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GPS+ Reference Manual

1. See Dilution of Precision DOP The shape of the earth if it were considered as a sea level surface extended continuously through the continents The geoid is an equipotential surface coincident with mean sea level to which at every point the plumb line direction in which gravity acts is perpendicular The geoid affected by local gravity disturbances has an irregular shape The reference ellipsoid surface that defines the coordinate system A satellite orbit along the equator that results in a constant fixed position over a particular reference point on the earth s surface GPS satellites are not geostationary GPS Reference Manual Glossary Global Positioning System GPS Great Circle Handshaking Heading Horizontal Dilution of Precision HDOP Horizontal and Time Dilution of Precision HTDOP Integer Ambiguity Estimates Iono Free Carrier Phase Observation Kinematic L Band L1 Frequency L2 Frequency Chapter 12 Full name is NAVSTAR Global Positioning System A space based radio positioning system which provides suitably equipped users with accurate position velocity and time data GPS provides this data free of direct user charge worldwide continuously and under all weather conditions The GPS constellation consists of 24 orbiting satellites four equally spaced around each of six different orbital planes The system is being developed by the Department of Defence under U S Air Fo
2. The GPS positioning velocity and time service which is available on a continuous worldwide basis to users authorized by the U S Department of Defence typically using P Code A number assigned by the GPS system designers to a given set of pseudorandom codes Typically a particular satellite will keep its PRN and hence its code assignment indefinitely or at least for a long period of time It is commonly used as a way to label a particular satellite An Earth based transmitter designed to mimic a satellite The calculated range from the GPS receiver to the satellite determined by taking the difference between the measured satellite transmit time and the receiver time of measurement and multiplying by the speed of light Contains several sources of error Measurements made using one of the pseudorandom codes on the GPS signals They provide an unambiguous measure of the range to the satellite including the effect of the satellite and user clock biases GPS Reference Manual 51 Chapter 12 Receiver Channels Reference Satellite Reference Station Relative Bearing Remote Station Residual Root Mean Square RMS Route Rover Station RT 20 Radio Technical Commission for Aeronautics RTCA Radio Technical Commission for Maritime Services RTCM Real Time Kinematic RTK SafeTrak Satellite Based Augmentation System SBAS Selective Availability SA Selected Waypoint 52 Glossary A GPS recei
3. Only L1 measurements are included in the set The observation set is assumed to contain information indicating how many satellites it contains and which ones have L1 only and which ones have L1 L1 pairs A wide area GPS correction service using L band satellite broadcast frequencies 1525 1560 MHz Data from many widely spaced Reference Stations is used in a proprietary multi site solution OmniSTAR Virtual Base Station VBS types achieve sub meter positioning over most land areas worldwide while OmniSTAR High Performance HP types achieve 10 cm accuracy Use of the OmniSTAR service requires a subscription The starting point of the present navigation leg expressed in latitude and longitude A receiver that monitors four or more satellites simultaneously with independent channels The even or odd quality of the number of ones or zeroes in a binary code Parity is often used to determine the integrity of data especially after transmission The point in a body s orbit at which it is nearest the earth Precise code or protected code A pseudorandom string of bits that is used by GPS receivers to determine the range to the transmitting GPS satellite P code is replaced by an encrypted Y code when Anti Spoofing is active Y code is intended to be available only to authorized primarily military users See Anti Spoofing C A Code and Y Code Position Dilution of Precision See Dilution of Precision DOP
4. See Dilution of Precision DOP By NMEA standards a data field which may or may not contain a decimal point and which may vary in precision following the decimal point depending on the requirements and the accuracy of the measuring device A reference point on a track A particular integer ambiguity value on one carrier phase range measurement or double difference carrier phase observation when the difference of the L1 and L2 measurements is used It is a carrier phase observable formed by subtracting L2 from L1 carrier phase data MD D gt The corresponding wavelength is 86 2 cm An ellipsoid designed to fit the shape of the entire Earth as well as possible with a single ellipsoid It is often used as a reference on a worldwide basis while other ellipsoids are used locally to provide a better fit to the Earth in a local region GPS uses the centre of the WGS84 ellipsoid as the centre of the GPS ECEF reference frame An encrypted form of P Code Satellites transmit Y Code in replace of P Code when Anti Spoofing is in effect See P Code and Anti Spoofing GPS Reference Manual 55 A accuracy 21 23 47 acquisition 39 45 46 49 almanac data 6 29 45 ambiguity 22 54 antenna 23 24 27 anti static 36 38 ascii 45 B base station 23 bearing 23 broadcast overview 6 buffer 49 C C A code 6 22 23 27 53 carrier phase 22 54 CDGPS 14 19 choke ring 27 circuit
5. 3 D or 3D Three Dimensional AC Alternating Current A D Analog to Digital ADR Accumulated Doppler Range ADR Accumulated Delta Range AGC Automatic Gain Control AL Alarm Limit AMSAT American Satellite APC Aircraft Power Conditioner ARNS Aeronautical Radio Navigation Services ARP Antennna Reference Point AS Anti Spoofing ASCII American Standard Code for Information Interchange ASIC Application Specific Integrated Circuits AVL Automated Vehicle Locations BCD Binary Coded Decimal BDE Borland Database Engine BDS Black Diamond System BIH Bureau International de l Heure BIST Built In Self Test BIT Built In Test BNR Binary Numerical Representation BPS Bits per Second BPSK Bi Phase Shift Key BSG Baseband Signal Generator BTS Conventional Terrestrial System BIH defined BW Bandwidth C A Code Coarse Acquisition Code CAN Controller Area Network CASM Coherent Adaptive Subcarrier Modulation CBIT Continuous Built In Test cc Cubic Centimeters CCITT Command Control and Intelligence Technical Test CD Clock Drift CD Compact Disc cd Change Directory CDGPS Canada Wide Differential Global Positioning System CDMA Code Division Multiple Access CDPD Cellular Digital Packet Data CE Conformit Europ enne CEP Circular Error Probable CISPR International Special Committee On Radio Interference CKSC Clock Status Card CLK System Clock CMG Course Made Good GPS Reference Manual 39 Chapter 11 40 CMP CMR
6. C No CoCom COG CPLD CPU CR CRC CRR CSA CTP CTS CTS CW dB dBm DC DCD DCE DCO DDS DGNSS DGPS DHCP DLL DoD DOP DPB DR DRAM DRMS DSP DSR DTE DTR D U ECEF EEPROM EGNOS EMC ESD ESN FAA FCC FDA FEC FEPROM FIFO FMEA Acronyms Comparator Message Processor Compact Measurement Record Post Correlation Carrier to Noise Ratio in dB Hz Coordinating Committee on Multilateral Export Controls Course Over Ground Complex Programmable Logic Device Central Processing Unit Carriage Return Cyclic Redundancy Check Common Reference Receiver Canada Shipping Act Conventional Terrestrial Pole Clear To Send Conventional Terrestrial System Continuous Wave Decibel Decibel Relative to 1 milliWatt Direct Current Data Carrier Detected Data Communications Equipment Modem Digitally Controlled Oscillator Direct Digital Sampling Differential Global Navigation Satellite System Differential Global Positioning System Dynamic Host Configuration Protocol Delay Lock Loop Department of Defence U S Dilution Of Precision Digital Pulse Blanking Dead Reckoning Dynamic Random Access Memory Distance Root Mean Square Digital Signal Processor Data Set Ready Data Terminal Equipment Data Terminal Ready Desired Undesired Eccentricity Earth Centred Earth Fixed Electrically Erasable Programmable Read Only Memory European Geo Stationary Navigation Overlay System Electromagnetic Compatibility Elect
7. antennas in general are more susceptible to the problems resulting from low angle multipath reception So for marine vessels this type of antenna encourages multipath reception However the advantages of good low angle reception also means that satellites can be acquired more easily while rising in the horizon As well vessels subject to pitch and roll conditions will experience fewer occurrences of satellite loss of lock Examples of the above antennas may be seen in Figure 11 Illustration of Quadrifilar vs Microstrip Patch Antennas on Page 25 A good antenna design will also incorporate some form of left hand circular polarization LHCP rejection Multipath signals change polarization during the refraction and reflection process This means that generally multipath signals may be LHCP oriented This property can be used to advantage by GPS antenna designers If a GPS antenna is well designed for RHCP polarization then LHCP multipath signals will automatically be attenuated somewhat during the induction into the antenna To further enhance performance antennas can be designed to increase the rejection of LHCP signals The Model 700 series of GPSAntennas are active antennas designed to operate at the GPS L1 and L2 frequencies 1575 42 and 1227 60 MHz The microstrip receiving elements are coupled to filters and a low noise amplifier LNA The units are optimized to receive right hand circularly polarized signals and their radiation patter
8. board 38 clock 6 8 47 51 constellation 5 49 conversion 7 33 35 45 coordinated universal time UTC 54 copyright 2 D data link 9 datum 48 delay lock loop 26 differential positioning 8 dilution of precision DOP 40 47 49 distance 33 Doppler 39 47 double differencing 27 E earth centered earth fixed ECEF 47 electrostatic discharge ESD 36 38 elevation 23 24 ellipsoid 53 54 ephemeris 6 29 52 errors in single point positioning 8 multipath 22 50 pseudorange 47 ESD see electrostatic discharge F frequency 25 47 G GDOP see dilution of precision GEO SBAS 12 geodetic datum see datum Geodetic Survey of Canada 32 geoid 47 53 GPS overview 5 9 standards and references 31 time 28 29 35 ground plane 23 25 H handshaking 49 HDOP see dilution of precision height antenna 23 dilution of precision 47 relationships 6 7 HTDOP see dilution of precision I initialization 29 K kinematic 10 26 GPS Reference Manual Index L latitude and longitude 5 47 L Band 6 17 19 loss of lock 29 M master control station 6 46 mean sea level 5 42 misclosure 52 mode navigation 29 multipath 21 27 N navigation 3 D 53 ephemeris 48 gps overview 5 mode 29 satellite system 40 NAVSTAR satellites 5 42 49 NMEA 32 noise number 43 non volatile memory NVM 28 50 NovAtel Inc 2 31 O OmniSTA
9. determine the day and time from that value calculations are performed to break down the number of seconds into day hour minute and second values For example starting with a GPS Time of Week of 511200 seconds the calculations are done as follows 511200 seconds Day of Week 511200 86400 seconds per day 5 916666667 days Hour 0 916666667 x 86400 3600 seconds per hour 22 0000 hours Minute 0 000 x 3600 60 seconds per minute 0 000 minutes Second 0 000 x 60 seconds per minute 0 000 seconds Therefore 511200 seconds represents day 5 Thursday 22 hours 0 minutes 0 seconds into Friday 9 6 2 Calendar Date to GPS Time Converting a calendar date to GPS Time is calculated as shown in the example below using the calendar date 13 30 hours January 28 2005 Years from January 6 1980 to January 28 2005 Number of days in 25 years 25 years x 365 days year Add one day for each leap year a year which is divisible by 4 but not by 100 unless it is divisible by 400 as every 100 years a leap year is skipped Add days from January 6 to January 27 January 28th is not finished Total days Total number of seconds 9154 days x 86400 seconds day Total number of weeks 790 905 600 seconds 604 800 seconds week Days into week 0 714285 x 7 days week Number of seconds in 5 days 5 days x 86400 seconds day Add number of seconds into the 6th day January 28th 13 5 hours x 3600 seconds hour Total seconds into week The res
