Lecture 7:Global Positioning
System (GPS)
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Learning Outcomes
• At the end of this lecture, the student should be able to:– Explain the basic working principle of GPS
– Describe the advantages of GPS
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Introduction
• GPS is stands for Global Positioning System.
• Official name of GPS is Navigational Satellite Timing And Ranging Global Positioning System (NAVSTAR GPS)
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Introduction
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What is GPS-Global Positioning System?
• 4 satellites/orbit. Total orbit = 6. Thus, GPS consists of 24 satellites.
• Each satellite orbits the earth every 12 hours (2 complete rotations every day).
• Thus, every point on the Earth will always be in radio contact with at least 4 satellites.
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GPS Segment
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What is the purpose of GPS
• The purpose of GPS is to show you your exact position on the Earth anytime, in any weather, anywhere.
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Who developed GPS?
• First developed by the US DOD (United States Department of Defense)
• Feasibility studies begun in 1960’s.Pentagon appropriates funding in 1973.
• First satellite launched in 1978. System declared fully operational in April, 1995.
• Open to the public, 2000. Currently controlled by the United States Air Force.
• It costs about $750 million to manage and maintain the system per year
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Help Who Can Use GPS
Military
Automobile
Aircraft Navigation
Marine
Individual
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Who can use GPS?
• Automobiles: show moving maps (highways, buildings)
• Military: target detection.
• Aviation: for aircraft navigation
• Marine: Provides precise navigation information to boaters.
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Why do we need GPS?
One drawback of using radio waves generated on the ground (like NDB,VOR,DME or ILS) is that you have only two choices:
• A system that is very accurate but doesn’t cover a wide area
• A system that covers a wide area but is not very accurate
• We need a powerful system such GPS because GPS can provide accurate information and cover wide area.
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GPS Frequency • GPS operates in the UHF band.
• There are two types of services available:
1. For Civilian/Research Use Standard Positioning System
– L1 (1575.42 MHz), L2 (1227.60 MHz), L5 (1176.45 MHz) – For Civilian
– L4 (1379.913 MHz) – For Research
2. For Military Use Precise Positioning System
– L3 (1381.05 MHz)
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GPS Receiver
Handheld GPS ReceiversCasio GPS wristwatch
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HOW GPS WORKS?
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How GPS works• GPS receivers tuned to the frequencies of GPS satellites.• Each GPS satellites then transmit signals to the GPS
receivers . The signals, moving at the speed of light, c = 3 x 10⁸ m/s.
• These signals indicates satellite’s location and the current time.
• The GPS receiver measures the time taken for a signal to travel from satellite to receiver.
• The distance to each GPS satellites can be calculated:
Distance = Speed of Light x Time• Knowing the distance from at least 4 GPS satellites, the GPS
receiver can calculate the position (latitude, longitude and altitude )
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GPS IN AVIATION
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GPS receiver in the aircraft’s cockpit
Can provide the pilot with navigational information in terms of longitude, latitude and altitude.
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What GPS can tell you?
• GPS also can tell you
– What direction you are heading
– Speed (How fast you are going)
– Your altitude
– A map to help you arrive at a destination
– Distance (How far you have traveled)
– Time (How long you have been traveling)
– Estimated time of arrival (When you will arrive)
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Help ADVANTAGES OF GPSIN AIRCRAFT NAVIGATION
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ADVANTAGES OF GPSin AIRCRAFT NAVIGATION
• GPS can reduce the aircraft delays problem,
• GPS can reduce journey time and fuel consumption
• GPS can maintain high levels of flight safety.
• GPS can increase airway & landing capacity for aircraft.
• GPS more economical
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A GPS receiver in the cockpit provides the pilot with
accurate position data and helps him keep the airplane on
course.
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Using GPS, aircraft can fly the most direct routes
between airports
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Advantages of using GPS in Aircraft Navigation
• GPS can reduce the aircraft delays problem– GPS can provide accurate & continuous data
during all-weather condition.– This can avoid flight delays.
• GPS can reduce fuel consumption– Civil aircraft typically fly from one waypoint to
another.– With GPS, an aircraft's computers can be
programmed to fly a direct route to a destination. – This can save fuel and time
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Advantages of using GPS in Aircraft Navigation
• GPS can maintain high levels of flight safety.– Improved situational awareness (quick alert
about emergency)– GPS also can simplify and improve the
method of guiding planes to a safe landing, especially in poor weather.
• GPS can increase airway & landing capacity for aircraft.
– GPS system more flexible. Many aircrafts can depend on GPS system at one time.
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Advantages of using GPS in Aircraft Navigation
• GPS more economical
– Maintain economies from reduced maintenance and operation of ground-based systems (such as VOR/DME/NDB station)
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Waypoints
• Waypoints are locations or landmarks that can be stored in your GPS.
• Waypoints may be entered directly by taking a reading with the unit at the location itself, giving it a name, and then saving the point.
• Once entered and saved, a waypoint remains unchanged in the receiver’s memory until edited or deleted.
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Waypoints
Latitude and Longitude
Your location
Direction of waypoint
Date and
Time
Waypoint
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Help GPS APPLICATION FOR NAVIGATION SYSTEM
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GPS NAVIGATION SYSTEM
• There are two advanced GPS NAVIGATION System which are
1.LAAS - Local Area Augmentation System.
2.WAAS - Wide Area Augmentation System
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Local Area Augmentation System (LAAS)
• “LAAS is a precision approach and landing system that relies on the Global Positioning System (GPS) to broadcast highly accurate information to aircraft on the final phases of a flight.
• LAAS support precision approaches and landing capability to aircraft operating within a 20- to 30-mile radius of the airport.
• LAAS approaches will be designed to avoid obstacles, restricted airspace, noise-sensitive areas, or congested airspace.”
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Local Area Augmentation System (LAAS)
• One LAAS covers multiple runway ends
• Contributing technology for high precision terminal area navigation services.
• Quick data transferring among LAAS, Aircraft and GPS satellites
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Benefits of LAAS
• Replaces ILS systems that are expensive to maintain
• Increases efficiency of arrival and departure operations and improves usage of runway capacity
• Supports fuel efficiency.
• Improves access to airports during extremely low visibility operations
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Wide Area Augmentation System Wide Area Augmentation System (WAAS)(WAAS)
38 Reference Stations
3 Master Stations
4 Ground Earth Stations
2 Geostationary Satellite Links
2 Operational Control Centers
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WAAS Benefits
• Serves all classes of aircraft during flight operations in all weather conditions at all locations.
• Provides precise navigation and landing guidance to pilots at all airports, including thousands that have no ground-based navigation aids
• Overcomes obstacles to ground-based systems, such as mountainous terrain
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WAAS Benefits
• Reduces operating and maintenance costs associated with ground-based navigation aids
• Makes more airspace usable to pilots, provides more direct en-route paths, and provides new precision approach services to runway ends
• Through international cooperation provides a global navigation system for all users
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GPS Limitations
• The GPS must “see” the satellites, so it does not work well in dense forests, inside caves, underwater, or inside buildings.
• Signal Interference: Sometimes the signals interfered before they reach the receivers.
• Changing atmospheric conditions change the speed of the GPS signals as they pass through the Earth's atmosphere
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Obstruction
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Earth’s Atmosphere
Solid Structures
Metal Electro-magnetic Fields
Signal Interference
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Question Bank
1. Explain how GPS works. (9m)
2. Describe 3 advantages of GPS. (6m)
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