From pseudorange overbounding to integrity risk overbounding
Résumé
Degradations of the pseudorange measurements, even when bounded, can lead to unacceptable positioning errors, especially when considering reduced alert limits—like those provided by GBAS, SBAS, and, in the future, ARAIM. The solution consists of the passive integrity method called “overbounding.” The overbounding approach allows all measurements in the position solution. The idea of the approach is to get a conservative bound for the integrity risk. The known methods of overbounding are applicable to the calculation of conservative bounds for a linear combination of several random variables. These methods are used to calculate the instantaneous integrity risk overbounding for vertical positioning, and they can be used for horizontal positioning only after some conservative steps. The original contribution is twofold: (a) new conservative upper bounds for the integrity risk in the horizontal plane; (b) new conservative upper bounds for the horizontal/vertical integrity risks per a given period of time.