Predicting the availability of (A)GPS in indoor places by simulations

Inhalt:
The availability of GPS fixes depends sensitively on the geometry and materials of the building, the exact position of the receiver and the satellite constellation. Thus, it is practically impossible to derive it theoretically, nor is it easy to obtain experimentally. A simulation environment and measurements for the availability of GPS navigation in indoor places is presented. The simulator calculates the receive power for different positions and times, so that the availability of satellite signals can be predicted and the performance of different GPS receivers can be compared. This can be done without any additional measurements. The simulation environment contains the calculation of the orbit and position of each satellite and a data model that describes the receive situation and the properties of rooms and buildings (geometry, walls, windows, attenuation factors). The basis for the simulation is a link budget of the satellite signals between the GPS satellites and the GPS receiver. The propagation of each signal on its way to the receiver and its attenuation by walls, windows and air, including one reflection, is simulated for several points in a building. The simulation was verified by reference measurements with a standard GPS receiver. Varying the threshold sensitivity, different GPS receivers can be compared by simulation. It is also possible to model Assisted GPS, which effectively decreases the required signal level. A time- and space-averaged availability probability for a concrete room can be obtained. The simulation shows the performance gain of high sensitivity receivers like Assisted GPS in indoor places.