EE587Spring – 2003

M12 - GPSPresented by,

Kishore Mogatadakala

02/04/03.

1) GPS and the satellite constellation2) Principle - segments and operation3) GPS equations and different coordinate systems4) GPS applications5) M12 GPS on-core7) M12 technical characteristics8) NMEA protocol9) Different Global positioning systems10) References

GPS and Satellite constellation

GPS (Global Positioning System)is a remarkable navigation technology that provides precise time and location. GPS provides the exact time and location anywhere, anytime, and under any atmospheric conditions.

GPS is the acronym for NAVSTAR(Navigation Satellite Timing And Ranging) Global Positioning System. NAVSTAR is the name given to GPS satellites.

GPS is funded by and controlled by the U. S. Department of Defense (DOD). While there are many thousands of civil users of GPS world-wide, the system was designed for and is operated by the U. S. military.

GPS Segments

* Space segmentGPS Space Segment consists

of at least four equally-spaced GPS satellites in a constellation of six orbiting planes at an altitude of 20, 200km. GPS satellites orbit at a 55 degree inclination to the equatorial plane

* Control segmentTo launch and arrange GPS

satellites properly in space to provide an optimal GPS system for safety applications.

to handle unexpected accidents and to provide exact information in different situations.

* User segmentGPS User Segment consists

of antenna for receiving satellite signals, a GPS receiver for collecting navigation data and for calculating time and location, and other specialized equipment for special purposes

GPS Operation

GPS Equations

where •c = speed of light (3 108 m/s) •tt,1, tt,2, tt,3, tt,4 = times that GPS satellites 1, 2, 3, and 4, respectively, transmitted their

signals (these times are provided to the receiver as part of the information that is transmitted). •tr,1, tr,2, tr,3, tr,4 = times that the signals from GPS satellites 1, 2, 3, and 4, respectively, are

received (according to the inaccurate GPS receiver’s clock) •x1, y1, z1 = coordinates of GPS satellite 1 (these coordinates are provided to the receiver as

part of the information that is transmitted); similar meaning for x2, y2, z2, etc

ECEF and Geodetic Coordinates

GPS Applications

M12 – On-core receiver

NMEA Protocol

The NMEA 0183 v2.0 protocol is implemented by most GPS equipment, but is in fact a general purpose standard used in marine electronics for navigation and other functions

NMEA 0180 & 0182 recommend that the talker output can be either RS-232 (polar) or TTL (0/5V). NMEA 0183 retains this but recommends RS-422 in addition. (M12-TTL)

The NMEA 0183 protocol supports serial communications at 4800 bps (fixed) using printable ASCII characters only The data is presented as "sentences” . Each sentence

starts with a "$" character followed by a two-character talker ID followed by a three-character sentence ID followed by data content (a series of comma delimited fields )The checksum comprises a field starting with a "*" character and two hexadecimal digits (expressed in ASCII) representing the exclusive OR of all characters appearing between the "$" and "*" exclusivelyEach sentence can have up to 82 characters including the header, the data and an optional checksum field at the end.If a field is blank, all the comma delimiters remain but no data appears between commas corresponding to the blank field.

Sentence GGAFunction: Global Positioning Fix Data

Example: $GPGGA,120757,5152.985,N,00205.733,W,1,06,2.5,121.9,M,49.4,M,,*52Synopsis: time of fix (hhmmss), latitude, N/S, longitude, E/W, Fix quality (0=invalid, 1=GPS fix, 2=DGPS fix), number of satellites being tracked, horizontal dilution of position, altitude above sea level, M (meters), height of geoid (mean sea level) above WGS84 ellipsoid, time in seconds since last DGPS update, DGPS station ID number, checksum

http://yona_n.tripod.com/gps/gps-survey.html#topDifferent GPS Modules

 

Company Product Diagram Dimension(mm) Weight(gm)

Garmin GPS 25 Series gps engine

46.5x70x11.4 38

Motorola M12 Oncore GPS Receiver

40x60x10 25

Trimble Lassen SK-II gps module

83x31x10.2 19.6

U-box TIM gps module (SiRF based)

25x25x3 3

 

Company Product Picture Dimensions(mm) Weight(gms)

EMTAC GPSPCMCIA Receiver Card

Compatible With most of PDA/Notebook !

Type - II N/A

Teletype GPS

GPS WorldNavigator PCMCIA GPS Receiver

Type – II 30

Agis PteLtd

CF Type I 103x48x23 60

EMTAC D157N CF Type - I N/A

References

* List of companies and their products ( Including dimensions and weights)

http://yona_n.tripod.com/gps/gps-survey.html#top

* NMEA 0183 Protocol

http://www.scnt01426.pwp.blueyonder.co.uk/Articles/GPS/NMEA.htm

* GPS Fundamentals

http://www.navicom.co.kr/english/gps/fundamental.asp

* M-12 On-core and characteristics

http://www.motorola.com/ies/GPS/download/gpsusersguide/gpsusersguidev5chap3.pdf