1. Presented by : DEBANJALI BANERJEE 2 nd year, CSE Department Swami Vivekananda Institute of Science and Technology West Bengal.

2. GPS, that is, Global Positioning System is a satellite-based navigation system made up of a network of 24 satellites placed into orbit. GPS measures 3-D locations on Earth surface using satellites. GPS operates using radio signals sent from satellites orbiting the Earth. The orbital height is 20,200km approximately. The systems as a whole consists of three segments – 1. Satellites (space segment) 2. Receivers (user segment) 3. Ground stations (control segment)

3. 1. Global Positioning Systems (GPS) is a form of Global Navigation Satellite System (GNSS) 2. Official name of GPS is NAVigational Satellite Timing And Ranging Global Positioning System (NAVSTAR -GPS) 3. First developed by the United States Department of Defense for military purpose on February, 1973 and became fully functional from 1995. 4. Consists of two dozen GPS satellites in medium Earth orbit (The region of space between 2000km and 35,786 km) 5. Till 31 st of January 2016 the total number of launches are 65.

4. As said earlier, GPS architecture consists of three segments : Space, User and Ground (control) segment. The Space Segment transmits radio-navigation signals, stores and retransmits navigation signal sent by the Control Segment. The Ground or Control Segment is mainly responsible for the proper operation of the GPS signals. User Segment receives the GPS signal and solve navigation equations. These transmissions are controlled by highly stable atomic clocks on board the satellites. Space Segment is formed by a satellite constellation, Control Segment is composed by a network of Monitor Stations, a Master Control Station and the Ground Antennas. User Segment is composed by GPS Receivers.

5. Space Segment : Currently: 26 Block II, 2 Block IIR, no Block I satellites are active. (Picture of a Block II Satellite as follows :)

6. Control Segment has 5 major stations which measure the distances of the overhead satellites every 1.5 seconds and send the corrected data to Master control and these Master control and Monitor Station are :

7. There are two services SPS and PPS :  The Standard Positioning Service –  SPS- is position accuracy based on GPS measurements on single L1 frequency C/A code  C/A ( coarse /acquisition or clear/access) GPs code sequence of 1023 pseudo random bi phase modulation on L1 freq User Segment :

8.  The other type of service is The Precise Position Service –  PPS is the highest level of dynamic positioning based on the dual freq P-code  The P-code is a very long pseudo- random bi phase modulation on the GPS carrier which does not repeat for 267 days  Only authorized users, this consists of SPS signal plus the P code on L1 and L2 and carrier phase measurement on L2

9. GPS functioning have 5 basic steps :  Triangulation.  Distance Measurement.  Timing.  Satellite Positioning.  Correction of Errors.

10.  Triangulation is a process by which the location of a radio transmitter can be determined by measuring either the radial distance, or the direction, of the received signal from two or three different points. Triangulation is sometimes used in cellular communications to pinpoint the geographic position of a user.  The position is calculated from distance measurement. Mathematically we need four satellites but three are sufficient by rejecting the ridiculous answer.

11. How Triangulation works.. This picture and the chart exactly shows how triangulation works : IntersectionEquivalencyResult Intersection of two spheres Circle Intersection of three spheres Circle SphereTwo points Intersection of four spheres (Not in the picture) Two points Spheres One point

12. Distance to a satellite is determined by measuring how long a radio signal takes to reach us from that satellite. To make the measurement we assume that both the satellite and our receiver are generating the same pseudo-random codes at exactly the same time. By comparing how late the satellite's pseudo-random code appears compared to our receiver's code, we determine how long it took to reach us. Multiply that travel time by the speed of light and you've got distance.

13. If the clocks are perfect sync the satellite range will intersect at a single point. But if imperfect the four satellite will not intersect at the same point. The receiver looks for a common correction that will make all the satellite intersect at the same point

14. 1.The Air Force has put each GPS satellite into a very precise orbit, according to the GPS master plan. 2.11,000 mile altitude is important because something that high is well clear of the atmosphere and it will orbit according to very simple mathematics. 3.On the ground all GPS receivers have an almanac programmed into their computers that tells them where in the sky each satellite is, moment by moment. 4.The basic orbits are quite exact but just to make things perfect the GPS satellites are constantly monitored by the Department of Defense. 5.They use very precise radar to check each satellite's exact altitude, position and speed. 6.The errors they're checking for are called "ephemeris errors" because they affect the satellite's orbit or "ephemeris.” 7.These errors are caused by gravitational pulls from the moon and sun and by the pressure of solar radiation on the satellites.

