Research On Related Technologies Of Multi-mode Local Difference Augment System

With the rapid development of GNSS, Augmentation system have be studied by more andmore countries，but Multi-Mode Local Difference Augment System (MLDAS) have not enteredinto the system research. The center of thesis is MLDAS. The main contents of paper are: designof MLDAS and multi-mode GNSS systems performance analysis, cycle slip detection and repairtechnology, differential correction algorithms and carrier phase smoothed pseudo rangetechnology, MLDAS system integrity and RAIM.The main achievements of the thesis are summarized as follows:1. In order to achieve the function, the thesis designed an overall structure and subsystemdetail of MLDAS, and discussed the differential format and error correction coding techniques.2. The thesis analyzed on the characteristics of the combination of the multi-GNSSsystems deeply, and compared the similarities and differences of the various GNSS systems,discussed the time reference coordinates、the spatial reference coordinates, and their interfrequency interference. Based on the GPS and GALILEO system, the thesis analyzed thenumber of visible satellites, DOP factor, the minimum detection bias, by comparing theseperformance, it can be find that the multi-mode system performance is better than system alone.3. The thesis discussed the cycle slip detection and repair methods: high-differencemethod, polynomial fitting method, Doppler method, ionosphere residual method, pseudo rangephase combination method, and then some experiments were carried out to analyze thesemethods precision, and the applicable conditions were gave for each method. And then the cycleslip detection algorithm using tri-frequency combination was discussed. The cycle slip detectionby Tri-frequency combination need to take into account the noise、ionosphere factor and noiseamplification factor. And the select principle of the Tri-frequency pseudorange carriercombination is the least variance of the cycle slip float resolution. And the thesis did anexperiment to test a group combination of cycle slip detection which are based on the leastvariance of the circle slip float resolution, and the experimental results can detect all the cycleslip.4. Ionosphere TEC rate of cycle slip detection and repair method was proposed which canbe used in ionosphere storms. The formula of TEC rate algorithm was proposed. Theexperiments show that the storm can’t affect the useage of the TEC rate algorithm for1seccondsampling interval data. In order to detect some cycle slip which were difficult fot TEC ratealgorithm, a combined algorithm was proposed. Combined with MW method has a very highpossibility on the combination of cycle slips, which are very difficult to be detected by them alone.5. The thesis studied the MLDAS’s corrections algorithm-the weighted average method,linear interpolation, low-surface model method and triangle interpolation method.And analyzedthe similarities and differences of various algorithms.And a simulation reference station networkwas build in order to analysis each algorithm performance.6. The classical Hatch filter in carrier phase smoothed pseudorange difference was studied.The relationship among the filtering error and smoothing times、noise、ionosphere rate wasderived, from the formula we can knew,the more smooth time,the small noise error, but whenthe smoothing time become long, the ionosphere effect can not be ignored. It may lead to filterdivergence.7. In order to reduce the classical Hatch filter divergence problem, The paper proposed anew Hatch filter method, Which take into account the ionosphere delay variation, It obtained thenoise error by empirical formula and get the ionosphere error by Klobuchar model，and deducedcalculated the smoothing time by cardaro. The improved Hatch filter algorithm works on eachsatellite at each epoch to get the optimal smooth time. The experiments show that the newalgorithm not only improved the positioning accuracy, but also enhance the robustness.8. Thesis designed the integrity monitoring system of MLDAS. It includes Signal QualityMonitoring、Data Quality Monitoring、Measurement Quality Monitoring、Multiple ReferenceConsistency Check、mean and standard deviation Monitoring、Message Field Range Monitoring.the alarm can be issued for monitoring module logic, fault channel can be isolated, and theintegrity of the system will be get.9. Accumulated algorithm was proposed which is use in the mean and standard deviationmonitoring. Accumulated algorithm can have good performance in accumulated error, but itcan’t quickly detect the large deviation, the improved algorithm which combined general controlcharts can rapid detection large deviation.It was introduced to the mean and standard deviationmonitoring to make it up for classical accumulated algorithms’ shortcoming. Experimentalresults show that the improved algorithm could not only monitor small medium cumulativedeviation but also to detect the large deviation.10. The least squares residual RAIM and parity space vector RAIM were introduced. Andthe integrity of these algorithms was discussed. The least squares residual experimental resultsshow that, the least squares residual RAIM has a better detection capability to single fault. Thethesis proposed an improved method based on least squares residuals to detection multiple faults.This method assumed that the fault number and size were unknown. And assumed the fault ispositive errors caused by ionosphere and tropospheric delay, which can restrict the solver arepositive. Under the condition, the fault can be found which have the minimum least squares residual sum.