Holdover time in GNSS outage analysis depends on which factors most?

• A. Holdover time is the time GNSS is unavailable.
• B. Holdover time depends on INS performance and process noise to keep position within bound.
• C. Holdover time is the time required to reacquire satellites.
• D. Holdover time is a fixed constant.

Answer: (B)

Holdover time is about how long the navigation solution can stay within a specified position error bound when GNSS signals are lost. During an outage, the system relies on the inertial navigation system to propagate the last known state using accelerometer and gyro data. The rate at which the position error grows depends on the INS performance (how accurate and stable the sensors are) and the process noise that the navigation filter assumes. If the INS has low drift and noise and the filter’s process noise is small, the error grows slowly, so you can maintain the required accuracy for a longer period. If the INS degrades or the process noise is larger, the error accumulates faster and the holdover time shortens.

Other statements miss the point: holdover isn’t simply the outage duration, nor the time to reacquire satellites, nor a fixed constant. It’s determined by how quickly INS errors accumulate under the given sensor quality and filter model, relative to the allowable position bound.