Novatel OM-20000077 user manual Message Formats, RTCM-Format Messages

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Chapter 5

Message Formats

The chapter discusses the industry-standard message formats that can be used with your SUPERSTAR II receiver, including RTCM and NMEA. Refer to the L1 GPS Firmware Reference Manual for more information on using these message formats.

5.1RTCM-Format Messages

The Radio Technical Commission for Maritime Services (RTCM) was established to facilitate the establishment of various radio navigation standards, which includes recommended GPS differential standard formats.

The standards recommended by the Radio Technical Commission for Maritime Services Special Committee 104, Differential GPS Service (RTCM SC-104,Washington, D.C.), have been adopted by NovAtel for implementation into the receiver. Because the receiver is capable of utilizing RTCM formats, it can easily be integrated into positioning systems around the globe.

As it is beyond the scope of this manual to provide in-depth descriptions of the RTCM data formats, it is recommended that anyone requiring explicit descriptions of such, should obtain a copy of the published RTCM specifications. See Appendix D, Standards/References on Page 62 for reference information.

Message ID# 83, DGPS Configuration contains one or part of a RTCM message. The message type selected in the Set DGPS Configuration message (Message ID# 83, bytes 9 to 16) is retransmitted through this message. Message length is variable and a message can be transmitted up to once every 100 ms. A RTCM message always starts as the first byte of a message and always ends as the last byte of a message. Thus, a RTCM message can be output in one or many messages but a message block cannot contain more than one RTCM message. The control byte is used to determine the start and the end of a RTCM message. The sequence number of the control byte can be used to detect the loss of a message block on the transmitter side. It starts at 0 and increments by one for each consecutive message block (0,1,2,3,0,1,2,3,0,1,...). Refer also to the L1 GPS Firmware Reference Manual for details on this message.

All receiver messages adhere to the structure recommended by RTCM SC-104. Thus, all RTCM messages are composed of 30 bit words. Each word contains 24 data bits and 6 parity bits. All RTCM messages contain a 2- word header followed by 0 to 31 data words for a maximum of 33 words (990 bits) per message.

Message Frame Header

 

Data

Bits

Word 1

Message frame preamble for synchronization

8

 

 

 

 

 

Frame/message type ID

6

 

 

 

 

 

Base station ID

10

 

 

 

 

 

Parity

6

 

 

 

 

Word 2

Modified z-count (time tag)

13

 

 

 

 

 

Sequence number

3

 

 

 

 

 

Length of message frame

5

 

 

 

 

 

Base health

3

 

 

 

 

 

Parity

6

 

 

 

 

The remainder of this section will provide further information concerning receiver RTCM data formats.

5.1.1RTCM1 Differential GPS Corrections (Fixed)

This is the primary RTCM message used for pseudorange differential corrections. This message follows the RTCM Standard Format for a Type 1 message. It contains the pseudorange differential correction data

SUPERSTAR II User Manual Rev 3

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Contents Superstar Proprietary Notice Table of Contents Appendices Tables Figures Software License Software License Contact Information Firmware UpdatesElectrostatic Discharge CE Notice Warranty Policy Related Publications Congratulations ScopeRelated Publications Superstar II GPS Card IntroductionIntroduction Chapter FlexPak-SSIIChapter Introduction Radio Frequency RF Section Receiver SpecificationsPhysical Characteristics System ArchitectureGPS Antenna Enclosure and Wiring HarnessPrincipal Power Supply Optional LNA Power SupplyTypical System Configuration Reference Description InstallationSerial Connection Chapter InstallationElectrostatic Discharge Equipment InterconnectionAntenna Location Installation ConsiderationsPower Connection Installation ChapterBase Station and Rover Units Separation Connectors and Connector Pins Assignment1 J1 Interface and Power Connector Data LinkSerial Data Interface RF Connector J2RF Input Preamplifier Power Pass-Through Antenna SupplyProtocol Selection and Non Volatile Memory Memory Back-UpDiscretes IP2 and IP3 functions Use of DiscretesNon-Volatile Memory Data Default ConfigurationNon Volatile Memory Description Reference Installation OverviewOperation Typical Operational Configuration Reference DescriptionOperation Chapter Serial Port Default SettingsCommunications with the Receiver Getting StartedChapter Operation Power-Up InformationBoot Information Operational InformationReceiver States Configurable ParametersData Requests Self-Test Mode Built-In Status Tests Dead-Reckoning ModeDatum Support RTCM1 Differential GPS Corrections Fixed Message FormatsRTCM-Format Messages Chapter Message Formats RTCM2 Delta Differential GPS Corrections FixedRTCM9 Partial Satellite Set Differential Corrections Message Formats Chapter Nmea Format Data MessagesSingle-Point or Autonomous GPS System ErrorsPositioning Modes of Operation Positioning Modes of Operation Chapter Satellite-Based Augmentation System SbasChapter Positioning Modes of Operation Sbas ReceiverSbas Messages Positioning Modes of Operation Chapter Cable Lengths Vs. Gain TroubleshootingTroubleshooting Chapter Superstar II Family Performance Technical SpecificationsAppendix a Output Messages Technical Specifications Appendix aMechanical Drawing Appendix a Technical SpecificationsJ1 Interfaces and Power Connector Pin Assignment Connector Pin AssignmentO Signals Voltage Limits 3 I/O Electrical CharacteristicsAppendix B FlexPak-SSII SpecificationsPort Pin-Outs Status IndicatorsAppendix B FlexPak-SSII Specifications FlexPak Status IndicatorsCables FlexPak-SSII Specifications Appendix BAutomobile Power Adapter Cable NovAtel part number FlexPak 13-Pin Serial Cable 3.2 13-Pin Deutsch to DB9 Serial Cable NovAtel part numberDescription Setup and OperationNormal Setup Development KitDifferential GPS Setup Dgps Setup with the FlexPak-SSIIStarView Software Installation Cable Selection Antenna SpecificationsCoaxial Cable Specifications Appendix CTypical Current Consumption Versus Antenna Gain Antenna Specifications Appendix CGeodetic Active Antenna Antenna Gain Depending on Cable Length RequiredRecommended Geodetic Active Antennas Appendix C Antenna SpecificationsActive Antenna Passive AntennaGPS Antenna 201-990146-716 MCX, +12 dB Passive Antenna Specifications Patch ElementGPS Antenna 201-990147-606 +26 dB Antenna Specifications Appendix C Standards/References Appendix DRe-Acquisition Appendix ETtff and Satellite Acquisition Time-To-First-Fix TtffSystem Requirements Utility InstallationAppendix F Updating Receiver FirmwareUpdating Receiver Firmware Appendix F Starting Software and Options UpdateRegistration Key Accepted Appendix F Updating Receiver Firmware Programming SuccessSpace Segment Appendix GGPS Overview GPS System DesignAppendix G GPS Overview Height RelationshipsControl Segment User SegmentGPS Overview Appendix G GPS PositioningAccuracy versus Precision1 Single-Point vs. Relative PositioningReal-time vs. Post-mission Data Processing MultipathStatic vs. Kinematic Positioning Consequences of Multipath Reception Why Does Multipath Occur?Antenna Site Selection Hardware Solutions For Multipath ReductionAntenna Designs GPS Signal Multipath vs. Increased Antenna HeightGPS Overview Appendix G Glossary of Terms Appendix HGlossary of Terms Appendix H Appendix H Glossary of Terms Glossary of Terms Appendix H Acronyms AppendixAcronyms Appendix Appendix Acronyms Index Index GEO, SbasIndex Index OM-20000077 Rev 2004/03/11