Atmospheric noise mitigation for Loran

While aircraft users increasingly rely on the Global Positioning System (GPS) for navigation, the received signal strength from these distant satellites is low and hence may easily be jammed. Of the alternative systems available to provide aircraft with a backup to GPS for non-precision approach (NPA), Loran promises to be an exceptional candidate since its signal is present over the continental United States (CONUS).;Loran, a low-frequency hyperbolic radio-navigation system, provides positioning with quarter nautical mile accuracy, 95% of the time. Since it was not originally designed for aircraft navigation, the system requires upgrades to both the transmitters and user receivers to meet NPA requirements. Furthermore, to be viable, Loran's coverage area, defined as where it meets the NPA requirements, must be across most of CONUS. Impeding its success is Loran's susceptibility to lightning and other atmospheric noise.;Determining Loran's coverage requires the estimation of atmospheric noise and the processing gain or credit for noise reduction due to non-linear processing techniques within a typical receiver. The traditional method uses the standard atmospheric noise model from the International Telecommunications Union (ITU), and estimates the processing gain as a constant. While easy to implement, such an analysis produces overly conservative results and, therefore, a poor estimate of coverage area.;This dissertation presents a new method for predicting coverage by extending the ITU model and by demonstrating empirically that a lower bound on atmospheric noise impulsivity is proportional to the noise strength. Since it is well known that the gain in signal-to-noise ratio (SNR) in a receiver produced by non-linear signal processing is proportional to the noise impulsivity, then the correlation of noise impulsivity to noise strength implies that the processing gain is also proportional to noise strength and is not simply constant as previously predicted.;The new method results in an increase of 8 dB to the SNR over those predicted by the traditional method. The result is an increase in system availability across most of CONUS, thereby increasing the likelihood that a modernized Loran can become certified for NPA.