Responding to demands by high tech companies for more so-called “mid-band” unlicensed spectrum to augment that already made available in the 5 GHz Band, which accommodates Wi-Fi, Internet of Things (“IoT”), and other Unlicensed National Information Infrastructure (“U-NII”) applications as well as Licensed Assisted Access and LTE-Unlicensed solutions, the FCC will vote on a draft Notice of Proposed Rulemaking (“NPRM”) at its October 26 Open Meeting to make up to 1200 megahertz of nearby spectrum available for similar purposes. The draft leaves no doubt that, to make the 5.925-7.125 GHz band (the “6 GHz Band”) available for unlicensed use, sophisticated sharing mechanisms will need to be in place. Various parts of this frequency range are already used by fixed, mobile, and satellite services, and the draft item commits to protecting these incumbents and allowing these services to grow while at the same time opening the band to increased numbers of unlicensed devices. To achieve this, the Commission is considering drawing upon its experience with white spaces and the Citizens Broadband Radio Service (at 3550-3750 MHz), and would seek comment on numerous subjects before adopting rules. The draft item would be a stepping stone to enabling unlicensed devices to operate with wider bandwidths and higher data rates, which the Commission hopes would set off a new wave of innovation in consumer devices complementing its recent moves to spur the rollout of next-generation 5G networks. The NPRM, when adopted, will be sure to generate a wave of comments from both equipment manufacturers and broadband providers hungry for more spectrum as well as incumbent public safety organizations, utilities, satellite companies, and various other fixed and mobile services licensees seeking to protect and hoping to expand their existing operations in the 6 GHz Band, particularly as relocation options for other similar spectrum are increasingly scarce.
Currently, the Commission’s unlicensed rules permit operations in the 6 GHz Band for wideband systems (e.g., sensor/tag systems used to locate objects) and ultra-wideband operations. In general, the draft NPRM would allow other unlicensed devices to be introduced to the 6 GHz Band by splitting the spectrum into four sub-bands that pair technical and operational parameters with certain 5 GHz U-NII sub-bands, while incorporating features designed to protect incumbent licensees in those sub-bands. The Commission hopes that by mirroring the operational and technical parameters that already exist for unlicensed devices in the 5 GHz Band, it will “create an enhanced ecosystem of unlicensed use in the 6 GHz band and the nearby U-NII bands” (which are spread over 580 megahertz within the 5150-5850 MHz range).
5.925-6.425 and 6.525-6.875 GHz: Automated Frequency Control
Unlicensed devices using the 5.925-6.425 GHz and 6.525-6.875 GHz sub-bands would be able to operate both outdoors and indoors at power levels permitted for unlicensed use in the U-NII-1 and U-NII-3 sub-bands (5150-5250 and 5725-5850 MHz, respectively). But the NPRM envisions that unlicensed devices in the 6 GHz sub-bands labeled U-NII-5 and U-NII-7 by the draft item would only be allowed to transmit if an automated frequency control (“AFC”) system determines that such transmissions are permitted, so as to avoid harmful interference to licensed operations. The AFC system, or systems, would communicate with an unlicensed device that acts as a “standard-power access point,” which, in addition to operating itself, would control operational permissions for client devices as well as devices accessing a wireless router in the home or an access point at a public location.
