The Signal Quality Monitoring Method based on Multi-correlation Algorithm for GNSS Modernized Signals

Abstract

Satellite signal anomalies result from a failure of the signal generating hardware on one of the GNSS space vehicles. These anomalies may cause severe distortions of the autocorrelation peak inside GNSS receivers, which could threaten the position accuracy and integrity of GNSS, especially for safety critical applications. Digital distortion caused by failures inside the baseband generation unit is an important kind of deformations. Multi-correlator technique, as a prevalent Signal Quality Monitoring (SQM) method, has shown good performance on detecting digital distortion of BPSK modulated signals. However, traditional multi-correlator technique, which depends on detecting correlation peak, is not applicable for modernized BOC signals because of their different characteristics in correlation domain. Hence, we give a modified multi-correlator method that combines BPSK-LIKE algorithm and multi-correlator technique to detect the distortion. The proposed method can be achieved easily in a modified GNSS receiver. Firstly, we utilize BPSK-LIKE tracking loop to deal with received signals so that the impact of the sub-carrier on BOC signals is eliminated and ambiguity problem on correlation functions is avoided. The values of correlation and the code phases in tracking loop are output to detection module. Then, a modified correlation-domain detection algorithm is presented to achieve digital distortion detection for BOC signals. Considering that, for BOC signals, the generation of pseudo-noise (PN) code and subcarrier are two separate procedures onboard navigation satellites, two detection methods including Ratio Tests and Symmetry Tests are used to monitor PN code distortion and subcarrier distortion respectively. The results show that the proposed method can detect digital deformation of BOC-modulated signals effectively. By increasing correlators and the length of input signals, the detection performance can be improved. In addition, correlator space has a significant impact on detecting PN code distortion. Compared with traditional multi-correlator technique, the modified method has shown similar performance on detecting PN code distortion.