Anyone who has tried to use GPS in downtown Los Angeles knows that the indicated GPS location can vary greatly from the actual location. This is caused by GPS satellite signals bouncing off city buildings and adding multipath and delay to the signals. As GPS operation relies on precise timing of the signals from a constellation of satellites, such delays cause the receivers to miscalculate their positions.
A new antenna design being tested by the U.S. Air Force could reduce the multipath problem and make GPS significantly more reliable and able to function in dense urban areas. It might also allow GPS to work indoors in some cases. The Air Force Institute of Technology system builds on a design invented by a Canberra, Australia company, Locata, and a soccer-ball-sized proof of concept prototype.
“The requirements of the military are now converging with the requirements of Apple and Google,” said Munzio Gambale, co-founder and chief executive officer of Locata. “Everyone wants to use these location tracking-devices indoors and in urban areas where people say GPS will never work.”
Locata's design is different from that used by other companies in that it uses multiple element GPS antennas with all elements connected to a single radio, rather than to individual radios. This reduces cost, but requires a large receiver. Todd Humphreys, a professor at the University of Texas geopositioning lab, cautions that because of the large receiver, the approach will only be practical in military applications.
While it wasn't mentioned in the MIT Technology Review article A Cure for Urban GPS: a 3D Antenna, this new GPS antenna design should also be able to configured to be less sensitive to GPS jamming and spoofing.
