Unit1 GPS Introduction

Basic concept, System Architecture, GPS and GLONASS Overview, Satellite Navigation, Time and GPS, User Position and Velocity Calculations, GPS Satellite Constellation, Operation Segment, User Receiving Equipment, Space Segment Phased Development, GPS Aided Geo augmented Navigation (GAGAN) Architecture.

1. GlobalPositioningSystem
UNIT-I
Introduction
-By
GVNSKSravya
AssistantProfessor
ECEDept.
GNITS

2. Contents
▶Basicconcept
▶SystemArchitecture
▶GPSandGLONASSOverview
▶SatelliteNavigation
▶TimeandGPS
▶UserPositionandVelocityCalculations
▶GPSSatelliteConstellation
▶OperationSegment
▶UserReceivingEquipment
▶SpaceSegmentPhasedDevelopment
▶GPSAidedGeoaugmentedNavigation(GAGAN)Architecture.
2

3. BasicConceptofGPS
▶Navigationreferstotheartofdeterminingthe
currentlocationofanobjectwhichcouldbein
space,intheair,onland,onorunderthesurfaceof
abodyofwater,orunderground.
3

4. Contd…
▶NavigationModesInordertogetfromAtoBthereare
basicallyfivebasicnavigationmodes:
▶Pilotage
▶CelestialNavigation
▶DeadReckoning
▶RadioNavigation
▶InertialNavigation
4

5. Contd…
▶SatelliteNavigationorSatnavSystemisasystemthatuses
satellitestoprovideautonomousgeo-spatialpositioning.
▶Itallowssmallelectronicreceiverstodeterminetheirlocationto
highprecisionusingtimesignalstransmittedalongalineofsight
byradiofromsatellites.
5

6. Contd…
▶GNSSstandsforGlobalNavigationSatelliteSystem,andisthestandard
generic term for satellite navigation systems that provide autonomousgeo-
spatialpositioningwithglobalcoverage.Thistermincludese.g.theGPS,
GLONASS,Galileo,Beidou,IRNSSandotherregionalnavigationsystems.
6

7. GPS
▶GPSTheGPSispartofasatellite-basednavigationsystem
developedbytheU.S.DepartmentofDefensein1995.
7

8. Contd…
▶OfficialnameofGPSisNavigationalSatelliteTimingAnd
RangingGlobalPositioningSystem(NAVSTARGPS).
▶GlobalPositioningSystems(GPS)isaformofGlobal
NavigationSatelliteSystem(GNSS).
▶ConsistsoftwodozenGPSsatellitesinMediumEarthOrbit
(Theregionofspacebetween2000kmand35,786km)
8

9. Contd…
knownasasatellite
▶Twodozensatellitesworkinginunisonare
constellation
StatesAir
▶Thisconstellation iscurrently controlled by theUnited
Force50thSpaceWing
▶Itcostsabout$750milliontomanageandmaintainthesystemper
year
▶Mainlyusedfornavigation,map-makingandsurveying
9

10. WorkingofGPS
▶Eachsatellitesbroadcastradiosignalswiththeirlocationandtime.
▶GPSreceiversreceivesradiosignals,andusedthesedatatocalculateitsdistancefromatleast
foursatellites.
▶Distance=Speed*Travel time
▶GPSradiosignalsaretravelatthespeed oflight.
▶Bothsatellitesandreceivergeneratethesamepseudocodesignals.
▶Differenceb/wthe2signalsisthetraveltime.
▶ThenthereceiverusesTrilaterationmethodtodefineitsexactlocationonEarth.
10

11. Trilateration Process
▶Ifweknowthedistanceb/wthesatelliteandthereceiverfor:1
satellite,thereceiver’slocationisknownwithinasphere.
11

12. Contd…
▶2satellite,thereceiver’slocationisknownwithin3Dring.
12

13. Contd…
▶3satellite,thereceiver’slocationissomewhereonatmosttwo
3Dregions.
13

14. Contd…
▶4satellite,theregiongetssmallerbecauseofthesphereofthe
newsatellite.
14

15. Architecture of GPS
▶ArchitectureofGPSconsistsofthreesegments:
Spacesegment(SS)
Sontrolsegment(CS)
Usersegment(US)
15

