What is GPS ?The Global Positioning System (GPS) can show you your exact position on Earth any time, anywhere, in any weather. The system consists of a constellation of 24 satellites (with about 7 "spares") that orbit 20372 km (11,000 n.m)above Earth’s surface and continuously send signals to ground stations that monitor and control GPS operations.
Origination of GPSAfter the Successive use of LORAN(LOng RAnge Navigation and Decca Navigator System, in world war II, more efficient and sophisticated system was required not only to find the friendly area but the exact location of the aircraft so pilot and control tower will not waste time to declare area or premises.
Origination of GPS SputniK 1So to achieve this goal, Soviet Union launched first satellite in 1957 named Sputnik 1.From here the cold war begun when two American physicists decided their own to monitor Sputniks radio transmissions.
Origination of GPS TransitThe first satellite navigation system, Transit, used by the United States Navy, was first successfully tested in 1960. It used a constellation of five satellites and could provide a navigational fix approximately once per hour.
Origination of GPSIn Civilians Use : After Korean Air Lines Flight007, carrying 269 people, was shot down in1983 after straying into the USSRs prohibitedairspace, in the vicinity of Sakhalin andMoneron Islands, President Ronald Reaganissued a directive making GPS freely availablefor civilian use, once it was sufficientlydeveloped, as a common good. The firstsatellite was launched in 1989, and the24th satellite was launched in 1994.
Fundamentals of GPS• Orbiting navigational satellites – Transmit position and time data• Handheld receivers calculate – latitude – longitude – altitude – velocity
Fundamentals of GPSOrbiting navigational satellites :a system of satellites that provide autonomous geo- spatial positioning with global coverage and allows small electronic receivers to determine their location.
Fundamentals of GPSHandheld receivers:Calculate latitude, longitude, Altitude some may also calculate Velocity after receiving signals from satellite.
Working of GPS• Satellite ranging – Satellite locations – Satellite to user distance – Need four satellites to determine position• Distance measurement – Radio signal traveling at speed of light – Measure time from satellite to user• Low-tech simulation
Working of GPS• Distance to a satellite is determined by measuring how long a radio signal takes Pseudo-Random to reach us from that satellite. Code:• To make the measurement we assume • Complex signal that both the satellite and our receiver • Unique to each are generating the same pseudo-random satellite codes at exactly the same time. • All satellites• By comparing how late the satellites use same pseudo-random code appears compared frequency to our receivers code, we determine how long it took to reach us.• Multiply that travel time by the speed of light and youve got distance.
Working of GPS• Accurate timing is the key to measuring distance to satellites.• Satellites are accurate because they have four atomic clocks on board.• Receiver clocks dont have to be too accurate because an extra satellite range measurement can remove errors.
Working of GPS• To use the satellites as references for range measurements we need to know exactly where they are.• GPS satellites are so high up their orbits are very predictable.• All GPS receivers have an almanac programmed into their computers that tells them where in the sky each satellite is, moment by moment.• Minor variations in their orbits are measured by the Department of Defense.• The error information is sent to the satellites, to be transmitted along with the timing signals.
GPS System PerformanceStandard Positioning Precise Positioning System: System: – 100 meters horizontal – 22 meters horizontal accuracy accuracy – 156 meters vertical – 27.7 meters vertical accuracy accuracy – Designed for civilian use – Designed for military – No user fee or use restrictions
GPS System PerformanceSelective availability• Intentional degradation of signal• Controls availability of system’s full capabilitiesReasons – Enhanced Emergency services – Vehicle navigation – Adoption of GPS time standard
GPS System Performance• The earths ionosphere and atmosphere cause delays in the GPS signal that translate into position errors.• Some errors can be factored out using mathematics and modeling.• The configuration of the satellites in the sky can magnify other errors.• Differential GPS can reduce errors.
GPS’ Applications• Location - determining a basic position• Navigation - getting from one location to another• Tracking - monitoring the movement of people and things• Mapping - creating maps of the world• Timing - bringing precise timing to the world
GPS’ Applications• Private and recreation – Traveling – Hiking, climbing, biking – Vehicle control• Mapping, survey, geology• English Channel Tunnel• Aviation – General and commercial – Spacecraft• Maritime
Military ExampleOperation - Desert Storm:• Featureless terrain• Initial purchase of 1000 portable commercial receivers• More than 9000 receivers in use by end of the conflict• Foot soldiers• Vehicles• Aircraft• Marine vessels
Cell Phones with GPSDue in part to regulations encouraging Cell phone tracking, including E911, the majority of GPS receivers are built into mobile telephones, with varying degrees of coverage and user accessibility. Commercial navigation software is available for most 21st century Smartphone as well as some Java-enabled phones that allows them to use an internal or external GPS receiver.
Parallel SystemsNot only GPS shares MEO at 20,200km, the two other Navigation systems are also running parallel to GPS.1. Glonass -19,100 km.2. Galileo – 23,22 km.
Parallel SystemsGalileo: is a satellite navigation system currently being built by the European Union (EU) and European Space Agency (ESA). This project is named after the famous Italian astronomer Galileo Galilei.
Parallel SystemsGLONASS: Global GLONASS logo : Navigation Satellite System, is a radio- based satellite navigation system operated for the Russian governmen t by the Russian Space Forces.
Message format• Each GPS satellite continuously broadcasts a navigation message at a rate of 50 b/s. Each complete message is composed of 30-second frames, distinct groupings of 1,500 bits of information. Each frame is further subdivided into 5 sub-frames of length 6 seconds and with 300 bits each. Each sub-frame contains 10 words of 30 bits with length 0.6 seconds each. Each 30 second frame begins precisely on the minute or half minute as indicated by the atomic clock on each satellite.• The first part of the message encodes the week number and the time within the week, as well as the data about the health of the satellite. The second part of the message, the ephemeris, provides the precise orbit for the satellite. The last part of the message, the almanac, contains coarse orbit and status information for all satellites in the network as well as data related to error correction.
Random CodeThe Pseudo Random Code is a fundamental part of GPS. Physically its just a very complicated digital code, or in other words, a complicated sequence of "on" and "off" pulses
Atomic Clocks• Most Accurate• The principle of operation of an atomic clock is not based on atomic physics and using the microwave signal that electrons in atoms emit when they change energy levels.• Example is NIST-F1
Satellite Orbits• LEO – Low earth Orbit, the commonly accepted definition for LEO is between 160 – 2,000 km.• MEO – Medium Earth Orbit , lies between altitude of 2,00km to 35,786 km.• GEO - Geostationary Earth Orbit, from 35,786 km to 265,000 km (Clarke Orbit).