An inertial (“INS”) /
GPS receiver includes an INS sub-
system which incorporates, into a modified
Kalman filter, GPS observables and / or other observables that span previous and current times. The INS filter utilizes the observables to update position information relating to both the current and the previous times, and to propagate the current position, velocity and attitude related information. The GPS
observable may be
delta phase measurements, and the other observables may be, for example, wheel pick-offs (or counts of wheel revolutions) that are used to calculate along track differences, and so forth. The inclusion of the measurements in the filter together with the current and the previous position related information essentially eliminates the effect of
system dynamics from the
system model. A position difference can thus be formed that is directly
observable by the
phase difference or along track difference measured between the previous and
current time epochs. Further, the
delta phase measurements can be incorporated in the INS filter without having to maintain GPS carrier
ambiguity states. The INS sub-system and the GPS sub-system share GPS and INS position and
covariance information. The
receiver time tags the INS and any other non-
GPS measurement data with GPS time, and then uses the INS and GPS filters to produce INS and GPS position information that is synchronized in time. The GPS / INS
receiver utilizes GPS position and associated
covariance information and the GPS and / or other observables in the updating of the INS filter. The INS filter, in turn, provides updated
system error information that is used to propagate inertial current position, velocity and attitude information. Further, the
receiver utilizes the inertial position, velocity and
covariance information in the GPS filters to speed up GPS
satellite signal re-acquisition and associated
ambiguity resolution operations