A myriad of stakeholders have offered the FCC advice on a notice of proposed rulemaking adopted in October that proposed to free up as much of 1,200 megahertz of spectrum for unlicensed use in the 6 gigahertz band (5.925-7.125 GHz band), with commercial, public safety, critical infrastructure, and scientific incumbents and prospective new entrants disagreeing on whether unlicensed operations can be permitted in the band without causing harmful interference to incumbents.
Incumbents say that if the FCC decides to permit unlicensed use of the band, it should adopt more stringent rules than those supported by unlicensed advocates. There is also disagreement about whether the Commission should permit any licensed use of the 6 GHz band.
“The proposed rules are designed to allow unlicensed devices to operate in the 6 GHz band without interfering with the operation of the licensed services that will continue to use this spectrum. In those portions of the 6 GHz band that are heavily used by point-to-point microwave links [5.925-6.425 GHz and 6.525-6.875 GHz], the Commission proposes to allow unlicensed devices to operate where permitted by an automated frequency coordination system and invites comment as to whether this is necessary for devices operated only indoors,” the agency said in a news release on the item, which was adopted in ET docket 18-295 and GN docket 17-183 (TR Daily, Oct. 23, 2018). “In the other portions of the band [6.425-6.525 GHz and 6.875-7.125 GHz] where licensed mobile services, such as the Broadcast Auxiliary Service and Cable Television Relay Service, operate, the unlicensed devices would be restricted to indoor operations at lower power. These proposed rules will allow a valuable spectrum resource to be more intensively used to benefit consumers while allowing the existing licensed uses of the 6 GHz band to continue uninterrupted.”
In 2017, the Commission adopted a notice of inquiry in its mid-band proceeding that included spectrum in the 3.7-4.2 GHz and 6 GHz bands (TR Daily, Aug. 3, 2017). A number of incumbents expressed concern in response to the NOI that use of the 6 GHz band by unlicensed devices would cause interference to their operations. Some reiterated those concerns in comments on the NPRM, while potential new entrants said the interference concerns were overblown.
In joint comments, Apple, Inc., Broadcom, Inc., Cisco Systems, Inc., Facebook, Inc., Google LLC, Hewlett Packard Enterprise, Intel Corp., Marvell Semiconductor, Inc., Microsoft Corp., Qualcomm, Inc., and Ruckus Networks said, “The Commission’s proposal to open the entire 6 GHz band for unlicensed technologies will expand access to broadband, promote innovation, and spur economic growth — while protecting existing users. The NPRM is a crucial step in making more unlicensed spectrum available to address exploding consumer demand for wireless technologies. The Commission has wisely proposed to make spectrum available under a regulatory structure based on the successful and time-tested Unlicensed National Information Infrastructure (U-NII) rules, while adding an additional set of conservative restrictions that will protect incumbent operations. These proposed rules accomplish this goal by creating different categories of unlicensed devices in four unlicensed 6 GHz sub-bands: 5.925-6.425GHz (U-NII-5); 6.425-6.525 GHz (U-NII-6); 6.525-6.875 GHz (U-NII-7); and 6.875-7.125 GHz (U-NII-8). In these comments, we explain how the Commission can adopt final rules for the band that promote efficient spectrum use, facilitate rapid deployment, and protect incumbent services from interference. Because access to this spectrum is so critical, both to meet growing consumer demand for Wi-Fi and to support other 5G investments, we ask that the Commission move quickly to resolve this proceeding and adopt rules that allow for rapid product deployment to maximize the value of the 6 GHz band for the country.”
The tech companies said that the FCC should “[i]mprove efficiency and intensity of use by permitting unlicensed operations to share the entire 5975-7125 MHz frequency range with incumbents — and reject introducing a new licensed mobile service in any portion of the band, which would displace incumbents.”
The Commission also should “[p]ermit standard-power AFC-controlled devices and LPI [low-power indoor] devices without AFC — while (1) allowing LPI devices to operate in all four sub-bands, (2) adding a 14-dBm very-low-power device class that can operate indoors or outdoors in U-NII-5, U-NII-7, and the bottom 100 megahertz of U-NII-8, (3) authorizing standard-power operations in U-NII-8 on a limited basis, and (4) revising proposed client-device power levels to permit symmetric operation,” according to the filing.
They also called on the FCC to “[a]dopt rigorous but flexible AFC rules that require careful protection of incumbents, while rejecting calls to over-regulate or dictate specific elements of AFC implementation, by permitting (1) portable and in-vehicle operation, (2) flexible geolocation strategies, (3) interference protection calculations that take FS and RLAN device height into account, and (4) operation without professional installation, device registration, ID transmission, or tracking of consumer devices or APs.”
The agency should also “[a]dopt technical rules based on the successful U-NII band, while also (1) adjusting power spectral density and client-device power levels to permit manufacturers to bring the latest wireless innovations to American consumers and (2) supporting WISPs’ efforts in rural communities by permitting greater directional gain for AFC-controlled devices and facilitating P2P and P2MP operations,” the companies added.
The Wi-Fi Alliance agreed “with the Commission’s proposal to divide the 6 GHz band into the U-NII-5 (5.925-6.425 GHz), U-NII-6 (6.425-6.525 GHz), U-NII-7 (6.525-6.875 GHz) and U-NII-8 (6.875-7.125 GHz) sub-bands, based on the characteristics of incumbent services.” It expressed support for regulating “unlicensed use in the 6 GHz band based on a ‘two-class approach,’ which differentiates between low-power, indoor-only (LPI) AP and standard-power AP devices.”
