Nextel GPS vehicle tracking system

What is GPS?

GPS is the Global Positioning System. The US military calls it NAVSTAR GPS. It is a satellite navigation system and is used to determining one's precise location. GPS provides a highly accurate time reference, almost anywhere on Earth or in Earth orbit. It uses an intermediate circular orbit (ICO) satellite constellation, of at least 24 satellites.

The GPS was designed and controlled by the United States Department of Defense. It is available to anyone and is free of charge. The system is divided into three segments: space, control, and user.

Different parts of GPS.

The space segment is the GPS satellite constellation.

The control segment is ground stations around the world. These stations are responsible for monitoring the flight paths of the GPS satellites. They synchronize the satellites' onboard atomic clocks, and upload data for transmission by the satellites.

The user segment is GPS receivers. They are used for both military and civilian applications. A GPS receiver decodes time signal transmissions from multiple satellites. Next, it calculates position using trilateration.

Why does GPS exist?

The primary military purpose, of the GPS, is allowing improved command, and control, of forces. This is done through an enhanced ability to accurately specify target locations, for cruise missiles or troops. The satellites carry nuclear detonation detectors. This forms a major portion of the United States Nuclear Detonation Detection System.

Other Applications of GPS.

The GPS is used by many, outside of the military. Consumers use the GPS's Standard Positioning Service worldwide, free of charge. Low-cost GPS receivers (price $100 to $200) are widely available. They are combined in a bundle, with a PDA or car computer.

The system is used as a navigation aid in aircraft, sea-going vessels, and cars. The system is used by computer-controlled harvesters, mine trucks, and other vehicles. Hand-held devices are used by mountain climbers and hikers. Glider pilots use the logged-signal to verify arrival at turnpoints, in competitions. Nextel GPS vehicle tracking system

GPS and the Military.

On May 1, 2000, US President Bill Clinton announced this "Selective Availability" would be turned off. However, for military purposes, "Selective Deniability" is still available. It effectively jams civilian GPS units while in a war zone or global alert. However, it still allows military units to have full functionality.

At a time, there was a shortage of military GPS units compared to civilian ones, among military personnel. This resulted in disabling the Selective Availability, at the time of the Gulf War. Nextel GPS vehicle tracking system

GPS in Europe.

European concern of control over the GPS network, and commercial issues, resulted in the planned GALILEO positioning system. Russia operates an independent system, called GLONASS (global navigation system). It only has twelve active satellites, as of 2004. The system is of limited usefulness.

Special benefits of GPS.

Military (and selected civilian) users enjoy some technical advantages. These give quicker satellite lock and increased accuracy. The increased accuracy comes from using both the L1 and L2 frequencies.

This better compensates for varying signal delay, in the ionosphere. Commercial GPS receivers have limits on the velocities, and altitudes, for reporting fixed coordinates. This prevents them from use in improvised cruise or ballistic missiles.

Many synchronization systems use GPS to keep accurate time. Hence, one of its most common applications is as a reference clock, for time code generators or NTP clocks. For instance, GPS is used when deploying sensors (for seismology or other monitoring application). It provides each recording apparatus with a precise time source. Therefore, the time of events is recorded, accurately. Nextel GPS vehicle tracking system

Nextel GPS vehicle tracking system.

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