4

Metrology for Advanced Communications

The second main category of CTL’s work addressed by the panel, Metrology for Advanced Communications, is discussed in this chapter. This category is implemented through three of the four CTL priority areas: (1) Trusted Spectrum Testing, (2) Fundamental Metrology for Communications, and (3) Next Generation Wireless (5G and Beyond). As may be seen from Table 4.1, three of the organizational units in CTL address priority areas that comprise the main category of CTL work treated in this chapter. In the discussion below, the assessment of the work of the aforementioned three organizational units is subsumed within the discussion of each priority.

OVERALL METROLOGY DISCUSSION AND RECOMMENDATIONS

CTL has adequate and stable funding to carry out its metrology mission. The scientific and technical quality of the team is excellent and the communication between team members is highly supportive of a collaborative, highly productive and interdisciplinary culture.

CTL staff has identified an excellent set of metrology projects to support future communications needs. This work is centered on solving fundamental and near-term applicable measurement challenges for emerging communications standards. Some of the projects clearly emerge from fundamental metrology scientific advances of clear practical import, and others seem to be (appropriately) driven by short term needs resulting from emerging national policy initiatives. The process for the future strategic selection of new projects—to maximize CTL impact—is unclear.

The CTL has capacity to grow in important metrology areas in order to address emerging communication needs in new technology and application areas, and the nation would be well served by this growth.

The CTL metrology staff are consistently and diligently engaged in the important task of dissemination of their scientific and technical findings to the broader community of technical professionals and stakeholders.

The CTL is a unique national resource, and its scientific output and test infrastructure need to be better publicized and made clearly available in order to have the highest impact.

The CTL physical infrastructure is mostly adequate for the current programs in its highly ambitious metrology mission.

There is substantial evidence that CTL has accomplished a significant amount in multiple areas of interest to its stakeholders on a relatively limited and uncertain budget in a short period of time.

Based on its significant accomplishments in a diverse portfolio of technical areas in a short period of time, the CTL is poised to capitalize on a number of timely and impactful opportunities, including: quantum-enabled metrology with applications in QISE; a new framework for channel metrology and modeling with the capability of predictive performance analysis to inform the design and deployment of next generation wireless networks; innovative hardware and platforms for testing and metrology of next generation wireless technology; continuing the growth and development of the NASCTN testbed and operational processes; leveraging machine learning, data science and statistical techniques to fully utilize the range of metrology capabilities at CTL and NIST to significantly increase, enhance and broaden the scope of its contributions and output to its stakeholders.

The stakeholders of CTL represent diverse communities (industry, government, academia and research communities in the various technical areas reflected in CTL’s projects) and have different needs ranging from basic science and engineering to applied research for design and technology development to offering its test and measurement facilities for stakeholder projects. A range of metrics are needed to evaluate NIST CTL.

CTL—with the diverse expertise of its world-class staff—has significant latent capacity that it can leverage to capitalize on timely and impactful opportunities in collaboration with other NIST laboratories (e.g., the Physical Measurement Laboratory [PML], the Information Technology Laboratory [ITL], and the Engineering Laboratory).

FUNDAMENTAL METROLOGY FOR COMMUNICATIONS

Assessment of Technical Programs

Nearly a decade ago, NIST CTL researchers began investigations on better, more accurate ways to measure electric fields. This was done with an aim toward making such measurements more “traceable” to fundamental SI quantities.¹ Subsequent years of effort have borne impressive results.

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¹ The International System of Units (SI) is made up of 7 base units: kilogram (kg) mass, kelvin (K) temperature, candela (cd) luminous intensity, ampere (A) electric current, meter (m) length, second (s) time, and mole (mol)

The primary result is a practical, demonstrated, Rydberg atom-based, SI-traceable measurement method (and prototype devices) for precision electric field (E-field) and power measurements. This result extends the amplitude range, frequency range, and accuracy of E-field measurements. Through the use of lasers and microwave signals to induce transparency in a closed cell containing a vapor of particular atoms (rubidium or cesium), one or two electrons are excited to states causing their host atoms to have large dipole moments, allowing them to be used as very sensitive E-field detectors. Initial results indicate multiple orders of magnitude improvement in the measurement sensitivity compared to the state of the art.

