GPS, or Global Positioning System, was developed in the early 1960s by the U. S. Department of Defense as a satellite-based radio navigation system. Paid for by U. S. tax dollars, GPS provides precise time and location of signal receivers anywhere, anytime and under any atmospheric conditions through the use of a specific network of satellites known as NAVSTAR (Navigation Satellite Timing and Ranging). GPS meets both civil and military user requirements, though there were originally two very different levels of service that separated such interests.

Until 2000, there was distinct GPS Service for civilians and separate GPS Service for the Government, which had drastic differences in accuracy and range. For public GPS access, utilized the Standard Positioning Service (SPS) and an encoded Precise Positioning Service (PPS), primarily intended for use by the Department of Defense, met the Government's unique needs. In 2000, President Bill Clinton ordered that Selective Availability, which had been often used to scramble and weaken the SPS signal, be turned off, thus opening up the full power of GPS to everyone. This sharply increased national and international interest in GPS and even allowed the end of SA to have little negative effect on national security as the Military was able to quickly develop and test their ability to selectively block accurate GPS transmissions in areas of conflict or where U. S. security was at risk.

The civilian-oriented Standard Positioning Service (SPS) signal accuracy was intentionally weakened in order to protect the interests of the Federal Government and national security. This process is known as Selective Availability (SA) and it controls the availability of the system's full ability.

SPS provides accuracy within: 100 meters, SPS provides accuracies of (for position, the accuracy with respect to geographic, or geodetic coordinates of the Earth) within: 100 meters (2 drms) horizontal 156 meters (2 Sigma) vertical 300 meters (99.99% prob.) horizontal 340 nanoseconds time (95% prob.).

The full strength of the GPS System is only accessible through the Precise Positioning Service (PPS) and is strictly enforced in the name of Governmental interest and national security.

Since President Clinton ended Selective Availability in May of 2000, GPS Tracking Systems have been used for a wide range of activity employing its strengths to help make life safer and easier for everything from 9-1-1 dispatchers to worried pet owners.

Farmers can use GPS data to improve crop yield and prevent hazardous ground-water runoff. Farming soil sensors and other monitors help pinpoint locations where changes in watering, fertilization or weed control are necessary in the farmers' fields.

Some other common uses of GPS tracking are: Personal emergencies, roadside assistance, landscaping, architecture, endangered animal preservation, animal migration tracking, stolen vehicle location, fleet management, and business logistics. These are all practical uses for GPS that are relatively simple and extremely effective.

GPS Technology is divided into three different segments: Space, Ground, and User.

The Space Segment consists of a minimum of 24 operational satellites. The satellites are spaced in orbit so that at any given time a minimum of 6 satellites will be in view of users anywhere in the world. The satellites are continuously broadcasting position and time information to users throughout the world.

The Ground Segment incorporates a control station in Colorado Springs, with five monitor stations and three ground antennas located throughout the world. These five monitor stations track all GPS satellites in its view as well as collect information from each satellite’s broadcast.

The User Segment consists of the receivers, processors, and antennas that allow land, sea, or airborne operators to receive the GPS satellite broadcasts and pinpoint their exact velocity, time and position.

The GPS System is extremely accurate depending on the amount of clearance from the U.S. Department of Defense. In certain instances, the Department of Defense may occasionally jam the GPS signals for civilians (SPS) on a short-term basis in order to insure the maximum level of national security. However, several other variables may cause a disruption in ones signal as well.

GPS Receivers can be purchased and installed into personal vehicles rather easily and affordably. Most companies that manufacture GPS Receivers build them to work in a wide range of vehicles. Some companies such as OnStar, are specific to certain vehicles and are factory-installed only. OnStar has been working exclusively with GM sine the new line of Cadillacs was introduced in 1997. OnStar is undoubtedly one of the biggest names in GPS technology, however it is certainly not the only reliable system.

Some inexpensive systems simply plug in to your car's cigarette lighter and are small enough to store in your glove compartment. However, these systems are not recommended if you intend to use the GPS frequently as they are not as user-friendly. Garmin and TomTom are just two of the major portable GPS Systems that are made to be as easy to use as they are effective in navigation as well as vehicle tracking.

WAAS stands for Wide Area Augmentation System and is based on a network of approximately 25 ground reference stations that cover a very large service area. Each of these precisely surveyed reference stations receive GPS signals and determine if any errors exist. Each wide area ground reference station in the network relays the data to the Wide Area Master Station (WMS) where correction information is computed. The WMS calculates correction algorithms and assesses the integrity of the system. A correction message is prepared and then uplinked to a satellite via a Ground Uplink System (GUS). The message is then broadcast from the satellite on the same frequency as GPS to GPS receivers, which are within the broadcast coverage area of the WAAS.

With technology always advancing, the future of GPS is extremely bright. With the development of Europe’s NAVSTAR equivalent, the GALILEO System, GPS developers and users have increasingly anticipated the benefits of combining the operation of both the NAVSTAR and GALILEO Systems. Some of the more important potential advantages would be: more available signals that will allow GPS users to access more satellites from remote areas. Additional signal power and spectrum diversity will lessen the impact of expected signal noise and interference. And also, improved signal redundancy.

However some people are also aware of the drawbacks that could come from a NAVSTAR/GALILEO cooperative system. Many fear that this would increase equipment cost to the user in order to be able to access both systems. Also, there would potentially be more additional noise and interference environment. And finally there is concern as to how the co-operative system could set the satellite orbits to ensure that interoperability actually benefits the user.

GNSS (Global Navigation Satellite System) is expected by many experts to be developed soon and capitalize on the compatibility of technology from the NAVSTAR (United States) GPS system and the GALILEO GPS (Europe) system. This comprehensive support system would provide users with navigation information that covers a broader area with higher accuracy data. GPS users across the world would potentially benefit from the access to more satellites due to the availability of two or more satellite constellations.