Abstract: Positioning dilution of precision (PDOP) availability of navigation constellation is one of the important specifications in the phase of general system design. Effects of different distributions of fault satellites on PDOP availability of global navigation constellation are studied. Firstly, a statistical evaluation model of PDOP availability is suggested using probability and combination method. Using this model, simulation and analysis for variation of PDOP availability of navigation constellations with typical Walkerδ configurations are performed, considering that a given number of fault satellites distribute in one or more orbital planes. The simulation results indicate that the distribution of fault satellites and the number of orbital planes have notable effects on PDOP availability of constellation, and that it is advantageous to reduce the number of orbital planes properly to improve PDOP availability of global navigation constellation. The proposed model has explicit physical meaning and can avoid the subjectivity and ensure the effectiveness of specification evaluation.

Key words: global navigation constellation, PDOP availability, distribution of fault satellites, evaluation model, probability and combination