Processing of WA-DGNSS Correction Messages: A Functional Perspective

Abstract

Satellite Based Augmentation Systems (SBAS) broadcast standard correction messages for aiding GNSS receivers. The SBAS implementation is envisaged under Development Wide Area Differential GNSS (WA-DGNSS) Systems project. WA-DGNSS correction messages are meant to provide an extensive set of information on corrections along with the confidence bounds. The end-user receiver should decode and interpret these messages every second. An individual message is composed of 250 bits. This levies strict limitation on information carrying capacity of each message. Therefore all correction information is distributed into several interconnected messages and each message is designed to carry certain portion of the corrections. It is responsibility of the end-user receiver not only to decode and interpret a message but also interconnect with other messages in order to obtain complete set of corrections. A comprehensive discussion on design, content and interconnections of WA-DGNSS broadcast messages can be found in relevant Minimum Operational Performance Standards (MOPS). It requires firm background knowledge about architecture and key sub-systems of WA-DGNSS to understand all the information provided in standards document. Since the document is outcome of extended discussions of diverse members; its narrative is legal and focused on detail. Despite being the standard reference, it is difficult to develop a WA-DGNSS receiver program using the standards document. The basic intent of this paper is to discuss functional aspects of how a WA-DGNSS capable receiver may process the correction messages. Understanding the functional perspective can be easily translated into receiver logic and then program code.