This invention has been shown to enable several other applications, including measurement of phase and modulation of fields for communications transmitters and receivers, quantum-enabled imaging for medical and near-field applications, power calibrations and more.

The measurement capabilities developed by CTL using Rydberg atoms also offer a promising bridge to future research directions mentioned by the CTL director: quantum computing and optical communication networks. Rydberg atoms are being explored as promising candidates for physical realization of qubits (quantum bits) and CTL is well-positioned to build on their recent successes to initiate a research program in QISE in collaboration with other NIST laboratories, such as the PML, which are already engaged in QISE-related research. This is a timely opportunity given the recent announcement of the National Quantum Initiative (NQI) in December 2018 and the worldwide attention QISE is receiving. In this endeavor, CTL is well-positioned to identify strategic collaborative opportunities with PML (and other laboratories, such as ITL) that draw on its unique strengths in communication metrology and technology to advance the science, engineering and technology frontiers of quantum computing, quantum communication and quantum sensing.

The technical area of optical communication technology also represents a synergistic direction that CTL is interested in adding to its research portfolio in the future. On the one hand, the need for higher bandwidths, which is driving emerging wireless technologies (5G and beyond), is also driving new technologies and innovations in fiber-optic and free-space optical communications to which CTL can fruitfully contribute. On the other hand, optical and microwave communication techniques and technologies are expected to play a key role in the emerging QISE technologies, and this provides further impetus for CTL to develop core expertise in this area, possibly by hiring new scientists and engineers with the requisite expertise.

The RFT Division continues to perform fundamental metrology research and development of techniques for high-frequency measurements applicable to a wide array of industry and government stakeholders. This high impact work has significant impact on 5G integrated circuit development, a field of high national priority. Related work is in advanced vector network analysis and calibration. NIST is viewed as a best in the world resource in this area. They have also developed a “microwave uncertainty framework.” This framework will have much broader application than only the microwave frequency band.

The technological trend towards fully integrated communication devices, in which the digital processing, analog-digital converters, and RF hardware and antennas are all integrated onto a single board with multiple chips, is radically changing the paradigm for testing and characterizing the performance of these new devices. NIST CTL is at the forefront of pioneering a new approach to testing next generation wireless devices and systems that would combine on-wafer measurements of individual components with over-the-air (OTA) testing of integrated devices and complement them with new approaches for making near-field measurements of various components in an integrated board.

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amount of substance. SOURCE: NIST, 2017, SI Measurement System, NIST SP 304A, U.S. Department of Commerce, Washington, D.C., July.

Accomplishments

The quality of the quantum SI-traceable measurements and application research is outstanding. The team is defining the state of the art in E-field amplitude, phase and polarization metrology. Among others, the developed Rydberg-atom-based methods are able to measure E-fields with amplitudes as low as 10 millivolt per meter (mV/m) at room temperature, over frequency bands ranging from tens of megahertz (MHz) to hundreds of gigahertz (GHz) or even terahertz (THz), with an instantaneous bandwidth of tens of megahertz. The team has also demonstrated the ability to accurately measure the phase of the E-field over a wide frequency range relying on the same fundamental principles. Several proof-of-concept demonstrators have been implemented, including analog (stereo AM/FM) as well as digital (up to 64 quadrature amplitude modulation [QAM]) modulation and demodulation.

The developed technology is also an enabler for high frequency (>110 GHz) calibration procedures. This is a field in which NIST is playing a key role in different ways, including the development of high-fidelity on-wafer measurement techniques and integrating these with on-board and over-the-air measurements to invent the future of vector network analyzers. The need for these new classes of measurements and network analyzers is driven by the advances in integrated circuit (IC) technology for communication applications in which the IC chips for various subsystems (e.g., RF transceivers, analog-digital convertors, and digital processors) are all integrated onto a single printed circuit board (PCB) with no connectors available for testing the individual systems. This is a stark departure from current testing methodologies that are based on conductive measurements of individual components. This area also ties in well with the increasing use of machine learning and data science techniques at CTL as evidenced by the newly-established laboratory space on the third floor of Building 3 that included a dedicated server for machine learning and high-intensity data analytics.

