Tsn

UNIT – I GPS Fundamentals

Introduction  Navigation is a art of science of conducting an aircraft/vehicle from one point to another point.  U.S. Dept of Defense decided to establish, develop, test, acquire and deploy GPS -1973  NAVSTAR GPS (Navigation Satellite Timing And Ranging Global Positioning System)  GPS is a all weather Space based Navigation System  GPS Satellites contains Radio transmitters, Atomic clocks, Various Equipment for Positioning, Military projects (atomic flash detection)

 GPS system: Universal Accessibility to air navigation, safety communications from harmful interferences.  It is a Satellite Aided Communication, Navigation and Surveillance system.  Navigation tells the pilot where he is.  Surveillance tells the air traffic controller where the pilot is.  Communication allows the two to exchange information including where the pilot is.

Position from one satellite (Triangularization Method)

Sat. 1 10,000 miles

Rec. A

Receiver A is somewhere on the perimeter of a 10,000 miles circle

Rec. A

Sat. 1

Sat. 2 12,000 miles

10,000 miles

Rec. A

The receiver A could be at either of the positions

Sat. 1

Sat. 2

10,000 miles

12,000 miles Rec. A Sat. 3 8,000 miles

Three known distances give a definite position for receiver A

How GPS works? (In 5 easy steps) Step 3: To measure travel time, GPS needs very accurate clocks.

Step 4: Once you know distance to a satellite, you then need to know where the satellite is in the space.

Step 5: As the GPS signal travels through the Earth’s atmosphere, it gets delayed.

Step 2:To triangulate, GPS measures distance using the travel time a radio message. Step 1:Triangulation from satellites is the basis of the GPS system.

GPS System Architecture SPACE SEGMENT

4 SELECTED SATELLITES EACH WITH PRECISION TIME STANDARD PSEUDO-RANDOM DATA TELEMETRY DATA

EPHEMERIS CLOCK CORRECTIONS IONOSPHERIC DATA

(L1, L2) PSEUDO-RANGE DATA

CONTROL

MONITOR STATIONS HAWAII ACSNSION ISLAND DIEGO GARCIA KWAJALEIN COLORADO SPRINGS CAPE CANAVERAL*

(L1, L2) PSEUDO-RANGE DATA CURRENT EPHEMERIS CLOCK CORRECTIONS IONOSPHERIC DATA

SEGMENT

MASTER CONTROL STATION

COLORADO SPRINGS

UPLOAD STATIONS

RECEIVER

ACSNSION ISLAND DIEGO GARCIA KWAJALEIN CAPE CANAVERAL

ACCURATE POSITION VELOCITY TIME

GPS Satellite Constellation

Control Segment

Impact of GPS

 All weather, works in rain, clouds, sun and snow.  High accuracy 3D position, velocity and time. 24 hours and world-wide availability.  GPS has an impact in all related fields in geo-sciences and engineering.  GPS equipment is very expensive compared with other equipment.

Position from four satellites Satellite 1

Satellite 2

Satellite 3 Z WGS-84

Receiver

Satellite 4

(0, 0, 0)

Local

X

Y

GPS Principle of Operation (x2 y2 z2) (x1 y1 z1)

(xu yu zu)

(x3 y3 z3) (x4 y4 z4)

EARTH

Solving of four independent equations leads to estimation of user location and time offset :

(xu-x1)2 + (yu-y1)2 + (zu-z1)2 = C2 (tu1 – tsv1 + tbias)2 (xu-x2)2 + (yu-y2)2 + (zu-z2)2 = C2 (tu2 – tsv2+ tbias)2 (xu-x3)2 + (yu-y3)2 + (zu-z3)2 = C2 (tu3 – tsv3+ tbias)2 (xu-x4)2 + (yu-y4)2 + (zu-z4)2 = C2 (tu4 – tsv4+ tbias)2

GPS Transmission frequency band selection considerations Performance parameter

UHF= ( 3001000 MHz )

L-band ( 1-2GHz )

C-band ( 4-6GHz )

