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)