On ionosphere-induced error detection for GNSS integrity monitoring

This work compares the design and performance of three ionospheric gradient monitors, based on code-only observations, on phase-only observations and on the combination of both observables. It is shown that the detection capabilities are considerably enhanced by exploiting carrier-phase measurements. However, these are ambiguous by an unknown number of integer cycles, and differential ionospheric delays close to integer multiples of the wavelength may potentially remain undetected by the monitor. It is shown how this can be avoided by designing ad-hoc relative baseline geometries between the elements of an antenna array. A theoretical evaluation of the performance of each ionospheric gradient monitor is provided through inspection of the associated acceptance region, that defines which values of the ionospheric gradient cannot be detected with given integrity requirements.