The alliance asked the agency to consider these “adjustments and clarifications” to the proposed rules: (1) “[a]llow LPI AP operations across the entire 6 GHz band, including the U-NII-5 and U-NII-7 bands, without an unnecessary automatic frequency coordination (‘AFC’) requirement for those bands”; (2) “[a]llow standard-power AP operations in U-NII-8 band using AFC technology to avoid transmissions in areas where TV pickup operations are licensed”; (3) “[a]llow client devices that operate under the control of an AP to operate at the same power level as the AP (whether standard-power or LPI)”; (4) “allow operation of fixed point-to-point operations with higher-gain antennas”; and (5) “allow mobile and transportable U-NII operations based on regulatory conditions comparable to LPI U-NII devices (i.e., applying very low power transmit power levels) or by using AFC technology.”
The Dynamic Spectrum Alliance said it “appreciates the Commission’s forward-thinking 6 GHz-band proposal and is eager to work with the Commission to ensure that dynamic spectrum access is a success in the band. The AFC approach the Commission proposes is only the most recent example of use of effective spectrum-sharing technologies to increase access to spectrum, and it is the result of hard work by Commission staff and a wide array of companies dedicated to making the most of the United States’ spectrum resources. DSA encourages the Commission to adopt its proposed framework, and to enact simple, flexible rules to support investment and innovation in the 6 GHz band.”
“The Commission should carefully craft technical rules to facilitate both incumbent and new unlicensed uses of the 6 GHz sub-bands. Protecting incumbents should remain the primary focus, but any new rules should, where possible, be harmonized with technical rules applicable to Unlicensed National Information Infrastructure (U-NII) devices that already operate in the 5 GHz band,” NCTA said.
NCTA said that the FCC should (1) “[p]ermit standard-power access points (APs) in the 5.925-6.425 GHz (U-NII-5) and 6.525-6.875 GHz (U-NII-7) sub-bands to use power levels permitted for unlicensed use in the U-NII-1 and U-NII-3 bands to operate on frequencies determined by an Automated Frequency Coordination (AFC) system;” and (2) “[p]ermit indoor, low-power AP operation in the 6.425-6.525 GHz (U-NII-6) and 6.875-7.125 GHz (U-NII-8) sub-bands using lower, more restricted power levels applicable to operations in the U-NII-2 band, so long as those operations do not cause harmful interference to incumbent users.”
NCTA also called on the Commission to (1) “[a]dopt higher permissible power limits for all client devices across the 6 GHz band;” and (2) “[p]ermit AP operations in the U-NII-5 and U-NII-7 bands under the same conditions as proposed for the U-NII-6 and U-NII-8 bands; i.e., low-power, indoor-only use without the need for authorization from an AFC system.” NCTA added that “[t]echnical analysis on the record suggests that these proposals can likely be adopted while still protecting incumbent operations. However, if additional technical analysis in the record suggests that incumbents would not in fact be protected from harmful interference, in either the near or long term, NCTA would no longer support the adoption of such rules.”
Starry, Inc., said that it “strongly supports the Commission’s quick action to make the 6 GHz band available for unlicensed operation, and largely supports the proposals in the 6 GHz NPRM. We believe that by allowing higher gain antennas and higher power client devices, along with deployment flexibility at any elevation, the Commission can ensure that this band will become part of the critical unlicensed backbone powering the U.S. wireless ecosystem, including for fixed wireless broadband.”
“The Commission should be commended for initiating this proceeding seeking comment on ways that 1200 megahertz of the 6 GHz band can be shared for unlicensed use. In particular, the Commission should make the U-NII-5 and U-NII-7 bands available at higher power to facilitate outdoor use under the control of the AFC and with the technical requirements described above,” said the Wireless Internet Service Providers Association. “With such rules in place, WISPs can take great strides to helping extend broadband access to more rural and unserved areas with less threat of harmful interference, and without causing interference to licensed links. The Commission also should adopt rules enabling lower-power indoor operations across the entire 6 GHz band.”
“As long as valuable incumbent uses are protected, unlicensed use in 6 GHz spectrum holds substantial promise to develop new services and enhance existing ones,” Verizon Communications, Inc., said. “Unlicensed versions of LTE (e.g., LAA, LTE-U, or newer versions) and WiFi will help expand capacity, relieve congestion on licensed wireless networks, and offer new broadband access points. To preserve a dynamic unlicensed ecosystem, any rules governing unlicensed operation in the band must maintain a technology-neutral approach that ensures permission-less innovation subject to compliance with all technical rules. The key to promoting unlicensed use in the 6 GHz band is a sharing model that protects incumbents through a cloud-based, IP-connected Automated Frequency Coordination (‘AFC’) manager. Unlike traditional unlicensed approaches that involve free-standing unmanaged devices, the AFC should use a ‘closed loop’ network framework that positively controls unlicensed radio access to the band and thereby protects incumbent operations. Active AFC management of unlicensed access points will enable greater security and protection and, in turn, allow for higher powered unlicensed use.”
“In principle we support the Commission’s approach to merge licensed and unlicensed services. If this can be successfully implemented, it will usher in a new, highly efficient, approach to frequency management. As expected, however, the devil is lurking in the details,” said the National Spectrum Management Association. “Given this new approach is unproven, we should proceed cautiously. A key component of the process will be the AFC function. The authorized agencies must meet the needs of all parties but be limited in number to avoid difficulty in determining the responsible agency for problem resolution. Another key component is a technical organization with extensive technical oversight and authority. An independent industry organization which is responsive to the needs of all interested parties should be used to develop the myriad of details needed to successfully implement these proposals. Among these would be the development of an appropriate path attenuation model adequate to protect licensed users. The organization’s responsibility should extend several years into the implementation phase. This organization should be allowed to develop technical details acceptable to operators and service providers and periodically report progress to the Commission.”
NSMA said that it “is one of a few organizations qualified to participate in this function. Field trials, monitored by all interested parties, should precede large scale implementation. The field trials should be based upon substantial agreement among all users. Large scale deployment should not begin until the field trials have been successfully completed to the substantial satisfaction of all parties.”
