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FCC Releases R&O Revising Emissions Limits for the 24 GHz Spectrum Band

On December 2, 2024, the FCC released a Report and Order (Order) revising emission limits for the 24 GHz spectrum band to align with international standards (Resolution 750) set by the World Radiocommunication Conference 2019 (WRC-19).  These changes are primarily intended to protect critical scientific and weather services using the adjacent 23.6-24.0 GHz passive band, such as Earth Exploration Satellite Services (EESS), from harmful interference caused by active services in the 24 GHz band.  The Order adopts the following:

  • Mobile Services:
    • The Resolution 750 limits will be applied to all mobile operations in the 24 GHz band, including International Mobile Telecommunications (IMT) and non-IMT services.
    • These limits ensure that the out-of-band emission (OOBE) levels of mobile base stations and devices do not interfere with the adjacent 23.6-24.0 GHz passive band used for scientific and weather-related purposes.
  • Two-Phase Emission Limit Standards:
    • Phase 1 (Current Limits):
      • Applies immediately upon the Order becoming effective (30 days after Fed Reg publication).
      • Retains less stringent OOBE limits (-33 dBW/200 MHz for base stations, -29 dBW/200 MHz for mobile devices).
      • These Phase 1 OOBE limits are currently applicable to all mobile operations in the 24 GHz band.  They will continue to apply to equipment brought into use before September 1, 2027, even after the stricter Phase 2 OOBE limits come into effect for new equipment deployed after that date.
    • Phase 2 (Stricter Limits):
      • Applies to equipment brought into use after September 1, 2027.
      • Sets stricter OOBE limits (-39 dBW/200 MHz for base stations, -35 dBW/200 MHz for mobile devices).
  • Existing Equipment:
    • Equipment compliant with Phase 1 limits may continue to operate beyond the 2027 deadline but cannot be deployed or significantly modified in ways that affect emission characteristics without adhering to Phase 2 limits.
  • Fixed Services:
    • Fixed operations, such as point-to-point and point-to-multipoint systems, are not required to comply with Resolution 750 limits.
    • The FCC noted that fixed systems typically use directional antennas and operate with greater frequency separation, reducing the likelihood of interference.
  • Indoor Small-Cell Systems:
    • Proposals to exempt indoor small-cell systems from the limits were rejected.  The FCC determined that additional research is necessary to justify such an exemption, as signal attenuation through building materials varies and enforcement of indoor-only rules could be challenging.
  • Measurement Standards:
    • The FCC allows equipment manufacturers flexibility in demonstrating compliance, permitting both Total Radiated Power (TRP) and conductive power measurements.
    • TRP measurements account for the actual radiated power from the antenna, while conducted power measurements are a conservative alternative that does not factor in antenna efficiency.
  • Timeline Considerations:
    • The September 1, 2027, deadline ensures a clear transition to Phase 2 limits while giving stakeholders sufficient time to adapt their equipment and deployment strategies.
  • Monitoring and Future Adjustments:
    • The FCC will monitor interference effects and consider further adjustments to rules if necessary.

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