10. for auto correlation of signals with a propagation delay of less than one C A code chip 300 meters E Figure 10 GPS Signal Multipath vs Increased Antenna Height GPS Reference Manual 23 Chapter 6 Multipath 6 4 24 When the antenna is in an environment with obstructions and reflective surfaces in the vicinity it is advantageous to mount the antenna as high as possible to reduce the obstructions as well as reception from reflective surfaces as much as possible See Figure 10 GPS Signal Multipath vs Increased Antenna Height on Page 23 for an example Water bodies are extremely good reflectors of GPS signals Because of the short wavelengths at GPS frequencies even small ponds and water puddles can be a strong source of multipath reception especially for low angle satellites Thus it can be concluded that water bodies such as lakes and oceans are among the most troublesome multipath environments for low angle signal reception Obviously water body reflections are a constant problem for ocean going vessels Antenna Designs Low angle reflections such as from water bodies can be reduced by careful selection of the antenna design For example flat plate microstrip patch antennas have relatively poor reception properties at low elevation angles near their radiation pattern horizon Quadrifilar helix antennas and other similar vertically high profile antennas tend to have high radiation gain patterns at the horizon These
11. is receiving corrections from multiple base stations Several L Band specific logs also exist and are prefixed by the letters RAWLBAND LBAND or OMNI CDGPS corrections are output similarly to SBAS corrections There are four SBAS fast corrections logs WAAS32 WAAS35 and one slow corrections log WAAS45 for CDGPS The CDGPS PRN is 209 lt In addition to a NovAtel receiver with L Band capability a subscription to the OmniSTAR or use of the free CDGPS service is required Consult Volume 2 of the OEM4 Manual set for more details on individual L Band commands and logs GPS Reference Manual 19 Chapter 5 L5 Overview The United States plans to implement a third civil GPS frequency L5 at 1176 45 MHz beginning with GPS satellites to be launched in 2005 This frequency is located within the 960 1215 MHz frequency band already used worldwide for Aeronautical Radio Navigation Services ARNS as well as by the Department of Defense DoD Certain measures have been taken within the United States to ensure that L5 can coexist with government systems operating at the same or nearby frequencies The carriers of the LS signal are modulated by two bit trains in phase quadrature The LS signal is contained within a 24 MHz band centered about L5 L5 power is increased by 6 dBW compared to the L1 signal 154 dBW versus 160 dBW This is equally split between an in phase I data channel and a quadrature Q data free channel which improves re
12. railway tracks soil with high moisture content water bodies etc One of the drawbacks of a flat plate ground plane is that it gives a hard boundary condition This means it allows electromagnetic waves to propagate along the ground plane and diffract strongly from its edge The soft boundary condition on the other hand will prevent the wave from propagating along the surface of the ground plane and thereby reducing the edge diffraction effects As a result the antenna will exhibit a completely different radiation pattern The soft boundary condition is typically achieved by a quarter wavelength deep transversely corrugated ground plane surface denoted as choke ring ground plane When the depth of the corrugation choke rings is equal to a quarter wavelength the surface wave vanishes and the surface impedance becomes infinite and hence provides the soft boundary condition for the electromagnetic field This results in modifications to GPS Reference Manual 25 Chapter 6 Multipath 6 6 the antenna radiation pattern that is characterized by low back lobe levels no ripples in the main lobe sharper amplitude roll off near the horizon and better phase center stability there are smaller variations in 2 axes This is what makes NovAtel s GPS antennas so successful when used with the NovAtel GPSAntenna choke ring ground plane NovAtel s Receiver Solutions for Multipath Reduction The multipath antenna har
13. the point where the frequency must be changed is not critical The North American OmniSTAR Network currently consists of ten permanent base stations in the Continental U S plus one in Mexico These eleven stations track all GPS satellites above 5 degrees elevation and compute corrections every 600 milliseconds The corrections are sent to the OmniSTAR Network Control Center NCC in Houston via wire networks At the NCC these messages are checked compressed and formed into packets for transmission up to the OmniSTAR satellite transponder This occurs approximately every few seconds A packet will contain the latest corrections from each of the North American base stations All of the eastern Canadian Provinces the Caribbean Islands Central America south of Mexico and South America is covered by a single satellite AM Sat A single subscription is available for all the areas covered by this satellite OmniSTAR currently has several high powered satellites in use around the World They provide coverage for most of the World s land areas Subscriptions are sold by geographic area Any Regional OmniSTAR service center can sell and activate subscriptions for any area They may be arranged prior to traveling to a new area or after arrival Contact OmniSTAR at www omnistar com for further details GPS Reference Manual L Band Positioning Chapter 4 4 1 2 Canada America Wide CDGPS The CDGPS service utilizes the MSAT 1 and MSAT 2 communicati
14. 0 6 A 1010 10 E 1110 14 3 0011 3 7 0111 7 B 1011 11 F 1111 15 Binary Decimal Binary Decimal Binary Decimal Binary Decimal 10000 16 100101 37 111010 58 1001111 79 10001 17 100110 38 111011 59 1010000 80 10010 18 100111 39 111100 60 1010001 81 10011 19 101000 40 111101 61 1010010 82 10100 20 101001 41 111110 62 1010011 83 10101 21 101010 42 111111 63 1010100 84 10110 22 101011 43 1000000 64 1010101 85 10111 23 101100 44 1000001 65 1010110 86 11000 24 101101 45 1000010 66 1010111 87 11001 25 101110 46 1000011 67 1011000 88 11010 26 101111 47 1000100 68 1011001 89 11011 27 110000 48 1000101 69 1011010 90 11100 28 110001 49 1000110 70 1011011 91 11101 29 110010 50 1000111 71 1011100 92 11110 30 110011 51 1001000 72 1011101 93 11111 31 110100 52 1001001 73 1011110 94 100000 32 110101 53 1001010 74 1011111 95 100001 33 110110 54 1001011 75 1100000 96 100010 34 110111 55 1001100 76 1100001 97 100011 35 111000 56 1001101 77 1100010 98 100100 36 111001 57 1001110 78 1100011 99 1100100 100 a These binary to decimal equivalents only go up to decimal 100 for the purpose of example Please use a calculator for other conversions 34 GPS Reference Manual 9 6 1 Unit Conversion 9 6 GPS Time Conversions Chapter 9 The following sections provided examples for converting to and from GPS time GPS Time of Week To Day of Week with Time of Day The value given for GPS Time of Week represents the number of seconds into the week Therefore to
15. 1 Fax 724 776 0790 E Mail CustomerService sae org Website http www sae org servlets index 32 GPS Reference Manual Chapter 9 Unit Conversion Sections 9 1 to 9 4 list commonly used equivalents between the SI Syst me Internationale units of weights and measures used in the metric system and those used in the imperial system A complete list of hexadecimal values with their binary equivalents is given in Section 9 5 while an example of the conversion from GPS time of week to calendar day is shown in Section 9 6 9 1 Distance 1 meter m 100 centimeters cm 1000 millimeters mm 1 kilometer km 1000 meters m 1 nautical mile 1852 m 1 international foot 0 3048 m 1 statute mile 1609 344 m 1 US survey foot 0 3048006096 m 1 inch 25 4 mm 9 2 Volume 1 liter 1 1000 cubic centimeters cc 1 gallon Imperial 4 546 liters 1 gallon US 3 785 liters 9 3 Temperature degrees Celsius 5 9 x degrees Fahrenheit 32 degrees Fahrenheit 9 5 x degrees Celsius 32 9 4 Weight 1 kilogram kg 1000 grams 1 pound 0 4536 kilogram kg GPS Reference Manual 33 Chapter 9 Unit Conversion 9 5 Hexadecimal Binary and Decimal Equivalents Hex Binary Decimal Hex Binary Decimal Hex Binary Decimal Hex Binary Decimal 0 0000 0 4 0100 4 8 1000 8 C 1100 12 1 0001 1 5 0101 5 9 1001 9 D 1101 13 2 0010 2 6 011
16. Current Volts Direct Current Variable Frequency Virtual Base Station standard OmniSTAR service Voltage Controlled Temperature Compensated Crystal Oscillator Vertical Dilution of Precision Vacuum Fluorescent Display Vertical Figure of Merit Voltage Standing Wave Ratio Wide Area Augmentation System WAAS Reference Receiver G H Wide Area DGPS World Geodetic System Windows Hardware Quality Lab Microsoft WAAS Message Processor Week number of almanac Waypoint Crosstrack Error Zero Velocity Update GPS Reference Manual Chapter 12 Glossary Acquisition Address Field Almanac Almanac Data Anti Spoofing ASCII Attenuation Azimuth Base Station Bearing Carrier Carrier Phase Ambiguity Carrier Phase Measurements The process of locking onto a satellite s C A code and P code A receiver acquires all available satellites when it is first powered up then acquires additional satellites as they become available and continues tracking them until they become unavailable For sentences in the NMEA standard the fixed length field following the beginning sentence delimiter HEX 24 For NMEA approved sentences composed of a two character talker identifier and a three character sentence formatter For proprietary sentences composed of the character P HEX 50 followed by a three character manufacturer identification code A set of orbit parameters that allows calculation of approximate
17. GPS Reference Manual 2 NX ovAtgei GPS Reference Manual Rev 0C Proprietary Notice GPS Reference Manual Revision Level OC Revision Date 2005 01 31 Proprietary Notice No part of this manual may be reproduced or transmitted in any form or by any means electronic or mechanical including photocopying and recording for any purpose without the express written permission of a duly authorized representative of NovAtel Inc The information contained within this manual is believed to be true and correct at the time of publication NovAtel MEDLL GPSolution Narrow Correlator tracking technology ProPak RT 20 and RT 2 are registered trademarks of NovAtel Inc SafeTrak SPAN technology PAC GPSCard and GPSAntenna are trademarks of NovAtel Inc All other brand names are trademarks of their respective holders Copyright 2000 2005 NovAtel Inc All rights reserved Unpublished rights reserved under International copyright laws 2 GPS Reference Manual Rev 0C Table of Contents Proprietary Notice 2 1 GPS Overview 5 1 1 GPS System Desin aet ha aa a aa E a a a a aai 5 TTA TNE Spaca EE 5 1 1 2 The Control Segment sssssssesseeesseesseseresttisstrssirrssinnstrnsstnnntnnntnnnennnntnnnt 6 1 173 The User Segment a aee a nae uar ena aa etanan eae Nap eea Ee a eee 6 1 2 Height Relationships sie aira AEEA EAEE 6 KS GPS Die len BETEN H 1 3 1 Single Point vs Relative Positioning cccccccceeeeee
18. GPS satellite positions and velocities The almanac is used by a GPS receiver to determine satellite visibility and as an aid during acquisition of GPS satellite signals A set of data which is downloaded from each satellite over the course of 12 5 minutes It contains orbital parameter approximations for all satellites GPS to universal standard time UTC conversion parameters and single frequency ionospheric model parameters Denial of the P code by the Control Segment is called Anti Spoofing It is normally replaced by encrypted Y code see P Code and Y Code A 7 bit wide serial code describing numbers upper and lower case characters special and non printing characters Typically used for textual data Reduction of signal strength The horizontal direction of a celestial point from a terrestrial point expressed as the angular distance from 000 reference clockwise through 360 The reference point is generally True North but may be Magnetic North or Relative ship s head The GPS receiver which is acting as the stationary reference It has a known position and transmits messages for the rover receiver to use to calculate its position The horizontal direction of one terrestrial point from another terrestrial point expressed as the angular distance from a reference direction usually measured from 000 at the reference direction clockwise through 360 The reference point may be True North Magnetic North or Rel
19. L Band Geostationary Satellite 6 L Band DGPS signal 7 Correction data are received and applied real time 8 DGPS uplink 18 GPS Reference Manual L Band Positioning Chapter 4 4 3 L Band Commands and Logs The ASSIGNLBAND command allows you to set OmniSTAR or CDGPS base station communication parameters It should include relevant frequencies for example assignlband omnistar 1551489 1200 or assignlband cdgps 1547547 4800 The PSRDIFFSOURCE command lets you identify from which base station to accept RTCA1 RTCM1 CDGPS or OmniSTAR VBS differential corrections For example in the PSRDIFFSOURCE command OMNISTAR enables OmniSTAR VBS and disables other DGPS types OmniSTAR VBS produces RTCM type corrections CDGPS produces WAAS type corrections AUTO means the first received RTCM or RTCA message has preference over an OmniSTAR VBS or CDGPS message The RTKSOURCE command lets you identify from which base station to accept RTK RTCM RTCA CMR and OmniSTAR HP differential corrections For example in the RTKSOURCE command OMNISTAR enables OmniSTAR HP if allowed and disables other RTK types OmniSTAR HP computes corrections in RTK float mode or within about 10 cm accuracy For RTK models AUTO means the NovAtel RTK filter is enabled and the first received RTCM RTCA or CMR message is selected For non RTK models AUTO means the OmniSTAR HP message if allowed is enabled The PSRDIFFSOURCE and RTKSOURCE commands are useful when the receiver
