Impact of Ionospheric Scintillation on GPS/WAAS System and its Mitigation Techniques

Rajendra Kumar

Abstract:	Small-scale variations in ionospheric electron density result in amplitude and phase scintillation (rapid variations) of the received GPS signal. It is known that these effects get more severe during times of peak solar activity and in equatorial and polar regions. Possible effects of this phenomenon on the overall performance will appear via degraded measurement accuracy obtained by the user receiver and by the reference receivers in case of Wide Area Augmentation systems such as FAA WAAS. Further effects are in terms of frequent receiver loss of lock and longer acquisition times. This paper presents simulation results on the degradation of receiver performance due to amplitude and phase scintilla-tion. It is shown that under Rayleigh fading conditions representing strong scintillation, there is a performance degradation of up to about 6- 7 dB due to amplitude scintillation. The paper also presents adaptive and optimum smoothing techniques to compensate for fading and shows that the proposed techniques more than compensate for the degradation due to fading. Moreover, even when there is no fading, the smoothing technique can be applied to improve the system performance by about 6 dB as the required smoother delay is only a small fraction of 1 sec and can be easily compensated for in most GPS applications. Under relatively high phase scintillation condition, the possible performance loss is even more severe, i.e. 10-15 dB possible loss. For this case a multistage estimator is presented. From simulation examples it is observed that a second estimation stage results in improvement of about 6.5 dB. If this method is combined with the smoother technique, the combined improvement due to both two-stage estimator and smoother may completely offset the scintillation impact.
Published in:	Proceedings of the 1999 National Technical Meeting of The Institute of Navigation January 25 - 27, 1999 Catamaran Resort Hotel San Diego, CA
Pages:	809 - 823
Cite this article:	Kumar, Rajendra, "Impact of Ionospheric Scintillation on GPS/WAAS System and its Mitigation Techniques," Proceedings of the 1999 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 1999, pp. 809-823.
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