GLOBAL POSITIONING SYSTEM

By:Taher K D

GPSGPS means Global Positioning

System.GPS is a space-based satellite

navigation system.GPS provides location and

information and time information of an object in all

weather conditions.The system provides critical

capabilities to civil and commercial users around the

world.

Every point on earth is monitored by

atleast 4 satellite every second.

The current system became fully operational June 26, 1993

when the 24th satellite was lunched.

GPS provides specially coded satellite signals that can be

processed with a GPS receiver, enabling the receiver to

compute position, velocity and time.

A minimum of four GPS satellite signals are required to

compute positions in three dimensions and the time offset

in the receiver clock.Accuracy and precision of data increases with more

satellites.

HISTORYIn 1956, the German-American

physicist Friedwardt Winterberg proposed a test of general relativity which was used in the design of GPS.

The US began the project of GPS in 1973 to overcome the

limitations of previous navigation systems. In 1978, the first

experimental Block-1 GPS satellite was launched.

STRUCTUREThe current GPS consists of three

major components-space segment(SS), User segment(US)

and a control segment.The U.S. Air force develops ,

maintains and operates the space and control segments.

Each GPS user receives these signals to calculate it's three

dimensional location (latitude, longitude and altitude).

SPACE SEGMENTThe space segment is composed of 24 to 32 satellites in medium

earth orbit.It is also composed of orbiting GPS satellites in GPS parlance.

As of December 2012, there are 32 satellites in the GPS

constellationThe additional satellites improves

the precision of GPS receiver calculations by providing

redundant measurements.

SPACE SEGMENTThe GPS uses a constellation of

24 satellites that orbit the earth at about 11,000 nautical miles, once

every 12 hours.The orbital position is constantly

monitored and updated by the ground stations.

Each satellite is identified by number and broadcasts a unique

signal.The signal travels at the speed of

light.Each satellite has a very accurate

clock, 0.000000003 seconds

SPACE SEGMENT-PHASING RANGING Each satellite has a unique signal.

It continuously broadcasts its signal and also sends out a time stamp every time it starts.

The receiver has a copy of each satellite signal and determines the distance by recording the time between when the satellite says it starts

its signal and when the signal reaches the receiver.

Factors Influencing Position Accuracy

The system errors that are occurring during the time the receiver is operating.The GPS system has several errors that have the potential to reduce the accuracy.

To achieve high levels of precision, differential GPS must be used.

Differential GPS uses one unit at a known location and a rover.The stationary unit compares its calculated GPS location with the actual location and computes the error.

The rover data is adjusted for the error. Real Time Kinematic (RTK) Post processing

CONTROL SEGMENTThe control segment is composed

of –MASTER CONTROL STATION(MCS)

Alternative master control station

Four dedicated ground antennasSix dedicated monitor stations

USER SEGMENTThe user segment is composed of hundreds of thousands of U.S. and allied military users of the secure GPS Precise Positioning Service.

In general, receivers are composed of an antenna, tuned to

the frequencies transmitted by the satellites , receiver-processors

and a highly stable clock.They may also include a display for providing location and speed

information to the user.

Signal From One SatelliteSignal From One Satellite

The receiver is somewhere on this sphere.

Signals From Two SatellitesSignals From Two Satellites

Three Satellites (2D Positioning)

Three Satellites (2D Positioning)

Triangulating Correct Position Triangulating Correct Position

Three Dimensional (3D) PositioningThree Dimensional (3D) Positioning

GPS ERRORSSatellite geometry

Satellite orbits

Multipath

Atmospheric effects

Clock

APPLICATION Astronomy: both positional and clock

synchronization data is used in astrometry and celestial mechanics calculations.

Cartography: both civilian and military cartographers use GPS extensively.

Clock synchronization: the accuracy of GPS time signals (±10 ns) is second only to the

atomic clocks they are based on.Disaster relief/emergency services: depend upon GPS for location and timing capabilities.

Recreation: for example, geocaching, geodashing, GPS

drawing and waymarking.Telematics: GPS technology integrated with computers and

mobile communications technology in automotive

navigation systemsPhasor measurements: GPS enables highly accurate time stamping of power system measurements, making it

possible to compute phasors.Navigation: navigators value digitally precise velocity and orientation measurements.Reconnaissance: Patrol

movement can be managed more closely.

Thank You