The 5G Automotive Association said it “supports the Commission’s efforts in these proceedings to identify new opportunities for unlicensed use in the 6 GHz band, and believes that the 6 GHz band – and not the 5.9 GHz band – represents the best opportunity for providing for more spectrum for unlicensed uses. However, without proper safeguards in place, out-of-band emissions (‘OOBE’) from secondary 6 GHz unlicensed operations will degrade primary licensed vehicle safety communications operations in the 5.9 GHz band. To prevent such an outcome, the Commission should adopt the protection criteria proposed by 5GAA herein.”
Motorola Solutions, Inc., said it “believes that the 6 GHz band has the potential to support a wide range of new and innovative applications. Therefore, MSI generally supports the Commission’s pursuit of a carefully crafted spectrum sharing approach that will accomplish the goal of expanded use of the 6 GHz band by secondary devices while providing sufficient protection for existing and future incumbent operations. As a critical component of this approach, MSI supports employing cloud-based AFC mechanisms that will allow rapid and uniform updates to incumbent protection information. MSI strongly believes that a carefully selected interference-to-noise (I/N) protection ratio is essential and recommends that the ratio for protecting critical incumbent links be set no higher than -12 dB I/N levels. Finally, the Commission should take several steps to enable the efficient and safe use of this band including by requiring AFC functions to record the operational frequencies and identifiers of authorized unlicensed devices operating in the band, and providing a mechanism for timely remediation of interference events.”
The Boeing Co. said it “supports the identification of additional spectrum resources in the 6 GHz band for [use] by unlicensed systems and devices. To ensure that this unlicensed spectrum is used for the greatest benefit, the Commission should refrain from imposing operating restrictions that are unnecessary to prevent harmful interference. Specifically, the Commission should permit all 6 GHz unlicensed devices to be used indoors without AFC control. The Commission should treat the inside of aircraft as indoor spaces for purposes of these rules and the Commission should permit the use of 6 GHz unlicensed spectrum for transmissions involving aircraft parked at airport facilities. Each of these measures will expand the use of unlicensed spectrum in the 6 GHz band without resulting in harmful interference to incumbent services. At the same time, the Commission should strive to ensure that the proposed additional unlicensed uses of the 6 GHz band do not prevent the continued operation of UWB devices that are also authorized in this spectrum.”
In joint comments, Intelsat License LLC and SES Americom, Inc., said they support the FCC’s “commitment that rules allowing new unlicensed use of the 5.925-7.125 GHz (‘6 GHz’) band will be designed to ensure that licensed services operating in the band, such as the Fixed-Satellite Service (‘FSS’), continue to thrive. To adequately protect critical FSS systems, the Commission must take steps to prevent unlicensed devices in the 6 GHz band from causing harmful interference into licensed FSS uplinks in the band. Only by adopting a limit on the aggregate power at the satellite receiver and employing a robust automated frequency coordination (‘AFC’) system to implement that limit can the Commission successfully make 6 GHz spectrum available to unlicensed devices while protecting licensed conventional and extended C-band FSS operations from harmful interference.”
“The Commission should apply current – and increasingly stringent – national, state and local building codes for new homes when calculating outdoor emissions from indoor devices using all of the unlicensed 6 GHz band,” said Leading Builders of America. “The ITU reports cited by the Commission in the Notice identified building elements that impact building entry loss, including materials used in siding, roofing, flooring, walls, insulation, and window elements. Contemporary building codes result in ever-increasing use of materials the ITU found to increase building entry loss. The Commission should consider these factors when calculating building entry loss due to unlicensed spectrum use throughout the 6 GHz band.”
Comsearch said it “supports efforts to create opportunities for unlicensed use of the 6 GHz band so long as there are adequate protections for incumbent users that allows for continuous interference free operation and growth for the many important services that rely on Part 101 microwave services. In support of such goals, the Commission should make sure that all unlicensed 6 GHz devices (both low-power indoors and outdoors) use a frequency coordination system, that the coordination system must be designed to effectively avoid interference with the primary microwave service licensees, and that no burden of interference avoidance or after-the-fact mitigation be placed on the incumbent point-to-point microwave users. Finally, it is critical that the coordination system must utilize an accurate and frequently updated database. … With respect to the proposed Automated Frequency Coordination (‘AFC’) system, Comsearch agrees with the Commission’s proposal that the AFC system should serve as the repository for unlicensed device registration data in the 6 GHz band and that AFC operators should maintain exclusion zones protecting incumbent microwave operations pursuant to the propagation modeling and IPC methodologies eventually adopted by the Commission. With respect to the AFC testing and certification process, Comsearch urges the Commission to seek separate comment via public notice after finalizing the rules for unlicensed 6 GHz operation, but anticipates that a happy medium can be struck between the relatively informal process used in the TV White Space context and the more elaborate requirements governing the CBRS band.”
Cambium Networks Ltd. applauded “the Commission for inviting public inquiry on these matters and for recognizing the vital importance of unlicensed spectrum in the broadband ecosystem. Cambium concurs in the need for more spectrum for unlicensed use in the 6 GHz band and in the potential utility of AFC for managing spectral interference and for protecting incumbent uses in the band. That said, higher power limits for outdoor use and the authorization of higher-power client devices, subject to appropriate operating conditions and managed via AFC, are necessary for these bands to more fully advance the Commission’s objectives and the public interest. For these reasons, Cambium encourages the FCC to adopt the proposals set forth herein.”
Federated Wireless, Inc., encouraged “the Commission to act expeditiously to make the 6 GHz band available for unlicensed use as broadly as possible and leverage the lessons learned in implementing other sharing regimes to ensure that the AFC system in the 6 GHz band best meets the present and future needs of incumbents and newly authorized unlicensed users. To these ends, the FCC should adopt rules that (A) reflect the characteristics of the band and its users in order to best enable the AFC systems to protect incumbent operations, (B) leverage the capabilities of the cloud to optimize the functionality of AFC systems and simplify the development and deployment of unlicensed devices, (C) leverage industry incentives to create a successful sharing regime by empowering multi-stakeholder bodies to develop consensus standards that foster the development of new services and protect incumbent operations, and (D) promote competition and innovation among AFC system operators.”
