initiate multi-stakeholder groups of relevant  industry and government representatives to work out issues and  implementation choices for these pieces of spectrum. PCAST  recommended that NTIA and FCC take steps to consider both  transmitters and receivers in its spectrum management policies and  specified that an initial step should be trying interference limits. Other  approaches to interference rights have been proposed, including one that  aims to replace FCC’s current policy of first-in-time rights—whereby FCC  protects incumbent users and thus receivers from interference as a result  of rule changes—to a policy where users would have to self-protect  against interference in adjacent bands.
The advantages of this option cited by stakeholders and reports that we  reviewed are that it would provide spectrum users with greater certainty,  as it sets a criterion for harmful interference. In addition, this option could  help enable private negotiation rather than FCC involvement to resolve  potential and realized interference. Another advantage is that this option  does not mandate a specific technology or design, leaving such choices  to manufacturers and others. Among the disadvantages cited by  stakeholders and reports are that this option would be more complex to  develop and enforce compared to standards. Also, this option has not  been used or tested, so it could take considerable time and resources to  test and considerable time to implement and the practical effects and  outcomes are unknown.
section_title: Additional Information on Spectrum Use
paragraphs: Many stakeholders we interviewed said that additional transparency and  sharing of information on spectrum use and system characteristics by  FCC and NTIA could help mitigate interference problems involving  receivers by facilitating greater understanding of the systems already in  place and thus the potential for interference to arise from the deployment  of a new system in adjacent spectrum. In general, stakeholders identified  two ways that additional information could be made available.
First, FCC and NTIA could make more information available on the  characteristics of transmitters and receivers in use, potentially in  conjunction with a spectrum inventory. The CSMAC Interference  and Dynamic Spectrum Access Subcommittee recommended that  NTIA, FCC, or other government entities responsible for managing  spectrum establish a clearinghouse to make information available to  those seeking to obtain access to spectrum; this will give entities  considering new services visibility about the potential for interference  for such equipment before they acquire spectrum and deploy  equipment. NTIA said that resources for implementing this and other  CSMAC recommendations were not included in recent budgets, but  some of its ongoing band-specific and other initiatives correspond with  these recommendations.
Second, FCC could also compile and share information on existing  industry standards for receivers. The TAC working group on receivers  and spectrum found that industry and government receiver standards  and recommended practices may exist but are often unknown to  manufacturers and users operating in adjacent bands. Therefore, the  TAC working group recommended that FCC enhance its Spectrum  Dashboard—a tool on FCC’s website that provides information on  how different frequency bands are being used and allows the public to  search, map, and download data on licenses—to include receiver  standards.
In terms of advantages, making additional information available would  enable more informed decision-making by NTIA, FCC, and spectrum  users through enhanced planning and testing. Moreover, additional  information could help new entrants better understand the spectrum  environment and potential interference concerns before committing  resources; as part of its report, the CSMAC Interference and Dynamic  Spectrum Access Subcommittee stated that some of the interference  problems in recent years were not anticipated by new entrants and might  have been avoided by providing new entrants with the interference  characteristics of receiving and transmitting equipment used in adjacent  bands. FCC and NTIA could also take action on this option quickly,  compared to other options. However, several stakeholders said that  concerns about proprietary and classified information could make it  difficult to implement this option. In addition, it would require resources,  both from federal spectrum management agencies and spectrum users,  to implement this option and keep it up to date. Finally, making additional  information on spectrum use available may be insufficient on its own to  address the challenges to improving receiver performance.
section_title: Research and Development
paragraphs: To improve receiver performance and increase spectrum efficiency, the  federal government could promote research and development for receiver  technologies and modeling. FCC officials told us that not much is known  about the actual performance of receivers. A 2010 report prepared by the  CSMAC Interference and Dynamic Spectrum Access Subcommittee  found that more research is needed to evaluate advances in technologies  and what standards will yield more spectrally efficient equipment, since  such advances may significantly alter cost-performance trade-offs. More  specifically, it recommended that the federal government could fund  research to accelerate the development of filters to improve the  performance of receivers, such as the ability to reject an undesired signal  at frequencies close to the desired signal frequency, without affecting size  or power consumption. The report also noted that a better dialogue  between the filter community and spectrum managers is essential as filter  performance has a large impact on spectrum efficiency. One licensee we  interviewed said that more investment is needed to improve technology  for receivers and that new technology could help lower the cost and  increase the flexibility of devices. A group like the Wireless Spectrum  Research and Development’s Senior Steering Group could be used to  help coordinate research in this area across the federal government.
Additional information gleaned through research could enable spectrum  managers and users to better understand the current state of receiver  performance and help inform future choices.