20. R 14 17 orbit period 6 oscillators 42 44 overview 20 P P code 45 parity 51 phase lock 22 polarity 21 poor reception 24 position 29 power 28 30 precision 6 7 9 processing 6 Doppler aiding 47 post mission 10 real time 7 10 propagation 21 23 27 56 pseudorange 8 22 51 pulse 39 43 R radio frequency RF 21 25 45 re acquisition 28 real time 7 9 10 residual 52 RF see radio frequency RMS see root mean square root mean square RMS 52 rover station 9 RTCA 31 RTCM 31 S satellite 30 acquisition 28 almanac 45 multipath 21 24 orbit arrangement 5 visibility 28 29 SBAS 12 13 segment 5 6 45 46 self test 29 39 signals 28 space vehicle number SVN 6 speed 51 static 36 38 support 31 surveying 7 8 SVN see space vehicle number T time to first fix TTFF 28 29 tracking 45 46 51 triangulation 22 trilateration 22 TTFF see time to first fix U U S National Geodetic Survey 32 UTC see coordinated universal time GPS Reference Manual Index NM velocity 5 6 47 51 W website 31 32 WGS84 54 Y Y code 45 GPS Reference Manual 57
21. RTK solution convergence The advantages of using SPAN technology are its ability to e Provide a full attitude solution roll pitch and azimuth e Provide continuous solution output in situations when a GPS only solution is impossible e Provide faster signal reacquisition and RTK solution resolution over stand alone GPS because of the tightly integrated GPS and IMU observations e Output high rate up to 100 Hz position velocity and attitude solutions for high dynamic applications e Use raw phase observation data to constrain INS solution drift even when too few satellites are available for a full GPS solution 11 GPS Reference Manual Chapter 3 Satellite Based Augmentation System A Satellite Based Augmentation System SBAS is a type of geo stationary satellite system that improves the accuracy integrity and availability of the basic GPS signals Accuracy is enhanced through the use of wide area corrections for GPS satellite orbits and ionospheric errors Integrity is enhanced by the SBAS network quickly detecting satellite signal errors and sending alerts to receivers to not use the failed satellite Availability is improved by providing an additional ranging signal to each SBAS geostationary satellite SBAS includes the Wide Area Augmentation System WAAS the European Geo Stationary Navigation System EGNOS and the MTSAT Satellite Based Augmentation System MSAS At the time of publication there are two WAAS satell
22. S SPS SIGNAL SPECIFICATION REFERENCE For copies of the Interface Control Document ICD GPS 200 contact ARINC Research Corporation 2551 Riva Road Annapolis MD 21401 7465 Phone 800 633 6882 Fax 410 573 3300 Website http www arinc com GPS Reference Manual 31 Chapter 8 Standards References NMEA REFERENCE National Marine Electronics Association 0183 Standard for Interfacing Marine Electronic Devices NMEA Executive Director Seven Riggs Avenue Severna Park MD 21146 Phone 410 975 9425 Fax 410 975 9450 E Mail info nmea org Website http www nmea org GEODETIC SURVEY OF CANADA Natural Resources Canada Geodetic Survey Division Geomatics Canada 615 Booth Street Room 440 Ottawa Ontario Canada K1A OPO Phone 613 995 4410 Fax 613 995 3215 E Mail information geod nrcan gc ca_ Website http www geod nrcan gc ca U S NATIONAL GEODETIC SURVEY NGS Information Services NOAA N NGS12 National Geodetic Survey SSMC 3 9202 1315 East West Highway Silver Spring MD 20910 3282 Phone 301 713 3242 Fax 301 713 4172 E Mail ngs infocenter noaa gov Website http www ngs noaa gov NAVSTAR GPS NAVSTAR GPS United States Naval Observatory USNO 3450 Massachusetts Avenue NW Washington DC 20392 5420 Phone 202 762 1467 Website http tycho usno navy mil gps html SOCIETY OF AUTOMOTIVE ENGINEERING SAE World Headquarters 400 Commonwealth Drive Warrendale PA 15096 0001 USA Phone 724 776 484
23. Track Made Good however Course Made Good is the more correct term The actual path of a vessel with respect to the Earth a misnomer in that courses are directions steered or intended to be steered through the water with respect to areference meridian this will not be a straight line if the vessel s heading yaws back and forth across the course The distance from the vessel s present position to the closest point on a great XTE Circle line connecting the current waypoint coordinates If a track offset has been specified in the receiver SETNAV command the cross track error will be relative to the offset track great circle line When the carrier phase measurement jumps by an arbitrary number of integer cycles It is generally caused by a break in the signal tracking due to shading or some similar occurrence GPS Reference Manual Glossary Dead Reckoning Destination Differential GPS DGPS Dilution of Precision DOP Doppler Doppler Aiding Double Difference Double Difference Carrier Phase Ambiguity Earth Centred Earth Fixed ECEF Eccentricity e Elevation Ellipsoid Ellipsoidal Height Chapter 12 The process of determining a vessel s approximate position by applying DR from its last known position a vector or a series of consecutive vectors representing the run that has since been made using only the courses being steered and the distance run as determined by log engine rpm or calc
24. aeeeseeaeseeeeeeesaeeseeeees 29 8 Standards References 31 9 Unit Conversion 33 GPS Reference Manual Table of Contents O TDIStANCE aaa views EE RE T oad olds deed ER tasbin ERAN 33 Te NODEEL a rete eda EE Mareen eebe 33 T3 Temperat Erie a ee D ee EE ee dese Ee 33 OF NN eebe ege n e ELE coher Deele ee DEE e ele ea 33 9 5 Hexadecimal Binary and Decimal Eouivalemts AA 34 GE Neel E 35 9 6 1 GPS Time of Week To Day of Week with Time of Day 35 9 6 2 Calendar Date to GPS Time nnet 35 10 Electrostatic Discharge Control ESD Practices 36 MOET OVGIVIOW Soe ee eer ee ad eee 36 10 2 Handling ESD Sensitive Devices ccceccececeeeeeeeeneeeeeeeeecaaeeeeeneeeseaeeeseeeeesaees 36 10 3 Prime Static Accumulators 0 0cceeeececeeeeeeeeeeceeeeeeceaeeeeeeeeseaaeseeaaeeseeeeesaaesseness 37 10 4 Handling Printed Circuit Boards eccccecseeceeeeceeeeeeeeeeeeeeeaeeeeaaeeseeeessaeeeeenees 38 11 Acronyms 39 12 Glossary 45 GPS Reference Manual Chapter 1 GPS Overview The Global Positioning System GPS is a satellite navigation system capable of providing a highly accurate continuous global navigation service independent of other positioning aids GPS provides 24 hour all weather worldwide coverage with position velocity and timing information The system uses the NAVSTAR NAVigation Satellite Timing And Ranging satellites which consists of 24 operational satellites to provide a GPS receiver with at least six satellites i
25. aligning it with the received PRN code A cross correlation check is performed to check alignment and the cross correlation channel shifts its code phase repeatedly to measure the power If neccessary the tracking channel re acquires the satellite to remove the cross correlation error A type of geo stationary satellite system that improves the accuracy integrity and availability of the basic GPS signals This includes WAAS EGNOS and MSAS The method used by the United States Department of Defence to control access to the full accuracy achievable by civilian GPS equipment generally by introducing timing and ephemeris errors The waypoint currently selected to be the point toward which the vessel is travelling Also called to waypoint destination or destination waypoint GPS Reference Manual Glossary Sequential Receiver Signal Quality Monitoring SQM Spherical Error Probable SEP Spheroid Standard Positioning Service SPS Space Vehicle ID SV TDOP Three Dimensional Coverage hours Three Dimensional 3D Navigation Time To First Fix TTFF Track Made Good True Bearing True Heading Two Dimensional 2D Coverage Two Dimensional Navigation Undulation Chapter 12 A GPS receiver in which the number of satellite signals to be tracked exceeds the number of available hardware channels Sequential receivers periodically reassign hardware channels to particular satellite signals in a predeterm
26. asurements Obviously anything other than direct line of sight reception will skew and bias the range measurements and thus the positioning triangulation or more correctly trilateration Unfortunately multipath is almost always present to some degree due to real world conditions When a GPS multipath signal converges at the GPS antenna there are two primary problems that occur 1 a multiple signal with amplitude and phase shifting and 2 a multiple signal with differing ranges When a direct signal and multipath signal are intercepted by the GPS antenna the two signals will sum according to the phase and amplitude of each This summation of signals causes the composite to vary greatly in amplitude depending on the degree of phase shift between the direct signal versus the multipath signal If the multipath signal lags the direct path signal by less than 90 the composite signal will increase in amplitude relative to the direct signal depending on the degree of phase shift between 0 and 90 As well if the multipath signal lags the direct path signal by greater than 90 but less than 270 the composite signal will decrease in amplitude Depending on the relative amplitude of the multipath signal or signals the composite signal being processed by the receiver correlator may experience substantial amplitude variations A worst case scenario is when the multipath signal experiences a lag of 180 and is near the same strength as the d
27. atellites For example if a user views 10 satellites but has 90 coverage then there are no corrections available for one of the satellites In that case our firmware shows that a correction is missing for that SV and excludes it from the position calculation 16 GPS Reference Manual L Band Positioning Chapter 4 4 2 L Band Service Levels Two levels of service are available Standard Sub meter accuracy from OmniSTAR VBS and CDGPS High Performance Sub decimeter accuracy from OmniSTAR HP 4 2 1 Standard Service The OmniSTAR VBS service uses multiple GPS base stations in a solution and reduces errors due to the GPS signals traveling through the atmosphere It uses a wide area DGPS solution WADGPS and data from a relatively small number of base stations to provide consistent accuracy over large areas A unique method of solving for atmospheric delays and weighting of distant base stations achieves sub meter capability over the entire coverage area regardless of your location relative to any base station This achieves a truly wide area system with consistent characteristics CDGPS is able to simultaneously track two satellites and incorporate the corrections into the position The output is SBAS like see WAAS32 WAAS45 in Volume 2 of the OEM4 Manual set and can incorporate these corrections to generate differential quality position solutions CDGPS allows anyone within the area of coverage to take advantage of its benefits NovAte
28. ative ship s head The steady transmitted RF signal whose amplitude frequency or phase may be modulated to carry information The number of integer carrier phase cycles between the user and the satellite at the start of tracking Sometimes ambiguity for short These are accumulated doppler range ADR measurements They contain the instantaneous phase of the signal modulo 1 cycle plus some arbitrary number of integer cycles Once the receiver is tracking the satellite the integer number of cycles correctly accumulates the change in range seen by the receiver When a lock break occurs this accumulated value can jump an arbitrary integer number of cycles this is called a cycle slip GPS Reference Manual 45 Chapter 12 Checksum Circular Error Probable CEP Coarse Acquisition C A Code Communication Protocol Control Segment Coordinated Universal Time UTC Course Course Made Good CMG Course Over Ground COG Cross Track Error XTE Cycle Slip 46 Glossary By NMEA standard a validity check performed on the data contained in the sentences calculated by the talker appended to the message then recalculated by the listener for comparison to determine if the message was received correctly Required for some sentences optional for all others Circular error probable the radius of a circle such that 50 of a set of events occur inside the boundary A pseudorandom string of bi
29. ay wish to refer to NAVSAT GPS L5 Signal Specification Document No RTCA DO 261 20 GPS Reference Manual Chapter 6 6 1 Multipath signal reception is one of the most plaguing problems that detracts from the accuracy potential of GPS pseudorange differential positioning systems This section provides a brief look at the problems of multipath reception and some solutions Multipath occurs when an RF signal arrives at the receiving antenna from more than one propagation route multiple propagation paths see Figure 9 Figure 9 Illustration of GPS Signal Multipath Why Does Multipath Occur When the GPS signal is emitted from the satellite antenna the RF signal propagates away from the antenna in many directions Because the RF signal is emitted in many directions simultaneously and is traveling different paths these signals encounter various and differing natural and man made objects along the various propagation routes Whenever a change in medium is encountered the signal is either absorbed attenuated refracted or reflected Refraction and reflection cause the signals to change direction of propagation This change in path directions often results in a convergence of the direct path signal with one or more of the reflected signals When the receiving antenna is the point of convergence for these multipath signals the consequences are generally not favorable Whenever the signal is refracted some signal polarity shif
