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Introduction to gps and gnss

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Introduction to gps and gnss

  1. 1. Introduction to GPS and GNSS Vivek Srivastava viveksrivastava09@gmail.com
  2. 2. Early Space-Based Radio Navigation System Launch of Sputnik – Tracking? -------------Doppler Shift. Altitude: 985km; revolution period: 98 min Frank McClure, of the Applied Physics Laboratory, made a suggestion: would it be possible to invert this problem? – given rise to TRANSIT in late 1950’s (US- 6 sat; Altitude: 1100km; revolution period: 108 min) / TSYKLON(USSR-10 sat; 6- PARUS: Military; 4- TSIKADA-commercial/civilian; Altitude: 1000km) The Navy Navigational Satellite System or TRANSIT, used observed measurements in Doppler shift to calculate distance and position to satellites (till 31-12-96). A fix requires 40 minutes for a static user-2D.
  3. 3. “ It is an all-weather, space based navigation system development by the U.S. DOD to satisfy the requirements for the military forces to accurately determine their position, velocity, and time in a common reference system, anywhere on or near the Earth on a continuous basis. ” Module 2 - GPS # In 1973 the U.S. DOD decided to establish, develop, test, acquire, and deploy a spaceborne Global Positioning System (GPS), resulting in the NAVSTARGPS (NAVigation Satellite Timing And Ranging Global Positioning System). NAVSTAR Global Positioning System
  4. 4. GPS General CharacteristicsGPS General Characteristics Module 2 - GPS Global Positioning System Developed by the US DOD Provides Accurate Navigation 10 - 20 m Worldwide Coverage 24 hour access Common Coordinate System Designed to replace existing navigation systems Accessible by Civil and Military
  5. 5. Introduction – GNSS The theoretical definition: “GNSS. A worldwide position and time determination system that includes one or more satellite constellations, aircraft receivers and system integrity monitoring, augmented as necessary to support the required navigation performance for the intended operation.” [from ICAO Annex 10, Volume I] Module 2 - GPS • USA’s GPS (+ WAAS) • Russian GLONASS(+SBAS) • EU’s Galileo (+ EGNOS); • Japan’s QZSS (+ MSAS); • India’s IRNSS (+ GAGAN); • China’s Beidou; Compass; • Australian Augmentations GNSS is the result of a recognition by the civilian community of the benefits that can be derived from the development of a 'true' civilian global positioning system that is: Multimodal (air, sea and land users), Capable of meeting future navigation & timing requirements, Global standard, Cost effective, Easy to use, Fundamentally based around the integration and augmentation of technologies. GNSS elements: GPS and augmentation systems (based on aircraft /satellite/ground inst.)
  6. 6. How Well Does It Work? Navigation Accuracy Comparisons Omega- 2 km Inertial- 1 km Tactical Air Navigation (TACAN)- 400m Transit- 200m LORAN C- 180m GPS- 15m Module 2 - GPS
  7. 7. GPS Constellation Module 2 - GPS
  8. 8. Space Segment ( Initial Operational Capability(IOC)-1993) (Full Operational Capability(FOC)-1995) Block I First Launch: 22 Feb 78(78-85) On-Orbit: None, Total=11 Block IIR / IIR-M(L2C civil signal & new military code M on both L1& L2) Block II/IIA First Launch: 14 Apr 89(89-97) Total: 28 First Launch: 2009 Acquiring up to 19 SV’s Block IIF First Launch: 22 Jul 1997/25Sep2005 Total=21/8 (R: Replenishment; M: Modernized) Module 2 - GPS Block III
  9. 9. GPS System ComponentsGPS System Components 24 Satellites 4 satellites in 6 Orbital Planes inclined at 55 Degrees 20200 Km above the Earth • 12 Hourly orbits – In view for 4-5 hours • Designed to last 7.5 years • Different Classifications – Block 1, 2, 2A, 2R & 2 F EquatorEquator 55 Module 2 - GPS Managed by the US National Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee SpaceSpace SegmentSegment
  10. 10. Master Control Station Responsible for collecting tracking data from the monitoring stations and calculating satellite orbits & clock parameters 5 Monitoring Stations Responsible for measuring pseudorange data. This orbital tracking network is used to determine the broadcast ephemeris and satellite clock modeling Ground Control Stations Responsible for upload of information to SV’s Module 2 - GPS
