An Alternative to GPS?

Outdoor-GPS-Unit1A few weeks ago DARPA (Defense Advanced Research Projects Agency) issued a request to the electronics and aviation industries to consider if there can and ought to be an alternative to GPS (Global Positioning System). DARPA has several concerns about GPS: It doesn’t work underground or underwater. It can be severely degraded by solar flares. And, since GPS is satellite-based, it is susceptible to being jammed or knocked out of commission by an enemy. And so DARPA asks if we should be exploring an alternative to GPS that overcomes these deficiencies. Since a lot of things we do relies on GPS any replacement has to be at least as accurate as GPS, which can pinpoint anything within 25 feet anywhere on earth 95% of the time. When coupled with land-based GPS augmentation technologies the accuracy can be narrowed in the best cases to within a few centimeters for land-based locations.

GPS was developed by the military in the late 1970s as a needed component of more accurately firing missiles from atomic submarines. The submarines needed to know exactly where they were located in order to calculate the desired path of a missile. But in 1983 after the Soviet Union shot down a civilian airliner KAL 007 that had strayed into their airspace, Ronald Reagan ordered that GPS be made available to all commercial aircraft.

GPS basically works by triangulation. Today there are a series of thirty GPS satellites at about 12,500 miles above the earth. To get the most accurate reading a location must be able to see at least four of these satellites. Each GPS satellite contains a very accurate clock which is almost as accurate as the atomic clock that is the basis for keeping official time. Each GPS satellite continuously transmits a message that includes the time the message was transmitted and the position of the satellite at the time it was sent. On the earth, a GPS device reads these transmissions and does a calculation to determine the coordinates of the GPS device. The math is somewhat complex in that a sphere is calculated around each of the received GPS signals and where those spheres intersect is the location of the GPS device.

In 1996 President Clinton authorized GPS to be used for any commercial use and by around 2000 it became widely adopted. Since then the number of ways that GPS is used has mushroomed. Following are some of the more important uses today of GPS, with the telecom uses listed first:

  • Cellular telephony. GPS is essential today in cellular roaming in handing cell phone calls from one tower to the next. GPS is also used for determining the caller location for cellular calls to 911.
  • Telematics. GPS is used to determine the location of moving vehicles. Telematics enables technologies like using Siri to help you with driving directions. This is also used for tracking and locating ships. This same technology enables stores to track the location of shoppers based upon their cellphone signal.
  • Geotagging. This is used in modern mapping systems to overlay photographs over maps.
  • Surveying and mapping. We now use GPS when mapping the routes of proposed fiber or other utilities and to determine property boundaries.
  • Geofencing. This is the technology used in fitness trackers, dog collars and other systems used today to track the location and travel history of a GPS device.
  • Clock synchronization. The accuracy of GPS time signals (±10 ns) is second only to the atomic clocks upon which they are based and many of our telecom devices get their timing from the GPS satellites.
  • Automated vehicles. GPS is going to be key in developing automated vehicle and drones.
  • Meteorology. GPS is used in sensors and balloons used measure and calculate atmospheric pressure, wind speed and direction in the upper atmosphere.
  • Aircraft tracking and navigation.
  • Tectonics. GPS enables direct fault motion measurements to pinpoint the epicenter of an earthquake.

This partial list shows you how quickly GPS has been integrated into our everyday lives in just the last decade. GPS is now a key component of huge number of industry and functions that we count on daily. I can see why DARPA is concerned about the security of GPS. The thought that the GPS system could be disabled in an attack on the country is scary. Luckily DARPA thinks there are alternatives and suggest some possibilities including “electro-optic/infrared (EO/IR) and radio frequency (RF) imaging (active or passive imaging), active/semi- active/passive guidance by EO/IR and/or RF signals, and tracking by exploitation of signals of opportunity.”

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