30. being tracked The position solution generated by the receiver is initially developed in earth centered coordinates which can subsequently be converted to any other coordinate system With as few as four GPS satellites in view the absolute position of the receiver in three dimensional space can be determined Only one receiver is needed In relative positioning also known as differential positioning the coordinates of a GPS receiver at an unknown point the rover station are sought with respect to a GPS receiver at a known point the base station The concept is illustrated in Figure 4 Example of Differential Positioning on Page H The relative position accuracy of two receivers locked on the same satellites and not far removed from each other up to tens of kilometers is extremely high The largest error contributors in single point positioning are those associated with atmospheric induced effects These errors however are highly correlated for adjacent receivers and hence cancel out in relative measurements Since the position of the base station can be determined to a high degree of accuracy using conventional surveying techniques any differences between its known position and the position computed using GPS techniques can be attributed to various components of error as well as the receiver s clock bias Once the estimated clock bias is removed the remaining error on each pseudorange can be determined The base station sends inf
31. ces starting on Page 31 Why is this important for GPS users The above formula is critical for GPS users as they typically obtain ellipsoid heights and need to convert these into mean sea level heights Once this conversion is complete users can relate their GPS derived heights to more usable mean sea level heights 1 3 GPS Positioning GPS positioning can be categorized as follows 1 single point or relative 2 static or kinematic 3 real time or post mission data processing A distinction should be made between accuracy and precision Accuracy refers to how close an GPS Reference Manual 7 Chapter 1 GPS Overview estimate or measurement is to the true but unknown value precision refers to how close an estimate is to the mean average estimate Figure 3 illustrates various relationships between these two parameters the true value is located at the intersection of the cross hairs the centre of the shaded area is the location of the mean estimate and the radius of the shaded area is a measure of the uncertainty contained in the estimate High accuracy Low accuracy high precision high precision High accuracy Low accuracy low precision low precision Figure 3 Accuracy versus Precision 1 3 1 Single Point vs Relative Positioning In single point positioning coordinates of a GPS receiver at an unknown location are sought with respect to the earth s reference frame by using the known positions of GPS satellites
32. d by an IMU to calculate acceleration velocity and attitude This capability is embedded in the firmware of our plus series of receivers Forces are measured by accelerometers in three perpendicular axes within the IMU and the gyros measure rotations around those axes Over short periods of time inertial navigation gives very accurate acceleration velocity and attitude output The IMU must have prior knowledge of its initial position initial velocity initial attitude Earth rotation rate and gravity field Since the IMU sensor measures changes in orientation and acceleration the INS determines changes in position and attitude but initial values for these parameters must be provided from an external source Once these parameters are known an INS is capable of providing an autonomous solution with no external inputs However because of errors in the IMU sensor measurements that accumulate over time an inertial only solution will degrade with time unless external updates such as position velocity or attitude are supplied NovAtel s SPAN system s combined GPS INS solution integrates the raw inertial measurements with all available GPS solution and raw measurement information to provide the optimum solution possible in any situation By using the high accuracy of the GPS solution the INS measurement errors can be modeled and mitigated Conversely the continuity and relative accuracy of the INS solution enables faster GPS signal reacquisition and
33. dware solutions described in the previous paragraphs are capable of achieving varying degrees of multipath reception reduction These options however require specific conscious efforts on the part of the GPS user In many situations especially kinematic few if any of the above solutions may be effective or even possible to incorporate By far the best solutions are those which require little or no special efforts in the field on the part of the GPS user This is what makes NovAtel s internal receiver solutions so desirable and practical NovAtel has placed long term concerted effort into the development of internal receiver solutions and techniques that achieve multipath reduction all of which are transparent to the receiver user These achievements have led first to Narrow Correlator tracking technology and now PAC technology It utilizes innovative patented correlator delay lock loop DLL techniques As it is beyond the scope of this manual to describe in detail how the correlator techniques achieve the various levels of performance the following paragraphs will provide highlights of the advantages of PAC technology 6 6 1 Pulse Aperture Correlator Technology PAC 26 NovAtel s OEM4 family of receivers achieve a higher level of pseudorange positioning performance versus standard wide or narrow correlator receivers by virtue of its celebrated PAC technology By utilizing PAC tracking techniques the receiver is capable of pseudorange
34. e Frequency International Geometric Reference Field Intermodulation Integrated Multipath Limiting Antenna Inertial Measuring Unit Inhibit Inertial Navigation System Input Output Issue of Data Ephemeris Internet Protocol Interrupt Request IF Signal Generator International Standards Organization Klystron Power Amplifier The 1575 42 MHz GPS carrier frequency including C A and P Code The 1227 60 MHz 2nd GPS carrier frequency P Code only The 1176 45 MHz 3rd civil GPS frequency that tracks carrier at low signal to noise ratios GPS Reference Manual 41 Chapter 11 42 LAAS LCD LED LF LGF LHCP LNA LO LSB MAT MEDLL MET MGRS MHz MINOS MKI MMCX MOPS MPC MPM ms MSAS MSB MSL MSR MTBF MTSAT NAS NAV NAVSTAR N C NCC NCO NH NMEA NOC ns NVM OBS OCXO OEM PAC PC P Code PCB PCMCIA PDF PDF PDOP PIN Acronyms Local Area Augmentation System Liquid Crystal Display Light Emitting Diode Line Feed LAAS Ground Facility Left Hand Circular Polarization Low Noise Amplifier Local Oscillator Least significant bit Multipath Assessment Tool Multipath Estimating Delay Lock Loop Multipath Elimination Technology Military Grid Reference System MegaHertz Multiple Independent NOmadic Stargazer Mark Input Multimedia Communications Exchange Lucent Minimum Operational Performance Standard Modulated Precision Clock Multipath Meter Millisecond MTSAT Satellite Based Augmentation S
35. eeeeeeeeeeeeeeseeeseeeeeeeneees 8 1 3 2 Static vs Kinematic Positionimg 10 1 3 3 Real time vs Post mission Data Proceseimg 10 2 INS Overview 11 3 Satellite Based Augmentation System 12 EEN EE 13 4 L Band Positioning 14 A Ni COVELAGE EE 14 4 1 1 Worldwide OmnTAb 14 4 1 2 Canada America Wide CDR 15 4 2 L Band Service Levels cccscceceeeceeseeeeceeaeeeeaaeeeeceeeeeeaaeeseeeeseaaeeeeeeeeeeiaaeeneaees 17 NEE Elte BET 17 4 2 2 High Performance Genice 17 4 3 L Band Commands and COQS escissrirena etnian aiana eae aeina paaa iaeiei ae naiaiae 19 5 L5 Overview 20 6 Multipath 21 6 1 Why Does Multipath Occur ceecceeececeeeneeeeeceeeeeaeeeceaaeeeseaeesseaeeeseaaeeseeaeeeeaeees 21 6 2 Consequences of Multipath Reception ceecceeeeceeeeeeeceseeeeeseaeeeeeeeeessaeeenennees 22 6 3 Hardware Solutions For Multipath Reduction cccccceeseeeeseeeeseeeseeteeeenaeees 23 6 3 1 Antenna Site Selection cccceccceceseeeeeeeeeeeneeeeeeeeeeeaeeseaeessaaeeseeeeeetaaeeeea 23 6 4 ul EE 24 6 5 Antenna Ground Planes 25 6 6 NovAtel s Receiver Solutions for Multipath Reduction ssessssesseeesseeesreeereeenn 26 6 6 1 Pulse Aperture Correlator Technology PAC sseseeeseeesessreereseresnnsns 26 6 6 2 SUMMARY haste seen Ge aleve ih dale Qala aia Maeve 27 7 TTFF and Satellite Acquisition 28 7 1 OEM4 based Producls AA 28 7 2 SUPERSTAR Il based Products cc cccceeeeeeeeeeeeeceeeeeaeeese
36. efits of PAC technology becomes most significant during pseudorange DGPS operation where the GPS system biases are largely removed Receivers operating DGPS with standard correlators typically achieve positioning accuracies in the two to five meter CEP range low multipath environment and using a choke ring ground plane or GPS Reference Manual Multipath Chapter 6 GPS 702 antenna NovAtel s Narrow Correlator tracking technology receivers are able to achieve accuracies in the order of 0 75m CEP while NovAtel s PAC technology receivers are able to achieve accuracies in the 0 35 to 0 5 m CEP PAC technology achieves this higher accuracy through a combination of low noise ranging measurements combined with a very narrow correlation window that dramatically reduces the effects of multipath interference and distortion Wide Correlator D Narrow Correlator Pseudorange Error m Multipath induced tracking etror in the pressence of a Half Power Multipath Signal Multipath Delay C A code chip Figure 12 Comparison of Multipath Envelopes 6 6 2 Summary Any localized propagation delays or multipath signal reception cause biases to the GPS ranging measurements that cannot be differenced by traditional DGPS single or double differencing techniques Multipath is recognized as the greatest source of errors encountered by a system operating in single point or differential mode It has been discussed that car
37. eful site selection and the GPSAntenna Model 700 or good antenna design combined with a choke ring ground plane are fairly effective means of reducing multipath reception Internal receiver solutions for multipath elimination are achieved through various types of correlation techniques where the standard correlator is the reference by which all other techniques can be compared PAC technology has a four fold advantage over standard correlators improved ranging measurements due to a sharper less noisy correlation peak and reduced susceptibility to multipath due to rejection of C A code delays of greater than 1 0 chip When used with a choke ring ground plane PAC technology provides substantial performance gains over standard or narrow correlator receivers operating in differential mode GPS Reference Manual 27 Chapter 7 TTFF and Satellite Acquisition 7 1 Time to First Fix or TTFF is the time it takes the receiver to calculate a position after a reset or upon power up The TTFF varies and depends on what is stored in non volatile memory NVM at the time of power up and on what other information is available The speed at which the receiver locates and locks onto new satellites is improved if the receiver has approximate time and position as well as an almanac This allows the receiver to compute the elevation of each satellite so it can tell which satellites are visible and their Doppler offsets improving TTFF Without thi
38. ellites greater than 5 elevation above the horizon HDOP lt 6 Bo O The time allowed for self test and device initialization is less than 5 seconds In the case where the following additional conditions are met the TTFF is reduced to 15 seconds e Unit has not been off for more than a week before nominal power is re applied e Last navigation fix occurred within the last 2 hours e Valid ephemeris data less than 4 hours old for at least 5 satellites GPS Reference Manual 29 Chapter 7 TTFF and Satellite Acquisition 30 With no initialization the time from power application to valid navigation output is typically 2 minutes There is no disruption of navigation data output when a satellite signal is lost unless there is a power interruption for a period of less than or equal to 200 ms Also the receiver re acquires the satellite signal within 0 3 seconds after satellite visibility has been restored When a satellite signal is lost due to signal masking the signal is typically re acquired within 2 3 seconds after the satellite signal meets the minimum input levels The vehicle dynamics during the masking period are assumed to be less than or equal to 0 5 g acceleration and 100 m s velocity When total signal masking occurs navigation resumes within 3 5 seconds of a Navigation mode criteria being met The receiver is capable of acquiring satellite signals with a minimum input carrier to noise density ratio C NO to the correlat
