DELIVERING BY: MOHAMMED MOIZUDDIN ZEESHAN

Department of Computer Science,Gulbarga University, Kalaburagi

Global Positioning System (GPS)UNDER THE GUIDANCE: ASST. PROF. SHIVANAND RUMMA

Global Positioning System (GPS)DELIVERING BY: MOHAMMED MOIZUDDIN ZEESHAN

Department of Computer Science,Gulbarga University, Kalaburagi

UNDER THE GUIDANCE: PROF. SHIVANAND S. RUMMA

CONTENTS• HISTORY.

• WHAT IS GPS?

• GPS ELEMENTS.

• HOW IT WORKS?

• GPS SIGNALS & FREQUENCIES.

• SOURCES OF GPS SIGNAL ERRORS.

• HOW TO IMPROVE THE ACCURACY OF GPS.

• APPLICATIONS(VEHICLE TRACKING).

• FUTURE OF GPS.

• LIMITATIONS.

• CONCLUSION.

HISTORY• Navigating by stars (requires clear nights and careful

measurements)

most widely used for centuries

• The GPS project was developed in 1973 to overcome the limitations of previous navigation systems.

• GPS was created and realized by the U.S. Department of Defense (DOD) and was originally run with 24 satellites.

• It became fully operational in 1995. “Bradford Parkinson”, “Roger L. Easton”, and “Ivan A. Getting” are credited with inventing it.

WHAT IS GPS?• Global Positioning System (GPS)

• A space-based satellite navigation system provides accurate location and time information 24 hours a day in all weather anywhere in the world.

• Maintained by the United States government and is freely accessible by anyone with a GPS receiver.

• GPS satellites also called NAVSTAR (Navigational Satellite Timing And Ranging), the official U.S. Department of Defense (DOD) name for GPS.

OVERVIEW• Official name : “Navigational Satellite Timing And Ranging

Global Positioning System” (NAVSTAR GPS)

• Consists of 30+ GPS satellites in medium Earth orbit (2000km - 35,000 km).

• Made up of two dozen satellites working in harmony are known as a satellite constellation.

• Mainly used for navigation, map-making and surveying.

Official logo for NAVSTAR GPS

SEGMENTSGPS uses radio transmissions. The satellites transmit timing information and satellite location information. The system can be separated into three parts: 1. Space Segment2. Control Segment3. User Segment

Space Segment

Control Segment

THE FOLLOWING FIGURE ILLUSTRATES HOW THE THREE SEGMENTS FIT TOGETHER

SPACE SEGMENTThe space segment consists of the satellites themselves. According to the United States Naval Observatory, there are currently 27 operational GPS satellites about 11,000 miles up in space. This constellation provides between five and eight GPS satellites visible from any point on the earth. The next scheduled launch is May 10, 2000.

It takes each satellite about twelve hours to orbit the earth. There are six orbital planes with at least four satellites in each plane.

CONTROL SEGMENTThe control segment is a group of ground stations that monitor and operate the GPS satellites. There are monitoring stations spaced around the globe and one Master Control Station located in Colorado Springs, Colorado. Each station sends information to the Control Station which then updates and corrects the navigational message of the satellites. There are actually five major monitoring systems, the figure below does not include the Hawaiian station.

USER SEGMENT• The user requires a GPS receiver in order to receive the

transmissions from the satellites.

• The GPS receiver calculates the location based on signals from the satellites.

• The user does not transmit anything to the satellites and therefore the satellites don't know the user is there.

• The only data the satellites receive is from the Master Control Station in Colorado. The users consist of both the military and civilians.

WORKING PRINCIPLE(HOW GPS DETERMINES LOCATION)Things which need to be determined: • Current Locations of GPS Satellites

• The Distance Between Receiver’s Position and the GPS Satellites

CURRENT LOCATION OF GPS SATELLITES• GPS satellites are orbiting the earth at an altitude of

11,000 miles.• The orbits, and the locations of the satellites, are

known in advance.• GPS receivers store this orbit information for all of the

GPS satellites in an ALMANAC*.

* the Almanac is a file which contains positional information for all of the GPS satellites

• All 24 satellites are divided into 6 parts.

• There are 4 satellites in each part.

• A definite orbit is defined for each part.

• Each of these 3,000- to 4,000-pound solar-powered satellites.

DISTANCE BETWEEN RECEIVER’S POSITION & THE GPS SATELLITES

• By measuring the amount of time taken by radio signal (the GPS signal) to travel from the satellite to the receiver.

• Radio waves travel at the speed of light, i.e. about 186,000 miles per second.

