Key Policy Considerations in Fashioning Indoor-Only Use Rights

Authorizing indoor-only access to frequency bands already in use by one or more incumbent services, whether federal or non-federal, involves weighing a variety of factors, some band-specific and some more generic. The Federal Communications Commission’s authorization of unlicensed indoor-only (LPI) device use across the entire 1,200 megahertz of the 6 GHz band included both types of considerations. For example, while the signal attenuation of the typical structure is generic (and the FCC used a conservative International Telecommunication Union, or ITU, value for building entry loss, or BEL), the FCC also set the maximum power level based on the outdoor signal threshold that the most vulnerable incumbents reported needing to protect the performance of fixed microwave links at a “five 9s” (99.999 percent) level of reliability. In contrast, the form factor restrictions imposed on LPI access points (e.g., no battery operation or no weatherized containment) are more generic in the sense that they will quite possibly characterize future indoor-only authorizations in any band since what’s most crucial is ensuring the transmitting devices only operate indoors.

Frequency bands that can accommodate additional uses indoors without undue risk of harmful interference to band incumbents offer the equivalent of a spectrum ‘free lunch’ that can potentially spur innovation and meet the rapidly growing demands of venues and enterprises for direct access and control of wireless bandwidth. Most recently, in its proposal to revisit the concept of authorizing Contained Access Facilities (CAFs) for low-power, indoor use in Citizens Broadband Radio Service (CBRS), the FCC’s new Notice of Proposed Rulemaking (NPRM) (released in August 2024) observes that “industry forecasts indicate that the private [Long Term Evolution] market is continuing to expand.”¹ As Internet of Things networks proliferate and artificial intelligence makes wireless connectivity even more valuable, the need for more spectrum resources at a variety of frequencies will only grow. More generally, America’s “5G” and future “6G” wireless ecosystems will rely on a combination of big national or regional carrier networks for truly “mobile” connections (for use ‘on the go’) and a far larger number of high-capacity and customized networks deployed by individual enterprises, households, and community anchor institutions to meet their particular needs at a lower cost.

The imperative to identify bands where a sharing framework can unlock fallow spectrum has its roots in the 2012 report of the President’s Council of Advisors on Science and Technology (PCAST), which recommended that a three-tier sharing framework in the Navy’s then-exclusive use of the 3.5–3.6 GHz band for radar could offer enormous localized and low-power spectrum access for commercial use.² President Obama’s subsequent 2013 Executive Memorandum stated in its preamble that: “Where technically and economically feasible, sharing can and should be used to enhance efficiency among all users and expedite commercial access to additional spectrum bands, subject to adequate interference protection for federal users, especially users with national security, law enforcement, and safety-of-life responsibilities.”³ The PCAST report and Executive Memorandum led directly to the FCC’s collaboration with the National Telecommunications and Information Administration (NTIA) and Department of Defense—and, ultimately, to the 2015 Order adopting CBRS.

Picking up again where the PCAST report and the Obama NTIA left off, the National Spectrum Strategy released in late 2023 acknowledged the need for new and more dynamic spectrum-sharing efforts to accommodate the rapidly growing needs of both the private sector and federal users. “Next-generation wireless technologies such as 5G, 6G, and Wi-Fi necessitate additional spectrum resources with the capacity for wider channels, resulting in benefits beyond increased capacity, including enhanced energy efficiency, improved reliability, and reduced latency,” the report stated.⁴ The National Spectrum Strategy is currently studying the degree to which certain federal bands—most notably the 3.1–3.45 GHz and 7125–8400 MHz bands, both of which are primarily occupied by military systems—can be reallocated or shared with the private sector.