39. ent to a repair center having complete facilities or to the manufacturer for exchange or repair GPS Reference Manual 36 Electrostatic Discharge Control ESD Practices Chapter 10 Where protective measures have not been installed a suitable alternative would be the use of a Portable Field Service Grounding Kit for example 3M Kit 8501 or 8507 This consists of a portable mat and wrist strap which must be attached to a suitable ground A circuit board in a static shielding bag or clamshell may be shipped or stored in a cardboard carton but the carton must not enter a static controlled area such as a grounded or dissipative bench top or repair zone Do not place anything else inside the bag for example repair tags Treat all PCBs and components as ESD sensitive Assume that you will damage the PCB or component if you are not ESD conscious Do not use torn or punctured static shielding bags A wire tag protruding through the bag could act as a lightning rod funneling the entire charge into the components inside the bag e Do not allow chargeable plastics such as binders within 0 6 m of unshielded PCBs e Do not allow a PCB to come within 0 3 m of a computer monitor 10 3 Prime Static Accumulators Table 3 provides some background information on static accumulating materials Table 3 Static Accumulating Materials Work Surfaces formica waxed or highly resistive finished wood synthetic mats writing material
40. heights are referenced to this surface What is an ellipsoid An ellipsoid also known as a spheroid is a mathematical surface which is sometimes used to represent the earth Whenever you see latitudes and longitudes describing the location this coordinate is being referenced to a specific ellipsoid GPS positions are referred to an ellipsoid known as WGS84 World Geodetic System of 1984 What is the relationship between a geoid and an ellipsoid The relationship between a geoid and an ellipsoid is shown in Figure 2 Illustration of Receiver Height Measurements on Page 7 GPS Reference Manual GPS Overview Chapter 1 References 1 Topography 2 Geoid mean sea level 3 Spheroid ellipsoid H Receiver computed height above below geoid N Geoidal Height undulation h GPS system computed height above the spheroid N h H Figure 2 Illustration of Receiver Height Measurements From the above diagram and the formula h H N to convert heights between the ellipsoid and geoid we require the geoid ellipsoid separation value This value is not easy to determine A world wide model is generally used to provide these values NovAtel GPS receivers store this value internally This model can also be augmented with local height and gravity information A more precise geoid model is available from government survey agencies for example U S National Geodetic Survey or Geodetic Survey of Canada see Chapter 8 Standards Referen
41. ined sequence Signal Quality Monitoring SQM technology is used to monitor GPS and GEO signals in space for anomalous behavior The radius of a sphere centred at the user s true location that contains 50 percent of the individual three dimensional position measurements made using a particular navigation system Sometimes known as ellipsoid a perfect mathematical figure which very closely approximates the geoid Used as a surface of reference for geodetic surveys A positioning service made available by the United States Department of Defence which is available to all GPS civilian users on a continuous worldwide basis typically using C A Code Sometimes used as SVID A unique number assigned to each satellite for identification purposes The space vehicle is a GPS satellite Time Dilution of Precision See Dilution of Precision DOP The number of hours per day when four or more satellites are available with acceptable positioning geometry Four visible satellites are required to determine location and altitude Navigation mode in which altitude and horizontal position are determined from satellite range measurements The actual time required by a GPS receiver to achieve a position solution This specification will vary with the operating state of the receiver the length of time since the last position fix the location of the last fix and the specific receiver design The single resultant direction from a po
42. int of departure to a point of arrival or subsequent position at any given time may be considered synonymous with Course Made Good Bearing relative to true north compass bearing corrected for compass error Heading relative to true north The number of hours per day with three or more satellites visible Three visible satellites can be used to determine location if the GPS receiver is designed to accept an external altitude input Navigation mode in which a fixed value of altitude is used for one or more position calculations while horizontal 2D position can vary freely based on satellite range measurements The distance of the geoid above positive or below negative the mathematical reference ellipsoid spheroid Also known as geoidal separation geoidal undulation geoidal height GPS Reference Manual 53 Chapter 12 Universal Time Coordinated Update Rate UTC VDOP Variable Field Waypoint Wide Lane World Geodetic System 1984 WGS84 Y Code 54 Glossary This time system uses the second defined true angular rotation of the Earth measured as if the Earth rotated about its Conventional Terrestrial Pole However UTC is adjusted only in increments of one second The time zone of UTC is that of Greenwich Mean Time GMT The GPS receiver specification which indicates the solution rate provided by the receiver when operating normally See Universal Time Coordinated Vertical Dilution of Precision
43. irect path signal this will cause the multipath signal to almost completely cancel out the direct path signal resulting in loss of satellite phase lock or even code lock Because a multipath signal travels a greater distance to arrive at the GPS antenna the two C A code correlations are by varying degrees displaced in time which in turn causes distortion in the correlation peak and thus ambiguity errors in the pseudorange and carrier phase if applicable measurements As mentioned in previous paragraphs it is possible that the received multipath signal has greater amplitude than the direct path signal In such a situation the multipath signal becomes the dominant signal and receiver pseudorange errors become significant due to dominant multipath biases and may exceed 150 meters For single point pseudorange positioning these occasional levels of error may be tolerable as the accuracy expectations are at the 1 to 5 meter CEP level depending on the GPS card model and using a standard correlator However for pseudorange single differencing DGPS users the accuracy expectations are at the one to 0 45 to 1 meter CEP level depending on the GPS card GPS Reference Manual Multipath Chapter 6 model and with no multipath Obviously multipath biases now become a major consideration in trying to achieve the best possible pseudorange measurements and position accuracy If a differential base station is subject to significant multipath cond
44. ites over the western Atlantic Ocean and the Pacific PRN 122 and PRN 134 respectively and one EGNOS satellite over the eastern Atlantic Ocean PRN 120 SBAS data is available from any of these satellites and more satellites will be available in the future The primary functions of SBAS include edata collection edetermining ionospheric corrections edetermining satellite orbits edetermining satellite clock corrections edetermining satellite integrity independent data verification SBAS message broadcast and ranging system operations amp maintenance As shown in Figure 5 The SBAS Concept on Page 13 the SBAS is made up of a series of Reference Stations Master Stations Ground Uplink Stations and Geostationary Satellites GEOs The Reference Stations which are geographically distributed pick up GPS satellite data and route it to the Master Stations where wide area corrections are generated These corrections are sent to the Ground Uplink Stations which up link them to the GEOs for re transmission on the GPS L1 frequency These GEOs transmit signals which carry accuracy and integrity messages and which also provide additional ranging signals for added availability continuity and accuracy These GEO signals are available over a wide area and can be received and processed by NovAtel receivers with appropriate firmware GPS user receivers are thus able to receive SBAS data in band and use not only differential corrections but also integrit
45. itions this in turn will bias the range corrections transmitted to the differential rover receiver And in turn if the rover receiver also experiences a high level of multipath the rover receiver position solutions will be significantly biased by multipath from both stations Thus when the best possible position solutions are required multipath is certainly a phenomenon that requires serious consideration 6 3 Hardware Solutions For Multipath Reduction A few options exist by which GPS users may reduce the level of multipath reception Among these include antenna site selection special antenna design and ground plane options 6 3 1 Antenna Site Selection Multipath reception is basically a condition caused by environmental circumstances Some of these conditions you may have a choice about and some you may not Many GPS reception problems can be reduced to some degree by careful antenna site selection Of primary importance is to place the antenna so that unobstructed line of sight reception is possible from horizon to horizon and at all bearings and elevation angles from the antenna This is of course the ideal situation which may not be possible under actual operating conditions Try to place the antenna as far as possible from obvious reflective objects especially reflective objects that are above the antenna s radiation pattern horizon Close in reflections will be stronger and typically have a shorter propagation delay allowing
46. ity value on one carrier phase range measurement or double difference carrier phase observation The type of measurement is not specified L1 L2 L1 L2 iono free An observation set as described below taken by the receiver on which the software is operating A coordinate system based on a plane tangent to the ellipsoid s surface at the Planeuser s location The three coordinates are east north and up Latitude longitude and height positions operate in this coordinate system A position solution which is based on a prediction A model based on previous base station observations is used to estimate what the observations will be at a given time epoch These estimated base station observations are combined with actual measurements taken at the rover station to provide a position solution Bearing relative to magnetic north compass bearing corrected for deviation Heading relative to magnetic north The angle between the magnetic and geographic meridians at any place expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north The minimum GPS satellite elevation angle permitted by a particular receiver design Satellites below this angle will not be used in position solution Observations from both the base station and the local receiver which have been matched by time epoch contain the same satellites and are corrected for any known offsets The square of the standard deviation
47. l s ProPak LBplus provides GPS with L Band corrections in one unit using a common antenna This means that with CDGPS or a subscription to the OmniSTAR VBS service the ProPak LBplus is a high quality receiver with sub meter capabilities The position from the GPSCard in the receiver is used as the L Band system s first approximation After the L Band processor has taken care of the atmospheric corrections it then uses its location versus the base station locations in an inverse distance weighted least squares solution L Band technology generates corrections optimized for the location It is this technique that enables the L Band receiver to operate independently and consistently over the entire coverage area without regard to where it is in relation to the base stations 4 2 2 High Performance Service The OmniSTAR High Performance HP service gives you more accuracy than the OmniSTAR VBS or CDGPS services OmniSTAR HP computes corrections in dual frequency RTK float mode within about 10 cm accuracy To obtain OmniSTAR HP corrections your receiver must have an HP subscription from OmniSTAR GPS Reference Manual 17 Chapter 4 L Band Positioning 5 DAIS W D O O A ee A ge i ee Figure 8 OmniSTAR Concept Reference Description 1 GPS satellites 2 Multiple L Band ground stations 3 Send GPS corrections to 4 4 Network Control Center where data corrections are checked and repackaged for uplink to 5 5