16. Contd…
16

17. Space Segment
▶Minimumof24satellites
(currently32)inorbit
aroundearthataltitude
20,000km.
▶Ittransmitradio-
navigationsignals,and
storeandretransmitthe
navigationmessagesent
bythecontrolsegment.
17

18. ControlSegment
controlstation,
▶Combinationofamaster
four
dedicatedgroundantennas
andsixdedicatedmonitor
stations.
▶Responsiblefortheproper
functioningofallthe
operationofGPSsuchas
changingunhealthysatellite
withahealthyone.
18

19. Components of ControlSegment 19

20. UserSegment
▶Comprises of thousand of
military users who uses the
secure GPS Precise Positioning
service, and millions of civil,
commercialandscientificusers.
20

21. GLONASS
GLONASS
▶AsecondconfigurationforglobalpositioningistheGlobalOrbiting
NavigationSatelliteSystem(GLONASS),placedinorbit bythe
formerSovietUnion,andnowmaintainedby the RussianRepublic.
20

22. GPSandGLONASSOverview
GPSOrbits
▶ThefullyoperationalGPSincludes
32ormoreactivesatellites
approximatelyuniformlydispersed
aroundsixcircularorbitswithfour
ormoresatelliteseach.
GLONASSOrbits
▶GLONASShas24satellites,distributed
approximatelyuniformlyinthreeorbital
planes(asopposedtosixforGPS)of
eightsatelliteseach(fourforGPS).
21

23. Contd…
GPSOrbits
▶Theorbitsareinclinedatanangle
of 55°relative to the equator and
are separated from each other by
60°.
GLONASSOrbits
▶Each orbital plane has a
nominal inclination of 64.8°
relativetotheequator,andthe
three orbital planes are
separated from each other by
multiples of 120°right
ascension.
22

24. Contd…
GPSOrbits
▶Theorbitsarenongeostationary
andapproximatelycircular,with
radii of 26,560 km and orbital
periods of one-half sidereal day
(≈11.967h).
GLONASSOrbits
▶GLONASS orbits have smaller
radii than GPS orbits, about
25,510 km, and a satellite
period of revolution of
approximately 8/17 of a
siderealday.
23

25. Contd…
▶Theoretically, three or more GPS satellites will always be visible
frommostpointson theearth’ssurface.
▶FourormoreGPSsatellitescanbeusedtodetermineanobserver’s
positionanywhereontheearth’ssurface24h/day.
24

26. Contd…
GPSSignals
▶The GPS system uses Code
division multiplexing of
independentsatellitesignals.
GLONASSSignals
▶TheGLONASSsystemusesfrequency-
division multiplexing of independent
satellitesignals.
25

27. Contd…
GPS Signals
Each GPS satellite transmits two
spread spectrum, L-band carrier
signals on two of the legacy L-
band frequencies—an L1 signal
with carrier frequency f1 = 1575.42
MHz and an L2 signal with carrier
frequency f2 = 1227.6 MHz.
GLONASSSignals
▶Its two carrier signals corresponding to
L1 and L2 have frequencies f1 = (1.602 +
9k/16) GHz and f2 = (1.246 + 7k/16)
GHz, where k = −7, −6, . . . 5, 6 is the
satellite number. These frequencies lie in
two bands at 1.598–1.605 GHz (L1) and
1.242–1.248GHz(L2).
26

28. Contd…
GPSSignals
▶Thesetwofrequenciesareintegral
multiplesf1=1540f0andf2=1200f0
ofabasefrequency f0=1.023MHz
▶TheL1signalfromeachsatelliteuses
binaryphase-shiftkeying(BPSK),
modulatedbytwopseudorandom
noise(PRN).
GLONASSSignals
▶The L1 code is modulated by a C/A-
code(chiprate=0.511MHz)andbya
P-code (chip rate = 5.11 MHz). L2
code is presently modulated only by
theP-code.
27

