Many people are regularly using the Global Positioning System (GPS), based on 24 satellites. Major users are the military or trucking companies tracking their fleet. But the technology is aging and apparently reaching some limits. In this article, Scientific American looks at the next generation of GPS technology, GPS III.
U.S. officials have begun planning the next generation of satellite navigation technology, known as GPS III (the current system is the second generation). The driving forces are better accuracy and reliability, concern about more effective signal-jamming techniques, alternative geolocation services [like Galileo, the European program], and new, more sophisticated applications, such as intelligent highway and traffic-safety systems.
GPS III satellites will start to be launched in 2010, in what will be a multibillion-dollar market eyed by Boeing or Lockheed Martin.
Per Enge, director of Stanford University's GPS Laboratory, thinks that the evolution of the technology will be driven by three factors.
The first is frequency diversity, which in fact is already being addressed as aging GPS II satellites are replaced periodically. When completed, the constellation of modernized orbiters will furnish civilian users with three new positioning signals. It will, moreover, provide U.S. armed forces with two additional signals that, being higher power, can better resist jamming.
The second big trend concerns overcoming radio-frequency interference (RFI). "GPS broadcasts are extremely low power -- equivalent to that of five lightbulbs," Enge explains. "With received power levels of 10-16 watt, the signal can be easily overwhelmed by nearby radio emitters." When deployed, so-called RFI hardening will permit the GPS receiver to double-check its calculations.
[The third one] revolves around the installation of "integrity machines -- systems that guarantee that the positioning error is smaller than a stated size." Called the Wide Area Augmentation System, the concept was developed by the FAA in cooperation with researchers at Enge's Stanford lab and elsewhere.
Source: Steven Ashley Scientific American, August 25, 2003
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