A group of public interest organizations (PIOs) endorsed “the Commission‘s proposal to allow low power, indoor-only operations on an unlicensed basis in the U-NII-6 and U-NII-8 bands. The PIOs urge the Commission to likewise authorize low power, indoor-only unlicensed use across the U-NII-5 and U-NII-7 band segments without the cost and complexity of AFC coordination. The overwhelming majority of consumer welfare and economic value generated by unlicensed spectrum – and particularly by Wi-Fi – is indoors, in homes and businesses literally walled off from incumbent receivers in the U-NII-5 and U-NII-7 band segments. Although expensive, professionally-installed, higher-power and AFC-controlled unlicensed access is important for enterprise and outdoor deployments, the failure to set a power level at which Wi-Fi can operate indoors across the entire 6 GHz band, using off-the-shelf routers and low-cost devices, will sacrifice what is likely to be the greatest benefit of this rulemaking. Without affordable, do-it-yourself access to the 850 megahertz in U-NII-5 and U-NII-7, a majority of homes and small businesses in particular will likely be limited to a single 160 megahertz channel between 6.875 and 7.125 GHz (U-NII-8 segment).”
The filing added, “There are at least three reasons the PIOs believe the Commission can adopt a rebuttable presumption that low-power, indoor-only unlicensed access to the U-NII-5 and U-NII-7 band segments does not create an undue risk of harmful interference to incumbents: First, harmful interference from low power, indoor-only RLANs into FS receivers would be extremely rare even without frequency coordination by an AFC. The two operate in entirely different locations and with transmit characteristics that are complementary. Second, the record demonstrates that FS links are high power and use high-quality, highly-directional antenna, whereas indoor home Wi-Fi and other unlicensed devices operate at very low duty cycles with low EIRP. Third, moving Wi-Fi and other unlicensed traffic onto networks required to be low power and indoors could reduce the overall risk of interference to FS incumbents. The less obvious reason is that by making 1,200 contiguous megahertz available inside every building, unlicensed routers and other devices will spread their transmissions over multiple and much wider channels.”
The PIOs urged the FCC “to adopt rules for outdoor, AFC-controlled fixed wireless deployments that are harmonized with Part 15 rules allowing higher gain antennas in the 5 GHz bands currently in use for rural broadband, enabling higher EIRP operations that cover larger areas more affordably. Equipment already widely deployed in the 5 GHz band is easily adaptable to operate in the 6 GHz band. Further, although rural broadband deployment would be a primary beneficiary of a rule permitting higher-power operations, the Commission should not impose any limitation that would prevent higher-power operations from being used wherever the AFC authorizes interference-free access. We also suggest the Commission open more contiguous bandwidth for fixed wireless providers by authorizing AFC-controlled use of those portions of the U-NII-8 segment that are not currently populated by BAS operations. The PIOs concur that in this band Automated Frequency Control (AFC) systems can be relatively simple databases that are easy to implement. AFC is well-established and reliable in bands, such as U-NII-5 and U-NII-7, where incumbent operations are geographically fixed, technically well-characterized, and change location or operating parameters infrequently. We recommend that the Commission adopt a flexible approach that allows both centralized and decentralized models for device and end-user coordination. The Commission should also give all certified AFC systems the flexibility to incorporate real-world GIS data (e.g., terrain, clutter, building heights) and a range of advanced propagation models that facilitate both a more intensive use of the band and a more precise protection of incumbent operations. Variation among AFC operators is positive for innovation and to encourage a diversity of use cases and service tiers. Cost recovery for AFC operators should be a given; but the Commission should also strive to minimize transaction costs, or arrangements that exclude or deter ordinary consumers.”
Signing onto the filing were the New America Foundation’s Open Technology Institute, the American Library Association, the Consumer Federation of America, the Consortium for School Networking, Public Knowledge, and Access Humboldt.
“In the 6 GHz band covering 1.2 gigahertz of spectrum, there are both existing services with important incumbent operations and promise for new, highly valued services – unlicensed and licensed,” CTIA said. “CTIA therefore urges the Commission to revisit the approach to the 6 GHz band proposed in the NPRM and pursue a framework that balances multiple interests: protecting incumbent operations, devising a robust regime that will enable new unlicensed opportunities, and repurposing spectrum for exclusive use, flexible rights licensed stakeholders.”
“First, the Commission should promptly issue a further notice of proposed rulemaking to repurpose the upper portion of the 6 GHz band for exclusive use, flexible rights licensing,” CTIA suggested. “It should assign the repurposed spectrum by auction and require winning bidders to relocate point-to-point fixed service and electronic news gathering incumbents pursuant to the framework adopted in the Emerging Technologies proceeding, while ensuring that fixed satellite service operations are accommodated. The Commission should also work with the National Telecommunications and Information Administration (‘NTIA’) to add a non-federal allocation to a portion of the 7.125-8.4 GHz band to expand opportunities for fixed service relocation and enhance the efficient use of spectrum in that band. The Commission can and should ensure that such actions do not inhibit or delay access to the lower portion of the 6 GHz band for unlicensed services.
“Second, the Commission should adopt a spectrum sharing regime for unlicensed operations in the lower portion of the 6 GHz band by implementing a rigorous interference protection framework that permits unlicensed use while fully protecting incumbent operations,” CTIA added. “The Commission can take this action even as the further notice is pending, so as not to delay the introduction of a spectrum sharing regime in the lower portion of the band. CTIA supports adoption of an Automated Frequency Control (‘AFC’) framework that serves as a positive control mechanism to authorize unlicensed access point operations, both outdoor and indoor, with robust security requirements to ensure operations comply with the AFC. The rules for unlicensed operations in the 6 GHz band should continue to be technologically neutral and avoid technical restrictions or requirements that favor one unlicensed technology over another.”
