The orbital spacing for Direct Broadcast Satellite (DBS) has been nine degrees since the 1990's. Most C-band and Ku-band communications satellites are spaced only two degrees apart. Wider spacing is required for DBS because the small receive dishes consumers use have a wider beamwidth and are likely to suffer some misaiming. While the nine-degree spacing limits the number of DBS satellites that can cover the U.S., DBS operators have been able to increase capacity by using high power spot beams and more complex higher-order modulation schemes to increase data throughput. Two satellite operators are now looking to add capacity by reducing the DBS orbital spacing to 4.5 degrees.
SES AMERICOM has filed an application with the FCC for a satellite located at 105.5 degrees West Longitude (WL), in between the current DBS orbital locations at 110 degrees WL and 101 degrees WL. EchoStar has filed applications for DBS satellites at the 123.5 degree, 96.5 degree and 86.5 degree West Longitude orbital locations. DirecTV, concerned about the impact these "tweener" satellites would have on existing DBS operations, filed a petition for Rulemaking on the Feasibility of Reduced Orbital Spacing in the U.S. Direct Broadcast Satellite Service.
In Public Notice DA 03-3903, released Dec. 16, the FCC International Bureau sought comment on these proposals for reduced DBS spacing. Comments are due January 23, 2004 and reply commends are due February 13, 2004.
The FCC asks "What would be the technical issues associated with reduced DBS orbital spacing, for example, to interference levels, new technology, and operational flexibility, assuming that adjacent satellite systems would be engineered to address interference between systems?" and "In a reduced DBS orbital spacing environment, what would be an appropriate orbital spacing between DBS satellites?"
While the FCC sees the benefit of providing more orbital locations for DBS, it notes that the proponents or reduced orbital spacing for DBS acknowledge that "any potential benefits must be achieved in a way that ensures that consumers continue to enjoy the benefits of existing DBS services. In addition, other co-primary services sharing the same frequency band, including both current and future services, such as non-geostationary satellite orbit fixed-satellite service ("NGSO-FSS") and multichannel video data distribution service ("MVDDS") must also be considered and accommodated. Further, it should be noted that the International Telecommunication Union ("ITU") Region 2 BSS Band Plan would need to be modified for the U.S. to assign licenses at orbital positions other than those currently assigned to the U.S. under the Plan."
The filings for the "tweener" satellites propose different methods to avoid interference to existing DBS operations. These include:
* Lower power (EIRP);
* Coordination of power levels and frequencies delivered to a certain area by the new satellites to manage the carrier to interference (C/I) ratios;
* Use of beam shaping and power roll-off to address interference to adjacent satellites;
* Use of opposite polarization with frequency offset on interleaved satellites with respect to current DBS satellites.
The FCC asks if there are other technologies to allow closer spacing that should be considered. It asks commenters to supply detailed technical analysis of any proposed solutions. The Public Notice also asks what reference pattern, pointing error and dish size should be used for existing DBS consumer antennas and for new DBS systems. What impact would new DBS systems located at less than nine degrees have on existing multi-satellite subscriber Earth stations? Would the impact vary with the geographic location of the subscriber?
Refer to the Public Notice DA 03-3903 for more details and a copy of the DirecTV Petition for Rulemaking, which contains graphs showing the impact of closer spacing on the C/I ratio for various sizes of DBS subscriber antennas.