Stakeholders said that an advantage of research and development would  be to provide FCC and NTIA with more accurate information on  interference mitigation technologies that are feasible. Stakeholders said  that research could also help enable improvements to receivers to help  prevent interference problems across bands. Conversely, this option  would require resources, not only to fund but also to coordinate research  efforts across the federal government and the private sector. Also, certain  advancements through research, like those in filtering, may not be  applicable across spectrum uses. A few members from one industry  association we interviewed also said that filters can help solve some but  not all problems of adjacent band interference. Finally, the federal  government may lack infrastructure (e.g., test bed, labs) to directly  support research.
section_title: Conclusions
paragraphs: As demand for and use of spectrum continues to increase, improving the  performance of receivers is one of several ways to more efficiently use  spectrum and accommodate new services. To date, there have been a  limited number of instances where interference concerns driven by  receiver performance have impeded a licensee’s planned use of adjacent  spectrum. Even so, PCAST and FCC, among others, have recognized the  growing impact of receivers on efficient spectrum use, and adjacent-band  interference concerns may increase in years to come as spectrum  management agencies look to allocate additional spectrum for wireless  broadband and other new services in an already crowded environment.
Therefore, many stakeholders feel that more can and should be done to  improve receiver performance in concert with other efforts to increase  spectrum efficiency—the status quo is increasingly becoming untenable.  Stakeholders have identified and studied several options to improve  receiver performance and the efficient use of spectrum. In some  instances, these options entail direct federal intervention, such as  imposing mandatory standards for receivers, whereas in others, federal  policy creates an environment where industry participants’ individual and  collective actions can improve receiver performance. Each of these  options entail advantages, including reduced actual and potential  interference and improved spectrum efficiency, and disadvantages,  including possibly higher equipment costs. FCC and NTIA have each  explored receiver performance in the past, and recent recommendations  from advisory committees specific to this topic provide Congress, NTIA  and FCC, and industry stakeholders with options for further consideration  and testing. Since the topic has been the subject of considerable study,  the potential advantages and disadvantages of various options are  generally understood. However, less is known about the practical effects  of implementing these options to address interference. Several options  have not been implemented, such as safe harbor standards and  interference limits, and others, such as mandatory standards, have only  been implemented for certain federal users, and it is unclear how these  experiences would translate to nonfederal users. Greater understanding  of the practical effects of these options will allow FCC to make more  informed spectrum-management decisions moving forward to ensure the  efficient and effective use of spectrum.
section_title: Recommendation for Executive Action
paragraphs: To improve receiver performance and spectrum efficiency, we  recommend that the Chairman of the Federal Communications  Commission consider collecting information on the practical effects of  various options to improve receiver performance, including consideration  of small-scale pilot tests of these options.
section_title: Agency Comments and Our Evaluation
paragraphs: We provided a draft of this report to the Department of Commerce  (Commerce) and FCC for review and comment. In response to the draft  report, Commerce and FCC provided written comments, which are  reprinted in appendixes II and III, respectively. In its letter, Commerce  said that it will continue to work with FCC on issues of potential  interference. Commerce also emphasized the federal government’s use  of standards to improve receiver performance and the benefits of receiver  performance characteristics as a factor in improving spectrum efficiency.  In its letter, FCC said that the Commission has already initiated a process  to gather information on the effects of options to improve receiver  performance; FCC discussed various actions under way, which we  describe in this report, including that FCC’s TAC recently submitted to the  Commission for consideration recommendations to improve receiver  performance. These actions will help FCC to understand the potential  advantages and disadvantages of various options to improve receiver  performance. However, we do not believe that these actions will provide  information on the practical effects of options that FCC might get from a  pilot test or other information-collection efforts, which, as we note in the  report, will allow FCC to make more informed spectrum-management  decisions. Commerce and FCC also provided technical corrections to the  draft report that we incorporated as appropriate.
We are sending copies of this report to the Secretary of Commerce, the  Chairman of the Federal Communications Commission, and the  appropriate congressional committees. In addition, the report will be  available at no charge on GAO’s website at http://www.gao.gov.