Path Loss for omni directional antenna

Lowest of the three

Acceptable

Path loss≈ 10dB larger than at Lband

Large group delay,201500ns

2-150ns at 1.5GHz

≈0-15ns

~f2 Ionospheric group delay

Spread Spectrum Technology for GPS Main Advantages (a) Jamming (b) Interference from other signals (c) Self interference due to multi-path propagation Allows all SVs to operate on the same frequencies. SST Spreading factor = Chipping Rate/ Information Bandwidth for L1 and L2 = 2 and 20MHz Noise floor of any Communication System = KTB For 1 Hz BW = -174 dBm

Graphical representation of Keplerian elements z

equatorial plane

y

r uk

Ω x

Fig. 2 Keplerian orbital elements

i

Keplerian orbit elements of satellite position Paramet er

Notation

a

Semi major axis

e

Eccentricity

ω

Argument of perigee

Ω

Drift of node’s right ascension / second

i

Inclination

v

True anomaly

Description

Size and shape of orbit

The orbital plane in the apparent system

Position in the plane

Getting perfect timing  The precise timing is important because the receiver must determine exactly how long it takes for signals to travel from each GPS receiver. The receiver uses this information to calculate its position.  How do we know both our receiver and the satellite are generating their codes at exactly the same time?  The satellites have atomic clocks on board  They are unbelievably precise and expensive that keep accurate time to within three nanoseconds (0.000000003 of a second). Each satellite has four clocks, just to be sure one is always working. The cost of each clock is $100,000. It is impossible to have a $100,000 atomic clock in every GPS receiver.

Getting perfect timing

Sat. 1

4 Secs

Sat. 2

X

6 Secs

Let’s say that, in reality, we are 4 Sec. From Sat.1 and 6 Sec. From Sat.2. In two dimensions, those two ranges would be enough to locate us at “X” point. So “X” is where we really are and is the position we would get if all the clocks were working perfectly.

But now what if used our “imperfect” receiver, which is a Sat. 1 Sat. 2 second fast? It would call the distance to Sat. 1, 5 4 Sec. 6 Sec. Sec. and to Sat.2, 7 Sec. and that causes the two circles to intersect at a different point “XX”. 7 Sec. 5 Sec. XX So, XX is where our imperfect (Wrong time) (Wrong time) receiver would put us, since there is no way of knowing that our receiver was a little fast. XX is a wrong position caused by wrong time measurements

But it would be miles off.

Sat. 1

4 Seconds

X

8 Seconds

Sat. 3

Sat. 2 Let’s add another measurement to the calculation (third satellite). Let’s say in reality (if we had perfect clocks) sat. 3 is 8 seconds 6 Seconds from the true position. All three circles intersect at X because those circles represent the true ranges to the three satellites.

Sat. 1

Sat. 2

4 Sec.

6 Sec.

5 Sec.

7 Sec.

X

(Wrong time)

(Wrong time)

XX 8 Sec.

9 Sec. (Wrong time)

Sat. 3

But now what if we used our “imperfect” receiver, which is a second fast? The dotted lines describes ranges that contain timing errors “pseudorange”. While Sat.1’s and Sat. 2’s fast times still intersect at XX, Sat.3’s fast time is nowhere near that point. There is no physical way those measurement can intersect

Geometric Dilution of Position

Poor GDOP 20

Good GDOP 2

UNIT – II Coordinate Systems

GPS Co-ordinate Systems  Knowledge of various coordinate systems is necessary to represent the position of a point on the earth, and the position and velocity of a GPS satellite orbiting the earth.  User position expressed in Earth-centered Earth-fixed (ECEF) coordinate system.  Satellite position expressed in Earth Centered Inertial Coordinate (ECI) system.

Geodetic Datum  As the surface of the earth is highly irregular, it is difficult to determine the user position accurately.  To overcome this problem, a hypothetical geometric reference surface called Geodetic Datum is defined, that approximates the shape of the earth.  For high accuracy positioning such as GPS, the best mathematical surface that approximates the surface of the earth is the biaxial ellipsoid or oblate ellipsoid.  A geodetic datum is uniquely determined by specifying eight parameters.  It is more common to characterize the ellipsoid by specifying the semi-major axis and flattening, denoted as f and defined as f=(a-b)/a .

