HOW GPS WORK?

Each satellite transmits two signals, namely L1 (1575.42 MHz) and L2 (1227.60 MHz). L1 signal is modulated with two pseudo-random signal that is the code P (Protected) code and C / A (coarse / Acquisition). L2 signal only bring the code P. Each satellite transmits a unique code so that the receiver (GPS devices) to identify the signal from each satellite. At the time of the "Anti-Spoofing" is activated, the code P will be encrypted and subsequently known as the code P (Y) or Y-code

GPS devices that are specific for only civilian to receive the code C / A on L1 signal (although in a sophisticated GPS devices can take advantage of the L2 signal to obtain a more precise measurement.

GPS devices receive signals transmitted by GPS satellites. In determining the position, we need at least 3 satellites for the determination of 2-dimensional position (latitude and longitude) and 4 satellites for the determination of 3-dimensional position (latitude, longitude, and altitude). More and more satellites are obtained, the accuracy of our position will be higher. To get these signals, the GPS device must be open space. If your GPS device we are in a room or a dense canopy and the area we are surrounded by tall buildings, the signal obtained will be further reduced so that it would be difficult to determine precisely the position or even not able to determine position.

Clasification GPS Segment

GPS (Global Positioning System) be devided in three segments 

1. Control Segment
Is the core of the GPS system that is satellite control stations are always doing the monitor to know the exact position, altitude, and speed of the satellite. The information was information was sent back to the satellite, and satellite will transmit information to receivers on earth. This control station operated by the United States Department of Defense.

2. Space Segment
The composition of the GPS satellites that transmit signals to earth, now there are 24 satellites NAVSTAR (Navigation Satellite for Time and Ranging) that orbited the earth and used for GPS.

3. User Segment
GPS signals from satellites used by the user on Earth to perform calculations in order to position a variety of purposes.

GPS Usage

GPS function when developed first is to determine the position and navigation but in line with the development of Geographic Information Systems (GIS), the GPS function increases with appearance information (data cupture), to present a picture and calculate the area of a form of specific features, and is a system information that can diakseske various GIS software.

The development of GPS is of course demands a certain uniformity for positioning and spacing system used in the geographic reference is used, in this case is WGS 84 (World Geodetic Survey 84) that is used now.

History

GPS is now used for a variety of purposes-some never even imagined by the makers of GPS. GPS can be used in almost all locations in the world except in places where GPS satellite signals can not be accepted, for example, inside buildings, inside caves, underground, and underwater.
GPS is actually a project the United States Department of Defense (USA) who gave the official name of the NAVSTAR (Navigation Satellite Timing And Ranging). The main part of the system is 24 GPS satellites orbiting the Earth at an altitude of 20,200 kilometers. Satellite orbit is designed so that every point on Earth can see at least four satellites at any time.
Each satellite orbit the earth approximately once in 12 hours with a speed of about 11,000 kilometers per hour. GPS satellites have panels solar power collectors to generate electricity it needs. There was also a battery that stores electric power and used it as a satellite does not get sunlight.
The first GPS satellite was launched in 1978 and the constellation of 24 satellites successfully completed in 1994. After that new satellites routinely launched to upgrade or replace old satellites Satellite damaged / not working anymore. Each satellite transmits navigation data in a signal of CDMA (Code Division Multiple Access)-same as the type of signal for CDMA cellular phone. CDMA signal using a code on the transmission so that the GPS receiver can still recognize the GPS navigation signals, although there is interference at the same frequency. The frequency used is the L1 (1575.42 MHz) and L2 (1227.6 MHz).
Information is transmitted from the satellite to a GPS receiver consists of two types. The first is called "almanac", ie the position of all GPS satellites. The second type of information called "efemeris", ie the almanac correction data. "If the 'almanac' is updated approximately once a week, the data 'eferemis' usually is updated every half hour. Instrument GPS receiver is switched on again after a day off can still use the almanac data before.

Introduction

Humans have long been trying to find a way to know with certainty the existence of (position) on the surface of the earth itself, where she was and where he would go. Humans have developed ways to determine its position on the surface of the earth from a simple way by using the signs of nature on earth, with a view to the position of the stars using a compass and some fairly sophisticated electronic perlalatan.

But these methods have yet to include many activities on the surface of the earth, and the accuracy of the resulting highly variable. The last system was developed human being is a GPS (Global Positioning System) which utilizes the position and the signals emitted by satellites orbiting in space and captured the receiver in the earth's surface.