A preventative approach to mitigating CW interference in GPS receivers |
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| Authors: | Asghar Tabatabaei Balaei Beatrice Motella Andrew Dempster |
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| Institution: | (1) Surveying and Spatial Information System, University of New South Wales, Sydney, 2052, Australia |
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| Abstract: | In the global positioning system (GPS), code division multiple access (CDMA) signals are used. Because of the known spectral
characteristics of the CDMA signal, continuous wave (CW) interference has a predictable effect on the different pseudo random
noise (PRN) spreading codes (unique to each satellite) depending on the Doppler frequency of the signal. The Doppler frequency
for each signal is also predictable once the receiver position is known. As different satellite signals have different Doppler
frequencies, the effect on the signal quality is also different. In this paper first the effect is studied analytically. The
concept of an “exclusion zone” is defined and analyzed for each satellite. This exclusion zone, where that satellite should
not be used due to interference degradation, is shown to be predictable for each satellite as a function of time. Using this
prediction, the CW interference effect on the positioning quality of the receiver can be mitigated by ignoring the affected
satellites within exclusion zones when performing position evaluation. The threshold beyond which a satellite should be excluded
is then derived by studying the mutual effects of the geometry and the signal quality of that satellite on the positioning
quality. Receiver autonomous integrity monitoring (RAIM) uses redundancy in measurements to perform an internal consistency
check to see if all of the measurements are satisfactory. In this paper this technique is also used to mitigate the effect
of CW interference on the positioning accuracy. Finally it is shown that the prediction of the exclusion zone for each satellite
outperforms the RAIM algorithm in mitigation the effect of the interference when 5 satellites are visible.
An erratum to this article can be found at |
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| Keywords: | GPS receiver CW interference RAIM algorithm Carrier to noise ratio (C/No) |
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