29. Contd…
GPSSignals
▶Theinitialsatelliteconfigurationused
SAwithpseudorandomditheringof
theonboardtimebutthiswas
discontinuedonMay1,2000.
GLONASSSignals
▶GLONASSdoesnotuseanyformof
SA.
28

30. GPS Satellite Constellation 29
Fig.GPSSatelliteConstellation

31. Contd… 30
Fig.GPS SatelliteConstellationPlanarProjection

32. Contd…
OrbitsandSatelliteConstellation
▶GPSSatelliteConstellationconsistsof24 operationalsatellitesin6orbitalplanes.
▶Orbitalperiodisof1 siderealday(11hr.58mins.).
▶AngleofInclinationis55degreesw.r.tequator.
▶Equallyspacedaroundtheequatorata60degreesseparation.Orbitalradius
26,600km.(distancefromcenter oftheearthtosat.)
▶Satellitegeometrytoprovidegoodobservabilitytousersthroughout theworld
31

33. Contd…
OrbitsandSatelliteConstellation
▶Thisgeometry ismeasuredbyaparametercalledDoP(DilutionOfPrecision).
▶Atleast4SV’sineachorbit.
▶Orbitalperiodis12hours.
▶ReceivesinformationfromCS.
▶Broadcastsone-wayrangingsignals.
32

34. Space Segment Phased Development
▶Thecontinuingdevelopmentofthecontrolandspacesegmentshas
beenphasedin overmanyyears,startinginthemid-1970s.
▶Thisdevelopmentstartedwithaconceptvalidationphaseandhas
progressedtoseveralproductionphases.
▶Thesatellitesassociatedwitheachphaseofdevelopmentarecalleda
block ofsatellites.
33

35. SatelliteBlockDevelopment
▶Fivesatelliteblocks havebeen developedtodate.
▶TheinitialconceptvalidationsatelliteswerecalledBlock I.
▶ThelastremainingprototypeBlockIsatellitewasdisposedof in late1995.
▶BlockIIsatellitesaretheinitialproductionsatellites,whileBlockIIAreferstoupgraded
productionsatellites.
▶BlockIIRsatellites,denotedas thereplenishmentsatellites.
▶ModifiedBlockIIRversionofsatellitesisdenotedasBlockIIR-M.
▶BlockIIFsatellitesarereferredtoas thefollow-onor sustainmentsatellites.
▶Sincesatellitesarelaunchedonlyasreplacementsforasatellitefailure,theirschedulingis
difficulttopredict,especiallywhen mostsatelliteshavefaroutlivedtheirdesignlifetime.
34

36. BlockI,Navigationdevelopment
Satellites
▶Fivesatelliteblockshavebeendeveloped todate.
▶Elevensatellitesof thiskindwerelaunchedbetween1978and1985.
▶TheSelectiveAvailability(S/A)wasnotimplemented.
▶Theyweighedabout845Kgandhadaplannedaveragelifeof4.5years,
although someofthemlastedup to 10.
▶Theywerecapableofgivingpositioningservicefor3or4dayswithout
anycontact withtheControlCentre.
35

37. BlockIIandIIA,OperationalSatellites
▶Theyconsistof 28satellitesintotalthatwerelaunchedfrom1989onand
manyarestilloperating.
▶They weighabout1500 Kgandhaveaplannedaveragelifeof7.5years.
▶Since1990, animprovedversionwasused,BlockIIA(advanced),with
capabilityofmutualcommunication.
▶Theyare abletosupplypositioningservicefor180 dayswithnocontact
withthecontrolsegment.
▶However,undernormaloperatingmode,theycommunicatedaily.
36

38. Block IIR, Replacement Operational
Satellites
▶From1997,these satellitesarebeingusedassparesforBlockII.
▶BlockIIRisformedbyasetof20satellites,althoughitcouldbe
increasedby 6 more.
▶They weighabout2000Kgandhaveaplannedaveragelifespanof10
years.
▶Thesesatellitescandeterminetheirorbitsandcomputetheirown
navigationmessageautonomously.
37

