Finding frequencies for new GPS signals proves difficult
- By Bob Brewin
- Apr 06, 1998
ALEXANDRIA, Va.—- The departments of Defense and Transportation need to resolve a number of key issues before the two agencies can go ahead with a plan announced last week to add two new civilian frequencies to the Global Positioning System, according to DOT.
Joe Canny, chairman of the DOT Civil GPS Service Interface Committee (CGSIC), said that while the administration has solidly backed the two new civilian frequencies, which are essential to ensuring reliable aerial navigation as well as providing increased accuracy to scientific users, the Pentagon has concerns about how the second civilian frequency can be added to the existing military band. CGSIC is the DOT group responsible for communicating and dealing with civilian GPS users.
Last week Vice President Al Gore announced that DOD and DOT agreed to add for civilian use two additional signals on the GPS satellites slated to go into service in 2005. GPS satellites provide precise positioning and navigation signals from a constellation developed by the Pentagon at a cost of more than $10 billion. Gore said the additional signals would improve navigation and other operations that depend on precise positioning, and the United States would provide these signals free of charge to anyone in the world equipped with a GPS receiver. DOD provides civilian users with accuracy of 100 meters or better on a frequency known as L1, while military users can tap into accuracy of 25 meters or better on the GPS L2 band.
But Canny said DOD and the Federal Aviation Administration, a DOT agency, have not yet reached agreement on the spectrum that will be used for the third civilian frequency. "There is substantial disagreement" between the two agencies on the new frequency, Canny told a CGSIC meeting here.
One proposal under consideration, Canny said, is to "replicate" the civilian frequency on the L2 band. But he added DOD is concerned that this would limit the capability of military-specific applications, such as precise weapons targeting. A more acceptable solution for DOD, Canny added, would be to split the new second civilian frequency in two and position the two parts at opposite ends of the military L2 band.
DOD and the FAA have developed opposing positions on the third frequency, Canny said, with the FAA pushing for a spectrum allocation at 1,205 MHz in the aeronautical band. The Pentagon opposes this frequency because the military uses it for tactical data link applications between aircraft. Canny said the two agencies need to resolve these issues so the United States can gain protection from interference through an administrative process managed by the International Telecommunications Union.
The joint interagency GPS executive board, which is staffed by DOT and DOD representatives, has tentatively set a meeting to resolve the frequency issues by mid-August, Canny said.