Shape of the Earth  We think of the earth as a sphere  It is actually a spheroid, slightly bulged at the equator and flattened slightly at the poles

ECEF Coordinate System  Also known as Conventional Terrestrial Reference System.  User position expressed in Earth-centered, Earth-fixed (ECEF) coordinate system.  It is a geocentric coordinate system, i.e., its origin coincides with the center of the earth.  It is rigidly tied to the earth, i.e., it rotates with the earth.  Orientation of the axes: Origin is the center of mass of the earth. xy-plane is coincident with earth’s equatorial plane. x-axis points in the direction of Greenwich meridian. z-axis is chosen normal to the equatorial plane in the direction of the geographic north pole. y-axis completes the right handed coordinate system.

ECI Coordinate System  Satellite position is expressed in Earth Centered Inertial (ECI) coordinate system.  An Inertial coordinate system is defined to be stationary in space, or moving with a constant velocity (no acceleration).  Orientation of the axes: Origin is the center of mass of the earth. xy-plane is coincident with the earth’s equatorial plane. x-axis is permanently fixed in a particular direction relative to the celestial sphere (along vernal equinox). z-axis is chosen normal to the xy-plane in the direction of the geographic north pole. y-axis completes the right handed coordinate system.

Geodetic coordinates  Cartesian (ECEF) coordinates are cumbersome in daily use.  An alternative is to limit the information to horizontal position only, and express it as angular coordinates - latitude and longitude.

Geographic Coordinates (Φ, λ , z )  Cartesian (ECEF) coordinates are cumbersome in daily use. An alternative is to represent the position information in geodetic coordinates – latitude, longitude and height or elevation. Latitude (Φ) and Longitude ( λ) defined using an ellipsoid, (i.e.), an ellipse rotated about an axis. Elevation (z) defined using geoid, a surface of constant gravitational potential. Earth datums define standard values of the ellipsoid and geoid

Datum Classification  Global Datum vs. Regional Datum • Global datum is geocentric, whereas local or regional datum is non-geocentric. • The geodetic coordinates based on a local datum differ considerably (up to hundreds of meters) as compared to that based on a global datum.

World Geodetic System 1984 (WGS 84)  WGS84 is a realization of the CTRS developed by National Imagery and Mapping Agency (NIMA), of the U.S Department of Defense (DoD). It is an earth-fixed global reference frame, including an earth model.  WGS-84 is the official geodetic system for all mapping, charting, navigation and geodetic products used through the DoD. GPS measurements are based on WGS-84 reference frame. Table 1. Fundamental parameters of WGS-84 ellipsoid Parameter Semi-major axis (a) Reciprocal flattening (1/f)

Value 6378137 m 298.25722356

Indian Geodetic Datum (IGD)  Indian Geodetic Datum is a local geodetic datum based on Everest spheroid and best fits the Indian subcontinent.  Everest spheroid parameters: Origin

: Kalianpur

Latitude of Origin

: 24°07'11.26"

Longitude of Origin

: 77°39'17.57"

Semi-major Axis (a)

: 6377301.243 m

Inverse Flattening (1/f) : 300.8017

Need for Datum Conversion  Before the advent of satellite navigation and development of global datum, regional datum were used for navigation, and mapping applications.  As geographic information is exchanged both locally and globally, position information need to be available, both in terms of a local and global datum.  Hence there is a need for Datum Conversion.

Datum transformation between WGS-84 and IGD  The GPS derived coordinates (WGS-84) and local geodetic coordinates of collocated points may be processed together using appropriate transformation models to obtain the datum transformation parameters.  Datum transformation parameters define the functional relationship between two reference frames.  Three mathematical models namely, (1) Molodensky (2) Bursa-Wolf, and (3) Veis are used extensively around the world for determining the Datum transformation parameters.

 The transformation parameters for the Indian subcontinent are specified by National Imagery and Mapping Agency (NIMA) of the U.S Department of Defense. These parameters are obtained using Molodensky equations. Table 1. Datum transformation parameters between WGS-84 and IGD dx (metres)

dy (metres)

dz (metres)

295

736

257

dx, dy and dz represent the shifts between centres of Everest datum and WGS-84 datum.

