Test Bed for Evaluation of GPS Receivers Performance in Ionospheric Scintillation - A Progress Report

Gregory Bishop, Dana Howell, Clayton Coker, Andrew Mazzella, Denice Jacobs, Edward Fremouw, James Secan, Bruce Rahn, Carlton Curtis Jr., John Quinn, Keith Groves, Santimay Basu, and Matthew Smitham

Abstract:	In May 1996 Wright Laboratory (WL) and Phillips Laboratory (PL), (now parts of the Air Force Research Laboratory [AFRL]) initiated a joint effort to quantify possible impacts of ionospheric scintillation on GPS during the upcoming solar maximum (reported at ION GPS-96). Ionospheric scintillation is caused by small-scale irregularities in the ionospheric electron density that can disturb, or scintillate, the amplitude and phase of radio signals that traverse it. Scintillation is reported to have caused GPS receiver loss-of-lock conditions, yet no hard data is known that confmed or quantified this. Thus, the GPS Joint Program Office (JPO) had recommended characterizing GPS receivers’ acquisition navigation capabilities under solar maximum ionospheric scintillation conditions. Since 1996-97 was at the low point of solar activity in the 11-year cycle, it was not possible to ‘go out and measure’ the effects. The Test Bed was developed to overcome this difficulty, and to obtain controlled and quantified performance measurement. The project coupled WL’s unique Antenna Wavefront Simulator (AWFS) hardware and testing expertise, with PL’s expertise in understanding of ionospheric scintillation and effects on AF systems. A limited definition phase effort has now been completed. The effort focused on characterizing the receivers’ response to scintillation, and identifying a threshold of pain for classes of receivers. To support the Test Bed, an analytic process for synthesizing physically realistic scintillation with essentially constant disturbance strength was developed. The extended test data sets produced by this process allowed statistical assessment of impacts of different levels of scintillation. However, the initial test effort could not support development of full-sky scenarios, with the accompanying variations in geometry, velocities and scintillation. The results of tests on several types of receivers suggest that some receivers may be significantly affected in strong scintillation, while other receivers may be quite robust This paper reviews the Test Bed hardware, sohare and test process. Discussion is presented of operational implications at solar maximum, and recommendations are given for validation and extension of the initial test results.
Published in:	Proceedings of the 1998 National Technical Meeting of The Institute of Navigation January 21 - 23, 1998 Westin Long Beach Hotel Long Beach, CA
Pages:	637 - 648
Cite this article:	Bishop, Gregory, Howell, Dana, Coker, Clayton, Mazzella, Andrew, Jacobs, Denice, Fremouw, Edward, Secan, James, Rahn, Bruce, Curtis, Carlton, Jr., Quinn, John, Groves, Keith, Basu, Santimay, Smitham, Matthew, "Test Bed for Evaluation of GPS Receivers Performance in Ionospheric Scintillation - A Progress Report," Proceedings of the 1998 National Technical Meeting of The Institute of Navigation, Long Beach, CA, January 1998, pp. 637-648.
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