Overall, this program is an excellent example of how timely investment of resources for the exploration of very fundamental physics principles (Rydberg atoms) can lead to transformative practical solutions (SI traceable E-field measurements) for industry/societal problems (calibration of equipment). This is also an excellent example of how such investment of resources can also lead to serendipitous dividends in terms of new unanticipated opportunities; new programs in QISE and optical communication technologies, in this case. CTL’s success in winning multiple Institute of Electrical and Electronics Engineers Instrumentation and Measurement Society (IMS) awards in these areas, in collaboration with other laboratories (e.g., PML and ITL), is commendable and reflective of the excellence of technical programs and the expertise of the staff.

A significant accomplishment has been the development of three different types of sounders, operating in 28 GHz, 60 GHz, and 83 GHz bands, with directional measurement capabilities using a variety of antenna architectures, including switched arrays and phased arrays. The measurements taken by these sounders have led to a set of “ground truth” propagation data that can be used for evaluating the performance of different sounders.² These measurement technologies, facilities, and advanced data processing capabilities are at the forefront of advanced metrology for next generation wireless communications.

Challenges and Opportunities

Several technical challenges must be overcome before the Rydberg-atom based devices can become widely useable. These include further miniaturization and eventual embedding of the system in a compact probe, widening of modulation bandwidths (currently in the order of 20 MHz, set by the electron/atom relaxation time), application of filtering, etc. The team is well aware of these challenges, and is currently at work on addressing them.

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² Data are available at NIST, “5G mmWave Channel Model Alliance,” https://5gmm.nist.gov/.

The accomplishments in quantum-enabled measurements also offer new opportunities in the growing and important area of QISE, in addition to new avenues in quantum-enabled sensing that team is already pursuing—for example, building on the measurement work to create higher-fidelity Rydberg atom-based qubits with longer coherence times. CTL’s expertise in optical and microwave metrology techniques would also be valuable in realizing high-fidelity signals for controlling the initialization and evolution of qubit states. A related opportunity is in the development of optical quantum communication techniques for exchanging qubits across multiple quantum processors (with tens to hundreds of qubits) to create a distributed quantum computer with larger number of qubits. NIST and CTL have made fundamental contributions to optical communications in the past and these potential opportunities align well with the CTL’s plan to re-establish its program in the area of optical communications. An important related research challenge is transduction of quantum states across multiple modalities—for example, between Rydberg atom-based qubits (for use within a quantum processor) and photonic qubits (for transporting qubits across quantum processors).

Another opportunity for the CTL within the quantum realm relates to new applications in quantum information science, supported by optical communications, the latter being a field in which NIST has made many fundamental contributions in the past. As the need for communication between quantum computing increases, developing technologies to support the reliable exchange of quantum bits is needed.

The CTL team has delivered exemplary results noted above. The Rydberg atom E-field sensor appears to have breakthrough potential.

The CTL team has proactively identified Optical Communications and Quantum Information Science and Engineering as promising new areas for research that synergistically build on the quantum-enabled sensing work.

Portfolio of Scientific Expertise

The RFT Division’s scientific expertise in SI-traceable measurements is closely matched to the program’s technical needs and strongly positions CTL at the forefront of the field, as evinced by the visibility and citations on this work.

Challenges and Opportunities

While expanding CTL’s capabilities into the synergistic areas of QISE and optical communications is timely and potentially impactful, it would likely require hiring new scientists and engineers with requisite expertise that can provide a bridge between CTL’s capabilities in communication technology and metrology and the capabilities of the collaborating laboratories, such as PML, in quantum information science.

Future technical staff hiring may require expertise that can provide a bridge between CTL’s capabilities in communication technology and metrology and the capabilities of the collaborating laboratories, such as PML, in QISE.

Adequacy of Facilities, Equipment, and Human Resources

Accomplishments

CTL has made significant progress in developing in-house capabilities for fundamental metrology in the context of next generation wireless technologies, including those for channel modeling and measurement. In the work led by the RFT Division; a number of new measurement and testing facilities have been developed, including anechoic chambers with robotic arms for radiation pattern measurements in static and mobile scenarios, a robotic aperture scanning testbed for making measurements appropriate for antenna arrays, reverberation chambers for creating different multipath propagation environments, and new methodologies and testbeds for characterizing the performance of channel sounders, including angular measurements. (The complementary work by the WN Division on channel modeling is discussed below in the section, Next Generation Wireless.)

