Hardware-in-the-Loop – sometimes called HIL or HWIL – is a simulation approach that incorporates hardware interfaces with software. Typically, hardware components will emulate a subsystem or portion of the system/device/vehicle being modeled. Although the Hardware-in-the-Loop approach is often used to test complex, embedded systems such as aerospace components, using a hardware-in-the-loop approach is much more straightforward than that.
HWIL testing is a process in which real signals from a controller (such as a radar, IR sensor, or autopilot system) are connected to a test system that simulates reality, tricking the controller into thinking it is in the assembled product in a real environment. Manufacturers can then easily run through thousands of possible scenarios to test the controller without the cost and time associated with actual physical tests.
Today, HWIL is widely used in aerospace and autonomous vehicles to help mitigate the time and cost of performing real, physical tests.