Managing Limited Spectrum for Unlimited Applications

Managing Limited Spectrum for Unlimited Applications

The wireless frequency spectrum extends to 300 GHz and beyond, but with the ever-growing number of wireless applications, that spectrum must be managed for its most efficient use.

Frequency spectrum might seem unlimited, considering the wide range of radio frequencies from 9 kHz to 300 GHz. But with more people and things using radio spectrum, portions of it, including smartphones in 4G LTE and soon 5G wireless networks, billions of Internet of Things sensors, and in connected smart cars, even the millimeter-wave (mmWave) frequencies (30 GHz and above) are being used up.

Spectrum management is the process of getting the most efficient use of available radio frequencies and with minimum interference. It involves commercial and military management, at national and international levels. Spectrum management is an ongoing process, since the demand for frequency spectrum grows with the number of wireless devices. Can radio frequency spectrum run out? If not properly managed, it can. But with proper management, even 6G will be possible.

Spectrum management has been going on since radio waves were first used for AM and FM broadcast radios, maintaining signals for these radios in the ranges of 540 to 1600 kHz and 88 to 108 MHz, respectively. In the U.S., broadcast television services occupied VHF and UHF bands at roughly 54 to 806 MHz, and the radio spectrum allocation chart started to fill with these early commercial uses of electromagnetic (EM) energy and radio spectrum.

Today, the radio-spectrum allocation chart for the U.S. is a densely populated map of commercial, military, and government applications with rapidly shrinking sections of available bandwidth. The U.S. table of frequency allocations covers the radio spectrum from 9 kHz to 300 GHz. In addition to those early radio and television applications, frequency bands are filled by cellular telephones, wireless communications networks, Global Positioning System (GPS) satellites, vehicle collision-avoidance radars, satellite communications (satcom) systems, and a variety of defense-related systems, such electronic-warfare (EW), electronic intelligence (ELINT), radar, and surveillance systems. Each application has its own allocated portion of the frequency spectrum, designed for its optimum use, but also for minimum interference with existing applications using other portions of the radio spectrum.

Allocating Frequencies

The various frequency bands are assigned by the process of spectrum authorization, handled by different organizations in different locations. The National Telecommunications and Information Administration (NTIA) is the organization that manages the U.S. federal government’s use of frequency spectrum, working with the Interdepartment Radio Advisory Committee (IRAC). The Federal Communications Commission (FCC) manages all domestic non-federal use of spectrum in the U.S.

Additional government organizations such as NASA work with these spectrum regulatory groups to ensure that spectrum will be available for present and future space-exploration missions. Internationally, the International Telecommunications Union (ITU) is part of the United Nations that manages terrestrial and satellite use of frequencies among different nations.

As spectrum continues to be consumed by different wireless applications, additional concepts have been proposed to ease the control of these organizations. This includes spectrum trading or sharing, in which a portion of bandwidth initially authorized for one type of application might also be used for a different application without need of authority from an organization like the FCC.

The FCC most recently issued a public notice (PN, May 1, 2018) on the feasibility of the licensed and unlicensed use or sharing the use of the frequencies between 3.7 to 4.2 GHz. The FCC notes that there’s currently no federal allocation for the band from 3.7 to 4.2 GHz, and is hoping to explore the effects of having commercial licensed and unlicensed users possibly share the band with federal users.

For federal U.S. applications, the NTIA will work with a federal government group or agency to review the expected characteristics and specifications for a new wireless system to ensure that the new system can operate effectively without disrupting existing radio-frequency systems. If it appears that the new system is safe, the NTIA will issue a Certificate of Spectrum Support, followed by a frequency authorization to the proposing group or agency that makes it possible to use the new system on a specific frequency and bandwidth or band of frequencies.

It’s then a matter for the proposing agency to put one or more of the new systems to use in the field. Therefore, actual use tests can be performed with available test equipment, such as signal generators and spectrum analyzers, to evaluate the effects of what might have been unforeseen problems (e.g., second- and third-harmonic interference from an antenna or signal source). The NTIA must review and approve any of these test results to ensure that the new application performs as expected and does not cause interference to existing applications. The NTIA works with guidance from other federal agencies, such as IRAC, as well as different federal departments like the U.S. Department of Transportation (DOT), as needed on spectrum-management issues.

Going to School

As part of the U.S. Department of Commerce, the NTIA works with many researchers on maintaining the database needed for effective spectrum management. The NTIA recently announced a five-year R&D agreement with the University of Colorado Boulder to develop a wireless test bed that essentially uses the university’s grounds (Fig. 1) as a laboratory for spectrum-management research. The NTIA and the university will benefit from the research, installing spectrum-monitoring sensors throughout the campus.

1. The NTIA is partnering with the University of Colorado Boulder on spectrum-management research over the course of a five-year R&D agreement. (Courtesy of the University of Colorado Boulder)

David Redl, Assistant Secretary of Commerce for Communications and Information and NTIA Administrator, says, “We’re excited that ITS is moving forward with this important test-bed research that will provide analytics on how real-world spectrum sharing could work. The scientists and engineers working at ITS are experts in the field of spectrum measurement, and we expect the collaboration with CU to lead to new opportunities for government users to share spectrum with other agencies and commercial users.” The test bed will help explore new wireless technologies, specifically how they occupy spectrum and interact with each other under real-world conditions.

