Session1 Er.N.namassivaya

7/24/2019 Session1 Er.N.namassivaya

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Introduction to Global

Positioning Systems (GPS)

Er Nuli Namassivaya

Associate Prof., ECE Dept.,

MVSR Engg. College, Nadergul, Hyd.Email : [email protected]

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as an aircraft or a person from one point to.

Radio navigation which makes use of

has an accuracy far superior compared to

.

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E rli r N vi i n m h

Celestial navigation

av ga on y ea rec on ng

Some of the Radio Navigation systes areVOR, ILS, MLS, LORAN, OMEGA, DECCA

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If a person wants to know

s pos on ..

send a signal to sky by the terminal.

the two satellites receive the signal. the two satellites send the accurate time when each

.

the ground station calculates the longitude and latitude of

the person. the ground station gets the altitude from a database for

relief map.

the round station sends the 3D osition to satellite.

the satellite transmits the position to the person's terminal.

the terminal could send and receive short messages with

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groun s a on.


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It has six low orbiting satellites and works on.

Limitations are : A fix can only be made in two dimensions

Interval between fixin ositions is ver lonand about 1.5 hours on an average

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Global Navigation Satellite

ys em GNSS is the standard generic term for satelli te navigation

sys ems a prov e au onomous geo-spa a pos on ng w

global coverage. A GNSS allow small electronic receivers to determine their location

lon itude latitude and altitude to within a few metres usin timesignals transmitted along a line of sight by radio from satellites.

Receivers on the ground with a fixed position can also be used to

calculate the precise time as a reference for scientific experiments. s o , e n e a es o a os on ng ys em

(GPS) is the only fully operational GNSS. The Russian GLONASS is a GNSS in the process of being restored

The European Union's Galileo positioning system is a nextgeneration GNSS in the initial deployment phase, scheduled to beoperational in 2010.

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China has indicated it may expand its regional Beidou navigationsystem into a global system


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GNSS-1 is the first generation system and is the combination of

ex s ng sa e e nav ga on sys ems an , w

Satellite Based Augmentation Systems (SBAS) or Ground BasedAugmentation Systems (GBAS). In the United States, thesatellite based com onent is the Wide Area Au mentationSystem (WAAS), in Europe it is the European GeostationaryNavigation Overlay Service (EGNOS), and in Japan it is the

Multi-Functional Satellite Augmentation System (MSAS). Ground

Augmentation System (LAAS). GNSS-2 is the second generation of systems that independently

rovides a full civilian satellite navi ation s stem exem lified b

the European Galileo positioning system. These systems willprovide the accuracy and integrity monitoring necessary for civilnavigation. This system consists of L1 and L2 frequencies for

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.progress to provide GPS with civil use L2 and L5 frequencies,

making it a GNSS-2 system.


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Core Satellite navigation systems, currently GPS, Galileo

an . Global Satellite Based Augmnetation Systems (SBAS) such

as Omnistar and Stafire. Regional SBAS including WAAS(US) , EGNOS (EU), MSAT

(Japan) and GAGAN (India).

Regional Satellite Navigation Systems such a QZSS(Japan), IRNSS (India) and Beidou (China).

Continental scale Ground Based Augmentaion Systems(GBAS) for example the Australian GRAS and the US

epar men o ranspor a on a ona eren a(DGPS) service. Regional scale GBAS such as CORS networks.

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Local GBAS typified by a single GPS reference station

operating Real Time Kinematic (RTK) corrections.


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Satellite navigation using a

ap op an a rece ver

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Current and proposed

sa e e nav ga on sys ems

Galileo Positioning System Beidou

DORIS

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The formerly Soviet, and now Russian, global navigationsystem is called GLONASS. It was a fully functionalnavigation constellation but since the collapse of the SovietUnion has fallen into disre air and is onl artialoperational. It is expected to become fully operational by2010 with the help of India, who is participating in therestoration ro ect.

GLONASS satellites transmit two types of signal: standardprecision (SP) and high precision (HP). The SP signal on

=1602 MHz + 0.5625n MHz, where n is a satellite'sfrequency channel number (n=0,1,2...).

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Galileo positioning system

It is named after the Italian astronomer GalileoGalilei. The Galileo positioning system is referredto as "Galileo" instead of as the abbreviation"GPS" to distin uish it from the existin UnitedStates system.

Built by the European Satellite NavigationSpace Agency (ESA) as an alternative to theUnited States operated Global Positioning System

. Galileo Operating Company, the concession holderand rivate consortium runnin Galileo, will have

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its main headquarters in Toulouse, France.


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orbital altitude: 23 222 km ,

satellites and one active spare per orbital plane)

>

satellite mass: 675 kg

. . .

span of solar arrays: 18.7 m

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l li i i nin m

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- The European Space Agency and the Galileo Joint

n er a ng success u y aunc e e rs a eo n- r

Validation Element test satellite, GIOVE-A, on 28 Dec 2005. GIOVE-A was built by Surrey Satellite Technology Ltd

ra er an uropean a e e av ga onIndustries. Operation of GIOVE-A ensured that Galieo mets

the frequency-filing allocation and reservation requirements,process that was required to be complete by June of 2006.

