Can you hear me now?

Satcom backers say WiMax signals Menace crucial C-Band links

A global organization that represents satellite communications companies has announced that stray radio signals from ground-based WiMax equipment can block transmissions between ground stations and orbiting satellites that relay popular and high-quality 'C-Band' signals used daily by the Defense Department and civilian agencies, as well as private companies.

The Satellite Users Interference Reduction Group (SUIRG) cited the results of its recent tests of the effect of WiMax transmissions on nearby C-Band uplink antennas. According to the industry association, the SUIRG study shows that WiMax transmissions can jam C-Band satcom links from as far as 12 kilometers from the affected satellite antenna.

Federal agencies rely on C-Band transmissions through both federal uplinks and commercial telecom companies to provide voice and data communications of all kinds. For example, commercial C-Band links become especially important to DOD during large-scale military operations.

The allocation of spectrum for use between the satcom industry's C-Band service and users of the WiMax service is controlled by the World Radiocommunications Conference, a global organization that allocates spectrum and adjudicates disputes about use of the ether.

"The C-band is in many ways the lifeline of the satellite industry and protecting that spectrum from the threat of interference posed by sharing it with broadband wireless access services is of paramount importance," said Robert Ames, SUIRG president.

In the spectrum allocation world, each specific type of transmission is known as a service, such as, the AM radio service, the digital television service, the land mobile radio service and so forth.

'The test, conducted in the latter quarter of 2007, conclusively demonstrated that WiMax communications pose a significant interference threat to satellite signals transmitted in the C-band frequency,' the satcom industry group said in a release that accompanied the study.

The association's test was intended to evaluate the accuracy of previous test results about interference to C-Band transmissions caused by ground-based WiFi services.

The association's plan called for the test to measure interference levels caused by fixed WiMax transmissions on a satellite ground station operating as a fixed frequency service as from a Fixed Satellite Service, or non-mobile, facility. The opposite of Fixed Satellite Service is Mobile Satellite Service, often referred to only by the acronym MSS.

The technical testing involved calculating the signal-to-noise changes in the C-Band transmissions caused by nearby WiMax services. The tests also calculated the proportion of interference, or unintelligible jamming, to the overall 'noise,' or undesirable and conflicting transmissions, that the WiMax services caused for the C-Band services. Additional tests include calculation of the 'bit error rate,' or proportion of garbled digital transmissions caused by the WiMax services.

The testing evaluated the threat of both mobile and fixed WiMax services near FSS ground stations.

The tests involving 'nomadic,' or randomly traveling, WiMax sources showed that the C-Band services could be completely mangled by the competing services' transmissions from as close as one kilometer. Fixed WiMax facilities could achieve the same undesirable signal blocking from as far as 12 kilometers, according to the SUIRG report.

The satcom industry managed to preserve its access to the C-Band during last year's WRC-07 conference. That meeting pitted the satcom transmissions community against the larger and better funded telecom companies that seek to deploy terrestrial WiMax networks extensively to upgrade mobile phone services, according to the trade association and published reports.

The complete interference study, titled 'Field Test Report, WiMAX Frequency Sharing with FSS Earth Stations, February 2008,' is available here.


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