“Given the present state of the record, AT&T remains highly doubtful that unlicensed uses could … harmlessly coexist with the critical licensed uses in the 6 GHz band,” said AT&T, Inc., which noted that it relies on 6 GHz microwave links to connect cell sites. “These essential services operate, by necessity, with a miniscule margin for error and are therefore highly vulnerable to harmful interference. Those seeking to introduce potentially disruptive, unlicensed uses into the 6 GHz band (‘RLAN advocates’) should therefore bear the burden of demonstrating, by clear and convincing evidence, that the proposed uses would cause no harmful interference.
“A review of the underlying NOI record demonstrates, however, that RLAN advocates have failed thus far to meet their high burden of proof. Indeed, RLAN advocates have derived their interference and margin analysis from a single RKF study that was prepared at the behest of RLAN advocates,” AT&T added. “Yet, this RKF study has drawn significant criticism regarding its methodology, assumptions, conclusions, and completeness. Accordingly, before adopting any rule allowing unlicensed use in the 6 GHz band, the Commission must insist that the record contain comprehensive and expertly crafted analyses detailing whether and what robust and near-perfect protections for preexisting licensed operations could be implemented to protect incumbent users. The Commission’s proposed AFC system must be just the beginning of an ongoing dialog among stakeholders.”
Ericsson said the Commission should “revisit its approach to the 6 GHz band and reiterates key points it raised in comments on the Commission’s Notice of Inquiry in GN Docket No. 17-183. In particular, the Commission should take the following actions: 1) Pursue unlicensed opportunities in the 5.925-6.425 GHz with an emphasis on rules that render the band neutral to choice of technology; 2) Explore the introduction of new licensed opportunities in the 6.425-7.125 GHz bands; 3) Ensure that incumbent operations are protected from harmful interference or accommodated; and 4) Examine whether to transition the 7.125-8.5 GHz band from an exclusive federal band to a shared one.”
Ericsson added that its “support for unlicensed use at 5.925-6.425 GHz is premised on Commission adoption of an automated frequency control (‘AFC’) regime that adequately protects incumbent fixed service (‘FS’) licensees from harmful interference. The AFC should serve as a positive controller with regard to unlicensed operations in the band. Each FS incumbent licensee should be protected by an exclusion zone determined by the individual FS receive antenna pattern, path loss and the equivalent isotropically radiated power (‘EIRP’) of the unlicensed device. In addition, it is critically important that unlicensed use of the 5.925-6.425 GHz band be technologically neutral. That is, the spectrum should not be a ‘Wi-Fi only’ band but should be available for any air interface technology, including LAA, LTE and NR-U.”
Nokia submitted with its comments a technical study that it said “demonstrates that FS operations can be disrupted not only from proposed outdoor unlicensed operations but also from indoor unlicensed operations. Based on the findings of our study, Nokia recommends that unlicensed access – both indoor and outdoor – be governed by an Automatic Frequency Coordination System (AFC) for the sub-bands most heavily used by fixed links, i.e., 5.925-6.425 GHz (U-NII-5) and 6.525-6.875 GHz (U-NII-7). For the 6.425-6.525 GHz (U-NII-6) and 6.875-7.125 GHz (U-NII-8) sub-bands which have no, or a very limited number of fixed links but have mobile services, restricting the U-NII devices to indoor low power use without an AFC system is acceptable. However, Nokia recommends studying if high power operation in U-NII-6 and U-NII-8 is also feasible via an AFC system.”
“This is the Commission’s first attempt at introducing very large numbers of unlicensed devices into a band whose services maintain the safety of life and property. We urge the Commission to proceed cautiously, and to resolve reasonable doubts in favor of protecting fixed Links,” said the Fixed Wireless Communications Coalition, citing the 96,604 FS links in the 6 GHz band.
“A study in the record, submitted by RLAN proponents, underestimates interference into the FS by using the shortcut of statistical modeling,” FWCC said. “The approach uses a computer program that populates an area with virtual FS receivers. It scatters RLANs at random, under some assumed distribution of locations and powers. The program tests to see how much RLAN/FS interference occurs. It then re-scatters the RLANs and tests again. Running a large number of such cases yields an overall estimated average probability of RLANs causing interference to FS receivers. Those estimates, unsurprisingly, depend on the assumed numbers: likely locations of RLANs, distributions of RLAN power levels, expected propagation losses, and so forth.”
“We see only one method of reliably preventing RLANs from interfering with FS receivers: (1) map out the three-dimensional “exclusion zone” around each FS receive antenna within which an RLAN could cause interference; (2) determine whether each RLAN that seeks to transmit is within one or more of those zones; (3) if so, use local propagation data to assess whether the RLAN signal threatens interference to an FS receiver; and (4) if so, prohibit the RLAN from operating on interfering frequencies,” FWCC added.
“Given the history of automated or dynamic spectrum sharing in TV whitespaces, interference that has occurred from unlicensed device operation in the 5 GHz band, and nascent sharing at 3.5 GHz through a spectrum access system and environmental sensing capability, NPSTC seriously questions whether unlicensed sharing in the critical 6 GHz band is sound spectrum policy,” said the National Public Safety Telecommunications Council. “However, given the Commission’s apparent interest in such sharing, NPSTC provides specific recommendations to help protect critical fixed microwave links in the band.
“NPSTC supports a centralized dynamic spectrum access approach incorporating important details as spelled out in these comments to protect both current and future fixed microwave links. Such a centralized approach with appropriate algorithms, protocols and up-to-date information on authorized microwave links is an essential part of the protection the Commission has promised. In addition, these comments address steps that need to be taken in testing, equipment authorization, and enforcement to help ensure proper protection to microwave links, and expeditious resolution of any interference problems that do occur.”
