Coordination For Satellite Networks

Presentation / Coordination For Satellite Networks

Date Submitted: 02 October 2001

Written by RPC Telecommunications. Website: http://www.rpctelecom.com

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Covers topics including Satellite Coordination Background, Satellite - Terrestrial and Satellite - Satellite Coordination and the role of the ITU in coordination.

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-Section 1
Satellite Coordination Background
-Section 2
What Is Coordination?
-Section 3
Key Issues
-Section 4
Frequency Allocations
-Section 5
Satellite - Terrestrial Coordination
-Section 6
Satellite - Satellite Coordination
-Section 7
Conclusions
Satellite - Terrestrial Coordination
Satellite-Terrestrial Sharing

Almost all FSS allocations are shared with terrestrial fixed and mobile services. 3 30 GHz (SHF) FSS bands share with point-to-point radio relay chains. Transportable line-of-sight (mobile) links above 40 GHz, FSS bands will share with HAPS (High Altitude Platform Stations).

Interference Management

ITU methods intend to ensure that interference to and from space and terrestrial systems does not produce more than a small fraction of the total allowable noise / BER in the end-to-end connection. Reference circuits define hypothetical links and allowable levels of noise due to interference.

Terrestrial Interference Modes

  • Satellite transmitters interfere with terrestrial station receivers
  • Terrestrial station transmitters interfere with satellite receivers
  • Earth station transmitters interfere with terrestrial station receivers
  • Terrestrial station transmitters interfere with earth station receivers
Earth Station <-> Terrestrial
For any given earth-station, it is possible to determine the likely interference to and from the earth-station and those terrestrial stations in overlapping frequency bands and close enough to be likely to be able to cause and receive interference. Then it is possible to find means to reduce the interference to acceptable levels. This is, of course, frequency coordination as already discussed - determining compatible assignments which may be recorded in the MIFR.
Satellite <-> Terrestrial
Because of wide coverage, one satellite footprint is likely to include very large numbers of terrestrial stations. Coordination is thus impractical (except in some specific cases). Inter-service sharing must thus be ensured by imposing "envelope" technical conditions in the shared bands determined by empirical and analytical study and defining limits on the power of satellite and terrestrial emissions.
Limits
Limits On Satellite Emissions

In bands shared with terrestrial services satellite emissions are constrained to a power flux density at the surface of the Earth which may not be exceeded. This is defined in a measurement bandwidth and elevation angle dependant - higher limits at higher elevation angles because terrestrial fixed stations have higher gain at lower elevation angles. Limits are mandatory and are in S21 of the Radio Regulations.

Limits On Terrestrial Station Emissions

S21 sets mandatory limits for terrestrial stations. The EIRP limited to 55 dBW. Power to the antenna input also limited to 13 dBW below 10 GHz and 10 dBW above 10 GHz.

The transmit beam is to be directed away from the GSO in the following way:

  • 1 - 10 GHz: 2 from the GSO unless EIRP less than 35 dBW
  • 10 - 15 GHz: 1.5 from the GSO unless EIRP less than 45 dBW
Earth Station <-> Terrestrial Coordination
This is a terrestrial sharing path. In addition to coordination there are some sharing constraints - limits on EIRP towards the horizon and earth-stations not to transmit below 3 elevation. The selection of an FSS transmitting earth-station site requires careful evaluation, to avoid the possible coordination problems. An increased number of FSS stations makes this more difficult
Coordination Steps
  • Resolution of potential interference problems within the jurisdiction of the same national frequency authority
  • Publication of information on potential international interference to or from the earth station
  • Foreign national authorities identify terrestrial stations at risk, prospective interference levels are calculated and problems are resolved
  • The ITU is notified of the coordinated frequency assignments and registers them in the MIFR
  • Changes which increase the risk of interference are re-coordinated and assignments to new local terrestrial stations are notified to the ITU and are subject to a technical examination for compatibility with registered assignments to the earth station
Identification Of Affected Stations
At "Stage 2" the administration responsible for the new earth-station prepares coordination maps of the coordination area based on pessimistic assumptions. Terrestrial stations in the contour could be affected.
If the coordination area includes the territory of a foreign administration the maps and technical data about the station must be sent to those administrations. Maps are prepared using the methodology of Radio Regulation Appendix S7.
Appendix S7 Procedure
WRC-2000 approved an updated methodology. 

The permissible level of interference is first defined and propagation for different modes is taken into account:

(mode 1): attenuation of signals due to tropospheric propagation (ducting) via near-great-circle paths.
(mode 2): attenuation of signals subject to scatter from hydrometeors (rain, etc.), which may not be along the great circle.

Next: Section 6 - Satellite - Satellite Coordination

 
 

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