The Federal Aviation Administration is currently developing the Local Area Augmentation System (LAAS) to transition from the current instrument landing system to satellite based navigation. Due to the single frequency nature of the current LAAS architecture for Category I approaches, spatial ionospheric decorrelation contributes significantly to the differential ranging error. During days of normal ionospheric activity, the LAAS Ground Facility (LGF) broadcasts a conservative standard deviation of the spatial ionospheric gradient (σ{sub}(vig)) to LAAS users. Under these normal circumstances, navigation integrity is ensured by incorporating σ{sub}(vig) into the computation of position domain protection levels. However, anomalies exhibiting abrupt changes in the ionospheric gradient have been observed during ionospheric storms in October and November 2003. Therefore, monitoring algorithms are necessary for LAAS to detect these hazardous ionospheric anomalies. A three parameter (front width, gradient, and front speed) ionospheric threat model has been proposed and significant research has been devoted to the development and analysis of LGF and airborne code-carrier divergence monitors in the past. However, there are limitations on the effectiveness of these monitors, as they depend on the rate of change of the delay with time. The most hazardous threat in this regard is a static ionospheric wave front. In previous work a differential carrier phase Receiver Autonomous Integrity Monitoring (RAIM) monitor to detect this threat was introduced. This work analyzes detection capabilities of the RAIM monitor for the whole spectrum of fronts within the threat model by showing what combinations of widths and gradients are detectable, and what is the associated availability cost to ensure detectability. Having the results in terms of combinations of fronts and widths is very advantageous, as it gives insight to the performance of this monitor when combined with a ground baseline monitor. It also provides an idea of how the availability would change with adjustments to the threat model. A new way of evaluating the availability is presented, using the actual GPS constellation in the sky for the full year 2004. The availability loss incurred by the implementation of the carrier phase RAIM monitor is presented for different locations in the US. It is shown that this loss is tolerable for most width-gradient combinations. It is also shown it is tolerable for all width-gradients combinations if the monitor only operates during a storm alarm. The availability gain in implementing a baseline ground monitor in conjunction with the RAIM monitor is also provided.
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