Earlier in 2023, the FCC reinforced its intention to promote more spectrum sharing by adopting a policy statement, Principles for Promoting Efficient Use of Spectrum, that embraces the principle of reciprocal obligations for transmitters and receivers (and of incumbents and entrants) to facilitate shared and more intensive spectrum use.⁵ Concerning interference realities, the policy statement clarifies the FCC’s recognition that: “The electromagnetic environment is highly variable, and zero risk of occasional service degradation or interruption cannot be guaranteed.”⁶ Indeed, the FCC noted that “the likelihood of harmful interference should be assessed under a range of operating conditions, but not on an expectation of 100% service availability, or in contemplation of exceptional events. The level of interference protection afforded to particular services under the Commission’s rules may vary, and some may require higher levels of service reliability than others.”⁷

All of this lays the groundwork for more innovative and aggressive efforts to achieve wireless bandwidth abundance, rather than scarcity, by authorizing the use of fallow spectrum capacity wherever feasible. Because of its emphasis on sharing, the National Spectrum Strategy studies of large bands currently occupied by the military and other federal users should, at a minimum, identify substantial opportunities for indoor, LPI-type commercial use. The FCC’s 2023 policy statement, for its part, helps lay to rest the traditional objection to shared or opportunistic use by incumbents claiming they are entitled to near-zero risk of interference or that they are not obligated to help accommodate new entrants. For example, in the 6 GHz Order, the FCC had to address and reject claims by AT&T and other incumbents that “the Commission’s rules generally prohibit the Commission from authorizing a service or type of unlicensed operation that can cause harmful interference, regardless of whether the probability of such interference is low.”⁸ The FCC disagreed, concluding that the agency “may authorize operations in a manner that reduces the possibility of harmful interference to the minimum that the public interest requires, and it will then authorize the service or unlicensed use to the extent that such authorization is otherwise in the public interest.”⁹

On a practical level, the FCC will need to examine proposals for LPI underlays on a band-by-band basis. Doing so can make bands with far more data capacity and diverse frequency characteristics available to enterprises, schools, factories, venues, office buildings, and many other locations that will need more and more wireless bandwidth in the future. This is no small thing. For example, there are nearly 130,000 K–12 schools in the United States,¹⁰ and there are more than 620,000 manufacturing facilities.¹¹ Still, crafting the right rules will involve some difficult trade-offs, some by necessity and others in the service of creating a sort of “portfolio” of options for direct local spectrum access.

The LPI approach adopted as a contiguous underlay across 1,200 megahertz in 6 GHz is just one possible approach—one that leans heavily toward unlicensed access by any household, business, or other facility with low-cost, off-the-shelf equipment. In contrast, the CAF concept outlined in the pending new CBRS NPRM suggests that only select categories or public or quasi-public (“critical”) facilities may be eligible for protected access for their indoor-only operations—and, given the CBRS sharing framework that will presumably entail a registration and approval process. The following are a few of the most basic (and overlapping) policy considerations and trade-offs that will need to be balanced to authorize additional LPI underlays in new bands.

The FCC can authorize indoor-only use of any frequency band on an unlicensed, licensed, or licensed-by-rule basis. The Commission’s choice is likely to be primarily a function of the intended use indoors (particularly the desired power level) and the nature of the incumbent licensees (or federal users) in the band. The propagation characteristics of the frequency band influence both of these. So, for example, even at a substantial power level, indoor-only use of a millimeter wave band (above 24 GHz) in a band used only or predominantly for satellite uplinks would seem to easily allow for an unlicensed authorization similar to LPI in 6 GHz. On the other hand, in a satellite downlink band—and especially where consumer dishes could be in almost any location—even at a much lower power, the Commission would be more likely to require the indoor facility to apply for a license, or at least register the location, as part of a coordinated, license-by-rule framework.

We have few precedents to inform this choice, but the 6 GHz band is illustrative. The FCC concluded it could make LPI Wi-Fi available inside any structure and at a power level sufficient for Wi-Fi (if only barely) while keeping any signal leakage comfortably below the lowest claimed threshold of harmful interference to an incumbent beyond the walls (namely, fixed microwave links). This has the benefit of allowing any home, business, or venue to continue doing what they have been doing with unlicensed devices (i.e., purchasing access points off the shelf or gateway routers from their internet service provider) without any need to get a license, register, or sign up or pay for coordination by the automated frequency coordination systems certified to control outdoor and full power operation. It’s also important to note that a Part 15 authorization (unlicensed) means that anyone can operate an LPI access point in a home, business, or other venue, but, in practice, the prohibition on battery power effectively gives the owner or manager exclusive rights to operate LPI on site.