Challenges and Opportunities

Sustainability of adequate personnel and facilities could present a programmatic challenge for building on recent accomplishments and expanding into new areas in quantum information science and optical communications. This effort will require strategic collaborations with other laboratories at NIST, such as PML and ITL. It is not clear whether the collective capabilities of CTL and other NIST laboratories, in terms of facilities, equipment and human resources will be adequate to successfully execute the potential new research activities. There appear to be multiple commercial opportunities for quantum-enabled metrology and potentially many future ones in the broader area of quantum information science. However, CTL will have to act in a thoughtful and strategic fashion to evaluate the resource needs and address them in a timely fashion.

The available resources in terms of facilities and staff seem to be adequate to sustain the current programs. However, growing into the new synergistic areas of optical communications and quantum information science will require strategic collaborations with other laboratories, such as the PML and the ITL, and likely require additional resources. The facilities and equipment being used for the quantum SI-traceable measurements are excellent. Overall RFT Division facilities are excellent.

Effective Dissemination of Outputs

The publications and patents from the quantum SI-traceable measurement research are first-rate in terms of venue, quantity, and visibility.

Accomplishments

This work has led to 17 journal publications in top-tier journals in the applied physics society, including Physical Review Applied, Applied Physics Letters, and Journal of Applied Physics, and 10 conference papers.³ These works have had, and are having, a high impact in the community, as shown by the very high number of downloads in the short term as well as citations in the long term.

Challenges and Opportunities

Opportunities exist in commercialization and development of applications. The novel modulation and musical demonstrations possible using the Rydberg atom could be used for outreach to K-12 student communities. Another opportunity may exist if the quantum SI-traceable measurement research could be connected with future applications in quantum information science and engineering.

NEXT GENERATION WIRELESS

Assessment of Technical Programs

CTL is tackling a diverse range of timely and significant problems in the area of 5G wireless technology, fundamental metrology, and applications, particularly on the topics of 5G Channel Modeling and Measurements. In addition, CTL is providing outstanding stewardship of the 5G mmWave Channel Model Alliance. This organization is a worldwide community of researchers engaged in research and development for new approaches to measurement and modeling of propagation channels at millimeter-wave frequencies. CTL also conducts work on other technologies that support 5G including for example, on massive multiple-input, multiple-output (MIMO) antennas on frequencies up to and including those of millimeter wave. Measurements of MIMO are enabled in the reverberation chambers of the National Broadband Interoperability Testbed on the Boulder campus as are over-the-air (OTA) measurements.

The CTL work on millimeter-wave channel measurements and modeling began in 2011, and CTL initiated the 5G mmWave Channel Model Alliance (the “Alliance”) in 2015. The Alliance has grown to include over 80 organizations from industry, academia, and government.

The Alliance has worked to develop multiple publications for the broader community, methodologies for channel measurements and model development, and has brought numerous individuals together for collaborations, who otherwise would likely not have interacted. The CTL team members have continued in a leading role in the Alliance, in direct response to a recommendation from the 2015 National Academies review.⁴

The CTL team has also taken several of their own measurement-based models and employed them in higher level network simulators, provided a commercial software vendor with code to enable the use of an 802.11 model by the wider community, and has also published widely. In addition to journal and conference papers, the Alliance has sponsored several workshops at major conferences.

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³ Christopher Holloway, Matt Simons, and Joshua Gordon, NIST CTL, “Quantum SI Traceable Measurements and Calibrations: Radio Frequency Electric Fields and Power,” presentation to the panel, June 26, 2019.

⁴ National Academies of Sciences, Engineering, and Medicine, 2015, Telecommunications Research and Engineering at the Communications Technology Laboratory of the Department of Commerce: Meeting the Nation’s Telecommunications Needs, The National Academies Press, Washington, D.C.

Accomplishments

The 5G mmWave Channel Model Alliance has achieved significant accomplishments since its inception in July 2015. The membership of the alliance has grown significantly to over 80 members from industry, academia and U.S. government agencies. Two comprehensive white papers have been developed by the two working groups—one on channel modeling techniques, and one of channel measurement and verification—capturing the diverse expertise of the Alliance members.⁵ NIST has also created a repository for sharing of data between the Alliance members and the wider research community.

