**UNITED STATES**

**PRELIMINARY VIEWS ON WRC-07**

**WRC-07 Agenda Item 1.18:** to review pfd limits in the band
17.7-19.7 GHz for satellite systems using highly inclined orbits, in
accordance with Resolution **141 (WRC‑03)**;

**ISSUES**:

1.  Whether the current pfd limits in Article 21 for non-geostationary
    (non-GSO) systems in the FSS are adequate to protect the fixed
    service in the 17.7-19.7 GHz band from non-GSO systems using Highly
    Inclined Orbits (HIO) having an apogee altitude greater than 18000
    km and an orbital inclination between 35^o^ and 145^o^, without
    unduly constraining the use of these non-GSO FSS systems.

2.  Whether there are technical and operational measures in the band
    17.7-19.7 GHz that could be implemented in the fixed service to
    mitigate interference from FSS space stations in HIO.

**BACKGROUND**: The ITU-R has been considering the sharing aspects of
highly elliptical orbit (HEO) satellite systems in a number of contexts
and under a number of different names in recent years. HEO systems are
non-geostationary satellite orbit (non-GSO) systems, and hence are
subject to all limitations that apply to non-GSO systems in the Radio
Regulations. All HEO systems are treated as non-GSO systems by the ITU
when they are examined for regulatory compliance. WRC-97 and WRC-2000
modified the Article **21** power flux-density (pfd) limits that apply
to non-GSO FSS systems to protect terrestrial systems in the 17.7-19.7
GHz frequency band.

In Resolution 141 (WRC-03), the ITU-R has been invited to determine
whether the current pfd limits for non-GSO FSS satellite systems in
Article 21 are adequate to protect the fixed service in the 17.7 to 19.7
GHz band from non-GSO systems using highly inclined orbits, without
unduly constraining the use of these non-GSO systems. Resolution 141
also calls for a determination to be made as to whether there are
technical and operational measures that could be implemented by the
fixed service to mitigate interference from FSS space stations.

In preparation for WRC-03 Agenda Item 1.37 on highly-elliptical orbit
(HEO) satellites, some studies were commenced on the subject of HEO
interference into FS systems in 17.7-19.7 GHz, but no conclusions were
reached in the ITU as whether it is technically appropriate to apply the
Art. 21 pfd limits for non-GSO satellites to HEO satellites. The ITU has
begun the process of responding to Resolution 141 (WRC-03). ITU-R
Working Party 4-9S has looked at prior work, and determined that the FS
and FSS parameters used in the collected studies, along with the FS
protection criteria and methodologies for developing/assessing pfd masks
all needed further review. It has begun the process of gathering the
relevant materials from the responsible working parties in ITU-R Study
Groups 4 and 9.

Resolution 141 (WRC-03) is a follow-on item from WRC-03 Agenda Item 1.37
on HEO satellites. Unfortunately, when it used the term "highly inclined
orbit" non-GSO satellite systems instead of the term HEO in Resolution
141, WRC-03 unintentionally introduced some ambiguity into the scope of
the studies it was requesting, as the term highly-inclined orbit, by
itself, can include not only the HEO systems that were under study
pursuant to the unfinished business from WRC-03 Agenda Item 1.37, but
also some circular-orbit non-GSO systems that were never part of the
Agenda Item 1.37 studies. This ambiguity already has been noted in early
discussions within the ITU-R Working Parties responsible for and
interested in this agenda item, and could prove to be an unwelcome
distraction if the intended scope of the agenda item is not readily
clarified.

It is noteworthy that at least one HEO system has been operating in the
17.7-19.7 GHz band for years at the power levels in the applicable
portion of Article 21, and that to date, there have been no reports of
interference from the non-GSO FSS into the fixed service.

**U.S. VIEWS**:

1\. The U.S., which has looked closely at this issue over the last three
years, believes now, as it did at WRC-03, that the non-GSO FSS pfd
limits for the 17.7-19.3 GHz band that were included in Art. 21 at
WRC-2000 remain adequate to protect the terrestrial services from
non-GSO FSS satellites in highly-elliptical orbits without unduly
constraining HEO non-GSO FSS systems.

2.  That Agenda Item 1.18 and its associated resolution, although
    ambiguously worded so as to encompass some circular-orbit non-GSO
    systems that meet the apogee altitude and orbital inclination
    criteria in *considering g)* of Resolution 141 (WRC-03), was
    intended to apply to highly-inclined (i.e., between 35º and 145º)
    non-circular-orbit non-GSO FSS satellite systems with orbital apogee
    altitudes greater than 18,000 km ***and orbital perigee altitudes
    that are less than the orbital apogee altitudes***. Consequently,
    there is no need to review the limits that apply to those non-GSO
    satellite systems using circular orbits, such as medium earth orbits
    (MEO) that satisfy both the apogee altitude criterion and the
    inclination criterion.

3\. ITU-R studies on sharing between non-GSO systems in the 17.7-19.7
GHz band using HIOs and FS networks in the same band should continue.
Studies will be improved by using realistic assumptions both for the
relevant characteristics of the fixed-satellite service -- including the
number of active HEO/HIO satellites in view of a particular fixed
service station -- and for the relevant characteristics of fixed service
systems.

4\. Satellite networks using HIOs should continue to be considered as
non-GSOs and have the same regulatory standing as other types of
non-GSOs such as those in low and medium earth orbits. There is no need
to modify the Radio Regulations in a way that categorizes HIO non-GSO
operations separately from other non-GSO systems.