What Simulation Repeatability Means for Your Program


Why Simulation Repeatability Matters

Given the same initial conditions, GNSS/INS simulations of the same mission scenario should produce the same result every time. Different results indicate a problem with the receiver. Or do they? Poor simulation repeatability can be subtle and hard to diagnose. Even worse, problematic simulations send investigations down the wrong path — a path that consumes time and resources.

In this article, we will discuss why simulation repeatability matters and the impact that misleading simulation results can have on a project. Then we will explain how choosing a CAST Navigation GNSS/INS simulator that can deliver 100% repeatability can make a difference to your project.

A simulator’s goal: generating repeatable simulations

GNSS/INS simulations are the most efficient ways to evaluate receivers. In the time it takes to fly one or two scenarios over a test range, a lab can perform four times as many simulations. The simulator’s output is more precise than radar checks and is never obscured by terrain. And since project budgets are always constrained, the financial benefits of GNSS/INS simulation make a difference — simulation time costs much less than flight time.

Yet the simulator must deliver on its productivity promise by reliably producing repeatable results. Under the same conditions, every simulation must start and stop at the same time. Every course and velocity change must happen at the same time. If the host vehicle uses an EGI, then the simulation must reproduce the real-world performance of that EGI and account for the unit’s drift, bias, and other factors.

You would be forgiven for assuming all simulators always produce the same results. After all, that is what simulators are supposed to do. But things are not that simple.

The problem with simulating the real world is that reality is continuous and digital systems are discrete. A change point in a simulation could arrive between the ticks of a digital system’s internal clock. When these mid-cycle events occur, they can create a microseconds-long delay before the change takes effect. These delays build upon each other during a simulation to alter the host vehicle’s path. In each run of the simulation, the delays occur at different times and produce different end results.

The consequences of inconsistent simulations

With imperfect repeatability, the differences between each simulation run look like problems with the receiver under investigation. If you are evaluating a receiver for procurement, you could assume that a good product did not meet requirements. If you are developing an INS, you may not be able to fine-tune the system. Your project team could waste valuable time troubleshooting a hardware issue that does not exist.

Identifying inconsistent simulation runs may require the help of an outside expert. Or it may force a project to turn to real-world flight testing — with all the costs associated with putting a vehicle in the air.

100% repeatability with CAST Navigation simulators

Over the past forty years, CAST Navigation has earned its reputation for GNSS and INS simulation solutions that produce 100% repeatable results with the most complex scenarios. Whether you are testing a single navigation unit or simulating an entire squadron, the same simulation will produce the same result every time.

Repeatability gives you the confidence to uncover issues in the lab without relying on flight testing. As a result, your investigations will focus on actual issues that can be fixed and quickly re-tested.

The repeatability of CAST simulators saves our customers time and resources by producing the right results the first time.

Learn more about CAST Navigation’s simulation solutions for GNSS, Inertial, Jamming, and CRPA.


August 5, 2021