39. Block IIR-M, Modernized Satellites
▶They include anewmilitarysignalandthemorerobustcivilsignal.
▶TherewillbeeightsatellitesintheBlockIIR-Mseries.
▶ThefirstsatelliteofthisblockwaslaunchedonSeptember26,2005.
38

40. Block IIF, Follow-on Operational
Satellites
▶Thefirstsatellite(SVN62)waslaunchedonMay28th2010.
▶Thesesatellitesincludethe third civilsignalon theL5band.
▶Theirtheoreticalaveragelifeisabout12 years,andtheywillhaveinertial
navigation.
39

41. Block III (GPS III)systems
▶ThenewgenerationofGPSsatellitesintroducessignificant
enhancementsinnavigationcapabilities,byimprovinginteroperability.
▶They providethefourthcivilsignalon L1band.
▶Thefirstlaunchis expectedasof2017.
40

42. Navigation Payload Overview
▶Thenavigationpayloadisresponsibleforthegenerationandtransmission
ofrangingcodesandnavigationdataontheL1,L2andL5frequenciesto
theusersegment.
▶Controlofthenavigationpayloadistakenfromreceptionofthepredicted
navigationdataandothercontroldatafromtheCSviathetracking,
telemetry,andcontrol(TT&C)links.
41

43. SatelliteNavigationPayload 42

44. Contd…
▶Atomicfrequencystandards(AFSs)areusedasthebasisforgenerating
theextremelystablerangingcodesandcarrierfrequenciestransmittedby
thepayload.
▶Thenavigationdataunit(NDU),knownasthemissiondataunitcontains
therangingcodegeneratorsthatgeneratetheC/AcodeandP(Y)codes.
43

45. Contd…
▶ThecombinedbasebandrangingsignalsarethensenttotheL-band
subsystemwheretheyaremodulatedontotheL-bandcarrierfrequencies
andamplifiedfortransmissiontotheuser.
44

46. Contd…
▶TheL-bandsubsystemcontainsnumerouscomponents,includingtheL1
andL2transmittersandassociatedantenna.
▶TheNDUprocessoralsointerfacestothecrosslinkreceiver/transmitter
forintersatellitecommunication,aswellasrangingonBlockIIRand
laterversions.
▶Thiscrosslinkreceiver/transmitterusesaseparateantennaandfeed
system.
45

47. Control Segment (Operating Segment)
▶CSComprisesof2Mastercontrolstations(MCS),16monitoringstations
and 12 groundantennas.
MonitoringStation
andtheir
▶Check position,speed,altitudeand healthoftrackedSV’s.
▶CollectsGPSsignals,navigationdata,atmosphericdata
variations
▶Sends collected informationtoMCS.
46

48. Contd…
MasterControlStation
▶ComputesspacecoordinatesofSV’s.
▶Evaluates healthofSV’s.
▶Generatesnavigationdata.
▶Performssatellitemaintenance.
▶Resolves satelliteperformances.
▶MaintainsGPSconstellation.
▶ThroughGroundAntennas,MCSprovidescommands,keepscontrolanduploadsnavigation
messagesandotherdatatotheGPSsatellites.
47

49. Contd…
GroundAntennas
▶Collects,storesdatafromMCS.
▶CSprovidescommands andkeeps controlonsatellites.
▶UploadstotheGPSsatellitesusingSbandsignals(2-4GHz)Computesspacecoordinatesof
SV’s.
48

50. UserSegment(UserReceiverEquipment)
▶TheusersegmentofGPSsystem
consistsofaGPSreceiver.
▶ProcessestheLbandsignals
transmittedfromsatellitestodetermine
PVT.
▶GPSreceiversfundamentallyconsistof
3basicconstituents-antenna,GPS
receiver andacontroller.
49

51. GAGAN(GPS aided GEO Augmented
Navigation) Architecture
50
Fig.ArchitectureofGAGAN

52. Contd… 51
▶Itisanimplementationofregionalsatellitebasedaugmentation
system(SBAS)jointlydevelopedbyISROandAAItoprovidethebest
possiblenavigationalservicesoverIndianFIR(FlightInformationRegion)
withthecapabilityofexpandingtoneighboringFIRs.
GroundSegment
▶DevelopedtoprovideaccuracyofGNSSreceiver
▶GAGANconsistsof3basiccomponents-Spacesegment
andUserSegment

