The paper considers the method of monitoring the integrity of global navigation satellite systems based on using the angle of arrival estimation. The method uses the differences between measured and calculated azimuths (“azimuth differences”) and elevations (“elevation differences”) respectively. The probability distributions of the differences are analyzed and probability-based integrity monitoring characteristics are obtained. The most important of them are the probability of false detection (false alarm probability) and the probability of missing the violation of integrity (missing probability). Three kinds of decision-making procedures are analyzed. The first one involves using only one of the differences for decision-making, whereas other procedures use each of them. In the latter case it is possible to use two ways of decision-making – when both differences exceed the thresholds simultaneously (logic “AND”) and at least one of them exceeds the threshold (logic “OR”). Both ways are analyzed and areas where parameter values, in either way, have advantages are obtained. As a result the probability-based characteristics improvement methods are suggested.