Simulation of GPS augmentation systems

High fidelity environmental simulators are required for the test and validation of GPS augmentation system software. Illgen Simulation Technologies, Inc. (ISTI) has developed the iWAASs simulation to address this requirement. The iWAASs simulation uses the GIPSY software package to provide accurate GPS and GEO orbits. Simulated signals, which include selective availability (SA), are propagated through the ionosphere and troposphere to a receiver simulation. Ionospheric models include a wide variety of storm scenarios. A detailed receiver model includes cycle slip models, receiver noise, and multipath. The output format is RINEX. In addition to nominal performance models, the iWAASs simulation can model a wide variety of fault conditions including range jumps, clock run-off, maneuvers, loss of attitude control, bad uploads, and ε-SA, to name a few. A detailed simulation of the GEO ranging signal control loop has also been developed. The iWAASs simulation is presently used by the WAAS prime contractor as its environmental simulator test tool. Applications are also being developed which integrate iWAASs into flight simulators with on-board receiver models