Hi I'm working on a GPS/INS model. Now I developped the mecanization equations for the INS. I have a kalman filter which estimate the error state (position error with respect to north and east). it takes as an input the diffrence between GPS and INS and gives its estimation . I have developped a gauss-markov process which very similar to sensor noise (after applying wavlet). Now, I don't know what can I do during the GPS outage ? Because the mesaures are not available during this periode; I can't use Kalman filter. Documentation that I have, doesn't say clearly what to do during GPS outage.