GPS: GPS: Working Principle and Working Principle and Interfacing - - PowerPoint PPT Presentation
GPS: GPS: Working Principle and Working Principle and Interfacing Interfacing Team D1 Team D1 Ranajeet Anand(200601186) Ranajeet Anand(200601186) Shashi Kumar(200601155) Shashi Kumar(200601155) Presentation Flow Presentation Flow
Land-based electronic navigation systems Land-based electronic navigation systems
In the 1930's radio beacons were used to provide
In the 1930's radio beacons were used to provide bearings from airfields bearings from airfields
Radio navigation systems like - LORAN, (Long Range
Radio navigation systems like - LORAN, (Long Range Aid to Navigation). Positions were determined by the Aid to Navigation). Positions were determined by the timing of signals timing of signals
In 1960s the Omega system provided worldwide
In 1960s the Omega system provided worldwide electronic navigation coverage for the first time electronic navigation coverage for the first time
In mid-1960's: US Navy's NAVigation SATellite System
In mid-1960's: US Navy's NAVigation SATellite System (NAVSAT), also known as TRANSIT, was developed to (NAVSAT), also known as TRANSIT, was developed to provide more accurate positions for ships and provide more accurate positions for ships and submarines. submarines.
Unavailability for the general public
Land based systems, so not much accurate
Low frequency of updating location
Lack of 24-hour availability
Definition: Definition: GPS stands for Global Positioning System GPS stands for Global Positioning System A “GPS System” usually means a GPS Receiver A “GPS System” usually means a GPS Receiver
GPS Components: GPS Components: There are three Components : There are three Components : 1) ground stations that controlled the system, 1) ground stations that controlled the system, 2) a "constellation" of satellites in Earth orbit, and 2) a "constellation" of satellites in Earth orbit, and 3) receivers carried by users. 3) receivers carried by users.
Solar-powered satellites orbit the earth at 19,300 km Solar-powered satellites orbit the earth at 19,300 km making two complete rotations every day making two complete rotations every day Arrangement of orbits such that at least four satellites Arrangement of orbits such that at least four satellites "visible" in the sky "visible" in the sky.
Job of Receiver Job of Receiver
Locate 4 or more satellites
Locate 4 or more satellites
figure out the distance to each,
figure out the distance to each,
Deduce its own location by the Trilateration Principle
Deduce its own location by the Trilateration Principle
2-D Trilateration
2-D Trilateration
2 circles intersect at 2
2 circles intersect at 2 points points
Intersection with 3
Intersection with 3rd
rd circle
circle => Accurate Location => Accurate Location
3-D Trilateration 3-D Trilateration Four spheres are needed Four spheres are needed
2 spheres intersect in a
2 spheres intersect in a circle circle
A 3
A 3rd
rd sphere intersects at
sphere intersects at 2 points of the circle 2 points of the circle
Intersection with 4
Intersection with 4th
th
sphere => Accurate sphere => Accurate Position Position
3 –D Trilateration
The 3 spheres are formed by 3 satellites
The 3 spheres are formed by 3 satellites
The earth itself acts as the 4
The earth itself acts as the 4th
th sphere
sphere
To improve accuracy and provide precise altitude
To improve accuracy and provide precise altitude information, receivers generally look to four or more information, receivers generally look to four or more satellites satellites
The satellites transmit high-frequency, low-power radio
The satellites transmit high-frequency, low-power radio signals signals
These signals are received by the GPS receiver
These signals are received by the GPS receiver Better units with multiple receivers can pick Better units with multiple receivers can pick up signals from several satellites up signals from several satellites
Radio waves travel at speed of light so receiver can
Radio waves travel at speed of light so receiver can calculate time taken by signal to arrive calculate time taken by signal to arrive
This is the distance of satellite from receiver This is the distance of satellite from receiver
To calculate distance, satellite and receiver clocks
To calculate distance, satellite and receiver clocks should be accurately synchronized should be accurately synchronized
The satellites contain atomic clocks which are extremely
The satellites contain atomic clocks which are extremely accurate, and accurate with respect to each other accurate, and accurate with respect to each other
So, the receiver also would need to have a highly
So, the receiver also would need to have a highly accurate atomic clock accurate atomic clock
This is not possible since atomic costs are very
This is not possible since atomic costs are very expensive expensive
The receiver itself uses an ordinary quartz clock, which it
The receiver itself uses an ordinary quartz clock, which it constantly resets constantly resets
Incoming signals from four or more satellites used to
Incoming signals from four or more satellites used to gauge its own inaccuracy gauge its own inaccuracy
The receiver sets its clock at a time value such that all
The receiver sets its clock at a time value such that all signals that it is receiving align at a single point in space signals that it is receiving align at a single point in space
Since a 4
Since a 4th
th satellite is used, all 4 spheres will not
satellite is used, all 4 spheres will not intersect at 1 point. intersect at 1 point.
