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To correct INS errors using cellular pseudoranges, an EKF framework similar to a traditional tightly coupled GNSS‐aided INS integration strategy can be adopted, with the added complexity that the cellular towers’ states (position and clock error states) are simultaneously estimated alongside the navigating vehicle’s states (position, velocity, attitude, IMU measurement error states, and receiver clock error states). This framework is composed of two modes:

 Mapping ModeThe EKF produces estimates and associated estimation error covariances of both the navigating vehicle and the cellular towers’ states (augmented in ) using both GNSS SV and cellular pseudoranges. Between aiding corrections, the EKF produces the state prediction and prediction error covariance P− using the INS and receiver and cellular transmitter clocks models. When an aiding source is available, either GNSS SV or cellular pseudoranges, the EKF produces a state estimate update and associated estimation error covariance P+.

 Radio SLAM ModeThe cellular‐aided INS framework enters a radio SLAM mode when GNSS pseudoranges become unavailable. In this mode, INS errors are corrected using cellular pseudoranges and the cellular transmitters’ state estimates that were last computed in the mapping mode. As the vehicle navigates, it continues to refine the cellular transmitters’ state estimates simultaneously with estimating the vehicle’s own states.

Figure 38.64 illustrates a high‐level diagram of the cellular‐aided INS framework.