ajal gps
DESCRIPTION
These 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 worldTRANSCRIPT
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: [email protected]
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.