Improving WAAS Receiver Radio Frequency Interference Rejection

Allan Manz, Karl Shallberg and Peter Shloss

Abstract:	The accuracy, availability and integrity of the Wide Area Augmentation System (WAAS), being developed for the FAA, is of significant concern because of its intended use in commercial aviation navigation applications. These performance criteria can be adversely affected by unintentional radio frequency interference (RFI) at the WAAS Reference Station (WRS) sites. This paper documents some of the efforts to improve the RFI rejection capability of the existing GPS receivers at the WRS sites. RFI rejection capability is determined primarily by the ability of the WRS receivers to maintain carrier phase tracking. The element most sensitive to RFI in tracking a GPS or WAAS signal is the phase lock loop (PLL). The fact that the WRS antennas are fixed can be exploited to enhance the RFI rejection capability of the PLL. This paper will document the performance improvements that can be achieved by narrowing the PLL bandwidth (BW) to 3 Hz or less from the 15 Hz BW currently used. The difference in achievable performance between GPS signals and WAAS signals due to the period of the navigation message data bits is highlighted. Significant attention is given to the methods used in testing receiver performance. This paper illustrates the sensitivity of RFI rejection capability testing to a number of factors. These factors include the PRN used and the nature of the interference signal.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	471 - 479
Cite this article:	Manz, Allan, Shallberg, Karl, Shloss, Peter, "Improving WAAS Receiver Radio Frequency Interference Rejection," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 471-479.
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