Signal Quality Monitoring: Correlation mask based on Ratio Test metrics for multipath detection

In any measurement process, the observation is error affected: calibration and careful measuring procedures can reduce the error components but are unable to completely eliminate them. The capability to monitor and to detect any disturbances on the spreading sequences transmitted by the satellites is then of primary importance. Quality Control techniques based on a modified tracking architecture, which provides a certain number of correlator outputs, are analysed in this paper. Such outputs are used to build a metric used to monitor in real-time the reliability of the signal being tracked. In literature, several definitions of metrics can be found. The mainly used metrics are based on the following ratios: Ratio Test, Delta Test and Lambda Test. Once the test metrics built, their values are compared to predetermined thresholds during the Signal Quality Monitoring (SQM) activity. Although a huge amount of work on those metrics is present in literature, this paper will present a new way of operation for the threshold settings. A threshold mask is built around the shape of the correlation function in order to detect in real time the presence or absence of a distortion guaranteeing a desired confidence level. The reliability of this design criterion will be proved in the paper. A simulations campaign is performed to determine and analyse the SQM techniques and their optimum parameters in order to obtain the so–called Receiver Operative Characteristic (ROC).