NPSTC added that maintaining the necessary levels of reliability for public safety links “is accomplished through link designs with requisite levels of fade margin. Contrary to the Commission’s proposal, such fade margins must not be eroded through the deployment of unlicensed devices.”
The Association of Public-Safety Communications Officials-International said it “understands the interest in expanding opportunities for unlicensed spectrum, but it is critical that both current and future public safety operations in the 6 GHz band remain reliable and free from interference. APCO is concerned that the proposed unlicensed use in the 6 GHz band will cause harmful interference to public safety operations. Spectrum bands housing public safety operations are not the appropriate arena to deploy new, unproven spectrum sharing and frequency coordination methods. Should the Commission proceed, it must substantially revise its proposal and ensure effective mechanisms are in place to mitigate potential interference and rapidly resolve any interference should it occur.”
APCO said that the FCC “must ensure that any Automated Frequency Coordination (AFC) system implemented is designed to protect new and existing public safety licensees from interference. This includes: limiting standard-power access point operation to a list of permissible frequencies provided by the AFC system; requiring access points to periodically verify whether frequency availability has changed, and to cease operation if a verification cannot be obtained or a channel is no longer available; and requiring device registration in the AFC database. The Commission should also prohibit client devices from transmitting in the 6 GHz band unless a device is actively associated with an access point that has verified permissible channels with the AFC system.”
APCO continued, “Entities interested in becoming AFC system operators should be required to submit a proposal to the Commission that includes a description of how the database will be designed, including security measures, and measures that will be taken to prevent and quickly resolve reports of potential interference. Further, APCO urges the Commission to take steps that will help to protect incumbents from interference such as adopting an interference protection criteria of no worse than an interference to noise ratio of -6 dB, and protecting fixed links operating on adjacent and second-adjacent channels. APCO opposes allowing the operation of low-power indoor access points that are not subject to a frequency coordination system in the 6 GHz band. Such unlicensed uses are likely to cause interference to public safety communications. Restricting low-power access points to indoor use would be difficult, if not impossible. Even if an indoor-only limitation could be enforced, differences in building construction make it impractical to draw assumptions for signal attenuation. Additionally, expanding unlicensed use as the Commission contemplates would make it difficult to determine the source of interference and whether the AFC system is working as planned.”
In joint comments, Los Angeles County, Calif.; the city and county of Denver, Colo.; the city of Kansas City, Mo.; Ozaukee County, Wis.; San Bernardino County, Calif.; the Regional Wireless Cooperative in the Phoenix area; and the Government Wireless Technology & Communications Association said they “are adamantly opposed to any ‘sharing’ of the 6 GHz band in which their microwave links exist. The risk to public safety is simply too great. While the Commission recognizes in paragraph 9 of the NPRM that these public safety links exist, the NPRM is devoid of any meaningful recognition of efforts, costs and consequences of interference to public safety operations.”
The entities added that they “appreciate that Automated Frequency Coordination (‘AFC’) systems create the potential for increased spectrum sharing. However, public safety should not be the innovation guinea pig. Interference from mobile devices is notoriously difficult to locate for mitigation and increasing the opportunities for mobile interference within the band is an unnecessarily high risk when balanced against the need to stream the next viral video. The Commission has only recently adopted final rules for the Citizens Broadband Radio Service (‘CBRS’). Expansion of that system is premature, at best, particularly when the expansion is to include public safety spectrum. However, should the Commission chose to go forward and place public safety systems at risk, there must be the ability to render interfering units inoperable. … The Commission has also failed to address the increased costs to public safety from having a new interference source to monitor. By way of reference, 800 MHz post-rebanding interference mitigation has cost the City of Oakland over a half million dollars. Unfortunately, Oakland is not alone in encountering such interference, post-rebanding.”
The city of Los Angeles said it “makes substantial use of the 6 GHz band, and has serious concerns about the harm that could arise from any interference with the Band’s vital public safety, utility monitoring, and infrastructure operations uses in and around the City of Los Angeles. The City relies on its more than one hundred and forty (140) 6 GHz microwave links to support: public safety and utility communications, emergency response, and critical infrastructure monitoring and management for one of the nation’s largest cities, and the country’s largest municipal utility. Any final sharing plan must ensure complete protection for incumbents, and address in detail: the Commission’s criteria for AFC operators; responsibility for harm caused by interference; and specific technical measures intended to prevent any interference with mission-critical public safety and critical infrastructure systems. The City hopes to ultimately be in a position to support a consensus sharing plan developed over the course of this proceeding, but such an outcome is only possible if any such plan preserves and protects existing essential public safety and utility communications operations.”
New York City urged “the Commission to take all necessary steps to protect incumbent 6GHz licensees, including the establishment of an accurate AFC database, updated daily and queried prior to device activation. The City urges the Commission to incorporate adjacent channel and second adjacent channel interference protection analysis into any AFC system it proposes. The City urges the Commission to require newly authorized unlicensed 6GHz access points to be location aware devices required to register with, and receive authorization from, the AFC prior to being placed into operation. The City urges the Commission to take swift enforcement action when appropriate, to ensure that interference to incumbent licensees does not occur.”
In joint comments, the Utilities Technology Council, the Edison Electric Institute, the American Public Power Association, the National Rural Electric Cooperative Association, the American Petroleum Institute, and the American Water Works Association argued that the FCC “should not allow unlicensed operations in the 6 GHz band because the potential for interference is unreasonably high and therefore likely to present significant adverse impact to critical infrastructure communications that would put at risk the safety of life, health and property that incumbent licensees help to protect. The 6 GHz band is uniquely suited to supporting highly reliable communications and therefore is already heavily used by electric, oil, natural gas, and water companies for mission critical operations. Moreover, these entities and other critical infrastructure industries (‘CII’) lack reasonable alternatives to the 6 GHz band, while there are other spectrum bands that could be opened to support the unlicensed operations envisioned by the FCC that would not raise the same likelihood of interference nor the unnecessary risk to critical infrastructure. Any benefit from the expansion of unlicensed operations in the 6 GHz band is outweighed by risking interference to mission-critical communications and therefore is not in the public interest.”