GIOVE-B, built by European Satellite Navigation Industries,- ,

after technical problems and launch delays is now targetedfor launch at end of 2007.

-

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for launch in the second half of 2008, to ensure continuous

reservation of Galileo frequency use with the ITU.


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-

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Beidou navigation system

Chinese constellation Bidu. Bidu, literallymeans "Northern Du", is named for its shape.Du is a type of traditional Chinese container used

for measuring grain volume. Bidu is equivalent to Big Dipperin other cultures.

Historically, these set of stars had been used in

.such, Beidou also serves as a metaphor for the

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.


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Beidou 1A was launched on 30 October 2000, Beidou 1Bfollowed on 20 December 2000, and Beidou 2A was putinto orbit on 24 May 2003. The latest Beidou navigationsatellite was successfull launched on 3 Februar 2007.

In September 2003, China joined the Galileo positioningsystem project. China will invest230 million (USD296

, .Galileo positioning system is currently not yet operational.

On November 2, 2006, China announced that from 2008

meters. This sent mixed messages to other investors of theEuropean Galileo project.

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Current Technology :

e uo

, ,

systems, which use intermediate circular-orbitin satellites, Beidou 1 uses satellites ingeostationary orbit.

This means that the system does not requirea large constellation of satellites, but it alsolimits the coverage to areas on Earth where

e sa e es are v s e. e area a canbe serviced is from 70E to 140E, and from

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.


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Future Plans :

e ou- or ompass The new system will be a constellation of 35 satellites, which

nc u e geos a onary or sa e es an me um

Earth orbit (MEO) satellites, that will offer complete coverage ofthe globe.

those in China, and licensed service for the military. The free service will have a 10 meter location-tracking accuracy,

will synchronize clocks with an accuracy of 50 ns, and measurespeeds within 0.2 m/s.

The licensed service will be more accurate than the free service,can be used for communication, and will supply information

. The satellite 2A is either a backup satellite for Beidou 1, or a

geostationary orbit satellites for Beidou 2.

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.next few years, China plans to continue experimentation and

system setup operations.


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DORIS

Radio- ositionin Inte rated bSatellite (DORIS) is a French

.

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IRNSS (Indian Regional

av ga ona a e e ys em

e n an eg ona av ga ona a e e ys em

is a proposed autonomous regional satellite navigation systemto be constructed and controlled by the Indian government.

than 20 meters throughout India and within a region extendingapproximately 1,500 to 2,000 km around it.

,space segment, ground segment and user receivers all beingbuilt in India.

The overnment a roved the ro ect in Ma 2006, with the

intention it be implemented within six to seven years. It is unclear if recent dealings with the Russian government to

restore their GLONASS system will supercede the IRNSS

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pro ec or ee a ona ec n ca suppor o ena e scompletion.


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The ro osed s stem would consist of a

constellation of seven satellites and a supportground segment.

placed in geostationary orbit and the remaining

four in geosynchronous inclined orbit of 29 . Such an arrangement would mean all seven

satellites would have continuous radio visibility with

n an contro stat ons. The navigation signals themselves would be

- -

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broadcast through a phased array antenna to

maintain required coverage and signal strength.


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The satellites would wei h a roximatel 1,330 k

and their solar panels generate 1,400 watts ofenergy.

consist of a Master Control Center (MCC), ground

stations to track and estimate the satellites' orbits

The MCC would estimate and predict the positionof all IRNSS satellites, calculate integrity, makes

necessary onosp er c an c oc correct ons anrun the navigation software.

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,Indian standard time infrastructure would also be

established.


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Uncertainities in position and time have been

vexing problems for the mankind for centuries.

WHERE AM I, WHERE ARE YOU, HOW DO I GETTHERE & HOW LONG WILL IT TAKE these uestionsin navigation and synchronization and any mistake inanswering these often have fatal consequences. The

GLOBAL POSITIONING SYSTEM GPS technolo ,which emerged in the late 1960s in the US and theformer USSR, answer all the aforesaid questionsaccuratel .

The GPS by the US is a satellite-base navigationsystem having a network of 24 satellites with four

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,circling the earth once every 24 hours.


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GPS operation is based on triangulation of satellite signals. Basically, it implements the

time-difference-of-arrival concept using precise

satellite position and on-board atomic clocks togenera e nav ga on messages a are

continuously broadcast from each of the GPS

.

and processed by users anywhere in the world

to determine their osition and time accuratel .

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The GPS is a universal positioning or navigation

system that provides 3-D positions accurate to within a

few meters, velocity accurate to 0.03 min/s, and timeaccurate to within a few nanosec. It performs threema or as s.1. Acquire signals from the four geometrically

o timum satellites.2. Process the satellite data, determine the position ofthe receiver and transform that information into acoordinate s stem latitude lon itude and altitude that

is familiar to the operator.3. Interface to the user and his vehicle by providing a

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both digital and analogue forms.


