Brief of GPS (Global Positioning System)

          In March 1994, NAVSTAR GPS satellites 24 units and 3 units have been in orbit operating reserve for the development of navigation technology, which can be used for materials research, Sport, Agriculture, Military, Pilot, Surveyor, mountain climber, Driver, skipper sailing, and much more usefulness of this tool. GPS is a satellite-based navigation system, a network consisting of 27 satellites (24 operational, 3 spare) are in place in earth orbit by the U.S. Department of Defense (U.S. DoD). GPS was originally intended for military purposes (NAVSTAR, the name given the U.S. DoD for GPS).

          The development of these GPS systems will cost approximately $ 12 milliard specifically made for the U.S. Military with the transmission line band "L.2". (1227.60 MHz). Furthermore, around the years 1983-1984, the U.S. government to allow the system was first developed for use by civilians. GPS can work in all weather, anywhere in the world, 24 hours a day 7 days a week, without having to pay subscription fees or setup for general use.

GPS Satellite Systems
         NAVSTAR GPS satellites Production of Rockwell International USA has a weight of ± 1900 lbs with a range of 5.66-meter solar panels, emitting a maximum of 50 Watt power. Each satellite is made with a period of 7.5 years of work. Twenty-four (24) which form a network of satellites that orbit 17,120 miles high. Constantly moving, orbiting around the Earth twice per day (Orbit Period setiap12 Hours) at ± 8500 km per hour.

          Orbits of satellites is designed in such a way that anytime, anywhere on earth, a GPS receiver will be able to access at least 4 satellites. The electric power to the GPS satellite dimemakai solar energy with solar panels, other than that the battery backup is available for satellite could keep working during a solar eclipse or when the sun's energy is not available.

          Serves as a small rocket booster to ensure the correct path and satellites orbiting the earth properly. Besides SystemGPS in orbit with the 24 satellites and 3 reserves will be required to support the surface of earth stations used to monitor the condition of the satellite and the satellite's orbit to match.

          NAVSTAR GPS system is controlled by the 5 Master Ground Stations that specifically monitors the GPS satellites in space satellites are located: Hawaii, Ascension Island, Diego Garcia, Kwajalein, and Colorado Springs

          GPS satellites around the earth twice a day in a very precise orbit while emitting signals to earth. GPS receivers (we call receiver only) receives this information using triangulation method to calculate exactly where the location of the receiver. Basically, the receiver compares the micro-second timing pulses in the time of the signal transmitted by satellite with the timing pulse time, received at the receiver by transmitting pseudo-random code. The time difference is what will tell the receiver how far and direction of the satellite is from it. After the distance was measured by a number of other GPS satellites, the receiver can. determine its position in latitude and longitude degrees. Receiver must be locked at least 3 satellites to calculate the 2-dimensional position (latitude and longitude) and track movement. With 4 or more satellites that can acess, the receiver can determine 3-dimensional position (+ height). Once the position of the user can be determined, the GPS receiver can also determine other information such as speed, trajectory that has been passed, the distance of travel that has been taken, the distance to the destination, time of sunrise and sunset and so forth.

          TriangulasiDengan method uses 3 Satellite NAVSTAR GPS systems and triangulation methods to determine the position of the GPS receiver on the surface of the earth is very accurate. For the first time 3 units NAVSTAR satellites to determine the distance between the satellite and the GPS receiver on the surface of the earth with a mathematical calculation. One Satellite NAVSTAR able to capture and calculate the direction and distance of signals from the GPS receiver as far as 11,000 miles or 17,600 kilometers.

          Satellite to the two determines the direction and distance of around 12,000 Miles (19.200km), from two satellites that determine the distance and direction of the GPS receiver has found common ground in the earth's surface, but more accurate for longer then the task into three NAVSTAR satellites to determine the direction and distance GPS Receiver as far as 13,000 miles (20.800km) and satellites in orbit each ID and always have a signal is transmitted to more complex calculations performed by the GPS Receiver.

          Calculating the Atomic Clock Atomic clock running does not use atomic energy, but it was only figurative name of the oscillations of a particular atom with the name "Metronome" and can work accurately as "Clock", is still being developed the technology.

          Trilangulasi in a rather complex three-dimensional space is described. Let's start with a simple explanation of two-dimensional triangulation. Imagine you are somewhere in America, and you really lost: (you meet a local resident and asked "Where was I now?". He replied "you're 625 miles from the city of Boise, Idaho". Information Good, but still not useful for you. you could be in any point covering 625 miles from Boise city.

