Message Type 28

Todd Walter, Andrew Hansen and Per Enge

Abstract:	The Wide Area Augmentations Syste (WAAS)and similar Satellite Based Augmentation Systems (SBASs) broadcast differential Global Positioning System (GPS) corrections and confidences.From this information a user can ore accurately determine position.Even ore i portantly,the users can determine the confidence they have in that position solution.The format of the messages containing these corrections is described in the WAAS Minimum Operational Performance Standards (MOPS)[1 ].A new message type is described that contains a relative clock and ephemeris covariance atrix for individual satellites.From this matrix users can reconstruct their location specific error bound rather than applying the largest bound in the service volume.By transmitting this information to the user,we can achieve two benefits:i proved availability within the service volume and improved integrity in the region outside.Message Type 28 contains matrices for two satellites per message,and each message is broadcast at the same rate as the long-ter corrections (Message Type 25).Message Type 28 is in the process of being incorporated into the WAAS and has been presented to RTCA and to the International Civil Aviation Organization (ICAO)for inclusion in the MOPS and the international Standards And Recommended Procedures (SARPS).Two issues have been identified with its implementation. Complexity is added t o t he syst e i n generating and monitoring the contents of the message.Additionally,the discretization error incurred when fitting the essage into the li ited bandwidth of the correction channel reduces some of the provided benefit.Nevertheless,we will show that application of this message achieves its goals.Clock and ephemeris errors are ore accurately bounded outside the service volume,and projected confidence factors inside the service volume are reduce by more than 25%.
Published in:	Proceedings of the 2001 National Technical Meeting of The Institute of Navigation January 22 - 24, 2001 Westin Long Beach Hotel Long Beach, CA
Pages:	522 - 532
Cite this article:	Walter, Todd, Hansen, Andrew, Enge, Per, "Message Type 28," Proceedings of the 2001 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 2001, pp. 522-532.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In