Lecture 7:Global Positioning System (GPS)

RAN 2204

Learning Outcomes

• At the end of this lecture, the student should be ableto:• Explain the basic working principle of GPS• Describe the advantages of GPS

Introduction

• GPS is stands for GlobalPositioning System.

• Official name of GPS isNavigational SatelliteTiming And RangingGlobal PositioningSystem (NAVSTAR GPS)

Introduction

What is GPS-Global Positioning System?

• 4 satellites/orbit. Total orbit =6. Thus, GPS consists of 24satellites.

• Each satellite orbits the earthevery 12 hours (2 completerotations every day).

• Thus, every point on the Earthwill always be in radio contactwith at least 4 satellites.

GPS Segment

Control Segment

Space Segment

User Segment

Three Segments of the GPS

Monitor Stations

GroundAntennas

Master Station

Three Segments of the GPS

What is the purpose of GPS

• The purpose of GPS is to show you your exactposition on the Earth anytime, in any weather,anywhere.

Who developed GPS?

• First developed by the US DOD (United StatesDepartment 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

Military

Automobile

Aircraft Navigation

Marine

Individual

Who use GPS?

• Automobiles: showmoving maps (highways,buildings)

• Military: targetdetection.

• Aviation: for aircraftnavigation

• Marine: Provides precisenavigation informationto boaters.

Why do we need GPS?

• One drawback of using radio wavesgenerated on the ground (like NDB,VOR,DMEor ILS) is that you have only two choices:

• A system that is very accurate but doesn’t covera wide area

• A system that covers a wide area but is notvery accurate

• We need a powerful system such GPS becauseGPS can provide accurate informationand cover wide area.

GPS Frequency

• GPS operates in the UHF band.

• There are two types of services available:• For Civilian/Research Use è Standard

Positioning System• L1 (1575.42 MHz) – For Civilian• L2 (1227.60 MHz) – For Civilian• L5 (1176.45 MHz) – For Civilian• L4 (1379.913 MHz) – For Research

• For Military Use è Precise Positioning System• L3 (1381.05 MHz)

GPS Receiver

Components of the System

• Space segment• 24 satellite vehicles• Six orbital planes

• Inclined 55o with respect toequator

• Orbits separated by 60o

• 20,200 km elevation aboveEarth

• Orbital period of 11 hr 55min

• Five to eight satellites visiblefrom any point on Earth

• Boeing Block I Satellite Vehicle

GPS Satellite Vehicle

• Three nickel-cadmiumbatteries

• Two solar panels• Battery charging• Power generation• 1136 watts

• S band antenna - satellitecontrol

• 12 element L band antenna -user communication

• Boeing - Block IIF satellitevehicle (fourth generation)

GPS Satellite Vehicle

• Weight• 2370 pounds

• Height• 16.25 feet

• Width• 38.025 feet including

wing span

• Design life -10 years• Block IIR satellite vehicle

assembly at LockheedMartin, Valley Forge, PA

GPS Satellite Vehicle

GPS Satellite Vehicle

GPS Satellite Vehicle

GPS Satellite Vehicle Launch

GPS Satellite Vehicle Launch

GPS Satellite Vehicle Launch

GPS Satellite Vehicle Modules

GPS Satellite Vehicle

Conventional Satellite Vehicle

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 = 3x 10⁸ m/s.

• These signals indicates satellite’s location and the currenttime.

• The GPS receiver measures the time taken for a signal totravel 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, longitudeand altitude )

Triangulation

• A GPS receiver's job is to locate four or more of thesesatellites, figure out the distance to each, and use thisinformation to deduce its own location.

•

• This operation is based on a simple mathematicalprinciple called triangulation or trilateration.

• Triangulation in three-dimensional space can be a littletricky, so we'll start with an explanation of simple two-dimensional trilateration.

An Example of 2D Triangulation

• Imagine you are somewhere in the United States and youare TOTALLY lost -- for whatever reason, you haveabsolutely no clue where you are.

• You find a friendly local and ask, "Where am I?" He says,"You are 625 miles from Boise, Idaho."

• This is a nice, hard fact, but it is not particularly useful byitself. You could be anywhere on a circle around Boise thathas a radius of 625 miles

Where in the U.S. am I?

• To pinpoint your location better, you ask somebody elsewhere you are.

• She says, "You are 690 miles from Minneapolis,Minnesota.“ If you combine this information with the Boiseinformation, you have two circles that intersect.

Where in the U.S. am I? (Cont’d)

• If a third person tells you that you are 615 miles fromTucson, Arizona, you can eliminate one of the possibilities,because the third circle will only intersect with one of thesepoints. You now know exactly where you are…

Where in the U.S. am I? (Cont’d)

• You are in Denver, CO!

• This same concept works in three-dimensional space, aswell, but you're dealing with spheres instead of circles.

