EE651 Term Project

8/8/2019 EE651 Term Project

1/35

GLOBAL POSITIONING SYSTEM (GPS)

SAMUEL DEKYEM

EE 651WS: INTRODUCTION TO SPREAD SPECTRUM

INSTRUCTOR: PROFESSOR YAO

4/13/2009 1


2/35

Outline

WHAT IS GPS

HISTORY

OVERVIEW

SYSTEM ARCHITECTURE SEGMENTS

SPACE SEGMENT

CONTROL SEGMENT

FUNCTIONS

USER SEGMENT

SIMPLIFIED GPS RECEIVER DIAGRAM GPS RECEIVER USES

GPS SATELLITE SIGNALS DEMODULATION

SIGNALS

GPS NAVIGATIONGPS DATADATA FORMAT

CODE GENERATORPOSITION CALCULATIONERROR SOURCES

SATELLITE GEOMETRY GOOD GEOMETRY POOR GEOMETRY

GPS SATELLITE VEHICLE

SUMMARY

REFERENCES

4/13/2009 2


3/35

WHAT IS GPS

GPS: Global Positioning System, is a GlobalNavigation Satellite System.

Developed by the United States Department of

Defense. It provides autonomous geo-spatial positioning

with global coverage.

The system consists of a constellation of between

24 and 32 Medium Earth Orbit satellites andground stations that monitor and control GPS

operations.

4/13/2009 3


4/35

The History of GPS

1960s - Feasibility studies begun

1973 - Pentagon appropriates funding

1978 - First satellite launched

April, 1995 - System declared fully

operational in

4/13/2009 4


5/35

OVERVIEW

yGPS satellites broadcast signals from space

ySignals picked up by GPS receivers

yGPS receiver provides three-dimensionallocation

1. Latitude

2. Longitude3. Altitude + time.

4/13/2009 5


6/35

SYSTEM ARCHITECTURE

4/13/2009 6

Sattelites

Users

Uplink StationsControl Station

GroundAntennas


7/35

SEGMENTS

The GPS is made up of three parts:

Satellites orbiting the Earth

Control and monitoring stations on Earth

GPS receivers owned by users.

Space Segment = Satellites

Control Segment = Earth Stations

User Segment = GPS Receivers

4/13/2009 7


8/35

GPS SEGMENTS DETAILS

4/13/2009 8

Space Segment

Users SegmentUplink Stations

Control Station

GroundAntennas

Control Segment

There are three segments of the GPS


9/35

SPACE SEGMENT

4/13/2009 9


10/35

SPACE SEGMENT

GPS satellites orbit around the globe.

Transmit radio signals from space to GPS

receivers. Repeat the same ground track as earth

Satellite are spaced to ensures that there willalways be at least 5 satellites in view, visible from

any point on the earth.

4/13/2009 10


11/35

CONTROL SEGMENT

Ground stations control the GPS-System

Communications with the space segment areconducted through ground antennas

There are Monitoring stations atKwajalein

Hawaii

Diego Garcia

Ascension IslandsColorado Spring

4/13/2009 11


12/35

FUNCTIONS

Signals from satellites are measured by theMonitoring

Compute precise orbital data

Clock corrections for each satellite.

Ephemeris uploaded by Master Control station

Master Control station uploads clock data to

the satellites.

4/13/2009 12


13/35

USER SEGMENT

Any GPS receiver and antennas

GPS receivers decode the signals

transmitted from the GPS satellites to

determineo Position

o Velocity

o Time

Most receivers used for real timemapping

4/13/2009 13


14/35

SIMPLIFIED GPS RECEIVER BLOCK DIAGRAM


15/35

GPS RECEIVER USES

GPS receiver uses include:1. Navigation2. Navigation systems for remotely piloted air,

land and water vehicles3. Time dissemination

4. Management and tracking of ship and landvehicle fleets5. Road and rail traffic monitoring6. Dispatch and monitoring of emergency services7. Aerial, seismic, and land surveying

8. Military9. Search and rescue10.Disaster relief

4/13/2009 15


16/35

GPS RECEIVER USES

11. Marine, aeronautical and terrestrial navigation12. Satellite positioning and tracking

13. Geographic Information Systems (GIS)

4/13/2009 16

Unmanned Aerial Vehicles


17/35

GPS Satellite Signals L1 Frequency(contains navigation code)

L2 Frequency is for ionosphere delays

L1 = 1575.42 MHZ

L2 = 1227.60 MHZ

The P-Code (Precise) modulates both theL1 and L2 carrier phases.