          Then you ask again to someone else, where you are, and he says "you're 690 miles from the city of Minneapolis, Minnesota." If you combine this information with information of Boise. You get two circles intersect. Now you know for sure you are in between the intersection of two circles.

         Then, if there is a third person to tell that you're 615 miles from the city of Tucson, Arizona; you can throw one of the two points above possibility, because the third circle will intersect in one point. Well now you know exactly where you are - in the city of Denver, Colorado.

          This triangulation method used by GPS satellites to determine the receiver location point. To support
calculation of triangulation, the receiver should know two things:
1. The location of at least 3 satellites which can be accessed
2. The distance between you and the satellites.

GPS Signal
         GPS satellites send two signal transmission by radio waves emissions "Code-Phase" and "Carrier-Phase" to calculate the distance and GPS Satellite Receiver for more accurate, with the L1 frequency (1.57542 GHz) GPS signal transmissions dedicated civilian users and L, 2. (1227.60 MHz) U.S. GPS signal transmission for military purposes with the specifications and Error Correction accuracy is better. NAVSTAR GPS satellite signals emanating highlighting the earth's surface in accordance with the character of microwave signals on the band around 1.2-1.5 GHZ, through clouds, glass and plastic but will not be able to penetrate solid objects / hardware such as buildings or mountains.

         GPS signal contains three pieces of information that is pseudorandom code, ephemeris data and almanac data. Transmission signals from GPS satellites is the satellite identification signal when it is sending information to the GPS Receiver. Furthermore, the GPS receiver calculates the timing wave propagation time from the NAVSTAR satellites by calculating the difference in timing pulses between the "pseudo random code" from the GPS receiver raised with the identical signal from the NAVSTAR GPS satellites. Breadth freqwensi (Bandwidth) needed to transmit pseudo random code is about 1 MHz, so that the transmission of GPS signals are transmitted in waves of 20 cm or about 1.2 -1.5 GHZ.

Calculation of pseudo-random code signals
          Ephemeris data is data that is always sent satellite, contains important information about the status of the satellite, data and current time from atomic clocks in GPS satellites, this is a very important part in determining the position.
          Almanac data tells the receiver where each satellite orbit should be at any time throughout the day.
Factors that lead to error on the receiver so that the lower the accuracy of information include:
Delay in the ionosphere and troposphere: disrupted satellite signal as it passes through Earth's atmosphere is contained in the surface layer of the earth at an altitude of 50-500 km. The ionized particles in this layer makes the effect on GPS signals resulting in one of the highest cause of error in determining the distance and location on the GPS Receiver. Because layers of the troposphere is a height of 50 km down to the earth's surface temperature is always changing cloud pressure, dust, only relatively few as disrupt the transmission signals from GPS satellites is the cause of error or miscalculation of the GPS Receiver.
Signal multipath: occurs when the GPS signal is reflected by tall buildings or solid surface such as mountains before the signal reaches the receiver. Does This adds the signal travel time (timing), because it causes an error in the calculation of the GPS Receiver.
           Error on the clock at the receiver. Built-in clock in the receiver are not as accurate atomic clocks in GPS satellites. Therefore, it would be easy in case of error in the determination of the time.
Orbital (ephemeris) error, this happens due to inaccuracies in location reports satelit.-Number of satellites visible: The more satellites that can acess by the receiver, the more accurate the information obtained. Building, the contour of the earth, electronic equipment interference or even dense foliage, can interfere with signal reception caused the error position. The receiver usually can not work indoors, underwater or underground.
          Satellite Geometry: This refers to the relative position of satellites at any given time. Ideal satellite geometry occurs when the satellite was in a wide angle relative to the other satellite. Geometry bad happens when the satellite is one line or the distance is too close to other calculations performed lead melesetnya GPS receiver

          GPS technology in Europe has been the trend since the year 2000, all types of vehicles have been equipped with GPS receivers as tools Automatic Navigator. GPS also has involved the development of the Russian state, which akhitr these days reached an agreement with America to synergize the GPS system that has been fully operational since 1994.

          In addition to these two satellite systems of the European Union also plans to name Galileo Navigation System. First launch conducted late 2006, launch of Galileo consists of 30 satellites orbiting the earth and is expected to be operational in 2012, Galileo GPS System is an improvement from previous technology with excess capacity to operate in the slits storey building and also in the room though.

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