Evaluation and Simulation of GPS Navigation Performance in Service Volume

The concept and partition of GPS service volume have been established and specified in GPS SPS PS(standard positioning service performance standard) published recently.And the terrestrial service volume(TSV) includs near-Earth space,in which spatial exploration is much active.The new changes give the point that the technology of satellite navigation and positioning is feasible and promising to support users in near-Earth space.Based on the partition of the GPS TSV and SSV(space service volume),we discussed the judgment of the visible satellites in the both space and the feasibility of the received signal power,and carried out the UERE budget of the GPS signal in near space under the standard positioning service condition.Then the navigation performance statistics at the different heights at the middle latitude single point and over the global volume were carried out respectively with the Monte-Carlo method.The results show that the navigation accuracy will improve gradually with the users' height increasing in TSV,and into SSV,the accuracy deteriorates rapidly,and the service interrupt will appear at some height.The conclusions also show that the GDOP at the certain height in TSV will change its precision dilution property,which means that the positioning accuracy is much higher than that of UERE,and that the vertical accuracy is becoming higher than the horizontal accuracy gradually with the users' height increasing in TSV.