CTL has also made significant progress in developing in-house capabilities in channel modeling and measurement. In the work led by the WN Division, channel models are being incorporated into network simulation software, and a framework for comparing the performance of different sounders is being developed. The measurement and verification work, led by the RFT Division, utilizes the testing facilities described above⁶—including anechoic chambers, a robotic aperture scanning testbed, and reverberation chambers.

A significant accomplishment has been the development of three different types of sounders, operating in 28 GHz, 60 GHz, and 83 GHz bands, with directional measurement capabilities using a variety of antenna architectures, including switched arrays and phased arrays. The measurements taken by these sounders, and extension of propagation parameters from those measurements, has led to a set of “ground truth” propagation data that can be used in the models for numerically evaluating the performance of different sounders

Challenges and Opportunities

There are a number of opportunities in the area of 5G channel modeling and measurements and next generation wireless networks that the CTL is poised to pursue, including: expanding the work to higher THz frequencies; expanding the work to UAV network channels; measurement campaigns for outdoor scenarios; quantifying the effects of human occupancy on indoor and outdoor channels and developing accurate channel models and an appropriate network modeling framework that has the capability to predict network performance in a given deployment area.

The microwave uncertainty framework (MUF) is a powerful approach for studying and quantifying the impact of different sources of uncertainty in measurements of future wireless devices and systems—not inherently limited to the microwave band. New capabilities of future wireless systems, including higher frequencies, larger bandwidths, and directional antennas, coupled with new approaches to analysis and processing of data, including machine learning techniques, present exciting new opportunities and challenges for further developing this uncertainty framework.

CTL is well positioned to grow the effort in next generation wireless technologies by building on their accomplishments at millimeter-wave frequencies. Additional measurements and models will be needed for other (higher) frequency bands and multiple outdoor settings. Planning for the future—for example, 6G (6th Generation Wireless)—is beginning in the wider community. Another challenge—for which NIST may be well suited in collaboration with the National Institutes of Health—is to address human health impacts of the use of these frequency bands.

The approaches developed by CTL for advancing the state of the art of modeling and measurement of millimeter-wave channels reflects a high level of creativity and ingenuity to complement commercially available hardware/software with internal development of antennas, hardware, automated measurement capability, and software for data processing and visualization.

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⁵ The white papers were undergoing peer review and final publication at the time of the panel’s review. Further information may be found at NIST, “5G mmWave Channel Model Alliance,” https://www.nist.gov/ctl/5g-mmwavechannel-model-alliance.

⁶ See the subsection “Accomplishments” in the section “Fundamental Metrology for Communications.”

Data science and machine learning offer a powerful new approach that CTL is beginning to leverage in its work on metrology of future highly integrated wireless devices, propagation channel modeling and measurement, and creating traceable measurements and associated uncertainty analysis.

Portfolio of Scientific Expertise

The CTL staff engaged in Next Generation Wireless are highly qualified and represent a diverse range of expertise (including in channel modeling and measurement) that is essential for this cross-disciplinary effort, including RF hardware design, testing and measurement expertise, channel and network modeling, and data processing and analysis. In FY 2019, 22 percent of CTL’s budget authority went to Next Generation Wireless priority area.

Adequacy of Facilities, Equipment, and Human Resources

The facilities and equipment being used for the next generation wireless metrology, including millimeter-wave and higher frequencies, are state of the art. This includes components and capabilities developed locally by CTL staff to augment commercial measurement equipment such as vector network analyzers. The CTL facilities fall into two categories: (1) very modern, well equipped, well maintained new infrastructure, and (2) one rather old building that houses valuable instrumentation and capabilities but suffers from lack of infrastructure such as high speed network connectivity, and modern HVAC. The panel did not make a site visit to Gaithersburg, Maryland, where the WN Division’s facilities are located so cannot comment on facilities located there.

CTL allows users outside of NIST to have access, on a supervised basis, through formal mechanisms, such as CRADAs, and informal collaborations. In addition CTL can also serve as a testing location for programs that need a neutral third party to serve as the technical evaluator, for example, the Defense Advanced Research Projects Agency. The precise rates of utilization through such agreements and arrangements are not readily available.

