GPS by Akash Adwani

8/14/2019 GPS by Akash Adwani

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PRESENTED BY-Akash Adwani

2008JE0303

GLOBAL POSITIONING SYSTEM


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Presentation OutlineI. Introduction

II. GPS History

III. GPS Forms

IV. Segments

V. How It Works

VI.Sources Of Error

VII.Applications


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What is GPS?The Global Positioning System (GPS)

A Constellation of Earth-OrbitingSatellites Maintained by the United

States Government for the Purpose ofDefining Geographic Positions On andAbove the Surface of the Earth. Itconsists of Three Segments:

Control Segment

Space Segment

User Segment


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GPS Satellites (Satellite Vehicles(SVs)) First GPS satellite launched in

1978

Full constellation achieved in 1994

Satellites built to last about 10years

Approximately 2,000 pounds,17

feet across


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GPS Lineage Phase 1: 1973-1979

CONCEPT VALIDATION

1978- First Launch of Block 1 SV

Phase 2: 1979-1985

FULL DEVELOPMENT AND TESTS

Phase 3: 1985-Present

PRODUCTION AND DEPLOYMENT


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Precise Positioning System (PPS) Authorized users ONLY

U. S. and Allied military

Requires cryptographicequipment, specially

equipped receivers

Accurate to 21 meters 95%of time


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Standard Positioning Service (SPS) Available to all users

Accuracy degraded bySelective Availability until 2May 2000 Horizontal Accuracy: 100m

Now has roughly sameaccuracy as PPS


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Space Segment 24+ satellites

6 planes with 55

inclination Each plane has 4

satellites

About 10 satellites are

visible Constellation has

spares


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Space Segment Very high orbit

20,200 km

1 revolution inapproximately 12 hrs

Travel approx. 7,000mph

Considerations

Accuracy

Survivability

Coverage


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Control Segment

Master Control Station

Monitor Station

Ground Antenna

Colorado

Springs

Hawaii Ascension

Islands

DiegoGarcia

Kwajalein

Monitor and Control


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Control Segment: Maintaining the System

(5) Monitor Stations

Correct Orbitand clockerrors Create newnavigation message

Observeephemerisand clock

MASTER CONTOLSTATION

Upload Station


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User Segment Over $19 Billion invested by DoD

Dual Use System Since 1985

(civil & military) Civilian community was quick to take

advantage of the system Hundreds of receivers on the market

3 billion in sales, double in 2 years DoD Executive Board sets GPS

policy


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How the system worksSpace Segment24+ Satellites

The CurrentEphemeris is

Transmitted toUsersMonitor

Stations Diego Garcia AscensionIsland

Kwajalein Hawaii ColoradoSprings

GPS ControlColorado Springs

EndUser


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TriangulationSatellite 1 Satellite 2

Satellite 3 Satellite 4


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Distance Measuring

Rate = 186,000 milesper second (Speed of

Light)

Time = time it takessignal to travel fromthe SV to GPS receiver

Distance = Rate xTime

Each satellite carriesaround four atomicclocks

Uses the oscillation of cesiumand rubidium atoms tomeasure time

Accuracy?

The whole systemrevolves around

time!!!


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SV and Receiver Clocks

SV Clocks 2 Cesium & 2 Rubidium in each SV $100,000-$500,000 each

Receiver Clocks Clocks similar to quartz watch Always an error between satellite and

receiver clocks ( t)

4 satellites required to solve for x, y,z, and t


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PROBLEM

Cant use atomic

clocks in receiver

SOLUTION

Receiver clocks

accurate over shortperiods of time

Reset often

4th

SV used torecalibrate receiverclock

Cesium Clock =$$$$$$$!!!

Size of PC

4


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Breaking the Code

Transmission Time

Receiver

The Carrier Signal...

combined with

The PRN code...

produces the

Modulated carrier signalwhich is transmitted...demodulated...

And detected by receiver,Locked-on, butWith a time delay...

Time delay

Satellite


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Accuracy and Precision in GPS

Accuracy

The nearness of a measurement to the

standard or true value Precision

The degree to which several

measurements provide answers very closeto each other.

What affects accuracy andprecision in GPS?


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Sources of Error

Selective Availability

Intentional degradation of GPSaccuracy

100m in horizontal and 160m invertical

Accounted for most error in

standard GPS Turned off May 2, 2000


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Sources of Error

Geometric Dilution ofPrecision (GDOP)

Describes sensitivity of receiver tochanges in the geometricpositioning of the SVs

The higher the DOP value, thepoorer the measurement

QUALITY DOP

Very Good 1-3

Good 4-5

Fair 6

Suspect >6


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Sources of Error

Clock Error Differences between satellite

clock and receiver clock

Ionosphere Delays Delay of GPS signals as they

pass through the layer ofcharged ions and free electronsknown as the ionosphere.

Multipath Error Caused by local reflections ofthe GPS signal that mix withthe desired signal

Dire

ctSigna

l

Refl

ected

Sign

al

GPSAntenna

Reflected

Sign

al

Hard Surface

Satellite


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Differential GPS Method of removing errors that affect GPS

measurements

A base station receiver is set up on a locationwhere the coordinates are known

Signal time at reference location is compared totime at remote location

Time difference represents error in satellitessignal

Post-Processing DGPS involves correcting at alater time

Referencelocation

Remotelocation

= Error


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Common Applications of GPS

Military Applications Navigation

Target Tracking

Missile and Projectile Guidance Search and rescue

Civilian Application Local velocity and Orientation

Research work

Measuring Earthquakes

Gps tours

Map-Making

Recreational Uses


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Cont.

Recreational activities Hiking ,Tracking ,Fishing, Sailing, Treasure hunt,

car racing and many more

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Wide Area Augmentation System (WAAS)

System of satellites and ground stations thatprovide GPS signal corrections

25 ground reference stations across US

Master stations create GPS correctionmessage

Corrected differential message broadcastthrough geostationary satellites to receiver

5 Times the accuracy (3m) 95% of time

Only requires WAAS enabled GPS


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Geodetic Latitude, Longitude

Prime Meridian and Equator are referenceplanes used to define latitude and longitude


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Mobile Mapping

Integrates GPS technologyand GIS software

Makes GIS data directlyaccessible in the field

Can be augmented withwireless technology


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Mobile Mapping Pros and Cons

Pros More efficient data entry

Ready access to GIS data

Less transcription error

Possible real-timeupload/download throughwireless

Cons Cost

Data storage limit

Digital data can be

lost/corrupted


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Hands on with GPS


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WORLD SCENARIO Developed by the united states department of defense , GPS is

officially named NAVSTAR GPS Other satellite navigation system in use or various states of

development include:

Beidou-Chinas regional system that China has proposed to expandinto a global system named Compass.

Galileo-A proposed global system being developed by the EuropeanUnion, joined by China, Israel, India, Morocco, Saudi Arabia, SouthKorea and Ukraine, planned to be operational by 2011-12.

Glonass-Russias global system which is being restored to to fullavailability in partnership with India.

Indian regional navigational Satellite System(IRNSS)- Indiasproposed regional system.

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IRNSS

The Indian Regional Navigational SatelliteSystem(IRNSS) is an autonomous regional satellitenavigation system being developed by Indian Spaceresearch organization which would be under totalcontrol of Indian Government.

Development

The government approved the project in May, 2006,with the intention it be implemented within six toseven years. The first satellite of the proposed

constellation, developed at a cost of Rupees 1,600crores(1.6 billion rupees) is expected to be launchedin 2009.

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THANK YOU

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