GPS from getting started to giving up (XIII), receiver autonomous integrity monitoring (RAIM)

Receiver autonomous integrity monitoring （RAIM: Receiver Autonomous Integrity Monitoring） It is based on the user receiver redundancy The observation value monitors the integrity of user positioning results , Its purpose is to detect the faulty satellite in the navigation process , And ensure the accuracy of navigation and positioning .

In order to monitor the autonomous integrity of the receiver , There must be redundant observations . Generally speaking , Number of visible satellites required 5 The integrity test can be carried out only when there are more than pieces ; Need to have 6 More than one satellite can be identified as faulty .RAIM The enhanced version of is RAIM-FDE（FDE: Fault Detection Exclusion）, That is, fault detection and troubleshooting Technology , Because we need to troubleshoot the satellite , So we must use at least 6 Visible satellites .RAIM Algorithms are very important for applications with strict security requirements , Such as civil aviation 、 Aviation and so on .

         RAIM There are different implementation algorithms ： Pseudo range residual decision method 、 Pseudo range comparison 、 Check vector method and maximum solution separation method .

One 、 Pseudo range residual decision method

In the solution of positioning equations, we talked about positioning equations
 

Two 、 Pseudo range comparison

Pseudo range comparison method is to directly use pseudo range to judge . Steps are as follows ：

1. When the number of observations is greater than 4 Under the circumstances , Yes n  Group by observation , One group is 4 individual , The other group is n − 4  individual .
2. Yes 4 The group of one is solved by the least square method to calculate the receiver position .
3. Yes n − 4 The group of calculates the satellite position .
4. The pseudo range is estimated according to the calculated receiver position and satellite position .
5. Compare the estimated pseudo range with the actual observed pseudo range . If the comparison results are very close , It shows that the observation results are ok , The first 2 The position of the solution in the step is no problem . Otherwise, there is a problem .
6. Deal with problematic situations . It depends on the situation . If there is only one comparison, the results differ greatly , There is a high probability that there is something wrong with that observation ; If the results of many comparisons are very different , Then there is a high probability that there is a problem with the least square solution . If necessary , You can regroup , Recalculate the comparison judgment .

3、 ... and 、 Check vector method

Four 、 Maximum solution separation method