4/13/2009 17


18/35

DEMODULATION

4/13/2009 18


19/35

SIGNALS

4/13/2009 19


20/35

Waypoint

Bearing =Course Over Ground (COG) =

Cross Track Error (XTE) =

Location Where GOTO

Was Executed

Bearing = 780

COG = 3500

XTE = 1/3 mi.

Bearing = 400

COG = 1040

XTE = 1/4 mi.

N

GPS NAVIGATION:ON GROUND

4/13/2009 20

Bearing =650 COG = 50

XTE = 1/2

mi.


21/35

GPS DATA

Navigation Message consists of time-tagged

data bits

Data bit frame consists of 1500 Frame consist of five 300-bit sub frames

Data frame is transmitted every thirty seconds.

Three six-second sub frames contain orbitaland clock data.

4/13/2009 21


22/35

GPS DATA

Twenty-five frames = one Navigation Message

T= 12.5 min (time of message)

Data frames (1500 bits) are sent every thirtyseconds. Each frame consists of five sub frames.

Data bit sub frames (300 bits transmitted over sixseconds) contain parity bits that allow for data

checking and limited error correction. Clock data parameters describe the SV clock and

its relationship to GPS time.

4/13/2009 22


23/35

DATA FORMAT

4/13/2009 23


24/35

CODE GENERATOR

4/13/2009 24


25/35

POSITION CALCULATION

x, y, and z components of position

Ti is the time message is sent

Tri is the time message is received Transit time=tri-ti

Distance =C*(transit time)

Calculation applies on 4 satellites

4/13/2009 25


26/35

ERROR SOURCES

yElectronics errorsyMultipath effects

ySignal delay

yAtmospheric effectsyClock errors

yIonospheric delay

yEphemeris Errors

4/13/2009 26


27/35

GPS SATELLITE GEOMETRY

Can affect the quality of GPS signals

Dilution of Precision (DOP) satellitesposition relative to the others

DOP value commonly is to determine thequality of a receivers position.

GPS receiver to pick satellites which

provide the best position triangulation.

4/13/2009 27


28/35

GOOD GEOMETRY

N

S

W E

4/13/2009 28


29/35

GOOD GEOMETRY

4/13/2009 29


30/35

BAD GEOMETRY

4/13/2009 30


31/35

BAD GEOMETRY

4/13/2009 31


32/35

GPS Satellite Vehicle

yS band antenna

ySolar Array Two solar panels

Battery charging

Power generationyGPS antenna

4/13/2009 32


33/35

GPS Satellite Vehicle

Typical Weight 900 Kg

Typical Height

5 meters

Typical Width

5 Meters

Approximate Design life10 years

4/13/2009 33


34/35

Summary

Considered requirements for good receiver reception morethe four GPS satellites shall be visible at receiver.

Analyzed GPS space segment

Defined GPS Segments

Discussed GPS Signal theory Discussed GPS Data format

Discussed space vehicle positioning calculations and errors

Analyzed satellite geometry

Describe typical Space Vehicle specification

4/13/2009 34


35/35

REFERENCES http://www.aero.org/education/primers/gps/ http://msl.jpl.nasa.gov/Programs/gps.html http://ares.redsword.com/gps/ http://www.novatel.com/Documents/Papers/Galileo_article.pdf www.tesaf.unipd.it/dmt/MatDidattico/Modulo3/0302f_MARCHI_GPSNeiRilieviP

ostEvento.pdf waas.stanford.edu/documents/Stanford%20GPS%20Lab%20Overview%20April%2

02006.pdf

www.unavco.org/community/announce_meetings/2005/antartic_meeting-DC-sept-05/pdf-talks/johns.pdf

www.navcen.uscg.gov/cgsic/meetings/EISubcommittee/2005_presentations/02%20Modern%20PRA.ppt

srma.stud.hive.no/nweb/navinstrumenter/Global%20Posision%20System.ppt http://waas.stanford.edu/~wwu/papers/gps/PDF/LoIONGNSS08.pdf http://waas.stanford.edu/~wwu/papers/gps/PDF/SeoIONGNSS08.pdf

netlab18.cis.nctu.edu.tw/html/paper/2001_11_06/Challenges%20in%20bringing%20GPS%20to%20Mainstream

4/13/2009 35