RTCM 10403.4, Differential GNSS (Global Navigation Satellite Systems) Services - Version 3 (December 01, 2023)

RTCM 10403.4 defines messages that are used improve the accuracy of location provided by Global Navigation Satellite Systems (GNSS) such as GPS, GLONASS, Galileo, QZSS, BeiDou (BDS), and NavIC. The method used is differential correction which involves the use of a reference station at a precisely known location, which communicates with “rover” receivers to refine their position using the messages in this standard.

This standard (referred to as Version 3) was first published by RTCM Special Committee 104 in 2004 as a more efficient alternative to the standards entitled "RTCM Recommended Standards for Differential Recommended Standards for Differential GNSS (Global Navigation Satellite Systems) Service, Version 2.x". (Current version is 2.3, now designated as RTCM 10402.3.) Service providers and vendors represented on the SC104 Committee wanted a new standard that would be more efficient, easy to use, and more easily adaptable to new situations. The main complaint was that the Version 2.x parity scheme, which uses words with 24 bits of data followed by 6 bits of parity, was wasteful of bandwidth. Another complaint was that the parity was not independent from word to word. Still another was that even with so many bits devoted to parity, the actual integrity of the message was not as high as it should be. Plus, 30-bit words are awkward to handle. Version 3 is recognized as correcting these weaknesses.

The standard has been revised several times since its original publication. It is now at version 3.4, designated RTCM 10403.4.

The significant changes in Version 3.4 are:

• Update of BeiDou ICD to 3.0.
• Changing QZSS "LEX" signal types to "L6".
• Changes and additions related to clarifications of transformation messages.
• Addition of normative references for the ICDs.
• Addition of Coordinate Reference Systems (CRS)/Datums Service Messages.
• Addition of BeiDou and Galileo Network RTK Residual Messages after successful interoperability testing.
• Incorporation of Amendments 1 -3, adding NavIC/IRNSS, Beidou BDS3 New Signals, and Coordinate Transformation clarifications.
• Grouping of ephemeris messages into one section.
• Grouping of legacy observation messages into one section.