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and Ranging)

Very high frequency 1200-1500 Mhzcommun ca on rave s cm n .seconds).

Satellites orbit in 6 orbital plates to providecomplete coverage

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Satellites orbit at 10,900 miles (2 orbits perda


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24+ satellites 6 planes with 55

nc na on

Each plane has 4-5

Broadcasting positionand time info on 2

frequencies Constellation has

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spares


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In addition to knowing the

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To measure traveltime, GPS needs very

accurate clocks.

distance to a satellite, a user

needs to know the satellites

location.

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As the GPS signal t ravels through

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the ionosphere and earths atmosphere,

it gets delayed(error sources).

Triangulation from

To triangulate, GPS measures

distance(pseudorange) using

the travel time of a radio signal.

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satellites is the

basis of the system.


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.

Satellite provides an electronic almanac to the

The speed of the radio signal from each

Timing allows the calculation of the distance

rom eac sa e e. Using triangulation, the position of the

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receiver is calculated.

H t


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How measurements are

poss e

information on its location and.

It sends a code that allows the

to the satellite.

our sa e es are v s e, asingle receiver can measure

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oca ons o w n me ers

95% of the time.


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S1

R2R1

R3

S3 Satellite Position(S1, S2, S3)

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(R1, R2, R3)


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GPS com rises of three se ments.

1. Space segment : Consisting of satellite themselves,transmitting time codes & orbital position information.

2. Control segment : along with master control

stations assumes the overall s stem erformanceand accuracy.

3. User segment : Consists the actual electronic,

satellites, compute the time differences anddetermines the position. This can be used by any

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arge num er o rece vers.


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pace egmen - a e es

Satellites provide navigationsignal and relay orbital and

.

Control Segment

Ground control tracks satellitesand measures and uploads

ephemeris and clock data.

User Segment

User tracks satellite signals,

downloads data, and computes

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pos on, ve oc y, an me.


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24+ satellites

6 planes with 55 inclination

Each plane has 4-5 satellites Constellation has spares

Very high orbit 20,200 km 1 revolution in approximately 12 hrs Travel a rox. 7 000m h

Considerations Accuracy

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urv va y Coverage


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Ground based se o rac an a us sa e es

Computes exact orbits (for location)

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Control Se ment Contd.

Colorado

Springs

Hawaii Ascension

Islands

Kwajalein

Master Control Station

Garcia

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Monitor Station

Ground Antenna

Control Segment :


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Control Segment :

a n a n ng e ys em

Correct Orbitand clock

Observe Create newnavigation message

ephemerisand clock

51(5) Monitor Stations Falcon AFB

Upload Station


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Units receive transmission from Satellites

Cost between $150 and $15000 (depends on accuracy)

Must be line of sight with satellites

ver on nves e y o

Dual Use System Since 1985

civil & militar Civilian community was quick to take advantage of the

system

3 billion in sales, double in 2 years 95% of current users

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o o xecu ve oar se s po cy


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Dilution of Precision (DOP) is a measure of the strength of

sa e e geome ry an s re a e o e spac ng an pos on

of the satellites in the sky. The final positional accuracy of a point is directly related toe geome r c s reng o e con gura on o sa e es

observed during the survey session.

GPS errors resulting from satellite-constellation geometry. In mathematical terms, DOP is the ratio of the standard

deviation of one coordinate to the measurement accuracy.

A low DOP factor is considered good while a high DOPfactor is considered bad.

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eren ypes o u on o prec s on or can ecalculated depending on the dimension.

Geometric Dilution of


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rec s on The main form of DOP used in absolute GPS

positioning is the geometric DOP (GDOP), which is

a measure of accuracy in a three-dimensionalosition and time.

The relationship between final positional accuracyin a three-dimensional position and time. The

,actual range error, and GDOP can be expressedas follows.

a =R

xwhere a = final positional accuracy and

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R


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Positional Dilution of Precision (PDOP) : Positional

Dilution of Precision (PDOP) is a measure of the

accuracy in three-dimensional position. This givesaccuracy degradation in the three-dimensional position.

PDOP = [E2 + N2 + U

2 ] 1/2 / RHorizontal Dilution of Precision (HDOP) : This is a

-position. Mathematically this can be defined as

HDOP = [E2 + N2 ] 1/2 / RVertical Dilution of Precision (VDOP) : VDOP is a

measurement of the accuracy in standard deviation invertical height. Mathematically VDOP is defined as

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= u / R



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rec s on

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GPS with SA off: 25 m - m o - cm

Better accuracy is achieved by samplingmore points (statistical)

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Improving Accuracy -


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Improving Accuracy

orrec ons -

same at each

The difference between know location andmeasure oca on s e error

Apply this error correction to the moving

receiver to improve accuracy

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Session1 Er.N.namassivaya

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