  11. 11. User Segment:User Segment: The most visible segment Module 2 - GPS Everyone! Merchant, Navy, Coast Guard vessels Forget about the sextant, Loran, etc. Commercial Airliners, Civil Pilots Surveyors Has completely revolutionized surveying Commercial Truckers Hikers, Mountain Climbers, Backpackers Cars now being equipped Communications and Imaging Satellites Space-to-Space Navigation Any system requiring accurate timing
  12. 12. Weather Independent Does not require line of sight Gives high Geodetic Accuracy Can be operated day and night Quicker and requires less manpower Economical advantages Common Coordinate System Wide Range of Applications Competitively Priced Why GPS ?Why GPS ? Module 2 - GPS
  13. 13. How It Works (In 5 Easy Steps) GPS is a ranging system (triangulation) The “reference stations” are satellites moving at 4 km/s 1. A GPS receiver (“the user”) detects 1-way ranging signals from several satellites Each transmission is time-tagged Each transmission contains the satellite’s position 1. The time-of-arrival is compared to time-of-transmission 2. The delta-T is multiplied by the speed of light to obtain the range 3. Each range puts the user on a sphere about the satellite 4. Intersecting several of these yields a user position Module 2 - GPS
  14. 14. Xll Vl Xl lll l ll lV V Vll Vlll X lX Range = Time Taken x Speed of Light Outline Principle : RangeOutline Principle : Range Module 2 - GPS Point Positioning:oint Positioning: Accuracy 10 - 100 mAccuracy 10 - 100 m A receiver in autonomous mode provides navigation and positioning accuracy of about 10 to 100 m due to the effects
  15. 15. Multi-Satellite Ranging 1 range puts user on the spherical face of the cone. Intersecting with a 2nd range restricts user to the circular arcs. A 3rd range constrains user to 1 of the 2 points. Pictures courtesy http://giswww.pok.ibm.com/gps Module 2 - GPS
  16. 16. The satellites are like “Orbiting Control StationsOrbiting Control Stations” Ranges (distances) are measured to each satellite using time dependent codes Typically GPS receivers use inexpensive clocks. They are much less accurate than the clocks on board the satellites A radio wave travels at the speed of light (Distance = Velocity x Time) Consider an error in the receiver clock 1/10 second error = 30,000 Km error 1/1,000,000 second error = 300 m error Outline Principle : PositionOutline Principle : Position Module 2 - GPS
  17. 17. Timing Accuracy of position is only as good as your clock To know where you are, you must know when you receive. Receiver clock must match SV clock to compute delta-T SVs carry atomic oscillators (2 rubidium, 2 cesium each) Not practical for hand-held receiver Accumulated drift of receiver clock is called clock bias The erroneously measured range is called a pseudorange To eliminate the bias, a 4th SV is tracked 4 equations, 4 unknowns Solution now generates X,Y,Z and b If Doppler also tracked, Velocity can be computed iirsiirs Module 2 - GPS
  18. 18. GPS Signal StructureGPS Signal Structure Each GPS satellite transmits a number of signals The signal comprises two carrier waves (L1-19cm and L2- 23cm) and two codes (C/A on L1 and P or Y on both L1 and L2) as well as a satellite orbit message Bandwidth allocated for L1-24 MHz, L2-22 MHz, & L5-28 MHz Fundamental Frequency 10.23 MHz Fundamental Frequency 10.23 MHz x 154 x 120 L1 1575.42 MHz L1 1575.42 MHz L2 1227.60 MHz L2 1227.60 MHz C/A Code 1.023 MHz C/A Code 1.023 MHz P (Y)-Code 10.23 MHz P (Y)-Code 10.23 MHz P (Y)-Code 10.23 MHz P (Y)-Code 10.23 MHz ÷ 10 50 BPS50 BPS Satellite Message (Almanac & Ephemeris)Satellite Message (Almanac & Ephemeris) iirsiirs Module 2 - GPS L3(1381.05MHz):L3(1381.05MHz): used only for a Nudet (Nuclear Detection)used only for a Nudet (Nuclear Detection) Detection System (NDS).Detection System (NDS).
  19. 19. Code Modulation Source: Peter Dana, http://www.colorado.Edu/geography/gcraft/notes/gps/gps_f.html iirsiirs Module 2 - GPS Selective Availability (SA):To deny high-accuracy realtime positioning to potential enemies, DoD reserves the right to deliberately degrade GPS performance (on C/A code: deactivated on 1 may, 2000).