In contrast, the FCC’s pending proposal to revisit the option of granting priority access “reservations” to specified categories of “Low-Power Indoor Facilities” would presumably be on a licensed-by-rule basis, consistent with the framework that applies to all Priority Access License (PAL) and General Authorized Access (GAA) users under Part 96 of the Commission’s rules. If the FCC decides to limit this to specific types of locations (e.g., hospitals, utilities, and schools) it will be walking a fine line with respect to the statutory obligation to assign spectrum by auction when “mutually exclusive applications are accepted for any license.”¹² Under the current CBRS framework, all users are required to register and operate only on channels granted by a Spectrum Access System (SAS). But while GAA users receive no protection from interference, PAL users had to purchase their rights at auction since they have mutually exclusive interference protection within the county they licensed. Although it’s not our intention here to go into this issue in depth, the Commission would likely be on firm grounds to establish qualifications for a Low-Power Indoor Facility (e.g., control of the facility or professional installation) that only the facility’s owner or lessee could satisfy. In that event, qualifying applicants would never be “mutually exclusive.”

A coordination requirement can be added to any of the options above (unlicensed, licensed, or licensed-by-rule) and used to give the indoor-only user either more flexibility (e.g., higher power or higher out-of-building emissions) or possibly even protection from at least some outdoor operators. Coordination could give indoor-only users—and perhaps even geographically remote campuses or multi-building facilities—far more latitude to deploy a private network. Depending on the frequency band (and hence the propagation), coordination could allow an indoor-only user that is sufficiently distant from incumbent licensees or federal users to take advantage of higher power, to transmit higher above ground level, or to avoid what might be expensive measures to completely contain the signal indoors (such as replacing or applying a special coating to windows).

This type of coordination would not require an automated geolocation database, such as the SASs certified to coordinate users in CBRS or the Automated Frequency Coordination (AFC) in 6 GHz. Indeed, by far, the largest number of licenses granted by the FCC are manually coordinated in shared bands. For example, tens of thousands of users hold licenses to locate a fixed link under Part 101, which requires the applicant to complete a manual coordination process prior to filing an application for authorization.¹³ And whether the coordination process is automated or manual, it could be used to authorize a hybrid indoor-outdoor private network. The Commission acknowledges this in its new CBRS 2024 NPRM, where it asks whether “a CAF-like GAA spectrum reservation system [can] be used to support some outdoor private networks in geographically contained areas (e.g., corporate campuses or manufacturing facilities)?”¹⁴ Depending on the nature of the incumbent service—and the location of the secondary user—this approach could give thousands of industrial, agricultural, military, Tribal, and other sites substantially more spectrum access and flexibility.

The possibility of using coordination (such as a SAS) to give indoor-only users interference protection is one option the FCC seems to suggest in its pending CBRS 2024 NPRM, which asks: “Should we allow operators to reserve some amount of GAA spectrum for private, low-power indoor operations—akin to the CAF approach . . .?”¹⁵ A “reservation” of rights to transmit on certain GAA channels and to interference protection on those channels within an approved facility would almost necessarily require a geolocation database (in CBRS, a SAS) to deny all other user requests to operate on those channels within a calculated protection area around the CAF. In theory, because the 6 GHz band similarly employs AFCs able to grant or deny channels for use in very specific locations, this same sort of reserved use and interference protection for a qualifying CAF—at a higher power than LPI—could be grafted onto the multi-tier framework for unlicensed operation in the 6 GHz band. It’s a better fit for a licensed-by-rule authorization, but it suggests the FCC has the tools to craft a wide variety of user environments.