The receiver makes necessary adjustments so that all 4
The receiver makes necessary adjustments so that all 4 spheres intersect at 1 point spheres intersect at 1 point
Based on this, it resets its clock to be in sync with the
Based on this, it resets its clock to be in sync with the satellite's atomic clock, thus ensuring that its clock is as satellite's atomic clock, thus ensuring that its clock is as accurate as the atomic clocks accurate as the atomic clocks
capable of displaying a user position within 4 minutes Initial Position Calculation Time user position will be updated every 10 seconds. LCD Updating Frequency no more than 5 watts of power. Power Consumption Accuracy of atleast1 meter per 22 mph. Accuracy vs. User Velocity Within 15 meters 99% of the time. Accuracy Description Name
:
Satellite errors
Satellite errors Errors in modeling clock offset Errors in modeling clock offset Latency in tracking Latency in tracking
Atmospheric propagation errors
Atmospheric propagation errors Through the ionosphere, carrier experiences phase Through the ionosphere, carrier experiences phase advance advance Dependent on Dependent on
Geomagnetic latitude
Geomagnetic latitude
Time of the day
Time of the day
Elevation of the satellite
Elevation of the satellite
Multipath
Multipath
Receiver Noise
Receiver Noise
Forces on the GPS satellite
Forces on the GPS satellite Earth is not a perfect sphere and hence Earth is not a perfect sphere and hence uneven uneven gravitational potential distribution gravitational potential distribution Other heavenly bodies attract the satellite, Other heavenly bodies attract the satellite, but but these are very well modeled these are very well modeled
Errors due to Geometry
Errors due to Geometry
TSIP (Trimble Standard Interface Protocol TSIP (Trimble Standard Interface Protocol ) ) TSIP is a powerful binary packet protocol that allows the system TSIP is a powerful binary packet protocol that allows the system designer maximum configuration control over the GPS receiver for designer maximum configuration control over the GPS receiver for
TAIP (Trimble ASCII Interface Protocol TAIP (Trimble ASCII Interface Protocol ) ) TAIP is the Trimble ASCII interface protocol designed specifically for TAIP is the Trimble ASCII interface protocol designed specifically for vehicle tracking applications. It is a bi-directional vehicle tracking applications. It is a bi-directional protocol
protocol using
using simple ASCII commands with the associated ASCII responses. simple ASCII commands with the associated ASCII responses.
NMEA (National Marine Electronic Association) NMEA (National Marine Electronic Association) NMEA 0183 is an industry standard protocol common to marine NMEA 0183 is an industry standard protocol common to marine
capable devices such as chart plotters, radars, etc. NMEA capable devices such as chart plotters, radars, etc. NMEA messages and output rates can be user selected as required. messages and output rates can be user selected as required.
DGPS ( DGPS (differential GPS differential GPS ) ) A technique used to improve positioning or navigation accuracy by A technique used to improve positioning or navigation accuracy by determining the positioning error at a known location and determining the positioning error at a known location and subsequently incorporating a corrective factor (by real-time subsequently incorporating a corrective factor (by real-time transmission of corrections or by post processing) into the position transmission of corrections or by post processing) into the position calculations of another receiver operating in the same area and calculations of another receiver operating in the same area and simultaneously tracking the same satellites. simultaneously tracking the same satellites. Above all protocols the NMEA protocol is the standard protocol Above all protocols the NMEA protocol is the standard protocol for all GPS. for all GPS.
protocols –
Rockwell binary message format NMEA ASCII message format
For NMEA compliance, The output of the GPS is fixed at 4800 bps, no parity, 8 data bits and 1 stop bit.
