Key Research Question
In the United States, the 5.925 to 7.125 GHz band (6 GHz band) is shared primarily by fixed microwave links (Fixed Service or FS), Mobile Services (MS), Fixed Satellite Services (FSS), and unlicensed operations. In November 2023, the Federal Communications Commission (FCC) allowed a new device class—very low power (VLP) devices—to operate in sub-bands U-NII-5 and U-NII-7. The FCC also asked if VLP devices could operate in the U-NII-6 and U-NII-8 sub-bands while still sufficiently protecting Broadcast Auxiliary Service (BAS) and Cable Television Relay Service (CARS).
In response to the FCC’s recent Second Further Notice of Proposed Rulemaking, this report examines the likelihood of harmful interference between VLP devices and the BAS TV Pickup (TP) service. TP service enables on-site reporters to transmit video from remote locations with truck-mounted transmitters back to the studio’s fixed central receive site for retransmission. This enables electronic newsgathering (ENG) as well as other remote production capabilities for broadcasters. This simulation seeks to study the interaction between VLP devices and TP links. Specifically, this simulation seeks to determine the probability of exceeding -6 dB I/N at TP Central Receivers. We agree with the FCC’s conclusion that exceeding -6 dB I/N does not constitute harmful interference, but the -6 dB I/N metric was used here as a conservative measurement threshold to align with incumbents’ studies and facilitate comparison.
Research Overview
A comprehensive Monte Carlo analysis with 100,000 iterations was performed over the contiguous United Stated (CONUS) to investigate the likelihood of harmful interference to TP Central Receivers from VLP devices. The simulation examined all 567 TP links listed in the FCC’s Universal Licensing System (ULS) for the CONUS region as a representative sample of all TP Central Receivers. The licensed Central Receivers’ locations, heights, and antenna peak gain were obtained from ULS. While the TP Central Receivers are static, the simulation modeled the dynamic orientation of these receivers to receive signals from truck-mounted transmitters at random locations.
The simulation modeled CONUS-wide VLP device deployment at an equivalent (slightly higher) density as the San Francisco and Houston studies that the Commission relied on in authorizing VLP devices in U-NII-5 and U-NII-7. The simulation applied the same assumptions as the San Francisco study submitted by Apple, Broadcom et al. to model the behavior and characteristics of VLP devices. A duty cycle of 2% was used. As a conservative approach, the simulation assumed that all VLP devices were operating outdoors. Simulated VLP devices included both outdoor devices at street level (90%) and outdoor devices on balconies and rooftops (10%). For VLP devices on balconies or rooftops, building penetration loss was applied to 50% of the devices to account for the potential positioning of VLP devices on the opposite side of the building from a TP Central Receiver.
In each simulation, the total aggregate VLP energy was calculated for each TP Central Receiver, based on azimuth/elevation/distance relative to each dropped VLP using standard propagation models.
A comparison of the registration data listed in ULS with images of the reported locations of Central Receivers demonstrated that, most (if not all) of the 99 Central Receivers with AGL heights of exactly 6.1 m were erroneous. The Central Receivers that listed a height of 6.1 m were actually located on towers and buildings much taller than 6.1 m. We compared the impact on the analysis of removing these sites versus attempting to estimate the correct heights. It was determined that the most appropriate approach would be to remove these likely erroneous TP links entirely from the analysis.
Key Findings
The analysis demonstrates that the risk that VLP devices will cause exceedances of -6 dB I/N is extremely low—lower than other scenarios where the Commission has determined that sharing between 6 GHz RLAN devices and incumbent licensees presented an “insignificant” risk of harmful interference by the FCC’s definition. This demonstrates that the risk of harmful interference to the TP Central Receivers in real-world situations is also insignificant.
- The large majority (95%) of TP links had no exceedance over 100,000 simulation iterations.
- The risk of harmful interference from VLP devices to TP links was exceedingly small with a 0.0001% average probability of an exceedance across all TP links.
- This extremely low probability of exceedances is lower than the likelihood of exceedances that the FCC found to be consistent with an “insignificant” risk of harmful interference when it authorized low-power indoor devices (LPI) in U-NII-6 and U-NII-8 as well as VLP in UNII-5 and U-NII-7. Specifically, this probability of exceedance is lower than the probabilities found in the San Francisco and Houston VLP studies that the FCC determined were sufficiently insignificant. Therefore, this low probability of exceedance is sufficient for the FCC to conclude that the risk of harmful interference to TP links from VLP devices in UNII-6 and U-NII-8 is also insignificant.
- The risk of harmful interference is further mitigated by the dynamic management of TP links. TP link operators can maximize the link quality by selecting transmit locations, antenna heights, and transmit power levels that account for various environmental factors.
- The risk of harmful interference is further reduced by the itinerant nature of both the VLP device as well as the central-receive-site link.
- Even in an extremely rare, worst-case scenario that results in an exceedance of -6 dB I/N, this would likely not cause harmful interference to a TP link because a TP link is configured to operate with sufficient SINR to operate robustly under prevailing local conditions.
Why This Matters
Results from this probabilistic simulation support the conclusion that the risk of harmful interference to TP links from VLP devices is insignificant. Results from this study may be used to help inform the FCC’s decision making to authorize VLP devices in U-NII-6 and U-NII-8.
Read the full report on FCC.gov
Prepared for Apple Inc., Broadcom Inc., Google LLC, Meta Platforms, Inc., and Qualcomm Inc.