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Federal Register / Vol. 86, No. 19 / Monday, February 1, 2021 / Proposed Rules Article 21 of the ITU Radio Regulations.
Since 25.140a contains rules to facilitate FSS operations in a two-degree orbital spacing environment, we believe that this rule section is a more appropriate place to include our proposed PFD limits, as they are intended to facilitate intra-service operation. Thus, rather than amending 25.208, we propose to include these new PFD requirements in 25.140a3.
Further, to improve the organizational coherence of our Part 25 rules, we also propose to likewise move the regional PFD limits for 17/24 GHz BSS space stations now contained in section 25.208w to 25.140b3. As a consequence of this move, we also propose conforming updates to other paragraphs in 25.140b3 42 and to rule sections that currently reference section 25.208w including 25.114d15i and ii, 25.140b5, and 25.262b1 and 2 and c and d.
We seek comment on these proposed rule changes generally, and on whether the proposed PFD limits for FSS space stations are appropriate.
Polarization and Full Frequency ReUse Requirements. Section 25.210f of our rules requires all space stations in the FSS operating in any portion of the bands specified therein to employ stateof-the-art full frequency reuse, either through the use of orthogonal polarizations within the same beam and/or the use of spatially independent beams.43 It similarly requires full frequency reuse for BSS space stations transmissions in the 17.317.8 GHz band space-to-Earth.44 We propose to amend this requirement to include 17.317.8 GHz in the list of specified frequencies, thereby extending the requirement to FSS space-to-Earth transmissions in the band. We seek comment on this proposal.
Cross-Polarization Isolation Requirements. Section 25.210i requires 17/24 GHz BSS transmitting space station antennas to provide crosspolarization isolation of at least 25 dB
within the primary coverage area. We note that a similar cross-polarization isolation requirement for transmitting 42 We propose renumbering of 25.140b3
generally as well as conforming updates to paragraphs b4, b5 and a new paragraph b6.
See infra Appendix A.
43 47 CFR 25.210f. The FSS bands listed include 36004200 MHz, 50915250 MHz, 58507025 MHz, 10.712.7 GHz, 12.7513.25 GHz, 13.7514.5 GHz, 15.4315.63 GHz, 18.320.2 GHz, 24.7525.25 GHz, or 27.530.0 GHz bands, including feeder links for other space services. This requirement does not apply to telemetry, tracking, and command operation.
44 47 CFR 25.210f. This requirement does not apply to telemetry, tracking, and command operation.

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FSS space stations was eliminated in the Part 25 Second Report and Order, although at that time the Commission did not address the cross-polarization isolation requirement for 17/24 GHz BSS. We propose to not extend the cross-polarization requirements to FSS
space station antennas transmitting in the 17.317.8 GHz band. We seek comment on this proposal. We also seek comment on whether this requirement might be obsolete in the current digital transmission environment and could be eliminated for 17/24 GHz BSS space station transmissions as well.45
Measures To Mitigate Space Path Interference In the 17.317.8 GHz reverse-band sharing environment, receiving DBS
space stations are vulnerable to space path interference 46 from nearby cofrequency 17/24 GHz BSS space station transmissions.47 In the 17/24 GHz Space Path Report and Order, the Commission adopted requirements to mitigate such space path interference. If we opt to permit FSS space-to-Earth transmissions in the 17.317.8 GHz band, analogous requirements will need to be adopted to mitigate space path interference from FSS space station transmissions into DBS satellite receivers. We propose to apply to FSS space stations the same antenna off-axis power flux density coordination trigger, antenna off-axis gain measurement requirements, twopart information submission process, and orbital inclination and eccentricity 45 Historically, the Commission adopted its 30 dB
FSS cross-polarization isolation requirement in an environment where satellites were predominantly using analog transmissions as it served to minimize the interference between adjacent satellites when both carried analog video signals with highly varying peaked power density levels. Although relaxed to 25 dB, a similar cross-polarization requirement, was later extended to 17/24 GHz BSS
systems. 17/24 GHz R&O and FNPRM, 22 FCC Rcd at 888889, paragraph 113.
46 This type of interference may occur when the off-axis downlinked signals from one space station are detected by the receiving antenna of a nearby co-frequency space station. The severity of space path interference will depend upon the transmitted signal power level; the off-axis gain discrimination characteristics of the transmitting and receiving antennas; and on the specific orientation of, and separation between, the transmitting and receiving antennas on both space stations. This latter factor in turn depends upon various inter-dependent parameters including longitudinal separation and the inclination and eccentricity of both space station orbits. Management of space path interference is typically more challenging when a receiving DBS space station is located within a few tenths of a degree in orbital longitude from a transmitting co-frequency space station.
47 Analogously, ground path interference arises between earth stations when the off-axis transmissions in the Earth-to-space direction of one service are received by a nearby co-frequency receiving earth station in another service. See infra at paragraphs 4958.

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constraints that 25.264 of our rules now applies to 17/24 GHz BSS space stations.
Off-Axis Power Flux Density Coordination Trigger. To avoid harmful levels of space path interference into DBS space station antennas from 17/24
GHz BSS transmissions, our rules provide a coordination trigger value, i.e., a PFD of 117 dBW/m2/100 kHz at the victim DBS space station receiving antenna above which coordination is required. To protect DBS space stations from space path interference arising from adjacent FSS space station downlinks, SES proposes modifications to 25.264 of our rules to extend the current PFD coordination trigger of 117
dBW/m2/100 kHz to downlinking FSS
space stations in the 17.317.7 GHz band. We further propose applying this coordination trigger to transmissions from FSS space stations is an appropriate approach to mitigate space path interference into DBS receivers and we propose to amend 25.264a through i of our rules accordingly. We also propose to apply this requirement to FSS downlinking space stations in the 17.717.8 GHz band, which could also be a source of space path interference into DBS receivers. We seek comment on these proposals.
In addition, we propose to amend 25.264b1 and 2 and e to require that the PFD calculations at the DBS
receiver consider the aggregate power flux density from all 17.317.8 GHz transmitting beams on the adjacent space station. Under our proposed new rules, this requirement would apply to both FSS and any new 17/24 GHz BSS
space station operations. Our space path mitigation rules were initially written considering the 17/24 GHz BSS space stations of an earlier generation as potential interference sources; at that time we did not contemplate todays space station design, that often employs multiple spot beams and may result in a cumulative interference level at the DBS receiver. We seek comment on these proposals.
Requirements for Antenna Off-Axis Gain, Angular Measurement Ranges, and Minimum Longitudinal Separation.
Our current rules require that 17/24
GHz BSS space stations maintain a minimum longitudinal separation of at least 0.2 from an adjacent DBS satellite.
This angular separation, in conjunction with limits on certain orbital parameters of space stations in both the DBS and 17/24 GHz BSS services, bounds the range over which 17/24 GHz BSS
applicants or licensees must provide off-

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