A study on the in-orbit environment of a GPS receiver for low/medium altitude satellites

In this paper, the in-orbit receiving environment of a GPS receiver for low/medium altitude satellites is studied and in particular, antenna characteristics of the GPS receiver for various antenna beam directions are examined. In addition, we propose a method to reduce error in calculating the position by reducing the geometric dilution of precision (GDOP). By computer simulations, the relation between the number of visible GPS satellites and GDOP is investigated and the fact that there must exist the most possible GPS satellites in order to reduce GDOP is also confirmed. Besides, since the error factor can be reduced if GDOP becomes smaller can yield the better performance of the GPS receiver. Another simulation result indicates that the heading angle of the GPS receiver antenna must be changed in proportion to the altitude of the receiver in order to obtain better receiving characteristics. The wider receiving range of the antenna can prevent from the situation that the direction of the satellite body must be changed. In this paper, even though we analyze the characteristics for GPS receivers with high inclination angle by computer simulations, we can also characterize the characteristics for GPS receivers with arbitrary inclination angle by considering the earth is a nearly sphere and GPS satellites are uniformly distributed.