Presentation By Prashanth Keni

PRESENTATION BY Prashanth keni

GLOBAL POSITIONING SYSTEM

The Global Positioning System (GPS) is a satellite-based navigation system made up of a network of 24 satellites placed into orbit . GPS is controlled and co-ordinated by the U.S. Department of Defense. GPS it is the only one system today we are able to show you your exact and precise position on the global orbit at any time ,anywhere and under any weather conditions. It provides reliable positioning, navigation, and timing services to worldwide users on a continuous basis.

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The first GPS satellite was launched in 1978.

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A full constellation of 24 satellites was achieved in 1994.

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Each satellite is built to last about 10 years. Replacements are constantly being built and launched into orbit.

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A GPS satellite weighs approximately 2,000 pounds and is about 17 feet across with the solar panels extended.

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Transmitter power is only 50 watts or less.

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The design of GPS is based partly on similar ground-based radio navigation systems, such as LORAN and the Decca Navigator developed in the early 1940s, and used during World War II.

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The first satellite navigation system, Transit, used by the UnitedStates Navy, was first successfully tested in 1960.

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It used a constellation of five satellites and could provide a navigational fix approximately once per hour.

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In the 1970s, the ground-based Omega Navigation System, became the first worldwide radio navigation system.

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A GPS receiver calculates its position by precisely timing the signals. Each satellite continuously transmits messages which include: The time the message was sent Precise orbital information (the ephemeris) The general system health and rough orbits of all GPS satellites (the almanac). Geometric triangulation is used to combine these distances with the satellites locations. The position is then displayed, which include latitude, longitude and elevation information. Even a very small clock error multiplied by the very large speed of light,results in a large positional error. Therefore receivers use four or more satellites to solve for the receiver's location and time.

GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location. 

Essentially, the GPS receiver compares the time a signal was transmitted by a satellite with the time it was received. The time difference tells the GPS receiver how far away the satellite is.

The receiver can determine the user's position and display it on the unit's electronic map.  A GPS receiver must be locked on to the signal of at least three satellites to calculate a 2D position (latitude and longitude) and track movement.  With four or more satellites in view, the receiver can determine the user's 3D position (latitude, longitude and altitude).  Once the user's position has been determined, the GPS unit can calculate other information, such as speed, bearing, track, trip distance, distance to destination, sunrise and sunset time and more.

The current GPS consists of three major segments. They are   

The space segment (SS). Control segment (CS) and User segment (US).

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The GPS design consists of 24 satellites, divided into six orbital planes with four satellites each.

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The six planes have approximately 55° inclination (tilt relative to Earth's equator) and are separated by 60°.Orbiting at an altitude of approximately 20,200 kilometers.

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The orbits are arranged so that at least six satellites are always within line of sight from almost everywhere on Earth's surface.

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The flight paths of the satellites are tracked by US Air Force monitoring stations in Hawaii,Colorado Springs, Colorado, along with monitor stations operated by the National Geospatial-Intelligence Agency (NGA).

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The tracking information is sent to the master control station at Schriever Air Force Base in Colorado Springs, which is operated by the 2nd Space Operations Squadron (2 SOPS) of the United States Air Force (USAF).

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Then 2 SOPS contacts each GPS satellite regularly with a navigational update These updates synchronize the atomic clocks on to within a few nanoseconds of each other, and adjust the ephemeris of each satellite's internal orbital model.

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The updates are created by a Kalman filter which uses inputs from the ground monitoring stations, space weather information, and various other inputs.

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GPS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver-processors, and a highly-stable clock (often a crystal oscillator). They may also include a display for providing location and speed information to the user.

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A receiver is often described by its number of channels. Originally limited to four or five, this has progressively increased over the years so that, as of 2007, receivers typically have between 12 and 20 channels.

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GPS satellites transmit two low power radio signals, designated L1 and L2. Civilian GPS uses the L1 frequency of 1575.42 MHz in the UHF band. The signals travel by line of sight, meaning they will pass through clouds, glass and plastic but will not go through most solid objects such as buildings and mountains. A GPS signal contains three different bits of information — a pseudorandom code, ephemeris data and almanac data.

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The pseudorandom code is simply an I.D. code that identifies which satellite is transmitting information.

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Ephemeris data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits ephemeris data showing the orbital information for that satellite and for every other satellite in the system.

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Almanac data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position.

Aviation  Roads and Highways  Railways  Marine  Space  Agriculture  Environment  Surveying & Mapping  Public Safety & Disaster Relief 

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Continuous, reliable, and accurate positioning information for all phases of flight.

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Safe, flexible, and fuel-efficient routes for airspace service providers and airspace users.

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Efficient air traffic management, particularly during inclement weather.

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Higher levels of safety and mobility for all surface transportation system users.

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Better location information with electronic maps to provide invehicle navigation systems for both commercial and private users.

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Increased efficiencies and reduced costs in surveying roads.

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Enhanced levels of safety. Increased capacity and efficiency for all rail users. Dependable schedule and equipment location awareness. Improved track, traffic, and train sensor information that flows together and produces a constantly updated plan to manage operations. Increased situational awareness for improved safety of trains and maintenance crews.

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Deliver disaster relief to areas in a more timely and accurate manner, saving lives and restoring critical infrastructure. Provide position information for mapping of disaster regions where little or no mapping information is available. Enhance capability for flood prediction and monitoring of seismic precursors and events. Provide positional information about individuals with mobile phones and in vehicles in case of emergency.

Civilian GPS receiver ("GPS navigation device") in a marine application.

GPS receivers are now integrated in many mobile phones.

Automotive navigation system in a taxicab.

A typical OEM GPS receiver module measuring 15×17 mm.

A typical GPS receiver with integrated antenna.

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