GPS URE/UE evolutionary improvements and end-user accuracy results

It has become evident that GPS must undergo evolutionary changes in order to fully satisfy both civil and military requirements in the next century. The end-user accuracy is an area where there is continual call for improvements to provide increasing accuracy for both tactical and strategic operations. The observed URE² performance which describes the error contributed by the Space and Control Segment portions has seen significant step improvements which have resulted in a current URE in the range of 2.5 m from the original spec of 6.0 m, a 60% reduction in the expected error. The continuing AII³ program efforts expect to drive this down to <1.5 m even before AUTONAV becomes operable with 6 functional IIR SV⁴