The New RTCM SC-104 Standard for Differential and RTK GNSS Broadcasts

R.M. Kalafus, K. Van Dierendonck

Abstract:	RTCM SC-104 has developed a new public standard, called Version 3, for differential and real-time kinematic (RTK) GNSS operations. It is designed to be highly efficient in terms of broadcast bandwidth, in order to accommodate the needs of RTK operations. It is also highly flexible, supporting conventional RTK, networked RTK, low bandwidth RTK, as well as all differential GNSS legacy applications. Now that Selective Availability has been set to zero, the new standard will enable existing low-bandwidth broadcast services to accommodate RTK operations, or add other services in addition to differential GNSS. The paper discusses the numerous applications of the standard, the transport layer format, and the presentation layer messages that have been developed to date. The transport layer includes a byte count and a 24-bit cyclic redundancy check (CRC). The messages are laid out in a data base format which is believed to be clearer than the previous standard, and which makes it easy to build new messages on top of old ones, for example, to readily accommodate SBAS signals. The initial version of the standard provides for real-time kinematic operation of GNSS, and includes a number of auxiliary messages which describe the antennas used by the reference stations, the antenna reference point, and system information that includes the messages processed by the reference station. A second supporting document defines the next group of messages currently in preparation for subsequent incorporation into the standard in future releases. The Committee has a process for establishing both completeness and interoperability. Each participating vendor checks the standard to ensure that the data fields, and their range and resolution, are adequate to support their intended applications. Then, each one develops reference station files that are distributed to the others to establish interoperability of the data. Finally, the vendors bring prototype equipment to a test site and perform interoperability tests in real time. In this way problems are dealt with prior to publication of the standard.
Published in:	Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003) September 9 - 12, 2003 Oregon Convention Center Portland, OR
Pages:	741 - 747
Cite this article:	Kalafus, R.M., Van Dierendonck, K., "The New RTCM SC-104 Standard for Differential and RTK GNSS Broadcasts," Proceedings of the 16th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS/GNSS 2003), Portland, OR, September 2003, pp. 741-747.
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