If you or members of your staff have any questions about this report,  please contact me at (202) 512-2834 or goldsteinm@gao.gov. Contact  points for our Offices of Congressional Relations and Public Affairs may  be found on the last page of this report. Major contributors to this report  are listed in appendix IV.
section_title: Appendix I: Objectives, Scope, and Methodology
paragraphs: This report examines efforts by commercial licensees, manufacturers,  and the federal government to ensure that transmission systems are  designed and operated so as to not compromise reasonable use of  adjacent spectrum, with a focus on receiver performance as it relates to  increasing the efficient use of spectrum. In particular, the report provides  information on (1) actions taken by selected manufacturers and  commercial licensees to improve receiver performance; (2) actions taken  by the federal government to improve receiver performance; (3)  challenges, if any, to improving receiver performance; and (4) options  identified by stakeholders and reports to improve receiver performance.
subsections: section_title: Scope and Methodology
paragraphs: To address the engagement’s objectives, we reviewed relevant statutes  and regulations, and Federal Communications Commission (FCC) and  National Telecommunications and Information Administration (NTIA)  documents related to spectrum management, interference, and  transmission systems, with a focus on receivers. FCC and NTIA  documents included presentations from FCC’s March 2012 workshop on  Spectrum Efficiency and Receiver Performance and NTIA’s Receiver  Spectrum Standards Phase 1–Summary of Research into Existing  Standards, as well as various notices, orders, advisory committee reports,  and other publications. We interviewed FCC and NTIA officials to learn  about actions the spectrum management agencies have taken to improve  receiver performance, with a focus on interference between adjacent  spectrum users, and reviewed reports and workshops held by the  agencies on the topic of receiver performance. We also interviewed  members of NTIA’s Interdepartment Radio Advisory Committee (IRAC),  which consists of representatives from federal departments and agencies,  and officials from the National Oceanic and Atmospheric Administration  (NOAA) to learn about federal spectrum users’ experiences with adjacent- band interference and actions to improve receiver performance to  increase spectrum efficiency.
We also interviewed a variety of other stakeholders outside the federal  government—specifically industry associations, commercial licensees  and manufacturers, and academics and representatives from research  organizations—to learn about receiver performance and spectrum  efficiency. We selected industry associations to cover a variety of  spectrum uses and provide the perspectives of both licensees and  manufacturers. We selected commercial licensees and manufacturers to  ensure variety in frequency and application and to correspond to  interference cases involving receiver concerns. We selected academics  and representatives from research organizations based on participation in  workshops on receiver performance, service on FCC or NTIA advisory  committees, and recommendations from other interviewees, among other  criteria. In addition, we interviewed officials from spectrum management  agencies in Canada and the United Kingdom to learn about steps taken in  those countries to improve receiver performance to increase spectrum  efficiency. Across these interviews, we discussed the advantages and  disadvantages of improving receiver performance to increase spectrum  efficiency; actions taken by the commercial licensees, manufacturers, and  the federal government to improve receiver performance; and options for  additional action to improve receiver performance.
Table 2 provides a complete list of those we interviewed for this report.  The information and perspectives that we obtained from the interviews  may not be generalized to all industry stakeholders that have an interest  in spectrum efficiency and receiver performance. Rather, comments and  views are reviewed in context with current literature on this topic.
We also analyzed literature on receiver performance, standards, and  interference from academic journals as well as workshop proceedings  and reports on receiver performance and interference conducted by FCC,  NTIA, and organizations like the Silicon Flatirons Center, Brookings  Institution, and Aspen Institute. To identify relevant literature, we  performed a search of papers and studies (from 2002 through 2012) from  major electronic databases, such as ProQuest and SciSearch. We  included studies that focused on interference between adjacent spectrum  users and spectrum efficiency. We only included papers from scholarly  peer-reviewed journals, government reports, conference papers, and  other working papers. We also conducted a targeted search for  proceedings from conferences that occurred between 2008 and 2012 that  covered receiver performance, spectrum, and interference. We reviewed  the relevant papers, studies, and conference proceedings to identify  options to improve receiver performance as well as the advantages and  disadvantages of taking action to improve receiver performance.
We also studied a judgmental sample of cases where receiver  performance played a role in cases of potential or realized interference  between adjacent spectrum users, to better understand the actions of  commercial licensees, manufacturers, and the federal government as well  as the trade-offs of solutions sought in each case. We selected cases to  ensure variation in application or use (e.g., cellular telephone, navigation),  federal and nonfederal users, and existence of receiver standards, among  other characteristics. To compile a list of possible cases, we reviewed  FCC and NTIA reports, including the FCC’s Technological Advisory  Council white paper on spectrum efficiency metrics that included an  appendix on receiver performance and NTIA published reports on  interference involving federal users, and discussed potential cases with  officials from FCC and NTIA. We selected two cases that primarily  involved nonfederal spectrum users: (1) interference between cellular and  public safety services in the 800 MHz band, and (2) potential interference  between satellite radio and wireless communication in the 2.3 GHz band.  We sought to select a third case of interference involving federal  spectrum users of radar systems. However, since our aim was to select  cases that involved receiver performance problems, and since NTIA  officials told us that many cases of interference involving federal spectrum  users are resolved without substantial NTIA involvement, we did not  select a particular interference case. Rather, we chose to study radar  systems more generally. For each case, we analyzed relevant rulemaking  proceedings, reports, and other documents to describe the types and  extent of actions taken by stakeholders to limit interference and increase  spectrum efficiency. In addition, we interviewed select licensees, industry  associations, and manufacturers to better understand the circumstances  of each case, actions taken to address interference, and the trade-offs of  these actions.
