What is a key advantage of a tightly coupled GNSS/INS fusion compared to a loosely coupled approach?

• A. It requires a full GNSS solution before fusion.
• B. It is always less robust in poor GNSS conditions.
• C. It can use partial satellite data and is more robust in degraded GNSS environments.
• D. It ignores INS data during outages.

Answer: (C)

Tightly coupled GNSS/INS fusion blends raw GNSS measurements with inertial data inside one estimation filter, rather than waiting for a full GNSS solution to fuse. By using measurements like pseudorange and Doppler directly along with high-rate INS data, the filter can estimate position, velocity, attitude, and biases even when not all satellites are visible. This means the system stays robust in degraded GNSS conditions because partial satellite data still contribute to updates, and the INS helps bridge gaps during outages. In contrast, requiring a full GNSS solution before fusion is a hallmark of looser coupling, which is less capable when satellite visibility is limited. The idea that INS data would be ignored during outages is incorrect in tight coupling, since the INS is continuously propagated and integrated to maintain the solution.