Lecture 4: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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Why do we need GPS?

One drawback of using radio waves generated on the ground is that you have only two choices:

• A system that is very accurate but doesn’t cover a wide area; or

• A system that covers a wide area but is not very accurate

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What is GPS & What the purpose of GPS?

• GPS is stands for Global Positioning System.

• Official name of GPS is Navigational Satellite Timing And Ranging Global Positioning System (NAVSTAR 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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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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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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Who can use GPS?

Handheld GPS ReceiversCasio GPS wristwatch

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HOW GPS WORKS?

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GPS: Global Positioning System

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Consists of two dozen GPS satellites in medium Earth orbit (The region of space between 2000km and 35,786 km)

•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.

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GPS components

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How GPS works

• GPS receivers are generally composed of an antenna, tuned to the frequencies transmitted by the GPS satellites.

• Each GPS satellites then transmit signals to the GPS receivers .

• 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.

• These signals indicates satellite’s location and the current time. – Each GPS satellite has special clocks to provide very

accurate time reference (atomic clocks).

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How GPS works

• The GPS receiver measures the time taken for a signal to travel from satellite to receiver.

• The distance to each GPS satellites can be determined by multiplication of speed of light and time.

Distance = Speed of Light x Time• Knowing the distance from at least 4 GPS satellites,

the GPS receiver can calculate their position in ground or in air (for aircraft).

• The position can be described in terms of latitude and longitude.

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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.

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How GPS works

• GPS 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 far you have traveled

– How long you have been traveling

– Estimated time of arrival

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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.

In addition, by observing the change in position and the rate of change, GPS calculates actual track, ground

speed and wind.

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Using GPS, aircraft can fly the most direct routes

between airports

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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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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.

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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