15. Error Sources : Satellite orbits - 1. IGS Final or Rapid orbits (available within 24h) virtually eliminate orbit errors (<.1m) for post- processing at any epoch 2. In real-time the broadcast orbit errors (~3m) can be reduced (< 1m) by DGPS (Differential GPS) or by using IGS Predicted or the Ultra-Rapid orbits Satellite clocks - 1. For relative positioning double differencing nearly eliminates satellite clock errors 2. IGS Final or Rapid satellite clocks (available within 24h) virtually eliminate satellite clock errors (<.1m) for post-processing (currently only at the 5 min epoch sampling) 3. In real time the broadcast clock errors (SA) reduced by DGPS Tropospheric refraction - 1. Virtually eliminated by estimating corrections to a model (also used in GPS meteorology); or at IGS stations, by using the IGS tropospheric delay products! 2. Nearly eliminated (<.1m) by using a model with measured met data 3. Reduced by a nominal model and/or differential positioning (e.g. DGPS) dt =Satellite clock error(s), d rel =relativity correction(s) af 2 =2nd order coefficient (s -1 ), af 1 =1st order coefficient (unitless), af 0 =Zero order coefficient (s) t =time of measurement(s), t oe =time of ephemeris(s), t gd =group delay(s)

16.  Ionospheric refraction - 1. For dual frequency receivers, the use of (P1, P2) or (L1, L2) virtually eliminates ionospheric refraction (also used for ionospheric delay determination/monitoring, e.g. by IGS, the IGS ionospheric delay products ) 2. For single frequency receivers, the use of IGS ionospheric delay products (available within a few weeks) significantly reduces ionospheric refraction errors 3. For single frequency receivers, ionospheric refraction errors reduced in differential (relative) positioning (e.g. DGPS) for baselines up to 100 km  Antenna phase center variations - 1. Virtually eliminated in relative positioning over moderate baseline lengths (<500km) when using the same antenna types 2. Antenna phase center corrections (e.g. IGS antenna phase center tables) must be used for different antenna types and precise positioning (<.1m)  Multipath - 1. Difficult to mitigate, errors can reach a few cm for the phase and up to a meter or more for pseudorange positioning/navigation 2. Reduced by improved site selections and hardware (receiver/antenna) designs f=frequency of L 1 or L 2 (Hz); λ=wavelength of L 1 or L 2 (m); L1,L2=Phase N=integer ambiguity on L 1 or L 2 (cycles); ɸ =carrier phase measurement on L 1 or L 2 (cycles)

18. A summative picture of how GPS works :

19. Dilution of precision is a term used in satellite navigation and geometric engineering to specify the additional multiplicative effect of navigation satellite geometry on positional measurement precision. Dilution of precision is may be of two types depending upon its values : GDOP (Good DOP) when the DOP value is between 2-5 and PDOP (Poor DOP) when the DOP value is greater than 20.

20. Dilution of Precision (Contd.) : Dilution of Precision may be of different values also which may be of 5 types. The types of Dilution of Precision is classified well in the picture below :

21. i.GPS receiver on getting a signal from satellite compares it with the known 37 codes to determine which satellite is sending the signal. ii.The receiver then decodes the timing information, multiplies by the speed of light to find the radius of the sphere. iii.After its completed for at least three(3) satellites the GPS can successfully determine the position. iv.This information is sent to the user via binary satellite codes. v.All these signals are run by some carrier signals and some pseudo- random code. vi.The signal travel time is given by, Signal travel time = offset between the satellite signal and the receiver signal. vii.The signal travel time is approximately 186 miles/second. Satellite Signal Receiver Signal

22. L1, L2 are two microwave carrier signal that are transmitted from Satellite Vehicle. L1 carriers the navigation message of frequency 1575.42 MHz and L2 measures the ionospheric delay of frequency 1227.6MHz. These are derived from the system clock of 10.23 MHz (phase quadrature). There are three (3) types of pseudo random code because they repeat themselves every 1023 bits. These codes are : i) C/A Code (Coarse Acquisition Code) that modulates L1 carrier phase with a frequency 1MHz, ii) NAV/System Code that modulates L1-C/A and describes the satellite orbit and clock corrections, iii) P-Code (Precise Code) AS (anti-spoofing) encrypts P-code into Y-code and the P-code modulates both L1 and L2. Modulation used is Direct Sequence Spread Spectrum.

23. Navigation : GPS satellites broadcast three different types of data in the primary navigation signal. – Almanac – sends time and status information about the satellites. – Ephemeris – has orbital information that allows the receiver to calculate the position of the satellite. This data is included in the 37,500 bit Navigation Message, which takes 12.5 minutes to send at 50 bps.

24. Navigation (Contd.) : Satellites broadcast two forms of clock information – Coarse / Acquisition code (C/A) - freely available to the public. The C/A code is a 1,023 bit long pseudo-random code broadcast at 1.023 MHz, repeating every millisecond. – Restricted Precise code (P- code) - reserved for military usage. The P-code is a similar code broadcast at 10.23 MHz, but it repeats only once a week. In normal operation, the anti-spoofing mode, the P code is first encrypted into the Y- code, or P(Y), which can only be decrypted by users a valid key.

