WiMax Industry Group Concedes on Interference Loss

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  Space News Business

WiMax Industry Group Concedes on Interference Loss

By PETER B. de SELDING
Space News Staff Writer
posted: 24 April 2007
10:28 am ET


PARIS — The principal industry association promoting broadband wireless services, in a major concession, has concluded that WiMax and similar technologies cannot coexist with satellite services in the C-band portion of the radio spectrum in nations where satellites are already well established.

The findings of the WiMax Forum, outlined in a position paper, represent a significant, if not yet final, victory for satellite operators, television broadcasters and others that have urged governments worldwide not to permit broadband wireless services into the C-band portion of radio spectrum in regions where satellites have been operating for decades.

“The WiMax forum’s White Paper is right on target and we welcome it,” said Matt Botwin, regulatory working group chairman of the Global VSAT Forum, an industry association representing satellite operators and dish-antenna builders. “I think that when they [broadband wireless proponents] first went into this, they didn’t realize how many dishes were out there.”

Botwin said April 17 that the two sides now hope to come together to test Forum-certified WiMax equipment near a C-band installation to put to rest any remaining doubts about how difficult it will be for a WiMax installation — even one located 30 kilometers from a C-band satellite antenna — to operate without wiping out the television or other signals from the satellite link.

In North and South America, Africa and many parts of Asia, C-band links are routinely used for television transmissions. But the scarcity of unused radio spectrum and the need for regulatory authorization of WiMax and other wireless technologies has caused some governments to approve WiMax installations in the lower portion of C-band.

Their reasoning has been that, while WiMax and satellite services cannot share the same segment of C-band, they could operate in different portions of the band.

India in particular authorized WiMax in the lower extended portion of the C-band, 3.4-3.7 gigahertz, in January and told satellite users to leave that section of the band or face interference. Under pressure from the Indian Space Research Organis ation, India’s Ministry of Communications suspended the ruling pending tests.

Field trials in Asia and South America have concluded that broadband wireless cannot occupy any portion of C-band without scrambling satellite signals, even if the two services occupy different portions of C-band.

The WiMax Forum position paper basically accepts this point.

Titled, “Compatibility of Services Using WiMax Technology with Satellite Services in the 2.3-2.7 GHz and 3.3-3.8 GHz Bands,” the paper says: “Even when the two services operate in separate, dedicated sub-bands … coexistence may prove difficult” unless the satellite stations are equipped with special filters or are surrounded by concrete or other shields.

The paper conceded that it is unrealistic to expect the thousands of C-band antennas already installed to be retrofitted with filters, and that shielding is also unfeasible.

The paper suggests that, in some regions, WiMax installations could use steerable antennas to avoid pointing in the direction of known satellite Earth stations. But it also says that a large majority of C-band satellite Earth stations worldwide are not registered with national regulatory authorities because such registration was not required.

Botwin said C-band is only one of several bandwidths for WiMax that are being explored, and that ultimately the satellite industry and WiMax operators will work together. For example, he said, satellite systems can be used to carry WiMax transmissions between users in Africa and the United States or Europe.

The Global VSAT Forum and the WiMax Forum met April 11 in London to talk about the position paper and determine how the two groups might work together.

Botwin said he hoped that a test site and test equipment might be agreed on soon.

Tim Hewitt, one of WiMax Forum’s directors and head of radio spectrum policy at the BT Group chief technology office, declined in an April 17 e-mail to discuss the April 11 meeting and declined to discuss the WiMax Forum paper.

The WiMax Forum has more than 400 member companies, including the biggest names in the technology and telecommunications industry. Whether these individual companies will abandon hope of a global C-band authorization for WiMax is unclear.

Spectrum regulators worldwide are scheduled to meet Oct. 22-Nov. 16 in Geneva to allocate radio spectrum during the World Radiocommunication Conference, organized every four years by the International Telecommunication Union, a United Nations affiliate.

At these meetings, governments vote on spectrum allocations. If WiMax operators by then are still lobbying for a C-band allocation, the satellite industry has an ally with a history of some success at these meetings: the U.S. Defense Department.

U.S. defense authorities for the past two years have been voicing concern that WiMax, if deployed anywhere near defense radar systems, would interfere with the use of the radars, which are located worldwide. “DoD’s ability to act globally and support our allies would be significantly impaired” if WiMax were given access to the 3.4-3.7-gigahertz bands, according to a July 2006 policy statement.

The statement also said that the U.S. Defense Department is a large customer of commercial satellite operators and would be affected if these commercial operators suffered WiMax interference.