Spectrum battles mire Defense in budget & safety straits (Part 2 of 2)

Defense Department officials have confirmed that last fall the United States came perilously close to losing its hold on a portion of the radio spectrum used for Global Positioning System transmissions.

Future use of the GPS spectrum—- which is critical to military and civilian aircraft navigation and Defense command and control systems—- remains in doubt because the European community is expected to resubmit a proposal in 1999 for extracting some frequencies within the spectrum for mobile satellite services.

According to industry sources, such a proposal not only would threaten the integrity of military and aviation GPS systems, but it also would impede the ability of these communities to further develop safety- and mission-critical applications. The proponents disagreed, asserting the spectrum reallocation would not have an impact on GPS systems. But Cindy Raiford, deputy director of communications and DOD spectrum manager in the Office of the Assistant Secretary for Defense for Command, Control, Communications and Intelligence, said the department found the European proposal technically flawed and one that could cause substantial interference with worldwide GPS applications. "This is a safety issue and not to be treated lightly," Raiford said.

Despite the U.S. government's objections, European representatives put the proposal forward last fall at the World Radiocommunications Conference (WRC), which is organized every two years by the International Telecommunications Union to discuss spectrum policy and related issues.

Sally Frodge, an engineer and policy analyst with the Transportation Department, said the Mobile Satellite Services (MSS) proposal was headed off after heavy lobbying from agencies, including the State Department, DOD and DOT.

Frodge said if a vote had been taken soon after the proposal was introduced, it would have had a good chance of passing. However, because debate and study of the proposal were allowed, the United States and the GPS users it had lobbied had time to persuade enough WRC members to table the MSS proposal for another two years, allowing further study.

The proposal would open up the only band of the spectrum—- 1559 MHz to 1567 MHz—- reserved exclusively for aeronautical radio navigation and navigation satellite services, including the primary GPS frequency. MSS providers have proposed reallocating a portion of that band for communications downlinks as a way to accommodate the growing demand for commercial telecommunications services.

According to DOD and other GPS users, the proposed arrangement could wreak havoc on GPS applications by interfering with GPS signals. The added traffic could make it difficult for GPS receivers to pick up, or "acquire," a satellite's signal, or it could introduce errors in tracking that signal, thereby affecting virtually any military or civil application.

Perhaps just as damaging, GPS industry sources say the potential for GPS interference would curtail further development of future GPS applications.

DOD, which built the GPS satellite system, is researching ways to open up the GPS system to further civil aviation use. Eventually, that may require reallocating some of the GPS spectrum band, according to aviation industry sources.

But the proposal would make the MSS providers a "co-primary" user of that band of the spectrum, which means the government would be required to seek permission to change spectrum allocation, which the GPS community sees as a major roadblock.

"By allowing sharing [of the band], you prohibit any future aviation application," said Larry Chesto, director of telecommunications at ARINC Inc., an organization that conducts aviation-related research.

Although DOD attendees were able to delay acceptance of the proposal, conference leaders said the issue deserves further study and will be revisited at the next conference in 1999.

Janet Dewar, vice president of corporate affairs at Comsat Corp., said her company opposed the issue when it was developed by the International Mobile Satellite Organization (Inmarsat), of which Comsat is the U.S. representative.

"We knew [the Inmarsat proposal] was a problem for GPS transmissions," Dewar said. "The proposal would have threatened the integrity of GPS transmissions worldwide. And you don't want any interference with that because it is such an important aspect of aeronautical safety."

Raiford said the government is already gearing up to fight the proposal when it arises again in 1999 and to challenge it on technical grounds. "We will have the technical [data] to show that it is not feasible," she said.