SBAS (WAAS, EGNOS & MSAS) Decoder

Project name:		SBAS decoder
Language:		ANSI C, also a VB6 version is available but is untested
Target platform:		PC or embedded, currently running on a Ti c6000 DSP
Abstract:		This software module processes raw SBAS messages and converts them into precision GPS corrections
Key features and advantages:		The software is a complete validated solution. It takes the full "high precision" approach and decodes all messages that can be used to improve GPS performance. The code is written in in ANSI C and is well structured and commented to a very high standard.

Full Description

SBAS (satellite based augmentation systems) satellites broadcast corrections to the standard data broadcast by the GPS satellites, in order to improve the accuracy of the solution obtained from the GPS data. The GPS solution obtained from the broadcast GPS data using a single frequency receiver will typically have an accuracy within about 3 - 5m most of the time. Using the SBAS corrections, the accuracy can be improved to around the 1m mark in typical operation.

The corrections are calculated using a network of accurately surveyed ground-based monitoring systems, uploaded to the SBAS satellites via radio link, and then broadcast by the SBAS satellites on the standard 1575.42MHz GPS L1 frequency. Current SBAS system implementations providing freely available broadcast data are the US Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Multi-functional Satellite Augmentation Service (MSAS). Standardisation of the SBAS message formats means that one decoder can be used for all SBAS implementations with minimal change.

The messages are transmitted from satellites as subframe messages in the same way as navigational data is received from standard GPS satellites. These subframes are then converted into useful sets of data that allow:

• fast corrections of the ranging data from standard satellites
• long term corrections of the ranging data from standard satellites
• atmospheric correction data that can be applied to measured ranges

The code checks the CRC on the data to make sure that it is valid, and converts it as required.

This code has been fully validated using the SISNeT EGNOS data broadcast in real time over the internet by the ESA (European Space Agency). The code has also been validated using a representative sample of WAAS messages.

This code is available in either binary or source form. The complete solution may be purchased, or alternatively the source code to decode any individual message may be purchased as reference source for that message. Please contact us with any purchasing or licensing enquires:

Tel: +44 (0)1773 537631

Email: sales@race-technology.com

Overview of SBAS (WAAS, EGNOS & MSAS) Decoder

Performance Parameters

SBAS (WAAS, EGNOS & MSAS) Decoder Application Programming Interface