53. Contd… 52
Spacesegmentconsistsof
(i)3GEOsatellites
(ii)GPSconstellation

54. Contd… 53
Groundsegmentconsistsof
▶INRES(IndianReferenceStations)
▶INMCC(IndianMasterControlStations)
▶INLUS(IndianNavigationlandearthuplinkstations)

55. Contd… 54
GAGANUserSegmentConsistsof
▶GAGAN-enabledGPSreceivers,withthesametechnologyas
WAASreceivers,capabletousetheGAGANSignal-in-Space
(SIS).

56. Satellites of GAGAN 55
▶GSAT-8isanIndiangeostationarysatellites,whichwas
successfullylaunchedon21May2011andispositionedin
geosynchronousorbitat55degreesElongitude.
▶GSAT-10isaugmentedtocarry12KuBand,12CBandand12
ExtendedCBandtranspondersandaGAGANpayload.

57. Contd… 56
▶Thespacecraftemployspowerhandlingcapabilityofaround6kW
withaliftoffmassof3400kg.GSAT-10wassuccessfullylaunched
on29September2012.
▶GSAT-15carries24KubandtransponderswithIndiacoverage
beamandaGAGANpayload,wassuccessfullylaunchedon10
November2015.

58. Time and GPS
CoordinatedUniversalTimeGeneration
▶CoordinatedUniversalTime(UTC)isthetimescalebasedontheatomic
second,butoccasionallycorrectedbytheinsertionofleapseconds,soasto
keepitapproximatelysynchronizedwiththeearth’srotation.
▶TheleapsecondadjustmentskeepUTCwithin0.9sofUT1,whichisa
timescalebasedontheearth’saxialspin.
▶UT1isameasureofthetrueangularorientationoftheearthinspace.
Becausetheearthdoesnotspinatexactlyaconstantrate,UT1isnota
uniformtimescale.
57

59. Time and GPS
GPSSystemTime
▶ThetimescaletowhichGPSsignalsarereferencedisreferredtoasGPS
time.
▶GPStimeisderivedfromacompositeor“paper”clockthatconsistsofall
operationalmonitorstationandsatelliteatomicclocks.
58

60. Time and GPS
GPSSystemTime
▶Overthelongrun,itissteeredtokeepitwithinabout1µsofUTC,as
maintainedbythemasterclockattheU.S.NavalObservatory,ignoringthe
UTCleapseconds.
▶Attheintegersecondlevel,GPStimeequaledUTCin1980.However,due
totheleapsecondsthathavebeeninsertedintoUTC,GPStimewasahead
ofUTCby14sinFebruary2006.
59

61. Time and GPS
ReceiverComputationOfUTC
▶TheparametersneededtocalculateUTCfromGPStimearefoundin
subframe4ofthenavigationdatamessage.
▶Thesedataincludeanoticetotheuserregardingthescheduledfuture
orrecentpast(relativetothenavigationmessageupload)valueof
thedeltatimeduetoleapseconds,togetherwiththeweeknumber
WNLSF(WeeknumberLeapsecondfuture)andthedaynumberDN
attheendofwhichtheleapsecondbecomeseffective.
60

62. Time and GPS
ReceiverComputationOfUTC
▶Thelattertwoquantitiesareknownastheeffectivitytimeof
theleapsecond.“Day1”isdefinedasthefirstdayrelativeto
theend/startofaweekandtheWNLSFvalueconsistsofthe
eightleastsignificantbits(LSBs)ofthefullweeknumber.
61

63. Satellite Navigation
▶TheGPSiswidelyusedinnavigation.Itsaugmentationwith
otherspace-basedsatellitesisthefutureofnavigation.
NavigationSolution(Two-DimensionalExample)
Antenna location in two dimensions can be calculated by
using range measurements.
62

64. Symmetric Solution Using Two
Transmitters on Land.
In this case, the receiver and
two transmitters are located
in the same plane, as shown
in Fig. with known positions
x1, y1 and x2, y2.
63
Fig. Two transmitters with known two
dimensional positions

