Study On The LAAS Integrity Under The Ionospheric Impact

Local Area Augmentation System(LAAS) is a differential GPS navigation system based on radio technology. It is mainly used in aviation during aircraft’s landing and precision approaching. LAAS Integrity refers to the capability of LAAS integrity monitoring the system abnormalities and alerting the user promptly. GPS satellite signals will be changed after passing through the ionosphere, the deformed GPS signals will cause huge impact on the LAAS GPS integrity.This paper firstly describes the characteristics and integrity monitoring methods of LAAS system, then depthly studys the ionospheric activity’s impact on LAAS integrity from a single reference station to multiple reference stations. For a single reference station, proposed an improved pseudocode-carrier deviation monitoring algorithm and an improved C/A code correlation peak symmetric algorithm. For multiple reference stations, established a LAAS ionospheric model to study the performance of the model influencing the LAAS system based on multiple reference stations, finally, designed a LAAS multiple reference station scheme base on the different spatial configuration, and analyzed the LAAS’s ionosphere monitoring performance under different scenarios.Specifically, the work areas are as followings:1. Proposed a pseudocode-carrier deviation monitoring algorithm based on the mixture Gaussian overbounding method to solve the problem that Gaussian function of the pseudocode-carrier measurements and the statistical distribution of actual data are not comprehensive at both the core and the tails of the curve. After collecting GPS data and analysising it, simulation experiments verified the effectiveness of the algorithm.2. Presented a virtual technology related to the C/A code correlation peak symmetric algorithms. Established a deformation signal model affected by ionosphere,using cubic curve fitting method to build a virtual C/A code correlator-pairs at the same time, calculated the virtual correlation-pairs threshold using the interpolation method.Through simulation experiments, compared the improved algorithm with the traditional algorithm, demonstrated the effectiveness of the improved algorithm.3. The establishment of an ionospheric model based on the LAAS architecture of multi-reference-station. Firstly, established the global ionospheric model using the traditional GAIM method, cited the concept of the ionospheric electron density,analysised the gradient anomalies of the ionospheric electron density when the ionosphere turmoil breaks out, according to the hypothesis, cited the ionospheric delay slope gradient model, finally simulated and analysised the impact of the model on the LAAS ground equipment and airborne receiver.4. Designed a scheme of building the reference stations for monitoring ionospheric delay gradient. By formula derivation, seted up a vertical and equal-length baseline reference station configuration, a vertical and unequal-length baseline reference station configuration and a non-vertical and unequal-length baseline reference station configuration. Though simulation, analysised the various performance of monitoring the ionospheric delay gradient of each LAAS scheme and verified its validity.