The draft item notes that the U-NII-5 and U-NII-7 sub-bands are home to point-to-point microwave links that support public safety, railroad, oil and gas pipeline, utilities, and wireless and wireline communications service, as well as some fixed satellite services. As the fixed service incumbents are at known, fixed locations, the FCC believes the AFC system could be a “simple database” which is automatically queried to determine which frequencies are available for an unlicensed device to use at a given location and time. The FCC seeks comment on numerous aspects of possible approaches to the AFC system concept, thereby highlighting the many technical and other issues that will need to be resolved. These include what are the basic eligibility requirements to be an AFC system operator; whether there should be more than one AFC system; whether the FCC’s ULS system is or can be made sufficiently reliable as the basis for AFC system operation and determination of available frequencies; whether and how AFC systems (assuming there are more than one) will need to exchange data; whether the AFC system(s) should be centralized or de-centralized; whether unlicensed devices will need to register with the AFC system(s) and will need to identify themselves to incumbents; how the location and height of an unlicensed 6 GHz Band device will be determined before frequencies are selected; what security needs to be in place to ensure proper operation of the AFC system(s); whether 6 GHz Band unlicensed devices might cause aggregate harmful interference to satellite space station receivers and, if so, how to mitigate that interference; how often unlicensed devices would need to check the AFC system to confirm the availability of the frequencies they are using; and whether and how AFC system operators can charge access fees. The FCC also requests input on the nature of and metrics for the appropriate interference standard to protect incumbent licensees, ensuring that unlicensed devices in the U-NII-5 and U-NII-7 sub-bands cannot operate co-channel to any fixed link within that link’s defined exclusion zone. In this area, the Commission faces a number of “real-world” challenges, such as properly allowing for multipath fading when an AFC system determines that a frequency is available, with the goal of maximizing spectrum utilization by licensed and unlicensed devices.
6.425-6.525 and 6.875-7.125 GHz: Low-Power, Indoor Operation
Meanwhile, unlicensed devices using the 6.425-6.525 GHz and 6.875-7.125 GHz sub-bands, which the NPRM terms the U-NII-6 and U-NII-8 sub-bands, respectively, would only be allowed to transmit indoors and at lower power levels than in the U-NII-5 and U-NII-7 sub-bands (equal to the same, more restricted, power levels already applicable to the 5 GHz U-NII-2 bands (i.e., 5250-5350 and 5470-5725 MHz)). However, as the draft NPRM would propose, unlicensed operations in the U-NII-6 and U-NII-8 sub-bands, by “low-power access points” and client devices, would not be subject to AFC system coordination before operation. The draft NPRM states that this sub-band is primarily used for mobile such as Broadcast Auxiliary Service television pick up stations (i.e., electronic news gathering and wireless video links), mobile and fixed Cable Television Relay Service links, several varieties of fixed television-service-related links which operate on a more restricted basis, licensed wireless microphone operations, and a limited number of satellite services. The itinerant operations of the foregoing mobile services make the use of an AFC system infeasible. The FCC inquires how indoor use effectively can be assured, asking, for example, whether it should adopt specific equipment restrictions to ensure indoor operations (e.g., requiring devices to have a direct connection to a power outlet) and how to address potential interference complaints.
The FCC’s draft item proposes a number of interference mitigation measures and potential limitations on unlicensed device use, indicating an openness to outside recommendations on how to best strike the balance between unlicensed and licensed use of the band. For example, would AFC system(s) permit operations on certain frequencies but at lower powers, whereas operation would be precluded if the unlicensed device’s maximum power were used to determine available frequencies? In addition, the NPRM would propose client devices be allowed to connect with both standard-power access points and low-power access points, and be permitted to operate across the entire band which should encourage the widespread availability of client devices. Similarly, to promote widespread adoption, the draft NPRM would also inquire whether there are ways to allow higher power and even outdoor operations in the U-NII-6 and U-NII-8 sub-bands without causing interference to mobile operations. Conversely, the Commission intends to ask whether non-AFC system operations by low-power access points should be permitted in the U-NII-5 and U-NII-7 sub-bands. Finally, the NPRM would propose to preclude operation of standard-power and low-power access points in moving vehicles, cars, trains, or aircraft (and implicitly raises the question whether sufficient spectrum is available for unlicensed operations in moving vehicles, in addition to certain 60 GHz unlicensed operations on aircraft pursuant to Commission decisions in the Spectrum Frontiers proceeding). The adoption of the NPRM would provide an opportunity for all stakeholders to weigh on the future use of the 6 GHz Band.