China and Australia Investigate Ground-Based GPS System
4 Mar 2013
Both China and Australia are investigating advanced technology of broadcasting global positioning signals from the ground, rather than, or in addition to, employing orbiting GPS satellites, which is currently used for GPS tracking and navigation. A ground-based location positioning system stands to not only save time and money, but pinpoint locations with more accuracy.
Satellite navigation systems are a global operation. Countries throughout the world are developing and utilizing the technology, including Russia with the GLONASS, China with the COMPASS, Japan with the Quasi Zenith Satellite System (QZSS) and India with the Indian Regional Navigational Satellite System (IRNSS), and of course the United States with the Global Positioning Satellite System (GPS).
It goes without saying that satellites provide a wealth of possibilities to the countries using them, but with advanced technology comes more time and money for developing, testing, building, and implementing them. For instance, funding for the U.S. GPS systems ran approximately $1.5 billion or more for developments, testing, and launching in 2012 alone.
Surely, there’s a less inexpensive solution, which is why several countries are experimenting with ground-based location positioning.
China
China is just one country looking into the possibility of building a location-based system on a shoestring budget. Currently, researchers from the National Astronomical Observatories in China are testing a way to use transmitters that are ground-based, rather than orbiting in the earth’s atmosphere. The idea is that these transmitters will mimic satellites. The observatories are part of the Chinese Academy of Sciences in Beijing and Hai-Fu Ji and colleagues are leading the research.
The navigation systems are being tested to use radio signals that are transmitted from ground satellites with a very high accuracy rate. The receivers on the ground currently have the same signal arrival times as many popular satellite systems, including GPS which uses 30 satellites to transmit signals. Hai-Fu has developed a way to transmit the time signals from the ground and then route them through geostationary satellites currently in orbit. Existing communications infrastructures already in orbit are being used, therefore allowing a significant savings.
The idea was first tested in 2005 with communications satellites in several cities throughout China. However, the geostationary satellites sit in a position along the equatorial plane allowing only for an east-west position. The north-south position required additional satellites below and above the equatorial plane. Hai-Fu says they have fixed the problem by taking advantage of the satellite’s fuel conservation method.
In order to conserve fuel, geostationary satellite operators will keep station in the east-west direction only which over time causes the satellites to incline, forming a figure-8 shape from the ground. Taking advantage of this north-south movement, Hai Fu and fellow researchers plan to broadcast the signals and let receivers on the ground triangulate the position in three dimensions.
Australia
China isn’t the only country investigating ground-based GPS systems. In Australia, a company named Locata has developed “LocataLites”, which is a constellation of ground-based transmitters the size of a book that enable devices to get a highly-accurate local location readout. While traditional GPS tracking and navigation devices can pinpoint a location within centimeters, LocataLites is said to be able to pinpoint locations within just a few centimeters. Because LocataLites are based in the ground versus tens of thousands of miles in space, it takes less time for the signals to reach the receivers. LocataLites is intended to meet particular locale needs, and as Locata puts it establish “GPS hotspots”.
United States
Meanwhile the U.S. has it’s own version of this technology — Ground Based Augmentation System (GBAS) . Currently, GBAS focuses on it’s technology on airports for more precise airplane approaches, terminal operations, and departure procedures through ground-based transmitters via very high frequency (VHF) radio data links.
Aside from improving accuracy and saving time and money, the new ground-based method of transmitting signals for satellite navigation systems could have additional benefits. They could be broadcasted over a wider range of frequencies, employed with a two-way communication link, combined with weather information, in addition to offering improved signal range and interference avoidance. Because the cost of testing the broadcast and routing system of these ground-based systems is relatively low, we may very well see more of this technology being explored and used in the future.
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