48. measurement improvements better than 4 1 when compared to standard wide correlation techniques and 2 1 when compared to narrow correlation techniques The PAC technology dramatically reduces multipath reception approaching a factor of 16 compared to standard correlators and 8 compared to narrow correlators by virtue of its very narrow correlation function Figure 12 Comparison of Multipath Envelopes on Page 27 illustrates relative multipath induced tracking errors encountered by the different correlation technologies As can be seen standard correlators are susceptible to substantial multipath biases for C A code chip delays of up to 1 5 chips with the most significant C A code multipath bias errors occurring at about 0 25 to 0 75 chips approaching 80 m error The Narrow Correlator tracking technology multipath susceptibility peaks at about 0 2 chips about 10 m error and remains relatively constant out to 0 95 chips where it rapidly declines to negligible error after 1 1 chips On the other hand the PAC technology multipath susceptibility peaks at about 0 1 chips about 5 m error then reduces to a negligible amount at about the 0 2 chip mark While positioning in single point mode the multipath and ranging improvement benefits of a PAC technology receiver versus narrow or standard correlators are overridden by a multitude of GPS system biases and errors In either case positioning accuracy will be in the order of 1 8 m CEP However the ben
49. n a simple measurement on that frequency The user s GPS antenna is moving In GPS this term is typically used with precise carrier phase positioning and the term dynamic is used with pseudorange positioning The range of radio frequencies that includes the GPS carrier frequencies L1 and L2 and the OmniSTAR satellite broadcast signal The 1575 42 MHz GPS carrier frequency which contains the course acquisition C A code as well as encrypted P code and navigation messages used by commercial GPS receivers The 1227 60 MHz secondary GPS carrier frequency containing only encrypted P code used primarily to calculate signal delays caused by the ionosphere GPS Reference Manual 49 Chapter 12 L5 Frequency Lane Local Observation Set Local Tangent Plane Low Latency Solution Magnetic Bearing Magnetic Heading Magnetic Variation Mask Angle Matched Observation Set Pair Measurement Error Variance Measurement Time Epoch Multipath Errors Nanosecond Non Volatile Memory Null Field 50 Glossary The third civil GPS frequency at 1176 45 MHz beginning with GPS satellites to be launched in 2005 This frequency is located within the 960 1215 MHz frequency band The L5 signal is equally split between an in phase I data channel and a quadrature Q data free channel which improves resistance to interference especially from pulse emitting systems in the same band as L5 A particular discrete ambigu
50. n is shaped to reduce signals arriving at low elevation angles These features decrease the errors associated with electromagnetic interference and multipath Also the model 700 gain roll off compares well to a patch antenna roll off mounted on a large choke ring ground plane This antenna provides comparable performance to the choke ring ground plane antenna while being much lighter and smaller GPS Reference Manual Multipath Chapter 6 Quadrifilar Elements Antenna Patch Dielectric Patch Ground Plane Quadrifilar Helix Antenna Microstrip Patch Antenna Figure 11 Illustration of Quadrifilar vs Microstrip Patch Antennas 6 5 Antenna Ground Planes Nearby objects can influence the radiation pattern of an antenna Thus one of the roles of the antenna ground plane is to create a stabilizing artificial environment on which the antenna rests and which becomes a part of the antenna structure and its resultant radiation pattern A small ground plane relative to one wavelength at the operating frequency may have minimal stabilizing effect whereas a large ground plane multiple wavelengths in size will have a highly stabilizing effect Large ground planes also exhibit a shielding effect against RF signal reflections originating below the antenna s radiation pattern horizon This can be a very effective low angle shield when the antenna is elevated on a hill or other structure above other reflecting surfaces such as vehicles
51. n view at all times A minimum of four satellites in view are needed to allow the receiver to compute its current latitude longitude altitude with reference to mean sea level and the GPS system time Figure 1 NAVSTAR Satellite Orbit Arrangement 1 1 GPS System Design The GPS system design consists of three parts e The Space segment e The Control segment e The User segment All these parts operate together to provide accurate three dimensional positioning timing and velocity data to users worldwide 1 1 1 The Space Segment The space segment is composed of the NAVSTAR GPS satellites The constellation of the system consists of 24 satellites in six 55 orbital planes with four satellites in each plane plus room for GPS Reference Manual Chapter 1 GPS Overview spares The orbit period of each satellite is approximately 12 hours at an altitude of 20 183 kilometers This provides a GPS receiver with at least six satellites in view from any point on earth at any particular time The GPS satellite signal identifies the satellite and provides the positioning timing ranging data satellite status and the corrected ephemerides orbit parameters of the satellite to the users The satellites can be identified either by the Space Vehicle Number SVN or the Pseudorandom Code Number PRN The PRN is used by the NovAtel receiver The GPS satellites transmit on two L band frequencies one centered at 1575 42 MHz L1 and the o
52. nels Carrier Phase and between the base and rover receivers They are estimated when Ambiguitya double difference mechanism is used for carrier phase positioning Sometimes double difference ambiguity or ambiguity for short This is a coordinate ordinate system which has the X coordinate in the earth s equatorial plane pointing to the Greenwich prime meridian the Z axis pointing to the north pole and the Y axis in the equatorial plane 90 from the X axis with an orientation which forms a right handed XYZ system A dimensionless measurement defined for a conic section where e 0 is a circle e is an ellipse O lt e lt 1 is a parabola and e gt is a hyperbola The angle from the horizon to the observed position of a satellite A smooth mathematical surface which represents the earth s shape and very closely approximates the geoid It is used as a reference surface for geodetic surveys Height above a defined ellipsoid approximating the surface of the earth GPS Reference Manual 47 Chapter 12 Ephemeris Ephemeris Data Epoch Field Figure of Merit Fixed Ambiguity Estimates Fixed Discrete Ambiguity Estimates Fixed Field Fixed Integer Ambiguity Estimates Flash ROM Geometric Dilution of Precision GDOP Geoid Geodetic Datum Geostationary 48 Glossary A set of satellite orbit parameters that are used by a GPS receiver to calculate precise GPS satellite positions and velocities The ephemeri
53. of a measurement quantity The standard deviation is representative of the error typically expected in a measured value of that quantity The point in time at which a receiver takes a measurement GPS positioning errors caused by the interaction of the GPS satellite signal and its reflections 1 x 10 second A type of memory device that retains data in the absence of a power supply By NMEA standard indicates that data is not available for the field Indicated by two ASCII commas for example HEX 2C2C or for the last data field in a sentence one comma followed by either the checksum delimiter HEX 2A or the sentence delimiters lt CR gt lt LF gt HEX ODOA Note the ASCII Null character HEX 00 is not to be used for null fields GPS Reference Manual Glossary Obscuration Observation Observation Set OmniSTAR Origin Waypoint Parallel Receiver Parity Perigee P Code PDOP Precise Positioning Service PPS PRN Number Pseudolite Pseudorange Pseudorange Measurements Chapter 12 Term used to describe periods of time when a GPS receiver s line of sight to GPS satellites is blocked by natural or man made objects Any measurement A set of receiver measurements taken at a given time which includes one time for all measurements and the following for each satellite tracked PRN number pseudorange or carrier phase or both lock time count signal strength and tracking status
54. olled locations Some recommendations for such handling practices follow e Handling areas must be equipped with a grounded table floor mats and wrist strap e A relative humidity level must be maintained between 20 and 80 non condensing e No ESD sensitive board or component should be removed from its protective package except in a static controlled location e A static controlled environment and correct static control procedures are required at both repair stations and maintenance areas e ESD sensitive devices must be handled only after personnel have grounded themselves via wrist straps and mats e Boards or components should never come in contact with clothing because normal grounding cannot dissipate static charges on fabrics e A circuit board must be placed into an anti static plastic clamshell before being removed from the work location and must remain in the clamshell until it arrives at a static controlled repair test center e Circuit boards must not be changed or moved needlessly Handles may be provided on circuit boards for use in their removal and replacement care should be taken to avoid contact with the connectors and components e On site repair of ESD sensitive equipment should not be undertaken except to restore service in an emergency where spare boards are not available Under these circumstances repair station techniques must be observed Under normal circumstances a faulty or suspect circuit board must be s
55. ons satellites In order to enable CDGPS positioning you must enable L band tracking to the CDGPS signal The CDGPS signal is broadcast on 4 different spot beams on the MSAT 1 satellite Depending on your geographic location there will be a different frequency for the CDGPS signal as shown in Figure 6 Figure 6 CDGPS Frequency Beams The following are the spot beam names and their frequencies East 1 547 646 Hz East Central 1 557 897 Hz West Central 1 557 571 Hz West 1 547 547 Hz The data signal is structured to perform well in difficult or foliated conditions so the service is available more consistently and has a high degree of service reliability CDGPS features wide area technology possible spatial integrity with all Government of Canada maps and surveys 1 24 hour 7 days a week built in network redundancies and an openly published broadcast protocol Figure 7 CDGPS Percentage Coverage Map on Page 16 is a conservative map of the coverage areas that CDGPS guarantee The coverage may be better in your area 1 If the coordinates are output using the CSRS datum Refer to the DATUM command in Volume 2 of the OEM4 Manual set GPS Reference Manual 15 Chapter 4 L Band Positioning 90 95 100 Figure 7 CDGPS Percentage Coverage Map In Figure 7 100 coverage means that a correction is received for every visible satellite at or above 10 degrees 90 coverage means that a correction is received for 90 of visible s
56. or of 34 dB Hz Once a signal has been acquired the receiver is capable of tracking satellite signals with a minimum input carrier to noise density ratio C NO to the correlator of 31 dB Hz GPS Reference Manual Chapter 8 Standards References DX Website addresses are subject to change however they are accurate at the time of posting NOVATEL INC Contact your local NovAtel dealer first for more information To locate a dealer in your area or if the problem is not resolved contact NovAtel Inc directly Customer Service Dept 1120 68 Avenue NE Calgary AB Canada T2E 8S5 Phone 1 800 NOVATEL U S amp Canada or 403 295 4900Fax 403 295 4901 E mail support novatel ca Website http www novatel com RTCM STANDARDS REFERENCE For detailed specifications of RTCM refer to RTCM SC104 Recommended Standards for Differential GNSS Global Navigation Satellite Systems Service Version 2 3 Radio Technical Commission For Maritime Services 1800 North Kent St Suite 1600 Arlington VA 22209 USA Phone 1 703 527 2000 Fax 1 703 351 9932 E Mail information rtcm org Website http www rtcm org RTCA STANDARDS REFERENCE For copies of the Minimum Aviation System Performance Standards DGNSS Instrument Approach System Special Category 1 SCAT 1 contact RTCA Inc 1828 L Street NW Suite 805 Washington DC 20036 Phone 202 833 9339 Fax 202 833 9434 E Mail info rtca org Website http www rtca org GP
