How does a tightly coupled system behave during partial GNSS outages?

• A. Loosely coupled enables operation during partial GNSS outages.
• B. Tightly coupled cannot operate during outages.
• C. Loosely coupled uses raw GNSS in the filter.
• D. Tightly coupled enables operation during partial GNSS outages by integrating raw measurements.

Answer: (D)

Tightly coupled GNSS/INS integration continuously feeds the navigation filter with raw GNSS measurements (pseudorange, Doppler, etc.) alongside inertial sensor data. This lets the system keep estimating position, velocity, and attitude even when not all satellites are visible or when the GNSS solution isn’t fully reliable. The filter uses whatever measurements are available and the inertial data to bridge short outages, so it can maintain an accurate estimate and quickly recover when satellites return.

Loosely coupled systems rely on a separate GNSS position/velocity solution from the receiver, so partial outages can prevent any update to the filter, making navigation more fragile. Tight coupling’s use of raw measurements is what enables operation during partial outages by continually constraining the state with GNSS observations directly in the filter.