  20. 20. Coarse Acquisition (C/A) Code 1023-bit Gold Code Originally intended as simply an acquisition code for P- code receivers Modulates the L1 only Chipping rate = 1.023 MHz (λ=290 meter) Sequence Length = 1023 bits, thus Period = 1 millisec Provides the data for Standard Positioning Service (SPS) The usual position generated for most civilian receivers Modulated by the Navigation/Timing Message code iirsiirs Module 2 - GPS
  21. 21. Precise (P) Code Generally encrypted into the Y-code (A.S.) Requires special chip to decode Modulates both L1 & L2 Also modulated by Nav/Time data message Chipping rate=10.23 MHz (λ=29.30m) i.e. 10 times faster than C/A code ensuring improved time measurement. Sequence Length = 2.35*1014 bits, thus Period = 266 days P-code rate is the fundamental frequency (provides the basis for all others) P-Code (10.23 MHz) /10 = 1.023 MHz (C/A code) P-Code (10.23 MHz) X 154 = 1575.42 MHz (L1). P-Code (10.23 MHz) X 120 = 1227.60 MHz (L2). iirsiirs Module 2 - GPS
  22. 22. Navigation Message In order to solve the user position equations, one must know where the SV is: The navigation and time code provides this 50 Hz signal modulated on L1 and L2 The SV’s own position information is transmitted in a 1500-bit data frame Pseudo-Keplerian orbital elements Determined by control center via ground tracking Receiver implements orbit-to-position algorithm Also includes clock data and satellite status And ionospheric / tropospheric corrections The International Telecommunication Union (ITU) has reserved 1559- 1610MHz band for satellite based navigation through World Radio Communication (WRC) conferences, held every three year. GPS bands (US Federal Communication Commission): (1215- 1240MHz, 1559-1610 MHz, L5- 1164-1188MHz) iirsiirs Module 2 - GPS
  23. 23. The Almanac In addition to its own nav data, each SV also broadcasts info about ALL the other SV’s In a reduced-accuracy format Known as the Almanac Permits receiver to predict, from a cold start, “where to look” for SV’s when powered up GPS orbits are so predictable, an almanac may be valid for months Almanac data is large 12.5 minutes to transfer in entirety iirsiirs Module 2 - GPS
  24. 24. GPS PositioningGPS Positioning • Point Positioning Methods using stand alone receivers provide 10 - 100 m accuracy – Dependent on SA – 1 Epoch solution • Differential Positioning Methods using 2 receivers, simultaneously tracking a minimum of 4 satellites (preferably 5) will yield 0.5 cm to 5 m accuracy with respect to a Reference Station • Differential Techniques using CodeCode will give metermeter accuracy • Differential Techniques using PhasePhase will give centimetercentimeter accuracy iirsiirs Module 2 - GPS
  25. 25. Topo and Locations Mapping Monitoring Volumes Photo control Construction Control and Stakeout Boundaries Seismic Stakeout Profiles Establishing Portable Control Stations (sharing with Total Stations) Agriculture - Slope Staking Tracking of people, vehicles Plate movements Sports (boating, hiking,…) Archeology Public Transport Emergency services ApplicationsApplications iirsiirs Module 2 - GPS
  26. 26. User requirements in positioning accuraciesUser requirements in positioning accuracies Accuracy Geomatics Land Marine Airborne Geodetic Infrastructure Earth Moving Dredging Cat II/III Fault Monitoring Road Grading Pylon Positioning Sensor positioning < 20 cm Construction Surveys Agriculture (air- spaceborne) Engineering Surveys Mining Geodynamics Urban cadastral survey Resource Mapping Facility Surveys GIS Database Mapping/GIS Docking 0.2 - 1.5 m Utility Mapping Highway Surveys Buoy Position Highway Surveys Rural cadastral survey Legal Surveys Precision farming GIS Data Collection Automobiles Channel Navigation Sensor navigation 1 - 5 m Site Specific Farming Emergency Cabling Oceanic Navigation Public Transport Research Tracking Harbor Entry Mapping 10 - 100 m Reconnaissance Navigation Harbor Approach Area Navigation Oceanic # Accuracy requirement depending on application iirs iirsiirs Module 2 - GPS
  27. 27. GPS Opportunities in India • Indian GPS market can be broadly divided in following segments • National Survey Agencies(NRSC, SOI,Mil. Survey,NHO,) • Land Records (Kerala,TN,J&K, Rajasthan,Gujrat, etc.) • Oil and Energy( OIL, ONGC, BPCL, HPCL) • Power(NHPC Assam, Himachal, J&K,Arunachal, Kaveri Basin) • Defense, Remote Sensing , GIS, Forestry AND Education • Scientific Institution(IIGM,CMMAC,WIHG, NGRI, SAC,GSI) • Mining and Geology(CMPDIL,WCL,MCL, SECL, NCL,BCCL) • Consultancy( CRRI, CBRI, NCB, CSMRS,WAPCOS) • Engineering /Infrastructure(IRCON,RITES,Delhi Metro, NHAI) • Private Surveying Companies (ICT, Theowell, Secon, etc. ) • Marine and Maritime Boards(Port Trust, MMB, NIO, etc.) iirsiirs Module 2 - GPS
  28. 28. Never get lost again Earth deformation measurement is the main application of GNSS. GPS is no longer primarily a military tool Now a product with vast commercial potential From aviation to outdoor recreational activities Applications will change our lives and save money GPS with computer mapping will help manage our natural resources Vehicle location and navigation lets us avoid congested freeways, find more efficient routes and save fuel, & air pollution Ships and aircraft are safer in all weather conditions Businesses with large outside plant (railroads, utilities) will manage resources more efficiently, reducing consumer costs The GPS technology is evolving rapidly More accurate and affordable TODAY than YESTERDAY. Conclusion iirsiirs Module 2 - GPS
  29. 29. References http://gps.gov/ http://www.glonass-ianc.rsa.ru/pls/htmldb/f? p=202:1:15000421459964108253 http://igscb.jpl.nasa.gov/ http://www.navcen.uscg.gov/?pageName=GPS Interface Control Documents: http://www.navcen.uscg.gov http://www.Glonass-ianc.ras.ru http://www.Galileoju.com iirsiirs Module 2 - GPS
  30. 30. Communications Surveying & Mapping Fishing & Boating Off shore Drilling Recreation Trucking & Shipping Personal Navigation Aviation Railroads Power Grid Interfaces Use of GPS Precision farming iirsiirs Module 2 - GPS