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Federal Register / Vol. 86, No. 19 / Monday, February 1, 2021 / Proposed Rules
Compliance with the two-degree orbital separation requirements for FSS space stations is verified by the information certifications and technical showings required by 25.140a of our rules.
In its Petition, SES includes proposed modifications to both rule 25.140, and 25.262. Under this proposed approach, FSS space stations would be required to maintain at least two degrees of separation from each other and would also be required to maintain a default orbital separation of at least four degrees from 17/24 GHz BSS space stations.32
In determining what orbital separation would be most appropriate for FSS space stations seeking to operate in the 17.317.8 GHz band in the spaceto-Earth direction, we consider not only accommodation of FSS operations in a manner most consistent with other FSS
bands, but also harmonization of the operations of the three different satellite services operating bi-directionally in the same frequency band. We therefore propose changes to 25.140a and b, d and 25.262 of our rules, to require GSO FSS and 17/24 GHz BSS applicants seeking to operate in the 17.317.8 GHz band, to demonstrate compliance with rules applicable to their services particular orbital spacing requirements, while simultaneously accommodating adjacent neighboring space stations in other services.33 We propose to adopt a two-degree orbital spacing approach for transmitting FSS space stations and require an FSS applicant to make different coordination showings depending upon the service of its adjacent neighbors. We believe that permitting two-degrees of separation between downlinking FSS space stations, while retaining four-degree separation from 17/24 GHz BSS space stations, would most efficiently use the orbital arc and associated spectrum resources. We seek comment on this proposal, and on its possible ramifications for the incumbent services.
We also seek comment on other alternatives, including whether we should apply the same orbital spacing requirements to downlinking FSS space stations as we currently apply to 17/24
GHz BSS stations, i.e., four-degree spacing. While this approach might yield a more homogeneous regulatory and operating environment and could or 3, or 25.222a1 or 3, 25.226a1 or 3, or 25.227a1 or 3.
32 The minimum four-degree separation requirement between 17/24 GHZ BSS space stations would be unchanged. SES Petition, Rule Appendix.
33 47 CFR 25.140a and b and 26.262. We also propose conforming changes to 25.114d15
which refers to the showings applicants must provide with their applications.

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be implemented using the coordination showings per 25.140b for both types of applicants, it may not, however, most effectively maximize use of the orbital arc and spectral resources, nor provide maximum flexibility for FSS or 17/24
GHz BSS operators. Commenters proposing other alternatives also should discuss any cost and benefits associated with their proposals, in addition to discussing any technical advantages.
Downlink Power Limits. The Commission has typically employed downlink PFD limits for space stations transmissions in order to facilitate both inter-service and intra-service sharing.
PFD limits for intra-service operations are generally imposed to ensure a relatively homogeneous transmitting environment which aids in protecting co-frequency receiving antennas from adjacent satellite interference.34 PFD
limits may also be imposed to facilitate inter-service operations, notably to protect terrestrial services from satellite transmissions.
The Commissions current rules include PFD limits for 17/24 GHz BSS
systems transmitting in the 17.317.7
GHz band.35 These PFD levels were established to accommodate four-degree spacing i.e., intra-service sharing between 17/24 GHz BSS networks. The regional variation was adopted, among other reasons, to account for geographic variations in rainfall characteristics.
Moreover, these limits are intended to protect BSS receiving antennas conforming to the requirements of 25.224 of our rules and are derived from antenna patterns in Recommendation ITUR BO.12131
which applies specifically to BSS
receiving antennas.36 FSS receiving antennas will likely exhibit different gain characteristics and may ultimately operate in an orbital spacing environment e.g., two degrees different from the four-degree separation approach established for 17/24 GHz BSS
34 The downlink power levels transmitted by adjacent co-frequency satellites, in combination with the sidelobe performance characteristics of the receiving earth station antenna, will determine the carrier-to-interference ratio that an operator experiences at the receive antenna as a result of adjacent satellite interference.
35 47 CFR 25.208w. Specifically, these PFD
limits are: 1 In the region of the contiguous United States, located south of 38 North Latitude and east of 100 West Longitude: 115 dBW/m2/MHz; 2 In the region of the contiguous United States, located north of 38 North Latitude and east of 100 West Longitude: 118 dBW/m2/MHz; 3 In the region of the contiguous United States, located west of 100
West Longitude: 121 dBW/m2/MHz; and 4 For all regions outside of the contiguous United States including Alaska and Hawaii: 115 dBW/m2/MHz.
Id.
36 In contrast, FSS receiving antennas in other frequency bands are typically subject to the requirements contained in 25.209.

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space stations. 17/24 GHz BSS and FSS
space stations transmitting in the 17.7
17.8 GHz band are also subject to the arrival-angle-dependent PFD limits contained in 25.208c that are intended to protect terrestrial systems in that band.37
At present, our rules do not include PFD limits for FSS space stations in the 17.317.7 GHz band. In its petition, SES
proposes PFD limits for FSS systems based on the existing regional PFD limit scheme, with some modifications.38 SES
proposes that in some geographic regions FSS downlink transmissions not exceed a PFD limit of 118 dBW/m2/
MHz which is more stringent than the limit imposed on 17/24 GHz BSS space stations in the same region.39 Although SES offers no explicit rationale for its proposal to apply this more stringent PFD limit to FSS transmissions, we recognize that it is identical to the PFD
limit our rules apply to FSS
transmissions in the nearby conventional Ka-band to allow twodegree spacing.40 We propose applying regional PFD limits to 17.317.8 GHz FSS space station transmissions, to harmonize them with those now applicable to the 17/24 GHz BSS, and propose adopting the specific regional limits advocated by SES. We tentatively conclude that these limits, including the maximum value of 118 dBW/m2/MHz will allow transmitting FSS space stations to operate in both a two-degree FSS spacing environment as well as alongside the four-degree 17/24 GHz BSS environment.41 We seek comment on these conclusions.
The PFD limits contained in 25.208
are largely intended to facilitate sharing between space and terrestrial services.
Most are angle-dependent and closely replicate the PFD limits contained in 37 47 CFR 25.208c. These limits are applicable in the 17.719.7 GHz band and must be met by FSS
and 17/24 GHz BSS space stations.
38 SES Petition at 10. SESs proposed requirements are: 1 In the region of the contiguous United States, located south of 38 North Latitude and east of 100 West Longitude: 118 dBW/m2/
MHz; 2 In the region of the contiguous United States, located north of 38 North Latitude and east of 100 West Longitude: 118 dBW/m2/MHz; 3 In the region of the contiguous United States, located west of 100 West Longitude: 121 dBW/m2/MHz.;
and 4 For all regions outside of the contiguous United States including Alaska and Hawaii: 118
dBW/m2/MHz.
39 This limit is more stringent compared with the most restrictive PFD limit of 115 dBW/m2/MHz required in the same geographic region from BSS
space stations.
40 47 CFR 25.140a3iii. The conventional downlink Ka-bands include 18.318.8 GHz spaceto-Earth and 19.720.2 GHz space-to-Earth.
41 We note that if the 118 dBW/m2/MHz regional PFD limit is met, then the angle-dependent PFD limits contained in 25.208c that are intended to protect terrestrial operations in the 17.717.8 GHz band will be met as well.

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