Various error sources in GPS

Sources of error in GPS Satellite Clocks Ephemeris

Selective Availability Atmospheric Delays Multipath Delays Receiver Clocks

Atmospheric Effects

Ephemeris

20,000 km

Atmospheric Delays

200 km

Ionosphere

Particles 50 km

Clouds

Troposphere

Earth

Atmospheric Errors         

Signal propagates through Ionosphere and Troposphere Ionosphere extends from 70 – 1000 km. Troposphere extends up to 20 km from the ground level Ionospheric delay is freq. Dependent and can be removed by dual freq. Receiver Kloubuchar model gives 50% of the delay Trophospheric delay is independent of frequency I t consists of dry component and Wet component Tropospheric delay can be successfully modeled Models by Hopfield, Black and Saastamonien are successful

1. Ionospheric group Path delay τ=

40.3 × TEC c× f 2

(sec)

2. RF Carrier Phase Advance 1.34 ×10−7 ×TEC ∆φ = f

(cycles)

3. Doppler Shift dφ 1.34 × 10− 7 d (TEC) Δf d = = (Hz) dt f dt

Multipath Error The reception of a signal along a direct path and along one or more reflected paths. The classical example of multipath is the “ghosting” that appears on TV when an a plane passes overhead Satellite

Reflected signal

Obstruction

A B

Direct signal

C Receiver Station D Multipath delay = AB + BC

Multipath Errors      

Signal reaches antenna via two or more paths Effect can be reduced in the antenna design process Can also be reduced in the signal processing step Higher chip rate – greater multipath immunity Pseudorange measurements 1- 5m Carrier phase measurements 1- 5 cms

Relativistic Effects

b Apogee

a

ae

r E

Satellite Perigee

ν

Focus Center of Mass

a semimajor axis b semiminor axis e eccentricity

ν True anomaly E Eccentric anomaly M Mean anomaly

 Relativistic correction for the slight Eccentricity of the satellite orbit  ∇tr = Fe√ a SinE     

F= -4.4442807633 x 10 –10 sec/m e= Eccentricity a= Semi major axis E= Eccentric anomaly Sagnac Effect

UERE (User Equivalent Range Error)  Effect of all the error sources on pseudorange measurement can be combined.  This combined error is referred as UERE  It is the root sum square of all the error components.

GPS Errors required to be reduced using Differential GPS techniques

Basic Positioning: Before May 2000

25­100 m

• C/A Code on L1 • Selective Availability

Basic Positioning: Today

10­20 m

• C/A Code on L1 • No Selective Availability

Basic Positioning: By 2009

5­10 m

• C/A Code on L1 • C/A Code on L2

Basic Positioning: By 2013

1­5 m

• C/A Code on L1 • C/A Code on L2 • New Code on L5

Better resistance to  interference

UNIT 3 GPS Measurements

Basic Functions Of GPS Receiver  Capture the RF signals by GPS Satellites  Separate the signals from satellites in view.  Measure transit time and Doppler shift.  Estimate the user position, velocity and time  Determine the satellite position, velocity and clock parameters.

The composite GPS signal transmitted by the satellite

 complete signal leaving the satellite antennas can be represented byA C (t ) D (t ) cos(2πf

+ φc ) Ap P (t ) D(t ) sin( 2πf L 2 + φ p 2 ) c

L1

+

Ap P (t ) D(t ) sin( 2πf L1 + φ p1 )

where Ac and Ap = amplitudes of the C/A and P code modulations C (t ) and P(t ) = C/A and P code PRN sequences D(t ) = Navigation Data φc , φ p1and φ p 2= the phases of the C/A code and P code on L1 and the b

L2 P code signal, respectively. First component is the modified C/A code signal, the second component is the modified P code on the L1 carrier, and the third

GPS Signal Structure

Ranging Codes

Coarse/acquisition code (C/A) • 1 Chip sequence = 1023 bits = 1ms.

Precision (encrypted) P(Y) Code  1Chip sequence or Period ≈ 1014 =38 weeks  PRN code is reset every week. Chipping rate =10.23 MHZ

• i.e., code period =1ms

 =10.23 Mcp/s

• chip λ= 300m

 Chip λ = 30m

• Chipping rate = 1.023 MHz • = Mega chip/sec = Mcp/s 1Mcp/s 1023 bits

Fig: C/A Code

GPS CODE GENERATION  Both C/A and P Codes are of a class called product codes.