The NMEA standard provides quite a range of sentences. Each
The NMEA standard provides quite a range of sentences. Each sentence starts with a $ and ends with a * and an optional 8-bit sentence starts with a $ and ends with a * and an optional 8-bit checksum expressed as two hexadecimal characters. checksum expressed as two hexadecimal characters. Sentence Description Sentence Description $GPRMC Recommended minimum specific GNSS data $GPRMC Recommended minimum specific GNSS data $GPGGA Global positioning system fixed data $GPGGA Global positioning system fixed data $GPGLL Geographic position - latitude / longitude $GPGLL Geographic position - latitude / longitude $GPGSA GNSS DOP and active satellites $GPGSA GNSS DOP and active satellites $GPGSV GNSS satellites in view $GPGSV GNSS satellites in view $GPVTG Course over ground and ground speed $GPVTG Course over ground and ground speed
$GPRMC,225446,A,4916.45,N,12311.12,W,000.5,054.7, $GPRMC,225446,A,4916.45,N,12311.12,W,000.5,054.7, 191107,020.3,E*68 191107,020.3,E*68 225446 Time of fix 22:54:46 UTC 225446 Time of fix 22:54:46 UTC A Navigation receiver warning A = Valid A Navigation receiver warning A = Valid position, V = Warning position, V = Warning 4916.45,N Latitude 49 deg. 16.45 min. North 4916.45,N Latitude 49 deg. 16.45 min. North 12311.12,W Longitude 123 deg. 11.12 min. West 12311.12,W Longitude 123 deg. 11.12 min. West 000.5 Speed over ground, Knots 000.5 Speed over ground, Knots 054.7 Course Made Good, degrees true 054.7 Course Made Good, degrees true 191107 UTC Date of fix, 19 November 2007 191107 UTC Date of fix, 19 November 2007 020.3,E Magnetic variation, 20.3 deg. East 020.3,E Magnetic variation, 20.3 deg. East *68 mandatory checksum *68 mandatory checksum
The signals available at the serial pins of the GPS are
The signals available at the serial pins of the GPS are TTL level. TTL level.
To read the GPS output on Hyper terminal, the TTL
To read the GPS output on Hyper terminal, the TTL signal is converted into RS 232 using a Max 232 IC signal is converted into RS 232 using a Max 232 IC
The input messages are sent to the GPS using a simple
The input messages are sent to the GPS using a simple C code C code
GPS systems that provide the driver with the current
GPS systems that provide the driver with the current position and a local map. position and a local map.
GPS devices that give the users a detailed map of the
GPS devices that give the users a detailed map of the terrain, rivers, hills and so forth, tracks and trails. terrain, rivers, hills and so forth, tracks and trails.
GPS devices that enable marine users to get specific
GPS devices that enable marine users to get specific information relating to the sea bed, navigable channels, information relating to the sea bed, navigable channels, and other pieces of maritime data that enables them to and other pieces of maritime data that enables them to navigate safely. navigate safely.
GPS devices that offer an inexpensive and reliable
GPS devices that offer an inexpensive and reliable supplement to existing navigation techniques for aircraft supplement to existing navigation techniques for aircraft
http://www.palowireless.com/gps/howgpsworks.asp http://www.palowireless.com/gps/howgpsworks.asp
http://electronics.howstuffworks.com/gadgets/travel/gps.htm http://electronics.howstuffworks.com/gadgets/travel/gps.htm
http://www.nasm.si.edu/gps/work.html http://www.nasm.si.edu/gps/work.html
http://www.8051projects.info/exp12.asp http://www.8051projects.info/exp12.asp
http://home.mira.net/~gnb/gps/nmea.html#interp http://home.mira.net/~gnb/gps/nmea.html#interp
http://www.psychologie.uni-regensburg.de/Zimmer/trafficresearch/NM http://www.psychologie.uni-regensburg.de/Zimmer/trafficresearch/NM
http://www.aero.org/education/primers/gps/uses.html http://www.aero.org/education/primers/gps/uses.html