History of GPS - - - - - is a space-based navigation system that provides location and time information. provides critical capabilitiesto military, civil, and commercial users around the world. was invented to fire the missiles accurately and minimize the risk of collateral damage. Their proposal was a network of radio transmitters, with each having an in-built clock. Civilian use was allowed from the 1980s. Ivan Getting - invented the first Global Positioning System with the help and contribution of Bradford Parkinson and Roger L. Easton. - ELEMENTS OF GPS - - - - - Maintained by the U.S. Government and is freely accessible by anyone with a GPS receiver. Official name: “Navigation Satellite Timing and Ranging Global Positioning System” (NAVSTAR GPS). Official name: “Navigation Satellite Timing and Ranging Global Positioning System” (NAVSTAR GPS). It is a technique by which the location of any object, velocity, direction and time can be known precisely at any time. Whether the object is on the ground, on the sea water or in the air. Transmit position and time data. BLOCk IRR-M - Launched in 2005-2009 7.5-year design lifespan 7 operational (PRESENT) Flexible power levels for military signals New military M code signals for enhanced jam resistance GPS III & IIIF The technical and operational characteristics of the GPS are organized into three distinct segments: space segment control segment user segment. SPACE SEGMENT - WHAT IS GPS - First launch in 2018 15-year design lifespan 6 operational (PRESENT) Enhanced signal reliability, accuracy, and integrity laser reflectors; search & rescue payload - GPS constellation consists of 24 satellites. Each satellite completes one orbit in one-half of a sidereal day, approximately 23 hours and 56 minutes. With this orbital configuration and number of satellites, a user at any location on Earth will have at least four satellites in view 24 hours per day. The main functions of the Space Segment are to transmit radionavigation signals, and to store and retransmit the navigation message sent by the Control Segment. These transmissions are controlled by highly stable atomic clocks on board the satellites. CONTROL SEGMENT - The GPS control segment consists of a global network of ground facilities that track the GPS satellites, monitor their transmissions, perform analyses, and send commands and data to the constellation. MASTER CONTROL STATION - Provides command and control of the GPS constellation. Uses global - - monitor station data to compute the precise locations of the satellites. Generates navigation messages for upload to the satellites. Monitors satellite broadcasts and system integrity to ensure constellation health and accuracy. located at Falcon Air Force Base in Colorado Springs, Colorado; remote monitoring stations, located in Hawaii The orbits of the satellites are sometimes disturbed by the interplay of the gravitational forces of the Earth and Moon. MONITOR STATION - - are very precise GPS receivers installed at known locations. They record discrepancies between known and calculated positions caused by slight variations in satellite orbits. the Master Control Center can modify satellite orbits by commands transmitted via the control segment's ground antennas. USER SEGMENT - refers to the component of GPS that directly involves and interacts with users. The user segment includes all GPS receivers and the user community. GPS receivers are devices that receive signals from satellites and calculate their own positions (latitude, longitude, altitude, and sometimes velocity and time) based on the signals received. HOW IT WORKS - CURRENT LOCATIONS OF GPS SATELLITE - You can find one’s location if you know its distance from other, alreadyknown locations. THINGS NEEDED TO BE DETERMINED - Current location of GPS satellites. GPS satellites are orbiting the earth at an altitude of 11,000 miles. The orbits, and the location of the satellites, are known in advance. GPS receivers store this orbit information for all of the GPS satellites in an almanac. TO GET THE DISTANCE TO EACH SATELLITE - - - - By measuring the amount of time taken by radio signals to travel from the satellite to the receiver. Radio waves travel at the speed of light, about 186,000 miles/sec. The distance from the satellite to the receiver can be determined by the formula distance = speed x time. Distance measurements from two satellites limits our location to the intersection of two spheres, which is circle. A third measurement narrows our location to just two points. A fourth measurement determines which point is our true location. ACCURACY - The position calculated by a GPS receiver relies on three accurate measurements: • * Current time * Position of the satellite * Time delay for the signal - GEOMETRIC PRINCIPLE - The distance between the receiver's position and the GPS satellites. The GPS signals in space will provide a "worst case" accuracy of 7.8 meters at a 95% confidence level GPS SIGNALS AND FREQUENCIES - transmits data on two frequencies, L1 (1575.42 Mhz) and L2 atomic clock aboard the satellite produces the fundamental L-band frequency - measured travel times of the signals from the satellites to the receivers are used to compute the pseudo ranges. COURSE- ACQUISITION (C/A) CODE - sometimes called the Standard Positioning Service A family of PRN codes transmitted by GPS satellites. Each satellite is assigned one of 32 unique codes in the family. Each code consists of 1,023 chips and is sent at a rate of 1.023 megabits per second. PRECISION (P) CODE - sometimes called the Precise Positioning Service A PRN code transmitted by GPS satellites. The code consists of about 2.35 3 1014 chips and is sent at a rate of 10.23 megabits per second. At this rate, it would take 266 days to transmit the complete code. SATELLITE CLOCK - RECEIVER CLOCK - made up of three major components. The first part contains the GPS date and time ephemeris data - allows the receiver to calculate the position of the satellite almanac - contains information and status concerning all the satellites ALMANAC - Almanac data is data that describes the orbital courses of the satellites. Every satellite will broadcast almanac data for each satellite. Almanac data includes a set of parameters for each GPS satellite that can be used to calculate its approximate location in orbit. SOURCES OF GPS SIGNAL ERRORS equipped with quartz crystal clocks that are less stable than the atomic clocks GPS JAMMING - is the process of using a frequency transmitting device to block or interfere with radio communications GPS FREQUENCIES - GPS Technology operates in the following frequency bands: NAVIGATION MESSAGE - satellites use atomic clocks, which are very accurate but can drift up to a millisecond GPS L1 Band: 1575.42 MHz with a bandwidth of 15.345 MHz GPS L2 Band: 1227.6 MHz with a bandwidth of 11 MHz GPS L5 Band: 1176.45 MHz with a bandwidth of 12.5 MHz ATMOSPHERIC ERRORS - atmosphere refract and slightly delays the signals MULTI – PATH ERRORS - results when the direct path to your receiver is blocked METHODS OF IMPROVING ACCURACY PRECISION MONITORING DUAL FREQUENCY MONITORING - Refers to systems that can compare two or more signals the receiver tracks more than one radio signal from each satellite on different frequencies, which can reduce errors caused by environmental interference. CARRIE- PHASE ENHANCEMENT (CPGPS) - CPGPS coupled with DGPS normally realizes between 20 and 30 cm Carrier-phase measurements, on the other hand, are like using a ruler with very fine markings, allowing for much more precise measurements. - GLOBAL DIFFERENTIAL GPS (GDGPS) - RELATIVE KINEMATIC POSITIONING (RTP) - - Determination of range signal can be resolved to an accuracy of less than 10 cm (4 inches). the receiver , called the base station, remains static while the rover is in movement. When the navigation starts, the DD vector direction depends on the movement direction of the rover receiver. AUGMENTATION - - is any system that aids GPS by providing accuracy, integrity, availability, or any other improvement to positioning, navigation, and timing Relies on external information being integrated into the calculation process. - - improves the accuracy, availability, and integrity of the GPS by constantly monitoring and broadcasting corrections to the GPS service. the systems are consisting of the maritime differential GPS system operated by the U.S. coast guard and an inland component funded by the department of transportation WIDE AREA AUGMENTATION SYSTEM (WAAS) - Satellite-based augmentation system operated by the federal aviation administration (FAA), supports aircraft navigation across north America High accuracy GPS augmentation system, developed by the NASA jet propulsion laboratory (IPL) to support the real-life positioning, timing, and determination requirements of NASA science missions. advanced GPS augmentation system that provides high-precision positioning information on a global scale. LIMITATIONS OF GPS - - NATIONWIDE DIFFERENTIAL GPS SYSTEM (NDGPS) - monitors and evaluates all GPS signals over North America to enable pilots to fly using augmented GPS data for safety of life missions there must be a (relatively) clear ‘line of sight’ between the receiver’s antenna and several orbiting satellites. Anything shielding the antenna from a satellite can potentially weaken the satellite’s signal Urban areas are especially affected by these types of difficulties. Bouncing of the signal off nearby objects or the ground may create another problem called multi-path interference. APPLICATION OF NAVSTAR GPS SURVEYING - - Surveyors used absolute locations to make maps and determine property boundaries. Surveying is the technique of determining the relative position of different features on, above or beneath the surface of the earth. TELEMATICS - - GPS Technology integrated with computers and mobile communications technology in automotive navigation systems. Telematics is a method of monitoring cars, trucks, equipment and other assets by using GPS technology and on-board diagnostics VEHICLE TRACKING - GPS car tracking system is the most effective way to locate a car. It consists of a receiver antenna and a box that consists of tracking chip and batteries. Exact location on the map Speed at which the vehicle is travelling Total distance travelled by the vehicle MILITARY APPLICATION - GPS integrated into fighters, tankers, helicopters, ships, submarines, tanks, jeeps and soldier’s equipment. Target tracking Search and Rescue