 Each is the product of two different code generators clocked at the same rate.

 Delay between the two code generators define the satellite code i.

 The specific component codes forming the product code for C/A and P are quite different but the principle is similar.

 The clock interval for the C/A code is Tcc=10Tc where Tc is the P-code clock interval.

GPS Code Generators

P-Code Generation  The P-code for satellite i is the product of two codes, X1(t) and X2(t+niT), where X1 has a period of 1.5s or 15,345,000 chips, and X2 has a period of 15,345,037 or 37 chips longer.

 Thus P-code is the product code of the form: Xpi(t)=X1(t)X2(t+niT), 0≤n ≤36  Both sequences are reset to begin the week at the same epoch time.

 Both X1and X2 are clocked in phase at a chip rate fc=1/Tc=10.23MHz.  The X1 and X2 codes are each generated as the products of two different pairs of 12-stage linear feedback shift registers X1A and X2B and X2A and X2B with polynomials:

Navigation data

1.0

0.5 6 Clock corrections & SV health/accuracy 1 2 12 Ephemeris parameters 3 18 Ephemeris parameters 24 Almanac, ionospheric model, dUTC 4 5 30 Almanac Sub frames

Fra me s

Time (seconds)

Ti

m e(

m in

ut es

)

12.5

Navigation Message Time and satellite clock information  Correction data to compensate for signal delay  Satellite orbit information  Satellite health status  Navigation message content superimposed on both the Pcode and C/A code  Data rate : 50 bits/sec.  Contains: ephemeris of the satellite, GPS time, Clock behaviour and system messages  Message Format(1500 bits), 5sub-frames (each 300 bits)  Each sub-frame : 10 words each 30 bits long  To receive 1 page : 30 secs, 25 data pages, 12.5 minutes  Sub-frames 1, 2 and 3 will have identical data on all 25 pages.  Satellite’s memory sufficient to 14 days of uploaded navigation data.

Desired Properties of GPS Signals  Tolerance to signals from other GPS satellites sharing the same frequency band; i.e., multiple access capability  Tolerance to some level of multipath interference.  Tolerance to reasonable levels of unintentional or intentional interference, jamming or spoofing by signal designed to mimic a GPS signal.  Ability to provide ionosphere delay measurements.  The GPS signal received on the earth be sufficiently low in power spectral density so as to avoid interference with terrestrial microwave line-of-sight communication.

GPS Measurements 1. Code phase measurement 2. Carrier phase measurement

Code Phase measurement 

GPS receiver determines the travel time of a signal from a satellite by comparing the "pseudo random code" it's generating, with an identical code in the signal from the satellite.

Satellite Receiver Time deference

 Apparent transit time of the signal from satellite to the receiver is measured.  ρ(t) = c[tu(t) - ts(t-τ)]  tu(t) =

Arrival time of the signal measured by

receiver clock  ts(t-τ) = emission time stamped on the signal  Both the receiver and satellite clocks can have biases with respect to GPS Time  tu(t) = t + δtu(t)  ts(t-τ) = (t-τ) + δts(t-τ)  δtu(t) and δts(t-τ) are the receiver and satellite clock biases with respect to GPS Time.

ρ = r + c[δtu − δt s ] + I p + Tp + ε p  Iρ(t) is the delay due to Ionosphere  Tρ(t) is the delay due to Tropospheres  ερ(t) = unmodelled error  Instead what we obtain is ρ the pseudorange, a noisy measurement of ‘r’  Accuracy with which r can be obtained depends upon how accurately we can estimate and eliminate these errors and compensate for clock biases.

Carrier Phase Measurement 

Survey receivers start with the pseudo random code and then move on to measurements based on the carrier frequency for that code.



This carrier frequency is much higher so its pulses are much closer together and therefore more accurate.



