Lecture 11:Global Positioning Global Positioning

System (GPS)System (GPS)

Lecture 11:Global Positioning Global Positioning

System (GPS)System (GPS)

Introduction to GPS

GPS is funded by and controlled by the US Department of Defense (DOD).

GPS provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity, and time.

What is GPS?

GPS, which stands for Global Positioning System, is the only system today able to show you your exact position on the Earth anytime, in any weather, anywhere.

GPS: Global Positioning GPS: Global Positioning SystemSystem

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GPS componentsGPS components

The three parts of GPS are:

GPS systems are made up of 3 segments Space Segment (SS) Control Segment (CS) User Segment (US)

Space SegmentSpace Segment

24 satellites in orbit dedicated to GPS that orbit the Earth in very precise orbits twice a day.

6 satellites are within view of any location at one time.

Satellites constantly transmit their location information and time data.

Control Segment Ground antennas monitor and track

the satellites. They also transmit correction

information to individual satellites.

Kwajalein Atoll

US Space Command

Control SegmentControl Segment

Hawaii

Ascension Is.

Diego Garcia

Cape Canaveral

Ground AntennaMaster Control Station Monitor Station

User Segment

GPS receivers include a display for showing location and speed information to the user.

User segmentUser segment GPS antennas & receiver/processorsGPS antennas & receiver/processors PositionPosition VelocityVelocity Precise timingPrecise timing Used byUsed by

AircraftAircraft Ground vehiclesGround vehicles ShipsShips IndividualsIndividuals

Handheld GPS ReceiversHandheld GPS Receivers

Casio GPS wristwatchCasio GPS wristwatch

GPS Applications

Military: fighters, bombers, detect missiles, weapons, nuclear.

Automobiles: show moving maps (highways, buildings)

Aviation: for aircraft navigation Marine: Provides precise navigation

information to boaters.

How GPS worksHow GPS works GPS uses satellites as reference points to

calculate accurate positions. Each satellite orbits the earth every 12

hours (2 complete rotations every day). This ensures that every point on the Earth

will always be in radio contact with at least 4 satellites.

Ground stations are used to precisely track each satellite's orbit.

How GPS worksHow GPS works GPS satellites transmit signals to equipment on

the ground. GPS receivers passively receive satellite

signals; they do not transmit. GPS operations depend on a very accurate time

reference, which is provided by atomic clocks. Each GPS satellite has atomic clocks on board.

Each GPS satellite transmits signals that indicates its location and the current time.

The signals, moving at the speed of light, arrive at a GPS receiver at slightly different times because some satellites are farther away than others.

How GPS worksHow GPS works The distance to the GPS satellites can be

determined by estimating the amount of time it takes for their signals to reach the receiver.

When the GPS receiver estimates the distance to at least four GPS satellites, it can calculate its position (in terms of latitude and longitude).

It also can tell you What direction you are heading How fast you are going Your altitude A map to help you arrive at a destination

How GPS worksHow GPS works

GPS also can tell you

How far you have traveledHow long you have been traveling

Estimated time of arrival

Calculating Distance

Velocity x Time = Distance

Radio waves travel at the speed of light, roughly 186,000 miles per second (mps)

If it took 0.06 seconds to receive a signal transmitted by a satellite floating directly

overhead, use this formula to find your distance from the satellite.

186,000 mps x 0.06 seconds = 11,160 miles

Latitude and Longitude Latitude and

Longitude are spherical coordinates on the surface of the earth.

Latitude is measured North or South of the Equator.

Longitude is measured East or West of Greenwich.

GPS uses Latitudes and Longitudes to reference locations.

Aircraft Navigation using GPS

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 GPS also can simplify and improve the

method of guiding planes to a safe landing, especially in poor weather.

With advanced GPS systems, airplanes can be guided to touchdown even when visibility is poor.

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.

Waypoints

Latitude and Longitude

Your location

Direction of waypoint

Date andTime

Waypoint

Using GPS, aircraft can fly the most direct routes

between airports

A GPS receiver in the cockpit provides the pilot

with accurate position data and helps him keep the

airplane on course.

Advantages of GPS in Aviation

GPS can provide accurate, continuous, all-weather coverage for aircraft position determination anywhere on the earth.

Thus, GPS can serve better air traffic management (ATM) system. GPS can maintain high levels of flight

safety GPS can reduce the aircraft delays

problem GPS can increase airway capacity. GPS can reduce fuel consumption

Advantages of GPS in Aviation

Reduced costs to each individual State while increasing overall benefits to individual States

Maintain economies from reduced maintenance and operation of ground-based systems (such as VOR/DME/NDB station)

Improved ground and cockpit situational awareness

Increased landing capacity for aircraft More efficient, optimized, flexible, and user-

preferred route structures

Time Difference

GPS Distance D = Speed of Light x Time;

or D = CT

D

GPS Limitations

Line of Sight Transmissions: Obstructions such as trees, buildings may prevent clear line of sight.

Refraction: GPS signal from the satellite doesn’t follow a straight line

Signal Interference: Sometimes the signals interfered before they hit the receivers.

Obstruction

Sources of Signal Sources of Signal InterferenceInterference

Sources of Signal Sources of Signal InterferenceInterference

Earth’s Atmosphere

Solid Structures

Metal Electro-magnetic Fields

GPS Frequencies

L1 (1575.42 MHz) - For CivilianL2 (1227.60 MHz) - For CivilianL3 (1381.05 MHz) – For MilitaryL4 (1379.913 MHz) – For ResearchL5 (1176.45 MHz) – For Civilian

Local Area Augmentation Local Area Augmentation System (LAAS)System (LAAS)

““LAAS is a precision approach and LAAS is a precision approach and landing system that relies on the Global landing system that relies on the Global Positioning System (GPS) to broadcast Positioning System (GPS) to broadcast highly accurate information to aircraft on highly accurate information to aircraft on the final phases of a flight. the final phases of a flight.

LAAS support precision approaches and LAAS support precision approaches and landing capability to aircraft operating landing capability to aircraft operating within a 20- to 30-mile radius of the within a 20- to 30-mile radius of the airport. airport.

LAAS approaches will be designed to LAAS approaches will be designed to avoid obstacles, restricted airspace, noise-avoid obstacles, restricted airspace, noise-sensitive areas, or congested airspace.”sensitive areas, or congested airspace.”

GPS Local Area Augmentation GPS Local Area Augmentation System (LAAS)System (LAAS)

One LAAS covers multiple runway endsOne LAAS covers multiple runway ends

LAAS

QuestionQuestion

The latest addition to The latest addition to navigational aid system is GPS.navigational aid system is GPS. Explain briefly how GPS works. Explain briefly how GPS works. Describe the advantages GPS has Describe the advantages GPS has

over the other navigational aids over the other navigational aids such as VOR/DME or NDB.such as VOR/DME or NDB.