TPRC 2024: The 52nd Research Conference on Communications, Information and Inter

Link to paper

Abstract:
This paper explores a tension in spectrum policy that is unnecessarily limiting public access to the airwaves and the benefits of more intensive spectrum sharing and connectivity. Most spectrum licenses (including Federal spectrum assignments) confer exclusive or at least primary rights to transmit on designated frequency bands at specific locations, or over defined geographic areas, including inside factories, office buildings and other facilities owned and controlled by others. This traditional form of licensing precludes property owners from using the spectrum inside buildings under their own control even if the transmissions are contained and would not cause harmful interference to the primary licensee’s operations outdoors. While unlicensed operations have been authorized, until very recently the rules have not been crafted to distinguish between how access rights could vary based on indoor-only use.

The potential benefits of different rules for indoor-only use are becoming more evident. In 2020, the Federal Communications Commission (FCC) adopted an order authorizing low power, indoor-only (LPI) use of 1,200 megahertz on an unlicensed basis across the entire 6 GHz band (5925-7125 MHz), which was already in use by incumbent licensees that include more than 50,000 high-power fixed microwave links. LPI use of this spectrum indoors is limited to roughly one-fourth the standard power of Wi-Fi, yet is considered extremely useful since the vast majority of internet data (including at least 80% of mobile device data traffic) is transmitted indoors and over Wi-Fi. LPI highlights the potential to authorize indoor-only use in many other bands where users comply with power, device form factor, or other requirements that protect the primary licensees from harmful interference. 

This paper explores the policy and technical considerations related to expanding indoor-only authorizations to more bands. For example, controlling the spectrum inside a facility is more practical at higher frequencies where transmissions do not readily penetrate building materials or travel long distances. This concept is particularly relevant now, as the National Telecommunications and Information Administration (NTIA) and FCC collaborate to implement the National Spectrum Strategy, which is premised on studying alternative means to expand private sector use of underutilized Federal bands, particularly bands occupied by U.S. military systems. Five Federal bands that may be prime candidates for indoor-only authorizations—1,675 megahertz in total—are discussed in this report. LPI underlays also provide another way to expand on the “use it or share it” approach to spectrum sharing, but without the need for control by a geolocation database.