Szu-chia Wang (Editor: Nancy Stubbs)

In August 1990, the American government sent thousands of military forces to the Middle East to protect Kuwait from an Iraqi invasion. Considering the unfamiliarity with the local terrain, American authorities decided to take advantage of the Global Positioning System (GPS), which was still under construction, in order to lead the forces to find the targets. The code name of this military action was Desert Storm. During this action, American troops forced Iraq to withdraw military forces from Kuwait successfully. Experts agree that part of the triumph can be attributed to the implementation of GPS. This was a vast public debut of this brand new tracking system.

GPS technology requires the cooperation of three parties: twenty-four satellites in space, the monitor stations, and GPS receivers. The first element is microwave signals transmitting from those satellites that orbit 20,200 km above sea level from the earth. The twenty-four satellites broadcast two sets of microwave signals every thirty seconds: L1 (1575.42 MHz) and L2 (1227.60 MHz). L1 consists of three messages: time, satellite position, and ephemeris (precise orbital data). And L2 is used to detect the delay of the signals when they pass through the ionosphere. The second element is American government owned monitor stations. By comparing microwave signals and their own information, monitor stations are able to check the accuracy of these messages and then adjust the messages by uploading the precise ephemeris and clock data. Therefore, the American government ensures the accuracy of these signals.

The key element in positioning technology is the computing function of GPS receivers. The mathematics applied here is the formula for spheres and circles. First, after obtaining L1 and L2 data, the receiver is capable of calculating the distance from the standing point to the emitting satellites (time difference ´ the speed of radio signals). Then the receiver uses the known distances as radiuses and the locations of satellites to be centers, so that the unknown location can be found in terms of the equations for circles and spheres. In order to estimate the exact information of the unknown spot, the receiver requires four satellites to gain its longitude, latitude, elevation, and time data.

After solving the equations, the receiver infers two opposite points resulting from the intersection of the four spheres. Because the two points are totally opposite, in terms of geographic locations, it is easy to reject the unreasonable one by pre-programming the computing system in the receivers. Without the distortion of signals, the accuracy of the location could be determined within 30 meters.

‘GPS is a model for dual-use systems,’ said General Dickman in a July 1995 news release. What the General suggested was to welcome everyone, including the military and civilians to utilize GPS. Since that day, there are a lot of manufacturers, including the telecommunication company Motorola, the consumer electronic manufacturer Pioneer, the semiconductor company, Rockwell, and the initial GPS provider Trimble, dedicated to this business and hoping to generate billions of dollars in revenues.

The prosperous GPS business has been operating for only three years, but it took over twenty years and $12 billion to finish its construction. The original idea was initiated by the Department of Defense in 1973 and the first experimental GPS satellite, Block I, was launched five years later. In February 1989, Block II, the first operational satellite, started to orbit the earth. The whole constellation of twenty-four satellites took four years to complete. It was not until July 1995 that the GPS and the detection system were completed and began operation. The whole works was then transferred to the America owned Navigation Satellite Time and Ranging (NAVSTAR) GPS joint program office, at the Los Angeles Air Force Base, which is in charge of managing and maintaining the GPS service.

A news release from the White House on 29 March 1996 stated "…rapid growth in a burgeoning civil and commercial GPS market…from $2 billion to $8 billion in annual sales by the year 2000." Over the past three years, the business has been flourishing. The main manufacturers continuously introduce various products based on GPS technology ranging from the $250 handheld navigational equipment for outdoor recreation by Magellan Systems Corp., to the $16,000 high-accuracy aviation locating system by Ashtech. Moreover, the market is not restricted to America. According to the 30 June 1997 issue of Computerworld magazine, the total sales of GPS related products in Japan 1996 reaped $1 billion. Experts believe that the increasing awareness of GPS and the decreasing price of GPS applications will accelerate the acceptance of market.