section_title: Case Study Descriptions
paragraphs: WCS/SDARS: In the 2.3 GHz band, interference concerns arose between  two different services—terrestrial-based Wireless Communications  Service (WCS) and chiefly satellite-based Satellite Digital Audio Radio  Service (SDARS, or satellite radio)—allocated to adjacent parts of the  bands with no guard bands separating the services. WCS allows a range  of terrestrial-based services, including fixed, mobile, portable, and  radiolocation services, though initial rules for the band made mobile  service impractical. SDARS is primarily a satellite-based service in which  programming is sent directly from satellites to receivers that are either at  a fixed location or in motion; however, SDARS licensees deployed  terrestrial repeaters to address situations where skyscrapers and other  impediments prevented a line-of-sight connection between satellites and  receivers. In general, SDARS receivers must be highly sensitive to  receive weak, satellite signals. Moreover, SDARS deployed before WCS,  so SDARS receivers did not have to tolerate high-powered mobile  operations in the adjacent WCS bands. SDARS licensees raised  concerns over interference from a request to change rules to enable  mobile services in the WCS spectrum, while WCS licensees and others  raised concern over potential interference from the SDARS terrestrial  repeaters.
FCC issued several notices of proposed rulemaking for both services  since their allocation in the mid 1990s. FCC also encouraged the parties  to negotiate an agreement to facilitate the adoption of rules for both  services that would resolve the potential for interference. However,  negotiations did not lead to a private resolution, and in 2007, FCC opened  a new proceeding to update the record on the potential interference. This  culminated in a 2010 Report and Order and Second Report and Order  that adopted rules addressing the potential interference. FCC adopted  rules that, among other things, effectively created 5 MHz guard bands on  each side of the SDARS spectrum to protect legacy SDARS receivers;  the rules did not include any requirements specific to receiver  performance. In 2012, FCC responded to petitions for reconsideration of  that decision with a new order that adopted an agreement reached by  AT&T and Sirius XM, which are now the primary license holders in the  band.  800 MHz band: Interference occurred between adjacent spectrum users  in the 800 MHz band primarily because of the use of two different types of  communications systems on interleaved channels. The two types of  communications systems were (1) cellular-architecture multi-cell systems  used by cellular telephone and enhanced specialized mobile radios and  (2) high site systems used by public safety and well as private wireless  and non-cellular specialized mobile radio licensees. Beyond the  difference in systems, two other factors exacerbated the potential for  interference: the close proximity of frequencies used by the commercial  and public safety users and insufficient selectivity of many land mobile  radios used by public safety users.
Interference from cellular systems to public safety systems began to  occur in the late 1990s as cellular licensees began deploying multi-cell  systems. Interference occurred even though all the licensees were  operating in compliance with FCC rules for transmitters. After interference  problems emerged, FCC brought together the relevant parties and  encouraged them to develop more definitive information on the scope and  severity of the problem and to recommend steps to mitigate interference.  As a result, a working group created a Best Practices Guide to help  prevent and mitigate interference in the band. Seeking a more  comprehensive solution to the interference problem, Nextel—the primary  license holder in the 800 MHz band—proposed reconfiguring the band to  separate the different systems and then worked with many public safety  and other industry associations to create an updated reconfiguration plan.  In addition, the public safety community and equipment manufacturers  recommended receiver performance specifications going forward that  would serve as criteria for qualifying for interference protection. FCC  adopted these recommendations in the rules it adopted for the 800 MHz  band in 2004, which reconfigured the band and defined a technical  standard for determining if a public safety or other non-cellular licensee is  entitled to interference protection.
section_title: Appendix II: Comments from the Department of Commerce
section_title: Appendix III: Comments from the Federal Communications Commission
section_title: Appendix IV: GAO Contact and Staff Acknowledgments
subsections: section_title: GAO Contact
section_title: Staff Acknowledgments
paragraphs: In addition to the contact person named above, Michael Clements,  Assistant Director; Nabajyoti Barkakati; Stephen Brown; Leia Dickerson;  Sharon Dyer; Ryan Eisner; David Goldstein; Richard Hung; Bert Japikse;  Joanie Lofgren; Maren McAvoy; Joshua Ormond; Amy Rosewarne;   Hai Tran; Elizabeth Wood; and Nancy Zearfoss made key contributions to  this report.