Global Navigation Satellite Systems PDF

Global Navigation Satellite Systems Week Week 6 Week 7 Outline Evolution of Navigation and Positioning Global Navigation Satellite Systems (GNSS) The Global Positioning System (GPS)...

Global Navigation Satellite Systems Week Week 6 Week 7 Outline Evolution of Navigation and Positioning Global Navigation Satellite Systems (GNSS) The Global Positioning System (GPS) GPS Segments Positioning Using GPS GPS Sources of Errors GPS Equipment GPS Application Evolution of Navigation and Positioning 1. Stone Age 2. Star Age 3. Radio Age 4. Satellite Age Stone Age Technique: Identifying and remembering objects and landmarks as points of reference. Points of reference used: big stones Global Navigation Satellite Systems 1  trees mountains Disadvantage: you can only use this method if it is in land and you are familiar in the place Star Age Technique: Using sun, moon, and stars (visible objects) as points of reference Why: you cannot use stone age reference to explore the ocean (no points of reference available) Disadvantages: there are certain time you cannot see the reference (sun at night, Polaris at the morning), you cannot see Polaris if you are in the Southern Hemisphere. Radio Age Received radio signals determine the location of the receiver. Transmitter to receiver to signal detection and measurement. However, one transmitter can only detect the distance, not the position Two transmitters can be focused on two location (two intersecting points of a circle. Three transmitters can find the exact location (= triangulation) Distance of the receiver to the tower = speed of light * time it took (D= cT) Limitation: can be easily interfered (causing some errors in location) if no transmitters, no signal local only Satellite Age Combination of star age and radio age concepts. Satellites act as the reference points that send signals to receivers Global Navigation Satellite Systems 2  The distances to receivers are measured to determine 3d positions Compared to Star Age, it works day/night and has global coverage. Can cover the whole planet several satellites orbiting the Earth Global Navigation Satellite Systems (GNSS) worldwide satellite-based positioning and navigation system. Accurate location, velocity, and time Utilize a work of satellites in space, ground-based control stations, user receivers handled by different countries/locations Global USA (NAVSTAR) - 32 operational EU (GALILEO) - 23 China (BeiDou) - 44 Russia (GLONASS) - 24 Regional India (NavIC (IRNSS)) - 7 Japan (QZSS) - 4 Global Positioning System (GPS) under GNSS old name: Navigation Satellite Time and Ranging Global Positioning System Developed by the US Department of Defense for very precise navigation and to protect the country Timeline: 1973 - project start 1978 - prototype 1993 - initial operational Global Navigation Satellite Systems 3  1995 - full operational Goal: to know: what time is it (precise) 1 * 10^-9 second precise distance between 2 points When is the sunset, and sunrise? how long does it take from A to B Meaning: the GPS satellites are nothing more than a set of clocks in the sky GPS Segments Space Segment the constellation of satellites Configuration: 24 Satellites in 6 orbital planes 55º inclination 4 satellites in each plane to get exact location Altitude: 22,000 km Period: about 12 hours (bumabalik sa same place) Design: durable and reliable solar panels + batteries Atomic clocks 10-15 years lifespan Payload: Inaattach na important components Atomic clock: provides highly accurate time measurements (error: 1 sec in 100 million years) Signal Generator: produces navigation signals that are essential for the system’s functionality Transponders: Amplify generated signals and received signals Control Segment Global Navigation Satellite Systems 4  Can be found in the Earth’s surface, controlling satellites Monitoring Stations track all GPS satellites in view collecting data on their signal strength, timing, and health Master Station controls all of the GPS satellite constellation Processing data sent by monitoring stations Located near Colorado Springs Ground Antennas communicate with the satellite for both receiving data from and transmitting commands to the satellite set signals to the satellite once it gets lost User Segment GPS user Handheld receivers stand-alone portable units designed for navigation/positioning purposes walang ibang usage Embedded receivers can be used as navigation and others ex. phone Specialized receivers precise receivers used for applications requiring greater accuracy for surveying, research, and military Positioning Using GPS Procedure: Global Navigation Satellite Systems 5  to control segment: satellite > monitoring station > master station > ground antenna > satellite. repeat to user segment: satellites have carrier signal that brings navigation messages to users What can this do: can determine the corresponding location. Solution: D = cT (this is only Pseudorange, there are errors in time) To lose this time error, we need to add clock error correction satellites. (triangulation (3D coordinates) + clock error correction = 4 satellites) How does GPS works? 1. There should be at least 24 operational satellites 2. 6 GPS satellites are always “Visible” from Earth 3. The satellites continuously transmit their precise location and time 4. GPS receivers pick up the satellite signals and determin the location using triangulation. Carrier Signals carries information (navigation message) GPS signals are transmitted in the L-band of the microwave radio spectrum primary L1 - civilian use - 1575.42 MHz L2 - military use - 1227.60 MHz L2C - civilian use - 1227.60 MHz L5 - aviation use - 1176 MHz Navigation Message Information about the satellite and other satellites Ephemeris Global Navigation Satellite Systems 6  prexice info of specific satellites (speed, loc, health) updated every 30 minutes Almanac coarse orbital position of all satellites less precise due to not updated real time (every 12 hours) main role: to know other satellites’ position (to avoid crashing) PRN Code Identifier of each satellite and ‘scrables’ the navigation message each satellite has ‘code’ and we need ‘code’ to identify it C/A or Coarse/Acquisition Code Civilian use P or Precise code Military use Cannot be interpreted using the cellphone Positioning Using GPS Differential GPS calculates the difference between the known position and the GPS position the data can be used to correct the positional errors in the data collected from the Rover GPS receivers 2 types of processing info from satellite 1. Post Processing Differential GPS 2. Real Time Differential GPS 2 Positioning Modes 1. Static steady (kaunting galaw, ulit) Global Navigation Satellite Systems 7  2. Kinematic continuously taking positions every steps. GPS Sources of Errors Denial of Accuracy in the past, US military denied users to have the accurate positioning pointless for creating GPS Solution: executive Availability civilians were given intentional error disregarding the position accuracy many people were protesting Another solution: anti-sproofing by encrypting P-code Selective Availability creating intentional errors to degrade the position accuracy of 100m eventually removed Satellite Clock 1 billionth of a second error - 30 cm error Solution: continuously monitoring by ground stations and compared with the master control clock system (more accurate) Calculating errors Receiver Clock causes inaccuracy in distance measurements Solution: make simultaneous measurements to 4 satellites Satellite Orbit caused by gravity, solar radiation pressure and models Atmospheric kapag nasa indoor or napapaligiran ng tall buildings Multipath Global Navigation Satellite Systems 8  Receiver Global Navigation Satellite Systems 9