GPS - Global Positioning System , a wonder technology developed and controlled by the U.S. Department of Defense (DoD), is making deep inroads into the consumer world as well. They require a minimum of 24 satellites orbiting at 11,000 nautical miles above the Earth. Each satellite takes 12 hours to complete an orbit. Receivers whether handheld, part of the car accessories or the more robust, highly precise military type, they calculate by extrapolating the transmitted satellite signals arriving from 4 GPS satellites to arrive at their present position in three dimensions.
Though it requires 3 satellites to find the latitude
and longitude of the receiver's position, it needs another
satellite signal to calculate the altitude. At the present
level of technology, a civilian GPS receiver can determine
the position to within about 300 feet which can be increased
further with corrections calculated by a GPS receiver
at a known fixed location.
GPS satellites use a frequency of 1575.42 MHz to transmit the Civilian Coarse/Acquisition Code (C/A Code) and the military specific P (Precision) Code where the data sent is encrypted. This L1 frequency implies that the antenna to receive this signal is barely about 45 mm wide which can be easily accommodate in a GPS receiver or in a mobile phone. There are other frequencies as well - L2 of 1227.6 MHz or L5 of 1176.45 MHz used for GPS.
GPS signals contain ephemeris (position information about the GPS satellites) data and the almanac (time and status information). It takes about 12.5 minutes for a receiver from the startup to obtain the almanac data from the GPS satellites as the data rate is very low. It is the reason why your GPS PNG (personal navigation device) takes so long to get a fix when you use it after a long time.
GPS Tracking System
GPS satellites deliberately add a fraction of inaccuracy to their signals to safeguard the interests of the US. But the error introduced is known and can be readily compensated by the US military hardware so that the GPS coordinates are accurate within a few meters. But the Europeans have started an independent Galileo GPS program to reduce their dependency on the US GPS satellite Navigation System.
The Russian GLONASS (Global Navigation Satellite System) has satellites orbiting at a slightly different angle. Because of this, GLONASS has better accuracy in high altitude conditions than the US GPS. At the time of writing this article, many GPS receivers including the mobile phones use GLONASS as well the normal GPS signals to compute their position.
GPS Vehicle Tracking System
Automatic Vehicle Locating (AVL) is an offshoot of the GPS Vehicle Tracking technology - an advanced method of remote vehicle tracking and monitoring. As per the scheme of things for using the Automatic Vehicle Locating, the targeted vehicle is equipped with an AVL unit that receives signals from the GPS satellites. The GPS receiver determines its current location, speed and heading which is stored locally for eventual analysis or transmitted to a central control center using GSM - Global standard of mobile communication or other suitable wireless technology. By a combination of these technologies you can protect and monitor your mobile assets like car, truck, bike, boat or ship virtually anywhere and then locate it to within a few meters. The central tracking station monitors your vehicle 24 hours per day for unauthorized intrusion, pilfering, breakdown, accident or even for any unforeseen emergency assistance.
Alternatively any unauthorized vehicle movement or any deviation from a predefined "Geo-fence" boundary can also trigger suitable measures as seen fit by the central control system.
Marine GPS International Maritime Bureau (IMB) in the worldwide fight against piracy in the high seas advocates the use of SHIPLOC.
SHIPLOC is a small GPS Vehicle Tracking device concealed on ships which allows owners to monitor the movement of their vessels. This satellite-tracking device integrates a GPS receiver, an Argos transmitter for exact and independent ship position measurement and enough battery backup power to last for several days.
GPS Vehicle Tracking System is not for locating ships or delivering nasty payloads targeting enemy positions alone. Closer to home, GPS equipped vehicles enable you to plan your trips precisely with moving maps display. Many emergency service units are using GPS receivers to determine the position of their resources - police cars, fire trucks, or ambulances nearest to an emergency, enabling the quickest possible response in life or death situations. GPS Vehicle tracking is one of the fastest-growing GPS applications. GPS equipped fleet vehicles, public transportation systems, delivery trucks, and courier services use GPS receivers to monitor their locations, helping to reduce wasted time - improving overall efficiencies and also for Mobile Asset Recovery. Whether you are stranded in the desert or in the deep blue ocean, GPS comes to the rescue.
Mobile asset recovery - an euphemism for techniques to recover your vehicle has been made easier with GPS technology. Advances in miniaturization of electronics coupled with rapid strides in GPS technology has resulted in small devices being used for GPS vehicle tracking. These devices when fitted in vehicles enable one to keep tabs on the position of the vehicles all the time. As we have seen earlier, they can send out data to remote locations for effective surveillance and administration of mobile assets.
GPS jamming: With the proliferation of low cost GPS tracking devices for personal as well for vehicle tracking use, some have come out with simple GPS jammers to 'confuse' the GPS signal data by transmitting a narrow band Gaussian noise signal. This type of Jamming devices may not work so well against many advanced anti-jam configured receivers or with receivers with multi frequency capabilities. This GPS jammers can jam signals only in the near vicinity. Dedicated high gain antenna aimed at the skies can mitigate the effects of a GPS jammer.