The groups added, “There are numerous reasons why the potential for interference cannot be sufficiently mitigated by an automated frequency coordination (‘AFC’) approach, as proposed by the FCC. AFC is a purely conceptual approach that has not been proven to perform as promised. The proposed AFC system is based upon false assumptions and inaccurate data about incumbent microwave systems in the band; and it does not account for sources of passive reflection and multipath fading that can increase the potential for interference. The FCC’s AFC proposal fails to account for the fact that similar spectrum sharing approaches have experienced performance flaws that have led to interference in other bands. Given that similar failures will occur with the proposed AFC approach, if the FCC goes forward with expanded unlicensed operations in the 6 GHz band, there must be a plan to address interference when the AFC system fails. Additionally, interference from unlicensed operations is expected to be intermittent, which will make it more difficult to trace and mitigate against. Moreover, it is unclear whether AFC will be centralized and whether the FCC will provide the enforcement mechanisms needed to enable incumbent licensees to remedy interference that is caused by unlicensed operations.”
The groups said that if the FCC “opens the 6 GHz band for unlicensed operations, it is critical that its rules will prevent interference a priori rather than rely on post hoc remedies that will be far too little too late to correct the consequences of interference to mission-critical communications microwave systems in the band. The Commission should require unlicensed operations to comply with prior coordination, which has proven to be effective at avoiding interference and has maximized the effective use of the band by microwave systems. Alternatively, the Commission must correct the underlying flaws in the AFC system, require AFC operators to be certified to comply with the FCC rules, and require unlicensed operators to register devices and provide identifying information to enable incumbent licensees to investigate interference and mitigate against it. To mitigate against interference, the Commission must also ensure that its rules protect incumbent operations against co-channel and adjacent channel interference from both indoor and outdoor unlicensed operations.”
The Critical Infrastructure Coalition said it “understands that the Commission intends to make new frequency bands available for wireless broadband services, but it should not do so at the expense of the nation’s critical infrastructure networks. The FCC’s proposed rule changes pose a threat not only to the Coalition’s private 6 GHz networks, but also to the common carrier networks that many Coalition members rely on to supplement internal operations. Outages to the Coalition’s existing 6 GHz systems are rare. Any rule changes proposed by the FCC should ensure this does not change. The FCC should adopt rules which prevent unlicensed users in the band from even slightly increasing the incidence of those outages. The Coalition agrees with the Fixed Wireless Communications Coalition (‘FWCC’) that the Commission should adopt rules which limit additional outages caused by unlicensed users in the band to no more than 3 seconds per year per incumbent fixed licensee receiver.”
The Association of American Railroads said, “Introduction of unlicensed services into the 5.925-7.125 GHz band (‘6 GHz band’) will create an intolerable risk of interference to incumbent communications systems, which relay mission-critical information for railway operations, other critical infrastructure industries, and public safety operators. The AAR recommends that the Commission reconsider allocating any portion of the 6 GHz band for unlicensed operations. If the Commission nonetheless proceeds with its proposal, these comments provide a number of prophylactic and mitigation measures to better protect incumbent licensed operations and the public interest.”
The filing said that if the FCC authorizes unlicensed operations, it should (1) “[p]roperly define exclusion zones using the free space path model and actual elevation (or, in the absence of actual elevation, worst-case elevation);” (2) “[p]rohibit co-channel, first adjacent channel, and second adjacent channel operations within the defined exclusion zones of any fixed link;” (3) “[i]mplement an Automated Frequency Coordination (‘AFC’) system that is centralized, relies on an accurate database, controls all unlicensed devices (whether indoors or outdoors), and establishes an initial connection with the unlicensed device in a band other than the 6 GHz band;” (4) “[r]equire unlicensed devices to determine their location via GPS and prohibit manual entry of a location by the device user;” (5) “[e]stablish protection criteria as an interference-to-noise power ratio (‘I/N ratio’) of -6 dB;” (6) “[l]imit the initial deployment of unlicensed devices;” and (7) “[i]mplement an interference resolution process that expeditiously resolves interference issues.”
RigNet Satcom, Inc., said “that opening the 6 GHz band to unlicensed use in the Gulf of Mexico would create an unreasonable risk of interference to existing critical communications systems. Therefore, RigNet urges the Federal Communications Commission (‘FCC’) to exclude the Gulf of Mexico from any expanded unlicensed use of 6 GHz. RigNet further urges the FCC to provide greater protections for backhaul systems used to carry traffic from the Gulf of Mexico through the 12-mile coastal zone and onto the beach.”
The Ultra Wide Band Alliance said, “The current proposed rules raise serious concerns that operation under the proposed rules may cause much more interference than anticipated with consumer, commercial, medical, and scientific applications in the 6 GHz spectrum. The rules seem tailored for the WLAN architecture and technologies specifically, and disadvantage other established technologies that currently utilize the subject bands providing proven coexistence with other spectrum users. These other users include both licensed and unlicensed users such as those complying with IEEE 802.15.4 standards established as far back a 2007. The conclusion by the Commission that such WLAN operation will not harm incumbent users – both licensed and licensed exempt – depend on assumptions that are not captured in the proposed rules. Our goal is mutual coexistence, to achieve the greatest possible value from the spectrum.”
The alliance suggested “changes to the proposed rules which will promote more efficient and effective use of the spectrum. Our suggestions satisfy the need for greater WLAN access while also promoting sharing of the spectrum with other equally important and valuable uses. We have focused on methods that benefit all users, including WLAN. Specifically we are asking the Commission to consider modifying the proposed rules as follows for all applications of the proposed rules: 1. Authorize new unlicensed broadband at the proposed standard power levels only in the sub-band 5.925 – 6.1 GHz (the lower 175 MHz of the proposed U-NII-5 band), and 2. Specify out of band emissions not to exceed -61 dBm/MHz; OR 1. Include maximum transmit duty cycle requirements for use of standard-power operation, and 2. Specify lower power levels for the remainder of the band (6.1 to 7.125 GHz).”