The phase difference between the receiver generated carrier and carrier transmitted by the satellite is measured

Where

φ (t ) == φPhase −φ (t − τ ) + N u (t )of thes receiver generated

carrier φu (t ) = Phase of the carrier transmitted by the satellite φs (tN− τ )= Whole number of carrier cycles that can’t be measured

 Writing phase (in cycles) in terms of freq. and time

φ (t ) = f ×τ + N = r (t ) / λ + N  Accounting for various biases the carrier phase measurement in units of cycles is

φ = λ−1[r + Iφ + Tφ ] + cλ−1 (δtu − δt s ) + N + ε φ

Combining code and carrier phase Measurements  The pseudorange due to code measurement is given by ρ (t ) = r (t ) + c[δt u (t ) − δt s t − τ )] + I (t ) + T (t ) + ε p (t )

 Carrier phase measurement in terms of cycles is φ = λ−1[r + Iφ + Tφ ] + cλ−1 (δtu − δt s ) + N + ε φ

 Carrier phase measurement in units of length is Φ (t ) = λφ (t ) = r (t ) + c[δtu (t ) − δt s (t − τ )] − I (t ) + T (t ) + λN + ε φ (t )

 This technique is popularly known as carrier smoothing of the code measurements  This combined measurement offers a modest improvement

Selective Availability (SA) (Intentional Signal Degradation)

SA consists of Dither & Epsilon  Dither is an intentional manipulation of the satellite clock frequency resulting in the generation of the carrier waves and the codes with varying wavelengths  Epsilon is an error imposed within the satellite orbit in the broadcast message

Anti-Spoofing (AS) (Intentional Signal Degradation)

 AS ( cross correlation) alters the GPS signal by changing the characteristics of the P code by mixing it with W code resulting in the Y code. Y code is designed to prevent the ability of the receiver to make P code measurements.  Many GPS receivers manufacturers have already developed techniques to still make P code measurements with only a small addition in added noise.

UNIT – IV GPS Augmentation systems

Differential GPS (DGPS)  DGPS can provide accuracy of +/-5m.  DGPS uses a known position, such as surveyed control point, as a reference point to correct the GPS position error.  DGPS provides pseudo-range corrections for each SV in view from a reference RX.  DGPS corrections are transmitted through a radio link. DGPS removes common-mode errors (not multipath or receiver noise).  Errors are common if users are close together (less than 100 km).  Position accuracies of 1-10 meters are possible with DGPS.

 Clear Line Of Sight (LOS) to the GPS satellites  GPS Ref. Station at precisely known position  Clear from nearby transmitters (Radar, TV etc)  Both Must track same GPS satellites

Differential Corrections  Upon removing the Receiver clock and multipath error, only locally common errors are left.  Troposphere usually decorrelates over relatively short distances. Special provision is made in the RTCM format for distant users to re-compute a tropospheric correction.  Ionopsheric and satellite orbit errors are two of the major drivers of the differential concept, because they are correlated over large distances.  Rare ionospheric and tropospheric disturbances can not be taken into account.

DGPS GPS Signal 1 GPS Signal 4

GPS Signal 2

Satellite

GPS Signal 3

GPS Signal RR Roving Receiver 1

Error correction message 2 Error correction message 3

Error correction message 1 Error correction message 4

Roving Receiver 2

Roving Receiver 4

Reference Receiver RR

Roving Receiver 3

DGPS APPLICATIONS * * * * * * * * * * *

Precision Agriculture Industrial Geodetic Surveying Marine and Air navigation Vehicle Guidance Military Fleet Management Forest/land asset Management Automatic Vehicle Location Aircraft landings GIS and Map Making

Need for Augmentation  GPS alone cannot support all aviation needs  Must maintain high aviation integrity requirement while providing more availability  GPS cannot provide vertical guidance

Augmentation Systems  Ground Based Augmentation System (GBAS) : LAAS  Ground Components Only  Greater PA Capability Over SBAS  Coverage Limited  Requires Ground Infrastructure  Can Be Included in Regional Architecture  Satellite Based Augmentation System (SBAS): WAAS,GAGAN  Ground and Satellite-Based Components  Improved Accuracy to Meet PA Requirements  Signal Corrections NOT Global  High Cost to Small Areas  Provides Additional Satellite Benefits

Why GPS / WAAS / LAAS?  To provide an inexpensive and reliable global area navigation capability. This is the cornerstone of free flight.  To provide an inexpensive precision approach capability everywhere. This is a significant safety benefit.  To do this, we have to deliver a navigation system capable of these services without reliance on other navigation systems. That is the purpose of WAAS and LAAS.