CTL’s measurement facilities can be of great use to users in the research and business communities in the United States and worldwide. For this to succeed, it is essential that the facilities be able to handle the data and infrastructure requirements of modern communications challenges.

Effective Dissemination of Outputs

The outputs of the millimeter-wave channel measurement and modeling work are numerous, and are of relevance and use to the community. These include the two white papers on modeling and measurement developed by the 5G mmWave Channel Model Alliance, contributions to standards bodies,

and hosting of a series of workshops on the topic over the last few years. In addition, various members of CTL have also disseminated this work through invited presentations and engagement in other organizations such as the National Science Foundation (NSF)-sponsored research coordination network on millimeter-wave wireless.

Accomplishments

The growth and outputs of the 5G Millimeter Wave Channel Model Alliance are substantial outcomes. At least one book is being published, datasets are being archived, and software and hardware instrument makers are likely to use some of the Alliance outputs. The three millimeter-wave channel sounders that CTL has developed are also a community asset. The new capabilities for testing and measurement being developed for next generation wireless system at the CTL would further build on these assets.

TRUSTED SPECTRUM TESTING

Assessment of Technical Programs

The CTL team’s work in the broad topic of shared use of federal spectrum by commercial systems has been enormously important. This work consists of (1) two NASCTN projects in the context of advanced wireless services (AWS)-3 spectrum sharing (1755-1780 MHz paired with 2155-2180 MHz), and (2) work in the WN Division on technologies for sharing of the 3550-3700 MHz band. The RFT Division provides expertise and collaboration in shared spectrum metrology on NASCTN projects using the National Broadband Interoperability Test Bed (NBIT) on the Boulder campus. Additionally, RFT works on spectrum sharing through contributions to the ANSI 63.27 standard and through research on techniques for quantifying the ability of wireless systems to coexist. The NASCTN projects also include independent measurements on the MITRE testbed and there are contributions from numerous other groups including NASA, NTIA and Johns Hopkins Applied Physics Laboratory.⁷

The projects in the context of AWS-3 sharing are very important as they aim to produce tools and methodology for characterizing interference of commercial LTE (long-term evolution [an early 4G protocol]) user equipment (UE) to Aeronautical Mobile Telemetry (AMT) systems and provide confidence to DoD and Commercial Service Providers (CSP) that their radio systems effectively co-exist in the band. This activity has two good projects: (1) Characterizing LTE User Equipment Emissions: Develop method for modeling LTE UE emissions, a component of the DoD aggregate interference model (proposed by the Defense Spectrum Organization [DSO]); and (2) LTE Impacts on AMT (proposed by Edwards Air Force Base).

The newly promulgated rules found in Part 96 of Title 47 of the Code of Federal Regulations (47 CFR Part 96) apply to use of 150 MHz of the 3550-3700 MHz band termed as Citizens Broadband Radio Service (CBRS). This represents significant regulatory policy innovation promoting shared use of valuable radio spectrum. As per these rules, incumbent systems such as naval radars, Fixed Earth Satellite Stations (FSS), government radio sites, and wireless Internet service providers (ISPs) share the spectrum with commercial radio networks. The rules require 3-tier spectrum access priority structure wherein (1) incumbent systems occupy the top tier and have highest priority access, (2) the bottom most tier called Generalized Authorized Access (GAA) provides lowest-priority access without interference protection, whereas (3) a middle tier called Priority Access License (PAL) provides protection from GAA devices. The rules also require a Spectrum Access System (SAS)—a network resident server to manage the

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⁷ Jason Coder, Adam Wunderlich, and Melissa Midzor, NIST CTL, “AWS-3 Spectrum Sharing,” presentation to the panel on June 25, 2019.

sharing in this tiered framework, and Environmental Sensing Capability (ESC)—a network of sensors to detect activity of dynamic incumbent and provide information to SAS for successful incumbent protection.

The development and advancement of CBRS spectrum sharing technologies based on this three-tier architecture has been undertaken in the Spectrum Sharing Committee—a multi-stake holder group consisting of industry and government members in the Wireless Innovation Forum (WinnForum) standards organization. The consensus standards developed in this forum are expected to drive rapid adoption of CBRS spectrum driving new business models and new use cases such as private wireless networks for diverse verticals and enterprises.

