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
Rec. A
10,000 miles

Receiver A is somewhere on the

perimeter of a 10,000 miles circle
 Rec. A

Sat. 1 Sat. 2

10,000 miles 12,000 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 4: Once you know distance to a
satellite, you then need to know
Step 3: To measure
where the satellite is in the space.
travel time, GPS needs
very accurate clocks. 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
(L1, L2)
CLOCK CORRECTIONS
IONOSPHERIC DATA PSEUDO-RANGE DATA
(L1, L2) CURRENT EPHEMERIS
PSEUDO-RANGE DATA CLOCK CORRECTIONS
IONOSPHERIC DATA

CONTROL SEGMENT

MONITOR MASTER UPLOAD RECEIVER

STATIONS CONTROL STATIONS
STATION
HAWAII ACSNSION ISLAND ACCURATE POSITION
ACSNSION ISLAND DIEGO GARCIA VELOCITY
DIEGO GARCIA KWAJALEIN TIME
KWAJALEIN CAPE CANAVERAL
COLORADO SPRINGS COLORADO SPRINGS
CAPE CANAVERAL*
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 Y

X
 GPS Principle of Operation
(x2 y2 z2) (x3 y3 z3)

(x1 y1 z1) (x4 y4 z4)

(xu yu zu)
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 UHF= ( 300- L-band C-band

parameter 1000 MHz ) ( 1-2GHz ) ( 4-6GHz )

Path Loss for Lowest of the Acceptable Path loss≈

omni directional three 10dB larger
antenna than at L-
~f2 band
Ionospheric Large group 2-150ns at ≈0-15ns
group delay delay,20- 1.5GHz
1500ns
 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

equatorial
r y
plane
uk

Ω i

Fig. 2 Keplerian orbital elements

 Keplerian orbit elements of satellite position

Paramet Notation Description

er

a Semi major axis

Size and shape of orbit

e Eccentricity

ω Argument of perigee
The orbital plane in the
Drift of node’s right ascension / apparent system
Ω second

i Inclination

True anomaly Position in the plane

v
 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

Let’s say that, in reality, we are 4

Sat. 1 Sat. 2
Sec. From Sat.1 and 6 Sec. From
Sat.2.
In two dimensions, those two
4 Secs X ranges would be enough to locate
6 Secs
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
7 Sec.
a different point “XX”.
5 Sec.
(Wrong time)
XX So, XX is where our imperfect
(Wrong time)
receiver would put us, since there is
no way of knowing that our receiver
XX is a wrong position was a little fast.
caused by wrong time
measurements
But it would be miles off.
 Sat. 1 Sat. 2 Let’s add another measurement to
the calculation (third satellite).
Let’s say in reality (if we had
4 Seconds X
6 Seconds perfect clocks) sat. 3 is 8 seconds
from the true position.
All three circles intersect at X
8 Seconds
because those circles represent the
true ranges to the three satellites.
Sat. 3
 Sat. 1 Sat. 2 But now what if we used our
“imperfect” receiver, which is a
4 Sec. 6 Sec.
5 Sec. 7 Sec.
second fast?
(Wrong time) X (Wrong time) The dotted lines describes ranges
that contain timing errors “pseudo-
XX range”.
While Sat.1’s and Sat. 2’s fast
8 Sec. 9 Sec.
(Wrong time) times still intersect at XX, Sat.3’s
fast time is nowhere near that point.
Sat. 3 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 Value
Semi-major axis (a) 6378137 m
Reciprocal flattening (1/f) 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

Troposphere Clouds

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
40.3
τ= × TEC (sec)
c× f 2
2. RF Carrier Phase Advance

1.34 ×10−7 ×TEC

∆φ = (cycles)
f

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

B
Direct signal

Receiver

Station

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

Satellite
b r
Apogee a ae E ν Perigee
Focus
Center of Mass

ν True anomaly
a semimajor axis E Eccentric anomaly
b semiminor axis
e eccentricity 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

Better resistance to 
interference
1­5 m

• C/A Code on L1
• C/A Code on L2
• New Code on L5
 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 L1 + φ p1 )

c L1

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

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
Precision (encrypted) P(Y) Code
 1Chip sequence or Period ≈ 1014
=38 weeks
Coarse/acquisition code (C/A)
 PRN code is reset every week.
• 1 Chip sequence = 1023 bits =
1ms. 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
12.5
)
es
ut
in
m
e(

1.0
m
Ti

0.5
6 Clock corrections & SV health/accuracy 1
2
Time (seconds)

12 Ephemeris parameters
18 Ephemeris parameters 3
24 Almanac, ionospheric model, dUTC 4
5

s
30 Almanac

me
Fra
Sub frames
 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 P-
code 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
u (t )of (t − τ ) + N
thes receiver generatedcarrier
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 2
Satellite
GPS Signal 4
GPS Signal 3
GPS Signal RR

Roving Receiver 1
Error correction message 2

Error correction message 1 Error correction message 3

Error correction message 4

Roving Receiver 2

Reference
Roving Receiver 4 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
GEO GEO Ranging
GPS +Integrity message
+WAD correction GPS

L1
C2
C1
L2 L1
L1/L2 L1/C2
L1
(GPS) (GEO) L2
L1 (GEO)

INRES

L
GEO
C1 GEO
C2

INLUS 1
INLUS 2
INMCC
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 E-
911 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 24 24
Number of orbital planes 6 3
Orbital inclination (deg) 55 65.8
Orbital radius (km) 26,560 25,510
Period (hr:min) 11:58 11:16
Ground track repeat sidereal day 8 sidereal days

Signal Characteristics
Carrier signal (MHz) L1:1575.42 L1:(1602+0.5625n),
L2:1227.60 L2:(1246+0.4375n),
n=1,2,…..,24
Code CDMA FDMA
C/A code on L1 C/A code on L1
P code on L1 and L2 P code on L1 and L2
Code frequency (MHz) C/A code:1.023 C/A code: 0.511
P code:10.23 P code: 5.11

Reference standards
Co-ordinate System WGS84 PZ90
Time UTC(USNO) UTC(SU)

Accuracy specification (95%)

Horizontal (m) 100 100
Vertical (m) 140 250
 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 GPS Techniques Application Area
Accuracy
<100 m SPS Using C/A code Point Positioning
>10m <30m PPS Using P code Point Positioning
<10 m PPS Using Dual Freq. Point/Limited
GPS or code DGPS Area Positioning
<3 m DGPS Code/Phase Local Area
<1 m & >10cm Carrier Phase DGPS Local Area survey
<50 cm & >1mm Carrier phase DGPS Local Area static
With Post processing & 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