Peter Mathys, Associate Professor in Electrical, Computer and Energy Engineering at the university, offers, “This will be a great motivator for students who use wireless devices on a daily basis but have little understanding of the underlying physical limitations associated with wireless technology. This testbed will enable measurement of the effects associated with the ever-growing demand for increased wireless communications.”

For its part, the FCC works on developing new uses for frequency spectrum with state and local government users as well as private and business users. For any new application, the FCC will first issue a Type Acceptance that identifies the authorized frequency band and the performance parameters, such as maximum transmit-power and frequency-channel bandwidth. Following the Type Acceptance, the FCC will issue the user a radio license for that frequency or group of frequencies, and the user must go through testing of the new equipment according to the FCCs requirements and recommended test methods.

The FCC works closely with the NTIA in managing spectrum in all conditions, in peacetime as well as war. As part of a 2010 presidential advisory, the FCC is collaborating with the NTIA to “find” or make available a total of 500 MHz of federal and non-federal communications spectrum for mobile and fixed broadband wireless use by the year 2020.

On a global basis, the ITU has mapped the world’s use of frequency spectrum into three main operating areas, and maintains a global Table of Allocations for the different nation members to follow. When new telecommunications designs or applications are developed, proposals for that new use of frequency spectrum must be submitted to the ITU. To assess the global need for spectrum management and any reorganization of the Table of Allocations, the ITU holds regular World Radiocommunications Conferences (WRCs) to invite new ideas for frequency-spectrum usage.

5G and Beyond

Much of the promise of 5G wireless networks depends on the availability of sufficient frequency bandwidth to support the many functions of this emerging wireless technology, and the NTIA will play a key role in finding the spectrum required for 5G in the U.S. What makes 5G somewhat unconventional is its use of scattered spectrum, at both lower and higher frequencies. For mmWave frequency access, for example, the NTIA has supported the FCC’s Spectrum Frontiers program, collaborating on a means of sharing the 37-GHz frequency band between federal and non-federal users. Both agencies feel that if the 37-GHz effort is successful, it could serve as a model for spectrum sharing of other mmWave bands, especially those needed for short-haul links in support of high-data-rate communications in 5G wireless networks. The NTIA is also working very closely with the FCC on the use of the 24- and 28-GHz frequency bands, which are under consideration for use in emerging 5G wireless networks.

At lower frequencies, the FCC has proposed the possibility of reusing the 2.5-GHz spectrum currently allocated to the Educational Broadband Service for the lower bands of 5G networks. At the same time, the NTIA has proposed repurposing the band of frequencies from 3450 to 3550 MHz for commercial use, perhaps as part of coming 5G wireless networks.

While the FCC is responsible for safeguarding the interests of non-Federal users for existing frequency bands, the NTIA must also watch for any conflicts that can cause interference with government and military users. It must ensure that the frequencies and bandwidths consumed by an emerging application such as 5G do not “steal” needed bandwidth from military communications or radar systems.

Much of the work to be done by the NTIA and FCC in finding spectrum for 5G must weigh not only the available spectrum, but the state of technology out there that can support the use of any available frequencies. Since 5G is being designed to make use of lower, mid-range, and higher (mmWave) frequencies, the economy of components for each different frequency range will vary with the frequency, with the most expensive components at the highest frequencies. Still, agencies such as the NTIA and FCC have traditionally used spectrum management to encourage the development of new technologies and more practical solutions that would allow the economical use of mmWave frequencies even above 95 GHz.

In recent remarks to the CTIA on that organization’s “Global Race to 5G” report, the NTIA’s David J. Redl, confirmed the importance of 5G as more than just a new generation of wireless communications equipment: “5G and the technologies it will enable promise transformative changes that will improve healthcare, advance manufacturing, and benefit public safety.”

Redl noted that maintaining a technological edge in 5G technology and modern communications in general is critical for the U.S. as a world leader. In addition to spectrum availability, security is one of the main concerns for the development of 5G wireless networks. Whereby the network and devices on that network can be made sufficiently secure to protect the information for users at all levels, from private citizens to the government and military users expected to share the many resources of 5G systems.

2. BroadbandUSA is an initiative and website organized by the NTIA to promote the use of broadband communications throughout the U.S. (Courtesy of the NTIA)

Along with its close ties to the FCC, the NTIA also works with many government organizations to promote effective use of frequency spectrum throughout the country. One of its newer initiatives, BroadbandUSA (Fig. 2), is aimed at helping communities throughout the U.S., no matter how remote, to develop the broadband communications capacity required for effective economic development, education, healthcare, and public safety. BroadbandUSA is expected to use webinars and other educational methods to reach citizens, and to encourage close coordination among federal agencies to promote broadband deployment and adoption.

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