Accomplishments

The CTL team members have been valued participants in the WinnForum standardization activities and have made contributions that have had significant impact on standards and component technologies. Their key contributions are in the following areas: (1) development of SAS test procedures for incumbent protection, (2) a “Move List Computation” methodology for assessing and limiting the impact of commercial systems to prospective locations of naval radars in the dynamic protection area (DPA) and development of SAS test procedures—this methodology will be adopted in all commercially operating SAS systems; (3) development of algorithms for selection of installation sites for ESC sensors to provide coverage of DPAs; (4) development of machine learning and statistical processing based algorithms for detection of naval radars in ESC sensors; and (5) extensive collection and analysis of naval radar data under a NASCTN project for characterization of incumbent signals. This work has provided valuable insights to community toward development of ESC sensors and availability of CBRS spectrum when radar is active.

Challenges and Opportunities

With demand for more sub-6 GHz spectrum for 5G networks in the United States continuing unabated, the Federal Communications Commission is considering opening up new bands such as 3.1-3.5 GHz and several new U-NII (unlicensed national information infrastructure) bands in 5.925 to 7.125 GHz range. Many of these spectrum bands have incumbent systems, and simplified spectrum sharing may be employed to accelerate availability of these bands for commercial use. The NIST CTL team has an opportunity to leverage its expertise and experience with CBRS to contribute to the development of solutions for these new bands, balancing the need for incumbent protection and the need for guaranteed spectrum access for commercial networks.

The CTL team might also make contributions to the design of solutions to the problem of coexistence of 5G new radio⁸ in unlicensed bands with other systems such as 802.11ax and WiFi-6.

The CTL team in the NASCTN program and WN Division have delivered exemplary results noted above, with a small staff. However, their activities have been opportunistic and reactive. A more strategic and proactive approach towards spectrum sensing and sharing would enhance the impact of the team in both regulatory actions and industry standardization activities.

The current operating model in NASCTN is to respond to requests for spectrum sensing and characterization from industry or other federal agencies. Given the level of current staffing, this is probably appropriate. In the future, the program could have a much broader impact if it would independently select “hot-button” spectrum issues on which to work and scale-up the number of staff appropriately.

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⁸ “5G New Radio (NR) is the global standard for a unified, more capable 5G wireless air interface” (Qualcomm, 2019, “We’re leading the charge to 5G NR,” https://www.qualcomm.com/invention/5g/5g-nr).

Portfolio of Scientific Expertise

The CTL staff engaged in NASCTN are highly qualified and represent a diverse range of expertise that is essential for this cross-disciplinary effort, including RF hardware design, testing and measurement expertise, spectrum measurements, and data processing and analysis. Their stated role as a neutral and unbiased testing source is adhered to carefully, and they have become a trusted source of information and expertise on spectrum management issues. The accomplishments of the group are especially impressive given their relatively small size—in FY 2019, 3 percent of CTL’s budget authority went to trusted spectrum testing.

Adequacy of Facilities, Equipment, and Human Resources

The review panel toured the anechoic chambers and reverberation chamber utilized by NASCTN, RFT, PSCR, and other NIST laboratories and located in Building 24. Together, these chambers comprise the aforementioned NBIT (see Figure 4.1) and the NIST Antenna and Communication Metrology Laboratory (ACML), which includes the Large Antenna Positioning System and the Configurable Robotic MilliMeter-wave Antenna Facility. The anechoic and reverberation chambers themselves are impressive and can be configured to provide a range of electro-magnetic environments by configuring absorbent and reflective materials as appropriate to the required testing. Staff noted the lack of high-speed data connections from Building 24 to other parts of the NIST-Boulder campus, necessitating that the large data sets generated be carried by hand on portable drives between buildings. In addition, the HVAC system has not been upgraded in some time and does not offer ideal temperature and humidity control.

Dissemination of Outputs

NASCTN has had a significant impact with its report on the effect of LTE deployments on GPS (Global Positioning System) receivers. The team also developed a curated set of LTE uplink waveforms, and made these widely available for use by the community. NASCTN led the effort to characterize the spectrum in the 3.5 GHz band and published the results of these tests widely. Overall, NASCTN has had a significant impact on the community thanks to the wide dissemination of its test results.