• The distance from the satellite to the receiver can be determined by the formula

“distance = speed * time”.

To get the distance to each satellite,

• Distance measurements from two satellites limits our location to the intersection of two spheres, which is a circle.

•A third

measurement narrows our location to just two points.

•A fourth measurement determines which point is our true location

GPS ERROR BUDGET

Different errors can cause a deviation of +/- 50 -100 meters from the actual GPS receiver position which are:

ATMOSPHERIC CONDITIONS:• Speed of GPS signal is affected by ionosphere & troposphere.

• Which cause a deviation of 0 to 30 m. from the actual position of receiver.

EPHEMERIS ERRORS:• The predicted changes in the orbit of a satellite.

• Which cause a deviation of 0 to 5 m. from the actual position of receiver

• CLOCK DRIFT:• Due to different code generations in satellite and receiver

simultaneously.

• Which cause a deviation of 0 to 1.5m. from the actual position of receiver

MULTIPATH: • Bouncing of GPS signal due to a reflecting surface before reaching

to receiver antenna.

• Which cause a deviation of 0 to 1 m. from the actual position of receiver

MEASURING GPS ACCURACYThe geometry of the constellation is evaluated by Dilution Of Precision, or DOP.

INCREASING ACCURACY OF GPS• Differential correction provides accuracy within 1-5 m.

• Coarse Acquisition receiver provides accuracy within 1-5m.

• Carrier Phase receivers provides accuracy within 10-30 cm.

• Dual-Frequency receivers are capable of providing sub-centimeter

GPS position accuracy.

APPLICATIONS

AVIATION AGRICULTURE

MARINE TIMING

SPACE RAILWAYS

ROADWAYS DISASTER RELIEF

APPLICATIONS OF GPS• The applications of the Global Positioning System fall into five

categories:

• Location• Navigation • Timing• Mapping, and • Tracking.

• Each category contains uses for the military, industry, transportation, recreation and science.

LOCATIONThis category is for position determination and is the most obvious use of the Global Positioning System.

GPS is the first system that can give accurate and precise measurements anytime, anywhere and under any weather conditions. Some examples of applications within this category are:

• Measuring the movement of volcanoes and glaciers.

• Measuring the growth of mountains.

• Measuring the location of icebergs - this is very valuable to ship captains helping them to avoid possible disasters.

NAVIGATION• Navigation is the process of getting from one location to

another. This was the what the Global Positioning System was designed for.

• The GPS system allows us to navigate on water, air, or land.

• It allows planes to land in the middle of mountains and helps medical evacuation helicopters save precious time by taking the best route.

TIMINGGPS brings precise timing to the us all.

Each satellite is equipped with an extremely precise atomic clock.

This is why we can all synchronize our watches so well and make sure international events are actually happening at the same time.

MAPPINGThis is used for creating maps by recording a series of locations.

The best example is surveying where the DGPS technique is applied but with a twist.

Instead of making error corrections in real time, both the stationary and moving receivers calculate their positions using the satellite signals.

Surveying: Surveyors use absolute locations

to make maps and determine property boundaries.

Telematics: GPS technology integrated with computers and mobile communications technology in automotive navigation systems.

TRACKING• The applications in this category are ways of monitoring

people and things such as packages.

• This has been used along with wireless communications to keep track of some criminals.

• The suspect agrees to keep a GPS receiver and transmitting device with him at all times.

• If he goes where he's not allowed to, the authorities will be notified.

• This can also be used to track animals.

VEHICLE TRACKING

MONITOR-TRACK-SPY

HOW IT WORKS?

Vehicle location and onboard information is sent via GPRS over the cell phone network every 2-10 minutes or when an event takes

place such as ignition ON/OFF.

Customer computers are updated continuously over the internet.

Information is stored on the host server – usually at the secure remote location

Satellites orbiting the earth tell the GPS locator in

the vehicle where it is.

LIMITATIONSGPS can provide worldwide, three-dimensional positions, 24 hours a day, in any type of weather.

But, There must be a relatively clear "line of sight" between the GPS antenna and four or more satellites.

Hence it becomes too difficult to ensure reliable positioning. These difficulties are particularly prevalent in urban areas.

The GPS signal may bounce off nearby objects causing another problem called multi path interference.

CONCLUSION

• The technology of the Global Positioning System is allowing for huge changes in society.

• The applications using GPS are constantly growing.

• The cost of the receivers is dropping while at the same time the accuracy of the system is improving.

• This affects everyone with things such as faster Internet speed and safer plane landings.

ANY QUESTIONS ?

Thank

you…