The National Association of Broadcasters said it “supports the Commission’s efforts to expand opportunities for spectrum use, including expanded opportunities for unlicensed use of the 6 GHz band. At the same time, broadcasters rely on important broadcast auxiliary services (BAS) operations in the 6425-6525 MHz (U-NII-6) and 6875-7125 MHz (U-NII-8) to cover major events. There are no ready substitutes available for this spectrum. Further, the proposals the Commission sets forth to protect these broadcast operations, such as limiting unlicensed use to low-power, indoor operation, will not protect these operations and will result in harmful interference. Mobile and low-power BAS operations in these bands will be particularly vulnerable to interference from unlicensed users.
“Accordingly, NAB urges the Commission not to permit unlicensed operations in the U-NII-6 and U-NII-8 bands unless a robust, reliable mechanism is developed to coordinate these operations with licensed BAS uses – including mobile uses,” the filing added. “The Commission can still consider making hundreds of megahertz of spectrum available for unlicensed operations in the U-NII-5 and U-NII-7 bands while preserving important broadcast operations in the U-NII-6 and U-NII-8 bands that consumers rely on today. If technical solutions develop that can reliably protect operations in the U-NII-6 and U-NII-8 bands, the Commission can consider additional unlicensed opportunities in those bands at a later date and in a separate proceeding.”
Engineers for the Integrity of Broadcast Auxiliary Services Spectrum (EIBASS) said it “continues to believe that this proposal is not a rational, feasible or compatible sharing of the 6.5 and 7 GHz TV BAS bands, and as proposed in the NPRM will result in chronic and difficult to locate intermittent interference. But, realizing that Congress has given the Commission its marching orders, regardless of the laws of Physics and reasonable and prudent spectrum management, EIBASS asks that the operational areas of 6.5 GHz and 7 GHz TV Pickup stations be protected (i.e., excluded), and that extraordinarily stringent steps be taken to ensure that U-NII-6 and U-NII-8 devices cannot be easily hacked to defeat their interference protection features.”
Sirius XM Radio, Inc., urged the FCC “to ensure that introduction of unlicensed devices in the 5.925-7.125 GHz (‘6 GHz’) band will not come at the expense of existing licensees that supply essential and desired communications services. Sirius XM requires ongoing, reliable access to 6 GHz frequencies in order to operate its business, since the only spectrum it can use for SDARS [satellite digital audio radio service] feeder links lies in the range that the Notice proposes for sharing with unlicensed devices, designated as the ‘U-NII-8’ band. Sirius XM also receives third party programming via conventional C-band satellites that use uplink spectrum in the ‘U-NII-5’ band and will rely on a portion of that band for telemetry, tracking and command during the phase following launch of its next-generation satellites.”
“Because SDARS spacecraft receive beams are extremely large, transmissions from devices anywhere in the contiguous U.S. would contribute to the aggregate interference reaching listeners’ satellite antennas. Moreover, unlicensed operations historically have proven to be very difficult for the Commission to police once devices are in the hands of consumers, providing further incentive for the Commission to exercise extreme caution before allowing consumer devices to use these bands,” Sirius XM added. “To maintain the integrity of SDARS feeder links, the Commission must adopt and enforce the power limits and indoor-only restriction that the Notice proposed for the U-NII-8 frequencies. The Commission must prohibit deployment in vehicles or on drones, and users must be fully advised of these policies. To reinforce the ban on outdoor use, the Commission should require devices to incorporate a cut-off based on GPS signal detection. In addition to these measures designed to prevent harmful aggregate interference, the Commission should adopt a backstop approach whereby further manufacture and sale of U-NII-8 band devices would be banned if the interference-to-noise ratio at any of the SDARS satellite receivers reaches -23 dB. Imposing this limit should not affect the legitimate interests of unlicensed device proponents, which have assured the Commission that such devices will not be deployed in numbers sufficient to trigger harmful interference to satellite reception.”
Sirius XM continued, “In the U-NII-5 band, the Commission should set limits on device pointing towards the geostationary arc and impose power constraints to protect satellite uplink operations. A backstop approach should be used in this band as well to address the potential for harmful aggregate interference. The Notice proposes to employ automated frequency coordination in this segment of the 6 GHz band, and coordinators should cease authorizing use of any frequency channel in which the protection threshold has been reached.”
“Opening up the 6 GHz band to unlicensed use can help address this growing need and alleviate congestion,” said GE Healthcare. “Not all healthcare applications require the same protection from interference as licensed healthcare services such as WMTS [wireless medical telemetry service]. These other applications can offer substantial efficiency gains for healthcare providers and improve patient experiences while operating on unlicensed spectrum. Meanwhile, mid-band spectrum is a ‘sweet spot’ for healthcare applications with greater throughput demands, such as high-resolution imaging transfers, because the frequencies at that range are low enough to cover large areas but offer greater bandwidth to support high-capacity services. By opening up the 6 GHz band for unlicensed use, the Commission can help ensure that these next-generation healthcare applications have the capacity and throughput necessary to reach their full potential.”
The National Academy of Sciences, through its Committee on Radio Frequencies (CORF), filed comments addressing “concerns regarding potential interference to protected passive scientific observations at 6-7 GHz” and making recommendations to protect these operations. For example, it said, “the Commission should include the locations of certain RAS [radio astronomy service] observatories in its proposed Automated Frequency Control (AFC) regime, and AFC should be set up to require unlicensed devices to avoid transmission between 6650.0 and 6675.2 MHz within a certain radius of those observatories.”- Paul Kirby’