Analysis of Maritime DGPS Malfunction by the Satellite Failure on PRN23

Abstract

The integrity function of maritime DGPS can ensure that the maritime DGPS users are safe against the position errors due to satellite failure. A good example to illustrate the integrity function of maritime DGPS is an anomaly of an atomic clock aboard the GPS satellite with PRN23 on January 1st 2004. At that time, the incorrect satellite was detected due to the high PRC and RRC values, and maritime DGPS system announced that DGPS user equipment should immediately stop using the detected incorrect satellite through RTCM messages. Therefore the DGPS users in the service coverage area of maritime DGPS were able to compute the user position using visible GPS satellites excluding PRN23. However unfortunately, some maritime DGPS systems recognized the other GPS satellites except PRN23 as the incorrect satellites, so that those systems didn’t provide DGPS users with the proper integrity function for retaining the normal DGPS position accuracy during the satellite failure on PRN23. This paper deals with the maritime DGPS malfunction by an anomaly such as satellite clock failure. In order to reproduce the anomaly of GPS satellite clock using GPS simulator, this paper carries out a study to analyze the pseudorange error on PRN23 and the impact on DGPS reference station at that time. And this paper makes a close investigation into the process of maritime DGPS malfunction under the reproduced anomaly circumstances. It is shown that the maritime DGPS malfunction resulted from the change in the PRC and RRC values of the correct satellites by PRN23 anomaly raised in process of computing the pseudorange corrections. Finally, this paper shows the validity of the analysis results using maritime DGPS RSIM and discusses a solution to make up the maritime DGPS malfunction by the satellite failure.