GPS/Inertial Coupling

Ultratight coupling is an effective way of integrating raw GPS measurements with raw inertial measurement unit (IMU) measurements. The technique eliminates conventional code and carrier tracking loops and many of their associated limitations. Instead, navigation measurements are obtained directly from the raw received GPS signals. Long measurement-smoothing times can reduce the effective bandwidth of the processing, thereby improving antijam performance and accuracy. With conventional unaided tracking loops (top), the wide bandwidth loop filter tracks all user and satellite motion. In a tightly coupled GPS/IMU tracking loop (middle), a narrower loop bandwidth is used to track errors in IMU, providing more noise rejection (and jam suppression). With ultratight coupling (bottom), a smoother transforms and smoothes thousands of correlator measurements into range and rate residual errors.

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