In yesterdays article I referenced the peculiar number of Compass satellites registered with the ITU. Naturally, such registrations also include the frequencies to be used. Things get very interesting when you compare Compass registrations to the GPS and Galileo allocationsIt is already well known that GPS and Galileo share some of the same frequencies. The rationale behind the frequency-sharing is simple the systems have the potential to be interoperable. To a civilian end-user, Galileo is merely an extension of the GPS constellation, providing better coverage and higher resolution. Yet each system retains some non-overlapping frequencies, such as GPSs military M-Code and Galileos Public Regulated Service. That way, the US military doesnt have to worry about Galileo interfering with its GPS signal.Many of you may remember that before this arrangement was agreed on, the DoD was afraid that they would not be able to jam Galileo without jamming its own GPS M-Code. This would have left the U.S. military planners in a difficult position to prevent the enemys use of satellite navigation (using civilian Galileo receivers) they would also have to deny it to themselves. Despite DARPAs efforts in recent years to build true precision-guided weapons independent of GPS, the military still remains heavily dependent on GPS.Six years of trans-Atlantic diplomacy finally resulted in the Binary Offset Carrier 1.1 standard, which was agreed upon in June 2004 by U.S. Secretary of State Colin Powell and EU Transport Commissioner Loyola de Palacio. Neither GPS nor Galileo is vulnerable to jamming targeting the other and the U.S. military retains the right, and the technical capability, to use ground jammers to knock out Galileo signals in war zones.Both GPS and Galileo are now experiencing deja vu, though, thanks to Compass. Without going into all the numbers, virtually all GPS and Galileo frequencies are overlain by Compass. Not only that, but Compass retains additional frequencies that are not touched by either of the U.S. or European systems (a caveat: satellites rarely use all the frequencies included in their ITU registrations, so this needs to be taken with a grain of salt). GPSs civilian and military channels, Galileos open, commercial, and Public Regulated channels are all within those ranges. Only the frequencies used onboard GPS satellites for missile warnings were avoided at least China was wise enough not to mess with that.Compass could jam GPS or Galileo even if Compass is only a regional system for Asia with a limited number of satellites. In a military flare-up regarding Taiwan, China could certainly benefit from a complete denial of positioning services to the U.S. and its allies. All it would take would be for the Chinese to program Compass to drown out the other systems with a stronger signal to start causing problems (there is debate as to whether or not such drowning can be overcome).More deceptively, Compass could masquerade as GPS and Galileo and transmit deceptive signals. Obviously, the specter of a Chinese finger on a big, red jamming button is giving the shivers to the U.S. military.However, frequency allocations do not indicate nefarious intent. These same allocations could allow Compass to work in harmony with GPS and Galileo. Overlapping frequencies are essential for making the American and European systems interoperabile the same would hold for Compass. There is precedent; both Japan and India have well-developed plans to augment the GPS network to suit their needs (in Japans case, high-latitude urban reception; in Indias an expanding aviation market). A global, multinational satellite navigation network comprising over 75 satellites would certainly provide remarkable coverage and high precision to all users during the vast majority of the time when there is not a military incursion.And, if worst comes to worst, everybody would have their own independent networks to fall back on assuming you dont get jammed first.Ryan Caron
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