Modeling of selective availability for global positioning system

To degrade location accuracy for unauthorized GPS users, US government applied Selective Availability (SA) to Global Positioning System (GPS). In this paper we discuss an anti-SA approach to improve location accuracy which is very important in landing position, and then we derived the SA error by eliminating almost all other errors including ionospheric and tropospheric time delays and clock errors both in satellites and in receiver, etc. By means of the system identification theory, an SA error, an SA error model with the second-order Gauss-Maukov stochastic process was derived and simulated. With the selected parameters of the stochastic process, the simulation results show that there is the excellent agreement between the simulated SA error model and that of really applied in GPS system.