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Slide 1:

February 5, 2011 1 JSM


February 5, 2011 2 CONTENTS Objectives of GPS History of GPS GPS Basics Measuring distance to satellites Sources of Error Conclusion JSM


February 5, 2011 3 OBJECTIVES OF GPS It provides users with the capability of determining, Position, Speed and Time, whether in motion or in rest. It also provides a continuous, global, 3-dimensional positioning capability with a high degree of accuracy, irrespective of the weather conditions. It had to offer potential for civilian use as well as military use. JSM


February 5, 2011 4 HISTORY OF GPS GPS (NAVSTAR-GPS : Navigation System with Timing And Ranging - Global Positioning System) was developed by US Department of Defense (DOD). Feasibility studies begun in 1960. First GPS satellite (Sputnik 1) was launched in 1978. System was declared fully operational in April, 1995 By DOD. JSM

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February 5, 2011 5 JSM


February 5, 2011 6 WHAT IS GPS? The Global Positioning System ( GPS ) is a navigation and precise-positioning tool. GPS is a technique used to locate position at any point on the Globe with high degree of accuracy. It can be used both by civilians and military personals. JSM

GPS in Technical terms:

February 5, 2011 7 GPS in Technical terms A network of satellites that continuously transmits coded information, which makes it possible to precisely identify locations on earth by measuring distance from the satellites. JSM


February 5, 2011 8 SEGMENTS OF GPS The GPS comprises three segments, The Space Segment (All functional satellites) The Control Segment (Master control station) The User Segment (Civil and military Users) JSM

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February 5, 2011 9 (satellites) (tracking stations) (receivers) JSM

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February 5, 2011 10 It consists of GPS satellites (Space vehicles : SVs) The SVs will send radio signals from space which is received by the master control station on the Earth. The GPS constellation, Consists of 24 satellites Orbiting 20,000 km above the Earth Traveling with the speed 7,000 miles per hour 12-hour circular orbits There are 6 orbital planes (four SVs in each orbit) Equally spaced at 60 degrees apart Inclined at about 55 degrees with respect to the equatorial plane Each satellite is built to last about 10 years. JSM

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February 5, 2011 11 Each satellite transmits low power radio signals on several frequencies, The L1 frequency (1575.42 MHZ) which carries, The navigation message The SPS (Standard Positioning Service) code signal. The L2 frequency (1227.60 MHZ) Used to measure the ionosphere delay by PPS (Precise Positioning Service) equipped receivers. JSM

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February 5, 2011 12 Two binary codes shift the L1 and L2 carrier phase, The C/A (Coarse Acquisition) code modulates the L1 carrier phase. The P (Precise) code modulates both the L1 and L2 carrier phase. These signals can pass through clouds or glass, but not through solid objects like buildings etc ( LoS ). JSM

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February 5, 2011 13 The GPS control segment consists of several ground stations located around the world, A master control station at Schriever Air Force Base in Colorado. Five monitoring stations: Hawaii and Kwajalein in the Pacific Ocean; Diego Garcia in the Indian Ocean; Ascension Island in the Atlantic Ocean; Colorado. Three large ground-antenna stations. JSM

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February 5, 2011 14 JSM

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February 5, 2011 15 Functions : The Monitor stations measure signals from the SVs. The Master Control Station determine any adjustments or updates to the navigation signals and update the satellites via the ground antennas. The Master Control Station send back the updated signal to SVs. JSM

Three Segments of the GPS:

16 Control Segment Space Segment User Segment Three Segments of the GPS Monitor Stations Ground Antennas Master Station February 5, 2011 JSM

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February 5, 2011 17 Updated data is transmitted to users Ground stations monitor and update satellite locations Space Segment JSM

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February 5, 2011 18 The GPS User Segment consists of GPS receivers and the user community. GPS receivers converts SV signals into position, velocity, and time estimates. Four satellites are required to compute the four dimensions of X,Y,Z (position) and Time. The GPS receivers are used for navigation and positioning. JSM

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February 5, 2011 19 JSM

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February 5, 2011 20 To calculate our position we need to know the satellite location and the satellite distance. Along with the radio signal, the GPS receiver picks up two kinds of coded information from the satellites, Almanac data contains the approximate position of the satellites stored in the memory of the GPS receiver, so it knows where each satellite is suppose to be. JSM

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February 5, 2011 21 From the Almanac and Ephemeris data GPS receiver knows location of satellites at all times. Corrected and exact position is ephemeris data. JSM

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February 5, 2011 22 JSM

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February 5, 2011 23 Receiver compares the two codes to determine how much it needs to shift (delay) its code to match the satellite code. JSM

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February 5, 2011 24 JSM

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February 5, 2011 25 JSM

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February 5, 2011 26 JSM

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February 5, 2011 27 Uses measurements from 4+ satellites, Distance = Travel time x Speed of light JSM

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February 5, 2011 28 Sources of Error 1. Atmospheric Interference Troposphere Ionosphere JSM

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February 5, 2011 29 Multipath means, the same radio signal is received several times through different paths. 2. Multipath Errors JSM

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February 5, 2011 30 The internal satellite and receiver clocks have limited accuracy, and they are not precisely synchronized. Since position computations are highly dependent on accurate timing information, small clock errors can cause significant errors in position computations. 3. Clock Limitations JSM

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February 5, 2011 31 4. Ephemeris Error (Orbital errors) JSM

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February 5, 2011 32 5. Selected Availability Scrambling of signal by military JSM

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February 5, 2011 33 Place a GPS receiver (reference or base station) at a known location. This base station receiver will calculate receiver errors by comparing its actual location to the location computed from the signals. Differential GPS JSM

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February 5, 2011 34 Differential GPS in Action 1. Compares field data to data collected at the same time at a nearby base station. 2. Error at base station known and subtracted from field data. JSM

Uses of GPS Technology:

February 5, 2011 35 Location - Determining a basic position. Navigation - Moving from one location to another. Tracking - Monitoring the movement of people and things. Mapping - Creating maps. Timing - Providing precise timing. Uses of GPS Technology JSM

GPS Competitors:

February 5, 2011 36 GLONASS GLONASS is the Russian Federation's satellite navigation system. GALILEO The Galileo satellite radio navigation system is an initiative launched by the European Union and the European Space Agency. GPS Competitors JSM


February 5, 2011 37 Conclusion GPS was originally designed to help US forces around the world to locate targets and move quickly from one place to another. GPS has evolved to fulfill tasks, which were never envisaged in its original designer’s requirements. GPS satellites are gradually revolutionizing driving, flying, hiking, exploring, rescuing, and map making. The list of uses is only set by the requirements we can think of applying GPS to. JSM


February 5, 2011 38 REFERENCES JSM

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February 5, 2011 JSM 39 Queries

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February 5, 2011 40 LOT OF THANKS ! JSM

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