The Innovations of WAAS Navigation Data Decoding and Signal Quality Monitoring in NovAtel WAAS-GII Receiver

Minmin Lin, Hua Huang, Michael Clayton

Abstract:	The GPS system was originally developed for military uses. It does not meet civil aviation requirements in terms of accuracy, continuity, and integrity. This has become the stimulus for the development of different satellitebased augmentation systems (SBAS), including the Wide Area Augmentation System (WAAS) by the Federal Aviation Administration (FAA) and EGNOS (European Geostationary Navigation Overlay System) by the European community [2]. Inside of all the SBAS infrastructures, the Ground Reference Receivers (RRx) became one of the most critical contributors to the system integrity and continuity. NovAtel has a rich experience as the world’s leading supplier of Ground Reference Receivers to satellite augmentation systems in Europe, the USA, Australia, Japan and China. NovAtel was awarded a contract to develop the second generation RRx for the WAAS system in 2002. The second generation WAAS-GII receiver features: enhanced Multipath Estimating Delay Lock Loop (MEDLL) performance; Signal Quality Monitoring (SQM) measurements; digital pulsed blanking; and Narrow CorrelatorTM Tracking Technology. This paper reviews the innovations, unique features and performance of the WAAS-GII receiver. One of the innovations lies in the Forward Error Correction (FEC) decoder for the Geostationary (GEO) Navigation message. The WAAS signal employs a rate ½ convolutional encoding when transmitting navigation data bits. This encoding inherits a symbol alignment problem. It relies on the receiver to determine the correct symbol alignment so that the navigation data bits can be decoded successfully. An algorithm is developed for the WAASGII receiver to quickly and reliably detect the symbol alignment with the minimum CPU resources. This paper also reviews another important feature of WAAS-GII: Signal Quality Monitor (SQM). The infamous “SV19” failure leads to the requirements for direct monitoring of the correlation function distortion of the signal in space. SQM has been thoroughly investigated in [1] and [3]. However, WAAS-GII is one of the few industrial GPS/WAAS receivers in the world which can provide real-time data to conduct GPS and GEO satellite signal quality. In this paper, the test to verify the SQM functionality is described. A tightly controlled simulator environment is created to form a determinate correlation function. The test results show that the measured correlation values agree with the theoretical expected values.
Published in:	Proceedings of the 2009 International Technical Meeting of The Institute of Navigation January 26 - 28, 2009 Disney's Paradise Pier Hotel Anaheim, CA
Pages:	917 - 923
Cite this article:	Lin, Minmin, Huang, Hua, Clayton, Michael, "The Innovations of WAAS Navigation Data Decoding and Signal Quality Monitoring in NovAtel WAAS-GII Receiver," Proceedings of the 2009 International Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2009, pp. 917-923.
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