25. Wide Area Augmented System : i) Wide Area Augmentation System (WAAS) is an experimental system designed to enhance and improve satellite navigation over the continental United States and portions of Mexico and Canada. ii) WAAS is a highly advanced real-time differential GPS that requires no additional equipment to work. iii) WAAS uses its own geostationary satellites in fixed orbit over North America. There are 25 ground reference stations positioned across the U.S. that monitor GPS satellite signals. iv) These stations continuously receive and correct GPS satellite information against their own known precise positions. v) Each WAAS ground station then sends its corrected GPS data to one of two master control stations located on U.S. These master control stations create a correction message that weeds out atmospheric distortion, GPS satellite orbit and clock errors and time errors which is then broadcast to 2 WAAS satellite. vi) These in turn rebroadcast the correction information using the basic GPS signal structure to any WAAS capable GPS receiver.

26.  The application of WAAS are improvement to aviation operation, software development that uses GPS and Space Segment upgrades.  The advantage of WAAS is it addresses all navigation problem and give highly accurate positioning.  The disadvantage of WAAS is that it is subjected to space weather and space debris threats Wide area augmented system :

27. Advantages of GPS : a) GPS is extremely easy to navigate to reach the desired navigation. b) GPS works in all weather. c) The GPS costs you very low in comparison other navigation systems, so it is very easy to integrate into other technologies like cell phone. d) The most attractive feature of this system is its 100% coverage on the planet and gives full time access. e) The system is updated regularly by the US government and hence is very advance. f) This is the best navigating system in water also.

28.  Sometimes the GPS signals are not accurate due to some obstacles to the signals such as buildings, trees.  If we are using the GPS on a battery operated system, then due to battery failure we may have a problem, so for that reason we must need to carry a external battery.  Sometimes GPS may fail due to certain reasons so we need to carry backup map for directions.  Launching satellites in orbit is too costly.  Impossibility to repair and maintain.

29.  GPS helps in road transport and heavy vehicle guidance.  The system helps in commercial aviation when aircrafts use GPS for route navigation.  GPS helps in environmental and atmospheric monitoring, animal behavior studies, botanical specimen location, meteorology and climate research.  GPS helps in tracking of vehicles and cargoes.  GPS helps in surveying, geophysics and mapping.  GPS timing is important for telecommunications applications, particularly for mobile telephone networks.  Global financial systems increasingly need precise timing systems to schedule and priorities local and international money transfers, settlements and trades and to provide an audit trail for financial transactions.  Last but not the least, GPS has immense importance in social networking.

30.  GPS is a space-based navigation system that transmit precise microwave signals, provides location and time information in all weather conditions where there is an unobstructed line of sight to four or more GPS satellites.  The system provides critical capabilities to military, civil, and commercial users around the world. Even in social networking also GPS plays an integral part.

31. * http://www.gps.gov/students/ http://www.gps.gov/students/ * https://en.wikipedia.org/wiki/Global_Positioning_System https://en.wikipedia.org/wiki/Global_Positioning_System * www.esf.edu/for/herrington/557/557pps/GPS.ppt www.esf.edu/for/herrington/557/557pps/GPS.ppt * www.nps.gov/gis/gps/gps4ics/2_prework/prework.ppt www.nps.gov/gis/gps/gps4ics/2_prework/prework.ppt * www.clarkson.edu/class/cs463/wireless.../GlobalPositioningSystem. ppt www.clarkson.edu/class/cs463/wireless.../GlobalPositioningSystem. ppt * www.casde.iitb.ac.in/IMSL/motion/gps/Seminar%20on%20GPS.ppt www.casde.iitb.ac.in/IMSL/motion/gps/Seminar%20on%20GPS.ppt * https://www.rgs.org/NR/rdonlyres/95D99DBD-CE9B-4B89-81F3- 22D12B3B976E/0/Chapter6TheGlobalPositioningSystemGPSPrinciples andConcepts.pdf https://www.rgs.org/NR/rdonlyres/95D99DBD-CE9B-4B89-81F3- 22D12B3B976E/0/Chapter6TheGlobalPositioningSystemGPSPrinciples andConcepts.pdf * http://www.nhdfl.org/library/pdf/Forest%20Protection/Introductio n%20to%20Global%20Positioning%20System.pdf http://www.nhdfl.org/library/pdf/Forest%20Protection/Introductio n%20to%20Global%20Positioning%20System.pdf * http://www.nhdfl.org/library/pdf/Forest%20Protection/Introductio n%20to%20Global%20Positioning%20System.pdf http://www.nhdfl.org/library/pdf/Forest%20Protection/Introductio n%20to%20Global%20Positioning%20System.pdf

32. I would like to thank all the people who helped me in completing this power point presentation starting from my Parents, my teachers, my guide, my friends and definitely a special thanks to those who created the challenge that initiated the urge in myself to complete this project which I finally did. Thank you everyone for all your support and cooperation throughout the project.