65. Contd…
Ranges R1 and R2 of two transmitters from the user position are calculated as
R1 = c AT1
R2 = c AT2
Where c = speed of light (0.299792458 m/ns)
AT1 = time taken for the radio wave to travel from transmitter 1 to the user
AT2 = time taken for the radio wave to travel from transmitter 2 to the user
(X , Y )= user position
64

66. Dilution of Precision
TheaccuracywithwhichapositioncanbedeterminedusingGPS
dependsontheaccuracyoftheindividualpseudorangemeasurements
andontheotherhanditalsodependsupontheGPSsatellite
geometry.
ThisistermedastheDilutionofPrecision(DOP).
SatelliteGeometrycanaffectthequalityofGPSsignalsandaccuracy
ofreceivertrilateration.
65

67. Contd…
There are 5 distinct kinds of DOP.
•GDOPGeometric Dilution of Precision
•PDOPPosition Dilution of Precision
•TDOPTime Dilution of Precision
•VDOPVertical Dilution of Precision
•HDOPHorizontal Dilution of Precision
66

68. Contd…
There are 5 distinct kinds of DOP.
•GDOPGeometric Dilution of Precision (Latitude, Longitude, Altitude and
clock)
•PDOPPosition Dilution of Precision (Latitude, Longitude, Altitude )
•TDOPTime Dilution of Precision (Clock)
•VDOPVertical Dilution of Precision (Altitude)
•HDOPHorizontal Dilution of Precision (Latitude and Longitude Positions)
67

69. Contd… 68

70. Computation of DOP Values
As a first step in computing DOP, consider the unit vectors from the receiver
to satellite i
Where,
(x,y,z) represents unknown position of the receiver
(xi,yi,zi) represents known positions of the satellite
69

71. Computation of DOP Values
Formulate the matrix, A, which (for 4 pseudo range measurement residual
equations) is
70

72. Computation of DOP Values
ThefirstthreeelementsofeachrowofAarethecomponentsofaunitvector
fromthereceivertotheindicatedsatellite.Thelastelementofeachrow
referstothepartialderivativeofpseudorangew.r.t.receiver'sclockbias.
Q, as thecovariance matrixresulting from theleast-squares normal matrix
 elements of Q are
71

73. Computation of DOP Values 72
PDOP, TDOP and GDOP are given by
GDOP is the square root of the diagonal elements of the matrix Q.

74. Contd… of DOP 73
DOP gives the geometric orientation of the satellites w.r.t the antennas.
Values of the DOPs are used for the GPS measurement quality
Smaller values of DOP gives the better satellite geometry and accurate user
positions, values greater than 5 suggest poor satellite geometry and least
accurate user positions.
Ideal satellite geometry has one satellite directly above the antenna and
remaining three satellites are spread by 120 degree apart.

75. Satellite Geometry 74
a) Ideal Satellite Geometry

76. Satellite Geometry 75
b) Poor Satellite Geometry

77. User Position Calculations With No Errors
Position calculation with no errors is given as
ρr= pseudorange(known),
x, y, z = satellite position coordinates (known),
X, Y, Z = user position coordinates (unknown),
where x, y, z, X, Y, Z are in the earth-centered, earth-fixed (ECEF) coordinate system.
76

78. Contd…
Squaring both sides yields
where r equals the radius of earth and Crris the clock bias correction.
77

79. Contd…
The four unknowns are (X, Y, Z, Crr).
position (x, y, z) is calculated from ephemeris data.
For four satellites, the above Eq becomes
78

80. Contd…
With four unknown state vectors X, Y, Z and Crr
We can rewrite the four equations in matrix form as
79

81. Contd…
Then we pre multiply both sides of above equation with M
-1
80

82. User Velocity Calculations With No Errors
The equation in this case is given as
81

83. Contd… 82

84. Contd…
The above equation is w.r.t one satellite,
Similarly the equation for 3 satellites is given as
83

85. Contd…
Uvis the User velocity
N is the Matrix
Pseudo range rate
84