Ashtech XII GPS technology

Several enhancements of GPS (Global Positioning System) technology are presented, including new data processing algorithms, enhanced application techniques, more hardware capabilities, and reduction in size and power consumption. The use of Doppler measurements for instantaneous (every one second) stationary position fixes is introduced. This technique has the potential of reducing the effect of selective availability in static point positioning. It is shown that the combination of Doppler and code phase measurements can provide two-dimensional deterministic static position fixes (and time) with only two satellites. It can also provide three-dimensional position fixes (and time) with three satellites. The proposed techniques expand the usage of GPS in areas with low satellite visibility and in the interim period while the GPS satellite constellation is not complete. The notion of multiple ramp smoothing of code phase with integrated Doppler is introduced. The results of implementation of this technique in Ashtech XII receivers for real-time differential GPS is given. Minimizing the errors in the use of GPS for aerial photogrammetry applications is discussed. A new technique implemented in Ashtech XII GPS is presented. A new generation of GPS receiver (Ashtech M-XII) is introduced. It is capable of performing precision survey, navigation, and time transfer. The 12-channel receiver uses a higher level of hardware integration. The results of Ashtech XII dual frequency receivers on the FGCC (Federal Geodetic Control Committee) test network are presented