DOT Raises Concerns on Part of FCC's Proposed Changes to 6 GHz Rules
With FCC commissioners set to vote Oct. 19, the Department of Transportation questioned whether the -27 dBm/MHz out-of-band emission limit allowed by the FCC for very-low power portable devices and mobile access points in the 6 GHz band will be harmful to cellular vehicle-to-everything operations in the adjacent 5.9 GHz band. The FCC’s draft order addresses the C-V2X concerns raised by DOT.
Sign up for a free preview to unlock the rest of this article
Communications Daily is required reading for senior executives at top telecom corporations, law firms, lobbying organizations, associations and government agencies (including the FCC). Join them today!
DOT has been expressing concern about protecting auto safety use of the 5.9 GHz band, and opposed a 2020 order reallocating the band (see 2011170058). Those concerns continued during the Biden administration (see 2103250071). The FCC didn’t comment Wednesday on the DOT complaint.
The NTIA letter includes a report on tests by DOT. “Based upon this testing, NTIA and DOT urge the Commission to set the out-of-band emission limit for VLP portable devices at -37 dBm/MHz (at 5.925 GHz) and to prioritize unlicensed operations in channels above 6 GHz,” said a filing Tuesday in docket 18-295. “This proposal is similar to one previously submitted by industry stakeholders,” NTIA said, citing a 2021 letter by Broadcom, Facebook, Intel, Cisco and Qualcomm.
The Alliance for Automotive Innovation also raised concerns. The alliance, in a series of recent meetings at the FCC, “reiterated concerns that, as unlicensed devices proliferate throughout the 6 GHz band over time and operation in the lower portion of the U-NII-5 band becomes likely, the OOBE limits put forth by the Commission will not sufficiently protect V2X operations,” said a filing posted Wednesday. The alliance urged the commission to “adopt an OOBE limit for the lower portion of the U-NII-5 band that is at least as restrictive as the -37 dBm limit previously proposed by a collection of VLP proponents and V2X proponents.” The filing also cites the 2021 letter.
The limits in the order “are intended to protect” C-V2X “operations below the 6 GHz band and federal operations above the band,” said the draft item circulated by FCC Chairwoman Jessica Rosenworcel (see 2309270064). “The Commission previously determined that the -27 dBm/MHz limit will sufficiently protect C-V2X operations from harmful interference from U-NII devices operating in other bands,” the draft says: “We remain convinced that the -27 dBm/MHz out-of-band emission level at the lower edge of U-NII-5 will protect C-V2X operations below 5925 MHz and adopt that level for VLP devices.” The limits “will create a consistent out-of-band limit for all 6 GHz unlicensed devices throughout the 6 GHz band,” the draft concludes.
The auto alliance also urged the FCC to act on an order more broadly allowing early C-V2X deployments, beyond an April waiver (see 2304240066). “While the recent vehicle-to-everything waiver grants have been helpful, the auto industry requires certainty,” the alliance said.
Also posted Wednesday was a joint letter from the alliance, the 5G Automotive Association and ITS America raising concerns about the -27 dBm/MHz limit. A limit of -37 dBm/MHz is “technically achievable, consistent with protections adopted in other countries, and necessary to ensure continued protection of C-V2X as unlicensed VLP devices proliferate,” the groups said.
The Open Technology Institute at New America questioned why the order reduces the proposed maximum power level of VLP devices from 1 dBm/MHz power spectral density (PSD) to -5 dBm/MHz in the U-NII-5 and U-NII-7 portions of the band. The group questioned whether that limit “is necessary to protect high-power fixed link incumbent operations from actual harmful interference.” A representative spoke with aides to Rosenworcel and Commissioner Geoffrey Starks.
The draft cites but rejects arguments by Wi-Fi advocates that VLP devices require a 1 dBm/MHz PSD limit “to meet expected consumer use cases, overcome on-body loss, and meet minimum throughput, latency, and power efficiency requirements.” The draft notes “the record is replete with many analyses and tests that come to widely different conclusions.”