There is widespread recognition that mmWave frequencies offer great promise for many wireless applications that will assist in enhancing U.S. infrastructure, expanding broadband services in rural areas, bringing new vertical industries to the communications network, and maintaining U.S. leadership and economic competitiveness.
Matching this recognition is a significant effort among academic, industry and government leaders to develop and test new wireless technologies and services, including efforts by the Federal Communications Commission to support 5G and 6G wireless in frequencies at the mmWave, sub-Terahertz, and Terahertz bands.
Today, extensive research and development for wireless devices above 95 GHz is underway, and there is a need for a suitable regulatory framework for their eventual use. Example areas that need to be addressed to foster commercial success and enhance the likelihood of success of investments at this spectral frontier:
- U.S. allocations extend up to 275 GHz as of 2021, but before March 2019, service rules stopped at 95 GHz. (FCC claims jurisdiction up to 3 THz)
- Use of technology above 95 GHz is governed by FCC ET Docket 18-21 in the United States
- ITU rules call for protection of primary passive spectrum by prohibiting “all emissions” in some bands. The mmWave coalition fully supports protecting all passive receivers and their spectrum. However, the ITU has made little progress in its WRC-2000 call for studies of possible sharing feasibility. If fundamental physics and engineering solutions offer fool-proof ways to share these passive bands with terrestrial users, these possibilities should be explored. Also, it is vital to understand the out-of-band emission (OOBE) sensitivity that passive users face in the spectrum above 95 GHz near the protected ITU bands.
- Worldwide, there is uncertainty regarding service rules in 95-275 GHz
- No provisions for terahertz spectroscopy exist today despite products on US market for domestic and foreign firms
95-275 GHz Image Screenshot: National Telecommunications and Information Administration United States Department of Commerce: U.S. Frequency Allocation Chart
Global regulatory agencies such as Japan’s Ministry of Internal Affairs and Communications (MIC), Conference of European Postal and Telecommunications (CEPT), the Federal Communications Commission (FCC), and England’s OFCOM have adopted rulemakings and have opened up the spectrum above 100 GHz.
As shown in the image above, in March 2019, the FCC under ET Docket 18-21 opened up four new unlicensed bands (shown in blue) and UK’s Ofcom followed suit. The mmWave coalition was formed to advocate and support the development and commercialization of frequencies above 100 GHz.
FCC also created in the same decision Spectrum Horizons (ET Docket 18-21) Experimental Radio Licenses “for experiments and demonstrations of equipment designed to operate exclusively on any frequency above 95 GHz”. FCC stated “Applicants for Spectrum Horizons Licenses may request authorization on any frequency within the 95 GHz to 3 THz frequency range” subject to 2 restrictions:
- “Each application must include a narrative statement describing in detail how its experiment could lead to the development of innovative devices and/or services on frequencies above 95 GHz and describe, as applicable, its plans for marketing such devices. This statement must sufficiently explain the proposed new technology/potential new service and incorporate an interference analysis that explains how the proposed experiment would not cause harmful interference to other services.” (47 C.F.R. § 5.702)
- “Spectrum Horizons License applicants that propose to use spectrum exclusively allocated for passive use(s), must provide an explanation why nearby bands with non-passive allocations are not appropriate or adequate for the experiment and also acknowledge that they intend to transition any potential long-term use to a band with appropriate allocations.” (FCC Decision at para. 14)
As seen in the image above, the International Telecommunications Union (ITU) Radio Regulation 5.340 (RR5.340 which was amended at the ITU World Radio Conference in 2000, WRC-2000 to include these bands) presently prohibits “all emissions” in ten passive bands (the dark gray bars) to protect passive environmental satellite sensors and radio astronomy from 100 GHz up to 252 GHz (e.g., see the dark grey protected bands at 100-102 GHz, 109.5-111.8 GHz, 114.25- 116 GHz, 148.5-151.5 GHz, 164-167 GHz, 182-185 GHz, 190- 191.8 GHz, 200-209 GHz, 226-231.5 GHz, and 250-252 GHz). The black double arrows show the amount of contiguous bandwidth between RR5.340 bands, (the largest chunk of contiguous spectrum block available is 32.5 GHz between 116-148.5 GHz) Other shared bands have less severe restrictions, such as the green segments in the bottom of Fig. 1 where Fixed and Mobile services have coprimary allocations.
So much more spectrum exists above 100 GHz. Currently RR 5.340 presently prohibits “all emissions” in several forbidden bands (shown in dark gray) to protect radio astronomy and passive satellite sensors which detect very low levels of energy and might be harmed by interference if special care was not taken to protect such passive systems. The ITU agreed in Resolution 731, at the request of the US and European countries, to study if and under what conditions sharing the ten forbidden bands may be shared. The issue of out of band emissions (OOBE) into the passive bands is also an important study area to assure that adjacent terrestrial transmissions do not leak into or interfere with satellite sensors and studies of limits on such emissions to protect nearby passive bands are beginning. The mmWave coalition is fostering a constructive and win-win approach to learning about these issues and developing technologies that will allow successful commercialization of the spectrum above 100 GHz in the coming years.