57. ormation about each satellite to the rover station which in turn can determine its 1 Environment Canada 1993 Guideline for the Application of GPS Positioning p 22 Minister of Supply and Services Canada 8 GPS Reference Manual GPS Overview Chapter 1 position much more exactly than would be possible otherwise The advantage of relative positioning is that much greater precision presently as low as 2 mm depending on the method and environment can be achieved than by single point positioning In order for the observations of the base station to be integrated with those of the rover station relative positioning requires either a data link between the two stations if the positioning is to be achieved in real time or else post processing of the data collected by the rover station At least four GPS satellites in view are still required The absolute accuracy of the rover station s computed position will depend on the accuracy of the base station s position GPS satellites aca P GPS antenna lt x n KH ger mme eee Differential a GPS antenna data shown with choke ring ground plane Radio RX GPS RX User with hand held computer Rover station Base station Figure 4 Example of Differential Positioning GPS Reference Manual 9 Chapter 1 GPS Overview 1 3 2 Static vs Kinematic Positioning Static and kinematic positioning refer to whether a GPS receiver is stationary or in m
58. otion while collecting GPS data Refer to Chapter 6 Volume 1 of the OEM4 Manual set for more details on static and real time kinematic positioning SUPERSTAR II based product manuals also contain a chapter on positioning modes of operation 1 3 3 Real time vs Post mission Data Processing Real time or post mission data processing refer to whether the GPS data collected by the receiver is processed as it is received or after the entire data collection session is complete Refer to Chapter 6 Volume 1 of the OEM4 Manual set for more details on static and real time kinematic positioning 10 GPS Reference Manual Chapter 2 INS Overview GPS positioning observes range measurements from orbiting Global Positioning System Satellites From these observations the receiver can compute position and velocity with high accuracy NovAtel GPS positioning systems have been established as highly accurate positioning tools however GPS in general has some significant restrictions which limit its usefulness in some situations Accurate GPS positioning requires line of site view to at least four satellites simultaneously If these criteria are met differential GPS positioning can be accurate to within a few centimetres If however some or all of the satellite signals are blocked the accuracy of the position reported by GPS degrades substantially or may not be available at all In general an Inertial Navigation System INS uses forces and rotations measure
59. rce management The shortest distance between any two points along the surface of a sphere or ellipsoid and therefore the shortest navigation distance between any two points on the Earth Also called Geodesic Line Predetermined hardware or software activity designed to establish or maintain two machines or programs in synchronization Handshaking concerns the exchange of messages or packets of data between two systems with limited buffers Hardware handshaking uses voltage levels or pulses in wires to carry the handshaking signals Software handshaking uses data units for example binary bits carried by some underlying communication medium The direction in which a vessel points or heads at any instant expressed in degrees 000 clockwise through 360 and may be referenced to True North Magnetic North or Grid North The heading of a vessel is also called the ship s head Heading is a constantly changing value as the vessel oscillates or yaws across the course due to the effects of the air or sea cross currents and steering errors See Dilution of Precision DOP See Dilution of Precision DOP Carrier phase ambiguity estimates which are only allowed to take on integer values A linear combination of L1 and L2 carrier phase measurements which provides an estimate of the carrier phase observation on one frequency with the effects of the ionosphere removed It provides a different ambiguity value non integer tha
60. rostatic Discharge Electronic Serial Number Federal Aviation Administration Federal Communication Commission Frequency Distribution Amplifier Forward Error Correction Flash Erasable Programmable Read Only Memory First In First Out Failure Mode Effects Analysis GPS Reference Manual Acronyms FOG GDOP GEO GIC GLONASS GMT GND GNSS GPAI GPS GUS GUST GUSTR HDOP hex HFOM HP HTDOP Hz Iand Q I Channel IBIT IC ICD ICP IEC IEEE IF IGRF IM IMLA IMU INH INS YO IODE IP IRQ ISG ISO KPA LI L2 L5 Chapter 11 Fibre Optic Gyro Figure of Merit Field Programmable Gate Array Factory Reset File Transfer Protocol Frequency and Time Standard Firmware Geometric Dilution Of Precision Geostationary Satellite GPS Integrity Channel Global Navigation Satellite System Greenwich Mean Time Ground Global Navigation Satellite System General Purpose Analog Input Global Positioning System Ground Uplink Station WAAS GUS Type 1 WAAS GUST Type 1 Receiver Horizontal Dilution Of Precision Hexadecimal Horizontal Figure of Merit High Performance standard OmniSTAR service Horizontal Position and Time Dilution Of Precision Hertz In Phase and Quadrature Channels In phase Data Channel Initiated Built In Test Integrated Circuit Interface Control Document Integrated Carrier Phase International Electrotechnical Commission Institute of Electrical amp Electronics Engineers Intermediat
61. s note pads etc Floors wax finished vinyl Clothes common cleanroom smocks personal garments all textiles non conductive shoes Chairs finished wood vinyl fiberglass Packing and handling common polyethylene bags wraps envelopes and bubble pack pack foam common plastic trays and tote boxes Assembly cleaning and repair areas spray cleaners common solder sucker common soldering irons common solvent brushes synthetic bristles cleaning drying and temperature chambers GPS Reference Manual 37 Chapter 10 Electrostatic Discharge Control ESD Practices 10 4 Handling Printed Circuit Boards 38 ESD damage to unprotected sensitive devices may occur at any time ESD events can occur far below the threshold of human sensitivity Follow this sequence when it becomes necessary to install or remove a circuit board 1 After you are connected to the grounded wrist strap remove the circuit board from the frame and place it on a static controlled surface grounded floor or table mat Remove the replacement circuit board from the static shielding bag or clamshell and insert it into the equipment Place the original board into the shielding bag or clamshell and seal it with a label Do not put repair tags inside the shielding bag or clamshell Disconnect the wrist strap GPS Reference Manual GUIOT Acronyms 1PPS One Pulse Per Second 2 D or 2D Two Dimensional
62. s information the receiver must blindly search through all possible satellite PRN codes and Doppler offsets as in a cold start Re acquisition is the resumption of tracking and measurement processing OEM4 based Products Once satellites are acquired the receiver will normally waits another 18 36 seconds before receiving broadcast ephemeris data to calculate a position To avoid this delay the receiver saves ephemeris data in its NVM and will use that data if it is less than 2 hours old Table 1 Typical Receiver TTFF for OEM4 Based Products Information Available to the Receiver Typical TIFF Approx Approx Almanac Recent Position Time Ephemeris Cold no no no no 50s Start Warm yes yes yes no 40s Start Hot yes yes yes yes 30s Start lt The TTFF numbers quoted assume an open environment Poor satellite visibility or frequent signal blockage increases TTFF GPS Reference Manual 28 TTFF and Satellite Acquisition Chapter 7 Upon power up the receiver does not know its position or time and therefore cannot use almanac information to aid satellite acquisition You can set an approximate GPS time using the SETAPPROXTIME command or RTCAEPHEM message The RTCAEPHEM message contains GPS week and seconds and the receiver will use that GPS time if the time is not yet known Several logs provide base station coordinates and the receiver will use them as an approximate position allowing it to compute
63. s is used in the determination of the navigation solution and is updated periodically by the satellite to maintain the accuracy of GPS receivers The data downlinked by a GPS satellite describing its own orbital position with respect to time Strictly a specific point in time Typically when an observation is made A character or string of characters immediately preceded by a field delimiter NovAtel SUPERSTAR II based L1 receivers provide an estimated accuracy level The accuracy level estimate is provided in the horizontal and vertical Figure of Merit FOM The FOM reflects a 95 confidence level for the position solution accuracy estimate The FOM accounts for all major sources of errors in the pseudoranges of the satellites used in the position solution The error sources which are included are ionospheric and tropospheric errors satellite position errors based on transmitted user range error and thermal noise Carrier phase ambiguity estimates which are set to a given number and held constant Usually they are set to integers or values derived from linear combinations of integers Carrier phase ambiguities which are set to values that are members of a predetermined set of discrete possibilities and then held constant A field in which the number of characters is fixed including the cyclic redundancy check CRC field Carrier phase ambiguities which are set to integer values and then held constant Programmable read only memory
64. satellite visibility Alternately you can set an approximate position by using the SETAPPROXPOS command Approximate time and position must be used in conjunction with a current almanac to aid satellite acquisition For a summary of the OEM4 family command and logs used to inject an approximated time or position into the receiver see Table 2 Table 2 Approximate Time and Position Methods Approximate Command Log Time SETAPPROXTIME RTCAEPHEM Position SETAPPROXPOS RTCAREF or CMRREF or RTCM3 Base station aiding can help in these environments A set of ephemerides can be injected into a rover station by broadcasting the RTCAEPHEM message from a base station This is also useful in environments where there is frequent loss of lock GPS ephemeris is three frames long within a sequence of five frames Each frame requires 6 seconds of continuous lock to collect the ephemeris data This gives a minimum of 18 s and a maximum of 36 s continuous lock time or when no recent ephemerides new or stored are available 7 2 SUPERSTAR Il based Products The receiver enters Navigation mode refer to the Operational States section of the SUPERSTAR IT User Manual and provides valid outputs in less than 45 seconds after completion of the self test and the following initialization criteria have been met Valid time 10 minutes and position data 100 km from actual position Valid almanac data less than a year old At least 4 sat
65. sistance to interference especially from pulse emitting systems in the same band as L5 Both I and Q channels are encoded with the Neuman Hoffman Codes The L5 signal is also Forward Error Correction FEC encoded Code Division Multiple Access CDMA techniques allow differentiating between the SVs since all SVs transmit the same LS frequency The benefits of the L5 signal include e Signal redundancy where the L5 signal is completely redundant to the L1 signal creates frequency diversity and includes a direct acquisition capability so that you do not have to rely on the L1 and L2 signals for initial acquisition e User capability to perform ionospheric delay corrections e Higher integrity level and continuity of service e Enhanced interference rejection capabilities e Coherent data free component allows the receiver to track the carrier at lower signal to noise ratios e Neuman Hoffman encoding reduces the effect of narrowband interference and improves the cross correlation properties between SV signals e FEC encoding permits a receiver to correct errors introduced in the transmission process due to noise or interference and makes it easier to extract the navigation message from weak signals e 6 dB stronger signal and more robust signal structure than L1 e Greater reliability for safety of life applications interference mitigation worldwide and position accuracies are provided 1 For further information on the L5 signal you m
66. ther at 1227 60 MHz L2 The L1 carrier is modulated by the C A code Coarse Acquisition and the P code Precision which is encrypted for military and other authorized users The L2 carrier is modulated only with the P code 1 1 2 The Control Segment The control segment consists of a master control station five base stations and three data up loading stations in locations all around the globe The base stations track and monitor the satellites via their broadcast signals The broadcast signals contain the ephemeris data of the satellites the ranging signals the clock data and the almanac data These signals are passed to the master control station where the ephemerides are re computed The resulting ephemerides corrections and timing corrections are transmitted back to the satellites via the data up loading stations 1 1 3 The User Segment 1 2 The user segment such as the NovAtel receiver consists of equipment which tracks and receives the satellite signals The user equipment must be capable of simultaneously processing the signals from a minimum of four satellites to obtain accurate position velocity and timing measurements Height Relationships What is a geoid An equipotential surface is any surface where gravity is constant This surface best represents mean sea level and not only covers the water but is projected throughout the continents In North America this surface is most commonly used at its zero value that is all