With the efforts of GPS manufacturers, GPS technology could be employed on anything that needed to determine a location. For example, by carrying a cellular phone integrated with a GPS receiver, snowboarders who go astray are able to pinpoint their standing site and inform the rescue team where they are. It can be applied to transportation systems as well, such as aircraft and vehicles. The latter one, car navigation systems, is the most popular GPS application today.

There are two ways to implement GPS technology in vehicles. Direct installation of GPS receivers in automobiles by car manufacturers like Toyota, Acura, General Motors Corp., BMW, Mercedes and Cadillac started in 1996. Avis car rental also has some cars available with navigation systems. Non-installed, portable GPS devices, charging $375 and above, is another way to implement GPS in cars (Brown 1998). Most of the devices contain a digital map which stores data from a CD-ROM or the Internet and a GPS receiver. Some products allow the attachment of laptop computers that can be used to download the directions of a desirable route. The device will indicate the right route with arrows on a map or with verbal direction.

For many reasons, such as customer’s need and the development of new technology, GPS industry participants are anticipating the growth of positioning markets, but it is the commitment of the American government in March 1996 that triggered the phenomena. An announcement by the Clinton administration demonstrated the U.S. global positioning system policy. The President promised that GPS will keep opening up to the worldwide public at no charge. Like the domino effect, after this document was released, lots of novel products and new applications emerged in the marketplace. This confirmation from Clinton reinforced many entrepreneurs’ willingness to continue to invest in enhancing the capabilities of the GPS receivers for the long term, resulting in the decline of prices and improved techniques.

Even though GPS can provide accuracy to around 30 meters, the commercial GPS receivers can only achieve accuracy of around 100 meters because of the intervention of the American government. What the America government is concerned about with the commercial applications is that they may affect military security. The authorities embedded the Selective Availability (SA) program in each GPS satellite to intervene in the transmitting of signals. Only the government and users with the cryptographic solution get exact information and are able to infer the site of the unknown spot. However, in 1996 the incumbent American government said they will re-evaluate the SA and the possibility of terminating the system on 22 August 1999. During this period, they will seek another method to protect the military security.

The overall evaluation of this industry is optimistic because the function of GPS is the same as a compass, which is considered to be one greatest inventions in human history, and we all know how prosperous the map business is. The only obstacle is how to meet different users’ demands of location precision. With the efforts of the GPS industry, there are several solutions to correct the errors such as the Differential Global Positioning System (DGPS) which provides the 1-to-10 meter accuracy.

Once the GPS products are accepted by mass consumers, it is certain that the issue of "Big Brother" will be raised. On one side, the GPS facility enables users to find their way home. On the other side, it also can be used to monitor the location of people. For example, last year 1997 Pro Tech Monitoring Inc. proposed a new system SMART, which allows police with GPS equipment to track prisoners wearing special bracelets. In the future, it is likely that bosses will want to use this device to track where sales people have been.

Anonymous (1998) ‘Consumer electronics show features slew of GPS-cellular security products’, Wireless Today v2n8.

Ayers, L. (1998) ‘Know the way to San Jose: TravRoute software’s door-to-door copilot in-car global positioning system for laptop computers’, PC/Computing v11n2.

Brown, B. (1998) ‘Gamin GPS III goes solo’, PC magazine v17n2.

Brush, M. (1996) ‘White House decision paves the way for new high-tech industry: military GPS technology is expected to become multi-billion dollar business by 2000’, Money Dailies.

[http://wwwhost.cc.utexas.edu/ftp/pub/grg/gcraft/notes/gps/gps.html] 27 February 1998.

[http://www.redsword.com/gps] 27 February1998.

[http://www.mto.gov.on.ca/english/teng/gps4.pdf] 29March 1998.

Nord, G., Jabon, D. and Nord, J. (1997) ‘The mathematics of the Global Positioning System’, Mathematics Teacher v90n6.

Siuru, B. (1998) ‘You’ll never be lost again’, Popular Electronics v15n3.

Back to Home Page