3D Triangulation

• Fundamentally, three-dimensional trilateration is not muchdifferent from two-dimensional trilateration, but it's a littletrickier to visualize.

• Imagine the radii from the examples in the last sectiongoing off in all directions. So instead of a series of circles,you get a series of spheres.

GPS Triangulation

• If you know you are 10 miles from satellite A in the sky, youcould be anywhere on the surface of a huge, imaginarysphere with a 10-mile radius.

Earth

10 miles

GPS Triangulation (Cont’d)

• If you also know you are 15 miles from satellite B, you canoverlap the first sphere with another, larger sphere. Thespheres intersect in a perfect circle.

10 miles15 miles

GPS Triangulation (Cont’d)

• The circle intersection implies that the GPS receiverlies somewhere in a partial ring on the earth.

PossibleLocations of GPS Receiver

Perfect circle formed fromlocating two satellites

GPS Triangulation (Cont’d)

• If you know the distance to a third satellite, you get athird sphere, which intersects with this circle at two points.

GPS Triangulation (Cont’d)

• The Earth itself can act as a fourth sphere -- only one ofthe two possible points will actually be on the surface ofthe planet, so you can eliminate the one in space.

• Receivers generally look to four or more satellites,however, to improve accuracy and provide precise altitudeinformation.

GPS in AVIATION

GPS receiver in the aircraft’s cockpitCan provide the pilot with navigationalinformation in terms of longitude, latitude andaltitude.

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)

ADVANTAGES OF GPSin AIRCRAFT NAVIGATION

• GPS can reduce the aircraft delays problem,

• GPS can reduce journey time and fuelconsumption

• GPS can maintain high levels of flight safety.

• GPS can increase airway & landing capacity foraircraft.

• GPS more economical

A GPS receiver in the cockpit provides thepilot with accurate position data andhelps him keep the airplane on course.

Using GPS, aircraft can fly the most direct routes between airports

Advantages of using GPS in Aircraft Navigation

1. GPS can reduce the aircraft delays problem• GPS can provide accurate & continuous data

during all-weather condition.• This can avoid flight delays.

2. 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

Advantages of using GPS in Aircraft Navigation

1. 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 poorweather.

2. GPS can increase airway & landing capacity foraircraft.• GPS system more flexible. Many aircrafts can

depend on GPS system at one time.

Advantages of using GPS in Aircraft Navigation

1. GPS more economical• Maintain economies from reduced maintenance and

operation of ground-based systems (such asVOR/DME/NDB station)

GPS NAVIGATION SYSTEM

• There are two advanced GPS NAVIGATION Systemwhich are

• LAAS - Local Area AugmentationSystem.

• WAAS - Wide Area AugmentationSystem

Local Area Augmentation System (LAAS)

• LAAS is a precision approach and landing systemthat relies on the Global Positioning System (GPS)to broadcast highly accurate information to aircrafton the final phases of a flight.

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

• LAAS approaches will be designed to avoidobstacles, restricted airspace, noise-sensitive areas,or congested airspace.

Local Area Augmentation System (LAAS)

• One LAAS coversmultiple runway ends

• Contributingtechnology for highprecision terminal areanavigation services.

• Quick datatransferring amongLAAS, Aircraft andGPS satellites

Benefits of LAAS

1. Replaces ILS systems thatare expensive to maintain

2. Increases efficiency ofarrival and departureoperations and improvesusage of runway capacity

3. Supports fuel efficiency.4. Improves access to

airports during extremelylow visibility operations

Wide Area Augmentation System (WAAS)

38 Reference Stations (WRS)

3 Master Stations(WMS)

4 Ground Earth Stations

2 Geostationary Satellite Links

2 Operational Control Centers

WAAS Components

WAAS Benefits

• Serves all classes of aircraft during flightoperations in all weather conditions at all locations.

• Provides precise navigation and landing guidanceto pilots at all airports, including thousands thathave no ground-based navigation aids

• Overcomes obstacles to ground-based systems, suchas mountainous terrain

WAAS Benefits

• Reduces operating and maintenance costsassociated with ground-based navigation aids

• Makes more airspace usable to pilots, providesmore direct en-route paths, and provides newprecision approach services to runway ends

• Through international cooperation provides aglobal navigation system for all users

GPS Limitations

1. The GPS must “see” the satellites, so it does notwork well in dense forests, inside caves,underwater, or inside buildings.

2. Signal Interference: Sometimes the signalsinterfered before they reach the receivers.

3. Changing atmospheric conditions change the speedof the GPS signals as they pass through the Earth'satmosphere

Obstruction

Earth’s Atmosphere

Solid Structures

Metal Electro-magnetic Fields

Signal Interference

QUIZ

1. UHF Bands for GPS ? From L1 – L5

2. Who uses GPS and for what ?

3. GPS Limitations ?

4. Benefits of LAAS and WAAS