Interference Monitoring at WAAS Reference Stations

Karl W. Shallberg and Donald T. Cox

Abstract:	The Wide Area Augmentation System (WAAS) is transitioning from concept phase to reality with the deployment this year of 25 Wide Area Reference Stations (WRS)s, two Wide Area Master Stations, and the integration of equipment at three Ground Uplink Stations. A key concern for the operation of WAAS, and for the GPS community in general, is the degree of unintentional RF interference present in the L1 and L2 bands. Interference has the potential of degrading GPS receiver measurement accuracy and, if severe enough, can prevent signal tracking altogether. Incorporation of a continuous RF interference monitoring function into WAAS is currently under program consideration and this paper investigates the use of the WAAS reference receiver in this role. Two receiver measurements having potential for reliably detecting the presence of interference are the carrier to noise power ratio for each satellite tracked and the accumulation bin levels from the adaptive multi-bit A-D. The response of these measurements to various types of interference has previously been demonstrated through laboratory testing and the results presented at the ¢98 National Technical Meeting [1]. This paper also investigates the level of interference present at WRSs using monitoring algorithms developed for these receiver measurements. The results of this interference survey will be used to identify reference stations that require more extensive RF surveys as well as assist in the selection of additional WRS interference mitigation measures. It is anticipated that the Local Area Augmentation System (LAAS) community will also benefit from the interference monitoring results since LAAS reference stations will most likely require a monitoring capability of their own.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	195 - 203
Cite this article:	Shallberg, Karl W., Cox, Donald T., "Interference Monitoring at WAAS Reference Stations," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 195-203.
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