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RTK Standards
Unlike other GNSS Augmentation systems as SBAS or GBAS, Real Time Kinematic (RTK) satellite navigation is a technique used in land survey and in hydrographic survey based on the use of carrier phase measurements of the GPS, GLONASS and/or Galileo signals where a single reference station provides the real-time corrections, providing up to centimetre-level accuracy. Therefore, the standards applying to RTK systems are the same of classical DGNSS systems, i.e. the ones of data transmission standards defined by the Special Committee 104 on DGNSS of the Radio Technical Commission for Maritime Services (RTCM). Besides RTCM, there exist other proprietary DGPS/RTK standards, such as Trimble Compact Measurement Record (CMR).
RTCM Standards
The internationally accepted data transmission standards for DGNSS are defined by RTCM, particularly by its Special Committee SC-104. RTCM SC-104 is a standard that defines the data structure for differential correction information for a variety of differential correction applications. It was developed by the Radio Technical Commission for Maritime Services (RTCM) and has become an industry standard for communication of correction information. Note that RTCM is a binary data protocol.
The applicable documents to DGNSS systems are listed in the following table and constitute the current version of the core set of documents to be used for the development of a new DGNSS system.
| Document Item | Reference | Issue | Comments |
|---|---|---|---|
| Recommended Standards for Differential GNSS (Global Navigation Satellite Systems) Service | RTCM 10402.3 | 2.3 | This standard is used around the world for differential satellite navigation systems, both maritime and terrestrial. |
| Differential GNSS (Global Navigation Satellite Systems) Services | RTCM 10403.0 | 3 | A more efficient alternative to RTCM 10402.3 |
| Standard for Networked Transport of RTCM via Internet Protocol (Ntrip) | RTCM 10410.0 | 1 | An application-level protocol that supports streaming Global Navigation Satellite System (GNSS) data over the Internet |
| Standard for Differential Navstar GPS Reference Stations and Integrity Monitors (RSIM) | RTCM 10401.2 | 2 | A companion to RTCM 10402.3, this standard addresses the performance requirements for the equipment which broadcasts DGNSS corrections |
The RTCM 10402.3 standards defined the messages for differential correction information. The messages 1 to 17 are available in older RTCM versions, while messages 18-21 have been added in version 2.3 to made the standard applicable to RTK corrections. The release of RTCM version 3.0 is developed to be more efficient in terms of broadcast bandwidth and also provides higher integrity.[1]
The RTCM DGNSS message types can be found in article DGNSS Standards.
Other Standards
The Compact Measurement Record (CMR) was developed by and initially used by Trimble in 1992. The format was developed as a method of transmitting code and carrier phase correction data in a compact format from GPS base stations to GPS rovers for RTK GPS surveying. In 2009, Trimble has introduced a new broadcast observation format called CMRx, this has been developed to support significant changes to GNSS constellations which are currently underway. CMRx will allow Real-Time Kinematic (RTK) users to utilize more constellations, satellites, and signals as they become available, to give users faster initializations, improved statistical outputs, and improved performance in canyons and under canopy.
In Europe, a particular type of Network RTK based on so-called FKP (Flaechen-Korrektur-Parameter, the German word for spatial correction parameter) corrections is widely used. FKP corrections[2] contain information, which allows the user to compensate satellite orbit and ionospheric errors as a function of baseline length and effectively fix ambiguities for longer baselines than with a usual RTK. These parameters can be transmitted to the users through the RTCM proprietary message type 59.
Notes
References
- ^ Lin Minmin (2006). RTCM 3.0 Implementation in Network RTK and Perfomance Analysis. Msc Thesis, University of Calgary, Dept of Geomatic Engineering.
- ^ Wubenna G., Bagge A., Seeber G., Volker B., Hankemeier P. (1996). Reducing Distance Dependent Errors for Real Time Precise DGPS Applications by Establishing Reference Station Networks. In Proc. Institute of Navigation National GPS 1996 Kansas, 17-20 September, Vol 2, 1845-1852.