LAAS

 Local Area Augmentation System (LAAS) provides a differential GPS augmentation navigation capability within the terminal area  Capabilities may include    

Precision approach to CAT I and CAT II Complex procedures Departure procedures Aircraft Surface movement navigation

 Augmentations enhance Parameters (RNP)  Accuracy, Integrity, Continuity ad Availability

WAAS

 WAAS has been available for recreational use and visual flight rules since August 2001  WAAS was approved for aviation instrument operations on July 10, 2003  Provides 100% coverage of Continental US & Alaska from 100,000ft. to surface  Continuing to develop the system to expand vertical navigation to most of North America  WAAS augments the GPS constellation to meet the necessary integrity, availability, accuracy, and continuity for use in all phases of flight

GAGAN is an INDIAN Satellite Based Augmentation system GAGAN will be executed in three phases

• Technology Demonstration System ( TDS) • Intial Operational Phase (IOP) • Final Operational Phase (FOP)

BENEFIT OF THE GAGAN PROJECT • IMPROVING ENROUTE / NPA /PA

SERVICE IN INDIA • SERVICE AVAIALBLE TO THE NEGHBORING COUNTRY

GAGAN ARCHITECTURE GEO

GPS

C1

L2 L1

L1

(GEO)

GEO

GEO Ranging +Integrity message +WAD correction

C2

GPS

L1

L1/L2 (GPS)

L1

L1/C2 (GEO)

L2

INRES GEO C1

L GEO C2

INLUS 1

INMCC

INLUS 2

WADGPS Ground Segment Concept

UNIT – V GPS Modernization and other satellite navigation systems

L2C Second Civil Signal  C/A code on L2 carrier (L2C)

 Benefits of L2C  Significant improvement for the ~ 50,000 current scientific and commercial dual frequency users.  Designed to aid safety-of-life wireless single frequency E911 applications since C/A code cross correlation protection is not as good.  Longer codes  Two codes, one with and one without message data time multiplexed (e.g. TDMA)

L5 Third Civil Signal  L5 signal definition in IS-GPS-705  Improved signal structure for enhanced performance  Higher power than other GPS signals (-154.9 dBW)  24 MHz broadcast bandwidth  Longer spreading codes at 10.23 Mbps with the navigation message  Aeronautical Radionavigation Services band  Co-primary allocation at WRC-2000 (1164-1215MHz)  DME compatibility achieved by frequency reallocation, if required

GLONASS(1996) Global Orbiting Navigation Satellite System  Three Orbital Planes, 8 satellites in each plane and equally separated.  Satellites are identified by FDMA.  Basic principle is same as GPS.  Altitude 25,510Km. Orbital period is 675.8minutes. Ground track repeat every 17orbits.  Base frequency is(L1) 1602MHz. +0.5625i, i=1…24.  L2=1246MHz,+0.4375i, i=1….24.  During 1996, fewer than 40 days showed that all 24 positions occupied by healthy satellites.  Presently 8 satellites are operational.  Likely to be revived by 2010.

GPS

GLONASS

GALILEO  European Union project.  Galileo would have put 30 satellites in orbit 23,000km above the Earth by 2007.  The whole project would cost upwards of 3bn Euros.  Concerns a new transport infrastructure and offering positioning and timing services.  For commercial, safety, security and government applications.  Signal and code structure more complex than GPS  Common signals L1 and L5 – interoperability  60 orbiting satellites  Four services Two free-to-air One commercial Public authorities – police http://www.galileo-pgm.org

/

A Comparison of GPS and Galileo Characteristic

GPS

Galileo

Combined Capability

Spacecraft in Orbit

28+3

30+3

58+6

Spacecraft availability(ever)

8-9

8-9

16-18

Integrity(autonomous)

Fair

Fair

Excellent

Coverage(Worldwide)

Good

Good

Excellent

Dilution of precision

1-3

1-3

0.7-2

Interference Susceptibility

Low

Low

Very Low

Safety Services Protection

2 Signals

4 Signals

6 Signals

Frequencies available(Civil)

1-3

1-5

2-8

Receiver Cost(Relative)

