GPSThese applications fall into five :Location - determining a basic position Navigation - getting from one location to another Tracking - monitoring the movement of people/things

Mapping - creating maps of the world Timing - bringing precise timing to the world

AJAL.A.J Assistant Professor –Dept of ECE, Federal Institute of Science And Technology (FISAT)TM  MAIL: ec2reach@gmail.com

Satellite OrbitsSatellite Orbits

F1

(GravitationalForce)

v (velocity)

Why do satellites stay moving and in orbit?

F2

(Inertial-Centrifugal Force)

GPS

Feasibility studies begun in 1960’s.Feasibility studies begun in 1960’s. Pentagon appropriates funding in Pentagon appropriates funding in

1973.1973. First satellite launched in 1978.First satellite launched in 1978. System declared fully operational in System declared fully operational in

April, 1995.April, 1995.

The History of GPSThe History of GPS

Radio Frequency SpectrumCommonly Used Bands

AM HF VHF UHF L S C X KuKa V Q

1 10 100 1

MHz GHz

Terrestrial Bands

Space Bands

Shared (Terrestrial and Space)

SHF

0.1 10010

GPS is a medium earth orbit (MEO) satellite system

GPS satellites broadcast pulse trains with very

accurate time signalsA receiver able to “see” four GPS satellites can calculate its position within 30 m anywhere in world24 satellites in clusters of four, 12 hour orbital period

“You never need be lost again”Every automobile and cellular phone will eventually have a GPS location read-out

Satellite Navigation: GPS

S p ace S eg m en t C on tro l S eg m en t U ser S eg m en t

G P S

Components of GPS

Control Segment

Space Segment

User Segment

Three Segments of the GPSThree Segments of the GPS

Monitor Stations

GroundAntennas

Master Station

Space Segment:

24 GPS space vehicles (SVs). Now 27

6 orbital planes inclined at 55 degrees with the equator.

This constellation provides 5 to 8 SVs from any point on the earth.

Control SegmentControl Segment

Ground Antenna

Master Control Station

Monitor Station

Functions of

Master control station estimates parameters describing satellites' orbit and clock performance,

It also assesses health status of the satellites and determines if any re-positioning may be required.

This information is then returned to three uplink stations which transmit the information to satellites.

Master Control Station

Functions of

These stations are the eyes and ears of GPS, monitoring satellites as they pass overhead by measuring distances to them every 1.5 seconds

This data is then smoothed using ionospheric and meteorological information and sent to Master Control Station at Colorado Springs.

The ionospheric and meteorological data is needed to get more accurate delay measurements, which in turn improve location estimation.

Monitor Station

Ground Antenna

GroundAntennas

User segment

GPS antennas & receiver/processors

Position

Velocity

Precise timing

Used byAircraftGround vehiclesShipsIndividuals

User Segment:It consists of receivers that decode the signals from the satellites.The receiver performs following tasks:

Selecting one or more satellitesAcquiring GPS signalsMeasuring and trackingRecovering navigation data

Position and coordinates.

The distance and direction between any two waypoints, or a position and a waypoint.

Travel progress reports.

Accurate time measurement.

Four Basic Functions of GPS

– Each GPS satellite transmits an accurate position and time signal.

– The user’s receiver measures the time delay for the signal to reach the receiver.

– Measurements collected from 4 satellites are processed to solve for the 3D position, velocity and time.

How does GPS Work?

Sources of Signal InterferenceSources of Signal Interference

Earth’s Atmosphere

Solid Structures

Metal Electro-magnetic Fields

Planning a Navigation RoutePlanning a Navigation Route

Start= Waypoint

Ideal Satellite GeometryIdeal Satellite GeometryN

S

W E

Good Satellite GeometryGood Satellite Geometry

Poor Satellite GeometryPoor Satellite GeometryN

S

W E

Wide Area Augmentation SystemWide Area Augmentation SystemGeostationary WAAS satellites

GPS Constellation

WAAS Control Station

Local Area System (LAAS)

WAAS Control Station

Important Terminology

Satellite transmits Ephemeris and Almanac Data to GPS receivers.

Ephemeris data : contains important information about status of satellite (healthy or unhealthy), current date and time. This part of signal is essential for determining a position.

Almanac data : tells GPS receiver where each GPS satellite should be at any time throughout day. Each satellite transmits almanac data showing orbital information for that satellite and for every other satellite in the system.

TOA Concept

GPS uses concept of time of arrival (TOA) of signals to determine user position.

This involves measuring time it takes for a signal transmitted by an emitter (satellite) at a known location to reach a user receiver.

Time interval is basically signal propagation time. By measuring propagation time of signals

broadcast from multiple satellites at known locations, receiver can determine its position.

Measuring Distance

The length of the delay is equal to the signal's travel time.

The receiver multiplies this time by the speed of light to determine how far the signal traveled.

Assuming the signal traveled in a straight line, this is the distance from receiver to satellite.

Sources of Unintentional Timing Errors

Typical Errors

Source of Error Typical Error in Meters (per satellite)

Satellite Clocks 1.5Orbit Errors 2.5Ionosphere 5.0Troposphere 0.5Receiver Noise 0.3Multipath 0.6

Real Time CommunicationsReal Time Communications

Local Area Wireless-RF

Wireless Wide Area Networks• UHF/VHF• GSM• Satellite

Monitoring• Container• Cargo • Personnel

Logistics• Inventory Management • Warehouse Management• Cross Dock• Wireless Download

Warehouse/

Hub Store

GPS

GPS BasedGPS Based ElectronicElectronic DoorDoor LockLock

Container solenoid door lock power up and data communication receptacle

User Identify GPS based PDA Having a receptacle to power up Container electronic door lock

and send GPS data to open door

Electronic Deadbolt lock releases whenContainer and hand PDA actual location address is same

as container door lock processor given destination address

34

N. Sokolova, B.Forssell, HSGPS Tracking Performance in Indoor Environments

GPS Signal Challenges Indoors

• Extremely weak LOS signal

• Shadowing and Fading effects• Heavy attenuation• Multipath (short delay

multipath)

• Signal level differences• Cross-correlation problems

• Interference from other RF systems

• Cellular transmission • Wireless internet

• Using radio tags to study the physiology, behavior, and demography of animals

• Telemetry- the transmission of information through the atmosphere usually by radio waves

Disadvantages-•high initial costs•relatively short-lived and applicable to mammals the size of a wolf or larger or to birds on which solar cells can be used

Advantages-•highly accurate•suited for studies where intensive and frequent data are needed •may not require frequent field visits.