67. ting takes place When full reflection occurs full polarity reversal results in the propagating wave The consequences of signal polarity shifting and reversal at the receiving antenna vary from minor to significant As well refracted and reflected signals generally sustain some degree of signal amplitude attenuation GPS Reference Manual 21 Chapter 6 Multipath 6 2 22 It is generally understood that in multipath conditions both the direct and reflected signals are present at the antenna and the multipath signals are lower in amplitude than the direct signal However in some situations the direct signal may be obstructed or greatly attenuated to a level well below that of the received multipath signal Obstruction of direct path signals is very common in city environments where many tall buildings block the line of sight to the satellites As buildings generally contain an abundance of metallic materials GPS signal reflections are abundant if not overwhelming in these settings Obstructions of direct path signals can occur in wilderness settings as well If the GPS receiver is in a valley with nearby hills mountains and heavy vegetation signal obstruction and attenuation are also very common Consequences of Multipath Reception Because GPS is a radio ranging and positioning system it is imperative that ground station signal reception from each satellite be of direct line of sight This is critical to the accuracy of the ranging me
68. ts that is used primarily by commercial GPS receivers to determine the range to the transmitting GPS satellite The 1023 chip C A code repeats every ms giving a code chip length of 300 m which is very easy to lock onto A method established for message transfer between a talker and a listener which includes the message format and the sequence in which the messages are to be transferred Also includes the signalling requirements such as bit rate stop bits parity and bits per character The Master Control Station and the globally dispersed Reference Stations used to manage the GPS satellites determine their precise orbital parameters and synchronize their clocks See Universal Time Coordinated The horizontal direction in which a vessel is to be steered or is being steered the direction of travel through the air or water Expressed as angular distance from reference North either true magnetic compass or grid usually 000 north clockwise through 360 Strictly the term applies to direction through the air or water not the direction intended to be made good over the ground see Track Made Good Differs from heading The single resultant direction from a given point of departure to a subsequent position the direction of the net movement from one point to the other This often varies from the track caused by inaccuracies in steering currents cross winds etc This term is often considered to be synonymous with
69. uare Residual Solution Status Real Time Clock Radio Technical Commission for Aviation Services Radio Technical Commission for Maritime Services Real Time Kinematic Request To Send Received Data SMART ANTENNA Selective Availability Satellite Based Augmentation System Safety Computer Special Category I Spherical Error Probable Signal Generator Systeme Internationale WAAS GUS Type 1 Signal Generator Serial Line Internet Protocol Signal to Noise Ratio Standard Positioning Service Signal Quality Monitoring Static Random Access Memory SUPERSTAR II Space Vehicle Space Vehicle Identifier Space Vehicle Number Software Transmission Control Protocol Temperature Compensated Crystal Oscillator Time Dilution Of Precision GPS Reference Manual 43 Chapter 11 TES TIL TNM TOA TOE TRAIM TTFF TTL TXD UART UDP UDRE UHF USB UTC VAC V DC VARF VBS VCTCXO VDOP VFD VFOM VSWR WAAS WAAS G II WADGPS WHQL WMP WNA WPT XTE ZUPT 44 Acronyms Time Estimator Status Time Integrity Limit Telecommunications Network Management Time of Almanac Time of Ephemeris Time Receiver Autonomous Integrity Monitor Time To First Fix Transistor Transistor Logic Transmitted Data Universal Asynchronous Receiver Transmitter User Datagram Protocol User Differential Range Error Ultra High Frequency Universal Serial Bus Universal Time Coordinated or Coordinated Universal Time Volts Alternating
70. ulations from speed measurements The immediate geographic point of interest to which a vessel is navigating It may be the next waypoint along a route of waypoints or the final destination of a voyage A technique to improve GPS accuracy that uses pseudorange errors at a known location to improve the measurements made by other GPS receivers within the same general geographic area A numerical value expressing the confidence factor of the position solution based on current satellite geometry The lower the value the greater the confidence in the solution DOP can be expressed in the following forms GDOP Uncertainty of all parameters latitude longitude height clock offset PDOP Uncertainty of 3 D parameters latitude longitude height HTDOP Uncertainty of 2 D and time parameters latitude longitude time HDOP Uncertainty of 2 D parameters latitude longitude VDOP Uncertainty of height parameter TDOP Uncertainty of clock offset parameter The change in frequency of sound light or other wave caused by movement of its source relative to the observer A signal processing strategy which uses a measured Doppler shift to help a receiver smoothly track the GPS signal to allow more precise velocity and position measurement A mathematical technique comparing observations by differencing between receiver channels and then between the base and rover receivers Carrier phase ambiguities which are differenced between receiver chan
71. ulting value for GPS Time is Week 1307 480 600 seconds GPS Reference Manual 25 years 9 125 days 7 days 22 days 9 154 days 790 905 600 seconds 1307 714285 weeks 5 days 432 000 seconds 48 600 seconds 480 600 seconds 35 AIE PCGEN Electrostatic Discharge Control ESD Practices 10 1 Overview Static electricity is electrical charge stored in an electromagnetic field or on an insulating body This charge can flow as soon as a low impedance path to ground is established Static sensitive units can be permanently damaged by static discharge potentials of as little as 40 volts Charges carried by the human body which can be thousands of times higher than this 40 V threshold can accumulate through as simple a mechanism as walking across non conducting floor coverings such as carpet or tile These charges may be stored on clothing especially when the ambient air is dry through friction between the body and or various clothing layers Synthetic materials accumulate higher charges than natural fibers Electrostatic voltage levels on insulators may be very high in the order of thousands of volts Various electrical and electronic components are vulnerable to electrostatic discharge ESD These include discrete components hybrid devices integrated circuits ICs and printed circuit boards PCBs assembled with these devices 10 2 Handling ESD Sensitive Devices ESD sensitive devices must only be handled in static contr
72. ume 2 of the OEM4 Manual set for details on SBAS commands and logs An SBAS capable receiver permits anyone within the area of coverage to take advantage of its benefits GPS Reference Manual 13 Chapter 4 L Band Positioning 4 1 The transmission of OmniSTAR or CDGPS corrections are from geostationary satellites The L Band frequency of geostationary satellites is sufficiently close to that of GPS that a common single antenna like the NovAtel GPS 600 LB may be used Both systems are portable and capable of sub meter accuracy over their coverage areas The OmniSTAR system is designed for worldwide coverage A subscription charge by geographic area is required The CDGPS system is a free Canada wide DGPS service that is accessible coast to coast beyond the U S border and into the Arctic Coverage The two systems provide different coverage areas e Worldwide OmniSTAR e Canada America Wide CDGPS 4 1 1 Worldwide OmniSTAR 14 In most world areas a single satellite is used by OmniSTAR to provide coverage over an entire continent or at least very large geographic areas In North America a single satellite is used but it needs three separate beams to cover the continent The three beams are arranged to cover the East Central and Western portions of North America The same data is broadcast over all three beams but the user system must select the proper beam frequency The beams have overlaps of several hundred miles so
73. ver specification which indicates the number of independent hardware signal processing channels included in the receiver design In a double difference implementation measurements are differenced between different satellites on one receiver in order to cancel the correlated errors Usually one satellite is chosen as the reference and all others are differenced with it See Base Station Bearing relative to heading or to the vessel See Rover Station In the context of measurement the residual is the misclosure between the calculated measurements using the position solution and actual measurements A probability level of 68 A planned course of travel usually composed of more than one navigation leg The GPS receiver which does not know its position and needs to receive measurements from a base station to calculate differential GPS positions The terms remote and rover are interchangeable NovAtel s Double Differencing Technology for real time kinematic RTK carrier phase floating ambiguity resolution An organization which developed and defined a message format for differential positioning An organization which developed and defined the SC 104 message format for differential positioning A type of differential positioning based on observations of carrier phase In NovAtel documents it is also used with reference to RT 2 and RT 20 The receiver tracks a satellite by replicating the satellite s PRN code and
74. y residual errors and ionospheric information for each monitored satellite The signal broadcast via the SBAS GEOs to the SBAS users is designed to minimize modifications to standard GPS receivers As such the GPS L1 frequency 1575 42 MHz is used together with GPS type modulation for example a Coarse Acquisition C A pseudorandom PRN code In addition the code phase timing is maintained close to GPS time to provide a ranging capability 12 GPS Reference Manual Satellite Based Augmentation System Chapter 3 Figure 5 The SBAS Concept Reference Description Reference Description 1 Geostationary Satellite GEO 8 C Band 2 GPS Satellite Constellation 9 SBAS Reference Station 3 L1 10 SBAS Master Station 4 L1 and C Band 11 Ground Uplink Station 5 L1 and L2 6 GPS User 7 Integrity data differential corrections and ranging control 3 1 SBAS Receiver Many models of the NovAtel receivers are equipped with an SBAS option The ability to simultaneously track two SBAS satellites and incorporate the SBAS corrections into the position is available in some models These models can output the SBAS data in log format and can incorporate these corrections to generate differential quality position solutions Standard SBAS data messages are analyzed based on RTCA standard DO 229B Change 1 Minimum Operational Performance Standards for GPS WAAS airborne equipment Please refer to your SUPERSTAR II Firmware Reference Manual or Vol
75. ystem Most significant bit Mean sea level Measure Output Mean Time Between Failures Multi Functional Transport Satellite National Airspace System United States RINEX Ephemeris File NAVigation Satellite Timing And Ranging synonymous with GPS Not Connected Network Control Center Numerically Controlled Oscillator Neumann Hoffman National Marine Electronics Association Network Operations Center Nanosecond Non Volatile Memory RINEX Observation File Oven Controlled Crystal Oscillator Original Equipment Manufacturer Pulsed Aperture Correlator Personal Computer Precise Code Printed Circuit Board Personal Computer Memory Card International Association Power Distribution Function Portable Document File Position Dilution Of Precision Position Indicator GPS Reference Manual Acronyms PLL PPM PPP PPS PRN PSR PV PVT Q Channel RAM SV SVID SVN SW TCP TCXO TDOP Chapter 11 Phase Lock Loop Parts Per Million Point to Point Protocol Precise Positioning Service or Pulse Per Second PseudoRandom Noise Number Pseudorange Position Valid Position Velocity Time Quadrature Data Free Channel Random Access Memory Remote Access Service Radio Frequency Radio Frequency Uplink Right Hand Circular Polarization Ring Indicator Receiver Independent Exchange Format Ring Laser Gyro Restriction of the use of Hazardous Substances Read Only Memory Return Material Authorization Root Mean Sq

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