1C

1C

1.2C

Accuracy

1-2m

1-2m

0.6-1.3m

Characteristic of GPS and GLONASS Systems. System

GPS (American)

GLONASS (Russian)

Constellation Number of satellite Number of orbital planes Orbital inclination (deg) Orbital radius (km) Period (hr:min) Ground track repeat

24 6 55 26,560 11:58 sidereal day

24 3 65.8 25,510 11:16 8 sidereal days

Signal Characteristics Carrier signal (MHz)

L1:1575.42 L2:1227.60

Code

CDMA C/A code on L1 P code on L1 and L2 C/A code:1.023 P code:10.23

Code frequency (MHz)

L1:(1602+0.5625n), L2:(1246+0.4375n), n=1,2,…..,24 FDMA C/A code on L1 P code on L1 and L2 C/A code: 0.511 P code: 5.11

Reference standards Co-ordinate System Time

WGS84 UTC(USNO)

PZ90 UTC(SU)

Accuracy specification (95%) Horizontal (m) Vertical (m)

100 140

100 250

GPS/INS Integration

• Integrated GPS receiver with a low cost IMU – GPS receiver outputs are combined with Inertial sensor outputs to provide more accurate and reliable navigation – GPS satellite signals are frequently blocked in Urban and Mountain areas and Tunnels – Inertial sensor outputs drift with time – Sensitivity of the GPS receiver can be increased using the velocity information from DR sensors

NAVIGATION ACCURACY REQUIREMENTS FOR DIFFERENT GPS TECHNIQUES Navigation Accuracy

GPS Techniques

<100 m

SPS Using C/A code Point Positioning

>10m <30m <10 m

PPS Using P code Point Positioning PPS Using Dual Freq. Point/Limited GPS or code DGPS Area Positioning

<3 m

DGPS Code/Phase

<1 m & >10cm Carrier Phase DGPS <50 cm & >1mm Carrier phase DGPS With Post processing

Application Area

Local Area Local Area survey Local Area static & Kinematic area

Future of GPS     

SA to be turned off. Reduced role of military Integration with Russian GLONASS Development of European Galileo Easier tie to national and international networks

GPS APPLICATIONS  Surveying and Mapping  Aviation  Fishing and boating  Forestry and Natural Resources  Public Safety  Vehicle Navigation  Civil Engineering Applications

Surveying and Mapping Geographic Information System, GIS  A GIS is a computer based tool capable of acquiring, storing, manipulating, analyzing and spatially referenced data.  Spatially referenced data is identified data according to its geographic location (such as streets, light poles and fire hydrants are linked by geography).  GIS stores GPS data as a collection of layers in the GIS data base.  GPS/GIS systems provide centimeter level to meter level accuracy

 Mapquest, Yahoo! Maps, GoogleEarth are examples of GIS

 Surveyors and map makers use GPS for precision positioning. GPS is often used to map the location of such facilities as telephone poles, sewer lines, and fire hydrants. Surveyors use GPS to map construction sites and property lines.

Aviation Pilots Use of GPS  Using GPS, aircraft can fly the most direct routes between airports. Pilots often rely on GPS to navigate to their destinations. A GPS receiver in the cockpit provides the pilot with accurate position data and helps him or her keep the airplane on course.

Fishing and boating 

A GPS unit tells you where you are and where you're going to within a few meters. Once considered a luxury, GPS is now an essential item in the fisher's arsenal.

 Combine the benefits of mapping with GPS by getting digital charts or scan in paper maps with GPS mapping software and then enter way points along your planed route.  A GPS unit can mark these fishing hot spots so that you can find it again easily.

Forestry and Natural Resources  Forestry, mineral ` exploration, and wildlife habitat management all use GPS/GIS to precisely define positions of important assets and to identify changes.

Public Safety  GPS is used for Location and status information provided to public safety systems offers managers a quantum leap forward in efficient operation of their emergency response teams. The ability to effectively identify and view the location of police, fire, rescue, and individual vehicles or boats means a whole new way of doing business.

Biking

 Download Hiking & Biking waypoints to use while traveling. Mark points of interest as you go or mark prior to trip by finding on the web.

 WAAS applications  GPS/Pseudolite applications  GPS/INS applications  LAAS applications

THE END