Future Dual-Frequency GPS Navigation System for Intelligent Air Transportation Under Strong Ionospheric Scintillation

GPS technology is essential for future intelligent air transportation systems such as the Next Generation Air Transportation System (NextGen) of the United States. However, observed deep and frequent amplitude fading of GPS signals due to ionospheric scintillation can be a major concern in expanding GPS-guided aviation to the equatorial area where strong scintillation is expected. Current civil GPS airborne avionics track signals at a single frequency (L1 frequency) alone because it was the only civil signal available in the frequency band for aviation applications. The first GPS Block IIF satellite was launched in May 2010. This next-generation satellite transmits a new civil signal at the L5 frequency, which can be used for air transportation. This paper investigates a possible improvement in the availability of GPS-based aircraft landing guidance down to 200 ft above the runway, which is also known as Localizer Performance with Vertical Guidance (LPV) 200, under strong ionospheric scintillation when dual-frequency signals are available. Based on the availability study, this paper proposes and justifies a GPS aviation receiver performance standard mandating fast reacquisition after a very brief signal outage due to scintillation. In order to support a temporary single-frequency operation under a single-frequency loss due to scintillation, a new vertical protection level (VPL) equation is proposed and justified. With this new performance requirement and new VPL equation in place, 99% availability of LPV-200 would be attainable, rather than 50% at the current standards, even under the severe scintillation scenarios considered in this paper.